The forest floor (FF) plays a key role in carbon, nutrient, and water cycling. It is the biologically most active compartment of forest soils, highly responsive to environmental conditions. Yet, its response to current changes in environmental conditions and forest management is understudied. Temperate forests are among the best studied ecosystems globally, providing the necessary ecological and biogeochemical background information to assess FF changes. Here, we focus on identifying existing knowledge and gaps in our understanding of the functioning of the FF. Interactions between FF biota and abiotic FF components show multifactorial dependencies with environmental conditions and drive FF turnover. Vice versa, the turnover of FF regulates carbon, nutrient, and water cycling. With slow litter decomposition and limited bioturbation, organic matter accumulates, nutrients cycle tightly within the FF, and water passes through this layer partly along preferential pathways. With rapid litter decomposition and intense bioturbation, FF accumulation is little, the mineral soil is the main nexus for plant nutrient uptake and organic matter transformation, and water infiltrates the mineral soil more homogeneously. The interconnectedness with the adjacent ecosystem compartments is a crucial feature of the FF, feeding back to its functioning and making it a central hub of forest processes. The FF morphology reflects these processes and therefore has untapped potential as an indicator of soil and ecosystem health. Under forest change, the FF might lose its functionality, with negative impacts on nutrient provision, water storage, and carbon sequestration. Consequences for forest growth could be strong and even detrimental. Hence, improved knowledge of FF characteristics and their linkages to mineral soils and aboveground ecosystem compartments is crucial for assessing forest resilience to progressing environmental changes.
Friederike Lang, J. Prietzel, Frank Hagedorn et al.· Global Change Biology· 0 citations
ABSTRACT Monosodium glutamate (MSG; L-glutamate monosodium salt) is among the most widely used flavor enhancers, yet its molecular effects on gut microbial physiology remain poorly understood. Here, we examined the strain-specific transcriptomic and metabolic responses of Clostridium butyricum and Bacteroides thetaiotaomicron grown in pure anaerobic culture with 0.1% (wt/vol) MSG. Although MSG exposure was not associated with major changes in total bacterial biomass dynamics, both species showed a temporal functional reprogramming. In C. butyricum, MSG rapidly intensified metabolic activity to capitalize on exogenous glutamate by activating central carbon metabolism, redox-balancing pathways, and the GABA shunt, thereby collectively enhancing butyrate synthesis, a metabolite associated with gut barrier integrity, energy regulation, and anti-inflammatory signaling. On the other hand, B. thetaiotaomicron adopted a conservative, homeostatic response, suppressing glycan utilization and central carbon and energy metabolism, and maintaining stable SCFA production through controlled regulation that buffered against abrupt dietary perturbations. Overall, MSG functioned as a potent metabolic signal, triggering distinct adaptive strategies in two dominant gut bacteria. IMPORTANCE The impact of monosodium glutamate (MSG) as a highly consumed food additive on the gut microbiome is often overlooked, and community-level analyses reveal little change, masking distinct phenotypic responses of individual strains. By combining gene expression and metabolite profiling using two key human gut bacteria, we show that MSG is sensed as a metabolic signal. A butyrate-producing gut bacterium increases energy metabolism and butyrate production, and a fiber-degrading gut bacterium transiently moderates metabolism to maintain stable fermentation products. These differences suggest that MSG's physiological effects may depend on which bacterial groups dominate an individual’s microbiome. The impact of monosodium glutamate (MSG) as a highly consumed food additive on the gut microbiome is often overlooked, and community-level analyses reveal little change, masking distinct phenotypic responses of individual strains. By combining gene expression and metabolite profiling using two key human gut bacteria, we show that MSG is sensed as a metabolic signal. A butyrate-producing gut bacterium increases energy metabolism and butyrate production, and a fiber-degrading gut bacterium transiently moderates metabolism to maintain stable fermentation products. These differences suggest that MSG's physiological effects may depend on which bacterial groups dominate an individual’s microbiome.
Nazanin Nematzadeh Somehsaraei, Joshua Lemuel Hadi, M. Khan Mirzaei et al.· Msphere· 0 citations