不同林龄华北落叶松土壤养分及酶活性变化规律研究

Study on the change of soil nutrients and enzyme activities of larix principis-rupprechtii in different forest ages

研究选择5年、10年、20年林龄的华北落叶松林地为调查对象,确定其各个生育期林地土壤中养分含量及酶活性的变化趋势。结果表明:各生育期林地土壤中有机质和有效磷含量均随着土壤深度的增加而呈现显著下降趋势。而对于相同土层不同林龄间,土壤有效磷含量随着林龄的增加而下降。在40～60cm处,以20年林龄有机质含量在7月时最低,为4.17g·kg^(-1),显著低于其他土层。同时,5年的土壤有效磷含量在7月时达到最大,平均为4.44mg·kg^(-1),高于5月和9月时土壤中有效磷含量,但三者间差异不显著。不同林龄林地土壤铵态氮、硝态氮含量随土层深度而产生的变化趋势基本一致,表现为下降趋势。在落叶松林的新叶生长期内,5年落叶松林地在20～40cm和40～60cm处的铵态氮为13.47 mg·kg^(-1)和9.09 mg·kg^(-1),分别较0～20cm(25.36mg·kg^(-1))下降了46.9%和64.2%。而20年林龄的林地土壤硝态氮为19.24mg·kg^(-1),较10年的25.93mg·kg^(-1)下降了25.8%,且达到显著差异(P<0.05)。土壤过氧化氢酶(CAT)、磷酸酶(ALP)和脲酶活性(Ure)随林龄的增加而下降,其中ALP下降趋势较缓,而CAT和Ure均显著下降。综合分析调查林龄范围内养分和酶活性的变化趋势,发现林地的地力随林龄的增加而衰退。

In this study,three different ages of larix principis-rupprechtii forests in 5a,10aand 20a were selected as the research objects to discover the changes of soil nutrient and soil enzyme activities in different growth stages were analyzed.The results showed that the contents of organic matter and available phosphorus in the soil of different growth stages showed a significant downward trend with the increase of soil depth.For different forest ages in the same soil layer,the soil available phosphorus content decreased with the increase of forest age.The organic matter content of 40~60cm in 20areached the lowest in the vigorous growth period,which was 4.17g·kg-1,which was significantly lower than other soil layers.At the same time,the soil available phosphorus content of 5areached the maximum in July,with an average of 4.44mg·kg-1,which was higher than the available phosphorus content in soil in May and September,but the difference between the three was not significant.The changes of ammonium nitrogen and nitrate nitrogen content in soils with different forest ages were consistent with soil depth,showing a downward trend.In the new leaf stage,the ammonium nitrogen content of the 5a alarch woodland at 20~40cm and 40~60cm was 13.47 mg·kg-1 and 9.09 mg·kg-1,respectively,which was lower than 0~20cm(25.36mg·kg-1)46.9%and 64.2%.The soil nitrate nitrogen content of 20awas 19.24mg·kg-1,which was 25.8%lower than that of 20a,and the difference between the two was significant(P<0.05).At the same time,with the increase of the age of larix principis-rupprechtii,soil catalase,phosphatase and urease decreased,and the decline of phosphatase was slow,while catalase and urease decreased significantly.All in all,it's concluded that the soil fertility of forest land declined with the increase of forest age on the basis of change trend of soil nutrient and soil enzyme activity in the surveyed forest age.