渭北旱塬不同龄苹果细根空间分布特征

以渭北旱塬3龄、10龄、15龄和20龄苹果树为对象,采用根钻法,沿3等分园半径方向(径向)、距树干1.0、1.5m和2 0m处设置采样点,研究了不同树龄的细根空间分布特征.结果表明,3龄苹果细根主要分布于径向1.5m以内和垂向0.5m以上,15龄和20龄苹果细根分布超出径向2.0m和垂向1.4m,10龄细根分布范围大于3龄,与15龄和20龄接近.在根系主要分布区内3龄和10龄细根分布稀疏,15龄和20龄细根分布密集;细根空间分布演化过程可分为3个阶段,即3～10龄为细根范围扩张阶段,10～15龄为细根密度扩张阶段,15～20龄为细根密度退化阶段;苹果细根空间分布无明显方向性差异;10龄、15龄和20龄苹果表层(0～20cm)平均根长密度低于下层(20～40cm),高峰值一般出现在40～80cm,此深度以下根长密度随深度递减,3龄苹果表层平均根长密度高于下层;在径向2.0m内随径向距离增大,3龄、15龄和20龄平均根长密度逐渐降低,而10龄根长密度逐渐增加.根长密度在径向变化上存在局部变异现象.

Distribution of the fine roots of different aged apple trees in Weibei rainfed tableland of the Loess Plateau

Root distribution and its resource demands of different aged apple trees are not same. Numerous studies focused on the spatial distribution of roots of specific aged trees and however, few studies were done for different aged apple trees. The spatial distribution of the fine roots of different aged apple trees in the Weibei rainfed tableland was investigated. The fine roots of the 3-aged apple tree were distributed mainly within a range of 1.5 m, horizontally, and within a thickness of 0.5 m, vertically, while those of the 20 and 15-aged apple trees exceeded 2 m in the radial direction and 1.4 m in the vertical direction. The dominated distribution range of the 10-aged tree was greater than that of the 3-aged tree, and it was close to those of the 15 and 20-aged trees. The fine roots of the 3 and 10 aged trees were sparsely distributed, while those of the 20 and 15-aged trees were densely distributed. Evolution of root length density (RLD) of the fine roots can be divided into three stages: range expanding stage (3 and 10-aged), density expanding stage (10 and 15-aged), and density degradation stage (15 and 20-aged). Directional difference in the RLD of fine roots was not distinct. The RLDs in 0-20 cm surface soil for 10, 15, and 20-aged trees were less than those in 20-40 cm soil layer. Peak values for the trees were observed in 40-80 cm soil layer below which the RLDs decreased gradually. The RLD of the 3-aged tree in 0-20 cm surface soil was higher than those in deeper layers. Within 2 m range in radial direction, the RLDs of the 3, 15, and 20-aged trees increased with distance, while that of the 10-aged tree decreased. Some variations of RLD in radial direction were found for all aged trees.