Soil nitrogen mineralization and nitrification under Caragana microphylla shrubs of different ages in the northwestern Shanxi Loess Plateau
Nitrogen (N) is a main limiting factor for plant growth and development in many regions.Soil organic N,accounting for up to 95％ of the soil N pool,cannot be used by plants directly,but can be absorbed and utilized by plants after being mineralized into nitrate N (NO3--N) and ammonium N (NH4+-N).Therefore,soil net N nitrification (Nnit) and net N mineralization (Nmin) rates have been considered two important indicators for evaluating the stability and function of an ecosystem.Caragana microphylla,a leguminous and sand-binding shrub,is a dominant species widely distributed in the Loess Plateau of northwestern Shanxi.Previous studies on soil N dynamics have mainly focused on forest,grassland,and farmland ecosystems to study the effect of environmental factors such as temperature and humidity on soil N mineralization and nitrification.However,few researchers have focused on soil N dynamic changes under shrub lands in arid and semiarid regions.The objective of this study was to explore the content of NO3--N and NH4+-N and the rate of soil net N nitrification and net N mineralization under Caragana microphylla shrubs as a function of plant age.We used a closed-top PVC tube in situ incubation method to detect the soil net N mineralization and net N nitrification in Caragana microphylla shrubs of different ages (5,10,20,30,and 40 a) in the northwest Shanxi Loess Plateau.The results indicated that NO3--N accounted for a larger proportion of mineral N in Caragana microphylla shrub soil.The NO3--N concentration was 1.5-15.4 times higher than NH4+-N in the same month of different years.Soil net N nitrification and net N mineralization rates increased as the Caragana microphylla shrubs' ages increased,with the greatest average rates from May to October (40.2 and 44.1 mg m-2 d-1,respectively) being observed under 30-year-old shrubs.The net N nitrification and mineralization rate increased faster in July and August relative other months during the growing season.The net N nitrification and mineralization rates were 86.9 and 93.1 mg m-2 d-1,respectively,at 30-year-old shrubs,which had the highest rates of all age classes (P＜ 0.05).The total net N nitrification and mineralization also increased with increased age of Caragana microphylla.The total net N nitrification and mineralization from May to October increased by 3.7-and 3.1-fold at 30-year-old shrubs,respectively,relative to 5-year-old shrubs.During the Caragana microphylla growing season from May to October,2.3％ of soil total N was mineralized into inorganic N,87％ of which was eventually transformed into NO3--N.The results of this study provide great insight for guiding shrub utility and land management in the establishment and development of shrub ecosystems in the Loess plateau.
Caragana microphylla shrubsnet N mineralization and nitrificationnorthwestern Shanxi Loess Plateau
国家科技期刊平台
NSTL
万方数据
维普
