树木根系衰老研究的意义与现状

Significance of senescence study on tree roots and its advances

树木根系是树木重要的组成部分 ,具有养分和水分的吸收、传输和储存、树体的固定与支撑等重要的生理功能 .在树木根系形成以后 ,常常遭遇到养分和水分胁迫 ,因此 ,其养分和水分的吸收功能尤其重要 .在森林土壤中 ,养分和水分具有很大的时间和空间异质性 .随着养分和水分在时间和空间上的变化 ,树木及时地主动调整其碳在根系中的分配 ,从而导致部分根系衰老或死亡 .在林学上 ,树木根系衰老与养分和水分吸收关系密切 ,因而与树木生产力有直接的关系 .在生态系统乃至全球尺度上 ,树木根系衰老影响碳循环和养分循环 ,因为根系对碳的消耗占树木通过光合作用所固定的碳的比例相当大 ,且含有丰富的养分 .树木根系衰老受许多环境因子的影响 ,生物因子有真菌、细菌、病毒、土壤小型动物等 ,非生物因子有水分、温度、土壤养分、重金属等 .这些因子对树木根系衰老的影响机制并不相同 .尽管在树木根系衰老研究领域取得了长足的进步 ,提出了许多不同的假设 ,但仍有许多问题尚未解决 ,这些假设也需要更多的实验来验证 .运用细胞学、生物化学、土壤科学、遗传学等多学科的交叉研究可进一步揭示根系衰老的本质 .

Root system is one of the important components of trees,and has some important physiological functions such as nutrient and water absorption,transport and storage,anchoring,and supporting.After tree root systems formed,roots often suffer from nutrient- and water-deficient stress,and thus,their absorption of nutrients and water appears more important.Soil nutrient and water have a great spatiotemporal heterogeneity.As the heterogeneity occurs,trees regulate carbon partitioning to roots,resulting in the senescence or death of some roots of the whole root system.In forestry,the senescence of tree roots is closely related to tree productivity,because there is a close relationship between the senescence of tree roots and the absorption of soil nutrient and water.At ecosystem and global scale,the senescence of tree roots influences the cycling of carbon and nutrients,because roots exhaust a great deal of carbon fixed by source leaves through photosynthesis,and there are great amounts of nutrients in tree roots.The senescence of tree roots is influenced by many environmental factors,biotic (e.g.,fungi,bacteria,viruses,small edaphic animals) and abiotic (e.g.,water,temperature,soil nutrients,heavy metals).These factors affect the senescence of tree roots by different mechanisms.Although we have much knowledge on the senescence of tree roots and some hypotheses have been proposed,some problems still remain to be resolved,and further experiments are needed to test these hypotheses.Interdisciplinary studies integrating cytology,biochemistry,soil science,and genetics are the prerequisite for rapid advances in understanding the essence of tree root senescence.