Plant species richness regulates soil respiration through changes in productivity

Soil respiration is an important pathway of the C cycle. However, it is still poorly understood how changes in plant community diversity can affect this ecosystem process. Here we used a long-term experiment consisting of a gradient of grassland plant species richness to test for effects of diversity on soil respiration. We hypothesized that plant diversity could affect soil respiration in two ways. On the one hand, more diverse plant communities have been shown to promote plant productivity, which could increase soil respiration. On the other hand, the nutrient concentration in the biomass produced has been shown to decrease with diversity, which could counteract the production-induced increase in soil respiration. Our results clearly show that soil respiration increased with species richness. Detailed analysis revealed that this effect was not due to differences in species composition. In general, soil respiration in mixtures was higher than would be expected from the monocultures. Path analysis revealed that species richness predominantly regulates soil respiration through changes in productivity. No evidence supporting the hypothesized negative effect of lower N concentration on soil respiration was found. We conclude that shifts in productivity are the main mechanism by which changes in plant diversity may affect soil respiration

The effects of leaf traits on litter rainfall interception with consequences for runoff and soil conservation

During rainfall, plant litter interception regulates overland flow with an impact on water runoff generation and sediment displacement. Besides the rainfall characteristics, the effects of litter mass, thickness, storage and drainage properties on rainfall interception are reasonably well understood. In contrast, less is known about the influence of leaf traits, which we hypothesized to affect interception, soil hydrology and conservation via litter structure assembly. We measured the runoff and soil loss generation as determined by litter layer structural and hydraulic properties of 16 coexisting tropical woody species with wide-range morphological leaf traits in a rainfall simulator experiment. Our results show that litter produced by coexisting species can differ in precipitation interception, thereby influencing runoff and soil loss. This is because there is important interspecific variation in litter water storage and drainage, which are negatively affected by leaf area (LA). Leaf water repellency positively affected litter water storage. Moreover, LA also negatively affected litter layer density. Litter density, in turn, increased runoff, but decreased soil loss, possibly due to protection against splash erosion. These results can be used to predict the effects of plant traits on the soil water balance and soil integrity protection through ecohydrological interception by the litter layer. The next research steps will be to extend our model to multiple-species litter layers, and to validate and calibrate our model in different field situations in different ecosystems. Synthesis: We revealed the direct and indirect effects of species leaf size and hydraulic traits on litter rainfall interception, runoff and soil loss. We propose a new litter-soil ecohydrological model, by using structural equation models, which can be used as a tool to predict ecosystem functioning, and guide management and restoration actions with water and soil conservation targets.</p

The effects of leaf traits on litter rainfall interception with consequences for runoff and soil conservation

During rainfall, plant litter interception regulates overland flow with an impact on water runoff generation and sediment displacement. Besides the rainfall characteristics, the effects of litter mass, thickness, storage and drainage properties on rainfall interception are reasonably well understood. In contrast, less is known about the influence of leaf traits, which we hypothesized to affect interception, soil hydrology and conservation via litter structure assembly. We measured the runoff and soil loss generation as determined by litter layer structural and hydraulic properties of 16 coexisting tropical woody species with wide-range morphological leaf traits in a rainfall simulator experiment. Our results show that litter produced by coexisting species can differ in precipitation interception, thereby influencing runoff and soil loss. This is because there is important interspecific variation in litter water storage and drainage, which are negatively affected by leaf area (LA). Leaf water repellency positively affected litter water storage. Moreover, LA also negatively affected litter layer density. Litter density, in turn, increased runoff, but decreased soil loss, possibly due to protection against splash erosion. These results can be used to predict the effects of plant traits on the soil water balance and soil integrity protection through ecohydrological interception by the litter layer. The next research steps will be to extend our model to multiple-species litter layers, and to validate and calibrate our model in different field situations in different ecosystems. Synthesis: We revealed the direct and indirect effects of species leaf size and hydraulic traits on litter rainfall interception, runoff and soil loss. We propose a new litter-soil ecohydrological model, by using structural equation models, which can be used as a tool to predict ecosystem functioning, and guide management and restoration actions with water and soil conservation targets

Le Brésil

L’histoire de l’art qui se forge au Brésil embrasse une variété d’objets exigeant des approches ambitieuses et expérimentales. Débattant avec les conventions historiographiques, elle se révèle ici connectée aux mondes anciens, nouveaux, parallèles et à venir puisqu’elle réinvente les catégories fécondes de l’art, des artefacts, de l’archéologie, du modernisme, du patrimoine, du baroque, du musée… Ce numéro est vente sur le site du Comptoir des presses d'universités

As relações econômicas internacionais do Brasil dos anos 1950 aos 80 Brazil's international economic relations, from 1950s to 1980s

Ensaio histórico sobre as relações econômicas internacionais do Brasil dos anos 1950 aos 80, evidenciando as mudanças nos principais fluxos comerciais e financeiros, no quadro da economia mundial. O Brasil preserva uma postura defensiva, em função de restrições cambiais e de fragilidades financeiras que são recorrentes nesse período.<br>Historical essay on international economic relations of Brazil since the 1950s up to the end of military regime, in 1985. Important changes are observed in the main flows in trade and finance, within world economy. Brazil keeps its defensive stance, in order to adjust to serious exchange restrictions and financial fragilities, a recurring trend during that period