Warming weakens facilitative interactions between decomposers and detritivores, and modifies freshwater ecosystem functioning

Abstract

Warming is among the major drivers of changes in biotic interactions and, in turn, ecosystem functioning. The decomposition process occurs in a chain of facilitative interactions between detritivores and microorganisms. It remains unclear, however, what effect warming may have on the interrelations between detritivores and microorganisms, and the consequences for the functioning of natural freshwater ecosystems. To address these gaps, we performed a field experiment using tank bromeliads and their associated aquatic fauna. We manipulated the presence of bacteria and detritivorous macroinvertebrates (control, "bacteria," and "bacteria + macroinvertebrates") under ambient and warming scenarios, and analyzed the effects on the microorganisms and ecosystem functioning (detritus mass loss, colored dissolved organic matter, and nitrogen flux). We applied antibiotic solution to eliminate or reduce bacteria from control bromeliads. After 60 days incubation, bacterial density was higher in the presence than in the absence of macroinvertebrates. In the absence of macroinvertebrates, temperature did not influence bacterial density. However, in the presence of macroinvertebrates, bacterial density decreased by 54% with warming. The magnitude of the effects of organisms on ecosystem functioning was higher in the combined presence of bacteria and macroinvertebrates. However, warming reduced the overall positive effects of detritivores on bacterial density, which in turn, cascaded down to ecosystem functioning by decreasing decomposition and nitrogen flux. These results show the existence of facilitative mechanisms between bacteria and detritivores in the decomposition process, which might collapse due to warming. Detritivores seem to contribute to nutrient cycling as they facilitate bacterial populations, probably by increasing nutrient input (feces) in the ecosystem. However, increased temperature mitigated these beneficial effects. Our results add to a growing research body that shows that warming can affect the structure of aquatic communities, and highlight the importance of considering the interactive effects between facilitation and climatic drivers on the functioning of freshwater ecosystems.

Biogeographic context dependence of trophic cascade strength in bromeliad food webs

“…The stronger influence of bacteria, relative to macroinvertebrates, on decomposition in the Brazilian restinga may be a result of the drier, warmer conditions than the other sites, influencing both leaf litter digestibility and microbial metabolic rates, and has recently been supported in manipulative experiments (Bernabé et al. ).…”

Arthropod–bacteria interactions influence assembly of aquatic host microbiome and pathogen defense

“…Environmental bacterial reservoirs may be particularly important to the microbiomes of aquatic hosts because the whole organism is in continual contact with bacteria in the water column [9]. Biotic community interactions are important drivers of environmental bacterial community structure [10,11]. For example, invertebrate detritivores are closely associated with environmental bacteria in aquatic ecosystems, and together they play a pivotal role in ecosystem functions such as detritus processing and nutrient cycling, with invertebrates both consuming and providing nutrients to bacterial communities [10,12].…”

“…Biotic community interactions are important drivers of environmental bacterial community structure [10,11]. For example, invertebrate detritivores are closely associated with environmental bacteria in aquatic ecosystems, and together they play a pivotal role in ecosystem functions such as detritus processing and nutrient cycling, with invertebrates both consuming and providing nutrients to bacterial communities [10,12]. However, the cascading effects of these biotic interactions on host microbiome structure and pathogen resistance are not well understood.…”

Changes in rainfall level and litter stoichiometry affect aquatic community and ecosystem processes in bromeliad phytotelmata

“…Also, changes in the litter N:P ratios can influence the survivorship (Migliorini, Srivastava, & Romero, 2018) and performance of aquatic insects living in tank bromeliads (González, Romero, & Srivastava, 2014). Tank bromeliads have been successfully used as natural microcosms to investigate the isolated impacts of environmental changes, such as rainfall regimes, warming and productivity, on community structure and ecosystem functioning (Amundrud & Srivastava, 2016;Antiqueira, Petchey, & Romero, 2018;Bernabé et al, 2018;Dézerald, Céréghino, Corbara, Dejean, & Leroy, 2015;Pires et al, 2016). These studies have reported that decreases in rainfall amount and more consecutive dry days lead to less dilution and leaching of nutrients from bromeliad phytotelmata (Richardson et al, 2000), concentrating the nutrients inside the tank.…”

“…In addition, due to the fact that bromeliad water derives from rainwater (Kitching, 2004), rises in rainfall will increase the water volume of the ecosystem, and reduce the risk of drought (Amundrud & Srivastava, 2016;Dézerald et al, 2015), increasing habitat availability for colonisation by new organisms (Srivastava, 2006). Such an increase is expected to stimulate an increase of zooplankton density and macroinvertebrate abundance, which, in turn, could trigger predation pressure upon bacteria populations (Bernabé et al, 2018), thus decreasing their density even more. Some of these changes will have a positive effect on ecosystem functioning by enhancing litter decomposition and N flux (Prediction 2).…”