Effect of disturbance by plateau pika on soil nitrogen stocks in alpine meadows

The presence of small burrowing herbivores often cause extensive disturbance to the grassland soil nutrient stocks. This study investigated the effect of small burrowing herbivore presence, the plateau pika (Ochotona curzoniae), and variation in disturbance intensity on soil nitrogen stocks at five alpine meadow sites. Disturbed plots occupied by plateau pikas consist of burrows and their associated bare soil patches in a matrix of continuous alpine meadow. The percentage of the bare soil area in a disturbed plot was used as a proxy for disturbance intensity of plateau pikas. This study showed that the soil total nitrogen stock was lower of bare soil than vegetated soil within disturbed plots, while ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), inorganic nitrogen and ammonium nitrogen/nitrate nitrogen ratio (ANR) were higher in bare soil than vegetated soil within the disturbed plots. This study further showed that the NH4+-N, inorganic nitrogen and ANR of disturbed plots were higher than those of undisturbed plots, whereas soil total nitrogen and the NO3--N stock was not different between disturbed plots and undisturbed plots. This study also showed that the soil total nitrogen, NH4+-N and inorganic nitrogen stocks of disturbed plots were higher at intermediate disturbance intensities of plateau pikas, whereas the NO3--N stock and ANR were not related to disturbance intensities. These results suggest that the NH4+-N and inorganic nitrogen stocks were higher in the presence of plateau pikas, and intermediate disturbance intensity of plateau pikas was beneficial for soil quality due to higher soil total nitrogen, NH4+-N and inorganic nitrogen stocks. The findings of this study present a possible approach for estimating how the presence of a small burrowing herbivore influences grassland soil nitrogen stock.