Di Tian

Nitrogen (N) and phosphorus (P) availability fundamentally regulate the structure and function of aquatic ecosystems. While global‐scale patterns of relative nutrient limitation have been increasingly documented, their responses to climate warming remain poorly quantified. To address this, we integrated a global meta‐analysis of nutrient enrichment experiments (spanning 510 sites and multiple trophic levels) with large‐scale datasets of water chemistry from 3403 lakes and 13,032 marine sites. Meta‐analysis showed that primary producers have the strongest responses to nutrient enrichment, especially NP co‐addition, with effects attenuating at higher trophic levels. Increasing temperature amplifies the response of primary producers to nutrient enrichment, but not for consumers, indicating that warming disrupts energy flow to higher trophic levels. Furthermore, relative N limitation of primary producers intensifies with increasing temperature and decreasing latitude in both freshwater and marine ecosystems. Global field observation of water chemistry supports such a pattern as water N:P mass ratios decrease with increasing temperature across lake and marine ecosystems. Our findings provide robust empirical evidence that the relative nutrient limitation of primary producers exhibits a strong latitudinal gradient and climate warming could fundamentally enhance nitrogen over phosphorus limitation in aquatic ecosystems, which have critical implications for ecosystem functioning and management in a warmer world.

羊草(Leymus chinensis)、紫花苜蓿(Medicago sativa)、燕麦(Avena sativa)和甜高粱(Sorghum bicolor)是我国北方4种常见的优势牧草，本研究梳理了国内外7个单位的牧草质量标准，并通过在内蒙古谢尔塔拉农牧场开展种植试验，解析了四种牧草全生育期的养分动态，并对比了其收获期品质与国内外标准的差异。结果发现：(1)以干草制作为主要利用方式，紫花苜蓿宜在盛花期收获，燕麦在蜡熟期收获，甜高粱和羊草分别在拔节末期和抽穗期收获，目前仅紫花苜蓿近乎达到我国或美国特级品质标准；(2)综合分析发现粗蛋白(CP)、瘤胃降解蛋白(RDP)、非纤维性碳水化合物(NFC)、非结构性碳水化合物(NSC)等是影响牧草品质的关键指标；(3)同时关注了牧草RDP: NFC、NFC: NDF、SFA: UFA等比值在生育期内的变化，以期将评价视角延伸至家畜对养分的吸收利用层面。本研究为构建我国北方优质饲草的标准化评价体系、推动“标准草”从概念走向实践奠定了科学基础。

Ecological stoichiometry in the plant–soil–microbial systems is crucial for regulating nutrient flow and sustaining ecosystem functions in forests. However, how rising atmospheric nitrogen (N) deposition induced by human activities impacts the stoichiometric relationships across ecosystem compartments remains poorly understood. We therefore conducted a 13‐year N‐addition experiment across eight forests from tropical to boreal zones in China, to assess the shifts in carbon:nitrogen:phosphorus (C:N:P) stoichiometry across live plant tissues, detritus, soil, and microbes. The N addition significantly elevated N concentrations in green leaves (+7.2% to 10.1%), twigs (+8.4%), fine roots (+20.2%), and leaf litter (+5.9%), while decreasing microbial N (−16.0%) and P concentrations (−20.2% to − 12.1%) across compartments. These changes triggered compartment‐specific responses, with greater stoichiometric variability in plants than in soils, particularly in high‐latitude forests. However, N addition did not significantly alter the intrinsic scaling relationships of P concentrations and N:P ratios among compartments or the N–P scaling patterns within individual compartments. Our findings provide new insights into the resilience and complexity of nutrient regulation in forests under chronic N deposition, with important implications for predicting long‐term ecosystem responses and developing sustainable nutrient management strategies.

Global vegetation growth is thought to be limited by nitrogen (N) more than by other nutrients. Here we document a stronger phosphorus (P) limitation on global photosynthesis compared with N over the last four decades. On the basis of more than 80,000 field observations of foliar nutrients and a machine learning method, we generated a long-term global dataset of foliar N and P concentrations for the period 1980–2017. We show a larger declining rate of foliar P concentration (−0.80 ± 0.008% yr⁻¹) than of N concentration (−0.31 ± 0.002% yr⁻¹). This decline has led to an increase in terrestrial areas limited by foliar P and a widespread constraint on vegetation photosynthesis, more than 1.5 times stronger than the constraint by foliar N. The increasing trend in global photosynthesis over the past 4 decades has been reduced by approximately 17.2% and 6.7% as a result of the decline in foliar P and N, respectively. This stronger P limitation on global photosynthesis implies a weakening of terrestrial carbon sinks due to an emerging P constraint and calls for stricter strategies for reducing anthropogenic emissions to mitigate climatic warming.

The role of plants in sequestering carbon is a critical component in mitigating climate change. A key aspect of this role involves plant nitrogen (N) uptake (Nup) and N use efficiency (NUE), as these factors directly influence the capacity of plants to store carbon. However, the additive contribution of N deposition, soil factors (biotic and abiotic), and climate to the plant N cycle remains inadequately understood, introducing significant uncertainties into climate change projections. Here, we used ground-based observations across 159 field experiments (including above and belowground information) to calculate Nup and NUE and identify their main drivers in natural ecosystems. We found that global plant Nup is primarily driven by N deposition, mean temperature, and precipitation, with Nup increasing in warmer and wetter areas. In contrast, NUE is driven by soil biotic and abiotic factors. Specifically, NUE decreased with the intensity of colonization by arbuscular mycorrhizal fungi and increased with soil pH and soil microbial stocks. Nup and NUE presented opposite latitudinal distributions, with Nup higher on tropical latitudes and NUE higher towards the poles. Total soil N stocks were not found to be a driver of Nup or NUE. We also compared our results with TRENDY models and found that models may overestimate Nup by ∼ 100 Tg N yr⁻¹ in the tropics and triple the standard deviation at boreal latitudes. Our findings emphasize the effect of N deposition and soil microbes that, in addition to climate and soil pH, are crucial for accurately predicting ecosystems' capacity to sequester carbon and mitigate climate change at a global scale.

Background: The ketogenic diet that forces adenosine triphosphate (ATP) production by beta-oxidation of fatty acids instead of carbohydrate glycolysis, has gained consensus on host metabolism. However, the mechanisms how a ketogenic diet alters gastrointestinal microbiome and its downstream consequences on microbial nutrient availability and energy metabolism remain to be elucidated. Here, we used the sheep model fed with fat-rich diet to evaluate the symbiotic microbiome across three regions of the gastrointestinal tract (rumen, ileum, and colon) to gain a comprehensive understanding of the microbial energy metabolism and microbe-mediated ATP biosynthesis. Results: Results showed that sheep fed a fat-rich diet had a greater ADG and increased reliance on fat oxidation for fuel utilization. Metagenomics analysis showed the loss of the specialized fiber-degrading bacteria (genus_Fibrobacter) in the rumen and enrichment of genera RUG420 and Eubacterium, which are involved in lipid metabolism and bile acid processing, in the ileum. A significant functional shift related to energy metabolism was shared across three regions of the gastrointestinal microbiomes. These shifts were dominated by glycolysis/gluconeogenesis and TCA cycle in the rumen and by fatty acid degradation and bile acid transformation in the ileum, indicating adaptation to nutrient availability and energy acquisition. Notably, the abundance of substrate-level phosphorylation (SLP) enzymes was significantly increased in the rumen, ileum and colon, while the ATP-producing capacity through electron transport phosphorylation (ETP) by family_Bacteroidaceae in rumen and Acutalibacteraceae in ileum of sheep with fat-rich diet. Conclusions: Altogether, the ATP-related microbiome encoding SLP and ETP in rumen, ileum, and colon contributed 36.95% to the host’s weight variation. Our study is the first one demonstrating the microbial potential in the ATP synthesis under the shift in dietary energy source, providing a new perspective on the energy metabolism and precise human macronutrients nutrition.

Summary: Allocation of leaf phosphorus (P) among different functional fractions represents a crucial adaptive strategy for optimizing P use. However, it remains challenging to monitor the variability in leaf P fractions and, ultimately, to understand P‐use strategies across diverse plant communities. We explored relationships between five leaf P fractions (orthophosphate P, P _i ; lipid P, P _L ; nucleic acid P, P _N ; metabolite P, P _M ; and residual P, P _R ) and 11 leaf economic traits of 58 woody species from three biomes in China, including temperate, subtropical and tropical forests. Then, we developed trait‐based models and spectral models for leaf P fractions and compared their predictive abilities. We found that plants exhibiting conservative strategies increased the proportions of P _N and P _M , but decreased the proportions of P _i and P _L , thus enhancing photosynthetic P‐use efficiency, especially under P limitation. Spectral models outperformed trait‐based models in predicting cross‐site leaf P fractions, regardless of concentrations ( R ² = 0.50–0.88 vs 0.34–0.74) or proportions ( R ² = 0.43–0.70 vs 0.06–0.45). These findings enhance our understanding of leaf P‐allocation strategies and highlight reflectance spectroscopy as a promising alternative for characterizing large‐scale leaf P fractions and plant P‐use strategies, which could ultimately improve the physiological representation of the plant P cycle in land surface models.

Plant-insect herbivore interactions are essential in shaping forest ecosystem health. The resource availability hypothesis (RAH) and the leaf economics spectrum (LES) theory predict that species in high-resource environments tend to adopt a "fast" strategy but are more susceptible to herbivory. However, this contradicts reports of increased insect herbivory in the context of global drought intensification, and hinders accurate prediction about how different plant species respond to herbivorous insect feeding.To fill this knowledge gap, we conducted an observational study in two temperate forests dominated by Quercus mongolica and Betula platyphylla in eastern China to compare their leaf herbivory patterns and explore possible mechanisms. We measured three leaf herbivory proxies (consumed leaf area, percent consumed, and herbivory frequency), some leaf traits (leaf area, specific leaf area, leaf water content, leaf nitrogen, phosphorus and non-structural carbohydrate contents), and soil properties (pH, soil water content, soil organic carbon content, soil nitrogen and phosphorus contents).We found that Q. mongolica, growing in poorer soil environments with lower water and nutrient contents, experienced higher leaf herbivory than B. platyphylla. Regarding leaf traits, Q. mongolica had a higher leaf area and non-structural carbohydrate content, but lower specific leaf area, leaf nutrient and water contents than B. platyphylla. At the leaf level, leaf area, rather than specific leaf area, of both tree species was positively correlated with leaf herbivory. At the tree level, species-specific patterns emerged, i.e., leaf herbivory of B. platyphylla was positively related to leaf area and negatively related to leaf nitrogen and water contents and soil phosphorus content, whereas that of Q. mongolica was only positively affected by soil phosphorus content.These findings challenge the predictions of RAH and LES theory, as Q. mongolica that grows in resource-poorer soil environments with a conservative strategy suffers higher leaf herbivory than B. platyphylla, shedding some light on the proverb that trouble follows the needy. Moreover, water-related factors (i.e., leaf and soil water contents) and leaf area showed an important effect on driving interspecific and intraspecific leaf herbivory variations here, implying that climate-induced droughts may exacerbate herbivore pressure in temperate forests.