Subjects: Biology >> Ecology submitted time 2017-11-29 Cooperative journals: 《中国生态农业学报》
Abstract： Nitrogen (N) mineralization is an important process of nitrogen cycling in terrestrial ecosystems and significantly influences the availability of soil N. In this paper, we studied the change of soil mineral N and the mineralization rates of N in sloping soils of the northern Loess Plateau respecting to the vegetation types, sampling locations (under canopy vs. outer canopy) and slope positions (upper, middle and lower positions) during the growing season. The objectives were to understand dynamics of N mineralization during growing season and their influencing factors. Sloping lands with Chinese Pine (Pinus tabulaeformis) and Korshinsk Peashrub (Caragana korshinskii), respectively, were selected in the Liudaogou catchment, and an in situ mineralization methods was used to measure the mineralization of soil N from April to October. The measurement were conducted in upper, middle and lower positions of the slope, under and outer of the canopy at the 0-10 and 10-20 cm soil depths. Soil mineral N in the growing season was dominated by ammonium, which accounted for 61% and 70% of total mineral N at the 0-10 and 10-20 cm soil depths, respectively. Meanwhile, the proportion of ammonium to total mineral N increased with the development of growing season. Soil ammonium in the upper and middle slope positions was significantly higher than that in the lower slope position for Chinese pine slopes, but was not affected by slope positions in for Korshinsk Peashrub slopes. Furthermore, soil ammonium was not affected by sampling locations in both Chinese Pine and Korshinsk Peashrub slopes. Soil nitrate and total mineral N were affected by vegetation type and sampling location, rather than by slope positions. Soil nitrate under canopy was similar to that from outer canopy in Chinese Pine slope, but was greater than that from outer canopy in Korshinsk Peashrub. The mineralization of soil N during growing season was mainly resulted from the nitrification at the 0-10 cm soil depth, but caused by both nitrification and ammonification at the 10-20 cm soil depth. Ammonification rate was significantly high at the early growing season, but low at the middle growing season. Moreover, ammonification rate was affected by slope position, vegetation type and sampling location. Nitrification and net N mineralization rate in soils under canopy were similar to soils of outer canopy in Chinese Pine slopes, but were greater than that in soils of outer canopy in Korshinsk Peashrub slopes. Additionally, when comparing with other slope positions, nitrification and net mineralization rate of N were the highest in lower slopes in soils under canopy, but the lowest in lower slopes in both Chinese Pine and Korshinsk Peashrub slopes. The results from this study suggested that Korshinsk Peashrub enhanced nitrification and mineralization of N in soils under canopy, while the effects of Chinese Pine on soil mineral N and mineralization were not affected by sampling location.
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