Publications by authors named "José Ignacio Querejeta"

16 Publications

  • Page 1 of 1

Vertical decoupling of soil nutrients and water under climate warming reduces plant cumulative nutrient uptake, water-use efficiency and productivity.

New Phytol 2021 05 11;230(4):1378-1393. Epub 2021 Mar 11.

Departamento de Conservación de Suelos y Agua, Centro de Edafología y Biología Aplicada del Segura - Consejo Superior de Investigaciones Científicas (CEBAS-CSIC), Murcia, 30100, Spain.

Warming-induced desiccation of the fertile topsoil layer could lead to decreased nutrient diffusion, mobility, mineralization and uptake by roots. Increased vertical decoupling between nutrients in topsoil and water availability in subsoil/bedrock layers under warming could thereby reduce cumulative nutrient uptake over the growing season. We used a Mediterranean semiarid shrubland as model system to assess the impacts of warming-induced topsoil desiccation on plant water- and nutrient-use patterns. A 6 yr manipulative field experiment examined the effects of warming (2.5°C), rainfall reduction (30%) and their combination on soil resource utilization by Helianthemum squamatum shrubs. A drier fertile topsoil ('growth pool') under warming led to greater proportional utilization of water from deeper, wetter, but less fertile subsoil/bedrock layers ('maintenance pool') by plants. This was linked to decreased cumulative nutrient uptake, increased nonstomatal (nutritional) limitation of photosynthesis and reduced water-use efficiency, above-ground biomass growth and drought survival. Whereas a shift to greater utilization of water stored in deep subsoil/bedrock may buffer the negative impact of warming-induced topsoil desiccation on transpiration, this plastic response cannot compensate for the associated reduction in cumulative nutrient uptake and carbon assimilation, which may compromise the capacity of plants to adjust to a warmer and drier climate.
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http://dx.doi.org/10.1111/nph.17258DOI Listing
May 2021

Nutrient limitation determines the suitability of a municipal organic waste for phytomanaging metal(loid) enriched mine tailings with a pine-grass co-culture.

Chemosphere 2019 Jan 25;214:436-444. Epub 2018 Sep 25.

Departamento de Ciencia y Tecnología Agraria, Escuela Técnica Superior de Ingeniería Agronómica, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, E-30203, Cartagena, Spain. Electronic address:

The suitable phytomanaging of mine tailings not only requires an improvement of soil fertility but also the assessment of the biotic interactions between the selected plant species. This study aimed to evaluate the effect of an organic amendment on the response of two plant species of contrasting habit, a tree, Pinus halepensis and a grass, Piptatherum miliaceum growing on a metal(loid)-contaminated substrate collected from mine tailings. Pots containing single plant individuals or their combination, with and without organic amendment (at 10% rate), were established and grown in a greenhouse for 13 months. Plant biomass, foliar ionome, leaf δN and metal(loid) concentrations were measured at the end of the experiment. The amendment alleviated P deficiency in the substrate and strongly stimulated biomass production by both plant species (10-fold for pine; 90-fold for the grass), leading to more balanced N/P ratios in leaves (especially for the grass). Co-culture with the grass negatively affected pine growth, decreasing total biomass and leaf δN values and inducing severe N deficiency (leaf N/P ratio<10). In contrast, co-culture with pine improved the nutrient status and growth of the grass, but only under non-amended conditions. Needle metal(loid) concentrations in P. halepensis were affected by both amendment addition and co-culture with the grass. High biomass growth with low metal(loid) concentrations in P. miliaceum leaves for the amended treatment makes this grass species suitable for the phytomanagement of metal(loid) polluted tailings, since it achieves high biomass production together with low concentrations of metal(loid)s in edible/senescent parts.
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http://dx.doi.org/10.1016/j.chemosphere.2018.09.147DOI Listing
January 2019

Poor plant performance under simulated climate change is linked to mycorrhizal responses in a semiarid shrubland.

J Ecol 2018 May 16;106(3):960-976. Epub 2017 Oct 16.

Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), Murcia, Spain.

Warmer and drier conditions associated with ongoing climate change will increase abiotic stress for plants and mycorrhizal fungi in drylands worldwide, thereby potentially reducing vegetation cover and productivity and increasing the risk of land degradation and desertification. Rhizosphere microbial interactions and feedbacks are critical processes that could either mitigate or aggravate the vulnerability of dryland vegetation to forecasted climate change.We conducted a four-year manipulative study in a semiarid shrubland in the Iberian Peninsula to assess the effects of warming (~2.5ºC; W), rainfall reduction (~30%; RR) and their combination (W+RR) on the performance of native shrubs () and their associated mycorrhizal fungi.Warming (W and W+RR) decreased the net photosynthetic rates of shrubs by ~31% despite concurrent increases in stomatal conductance (~33%), leading to sharp decreases (~50%) in water use efficiency. Warming also advanced growth phenology, decreased leaf nitrogen and phosphorus contents per unit area, reduced shoot biomass production by ~36% and decreased survival during a dry year in both W and W+RR plants. Plants under RR showed more moderate decreases (~10-20%) in photosynthesis, stomatal conductance and shoot growth.Warming, RR and W+RR altered ectomycorrhizal fungal (EMF) community structure and drastically reduced the relative abundance of EMF sequences obtained by high-throughput sequencing, a response associated with decreases in the leaf nitrogen, phosphorus and dry matter contents of their host plants. In contrast to EMF, the community structure and relative sequence abundances of other non-mycorrhizal fungal guilds were not significantly affected by the climate manipulation treatments. Our findings highlight the vulnerability of both native plants and their symbiotic mycorrhizal fungi to climate warming and drying in semiarid shrublands, and point to the importance of a deeper understanding of plant-soil feedbacks to predict dryland vegetation responses to forecasted aridification. The interdependent responses of plants and ectomycorrhizal fungi to warming and rainfall reduction may lead to a detrimental feedback loop on vegetation productivity and nutrient pool size, which could amplify the adverse impacts of forecasted climate change on ecosystem functioning in EMF-dominated drylands.
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http://dx.doi.org/10.1111/1365-2745.12888DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6071827PMC
May 2018

Importance of intra- and interspecific plant interactions for the phytomanagement of semiarid mine tailings using the tree species Pinus halepensis.

Chemosphere 2017 Nov 7;186:405-413. Epub 2017 Aug 7.

Departamento de Ciencia y Tecnología Agraria, Escuela Técnica Superior de Ingeniería Agronómica, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, E-30203, Cartagena, Spain. Electronic address:

The objective of this work was to evaluate the effects of plant interactions (intra- and interspecific) on the growth and metal(loid) uptake of the tree species Pinus halepensis to determine its suitability for the phytomanagement of semiarid mine tailings. The pioneer tailings colonizer grass Piptatherum miliaceum was selected for assessing interspecific interactions. The experiment was conducted following a pot experimental design employing mine tailings soil. Pots containing single individuals of P. halepensis or P. miliaceum and pots containing combinations with pines (two pines per pot, or one pine and one grass per pot) were used. The analyses included the determination of plant biomass, foliar element status and stable isotope composition, metal(loid) uptake and its translocation to different plant organs. P. halepensis strongly favoured the growth of P. miliaceum by increasing 9-fold the latter's biomass and alleviating its P limitation. In this interspecific treatment P. halepensis showed a strong N limitation (N/P = 7), which negatively affected its growth, (to about half the biomass of that obtained for the other treatments) and exhibited a significant increase in some metals translocation (especially Cd) into aerial parts. Interestingly, P. miliaceum showed a decrease in the root to leaves translocation factor for most of metals when growing together with pines. The effects of the intraespecific combination on growth and metal uptake in P. halepensis were less relevant than those obtained for the interspecific one. Further research should be focused on testing the behaviour of plant co-cultures under the addition of N or P amendments which could alleviate the negative effects of plant competition.
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http://dx.doi.org/10.1016/j.chemosphere.2017.08.010DOI Listing
November 2017

Nurse plants transfer more nitrogen to distantly related species.

Ecology 2017 May 19;98(5):1300-1310. Epub 2017 Apr 19.

Departamento de Ecología de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, A.P. 70-275, C.P. 04510, México D.F, México.

Plant facilitative interactions enhance co-occurrence between distant relatives, partly due to limited overlap in resource requirements. We propose a different mechanism for the coexistence of distant relatives based on positive interactions of nutrient sharing. Nutrients move between plants following source-sink gradients driven by plant traits that allow these gradients to establish. Specifically, nitrogen (N) concentration gradients can arise from variation in leaf N content across plants species. As many ecologically relevant traits, we hypothesize that leaf N content is phylogenetically conserved and can result in N gradients promoting N transfer among distant relatives. In a Mexican desert community governed by facilitation, we labelled nurse plants (Mimosa luisana) with N and measured its transfer to 14 other species in the community, spanning the range of phylogenetic distances to the nurse plant. Nurses established steeper N source-sink gradients with distant relatives, increasing N transfer toward these species. Nutrient sharing may provide long-term benefits to facilitated plants and may be an overlooked mechanism maintaining coexistence and increasing the phylogenetic diversity of plant communities.
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http://dx.doi.org/10.1002/ecy.1771DOI Listing
May 2017

Metal(loid) allocation and nutrient retranslocation in Pinus halepensis trees growing on semiarid mine tailings.

Sci Total Environ 2014 Jul 16;485-486:406-414. Epub 2014 Apr 16.

Universidad Politecnica de Cartagena, Departamento de Ciencia y Tecnología Agraria Paseo Alfonso XIII, Cartagena 48. 30203, Spain.

The goal of this study was to evaluate internal metal(loid) cycling and the risk of metal(loid) accumulation in litter from Pinus halepensis trees growing at a mine tailing disposal site in semiarid Southeast Spain. Internal nutrient retranslocation was also evaluated in order to gain insight into the ability of pine trees to cope with the low-fertility soil conditions at the tailings. We measured metal(loid) concentrations in the foliage (young and old needles), woody stems and fresh leaf litter of pine trees growing on tailings. The nutrient status and stable isotope composition of pine foliage (δ(13)C, δ(15)N, δ(18)O as indicators of photosynthesis and water use efficiency) were also analyzed. Tailing soil properties in vegetation patches and in adjacent bare soil patches were characterized as well. Significant amounts of metal(loid)s such us Cd, Cu, Pb and Sb were immobilized in the woody stems of Pinus halepensis trees growing on tailings. Leaf litterfall showed high concentrations of As, Cd, Sb, Pb and Zn, which thereby return to the soil. However, water extractable metal(loid) concentrations in tailing soils were similar between vegetation patches (mineral soil under the litter layer) and bare soil patches. The pines growing on mine tailings showed very low foliar P concentrations in all leaf age classes, which suggests severe P deficiency. Young (current year) needles showed lower accumulation of metal(loid)s, higher nutrient concentrations (P and K), and higher water use efficiency (as indicated by and δ(13)C and δ(18)O data) than older needles. Substantial nutrient resorption occurred before leaf litterfall, with 46% retranslocation efficiency for P and 89% for K. In conclusion, phytostabilization of semiarid mine tailings with Pinus halepensis is feasible but would require careful monitoring of the trace elements released from litterfall, in order to assess the long term risk of metal(loid) transfer to the food chain.
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http://dx.doi.org/10.1016/j.scitotenv.2014.03.116DOI Listing
July 2014

Usefulness of pioneer vegetation for the phytomanagement of metal(loid)s enriched tailings: grasses vs. shrubs vs. trees.

J Environ Manage 2014 Jan 20;133:51-8. Epub 2013 Dec 20.

Universidad Politecnica de Cartagena, Departamento de Ciencia y Tecnología Agraria, Paseo Alfonso XIII 48, ES-30203 Cartagena, Spain. Electronic address:

The goal of this work was to assess the selection of the most suitable combination of plant species for the phytomanagement of mine tailings, by comparing among different plant life-forms (grasses, shrubs and trees). A comparison on induced rhizosphere changes generated by four plant species (the grass Piptatherum miliaceum, the shrub Helichrysum decumbens, and the trees, Pinus halepensis and Tetraclinis articulata) and high density vegetation patches (fertility islands) at a mine tailing located at Southeast Spain and the description of their physiological status employing stable isotopes analyses were carried out. The edaphic niches for plant growth were determined by salinity, organic matter and total soil nitrogen while metal(loid)s concentrations played a minor role. Induced changes in plant rhizospheres had a significant impact in soil microbiology. While grasses and shrubs may play an important role in primary ecological succession, trees seem to be the key to the development of fertility islands. The low δ(15)N values (-8.00‰) in P. halepensis needles may reflect higher ectomycorrhizal dependence. Large differences in leaf δ(18)O among the plant species indicated contrasting and complementary water acquisition strategies. Leaf δ(13)C values (-27.6‰) suggested that T. articulata had higher water use efficiency than the rest of species (-29.9‰). The implement of a diverse set of plant species with contrasting life forms for revegetating tailings may result in a more efficient employment of water resources and a higher biodiversity not only in relation to flora but soil microbiology too.
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http://dx.doi.org/10.1016/j.jenvman.2013.12.001DOI Listing
January 2014

Isotopes reveal contrasting water use strategies among coexisting plant species in a Mediterranean ecosystem.

New Phytol 2012 Oct 23;196(2):489-496. Epub 2012 Aug 23.

Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), Campus Universitario de Espinardo, PO Box 164, 30100, Murcia, Spain.

Variation in the stable carbon and oxygen isotope composition (δ13C, Δ18O) of co-occurring plant species may reflect the functional diversity of water use strategies present in natural plant communities. We investigated the patterns of water use among 10 coexisting plant species representing diverse taxonomic groups and life forms in semiarid southeast Spain by measuring their leaf δ13C and Δ18O, the oxygen isotope ratio of stem water and leaf gas exchange rates. Across species, Δ18O was tightly negatively correlated with stomatal conductance (gs), whereas δ13C was positively correlated with intrinsic water use efficiency (WUEi). Broad interspecific variation in Δ18O, δ13C and WUEi was largely determined by differences in gs, as indicated by a strong positive correlation between leaf δ13C and Δ18O across species The 10 co-occurring species segregated along a continuous ecophysiological gradient defined by their leaf δ13C and Δ18O, thus revealing a wide spectrum of stomatal regulation intensity and contrasting water use strategies ranging from 'profligate/opportunistic' (high gs, low WUEi) to 'conservative' (low gs, high WUEi). Coexisting species maintained their relative isotopic rankings in 2 yr with contrasting rainfall, suggesting the existence of species-specific 'isotopic niches' that reflect ecophysiological niche segregation in dryland plant communities.
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http://dx.doi.org/10.1111/j.1469-8137.2012.04276.xDOI Listing
October 2012

Stand structure modulates the long-term vulnerability of Pinus halepensis to climatic drought in a semiarid Mediterranean ecosystem.

Plant Cell Environ 2012 Jun 30;35(6):1026-39. Epub 2011 Dec 30.

Centro de Edafología y Biología Aplicada del Segura, Campus Universitario de Espinardo, 30100 Murcia, Spain.

We investigated whether stand structure modulates the long-term physiological performance and growth of Pinus halepensis Mill. in a semiarid Mediterranean ecosystem. Tree radial growth and carbon and oxygen stable isotope composition of latewood (δ(13)C(LW) and δ(18)O(LW), respectively) from 1967 to 2007 were measured in P. halepensis trees from two sharply contrasting stand types: open woodlands with widely scattered trees versus dense afforested stands. In both stand types, tree radial growth, δ(13)C(LW) and δ(18)O(LW) were strongly correlated with annual rainfall, thus indicating that tree performance in this semiarid environment is largely determined by inter-annual changes in water availability. However, trees in dense afforested stands showed consistently higher δ(18)O(LW) and similar δ(13)C(LW) values compared with those in neighbouring open woodlands, indicating lower stomatal conductance and photosynthesis rates in the former, but little difference in water use efficiency between stand types. Trees in dense afforested stands were more water stressed and showed lower radial growth, overall suggesting greater vulnerability to drought and climate aridification compared with trees in open woodlands. In this semiarid ecosystem, the negative impacts of intense inter-tree competition for water on P. halepensis performance clearly outweigh potential benefits derived from enhanced infiltration and reduced run-off losses in dense afforested stands.
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http://dx.doi.org/10.1111/j.1365-3040.2011.02469.xDOI Listing
June 2012

No tillage affects the phosphorus status, isotopic composition and crop yield of Phaseolus vulgaris in a rain-fed farming system.

J Sci Food Agric 2011 Jan;91(2):268-72

CSIC, Centro de Edafología y Biología Aplicada del Segura, Department of Soil and Water Conservation, PO Box 164, Campus de Espinardo, E-30100 Murcia, Spain.

Background: Conservation tillage promotes the accretion of soil organic matter and often leads to improved soil fertility and moisture availability. However, few studies have looked at the physiological response of crop plants to different tillage practices. It was therefore hypothesised that measuring the nutrient concentrations and stable isotope composition (δ(13)C, δ(18)O, δ(15)N) of shoots could help evaluate the physiological response of common bean (Phaseolus vulgaris L.) to different tillage treatments (no tillage (NT) and mouldboard ploughing (MP)) in a rain-fed farming system in northern Mexico.

Results: NT significantly enhanced shoot phosphorus concentration in bean plants. Tillage exerted a negative effect on the extent of root colonisation (%) by arbuscular mycorrhizal fungi (AMF). Lower shoot δ(18)O but unchanged δ(13)C values in plants from the NT system suggest enhanced stomatal conductance but also enhanced photosynthetic rate, which overall resulted in unchanged water use efficiency. Bean plants in the NT system showed lower shoot δ(15)N values, which suggests that a larger proportion of total plant nitrogen was obtained through atmospheric nitrogen fixation in this treatment.

Conclusion: Greater diversity of AMF soil communities and heavier colonisation of roots by AMF in the NT compared with the MP system appeared to contribute to improved crop nutrition, water relations and yield in this rain-fed agroecosystem.
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http://dx.doi.org/10.1002/jsfa.4180DOI Listing
January 2011

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

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 transfer via ectomycorrhizal fungal hyphae to conifer seedlings.

Mycorrhiza 2007 Jul 1;17(5):439-447. Epub 2007 Mar 1.

Departamento de Conservación de Suelos y Aguas, Centro de Edafología y Biología Aplicada del Segura-CSIC, Campus de Espinardo, P.O. Box 4195, Murcia, 30100, Spain.

Little is known about water transfer via mycorrhizal hyphae to plants, despite its potential importance in seedling establishment and plant community development, especially in arid environments. Therefore, this process was investigated in the study reported in this paper in laboratory-based tripartite mesocosms containing the shrub Arctostaphylos viscida (manzanita) and young seedlings of sugar pine (Pinus lambertiana) and Douglas-fir (Pseudotsuga menziesii). The objectives were to determine whether water could be transported through mycorrhizal symbionts shared by establishing conifers and A. viscida and to compare the results obtained using two tracers: the stable isotope deuterium and the dye lucifer yellow carbohydrazide. Water containing the tracers was added to the central compartment containing single manzanita shrubs. The fungal hyphae were then collected as well as plant roots from coniferous seedlings in the other two compartments to determine whether water was transferred via fungal hyphae. In addition, the length of the hyphae and degree of mycorrhizal colonisation were determined. Internal transcribed spacer-restriction fragment length polymorphism (ITS-RFLP) analysis was used to identify the fungal species involved in dye (water) transfer. Results of the stable isotope analysis showed that water is transferred via mycorrhizal hyphae, but isotopically labelled water was only detected in Douglas-fir roots, not in sugar pine roots. In contrast, the fluorescent dye was transported via mycorrhizal hyphae to both Douglas-fir and sugar pine seedlings. Only 1 of 15 fungal morphotypes (identified as Atheliaceae) growing in the mesocosms transferred the dye. Differences were detected in the water transfer patterns indicated by the deuterium and fluorescent dye tracers, suggesting that the two labels are transported by different mechanisms in the same hyphae and/or that different fungal taxa transfer them via different routes to host plants. We conclude that both tracers can provide information on resource transfer between fungi and plants, but we cannot be sure that the dye transfer data provide accurate indications of water transfer rates and patterns. The isotopic tracer provides more direct indications of water movement and is therefore more suitable than the dye for studying water relations of plants and their associated mycorrhizal fungi.
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http://dx.doi.org/10.1007/s00572-007-0119-4DOI Listing
July 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

Direct nocturnal water transfer from oaks to their mycorrhizal symbionts during severe soil drying.

Oecologia 2003 Jan 18;134(1):55-64. Epub 2002 Oct 18.

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

Symbiotic mycorrhizal fungi play an important role in the absorption of soil nutrients and water by most plants. It has been suggested that hydraulically lifted water might maintain the integrity of the external mycorrhizal mycelium during drought. We tested this hypothesis in the obligately mycorrhizal species, coast live oak (Quercus agrifolia), using a microcosm system that separated the effects of hydraulic lift in roots from those in the external mycelium. Mycorrhizal oak seedlings were established in microcosms comprising three discrete compartments for (1) upper roots, (2) tap roots, and (3) external fungal mycelium. Eight months after planting, a drought treatment was initiated: irrigation to the upper root and fungal chambers was terminated and only irrigation to the taproot compartment was maintained. After 3, 12, 30, 50, 70 and 80 days of drought, tracers were injected into the taproot compartment at dusk. At dawn the following morning, mycorrhizal hyphae (EM and AM) and spores (AM) in upper root and fungal compartments were extensively labeled with the tracers. In contrast, no labeling was observed when tracers were injected into the taproot compartment during daytime. Nocturnal water translocation from plant to mycorrhizal fungi occurred in association with hydraulic lift. Saprotrophic/parasitic fungi in the microcosms were not labeled, suggesting a direct water transfer from plants to their mycorrhizal mutualists and not to other fungi in the soil. Even after prolonged drought (70-80 days), mycorrhizal hyphae persisted in soils with water potential values as low as -20 MPa. Maintaining mycorrhizal activity through direct water translocation could potentially improve the nutrient status of deep-rooted plants during periods when the fertile upper soil is dry.
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http://dx.doi.org/10.1007/s00442-002-1078-2DOI Listing
January 2003