The combined impact of soil tillage intensification and expansion of olive farming is resulting in soil degradation and biodiversity decline. We hypothesized that, instead of tilling, mowing to control the natural vegetation in spring can increase biodiversity and improve soil quality. We compared the effects of natural vegetation mowing (NVM) with those of tillage (NVT) on plant community composition and cover, soil water content and resistance to penetration, and olive yield over an 8-year period, in a Mediterranean rainfed olive orchard. NVM had an average of 28 more species and showed a strong positive correlation with Poaceae and Fabaceae, and also with geophytes and hemicryptophytes. In contrast, NVT was negatively correlated with species richness and diversity, with perennial life forms, and positively correlated with Convolvulaceae. Proportions of grass and straw cover in spring were higher in NVM from the beginning of the study (average difference was about 20%). In autumn, grass cover became higher in NVM than in NVT from year five (13% more) and straw cover from year two (30% more). Olive production did not differ between treatments in any of the years. Soil water was higher in NVM, at both soil depths, particularly in mid-summer and after the first autumn rains (1 to 2%). Soil resistance to penetration was 1 Mpa higher in NVM than in NVT. As compared to conventional tillage, natural vegetation cover mowed in spring seems to be an effective management practice to improve the overall rainfed olive orchard biodiversity and soil quality, without affecting production.

Assuming that dispersal modes or abilities can explain the different responses of organisms to geographic or environmental distances, the distance-decay relationship is a useful tool to evaluate the relative role of local environmental structuring versus regional control in community composition. Based on continuing the current theoretical framework on metacommunity dynamics and based on the predictive effect of distance on community similarity, we proposed a new framework that includes the effect of spatial extent. In addition, we tested the validity of our proposal by studying the community similarity among three biotic groups with different dispersal modes (macrofaunal active and passive dispersers and plants) from two pond networks, where one network had a small spatial extent, and the other network had an extent that was 4 times larger. Both pond networks have similar environmental variability. Overall, we found that environmental distance had larger effects than geographical distances in both pond networks. Moreover, our results suggested that species sorting is the main type of metacommunity dynamics shaping all biotic groups when the spatial extent is larger. In contrast, when the spatial extent is smaller, the observed distance-decay patterns suggested that different biotic groups were mainly governed by different metacommunity dynamics. While the distance-decay patterns of active dispersers better fit the trend that was expected when mass effects govern a metacommunity, passive dispersers showed a pattern that was expected when species sorting prevails. Finally, in the case of plants, it is difficult to associate their distance-decay patterns with one type of metacommunity dynamics.

Bacterial endophytes, a subset of a plant’s microbiota, can facilitate plant growth by a number of different mechanisms. The aims of this study were to assess the diversity and functionality of endophytic bacterial strains from internal root tissues of native legume species grown in two distinct sites in South of Portugal and to evaluate their ability to promote plant growth. Here, 122 endophytic bacterial isolates were obtained from 12 different native legume species. Most of these bacteria possess at least one of the plant growth-promoting features tested in vitro, with indole acetic acid production being the most common feature among the isolates followed by the production of siderophores and inorganic phosphate solubilization. The results of in planta experiments revealed that co-inoculation of chickpea plants with specific endophytic bacteria along with N₂-fixing symbionts significantly improved the total biomass of chickpea plants, in particular when these plants were grown under saline conditions. Altogether, this study revealed that Mediterranean native legume species are a reservoir of plant growth-promoting bacteria, that are also tolerant to salinity and to toxic levels of Mn. Thus, these bacterial endophytes are well adapted to common constraints present in soils of this region which constitutes important factors to consider in the development of bacterial inoculants for stressful conditions in the Mediterranean region.