Chao Wang

Summary: While eutrophication is known to alter community structure and functioning through ecological niche modification in grasslands, quantifying the contribution of realized niches to dynamics of plant diversity and ecosystem productivity remains challenging. Based on the biogeochemical niche (BN) hypothesis and the Price equation, we linked realized BN, estimated by leaf elemental composition, to diversity loss and productivity increases after fertilization in a long‐term alpine nutrient addition experiment and across 18 Nutrient Network grasslands. We found that fertilization compressed community‐wide realized BN hypervolume and reduced elemental diversity, yet expanded species realized BN hypervolume. These changes together decreased plant diversity in alpine grassland and Nutrient Network grasslands. Mechanistically, the alpine grassland experiment showed that the reduction in plant diversity after fertilization resulted from two simultaneous processes: first, the loss of species whose realized BNs closely resembled those of their close relatives; and second, the suppression of coexisting highly phylogenetically plastic species that continued to persist in the communities. Additionally, persistent species' BN expansion enhanced population productivity, scaling to ecosystem productivity increase after fertilization. Our findings formalize a predictive framework linking grassland biodiversity and ecosystem functions to global change through quantifiable ecological niche and species compositional dynamics.

Nutrient addition generally weakens the stabilizing effects of plant diversity on grassland productivity. However, whether this destabilizing effect is associated with species compositional changes and varies with nutrient input levels remains unclear. Here, we applied the Price equation to separate community species composition into lost, gained and persistent species, and quantified their contributions to the temporal stability of community productivity, defined as the ratio of temporal mean productivity to its standard deviation over year, in a 6‐year multi‐level nitrogen (N; 0, 5, 10, 15, 20 g N m ⁻² year ⁻¹ ) and phosphorus (P; 0, 2.5, 5, 7.5, 10 g P m ⁻² year ⁻¹ ) addition experiment in the Qinghai–Tibetan alpine grasslands. We found that community stability and species richness decreased with increasing N and P addition, with more rapid declines when both nutrients were applied together. The reduction in species richness resulted from fewer gained species and a decline in persistent species richness. Remarkably, species richness contributed only 5.3% to the observed variation in community stability along nutrient addition gradients. In contrast, the combined richness of gained and persistent species accounted for 53.1% of this variation. Importantly, fewer persistent species in the fertilized communities reduced the asynchronous dynamics among themselves, while fewer colonizing species decreased asynchronous dynamics between gained and persistent species, collectively weakening community stability along the nutrient addition gradients. Our results demonstrate that the destabilizing effects of nutrient addition are primarily driven by changes in species composition, which reduce compensatory dynamics among species that are persisting within the communities, rather than by the loss of species richness in grasslands. Read the free Plain Language Summary for this article on the Journal blog.

The biogeochemical niche (BN) hypothesis posits that each species performs species‐specific functions linked to its unique elemental composition. However, the relationship between BN and plant functions—such as biomass—remains to be fully understood. In our study, we assessed the shoot and root biomass, as well as the concentrations of 10 elements in the leaves and roots of 368 individuals from 18 species within the Potentillinae across northern grasslands in China. We tested the BN hypothesis for both leaves and roots and investigated the relationships between the BN and biomass in the above‐ and below‐ground in these grasslands. Our analysis revealed that legacy (phylogenetic + species) effects explained a significant proportion of the variation in leaf and root elemental composition among species within a narrower taxonomic range, and leaf elemental composition exhibited higher phylogenetic conservatism compared to roots. Moreover, we also identified a strong connection between species B and N that estimated by leaves and roots, along with positive associations between them and the shoot and root biomass. Synthesis. Our results underscore the strong connections between the BN size and plant biomass above‐ and below‐ground. We suggest that the BN could serve as a valuable framework for linking elemental composition to ecosystem functions in grasslands.

Summary: The biogeochemical niche (BN) hypothesis posits that each species has a specific elemental composition. However, the BN of roots and its interaction with leaf BN have largely been neglected until now across diverse environmental conditions. We investigated the relationships between the elemental compositions of leaves and roots, phylogeny, and environmental variables, as well as the connection between leaf and root BN. We analyzed the concentrations of carbon, nitrogen, phosphorus, potassium, calcium, and magnesium in the leaves and roots of 12 394 individuals from 1238 species. Consistent with the BN hypothesis, despite significant differences in elemental concentrations and their ratios between leaves and roots, we observed strong legacy (phylogenetic + species) signals in the species‐specific elemental compositions. This finding confirms that the elemental compositions of leaves and roots can contribute to identifying species niches. Our study revealed a higher phylogenetic conservatism for BN in leaves than in roots and provided evidence of a tight association between the species‐specific BN of leaves and roots. Our results underscore the broad applicability of the BN hypothesis across diverse species and biomes and demonstrate the critical role of evolutionary legacy in driving coordinated dynamics in both above‐ and belowground ecological niches.

Grassland vegetation phenology has undergone great changes under the influence of climate, which affects ecosystem functions and services. However, the mechanism of preseason climatic factors in driving phenological shifts is unclear. In this study, we determined the start (SOS) and peak (POS) of the growing season for Inner Mongolian grasslands using gross primary productivity data (2000–2018). We investigated the spatiotemporal changes of SOS and POS and elucidated the mechanisms behind these changes by analyzing how these phenological events were influenced by the specific preseason climatic requirements (precipitation, air temperature, and solar radiation). Our results revealed that the SOS significantly advanced at a rate of 0.65 days/a, while the POS was stable across the study area. At the pixel scale, areas with initially later SOS and POS exhibited stronger advanced trends. An earlier SOS and POS were associated with lower thermal requirements, including air temperature and solar radiation. Conversely, a delayed SOS and POS necessitated higher climatic requirements. The impact of preseason precipitation on both SOS and POS demonstrated notable spatial variability. Moreover, the effects of different climatic factors on phenology were not in sync due to regional environmental disparities. Our study provides insight into the mechanisms underlying phenological shifts in grassland ecosystems under climate change.

Drought can greatly impact the biodiversity of an ecosystem and play a crucial role in regulating its functioning. However, the specific mechanisms by which drought mediate the biodiversity effect (BE) on community biomass in above- and belowground through functional traits remain poorly understood. Here, we conducted a common garden experiment in a greenhouse, which included two plant species richness levels and two water addition levels, to analyze the effects of biodiversity on aboveground biomass (AGB), belowground biomass (BGB) and total biomass (TB), and to quantify the relationship between BEs and functional traits under drought conditions. Our analysis focused on partitioning BEs into above- and belowground complementarity effect (CE) and selection effect (SE) at the species level, which allowed us to better understand the impacts of biodiversity on community biomass and the underlying mechanisms. Our results showed that plant species richness stimulated AGB, BGB and TB through CEs. Drought decreased AGB, BGB and TB, simultaneously. In addition, the aboveground CE was positively associated with the variation in plant height. SEs in above- and belowground were negatively correlated with the community mean plant height and root length, respectively. Furthermore, drought weakened the aboveground CE by decreasing variation in plant height, resulting in a reduction in AGB and TB. Our findings demonstrate that the complementarity of species is an important regulator of community biomass in above- and belowground, the dynamics of biomass under environmental stress are associated with the response of sensitive compartments.

The relationship between metabolite changes and biological endpoints in response to cadmium (Cd) stress remains unclear. Fountain grass has good Cd enrichment and tolerance abilities and is widely used in agriculture and landscaping. We analyzed the metabolic responses by detecting the metabolites through UPLC-MS and examined the relationships between metabolite changes and the characteristics of morphology and physiology to different Cd stress in fountain grass. Our results showed that under Cd stress, 102 differential metabolites in roots and 48 differential metabolites in leaves were detected, with 20 shared metabolites. Under Cd stress, most of the carbohydrates in leaves and roots decreased, which contributed to the lowered leaf/root length and fresh weight. In comparison, most of the differential amino acids and lipids decreased in the leaves but increased in the roots. Almost all the differential amino acids in the roots were negatively correlated with root length and root fresh weight, while they were positively correlated with malondialdehyde content. However, most of the differential amino acids in the leaves were positively correlated with leaf length and leaf fresh weight but negatively correlated with malondialdehyde content. Metabolic pathway analysis showed that Cd significantly affects seven and eight metabolic pathways in the leaves and roots, respectively, with only purine metabolism co-existing in the roots and leaves. Our study is the first statement on metabolic responses to Cd stress and the relationships between differential metabolites and biological endpoints in fountain grass. The coordination between various metabolic pathways in fountain grass enables plants to adapt to Cd stress. This study provides a comprehensive framework by explaining the metabolic plasticity and Cd tolerance mechanisms of plants.

Anthropogenic eutrophication is known to impair the stability of aboveground net primary productivity (ANPP), but its effects on the stability of belowground (BNPP) and total (TNPP) net primary productivity remain poorly understood. Based on a nitrogen and phosphorus addition experiment in a Tibetan alpine grassland, we show that nitrogen addition had little impact on the temporal stability of ANPP, BNPP, and TNPP, whereas phosphorus addition reduced the temporal stability of BNPP and TNPP, but not ANPP. Significant interactive effects of nitrogen and phosphorus addition were observed on the stability of ANPP because of the opposite phosphorus effects under ambient and enriched nitrogen conditions. We found that the stability of TNPP was primarily driven by that of BNPP rather than that of ANPP. The responses of BNPP stability cannot be predicted by those of ANPP stability, as the variations in responses of ANPP and BNPP to enriched nutrient, with ANPP increased while BNPP remained unaffected, resulted in asymmetric responses in their stability. The dynamics of grasses, the most abundant plant functional group, instead of community species diversity, largely contributed to the ANPP stability. Under the enriched nutrient condition, the synchronization of grasses reduced the grass stability, while the latter had a significant but weak negative impact on the BNPP stability. These findings challenge the prevalent view that species diversity regulates the responses of ecosystem stability to nutrient enrichment. Our findings also suggest that the ecological consequences of nutrient enrichment on ecosystem stability cannot be accurately predicted from the responses of aboveground components and highlight the need for a better understanding of the belowground ecosystem dynamics.