纸坊沟流域退化土壤碳氮关系对植被恢复的时空响应

Spatio-temporal Response of Soil Carbon and Nitrogen Relation to the Process of Vegetation Restoration in the Gully Region of Loess Plateau

采用植被次生演替空间序列代替时间序列的方法研究黄土丘陵沟壑区纸坊沟流域退化土壤碳、氮关系对植被恢复的时空响应，旨在揭示坡耕地退化土壤植被恢复后土壤中碳、氮运移规律，为人工干预下群落的演替和土壤的生态修复提供理论依据。结果表明：与农地相比，植被恢复显著增加了土壤有机碳（SOC）和总氮（STN）的含量，且增加了其有效性，即活性有机碳（LOC）和碱解氮（SLN）的含量，后者变化幅度大于前者的。恢复12a以上人工林的0～20cm土层相比农地其C／N增加，而20～40cm和40-60cm土层的降低。SOC和LOC含量随恢复年限增加呈非直线上升，而STN和SLN含量随恢复年限增加呈直线上升。在土壤剖面上，0～20cm土层SOC和STN含量的增加主要与恢复年限有关，而20-40cm和40-60cm这2层主要与植被类型有关。在退耕土壤SOC的增加及其活化方面，均呈现出乔木〉灌木〉撂荒的趋势；自然恢复有利于STN的恢复，人工乔木和灌木林更有利于贫瘠退化土壤的SLN即可利用N的恢复。植被恢复显著优化了土壤SOC和STN之间的直线相关性，同一植被类型随恢复年限的增加相关性略有增加。人工干预恢复是短时间内加速土壤碳贮存，恢复土壤营养有效性和降低温室效应的首选。

The spatio-temporal difference of C and N relation were studied among various mode of vegeta- tion restoration in Zhifang gutter of Loess Plateau, China. Results indicated that vegetation restoration not only significantly increased soil organic C （SOC） and soil total N （STN）, but also greatly improved labile organic C （LOC） and alkali-hydrolyzable N （soil labile N SLN） contents. The organic matters （C and N） of 0-20 cm soil profile were changed significantly compared with both 200-40 cm and 40-60 cm soil pro- files, indicating that the shallow profile was more sensitive to land use change. Both STN and SLN in- creased linearly with the restoration time increasing, whereas both SOC and LOC presented a nonlinear ac- cumulation characteristic across time. The increases of both SOC and STN in 0-20 cm soil profile were mainly related with restoration time, whereas these in both 20-40 cm and 40-60 cm soil profile were sig- nificantly related with re-vegetation mode. The SOC increase and activities in different vegetation types were ordered as highwood 〉 shrubbery 〉 abandoned land. However, abandoned land was benefit of STN restoration, and artificial bighwood and shrubbery accelerated SLN restoration in degraded and barren soil. Vegetation restoration significantly increased the correlation between SOC and STN. In a word, the vege- tation restoration of degenerated farmland significantly increased C02 sequestration, restored soil nutrition availability, and improved the relationship of soil C and N. Human-assistant restoration was superior to natural restoration within a short re-vegetation time.