Plant traits and decomposition rates: Potential influences for forest carbon flux and fungal communities

Background/Question/Methods

Forests contain approximately half of the carbon (C) held in the terrestrial biosphere. A large fraction of this C is locked up in woody stems, both living and coarse woody debris. The rate of carbon release from these pools depends on two factors: plant senescence and wood decomposition. These factors, in turn, are modulated by wood traits. Vascular anatomy and chemical composition may predict mortality during drought. They also may influence saprophyte community structure and function. These important wood traits vary among species, with important consequences for forecasting the carbon balance of forests under climate change. As part of a larger project that integrates experiments and field observations with plant traits and fungal metagenomics, we established long-term experimental decomposition plots in forests at Tyson Research Center within the Ozark Highlands Ecoregion. Plots were situated at upland and lowland sites in four different watersheds. Each included replicate stem sections from 16 locally occurring, phylogenetically diverse, woody species with contrasting traits. After the first year of decomposition, we analyzed variation in mass loss across sites and species.

Results/Conclusions

Over the course of the first year, stems lost 12-50% of their mass. Mass loss varied between upland and lowland sites, with moister lowland sites decaying more quickly than drier upland sites. Mass loss also varied strongly among species.  Species differences alone explained 60% of the variation in initial decay rates. These species differed in a suite of functional traits, including leaf size, specific leaf area, leaf area to sapwood area ratio, wood density, C and N content, and C:N ratio.  Although each trait independently explained relatively little variation in decay rates, together they explained almost as much variation in decay rates as species identity alone. In addition to these measured trait differences, additional unmeasured differences between angiosperms and conifers (i.e. clade membership) contributed to variation in decay rates. On the whole, these results reinforce the well-known effect of environment on decomposition.  Furthermore, they strongly suggest that plant species’ functional traits and evolutionary histories play an extremely important role in wood decomposition.  Exactly how species’ differences influence saprophyte community structure and function will be the subject of future studies.