Leaf Decomposition Of Forest Litter In Different Environments

Forest litter is the main pathway of nutrient returns in forest ecosystems. Nutrient release in litter decomposition plays an important role in maintenance of soil fertility, nutrient availability for plant re-growth, and promotion nutrient cycling and nutrient balance of ecosystems. Studies on litter decomposition and nutrient release dynamics for the different forest types can help understanding the functional process of forest ecosystems. Litter decomposition, as a complicated physical and biochemical processes, was mainly controlled by soil microbial activities. if the soil conditions were good for microbial growth or activity, the decomposition of litter could be accelerated. Therefore, the rate of decomposition is closely related to the litter property litter and environmental conditions. The major objective of the study is to determine the major controls on decomposition process and nutrient release dynamics (including N, P, Ca, Na, Mg, K), and to reveal the relationships between decomposition rate and the soil and litter respiration. In this study, litter decomposition experiment was conducted using the litter-bag method at urban (Campus of Anhui Agricultural University) and suburban (Shushan Forest Park) area in Hefei. The foliar litter from three tree species, Cinnamonum camphora, Castanopsis eyrei and Pinus massoniana, were used through 18-month field decomposition experiment. The results are as follows.1 Decomposition rateDuring the experiment, the decomposition rates of the same species were somewhat different under different environments. Needle of Pinus massoniana decomposed fastest at both sites. During the 18-month decomposition, the dry mass loss was 92.5% at the park site, and 80.7% at the campus site. The rates of the dry mass loss for the three leaf litter decomposed at the Shushan Park ranked as decreasing order as P. massoniana > Cinnamonum camphora > Castanopsis eyrei. However, at the Campus site, the order was: P. massoniana > C. eyrei > C. camphora.Result from simulation of decomposition process based on Olson model showed that the decomposition coefficients were, respectively, 0.1112 for C. camphora and 0.1144 for C. eyrei in Shushan Park. However, at the Campus site, the decomposition coefficients were 0.0755 and 0.1255 for C. camphora and C. eyrei, respectively. The times for 95% decomposition were, respectively, 2.23 a and 3.33 a for C. camphora at the park and the campus sites; 2.18 a and 2.05 a for C. eyrei at the park and the campus sites.2 Nutrient dynamicsThe nutrient concentrations of foliar litter varied significantly amongst species. During the decomposition processes, notable differences in nutrient concentrations were observed amongst species at both sites, Shushan Park and the Campus. N concentration showed an increasing trend during the decomposition for C. eyrei and C. camphora, while for P. massoniana, N concentration increased slightly at the initial phase and kept almost constant at the late phase. P concentration increased slightly at the initial phase and decreased at the late phase for all species and two sites. During the decomposition process, Ca concentration showed an increasing trend at both Shushan Park and the campus site with greater increase for C. eyrei and C. camphora than for P. massoniana. Generally, K, Na and Mg concentrations showed a downward trend in both C. eyrei and C. camphora, while kept almost constant in P. massoniana during the decomposition.3 Relationship between decomposition rate and soil and litter respirationSoil respiration rates are different at both sites, Shushan Forest Park and the university. On Shushan Forest Park, the rate of soil respiration was peaked in May. However, at the campus site, the rate of soil respiration was peaked in July with consistency of the appearance of the maximum temperature. Result from the regression analysis demonstrated that the soil respiration was not significantly correlated to soil moisture in 0-10 cm layer at both sites.Due to the effects of temperature and soil moisture, the respiration rates of three foliar litter varied obviously with sites. At the campus site, the respiration rates of foliar litter in decomposition were reached maximum in September for all three species. However, at the campus site, there existed significant differences for the respiration of foliar litter amongst species.Both soil and liter respirations were determined by microbial biomass, species and physiological activities. Environmental conditions can also affect the soil and litter respirations. The results from the study showed that the seasonal course of both soil and litter respiration synchronized with that of the litter dry weight loss at the initial phase during decomposition. To a certain extent, the litter weight loss was not correlated with respiration rates of both soil and litter. This suggests that both soil and leaf respiration rates are not effective indicator for estimation of litter decomposition.