Expected shifts in tree species may alter the important C storage potential of the US eastern deciduous forest, particularly in below-ground pools. A critical knowledge gap exists in soil microbial community shifts resulting from large-scale forest biodiversity change and the mechanisms of microbial metabolism that influence soil C storage and dynamics. The objective in this research was to quantify the microbial processes leading to changes in C and N dynamics as a function of tree species using American chestnut, Northern red oak, and black cherry as model species at a 10-year-old plantation at Purdue University Martell Research Forest, with replicated plots of chestnut, cherry, and oak planted in monoculture. We hypothesize that chemical differences in organic substrates arising from the reintroduction of American chestnut into oak- and cherry-dominated forests will engender changes in the soil microbial metabolic processes involved in C and N cycling, ultimately resulting in landscape-level changes in the biogeochemical processing and below-ground storage of C. DNA was extracted from soil collected from beneath each tree species (n = 6) and metagenomic analysis and annotation was performed at the DOE Joint Genome Institute. Soil N mineralization, enzyme activity, respiration, litter decomposition, and soil oxidizable C were also measured.
Results/Conclusions
From the normalized gene abundance data, we find that chestnut soil contained the lowest gene abundance for the exoenzyme neopullanase for starch C degradation, and gentisate and superoxide dismutase enzymes for stress response. Chestnut soil also contained the greatest gene abundance for vanillate for aromatic C degradation, and for catalase and gentisate enzymes for stress response. Surprisingly, tree species did not cause differences in gene abundance related to lignin, cellulose, or chitin degradation. Chestnut soil contained the lowest gene abundance values for amoA functional gene related to nitrification and for the functional genes nirK, norB, and nosZ in the denitrification pathway. In the dissimilatory nitrate reduction to ammonium pathway, chestnut soils contained the lowest gene abundance for nitrate reductase genes narJ and napA and nitrite reductase nrfA and nrfH. Measured process and enzyme rates from incubated soil and litter reflect the low N gene abundance in chestnut soils, as N mineralization was lowest from chestnut soil (7.84) relative to cherry (11.51) and oak (12.02 mg N kg-1 soil). Overall, the soil ecosystem from chestnut plots has rapid decomposition with high nitrogen use efficiency, reflective of greater soil organic matter accumulation potential relative to black cherry and red oak.