Comparison of wood physical and mechanical traits between major gymnosperm and angiosperm tree species in China

Many wood physical and mechanical traits are important functional attributes for tree species, but variation in these traits among taxonomic categories such as between gymnosperms and angiosperms is still poorly documented. Here, the systematic differences in 12 traits and their allometric relationships between the two tree categories and the potential effects of phylogeny are explored based on a database for major gymnosperm and angiosperm tree species across China. The results are summarized below: (1) means of wood traits were all significantly lower in gymnosperms than in angiosperms. (2) Air-dried density (ADD) and tangential shrinkage coefficient (TSC) are key traits that summarize the correlations among wood traits for gymnosperms, while ADD and radial shrinkage coefficient (RSC) represent those for angiosperms. The allometric slopes of other traits, except for hardness of transverse section (HES), against ADD for gymnosperms were significantly steeper than or similar to the corresponding slopes for angiosperms. On the contrary, the slopes of other traits (except TSC) against RSC for gymnosperms were shallower than or similar to their counterparts for angiosperms. Generally, wood traits were positively related with each other, except that TSC was negatively related to density-related (ADD, BD) and hardness-related traits (HES, HRS and HTS) in gymnosperms. (3) Phylogeny had significant effects on some wood traits of gymnosperms, but had no effects on traits of angiosperms. The present analyses demonstrated a systematic difference in wood traits between two major plant categories, which suggests the evolutionary divergence (TSC, RSC) and convergence (ADD) in key functional traits among woody plants.