Short-term impacts of Frangula alnus litter on forest soil properties

Background/Question/Methods

If the litter of invasive plants differs from native species in its chemical composition, then invasion may alter the soil. The carbon (C) quality of invasive leaf litter is a potential mechanism for soil alteration. The objective of this study was to examine the short-term impacts various C additions have on soil microorganisms and soil properties with a particular focus on the litter of the invasive species Frangula alnus. In situ soil rings (6 cm in diameter) were identified in a native forest plot (Quercus rubra overstory). Subsets of soil rings received the following aqueous treatments: deionized water, dextrose (a labile C source), cellulose (a moderately labile C source), a water soluble extract of Q. rubra leaves (native species), and a water soluble extract of F. alnus leaves (n = 7).  Soil cores (top 10 cm) were collected prior to treatment and 1, 2, and 4 weeks after treatment and analyzed for microbial biomass C (MBC), extractable inorganic nitrogen (N), and permanganate oxidizable C (POXC). Data were tested with a 2-way ANOVA to determine differences among treatments and sampling events (α = 0.05).

Results/Conclusions

MBC was not different among C treatments at any sampling period, and MBC and POXC had no correlation (r² = 0.05; p = 0.389). Both of these results suggest that C quantity and quality were not driving microbial abundance in our study site. During weeks 1 and 2 extractable N in the soil that received F. alnus extract significantly increased from the pre-treatment level (7.5 mg N kg soil^-1) to 41 and 46 mg N kg soil^-1, respectively. Extractable N in the soil of the other treatments did not significantly increase from the pre-treatment level. Due to the F. alnus extract providing a negligible amount of total N (0.045 mg N kg soil^-1), we suspect that N mineralization was enhanced by the addition of the soluble fraction of F. alnus litter. This research suggests that F. alnus litter may alter soil properties by changing N cycling in invaded systems.