Effects Of Forest Gap Size On Litter Recalcitrant Components Of Two Tree Species In Pinus Massoniana Plantations

The objective of the study was to evaluate the dynamics of recalcitrant components during foliar litter decomposition at different forest gap size in Pinus massoniana plantation in the low hilly land, Sichuan basin. The experiment was set up by thinning P. massoniana plantation to establish seven different gap sizes(G1:100 m~2, G2:225 m~2, G3: 400 m~2, G4:625 m~2, G5:900 m~2, G6:1225 m~2, G7:1600 m~2). The effects of gap size on the degradation of four recalcitrant components, i.e., condensed tannins, total phenol, lignin and cellulose in foliar litter of two native species (Cinnamomum camphora and Toona ciliata) in the center, edge of the gap and closed canopy were evaluated. The litterbags placed under closed canopy were used as the control. Litterbags with air-dried litter of C. camphora and T. Ciliata were placed on forest floor from the center, edge of the gap to under the closed canopy. The results showed that:1) Forest gap size had significant effect on the degradation rate of condensed tannins, total phenol and lignin for T. ciliate and lignin in the litters of C. camphora However, the forest gap size had no significant effect on the degradation rate of the other three recalcitrant components in the litters of C. camphora and cellulose content of T. ciliata. The degradation rate of recalcitrant components in small and medium sized gaps center (G3-G5) was significantly higher than in other gaps. However, gap edge only in medium-sized gaps (G3, G4) showed the greatest degradation rate. Our results suggested that small and medium sized gaps (100-900 m~2) had a more significant effect on the degradation of litter recalcitrant components in the two native species in P. massoniana plantations, however, the effect was depended on species.2) The differences on the degradation rate of litter recalcitrant components in the two native species between gap center and gap edge were not significant. In spite of, the degradation rate, and the degradation of soil fauna to them had significant difference between gap center and gap edge a small number of forest gaps, there was no obvious change rule.3) The degradation rate of the four recalcitrant components in both species'foliar litter changed with time. The condensed tannins, total phenol, and lignin of C. camphora litter and the four recalcitrant components for T. ciliate exhibited an increment of degradation rate, however, the total phenol degradation rate decreased initially, and then increased. The degradation rate of condensed tannin was the fastest, followed by total phenol and cellulose, but the lignin degradation rate was the slowest. After the one-year decomposition, the degradation process of four recalcitrant components for T. ciliate had been basically completed, however C. camphora litter need two years. The degradation rate of four recalcitrant components for T. ciliate was significant faster than the degradation of C. camphora litter.4) With the increase of gap size, the degradation rate of the four recalcitrant components through soil fauna have no significant changes in gap center. Degradation rate of condensed tannins and total phenol did not change significantly with increasing forest gap sizes of gap edge. The degradation rate in G4 and G5 gap edge, and cellulose in G3 gaps edge, was significantly higher than in other gaps. Compared with small(G2) and large sized gaps(G6?G7), medium sized forest gaps(400-900m~2) is more conducive to lignin and cellulose biodegradation. Effects of soil fauna on lignin and cellulose is greater than condensed tannins and total phenols between gap center and gap edge.In summary, forest gap size had significant effect on the degradation rate of recalcitrant components for T. ciliate and C. camphora. The environmental heterogeneity of the gaps is main factors on regulation of decomposition dynamics of litter recalcitrant components, and the indirect influence of soil fauna during decomposition of leaf litter. Meanwhile, dependent on the initial litter quality. Therefore, small and medium sized gaps(400-900 m~2) could be the optimal gap size to promote the degradation of litter recalcitrant components for two species in P. massoniana plantations. The results presented in this paper provide a scientific basis to rebuild low-efficient plantations and to understand litter decomposition, maintaining element balance within forest.