Plant-plant competition outcomes are modulated by plant effects on the soil bacterial community.

Competition is a key process that determines plant community structure and dynamics, often mediated by nutrients and water availability. However, the role of soil microorganisms on plant competition, and the links between above- and belowground processes, are not well understood. Here we show that the effects of interspecific plant competition on plant performance are mediated by feedbacks between plants and soil bacterial communities. Each plant species selects a singular community of soil microorganisms in its rhizosphere with a specific species composition, abundance and activity. When two plant species interact, the resulting soil bacterial community matches that of the most competitive plant species, suggesting strong competitive interactions between soil bacterial communities as well. We propose a novel mechanism by which changes in belowground bacterial communities promoted by the most competitive plant species influence plant performance and competition outcome. These findings emphasise the strong links between plant and soil communities, paving the way to a better understanding of plant community dynamics and the effects of soil bacterial communities on ecosystem functioning and services.

Alpine cushion plants inhibit the loss of phylogenetic diversity in severe environments.

Biotic interactions can shape phylogenetic community structure (PCS). However, we do not know how the asymmetric effects of foundation species on communities extend to effects on PCS. We assessed PCS of alpine plant communities around the world, both within cushion plant foundation species and adjacent open ground, and compared the effects of foundation species and climate on alpha (within-microsite), beta (between open and cushion) and gamma (open and cushion combined) PCS. In the open, alpha PCS shifted from highly related to distantly related with increasing potential productivity. However, we found no relationship between gamma PCS and climate, due to divergence in phylogenetic composition between cushion and open sub-communities in severe environments, as demonstrated by increasing phylo-beta diversity. Thus, foundation species functioned as micro-refugia by facilitating less stress-tolerant lineages in severe environments, erasing a global productivity - phylogenetic diversity relationship that would go undetected without accounting for this important biotic interaction.

Environmental and physiological factors governing nutrient resorption efficiency in barley.

Barley plants (Hordeum vulgare cv. stepto) were grown in a greenhouse under two nutrient and water levels and four treatments intended to alter sourcesink relationships, in a factorial experiment designed to study factors governing efficiency of nutrient resorption from senescing leaves. Plant growth was enhanced in high-nutrient treatments, leading to higher concentrations of nitrogen (N) and phosphorus (P) in leaves and ears. Water stress reduced growth, but plants in waterstressed treatments had equal or higher nutrient concentrations than watered plants. Nutrient resorption efficiency was higher at low than at high nutrient availability, and was higher in watered than in water-stressed plants. Treatments in which sink strength was increased had enhanced resorption efficiency, as well as those in which the source activity was reduced. Our data show that the amount of nutrient resorbed and the efficiency of the resorption process depend on plant nutrient and water status, and that the presence of an active sink strongly enhances nutrient resorption.