Phosphorus mismanagement threatens food security, water quality, climate and biodiversity. This Comment outlines how countries may establish national working groups and action plans to tackle these challenges, considering context-specificities, local resilience and global commitments.

Lake eutrophication remains a significant challenge for water-quality management across the world. Many management strategies focus on reducing nutrient inputs, but other environmental factors can substantially influence the yield of algal biomass for a given level of nutrients. While various large-scale studies have explored how different lake characteristics impact eutrophication, there remains a need to integrate these factors into a comprehensive model capable of assessing nitrogen vs. phosphorus limitation. In this study, we refine chlorophyll-nutrient relationships across the conterminous United States by considering auxiliary variables (i.e., temperature, lake depth, and nutrient enrichment) within a Bayesian hierarchical framework. We leverage over 4000 sampling events of 2755 different lakes from the National Lakes Assessments (2007-2022) to inform model development. We first consider auxiliary variables independently, exploring how they influence the intercept, slope, and critical nutrient ratio (nitrogen : phosphorus) in a regression to predict chlorophyll based on the limiting nutrient. Next, we integrate significant auxiliary variables into a comprehensive model for chlorophyll prediction. Results indicate that the critical nutrient ratio increases in relation to increased lake depth, and the slope of the nutrient-chlorophyll relationship increases with increasing temperature. We apply the model to map mean summer conditions across US lakes and find that 23% and 16% of lakes are strongly limited by phosphorus and nitrogen, respectively (i.e., at > 90% probability). These proportions, however, vary substantially across different subregions. Overall, the probabilistic modeling approach and results can serve as an effective tool to inform water resources management, especially at large spatial scales.

The biodiversity-productivity relationship (BPR) is crucial for understanding the consequences of biodiversity loss; yet, how this relationship evolves over time in natural ecosystems remains unclear. Several long-term biodiversity experiments with artificially assembled communities suggest that the BPR escalates over time, however, whether this pattern applies to natural ecosystems has not been explored. Here, we present the results of a 15-y removal experiment in the Inner Mongolia grassland, where gradients of plant functional group (PFG) richness and species richness were created through targeted removals from 2006-2009, followed by natural recolonization from 2010 onward. We found that both the PFG richness-based and species richness-based BPRs diminished gradually during the removal period (years 2-4) and decoupled in 9 out of 12 y after the cessation of removal (years 5-16), suggesting that the negative impacts of biodiversity loss do not necessarily escalate over time; rather, they may decrease. We identified that the temporal shift in BPRs resulted first from compensatory growth of remaining species and subsequently from new colonization by external populations. These results highlight that the impacts of biodiversity loss in natural ecosystems are strongly modified by assembly processes such as compensation and colonization. Therefore, models predicting the ecosystem consequences of biodiversity loss should consider these mechanisms. Ignoring them may lead to an overestimation of the long-term impacts of biodiversity loss in natural communities, particularly where surrounding landscapes harbor species pools capable of recolonization.

Abstract Snow algae darken snowpacks and accelerate melt worldwide. Although elevation strongly structures the physical conditions of mountain snowfields, its influence on snow algal traits and their effects on snowpack reflectance remains unclear. Here, we investigated snow algal composition, cellular traits, and optical properties in summer blooms across an elevational range of 1,059–3,423 m a.s.l. in the western United States, spanning two elevational gradients in the Cascade Range (CA, OR, WA) and the Rocky Mountains (UT, WY, MT). Across all samples (n = 294), snow albedo declined strongly with increasing algal cell density, indicating that total biomass, rather than pigment composition, is the dominant driver of albedo reduction. However, within Sanguina-dominated blooms (117 of 206 samples bloom samples identified across the dataset), neither relative abundance nor algal cell density varied systematically with elevation. Instead, mean cell size increased with elevation, while per-cell pigment concentrations declined, leading to higher astaxanthin:chlorophyll-a ratios driven primarily by reductions in chlorophyll-a per cell. These elevation-dependent shifts in cell size and pigment balance were consistent across both mountain ranges, indicating phenotypic acclimation to increasing environmental stress with elevation. Together, these findings link cellular-scale acclimation of a widespread snow alga to radiative processes shaping mountain snowpacks.

Phosphorus sustains global food production and is, therefore, of crucial importance to human nutrition and health. However, its mismanagement can lead to water pollution and environmental degradation in addition to low crop yields. In many parts of sub-saharan Africa, phosphorus deficiency constrains agricultural productivity and exacerbates food insecurity. Despite these challenges, phosphorus remains a fragmented topic in global and African policy. To address these issues, the 8th Sustainable Phosphorus Summit (SPS8) was convened in Africa for the first time. SPS8 took place in Accra, Ghana, between 30th September and 3rd October 2025. The Summit was an international collaboration, with co-conveners from the Council for Scientific and Industrial Research (CSIR) – Ghana, the Forum for Agricultural Research in Africa (FARA), The UK Centre for Ecology & Hydrology West Africa Office, Lancaster University and Rothamsted Research. In this paper, we give a detailed overview of the key messages and insights that emerged from highlight talks, lectures, working groups and field trips. We also discuss and reflect on the challenges of delivering an inclusive summit, from designing solutions to benefit-sharing. SPS8 demonstrates that inclusive, cross-sector knowledge-exchange events are crucial to support and enable phosphorus sustainability on the continent of Africa and globally and to enable the next generation of interdisciplinary phosphorus researchers.

1. Nutrient limitation of phytoplankton growth in a lake has various effects on lake function and primary producer composition. There is a rich history of using short-term enrichment experiments to infer the type and degree of limitation in lakes. However, most experiments are analysed independently of one another, lack a common framework for expressing uncertainty, and only represent a single point in time. 2. We conducted a series of phytoplankton nutrient limitation experiments in mountain lakes across northwestern Montana, USA to (a) assess regional patterns of nutrient limitation and (b) examine limitation through time in one large lake. We use a multilevel Bayesian model to better characterise parameter uncertainty across all experiments. 3. The fertilisation effect of phosphorus was consistently larger than that of nitrogen, reflecting low phosphorus concentrations across lakes in this region. 4. Most experiments showed evidence for P limitation or serial P limitation, with some evidence for independent co-limitation as well. We also show that nutrient limitation in one lake changed over both a growing season and across years from strong P limitation to serial P limitation. 5. Future work should continue to explore methods for analysing collections of nutrient limitation experiments.

Snow algae darken snowpacks and accelerate melt world-wide. Although elevation strongly structures mountain snowfields, its influence on snow algal traits and their effects on snowpack reflectance remains unclear. Here, we investigated snow algal blooms across an elevational range of 1059-3423 m above sea level (asl) in the Cascade Range (California, Oregon, Washington) and the Rocky Mountains (Utah, Wyoming, Montana). We analyzed 294 snow samples and quantified algal community composition, algal cell density, cell size, pigment concentrations, and snow albedo. We further examined elevation-dependent patterns within Sanguina nivaloides-dominated blooms (117 of 206 bloom samples). Across samples spanning clean snow and algal blooms, algal cell density emerged as the strongest biological predictor of albedo, whereas pigment-related variables showed no consistent effects. Within Sanguina nivaloides-dominated blooms, neither relative abundance nor algal cell density varied systematically with elevation. Instead, mean cell size increased with elevation, while per-cell pigment concentrations declined, leading to higher astaxanthin ratios driven primarily by reductions in Chla per cell. These elevation-dependent shifts in cell size and pigment balance were consistent across both mountain ranges, indicating phenotypic acclimation to increasing environmental stress with elevation. Together, these findings link cellular-scale acclimation of a widespread snow algae to radiative processes shaping mountain snowpacks.

With diminishing availability of high-quality phosphate rock and increasing supply uncertainties, improving phosphorus (P) recovery, recycling, and waste reduction has become critical for sustaining agricultural production. We developed an integrated P cycling and soil dynamics model to quantify 7 circular strategies for reducing mineral P demand in the United States, using data for 91 major crops and 20 livestock types across 3,142 counties from 1866 to 2050. We show that soil residual P reuse has the largest potential to reduce mineral P demand in the United States. By 2023, total soil P stocks had accumulated to 99 Tg, equivalent to approximately 68% of mineral P inputs over 1866-2023. For 2024-2050, projections under various socioeconomic scenarios indicate that soil residual P reuse alone could potentially supply approximately 2.4 to 5.1 times projected US mineral P demand, with substantial residual P stocks accumulated in both cropland and pastureland soils. Recycling from sewage sludge and livestock and crop by-products could collectively offset an additional approximately 0.5 to 1.0 times mineral P demand, while food waste reduction could reduce requirements by approximately 0.3 times. Spatial analyses further highlight a mismatch between circular P availability and cropland P demand, with high mineral P avoidance potential concentrated in the South and West, but relatively low ratios of circular P supply to projected mineral P demand across most counties in the Midwest. These findings provide spatially explicit and decision-relevant insights into how circular P strategies can enhance the stability and resilience of US food systems under future resource constraints.

In this study, we examined the reflectance, pigment composition, and community composition of three snow algae blooms showing distinct colors in the same snowfield in Glacier National Park (USA). Each color bloom was dominated by a different algae, each exhibiting a unique pigment signature but with astaxanthin as the predominant pigment across all three blooms. The spectral reflectance of red snow algae was consistently lower than that of green algae, while orange algae had intermediate reflectance values. Specifically, red algae reduced reflectance by approximately 55% across the PAR range, while green algae reduced reflectance by 25%. Red algae also demonstrated the highest radiative forcing, double that of green algae, leading to increased energy re-emission into the surrounding environment, which likely contributes to the localized melting of adjacent ice crystals. The high absorbance around 680 nm in cells with high astaxanthin content, such as the orange algae, suggests that semi-automatic detection methods could effectively identify these algae, as their spectral features remain distinct despite the presence of secondary carotenoids. Our data demonstrate the impact of snow algae taxonomic and pigment composition on the radiative balance of snowfields, underscoring taxonomy as a key determinant of bloom color under similar environmental conditions ### Competing Interest Statement The authors have declared no competing interest. National Science Foundation, 2113783, 2113784

The nitrogen (N) and phosphorus (P) limitations in soil microorganisms have profound implications for key soil functions such as organic matter decomposition and soil carbon (C) sequestration. However, the extent and magnitude of microbial N and P limitation in soils worldwide remain largely unknown compared to N and P limitation in plants. Moreover, the spatial variability of microbial N and P limitation may lead to disproportionate responses of microbially driven soil processes and functions to global change factors along environmental gradients. Thus, better understanding of global patterns and drivers of microbial N and P limitation is urgently needed for predicting changes in soil functions and their consequences for terrestrial ecosystem functioning. Herein, we evaluated global patterns of microbial N and P limitation by combining profiles of extracellular enzymes (i.e. ecoenzymes; 5,259 observations) with multiple sets of observational and experimental data from natural (i.e. outside of agricultural and urban areas) terrestrial ecosystems. Our analyses reveal widespread indications of microbial P and N limitation (65 and 40% of observations, respectively) in soils worldwide, with unexpectedly frequent N and P co-limitation in the tropics. This co-limitation could be attributable to elevated microbial N demand for the synthesis of P-acquiring enzymes under P limitation, and thus likely as a secondary N limitation resulting from the inherent P deficiency in tropical soils. Upscaling prediction (0.1 × 0.1° spatial resolution) further indicated certain regions such as the Amazon Basin, Tibetan Plateau, and Siberian regions, which harbor substantial soil organic C, showed signs of strong N and P limitation in soil microorganisms, suggesting a high sensitivity of soil C cycling in these regions to nutrient perturbations. As the first global assessment of spatial variation in microbial N and P limitation, these findings provide clues to explain the long-standing “Tropical N Paradox” (i.e. the apparent up-regulation of ecosystem N cycling processes, such as biological N fixation, despite primary P limitation and high soil N levels in tropical ecosystems) and could be useful for understanding and predicting soil biogeochemical cycles in a changing world. [This study is a work that will be published in PNAS (revised stage)].

Glaciers are retreating, altering alpine ecosystems and creating new proglacial lakes. Compared to lakes fed by snowpack, glacial lakes are often enriched in nutrients and suspended solids that decrease light penetration. However, the microorganisms and biogeochemical conditions within these newly formed lakes are not well characterized. We describe the microbial communities in 14 glacial lakes in Glacier National Park, MT, USA using 16S rRNA gene amplicon sequencing and measurements of nutrient concentrations, water clarity, and other environmental properties. Microbial communities were distinct between lakes, including those connected to the same glacier, indicating the importance of site-specific biogeochemical and physical dynamics on these systems. Microbial community composition correlated with lake age (formation before or after the Little Ice Age) and conductivity but not with whether a lake was connected to a contemporaneous glacier > 0.1 km2. Heterotrophic lineages found in other glacial systems were abundant and widespread, while cyanobacteria only reached appreciable abundances in shallow lakes where light reached the benthos. Relative abundances of ammonia and nitrite oxidizers correlated with concentrations of nitrate and nitrite, suggesting nitrification may help control nitrogen forms and concentrations in glacial lakes. We show that as glaciers recede, unique glacial lake microbial communities will be formed and lost with them.

Phosphorus (P) is a critical biogenic element driving aquatic productivity and eutrophication in freshwater systems. However, monitoring total phosphorus (TP) in shallow, dynamic lakes remain challenging due to its pronounced spatiotemporal variability and complex interactions with optically active constituents. While remote sensing provides a cost-effective supplement to in situ monitoring of TP, accurately estimating TP -a non-optically active component- using remote sensing requires models that balance high precision, reliability, and interpretability. Therefore, this study develops an interpretable machine learning framework using the Light Gradient Boosting Machine Regressor (LGBMR), trained on multi-source data including MODIS satellite reflectance, in situ measurements and meteorological variables to estimate TP dynamics. The LGBMR outperformed 13 other algorithms on independent validation datasets (N = 609, R² = 0.70, MAPE = 27.9 %), demonstrating superior predictive performance. Shapley Additive Explanations (SHAP) analysis revealed mechanistic controls of input variables on TP dynamics, enabling the model to effectively capture both seasonal-spatial TP variability and climate-induced extremes. Long-term analysis of Lake Taihu revealed a significant declining trend in TP concentration over the past two decades (R2 = 0.26, P < 0.05, rate: -0.009 mg/L/decade), with an accelerated decline from 2017 to 2024 (R2 = 0.77, P < 0.05, rate: -0.059 mg/L/decade). SHAP analysis revealed a 12.4 % and 18.9 % decrease in pixel counts dominated by total suspended matter (TSM) and algal-associated P, respectively. The decline is attributed to reduced external loading due to improved watershed management and internal phosphorus release due to reduced algal biomass and sediment resuspension linked to weakened wind-driven mixing. These findings underscore the effectiveness of integrated modeling approaches for tracking phosphorus dynamics in shallow eutrophic lakes, providing actionable insights for eutrophication management. The proposed framework advances interpretable machine learning in environmental monitoring by elucidating mechanistic linkages between hydrological, meteorological, and biogeochemical drivers.

Snow algae darken the surface of snow, reducing albedo and accelerating melt. However, the impact of subsurface snow algae (e.g., when cells are covered by recent snowfall) on albedo is unknown. Here, we examined the impact of subsurface snow algae on surface energy absorption by adding up to 2 cm of clean snow to surface algal blooms and measuring reflectivity. Surprisingly, snow algae still absorb significant energy across an array of wavelengths when snow-covered. Furthermore, the scale of this effect correlates with algal cell densities and chlorophyll-a concentrations. Collectively, our results suggest that darkening by subsurface snow algae lowers albedo and thus potentially accelerates snowmelt even when the algae is snow-covered. Impacts of subsurface algae on melt await assessment. This implies that snow algae play a larger role in cryosphere melt than investigations of surface-only reflectance would suggest. IMPORTANCE:This study addresses a gap in research by examining the impact of subsurface snow algae on snow albedo, which affects snowmelt rates. Previous studies have focused on visible surface blooms, leaving the effects of hidden algae unquantified. Our findings reveal that snow algae beneath the surface can still absorb energy across various wavelengths, accelerating melt even when not visible to the naked eye. This suggests that spectral remote sensing can detect these hidden algae, although their biomass might be underestimated. Understanding how subsurface snow algae influence albedo and snowmelt is crucial for accurate predictions of meltwater runoff, which impacts alpine ecosystems, glacier health, and water resources. Accurate projections are essential for managing freshwater supplies for agriculture, drinking water, and other vital uses. Thus, further investigation into subsurface snow algae is necessary to improve our understanding of their role in snow albedo reduction and water resource management.

Drought and human land use have increased dust emissions in the western United States. However, the ecological sensitivity of remote lakes to dust deposition is not well understood and to date has largely been assessed through spatial and temporal correlations. Using in situ bioassays, we investigated the effects of dust enrichment on the production, chlorophyll a (Chl a) concentration, and taxonomic composition of phytoplankton and microbial communities in three western US mountain lakes. We found that dust-derived nutrients increased Chl a concentration in all three lakes, but the magnitude of the effect varied from 32% to 226%. This variation was related to pre-existing lake conditions, such as trophic status, pH, and nutrient limitation. In Castle Lake, co-limited by N and P, dust bioassays showed an increase in Chl a content per cell but suppressed primary production and increased dark 14C uptake. In contrast, both Flathead Lake and The Loch were primarily P-limited and exhibited increases in Chl a concentration. The contrasting Chl a and primary production results from Castle Lake are consistent with the alleviation of nitrogen limitation where energy Adenosine triphosphate (ATP) is used for nutrient assimilation instead of carbon fixation. Dust additions also altered the algal and microbial communities. The latter included the addition of new phyla (e.g., Deinococcota), indicating that dust-delivered microbes have the potential to thrive in receiving lakes. Our study provides the first short-term experimental in situ evidence of rapid ecosystem effects in mountain lakes following dust exposure. The results emphasize the need for continued research in this area to understand interactions of both the short- and long-term consequences of dust-induced perturbations in remote lakes in the context of global changes.

The availability of nitrogen (N) and phosphorus (P) is essential for soil microbial activity and growth, yet global patterns of N and P limitation in soil microbial metabolism remain largely unknown. We modeled ecoenzyme stoichiometry data from 5,259 field observations of natural ecosystems to assess microbial N and P limitation in global surface soils. We found that microbial P limitation, which was especially strong at low latitudes, was more prevalent globally than microbial N limitation, which prevailed in cold environments. We also found widespread N and P colimitation in soil microorganisms in the tropics, contradicting the long-held paradigm that P, and not N, is the primary limiting nutrient at low latitudes. This colimitation could be attributable to elevated microbial N demand for the synthesis of P-acquiring enzymes under P limitation. Upscaling (0.1 × 0.1° spatial resolution) suggested that soil microorganisms were limited by N and P in 39% and 57%, respectively, of natural terrestrial surface areas, with 21% of areas with N and P colimitation. As a global assessment of spatial variation in microbial N and P limitation, our results highlight the importance of N availability in supporting microbial P acquisition at low latitudes and improve our understanding of microbial nutrient limitation on a global scale.

Snow algal blooms decrease snow albedo and increase local melt rates. However, the causes behind the size and frequency of these blooms are still not well understood. One factor likely contributing is nutrient availability, specifically nitrogen and phosphorus. The nutrient requirements of the taxa responsible for these blooms are not known. Here, we assessed the growth of three commercial strains of snow algae under 24 different nutrient treatments that varied in both absolute and relative concentrations of nitrogen and phosphorus. After 38 days of incubation, we measured total biomass and cell size and estimated their effective albedo reduction surface. Snow algal strains tended to respond similarly and achieved bloom-like cell densities over a wide range of nutrient conditions. However, the molar ratio of nitrogen to phosphorus at which maximum biomass was achieved was between 4 and 7. Our data indicate a high requirement for phosphorus for snow algae and highlights phosphorus availability as a critical factor influencing the frequency and extent of snow algae blooms and their potential contribution to snow melt through altered albedo. Snow algae can thrive across a range of nitrogen (N) and phosphorus (P) conditions, with a higher P requirement for optimal growth. Our study suggests that increased N deposition may have a limited impact on snow algae bloom occurrence and size, emphasising P as a key factor influencing these blooms and their potential to accelerate snow melt by lowering albedo.

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.

ABSTRACT 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.