沙地云杉幼苗根表土体中NPK的梯度分布

采用水平根和垂直根两种处理方法对6年生沙地云杉幼苗进行栽培实验，应用分层取样方法对幼苗根表不同距离土体进行取样，并测定不同层次土体中速效N、速效P、速效K的含量。结果表明，在沙地云杉根表不同距离的土体中，速效N、P、K呈现有规律的梯度分布，即在根表近距离土体中营养元素由于根系的吸附作用而含量较高，同时根系生命活动对营养元素的大量消耗又使得营养元素随即出现严重的亏缺区，再向外延伸营养元素含量又逐渐上升而达到土壤本底值，在水平根处理中，由于沙地云杉对N、P、K吸收和利用的强度不同，亏缺区出现的位置不同，速效N和速效K的亏缺区出现在距离根表1cm处；速效P出现在距离根表0．5cm处，在垂直根处理中，速效N、速效P、速效K的梯度变化与水平根处理的相似速效N和速效K亏缺区出现在距离根表大约1cm处，而速效P在根表附近土壤中的含量始终少于根表远处，说明沙地云杉幼苗对速效P的吸收和利用强度大，速效P可能成为沙地云杉生长发育的限制因子。因此，在沙地云杉引种栽培时，应该选择含P丰富的土壤，或者对林地适当施用一些P肥。

Gradient distribution of soil N|P|and K along the distan ce from Picea mongolica seedlings root surface

Six years old seedlings of Picea mongolica were planted in pots with horizontal and vertical root treatments. Soil samples were stratified collected,and their available nitrogen (N),phosphorus (P),and potassium (K) contents were determined.The results showed that the available contents of N,P and K in soils along the distance from Picea mongolica seedlings root surface had a special gradient distribution. Near root surface,there was a depletion zone of soil available N,P,and K,and along the distance from it,the nutrient element contents increased gradually and reached their background values in the bulk soil. In the horizontal root treatment,the depletion zone of soil available N,P,and K existed in different distance from root surface,owing to the absorption and the use intensity of the seedlings to these nutrient elements. The depletion zone of soil available N and K appeared from 1 cm from root surface,and that of available P existed in 0.5 cm from root surface. In the vertical root treatment,the depletion zone of available N and K also appeared from 1 cm from root surface as in the horizontal root treatment,but the available P content near root surface was lower than that far away from root surface. It is proved that the absorption and the utilize intensity of soil available P by Picea mongolica seedlings was intense,which might become a limiting factor to its growth and development. Therefore, Picea mongolica should be planted on soils rich in phosphorus,or P and N fertilizers should be applied to improve the absorption and the use efficiency of available P by Picea mongolica .