Effects of seasonal warming on soil stoichiometry in semiarid grassland of Inner Mongolia

In this study, the effects of non-growing-season and growing-season warming on the soil nutrient content and ecological stoichiometric ratio of a northern temperate steppe ecosystem in China were determined through a warming experiment in Inner Mongolia. The ecological stoichiometric characteristics of soil in the 0－10 and 10－20 cm layers, including the contents of soil total organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N), and available phosphorus (AP), were analyzed in this experiment. The results showed that: 1) non-growing-season and growing-season temperature increases changed the nutrient contents and ecological stoichiometric ratio of the grassland soil in Inner Mongolia, and interaction effects were found for some indices. The effects of non-growing-season warming on soil nutrient content were mainly concentrated in the 0－10 cm soil layer. Non-growing-season warming significantly increased the total organic carbon content of the 0－10 cm soil (P < 0.05) and total phosphorus content of the 10－20 cm soil ( P < 0.05). The nitrate nitrogen content in the 0－10 cm soil was significantly decreased ( P < 0.05). The increased temperature during the growing season significantly increased the ammonium nitrogen content in the 0－20 cm soil ( P < 0.05), and significantly decreased the nitrate nitrogen content in the 0－10 cm soil and the total organic carbon content in the 10－20 cm soil ( P < 0.05). In addition, non-growing-season and growing-season warming interactively affected the contents of total organic carbon, total phosphorus, and ammonium nitrogen in the 0－10 cm soil ( P < 0.05). 2) Non-growin- season warming significantly reduced the N ꞉ P in the 10－20 cm soil layer soil ( P < 0.05). However, growing season warming had no significant effect on the stoichiometric ratio between C, N, and P ( P > 0.05). In addition, non-growing-season and growing-season warming interactively affected C ꞉ N, C ꞉ P, and N ꞉ P in the 0－10 cm soil and C ꞉ N in the 10－20 cm soil ( P < 0.05). The results of this study indicated that non-growing-season climate warming is as important as growing-season climate warming affects the stoichiometric characteristics of the soil of typical grasslands in northern China, and interactions occur between different seasons of climate warming on soil stoichiometry. Therefore, seasonal differences in climate warming should receive more attention in future global change studies.