半干旱沙区引进树种和乡土树种蒸腾耗水过程与机制比较研究

Protective or shelter forests play an important role in coping with natural disasters and ecological problems in ecological fragile areas. However, the artificial protective forests have emerged decline phenomenon, especially for the protective forests in semiarid sandy region. Previous studies have indicated that water imbalance was the major cause inducing the decline of protective forests, but the native tree species did not show obviously decline in the same precipitation condition. Therefore, determination of mechanisms in water use for the introduced and native tree species have become an important scientific issues, which further reveal mechanisms in the protective forests decline. In this study, we select the introduced tree species (Pinus sylvestris var. mongolica and Populus spp.) and native tree species (Pinus tabuliformis and Populus simonii) in the southern edge of Horqin Sandy Land as the objects of this study. Water condition, the most important factor influencing the survival and growth of the protective forests, is considered as the main topic in this project. Based on high pressure flow meter and heat dissipation approaches and so on, dynamic characteristics of hydraulic architecture, sap flow and its correlation with influencing factors and comparision of soil water and groundwater contribution to tree transpiration are studied for the introduced and native tree species with different ages. The specific objectives of this project are to 1) determine the trade-off between hydraulic safety and efficiency, tree transpiriaton patterns and sources of water for transpiraiton in the introduced and native tree speices, 2) to reveal the water use mechnisims for the introduced and native tree speices and their interspecific differences in hydraulics and ecophysiology. The results obtained in this project would have important theoretical and practical significances in tree species selection, stand structure configuration and water management for protective forests in semiarid sandy region.

防护林在应对生态脆弱区自然灾害和生态问题具有十分重要的地位，但人工营建的防护林出现了衰退现象，尤其是半干旱沙区防护林衰退更为严重。前期研究表明，水分失衡是衰退主要原因；但是，相同降水环境下乡土树种并未出现明显衰退。因而，明确引进树种和乡土树种水分利用机制便成为进一步揭示衰退机理的重要科学问题。本项目以科尔沁沙地南缘引进树种樟子松、杂交杨和乡土树种油松、小叶杨为对象，以影响防护林存活、生长的水分因子为主线，通过野外监测和定位试验相结合手段，利用高压流速仪和热扩散等方法，重点研究不同年龄引进树种和乡土树种水力结构动态特征、树干液流特性及其与环境因子关系，比较土壤水和地下水对蒸腾耗水的贡献；基于此，阐明不同树种水分传输有效性和安全性权衡机制、蒸腾耗水规律和蒸腾耗水来源，揭示不同树种水分利用及种间差异的水力学与生理生态学机理。研究结果对造林树种选择、林分结构配置和林地水分管理具有重要理论和现实意义

防护林衰退已经成为制约防护林功能高效稳定与可持续发挥的瓶颈。为揭示引进树种固沙林衰退机制，本项目以科尔沁沙地南缘引进树种樟子松、杂交杨和乡土树种油松、小叶杨为对象，研究不同年龄引进树种和乡土树种水力结构特征、树干液流特性及其与环境因子关系，土壤水和地下水对蒸腾耗水的贡献。主要结果如下：. 1）明确了引进树种与乡土树种水力结构差异：随着树龄增加，小钻杨和小叶杨比导率降低，表明随树龄增加不同树种输水效率降低；小钻杨和樟子松叶比导率分别高于小叶杨和油松，表明引进树种输水效率高于乡土树种。樟子松木材密度显著低于其他树种，表明樟子松具有较低的抗栓塞化能力。. 2）确定了引进树种与乡土树种蒸腾耗水量及其环境影响机制：18和40年生樟子松单株耗水量分别为7.8和15.7 kgd-1，7、14和22年生小钻杨单株耗水量分别17.4、38和34 kgd-1，18和48年生油松单株耗水量分别为5.8和13 kgd-1。将单株耗水量扩展到林分尺度，18和40年生樟子松人工林耗水量分别为0.7和1.9 mmd-1，生长季林分耗水量为128.8和299.4 mm。7、14和22年生小钻杨人工林耗水量分别为2、1.6和2.1 mmd-1，生长季林分耗水量为372、245和314 mm。18和48年生油松人工林耗水量为0.3和0.6 mmd-1，生长季林分耗水量为55.2和91.8 mm。随时间尺度增加，不同树种蒸腾耗水量与环境因子相关程度逐渐降低。随干旱程度增加，樟子松和油松冠层导度对水汽压亏缺敏感性显著降低，但樟子松降低程度高于油松，表明干旱条件下樟子松木质部栓塞化导致水力导度降低程度高于油松。. 3）量化了地下水和土壤水对引进树种和乡土树种蒸腾耗水贡献：18年生樟子松人工林生长季利用土壤水，40年生樟子松人工林生长季10%时间利用地下水，利用地下水比例介于8~70%，地下水利用量占同期蒸腾耗水量43%。7年生小钻杨人工林生长季15%时间利用地下水，比例介于4~93.4%；地下水利用量占同期蒸腾耗水量48.2%。22年生小钻杨人工林生长季13%时间利用地下水，比例介于4~97.2%，地下水利用量占同期蒸腾耗水量60%。不同年龄油松生长季利用土壤水。与乡土树种相比，引进树种更加依赖地下水。. 本项目发表SCI论文11篇，协助培养研究生2名。