荒漠绿洲过渡带不同年限雨养梭梭(Haloxylon ammodendron)对土壤水分变化的响应

Abstract

通过调查分析河西走廊荒漠绿洲过渡带不同种植年限（5、10、20、30和40a）人工梭梭生理生化变化（叶片渗透调节物质、丙二醛和叶绿素含量，根系活力）和个体形态特征（叶片、枝条和茎干生物量、枯枝落叶比、株高、冠幅等）以揭示不同种植年限雨养梭梭对土壤水分变化的响应机制。研究结果表明：随着梭梭种植年限增加，人工梭梭林内深层100-120cm和180-200cm土壤水分变化明显，在5-20a保持在3%-4%，而在种植后期（30-40a）土壤水分下降到1%-2%左右。在5-20a，梭梭主要通过显著提高叶片渗透调节物质可溶性糖和可溶性蛋白含量，维持叶片较低的丙二醛含量和较高的叶绿素含量，保持新叶光合能力；同时，显著提高0-20cm根系的活力，增强对表层土壤水分的吸收能力；但在30-40a，梭梭叶片渗透调节物质明显减少，梭梭叶片丙二醛含量增加，叶绿素含量下降，同时叶绿素a，b比例失调，渗透调节作用失效，梭梭叶片老化，老叶比例明显增加，光合作用能力下降，枝条和茎干退化严重，个体生物量进一步减少，在40a梭梭叶片、枝条和茎干生物量下降到最低值。研究表明在年降水100mm左右的荒漠绿洲过渡带，在种植梭梭5-20a土壤水分为3%-4%，梭梭可以通过生理调节适应土壤干燥，但是从30a土壤水分下降到1%-2%时，梭梭主要通过枯枝落叶降低个体蒸腾耗水量，在40a梭梭进入休眠（假死）状态，这暗示土壤水分下降到1%-2%，可能是梭梭的临界吸收土壤水分。;In a typical desert-oasis ecotone of the Hexi Corridor, we examined the eco-physiological and individual morphological responses of artificial rain-fed Haloxylon ammodendron in different plantation ages (5, 10, 20, 30, and 40a) under different soil water stresses imposed by high evapotranspiration and limited precipitation. The results showed that the soil moisture in 100-120 cm and 180-200 cm decreased sharply with the increase of Haloxylon ammodendron plantation age, especially after 30-40 years, the soil moisture decreased from 3%-4% to 1%-2%. In the early stages of 5-20a, Haloxylon ammodendron could respond to the fluctuations of soil moisture by increasing the osmotic adjustment substances (i.e. soluble sugar and soluble protein) and chlorophyll content and decreasing the Malondiadehyde (MDA) content of leaves to maintain the photosynthetic capacity of young leaves. Meanwhile, the vitality of feeder roots in the 0-20 cm increased significantly to absorb soil water at shallow depths. However, from 30 to 40 years, the osmotic adjustment substance and chlorophyll content in Haloxylon ammodendron leaves significantly decreased with the increase of MDA content, indicating that the function of eco-physiological regulation failed. The morphological adjustments of Haloxylon ammodendron occurred when the soil moisture decreased to 1%-2% after 30-40 years through reducing the biomass of leaf, branches and stems to lower the values of transpiration water consumption amount. These results indicated that in the arid desert-oasis ecotone with annual precipitation about 100 mm, Haloxylon ammodendron could alleviate the stress of soil moisture through physiological responses when the soil moisture kept at 3%-4% at the early ages of 5-20 years; however, after 30-40 years when the soil moisture decreased to 1%-2%, Haloxylon ammodendron could lose the old leaves, branches and stem to keep a dormant state (fake death).