Research Background

Plant leaf stable carbon isotope (δ¹³C) is a key indicator of water-use efficiency, providing critical insights into vegetation dynamics under climate change. However, the drivers of community-level leaf δ¹³C variation in arid and semi-arid grassland ecosystems remain unclear.

Methods

This study investigated meadow steppe, typical steppe, and desert steppe ecosystems along a decreasing moisture gradient in Inner Mongolia. Using data from 399 sites and 1,197 community plots, we calculated community-weighted

  mean leaf δ¹³C (δ¹³C_CWM) and leaf functional traits (LFTCWM) for 70 dominant species, along with climatic and edaphic factors. We assessed the responses of δ¹³C_CWM to leaf traits, environmental factors, and aboveground biomass (AGB).

Differences inδ¹³C_CWM among grassland types were compared using one-way ANOVA with post-hoc LSD tests, while relationships with climate, soil, leaf traits, and AGB were analyzed via least squares regression. Structural equation modeling (SEM) was employed to disentangle the regulatory roles of climate, soil, and leaf traits onδ¹³C_CWM and AGB.

Results

Leaf δ¹³C_CWM increased with decreasing precipitation, peaking in desert steppe and reaching the lowest values in meadow steppe.

At the regional scale, δ13CCWM showed no significant correlation with mean annual precipitation (MAP) but was positively correlated with mean annual temperature (MAT) in meadow and typical steppes.

In meadow and typical steppes, δ13CCWM increased with soil pH and bulk density (BD) but decreased with soil total nitrogen (STN) and soil organic carbon (SOC). In contrast, desert steppe δ13CCWM was unaffected by these soil factors.

Leaf δ13CCWM was positively correlated with acquisitive traits and negatively correlated with conservative traits.

AGB was negatively correlated with δ13CCWM across all grasslands except desert steppe.

Abiotic factors (climate & soil) dominated δ¹³C_CWM variation in meadow and typical steppes, whereas leaf functional traits outweighed abiotic drivers in desert steppe.

Conclusions

This study reveals divergent drivers of community-level leaf δ¹³C variation across Inner Mongolian grasslands: environmental factors (climate and soil) primarily regulate δ¹³C in meadow and typical steppes, whereas leaf functional traits dominate in desert steppe. These findings highlight distinct carbon-water balance mechanisms among grassland types and enhance predictive understanding of ecosystem responses to global change.

Notably, desert steppe plants exhibit low environmental sensitivity in δ¹³C, relying instead on trait-based drought adaptation—suggesting long-term evolutionary selection for high water-use efficiency (higher δ¹³C) under persistent aridity. Under future drying climates, high-δ¹³C species may gain competitive dominance, potentially driving meadow steppe contraction and desert steppe expansion, with profound implications for regional ecosystem functioning and services.