缺苞箭竹密度对养分元素贮量、积累与分配动态的影响

Effects of Fargesia denudate density on its nutrient element stocks, accumulation and allocation dynamics

研究了缺苞箭竹(Fargesiadenudate)-紫果云杉(Piceapurpurea)原始林下不同密度缺苞箭竹群落的养分元素贮量与分配动态以及养分元素在一个生长季节内的积累量。结果表明:地上、地下部分的N、P、K、Ca、Mg贮量均随着箭竹密度的增加而增大,养分元素贮量排序为:K>N>Ca>P>Mg。密度较大的箭竹群落(D1和D2)中,地上部分的N、P和K贮量大于地下部分,而密度较小的箭竹群落(D3)中P和K贮存于地下部分的比例较大,3个群落中的地下部分Ca和Mg贮量均大于地上部分,且地下部分的养分元素贮量的比例随着箭竹密度的增加而减少。养分元素的总积累量排序为:K>N>Ca>P>Mg,且地上部分和群落的总积累量随着箭竹密度的增加而增加,总积累率以D1群落最大,3个群落的养分元素积累率大小顺序为:Mg>Ca>P>N>K。地下部分(根系和鞭)养分元素贮量比例随着箭竹密度的增加而下降,而地上部分(叶、枝和竹杆)养分元素贮量比例随着箭竹密度增加而上升。密度对缺苞箭竹养分贮量、积累和分配动态有深刻影响。

Dwarf bamboo （Fargesia denudate）, a staple food bamboo for the giant panda, is the dominant synusia of the forest ecosystem in Wanglang National Nature Reserve, which plays an important role in forest ecosystem structure and function.The dynamics of nutrient stocks, accumulation and allocation is one of the most profound ecological processes in the forest ecosystem. Nutrient stocks, accumulation and allocation are regulated ultimately by the density itself besides biotic and abiotic factors. There have been many reports on nutrient cycle in bamboo community, forest regeneration driven by bamboo, bamboo regeneration, and bamboo population dynamics, but there is lack of information about the effects of the bamboo density on the nutrient stocks, accumulation and allocation. Therefore, in our study, these effects were studied by setting up 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, and by harvesting all the bamboo per unit over a growing period （from May to October 2003）, analyze the nutrient concentration （N, P, K, Ca and Mg） in bamboo components （leaf, branch, stem,rhizome and root）. Considering the complex effects of biotic and abiotic factors on the biomass, the plots were chosen according to the criteria with similar slope, direction, soil parent material and texture, tree canopy, etc, which was the prerequisite to realize the objectives here. The results indicated that all the total, above- and below-ground nutrient stocks increased with increasing stem density, and the order of nutrient stocks was K〉N〉Ca〉P〉Mg, N, P and K stored in above-ground more than in below-ground in bamboo communities with higher density （D1 and D2）, but more P and K stored in below-ground bamboo community with lower density （80±4 stems·m^-2）, below-ground system had more Ca and Mg stocks than above-ground in all the three communities, and the ratio of below-ground nutrient stocks decreased with increasing stem density. The total accumulation quantity in bamboo community over one growing period could put in the order of K〉N〉Ca〉P〉Mg. Furthermore, the total and above-ground nutrient accumulation quantity increased with increasing stem density, the accumulation ratio order was similar in different communities, and it was Mg〉Ca〉P〉N〉K, the bamboo community with highest density （220±11 stems·m^-2） had the highest accumulation ratio. The ratio of nutrient storages in below-ground system （root and rhizome） decreased with increasing stem density, nutrient storages in the root were higher than other bamboo components, increased from May to September, and decreased after September over one growing period. Rhizome nutrient storages ratio was highest in May and June, then declined, ascended in the end of growing season （October）;there were more N and Mg stored in leaves than other bamboo components except for root, but more P, K and Ca for stems. The nutrient storage in branch was less than other bamboo components. The ratio of nutrient storages in above-ground system （leaf. branch and stem） increased with increasing stem density. Density, therefore, greatly influenced the nutrient stocks, accumulation and allocation dynamics of the dwarf bamboo community.