Effects Of Simulating Light Intensity On Forest Litter Decomposition

Utilization and redistribution on light caused by the process of absorption, reflection and scattering of forest canopy, might make different light environments on the forest floor. As yet, little information has been available on the effects of light intensity on the forest litter decomposition. In order to deeply explore the influence of forest canopy on litter decomposition, a shading experiment using 50%-95% shading net in combination with litterbag method was therefore conducted to simulate the effects of different light intensity (the relative intensity were 72%,62%, 55%,45% and 32%) on litter decomposition in the subtropical evergreen broad-leaved forest of Sichuan Basin at the upper reaches of Yangtze River. Litterbags with dried leaf litter of Pinus massoniana, Cryptomeria fortunei, Cunninghamia lanceolata, Cinnamomum camphora, Toona ciliate and Quercus acutissima were incubated on soil surfaces under different light intensities in January, 2013. The incubated litterbags were taken back at different periods (drizzle period, spring light rainy period, early stage of rainy season, late stage of rainy season and winter rainy stage in the first year, and spring rainy stage, rainy stage and winter rainy stage of the second year), and mass loss, quality change, C, N and P releases and degradations of lignin and cellulose in litter were measured. The objectives were to deeply recognize the material cycling in the subtropical evergreen broad-leaved forest ecosystem, and to provide with certain theoretical basis for sustainable development management subtropical evergreen broad-leaved forest. The results showed that:(1) After two-year decomposition, needle litter lost 54.46%-88.37% of mass, while broadleaf litter lost 55.54%-100%. Litter decomposition occurred mainly in the first year for the half of total amount of decomposition. The K values from Olson decomposition model for three broad leaved tree species (C. camphora, T. ciliate, Q. acutissima) were higher than those of three coniferous species (P. massoniana, C. fortunei, C. lanceolata). Litter of broadleaved tree species decomposed more easily than coniferous species.(2) Light intensity significantly affected the litter mass loss rates of six species, but the responses of litter mass loss to light intensity varied with tree species. The responses of litter mass loss to shading treatments also varied with critical periods. Shading treatments obviously promoted litter decomposition of P. massoniana, C. camphora, and T. ciliate, but inhibited litter decomposition of C. fortunei, C. lanceolata and Q. acutissima. In the drizzle period of the first year, shading treatments did not give significant effects on litter decomposition of P. massoniana, C. lanceolata, and Q. acutissima, but did give strong effects on those of other three tree species. However, shading treatments gave significant effects on litter decomposition of six tree species at other critical periods. The effect of shading treatment on first year decomposition was more significant than that on the second year decomposition.(3) Changes of light intensity affected significantly litter substrate quality, depending on the different critical periods and tree species. Shading treatments had also affected significantly C, N, P, lignin and cellulose concentrations and C/N, C/P, N/P and lignin/N of litter in some extent in the whole decomposition process. In addition, by and large, the responses of litter N, P, lignin and cellulose concentrations, C/P, N/P and lignin/N to shading treatments were coincident in each decomposition stage. These quality indexes of litter put up increase or decrease coincidently in the same decomposition stage in the shading treatments. While, the responses of litter C contents and C/N to shading treatments were coincidently, and there were large differences between needle leaved and broad leaved litter.(4) Shading treatments significantly affected the release characteristics of C, N and P of six tree species litter, and C, N and P release dynamics of different species showed obvious differences in the different critical periods. The responses of litter C, N and P release to shading treatments were coincident in each critical decomposition stage. Shading treatments obviously promoted litter C and N releases of P. massoniana, C. lanceolata C. camphora and T. ciliate, but shading treatments inhibited litter C and N releases of Q. acutissima. Shading treatments obviously promoted litter P releases of P. massoniana, T. ciliate and C. camphora, but inhibited litter P releases of C. lanceolata and Q. acutissima. While shading treatments did not gave significant effects on litter N and P releases of C. fortunei. In addition, by and large, the release processes of C, N and P of needle leaved litter were faster than that of broad leaved litter. Two-factor variance analysis results indicated that light intensity and species factors and their interaction significantly affected litter C, N and P release processes of two years decomposition.(5) Shading treatments significantly affect the degradation characteristics of lignin and cellulose of six tree species litter, and the degradation characteristics of lignin and cellulose of different species showed obvious difference in the different critical periods. Shading treatments obviously promoted litter lignin degradation of C. fortunei, C. lanceolata and C. camphora, but did not gave significant effects on lignin degradations of P. massoniana, T. ciliate and Q. acutissima. While shading treatments obviously promoted litter cellulose degradations of P. massoniana, C. lanceolat, C. camphora and Q. acutissima, but did not gave significant effects on cellulose degradation of C. fortunei and T. ciliate. What’s more, light intensity and species factors and their interaction significantly affected litter lignin degradation processes of two-year decomposition, while that only significantly affected litter cellulose degradation processes in the first year decomposition.In summary, simulating light intensity significantly affected litter decomposition in the subtropical evergreen broad-leaved forest, and the responses of litter decomposition to shading treatments depended on the different critical periods and tree species. Changes of light intensity did affect litter C, N and P contents, lignin and cellulose concentrations, and its release characteristics. Our results also indicated that light intensity regulated litter decomposition through affected litter mass loss, element (C, N, and P) releases, lignin and cellulose degradations in the rainy stage. These results showed that changes of light intensity caused by forest canopy would significantly affect material cycling of forest ecosystem. In order to manage legitimately subtropical evergreen broad-leaved forest, we could effectively regulate the process of material cycling of forest ecosystem by intelligent cultivating and canopy trimming.