不同林龄和密度马尾松人工林针叶和根系的生态化学计量特征

Ecological stoichiometry characteristics of needle leaves and roots in different age and density stands of Pinus massoniana plantations

关键词:  马尾松, 林龄, 密度, 针叶, 根系, 养分限制

Key words:  Pinus massoniana, stand age, density, needle leaves, roots, nutrient limitation

摘要:

为了解不同林龄和密度马尾松人工林针叶和根系的养分变化特征,该文在广西南宁市横县镇龙林场选择了四种林龄(幼龄林、中龄林、成熟林和过熟林)和四种密度(低密度林、中低密度林、中高密度林和高密度林)马尾松林共八种林分,分析了马尾松针叶和根系的C、N、P含量和比值及其与土壤养分的关系。结果表明:(1)所有龄林与密度林的马尾松针叶N:P比值均大于16,表明该地区马尾松明显受P限制,幼龄林更加明显。(2)马尾松针叶C含量随着林龄增长逐渐增大后下降,N与P含量呈微弱下降趋势,导致C:N比值、C:P比值和N:P比值呈微弱上升趋势,但没达到显著水平; 根系C含量、P含量和C:N比值逐渐增大,N含量、C:P比值和N:P比值呈U字型且都在幼龄林最大; 针叶和根系在成熟林阶段均具有较高的P含量和最高的C含量。(3)中密度林的马尾松针叶的C和N含量较高且P含量最高,C:N比值较低且C:P比值和N:P比值最低; 根系的C、N和P含量较高,而C:N比值、C:P比值和N:P比值较低。(4)马尾松的根系养分尤其是P含量在不同龄林和不同密度林之间的变化比针叶更加剧烈,且其与土壤养分之间的相关性比针叶更强。综上结果表明,马尾松人工林受P限制,在低龄林加强P肥管理和选择合适的林分密度(中等密度)则有利于缓解马尾松受P限制的状态。

Abstract:

Ecological stoichiometries of leaves and roots are important factors responding to nutrient-limited soils, however, the patterns of needle leaves and roots in different age and density stands of Pinus massoniana plantations are unclear. To determinate the trends of needle leaves, roots, and soils and relationships between the three parts in these plantations, we selected total eight stands [including four age stands(young stand, half-mature stand, mature stand, and over-mature stand)and four density stands(low density, medium density, high density, and over-high density)] as the research object and measured C, N and P concentrations of needle leaves, roots, and soils in Zhenlong forest farm of Hengxian county, Nanning, Guangxi Zhuang Autonomous Region. The results were as follows:(1)N:P ratios of needle leaves in all stands were higher than 16.(2)The C concentrations of needle leaves increased and then decreased, and the C:N ratios, C:P ratios, and N:P ratios slightly(insignificantly)increased with the increasing stand ages, but the N and P concentrations were opposite. The C and P concentrations and C:N ratios of roots increased with the increasing stand ages, but the N concentrations, C:P ratios, and N:P ratios were the highest in young stand. Additionally, the C and P concentrations of needle leaves were the highest in mature stand, but the two parameters of roots were and relatively the highest in this stand.(3)Moreover, the highest P and relatively the highest C and N of needle leaves were found in medium density stand, as well as lowest C:P ratios and N:P ratios and relatively lowest C:N ratios. Simultaneously, the C, N, and P concentrations of roots were higher in medium density stand than in other stands, but the C:N ratios, C:P ratios, and N:P ratios of roots were opposite.(4)Root nutrients(especially P)of P. massoniana dramatically changed further than those of needle leaves in different age and density stands, as well as the relationships between root and soil nutrients. Our results suggest that P. massoniana is limited by P, and then, fertilization and management of phosphate in young stand and the appropriate density stand(medium)will be beneficial to relieve the P limitation in southern Guangxi.