Slope position affects growth and allometry of the endangered conifer Calocedrus macrolepis by mediating soil properties and microbial communities

Premise: The allometric relationships among growth traits are highly relevant for a tree’s fitness, however, the mechanism of how the slope position affects the plant growth and allometry remains poorly understood, hindering our understanding of the variation in allometry of trees along slope position in mountainous areas.

Methods: A typical slope of Calocedrus macrolepis plantation in southwest China was chosen to measure growth traits and their allometric relationships. In addition, spatial variations in soil properties and microbial communities were also investigated.

Results: Slope position altered the allometric growth pattern with the larger allometric exponents of the tree height, diameter and wood volume relative to the crown size and height under the branch for the downslope. Additionally, most of soil nutrients, microbial diversity and abundances were greater at mesoslope and downslope, especially at the surface soil layer. The relative abundance both in Chloroflexi and Actinobacteria differed significantly among slope positions, while fungal dominant phyla abundances varied little across slope positions, indicating that bacterial community was more sensitive to slope position than fungal community. The growth traits and allometry were affected by the slope position, which is mainly caused by the variations of soil properties and microbial communities, and bacteria were more important than fungi in their relationships to growth traits and allometry.

Conclusions: Together, results emphasized that slope position indirectly influences the growth traits and allometry of C. macrolepis by regulating soil nutrients and microbial communities, which will provide important theoretical basis for the plantation management of C. macrolepis.

Methods
We measured growth traits of C. macrolepis and their allometric relationships along the slope position. In addition, spatial variations in soil properties and microbial communities in soil depths of 0-20 cm, 20-40 cm and 40- 60 cm at upper, middle and down slope positions were investigated. We focused on the variations in growth and allometry along the slope position, and the effects of soil properties and microbial communities mediated by slope position on growth and allometry.