Net N mineralization and nitrification were determined using the closed_top PVC tube in situ incubation method in a subalpine meadow (Saussurea iodostegia Hance + Carex capillaris L.)→shagspine peashrub (Caragana jub...Net N mineralization and nitrification were determined using the closed_top PVC tube in situ incubation method in a subalpine meadow (Saussurea iodostegia Hance + Carex capillaris L.)→shagspine peashrub (Caragana jubata (Pall.) Poir) shrubland→ribbed birch (Betula costata Trautv.) successional sere. The ability of the three communities to supply available N was comparatively studied. The results showed that there were apparent seasonal changes in the inorganic N pools (including NH + 4_N and NO - 3_N) and net N mineralization and nitrification rates in the three sites. There were generally no significant differences in the inorganic N pools among sampling events. But the NH + 4_N concentration in both birch (P<0.01) and meadow (P<0.01) sites was significantly higher than that in peashrub site in June 1996, and the NO - 3_N concentration in peashrub site was significantly higher than that of meadow site (P<0.05) in August 1996. The annual net N mineralization and nitrification rates in peashrub site (16.01 kg·hm -2 ) were higher than in birch (12.05 kg·hm -2 ) and meadow sites (1.64 kg·hm -2 ). The annual net nitrification rate in peashrub site (11.37 kg·hm -2 ) was higher than in meadow site (10.90 kg·hm -2 ) and much lower than in birch site (14.36 kg·hm -2 ). We conclude that the ability of peashrub shrubland soil to supply available N for plant uptake and the ability to prevent available N from denitrification and leaching were higher than that of the other two sites. The leguminous peashrub might play a potential role in supplying more N, which in turn facilitate the invasion of birch saplings during the successional processes.展开更多
文摘Net N mineralization and nitrification were determined using the closed_top PVC tube in situ incubation method in a subalpine meadow (Saussurea iodostegia Hance + Carex capillaris L.)→shagspine peashrub (Caragana jubata (Pall.) Poir) shrubland→ribbed birch (Betula costata Trautv.) successional sere. The ability of the three communities to supply available N was comparatively studied. The results showed that there were apparent seasonal changes in the inorganic N pools (including NH + 4_N and NO - 3_N) and net N mineralization and nitrification rates in the three sites. There were generally no significant differences in the inorganic N pools among sampling events. But the NH + 4_N concentration in both birch (P<0.01) and meadow (P<0.01) sites was significantly higher than that in peashrub site in June 1996, and the NO - 3_N concentration in peashrub site was significantly higher than that of meadow site (P<0.05) in August 1996. The annual net N mineralization and nitrification rates in peashrub site (16.01 kg·hm -2 ) were higher than in birch (12.05 kg·hm -2 ) and meadow sites (1.64 kg·hm -2 ). The annual net nitrification rate in peashrub site (11.37 kg·hm -2 ) was higher than in meadow site (10.90 kg·hm -2 ) and much lower than in birch site (14.36 kg·hm -2 ). We conclude that the ability of peashrub shrubland soil to supply available N for plant uptake and the ability to prevent available N from denitrification and leaching were higher than that of the other two sites. The leguminous peashrub might play a potential role in supplying more N, which in turn facilitate the invasion of birch saplings during the successional processes.
