缺苞箭竹群落密度对土壤养分库的影响

研究了王朗自然保护区内缺苞箭竹(Fargesia denudata)群落3个密度在1个生长季(5～10月)内不同土壤层次的养分贮量及其季节动态.结果表明，土壤(0～30 cm)总P、速效P贮量均随密度的增加而显著减少(P<0.01)；而土壤总Ca、Mg贮量则随密度的增加而增加；土壤N、K(全量或速效)贮量密度间差异不大.在不同密度的箭竹群落样地内，除了D1样地土壤总钾贮量大于Ca外，土壤层(0～30 cm)不同养分贮量(全量)大小顺序均为Ca>K>Mg>N>P.表层(L1)速效N、P和K浓度在7月份均有显著降低的现象，随后又逐渐回升.养分的变化幅度则普遍存在着表层(L1)大于下层(L2、L3)，高密度(D3)大于低密度(D1)，速效P大于速效N、K的现象.土壤总养分贮量与浓度在土壤层次上的分布特征明显不同，3个密度样地中L1(0～10 cm)层的N、P、K、Ca、Mg贮量均低于L2(10～20 cm)和L3(20～30 cm)层.分析表明，箭竹群落土壤层养分贮量与密度密切相关，可能是由于密度影响到了箭竹对土壤养分的吸收、凋落物养分的归还、微生物活性等养分循环各个环节，从而导致了土壤养分贮量的改变.其中，密度对P、Ca贮量影响最大，Mg其次，对N、K影响最弱.随着箭竹密度的增加，越来越低的土壤总P、速效P贮量也表明，P素可能是箭竹生长发育的主要限制因子，P不足可能是导致箭竹开花的重要诱因.

Effects of Fargesia denudata density on soil nutrient pool

This paper studied the nutrient storage and its dynamics in different soil layers under three densities of Fargesia denudata communities in Wanglang National Nature Reserve, aimed to understand the effects of F. denudata density on the storage and dynamics of soil nutrients. The results showed that F. denudata density had a significant effect on the total and available nutrient contents in 0 - 30 cm soil layer. The total and available P contents decreased significantly with the increasing F. denudata density (P < 0. 01), being 0.274 kg m(-2) and 1.72 g x m(-2) at D1, 0.222 kg m(-2) and 1.50 g x m(-2) at D2, and 0.158 kg x m(-2) and 1.10 g x m(-2) at D3 sampling site, while the contents of total Ca and Mg increased with the increasing F. denudata density, being 2.64 and 1.70 kg x m(-2) at D1,4.42 and 1.80 kg x m(2-) at D2, and 4.85 and 2.12 kg x m(-2) at D3 sampling site, respectively. The contents of both total and available N and K did not change significantly with F. denudata density. Soil total and available N were 1.10 and 45.15 kg x m(-2) at D1, 1.04 and 44.38 kg x m(-2) at D2, and 1.06 and 42.02 kg x m(-2) at D3, while soil total and available K were 3.19 and 39.62 kg x m(-2) at D1, 3.30 and 36.23 kg x m(-2) at D2, and 3.19 and 37.18 kg x m(-2) at D3, respectively. The total nutrient storage was in order of Ca>K>Mg>N>P, except a higher K storage than Ca under D1 community. The available N, P and K concentration in surface soil (0-10 cm) decreased significantly in July, and then increased slowly in the later growth season. In general, the change magnitude of available nutrients was greater in surface soil (L1) than in lower soil layers (L2 and L3), under higher F. denudata density (D3) than under lower F. denudata density, and for P than for N and K. The distribution pattern of nutrient storage in soil layers differed greatly from that of nutrient concentration, regardless of F. denudata densities. The contents of total N, P, K, Ca and Mg in L (0-10 cm) were lower than those in L2 (10-20 cm) and L3 (20-30 cm). The differences of nutrient contents among soil layers varied with F. denudata density, and particularly with bio-elements. The results suggested that the nutrient storage in soil under F. denudata community was related to F. denudata density, because the density affects the processes of nutrient cycling, such as nutrient absorption, return through litter, and activity of soil microorganisms. It could be concluded that the density of F. denudata communities affected the storage of soil P and Ca significantly, but that of soil Mg, N and K slightly. Soil total and available P contents decreased with the increasing F. denudata density, implying that soil P could be one of the main factors limiting the growth and succession of F. denudata community in these stands, and affecting the flowering and death of bamboo.