• Energy Research

AbstractClimate variability and periodic droughts have complex effects on carbon (C) fluxes, with uncertain implications for ecosystem C balance under a changing climate. Responses to climate change can be modulated by persistent effects of climate history on plant communities, soil microbial activity, and nutrient cycling (i.e., legacies). To assess how legacies of past precipitation regimes influence tallgrass prairie C cycling under new precipitation regimes, we modified a long‐term irrigation experiment that simulated a wetter climate for >25 years. We reversed irrigated and control (ambient precipitation) treatments in some plots and imposed an experimental drought in plots with a history of irrigation or ambient precipitation to assess how climate legacies affect aboveground net primary productivity (ANPP), soil respiration, and selected soil C pools. Legacy effects of elevated precipitation (irrigation) included higher C fluxes and altered labile soil C pools, and in some cases altered sensitivity to new climate treatments. Indeed, decades of irrigation reduced the sensitivity of both ANPP and soil respiration to drought compared with controls. Positive legacy effects of irrigation on ANPP persisted for at least 3 years following treatment reversal, were apparent in both wet and dry years, and were associated with altered plant functional composition. In contrast, legacy effects on soil respiration were comparatively short‐lived and did not manifest under natural or experimentally‐imposed “wet years,” suggesting that legacy effects on CO2efflux are contingent on current conditions. Although total soil C remained similar across treatments, long‐term irrigation increased labile soil C and the sensitivity of microbial biomass C to drought. Importantly, the magnitude of legacy effects for all response variables varied with topography, suggesting that landscape can modulate the strength and direction of climate legacies. Our results demonstrate the role of climate history as an important determinant of terrestrial C cycling responses to future climate changes.

Scientists must have an integrative understanding of ecology and evolution across spatial and temporal scales to predict how species will respond to global change. Although comprehensively investigating these processes in nature is challenging, the infrastructure and data from long-term ecological research networks can support cross-disciplinary investigations. We propose using these networks to advance our understanding of fundamental evolutionary processes and responses to global change. For ecologists, we outline how long-term ecological experiments can be expanded for evolutionary inquiry, and for evolutionary biologists, we illustrate how observed long-term ecological patterns may motivate new evolutionary questions. We advocate for collaborative, multi-site investigations and discuss barriers to conducting evolutionary work at network sites. Ultimately, these networks offer valuable information and opportunities to improve predictions of species' responses to global change.

SummaryThe pattern of a few abundant species and many rarer species is a defining characteristic of communities worldwide. These abundant species are often referred to as dominant species. Yet, despite their importance, the term dominant species is poorly defined and often used to convey different information by different authors. Based on a review of historical and contemporary definitions we develop a synthetic definition of dominant species. This definition incorporates the relative local abundance of a species, its ubiquity across the landscape, and its impact on community and ecosystem properties. A meta‐analysis of removal studies shows that the loss of species identified as dominant by authors can significantly impact ecosystem functioning and community structure. We recommend two metrics that can be used jointly to identify dominant species in a given community and provide a roadmap for future avenues of research on dominant species. In our review, we make the case that the identity and effects of dominant species on their environments are key to linking patterns of diversity to ecosystem function, including predicting impacts of species loss and other aspects of global change on ecosystems.

La sécheresse extrême a un impact considérable sur la fonction et les processus de l'écosystème. Cependant, une compréhension globale de la façon dont la sécheresse extrême affecte la biomasse racinaire à l'échelle régionale reste insaisissable. Ici, nous avons étudié les effets sur six prairies avec un traitement de sécheresse extrême répliqué sur un gradient de précipitations en Mongolie intérieure, en Chine. Nous avons constaté que la biomasse racinaire et la productivité primaire nette souterraine (BNPP) étaient significativement corrélées positivement avec les précipitations à l'échelle réginale. La sécheresse extrême a diminué la pente de cette corrélation de 0 à 10 cm et a augmenté de 10 à 20 cm. La biomasse racinaire et le BNPP ont augmenté par la sécheresse extrême dans les quatre sites relativement arides et diminué dans les deux sites relativement mésiques de 0 à 10 cm, et le schéma inverse a été montré de 10 à 20 cm. Ces changements ont été entraînés par la réponse de l'humidité du sol. Nos résultats suggèrent que l'inclusion de réponses verticales de la productivité primaire souterraine à la sécheresse extrême devrait améliorer les prédictions des modèles de racines végétales au changement climatique futur. La sequía extrema afecta la función y los procesos del ecosistema de manera dramática. Sin embargo, una comprensión integral de cómo la sequía extrema afecta la biomasa de la raíz a escalas regionales sigue siendo difícil de alcanzar. Aquí, investigamos los efectos en seis pastizales con tratamiento de sequía extrema replicado en un gradiente de precipitación en Mongolia Interior, China. Encontramos que la biomasa de la raíz y la productividad primaria neta subterránea (BNPP) se correlacionaron significativamente de manera positiva con la precipitación a escala reginal. La sequía extrema disminuyó la pendiente de esta correlación en 0-10 cm y aumentó en 10-20 cm. La biomasa de la raíz y la BNPP aumentaron por la sequía extrema en los cuatro sitios relativamente áridos y disminuyeron en los dos sitios relativamente mesicos en 0-10 cm, y el patrón inverso mostrado en 10-20 cm. Estos cambios fueron impulsados por la respuesta de la humedad del suelo. Nuestros hallazgos sugieren que la inclusión de respuestas verticales de la productividad primaria subterránea a la sequía extrema debería mejorar las predicciones de los modelos de las raíces de las plantas al cambio climático futuro. Extreme drought impacts ecosystem function and processes dramatically.However, a comprehensive understanding of how extreme drought affects root biomass at regional scales remains elusive.Here, we investigated the effects across six grasslands with extreme drought treatment replicated across a precipitation gradient in Inner Mongolia, China.We found the root biomass and belowground net primary productivity (BNPP) were significantly positively correlated with precipitation at the reginal scale.Extreme drought decreased the slope of this correlation in 0-10 cm and increased in 10-20 cm.Root biomass and BNPP increased by extreme drought in the four relatively arid sites and decreased in the two relatively mesic sites in 0-10 cm, and the reverse pattern showed in 10-20 cm.These shifts were driven by the response of soil moisture.Our findings suggest that including vertical responses of belowground primary productivity to extreme drought should improve models predictions of plant roots to future climate change. يؤثر الجفاف الشديد على وظيفة النظام البيئي وعملياته بشكل كبير. ومع ذلك، فإن الفهم الشامل لكيفية تأثير الجفاف الشديد على الكتلة الحيوية للجذور على النطاقات الإقليمية لا يزال بعيد المنال. هنا، قمنا بالتحقيق في الآثار عبر ستة مراعي مع معالجة الجفاف الشديد التي تتكرر عبر تدرج هطول الأمطار في منغوليا الداخلية، الصين. وجدنا أن الكتلة الحيوية للجذور والإنتاجية الأولية الصافية تحت الأرض (BNPP) كانت مرتبطة بشكل إيجابي بشكل كبير مع هطول الأمطار على نطاق ريجنال. أدى الجفاف الشديد إلى انخفاض ميل هذا الارتباط في 0-10 سم وزاد في 10-20 سم. زادت الكتلة الحيوية للجذور و BNP بسبب الجفاف الشديد في المواقع الأربعة القاحلة نسبيًا وانخفضت في الموقعين المتوسطين نسبيًا في 0-10 سم، وأظهر النمط العكسي في 10-20 سم. كانت هذه التحولات مدفوعة باستجابة رطوبة التربة. تشير نتائجنا إلى أن بما في ذلك الاستجابات الرأسية للإنتاجية الأولية تحت الأرض للجفاف الشديد يجب أن تحسن نماذج جذور النباتات لتغير المناخ في المستقبل.

Plant biomass tends to increase under nutrient addition and decrease under drought. Biotic and abiotic factors influence responses to both, making the combined impact of nutrient addition and drought difficult to predict. Using a globally distributed network of manipulative field experiments, we assessed grassland aboveground biomass response to both drought and increased nutrient availability at 26 sites across nine countries. Overall, drought reduced biomass by 19% and nutrient addition increased it by 24%, resulting in no net impact under combined drought and nutrient addition. Among the plant functional groups, only graminoids responded positively to nutrients during drought. However, these general responses depended on local conditions, especially aridity. Nutrient effects were stronger in arid grasslands and weaker in humid regions and nitrogen-rich soils, although nutrient addition alleviated drought effects the most in subhumid sites. Biomass responses were weaker with higher precipitation variability. Biomass increased more with increased nutrient availability and declined more with drought at high-diversity sites than at low-diversity sites. Our findings highlight the importance of local abiotic and biotic conditions in predicting grassland responses to anthropogenic nutrient and climate changes.

Extreme droughts generally decrease productivity in grassland ecosystems1-3 with negative consequences for nature's contribution to people4-7. The extent to which this negative effect varies among grassland types and over time in response to multi-year extreme drought remains unclear. Here, using a coordinated distributed experiment that simulated four years of growing-season drought (around 66% rainfall reduction), we compared drought sensitivity within and among six representative grasslands spanning broad precipitation gradients in each of Eurasia and North America-two of the Northern Hemisphere's largest grass-dominated regions. Aboveground plant production declined substantially with drought in the Eurasian grasslands and the effects accumulated over time, while the declines were less severe and more muted over time in the North American grasslands. Drought effects on species richness shifted from positive to negative in Eurasia, but from negative to positive in North America over time. The differing responses of plant production in these grasslands were accompanied by less common (subordinate) plant species declining in Eurasian grasslands but increasing in North American grasslands. Our findings demonstrate the high production sensitivity of Eurasian compared with North American grasslands to extreme drought (43.6% versus 25.2% reduction), and the key role of subordinate species in determining impacts of extreme drought on grassland productivity.

AbstractPatterns of insect herbivory may follow predictable geographical gradients, with greater herbivory at low latitudes. However, biogeographic studies of insect herbivory often do not account for multiple abiotic factors (e.g., precipitation and soil nutrients) that could underlie gradients. We tested for latitudinal clines in insect herbivory as well as climatic, edaphic, and trait‐based drivers of herbivory. We quantified herbivory on five dominant grass species over 23 sites across the Great Plains, USA. We examined the importance of climate, edaphic factors, and traits as correlates of herbivory. Herbivory increased at low latitudes when all grass species were analyzed together and for two grass species individually, while two other grasses trended in this direction. Higher precipitation was related to more herbivory for two species but less herbivory for a different species, while higher specific root length was related to more herbivory for one species and less herbivory for a different species. Taken together, results highlight that climate and trait‐based correlates of herbivory can be highly contextual and species‐specific. Patterns of insect herbivory on dominant grasses support the hypothesis that herbivory increases toward lower latitudes, though weakly, and indicates that climate change may have species‐specific effects on plant–herbivore interactions.

A substantial body of evidence has demonstrated that biodiversity stabilizes ecosystem functioning over time in grassland ecosystems. However, the relative importance of different facets of biodiversity underlying the diversity-stability relationship remains unclear. Here we use data from 39 grassland biodiversity experiments and structural equation modelling to investigate the roles of species richness, phylogenetic diversity and both the diversity and community-weighted mean of functional traits representing the 'fast-slow' leaf economics spectrum in driving the diversity-stability relationship. We found that high species richness and phylogenetic diversity stabilize biomass production via enhanced asynchrony in the performance of co-occurring species. Contrary to expectations, low phylogenetic diversity enhances ecosystem stability directly, albeit weakly. While the diversity of fast-slow functional traits has a weak effect on ecosystem stability, communities dominated by slow species enhance ecosystem stability by increasing mean biomass production relative to the standard deviation of biomass over time. Our in-depth, integrative assessment of factors influencing the diversity-stability relationship demonstrates a more multicausal relationship than has been previously acknowledged.