近100年植被破坏加速侵蚀下土壤养分和 酶活性动态变化研究

选取不同开垦年限的阳坡梁坡农地为研究对象，研究子午岭地区近100年植被破坏加速侵蚀下土壤养分和酶活性动态变化。结果表明，林地被开垦近100年来，阳坡梁坡农地0―20和20―40 cm土层中土壤的有机碳、全氮含量，碱性磷酸酶和蔗糖酶活性皆随开垦年限的延长呈明显的下降趋势。与对照林地相比，不同开垦年限的农地土壤剖面0―20 cm土层的土壤有机碳、全氮含量，碱性磷酸酶和蔗糖酶活性分别下降了26.6 %～84 .4%、17.6%～76.9 %，15.7%～73.8%和37.6%～68.6 %；20―40 cm土层分别下降了30.7 %～81.0%、8.3 %～71.9%，17.3 %～96.9%和51.1%～92.6%。土壤有机碳、全氮含量，碱性磷酸酶和蔗糖酶活性在开垦初期（4 a）年均下降速率最大；而后，随开垦年限延长年均下降速率减少。土壤有机碳和全氮含量在0―20和20―40 cm土层之间差异随着开垦年限的延长呈减少趋势。土壤脲酶活性随开垦年限的延长呈先上升后下降的趋势，开垦9 a农地的土壤脲酶活性最高。受施用磷肥的影响，土壤速效磷含量随开垦年限延长，在0―20 cm土层呈波动变化，在20―40 cm土层呈微弱下降趋势。

Dynamic changes of soil nutrient and enzyme activities under accelerated soil erosion conditions caused by deforestation during the past 100 years

Taking croplands located at sunny hillslopes with different years of deforestation as a case study, dynamic changes of soil nutrient and soil enzyme activities following 100 years of deforestation were analyzed. Results showed that after 100 years of deforestation, soil organic C, total N, alkaline phosphates and invertase activities obviously decreased in both 0-20 cm and 20-40 cm layers of soil profile as deforested years increased. Compared with corresponding forestlands, soil organic C, total N, alkaline phosphates and invertase activities in 0-20 cm layer of soil profile reduced by 26.6%-84.4%,17.6%-76.9%, 15.7%～73.8% and 37.6%-68.6%, respectively; soil organic C, total N, alkaline phosphates and invertase activities in 20–40 cm layer of soil profile reduced by 30.7%-81.0%, 8.3%-71.9%, 17.3%-96.9% and 51.1%-92.6%, respectively. The reduction rates of soil organic C, total N, alkaline phosphates and invertase activities in the earlier years of deforestation were greater than those in the late years of deforestation. Meanwhile, the differences of soil organic C and total N between 0-20 cm and 20-40 cm of soil profile became less and less as deforested year increased. Soil urease activities increased in the earlier years of deforestation, then decreased in the later years of deforestation as deforested year increased. Soil urease activities were highest in the 9th year of deforestation. Due to P fertilizer application rates in top soil, change trend of soil available P in 0-20 cm layer of soil profile was fluctuant; but soil available P in 20-40 cm layer of soil profile decreased slightly with deforested years.