荒漠草原灌丛引入过程中土壤氮矿化的季节动态及其影响因子

Seasonal dynamics of soil nitrogen mineralization and their influencing factors during shrub anthropogenic introduction in desert steppe

选取封育草地、放牧草地、不同年限(引入柠条3、12、22年)/密度(间距2、6、40 m)的灌丛地为对象,研究荒漠草原-退化-灌丛引入过程中生长季(4—10月)土壤氮矿化的季节动态及其影响因子。结果表明:0~10 cm表层土壤水分具有明显的季节特征,0~200 cm剖面土壤水分随灌丛年限和密度增加而加剧消耗;与放牧草地和封育草地相比,灌丛对土壤碳氮磷养分的促进作用随灌丛年限和密度的增加呈现先强后弱趋势;生长季动态和草地变化对土壤氮矿化过程产生显著影响,土壤NO_(3)^(-)、微生物生物量碳和氮在生长季中期(6—8月)显著升高,其中NO_(3)^(-)占总无机氮的比值由封育草地30.5%增至灌丛地69.5%。NH_(4)^(+)受生长季动态影响大于草地变化,其含量在生长季后期(10月)升高。在草原-退化-灌丛引入过程中,灌丛年限和密度的增加显著增大荒漠草原土壤硝化和铵化作用的生长季动态差异,而对微生物生物量碳和氮的影响不显著;土壤NH_(4)^(+)和NO_(3)^(-)含量与全氮、有机碳和N/P呈显著正向相关,土壤碳氮磷主要以计量比(C/N和N/P)的形式直接调控氮矿化过程。

We selected enclosed grassland,grazed grassland and shrublands with different planting years(3,12,22 years)/densities(intervals of 2,6,40 m)to investigate soil N mineralization dynamics in the growing season(April-October)and its influencing factors during the process of desert steppe-degradation-shrub introduction.The results showed that soil moisture at 0-200 cm layer was decreased with increases of shrub age and density,and that the variations of soil moisture at 0-10 cm layer coincided with seasonal change.Compared with grazed grassland and enclosed grassland,the positive effect of shrubs on soil carbon,nitrogen and phosphorus contents first increased and then decreased with the increases of age and density.Moreover,soil N mineralization significantly varied across months and sites.Soil NO_(3)^(-)content and microbial biomass carbon and nitrogen were significantly higher from June to August.The proportion of NO_(3)^(-)to inorganic nitrogen significantly increased from 30.5%in enclosed grassland to 69.5%in shrublands.NH_(4)^(+)content was mainly affected by months compared with sites.In the process of steppe-degradation-shrub introduction,the increases of shrub age and density significantly enhanced seasonal differences of soil nitrification and ammonification,but not on the seasonal mineralization of microbial biomass carbon and nitrogen.Soil NH_(4)^(+)and NO_(3)^(-)contents were significantly and positively correlated with total nitrogen,organic carbon and N/P.Soil stoichiometric ratios(C/N and N/P)directly regulated N mineralization process.