Acetic acid plays a crucial role in the organoleptic balance of many fermented products. We have investigated the factors controlling the production of acetate by Saccharomyces cerevisiae during alcoholic fermentation by metabolic engineering of the enzymatic steps involved in its formation and its utilization. The impact of reduced pyruvate decarboxylase (PDC), limited acetaldehyde dehydrogenase (ACDH), or increased acetoacetyl coenzyme A synthetase (ACS) levels in a strain derived from a wine yeast strain was studied during alcoholic fermentation. In the strain with the PDC1 gene deleted exhibiting 25% of the PDC activity of the wild type, no significant differences were observed in the acetate yield or in the amounts of secondary metabolites formed. A strain overexpressing ACS2 and displaying a four-to sevenfold increase in ACS activity did not produce reduced acetate levels. In contrast, strains with one or two disrupted copies of ALD6, encoding the cytosolic Mg 2؉ -activated NADP-dependent ACDH and exhibiting 60 and 30% of wild-type ACDH activity, showed a substantial decrease in acetate yield (the acetate production was 75 and 40% of wild-type production, respectively). This decrease was associated with a rerouting of carbon flux towards the formation of glycerol, succinate, and butanediol. The deletion of ALD4, encoding the mitochondrial K ؉ -activated NAD(P)-linked ACDH, had no effect on the amount of acetate formed. In contrast, a strain lacking both Ald6p and Ald4p exhibited a long delay in growth and acetate production, suggesting that Ald4p can partially replace the Ald6p isoform. Moreover, the ald6 ald4 double mutant was still able to ferment large amounts of sugar and to produce acetate, suggesting the contribution of another member(s) of the ALD family.

In Europe, like in many temperate lowlands worldwide, forest has a long history of fragmentation and land use change. In many places, forest landscapes consist of patches of different quality, age, size and isolation, embedded in a more or less intensively managed agricultural matrix. As potential biodiversity islets, small forest patches (SFP) may deliver several crucial ecosystem services to human society, but they receive little attention compared to large, relatively intact forest patches. Beyond their role as a biodiversity reservoir, SFP provide important in situ services such as timber and wild food (game, edible plants and mushrooms) production. At the landscape scale, SFP may enhance the crop production via physical (obstacle against wind and floods) and biological (sources of pollinators and natural enemies) regulation, but may, on the other hand, also be involved in the spread of infectious diseases. Depending on their geographic location, SFP can also greatly influence the water cycle and contribute to supply high-quality water to agriculture and people. Globally, SFP are important carbon sinks and are involved in nutrient cycles, thus play a role in climate change mitigation. Cultural services are more related to landscape values than to SFP per se, but the latter may contribute to the construction of community identity. We conclude that SFP, as local biodiversity hotspots in degraded landscapes, have the potential to deliver a wide range of ecosystem services and may even be crucial for the ecological intensification of agroecosystems. There is thus an urgent need to increase our knowledge about the relationships between biodiversity and ecosystem services delivered by these SFP in agricultural landscapes.

Amount of semi‐natural habitats (permanent grasslands, woodlands and hedgerows) and their level of fragmentation are among the main determinants of wild bee diversity in agricultural landscapes. However, their impact on the distribution of bee ecological traits has received little attention. In this study, we aimed to explore whether changes in the distribution of bee ecological traits along gradients of habitat amount and fragmentation were due to a direct effect of landscape context on multiple traits (‘response traits’) or to a correlation of response traits with other ecological traits not involved in the response of bee species to landscape context. In two study regions in southwest France and southeast Australia, we used a RLQ analysis (three‐table ordination method) to link bee traits with habitat amount and fragment isolation measured at the landscape scale. We found that bee ecological traits shifted at the community‐level in association with landscape gradients, whereas species‐level associations among bee traits and phylogenetic clustering in bee communities were of only minor importance in determining such shifts. We found that traits such as body size and nest location were closely linked to habitat amount and fragmentation. We also observed regionally‐specific relationships among ecological traits, suggesting that the regional species pool can play an important role in determining the response of bee communities to habitat amount and fragmentation. Our findings suggest that improved knowledge about how trait‐based responses mediate the impact of landscapes on wild bee communities will allow better prediction and understanding of subsequent effects on ecosystem functioning.

Aim: Macroclimate is a major determinant of large-scale diversity patterns. However, the influence of smaller-scale factors on local diversity across large spatial extents is not well documented. Here, we quantify the relative importance of local (patch-scale), landscape-scale and macroclimatic drivers of herbaceous species diversity in small forest patches in agricultural landscapes across Europe. Location: Deciduous forest patches in eight regions along a macroclimatic gradient from southern France to central Sweden and Estonia. Methods: The diversity of forest specialists and generalists at three levels (whole forest patch, sampling plots within patches and between scales) was related to patch-scale (forest area, age, abiotic and biotic heterogeneity), landscape-scale (amount of forest, grasslands and hedgerows around the patch, patch isolation) and macroclimatic variables (temperature and precipitation) using generalized linear mixed models and variation partitioning for each group of variables. Results: The total amount of explained variation in diversity ranged from 8% for plot-scale diversity of generalists to 54% for patch-scale diversity of forest specialists. Patch-scale variables always explained more than 60% of the explained variation in diversity, mainly due to the positive effect of within-patch heterogeneity on patch-scale and between-scale diversities and to the positive effect of patch age on plot-scale diversity of forest specialists. Landscape-scale variables mainly contributed to the amount of explained variation in plot-scale diversity, being more important for forest specialists (21%) than for generalists (18%). Macroclimatic variables contributed a maximum of 11% to the plot-scale diversity of generalists. Main conclusions: Macroclimate poorly predicts local diversity across Europe, and herbaceous diversity is mainly explained by habitat features, less so by landscape structure. We show the importance of conserving old forest patches as refugia for typical forest species, and of enhancing the landscape context around the patches by reducing the degree of disturbance caused by agriculture

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