生物量是生态系统最基本的数量特征, 其在各器官间的分配反映了植物适应环境的生长策略, 是物种进化、生物多样性保护和生态系统碳循环研究的核心问题。檵木(Loropetalum chinense)灌丛是中国亚热带灌丛生态系统最具优势的一种灌丛类型, 该研究以该灌丛建群种檵木为研究对象, 采用整株收获法在个体水平上研究了器官间的异速生长、生物量在各器官间的分配以及与个体大小、灌丛更新起源和生境因子之间的关系。研究发现: 檵木地上-地下间相对生长关系符合等速生长规律, 但随径级增大其等速生长关系可能发生变化; 较小径级檵木叶-茎、叶-根间为等速生长, 随径级增大转换为异速生长。不同灌丛起源间, 檵木叶-茎、叶-根间相对生长存在显著差异。器官间相对生长的尺度系数与生境因子无显著相关关系, 灌木层盖度和坡度通过影响檵木生长初期器官间的相对生长影响其生物量在器官间的分配。檵木平均叶质比为0.11, 茎质比为0.55, 根质比为0.34, 根冠比为0.65。随径级的增大, 茎质比(0.50-0.64)逐渐增大, 叶质比(0.12-0.08)、根质比(0.38-0.28)和根冠比(0.91-0.43)逐渐减小。在次生灌丛中, 檵木叶质比为0.12, 根质比为0.33; 在原生灌丛中, 檵木叶质比为0.07, 根质比为0.36。生物量向地上部分的分配与灌木层盖度正相关, 叶质比与坡度负相关, 根质比与年平均气温正相关。研究结果表明: 随个体增大, 檵木器官间的相对生长关系由等速生长转换为异速生长, 生物量向地上部分的分配增加, 地上生物量更多地分配到茎干中; 干扰通过影响器官间的相对生长影响生物量在各器官间的分配, 干扰导致生物量向叶的分配增加, 向根的分配减少; 光照减少促进生物量向地上部分的分配, 坡度增加导致生物量向叶的分配减少, 年平均气温升高促进生物量向根系的分配, 年降水量的变化对生物量分配无显著影响。檵木生物量分配策略在一定程度上支持了最优分配假说。

Aims Biomass is the most fundamental quantitative character of an ecosystem. Biomass allocation patterns reflect the strategies of plants to adapt various habitat conditions and play a vital role in evolution, biodiversity conservation and global carbon cycle. Loropetalum chinense shrub is one of the most dominant shrub types in subtropical China. The objectives of this study were to quantify the allometric relationships and the biomass allocation pattern among organs, and to investigate the effects of body size, shrub regeneration origin and site factors on allometry and biomass allocation.
Methods Individual samples of L. chinense were harvested from shrublands in subtropical China and were further divided into leaves, stems and roots. The allometric relationships between different organs were modeled with standard major axis (SMA) regression and the biomass allocation to different organs was quantified. The effects of body size, shrub regeneration origin and other habitat factors on allometry and allocation were examined using Pearson’s correlation analysis and multiple linear regressions.
Important findings The isometric scaling relationships between shoot and root changed to allometric relationships with increasing basal diameter. The scaling relationships between leaf and stem and between leaf and root were isometric for smaller diameter classes, while for larger diameter classes they were allometric. These relationships were significantly different among shrub regeneration origin types. The scaling relationships between different organs were not affected by habitat factors; while the coverage of shrub layer and slope affected biomass allocation due to their influences on the allometric relationships between different organs at the initial stage of growth. The mean dry mass ratios of leaf, stem, root and the mean root to shoot ratio were 0.11, 0.55, 0.34 and 0.65, respectively. With the increase of basal diameter class, stem mass ratio (0.50-0.64) increased, while leaf mass ratio (0.12-0.08) and root mass ratio (0.38-0.28) decreased, and consequently root to shoot ratio (0.91-0.43) also decreased. In secondary shrublands, the leaf mass ratio was 0.12 and the root mass ratio was 0.33, while these values were 0.07 and 0.36 respectively in natural shrublands. The ratio of aboveground allocation was significantly correlated to shrub layer coverage (r = 0.44, p < 0.05). Leaf mass ratio was significantly correlated to slope (r = -0.36, p < 0.05) and root mass ratio was significantly correlated to mean annual temperature (r = 0.34, p < 0.05). Results showed that with the increase of body size, the scaling relationships between different organs of L. chinense changed from isometric to allometric, and more biomass was allocated to aboveground part, and concretely, to stems. Human disturbance affected biomass allocation by its influences on the allometric relationships between different organs, and by increasing biomass allocation to leaves and decreasing allocation to roots. Reduced light resource promoted the biomass allocation to aboveground part, and higher slope resulted in decreased biomass allocation to leaves, while higher mean annual temperature promoted biomass allocation to roots. The variation in annual precipitation had no significant influences on biomass allocation. The biomass allocation strategies of L. chinense partially support the optimal partitioning theory.