Research On Litter Decomposition Characteristics Of Rubber Plantation In Danzhou,Hainan

Rubber plantation is one of the most important forests for tropical area, and it's playing a key role in promoting regional economic development and increasing farmers' income. As the existing rubber plantations were established on the first or second generation rubber plantations, after60years of large-scale rubber planting, the soil nutrients of rubber plantation have a serious loss in spite of taking a variety of fertilizer and protective measures in production, making healthy and sustainable development of rubber forest ecosystems facing increasingly severe pressure. Litter is an important component of the ecosystem, and it's providing more than half of forest vegetation nutrients needed, therefore, researching on litter decomposition is a key process to knowing forest nutrient cycling. Although many researches have been caused on litter decomposition, some results can't fit rubber plantation ecosystem. For this reason, we studied the rubber leaf litter decomposition on different control measures, and results as follows:(1) The decomposition rate of litter was decreased and C/N ration was increased with ages. Apart from contents of C, lignin, and C/N ratio, the initial N content, P content, lignin/N ratio, C/P ratio, and lignin/P ratio of leaf-litter were significantly affected by plantation ages. The decomposition rates of rubber leaf litter in different ages were significant negatively correlated with the initial C/N ration, and a weak negatively correlated with other nutrients content. The times required for50%and95%of leaf decomposition by ages increased were0.43a,0.45a,0.47a,0.50a and1.86a,1.96a,2.03a,2.18a, respectively.(2) The decomposition rate of litter was closely related to soil fertility. Rates of litter decomposition with different control measures as follows:1.0mm>0.07mm mesh bags; comparison hole> ground> fertile hole; No significant influence was detected about rubber roots on litter decomposition at all stages; residues of leaf litter was significantly positively correlated with soil available phosphorus?available nitrogen and total nitrogen, a significant positive correlation with soil potassium, organic matter content, a significant negative correlation with soil total potassium, and there was no significant correlation with soil water content, total phosphorus.(3)The dynamics of nutrient concentrations were differ among different control measures. Above ground, the total contents of N, P, Ca, Mg fluctuated with an enrichment at initial phase and then released at late phase, lignin and K contents released from initial phase in two size bags, C contents in lmm size mesh bags fluctuated with an slight enrichment at initial phase and then released at late phase, but in0.07mm size mesh bags released from initial phase; under ground, apart from Ca?Mg fluctuated with an enrichment at initial phase and then released at late phase, other elements released from initial phase. Among different treatments, the average contents of nutrient decreased95.0%in comparison hole and71.50%in fertile hole treatments after240d; above ground, it decreased73.54%in1.00mm size mesh bag and75.68%in0.07size mesh bag, respectively.(4)Microbial populations were closely related to litter residues and decomposition environments. Over time, the group of microbial numbers has been rising after falling on the ground but directing drop underground. In general, microbial populations on different control measures as follows:0.07mm aperture mesh bag>1mm aperture mesh bag, comparison hole> fertile hole, underground group> ground group. During the entire process of decomposition, the quantity of bacteria holed absolute superiority, and then actinomycetes, finally was fungus. Through the correlation analysis, the total number of bacteria, fungi and microbial was significantly associated with the decomposition rate, but there was little correlation to actinomycetes, it's suggested that fungi and bacteria are the main participants in litter decomposition on the ground. Underground group, the microbial groups were significant or extremely significant correlation with the dry weight of residues, but no significant correlation with decomposition rate, it's suggested that litter provided food for underground microbes, and litter decomposition is more dependent on microbes, soil animals and soil environments comprehensive effect.(5) Enzyme activities also closely related to litter residues and decomposition environments. The cellulose and polyphenol oxidase activities of litter on the ground had an intermittent rising, and peak appears at the mid and late period of litter decomposition, respectively. Through the whole decomposition, the unease but sucrose activity had a continuous rising process. Underground group, the cellulase activity had an unmoral change process, sucrose and urease activities showed a decent trend, polyphenol oxidase showed an up-down-up trend. From the annual average value, the urease activity of underground group was25.73%higher than ground group, sucrase and polyphenol oxidase activity were56.01%and61.28%smaller than ground group, respectively. Cellulase activity had no significant different in two groups. From two sizes of mesh bag effects on enzyme activities, the activity of cellulase?polyphenol oxidase?urease and sucrase in1mm mesh bag were10.97%,15.99%,-8.73%and-18.90%higher than that in0.07mm mesh bag, respectively. From different soil fertility effects on enzyme activities, the activity of cellulose, polyphenol oxides,sucrase and urease in barren soils were14.89%,20.51%,8.63%and-12.33%higher than that in fertility soils.