Research On The Microbial Decomposition And Nutrient Release Feature Of The Pinus Massoniana Forest Litters In Jinyun Mountain

The decomposition of forest litter that maintained the material circulation and energy flowing in forest ecosystem is one of the main pathways for vegetations releasing nutritive elements back to soils. The litter decomposition rate is affected enormously by litter chemical composition, the activities of the decomposers such as microorganism, and climate conditions. It is well known that Pinus massoniana is an important kind of timber resource in the south of China, however, in recent years, some problems caused by slower litter decomposition, such as poor forest soil and low productivity, have seriously affected the sustainable development of forestry in the south of China.In this paper, in order to explore the underlying reasons and microbial mechanisms for the slower decomposition of pine litter, taking Pinus massoniana leaf litter and Quercus aliena leaf litter as the materials, using the method of Litter Bag of in situ decomposition in natural secondary pine forest of Jinyun Mountain, the quantity dynamics of main microbial groups, the activity variations of three enzymes and the release characteristics of main nutrient elements were researched of the proportion of their singleness and natural mixture during the process of the decomposition in one year. The results of this study are as follows:(1) The mixture of coniferous and broadleaved litter could significantly boost their decomposition. By the end of this experiment (360d), the remains of forest litter from lowest to highest were mixture (41.33%), pure leaf litter of Quercus aliena (43.49%) and pure leaf litter of Pinus massoniana (54.34%). This boosting effect appeared significantly at the later stage of forest litter decomposition (225d～315d). In this stage, the decomposition rate constant of mixture was from 0.61 to 0.78, which was faster than that of pure leaf litter of Quercus aliena (0.19～0.53) and pure leaf litter of Pinus massoniana (0.43～0.48).(2) Different nutritive elements demonstrated different release characteristics obviously in the process of forest litter decomposition.The highest content of the element in the leaf litter was C that accounted for above 40% of the initial quality, and its release characteristics were in accordance with the biomass loss of the litter. By the end of the study, the release rate of C was sequenced as:mixed leaf litter (for 67.36%)>pure leaf litter of Quercus aliena (for 62.06%)> pure leaf litter of Pinus massoniana (for 54.62%).K, Ca and Mg in three types of litter showed stronger liquidity and net release characteristics, while Fe was opposite which presented net accumulation characteristics. The elements including N, P, Cu, and Zn showed different release characteristics because of the difference of litter type. The accumulation of N and P during the early period of the decomposition adjusted the chemical composition of mixed leaf litter and promoted metabolic activities of the decomposers such as microorganism during the late period to accelerate the decomposition of mixed leaf litter.(3) Different microbes play different roles in different stages of forest litter decomposition. The percentage of fungi, bacteria and actinomyces was variable with the forest litter decomposition prolonging. Before the time of 180th day, the average account of fungi was more than 90% several times, while after the time of 180th day, the average account of bacteria increased to approaching that of fungi, and sometimes it was more than that of fungi in pure leaf litter of Pinus massoniana. In addition, on the 135th day of the forest litter decomposition, the total number of microorganism and the number of fungi reached the peak value, however, the number of bacteria and actinomyces was the lowest respectively. From this perspective, fungi which played an important role in early stage of litter decomposition, was the main group of microbe during the decomposition of forest litter, and there were fierce competitions among fungi, bacteria and actinomyces in this process. To some extent, the litter decomposition at latter stage might depend on the synergistic effect of fungi and bacteria. Through the whole process, the microbial quantity, especially the fungi quantity in pure leaf litter of Pinus massoniana,was less than that in pure leaf litter of Quercus aliena and mixture, except the time of 45th day and 135th day. So it might be an important reason for the slowness of the pine needles litter decomposition(4) The activities of cellulase, polyphenol oxidase and phosphatase showed special dynamic response to the process of litter decomposition. During the early period of the decomposition, the cellulase activities of pure leaf litter of Pinus massoniana and mixture had a transient rising, then was similar to the cellulase activity of pure leaf litter of Quercus aliena that declined gradually with the extension of decomposition time.and maintained at a constant level (about 1.50 mg·g-1·h-1) after 315 days. With the decomposition prolonging, the phosphatase activities of three types of litter decreased, while the activities of polyphenol oxidase of pure leaf litter of Pinus massoniana and mixture increased gradually. Therefore, cellulase and phosphatase were main enzymes that participated in the early decomposition of litter, while the collaboration between cellulase and polyphenol oxidase was needed during the late period of the decomposition. Through the whole decomposition, the polyphenol oxidase activity of pure leaf litter of Pinus massoniana was lower than that of pure leaf litter of Quercus aliena in each period significantly, and was lower than that of mixture in most periods. So the low activity of polyphenol oxidase may be another important reason for the slowness of pure leaf litter of Pinus massoniana decomposition.