Guiwu Zou

Competition is an important factor influencing the structure and dynamics of plant communities, and understanding species coexistence. Tree architectural traits, such as height-to-diameter (H-D) and branch length-to-diameter (L-d) relationships influence species competitiveness through affecting light capture by altering the occupation of space. Unfortunately, little is known about how the H-D and L-d scaling allometric exponent related to tree performance (growth vigour) in competition. We surveyed 1739 (1642 living and 97 dead) individual trees from an even-aged dense aerial seeding forest of Masson pine ( Pinus massoniana ), in which 51 trees with 1087 first-order branches were destructively sampled. Using the H-D and branch L-d scaling data, we determined (1) whether the H-D scaling exponent numerically differed across different levels of tree performance, and (2) whether the L-d scaling relationship differed across tree performance and branch vertical position in crowns. The results indicate that (1) the H-D scaling exponent numerically decreased as tree performance deteriorated; (2) the L-d scaling relationship differed across tree performance, and the numerical value of the scaling exponent of “inferior” trees was significantly larger than that of “moderate” and “superior” trees; (3) the L-d scaling exponent declined as branch position approached ground level, and it was significantly higher in upper branches; and (4) overall, the branch scaling exponent numerically decreased as tree vigour ameliorated in each canopy layer, but decreased significantly only in the intermediate layer. This study highlights the variation within (and linkage among) length-to-diameter scaling relationships across tree performance at the individual and branch levels. This linkage provides novel insights into tree competitive strategies and potential mechanisms of tree mortality in the competition of subtropical forests.

The unbridled expansion of moso bamboo (Phyllostachys edulis) occurs throughout the world and has a series of consequences. However, the effect of bamboo expansion on arbuscular mycorrhizal fungi (AMF) is still poorly understood. We assessed the changes in the AMF community during bamboo expansion into Japanese cedar (Cryptomeria japonica) forests by analyzing AMF in three forest types—Japanese cedar (JC), bamboo-cedar mixed (BC) and moso bamboo (MB)—using 454 pyrosequencing technology. We found that the AMF community composition differed significantly among forest types. The relative abundance of Glomerales decreased from 74.0% in JC to 61.8% in BC and 42.5% in MB, whereas the relative abundance of Rhizophagus increased from 24.9% in JC to 35.9% in BC and 56.7% in MB. Further analysis showed that soil characteristics explained only 19.2% of the AMF community variation among forest types. Hence, vegetation is presumably the main driver of the alteration of the AMF community. The α diversity of AMF was similar between JC and MB, although it was higher in BC. Overall, this research sheds more light on AMF community dynamics during moso bamboo expansion. Our results highlight that the consequences of bamboo expansion in monoculture forests differ from those in mixed forests.