氮素添加对贝加尔针茅草原土壤团聚体碳、氮和磷生态化学计量学特征的影响

Effects of nitrogen addition on ecological stoichiometric characteristics of carbon, nitrogen and phosphorus in Stipa baicalensis grassland soil aggregates

大气氮沉降增加作为全球气候变化的重要现象,其对草原生态系统的影响成为生态学研究热点之一。掌握氮沉降对草原土壤团聚体碳(C)、氮(N)和磷(P)生态化学计量学特征的影响,可为全面分析和评估氮沉降对草原生态系统的影响提供基础资料。自2010年起,在内蒙古贝加尔针茅草原典型地段设置N 0(0 kg N·hm^-2·yr^-1)、N 15(15 kg N·hm^-2·yr^-1)、N 30(30 kg N·hm^-2·yr^-1)、N 50(50 kg N·hm^-2·yr^-1)、N 100(100 kg N·hm^-2·yr^-1)、N 150(150 kg N·hm^-2·yr^-1)6个氮素添加处理模拟氮沉降野外控制试验。结果表明:氮素添加极显著提高了土壤团聚体的稳定性和>2 mm团聚体比例(P<0.01);各氮素添加处理中0.25~2 mm团聚体有机碳、全氮含量均显著高于其他粒径(P<0.05),全磷含量在各粒径团聚体中差异不显著;与对照相比,氮素添加显著提高了>0.25 mm土壤大团聚体有机碳和全氮含量(P<0.05),对全磷无显著影响;氮素添加导致>0.25 mm土壤大团聚体C/N降低,0.25~2 mm土壤团聚体C/P、N/P升高(P<0.05)。综合分析,氮添加在一定程度上促进了土壤的固碳潜力,提高了土壤团聚体有机质的矿化速率,随着氮素添加水平的提高,土壤团聚体中P元素成为限制草原植物生长的主要限制因子。

The influence of atmospheric nitrogen deposition on grassland ecosystems is an important component process of global climate change,and therefore has become a research hotspot in ecology.Our study aimed to understand the influence of nitrogen deposition on the carbon(C),nitrogen(N)and phosphorus(P)ecological stoichiometric characteristics of grassland soil aggregates,in order to provide fundamental research data for the comprehensive analysis and assessment of the impact of nitrogen deposition on grassland ecosystems.Since 2010,six simulated nitrogen deposition field control experiments of N 0(0 kg N·ha^-1·yr^-1),N 15(15 kg N·ha^-1·yr^-1),N 30(30 kg N·ha^-1·yr^-1),N 50(50 kg N·ha^-1·yr^-1),N 100(100 kg N·ha^-1·yr^-1)and N 150(150 kg N·ha^-1·yr^-1)were set up in an area of typical Stipa baicalensis grassland in Inner Mongolia.It was found that nitrogen addition significantly(P<0.01)increased the stability of soil aggregates and the proportion of aggregates>2 mm in diameter.In addition,the organic carbon and total nitrogen contents of 0.25-2 mm aggregates were significantly(P<0.05)higher than those of other particle sizes,but the total phosphorus contents did not differ significantly with different particle sizes.Compared with the control group,nitrogen addition significantly(P<0.05)increased the organic carbon and total nitrogen content of soil macroaggregates>0.25 mm diameter,but had no significant effect on total phosphorus.Nitrogen addition reduced the C∶N ratio of>0.25 mm aggregates,but increased C∶P and N∶P ratios of 0.25-2 mm aggregates(P<0.05).A comprehensive analysis shows that nitrogen addition promotes the carbon sequestration potential of soil to a certain degree and increases the mineralization rate of organic matter in soil aggregates.With the increase of nitrogen addition level,the elemental P level in soil aggregates becomes the main limiting factor restricting the growth of grassland plants.