• Energy Research

AbstractQuantifying landscape‐scale methane (CH4) fluxes from boreal and arctic regions, and determining how they are controlled, is critical for predicting the magnitude of any CH4 emission feedback to climate change. Furthermore, there remains uncertainty regarding the relative importance of small areas of strong methanogenic activity, vs. larger areas with net CH4 uptake, in controlling landscape‐level fluxes. We measured CH4 fluxes from multiple microtopographical subunits (sedge‐dominated lawns, interhummocks and hummocks) within an aapa mire in subarctic Finland, as well as in drier ecosystems present in the wider landscape, lichen heath and mountain birch forest. An intercomparison was carried out between fluxes measured using static chambers, up‐scaled using a high‐resolution landcover map derived from aerial photography and eddy covariance. Strong agreement was observed between the two methodologies, with emission rates greatest in lawns. CH4 fluxes from lawns were strongly related to seasonal fluctuations in temperature, but their floating nature meant that water‐table depth was not a key factor in controlling CH4 release. In contrast, chamber measurements identified net CH4 uptake in birch forest soils. An intercomparison between the aerial photography and satellite remote sensing demonstrated that quantifying the distribution of the key CH4 emitting and consuming plant communities was possible from satellite, allowing fluxes to be scaled up to a 100 km2 area. For the full growing season (May to October), ~ 1.1–1.4 g CH4 m−2 was released across the 100 km2 area. This was based on up‐scaled lawn emissions of 1.2–1.5 g CH4 m−2, vs. an up‐scaled uptake of 0.07–0.15 g CH4 m−2 by the wider landscape. Given the strong temperature sensitivity of the dominant lawn fluxes, and the fact that lawns are unlikely to dry out, climate warming may substantially increase CH4 emissions in northern Finland, and in aapa mire regions in general.

The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% of the Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2 fertilization4, with major implications for future carbon sequestration and forest resilience to climate change.

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.

AbstractTropical montane forests (TMFs) are biodiversity hotspots and provide vital ecosystem services, but they are disproportionately vulnerable to climate warming. In the Andes, cold‐affiliated species from high elevations are being displaced at the hot end of their thermal distributions by warm‐affiliated species migrating upwards from lower elevations, leading to compositional shifts. Leaf functional traits are strong indicators of plant performance and at the community level have been shown to vary along elevation gradients, reflecting plant adaptations to different environmental niches. However, the plastic response of such traits to relatively rapid temperature change in Andean TMF species remains unknown. We used three common garden plantations within a thermosequence in the Colombian Andes to investigate the warming and cooling responses of key leaf functional traits in eight cold‐ and warm‐affiliated species with variable thermal niches. Cold‐affiliated species shifted their foliar nutrient concentrations when exposed to warming, while all other traits did not significantly change; contrastingly, warm‐affiliated species were able to adjust structural, nutrient and water‐use efficiency traits from acquisitive to conservative strategies in response to cooling. Our findings suggest that cold‐affiliated species will struggle to acclimate functional traits to warming, conferring warm‐affiliated species a competitive advantage under climate change.

AbstractWhether the world can achieve the United Nations Sustainable Development Goals (SDGs) largely depends on the ability of less‐developed areas to cope with multiple socio‐economic changes. The challenges that hinterland areas would face during the realization of SDGs has not yet received enough attentions. In this study, a context‐based assessment of regional food balances was conducted, considering key challenges related to socio‐economic development as well as land use competition under the framework of the shared socioeconomic pathways (SSPs) and the implementation of reforestation. We examined one of the poorest hinterland provinces in China as a case study, projecting its food deficit and exploring the potential threats to and opportunities for SDG realization by 2030, including population growth, urbanization, urban land expansion and reforestation. The projections revealed a crop deficit of 4.9–9.8 million tonnes, corresponding to the food demands of 10.2–20.6 million people. Approximately 76%–81% of this deficit was expected to be caused by increased food demand, rather than reforestation policies. Therefore, for this less‐developed area with low agricultural productivity and large groups of vulnerable people, population growth and urbanization are likely to result in demands for food that cannot be met locally. In addition, large‐scale reforestation projects, while enhancing a number of key ecosystem services, will increase the local food deficit by promoting the abandonment of cropland. This will result in greater reliance on food imports, with potential impacts on SDG realization in other regions. These findings highlight the need for integrated governance across multiple scales to ensure hinterland sustainability.

Data collection protocol: in January – March 2022, Aci curves (i.e., CO2 response curves of net photosynthesis) were done at a pre-determined saturating light intensity of 1800 PAR (Qin in the database). Aci curves were done at different leaf temperature targets between 15 and 40 degree Celcius, with 5 degree celcius steps. Before starting any ACi curve, the leaf was allowed to acclimate at each temperature for at least 10 min and the ACi was initiated once both Anet and stomatal conductance were stable for at least 2 min. Throughout each Aci, the stability time at each CO2 reference concentration (410, 50, 100, 150, 250, 410, 800, 1200, 1600, and 2000 in this order) was set to 45 - 180 seconds, the automatic match was programmed before recording any data at each CO2 reference concentration. Measurements were taken with an LI6800 Portable Photosynthesis System under field conditions. LI6800 indicates whether there is a leak, but measurements were always done after ensuring there was no leak in the system, therefore, no subsequent leak correction was necessary. At the beginning of each measurement day, automatic warm-up test was run to detect any problem within the instrument, and only measurements were initiated when all errors have been fixed as suggested by the instrument system. The leaf temperature was derived from the thermocouple of the instrument. This dataset contains information about temperature response curves of ACi (i.e., CO2 response curves of net photosynthesis) that were collected on Colombian Andean forests tree species that were planted in three, common-garden tree plantations along a 2000m altitudinal gradient. Specifically, individuals of cold- and warm-affiliated species were planted under common soil and water conditions, exposing them to the hot and cold extremes of their thermal niches, respectively. This work was supported by the UK Natural Environment Research Council (NE/R001928/1)

AbstractHeterotrophic soil microorganisms are responsible for ~50% of the carbon dioxide released by respiration from the terrestrial biosphere each year. The respiratory response of soil microbial communities to warming, and the control mechanisms, remains uncertain, yet is critical to understanding the future land carbon (C)‐climate feedback. Individuals of nine species of fungi decomposing wood were exposed to 90 days of cooling to evaluate the medium‐term effect of temperature on respiration. Overall, the effect of temperature on respiration increased in the medium term, with no evidence of compensation. However, the increasing effect of temperature on respiration was lost after correcting for changes in biomass. These results indicate that C loss through respiration of wood‐decomposing fungi will increase beyond the direct effects of temperature on respiration, potentially promoting greater C losses from terrestrial ecosystems and a positive feedback to climate change.