关键词: 缺苞箭竹, 凋落物, 生物元素, 潜在内转移能力, 密度

Abstract:

Dwarf bamboo (Fargesia denudata), a staple food of the giant panda, is the dominant synusia of the forest ecosystem in Wanglang National Nature Reserve, which plays an important role in the maintenance of forest ecosystem structure and function. The seasonal changes of nutrients in bamboo litter and nutrient retranslocation is one of the most profound ecological processes in the forest system. The seasonal change of nutrients in bamboo litter and nutrient retranslocation is regulated by the density of the bamboo stand as well as by biotic and abiotic factors. Although there have been a number of studies on nutrient cycling in bamboo forests, the effects of the bamboo density has not been investigated. The influence of bamboo density on the dynamics on litterfall, nutrient concentrations in bamboo litter, the differences in nutrient concentrations between litter and fresh leaves, and potential nutrient retranslocation were studied in three bamboo communities with different densities (D₁ with (220±11) stems·m^-2, D₂ with (140±7) stems·m^-2, and D₃ with (80±4) stems·m^-2) beneath a bamboo-fir (Picea purpurea) forest. Plots were chosen that had similar slope, aspect, soil parent material and texture, tree canopy, etc. Bamboo litter was collected in each stand and fresh leaves collected over a growing period from May to October, 2003, and nutrient concentrations (C, N, P, K, Ca and Mg) analyzed. The results indicated that litterfall production of bamboo increased with stem density during the growing period. The concentrations of C, N, P and K in litter decreased with stem density, but Ca and Mg showed the opposite pattern. It was found that N, P and K concentrations were lower in litter than in fresh leaves, increased from May to July, and decreased after July. Carbon concentrations in both litter and fresh leaves did not vary with the stem densities and month. Calcium concentrations were higher in litter than in fresh leaves over the growing season, but there was no significant monthly variation. Litter had the lowest Mg concentrations in July (during the exponential growth period) whereas fresh leaves showed the opposite pattern. No significant monthly differences in nutrients were found among the three communities. The potential retranslocation capacity of P was strongly regulated by stem density, but N and K retranslocation was not influenced by stem density. The potential retranslocation capacity of N, P and K showed the ranked order as K>N>P. The retranslocation of C in bamboo was not significantly different among the three bamboo communities. The accumulation of Ca in litter increased with stem density. The accumulation of Mg in litter increased with stem density, but the retranslocation capacity decreased with stem density. Density, therefore, greatly influenced the seasonal changes of nutrient concentrations in litter and their potential retranslocation capacity.

Key words: Fargesia denudata, Litter, Bioelements, Potential retranslocation capacity, Density