دانلود رایگان مقاله اهمیت نمایندگی دقیق طول عمر برگ برای شبیه سازی اکوسیستم

Abstract

Leaf longevity and leaf turnover rate are important plant traits relating to plant growth, leaf photosynthesis and respiration, plant canopy dynamic and many other factors, but dynamic global vegetation models only set inaccurate values for these factors. In this study, we firstly investigated the leaf longevities at major vegetation types based on 418 field measurements from around the world. By replacing the default leaf longevities in the Lund-Potsdam-Jena model (LPJ) with the revised values, we examined the changes in simulated carbon cycle caused by the revised parameters. The results suggested that the compiled observations of leaf longevity were significantly different from the default values in LPJ. Both the vegetation production and respiration of the simulated natural ecosystems showed significant changes based on the revised leaf longevity compared with the predictions developed using default model parameters. Of all of the variables, the aboveground and belowground litter pools showed the largest changes (about 10% globally). Globally, the default parameters induced a significant overestimation of terrestrial carbon sink by 3%, compared with a simulation using the revised parameters. Furthermore, the uncertainties in leaf longevity caused various uncertainties (5–30%) in the simulated carbon fluxes and carbon pools. The offset of biases in intermediate variables might result in rational final model outputs. Overall, more accurate leaf longevities are critical for simulating the vegetation distribution and ecosystem carbon cycle.

Discussion

Leaf longevity and turnover rate have been used by LPJ to calculate several key processes of ecosystem carbon cycle. Many previous studies have reported significant correlations between leaf longevity and many other leaf structural and physiological properties such as leaf photosynthetic assimilation rate, leaf nitrogen and specific leaf area (SLA) (Wright, Thornton, Running, & Nemani, 2000; Wright et al., 2004; Reich, Wright, & Lusk, 2007). LPJ employed an empirical relationship derived by Reich et al. (1997) relating SLA to leaf longevity (Eq. 1). Because SLA was used to calculate the leaf area index (LAI) and foliage projective cover (FPC), leaf longevity would further determine the vegetation dynamics, plant photosynthesis and respiration (Koike, 1987; Matsuki and Koike 2006). The leaf turnover rate in LPJ was used to calculate the annual litter input, as well as to determine the size of the canopy biomass, the substrate of heterotrophic respiration (Hikosaka, 2005). Overall, leaf longevity and turnoverrate are involved inmany key variables and processes in LPJ.