Responses of microbial decomposers to drought in streams may depend on the environmental context

Abstract

A consequence of drought in streams is the emersion of decomposing leaf litter, which may alter organic matter recycling. We assessed the effects of emersion on decomposition of black poplar leaves and associated microbes (microbial biomass, extracellular enzyme activities and microbial diversity) in two streams with distinct characteristics, in particular nutrients, temperature and oxygen levels. Leaf decomposition rates, fungal biomass and extracellular enzyme activities were lower in the most impacted stream (high nutrients and temperature, low oxygen). Also, the structure of fungal and bacterial communities differed between streams. Emersion strongly affected all microbial functional measures. Leaf decomposition, fungal biomass and extracellular enzyme activities were more sensitive at the most pristine site, while fungal reproduction and bacterial biomass production were more affected by emersion at the most impacted stream. Microbial community structure was strongly altered after emersion. Although similar effects on leaf-associated microbes were found in both streams, functional responses to emersion differed probably as a consequence of different initial microbial communities with different sensitivity to the drying stress. Our study highlights the need of understanding the effects of drought in streams suffering from different environmental perturbations, since responses to emersion appear to depend on the environmental context.

Multi‐model assessment of hydrological and environmental impacts on streambed microbes in Mediterranean catchments

“…These microbial community responses might be a consequence of enhanced nutrient input from agricultural practices in the fields around the sites; this may induce bacterial growth and favour the spread of certain dominant species, thus reducing diversity, as expected in eutrophic conditions or nutrient‐contaminated systems (Zeglin, ; Li et al ., ). The negative effect of agricultural cover on bacterial diversity may be further enhanced by longer droughts (negative interaction T‐DRYxAGRI, Table ), as also suggested in previous studies on leaf litter decomposition and soils (Duarte et al ., ; Meisner et al ., ).…”

“…Physical characteristics, such as the type of streambed substrata (e.g. cobbles/bedrock, fine/coarse sediment, accumulation of leaf litter), can influence the microbial response to hydrological intermittency (Duarte et al, 2017;Arce et al, 2019). Headwaters are usually more heavily affected by natural intermittency than downstream areas, due to their hydro-morphological features (e.g.…”

Root Fungal Endophytes and Microbial Extracellular Enzyme Activities Show Patterned Responses in Tall Fescues under Drought Conditions

“…Bacteria and fungi both produce extracellular enzymes, and the increase in chitinase and phenol oxidase activities may signal a role in drought tolerance or recovery. Previous studies have shown that fungal and bacterial biomass and extracellular enzyme production often respond differently to drought and that they show distinct enzyme partitioning [50][51][52][53][54]. The interest in the role of drought in ecosystem functioning has not revealed a consistent response of microbial communities and extracellular enzyme activities to drought and recovery.…”

Response of stream fungi on decomposing leaves to experimental drying

“…Schlief and Mutz () noted slow breakdown and reduced microbial activity in a stream that became fragmented during a severe drought. Duarte, Mora‐Gómez, Romaní, Cássio, and Pascoal () found that breakdown rate and enzyme activities decreased in a stream following emersion.…”