【作者】 陈小红；

【导师】 李贤伟；

【作者基本信息】 四川农业大学 ， 森林培育学， 2002， 硕士

【摘要】 本研究以农耕地为对照，对三倍体毛白杨、杉木、杂交竹三种还林地的土壤氮素特征、变化规律、剖面特征和时间变化等时空动态进行了初步研究，结果表明： ①农耕地与还林地间有机质含量差异不明显，土壤氮素各形态均存在显著差异。还林地间土壤铵态氮、硝态氮和速效氮含量差异不明显，但全氮、水解氮含量差异明显，杉木林地含量最高。 ②与还林前相比，三种还林地土壤表层氮素的变化趋势不同。土壤有机质、铵态氮和速效氮含量有所增加；三倍体毛白杨、杂交竹林地全氮量在一定程度上有所提高，但杉木林地下降；硝态氮和水解氮的变化规律与全氮相反。 ③在农耕地和还林地中，土壤氮素含量的剖面分异特征不同。土壤上层有机质、全氮、水解氮含量明显高于下层；铵态氮同样表现为上层远高于下层，但杂交竹林地层间差异不明显；硝态氮的层间变化可分为增长型、降低型和平稳型三种类型；速效氮的剖面特征与铵态氮相似。 ④还林地不同土层氮素的时间变化有所差异。土壤上下层有机质、全氮量的时间变化趋势相同，层间差异量基本维持在恒量水平；春、秋季铵态氮含量上层明显高于下层，夏、冬季随还林措施不同而表现复杂；上下层硝态氮波谷、波峰的出现时间大致相同，但不同还林地的变化规律较复杂；速效氮的变化趋势与铵态氮类似；土壤上下层水解氮的时间变化几乎同步，在图上表现为两条近似的平行线。 ⑤还林地土壤氮素含量具有明显的时间动态特点。有机质含量秋季下降，冬季下降到低谷，随后逐步回升，夏、秋季达到最高水平；全氮的时间动态仅为小幅度的波动，变幅不足5％。铵态氮的变化趋势为：升高—降低—升高，高峰期出现在夏季，低峰期则出现在冬季；硝态氮的时间变化比铵态氮复杂，呈明显的波浪式起伏变化，最高峰出现在雨季；速效氮的时间变化与铵态氮类似，5月出现明显低谷；水解氮表现为小幅度的不规则波动，总的走势为平稳下降，全年没有明显高峰。 ⑥土壤的氮素的时空变化特点是多方面环境因素和植被因素综合作用的结果。降水、土壤理化性质、植被状况和农业活动在一定程度上都影响着土壤氮素含量，其具体影响程度有待进一步研究。更多还原

【Abstract】 The spatial and temporal changes of soil nitrogen in forest land where farmland was returned to Triploid Populus tomentosa, Cunninghamia Lanceolata, and Bambusapervariabilis X Dendrocalamopsisvalidus forest land were analyzed such as the characters of soil N, the rules of changes, the characters of soil profile and the temporal change, the results showed that:(1) The soil N had conspicuous difference between the forest land and farmland, but the soil organic matter content did not. Among the forest land NH4+-N, NOs’-N and available N content had conspicuous difference, but the total N and the hydrolysable N did not whose content in China fir land was the highest.(2) To compare after returning forest with before, the change tendency of soil N was complicate in the forest land. The organic matter, NH4+-N, available N content have conspicuously increased; the soil total N in Populus, Bamboo lands increased, conversely it reduced in China fir land; the variations of NOs’-N and the hydrolysable N were on the contrary to the total N.(3) In farmland and forest land, the profile character of soil N showed differently: the organic matter and total N content in the upper soil was much higher than hi the below; with the soil depth’s increasing the soil NFLj+-N content appeared reducing and its change was not obvious hi Bamboo land; the change of the soil NOa’-N content was complicate that was divided into increasing type, decreasing type, and moderate type; the available N’s variation was the same as NCV-N’s.(4) Temporal changes of each soil layer were different in farmland and forest lands. The organic matter and total N’s variation of the upper and below layer were identical whose range remained constant in each season; the soil NlV-N content in the upper layer was higher than hi the below in Spring and Autumn, but this change was complicated hi Summer and Winter owing to different forest measures; the peaks and valleys of NCV-N hi the upper and below soil layer appeared in the same tune, but the change showed no laws in different forest lands; the variation of the available N was approximate to NHU+-N; the range of each layer’s change of the hydrolysable N was identical that appearedparallel lines in figure.(5) Soil nitrogen’s temporal changes had obvious dynamic characters. The organic matter decreased in Autumn and reached to a valley in Winter, then it raised to the peak in Summer and Autumn; the total N fluctuated which change range is smaller than 5%; the soil NHt+-N rose firstly, reduced in Autumn and Winter, then rose in Spring; additionally, its peak appeared in Summer and valley in Winter; the soil NCV-N’s change was more complicated than NHU+-N and fluctuated with season whose peak appeared in rain season; the available N’s change tendency was similar to NH4+-N, it decreased in May; the hydrolysable N fluctuated in smaller range, and its content decreased steadily and showed no apparent peak in a year.(6) The spatial and temporal changes of soil nitrogen were the effects of environment and vegetation types. Rainfall, soil physical and chemical character, vegetation types and farming activities affected the soil nitrogen content in some degree, and the degree of effect should be researched deeply.更多还原