• Energy Research

AbstractFundamental axes of variation in plant traits result from trade-offs between costs and benefits of resource-use strategies at the leaf scale. However, it is unclear whether similar trade-offs propagate to the ecosystem level. Here, we test whether trait correlation patterns predicted by three well-known leaf- and plant-level coordination theories – the leaf economics spectrum, the global spectrum of plant form and function, and the least-cost hypothesis – are also observed between community mean traits and ecosystem processes. We combined ecosystem functional properties from FLUXNET sites, vegetation properties, and community mean plant traits into three corresponding principal component analyses. We find that the leaf economics spectrum (90 sites), the global spectrum of plant form and function (89 sites), and the least-cost hypothesis (82 sites) all propagate at the ecosystem level. However, we also find evidence of additional scale-emergent properties. Evaluating the coordination of ecosystem functional properties may aid the development of more realistic global dynamic vegetation models with critical empirical data, reducing the uncertainty of climate change projections.

Abstract. Extreme climatic events, such as droughts and heat stress induce anomalies in ecosystem-atmosphere CO2 fluxes, such as gross primary production (GPP) and ecosystem respiration (Reco), and, hence, can change the net ecosystem carbon balance. However, despite our increasing understanding of the underlying mechanisms, the magnitudes of the impacts of different types of extremes on GPP and Reco within and between ecosystems remain poorly predicted. Here we aim to identify the major factors controlling the amplitude of extreme event impacts on GPP, Reco, and the resulting net ecosystem production (NEP). We focus on the impacts of heat and drought and their combination. We identified hydrometeorological extreme events in consistently downscaled water availability and temperature measurements over a 30 year time period. We then used FLUXNET eddy-covariance flux measurements to estimate the CO2 flux anomalies during these extreme events across dominant vegetation types and climate zones. Overall, our results indicate that short-term heat extremes increased respiration more strongly than they down-regulated GPP, resulting in a moderate reduction of the ecosystem’s carbon sink potential. In the absence of heat stress, droughts tended to have smaller and similarly dampening effects on both GPP and Reco, and, hence, often resulted in neutral NEP responses. The combination of drought and heat typically led to a strong decrease in GPP, whereas heat and drought impacts on respiration partially offset each other. Taken together, compound heat and drought events led to the strongest C sink reduction compared to any single-factor extreme. A key insight of this paper, however, is that duration matters most: for heat stress during droughts, the magnitude of impacts systematically increased with duration, whereas under heat stress without drought, the response of Reco over time turned from an initial increase to a down-regulation after about two weeks. This confirms earlier theories that not only the magnitude but also the duration of an extreme event determines its impact. Our study corroborates the results of several local site-level case studies, but as a novelty generalizes these findings at the global scale. Specifically, we find that the different response functions of the two antipodal land-atmosphere fluxes GPP and Reco can also result in increasing NEP during certain extreme conditions. Apparently counterintuitive findings of this kind bear great potential for scrutinizing the mechanisms implemented in state-of-the-art terrestrial biosphere models and provide a benchmark for future model development and testing.

Policymakers in the Northwest Territories have introduced carbon pricing as a strategy to reduce fossil fuel consumption and CO2 emissions across various population segments and industries. This indirect approach, chosen for its acceptability, aims to influence behavior rather than directly limit carbon-intensive products. The main purpose of this study was to evaluate the economic and ecological impacts of this policy and its alignment with intended objectives. Using a CGE macroeconomic model incorporating economic structural and behavioral equations, we assessed the policy’s effects on NWT’s economy in general and on a subset of its key sectors. We also incorporated a few observed and simulated climate data for diverse climate change scenarios. The estimated results revealed that climate variables, especially precipitation, significantly influenced sectors like agriculture, construction, and manufacturing. The standardized precipitation evapotranspiration index (SPEI), which encompasses both temperature and precipitation, notably impacted the agriculture, oil, and gas sectors. However, temperature alone showed limited significance, except in the oil and gas sector. The simulation results indicated that, while carbon pricing reduced economic contributions of fossil fuel sector, household rebates could counteract these effects of the economic growth of NWT. Our findings offer valuable insights for shaping NWT’s environmental policies, aligning them with Canada’s goal of net-zero CO2 emissions by 2050.

Comprendre les relations entre le climat et l'échange de carbone par les écosystèmes terrestres est essentiel pour prédire les niveaux futurs de dioxyde de carbone atmosphérique en raison des effets d'accélération potentiels des rétroactions positives du cycle climat-carbone. Cependant, les relations directement observées entre le climat et l'échange de CO2 terrestre avec l'atmosphère à travers les biomes et les continents font défaut. Nous présentons ici des données décrivant les relations entre l'échange net de carbone par les écosystèmes (NEE) et les facteurs climatiques tels que mesurés à l'aide de la méthode de covariance de Foucault sur 125 sites uniques dans divers écosystèmes sur six continents avec un total de 559 années de site. Nous trouvons que le NEE observé aux sites de covariance tourbillonnaire est (1) une fonction forte de la température annuelle moyenne aux latitudes moyennes et élevées, (2) une fonction forte de la sécheresse aux latitudes moyennes et basses, et (3) une fonction à la fois de la température et de la sécheresse autour de la ceinture moyenne-latitudinale (45°N). La sensibilité du NEE à la température annuelle moyenne se décompose à ~ 16 °C (une valeur seuil de la température annuelle moyenne), au-delà de laquelle aucune augmentation supplémentaire de l'absorption de CO2 avec la température n'a été observée et la sécheresse influence les règles de dépassement de l'influence de la température. Comprender las relaciones entre el clima y el intercambio de carbono por parte de los ecosistemas terrestres es fundamental para predecir los niveles futuros de dióxido de carbono en la atmósfera debido a los posibles efectos aceleradores de las retroalimentaciones positivas del ciclo clima-carbono. Sin embargo, faltan relaciones directamente observadas entre el clima y el intercambio terrestre de CO2 con la atmósfera a través de biomas y continentes. Aquí presentamos datos que describen las relaciones entre el intercambio neto de carbono (NEE) del ecosistema y los factores climáticos medidos utilizando el método de covarianza de remolinos en 125 sitios únicos en varios ecosistemas de seis continentes con un total de 559 años-sitio. Encontramos que la NEE observada en los sitios de covarianza de remolinos es (1) una fuerte función de la temperatura media anual en latitudes medias y altas, (2) una fuerte función de sequedad en latitudes medias y bajas, y (3) una función tanto de la temperatura como de la sequedad alrededor del cinturón latitudinal medio (45°N). La sensibilidad de NEE a la temperatura media anual se rompe a ~ 16 °C (un valor umbral de la temperatura media anual), por encima del cual no se observó ningún aumento adicional de la absorción de CO2 con la temperatura y la influencia de la sequedad anula la influencia de la temperatura. Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate–carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid- and high-latitudes, (2) a strong function of dryness at mid- and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45°N). The sensitivity of NEE to mean annual temperature breaks down at ~ 16 °C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence. يعد فهم العلاقات بين المناخ وتبادل الكربون بواسطة النظم الإيكولوجية الأرضية أمرًا بالغ الأهمية للتنبؤ بالمستويات المستقبلية لثاني أكسيد الكربون في الغلاف الجوي بسبب التأثيرات المتسارعة المحتملة للتغذية المرتدة الإيجابية لدورة المناخ والكربون. ومع ذلك، لا توجد علاقات ملحوظة مباشرة بين المناخ والتبادل الأرضي لثاني أكسيد الكربون مع الغلاف الجوي عبر المناطق الحيوية والقارات. نقدم هنا بيانات تصف العلاقات بين صافي تبادل النظام البيئي للكربون (NEE) والعوامل المناخية كما تم قياسها باستخدام طريقة التباين الدوامي في 125 موقعًا فريدًا في أنظمة بيئية مختلفة عبر ست قارات بإجمالي 559 سنة موقع. نجد أن NEE التي لوحظت في مواقع التباين الدوامي هي (1) وظيفة قوية لمتوسط درجة الحرارة السنوية عند خطوط العرض المتوسطة والعالية، (2) وظيفة قوية للجفاف عند خطوط العرض المتوسطة والمنخفضة، و (3) وظيفة لكل من درجة الحرارة والجفاف حول حزام العرض المتوسط (45درجةشمالاً). تنهار حساسية NEE لمتوسط درجة الحرارة السنوية عند حوالي 16 درجة مئوية (قيمة عتبة لمتوسط درجة الحرارة السنوية)، والتي لم يلاحظ فوقها أي زيادة أخرى في امتصاص ثاني أكسيد الكربون مع درجة الحرارة ويتجاوز تأثير الجفاف تأثير درجة الحرارة.