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Nutrient limitation in terrestrial and freshwater ecosystems

Nutrient limitation in terrestrial and freshwater ecosystems


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In terms of primary production, it is often described in textbooks that nitrogen is the most limiting nutrient in terrestrial ecosystems, while phosphorus is the most limiting nutrient in freshwater ecosystems. What creates this difference?


The traditional explanation for this is that nitrogen compounds are more mobile than phosphorus compounds. As a result, nitrogen is more likely to flow through terrestrial ecosystems and accumulate in freshwater ecosystems, making P relatively more limiting than N in freshwater.

Phosphorus compounds (e.g., phosphate) are more "sticky" and tend to bind/sorb to compounds in the soil and aquatic sediments, e.g., ferric compounds. Thus, most phosphorus gets bound up in terrestrial ecosystems because it's less mobile than nitrogen, or gets bound up in aquatic sediments. As a result, nitrogen becomes relatively more limiting than phosphorus in terrestrial ecosystems, and the phosphorus that does enter freshwater ecosystems often becomes inaccessible to biological organisms like primary producers.

Note that this paradigm is a generalization, and is dependent on many other factors. Lake pH and concentration ferric compounds can regulate whether the sediments are sources or sinks of P; anoxic conditions can lead to denitrification, a loss of N that could offset N inputs. Anthropogenic additions of N and P (either to the freshwater system directly or to the terrestrial ecosystem that drains into it) could dramatically perturb the natural balance between N and P limitation in terrestrial and aquatic ecosystems in a way that does not conform to the paradigm.

Some references you might find useful:

Elser, J. J., Bracken, M. E.S., Cleland, E. E., Gruner, D. S., Harpole, W. S., Hillebrand, H., Ngai, J. T., Seabloom, E. W., Shurin, J. B. and Smith, J. E. (2007), Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems. Ecology Letters, 10: 1135-1142.

Vitousek, P.M. & Howarth, R.W. Biogeochemistry (1991) 13: 87.


Quantifying terrestrial nitrogen and phosphorus limitation

The story of nutrient limitation originated from 1840s, when the famous German chemist Justus Freiherr von Liebig first proposed the Liebig’s Law of the Minimum based on experiments that added essential nutrients to improve crop productivity (von Liebig, 1843). One hundred years later, Chapin III et al. (1986) investigated the concept of nutrient limitation in natural plant communities and proposed several differences from that in agriculture, especially the diverse nutrient use strategies for different plant species. In 1991, Vitousek and Howarth (1991) concluded that “there is substantial evidence that nitrogen limits net primary production much of the time in most terrestrial biomes and many marine ecosystems”. Since the 2000s, numerous ecologists assessed nitrogen and phosphorus limitation based on meta-analyses of global nutrient addition experiments and they concluded a global distribution of nitrogen and phosphorus limitation in terrestrial ecosystems (Elser et al., 2007 LeBauer and Treseder, 2008 Fay et al., 2015). Meanwhile, many others have also estimated nitrogen and phosphorus limitation via indirect indicators (Koerselman and Meuleman, 1996 Güsewell, 2004 Vergutz et al. 2012 Han et al., 2013). Although these efforts have greatly improved our understanding of nutrient limitation, global patterns of terrestrial nitrogen and phosphorus limitation still remain a fundamental question for the fields of terrestrial ecology and biogeochemistry.

I have been thinking about the answer to this question since the time when I conducted a nitrogen addition experiment in a boreal forest for my Ph.D thesis in Peking University (2008-2013). I found that nutrient addition experiments are costly, and a variety of growth response indicators were used by different researchers, complicating the challenging goal of disentangling the spatial patterns of global nutrient limitation. After completing my Ph.D work in Peking University, I moved to Beijing Normal University for a postdoc during 2013 and 2015. I continued to work in Beijing Normal University and became an associated professor in 2016. Since then, I have returned to the issue to solve the puzzle of global nitrogen and phosphorus limitation.

Mass ratios of leaf nitrogen and phosphorus have been used to indicate nitrogen and phosphorus limitation (Koerselman and Meuleman, 1996 Güsewell, 2004), but this approach has been shown to have large uncertainties by a recent assessment (Yan et al., 2017). Some other studies have tried to link leaf nitrogen and phosphorus resorption efficiencies to nutrient limitation (Vergutz et al. 2012 Reed et al., 2012 Han et al., 2013), but a theoretical framework is still lacking. As inspired by the stoichiometric homeostasis theory and Liebig’s Law of the Minimum, I proposed a theoretical framework to test nutrient limitation based on the ratio of plant leaf nitrogen and phosphorus resorption efficiencies at the ecosystem scale (see more details in Du et al., 2020). In nearly two years of work, I collected data of paired leaf nitrogen resorption efficiency and phosphorus resorption efficiency from literature and made initial assessments of patterns in nitrogen and phosphorus limitation.

In October, 2017, I made a short visit to Professor Rob Jackson at Stanford University, where we collaborated to improve the work and finished a first draft of our manuscript. His lab has long been interested in nutrient limitation across ecosystems and the role of plants in both structuring and responding to global nutrient availability (e.g., Jobbágy and Jackson 2001 Vergutz et al. 2012 Terrer et al. 2019). Our team was strengthened when Rob introduced his postdocs César Terrer, Adam Pellegrini and Anders Ahlström to join in various aspects of the analyses. We also involved Dr. Caspar J. van Lissa, an assistant professor of Methods & Statistics at Utrecht University, to improve our statistical analyses. We discussed new ideas, reanalyzed data, validated predictions of global nitrogen and phosphorus limitation by comparing to a newly constructed database of field nutrient addition experiments, and revised the manuscript at least ten times. I have enjoyed working with this great team and I really thank Rob for organizing it. I believe that we will work together more in the future.

Our results suggest that 18% of Earth’s land area, excluding cropland, urban, and glacial areas, is strongly limited by N alone, whereas 43 % is strongly P limited. The remaining 39% of natural terrestrial land area could be co-limited by N and P or weakly limited by either nutrient alone. Nitrogen limitation is more common in boreal forests, tundra, temperate coniferous forests and montane grasslands and shrublands, whereas phosphorous limitation is more common in tropical and subtropical forests, temperate broadleaf and mixed forests, deserts, Mediterranean biomes and grasslands, savannas and shrublands in tropical, subtropical and temperate regions. Our work provides a new framework for testing nutrient limitation and an empirical benchmark of N and P limitation for models to constrain predictions of the terrestrial C sink. It will help to improve representation of nutrient limitation in Earth system models and identify hotspots of future land C sinks in response to climate change and rising carbon dioxide concentrations. Although we looked at nutrient limitation in relatively natural ecosystems, there is a potential to extend our approach to human-dominated or managed ecosystems, such as commercial plantations and urban forests. This will lead to better nutrient management by diagnosing the limiting nutrients in these ecosystems.

Global patterns of terrestrial nitrogen and phosphorus limitation (Du et al., 2020, Nature Geoscience)

At the ecosystem scale, the ratio of average leaf nitrogen resorption efficiency (NRE) to phosphorus resorption efficiency (PRE) weighted by the leaf mass of all species is a theoretical indicator of N or P limitation. Because species-specific leaf mass is rarely reported together with NRE and PRE, in the current analysis we had to use the ratio of site-averaged NRE to site-averaged PRE of dominant species as an approximate indicator. Future studies would benefit from additional data to support analyses using ecosystem mean NRE/PRE weighted by species-specific leaf mass or abundance. We recommend researchers conducting field studies measure such variables whenever possible and compare results to those of nutrient fertilization experiments.

Combining paired field measurements and fertilization experiments to understand ecosystem nutrient limitation (Credit to Enzai Du).

To find out more, read the paper following the link: https://www.nature.com/articles/s41561-019-0530-4

Chapin III, F. S., Vitousek, P. M., & Van Cleve, K. The nature of nutrient limitation in plant communities. Am. Nat. 127, 48–58 (1986).

Du, E., et al. Global patterns of terrestrial nitrogen and phosphorus limitation. Nat. Geosci. https://www.nature.com/articles/s41561-019-0530-4 (2020).

Elser, J.J. et al. Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems. Ecol. Lett. 10, 1135–1142 (2007).

Fay, P. A. et al. Grassland productivity limited by multiple nutrients. Nat. Plants 1, 15080 (2015).

Güsewell, S. N:P ratios in terrestrial plants: variation and functional significance. New Phytol. 164, 243–266 (2004).

Han, W., Tang, L., Chen, Y. & Fang, J. Relationship between the relative limitation and resorption efficiency of nitrogen vs phosphorus in woody plants. PLoS One 8, e83366 (2013).

Jobbágy, E.G. & Jackson, R.B. The distribution of soil nutrients with depth: global patterns and the imprint of plants. Biogeochemistry 53:51-77 (2001).

Koerselman, W. & Meuleman, A.F. The vegetation N: P ratio: a new tool to detect the nature of nutrient limitation. J. Appl. Ecol. 33, 1441–1450 (1996).

LeBauer, D.S. & Treseder, K.K. Nitrogen limitation of net primary productivity in terrestrial ecosystems is globally distributed. Ecology 89, 371–379 (2008).

Reed, S.C., Townsend, A.R., Davidson, E.A. & Cleveland, C.C. Stoichiometric patterns in foliar nutrient resorption across multiple scales. New Phytol. 196, 173–180 (2012).

Terrer, C. et al. Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass. Nat. Clim. Change 9, 684-689 (2019).

Vergutz, L., Manzoni, S. Porporato, A., Novais, R.F. & Jackson, R.B. Global resorption efficiencies and concentrations of carbon and nutrients in leaves of terrestrial plants. Ecol. Monogr. 82, 205-220 (2012).

Vitousek, P. M., & Howarth, R. W. Nitrogen limitation on land and in the sea: how can it occur? Biogeochemistry 13, 87–115 (1991).

von Liebig, J. Die Chemie in ihrer Anwendung auf Agricultur und Physiologie. 3e Aufl., Braunschweig: F. Vieweg und Sohn (1843).

Yan, Z., Tian, D., Han, W., Tang, Z. & Fang, J. An assessment on the uncertainty of the nitrogen to phosphorus ratio as a threshold for nutrient limitation in plants. Ann. Bot-London 120, 937–942 (2017).


Abstract

Nitrogen (N) is considered the dominant limiting nutrient in temperate regions, while phosphorus (P) limitation frequently occurs in tropical regions, but in subtropical regions nutrient limitation is poorly understood. In this study, we investigated N and P contents and N:P ratios of foliage, forest floors, fine roots and mineral soils, and their relationships with community biomass, litterfall C, N and P productions, forest floor turnover rate, and microbial processes in eight mature and old-growth subtropical forests (stand age >80 yr) at Dinghushan Biosphere Reserve, China. Average N:P ratios (mass based) in foliage, litter (L) layer and mixture of fermentation and humus (F/H) layer, and fine roots were 28.3, 42.3, 32.0 and 32.7, respectively. These values are higher than the critical N:P ratios for P limitation proposed (16–20 for foliage, ca. 25 for forest floors). The markedly high N:P ratios were mainly attributed to the high N concentrations of these plant materials. Community biomass, litterfall C, N and P productions, forest floor turnover rate and microbial properties were more strongly related to measures of P than N and frequently negatively related to the N:P ratios, suggesting a significant role of P availability in determining ecosystem production and productivity and nutrient cycling at all the study sites except for one prescribed disturbed site where N availability may also be important. We propose that N enrichment is probably a significant driver of the potential P limitation in the study area. Low P parent material may also contribute to the potential P limitation. In general, our results provided strong evidence supporting a significant role for P availability, rather than N availability, in determining ecosystem primary productivity and ecosystem processes in subtropical forests of China.

Citation: Hou E, Chen C, McGroddy ME, Wen D (2012) Nutrient Limitation on Ecosystem Productivity and Processes of Mature and Old-Growth Subtropical Forests in China. PLoS ONE 7(12): e52071. https://doi.org/10.1371/journal.pone.0052071

Editor: Sandra Maria Feliciano de Oliveira Azevedo, Federal University of Rio de Janeiro, Brazil

Received: July 4, 2012 Accepted: November 15, 2012 Published: December 20, 2012

Copyright: © 2012 Hou et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This study was supported by National Natural Science Foundation of China (No. 31070409), Strategic Priority Research Program - Climate Change: Carbon Budget and Relevant Issues of the Chinese Academy of Sciences (No. XDA05050205 and the Australian Research Council (FT0990547). The support from China Scholarship Council through an overseas joint doctoral fellowship to Enqing Hou is also kindly acknowledged. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.


Phosphorus Cycle

Phosphorus is essential for the formation of nucleotides and is present as calcium phosphate and phospholipids in bones and lipid membranes. The phosphorus cycle is the process by which the element moves through the lithosphere, hydrosphere, and biosphere. This cycle is the slowest of all biogeochemical cycles. The main steps in a phosphorus cycle as follows:

In nature, phosphorus is mainly found as phosphate compounds in sedimentary rocks. When these rocks weather, these phosphate compounds leach into the soil and water.

The leached phosphates are then taken up by microbes, plants, and animals through water and soil.

When the plants and animals die, the phosphates in the remains of plants and animals (including their waste products) are decomposed by detritivores. These phosphates then return to the environment or are taken up by the detritivores.

The phosphates that return to the environment, upon reaching oceans, sink to the bottom of the ocean floor as sediments. Over time, the sediment layers get compressed into sedimentary rocks and are moved toward land through uplift.


Assistant Professor

Education

  • Ph.D., Ecology and Evolutionary Biology, University of Oklahoma, 2013
  • Postdoctoral research: Cornell University

Research Interests

Our lab is focuses on the role of organisms in maintaining vital ecosystem processes and how flow regime alterations and land use and climate change may interact to influence these processes. Through our work, we contribute to the understanding of freshwater ecological systems and the interaction and feedbacks between the surrounding terrestrial landscape. We are particularly interested in how species traits, especially stoichiometric traits, influence structure and function within aquatic systems. To do this, we employ combination of field observational and mesocosm studies to understand how body stoichiomtery, remineralization rates, trophic ecology, threshold elemental ratios, and growth efficiencies respond under various conditions and states of physiological distress. Research in my laboratory addresses both basic and applied ecology and currently follows two main themes:

Physiological Stress Due to Changed Thermal and Nutrient Regimes

Understanding the mechanistic linkages between land use and flow regime changes and biodiversity loss is an essential need for both scientists and managers. Our research aims to addresses these linkages by examining how multiple species physiologically respond to enhanced nutrient concentrations and altered thermal regimes. This trait-based approach will allow us to make linkages between organism-level processes to ecosystem-level Freshwater ecosystems support a disproportionate amount of species relative to the area they cover and are subject to declines in native biodiversity that far exceed those in the most impacted terrestrial ecosystems. Within North America, freshwater mussels (Bivalvia Unionidae) are the most imperiled faunal group in the world with approximately 70% of the more than 300 recognized species at risk of extinction. Evidence of the causes of extirpation of freshwater mussels has often been circumstantial and lacks a direct casual mechanism. We are coupling lab and field experiments with field observational approached to understand metabolic responses, growth, and survival of unionid mussels under altered nutrient and temperature regimes. We are also setting up a flow/temperature monitoring stations in nearby basins to make our work ecologically relevant for managers.


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Freshwater Ecology, Third Edition, covers everything from the basic chemical and physical properties of water, to the advanced and unifying concepts of community ecology and ecosystem relationships found in continental waters. Giving students a solid foundation for both courses and future fieldwork, and updated to include key issues, including how to balance ecological and human health needs, GMOs, molecular tools, fracking, and a host of other environmental issues, this book is an ideal resource for both students and practitioners in ecology and related fields.


At the root of nutrient limitation, ecosystems are not as different as they seem

TEMPE, Ariz. -- Anyone who has thrown a backyard barbecue knows that hot dogs are inexplicably packaged in different numbers than buns -- eight hot dogs per pack versus 10 hot dog buns. Put in ecological terms, this means that weenie roasts are "hot-dog limited" -- the extra buns are worthless without hot dogs to fill them.

Such limiting factors are a cornerstone of natural ecology, where phosphorus or nitrogen limits plant production in most ecosystems. According to the customary model, the relative importance of these two key nutrients varies by ecosystem but a group of researchers led by Arizona State University professor James Elser has found that this view might need to be updated.

Their paper, "Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems," is highlighted in the News and Views section of the October 25 edition of Nature. The most comprehensive study of its kind, this meta-analysis of more than 300 publications in the field of nutrient limitation in ecosystems was recently published online in the journal Ecology Letters.

Like all living things, plants require a number of chemical elements in order to flourish, including carbon, hydrogen and oxygen. They also need nitrogen, a building block of proteins and phosphorus, used to make the nucleotides that compose DNA and RNA. The interplay of these elements affects the growth of the food web's foundational plants, and so understanding their interplay is of vital environmental and commercial concern.

Nitrogen and phosphorus, both widely used in fertilizers, must be in proper balance to be effective. Adding nitrogen alone to an ecosystem is helpful only up to a point, after which plants stop benefiting unless phosphorus also is added. If such a system responds positively to the initial nitrogen addition, it is said to be "nitrogen-limited," because the availability of nitrogen instantaneously constrains the productivity of the ecosystem. The converse is true in "phosphorus-limited" systems.

Plant production in both cases is limited by the nutrient in shortest supply, a principle known as von Liebig's law of the minimum. Because of their characteristic differences in size, makeup, geology and other factors, different kinds of ecosystems have long been thought to differ widely in the strength and the nature of their nutrient limitation for example, conventional wisdom has held that freshwater lakes are primarily phosphorus-limited, while oceans along with terrestrial forests and grasslands were believed to be nitrogen-limited.

Yet that is not what Elser's group found. Rather, their data reveals that the three environments are surprisingly similar, and that the balance of nitrogen and phosphorus within each ecosystem conforms to a different pattern than previously expected.

"Our findings don't support conventional views of ecosystem nutrient limitation," said Elser, a professor of ecology, evolution and environmental science at ASU. "They don't, for example, confirm the rule of thumb that in freshwaters phosphorus is more limiting than nitrogen."

Instead, Elser's group found that nitrogen and phosphorus are in fact equally important in freshwater systems, and that phosphorus is just as important as nitrogen in terrestrial ecosystems as well.

"This is in contradiction to conventional wisdom, which seems to emphasize N on land while disregarding P," Elser said.

The determining factor, according to Elser, is simplicity. Underlying all of the splendid diversity of the world's ecosystems -- whether soggy, arid, terrestrial, aquatic, arboreal or algal -- is the simple unifying fact that all plants share a common core of biochemical machinery. That machinery is composed of proteins and nucleotides, meaning that all plants require nitrogen and phosphorus within a limited range of natural proportions.

"Thus, N and P both play a major role in limiting production, no matter where you look," Elser said.

Source: James Elser, 480-965-9747, [email protected]

Media Contacts: Nicholas Gerbis, (480) 965-9690, [email protected]
Skip Derra, (480) 965-4823, [email protected]

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


At The Root Of Nutrient Limitation, Ecosystems Are Not As Different As They Seem

Anyone who has thrown a backyard barbecue knows that hot dogs are inexplicably packaged in different numbers than buns -- eight hot dogs per pack versus 10 hot dog buns. Put in ecological terms, this means that weenie roasts are "hot-dog limited" -- the extra buns are worthless without hot dogs to fill them.

Such limiting factors are a cornerstone of natural ecology, where phosphorus or nitrogen limits plant production in most ecosystems. According to the customary model, the relative importance of these two key nutrients varies by ecosystem but a group of researchers led by Arizona State University professor James Elser has found that this view might need to be updated.

Like all living things, plants require a number of chemical elements in order to flourish, including carbon, hydrogen and oxygen. They also need nitrogen, a building block of proteins and phosphorus, used to make the nucleotides that compose DNA and RNA. The interplay of these elements affects the growth of the food web's foundational plants, and so understanding their interplay is of vital environmental and commercial concern.

Nitrogen and phosphorus, both widely used in fertilizers, must be in proper balance to be effective. Adding nitrogen alone to an ecosystem is helpful only up to a point, after which plants stop benefiting unless phosphorus also is added. If such a system responds positively to the initial nitrogen addition, it is said to be "nitrogen-limited," because the availability of nitrogen instantaneously constrains the productivity of the ecosystem. The converse is true in "phosphorus-limited" systems.

Plant production in both cases is limited by the nutrient in shortest supply, a principle known as von Liebig's law of the minimum. Because of their characteristic differences in size, makeup, geology and other factors, different kinds of ecosystems have long been thought to differ widely in the strength and the nature of their nutrient limitation for example, conventional wisdom has held that freshwater lakes are primarily phosphorus-limited, while oceans along with terrestrial forests and grasslands were believed to be nitrogen-limited.

Yet that is not what Elser's group found. Rather, their data reveals that the three environments are surprisingly similar, and that the balance of nitrogen and phosphorus within each ecosystem conforms to a different pattern than previously expected.

"Our findings don't support conventional views of ecosystem nutrient limitation," said Elser, a professor of ecology, evolution and environmental science at ASU. "They don't, for example, confirm the rule of thumb that in freshwaters phosphorus is more limiting than nitrogen."

Instead, Elser's group found that nitrogen and phosphorus are in fact equally important in freshwater systems, and that phosphorus is just as important as nitrogen in terrestrial ecosystems as well.

"This is in contradiction to conventional wisdom, which seems to emphasize N on land while disregarding P," Elser said.

The determining factor, according to Elser, is simplicity. Underlying all of the splendid diversity of the world's ecosystems -- whether soggy, arid, terrestrial, aquatic, arboreal or algal -- is the simple unifying fact that all plants share a common core of biochemical machinery. That machinery is composed of proteins and nucleotides, meaning that all plants require nitrogen and phosphorus within a limited range of natural proportions.

"Thus, N and P both play a major role in limiting production, no matter where you look," Elser said.

Their paper, "Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems," is highlighted in the News and Views section of the October 25 edition of Nature. The most comprehensive study of its kind, this meta-analysis of more than 300 publications in the field of nutrient limitation in ecosystems was recently published online in the journal Ecology Letters.

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At the root of nutrient limitation, ecosystems are not as different as they seem

TEMPE, Ariz. -- Anyone who has thrown a backyard barbecue knows that hot dogs are inexplicably packaged in different numbers than buns -- eight hot dogs per pack versus 10 hot dog buns. Put in ecological terms, this means that weenie roasts are "hot-dog limited" -- the extra buns are worthless without hot dogs to fill them.

Such limiting factors are a cornerstone of natural ecology, where phosphorus or nitrogen limits plant production in most ecosystems. According to the customary model, the relative importance of these two key nutrients varies by ecosystem but a group of researchers led by Arizona State University professor James Elser has found that this view might need to be updated.

Their paper, "Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems," is highlighted in the News and Views section of the October 25 edition of Nature. The most comprehensive study of its kind, this meta-analysis of more than 300 publications in the field of nutrient limitation in ecosystems was recently published online in the journal Ecology Letters.

Like all living things, plants require a number of chemical elements in order to flourish, including carbon, hydrogen and oxygen. They also need nitrogen, a building block of proteins and phosphorus, used to make the nucleotides that compose DNA and RNA. The interplay of these elements affects the growth of the food web's foundational plants, and so understanding their interplay is of vital environmental and commercial concern.

Nitrogen and phosphorus, both widely used in fertilizers, must be in proper balance to be effective. Adding nitrogen alone to an ecosystem is helpful only up to a point, after which plants stop benefiting unless phosphorus also is added. If such a system responds positively to the initial nitrogen addition, it is said to be "nitrogen-limited," because the availability of nitrogen instantaneously constrains the productivity of the ecosystem. The converse is true in "phosphorus-limited" systems.

Plant production in both cases is limited by the nutrient in shortest supply, a principle known as von Liebig's law of the minimum. Because of their characteristic differences in size, makeup, geology and other factors, different kinds of ecosystems have long been thought to differ widely in the strength and the nature of their nutrient limitation for example, conventional wisdom has held that freshwater lakes are primarily phosphorus-limited, while oceans along with terrestrial forests and grasslands were believed to be nitrogen-limited.

Yet that is not what Elser's group found. Rather, their data reveals that the three environments are surprisingly similar, and that the balance of nitrogen and phosphorus within each ecosystem conforms to a different pattern than previously expected.

"Our findings don't support conventional views of ecosystem nutrient limitation," said Elser, a professor of ecology, evolution and environmental science at ASU. "They don't, for example, confirm the rule of thumb that in freshwaters phosphorus is more limiting than nitrogen."

Instead, Elser's group found that nitrogen and phosphorus are in fact equally important in freshwater systems, and that phosphorus is just as important as nitrogen in terrestrial ecosystems as well.

"This is in contradiction to conventional wisdom, which seems to emphasize N on land while disregarding P," Elser said.

The determining factor, according to Elser, is simplicity. Underlying all of the splendid diversity of the world's ecosystems -- whether soggy, arid, terrestrial, aquatic, arboreal or algal -- is the simple unifying fact that all plants share a common core of biochemical machinery. That machinery is composed of proteins and nucleotides, meaning that all plants require nitrogen and phosphorus within a limited range of natural proportions.

"Thus, N and P both play a major role in limiting production, no matter where you look," Elser said.

Source: James Elser, 480-965-9747, [email protected]

Media Contacts: Nicholas Gerbis, (480) 965-9690, [email protected]
Skip Derra, (480) 965-4823, [email protected]

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


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