Toposequence variability in tree growth associated with leaf traits for Larix gmelinii

Intraspecific variations in leaf traits and tree growth along environmental gradients are crucial for survival and distribution of the tree species, but they are substantially less quantified than interspecific counterparts. Here, we examined the intraspecific variations in leaf hydraulics and economics traits and growth of Larix gmelinii Rupr. - the predominant tree species in the Eurasian boreal forests with a toposequence approach. The topo-sequence included three replicated 1000-m transects of the larch plantation (31-year-old), each of which consisted of three plots located at the toe-, mid-, and top-slope, respectively. We found that the leaf hydraulics traits showed a "high-low-high" pattern along the toposequence, while the leaf economics traits, total biomass (TB) and TB increment (TBI) displayed an opposite trend, largely consistent with changes in site conditions especially soil nitrogen concentration. This suggests that the intraspecific variation in tree growth is coupled with leaf traits and site conditions. Leaf mass per area explained 21.9% of the variability in TB, while and the ability of drought tolerance explained 22.5% of that in TBI; and the interactions of hydraulic and economic variables explained additional 23.1-26.2% of that in TB or TBI. This result indicates that leaf traits interactively affect TB and TBI, but the hydraulics and economics play major roles in the short-term growth rate and relatively long-term biomass stock, respectively. Together, our findings demonstrate that the larch trees acclimate the leaf traits and growth/biomass accumulation to site conditions, and provide insights into the mechanistic understanding of forest production.