天然胡杨林龄对营养元素空间分配格局的影响

Effect of the age of natural Populus euphratica forest on the spatial distribution pattern of nutrient elements

为了解胡杨林生长过程对主要营养元素在土壤全库、有效库及植被库之间运移规律的影响,以新疆轮台县轮南镇5个不同林龄(幼龄林、中龄林、近熟林、成熟林和过熟林)典型天然胡杨林为研究对象,采用时空替代方法,分析林下土壤和植被中C、N、P、K的空间分配特征。结果表明:(1)总体而言,土壤营养元素全库中全钾含量较富积,有机质、全氮、全磷相对缺乏。土壤有机质及全量养分受林龄影响较显著。土壤全氮量随着林龄的增长显著升高,至近熟林时达到最大值,然后下降。幼龄林土壤有机质、全钾含量较低,中龄林和近熟林含量较高。幼龄林、成熟林和过熟林土壤全磷含量相对较高。土壤垂直层中,土壤有机质、全钾含量深层土壤>浅层土壤,而全氮含量随着土壤深度的增加呈现下降趋势。全磷含量受土壤垂直层影响较小。(2)土壤有效养分库中碱解氮、速效磷含量较低,速效钾含量较高。土壤速效养分受林龄影响较大,碱解氮含量随着林龄的发育,呈现先显著升高到近熟林达到最大值,然后下降的趋势。速效钾、速效磷含量均呈现幼龄林和中龄林显著低于其它龄林。不同土壤垂直层显示,碱解氮、速效钾、速效磷含量均呈现浅层>深层土壤。速效钾、速效磷有明显的表层聚集现象。(3)从土壤养分有效性占全量比率分析,氮>钾>磷。氮素在不同龄级中有效率均较高。钾和磷有效率受林龄影响,呈现出成熟林>过熟林>近熟林>中龄林>幼龄林。土壤垂直层中0—10 cm、40—60 cm氮素有效率较高。钾和磷有效率随着土层深度的增加呈现递减的变化趋势,其中0—10 cm钾和磷有效率显著高于其他土层。(4)植被库中主要矿质养分积累量由大到小依次为N>K>P。除叶外,N、K、P积累量在胡杨各器官中均呈现随着林龄的增长而增加,到成熟林达到最大值,在过熟林降低。对树木不同器官,N、P累积量依次为干>根>枝,但K累积量依次为根>干>枝。

In order to understand effect of the growth process of Populus euphratica on the migration of main nutrient elements in soil available and total reservoir and vegetation reservoir,we investigated five typical natural P.euphratica forests with different ages(i.e.,young,mid-age,near-mature,mature,and over-mature forest).The spatial distribution characteristics of C,N,P,K in both soil and vegetation were analyzed,using the time-space substitution method.Results showed that:(1)In general,total K content in the soil nutrient element pool was relatively rich,while organic matter,total N and P contents were relatively poor.Soil organic matter and total nutrients were significantly affected by the forest age.Total soil N content increased significantly with the increasing of the forest age,with the maximum value occurring in near-mature forest.Organic matter and total P content were lower in young forests than in middle-age forests and near-mature forests.Total P content in soil was relatively high in young,mature,and over-mature forests.Organic matter and total K content was larger in deep soil layer than shallow soil.Total N content decreased with the increase of soil depth,while total P content was less affected by the soil layer.(2)The contents of alkali hydrolyzable N and available P were much lower than the content of available K in soil.Soil available nutrients were greatly affected by the age of the forest.With the increase of the age of the forest,the content of alkali hydrolyzable N increased continuously,reaching the maximum value in the near-mature forest,and then decreased.The contents of available K and P were significantly lower in young and middle-age forests than other forests.The content of alkali-hydrolyzable N,available K and P decreased with increasing of soil depth.The content of available K and P were mainly accumulated in the surface soil.(3)For the ratio of soil available nutrients to total amount,we found the pattern of N>K>P.The ratio of soil available N to total amount was relatively high in each class of forest age.The ratios of soil available K and P to total amount were significantly affected by the age of forest,following the rank:mature forest>over-mature forest>near-mature forest>middle-age forest>young forest.Among the different soil layers,ratios of soil available N to total amount in 0-10 cm and 40-60 cm were relatively high.The ratios of soil available K and P to total amount decreased with the increase of soil depth,and were significantly higher in surface(0-10cm)than those in other soil layers.(4)The highest accumulation of N in the vegetation reservoir was found,followed by K and P.Except for leaves,the accumulation of N,K,and P in various organs of P.euphratica plants increased with the increase of forest age,but decreased in the over-mature forest.Among the different organs in plants,the largest N and P accumulated in stem,followed by root and branch;while the largest K accumulated in root,followed by stem and branch.