Publications by authors named "Peter Vitousek"

61 Publications

Soil-Food-Environment-Health Nexus for Sustainable Development.

Research (Wash D C) 2021 29;2021:9804807. Epub 2021 Apr 29.

Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, Fujian 361021, China.

Changes in soil properties and processes can influence food and environmental quality, thus, affecting human health and welfare through biogeochemical cascades among soil, food, environment, and human health. However, because many soil properties change much more slowly than do management practices and pollution to soil, the legacy of past influences on soil can have long-term effects on both human health and sustainability. It is essential and urgent to manage soils for health and sustainability through building the soil-food-environment-health nexus.
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http://dx.doi.org/10.34133/2021/9804807DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8152674PMC
April 2021

Nitrogen deposition accelerates soil carbon sequestration in tropical forests.

Proc Natl Acad Sci U S A 2021 Apr;118(16)

Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China;

Terrestrial ecosystem carbon (C) sequestration plays an important role in ameliorating global climate change. While tropical forests exert a disproportionately large influence on global C cycling, there remains an open question on changes in below-ground soil C stocks with global increases in nitrogen (N) deposition, because N supply often does not constrain the growth of tropical forests. We quantified soil C sequestration through more than a decade of continuous N addition experiment in an N-rich primary tropical forest. Results showed that long-term N additions increased soil C stocks by 7 to 21%, mainly arising from decreased C output fluxes and physical protection mechanisms without changes in the chemical composition of organic matter. A meta-analysis further verified that soil C sequestration induced by excess N inputs is a general phenomenon in tropical forests. Notably, soil N sequestration can keep pace with soil C, based on consistent C/N ratios under N additions. These findings provide empirical evidence that below-ground C sequestration can be stimulated in mature tropical forests under excess N deposition, which has important implications for predicting future terrestrial sinks for both elevated anthropogenic CO and N deposition. We further developed a conceptual model hypothesis depicting how soil C sequestration happens under chronic N deposition in N-limited and N-rich ecosystems, suggesting a direction to incorporate N deposition and N cycling into terrestrial C cycle models to improve the predictability on C sink strength as enhanced N deposition spreads from temperate into tropical systems.
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http://dx.doi.org/10.1073/pnas.2020790118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8072245PMC
April 2021

Diversity of putative ericoid mycorrhizal fungi increases with soil age and progressive phosphorus limitation across a 4.1-million-year chronosequence.

FEMS Microbiol Ecol 2021 03;97(3)

Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA 94305-5020, USA.

Ericaceous plants rely on ericoid mycorrhizal fungi for nutrient acquisition. However, the factors that affect the composition and structure of fungal communities associated with the roots of ericaceous plants remain largely unknown. Here, we use a 4.1-million-year (myr) soil chronosequence in Hawaii to test the hypothesis that changes in nutrient availability with soil age determine the diversity and species composition of fungi associated with ericoid roots. We sampled roots of a native Hawaiian plant, Vaccinium calycinum, and used DNA metabarcoding to quantify changes in fungal diversity and community composition. We also used a fertilization experiment at the youngest and oldest sites to assess the importance of nutrient limitation. We found an increase in diversity and a clear pattern of species turnover across the chronosequence, driven largely by putative ericoid mycorrhizal fungi. Fertilization with nitrogen at the youngest site and phosphorus at the oldest site reduced fungal diversity, suggesting a direct role of nutrient limitation. Our results also reveal the presence of novel fungal species associated with Hawaiian Ericaceae and suggest a greater importance of phosphorus availability for communities of ericoid mycorrhizal fungi than is generally assumed.
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http://dx.doi.org/10.1093/femsec/fiab016DOI Listing
March 2021

Quantitative Analysis of Pedogenic Thresholds and Domains in Volcanic Soils.

Ecosystems 2019 Nov 1;22(7):1633-1649. Epub 2019 Apr 1.

Department of Biology, Stanford University, Stanford, CA 94305.

Pedogenic thresholds describe where soil properties or processes change in an abrupt/nonlinear fashion in response to small changes in environmental forcing. Contrastingly, soil process domains refer to the space between thresholds where soil properties are either unchanged, or change gradually, across a broad range of environmental forcing. Here, we test quantitatively for the presence of thresholds in patterns of soil properties across a climatic gradient on soils developed from ~20 ky old basaltic substrate on the Island of Hawai'i. From multiple soil properties, we quantitatively identified a threshold at ~750 mm/y of water balance (precipitation minus potential evapotranspiration), delineating the upper water balance boundary of soil fertility in these soils. From the threshold in the ratio of exchangeable Ca to total Ca we identified the lower water balance boundary of soil fertility in these soils at -1000 mm/y, however this threshold was qualitatively described as it lies near the limit of the climate gradient data where the statistical approach can not be applied. These two results represent the first time that pedogenic thresholds have been identified using statistically rigorous methods and the limitations of said methods, respectively. Comparing the 20 ky soils to soils that developed on basaltic substrates of 1.2 ky, 7.5 ky, 150 ky, and 4100 ky in a time-climate matrix, we found that our quantitative analysis supports previous qualitatively identified thresholds in the soils developed from older substrates. We also identified the 20 ky as the transition from kinetic to supply limitation for plant nutrients in soil in this system.
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http://dx.doi.org/10.1007/s10021-019-00361-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7079697PMC
November 2019

Changes in belowground biodiversity during ecosystem development.

Proc Natl Acad Sci U S A 2019 04 15;116(14):6891-6896. Epub 2019 Mar 15.

Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309.

Belowground organisms play critical roles in maintaining multiple ecosystem processes, including plant productivity, decomposition, and nutrient cycling. Despite their importance, however, we have a limited understanding of how and why belowground biodiversity (bacteria, fungi, protists, and invertebrates) may change as soils develop over centuries to millennia (pedogenesis). Moreover, it is unclear whether belowground biodiversity changes during pedogenesis are similar to the patterns observed for aboveground plant diversity. Here we evaluated the roles of resource availability, nutrient stoichiometry, and soil abiotic factors in driving belowground biodiversity across 16 soil chronosequences (from centuries to millennia) spanning a wide range of globally distributed ecosystem types. Changes in belowground biodiversity during pedogenesis followed two main patterns. In lower-productivity ecosystems (i.e., drier and colder), increases in belowground biodiversity tracked increases in plant cover. In more productive ecosystems (i.e., wetter and warmer), increased acidification during pedogenesis was associated with declines in belowground biodiversity. Changes in the diversity of bacteria, fungi, protists, and invertebrates with pedogenesis were strongly and positively correlated worldwide, highlighting that belowground biodiversity shares similar ecological drivers as soils and ecosystems develop. In general, temporal changes in aboveground plant diversity and belowground biodiversity were not correlated, challenging the common perception that belowground biodiversity should follow similar patterns to those of plant diversity during ecosystem development. Taken together, our findings provide evidence that ecological patterns in belowground biodiversity are predictable across major globally distributed ecosystem types and suggest that shifts in plant cover and soil acidification during ecosystem development are associated with changes in belowground biodiversity over centuries to millennia.
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http://dx.doi.org/10.1073/pnas.1818400116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6452688PMC
April 2019

Nitrogen dynamics along a climate gradient on geologically old substrate, Kaua'i, Hawai'i.

Oecologia 2019 Jan 30;189(1):211-219. Epub 2018 Oct 30.

Department of Geography, University of California, Santa Barbara, Santa Barbara, CA, 93106, USA.

We evaluated N dynamics on a climate gradient on old (> 4 million year) basaltic substrate on the Island of Kaua'i, Hawai'i, to evaluate the utility of pedogenic thresholds and soil process domains for understanding N cycling in terrestrial ecosystems. Studies of nitrogen dynamics on the climate gradient on a younger basaltic substrate (~ 150,000 year) had found a good match between soil process domains and N cycling processes. Here we measured net N mineralization and nitrification by incubation, and δN of total soil N, to determine whether the soil process domains on the older gradient were equally useful for interpreting N cycling and thereby to explore the general utility of the approach. Net N mineralization varied from 0 to 1.7 mg kg d across the old Kaua'i gradient, and δN varied from + 3 to + 11 /, both ranges similar to those on the younger substrate. However, while the pattern of variation with climate was similar for δN, the highest rates of mineralization on the old gradient occurred where forests were dominated by the native N fixer Acacia koa. This occurred in sites wetter than the process domain associated with high net N mineralization on the gradient on younger substrate. We conclude that soil process domains based on rock-derived nutrients are not always useful for evaluating N dynamics, especially where the distribution of biological N fixers is controlled by factors other than rock-derived nutrients.
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http://dx.doi.org/10.1007/s00442-018-4285-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6323096PMC
January 2019

Combining spectroscopic and isotopic techniques gives a dynamic view of phosphorus cycling in soil.

Nat Commun 2018 08 13;9(1):3226. Epub 2018 Aug 13.

Institute of Agricultural Sciences, ETH Zurich, 8315, Lindau, Switzerland.

Current understanding of phosphorus (P) cycling in soils can be enhanced by integrating previously discrete findings concerning P speciation, exchange kinetics, and the underlying biological and geochemical processes. Here, we combine sequential extraction with P K-edge X-ray absorption spectroscopy and isotopic methods (P and O in phosphate) to characterize P cycling on a climatic gradient in Hawaii. We link P pools to P species and estimate the turnover times for commonly considered P pools. Dissolved P turned over in seconds, resin-extractable P in minutes, NaOH-extractable inorganic P in weeks to months, and HCl-extractable P in years to millennia. Furthermore, we show that in arid-zone soils, some primary mineral P remains even after 150 ky of soil development, whereas in humid-zone soils of the same age, all P in all pools has been biologically cycled. The integrative information we provide makes possible a more dynamic, process-oriented conceptual model of P cycling in soils.
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http://dx.doi.org/10.1038/s41467-018-05731-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6089999PMC
August 2018

Policy distortions, farm size, and the overuse of agricultural chemicals in China.

Proc Natl Acad Sci U S A 2018 07 18;115(27):7010-7015. Epub 2018 Jun 18.

School of Agriculture and Food, The University of Melbourne, VIC 3010, Australia.

Understanding the reasons for overuse of agricultural chemicals is critical to the sustainable development of Chinese agriculture. Using a nationally representative rural household survey from China, we found that farm size is a strong factor that affects the use intensity of agricultural chemicals across farms in China. Statistically, a 1% increase in farm size is associated with a 0.3% and 0.5% decrease in fertilizer and pesticide use per hectare ( < 0.001), respectively, and an almost 1% increase in agricultural labor productivity, while it only leads to a statistically insignificant 0.02% decrease in crop yields. The same pattern was also found using other independently collected data sources from China and an international panel analysis of 74 countries from the 1960s to the 2000s. While economic growth has been associated with increasing farm size in many other countries, in China this relationship has been distorted by land and migration policies, leading to the persistence of small farm size in China. Removing these distortions would decrease agricultural chemical use by 30-50% and the environmental impact of those chemicals by 50% while doubling the total income of all farmers including those who move to urban areas. Removing policy distortions is also likely to complement other remedies to the overuse problem, such as easing farmer's access to modern technologies and knowledge, and improving environmental regulation and enforcement.
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http://dx.doi.org/10.1073/pnas.1806645115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6142251PMC
July 2018

Plant acclimation to long-term high nitrogen deposition in an N-rich tropical forest.

Proc Natl Acad Sci U S A 2018 05 1;115(20):5187-5192. Epub 2018 May 1.

Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China;

Anthropogenic nitrogen (N) deposition has accelerated terrestrial N cycling at regional and global scales, causing nutrient imbalance in many natural and seminatural ecosystems. How added N affects ecosystems where N is already abundant, and how plants acclimate to chronic N deposition in such circumstances, remains poorly understood. Here, we conducted an experiment employing a decade of N additions to examine ecosystem responses and plant acclimation to added N in an N-rich tropical forest. We found that N additions accelerated soil acidification and reduced biologically available cations (especially Ca and Mg) in soils, but plants maintained foliar nutrient supply at least in part by increasing transpiration while decreasing soil water leaching below the rooting zone. We suggest a hypothesis that cation-deficient plants can adjust to elevated N deposition by increasing transpiration and thereby maintaining nutrient balance. This result suggests that long-term elevated N deposition can alter hydrological cycling in N-rich forest ecosystems.
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http://dx.doi.org/10.1073/pnas.1720777115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5960300PMC
May 2018

Convergence and contrast in the community structure of Bacteria, Fungi and Archaea along a tropical elevation-climate gradient.

FEMS Microbiol Ecol 2017 05;93(5)

Department of Biology, Stanford University, Stanford, CA 94305, USA.

Changes in species richness along climatological gradients have been instrumental in developing theories about the general drivers of biodiversity. Previous studies on microbial communities along climate gradients on mountainsides have revealed positive, negative and neutral richness trends. We examined changes in richness and composition of Fungi, Bacteria and Archaea in soil along a 50-1000 m elevation, 280-3280 mm/yr precipitation gradient in Hawai'i. Soil properties and their drivers are exceptionally well understood along this gradient. All three microbial groups responded strongly to the gradient, with community ordinations being similar along axes of environmental conditions (pH, rainfall) and resource availability (nitrogen, phosphorus). However, the form of the richness-climate relationship varied between Fungi (positive linear), Bacteria (unimodal) and Archaea (negative linear). These differences were related to resource-ecology and limiting conditions for each group, with fungal richness increasing most strongly with soil carbon, ammonia-oxidizing Archaea increasing with nitrogen mineralization rate, and Bacteria increasing with both carbon and pH. Reponses to the gradient became increasingly variable at finer taxonomic scales and within any taxonomic group most individual OTUs occurred in narrow climate-elevation ranges. These results show that microbial responses to climate gradients are heterogeneous due to complexity of underlying environmental changes and the diverse ecologies of microbial taxa.
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http://dx.doi.org/10.1093/femsec/fix045DOI Listing
May 2017

Controls of nitrogen cycling evaluated along a well-characterized climate gradient.

Ecology 2017 Apr;98(4):1117-1129

Department of Biology, Stanford University, Stanford, California, 94305, USA.

The supply of nitrogen (N) constrains primary productivity in many ecosystems, raising the question "what controls the availability and cycling of N"? As a step toward answering this question, we evaluated N cycling processes and aspects of their regulation on a climate gradient on Kohala Volcano, Hawaii, USA. The gradient extends from sites receiving <300 mm/yr of rain to those receiving >3,000 mm/yr, and the pedology and dynamics of rock-derived nutrients in soils on the gradient are well understood. In particular, there is a soil process domain at intermediate rainfall within which ongoing weathering and biological uplift have enriched total and available pools of rock-derived nutrients substantially; sites at higher rainfall than this domain are acid and infertile as a consequence of depletion of rock-derived nutrients, while sites at lower rainfall are unproductive and subject to wind erosion. We found elevated rates of potential net N mineralization in the domain where rock-derived nutrients are enriched. Higher-rainfall sites have low rates of potential net N mineralization and high rates of microbial N immobilization, despite relatively high rates of gross N mineralization. Lower-rainfall sites have moderately low potential net N mineralization, relatively low rates of gross N mineralization, and rates of microbial N immobilization sufficient to sequester almost all the mineral N produced. Bulk soil δ N also varied along the gradient, from +4‰ at high rainfall sites to +14‰ at low rainfall sites, indicating differences in the sources and dynamics of soil N. Our analysis shows that there is a strong association between N cycling and soil process domains that are defined using soil characteristics independent of N along this gradient, and that short-term controls of N cycling can be understood in terms of the supply of and demand for N.
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http://dx.doi.org/10.1002/ecy.1751DOI Listing
April 2017

Strengthening Agronomy Research for Food Security and Environmental Quality.

Environ Sci Technol 2016 Feb 1;50(4):1639-41. Epub 2016 Feb 1.

Key Laboratory of Plant-Soil Interactions, Ministry of Education, Center for Resources, Environment and Food Security, China Agricultural University , Beijing 100193, China.

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http://dx.doi.org/10.1021/acs.est.6b00267DOI Listing
February 2016

Evidence for a Historic Change Occurring in China.

Environ Sci Technol 2016 Jan 28;50(2):505-6. Epub 2015 Dec 28.

College of Resources and Environmental Sciences, China Agricultural University , Beijing 100193, China.

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http://dx.doi.org/10.1021/acs.est.5b05972DOI Listing
January 2016

Integrated reactive nitrogen budgets and future trends in China.

Proc Natl Acad Sci U S A 2015 Jul 29;112(28):8792-7. Epub 2015 Jun 29.

Department of Biology, Stanford University, Stanford, CA 94305

Reactive nitrogen (Nr) plays a central role in food production, and at the same time it can be an important pollutant with substantial effects on air and water quality, biological diversity, and human health. China now creates far more Nr than any other country. We developed a budget for Nr in China in 1980 and 2010, in which we evaluated the natural and anthropogenic creation of Nr, losses of Nr, and transfers among 14 subsystems within China. Our analyses demonstrated that a tripling of anthropogenic Nr creation was associated with an even more rapid increase in Nr fluxes to the atmosphere and hydrosphere, contributing to intense and increasing threats to human health, the sustainability of croplands, and the environment of China and its environs. Under a business as usual scenario, anthropogenic Nr creation in 2050 would more than double compared with 2010 levels, whereas a scenario that combined reasonable changes in diet, N use efficiency, and N recycling could reduce N losses and anthropogenic Nr creation in 2050 to 52% and 64% of 2010 levels, respectively. Achieving reductions in Nr creation (while simultaneously increasing food production and offsetting imports of animal feed) will require much more in addition to good science, but it is useful to know that there are pathways by which both food security and health/environmental protection could be enhanced simultaneously.
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http://dx.doi.org/10.1073/pnas.1510211112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4507225PMC
July 2015

Variation in Rapa Nui (Easter Island) land use indicates production and population peaks prior to European contact.

Proc Natl Acad Sci U S A 2015 Jan 5;112(4):1025-30. Epub 2015 Jan 5.

Te Pūnaha Matatini and Department of Anthropology, University of Auckland, Auckland, New Zealand 1142.

Many researchers believe that prehistoric Rapa Nui society collapsed because of centuries of unchecked population growth within a fragile environment. Recently, the notion of societal collapse has been questioned with the suggestion that extreme societal and demographic change occurred only after European contact in AD 1722. Establishing the veracity of demographic dynamics has been hindered by the lack of empirical evidence and the inability to establish a precise chronological framework. We use chronometric dates from hydrated obsidian artifacts recovered from habitation sites in regional study areas to evaluate regional land-use within Rapa Nui. The analysis suggests region-specific dynamics including precontact land use decline in some near-coastal and upland areas and postcontact increases and subsequent declines in other coastal locations. These temporal land-use patterns correlate with rainfall variation and soil quality, with poorer environmental locations declining earlier. This analysis confirms that the intensity of land use decreased substantially in some areas of the island before European contact.
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http://dx.doi.org/10.1073/pnas.1420712112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4313829PMC
January 2015

Grassland ecology: Complexity of nutrient constraints.

Authors:
Peter M Vitousek

Nat Plants 2015 Jul 7;1:15098. Epub 2015 Jul 7.

Department of Biology, Stanford University, Stanford, California 94305, USA.

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http://dx.doi.org/10.1038/nplants.2015.98DOI Listing
July 2015

Producing more grain with lower environmental costs.

Nature 2014 Oct 3;514(7523):486-9. Epub 2014 Sep 3.

College of Resources &Environmental Sciences, China Agricultural University, Beijing 100193, China.

Agriculture faces great challenges to ensure global food security by increasing yields while reducing environmental costs. Here we address this challenge by conducting a total of 153 site-year field experiments covering the main agro-ecological areas for rice, wheat and maize production in China. A set of integrated soil-crop system management practices based on a modern understanding of crop ecophysiology and soil biogeochemistry increases average yields for rice, wheat and maize from 7.2 million grams per hectare (Mg ha(-1)), 7.2 Mg ha(-1) and 10.5 Mg ha(-1) to 8.5 Mg ha(-1), 8.9 Mg ha(-1) and 14.2 Mg ha(-1), respectively, without any increase in nitrogen fertilizer. Model simulation and life-cycle assessment show that reactive nitrogen losses and greenhouse gas emissions are reduced substantially by integrated soil-crop system management. If farmers in China could achieve average grain yields equivalent to 80% of this treatment by 2030, over the same planting area as in 2012, total production of rice, wheat and maize in China would be more than enough to meet the demand for direct human consumption and a substantially increased demand for animal feed, while decreasing the environmental costs of intensive agriculture.
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http://dx.doi.org/10.1038/nature13609DOI Listing
October 2014

Litter quality versus soil microbial community controls over decomposition: a quantitative analysis.

Oecologia 2014 Jan;174(1):283-94

The possible effects of soil microbial community structure on organic matter decomposition rates have been widely acknowledged, but are poorly understood. Understanding these relationships is complicated by the fact that microbial community structure and function are likely to both affect and be affected by organic matter quality and chemistry, thus it is difficult to draw mechanistic conclusions from field studies. We conducted a reciprocal soil inoculum × litter transplant laboratory incubation experiment using samples collected from a set of sites that have similar climate and plant species composition but vary significantly in bacterial community structure and litter quality. The results showed that litter quality explained the majority of variation in decomposition rates under controlled laboratory conditions: over the course of the 162-day incubation, litter quality explained nearly two-thirds (64%) of variation in decomposition rates, and a smaller proportion (25%) was explained by variation in the inoculum type. In addition, the relative importance of inoculum type on soil respiration increased over the course of the experiment, and was significantly higher in microcosms with lower litter quality relative to those with higher quality litter. We also used molecular phylogenetics to examine the relationships between bacterial community composition and soil respiration in samples through time. Pyrosequencing revealed that bacterial community composition explained 32 % of the variation in respiration rates. However, equal portions (i.e., 16%) of the variation in bacterial community composition were explained by inoculum type and litter quality, reflecting the importance of both the meta-community and the environment in bacterial assembly. Taken together, these results indicate that the effects of changing microbial community composition on decomposition are likely to be smaller than the potential effects of climate change and/or litter quality changes in response to increasing atmospheric CO2 concentrations or atmospheric nutrient deposition.
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http://dx.doi.org/10.1007/s00442-013-2758-9DOI Listing
January 2014

The global nitrogen cycle in the twenty-first century.

Philos Trans R Soc Lond B Biol Sci 2013 Jul 27;368(1621):20130164. Epub 2013 May 27.

NERC Centre for Ecology and Hydrology, Penicuik, UK.

Global nitrogen fixation contributes 413 Tg of reactive nitrogen (Nr) to terrestrial and marine ecosystems annually of which anthropogenic activities are responsible for half, 210 Tg N. The majority of the transformations of anthropogenic Nr are on land (240 Tg N yr(-1)) within soils and vegetation where reduced Nr contributes most of the input through the use of fertilizer nitrogen in agriculture. Leakages from the use of fertilizer Nr contribute to nitrate (NO3(-)) in drainage waters from agricultural land and emissions of trace Nr compounds to the atmosphere. Emissions, mainly of ammonia (NH3) from land together with combustion related emissions of nitrogen oxides (NOx), contribute 100 Tg N yr(-1) to the atmosphere, which are transported between countries and processed within the atmosphere, generating secondary pollutants, including ozone and other photochemical oxidants and aerosols, especially ammonium nitrate (NH4NO3) and ammonium sulfate (NH4)2SO4. Leaching and riverine transport of NO3 contribute 40-70 Tg N yr(-1) to coastal waters and the open ocean, which together with the 30 Tg input to oceans from atmospheric deposition combine with marine biological nitrogen fixation (140 Tg N yr(-1)) to double the ocean processing of Nr. Some of the marine Nr is buried in sediments, the remainder being denitrified back to the atmosphere as N2 or N2O. The marine processing is of a similar magnitude to that in terrestrial soils and vegetation, but has a larger fraction of natural origin. The lifetime of Nr in the atmosphere, with the exception of N2O, is only a few weeks, while in terrestrial ecosystems, with the exception of peatlands (where it can be 10(2)-10(3) years), the lifetime is a few decades. In the ocean, the lifetime of Nr is less well known but seems to be longer than in terrestrial ecosystems and may represent an important long-term source of N2O that will respond very slowly to control measures on the sources of Nr from which it is produced.
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http://dx.doi.org/10.1098/rstb.2013.0164DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3682748PMC
July 2013

Biological nitrogen fixation: rates, patterns and ecological controls in terrestrial ecosystems.

Philos Trans R Soc Lond B Biol Sci 2013 Jul 27;368(1621):20130119. Epub 2013 May 27.

Department of Biology, Stanford University, Stanford, CA 94305, USA.

New techniques have identified a wide range of organisms with the capacity to carry out biological nitrogen fixation (BNF)-greatly expanding our appreciation of the diversity and ubiquity of N fixers-but our understanding of the rates and controls of BNF at ecosystem and global scales has not advanced at the same pace. Nevertheless, determining rates and controls of BNF is crucial to placing anthropogenic changes to the N cycle in context, and to understanding, predicting and managing many aspects of global environmental change. Here, we estimate terrestrial BNF for a pre-industrial world by combining information on N fluxes with (15)N relative abundance data for terrestrial ecosystems. Our estimate is that pre-industrial N fixation was 58 (range of 40-100) Tg N fixed yr(-1); adding conservative assumptions for geological N reduces our best estimate to 44 Tg N yr(-1). This approach yields substantially lower estimates than most recent calculations; it suggests that the magnitude of human alternation of the N cycle is substantially larger than has been assumed.
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http://dx.doi.org/10.1098/rstb.2013.0119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3682739PMC
July 2013

Chinese agriculture: An experiment for the world.

Nature 2013 May;497(7447):33-5

Center for Resources, Environment and Food Security, China Agricultural University, Beijing, China.

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http://dx.doi.org/10.1038/497033aDOI Listing
May 2013

Enhanced nitrogen deposition over China.

Nature 2013 Feb 20;494(7438):459-62. Epub 2013 Feb 20.

College of Resources & Environmental Sciences, China Agricultural University, Beijing 100193, China.

China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen. These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity. However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8 kilograms of nitrogen per hectare (P < 0.001) between the 1980s (13.2 kilograms of nitrogen per hectare) and the 2000s (21.1 kilograms of nitrogen per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s, before the introduction of mitigation measures. Nitrogen from ammonium (NH4(+)) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO3(-)), in agreement with decreased ratios of NH3 to NOx emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized croplands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment.
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http://dx.doi.org/10.1038/nature11917DOI Listing
February 2013

Introduction to a Virtual Special Issue on ecological stoichiometry and global change.

New Phytol 2012 Nov;196(3):649-651

Stanford University, Calfornia, USA.

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http://dx.doi.org/10.1111/j.1469-8137.2012.04376.xDOI Listing
November 2012

Fungal endophyte communities reflect environmental structuring across a Hawaiian landscape.

Proc Natl Acad Sci U S A 2012 Aug 25;109(32):13022-7. Epub 2012 Jul 25.

Department of Biology, Stanford University, Stanford, CA 94305, USA.

We surveyed endophytic fungal communities in leaves of a single tree species (Metrosideros polymorpha) across wide environmental gradients (500-5,500 mm of rain/y; 10-22 °C mean annual temperature) spanning short geographic distances on Mauna Loa Volcano, Hawai'i. Using barcoded amplicon pyrosequencing at 13 sites (10 trees/site; 10 leaves/tree), we found very high levels of diversity within sites (a mean of 551 ± 134 taxonomic units per site). However, among-site diversity contributed even more than did within-site diversity to the overall richness of more than 4,200 taxonomic units observed in M. polymorpha, and this among-site variation in endophyte community composition correlated strongly with temperature and rainfall. These results are consistent with suggestions that foliar endophytic fungi are hyperdiverse. They further suggest that microbial diversity may be even greater than has been assumed and that broad-scale environmental controls such as temperature and rainfall can structure eukaryotic microbial diversity. Appropriately constrained study systems across strong environmental gradients present a useful means to understand the environmental factors that structure the diversity of microbial communities.
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http://dx.doi.org/10.1073/pnas.1209872109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3420199PMC
August 2012

Integrated soil-crop system management for food security.

Proc Natl Acad Sci U S A 2011 Apr 28;108(16):6399-404. Epub 2011 Mar 28.

College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China.

China and other rapidly developing economies face the dual challenge of substantially increasing yields of cereal grains while at the same time reducing the very substantial environmental impacts of intensive agriculture. We used a model-driven integrated soil-crop system management approach to develop a maize production system that achieved mean maize yields of 13.0 t ha(-1) on 66 on-farm experimental plots--nearly twice the yield of current farmers' practices--with no increase in N fertilizer use. Such integrated soil-crop system management systems represent a priority for agricultural research and implementation, especially in rapidly growing economies.
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http://dx.doi.org/10.1073/pnas.1101419108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3080987PMC
April 2011

Cellulose (delta)18O is an index of leaf-to-air vapor pressure difference (VPD) in tropical plants.

Proc Natl Acad Sci U S A 2011 Feb 18;108(5):1981-6. Epub 2011 Jan 18.

Center for Stable Isotope Biogeochemistry, Department of Integrative Biology, University of California, Berkeley, CA 94720, USA.

Cellulose in plants contains oxygen that derives in most cases from precipitation. Because the stable oxygen isotope composition, δ(18)O, of precipitation is associated with environmental conditions, cellulose δ(18)O should be as well. However, plant physiological models using δ(18)O suggest that cellulose δ(18)O is influenced by a complex mix of both climatic and physiological drivers. This influence complicates the interpretation of cellulose δ(18)O values in a paleo-context. Here, we combined empirical data analyses with mechanistic model simulations to i) quantify the impacts that the primary climatic drivers humidity (e(a)) and air temperature (T(air)) have on cellulose δ(18)O values in different tropical ecosystems and ii) determine which environmental signal is dominating cellulose δ(18)O values. Our results revealed that e(a) and T(air) equally influence cellulose δ(18)O values and that distinguishing which of these factors dominates the δ(18)O values of cellulose cannot be accomplished in the absence of additional environmental information. However, the individual impacts of e(a) and T(air) on the δ(18)O values of cellulose can be integrated into a single index of plant-experienced atmospheric vapor demand: the leaf-to-air vapor pressure difference (VPD). We found a robust relationship between VPD and cellulose δ(18)O values in both empirical and modeled data in all ecosystems that we investigated. Our analysis revealed therefore that δ(18)O values in plant cellulose can be used as a proxy for VPD in tropical ecosystems. As VPD is an essential variable that determines the biogeochemical dynamics of ecosystems, our study has applications in ecological-, climate-, or forensic-sciences.
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http://dx.doi.org/10.1073/pnas.1018906108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3033288PMC
February 2011

Terrestrial phosphorus limitation: mechanisms, implications, and nitrogen-phosphorus interactions.

Ecol Appl 2010 Jan;20(1):5-15

Department of Biological Sciences, Stanford University, Stanford, California 94305, USA.

Nutrient limitation to primary productivity and other biological processes is widespread in terrestrial ecosystems, and nitrogen (N) and phosphorus (P) are the most common limiting elements, both individually and in combination. Mechanisms that drive P limitation, and their interactions with the N cycle, have received less attention than mechanisms causing N limitation. We identify and discuss six mechanisms that could drive P limitation in terrestrial ecosystems. The best known of these is depletion-driven limitation, in which accumulated P losses during long-term soil and ecosystem development contribute to what Walker and Syers termed a "terminal steady state" of profound P depletion and limitation. The other mechanisms are soil barriers that prevent access to P; transactional limitation, in which weathering of P-containing minerals does not keep pace with the supply of other resources; low-P parent materials; P sinks; and anthropogenic changes that increase the supply of other resources (often N) relative to P. We distinguish proximate nutrient limitation (which occurs where additions of a nutrient stimulate biological processes, especially productivity) from ultimate nutrient limitation (where additions of a nutrient can transform ecosystems). Of the mechanisms that drive P limitation, we suggest that depletion, soil barriers, and low-P parent material often cause ultimate limitation because they control the ecosystem mass balance of P. Similarly, demand-independent losses and constraints to N fixation can control the ecosystem-level mass balance of N and cause it to be an ultimate limiting nutrient.
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http://dx.doi.org/10.1890/08-0127.1DOI Listing
January 2010

Landscape-level variation in forest structure and biogeochemistry across a substrate age gradient in Hawaii.

Ecology 2009 Nov;90(11):3074-86

Department of Biology, Stanford University, Stanford, California 94305, USA.

We compared forest canopy heights and nitrogen concentrations in long-term research sites and in 2 x 2 km landscapes surrounding these sites along a substrate age gradient in the Hawaiian Islands. Both remote airborne and ground-based measurements were used to characterize processes that control landscape-level variation in canopy properties. We integrated a waveform light detection and ranging (LiDAR) system, a high-resolution imaging spectrometer, and a global positioning system/inertial measurement unit to provide highly resolved images of ground topography, canopy heights, and canopy nitrogen concentrations (1) within a circle 50 m in radius focused on a long-term study site in the center of each landscape; (2) for the entire 2 x 2 km landscape regardless of land cover; and (3) after stratification, for our target cover class, native-dominated vegetation on constructional geomorphic surfaces throughout each landscape. Remote measurements at all scales yielded the same overall patterns as did ground-based measurements in the long-term sites. The two younger landscapes supported taller trees than did older landscapes, while the two intermediate-aged landscapes had higher canopy nitrogen (N) concentrations than did either young or old landscapes. However, aircraft-based analyses detected substantial variability in canopy characteristics on the landscape level, even within the target cover class. Canopy heights were more heterogeneous on the older landscapes, with coefficients of variation increasing from 23-41% to 69-78% with increasing substrate age. This increasing heterogeneity was associated with a larger patch size of canopy turnover and with dominance of most secondary successional stands by the mat-forming fern Dicranopteris linearis in the older landscapes.
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http://dx.doi.org/10.1890/08-0813.1DOI Listing
November 2009

Sources of nutrients to windward agricultural systems in pre-contact Hawai'i.

Ecol Appl 2009 Sep;19(6):1444-53

Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA.

Prior to European contact in 1778, Hawaiians developed intensive irrigated pondfield agricultural systems in windward Kohala, Hawai'i. We evaluated three potential sources of nutrients to windward systems that could have sustained intensive agriculture: (1) in situ weathering of primary and secondary minerals in upland soils; (2) rejuvenation of the supply of rock-derived nutrients on eroded slopes and in alluvium; and (3) transport of rock-derived nutrients to crops via irrigation water. Our results show that most windward soils are infertile and suggest that weathering of minerals within upland soils was insufficient to sustain intensive agriculture without substantial cultural inputs. Erosion enhances weathering and so increases nutrient supply, with soils of the largest alluvial valleys (>200 m deep) retaining 37% of calcium from parent material (compared to 2% in upland sites). However, soils of smaller valleys that also supported pre-contact agricultural systems are substantially less enriched. Isotopic 87Sr/86Sr analyses of stream water demonstrate that at low to moderate stream flow over 90% of dissolved strontium derives from weathering of basalt rather than deposition of atmospheric sources; most other dissolved cations also derive from basalt weathering. We calculate that irrigation water could have supplied approximately 200 kg ha(-1) yr(-1) of calcium to pondfield systems, nearly 100 times more than was supplied by weathering in soils on stable geomorphic surfaces. In effect, irrigation waters brought nutrients from rocks to the windward crops.
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http://dx.doi.org/10.1890/08-0983.1DOI Listing
September 2009

N:P stoichiometry and protein:RNA ratios in vascular plants: an evaluation of the growth-rate hypothesis.

Ecol Lett 2009 Aug 8;12(8):765-71. Epub 2009 Apr 8.

Department of Environmental Studies, California State University, 6000 J Street, Sacramento, CA 95819, USA.

The growth-rate hypothesis states that fast-growing organisms need relatively more phosphorus-rich RNA to support rapid rates of protein synthesis, and therefore predicts, within and among taxa, increases in RNA and phosphorus content (relative to protein and nitrogen content) with increased growth rate. Here, we present a test of this hypothesis in vascular plants. We determined nitrogen : phosphorus ratios and protein:RNA ratios in pines growing at different rates due to nutrient conditions. In general, when comparing leaves of the same species at low and high growth rates, the faster-growing plants had higher RNA content, higher %N and %P, and lower protein:RNA ratios, but not consistently lower N:P ratios. We found no link between growth rate and foliar N:P or protein:RNA when comparing multiple species of different inherent growth rates. We conclude that plants adjust the balance of protein and RNA to favour either speed or efficiency of protein synthesis, but this balance does not alone dictate leaf stoichiometry.
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http://dx.doi.org/10.1111/j.1461-0248.2009.01310.xDOI Listing
August 2009
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