Dynamic Changes Of Litter And Decomposition Process Of Pine Needles In Different Types Of Masson Pine Community

Masson pine(Pinus massoniana)is the main afforestation tree species in southern China, which plays an important role on forestry construction for its widespread, well-adapted and fast growing features. Learning the dynamic changes of litter and decomposition Process of pine needles of different types of Masson pine community can help us understanding the Masson pine forest ecosystem nutrient cycling processes, providing strong support for the scientif ic management and maintaining the site’s long-term productivity of Masson pine.In this paper, we employed long-term sentinel surveillance to study the dynamic changes of the litter and decomposition Process of pine needles in three artificial forests of different densities and three forests of different communities. For artificial forests, we set litter nets and bags for a year to collect litters and then analyzed the seasonal variation of litter volume. Besides, we recycled the litter bags continuously 18 months and analyzed the variation of weight and nutrient content. For Masson pine forests consists of different communities, litter bags also have been set for a year and weight change and nutrient contents have been recorded. Orthogonal test of four factors and three levels was used to regulate pine need les decomposion and then the variation of decomposition rate was analyzed. Biomass of litter, nutrient content and other factors were calculated by Excel and SPSS. The results showed that:(1) Annual amount of litter in medium density forest was significantly greater than that in low and high density(P<0.05), but not significant different between low and high density. The amount of litter varied among different months and peaked in autumn. Pine needles had the largest proportion in different litter components(>70%). The nutrient concentrations in pine needles had an obvious seasonal variation, and the concentrations between largest and smallest was signif icant different(P<0.05). In forests of different densities, annual amount of nutrient return in medium density was significantly greater than that in low and high density(P<0.05), but there was no signif icant differences between low and high density. The nutrient restitution amount had an obvious seasonal variation,largest in autumn, followed by summer, small and showed no signif icant differences in winter and spring. And the differences between largest and smallest season was significant(P<0.05).(2) Decomposition rate of pine needles in prophase was slow in three Masson pine artificial forests, which is different from previous studies. This may due to the remove of the surface litter and humus layer before laying litterbags in this study. Then the contact between Needles and microbes was cut off and need time to re-build,so the decomposition rate of pine needles increased rapidly after a period of time. Pine needles decomposed rapidly in summer and autumn. The weight loss rate of pine needles in forests of high, middle and low density were 40.15%,47.85% and 43.5% respectively after 18 months of decomposition. And the decomposition rate were 0.342,0.434 and 0.381 respectively and showed significant difference between any two densities. Needles in medium density(the 6th forest) decayed fastest, which indicates that the density of Masson pine artificial forests may accelerate the decomposition rate of litter within a certain range.But to a certain extent, will restrict the decomposition rate. Therefore, appropriate density stand can effectively accelerate the decomposition rate of litter in Masson pine artificial forests management and promote the forest nutrient cycling. The half-period of pine needles decompose in three kinds of density stands were 2.0a,1.6a and 1.8a, turnover were 8.8a,6.9a and 7.9a.Both half-period and turnover showed significant differences.(3) Pine needles decomposed fastest at the beginning of the decompositions, then gradually slow down and the weight loss rate of pine needles in three different types of stands were 45.70%,52.50% and 48.10% after one year of decomposition The decomposition rate of pine needles in three different types of stands were 0.611,0.744 and 0.656 and it shows signif icant difference between any two densities. Needles in Natural secondary forest decayed fastest, followed in P inus-Liriodendron conifer and Masson pine artif icial forests decayed slowest. This is closely related to forest biodiversity: the species richness of three different types of stands were 4.12,4.34 and 3.69. The more abundant species diversity, the more forest soil microbial species and quantity and the sooner litter decomposes. Thus, appropriate replanting broadleaf shrub-like in Masson pine artif icial forests can speed up forest nutrient cycling speed and improve the productivity without changing the current mode of operation. The half-period of pine needles decomposed in three different types of stands were 1.1a, 0.9a, 1.1a, Turnover were 4.9a, 4.0a, 4.6a and showed significant differences.(4) The element content is constantly changing in Pine needles decomposition process but the release mode of the element in two different levels of pine needles decompose test is roughly the same. C was released directly; K, Ca, Mg had a leaching-release mode;N, P, Mn, Cu showed enrichment-release mode while Fe, Zn showed enrichment-release mode in different density test but performed leaching-enrichment-release mode in different type test.This may be related to the test time and stand compositional differences. Different test time will cause the difference on temperature and rainfall and then leading to the changes of the element release mode. Besides, various of stand consisting could lead to different microbial structure and cause the changes of the element release mode.(5) In four kinds of factors, agents factor was the most pivotal one in pine needles decom pose, followed by organic matter, and finally surfactant and C/N. Therefore, agents and organic matter was the main factor affecting the decomposition of pine needles, and surfactant and C/N were the minor factor. By selecting the optimal level of each fac tor, we can find out the best collaboration treatment to regulate pine needles decompose, such as inoculating decomposing agent 2(complex bacteria), adding chicken manure, no surfactant treatment and spraying NH4 Cl.