Tan sheep excrement type and supply level can alter community parameters through population transformation in a...

Livestock grazing and their excrement regulate vegetation structure and species competition in climate-sensitive semi-arid steppes. While grazing-nutrient dynamics are well documented in humid and mesic savannas, however, the ecological roles of distinct excrement types and their deposition intensities remain poorly understood in semi-arid grasslands. To address this gap, we conducted a two-year field experiment with two excrement types (urine and dung) at three levels (0.5, 1, and 1.5 l/m² for urine and 4.72, 9.44, and 14.16 g/m² for dung), along with a control (no treatment application) in the typical steppe on Loess Plateau of China. Thus, a total of 21 treatments were analysed. All treatments were replicated thrice to understand their effects on plant traits, with a consequent change in community parameters (i.e., aboveground biomass and plant diversity). We found that with the increase in urine gradient, the above-ground biomass (AGB) of three dominant species, i.e., Artemisia capillaris, Lespedeza davurica and Stipa bungeana displayed a significant increase, approximately 25 %, 20 % and 50 % variance was explained by year × excrement gradient, respectively, due to abundant nitrogen supply; however, climate-driven volatility caused an uneven change in the second year for urine application treatments. However, dung application had stable effects on the population biomass of these three species, this could be due to its slower decomposition and gradual nutrient release. Plant traits (height, crown width) showed temporal and excrement-type variability. Urine and dung enhanced A. capillaris height and crown width temporarily, however, S. bungeana height was not affected. Trade-off analysis between height and width has shown that under urine application, the three species invested longer in height, while dung application encouraged them to prioritise width as well. Population biomass and community biomass showed a positive correlation with annual precipitation under both excrement additions in A. capillaris. Partial Least Squares Path Modeling (PLS-PM) revealed the direct effects of A. capillaris biomass on community biomass, while diversity and population biomass interchangeably affected community biomass for L. davurica and S. bungeana under excrement additions. Hence, adding animal manure to degraded grassland can help plants fight climatic extremes while maintaining their productivity.