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AbstractAcross the world, social‐ecological rangeland systems have been transformed from a preindustrial extensive status to intensive exploitation, often leading to long‐term livestock population booms, overgrazing, and rangeland degradation. To understand the regulatory mechanisms involved in such historical social‐ecological transformations, we collected population data on the native sheep of the last nomadic county in the Inner Mongolia Autonomous Region (1961–2005). We detected changes in internal feedbacks (e.g., density‐dependent effects) and external disturbance (e.g., winter harshness, rainfall, harvest) between the extensive and intensive management periods using regression models of sheep population growth rate and counterfactual analyses. We found that, in the extensive period, sheep populations were regulated during harsh winters by climate, while they were regulated during mild winters by negative density dependence. In the intensive period, the negative feedback of density dependence was removed through the provision of additional forage and shelter, and only winter climate and growing season rainfall regulated sheep populations. Counterfactual analyses also confirmed the irreplaceable role of density‐dependence in maintaining a sustainable rangeland ecosystem. Although herders attempted to adapt to the removal of negative feedbacks by improving livestock harvest, overgrazing and grassland degradation remain a challenge in this system. We conclude that internal feedbacks within social‐ecological systems should be carefully anticipated and accounted for when managing rangelands for sustainability.

Liu, X., Burras, C. L., Kravchenko, Y. S., Duran, A., Huffman, T., Morras, H., Studdert, G., Zhang, X., Cruse, R. M. and Yuan, X. 2012. Overview of Mollisols in the world: Distribution, land use and management. Can. J. Soil Sci. 92: 383–402. Mollisols – a.k.a., Black Soils or Prairie Soils – make up about 916 million ha, which is 7% of the world's ice-free land surface. Their distribution strongly correlates with native prairie ecosystems, but is not limited to them. They are most prevalent in the mid-latitudes of North America, Eurasia, and South America. In North America, they cover 200 million ha of the United States, more than 40 million ha of Canada and 50 million ha of Mexico. Across Eurasia they cover around 450 million ha, extending from the western 148 million ha in southern Russia and 34 million ha in Ukraine to the eastern 35 million ha in northeast China. They are common to South America's Argentina and Uruguay, covering about 89 million and 13 million ha, respectively. Mollisols are often recognized as inherently productive and fertile soils. They are extensively and intensively farmed, and increasingly dedicated to cereals production, which needs significant inputs of fertilizers and tillage. Mollisols are also important soils in pasture, range and forage systems. Thus, it is not surprising that these soils are prone to soil erosion, dehumification (loss of stable aggregates and organic matter) and are suffering from anthropogenic soil acidity. Therefore, soil scientists from all of the world's Mollisols regions are concerned about the sustainability of some of current trends in land use and agricultural practices. These same scientists recommend increasing the acreage under minimum or restricted tillage, returning plant residues and adding organic amendments such as animal manure to maintain or increase soil organic matter content, and more systematic use of chemical amendments such as agricultural limestone to replenish soil calcium reserves.

Abstract Grassland ecosystems play an essential role in climate regulation through carbon (C) storage in plant and soil. But, anthropogenic practices such as livestock grazing, grazing related excreta nitrogen (N) deposition, and manure/fertilizer N application have the potential to reduce the effectiveness of grassland C sink through increased nitrous oxide (N2O) and methane (CH4) emissions. Although the effect of anthropogenic activities on net greenhouse gas (GHG) fluxes in grassland ecosystems have been investigated at local to regional scales, estimates of net GHG balance at the global scale remains uncertain. With the data-model framework integrating empirical estimates of livestock CH4 emissions with process-based modeling estimates of land CO2, N2O and CH4 fluxes, we examined the overall global warming potential (GWP) of grassland ecosystems during 1961–2010. We then quantified the grassland-specific and regional variations to identify hotspots of GHG fluxes. Our results show that, over a 100-year time horizon, grassland ecosystems sequestered a cumulative total of 113.9 Pg CO2-eq in plant and soil, but then released 91.9 Pg CO2-eq to the atmosphere, offsetting 81% of the net CO2 sink. We also found large grassland-specific variations in net GHG fluxes, with pasturelands acting as a small GHG source of 1.52 ± 143 Tg CO2-eq yr−1 (mean ± 1.0 s.d.) and rangelands a strong GHG sink (−442 ± 266 Tg CO2-eq yr−1) during 1961–2010. Regionally, Europe acted as a GHG source of 23 ± 10 Tg CO2-eq yr−1, while other regions (i.e. Africa, Southern Asia) were strong GHG sinks during 2001–2010. Our study highlights the importance of considering regional and grassland-specific differences in GHG fluxes for guiding future management and climate mitigation strategies in global grasslands.

Schizochytrium strains are usually studied as oil-producing strains, but they can also synthesize other secondary metabolites, such as astaxanthin. In this study, methanol was used as an inducer, and we explored its effects on the production of astaxanthin, a highly valuable substance in Schizochytrium . Methanol induced Schizochytrium to synthesize large amounts of astaxanthin. Transcriptomic analysis was used to investigate the regulation of signaling and metabolic pathways (mainly relative gene expression) in Schizochytrium grown in the presence of various concentrations of methanol. These results contribute to the understanding of the underlying molecular mechanisms and may aid in the future optimization of Schizochytrium for astaxanthin biosynthesis.

Understanding the interactions between drought and tree ontogeny or size remains an essential research priority because size-specific mortality patterns have large impacts on ecosystem structure and function, determine forest carbon storage capacity, and are sensitive to climatic change. Here we investigate a xerophytic tree species (Haloxylon ammodendron (C.A. Mey.)) with which the changes in biomass allocation with tree size may play an important role in size-specific mortality patterns. Size-related changes in biomass allocation, root distribution, plant water status, gas exchange, hydraulic architecture and non-structural carbohydrate reserves of this xerophytic tree species were investigated to assess their potential role in the observed U-shaped mortality pattern. We found that excessively negative water potentials (<-4.7MPa, beyond the P50leaf of -4.1MPa) during prolonged drought in young trees lead to hydraulic failure; while the imbalance of photoassimilate allocation between leaf and root system in larger trees, accompanied with declining C reserves (<2% dry matter across four tissues), might have led to carbon starvation. The drought-resistance strategy of this species is preferential biomass allocation to the roots to improve water capture. In young trees, the drought-resistance strategy is not well developed, and hydraulic failure appears to be the dominant driver of mortality during drought. With old trees, excess root growth at the expense of leaf area may lead to carbon starvation during prolonged drought. Our results suggest that the drought-resistance strategy of this xeric tree is closely linked to its life and death: well-developed drought-resistance strategy means life, while underdeveloped or overdeveloped drought-resistance strategy means death.

AbstractFuture climate may profoundly impact the functioning of terrestrial ecosystems. However, we do not know well how the functioning of different types of grassland ecosystems is associated with variation in temperature and precipitation. Here, we used long‐term field measurements to examine how climatic changes between the 1980s and the 2010s (i.e., growing season temperature, precipitation, habitat moisture index, solar radiation, and sunshine duration) have affected aboveground net primary productivity (ANPP) for all major grassland types in northern China. We found that ANPP consistently declined over the 30‐year period across all types of grassland, on average by about 6.1%. Warming, associated with increased solar radiation and, hence, soil temperature, was the primary factor driving the decrease of ANPP. We further show that ANPP was more sensitive to climate change in alpine and lowland grasslands than in temperate grasslands. Together, our findings indicate that climate warming consistently reduces plant productivity of different types of grassland ecosystems, and emphasize the importance of soil temperature in driving the decline in grassland productivity under climate change.

AbstractAimOur aim is to use elevational gradients to quantify the relationship between temperature and ecosystem functioning. Ecosystem functions such as decomposition, nutrient cycling and carbon storage are linked with the amount of microbial biomass in the soil. Previous studies have shown variable relationships between elevation and soil microbial biomass (SMB). Understanding the biological mechanisms linking SMB with elevational gradients will shed light on the environmental impacts of global warming.LocationGlobal.Time period2002–2018.Major taxa studiedSoil microbes.MethodWe performed a global meta‐analysis of the relationships between SMB and elevation. Data were collected from 59 studies of 73 elevational transects from around the world.ResultsWe found no consistent global relationship between SMB and elevation. SMB increased significantly with elevation in the tropics and subtropics, but not in other climate zones. However, we found consistent positive relationships between SMB, soil organic carbon and total nitrogen concentrations.Main conclusionsOur results suggest that global warming will impact tropical and subtropical ecosystems more severely than colder regions. Tropical ecosystems, already at risk from species extinctions, will likely experience declines in SMB as the climate warms, resulting in losses of fundamental ecosystem functions such as nutrient cycling and carbon storage.

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.