混交比例对桉树-乡土树种混交林优势树种叶片资源获取性状的影响

Effect of Mixed Proportions on Leaf Resource Acquisition Capability in Mixed Plantations of Eucalyptus and Native Trees

摘要:

桉树-乡土树种混交林在提高林分生产力和生态系统功能等方面具有较大潜力。该研究以南亚热带4种桉树-乡土树种混交林(桉树与乡土树种混交比例分别为5:5、6:4、7:3、8:2)和桉树纯林为研究对象，研究了3种优势乡土树种华润楠(Machilus chinensis)、阴香(Cinnamomum burmannii)、灰木莲(Manglietia glauca)和速生树种尾叶桉(Eucalyptus urophylla)的叶片生理、结构和化学性状在不同比例混交林中的差异。结果表明, 4优势造林树种的叶片性状存在明显的种间差异，其中灰木莲的比叶面积(SLA)、光合磷利用效率(PPUE)、单位质量叶片最大光合速率(A_mass)和蒸腾速率(T_mass)以及叶片养分含量最高，说明灰木莲采取资源获取型的生态策略；尾叶桉的SLA、A_mass、T_mass及叶片养分含量最低，但具有最高的PPUE，说明尾叶桉兼顾了资源获取型和保守型的物种特征。灰木莲与尾叶桉在SLA、A_mass、T_mass、PPUE、叶片氮含量和氮磷比等叶片性状上几乎没有任何重叠，说明灰木莲与尾叶桉之间的叶片资源利用高度互补，可能是与尾叶桉混交的理想树种。物种水平上，灰木莲叶片氮含量、华润楠叶片磷含量以及干季时阴香叶片A_mass和PPUE随乡土树种混交比例增加有增加的趋势，但总体上树种混交比例对于4造林树种的叶片结构、化学和生理性状的影响不大；林分水平上，桉树-乡土树种混交林的比叶面积、光合能力以及叶片氮磷比显著高于尾叶桉纯林，说明桉树与乡土树种混交能够提高林分整体的光捕获和光合能力，但同时也加剧了植物生长的磷限制。因此，建议在未来南亚热带桉树人工林的构建与改造中，应优先挑选与桉树资源利用互补并能够优化混交林磷素循环利用的乡土树种。

Abstract:

Mixed-species plantations composed of Eucalyptus and native tree species have great potential in improving stand productivity and ecosystem functions. In this study, we investigated leaf physiological, structural and chemical traits of three dominant native tree species (Machilus chinensis, Cinnamomum burmannii and Manglietia glauca) and Eucalyptus urophylla in Eucalyptus monocultures (EM) and four mixtures of Eucalyptus (EU) and native trees species (NS) with different mixed proportions (EU:NS=5:5, 6:4, 7:3, 8:2, respectively) in south China. The results showed that there was substantial interspecific variation in leaf traits among four dominant tree species. On average, M. glauca had the highest SLA, PPUE, A_mass, T_mass, N_mass and P_mass, indicating that M. glauca adopts resource acquisition strategies. E. urophylla had the lowest SLA, PPUE, A_mass, T_mass, N_mass, P_mass but the highest PNUE, indicating that E. urophylla occupies characteristics typical of fast-growing and nutrient-conserving in order to adapt nutrient-poor environments. There was nearly no overlap between M. glauca and E. urophylla in leaf traits, such as SLA, N:P, A_mass, T_mass, PPUE and N_mass, indicating that M. glauca and E. urophylla were highly complementary in the leaf resource use. Manglietia glauca may be an ideal candidate tree species for establishing mixed plantations of Eucalyptus and native tree species. At the species level, N_mass of M. glauca, P_mass of M. chinensis, A_mass and PPUE of C. burmannii in dry season increased with the mixed proportion of native species, but leaf traits of four dominant tree species were generally not affected by the mixed proportion as a whole. At the stand level, SLA, PPUE, A_mass, T_mass and N:P in mixtures of Eucalyptus and native species were significantly higher than those in Eucalyptus monocultures. Thus, plantations established with Eucalyptus and high diversity native tree species can improve the light capture and photosynthetic capability from the stand level, but also aggravate the phosphorus limitation of plant growth. Overall, it was suggested that native species with complementary resource use to Eucalyptus and capability of optimizing phosphorus biogeochemical cycle of mixed plantations should be prioritized in designing and improving the Eucalyptus plantations in south China.