氮添加速率和频率对草原土壤-植物化学计量的影响OA

Nitrogen(N)is a key limiting factor for plant growth,and the increase in N deposition has become a crucial driver influencing the soil-plant nutrient cycle in grasslands.However,the mechanisms underlying the effects of different N addition rates and frequencies on soil-plant stoichiometric relationships remain unclear.A field experiment was conducted in a temperate typical grassland to examine the effects of three N addition rates:0,10,and 20 g N/(m2·a)and two N addition frequencies(twice a year and twelve times a year)on the nutrient stoichiometric characteristics of surface soil and on the relationship between plant biomass and carbon(C),nitrogen(N),and phosphorus(P)contents in the dominant plants Leymus chi-nensis and Stipa grandis.Results showed that N addition significantly increased soil C and N contents while decreasing soil P content,thereby reducing the C∶N ratio and increasing the C∶P and N∶P ratios.Under the high-frequency addition,the decrease in soil P content and the increases in C∶P and N∶P ratios in the 20 g N/(m2·a)treatment were lower than those in the 10 g N/(m2·a)treatment.In addition,increas-ing the N addition rates elevated plant N content while reducing plant P content,resulting in a decreased plant C∶N ratio and increased plant N∶P and C∶P ratios.However,N addition frequencies had no signifi-cant effects on plant or soil nutrient contents or their stoichiometric ratios.Partial least squares path model revealed that N addition rates indirectly regulated plant stoichiometric ratios by modifying soil and plant nutrient contents,thereby promoting increases in the aboveground and belowground biomass of the two dominant plant species.In contrast,N addition frequencies had no significant impact.This study demon-strated that N addition transitions plants from N limitation to N saturation and further intensifies P limita-tion,which may become a critical process constraining the productivity increases in grassland ecosystems.