Interactive effects of tree species mixture and climate on foliar and woody trait variation in in a widely distributed deciduous tree

Despite increasing reports of severe drought and heat impacts on forest ecosystems, community-level processes, which could potentially modulate tree responses to climatic stress, are rarely accounted for. While numerous studies indicate a positive effect of species diversity on a wide range of ecosystem functions and services, little is known about how species interactions influence tree responses to climatic variability. We quantified the intraspecific variation in 16 leaf and wood physiological, morphological, and anatomical traits in mature beech trees (Fagus sylvatica L.) at six sites located along a climatic gradient in the French Alps. At each site, we studied pure beech and mixed stands with silver fir (Abies alba Mill.) or downy oak (Quercus pubescens Willd.). We tested how functional traits differed between the two species mixtures (pure vs. mixed stands) within each site and along the climatic gradient. We found significant changes in many traits along the climatic gradient as conditions progressively got drier and warmer. Independent of the mixture, reduced leaf-level CO2 assimilation, stomatal size, and thicker leaf cuticles, consistent with a more conservative resource use strategy, were found. At the drier sites, higher foliar stable carbon isotopic composition (δ13C), thicker mesophyll tissues, and lower specific leaf area (SLA) in pure stands suggests that beech had more acquisitive traits there compared to mixed stands. At the wetter sites, trees in beech-silver fir mixtures had higher chlorophyll concentration, lower δ13C, larger xylem vessels, and higher SLA, suggesting a more acquisitive resource use strategy in mixed stands than in pure stands. Our work revealed that species interactions are significant modulators of functional traits, and that they can be just as important drivers of intraspecific trait variation as climatic conditions. We show that downy oak mixtures lead to an adaptive drought response by common beech in dry environments. In contrast, in milder climates, interactions with silver fir seem to increase beech’ resource acquisition and productivity. These findings highlight a strong context-dependency and imply that incorporating local interspecific interactions in research on climate impacts could improve our understanding and predictions of forest dynamics.MD and CG were supported by the Swiss National Science Foundation SNF (PZ00P3_174068). CG is supported by the Sandoz Family Foundation. The plot design used in this study is part of the GMAP plot network (https://oreme.org/observation/foret/gmap/), partly funded by the OSU OREME in Montpellier, France

Warming may extend tree growing seasons and compensate for reduced carbon uptake during dry periods

1. Warming and drought alter plant phenology, photosynthesis and growth with important consequences for the global carbon cycle and the earth’s climate. Yet, few studies have attempted to tease apart their effects on tree phenology, particularly leaf senescence, and on source and sink activity. 2. We experimentally assessed the single and combined effects of warming and reduced soil moisture on the phenology (leaf-out and senescence date, growing season length) and aboveground sink (height and diameter growth, leaf area and Huber values) and source activity (net photosynthesis, photosynthetic efficiency, chlorophyll concentration and total carbon (C) uptake) of two tree species with distinct strategies to deal with drought: European beech and pubescent oak. 3. Warming advanced leaf-out, irrespective of soil moisture levels, particularly in oak and to a lower extent in beech, leading to a prolonged growing season in oak but not beech. No impacts of warming on senescence timing were found for both species. Reduced moisture had little impact on the phenology of both species. Warming-induced advances in phenology and higher photosynthetic efficiency increased the annual C uptake for oak and compensated for the reduced photosynthetic activity in the presence of reduced moisture. Conversely, for beech, source activity, including yearly C uptake, was lower in all treatments than the control, indicating no compensation of the C budget by phenological shifts. 4. Synthesis. Our results demonstrate that a warming-driven earlier activity and higher photosynthetic efficiency compensates for reduced photosynthesis during hot and dry periods, but only for pubescent oak, which is a rather drought tolerant species. Current predictions of warming-induced mitigation effects through extended C uptake seem incorrect for beech

A Conclusive Concept for Three-Dimensional Imaging Based on Efficient Steering and Focusing of an Ultrasonic 2D-Array

Abstract. A 16-by-16 element array is operated at a center frequency of 2.25 MHz using a 256-channel transmitter system. Reception is performed with a subset of elements of the array or with a separate single element probe. The beam fields generated in water have been simulated and compared to experiments with excellent agreement. 3D imaging of defects inside components has been addressed only by electronic steering and focusing to various depths of the inspected component. Work has also been done using an 8-by-8 element array

Interactive effects of tree species mixture and climate on foliar and woody trait variation in a widely distributed deciduous tree

1. Despite increasing reports of severe drought and heat impacts on forest ecosystems, community-level processes, which could potentially modulate tree responses to climatic stress, are rarely accounted for. While numerous studies indicate a positive effect of species diversity on a wide range of ecosystem functions and services, little is known about how species interactions influence tree responses to climatic variability. 2. We quantified the intraspecific variation in 16 leaf and wood physiological, morphological and anatomical traits in mature beech trees (Fagus sylvatica L.) at six sites located along a climatic gradient in the French Alps. At each site, we studied pure beech and mixed stands with silver fir (Abies alba Mill.) or downy oak (Quercus pubescens Willd.). We tested how functional traits differed between the two species mixtures (pure vs. mixed stands) within each site and along the climatic gradient. 3. We found significant changes in many traits along the climatic gradient as conditions progressively got drier and warmer. Independent of the mixture, reduced leaf-level CO2 assimilation, stomatal size and thicker leaf cuticles, consistent with a more conservative resource use strategy, were found. At the drier sites, higher foliar stable carbon isotopic composition (δ13C), thicker mesophyll tissues and lower specific leaf area (SLA) in pure stands suggest that beech had more acquisitive traits there compared to mixed stands. At the wetter sites, trees in beech-silver fir mixtures had higher chlorophyll concentration, lower δ13C, larger xylem vessels and higher SLA, suggesting a more acquisitive resource use strategy in mixed stands than in pure stands. 4. Our work revealed that species interactions are significant modulators of functional traits, and that they can be just as important drivers of intraspecific trait variation as climatic conditions. We show that downy oak mixtures lead to an adaptive drought response by common beech in dry environments. In contrast, in milder climates, interactions with silver fir seem to increase beech resource acquisition and productivity. These findings highlight a strong context dependency and imply that incorporating local interspecific interactions in research on climate impacts could improve our understanding and predictions of forest dynamics.ISSN:0269-8463ISSN:1365-243

Deletion of the ageing gene p66Shc reduces early stroke size following ischaemia/reperfusion brain injury

Aims: Stroke is a leading cause of morbidity and mortality, and its incidence increases with age. Both in animals and in humans, oxidative stress appears to play an important role in ischaemic stroke, with or without reperfusion. The adaptor protein p66(Shc) is a key regulator of reactive oxygen species (ROS) production and a mediator of ischaemia/reperfusion damage in ex vivo hearts. Hence, we hypothesized that p66(Shc) may be involved in ischaemia/reperfusion brain damage. To this end, we investigated whether genetic deletion of p66(Shc) protects from ischaemia/reperfusion brain injury. Methods and results: Transient middle cerebral artery occlusion (MCAO) was performed to induce ischaemia/reperfusion brain injury in wild-type (Wt) and p66(Shc) knockout mice (p66(Shc-/-)), followed by 24 h of reperfusion. Cerebral blood flow and blood pressure measurements revealed comparable haemodynamics in both experimental groups. Neuronal nuclear antigen immunohistochemical staining showed a significantly reduced stroke size in p66(Shc-/-) when compared with Wt mice (P < 0.05, n = 7-8). In line with this, p66(Shc-/-) mice exhibited a less impaired neurological function and a decreased production of free radicals locally and systemically (P < 0.05, n = 4-5). Following MCAO, protein levels of gp91phox nicotinamide adenine dinucleotide phosphate oxidase subunit were increased in brain homogenates of Wt (P < 0.05, n = 4), but not of p66(Shc-/-) mice. Further, reperfusion injury in Wt mice induced p66(Shc) protein in the basilar and middle cerebral artery, but not in brain tissue, suggesting a predominant involvement of vascular p66(Shc). Conclusion: In the present study, we show that the deletion of the ageing gene p66(Shc) protects mice from ischaemia/reperfusion brain injury through a blunted production of free radicals. The ROS mediator p66(Shc) may represent a novel therapeutical target for the treatment of ischaemic stroke