植被恢复过程中芒萁覆盖对侵蚀红壤氮组分的影响

Effects of Dicranopteris dichotoma coverage on nitrogen components during the vegetation restoration process in eroded red soil

氮素是限制陆地生态系统生产力的重要因子。采用时空代换法,以红壤侵蚀区未治理、恢复12年和30年的马尾松林为研究对象,对比分析了林下芒萁覆盖地与裸地表层土壤之间氮同位素、不同形态氮组分含量以及不同组分氮含量所占比例之间的差异。结果表明:在所有马尾松林中,芒萁覆盖增加了表层土壤的全氮含量,δ^(15)N值则比林下裸地显著降低了33. 8%—83.1%(P<0.05)。随着恢复年限增加,林下芒萁覆盖地表层土壤δ^(15)N值显著下降,而林下裸露地δ^(15)N值没有显著变化(P>0.05)。不同恢复年限马尾松林的芒萁覆盖地表层土壤微生物生物量氮、可溶性有机氮和铵态氮含量显著高于林下裸地(P <0.05),而硝态氮含量则显著低于林下裸地(P<0.05)。随恢复年限增加,表层土壤微生物生物量氮、可溶性有机氮、铵态氮含量均呈增加趋势,而硝态氮含量则呈下降趋势,不同形态氮占全氮比例表现为:微生物生物量氮>铵态氮>可溶性有机氮>硝态氮。相关分析表明土壤δ^(15)N值与硝态氮极显著正相关,与其他氮组分极显著负相关(P<0.01)。由此可见,与林下裸地相比,芒萁覆盖在植被恢复过程中有助于提高表层土壤中全氮、微生物生物量氮、可溶性有机氮和铵态氮含量,降低硝态氮的淋溶损失风险,促进土壤氮保持和积累,从而有利于退化红壤生态系统的恢复。

Nitrogen is an important factor limiting the productivity of terrestrial ecosystems. We used the method of spatiotemporal substitution and Pinus massoniana woodlands with different restoration history lengths as the research subject. In order to understand the effects of Dicranopteris dichotoma on nitrogen fixation during the vegetation restoration process, we measured the stable isotope 15N, the nitrogen content of different components, and the ratios of different components of nitrogen to total nitrogen in the topsoil between D. dichotoma soft （WD） and non-D, dichotoma soil （ND）. The results showed that Dicranopteris dichotoma coverage increased the total nitrogen （TN） content of the topsoil in all Pinus massoniana woodlands. The δ15N values of WD were significantly decreased, from 33.8% to 83.1%, compared with those of ND （P〈0.05）. With the increase of restoration time, the δ15N value of WD significantly decreased, while the δ15N value of ND did not significantly change （P〉0.05）. The average contents of microbial biomass nitrogen （ MBN）, dissolved organic nitrogen （DON）, and ammonium nitrogen （NH4＋-N） of WD were significantly higher than those of the ND under different restoration years （P〈0.05）, but the content of nitrate nitrogen （NO3- -N） had the complete opposite trend （P〈0.05）. With the increase in the duration of restoration, the contents of MBN, DON, and NH4＋ in topsoil increased, while NO3--N content decreased. The ratios of different components of nitrogen to total nitrogen were in the following order： MBN〉NH4-N〉DON〉 NO3--N. Correlation analysis showed that the δ15N values of topsoil had highly significant positive correlations with the content of NO3--N, and highly significant negative correlations with the others （P〈 0.01 ）. Thus, compared with ND, Dicranopteris dichotoma coverage was helpful in improving the contents of TN, MBN, DON, and NH4-N in topsoil and reducing the risk of nitrate leaching loss during the vegetation restoration process, and promoted the retention and accumulation of soil nitrogen, which was beneficial to the restoration of the degraded red soil ecosystem.