Ning Zong

The alpine grassland ecosystem of the Tibetan Plateau is a vital base for animal husbandry and a key ecological security barrier in China. Phosphorus (P), an essential nutrient, is among the primary factors limiting grassland productivity. However, the spatial distribution of soil P fractions across alpine grasslands on the Tibetan Plateau and their environmental drivers remain unclear, limiting our understanding of P cycling and grassland productivity. This study examined the composition and distribution of soil P in three representative alpine grasslands (meadow, steppe, and desert) using a combination of chemical fractionation and ³¹P nuclear magnetic resonance (NMR) spectroscopy. The results revealed pronounced spatial heterogeneity, with total soil P content varying by approximately 2.4-fold among the grassland types. Alpine meadows had the highest total P (0.73 g kg⁻¹) and available P (4.02 mg kg⁻¹) concentrations, with the latter being nearly twice that of alpine steppes and deserts. Alpine meadows were characterized by a predominance of labile and moderately labile organic P (e.g., NaOH-Po) and a diverse array of phosphate monoesters and diesters, whereas alpine deserts were dominated by stable, calcium-bound inorganic P (HCl-Pi). Temperature, precipitation, pH, and phosphatase activity were identified as key factors regulating the distribution and transformation of P fractions. The distinct P fractions and availability uncovered in this study are essential for predicting grassland ecosystem responses to environmental change and guiding sustainable pasture management on the Tibetan Plateau.

Phosphorus (P) is a key limiting nutrient in alpine meadows. Analyzing the spatial distribution of soil P and its forms along altitudinal gradients is crucial to understand soil nutrient cycling and sustain productivity under climate change. In this study, changes in the total P, available P, inorganic P (Pi), and organic P (Po) contents in soil along an altitudinal gradient of 4400–5200 m on the Qinghai–Tibetan Plateau were investigated using sequential chemical fractionation and solution ³¹P nuclear magnetic resonance (NMR). The results showed that the contents of total soil P, available P, Pi, and Po forms showed vertical distribution patterns. At an altitude of 4400–4950 m, the dominance of NaOH-Po was observed, whereas HCl-Pi was predominant at 5200 m. With increasing elevation, total soil P, orthophosphate, NaHCO₃-Pi, NaOH-Pi, HCl-Pi, and HCl-Po contents increased gradually. In contrast, the concentrations of available P, H₂O-Pi, H₂O-Po, NaHCO₃-Po, NaOH-Po, pyrophosphate, orthophosphate monoester, and diester initially increased, peaked at approximately 4950 m, and subsequently decreased. Both climatic factors (i.e., mean annual temperature and precipitation) and biological factors (aboveground biomass and enzyme activity) jointly regulated the vertical distribution of soil P forms in the alpine ecosystems.

Increased Nitrogen (N) input exerts significant impact on the functional integrity of terrestrial ecosystems, with alpine grasslands being particularly susceptible. Soil microbes are intricately intertwined with nearly all facets of essential biogeochemical cycle, underscoring their pivotal role in ecosystem processes. To elucidate how N enrichment modulates soil microbes and their diversity, 11-year N addition experiments were conducted in a semi-humid alpine meadow (AM) and an arid alpine steppe (AS) on the Northern Tibetan Plateau. We measured soil properties, aboveground net primary productivity (ANPP), plant diversity, microbial composition and diversity, as well as microbial co-occurrence networks. The results revealed that N additions profoundly reshaped microbial co-occurrence in alpine grasslands, albeit via divergent mechanisms in different ecosystems. In AM, N enrichment destabilized microbial networks mainly through reduced bacterial diversity linked to plant diversity loss. Conversely, in the harsher AS, N addition fostered closer microbial interactions, forming a more stable co-occurrence network despite lower plant richness, predominantly attributed to increased soil nutrient availability. Our results highlight the significance of co-occurrence networks as a key component of microbial biodiversity and emphasize the imperative of deciphering microbial interaction mechanisms to unravel soil functional dynamics under global nitrogen enrichment.

A community functional structure may respond to environmental changes such as nitrogen (N) enrichment by altering intraspecific and interspecific trait variations. However, the relative contributions of both components in determining the community response to N enrichment are unclear. In this study, we measured the plant height (H), leaf area (LA), leaf dry matter content (LDMC), and specific leaf area (SLA) based on a nine-year N addition gradient experiment in an alpine meadow on the Tibetan Plateau. We examined the intraspecific and interspecific variations within and among the communities, the responses of traits in terms of community weighted mean (CWM) and non-weighted mean (CM) to N addition, and the effects of these trait variations on aboveground net primary productivity (ANPP). Our results show that N addition increased the interspecific variation in H while decreasing that of LA within the community, whereas it had no significant effects on the intraspecific variations in the four traits within the community. In contrast, N addition significantly increased the intraspecific variation in H and decreased that of LA among the communities. Moreover, the contribution of intraspecific variation was greater than that of the interspecific variation in terms of CWM for all traits, while the opposite contribution was observed in terms of CM, suggesting that the dominant species would have greater resilience while subdominant species would become less resistant to N addition. Further, intraspecific variations of LA and LDMC within the community played an important role in explaining community productivity. Our results highlight the importance of both intraspecific and interspecific variations in mediating functional trait responses to N enrichment, and intraspecific variation within the communities has important implications for community functioning that should be considered to better understand and predict the responses of the alpine grasslands to N enrichment.

Asymmetric seasonal warming, characterized by more pronounced temperature increases in winter than in summer, has become a critical feature of global warming, especially in cold and high-altitude regions. Previous studies have primarily focused on year-round warming, while comparatively less attention was paid to winter warming. However, a significant knowledge gap exists regarding the impacts of winter warming on ecosystem functions. To address this, we conducted an 8-year manipulated warming experiment in an alpine grassland on the Tibetan Plateau, employing three treatments: no warming, year-round warming and winter warming. We found that neither year-round warming nor winter warming significantly alters species richness at the community level. Notably, community biomass stability was maintained via species asynchrony. However, warming exerted significant effects on the plant abundance groups (dominant, common and rare species). Specifically, winter warming enhanced the stability of dominant species by increasing species asynchrony of dominant species, as the compensatory dynamics occurred between the grass and forbs. In contrast, year-round warming reduced the stability of common species, correlated with an increase in species richness and a decline in asynchrony among common species. Thus, our study underscores the capacity of alpine grassland to maintain community biomass stability via asynchrony dynamics of species under different warming conditions, although the stability of different abundance groups would be changed. Importantly, our results provide valuable insights for understanding the alpine grassland ecosystem on the Tibetan Plateau.

Anthropogenic nutrient additions are influencing the structure and function of alpine grassland ecosystems. However, the underlying mechanisms of the direct and indirect effects of nutrient additions on aboveground net primary productivity (ANPP) are not well understood. In this study, we conducted an eight-year field experiment to explore the ecological consequences of nitrogen (N) and/or phosphorous (P) additions on the northern Tibetan Plateau. ANPP, species diversity, functional diversity, and functional groups were used to assess species’ responses to increasing nutrients. Our results showed that nutrient additions significantly increased ANPP due to the release in nutrient limitations. Although N addition had a significant effect on species richness and functional richness, and P and N + P additions altered functional diversity, it was functional groups rather than biodiversity that drove changes in ANPP in the indirect pathways. We identified the important roles of N and P additions in begetting the dominance of grasses and forbs, respectively. The study highlights that the shift of functional groups should be taken into consideration to better predict the structure, function, and biodiversity–ANPP relationship in grasslands, particularly under future multifaceted global change.

Dominant species may strongly influence biotic conditions and interact with other species, and thus are important drivers of community dynamics and ecosystem functioning, particularly in the stressed environment of alpine grasslands. However, the effects of dominant species on the community stability of different ecosystems remain poorly understood. We examined the mechanisms underlying temporal stability (2014–2020 year) of aboveground productivity and community stability in four alpine grasslands (alpine meadow, alpine meadow steppe, alpine steppe and alpine desert steppe) of the northern Tibetan with different species composition and dominance. Our results showed that community stability was significantly higher in the alpine meadow than in the other three types of grasslands. This difference was mainly attributed to the higher compensatory effect and selection effect in the alpine meadows. Furthermore, dominant species strongly affected community stability by increasing dominant species stability and species asynchrony. However, species richness had little effect on community stability. Our findings demonstrate that dominant species, as foundation species, may play leading roles in shaping community stability in the alpine grasslands, highlighting the importance of conserving dominant species for stable ecosystem functioning in these fragile ecosystems under increasing environmental fluctuations.