Publications by authors named "Michael F Allen"

35 Publications

Precipitation-drainage cycles lead to hot moments in soil carbon dioxide dynamics in a Neotropical wet forest.

Glob Chang Biol 2020 Sep 10;26(9):5303-5319. Epub 2020 Jul 10.

Environmental Systems Graduate Program , Department of Civil & Environmental Engineering, University of California Merced, Merced, CA, USA.

Soil CO concentrations and emissions from tropical forests are modulated seasonally by precipitation. However, subseasonal responses to meteorological events (e.g., storms, drought) are less well known. Here, we present the effects of meteorological variability on short-term (hours to months) dynamics of soil CO concentrations and emissions in a Neotropical wet forest. We continuously monitored soil temperature, moisture, and CO for a three-year period (2015-2017), encompassing normal conditions, floods, a dry El Niño period, and a hurricane. We used a coupled model (Hydrus-1D) for soil water propagation, heat transfer, and diffusive gas transport to explain observed soil moisture, soil temperature, and soil CO concentration responses to meteorology, and we estimated soil CO efflux with a gradient-flux model. Then, we predicted changes in soil CO concentrations and emissions under different warming climate change scenarios. Observed short-term (hourly to daily) soil CO concentration responded more to precipitation than to other meteorological variables (including lower pressure during the hurricane). Observed soil CO failed to exhibit diel patterns (associated with diel temperature fluctuations in drier climates), except during the drier El Niño period. Climate change scenarios showed enhanced soil CO due to warmer conditions, while precipitation played a critical role in moderating the balance between concentrations and emissions. The scenario with increased precipitation (based on a regional model projection) led to increases of +11% in soil CO concentrations and +4% in soil CO emissions. The scenario with decreased precipitation (based on global circulation model projections) resulted in increases of +4% in soil CO concentrations and +18% in soil CO emissions, and presented more prominent hot moments in soil CO outgassing. These findings suggest that soil CO will increase under warmer climate in tropical wet forests, and precipitation patterns will define the intensity of CO outgassing hot moments.
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http://dx.doi.org/10.1111/gcb.15194DOI Listing
September 2020

Differences in root phenology and water depletion by an invasive grass explains persistence in a Mediterranean ecosystem.

Am J Bot 2019 09 9;106(9):1210-1218. Epub 2019 Sep 9.

Department of Botany and Plant Sciences, University of California Riverside, 900 University Ave., Riverside, California, 92521, USA.

Premise: Flexible phenological responses of invasive plants under climate change may increase their ability to establish and persist. A key aspect of plant phenology is the timing of root production, how it coincides with canopy development and subsequent water-use. The timing of these events within species and across communities could influence the invasion process. We examined above- and belowground phenology of two species in southern California, the native shrub, Adenostoma fasciculatum, and the invasive perennial grass, Ehrharta calycina to investigate relative differences in phenology and water use.

Methods: We used normalized difference vegetation index (NDVI) to track whole-canopy activity across the landscape and sap flux sensors on individual chaparral shrubs to assess differences in aboveground phenology of both species. To determine differences in belowground activity, we used soil moisture sensors, minirhizotron imagery, and stable isotopes.

Results: The invasive grass depleted soil moisture earlier in the spring and produced longer roots at multiple depths earlier in the growing season than the native shrub. However, Adenostoma fasciculatum produced longer roots in the top 10 cm of soil profile in May. Aboveground activity of the two species peaked at the same time.

Conclusions: The fact that Ehrharta calycina possessed longer roots earlier in the season suggests that invasive plants may gain a competitive edge over native plants through early activity, while also depleting soil moisture earlier in the season. Depletion of soil moisture earlier by E. calycina suggests that invasive grasses could accelerate the onset of the summer drought in chaparral systems, assuring their persistence following invasion.
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http://dx.doi.org/10.1002/ajb2.1344DOI Listing
September 2019

Dust Sources in the Salton Sea Basin: A Clear Case of an Anthropogenically Impacted Dust Budget.

Environ Sci Technol 2019 Aug 6;53(16):9378-9388. Epub 2019 Aug 6.

Department of Environmental Sciences , University of California , Riverside , California 92521 , United States.

The Salton Sea Basin in California suffers from poor air quality, and an expanding dry lakebed (playa) presents a new potential dust source. In 2017-18, depositing dust was collected approximately monthly at five sites in the Salton Sea Basin and analyzed for total elemental and soluble anion content. These data were analyzed with Positive Matrix Factorization (PMF). The PMF method resolved seven dust sources with distinct compositional markers: (Mg, SO, Na, Ca, Sr), (U, Ca), (Al, Fe, Ti), (K, PO), (Na, Cl, Se), (Sb, As, Zn, Cd, Pb, Na), and (Cu). All sources except are influenced or caused by current or historic anthropogenic activities. PMF attributed 55 to 80% of the measured dust flux to these six sources. The dust fluxes at the site where the playa source was dominant (89 g m yr) were less than, but approaching the scale of, those observed at Owens Lake playas in the late 20th century. emissions in the Salton Sea region were most intense during the late spring to early summer and contain high concentrations of evaporite mineral tracers, particularly Mg, Ca, and SO.
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http://dx.doi.org/10.1021/acs.est.9b02137DOI Listing
August 2019

A pulse of summer precipitation after the dry season triggers changes in ectomycorrhizal formation, diversity, and community composition in a Mediterranean forest in California, USA.

Mycorrhiza 2018 Oct 13;28(7):665-677. Epub 2018 Aug 13.

Center for Conservation Biology, University of California, Riverside, CA, 92521, USA.

Rapid responses of microbial biomass and community composition following a precipitation event have been reported for soil bacteria and fungi, but measurements characterizing ectomycorrhizal fungi remain limited. The response of ectomycorrhizal fungi after a precipitation event is crucial to understanding biogeochemical cycles and plant nutrition. Here, we examined changes in ectomycorrhizal formation, diversity, and community composition at the end of a summer drought and following precipitation events in a conifer-oak mixed forest under a semiarid, Mediterranean-type climate in CA, USA. To study the effects of different amounts of precipitation, a water addition treatment was also undertaken. Ectomycorrhizal fungal diversity and community composition changed within 6 days following precipitation, with increased simultaneous mortality and re-growth. Ectomycorrhizal diversity increased and community composition changed both in the natural rainfall (less than 10 mm) and water addition (50 mm) treatments, but larger decreases in ectomycorrhizal diversity were observed from 9 to 16 days after precipitation in the water addition treatment. The changes were primarily a shift in richness and abundance of Basidiomycota species, indicating higher drought sensitivity of Basidiomycota species compared with Ascomycota species. Our results indicate that ectomycorrhizal formation, diversity, and community composition rapidly respond to both precipitation events and to the amount of precipitation. These changes affect ecosystem functions, such as nutrient cycling, decomposition, and plant nutrient uptake, in semiarid regions.
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http://dx.doi.org/10.1007/s00572-018-0859-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6182365PMC
October 2018

Land-Sparing Opportunities for Solar Energy Development in Agricultural Landscapes: A Case Study of the Great Central Valley, CA, United States.

Environ Sci Technol 2017 Dec;51(24):14472-14482

Land, Air, and Water Resources, University of California , Davis, California 95616, United States.

Land-cover change from energy development, including solar energy, presents trade-offs for land used for the production of food and the conservation of ecosystems. Solar energy plays a critical role in contributing to the alternative energy mix to mitigate climate change and meet policy milestones; however, the extent that solar energy development on nonconventional surfaces can mitigate land scarcity is understudied. Here, we evaluate the land sparing potential of solar energy development across four nonconventional land-cover types: the built environment, salt-affected land, contaminated land, and water reservoirs (as floatovoltaics), within the Great Central Valley (CV, CA), a globally significant agricultural region where land for food production, urban development, and conservation collide. Furthermore, we calculate the technical potential (TWh year) of these land sparing sites and test the degree to which projected electricity needs for the state of California can be met therein. In total, the CV encompasses 15% of CA, 8415 km of which was identified as potentially land-sparing for solar energy development. These areas comprise a capacity-based energy potential of at least 17 348 TWh year for photovoltaic (PV) and 2213 TWh year for concentrating solar power (CSP). Accounting for technology efficiencies, this exceeds California's 2025 projected electricity demands up to 13 and 2 times for PV and CSP, respectively. Our study underscores the potential of strategic renewable energy siting to mitigate environmental trade-offs typically coupled with energy sprawl in agricultural landscapes.
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http://dx.doi.org/10.1021/acs.est.7b05110DOI Listing
December 2017

Environmental change, shifting distributions, and habitat conservation plans: A case study of the California gnatcatcher.

Ecol Evol 2017 12 28;7(23):10326-10338. Epub 2017 Oct 28.

University of California Riverside CA USA.

Many species have already experienced distributional shifts due to changing environmental conditions, and analyzing past shifts can help us to understand the influence of environmental stressors on a species as well as to analyze the effectiveness of conservation strategies. We aimed to (1) quantify regional habitat associations of the California gnatcatcher (); (2) describe changes in environmental variables and gnatcatcher distributions through time; (3) identify environmental drivers associated with habitat suitability changes; and (4) relate habitat suitability changes through time to habitat conservation plans. Southern California's Western Riverside County (WRC), an approximately 4,675 km conservation planning area. We assessed environmental correlates of distributional shifts of the federally threatened California gnatcatcher (hereafter, gnatcatcher) using partitioned Mahalanobis niche modeling for three time periods: 1980-1997, 1998-2003, and 2004-2012, corresponding to distinct periods in habitat conservation planning. Highly suitable gnatcatcher habitat was consistently warmer and drier and occurred at a lower elevation than less suitable habitat and consistently had more CSS, less agriculture, and less chaparral. However, its relationship to development changed among periods, mainly due to the rapid change in this variable. Likewise, other aspects of highly suitable habitat changed among time periods, which became cooler and higher in elevation. The gnatcatcher lost 11.7% and 40.6% of highly suitable habitat within WRC between 1980-1997 to 1998-2003, and 1998-2003 to 2004-2012, respectively. Unprotected landscapes lost relatively more suitable habitat (-64.3%) than protected landscapes (30.5%). Over the past four decades, suitable habitat loss within WRC, especially between the second and third time periods, was associated with temperature-related factors coupled with landscape development across coastal sage scrub habitat; however, development appears to be driving change more rapidly than climate change. Our study demonstrates the importance of providing protected lands for potential suitable habitat in future scenarios.
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http://dx.doi.org/10.1002/ece3.3482DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5723624PMC
December 2017

Plant hydraulic responses to long-term dry season nitrogen deposition alter drought tolerance in a Mediterranean-type ecosystem.

Oecologia 2016 07 26;181(3):721-31. Epub 2016 Mar 26.

Center for Conservation Biology, University of California Riverside, Riverside, CA, 92521, USA.

Anthropogenic nitrogen (N) deposition represents a significant N input for many terrestrial ecosystems. N deposition can affect plants on scales ranging from photosynthesis to community composition, yet few studies have investigated how changes in N availability affect plant water relations. We tested the effects of N addition on plant water relations, hydraulic traits, functional traits, gas exchange, and leaf chemistry in a semi-arid ecosystem in Southern California using long-term experimental plots fertilized with N for over a decade. The dominant species were Artemisia california and Salvia mellifera at Santa Margarita Ecological Reserve and Adenostoma fasciculatum and Ceanothus greggii at Sky Oaks Field Station. All species, except Ceanothus, showed increased leaf N concentration, decreased foliar carbon to N ratio, and increased foliar N isotopic composition with fertilization, indicating that added N was taken up by study species, yet each species had a differing physiological response to long-term N addition. Dry season predawn water potentials were less negative with N addition for all species except Adenostoma, but there were no differences in midday water potentials, or wet season water potentials. Artemisia was particularly responsive, as N addition increased stem hydraulic conductivity, stomatal conductance, and leaf carbon isotopic composition, and decreased wood density. The alteration of water relations and drought resistance parameters with N addition in Artemisia, as well as Adenostoma, Ceanothus, and Salvia, indicate that N deposition can affect the ability of native Southern California shrubs to respond to drought.
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http://dx.doi.org/10.1007/s00442-016-3609-2DOI Listing
July 2016

Solar energy development impacts on land cover change and protected areas.

Proc Natl Acad Sci U S A 2015 Nov 19;112(44):13579-84. Epub 2015 Oct 19.

Center for Conservation Biology, University of California, Riverside, CA 92521; Department of Biology, University of California, Riverside, CA 92521; Department of Plant Pathology, University of California, Riverside, CA 92521.

Decisions determining the use of land for energy are of exigent concern as land scarcity, the need for ecosystem services, and demands for energy generation have concomitantly increased globally. Utility-scale solar energy (USSE) [i.e., ≥ 1 megawatt (MW)] development requires large quantities of space and land; however, studies quantifying the effect of USSE on land cover change and protected areas are limited. We assessed siting impacts of >160 USSE installations by technology type [photovoltaic (PV) vs. concentrating solar power (CSP)], area (in square kilometers), and capacity (in MW) within the global solar hot spot of the state of California (United States). Additionally, we used the Carnegie Energy and Environmental Compatibility model, a multiple criteria model, to quantify each installation according to environmental and technical compatibility. Last, we evaluated installations according to their proximity to protected areas, including inventoried roadless areas, endangered and threatened species habitat, and federally protected areas. We found the plurality of USSE (6,995 MW) in California is sited in shrublands and scrublands, comprising 375 km(2) of land cover change. Twenty-eight percent of USSE installations are located in croplands and pastures, comprising 155 km(2) of change. Less than 15% of USSE installations are sited in "Compatible" areas. The majority of "Incompatible" USSE power plants are sited far from existing transmission infrastructure, and all USSE installations average at most 7 and 5 km from protected areas, for PV and CSP, respectively. Where energy, food, and conservation goals intersect, environmental compatibility can be achieved when resource opportunities, constraints, and trade-offs are integrated into siting decisions.
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http://dx.doi.org/10.1073/pnas.1517656112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4640750PMC
November 2015

Diurnal patterns of productivity of arbuscular mycorrhizal fungi revealed with the Soil Ecosystem Observatory.

New Phytol 2013 Oct 12;200(2):547-557. Epub 2013 Jul 12.

Center for Conservation Biology, University of California, Riverside, CA, 92521, USA.

Arbuscular mycorrhizal (AM) fungi are the most abundant plant symbiont and a major pathway of carbon sequestration in soils. However, their basic biology, including their activity throughout a 24-h day : night cycle, remains unknown. We employed the in situ Soil Ecosystem Observatory to quantify the rates of diurnal growth, dieback and net productivity of extra-radical AM fungi. AM fungal hyphae showed significantly different rates of growth and dieback over a period of 24 h and paralleled the circadian-driven photosynthetic oscillations observed in plants. The greatest rates (and incidences) of growth and dieback occurred between noon and 18:00 h. Growth and dieback events often occurred simultaneously and were tightly coupled with soil temperature and moisture, suggesting a rapid acclimation of the external phase of AM fungi to the immediate environment. Changes in the environmental conditions and variability of the mycorrhizosphere may alter the diurnal patterns of productivity of AM fungi, thereby modifying soil carbon sequestration, nutrient cycling and host plant success.
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http://dx.doi.org/10.1111/nph.12393DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4288973PMC
October 2013

In situ high-frequency observations of mycorrhizas.

New Phytol 2013 Oct 17;200(1):222-228. Epub 2013 Jun 17.

Center for Conservation Biology, University of California, Riverside, CA, 92521-0334, USA.

Understanding the temporal variation of soil and root dynamics is a major step towards determining net carbon in ecosystems. We describe the installation and structure of an in situ soil observatory and sensing network consisting of an automated minirhizotron with associated soil and atmospheric sensors. Ectomycorrhizal hyphae were digitized daily during 2011 in a Mediterranean climate, high-elevation coniferous forest. Hyphal length was high, but stable during winter in moist and cold soil. As soil began to warm and dry, simultaneous mortality and production indicating turnover followed precipitation events. Mortality continued through the dry season, although some hyphae persisted through the extremes. With autumn monsoons, rapid hyphal re-growth occurred following each event. Relative hyphal length is dependent upon soil temperature and moisture. Soil respiration is related to the daily change in hyphal production, but not hyphal mortality. Continuous sensor and observation systems can provide more accurate assessments of soil carbon dynamics.
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http://dx.doi.org/10.1111/nph.12363DOI Listing
October 2013

Above- and belowground responses to nitrogen addition in a Chihuahuan Desert grassland.

Oecologia 2012 May 1;169(1):177-85. Epub 2011 Nov 1.

Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA.

Increased available soil nitrogen can increase biomass, lower species richness, alter soil chemistry and modify community structure in herbaceous ecosystems worldwide. Although increased nitrogen availability typically increases aboveground production and decreases species richness in mesic systems, the impacts of nitrogen additions on semiarid ecosystems remain unclear. To determine how a semiarid grassland responds to increased nitrogen availability, we examined plant community structure and above- and belowground net primary production in response to long-term nitrogen addition in a desert grassland in central New Mexico, USA. Plots were fertilized annually (10 g N m(-2)) since 1995 and NPP measured from 2004 to 2009. Differences in aboveground NPP between fertilized and control treatments occurred in 2004 following a prescribed fire and in 2006 when precipitation was double the long-term average during the summer monsoon. Presumably, nitrogen only became limiting once drought stress was alleviated. Belowground NPP was also related to precipitation, and greatest root growth occurred the year following the wettest summer, decreasing gradually thereafter. Belowground production was unrelated to aboveground production within years and unrelated to nitrogen enrichment. Species richness changed between years in response to seasonal precipitation variability, but was not altered by nitrogen addition. Community structure did respond to nitrogen fertilization primarily through increased abundance of two dominant perennial grasses. These results were contrary to most nitrogen addition studies that find increased biomass and decreased species richness with nitrogen fertilization. Therefore, factors other than nitrogen deposition, such as fire or drought, may play a stronger role in shaping semiarid grassland communities than soil fertility.
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http://dx.doi.org/10.1007/s00442-011-2173-zDOI Listing
May 2012

First report of the ectomycorrhizal status of boletes on the Northern Yucatan Peninsula, Mexico determined using isotopic methods.

Mycorrhiza 2011 Aug 6;21(6):465-471. Epub 2011 Jan 6.

Center for Conservation Biology, University of California, Riverside, CA, 92521, USA.

Despite their prominent role for tree growth, few studies have examined the occurrence of ectomycorrhizal fungi in lowland, seasonally dry tropical forests (SDTF). Although fruiting bodies of boletes have been observed in a dry tropical forest on the Northern Yucatan Peninsula, Mexico, their occurrence is rare and their mycorrhizal status is uncertain. To determine the trophic status (mycorrhizal vs. saprotrophic) of these boletes, fruiting bodies were collected and isotopically compared to known saprotrophic fungi, foliage, and soil from the same site. Mean δ(15)N and δ(13)C values differed significantly between boletes and saprotrophic fungi, with boletes 8.0‰ enriched and 2.5‰ depleted in (15)N and (13)C, respectively relative to saprotrophic fungi. Foliage was depleted in (13)C relative to both boletes and saprotrophic fungi. Foliar δ(15)N values, on the other hand, were similar to saprotrophic fungi, yet were considerably lower relative to bolete fruiting bodies. Results from this study provide the first isotopic evidence of ectomycorrhizal fungi in lowland SDTF and emphasize the need for further research to better understand the diversity and ecological importance of ectomycorrhizal fungi in these forested ecosystems.
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http://dx.doi.org/10.1007/s00572-010-0355-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3134708PMC
August 2011

Looking deeper into the soil: biophysical controls and seasonal lags of soil CO2 production and efflux.

Ecol Appl 2010 Sep;20(6):1569-82

Department of Environmental Science, Policy, and Management, 137 Mulford Hall, University of California, Berkeley, California 94720, USA.

We seek to understand how biophysical factors such as soil temperature (Ts), soil moisture (theta), and gross primary production (GPP) influence CO2 fluxes across terrestrial ecosystems. Recent advancements in automated measurements and remote-sensing approaches have provided time series in which lags and relationships among variables can be explored. The purpose of this study is to present new applications of continuous measurements of soil CO2 efflux (F0) and soil CO2 concentrations measurements. Here we explore how variation in Ts, theta, and GPP (derived from NASA's moderate-resolution imaging spectroradiometer [MODIS]) influence F0 and soil CO2 production (Ps). We focused on seasonal variation and used continuous measurements at a daily timescale across four vegetation types at 13 study sites to quantify: (1) differences in seasonal lags between soil CO2 fluxes and Ts, theta, and GPP and (2) interactions and relationships between CO2 fluxes with Ts, theta, and GPP. Mean annual Ts did not explain annual F0 and Ps among vegetation types, but GPP explained 73% and 30% of the variation, respectively. We found evidence that lags between soil CO2 fluxes and Ts or GPP provide insights into the role of plant phenology and information relevant about possible timing of controls of autotrophic and heterotrophic processes. The influences of biophysical factors that regulate daily F0 and Ps are different among vegetation types, but GPP is a dominant variable for explaining soil CO2 fluxes. The emergence of long-term automated soil CO2 flux measurement networks provides a unique opportunity for extended investigations into F0 and Ps processes in the near future.
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http://dx.doi.org/10.1890/09-0693.1DOI Listing
September 2010

Water relations of evergreen and drought-deciduous trees along a seasonally dry tropical forest chronosequence.

Oecologia 2010 Dec 24;164(4):881-90. Epub 2010 Jul 24.

Department of Forest Ecology and Management, Swedish University of Agriculture Sciences (SLU), Umea, Sweden.

Seasonally dry tropical forests (SDTF) are characterized by pronounced seasonality in rainfall, and as a result trees in these forests must endure seasonal variation in soil water availability. Furthermore, SDTF on the northern Yucatan Peninsula, Mexico, have a legacy of disturbances, thereby creating a patchy mosaic of different seral stages undergoing secondary succession. We examined the water status of six canopy tree species, representing contrasting leaf phenology (evergreen vs. drought-deciduous) at three seral stages along a fire chronosequence in order to better understand strategies that trees use to overcome seasonal water limitations. The early-seral forest was characterized by high soil water evaporation and low soil moisture, and consequently early-seral trees exhibited lower midday bulk leaf water potentials (Ψ(L)) relative to late-seral trees (-1.01 ± 0.14 and -0.54 ± 0.07 MPa, respectively). Although Ψ(L) did not differ between evergreen and drought-deciduous trees, results from stable isotope analyses indicated different strategies to overcome seasonal water limitations. Differences were especially pronounced in the early-seral stage where evergreen trees had significantly lower xylem water δ(18)O values relative to drought-deciduous trees (-2.6 ± 0.5 and 0.3 ± 0.6‰, respectively), indicating evergreen species used deeper sources of water. In contrast, drought-deciduous trees showed greater enrichment of foliar (18)O (∆(18)O(l)) and (13)C, suggesting lower stomatal conductance and greater water-use efficiency. Thus, the rapid development of deep roots appears to be an important strategy enabling evergreen species to overcome seasonal water limitation, whereas, in addition to losing a portion of their leaves, drought-deciduous trees minimize water loss from remaining leaves during the dry season.
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http://dx.doi.org/10.1007/s00442-010-1725-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2981736PMC
December 2010

Characterizing urbanization, and agricultural and conservation land-use change in Riverside County, California, USA.

Ann N Y Acad Sci 2010 May;1195 Suppl 1:E164-76

Department of Botany and Plant Sciences, University of California, Riverside, California, USA.

Monitoring trends in urbanization and land use related to population growth and changing social and economic conditions is an important tool for developing in land use and habitat conservation policy. We analyzed urbanization and agricultural land-use change in Riverside County, California from 1984 to 2002, comparing maps every two years on the basis of aerial photographs. Matrix analysis combined with information theory was applied to study land type conversion. Results showed that the total area of "Urban and Built-Up Land" increased the most whereas total area of "Prime Farmland" decreased most. Land-use characterized as "Grazing Land,"Farmland of Local Importance," and "Farmland of Statewide Importance" also decreased. Mean patch size also decreased for "Grazing Land,"Water Area,"Other Land," and "Prime Farmland." The diversity of land types decreased dramatically after 1992. Urbanization patterns were different among three city groups (Riverside City, Coachella Valley, and Blythe), indicating the different times for "leapfrog" development in the three areas. Furthermore, the unpredictability and change in composition of land use increased after 1996 due to intensified urbanization. If the current driving forces continue, our model projects that in 2020 the area of "Urban and Built-Up Land" may increase between 25% and 39% in comparison with 2002. Percentages of most agricultural land types are projected to decrease, especially "Farmland of Local Importance,"Prime Farmland," and "Farmland of Statewide Importance." If the county's goal is to preserve agricultural lands and natural biodiversity, while maintaining sustainable development, current land-use policies and practices should be changed. This study demonstrates new useful methods for monitoring and detection of change of land-use processes.
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http://dx.doi.org/10.1111/j.1749-6632.2009.05403.xDOI Listing
May 2010

Carbon stable isotopic composition of soluble sugars in Tillandsia epiphytes varies in response to shifts in habitat.

Oecologia 2010 Jul 13;163(3):583-90. Epub 2010 Feb 13.

Biology Department, University of California, Riverside, CA 92521, USA.

We studied C stable isotopic composition (delta(13)C) of bulk leaf tissue and extracted sugars of four epiphytic Tillandsia species to investigate flexibility in the use of crassulacean acid metabolism (CAM) and C(3) photosynthetic pathways. Plants growing in two seasonally dry tropical forest reserves in Mexico that differ in annual precipitation were measured during wet and dry seasons, and among secondary, mature, and wetland forest types within each site. Dry season sugars were more enriched in (13)C than wet season sugars, but there was no seasonal difference in bulk tissues. Bulk tissue delta(13)C differed by species and by forest type, with values from open-canopied wetlands more enriched in (13)C than mature or secondary forest types. The shifts within forest habitat were related to temporal and spatial changes in vapor pressure deficits (VPD). Modeling results estimate a possible 4% increase in the proportional contribution of the C(3) pathway during the wet season, emphasizing that any seasonal or habitat-mediated variation in photosynthetic pathway appears to be quite moderate and within the range of isotopic effects caused by variation in stomatal conductance during assimilation through the C(3) pathway and environmental variation in VPD. C isotopic analysis of sugars together with bulk leaf tissue offers a useful approach for incorporating short- and long-term measurements of C isotope discrimination during photosynthesis.
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http://dx.doi.org/10.1007/s00442-010-1577-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2886131PMC
July 2010

Ecosystem CO2 fluxes of arbuscular and ectomycorrhizal dominated vegetation types are differentially influenced by precipitation and temperature.

New Phytol 2010 Jan 13;185(1):226-36. Epub 2009 Oct 13.

Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, USA.

Here, we explore how interannual variations in environmental factors (i.e. temperature, precipitation and light) influence CO(2) fluxes (gross primary production and ecosystem respiration) in terrestrial ecosystems classified by vegetation type and the mycorrhizal type of dominant plants (arbuscular mycorrhizal (AM) or ectomycorrhizal (EM)). We combined 236 site-year measurements of terrestrial ecosystem CO(2) fluxes and environmental factors from 50 eddy-covariance flux tower sites with information about climate, vegetation type and dominant plant species. Across large geographical distances, interannual variations in ecosystem CO(2) fluxes for EM-dominated sites were primarily controlled by interannual variations in mean annual temperature. By contrast, interannual variations in ecosystem CO(2) fluxes at AM-dominated sites were primarily controlled by interannual variations in precipitation. This study represents the first large-scale assessment of terrestrial CO(2) fluxes in multiple vegetation types classified according to dominant mycorrhizal association. Our results support and complement the hypothesis that bioclimatic conditions influence the distribution of AM and EM systems across large geographical distances, which leads to important differences in the major climatic factors controlling ecosystem CO(2) fluxes.
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http://dx.doi.org/10.1111/j.1469-8137.2009.03040.xDOI Listing
January 2010

Evidence of old carbon used to grow new fine roots in a tropical forest.

New Phytol 2009 ;182(3):710-718

Center for Conservation Biology, University of California, Riverside, CA 92521, USA.

In this study, we explore how a hurricane disturbance influenced carbon allocation for the production of new fine roots. Before and after a hurricane, we measured the age of carbon (time since fixation from the atmosphere) in fine root structural tissues using natural abundance radiocarbon (14C) measured by accelerator mass spectrometry. Roots were sampled from five seasonally dry tropical forests ranging in age from 6 yr to a mature forest. Structural carbon in combined live + dead roots picked from soil cores sampled 1 month before the hurricane had mean ages ranging from 4 to 11 yr, whereas live roots alone had ages of 1-2 yr. Structural carbon in new live fine roots produced over a period lasting from 3 wk before the hurricane to 2 months after the event had mean ages of between 2 and 10 yr. Contrary to expectations, our results showed that plants allocate long-lived storage carbon pools to the production of new fine roots after canopy defoliation and root mortality. The age of the carbon allocated for new roots increased with forest age and forest above-ground biomass, suggesting an adaptation of plants to survive and recover from severe disturbances.
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http://dx.doi.org/10.1111/j.1469-8137.2009.02789.xDOI Listing
July 2009

Environmental sensor networks in ecological research.

New Phytol 2009 ;182(3):589-607

School of Engineering, University of California, Merced, CA 95344, USA.

Environmental sensor networks offer a powerful combination of distributed sensing capacity, real-time data visualization and analysis, and integration with adjacent networks and remote sensing data streams. These advances have become a reality as a combined result of the continuing miniaturization of electronics, the availability of large data storage and computational capacity, and the pervasive connectivity of the Internet. Environmental sensor networks have been established and large new networks are planned for monitoring multiple habitats at many different scales. Projects range in spatial scale from continental systems designed to measure global change and environmental stability to those involved with the monitoring of only a few meters of forest edge in fragmented landscapes. Temporal measurements have ranged from the evaluation of sunfleck dynamics at scales of seconds, to daily CO2 fluxes, to decadal shifts in temperatures. Above-ground sensor systems are partnered with subsurface soil measurement networks for physical and biological activity, together with aquatic and riparian sensor networks to measure groundwater fluxes and nutrient dynamics. More recently, complex sensors, such as networked digital cameras and microphones, as well as newly emerging sensors, are being integrated into sensor networks for hierarchical methods of sensing that promise a further understanding of our ecological systems by revealing previously unobservable phenomena.
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http://dx.doi.org/10.1111/j.1469-8137.2009.02811.xDOI Listing
July 2009

Topographic position modulates the mycorrhizal response of oak trees to interannual rainfall variability.

Ecology 2009 Mar;90(3):649-62

Center for Conservation Biology, The University of California, Riverside, California 92521-0124, USA.

California coast live oak (Quercus agrifolia) forms tripartite symbiotic associations with arbuscular (AMF) and ectomycorrhizal (EMF) fungi. We selected oak individuals differing in topographic position and depth to groundwater (mesic valley vs. xeric hill sites) to investigate changes of tree mycorrhizal status in response to interannual rainfall variability. EMF root colonization, as well as hyphal abundance and viability in upper rhizosphere soil (0-30 cm), were negatively affected by severe multi-year drought, although not to the same extent in each topographic location. Oak trees growing in hill sites showed EMF colonization levels <1% in upper roots during drought. By contrast, oaks in valley sites maintained much higher EMF colonization (>19%) in upper roots during drought. EMF root colonization increased sharply at both topographic positions during the ensuing wet year (78% in valley, 49% in hill), which indicates that the mycorrhizal status of roots in upper rhizosphere soil is highly responsive to interannual rainfall variability. Across sites and years, percentage EMF colonization and soil hyphal density and viability were strongly positively correlated with soil moisture potential, but percentage AMF root colonization was not. Interestingly, changes in percentage EMF root colonization and density of viable hyphae between a wet and a dry year were proportionally much greater in xeric hill sites than in mesic valley sites. The mycorrhizal status of oak trees was particularly responsive to changes in soil moisture at the hill sites, where roots in upper rhizosphere soil shifted from almost exclusively AMF during severe drought to predominantly EMF during the ensuing wet year. By contrast, the mycorrhizal status of oaks in the valley sites was less strongly coupled to current meteorological conditions, as roots in upper soil layers remained predominantly EMF during both a dry and a wet year. Canopy shading and hydraulic lift by oaks in valley sites likely contributed to maintain the integrity and viability of EMF roots and extraradical hyphae in upper rhizosphere soil during extended drought. Our results suggest that oak woodlands in water-limited ecosystems may become increasingly reliant on the AMF symbiosis under future climate change scenarios for the U.S. southwest and other world regions.
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http://dx.doi.org/10.1890/07-1696.1DOI Listing
March 2009

Bidirectional water flows through the soil-fungal-plant mycorrhizal continuum.

Authors:
Michael F Allen

New Phytol 2009 ;182(2):290-293

Center for Conservation Biology, University of California, Riverside, CA 92521, USA (tel +1 951 8275494; email

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http://dx.doi.org/10.1111/j.1469-8137.2009.02815.xDOI Listing
July 2009

Increasing demands on limited water resources: Consequences for two endangered plants in Amargosa Valley, USA.

Am J Bot 2009 Mar 12;96(3):620-6. Epub 2009 Feb 12.

Center for Conservation Biology, University of California-Riverside, Riverside, California 92521 USA.

Recent population expansion throughout the Southwest United States has created an unprecedented demand for already limited water resources, which may have severe consequences on the persistence of some species. Two such species are the federally protected Nitrophila mohavensis (Chenopodiaceae) and Grindelia fraxino-pratensis (Asteraceae) found in Amargosa Valley, one valley east of Death Valley, California. Because both species are federally protected, no plant material could be harvested for analysis. We therefore used a chamber system to collect transpired water for isotopic analysis. After a correction for isotopic enrichment during transpiration, δ(18)O values of plant xylem water were significantly different between N. mohavensis and G. fraxino-pratensis throughout the study. Using a multisource mixing model, we found that both N. mohavensis and G. fraxino-pratensis used soil moisture near the soil surface in early spring when surface water was present. However, during the dry summer months, G. fraxino-pratensis tracked soil moisture to deeper depths, whereas N. mohavensis continued to use soil moisture near the soil surface. These results indicate that pumping groundwater and subsequently lowering the water table may directly prevent G. fraxino-pratensis from accessing water, whereas these same conditions may indirectly affect N. mohavensis by reducing surface soil moisture and thus its ability to access water.
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http://dx.doi.org/10.3732/ajb.0800181DOI Listing
March 2009

Environmental controls and the influence of vegetation type, fine roots and rhizomorphs on diel and seasonal variation in soil respiration.

New Phytol 2008 Jul;179(2):460-471

Center for Conservation Biology, University of California, Riverside, CA 92521, USA.

Characterization of spatial and temporal variation of soil respiration coupled with fine root and rhizomorph dynamics is necessary to understand the mechanisms that regulate soil respiration. A dense wireless network array of soil CO2 sensors in combination with minirhizotron tubes was used to continuously measure soil respiration over 1 yr in a mixed conifer forest in California, USA, in two adjacent areas with different vegetation types: an area with woody vegetation (Wv) and an area with scattered herbaceous vegetation (Hv). Annual soil respiration rates and the lengths of fine roots and rhizomorphs were greater at Wv than at Hv. Soil respiration was positively correlated with fine roots and rhizomorphs at Wv but only with fine roots at Hv. Diel and seasonal soil respiration patterns were decoupled with soil temperature at Wv but not at Hv. When decoupled, higher soil respiration rates were observed at increasing temperatures, demonstrating a hysteresis effect. The diel hysteresis at Wv was explained by including the temperature-dependent component of soil respiration and the variation dependent on photosynthetically active radiation. The results show that vegetation type and fine root and rhizomorph dynamics influence soil respiration in addition to changes in light, temperature and moisture.
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http://dx.doi.org/10.1111/j.1469-8137.2008.02481.xDOI Listing
July 2008

Efflux of hydraulically lifted water from mycorrhizal fungal hyphae during imposed drought.

Plant Signal Behav 2008 Jan;3(1):68-71

Center for Conservation Biology; University of California; Riverside, California USA.

Apart from improving plant and soil water status during drought, it has been suggested that hydraulic lift (HL) could enhance plant nutrient capture through the flow of mineral nutrients directly from the soil to plant roots, or by maintaining the functioning of mycorrhizal fungi. We evaluated the extent to which the diel cycle of water availability created by HL covaries with the efflux of HL water from the tips of extramatrical (external) mycorrhizal hyphae, and the possible effects on biogeochemical processes. Phenotypic mycorrhizal fungal variables, such as total and live hyphal lengths, were positively correlated with HL efflux from hyphae, soil water potential (dawn), and plant response variables (foliar (15)N). The efflux of HL water from hyphae was also correlated with bacterial abundance and soil enzyme activity (P), and the moistening of soil organic matter. Such findings indicate that the efflux of HL water from the external mycorrhizal mycelia may be a complementary explanation for plant nutrient acquisition and survival during drought.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2633966PMC
http://dx.doi.org/10.4161/psb.3.1.4924DOI Listing
January 2008

Corrigendum to: Plant isotopic composition provides insight into mechanisms underlying growth stimulation by AM fungi in a semiarid environment.

Funct Plant Biol 2007 Sep;34(9):860

Departamento de Conservación de Suelos y Aguas, Centro de Edafología y Biología Aplicada del Segura-Consejo Superior de Investigaciones Científicas (CEBAS-CSIC), PO Box 4195, Campus Universitario de Espinardo 30100 Murcia, Spain.

We hypothesised that improved plant water status and enhanced transpiration are key mechanisms involved in plant growth stimulation by native arbuscular mycorrhizal fungi (AMF) in semiarid calcareous soils. Seedlings of the dryland shrubs Pistacia lentiscus L. and Retama sphaerocarpa L. were pre-inoculated with a mixture of eight native Glomus spp. fungi, or left un-inoculated, before transplanting into a degraded site in south-eastern Spain. Pre-inoculated Pistacia and Retama shrubs grew faster after transplanting, despite spontaneous colonisation of control plants by local AMF. Pre-inoculation enhanced shoot water content and shoot ´N in both shrub species. Increased potassium uptake and improved water relations were key mechanisms behind growth stimulation by native AMF in Pistacia. Shoot ´O (a proxy measure of stomatal conductance) was significantly less negative in AMF-inoculated than in control Pistacia seedlings, indicating enhanced cumulative transpiration in the former. In contrast, shoot ´O was unaffected by AMF inoculation in Retama, a leafless leguminous shrub with photosynthetic stems. Growth stimulation by native AMF in Retama was attributed to increased phosphorus uptake, enhanced atmospheric nitrogen fixation and a largely nutrient-mediated improvement of plant water status. Shoot ´C was not significantly influenced by AMF inoculation in either shrub species, thus suggesting roughly parallel upshifts in photosynthetic and transpiration rates which did not affect plant water use efficiency.
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http://dx.doi.org/10.1071/FP07061_CODOI Listing
September 2007

Plant isotopic composition provides insight into mechanisms underlying growth stimulation by AM fungi in a semiarid environment.

Funct Plant Biol 2007 Aug;34(8):683-691

Departamento de Conservación de Suelos y Aguas, Centro de Edafología y Biología Aplicada del Segura-Consejo Superior de Investigaciones Científicas (CEBAS-CSIC), PO Box 4195, Campus Universitario de Espinardo 30100 Murcia, Spain.

We hypothesised that improved plant water status and enhanced transpiration are key mechanisms involved in plant growth stimulation by native arbuscular mycorrhizal fungi (AMF) in semiarid calcareous soils. Seedlings of the dryland shrubs Pistacia lentiscus L. and Retama sphaerocarpa L. were pre-inoculated with a mixture of eight native Glomus spp. fungi, or left un-inoculated, before transplanting into a degraded site in south-eastern Spain. Pre-inoculated Pistacia and Retama shrubs grew faster after transplanting, despite spontaneous colonisation of control plants by local AMF. Pre-inoculation enhanced shoot water content and shoot δN in both shrub species. Increased potassium uptake and improved water relations were key mechanisms behind growth stimulation by native AMF in Pistacia. Shoot δO (a proxy measure of stomatal conductance) was significantly less negative in AMF-inoculated than in control Pistacia seedlings, indicating enhanced cumulative transpiration in the former. In contrast, shoot δO was unaffected by AMF inoculation in Retama, a leafless leguminous shrub with photosynthetic stems. Growth stimulation by native AMF in Retama was attributed to increased phosphorus uptake, enhanced atmospheric nitrogen fixation and a largely nutrient-mediated improvement of plant water status. Shoot δC was not significantly influenced by AMF inoculation in either shrub species, thus suggesting roughly parallel upshifts in photosynthetic and transpiration rates which did not affect plant water use efficiency.
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http://dx.doi.org/10.1071/FP07061DOI Listing
August 2007

Wide geographical and ecological distribution of nitrogen and carbon gains from fungi in pyroloids and monotropoids (Ericaceae) and in orchids.

New Phytol 2007 ;175(1):166-175

Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.

* Stable isotope abundance analyses recently revealed that some European green orchids and pyroloids (Ericaceae) are partially myco-heterotrophic, exploiting mycorrhizal fungi for organic carbon and nitrogen. Here we investigate related species to assess their nutritional mode across various forest and climate types in Germany and California. * C- and N-isotope signatures of five green pyroloids, three green orchids and several obligate myco-heterotrophic species (including the putatively fully myco-heterotrophic Pyrola aphylla) were analysed to quantify the green plants' nutrient gain from their fungal partners and to investigate the constancy of enrichment in (13)C and (15)N of fully myco-heterotrophic plants from diverse taxa and locations relative to neighbouring autotrophic plants. * All green pyroloid and one orchid species showed significant (15)N enrichment, confirming incorporation of fungi-derived N compounds while heterotrophic C gain was detected only under low irradiance in Orthilia secunda. Pyrola aphylla had an isotope signature equivalent to those of fully myco-heterotrophic plants. * It is demonstrated that primarily N gain from mycorrhizal fungi occurred in all taxonomic groups investigated across a wide range of geographical and ecological contexts. The (13)C and (15)N enrichment of obligate myco-heterotrophic plants relative to accompanying autotrophic plants turned out as a fairly constant parameter.
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http://dx.doi.org/10.1111/j.1469-8137.2007.02065.xDOI Listing
October 2007

Common mycorrhizal networks provide a potential pathway for the transfer of hydraulically lifted water between plants.

J Exp Bot 2007 8;58(6):1473-83. Epub 2007 Mar 8.

Centre for Conservation Biology, The University of California, Riverside, CA 92521, USA.

Plant roots may be linked by shared or common mycorrhizal networks (CMNs) that constitute pathways for the transfer of resources among plants. The potential for water transfer by such networks was examined by manipulating CMNs independently of plant roots in order to isolate the role(s) of ectomycorrhizal (EM) and arbuscular mycorrhizal fungal (AMF) networks in the plant water balance during drought (soil water potential -5.9 MPa). Fluorescent tracer dyes and deuterium-enriched water were used to follow the pathways of water transfer from coastal live oak seedlings (Quercus agrifolia Nee; colonized by EM and AMF) conducting hydraulic lift (HL) into the roots of water-stressed seedlings connected only by EM (Q. agrifolia) or AMF networks (Q. agrifolia, Eriogonum fasciculatum Benth., Salvia mellifera Greene, Keckiella antirrhinoides Benth). When connected to donor plants by hyphal linkages, deuterium was detected in the transpiration flux of receiver oak plants, and dye-labelled extraradical hyphae, rhizomorphs, mantles, and Hartig nets were observed in receiver EM oak roots, and in AMF hyphae of Salvia. Hyphal labelling was scarce in Eriogonum and Keckiella since these species are less dependent on AMF. The observed patterns of dye distribution also indicated that only a small percentage of mycorrhizal roots and extraradical hyphae were involved with water transfer among plants. Our results suggest that the movement of water by CMNs is potentially important to plant survival during drought, and that the functional ecophysiological traits of individual mycorrhizal fungi may be a component of this mechanism.
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http://dx.doi.org/10.1093/jxb/erm009DOI Listing
October 2007

Water source partitioning among trees growing on shallow karst soils in a seasonally dry tropical climate.

Oecologia 2007 May 10;152(1):26-36. Epub 2007 Jan 10.

Center for Conservation Biology, University of California, Riverside, CA 92521, USA.

The sources of water used by woody vegetation growing on karst soils in seasonally dry tropical regions are little known. In northern Yucatan (Mexico), trees withstand 4-6 months of annual drought in spite of the small water storage capacity of the shallow karst soil. We hypothesized that adult evergreen trees in Yucatan tap the aquifer for a reliable supply of water during the prolonged dry season. The naturally occurring concentration gradients in oxygen and hydrogen stable isotopes in soil, bedrock, groundwater and plant stem water were used to determine the sources of water used by native evergreen and drought-deciduous tree species. While the trees studied grew over a permanent water table (9-20 m depth), pit excavation showed that roots were largely restricted to the upper 2 m of the soil/bedrock profile. At the peak of the dry season, the delta(18)O signatures of potential water sources for the vegetation ranged from 4.1 +/- 1.1 per thousand in topsoil to -4.3 +/- 0.1 per thousand in groundwater. The delta(18)O values of tree stem water ranged from -2.8 +/- 0.3 per thousand in Talisia olivaeformis to 0.8 +/- 1 per thousand in Ficus cotinifolia, demonstrating vertical partitioning of soil/bedrock water among tree species. Stem water delta(18)O values were significantly different from that of groundwater for all the tree species investigated. Stem water samples plotted to the right of the meteoric water line, indicating utilization of water sources subject to evaporative isotopic enrichment. Foliar delta(13)C in adult trees varied widely among species, ranging from -25.3 +/- 0.3 per thousand in Enterolobium cyclocarpum to -28.7 +/- 0.4 per thousand in T. olivaeformis. Contrary to initial expectations, data indicate that native trees growing on shallow karst soils in northern Yucatan use little or no groundwater and depend mostly on water stored within the upper 2-3 m of the soil/bedrock profile. Water storage in subsurface soil-filled cavities and in the porous limestone bedrock is apparently sufficient to sustain adult evergreen trees throughout the pronounced dry season.
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http://dx.doi.org/10.1007/s00442-006-0629-3DOI Listing
May 2007

Differential response of delta13C and water use efficiency to arbuscular mycorrhizal infection in two aridland woody plant species.

Oecologia 2003 May 28;135(4):510-5. Epub 2003 Mar 28.

Center for Conservation Biology, The University of California, Riverside, CA 92521-0124, USA.

During a revegetation field experiment in Southeast Spain, we measured foliar carbon isotope ratios (delta13C) and gas exchange parameters in order to evaluate the influence of arbuscular mycorrhizal (AM) infection on the water use efficiency (WUE) of two semiarid woodland species. WUE during drought was significantly enhanced by inoculation with Glomus intraradices in Olea europaea ssp sylvestris, but not in Rhamnus lycioides. While Olea is a long-lived, slow-growing evergreen tree with a conservative water use strategy, Rhamnus is a drought-deciduous shrub with a shorter lifespan; these differences may explain their dissimilar patterns of physiological response to inoculation with the same AM fungus. Differences in delta13C and WUE between Olea and Rhamnus were larger when comparing AM inoculated than non-inoculated seedlings. This result suggests that some of the interspecific variability in delta13C observed for aridland plant communities may be due to different physiological responses to mycorrhization.
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http://dx.doi.org/10.1007/s00442-003-1209-4DOI Listing
May 2003