干旱沙区固沙灌木衰退的年龄效应研究

The decline of the initially planted sand-binding shrubs in arid desert regions has affected the stability and ecological effect of sand-binding vegetation. The degradation of artificial stands is closely related to the viability of the individual trees. The study of age-related decline in photosynthesis and growth and even death of woody plants has become a focus recently. The aging of woody plants would be accelerated by the environmental stress such as drought. According to the present studies, the reduced soil water availability is the main reason for the degradation of revegetated sand-binding shrubs. In addition to water limitation, does specific biological trait of the plant itself, such as aging, has the effect on the degradation of revegetated sand-binding plants, and what is the corresponding mechanism? In this proposal, we select Caragana korshinskii, widely-used sand-binding shrubs in the Shapotou area which is located in the southeastern fringe of the Tengger desert, to examine the age effect of the shrubs by combined methods of in situ field measurements and laboratory testing. The specific objectives of the present study are to (1) compare the differences among the growth, water relations, photosynthesis biochemical features and leaf morphological structures of the different-aged aritificial C. korshinskii; (2) analyze the relationships between eco-physiological characters and shrub age; (3) reveal physiological and ecological mechanisms on age effect of plants in degradation of artificial stands in arid desert regions. At last, we aim to provide a scientific basis for ecological management artificial stands in arid desert regions.

干旱沙区早期建植的人工灌木林的衰退，直接影响到固沙植被的稳定性和生态效应的发挥。人工林林分的退化与林木个体的生存能力紧密相关。由林龄增加引起木本植物光合下降、生长衰退乃至死亡的研究已成为近些年的热点，而且环境胁迫如水分的限制等会加速木本植物老龄化的进程。现有研究认为导致固沙人工林衰退的主要因素是土壤有效水分的减少。那么，除了水分限制外，林木本身的生物学特性比如植物年龄是否起作用以及如何起作用？对该问题还没有明确答案。本项目拟以腾格里沙漠东南缘沙坡头地区的主要固沙灌木柠条为研究对象，通过控制土壤水分以排除水分的限制作用，采用野外原位观测和室内分析相结合的方法，比较不同林龄人工柠条的生长动态、水分生理、光合性能、生化指标及叶形态的差异，分析其生理生态特征等的变化与柠条年龄的关系，揭示林龄增加在干旱沙区人工柠条林退化中的作用及生理生态学机理，为干旱沙区人工灌木林的生态管理提供科学依据。

干旱沙区早期建植的人工灌木林的衰退，直接影响到固沙植被的稳定性和生态效应的发挥。人工林林分的退化与林木个体的生存能力紧密相关。由林龄增加引起木本植物光合下降、生长衰退乃至死亡的研究已成为近些年的热点，而且环境胁迫如水分的限制等会加速木本植物老龄化的进程。现有研究认为导致固沙人工林衰退的主要因素是土壤有效水分的减少。排除水分限制的因素，林木本身的生物学特性比如植物年龄是否起作用以及如何起作用?本研究选取不同年龄的人工栽植的固沙灌木柠条、油蒿、花棒，通过监测其生长动态，并结合植物水分生理、水力特征、光合性能及生理生化特征研究，探讨了植物年龄是否是引起人工固沙灌木衰退的因素之一。结果表明，植物年龄是导致固沙灌木柠条衰退的因素之一，植物导水率的降低是引起老龄柠条光合能力下降的主要因素。研究结果表明，随植物年龄增加，植物水力结构的变化引起水力限制增加，如木质部栓塞的增加导致植物水分运输功能的丧失，是干旱区植物年龄增加导致固沙灌木衰退的主要驱动因素。同时，研究结果并不支持干旱导致植物死亡的“碳饥饿”假说。本研究初步阐明了植物年龄在人工固沙灌木衰退中的作用及其生理生态学机制，为维持干旱沙区人工植被的稳定性和固沙灌木林的生态建设与管理提供了科学依据。