Fig 1.
Conceptual framework of drought effects on fungal functional genes related to acquisition of carbon (e.g., cellulose-targeting AA9 genes) and nitrogen cycling (e.g., extracellular chitinase, amino acid permease, and ammonium transporter genes).
Drought can directly alter gene profiles via changes in the plot environment, or indirectly shift them via changes in the microbial community or plant litter chemistry (a). We tested predictions from three hypotheses, each related to a specific effect (b). Only the direct effect of drought in the plot environment altered fungal functional genes as predicted.
Fig 2.
Reciprocal transplant design for decomposition experiment.
We crossed plot environment, microbe origin, and litter origin in a fully factorial design. There were two levels for each treatment: control and drought. Control plots were unmanipulated, while drought plots received ~50% less rainfall.
Fig 3.
Frequencies of fungal functional genes related to N acquisition in the reciprocal litter transplant.
For each gene family, plot environment significantly altered gene frequencies (P < 0.001 in all cases, S1 Table). Microbial origin and litter origin were not significant in any case. Treatment combinations associated with different letters were significantly different from one another. Bars are means +1SE of 2 replicates. Asco = ascomycete, basidio = basidiomycete.
Fig 4.
Frequencies of fungal functional genes related to C acquisition in the reciprocal litter transplant.
Cellulose-targeting AA9 is an enzyme that targets crystalline cellulose. For each gene family, plot environment significantly altered gene frequencies (S1 Table, P < 0.001 in both cases). Microbial origin and litter origin were not significant in any case. Treatment combinations associated with different letters were significantly different from one another. Bars are means +1SE of 2 replicates. Asco = ascomycete, basidio = basidiomycete.
Fig 5.
Fungal hyphal lengths (an index of abundance) in litter from a reciprocal transplant.
Hyphal lengths were significantly greater in drought versus control plots (P = 0.026), and significantly lower in drought-derived versus control-derived microbial communities (P = 0.002). In addition, there was a significant plot environment x microbe origin x litter origin interaction (P = 0.018, S1 Table). Treatment combinations associated with different letters were significantly different from one another. Bars are means +1SE of 2 replicates.