ADVANCES IN ECOLOGICAL STUDIES ON LEAF LIFESPAN AND ASSOCIATED LEAF TRAITS

Abstract

It is well known that plants with long leaf lifespans are found to grow mostly in habitats where nutrient availability is low and/or water is limited, while plants with short leaf lifespans usually occur on sites with relatively h igh nutrient availability. Considerable research conducted worldwide indicates t hat leaf mass-based nitrogen concentrations (N mass ) are positively rel ated to ma ximum photosynthetic rates, and specific leaf area (leaf area per unit dry weigh t) shows a negative relationship with leaf construction cost, and both decrease with increased leaf lifespan. These relationships among leaf traits generally ex ist across wide ranges of plant populations, communities and biomes, apparently reflecting convergent adaptation of plants to the given climate and/or other env ironmental constraints. Therefore, knowledge about leaf traits is important t o further understand the structure and function of plant ecosystems. With increasing altitude, leaf lifespan generally increases. Associated leaf tra its also show general altitudinal trends: leaf area-based nitrogen concentration s and maximum photosynthetic rates both increase, whereas specific leaf area dec reases with increasing elevation. Plants with long leaf lifespans are thought to be adapted to environmental stresses, such as low temperatures, short growing s e ason length or low light and nutrient availability, while those with short leaf lifespans tend to be associated with fast rates of relative growth and carbon fi xation in response to seasonal stresses of drought and/or cold winters. Under gi ven environmental constraints, the cost-benefit hypothesis explains that variati ons in leaf lifespan are controlled by the trade-offs between leaf carbon costs and benefits for maximizing carbon gain of plants. Cost-benefit simulations nice ly predict a global bimodal distribution of evergreen forests. Accordingly, leaf lifespan and its related leaf traits appear to provide a conceptual link betwee n processes at short-term leaf scales and long-term whole plant and stand-level scales. Knowledge about patterns of leaf lifespan and associated leaf traits acr oss biomes would help us to develop a processing link between biogeography model s and biogeochemistry models and to further understand mechanisms of vegetation dynamics in response to global change. However, there is limited knowledge on ho w leaf characteristics might be used to deduct ecosystem function information and how this scaling task could be accomplished. The traditional focus of plant ecophysiology, understanding how plants cope with often-stressful habitats, is organism centered. It is still difficult to quantitatively describe the relati onships among community characteristics, climatic factors and leaf characteristi cs due to a lack of field data at the ecosystem level. In China, there has been very little work on the ecology of leaf lifespan and its related traits, so it's a challenge and fruitful area for the future research.