Interactive effects of past land use and recent forest management on the understorey community in temperate oak forests in South Sweden

Questions: Past agricultural land use and forest management have shaped and influenced the understorey composition in European forests for centuries. We investigated whether understorey vegetation assemblages are affected by (a) legacies from a historical infield/outland agricultural system (i.e., a system with nutrient-enriched vs nutrient-depleted areas), (b) recent management intensity (i.e., thinning/felling activities), and (c) the interaction of recent management and potential legacies. Location: Oak forests in Skane, south Sweden. Methods: We use three vegetation surveys (1983, 1993/94 and 2014) and notes on management and land-use history, available for 62 permanent 500 m(2) plots. We conducted linear mixed effect modelling to detect both main and interactive effects of past land use and recent management on understorey diversity measures and vegetation indicator values for light and fertility. We combined nonmetric multidimensional scaling with permutational multivariate analysis of variance and indicator species analysis to detect compositional differences caused by past land use and/or recent management. Results: Understorey diversity was mainly affected by management activities, but the former infield/outland agricultural system was an important determinant of understorey composition. Understorey composition of former infields reflected higher nutrient availability and lower light availability compared to former outland. Past land use and recent management had interactive effects on light-related understorey variables: for the less intensively managed plots, the outland plots contained more light-demanding species than the infield plots, while for the more intensively managed plots, the light-demanding signature of the understorey was similar for infield and outland plots. Conclusions: Different intensities of past land use as well as recent forest management influenced the composition of the forest understorey, and interactions were present. Therefore, careful consideration of both the long-term land-use history and the more recent disturbances due to forest management are necessary when making future predictions of understorey composition and diversity

Antimicrobial Actions of Reactive Oxygen Species

Everything should be as simple as it can be, but not simpler.—Attributed to Albert Einstein (1

Tree species identity outweighs the effects of tree species diversity and forest fragmentation on understorey diversity and composition

Background & aim – In general, biodiversity has positive effects on ecosystem functioning. In forests, understorey vegetation is influenced by both the composition and species richness of the overstorey through species-specific effects on environmental conditions at the forest floor. Forest fragmentation is also known to influence understorey vegetation composition and richness. However, the combined effects of tree species diversity and forest fragmentation have not been studied yet. With the TREEWEB research platform, consisting of 53 forest plots along a tree species diversity and forest fragmentation gradient, we aim to unravel the combined effects of tree species diversity, tree species identity and forest fragmentation on the understorey composition and diversity.Methods – The TREEWEB platform includes forest plots of three tree species richness levels, containing all possible species combinations of Quercus robur, Quercus rubra and Fagus sylvatica. Complete dilution is avoided in the design, allowing separation between tree species identity and diversity effects. Vegetation surveys were conducted in all plots to investigate the species richness, species diversity, compositional turnover and cover of the herb layer as well as the shrub layer cover.Key results – Within the TREEWEB platform, overstorey-understorey diversity relationships were mainly characterised by tree species identity effects. No clear effects of tree species diversity and forest fragmentation on understorey composition and diversity were found.Conclusion – Tree species identity effects were most important in explaining the observed patterns in the understorey vegetation. Further in-depth research will allow us to disentangle which mechanisms underlie these patterns and whether effects of fragmentation are more pronounced at higher trophic levels

Salmonella Mitigates Oxidative Stress and Thrives in the Inflamed Gut by Evading Calprotectin-Mediated Manganese Sequestration

Neutrophils hinder bacterial growth by a variety of antimicrobial mechanisms, including the production of reactive oxygen species and the secretion of proteins that sequester nutrients essential to microbes. A major player in this process is calprotectin, a host protein that exerts antimicrobial activity by chelating zinc and manganese. Here we show that the intestinal pathogen Salmonella enterica serovar Typhimurium employs specialized metal transporters to evade calprotectin sequestration of manganese, allowing the bacteria to outcompete commensals and thrive in the inflamed gut. The pathogen’s ability to acquire manganese in turn promotes function of SodA and KatN, enzymes that utilize the metal as a cofactor to detoxify reactive oxygen species. This manganese-dependent SodA activity allows the bacteria to evade neutrophil killing mediated by calprotectin and reactive oxygen species. Thus, manganese acquisition enables S. Typhimurium to overcome host antimicrobial defenses and support its competitive growth in the intestine