• Energy Research

Les communautés microbiennes du sol sont influencées par les facteurs du changement climatique tels que le réchauffement et l'altération des précipitations. Ces changements créent des stress abiotiques, y compris la dessiccation et la limitation des nutriments, qui agissent sur les microbes. Cependant, notre compréhension des réponses des communautés microbiennes aux facteurs concomitants du changement climatique est limitée. Nous avons étudié la diversité et la composition des bactéries et des champignons du sol après un réchauffement d'un an et une manipulation altérée des précipitations dans les prairies alpines du plateau tibétain. Dans l'isolement, les traitements de réchauffement et de diminution des précipitations n'ont eu aucun effet significatif sur la structure de la communauté bactérienne du sol ; cependant, en combinaison avec les deux traitements, la structure de la communauté bactérienne a été modifiée (p = 0,03). Le principal effet de l'altération des précipitations a spécifiquement eu un impact sur l'abondance relative des Bactéroïdes et des Gammaprotéobactéries par rapport au témoin, tandis que le principal effet du réchauffement a eu un impact sur l'abondance relative des Bétaprotéobactéries. En revanche, la communauté fongique n'a pas eu de réponse significative aux traitements après 1 an. En utilisant la modélisation par équation structurelle (MEB), nous avons trouvé que la composition de la communauté bactérienne était positivement liée à l'humidité du sol. Nos résultats indiquent que le changement climatique à court terme pourrait provoquer des changements dans la communauté bactérienne du sol par le biais de changements taxonomiques. Notre travail fournit de nouvelles informations sur les réponses microbiennes immédiates du sol aux facteurs de stress à court terme agissant sur un écosystème particulièrement sensible au changement climatique mondial. Las comunidades microbianas del suelo están influenciadas por los impulsores del cambio climático, como el calentamiento y las precipitaciones alteradas. Estos cambios crean tensiones abióticas, incluida la desecación y la limitación de nutrientes, que actúan sobre los microbios. Sin embargo, nuestra comprensión de las respuestas de las comunidades microbianas a los factores coexistentes del cambio climático es limitada. Estudiamos la diversidad y composición bacteriana y fúngica del suelo después de un calentamiento de 1 año y una manipulación alterada de las precipitaciones en los pastizales alpinos de la meseta tibetana. De forma aislada, el calentamiento y la disminución de los tratamientos de precipitación no tuvieron efectos significativos en la estructura de la comunidad bacteriana del suelo; sin embargo, en combinación de ambos tratamientos, la estructura de la comunidad bacteriana se alteró (p = 0,03). El efecto principal de la precipitación alterada impactó específicamente las abundancias relativas de Bacteroidetes y Gammaproteobacterias en comparación con el control, mientras que el efecto principal del calentamiento impactó la abundancia relativa de Betaproteobacterias. Por el contrario, la comunidad fúngica no tuvo una respuesta significativa a los tratamientos después de 1 año. Usando el modelado de ecuaciones estructurales (SEM), encontramos que la composición de la comunidad bacteriana estaba positivamente relacionada con la humedad del suelo. Nuestros resultados indican que el cambio climático a corto plazo podría causar cambios en la comunidad bacteriana del suelo a través de cambios taxonómicos. Nuestro trabajo proporciona nuevos conocimientos sobre las respuestas microbianas inmediatas del suelo a los factores estresantes a corto plazo que actúan sobre un ecosistema que es particularmente sensible al cambio climático global. Soil microbial communities are influenced by climate change drivers such as warming and altered precipitation. These changes create abiotic stresses, including desiccation and nutrient limitation, which act on microbes. However, our understanding of the responses of microbial communities to co-occurring climate change drivers is limited. We surveyed soil bacterial and fungal diversity and composition after a 1-year warming and altered precipitation manipulation in the Tibetan plateau alpine grassland. In isolation, warming and decreased precipitation treatments each had no significant effects on soil bacterial community structure; however, in combination of both treatments altered bacterial community structure (p = 0.03). The main effect of altered precipitation specifically impacted the relative abundances of Bacteroidetes and Gammaproteobacteria compared to the control, while the main effect of warming impacted the relative abundance of Betaproteobacteria. In contrast, the fungal community had no significant response to the treatments after 1-year. Using structural equation modeling (SEM), we found bacterial community composition was positively related to soil moisture. Our results indicate that short-term climate change could cause changes in soil bacterial community through taxonomic shifts. Our work provides new insights into immediate soil microbial responses to short-term stressors acting on an ecosystem that is particularly sensitive to global climate change. تتأثر المجتمعات الميكروبية للتربة بعوامل تغير المناخ مثل الاحترار وتغير هطول الأمطار. تخلق هذه التغييرات ضغوطًا غير حيوية، بما في ذلك الجفاف والحد من المغذيات، والتي تؤثر على الميكروبات. ومع ذلك، فإن فهمنا لاستجابات المجتمعات الميكروبية للدوافع المشتركة لتغير المناخ محدود. قمنا بمسح التنوع البكتيري والفطري للتربة وتكوينها بعد ارتفاع درجة الحرارة لمدة عام وتغيير التلاعب في هطول الأمطار في الأراضي العشبية في جبال الألب في هضبة التبت. في العزلة، لم يكن لكل من علاجات الاحترار وانخفاض هطول الأمطار آثار كبيرة على بنية المجتمع البكتيري للتربة ؛ ومع ذلك، في مزيج من كلا العلاجين تغير بنية المجتمع البكتيري (ص = 0.03). أثر التأثير الرئيسي لهطول الأمطار المتغير على وجه التحديد على الوفرة النسبية للبكتيرويدات وجامابروتوباكتريا مقارنة بالتحكم، في حين أثر التأثير الرئيسي للاحترار على الوفرة النسبية لبكتريا بيتا بروتيوباكتريا. في المقابل، لم يكن لدى المجتمع الفطري استجابة كبيرة للعلاجات بعد عام واحد. باستخدام نمذجة المعادلة الهيكلية (SEM)، وجدنا أن تكوين المجتمع البكتيري كان مرتبطًا بشكل إيجابي برطوبة التربة. تشير نتائجنا إلى أن تغير المناخ على المدى القصير يمكن أن يسبب تغيرات في مجتمع بكتيريا التربة من خلال التحولات التصنيفية. يوفر عملنا رؤى جديدة حول الاستجابات الميكروبية الفورية للتربة للضغوط قصيرة الأجل التي تعمل على نظام بيئي حساس بشكل خاص لتغير المناخ العالمي.

Abstract Key Message The first bottleneck in Spanish black pine survival through afforestation is the lack of resistance to drought in their initial life stages. Abstract Spanish black pine (Pinus nigra Arn ssp. salzmannii) is the most widely distributed pine species in mountain areas of the Mediterranean Basin and is commonly used for afforestation in endangered and degraded areas. Despite its importance, little is known regarding the factors driving seedling survival for this species, which may hamper afforestation success in Mediterranean areas. In this study, we assessed the effects of seed origin and plantation site along a natural gradient with contrasting elevation and climatic conditions in a Mediterranean forest in Central-Eastern Spain. Our results showed: (1) higher seedling survival rates when seed origin differed from plantation site (25.3 ± 5.4%) compared to same origin and plantation site (5.3 ± 2.7%); (2) higher survival probability (~ 20%) for high and medium elevation seeds (colder and wetter locations) compared to the warmer and drier low elevation sites (15%); (3) higher seedling survival (~ 40%) at higher elevation sites compared to low-elevation sites (< 20%); and (4) increased hazard of seedling death with decreasing elevation of the plantation site. We also reported a complete mortality at the drier sites after the first summer following the plantation. Overall, the combination of seeds from medium elevation and high elevation plantation sites increased the survival of Spanish black pine. These results have direct implications for forest management of Spanish black pine in Mediterranean regions, particularly in current and future climate change scenarios.

Tree species diversity promotes multiple ecosystem functions and services. However, little is known about how above- and belowground resource availability (light, nutrients, and water) and resource uptake capacity mediate tree species diversity effects on aboveground wood productivity and temporal stability of productivity in European forests and whether the effects differ between humid and arid regions. We used the data from six major European forest types along a latitudinal gradient to address those two questions. We found that neither leaf area index (a proxy for light uptake capacity), nor fine root biomass (a proxy for soil nutrient and water uptake capacity) was related to tree species richness. Leaf area index did, however, enhance productivity, but negatively affected stability. Productivity was further promoted by soil nutrient availability, while stability was enhanced by fine root biomass. We only found a positive effect of tree species richness on productivity in arid regions and a positive effect on stability in humid regions. This indicates a possible disconnection between productivity and stability regarding tree species richness effects. In other words, the mechanisms that drive the positive effects of tree species richness on productivity do not per se benefit stability simultaneously. Our findings therefore suggest that tree species richness effects are largely mediated by differences in climatic conditions rather than by differences in above- and belowground resource availability and uptake capacity at the regional scales.

Little is known about the structure of plant communities across the vast Tibetan Plateau, which supports at least 12,000 species of alpine vascular plants including over 2000 endemics. We recorded species abundance in 485 sites stretching across 6000 km of the plateau. At each site, species abundance was measured in three quadrats that were 40 m apart, allowing us to quantify local β-diversity within the site. We found that local β-diversity in alpine meadows and steppes was significantly higher than expected by chance, indicating intraspecific aggregation within the sites. After controlling for random sampling effects, the magnitude of local β-diversity varied across the plateau: there was a positive relationship from west to east corresponding to increased rainfall; there were hump-shaped relationships with elevation and latitude. These patterns were driven mainly by regional variation in climate, but also by local soil properties and grazing regimes (our structural equation models (SEMs) explained 27 % and 26 % of variation in alpine meadows and steppes, respectively). Unexpectedly, precipitation-related variables were the strongest predictors in cold-wet alpine meadows while temperature-related variables were the strongest predictors in dry-warm alpine steppes. Our findings support the hypothesis that environmental filtering is largely responsible for local β-diversity of alpine grasslands across the Tibetan Plateau. We discuss how these findings inform efforts to conserve fragile alpine ecosystems threatened by rapid climate warming and overgrazing.

AbstractPlant biodiversity is often correlated with ecosystem functioning in terrestrial ecosystems. However, we know little about the relative and combined effects of above- and belowground biodiversity on multiple ecosystem functions (for example, ecosystem multifunctionality, EMF) or how climate might mediate those relationships. Here we tease apart the effects of biotic and abiotic factors, both above- and belowground, on EMF on the Tibetan Plateau, China. We found that a suite of biotic and abiotic variables account for up to 86% of the variation in EMF, with the combined effects of above- and belowground biodiversity accounting for 45% of the variation in EMF. Our results have two important implications: first, including belowground biodiversity in models can improve the ability to explain and predict EMF. Second, regional-scale variation in climate, and perhaps climate change, can determine, or at least modify, the effects of biodiversity on EMF in natural ecosystems.

Summary Recent droughts have strongly impacted forest ecosystems and are projected to increase in frequency, intensity, and duration in the future together with continued warming. While evidence suggests that tree diversity can regulate drought impacts in natural forests, few studies examine whether mixed tree plantations are more resistant to the impacts of severe droughts. Using natural variations in leaf carbon (C) and nitrogen (N) isotopic ratios, that is δ13C and δ15N, as proxies for drought response, we analyzed the effects of tree species richness on the functional responses of tree plantations to the pan‐European 2018 summer drought in seven European tree diversity experiments. We found that leaf δ13C decreased with increasing tree species richness, indicating less drought stress. This effect was not related to drought intensity, nor desiccation tolerance of the tree species. Leaf δ15N increased with drought intensity, indicating a shift toward more open N cycling as water availability diminishes. Additionally, drought intensity was observed to alter the influence of tree species richness on leaf δ15N from weakly negative under low drought intensity to weakly positive under high drought intensity. Overall, our findings suggest that dual leaf isotope analysis helps understand the interaction between drought, nutrients, and species richness.