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Phosphorus (P) is essential for growing crops, but the supply of high-quality phosphate rock reserves used for fertilizer production is finite while losses of P from the food/waste system cause considerable environmental damage. A variety of emerging approaches in biotechnology are reviewed that hold promise for improving the sustainability of P use in the food/water systems. These include improved sensors, cell culture approaches to meat production, bio-based P adsorption and transformation strategies, advancements in understanding of polyphosphate-accumulating organisms, and new approaches involving biomineralization and anaerobic treatment. By advancing these technologies to scale, progress can be made in developing a circular phosphorus economy that improves food security while protecting drinking water and aquatic ecosystems., Competing Interests: Declaration of Competing Interest James Elser reports financial support was provided by National Science Foundation. Douglas F. Call, Jessica A. Deaver, Owen W. Duckworth, Brooke K. Mayer, Eric S. McLamore, Bruce E. Rittmann, Maheen Mahmood, and Paul Westerhoff report financial support was provided by National Science Foundation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Microorganisms grow despite imbalances in the availability of nutrients and energy. The biochemical and elemental adjustments that bacteria employ to sustain growth when these resources are suboptimal are not well understood. We assessed how Pseudomonas putida KT2440 adjusts its physiology at differing dilution rates (to approximate growth rates) in response to carbon (C), nitrogen (N), and phosphorus (P) stress using chemostats. Cellular elemental and biomolecular pools were variable in response to different limiting resources at a slow dilution rate of 0.12 h -1 , but these pools were more similar across treatments at a faster rate of 0.48 h -1 . At slow dilution rates, limitation by P and C appeared to alter cell growth efficiencies as reflected by changes in cellular C quotas and rates of oxygen consumption, both of which were highest under P- and lowest under C- stress. Underlying these phenotypic changes was differential gene expression of terminal oxidases used for ATP generation that allows for increased energy generation efficiency. In all treatments under fast dilution rates, KT2440 formed aggregates and biofilms, a physiological response that hindered an accurate assessment of growth rate, but which could serve as a mechanism that allows cells to remain in conditions where growth is favorable. Our findings highlight the ways that microorganisms dynamically adjust their physiology under different resource supply conditions, with distinct mechanisms depending on the limiting resource at slow growth and convergence toward an aggregative phenotype with similar compositions under conditions that attempt to force fast growth., Importance: All organisms experience suboptimal growth conditions due to low nutrient and energy availability. Their ability to survive and reproduce under such conditions determines their evolutionary fitness. By imposing suboptimal resource ratios under different dilution rates on the model organism Pseudomonas putida KT2440, we show that this bacterium dynamically adjusts its elemental composition, morphology, pools of biomolecules, and levels of gene expression. By examining the ability of bacteria to respond to C:N:P imbalance, we can begin to understand how stoichiometric flexibility manifests at the cellular level and impacts the flow of energy and elements through ecosystems., Competing Interests: The authors declare no conflict of interest.

Uneven global distribution of phosphate rock deposits and the supply chains to transport phosphorus (P) make P fertilizers vulnerable to exogenous shocks, including commodity market shocks; extreme weather events or natural disasters; and geopolitical instability, such as trade disputes, disruption of shipping routes, and war. Understanding bidirectional risk transmission (global-to-local and local-to-global) in P supply and consumption chains is thus essential. Ignoring P system interdependencies and associated risks could have major impacts on critical infrastructure operations and increase the vulnerability of global food systems. We highlight recent unanticipated events and cascading effects that have impacted P markets globally. We discuss the need to account for exogenous shocks in local assessments of P flows, policies, and infrastructure design choices. We also provide examples of how accounting for undervalued global risks to the P industry can hasten the transition to a sustainable P future. For example, leveraging internal P recycling loops, improving plant P use efficiency, and utilizing legacy soil P all enhance system resiliency in the face of exogenous shocks and long-term anticipated threats. Strategies applied at the local level, which are embedded within national and global policy systems, can have global-scale impacts in derisking the P supply chain., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Growth is a function of the net accrual of resources by an organism. Energy and elemental contents of organisms are dynamically linked through their uptake and allocation to biomass production, yet we lack a full understanding of how these dynamics regulate growth rate. Here, we develop a multivariate imbalance framework, the growth efficiency hypothesis, linking organismal resource contents to growth and metabolic use efficiencies, and demonstrate its effectiveness in predicting consumer growth rates under elemental and food quantity limitation. The relative proportions of carbon (%C), nitrogen (%N), phosphorus (%P), and adenosine triphosphate (%ATP) in consumers differed markedly across resource limitation treatments. Differences in their resource composition were linked to systematic changes in stoichiometric use efficiencies, which served to maintain relatively consistent relationships between elemental and ATP content in consumer tissues and optimize biomass production. Overall, these adjustments were quantitatively linked to growth, enabling highly accurate predictions of consumer growth rates., Competing Interests: Competing interests statement:The authors declare no competing interest.

With the ongoing differential disruption of the biogeochemical cycles of major elements that are essential for all life (carbon, nitrogen, and phosphorus), organisms are increasingly faced with a heterogenous supply of these elements in nature. Given that photosynthetic primary producers form the base of aquatic food webs, impacts of changed elemental supply on these organisms are particularly important. One way that phytoplankton cope with the differential availability of nutrients is through physiological changes, resulting in plasticity in macromolecular and elemental biomass composition. Here, we assessed how the green alga Chlamydomonas reinhardtii adjusts its macromolecular (e.g., carbohydrates, lipids, and proteins) and elemental (C, N, and P) biomass pools in response to changes in growth rate and the modification of resources (nutrients and light). We observed that Chlamydomonas exhibits considerable plasticity in elemental composition (e.g., molar ratios ranging from 124 to 971 for C:P, 4.5 to 25.9 for C:N, and 15.1 to 61.2 for N:P) under all tested conditions, pointing to the adaptive potential of Chlamydomonas in a changing environment. Exposure to low light modified the elemental and macromolecular composition of cells differently than limitation by nutrients. These observed differences, with potential consequences for higher trophic levels, included smaller cells, shifts in C:N and C:P ratios (due to proportionally greater N and P contents), and differential allocation of C among macromolecular pools (proportionally more lipids than carbohydrates) with different energetic value. However, substantial pools of N and P remained unaccounted for, especially at fast growth, indicating accumulation of N and P in forms we did not measure., (© 2024 The Authors. Journal of Phycology published by Wiley Periodicals LLC on behalf of Phycological Society of America.)

Nitrogen (N) and phosphorus (P) are two critical nutrients for agroecosystems. In meeting food demands, human use of both nutrients has crossed planetary boundaries for sustainability. Further, there has been a dramatic shift in their relative inputs and outputs, which may generate strong N:P imbalances. Despite enormous efforts on agronomic N and P budgets, the spatio-temporal characteristics of different crop types in using nutrients are unknown as are patterns in the stoichiometric coupling of these nutrients. Thus, we analyzed the annual crop-specific N and P budgets and their stoichiometric relations for producing ten major crops at the provincial level of China during 2004-2018. Results show that, China has generally witnessed excessive N and P input over the past 15 years, with the N balance remaining stable while the P balance increasing by more than 170%, thus resulting in a decline in the N:P mass ratios from 10.9 in 2004 to 3.8 in 2018. Crop-aggregated nutrient use efficiency (NUE) of N has increased by 10% in these years while most crops have shown a decreasing trend of this indicator for P, which reduced NUE of P from 75% to 61% during this period. At the provincial level, the nutrient fluxes of Beijing and Shanghai have obviously declined, while the nutrient fluxes of provinces such as Xinjiang and Inner Mongolia have increased significantly. Although N management has made progress, P management should be further explored in the future due to eutrophication concerns. More importantly, N and P management strategies for sustainable agriculture in China should take account of not only the absolute nutrient use, but also their stoichiometric balance for different crops in different locations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The growth rate hypothesis (GRH) posits that variation in organismal stoichiometry (C:P and N:P ratios) is driven by growth-dependent allocation of P to ribosomal RNA. The GRH has found broad but not uniform support in studies across diverse biota and habitats. We synthesise information on how and why the tripartite growth-RNA-P relationship predicted by the GRH may be uncoupled and outline paths for both theoretical and empirical work needed to broaden the working domain of the GRH. We found strong support for growth to RNA (r 2  = 0.59) and RNA-P to P (r 2  = 0.63) relationships across taxa, but growth to P relationships were relatively weaker (r 2  = 0.09). Together, the GRH was supported in ~50% of studies. Mechanisms behind GRH uncoupling were diverse but could generally be attributed to physiological (P accumulation in non-RNA pools, inactive ribosomes, translation elongation rates and protein turnover rates), ecological (limitation by resources other than P), and evolutionary (adaptation to different nutrient supply regimes) causes. These factors should be accounted for in empirical tests of the GRH and formalised mathematically to facilitate a predictive understanding of growth., (© 2022 The Authors. Ecology Letters published by John Wiley & Sons Ltd.)

Microplastics are contaminants that are closely associated with human activity and are often abundant even in remote areas. As the largest natural freshwater lake in the western USA, Flathead Lake is a suitable site to study microplastics in lakes in less-populated areas of North America. Our assessment of microplastics in lake surface water samples showed that microplastic densities and concentrations in Flathead Lake were similar to those in other lakes located in less-populated areas around the world, with densities ranging from 8.00 × 10 4 to 4.22 × 10 5 particles/km 2 with a mean concentration of 1.89 × 10 5 particles/km 2 . Dry deposition rates for microplastics ranged from 4 to 140 particles/m 2 /day with an average of 69 particles/m 2 /day and were significantly higher in the fall. Microplastic concentrations in wet deposition ranged from 0.006 particles/mL to 0.050 particles/mL with highest concentrations in winter and lowest in summer. Fibrous microplastics were predominant in both lake water and atmospheric deposition. The high densities of microplastics in the sample sites located near the Flathead River inlet suggests that the river is an important source of microplastics to Flathead Lake. The high densities of microplastics and high proportions of non-fibrous microplastics near populated areas of the lake imply that local human activities also affect microplastics in Flathead Lake. Although the annual flux of microplastics in dry deposition was higher than that in wet deposition, the relatively modest difference suggests that precipitation might enhance the deposition of microplastics. The results of this study indicate that instituting increased control measures that target both reducing the microfibers generated by laundry and improving the overall level of plastic waste management in the watershed may help in controlling microplastic levels in Flathead Lake., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Considerable attention is given to absolute nutrient levels in lakes, rivers, and oceans, but less is paid to their relative concentrations, their nitrogen:phosphorus (N:P) stoichiometry, and the consequences of imbalanced stoichiometry. Here, we report 38 y of nutrient dynamics in Flathead Lake, a large oligotrophic lake in Montana, and its inflows. While nutrient levels were low, the lake had sustained high total N: total P ratios (TN:TP: 60 to 90:1 molar) throughout the observation period. N and P loading to the lake as well as loading N:P ratios varied considerably among years but showed no systematic long-term trend. Surprisingly, TN:TP ratios in river inflows were consistently lower than in the lake, suggesting that forms of P in riverine loading are removed preferentially to N. In-lake processes, such as differential sedimentation of P relative to N or accumulation of fixed N in excess of denitrification, likely also operate to maintain the lake's high TN:TP ratios. Regardless of causes, the lake's stoichiometric imbalance is manifested in P limitation of phytoplankton growth during early and midsummer, resulting in high C:P and N:P ratios in suspended particulate matter that propagate P limitation to zooplankton. Finally, the lake's imbalanced N:P stoichiometry appears to raise the potential for aerobic methane production via metabolism of phosphonate compounds by P-limited microbes. These data highlight the importance of not only absolute N and P levels in aquatic ecosystems, but also their stoichiometric balance, and they call attention to potential management implications of high N:P ratios.

Background: On the front lines of climate change, glacier termini play crucial roles in linking glaciers and downstream ecosystems during glacier retreat. However, we lack a clear understanding of biological processes that occur in surface and basal ice at glacier termini., Methods: Here, we studied the bacterial communities in surface ice and basal ice (the bottom layer) of a glacier terminus in the Yangtze River Source, Qinghai-Tibet Plateau., Results: Surface and basal ice harbored distinct bacterial communities but shared some core taxa. Surface ice communities had a higher α-diversity than those in basal ice and were dominated by Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, and Cyanobacteria while basal ice was dominated by Firmicutes and Proteobacteria. The bacterial communities were also substantially different in functional potential. Genes associated with functional categories of cellular processes and metabolism were significantly enriched in surface ice, while genes connected to environmental information processing were enriched in basal ice. In terms of biogeochemical cycles of carbon, nitrogen, phosphorus, and sulfur, bacterial communities in surface ice were enriched for genes connected to aerobic carbon fixation, aerobic respiration, denitrification, nitrogen assimilation, nitrogen mineralization, sulfur mineralization, alkaline phosphatase, and polyphosphate kinase. In contrast, bacterial communities in basal ice were enriched for genes involved in anaerobic carbon fixation, fermentation, nitrate reduction, 2-aminoethylphosphonic acid pathway, G3P transporter, glycerophosphodiester phosphodiesterase, and exopolyphosphatase. Structural equation modeling showed that total nitrogen and environmental carbon:phosphorus were positively while environmental nitrogen:phosphorus was negatively associated with taxonomic β-diversity which itself was strongly associated with functional β-diversity of bacterial communities., Conclusions: This study furthers our understanding of biogeochemical cycling of the mountain cryosphere by revealing the genetic potential of the bacterial communities in surface and basal ice at the glacier terminus, providing new insights into glacial ecology as well as the influences of glacier retreat on downstream systems., (© 2022. The Author(s).)

Species invasions can have substantial impacts on native species and ecosystems, with important consequences for biodiversity. How these disturbances drive changes in the trophic structure of native food webs through time is poorly understood. Here, we quantify trophic disruption in freshwater food webs to invasion by an apex fish predator, lake trout, using an extensive stable isotope dataset across a natural gradient of uninvaded and invaded lakes in the northern Rocky Mountains, USA. Lake trout invasion increased fish diet variability (trophic dispersion), displaced native fishes from their reference diets (trophic displacement), and reorganized macroinvertebrate communities, indicating strong food web disruption. Trophic dispersion was greatest 25 to 50 y after colonization and dissipated as food webs stabilized in later stages of invasion (>50 y). For the native apex predator, bull trout, trophic dispersion preceded trophic displacement, leading to their functional loss in late-invasion food webs. Our results demonstrate how invasive species progressively disrupt native food webs via trophic dispersion and displacement, ultimately yielding biological communities strongly divergent from those in uninvaded ecosystems., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

Alpine regions are changing rapidly due to loss of snow and ice in response to ongoing climate change. While studies have documented ecological responses in alpine lakes and streams to these changes, our ability to predict such outcomes is limited. We propose that the application of fundamental rules of life can help develop necessary predictive frameworks. We focus on four key rules of life and their interactions: the temperature dependence of biotic processes from enzymes to evolution; the wavelength dependence of the effects of solar radiation on biological and ecological processes; the ramifications of the non-arbitrary elemental stoichiometry of life; and maximization of limiting resource use efficiency across scales. As the cryosphere melts and thaws, alpine lakes and streams will experience major changes in temperature regimes, absolute and relative inputs of solar radiation in ultraviolet and photosynthetically active radiation, and relative supplies of resources (e.g., carbon, nitrogen, and phosphorus), leading to nonlinear and interactive effects on particular biota, as well as on community and ecosystem properties. We propose that applying these key rules of life to cryosphere-influenced ecosystems will reduce uncertainties about the impacts of global change and help develop an integrated global view of rapidly changing alpine environments. However, doing so will require intensive interdisciplinary collaboration and international cooperation. More broadly, the alpine cryosphere is an example of a system where improving our understanding of mechanistic underpinnings of living systems might transform our ability to predict and mitigate the impacts of ongoing global change across the daunting scope of diversity in Earth's biota and environments., (© 2020 John Wiley & Sons Ltd.)

Grasslands across the world are being degraded due to the impacts of overgrazing and climate change. However, the influences of grassland degradation on carbon (C), nitrogen (N), and phosphorus (P) dynamics and stoichiometry in soil ecosystems are not well studied, especially at high elevations where ongoing climate change is most pronounced. Ecological stoichiometry facilitates understanding the biogeochemical cycles of multiple elements by studying their balance in ecological systems. This study sought to assess the responses of these soil elements to grassland degradation in the Qinghai Lake watershed on the Qinghai-Tibet Plateau (QTP), which has an average elevation of >4000 m and is experiencing serious grassland degradation due to its sensitivity and vulnerability to external disturbances. Substituting space for time, we quantified normalized difference vegetation index to gauge grassland degradation. C, N, and P concentrations and their molar ratios in soil and in soil microbial biomass were also measured. The results showed that grassland degradation decreased the concentrations of C and N, as well as the ratios of C:P and N:P in soil. The soil became relatively more P rich and thus N limitation is anticipated to be more apparent with grassland degradation. Moreover, C, N, and P concentrations in soil microbial biomass decreased with increased grassland degradation. C:N:P ratios of soil microbial biomass were highly constrained, suggesting that soil microorganisms exhibited a strong homeostatic behavior, while the variations of microbial biomass C:N:P ratios suggest changes in microbial activities and community structure. Overall, our study revealed that grassland degradation differentially affects soil C, N, and P, leading to decreased C:N and N:P in soil, as well as decreased C, N, and P concentrations in soil microbial biomass. This study provides insights from a stoichiometric perspective into microbial and biogeochemical responses of grassland ecosystems as they undergo degradation on the QTP., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Grassland is among the largest terrestrial biomes and is experiencing serious degradation, especially on the Qinghai-Tibet Plateau (QTP). However, the influences of grassland degradation on microbial communities in stream biofilms are largely unknown. Using 16S rRNA gene sequencing, we investigated the bacterial communities in stream biofilms in sub-basins with different grassland status in the Qinghai Lake watershed. Grassland status in the sub-basins was quantified using the normalized difference vegetation index (NDVI). Proteobacteria, Bacteroidetes, Cyanobacteria, and Verrucomicrobia were the dominant bacterial phyla. OTUs, 7,050, were detected in total, within which 19 were abundant taxa, and 6,922 were rare taxa. Chao 1, the number of observed OTUs, and phylogenetic diversity had positive correlations with carbon (C), nitrogen (N), and/or phosphorus (P) in biofilms per se . The variation of bacterial communities in stream biofilms was closely associated with the rate of change in NDVI, pH, conductivity, as well as C, N, P, contents and C:N ratio of the biofilms. Abundant subcommunities were more influenced by environmental variables relative to the whole community and to rare subcommunities. These results suggest that the history of grassland degradation (indicated as the rate of change in NDVI) influences bacterial communities in stream biofilms. Moreover, the bacterial community network showed high modularity with five major modules (>50 nodes) that responded differently to environmental variables. According to the module structure, only one module connector and 12 module hubs were identified, suggesting high fragmentation of the network and considerable independence of the modules. Most of the keystone taxa were rare taxa, consistent with fragmentation of the network and with adverse consequences for bacterial community integrity and function in the biofilms. By documenting the properties of bacterial communities in stream biofilms in a degrading grassland watershed, our study adds to our knowledge of the potential influences of grassland degradation on aquatic ecosystems., (Copyright © 2020 Ren, Niu, Ma, Wang, Wang, Fu and Elser.)

Large-scale and rapid improvement in wastewater treatment is common practice in developing countries, yet this influence on nutrient regimes in receiving waterbodies is rarely examined at broad spatial and temporal scales. Here, we present a study linking decadal nutrient monitoring data in lakes with the corresponding estimates of five major anthropogenic nutrient discharges in their surrounding watersheds over time. Within a continuous monitoring dataset covering the period 2008 to 2017, we find that due to different rates of change in TN and TP concentrations, 24 of 46 lakes, mostly located in China's populated regions, showed increasing TN/TP mass ratios; only 3 lakes showed a decrease. Quantitative relationships between in-lake nutrient concentrations (and their ratios) and anthropogenic nutrient discharges in the surrounding watersheds indicate that increase of lake TN/TP ratios is associated with the rapid improvement in municipal wastewater treatment. Due to the higher removal efficiency of TP compared with TN, TN/TP mass ratios in total municipal wastewater discharge have continued to increase from a median of 10.7 (95% confidence interval, 7.6 to 15.1) in 2008 to 17.7 (95% confidence interval, 13.2 to 27.2) in 2017. Improving municipal wastewater collection and treatment worldwide is an important target within the 17 sustainable development goals set by the United Nations. Given potential ecological impacts on biodiversity and ecosystem function of altered nutrient ratios in wastewater discharge, our results suggest that long-term strategies for domestic wastewater management should not merely focus on total reductions of nutrient discharges but also consider their stoichiometric balance., Competing Interests: The authors declare no competing interest.

Eutrophication mitigation is an ongoing priority for aquatic ecosystems. However, the current eutrophication control strategies (phosphorus (P) and/or nitrogen (N)) are guided mainly by nutrient addition experiments in small waters without encompassing all in-lake biogeochemical processes that are associated largely with lake morphological characteristics. Here, we use a global lake data set (573 lakes) to show that the relative roles of N vs P in affecting eutrophication are underpinned by water depth. Mean depth and maximum depth relative to mixing depth were used to distinguish shallow (mixing depth > maximum depth), deep (mixing depth < mean depth), and transitional (mean depth ≤ mixing depth ≤ maximum depth) lakes in this study. TN/TP ratio (by mass) was used as an indicator of potential lake nutrient limitation, i.e., N only limitation if N/P < 9, N + P colimitation if 9 ≤ N/P < 22.6, and P only limitation if N/P ≥ 22.6. The results show that eutrophication is favored in shallow lakes, frequently (66.2%) with N limitation while P limitation predominated (94.4%) in most lakes but especially in deep ones. The importance of N limitation increases but P limitation decreases with lake trophic status while N and P colimitation occurs primarily (59.4%) in eutrophic lakes. These results demonstrate that phosphorus reduction can mitigate eutrophication in most large lakes but a dual N and P reduction may be needed in eutrophic lakes, especially in shallow ones (or bays). Our analysis helps clarify the long debate over whether N, P, or both control primary production. While these results imply that more resources be invested in nitrogen management, given the high costs of nitrogen pollution reduction, more comprehensive results from carefully designed experiments at different scales are needed to further verify this modification of the existing eutrophication mitigation paradigm.

Several universal genomic traits affect trade-offs in the capacity, cost, and efficiency of the biochemical information processing that underpins metabolism and reproduction. We analyzed the role of these traits in mediating the responses of a planktonic microbial community to nutrient enrichment in an oligotrophic, phosphorus-deficient pond in Cuatro Ciénegas, Mexico. This is one of the first whole-ecosystem experiments to involve replicated metagenomic assessment. Mean bacterial genome size, GC content, total number of tRNA genes, total number of rRNA genes, and codon usage bias in ribosomal protein sequences were all higher in the fertilized treatment, as predicted on the basis of the assumption that oligotrophy favors lower information-processing costs whereas copiotrophy favors higher processing rates. Contrasting changes in trait variances also suggested differences between traits in mediating assembly under copiotrophic versus oligotrophic conditions. Trade-offs in information-processing traits are apparently sufficiently pronounced to play a role in community assembly because the major components of metabolism-information, energy, and nutrient requirements-are fine-tuned to an organism's growth and trophic strategy., Competing Interests: JO, AP, ZL, AR, LA, LE, JS, VS, CD, JE No competing interests declared, (© 2020, Okie et al.)

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives., (© 2019 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

It is vital to understand processes of microplastic ingestion and egestion by aquatic organisms in order to evaluate the potential effects and impacts of microplastics in aquatic ecosystems. In this study, goldfish ( Carassius auratus ) was used to investigate ingestion and egestion of polyethylene (PE) microplastics and how these processes were affected by size, color, and shape of microplastics. Results showed that goldfish ingested white PE microplastics only in the presence of fish feed and that microplastics larger than 2 mm were rejected even after being ingested. However, in the presence of food, more green and black microplastics were ingested compared with red, blue, and white microplastics while significantly higher amounts of microplastic films were ingested compared with fragments and filaments. Microplastics ingested by goldfish were egested within 72 h. However, the egestion rate of filaments was the lowest among all tested microplastic shapes. The presence of food appeared to reduce film and filament residues in fish after 72 h. Results of this study imply that different features of microplastics result in different exposure risks for fish. Thus, the specific features of microplastics (e.g. their shape, color, and size) should be considered in future ecotoxicological studies., (© 2019 The Authors. Published by Elsevier Ltd.)

The processes of urbanization and industrialization within geological phosphorus-rich mountains (GPMn) have resulted in water degradation within southwest China. Lake Dianchi, one of the most eutrophicated lakes in China, has epitomized this issue. Clear understandings of phosphorus (P) mitigation efforts, the evolution of P budgets, and possible risks in the Dianchi system will benefit future eutrophication control, providing valuable lessons for other plateau freshwater lakes. In this study, we applied systematic review methodology to investigate the above questions, and then compared the results with other lakes worldwide. Generally, meta-analytical approaches have indicated P levels remain a key factor in causing algal blooms. Post-2015, the P budget of the Dianchi system, especially in Caohai section, was modified. However, it's still experiencing high pressures from P enrichment (Caohai: 0.4 mg·l -1 ; Waihai: 0.2 mg·l -1 ). The flux of P in Dianchi remains high, both through the external P load (556 ton·a -1 ), and an internal cycle (304 ton·a -1 associated with the absorption, deposition and removal of algae biomass; and 380 ton·a -1 associated with sediment exchange). Meanwhile, significant P retention has been observed in the lake, in particular within the Waihai section (211 ton·a -1 ). Currently, water diversion (from external watersheds), sewage diversion, and sediment-dredging projects have benefited Dianchi. However, continuous urbanization and GPMn ecological degradation could introduce hundreds of tons of additional P, leading to subsequent algal blooms. Furthermore, beyond Lake Dianchi, other lakes and reservoirs in southwest China are facing similar issues regarding P mitigation, especially in GPMn regions, though corresponding knowledge is still limited. Therefore, effective and flexible sub-regional protection strategies and research related to external and internal P mitigations have become key requirements for Lake Dianchi management. Meanwhile, ecologically sensitive approaches to GPMn regions, as well as city development within basin and market driven treatments, should be incorporated into regional water source protection for southwest China., (Copyright © 2019. Published by Elsevier B.V.)

Nitrogen (N) and phosphorus (P) are key growth-limiting nutrients for organisms and their absolute and relative supplies regulate the structure and function of ecosystems. Landcover changes lead to modifications of terrestrial biogeochemistry, consequently influencing aquatic nutrient conditions. This study sought to evaluate the potential impacts of grassland degradation on nutrient availability and nutrient limitation in the Qinghai Lake (China) and its inflow streams. We sampled nutrient concentrations and tested stream nutrient limitation by conducting nutrient diffusing substrata (NDS) bioassays in streams flowing through subbasins with different grassland status. To test nutrient limitation and the responses of lake phytoplankton to stream inflows, bioassays were conducted by adding different nutrients (N, P, and joint NP) as well as water from different streams to lake water with phytoplankton, respectively. In general, N concentrations as well as N:P ratios decreased while P concentrations increased with decreased normalized difference vegetation index (NDVI, an index of vegetation status), especially in September, suggesting that grassland degradation (low NDVI) has the potential to differentially decrease N availability and increase P availability in streams. Consistent with this, relative responses (RR) of stream periphyton to P and combined NP enrichments in the NDS bioassays decreased with stream P concentrations while increased with stream water N:P ratios. Lake phytoplankton responded strongly to P and combined NP addition indicating strong P-limitation of lake phytoplankton. RR of lake phytoplankton to stream water decreased with nitrate concentration and N:P ratios in stream water and increased with the concentrations of ammonium, total phosphorus, and soluble reactive phosphorus, indicating that stream water with higher P but lower N and N:P from degraded subcatchments is associated with increased impact on P-limited Lake phytoplankton. Overall, this study suggests that grassland degradation has the potential to differentially influence the nutrients delivered to streams with substantial increases in P but decreases in N and N:P, alleviating P limitation of stream periphyton and, ultimately, stimulating P-limited phytoplankton growth in the lake., (© 2019 by the Ecological Society of America.)

Decadal-scale increases in fire frequency have the potential to deplete ecosystems of essential nutrients and consequently impede nutrient-limited biological processes via stoichiometric imbalance. Decomposition, a fundamental ecosystem function and strong driver of future fire occurrence, is highly sensitive to nutrient availability and is, therefore, particularly important in this context. Here we show that 40 yr of quadrennial (4yB) and biennial (2yB) prescribed burning result in severely P- and N-depleted litter stoichiometry, respectively, relative to fire exclusion. These effects exacerbated the nutrient limitation of microbial activities, constraining litter decomposition by 42.1% (4yB) and 23.6% (2yB) relative to unburned areas. However, invertebrate-driven decomposition largely compensated for the diminished capacity of micro-organisms under 4yB, suggesting that invertebrates could have an important stabilizing influence in fire-affected ecosystems. This effect was strongly positively coupled with the strength of microbial P-limitation and was not obviously or directly driven by fire regime-induced changes in invertebrate community assemblage. Together, our results reveal that high-frequency fire regimes promote nutrient-poor, carbon-rich ecosystem stoichiometry and, in doing so, disrupt ecosystem processes and modify the relative functionality of micro-organisms and invertebrates., (© 2019 by the Ecological Society of America.)

Based on field investigations and modeling estimates, rivers are considered an important route taken by microplastics to reach the sea. However, only a few studies have directly assessed occurrence and fate of microplastics in rivers. In this study, we surveyed the occurrence and fate of microplastic debris in the middle and lower reaches of the Yangtze River, which was estimated to be the largest riverine source of plastic debris to the sea. The abundance of microplastics at 15 sites along the middle and lower reaches of the Yangtze River ranged from 1.95 × 10 5 to 9.00 × 10 5  items/km 2 with an average of 4.92 × 10 5  items/km 2 . The abundance of microplastics was positively correlated with the abundance of mesoplastics. Megacities, large riparian lakes, and seawater encroachment appeared to be main factors affecting the distribution of microplastics in the Yangtze River, while the deposition to benthic and riparian sediments likely led to observed decreases in microplastics in some sections of the river. The results of this study indicate that a considerable amount of microplastics generated in large river catchments are not transported to the sea and past modeling estimates of microplastic flux may contain biases. The flux of microplastics reaching the sea should be calculated based on long-term monitoring at the tidal limit of rivers. More importantly, the fate and effects of microplastics retained in the river system should receive more attention., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Nitrogen (N) and phosphorus (P) limit primary production in many aquatic ecosystems, with major implications for ecological interactions in plankton communities. Yet it remains unclear how evolution may affect the N∶P stoichiometry of phytoplankton-zooplankton interactions. Here, we address this issue by analyzing an eco-evolutionary model of phytoplankton-zooplankton interactions with explicit nitrogen and phosphorus dynamics. In our model, investment of phytoplankton in nitrogen versus phosphorus uptake is an evolving trait, and zooplankton display selectivity for phytoplankton with N∶P ratios matching their nutritional requirements. We use this model to explore implications of the contrasting N∶P requirements of copepods versus cladocerans. The model predicts that selective zooplankton strongly affect the N∶P ratio of phytoplankton, resulting in deviations from their optimum N∶P ratio. Specifically, selective grazing by nitrogen-demanding copepods favors dominance of phytoplankton with low N∶P ratios, whereas phosphorus-demanding cladocerans favor dominance of phytoplankton with high N∶P ratios. Interestingly, selective grazing by nutritionally balanced zooplankton leads to the occurrence of alternative stable states, where phytoplankton may evolve either low, optimum, or high N∶P ratios, depending on the initial conditions. These results offer a new perspective on commonly observed differences in N∶P stoichiometry between plankton of freshwater and those of marine ecosystems and indicate that selective grazing by zooplankton can have a major impact on the stoichiometric composition of phytoplankton.

Consumer-driven nutrient recycling can have substantial effects on primary production and patterns of nutrient limitation in aquatic ecosystems by altering the rates as well as the relative supplies of the key nutrients nitrogen (N) and phosphorus (P). While variation in nutrient recycling stoichiometry has been well-studied among species, the mechanisms that explain intraspecific variation in recycling N:P are not well-understood. We examined the relative importance of potential drivers of variation in nutrient recycling by the fish Gambusia marshi among aquatic habitats in the Cuatro Ciénegas basin of Coahuila, Mexico. There, G. marshi inhabits warm thermal springs with high predation pressure as well as cooler, surface runoff-fed systems with low predation pressure. We hypothesized that variation in food consumption among these habitats would drive intraspecific differences in excretion rates and N:P ratios. Stoichiometric models predicted that temperature alone should not cause substantial variation in excretion N:P, but that further reducing consumption rates should substantially increase excretion N:P. We performed temperature and diet ration manipulation experiments in the laboratory and found strong support for model predictions. We then tested these predictions in the field by measuring nutrient recycling rates and ratios as well as body stoichiometry of fish from nine sites that vary in temperature and predation pressure. Fish from warm, high-predation sites excreted nutrients at a lower N:P ratio than fish from cool, low-predation sites, consistent with the hypothesis that reduced consumption under reduced predation pressure had stronger consequences for P retention and excretion among populations than did variation in body stoichiometry. These results highlight the utility of stoichiometric models for predicting variation in consumer-driven nutrient recycling within a phenotypically variable species., (© 2018 by the Ecological Society of America.)

Increasing atmospheric nitrogen (N) deposition may affect plant biodiversity, subsequently altering ecosystem stability. While a few studies have explored how simulated N deposition affects community stability and its underlying mechanisms, the experimental levels of N addition used are usually higher than current and future N deposition rates. Thus, their results could produce highly uncertain predictions of ecosystem function, especially if the responses to N deposition are nonlinear. We conducted a manipulative experiment that simulated elevated atmospheric N deposition with several N addition levels to evaluate the effect of N deposition on ecosystem stability and its underlying mechanisms in a semiarid grassland in northern China. Here we show that N addition altered community diversity, reducing species richness, evenness, diversity and dominance. In addition, we found that N addition at current N deposition levels had no significant impact on community stability. In contrast, N addition at levels from 4.6 to 13.8gNm -2 yr -1 significantly decreased community stability, although community stability for the 13.8gNm -2 yr -1 treatment was higher than that for the 4.6gNm -2 yr -1 treatment. These results indicate that the response of community stability to N enrichment is nonlinear. This nonlinear change in community stability was positively correlated with species asynchrony, species richness, and species diversity as well as the stability of dominant species and the stability of the grass functional group. Our data suggest a need to re-evaluate the mechanisms responsible for the effects of N deposition on natural ecosystem stability across multiple levels of N enrichment and that additional experimentation with gradients of N loads more similar to future atmospheric N deposition rates is needed., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The biogeochemical and stoichiometric signature of vegetation fire may influence post-fire ecosystem characteristics and the evolution of plant 'fire traits'. Phosphorus (P), a potentially limiting nutrient in many fire-prone environments, might be particularly important in this context; however, the effects of fire on P cycling often vary widely. We conducted a global-scale meta-analysis using data from 174 soil studies and 39 litter studies, and found that fire led to significantly higher concentrations of soil mineral P as well as significantly lower soil and litter carbon:P and nitrogen:P ratios. These results demonstrate that fire has a P-rich signature in the soil-plant system that varies with vegetation type. Further, they suggest that burning can ease P limitation and decouple the biogeochemical cycling of P, carbon and nitrogen. These effects resemble a transient reversion to an earlier stage of ecosystem development, and likely underpin at least some of fire's impacts on ecosystems and organisms., (© 2018 John Wiley & Sons Ltd/CNRS.)

Understanding microbial communities in terms of taxon and function is essential to decipher the biogeochemical cycling in aquatic ecosystems. Lakes and their input streams are highly linked. However, the differences between microbial assemblages in streams and lakes are still unclear. In this study, we conducted an intensive field sampling of microbial communities from lake water and stream biofilms in the Qinghai Lake watershed, the largest lake in China. We determined bacterial communities using high-throughput 16S rRNA gene sequencing and predicted functional profiles using PICRUSt to determine the taxonomic and functional differences between microbial communities in stream biofilms and lake water. The results showed that stream biofilms and lake water harbored distinct microbial communities. The microbial communities were different taxonomically and functionally between stream and lake. Moreover, streams biofilms had a microbial network with higher connectivity and modularity than lake water. Functional beta diversity was strongly correlated with taxonomic beta diversity in both the stream and lake microbial communities. Lake microbial assemblages displayed greater predicted metabolic potentials of many metabolism pathways while the microbial assemblages in stream biofilms were more abundant in xenobiotic biodegradation and metabolism and lipid metabolism. Furthermore, lake microbial assemblages had stronger predicted metabolic potentials in amino acid metabolism, carbon fixation, and photosynthesis while stream microbial assemblages were higher in carbohydrate metabolism, oxidative phosphorylation, and nitrogen metabolism. This study adds to our knowledge of stream-lake linkages from the functional and taxonomic composition of microbial assemblages.

Benthic biofilms in glacier-fed streams harbor diverse microorganisms driving biogeochemical cycles and, consequently, influencing ecosystem-level processes. Benthic biofilms are vulnerable to glacial retreat induced by climate change. To investigate microbial functions of benthic biofilms in glacier-fed streams, we predicted metagenomes from 16s rRNA gene sequence data using PICRUSt and identified functional genes associated with nitrogen and sulfur metabolisms based on KEGG database and explored the relationships between metabolic pathways and abiotic factors in glacier-fed streams in the Tianshan Mountains in Central Asia. Results showed that the distribution of functional genes was mainly associated with glacier area proportion, glacier source proportion, total nitrogen, dissolved organic carbon, and pH. For nitrogen metabolism, the relative abundance of functional genes associated with dissimilatory pathways was higher than those for assimilatory pathways. The relative abundance of functional genes associated with assimilatory sulfate reduction was higher than those involved with the sulfur oxidation system and dissimilatory sulfate reduction. Hydrological factors had more significant correlations with nitrogen metabolism than physicochemical factors and anammox was the most sensitive nitrogen cycling pathway responding to variation of the abiotic environment in these glacial-fed streams. In contrast, sulfur metabolism pathways were not sensitive to variations of abiotic factors in these systems.

Surveys of carbon:nitrogen:phosphorus ratios are available now for major groups of biota and for various aquatic and terrestrial biomes. However, while fungi play an important role in nutrient cycling in ecosystems, relatively little is known about their C:N:P stoichiometry and how it varies across taxonomic groups, functional guilds, and environmental conditions. Here we present the first systematic compilation of C:N:P data for fungi including four phyla (Ascomycota, Basidiomycota, Glomeromycota, and Zygomycota). The C, N, and P contents (percent of dry mass) of fungal biomass varied from 38 to 57%, 0.23 to 15%, and 0.040 to 5.5%, respectively. Median C:N:P stoichiometry for fungi was 250:16:1 (molar), remarkably similar to the canonical Redfield values. However, we found extremely broad variation in fungal C:N:P ratios around the central tendencies in C:N:P ratios. Lower C:P and N:P ratios were found in Ascomycota fungi than in Basidiomycota fungi while significantly lower C:N ratios ( p < 0.05) and higher N:P ratios ( p < 0.01) were found in ectomycorrhizal fungi than in saprotrophs. Furthermore, several fungal stoichiometric ratios were strongly correlated with geographic and abiotic environmental factors, especially latitude, precipitation, and temperature. The results have implications for understanding the roles that fungi play in function in symbioses and in soil nutrient cycling. Further work is needed on the effects of actual in situ growth conditions of fungal growth on stoichiometry in the mycelium.

For many species, migration evolves to allow organisms to access better resources. However, the proximate factors that trigger these developmental changes, and how and why these vary across species, remain poorly understood. One prominent hypothesis is that poor-quality food promotes development of migratory phenotypes and this has been clearly shown for some polyphenic insects. In other animals, particularly long-distance bird migrants, it is clear that high-quality food is required to prepare animals for a successful migration. We tested the effect of diet quality on the flight behaviour and morphology of the Mongolian locust, Oedaleus asiaticus . Locusts reared at high population density and fed low-N grass (performance-enhancing for this species) had enhanced migratory morphology relative to locusts fed high-N grass. Furthermore, locusts fed synthetic diets with an optimal 1 : 2 protein : carbohydrate ratio flew for longer times than locusts fed diets with lower or higher protein : carbohydrate ratios. In contrast to the hypothesis that performance-degrading food should enhance migration, our results support the more nuanced hypothesis that high-quality diets promote development of migratory characteristics when migration is physiologically challenging., Competing Interests: We declare we have no competing interests.

Nutrient availability and ratios can play an important role in shaping microbial communities of freshwater ecosystems. The Cuatro Ciénegas Basin (CCB) in Mexico is a desert oasis where, perhaps paradoxically, high microbial diversity coincides with extreme oligotrophy. To better understand the effects of nutrients on microbial communities in CCB, a mesocosm experiment was implemented in a stoichiometrically imbalanced pond, Lagunita, which has an average TN:TP ratio of 122 (atomic). The experiment had four treatments, each with five spatial replicates - unamended controls and three fertilization treatments with different nitrogen:phosphorus (N:P) regimes (P only, N:P = 16 and N:P = 75 by atoms). In the water column, quantitative PCR of the 16S rRNA gene indicated that P enrichment alone favored proliferation of bacterial taxa with high rRNA gene copy number, consistent with a previously hypothesized but untested connection between rRNA gene copy number and P requirement. Bacterial and microbial eukaryotic community structure was investigated by pyrosequencing of 16S and 18S rRNA genes from the planktonic and surficial sediment samples. Nutrient enrichment shifted the composition of the planktonic community in a treatment-specific manner and promoted the growth of previously rare bacterial taxa at the expense of the more abundant, potentially endemic, taxa. The eukaryotic community was highly enriched with phototrophic populations in the fertilized treatment. The sediment microbial community exhibited high beta diversity among replicates within treatments, which obscured any changes due to fertilization. Overall, these results showed that nutrient stoichiometry can be an important factor in shaping microbial community structure.

Combined effects of cumulative nutrient inputs and biogeochemical processes that occur in freshwater under anthropogenic eutrophication could lead to myriad shifts in nitrogen (N):phosphorus (P) stoichiometry in global freshwater ecosystems, but this is not yet well-assessed. Here we evaluated the characteristics of N and P stoichiometries in bodies of freshwater and their herbaceous macrophytes across human-impact levels, regions and periods. Freshwater and its macrophytes had higher N and P concentrations and lower N : P ratios in heavily than lightly human-impacted environments, further evidenced by spatiotemporal comparisons across eutrophication gradients. N and P concentrations in freshwater ecosystems were positively correlated and N : P was negatively correlated with population density in China. These results indicate a faster accumulation of P than N in human-impacted freshwater ecosystems, which could have large effects on the trophic webs and biogeochemical cycles of estuaries and coastal areas by freshwater loadings, and reinforce the importance of rehabilitating these ecosystems., (© 2016 John Wiley & Sons Ltd/CNRS.)

Understanding the impacts of biodiversity loss on ecosystem functioning and services has been a central issue in ecology. Experiments in synthetic communities suggest that biodiversity loss may erode a set of ecosystem functions, but studies in natural communities indicate that the effects of biodiversity loss are usually weak and that multiple functions can be sustained by relatively few species. Yet, the mechanisms by which natural ecosystems are able to maintain multiple functions in the face of diversity loss remain poorly understood. With a long-term and large-scale removal experiment in the Inner Mongolian grassland, here we showed that losses of plant functional groups (PFGs) can reduce multiple ecosystem functions, including biomass production, soil NO 3 -N use, net ecosystem carbon exchange, gross ecosystem productivity, and ecosystem respiration, but the magnitudes of these effects depended largely on which PFGs were removed. Removing the two dominant PFGs (perennial rhizomatous grasses and perennial bunchgrasses) simultaneously resulted in dramatic declines in all examined functions, but such declines were circumvented when either dominant PFG was present. We identify the major mechanism for this as a compensation effect by which each dominant PFG can mitigate the losses of others. This study provides evidence that compensation ensuing from PFG losses can mitigate their negative consequence, and thus natural communities may be more resilient to biodiversity loss than currently thought if the remaining PFGs have strong compensation capabilities. On the other hand, ecosystems without well-developed compensatory functional diversity may be much more vulnerable to biodiversity loss., (© 2016 by the Ecological Society of America.)

Unlabelled: Phosphorus (P) plays a fundamental role in the physiology and biochemistry of all living things. Recent evidence indicates that organisms in the oceans can break down and use P forms in different oxidation states (e.g., +5, +3, +1, and -3); however, information is lacking for organisms from soil and sediment. The Cuatro Ciénegas Basin (CCB), Mexico, is an oligotrophic ecosystem with acute P limitation, providing a great opportunity to assess the various strategies that bacteria from soil and sediment use to obtain P. We measured the activities in sediment and soil of different exoenzymes involved in P recycling and evaluated 1,163 bacterial isolates (mainly Bacillus spp.) for their ability to use six different P substrates. DNA turned out to be a preferred substrate, comparable to a more bioavailable P source, potassium phosphate. Phosphodiesterase activity, required for DNA degradation, was observed consistently in the sampled-soil and sediment communities. A capability to use phosphite (PO3 (3-)) and calcium phosphate was observed mainly in sediment isolates. Phosphonates were used at a lower frequency by both soil and sediment isolates, and phosphonatase activity was detected only in soil communities. Our results revealed that soil and sediment bacteria are able to break down and use P forms in different oxidation states and contribute to ecosystem P cycling. Different strategies for P utilization were distributed between and within the different taxonomic lineages analyzed, suggesting a dynamic movement of P utilization traits among bacteria in microbial communities., Importance: Phosphorus (P) is an essential element for life found in molecules, such as DNA, cell walls, and in molecules for energy transfer, such as ATP. The Valley of Cuatro Ciénegas, Coahuila (Mexico), is a unique desert characterized by an extreme limitation of P and a great diversity of microbial life. How do bacteria in this valley manage to obtain P? We measured the availability of P and the enzymatic activity associated with P release in soil and sediment. Our results revealed that soil and sediment bacteria can break down and use P forms in different oxidation states and contribute to ecosystem P cycling. Even genetically related bacterial isolates exhibited different preferences for molecules, such as DNA, calcium phosphate, phosphite, and phosphonates, as substrates to obtain P, evidencing a distribution of roles for P utilization and suggesting a dynamic movement of P utilization traits among bacteria in microbial communities., (Copyright © 2016, American Society for Microbiology. All Rights Reserved.)

Phosphorus (P) is an essential nutrient for living systems with emerging sustainability challenges related to supply uncertainty and aquatic eutrophication. However, its long-term temporal dynamics and subsequent effects on freshwater ecosystems are still unclear. Here, we quantify the P pathways across China over the past four centuries with a life cycle process-balanced model and evaluate the concomitant potential for eutrophication with a spatial resolution of 5 arc-minutes in 2012. We find that P cycling in China has been artificially intensified during this period to sustain the increasing population and its demand for animal protein-based diets, with continuous accumulations in inland waters and lands. In the past decade, China's international trade of P involves net exports of P chemicals and net imports of downstream crops, specifically soybeans from the United States, Brazil, and Argentina. The contribution of crop products to per capita food P demand, namely, the P directly consumed by humans, declined from over 98% before the 1950s to 76% in 2012, even though there was little change in per capita food P demand. Anthropogenic P losses to freshwater and their eutrophication potential clustered in wealthy coastal regions with dense populations. We estimate that Chinese P reserve depletion could be postponed for over 20 y by more efficient life cycle P management. Our results highlight the importance of closing the P cycle to achieve the cobenefits of P resource conservation and eutrophication mitigation in the world's most rapidly developing economy.

The ribosomal RNA (rrn) operon is a key suite of genes related to the production of protein synthesis machinery and thus to bacterial growth physiology. Experimental evidence has suggested an intrinsic relationship between the number of copies of this operon and environmental resource availability, especially the availability of phosphorus (P), because bacteria that live in oligotrophic ecosystems usually have few rrn operons and a slow growth rate. The Cuatro Ciénegas Basin (CCB) is a complex aquatic ecosystem that contains an unusually high microbial diversity that is able to persist under highly oligotrophic conditions. These environmental conditions impose a variety of strong selective pressures that shape the genome dynamics of their inhabitants. The genus Bacillus is one of the most abundant cultivable bacterial groups in the CCB and usually possesses a relatively large number of rrn operon copies (6-15 copies). The main goal of this study was to analyze the variation in the number of rrn operon copies of Bacillus in the CCB and to assess their growth-related properties as well as their stoichiometric balance (N and P content). We defined 18 phylogenetic groups within the Bacilli clade and documented a range of from six to 14 copies of the rrn operon. The growth dynamic of these Bacilli was heterogeneous and did not show a direct relation to the number of operon copies. Physiologically, our results were not consistent with the Growth Rate Hypothesis, since the copies of the rrn operon were decoupled from growth rate. However, we speculate that the diversity of the growth properties of these Bacilli as well as the low P content of their cells in an ample range of rrn copy number is an adaptive response to oligotrophy of the CCB and could represent an ecological mechanism that allows these taxa to coexist. These findings increase the knowledge of the variability in the number of copies of the rrn operon in the genus Bacillus and give insights about the physiology of this bacterial group under extreme oligotrophic conditions.

Comparisons of the carbon, nitrogen and phosphorus (P) content of plants and insect herbivores suggests that P limitation and herbivore foraging to balance P intake could be common. However, the lack of synthetic diets for testing the effects of lower ranges of dietary P has been a major impediment to experimental assessment of the ecological importance of, and physiological responses to, P limitation for terrestrial herbivores. We manipulated dietary P content (%P) over its observed range in terrestrial foliage using artificial diets containing near-optimal content of other nutrients for the grasshopper Schistocerca americana. Over much of the ecologically relevant range, when consuming single diets over a lifetime, higher P stimulated growth rates and increased survival, with an optimal dietary %P of 0.25-0.50% when measured throughout development. Excessive dietary P (1%) reduced growth and survival. However, with only short-term (3 day) confinement to single diets, dietary P had no effect on food consumption or growth rates. During these short exposures, fifth (but not third) instar hoppers increased the proportion of P excreted relative to P assimilated as dietary P increased. Target experiments demonstrated that, when given a choice, grasshoppers select among foods to attain a P intake target of 0.6%. These data suggest that P limitation could be common for terrestrial insect herbivores and that they can exhibit ingestive and post-ingestive mechanisms to attain sufficient but not excessive P., (© 2016. Published by The Company of Biologists Ltd.)

Increasing atmospheric CO2 concentrations generally alter element stoichiometry in plants. However, a comprehensive evaluation of the elevated CO2 impact on plant nitrogen: phosphorus (N:P) ratios and the underlying mechanism has not been conducted. We synthesized the results from 112 previously published studies using meta-analysis to evaluate the effects of elevated CO2 on the N:P ratio of terrestrial plants and to explore the underlying mechanism based on plant growth and soil P dynamics. Our results show that terrestrial plants grown under elevated CO2 had lower N:P ratios in both above- and belowground biomass across different ecosystem types. The response ratio for plant N:P was negatively correlated with the response ratio for plant growth in croplands and grasslands, and showed a stronger relationship for P than for N. In addition, the CO2-induced down-regulation of plant N:P was accompanied by 19.3% and 4.2% increases in soil phosphatase activity and labile P, respectively, and a 10.1% decrease in total soil P. Our results show that down-regulation of plant N:P under elevated CO2 corresponds with accelerated soil P cycling. These findings should be useful for better understanding of terrestrial plant stoichiometry in response to elevated CO2 and of the underlying mechanisms affecting nutrient dynamics under climate change.

Large quantities of sodic and alkaline bauxite residue are produced globally as a by-product from alumina refineries. Ecological stoichiometry of key elements [nitrogen (N) and phosphorus (P)] plays a critical role in establishing vegetation cover in bauxite residue sand (BRS). Here we examined how changes in soil chemical properties over time in rehabilitated sodic and alkaline BRS affected leaf N to P stoichiometry of native species used for rehabilitation. Both Ca and soil pH influenced the shifts in leaf N:P ratios of the study species as supported by consistently significant positive relationships (P < 0.001) between these soil indices and leaf N:P ratios. Shifts from N to P limitation were evident for N-fixing species, while N limitation was consistently experienced by non-N-fixing plant species. In older rehabilitated BRS embankments, soil and plant indices (Ca, Na, pH, EC, ESP and leaf N:P ratios) tended to align with those of the natural ecosystem, suggesting improved rehabilitation performance. These findings highlight that leaf N:P stoichiometry can effectively provide a meaningful assessment on understanding nutrient limitation and productivity of native species used for vegetating highly sodic and alkaline BRS, and is a crucial indicator for assessing ecological rehabilitation performance.

Recent work has indicated that stoichiometric food quality in terms of the carbon:phosphorus (C:P) ratio affects consumers whether the imbalance involves a deficit or an excess of nutrients; hence, organisms exist on a "stoichiometric knife edge". While previous studies have focused primarily on autotroph-herbivore trophic transfer, nutritional imbalances may also affect the interactions between species at higher trophic levels. Since the foods of carnivores are normally stoichiometrically similar to the body compositions of those carnivores, they may be more severely affected than herbivores if imbalances become pronounced. We analysed the response of the predatory copepod Parabroteas sarsi to monospecific diet treatments consisting of high and low C:P prey items. These dietary treatments strongly affected the predator's elemental composition and growth, although prey selection, excretion, egestion, and respiration rates were not affected. We suggest that, due to their low threshold elemental ratio and a narrow C:P stoichiometric knife edge, these predators are highly vulnerable to stoichiometric imbalances, whether an excess or a deficit of nutrients is involved. Our results demonstrating this high sensitivity to prey C:P ratio show that the stoichiometric knife edge may apply to not only herbivores but also higher trophic levels. Thus, predators such as P. sarsi, with a much narrower range of food quality, may also be strongly affected by fluctuations in the quality of their prey, with negative consequences for their secondary production.

Cuatro Ciénegas Basin (CCB) is a desert ecosystem that hosts a large diversity of water bodies. Many surface waters in this basin have imbalanced nitrogen (N) to phosphorus (P) stoichiometry (total N:P > 100 by atoms), where P is likely to be a limiting nutrient. To investigate the effects of nutrient stoichiometry on planktonic and sediment ecosystem components and processes, we conducted a replicated in situ mesocosm experiment in Lagunita, a shallow pond located in the southwest region of the basin. Inorganic N and P were periodically added to mesocosms under three different N:P regimes (P only, N:P = 16 and N:P = 75) while the control mesocosms were left unamended. After three weeks of fertilization, more than two thirds of the applied P was immobilized into seston or sediment. The rapid uptake of P significantly decreased biomass C:P and N:P ratios, supporting the hypothesis that Lagunita is P-limited. Meanwhile, simultaneous N and P enrichment significantly enhanced planktonic growth, increasing total planktonic biomass by more than 2-fold compared to the unenriched control. With up to 76% of added N sequestered into the seston, it is suspected that the Lagunita microbial community also experienced strong N-limitation. However, when N and P were applied at N:P = 75, the microbes remained in a P-limitation state as in the untreated control. Two weeks after the last fertilizer application, seston C:P and N:P ratios returned to initial levels but chlorophyll a and seston C concentrations remained elevated. Additionally, no P release from the sediment was observed in the fertilized mesocosms. Overall, this study provides evidence that Lagunita is highly sensitive to nutrient perturbation because the biota is primarily P-limited and experiences a secondary N-limitation despite its high TN:TP ratio. This study serves as a strong basis to justify the need for protection of CCB ecosystems and other low-nutrient microbe-dominated systems from anthropogenic inputs of both N and P.

The increase of nutrients in water bodies, in particular nitrogen (N) and phosphorus (P) due to the recent expansion of agricultural and other human activities is accelerating environmental degradation of these water bodies, elevating the risk of eutrophication and reducing biodiversity. To evaluate the ecological effects of the influx of nutrients in an oligotrophic and stoichiometrically imbalanced environment, we performed a replicated in situ mesocosm experiment. We analyzed the effects of a N- and P-enrichment on the bacterial interspecific interactions in an experiment conducted in the Cuatro Cienegas Basin (CCB) in Mexico. This is a desert ecosystem comprised of several aquatic systems with a large number of microbial endemic species. The abundance of key nutrients in this basin exhibits strong stoichiometric imbalance (high N:P ratios), suggesting that species diversity is maintained mostly by competition for resources. We focused on the biofilm formation and antibiotic resistance of 960 strains of cultivated bacteria in two habitats, water and sediment, before and after 3 weeks of fertilization. The water habitat was dominated by Pseudomonas, while Halomonas dominated the sediment. Strong antibiotic resistance was found among the isolates at time zero in the nutrient-poor bacterial communities, but resistance declined in the bacteria isolated in the nutrient-rich environments, suggesting that in the nutrient-poor original environment, negative inter-specific interactions were important, while in the nutrient-rich environments, competitive interactions are not so important. In water, a significant increase in the percentage of biofilm-forming strains was observed for all treatments involving nutrient addition.

Nitrogen (N) and phosphorus (P) are important limiting nutrients for plant production and consumer performance in a variety of ecosystems. As a result, the N:P stoichiometry of herbivores has received increased attention in ecology. However, the mechanisms by which herbivores maintain N:P stoichiometric homeostasis are poorly understood. Here, using a field manipulation experiment we show that the grasshopper Oedaleus asiaticus maintains strong N:P stoichiometric homeostasis regardless of whether grasshoppers were reared at low or high density. Grasshoppers maintained homeostasis by increasing P excretion when eating plants with higher P contents. However, while grasshoppers also maintained constant body N contents, we found no changes in N excretion in response to changing plant N content over the range measured. These results suggest that O. asiaticus maintains P homeostasis primarily by changing P absorption and excretion rates, but that other mechanisms may be more important for regulating N homeostasis. Our findings improve our understanding of consumer-driven P recycling and may help in understanding the factors affecting plant-herbivore interactions and ecosystem processes in grasslands.

Fire is a major driver of ecosystem change and can disproportionately affect the cycling of different nutrients. Thus, a stoichiometric approach to investigate the relationships between nutrient availability and microbial resource use during decomposition is likely to provide insight into the effects of fire on ecosystem functioning. We conducted a field litter bag experiment to investigate the long-term impact of repeated fire on the stoichiometry of leaf litter C, N and P pools, and nutrient-acquiring enzyme activities during decomposition in a wet sclerophyll eucalypt forest in Queensland, Australia. Fire frequency treatments have been maintained since 1972, including burning every 2 years (2yrB), burning every 4 years (4 yrB) and no burning (NB). C : N ratios in freshly fallen litter were 29-42% higher and C : P ratios were 6-25% lower for 2 yrB than NB during decomposition, with correspondingly lower 2yrB N : P ratios (27-32) than for NB (34-49). Trends in litter soluble and microbial N : P ratios were similar to the overall litter N : P ratios across fire treatments. Consistent with these, the ratio of activities for N-acquiring to P-acquiring enzymes in litter was higher for 2 yrB than NB, whereas 4 yrB was generally intermediate between 2 yrB and NB. Decomposition rates of freshly fallen litter were significantly lower for 2 yrB (72 ± 2% mass remaining at the end of experiment) than for 4 yrB (59 ± 3%) and NB (62 ± 3%), a difference that may be related to effects of N limitation, lower moisture content, and/or litter C quality. Results for older mixed-age litter were similar to those for freshly fallen litter although treatment differences were less pronounced. Overall, these findings show that frequent fire (2 yrB) decoupled N and P cycling, as manifested in litter C : N : P stoichiometry and in microbial biomass N : P ratio and enzymatic activities. Furthermore, these data indicate that fire induced a transient shift to N-limited ecosystem conditions during the postfire recovery phase., (© 2013 John Wiley & Sons Ltd.)