不同林龄和密度对马尾松人工林凋落叶养分变化的影响

该文选择广西南宁市横县镇龙林场的4种林龄(幼龄林、中龄林、成熟林和过熟林)和4种密度(低密度林、中低密度林、中高密度林和高密度林)马尾松人工林共8种林分作为研究对象,分析了未破碎和破碎两个不同降解阶段的凋落叶C、N、P含量及其生态化学计量学特征。结果表明:(1)不同林龄中,凋落叶初始C、N含量在过熟林和成熟林中较高,P含量没有显著变化,且C∶N比值和C∶P比值从幼龄林到成熟林逐渐升高,说明较高林龄马尾松对N和P重吸收较低,而较低林龄马尾松对N和P重吸收较强,需要较大。(2)不同密度林中,随着林木密度的增加,凋落叶初始C含量逐渐升高,N含量无显著变化,P含量降低;高密度林凋落叶的初始C∶P比值和N∶P比值较高,说明高种植密度下马尾松可能对N和P养分的需求较大,P重吸收较强。(3)不同林龄和不同密度马尾松林的破碎凋落叶C含量、C∶N比值、C∶P比值和N∶P比值比未破碎凋落叶的低,N和P含量较高,说明凋落物在降解过程中出现N和P养分的富集现象。(4)中林龄和较高种植密度的马尾松破碎凋落叶与未破碎凋落物的C含量差值最大,C∶N比值和C∶P比值较低,说明这两种林分的凋落叶C的降解速率可能较大。上述结果说明,中龄林和中高、高密度林的马尾松可能对N和P养分的需求较大,重吸收效率较高,且凋落叶C的潜在分解速率较高,可能利于有机碳较快进入土壤中。

Stand age and density affected litter nutrient changes in planted Pinus massoniana forests

In order to relieve the effects of stand ages and densities on litter nutrient changes and its returns in planted Pinus massoniana forests, we selected four forest types of stand ages(young stand, half-mature stand, mature stand, and over-mature stand)and four forest types of stand densities(low density, middle-low density, middle-high density, and jigh density)as the research objects(total eight stands)in Zhenlong Forest Farm of Hengxian County, Nanning, Guangxi Zhuang Autonomous Region, and we measured litter carbon(C), nitrogen(N)and phosphorus(P)contents and their ratios in the early and latter degradation periods of litter. The results were as follows:(1)C contents in early degradation period of litter were relatively higher in mature and over-mature stands, N contents were relatively higher in over-mature and half-mature stands, but P contents and N:P ratios were not different among four stands, C:N and C:P ratios increased from young stand to nature stand. It indicated that the growth rates were relatively faster in young stand and half-mature stand, resulting in Pinus massoniana needing large amounts of N and P in the two stands.(2)In early degradation period of litter, C contents increased but P contents decreased with the increasing of stand densities, N contents were not different among four densities of stands. C:P and N:P ratios were relatively higher in middle-high and high density stands, resulting in Pinus massoniana needing large amounts of N and P and higher P reabsorption in these stands.(3)C contents and C:N, C:P, and N:P ratios in latter degradation periods of litter were lower than those in early degradation period of litter, but N and P contents were adverse. It indicated that N and P were enriched to litters along the advancing degradation periods.(4)The difference of C contents between the early and the latter degradation periods of litter was relatively higher in half-mature, middle-high, and high density stands, but C:N and C:P ratios were relatively lower, indicating that the degradation rates of litters C were relatively higher in these stands. The above results suggested that Pinus massoniana may need large amounts of N and P in half-mature, middle-high and high densities of stands, resulting in high nutrient resorption efficiency; additionally, there were high potential degradation rates of litter carbon, which was beneficial to return litter C to soils in these forest stands.