Abstract:

Four treatments of Chinese Fir needle litter, Chinese Fir needle litter with addition of 2 g and 4 g NaNO₃ respestively, and Chinese Fir needle litter mixed with leaves from understorey plants were designed to investigate the effects of nutrient status on the decomposition rates and nutrient releases of Chinese Fir needle litter using the litter bag technique. The results showed that both adding NO^-₃-N and mixing with leaves from understorey plants to some extent accelerated the decomposition rate of Chinese Fir needle. The dry mass loss percentage, decomposition rate and half-life time of Chinese Fir needle were 20.49%, 0.001 6 per day and 1.2 a, respectively. Chinese Fir needle litter mixed with leaves from understorey plants had the highest decomposition rate with dry mass loss percentage of 43.67%, decomposition rate of 0.004 3 per day and half life time of 0.44 a. In the whole decomposition processes, there was a significant difference of decomposition rate between Chinese Fir needle litter mixed with leaves from understorey plants and Chinese Fir needle litter. The amount of NaNO₃ addition also affected the decomposition rate. Addition of 4 g NaNO₃ had higher decomposition rate with dry mass loss percentage of 42.07%, decomposition rate of 0.003 7 per day and half life time of 0.51 a than addition of 2 g NaNO₃ with dry mass loss percentage of 29.13%, decomposition rate of 0.002 2 per day and half life time of 0.86 a. The decomposition rate accelerations could be attributed to improvement in litter quality, in particular N content increase and C∶N ratio decline, because the relationship between the initial litter C∶N ratio and the proportion of dry mass remaining was significant. The N content in litter after NO^-₃-N addition and shrub leaves mixing had been increased as many 0.6～1.6 times as that in Chinese Fir needle litter. The reduction of C∶N ratios was 0.4～0.6 times. Nitrogen immobilization was observed in the decomposition processes of Chinese Fir needle while N mineralization followed by stabilization were found in the litter of treatments of NaNO₃ addition and mixing leaves from understorey plants. Understorey plants management and appropriate amount of NO^-₃-N fertilizer application would accelerate Chinese Fir needle litter decomposition and provide soil nutrient supply for plant growth.

Key words: Chinese Fir plantation, needle litter, decomposition rate, understorey plants, nitrogen concentration, C∶N ratio