川南天然常绿阔叶林人工更新后枯落物对土壤供氮潜力的影响

该文通过实验室土壤培养试验,研究了天然常绿阔叶林及其人工更新成檫木林、柳杉林后0~20cm土层土壤在25℃、自然含水量和添加不同枯落物条件下,培养15、30、45、60、75、90d土壤供氮能力的差异.结果表明:在不添加枯落物时,土壤铵态氮、硝态氮、总无机氮和微生物量氮含量以及硝化速率、氮净矿化速率,均为天然常绿阔叶林>檫木林>柳杉林;各林分土壤添加其枯落物后,土壤铵态氮、硝态氮和总无机氮含量以及氨化速率、硝化速率、氮净矿化速率均高于不添加枯落物土壤,而且在檫木林、柳杉林土壤中添加天然常绿阔叶林枯落物比添加其自身林地枯落物高;微生物量氮含量与铵态氮、硝态氮和总无机氮含量以及硝化速率、氮净矿化速率均存在显著相关性.这说明了天然常绿阔叶林人工更新后土壤供氮能力和微生物生物量下降,天然常绿阔叶林枯落物与檫木林和柳杉林枯落物相比,对土壤供氮能力和微生物生物量的影响作用更大,微生物量氮含量的变化能较好地反映土壤供氮能力的变化.因此,枯落物数量和质量对林地土壤供氮能力和微生物生物量具有重要作用,研究结果为保护天然常绿阔叶林、选择适宜的更新树种和天然常绿阔叶林人工更新后林地土壤的科学管理提供依据,也为退耕还林中树种的选择提供参考.

Impacts of litter on soil nitrogen supply potential of the natural evergreen broadleaved forests after artificial regeneration in southern Sichuan Province

To determine soil nitrogen supply potential in the 0-20 cm soil layer in natural evergreen broadleaved forests and two plantations, Sassafras tzumu and Cryptomeria fortunei plantations formed by natural evergreen broadleaved forests after artificial regeneration, soils were collected and incubated in the laboratory at 25℃ with natural water content and different litter covering for 15, 30, 45, 60, 75 and 90 days. The results indicated that the content of soil NH~+_4-N, NO~-_3-N, total inorganic nitrogen and microbial biomass nitrogen, and the rates of nitrification and net nitrogen mineralization were natural evergreen broadleaved forests>S. tzumu plantation>C. fortunei plantation when without litter addition in soil. When litter was added in soil,the content of soil NH~+_4-N, NO~-_3-N, total inorganic nitrogen and microbial biomass nitrogen, and the rates of ammonification, nitrification and net nitrogen mineralization were higher than those without litter addition in soil, and the natural evergreen broadleaved forest litter addition in soil has greater effect than S. tzumu plantation and C. fortunei plantation litter addition in soil. There existed close relationship between the content of microbial biomass nitrogen and that of soil NH~+_4-N, NO~-_3-N and total inorganic nitrogen, as well as the rates of nitrification and net nitrogen mineralization. The results suggest that the nitrogen supply potential and microbial biomass will decline with conversion from natural evergreen broadleaved forest to S. tzumu plantation and C. fortunei plantation, and natural evergreen broadleaved forest litter has greater effects on soil nitrogen supply potential and microbial biomass than those of S. tzumu plantation and C. fortunei plantation litter, and microbial biomass nitrogen can be used to evaluate the soil nitrogen supply potential. In addition, the quantity and quality of forest litter have important impacts on soil nitrogen supply potential and microbial biomass, so the study results will lay a solid foundation for protecting natural evergreen broadleaved forests, choosing appropriate trees for artificial regeneration, and soil management after being artificially regenerated, also providing the advices for trees choosing in the process of converting farmland to forestland.