水分再分配对土壤-植物系统养分循环的生态意义

Ecological implications of hydraulic redistribution in nutrient cycling of soil-plant system

水分再分配(hydraulic redistribution,HR)作为一个普遍存在的生物物理过程,在缓解植物干旱胁迫、调节植物种间关系和群落组成、影响生态系统水碳平衡等方面具有重要的生态意义。近年来,同位素标记示踪技术的应用促进了HR的深入研究,该文综述了HR对土壤-植被系统养分循环的影响。HR能改善干燥土层的水分状况,防止根系栓塞,促进细根存活与生长,提高微生物活性,从而促进植物对表层土壤养分(尤其是氮)的吸收;HR还通过水分下传作用促进植物对深层土壤中磷和金属离子的吸收。HR促进土壤养分库的上下交换与流动,调节植物与土壤的氮磷比,因此其影响可能具有全球意义。在全球变化(如氮沉降)背景下,有必要深入探索HR在生物地球化学循环过程中的影响和作用,并将其纳入生态系统模型中。

Hydraulic redistribution （HR）, one of the common bio-physical processes, plays key roles in mediating plant drought stress, regulating plant interspecific relations and community composition, as well as in influencing water and carbon balance of ecosystems. Great improvements have been achieved in HR research with fast development of isotopic labelling and tracing technologies. This paper summarizes the effects of HR on nutrient cycling of soil-plant system, based on studies over the past decade. HR increases soil water content in dry soil layers, thus helping to prevent embolism in roots, increasing the survival rate and the growth rate of fine roots and improving microbial activities. Such effects improve plant nutrient uptake, i.e., hydraulic lift promotes nitrogen uptake from upper soil layers and hydraulic descent promotes phosphorus uptake from deep soil layers. HR may facilitate nutrient exchange between upper and lower soil nutrient pools, improve nutrient flows and regulate the N：P ratio in both plants and soil. These effects may ultimately affect global ecosystems. Under the global change scenarios （e.g. nitrogen deposition）, it is necessary to further explore the effects of HR on biogeochemical cycles. HR should be taken into account when using ecosystem models for future predictions.