Physiological adaptations of leaf litter microbial communities to long-term drought

Abstract

Drought represents a significant stress to soil microorganisms and is known to reduce microbial activity and organic matter decomposition in Mediterranean ecosystems. However, we still lack a detailed understanding of the drought stress adaptations of microbial decomposers. We hypothesised that drought causes greater microbial allocation to stress tolerance relative to growth pathways. Here we present metatranscriptomic and metabolomic data on the physiological response of in situ microbial communities on plant leaf litter to long-term drought and pulse wetting in Californian grass and shrub ecosystems. Wetting litter after a long dry summer caused only subtle shifts in gene expression. On grass litter, communities from the decade-long ambient and reduced precipitation treatments had distinct functional profiles. The most discernable physiological adaptations to drought were production or uptake of compatible solutes to maintain cellular osmotic balance, and synthesis of capsular and extracellular polymeric substances as a mechanism to retain water. The results show a clear functional response to drought in grass litter communities with greater allocation to survival relative to growth that could affect decomposition under drought. In contrast, communities on chemically more diverse and complex shrub litter had smaller physiological differences in response to long-term drought but higher investment in resource acquisition traits across treatments, suggesting that the functional response to drought is constrained by substrate quality. Our findings suggest, for the first time in a field setting, a trade-off between microbial drought stress tolerance, resource acquisition and growth traits in leaf litter microbial communities.Introduction:

Ocean acidification induces subtle shifts in gene expression and DNA methylation in mantle tissue of the Eastern oyster (Crassostrea virginica)

“…The subtle molecular responses of C. virginica found in this study contrasted the more severe transcriptomic responses exhibited by other marine calcifying taxa in response to OA (e.g., Li et al 2016). However, other examples of subtle gene expression shifts in response to environmental change do exist (Malik et al, 2019) , and these minor shifts can still have phenotypic consequences (Wu et al, 2010) . In C. virginica , these subtle molecular responses may be the result of; (i) extended evolution under regular extreme OA conditions, (ii) constrained plasticity of the mantle (e.g., an evolved canalization of gene expression in response to OA), and/or (iii) a highly polygenic genetic response architecture.…”

Bacterial Tradeoffs in Growth Rate and Extracellular Enzymes

“…All PB was made using the same litter batch to ensure consistent nutrient conditions. Although we did not analyze PB directly, metabolomic analysis on cold water extracts from grass litter suggests that PB composition is dominated by amino acids, organic acids, nucleosides, and other low molecular weight compounds (Malik et al, 2019b). Therefore, compared to LB, PB is likely more representative of the environment from which the bacteria were originally isolated.…”

Disentangling drivers of soil microbial potential enzyme activity across rain regimes: An approach based on the functional trait framework

“…Such trade-off (Fig. 1) needs further investigations using molecular and culturing approaches (Malik et al, 2019c;Ramin and Allison, 2019). Even if such trade-off across microbial diversity could justify to interpret these SEM paths accordingly (community composition affecting biomass-C), we acknowledge that a feedback might exist between community composition and biomass-C, with high biomass-C potentially influencing community composition by favouring competitive microbes.…”

“…However, oligotrophic communities as indicated by PCoA-1 were likely characterized by a lower investment in biomass production (Fig. 1) (Malik et al, 2019a(Malik et al, , 2019c. The positive effect of bacterial community composition on biomass-specific activity, translating into a negative effect on biomass suggests that oligotrophic communities invest relatively more C in non-growth products such as enzymes (Malik et al, 2019a).…”

“…However, Piton et al (2020) demonstrated that measuring biomass-specific potential enzyme activity (potential activity per unit of microbial biomass) and enzyme stoichiometry give a direct approximation of community-weighted mean (CWM) traits representative of the dominant strategy in the microbial community. Using such indicators, Malik et al (2019c) and Piton et al (2020) observed decreases in mass-specific extracellular potential enzyme activity along soil resource gradients. Their results indicate that oligotrophic microbes invest more in the production of extracellular enzymes as compared to copiotrophic Fig.…”