The once-dominant American chestnut tree (Castenea dentata) was functionally extirpated from the US eastern hardwood forest resulting from the chestnut blight fungus in the early 1900’s, in what is considered the largest disturbance event since glaciation. However, back-cross breeding and transgenic approaches have resulted in the production of blight resistant trees, and the reintroduction of American chestnut is considered imminent. In the event of a successful reintroduction, significant ecosystem changes in carbon (C) and nutrient cycling are expected, but have yet to be understood or quantified at a landscape level. This study aims to assess changes in ecosystem C and nitrogen (N) cycling between chestnut and two contemporary species, northern red oak and black cherry, in soils from a 10-yr old plantation at Purdue University’s Martell Forest. We measured select pools and fluxes of C and N in field plots and implemented a one-year laboratory incubation of soil and litter material. From field plots, we measured total C and N in mineral soil, leaf litter and forest floor material, and standing biomass. From incubation cores, we measured cumulative CO2 respiration, N mineralization, and dissolved organic C from successive leaching events, and litter mass loss rates. Explanatory variables measured from the incubation include oxidizable C content, a suite of microbial extracellular enzymes, and tannin and lignin content to assess differences in organic matter chemistry and microbial function related to C cycling.
Results/Conclusions
From the incubation cores, tree species had no significant effect on cumulative CO2 respiration (p>0.05). N mineralization was lowest from soils with chestnut soil and litter (7.84) relative to cherry (11.51) and oak (12.02 mg N kg-1 soil). Mass loss of litter was greatest from chestnut (18.97%), relative to cherry (14.18%) and oak (10.83%), related to the differences in litter C:N ratio, where chestnut C:N was highest (40.82), relative to cherry (32.99) and oak (26.04). Oxidizable C content, reflective of microbial biomass, was also greatest in chestnut soils (334.31), relative to cherry (273.39) and oak (294.35 mg C kg-1 soil). Microbial extracellular enzyme activities reflect an N limitation in chestnut soil, as β-1,4-N-acetylglucosaminidase (NAG) activity was greatest in chestnut soil (2.10) relative to cherry (0.91) and oak (1.91 mmol h-1 g-1 soil). Overall, the soil ecosystem from chestnut plots has an accumulating microbial biomass with high nitrogen use efficiency (NUE), reflective of greater soil organic matter accumulation potential relative to co-occurring tree species black cherry and red oak.