外源氮添加对高寒草地门源草原毛虫种群密度的影响

近几十年以来，中国陆地生态系统的大气氮沉降持续增加。这种外源氮输入会影响植物多样性和生产力，进而影响植食性昆虫的种群动态。门源草原毛虫(Gynaephora menyuanensis)是青藏高原东北部高寒草地的主要植食性昆虫，种群数量爆发时会造成巨大的生态经济损失。为了探明草原毛虫种群密度如何响应氮沉降加剧，依托青海海北高寒草地“外源氮添加梯度”控制实验平台(0、25、50、100 kg N hm^-2 a^-1),详细调查了门源草原毛虫的种群密度及其相关的食物数量、质量和栖息地环境变化。结果表明：(1)外源氮添加显著影响门源草原毛虫的虫口密度(ANOVA:F=3.29,P=0.04),且草原毛虫虫口密度随氮添加量的增加呈线性增加趋势(R~2=0.31,P=0.005)。(2)外源氮添加梯度下，食物质量(叶片氮含量),而非食物数量(植物地上生物量和禾草地上生物量)和栖息地环境(土壤温度、湿度和光照条件),是草原毛虫虫口密度变化的关键影响因素。基于上述结果，可以预测：未来氮沉降的加剧可能促进青藏高原高寒草地门源草原毛虫的虫害爆发。研究将为全球变化背...

Effects of nitrogen addition on the population density of Gynaephora menyuanensis in Tibetan alpine grassland

Atmospheric nitrogen deposition has continued to increase in the Chinese terrestrial ecosystems over the past several decades. The input of exogenous nitrogen can alter the productivity and diversity of plant community, thus influencing the population dynamics of herbivorous insects. The grassland caterpillar (Gynaephora menyuanensis) is one of the main herbivorous insects of alpine grasslands in the northeast of the Qinghai-Tibet Plateau, and its outbreak can cause enormous ecological and economic losses. To explore whether increasing nitrogen deposition exacerbates or alleviates the outbreak of grassland caterpillar, we investigated the larval density of G. menyuanensis and their food quantity, food quality and habitat conditions by a nine-year nitrogen addition experiment in an alpine grassland on the Qinghai-Tibet Plateau. In the manipulative field experiment, a randomized block design was used with six blocks, and each block contained four levels of nitrogen addition including control (0 kg N hm^-2 a^-1), low nitrogen (25 kg N hm^-2 a^-1), medium nitrogen (50 kg N hm^-2 a^-1), and high nitrogen (100 kg N hm^-2 a^-1). The low, medium, and high nitrogen addition treatments were approximately 2.5, 5 and 10 times the ambient nitrogen deposition, respectively. Nitrogen was added using urea after sunset at the beginning of June, July, and August each year. Larval density of G. menyuanensis was investigated in sunny weather of July 2019. Our results showed that:(1) Nitrogen addition treatments altered the larval density of G. menyuanensis (ANOVA:F=3.29, P=0.04), and the larval density increased linearly with increasing rate of nitrogen addition (R²=0.31, P=0.005). Among them, the high nitrogen addition treatment increased the larval density by 85.4% (P<0.01). (2) Food quality (i.e., community-level leaf nitrogen content) played a main role in driving the responses of larval density of G. menyuanensis to nitrogen addition, while food quantity (i.e., aboveground plant biomass and aboveground graminoid mass) and habitat conditions (i.e., soil temperature and moisture and light condition) contributed less to the changes in larval density. Specifically, the pure effect of food quality accounted for 26.8% of variation in the larval density across different nitrogen addition treatments, and the joint effect of food quality and habitat conditions accounted for 18.3% of variation. The pure effects of food quantity and habitat conditions accounted for 1.7% and 12.2% of variation, respectively. Overall, these findings suggest that increasing nitrogen deposition may promote the outbreak of grassland caterpillars on the Qinghai-Tibet Plateau. They will also enhance our understanding of the interaction between plants and herbivores and provide practical advice on the adaptive management and pest control of alpine grasslands.