Fagus sylvatica seedlings show provenance differentiation rather than adaptation to soil in a transplant experiment.

BACKGROUND: Understanding and predicting the response of tree populations to climate change requires understanding the pattern and scale of their adaptation. Climate is often considered the major driver of local adaptation but, although biotic factors such as soil pathogens or mutualists could be as important, their role has typically been neglected. Biotic drivers might also interact with climate to affect performance and mycorrhizae, in particular, are likely to play a key role in determining drought resistance, which is important in the context of adaptation to future environmental change. To address these questions, we performed a fully reciprocal soil-plant transplant experiment using Fagus sylvatica seedlings and soils from three regions in Germany. To separate the biotic and abiotic effects of inoculation, half of the plants were inoculated with natural soil from the different origins, while the rest were grown on sterilized substrate. We also imposed a drought stress treatment to test for interactions between soil biota and climate. After 1 year of growth, we measured aboveground biomass of all seedlings, and quantified mycorrhizal colonization for a subset of the seedlings, which included all soil-plant combinations, to disentangle the effect of mycorrhiza from other agents. RESULTS: We found that plant origin had the strongest effect on plant performance, but this interacted with soil origin. In general, trees showed a slight tendency to produce less aboveground biomass on local soils, suggesting soil antagonists could be causing trees to be maladapted to their local soils. Consistently, we found lower mycorrhizal colonization rate under local soil conditions. Across all soils, seedlings from low elevations produced more annual biomass than middle (+ 290%) and high (+ 97%) elevations. Interestingly, mycorrhizal colonization increased with drought in the two provenances that showed higher drought tolerance, which supports previous results showing that mycorrhizae can increase drought resistance. CONCLUSIONS: Our findings suggest that soil communities play a role in affecting early performance of temperate trees, although this role may be smaller than that of seed origin. Also, other effects, such as the positive response to generalists or negative interactions with soil biota may be as important as the highly specialized mycorrhizal associations.

Gastric residual volume during enteral nutrition in ICU patients: the REGANE study.

OBJECTIVE: To compare the effects of increasing the limit for gastric residual volume (GRV) in the adequacy of enteral nutrition. Frequency of gastrointestinal complications and outcome variables were secondary goals. DESIGN: An open, prospective, randomized study. SETTING: Twenty-eight intensive care units in Spain. PATIENTS: Three hundred twenty-nine intubated and mechanically ventilated adult patients with enteral nutrition (EN). INTERVENTIONS: EN was administered by nasogastric tube. A protocol for management of EN-related gastrointestinal complications was used. Patients were randomized to be included in a control (GRV = 200 ml) or in study group (GRV = 500 ml). MEASUREMENTS AND RESULTS: Diet volume ratio (diet received/diet prescribed), incidence of gastrointestinal complications, ICU-acquired pneumonia, days on mechanical ventilation and ICU length of stay were the study variables. Gastrointestinal complications were higher in the control group (63.6 vs. 47.8%, P = 0.004), but the only difference was in the frequency of high GRV (42.4 vs. 26.8%, P = 0.003). The diet volume ratio was higher for the study group only during the 1st week (84.48 vs. 88.20%) (P = 0.0002). Volume ratio was similar for both groups in weeks 3 and 4. Duration of mechanical ventilation, ICU length of stay or frequency of pneumonia were similar. CONCLUSIONS: Diet volume ratio of mechanically ventilated patients treated with enteral nutrition is not affected by increasing the limit in GRV. A limit of 500 ml is not associated with adverse effects in gastrointestinal complications or in outcome variables. A value of 500 ml can be equally recommended as a normal limit for GRV.