The Effect Of UV-B Radiation On Decomposition Of Leaf Litter Of Main Tree Species In Subtropical Region

Forest litter plays a key role in maintaining soil fertility, nutrient and carbon recycling in forest ecosystems. The forest litter decomposition and nutrient mineralization is the main way of material cycle and energy conversion in terrestrial ecosystems, and an important component of the global carbon budget. Under the background of global environment change, studying the effect of UV-B radiation on litter decomposition is important to elucidate the litter turnover, biogeochemical cycle and forest soil nutrient dynamics. In this study, under elevated UV-B (31.5% of ambient UV-B), reduced UV-B (22.1% of ambient UV-B) and ambient UV-B condition, the decomposition of leaf litter of Cinnamanun camphora and Cyclobalanopsis glauca, including decomposition rate, the concentration and releasing dynamics of C, N, P, K and lignin was investigated with litter-bag method. Main results are as follows:Elevated UV-B radiation significantly accelerates the litter decomposition rate of C. camphora and C. glauca, and reduced UV-B radiation significantly decreases the litter decomposition rate of two species. The leaf litter decomposition rate of C. camphora increases 16.67% under elevated UV-B than under ambient UV-B, consequently the time of half and 95% decomposition shortens 0.34a and 1.48a respectively. The leaf litter decomposition rate of C. camphora decreases 33% under reduced UV-B than under ambient UV-B, consequently the time of half and 95% decomposition long 1.43a and 6.17a respectively. The leaf litter decomposition rate of C. glauca increases 27.78% under elevated UV-B than under ambient UV-B, consequently the time of half and 95% decomposition shortens 0.29a and 1.22a respectively. The leaf litter decomposition rate of C. glauca decreases 57.41% under reduced UV-B than under ambient UV-B, consequently the time of half and 95% decomposition long 1.69a and 7.32a respectively.During the decomposition, elevated UV-B radiation decreases the N concentration in leaf litter of C. camphora, and inhibits the increasing of N concentration in leaf litter of C. glauca, and accelerate the N release of leaf litter of two species.The increased trend of P concentration in leaf litter of C. camphora is investigated under elevated, reduced and ambient UV-B condition, however, P is net immobilization in general. The UV-B radiation change has no obvious effect on concentration and release of P in leaf litter of C. camphora. Elevated UV-B decreases the P concentration and accelerates the P release in leaf litter of C. glauca. However, reduced UV-B increases the P concentration and blocks the P release in leaf litter of C. glauca.Elevated UV-B radiation accelerates the decline of K concentration and the net release of both C. camphora and C. glauca. But reduced UV-B radiation blocks the decline of K concentration and the net release of both C. camphora and C. glauca.The C of C. camphora and C. glauca shows net release under 3 UV-B conditions. The elevated UV-B radiation has no obvious effect on C release of leaf litter of two tree species, but reduced UV-B radiation decrease the C release of leaf litter of C. glauca.The lignin concentration of leaf litter of C. camphora and C. glauca increases in different degree under three UV-B radiation conditions. The elevated UV-B radiation has no obvious effect on lignin decay but increases the lignin/N ratio in leaf litter of both C. camphora and C. glauca. Multiple regression analysis shows that the leaf litter decomposition rate of both C. camphora and C. glauca are all significantly correlated with lignin concentration dynamics under elevated, reduced and ambient UV-B condition.