外源性养分添加对高寒草甸土壤节肢动物群落的影响

为了查明外源性养分添加对高寒草甸土壤动物群落的影响，2012年5月在川西北的高寒草甸上用随机区组方式设置添加氮（N）、磷（P）和氮磷混加（NP）3种处理试验样地，每种添加处理均设置10、20和30 g·m^-2三个处理梯度，以未添加养分的高寒草甸为对照样地（CK）。于2017和2020年的8月先后两次对各样地内的土壤节肢动物和土壤理化性质进行调查。结果表明：1）N、P和NP添加均能增加高寒草甸土壤节肢动物的密度和多样性，以梯度为20 g·m^-2和NP混加处理效果最明显；2）N、P添加土壤节肢动物群落的密度、类群数和Shannon多样性指数均表现为2020年显著高于2017年（P<0.05），而NP混加土壤节肢动物群落的密度和类群数则表现为2020年显著低于2017年（P<0.05），但Shannon多样性指数表现为无显著差异（P>0.05）；3）N、P添加显著提高长角?目密度（P<0.05），NP混加显著提高甲螨亚目和中气门亚目密度（P<0.05）；4）多元回归分析和典范对应分析表明，影响土壤节肢动物群落组成结构和多样性的主要环境因素是土壤全N、全P、土壤有机质、pH、地上生物量和植物群落盖度。研究结果表明，土壤节肢动物群落对添加不同的外源性养分及添加量处理存在差异；高寒草甸上连续8年添加外源性氮、磷养分能提高土壤节肢动物多样性，而氮磷混加则起抑制作用。建议对高寒草甸进行外源性氮磷混加控制在每年20 g·m^-2，且连续添加年限不宜超过8年。

Effects of exogenous nutrient addition on alpine meadow soil arthropod communities

This study aimed to determine the effects of exogenous nutrient addition on soil arthropod communities in the alpine meadows. Three nutrient addition treatments （nitrogen， N； phosphorus， P； and combined nitrogen and phosphorus， NP） were established in Hongyuan County， northwest Sichuan， China， in late May 2012. Each nutrient treatment was applied at three concentrations： 10 g·m^–2 （N₁₀， P₁₀， and NP₁₀）， 20 g·m^–2 （N₂₀， P₂₀， and NP₂₀）， and 30 g·m^–2 （N₃₀， P₃₀， and NP₃₀）， with six replicate plots of 3 m×3 m. Another six 3 m×3 m plots in natural alpine meadow served as control plots. The nutrient treatments were added every year for continued eight years. The soil arthropods and soil environmental factors in each plot were evaluated in August 2017 and 2020. Soil arthropods were extracted from the soil samples for 48 h at 38 ℃ using the Tullgren method in the laboratory. The main findings were as follows： 1） N， P， and NP additions in the alpine meadow increased the individual density and diversity of soil arthropods， with the strongest effects in the 20 g·m^-2 and NP treatments； 2） The abundances， taxonomic richness， and Shannon’s diversity index of the soil arthropod communities in the N-addition and P-addition treatments increased significantly from 2017 to 2020 （P<0.05）， while the abundance and taxonomic richness of soil arthropod communities in the NP-addition treatment declined significantly from 2017 to 2020 （P<0.05）， but no significant change was detected for Shannon’s diversity index （P>0.05）； 3） The abundance of Entomobryomorpha was significantly increased in the N-addition and P-addition treatments （P<0.05） and the abundances of Oribatida and Mesostigmata were significantly increased in the NP-addition treatment （P<0.05）； 4） The results of multiple regression analysis and canonical correspondence analysis showed that the main environmental factors influencing the composition of soil arthropod communities were the contents of soil total N， total P and soil organic matter， pH， aboveground biomass， and plant community cover. Our results showed that the soil arthropod communities respond differently to different exogenous nutrient additions and nutrient gradients； and that the diversity of soil arthropods in alpine meadows can be promoted by N-addition and P-addition but restrained by mixed N and P additions after continued eight years additions. We recommend that the additions of mixed N and P to the alpine meadows should be controlled at 20 g·m^–2 per year and should not exceed eight years.