Abstract:

Aims: Nitrogen (N) enrichment can reduce grassland plant diversity, while dung decomposition and nutrient release are important for maintaining plant diversity in native grassland ecosystems. Grasslands have been subjected to both atmospheric N deposition and dung inputs. However, it remains unclear how these factors affect plant richness and species–area relationship (SAR). 

Methods: In 2022, we conducted a field experiment at the Inner Mongolia Grassland Ecosystem Research Station, Chinese Academy of Sciences. A split–plot completely randomized design was used, with enclosure and grazing as the two main effects. Within each main effect, four treatments were applied: control, cow dung addition (Dung), N addition (N), combined cow dung and N addition (Dung + N). In August 2024, species richness was recorded at four spatial scales (1 m², 2 m², 4 m², and 8 m²). At the same time, aboveground net primary productivity (ANPP) and relevant soil physicochemical indicators were measured. 

Results: We found that enclosure significantly reduced the mean plant species richness at multiple spatial scales by 18.9%. Enclosure significantly reduced the intercept of the species–area relationship (i.e., plant diversity per unit area), but did not affect the minimum area for species coexistence or the slope (i.e., spatial heterogeneity of community composition). Neither N nor dung addition significantly changed the intercept, or slope of the species–area relationship. Results from the structural equation model showed that enclosure had a positive effect on the slope by lowering soil pH. It also exerted a negative effect on the intercept by increasing aboveground net primary productivity. Dung addition had a negatively affected on both the slope and intercept of the species–area relationship by increasing soil ammonium nitrogen content. 

Conclusions: Our findings suggest that dung inputs in typical steppe ecosystems can facilitate species coexistence through moderate nutrient supplementation, highlighting the importance of evaluating the ecological, productive, and livelihood benefits of dung coverage under the premise of grass–livestock balance.

Key words: grassland, plant diversity, cow dung, nitrogen deposition, species–area relationship