恢复年限、林下植被及季节对马尾松林土壤氮转化的影响

Effects of restoration duration,understory vegetation and seasons on soil nitrogen transformation in Pinus massoniana forests

侵蚀红壤区植被恢复能有效防治土壤侵蚀,改善生态环境。提高侵蚀退化地土壤氮矿化潜力、增加氮有效性是改善贫瘠土壤植被生长发育的关键途径,对恢复侵蚀地生态系统具有重要意义。采用顶盖埋管培养法研究了不同恢复年限(Y0、Y16、Y34)不同芒萁处理的马尾松林土壤净氮矿化量和净氮矿化速率的季节变化特征,分析了植被恢复年限、林下植被覆盖及季节变化对土壤氮矿化的交互影响。结果表明,植被恢复能使侵蚀退化地土壤养分条件得到改善。不同恢复年限马尾松林净氮矿化最高值出现在夏秋季,而在春季为负值。植被恢复能使土壤净氮矿化量显著增加,且净氮矿化过程以氨化作用为主。净氨化速率与净矿化速率具有相似的季节变化,硝化速率随着恢复年限增加季节变化减小。林下裸露地净氮矿化量及速率低于芒萁覆盖地,且去除芒萁可以降低净氮矿化量及速率。方差分析表明,恢复年限、季节变化及其交互作用能显著影响土壤净氮矿化量及矿化速率(P<0.001),而芒萁处理未能达到显著水平(P>0.05)。马尾松林土壤氮转化过程季节变化明显,林分管理应按季节变化进行,林下芒萁覆盖对侵蚀退化地马尾松林土壤氮恢复具有重要作用。

Vegetation restoration can effectively prevent soil erosion and improve ecological environment in eroded red soil regions.Enhancement of soil nitrogen(N)mineralization capacity and N availability is a key pathway to improve the growth and development of vegetation in barren soil,which is of great significance to ecosystem restoration of eroded land.The amount and rate of soil net N mineralization in Pinus massoniana forests under different recovery years(Y0,Y16,and Y34)and different treatments of understory vegetation(Dicranopteris dichotoma)were examined by in situ closed-top core incubation method.The interactive effects of vegetation restoration years,understory vegetation cover,and seasonal changes on soil N mineralization were analyzed.The results showed that vegetation restoration improved soil nutrients in the erosion-degraded land.The highest value of net N mineralization appeared in summer and autumn,but negative value was observed in spring.Vegetation restoration significantly increased the amount of soil net N mineralization,with ammonification playing a dominant role in the process of net N mineralization.The net ammonification rate and net mineralization rate showed similar seasonal pattern.The nitrification rate decreased with increasing recovery years.The amount and rate of net N mineralization in the forest gap without vegetation cover were lower than that in the forest covered with D.dichotoma.The removal of D.dichotoma reduced the amount and rate of net N mineralization.Results of analysis of variance showed that recovery years,seasons,and their interaction significantly affected the amount and rate of soil net N mineralization(P<0.001),but the manipulation of D.dichotoma had no effects(P>0.05).Soil N transformation in P.massoniana forest changed seasonally,and thus forest management should be carried out in accordance with seasonal change.D.dichotoma coverage under the forest plays an important role in the soil N recovery of P.massoniana forest.