关键词: 福建柏, 杉木, 凋落物, 分解, 养分释放

Abstract:

Decomposition of forest litter and simultaneous release of bioelements is one of the fundamental pathway of the flow of nutrient and energy in forest ecosystems. This study was related to rate of litter weight loss and release of nutrient elements in plantations of Fokienia hodginsii and Cunninghamia lanceolata in Fujian. Needles and branches of the two species were involved in the 750-day period of litter bag studies. Litter decay is regulated by an array of factors, of which the two most important are probably climate and the chemical composition of the litter, termed `substrate quality'. N content, C: N ratio, lignin content and lignin: N ratio have been seen to be of critical importance. The high precipitation and temperature of subtropical climates yield a general high rate of decomposition. Rate of weight loss showed exponential relationship with time for litter of needle and branch, with percent initial weight loss of 83.47% and 19.43% for needle and branch litter of F. hodginsii at the first year. The corresponding values were 60.78% and 25.02% for litter of C. lanceolata. Generally, the course of nutrient dynamics during decomposition follows three phases: (1)Initial nutrient release through leaching; (2) Net immobilization when decomposer microorganisms retain or import nutrients, followed by (3) Nutrient release when nutrients are released from the litter at a rate paralleling mass loss. However, this general pattern can vary depending on litter type, species, and ecosystem. For example, in conifers the leaching phase is typically short or absent. In this study, concentration of P in needle litter appeared to increase and concentrations of K and C appeared to decrease during the decomposition, while change of N concentration was different for two types of needle litter, especially in initial phase of decomposition. There was an obvious increase of N concentration at 60-day period followed by a decrease for F. hodginsii, while this pattern was not found for C. lanceolata. As to changes of nutrient concentration in branches, the two species were the same, with consistent increase for N, decrease for K and C and increase followed by decrease for P. The highest decay rate of nutrients was found for K, due to its leaching and the lowest for N. Annual decay rates of N, P and C in needle litter of F. hodginsii were faster than those of C. lanceolata, while the reverse was true for K. Comparison of annual decay rate of nutrients in branch litter between the two species, the greater values of C and N was for F. hodginsii, while values of P and K was higher for C. lanceolata. Productivity of forest ecosystems has been widely assessed by release of nutrients from decomposing litter. Owing to higher nutritional quality, the annual nutrient release by litter of F. hodginsii was much greater than that of C. lanceolata. The total annual nutrient release of leaf litter and twig litter was N, 2.630 g·m^-2a^-1; P, 0.162 g·m^-2a^-1 and K, 1.601 g·m^-2a^-1 respectively in the plantation of F. hodginsii, being 2.18, 1.13 and 1.42 times as much as in the plantation of C. lanceolata. It was concluded that the greater amount of nutrient release from litter and the ratio of release to return in F. hodginsii plantation indicated the faster turnover of nutrients, which in turn would be beneficial for maintenance of soil fertility.

Key words: Fokienia hodginsii, Cunninghamia lanceolata, Litter fall, Decomposition, Nutrient release