Effect of grazing intensity on temperature sensitivity of soil nitrogen mineralization in Zoigë alpine meadow

Abstract

Overgrazing, climate changes, and drainage are the important disturbances and critical environmental problems for Zoigë alpine meadow. These factors play an important role in regulating the soil nitrogen (N) cycle and to some extent influence alpine meadow ecosystem structure and function. In this study, we investigated the effect of grazing intensity on soil N mineralization and its temperature sensitivity (Q10), by incubating soil samples collected during field grazing experiments in the Zoigë alpine meadow. The results showed that grazing significantly influenced soil nitrification and net N mineralization rates, which followed the order of light grazing (L) > moderate grazing (M) > heavy grazing (H) > no grazing (CK). No differences were observed in the nitrification and net N mineralization rates at low temperatures (5— 10ºC); however, significant differences were observed at high temperatures (15—25ºC). The accumulations of NO-3 -N and total inorganic N increased with increasing incubation time, whereas no significant differences were observed in the accumulations of soil NH+4 -N. Moreover, we found that the Q10 value for soil N mineralization significantly increased with increase in grazing intensity. Further, the Q10value in heavily grazed grasslands (Q10 = 2.72) was significantly higher than that in other areas with lower grazing intensities. Thus, our results highlighted that grazing intensity has an important effect on the Q10 value in the Zoigë alpine meadow, which is important for the N cycles in the area when considering heavy grazing and future scenarios on climate change. Further, we showed that the high acceleration of N mineralization rates in heavily grazed grasslands under the tendency of increasing temperatures in Zoigë would be in favor of plant growth in a short-term view. However, in a long-term view, the situation would accelerate nitrogen loss in the Zoigë alpine meadow and may negatively affect plant growth and maintenance of the ecosystem structure and function.