Linking leaf traits to the temporal stability of above- and belowground productivity under global change and land use scenarios in a semi-arid grassland of Inner Mongolia

Plant Acquisitive Strategies Promote Resistance and Temporal Stability of Semiarid Grasslands

Among ecologists, it is widely believed that conservative growth strategies of plants are crucial for sustaining ecosystem stability, while the potential stabilising role of acquisitive strategies has received little attention. We investigated the relationships between plant traits and three stability dimensions-temporal stability, resistance and resilience-using two complementary datasets from drought-affected semi-arid grasslands: a temporal plant community survey from a single site and a 1000-km transect survey with satellite-derived productivity estimates. We found strikingly consistent patterns from the two datasets, with grasslands dominated by acquisitive strategies exhibiting greater resistance and temporal stability of productivity. Acquisitive strategies enhance stability by facilitating drought escape and avoidance, rather than drought tolerance typically associated with conservative strategies. These results highlight the important but underappreciated role of acquisitive strategies in enhancing ecosystem resistance to disturbances and maintaining temporal stability in semi-arid grasslands.

Dominant species modulates nitrogen effects on the temporal stability of above- and below-ground biomass in a temperate desert steppe

The temporal stability of above-ground biomass (AGB) and below-ground biomass (BGB) in grasslands is crucial for maintaining a continuous supply of ecosystem functions and services, particularly in the context of global changes. Nitrogen (N) addition is well known to affect AGB stability, however, we still lack knowledge of how N addition affect BGB stability. Furthermore, a crucial knowledge gap remains regarding which underlying mechanisms drive AGB and BGB stability, which obstructs our comprehensive awareness of biomass stability from both above- and below-ground perspectives simultaneously. Through a five-year manipulative experiment with seven N addition levels, we tested how AGB and BGB stability responded to N addition and which factors modulated the effects of N addition on stability. Using a framework developed to quantify changes in biomass stability, we investigated the relative contributions of dominant species, taxonomic diversity, functional diversity, species asynchrony, species stability and soil properties in driving AGB and BGB stability. We found that N addition enhanced AGB stability directly and indirectly through the modulatory effects of dominant species. N addition increased dominance of fast species, causing high community-weighted mean (CWM) fast-slow and further high species asynchrony. Large increases in species asynchrony and weak decreases in dominant species stability, rather than decreases in species richness, were crucial factors driving AGB stability. Additionally, increased CWM fast-slow enhanced BGB stability, although this positive effect was partially offset by a slight decrease in soil water content (SWC). Our results broaden the insurance hypothesis and the mass ratio hypothesis, providing new insights into how N addition affects biomass stability and underlying driving mechanisms in a temperate desert steppe. These findings emphasize that dominant species and CWM fast-slow play crucial modulatory roles in driving biomass stability. Therefore, it is very necessary to pay attention to dominant species and functional diversity, in order to provide guidance for the sustainable functions and services in species-poor drylands.

High species richness of sheep-grazed sand pastures is driven by disturbance-tolerant and weedy short-lived species

We selected 15 sheep-grazed sand pastures along a gradient of increasing grazing intensity to study the fine-scale patterns of main biomass fractions (green biomass, litter) and that of plant species and functional groups (life forms and social behaviour types). We classified them into five grazing intensity levels based on stocking density, proximity to drinking and resting places and the number of faeces. We aimed to answer the following questions: (i) How does increasing intensity of sheep grazing affect the amount of green biomass, the species richness and their relationship in sand pastures? (ii) How does increasing intensity of sheep grazing affect the biomass of perennial and short-lived graminoids and forbs? (iii) How does the disturbance value-expressed in the biomass ratio of disturbance-tolerant and ruderal species-change along the gradient of grazing intensity? A unimodal relationship between green biomass and species richness was detected; however, the ordination (canonical correspondence analysis, CCA) showed no clustering of pastures subjected to the same levels of grazing intensity. Along the grazing intensity gradient we found an increasing trend in species richness and significant differences in green biomass (decreasing trend), litter (decreasing trend), graminoids (decreasing trend) and short-lived forbs (increasing trend). We found an increasing amount of disturbance-tolerant and ruderal species with increasing grazing intensity. We suggest that we might need to use multiple scales for sampling and a fine-scale assessment of grazing intensity. Our findings might be instructive for pastures in densely populated regions, which are prone to the encroachment of disturbance-tolerant and ruderal species.

Opposing responses of temporal stability of aboveground and belowground net primary productivity to water and nitrogen enrichment in a temperate grassland

Changes in water and nitrogen availability, as important elements of global environmental change, are known to affect the temporal stability of aboveground net primary productivity (ANPP). However, evidences for their effects on the temporal stability of belowground net primary productivity (BNPP), and whether such effects are consistent between belowground and aboveground, are rather scarce. Here, we investigated the responses of temporal stability of both ANPP and BNPP to water and nitrogen addition based on a 9-year manipulative experiment in a temperate grassland in northern China. The results showed that the temporal stability of ANPP increased with water addition but decreased with nitrogen addition. By contrast, the temporal stability of BNPP decreased with water addition but increased with nitrogen enrichment. The temporal stability of ANPP was mainly determined by the soil moisture and inorganic nitrogen, which modulated species asynchrony, as well as by the stability of dominant species. On the other hand, the temporal stability of BNPP was mainly driven by the soil moisture and inorganic nitrogen that modulated ANPP of grasses, and by the direct effect of soil water availability. Our study provides the first evidence on the opposite responses of aboveground and belowground grassland temporal stability to increased water and nitrogen availability, highlighting the importance of considering both aboveground and belowground components of ecosystems for a more comprehensive understanding of their dynamics.