Abstract
Although water is a critical resource for organisms, microbially-mediated processes such as decomposition and nitrogen (N) transformations can endure within ecosystems even when water is scarce. To identify underlying mechanisms, we examined the genetic potential for fungi to contribute to specific aspects of carbon (C) and N cycling in a drought manipulation in Southern California grassland. In particular, we measured the frequency of fungal functional genes encoding enzymes that break down cellulose and chitin, and take up ammonium and amino acids, in decomposing litter. Furthermore, we used “microbial cages” to reciprocally transplant litter and microbes between control and drought plots. This approach allowed us to distinguish direct effects of drought in the plot environment versus indirect effects via shifts in the microbial community or changes in litter chemistry. For every fungal functional gene we examined, the frequency of that gene within the microbial community increased significantly in drought plots compared to control plots. In contrast, when plot environment was held constant, frequencies of these fungal functional genes did not differ significantly between control-derived microbes versus drought-derived microbes, or between control-derived litter versus drought-derived litter. It appears that drought directly selects for fungi with the genetic capacity to acquire these specific C- and N-containing compounds. This genetic trait may allow fungi to take advantage of ephemeral water supplies. Altogether, proliferation of fungi with the genetic capacity for C and N acquisition may contribute to the maintenance of biogeochemical cycling under drought.
Highlights
Fungi can be remarkably drought tolerant—they can remain active and even grow under extremely dry conditions [1, 2]
We had hypothesized that drought in the plot environment would directly induce an increase in frequencies of fungal functional genes related to Cand N-acquisition
This response was consistent across taxonomic groups; ascomycetes and basidiomycetes each displayed significant increases in chitinase (Fig 3) and cellulose-targeting AA9 gene frequencies (Fig 4)
Summary
Fungi can be remarkably drought tolerant—they can remain active and even grow under extremely dry conditions [1, 2]. Fungal abundance can increase under drought [3,4,5,6,7,8]. Fungi have a number of traits that can mitigate drought stress, including osmolytes, thick cell walls, and melanin [9,10,11]. Drought and fungal functional genes (www.energy.gov), under Award Numbers DEPS02-09ER09-25 and DE-SC001641 to SDA, ACM, and KKT
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