Danielle A. Way

Peatlands store one-third of the global soil carbon (C) on only ∼3% of Earth’s land surface but risk becoming C sources to accelerate climate change due to warming-induced C loss. Elevated CO ₂ (eCO ₂ ) may mitigate this loss by boosting plant C uptake. However, how eCO ₂ and climate warming interact to influence peatland C dynamics remains unclear. Here, we investigated peatland C fate at five warming levels (+0°, +2.25°, +4.5°, +6.75°, and + 9°C), each under ambient CO ₂ (aCO ₂ ) and eCO ₂ (+500 parts per million), by model-guided synthesis of 18 measured variables for each of the 10 treatments from an experiment. Our results showed that the peatland C loss increased with warming at a rate of 62.6 g C m ⁻² year ⁻¹ °C ⁻¹ , reaching 476.5 ± 104.7 g C m ⁻² year ⁻¹ at +9°C under aCO ₂ , primarily because of increased Sphagnum mortality and accelerated decomposition. eCO ₂ reduced the loss rate to 17.3 g C m ⁻² year ⁻¹ °C ⁻¹ , nearly halving the C loss at +9°C (269.4 ± 80.5 g C m ⁻² year ⁻¹ ), mainly due to enhanced tree and shrub growth. Methane emissions increased with warming, similarly under aCO ₂ and eCO ₂ . Our findings suggest that northern peatlands likely become major C sources under climate warming, although rising atmospheric CO ₂ concentration may partially slow down the C loss. Climate-driven shifts in plant community structure, rather than peat decomposition alone, play a critical role in regulating peatland C fate and may threaten the stability of peatland ecosystem functions and services in the future.

SUMMARY: Future climatic conditions are projected to become warmer and drier, critically challenging tree growth and survival. Understanding how photosynthesis and respiration of tree seedlings acclimate to warming is pivotal for predicting seedling responses to climate change and tree carbon dynamics. However, the photosynthetic capacity parameters of thermal acclimation remain unresolved; particularly their interaction with water availability constraints and local climate adaptation needs to be fully explored. Here, we grew seedlings of a widely planted timber species in subtropical China, Pinus massoniana , with two provenances from contrasting climates of origin (cooler‐drier and warmer‐wetter), under three growth temperatures (22°C, 26°C, and 30°C) and two water conditions (well‐watered and drought). Temperature responses of gas exchange and nutrient status were investigated, together with a data synthesis of meta‐analysis. The experimental results showed that under well‐watered conditions, the optimal temperature for photosynthesis ( T _optA ), the net photosynthetic rate ( A ₂₅ ) and dark respiration rate ( R ₂₅ ) at 25°C, and respiratory sensitivity parameters ( Q ₁₀ ) remained unexpectedly stable under warming for both provenances, contrasting with our hypotheses; however, data synthesis shows that the T _optA from the cooler region increased with warming. Drought reduced T _optA and A ₂₅ , largely related to the magnitude of warming. Compared to drought‐only conditions, warming and drought in combination induced an increase in T _optA and the optimal temperature for photosynthetic electron transport rate ( T _optJ ) in the provenance from the warmer‐wetter region and a reduction in Q ₁₀ for both provenances, but did not affect A ₂₅ and R ₂₅ . Collectively, our results indicated that thermal acclimation of photosynthesis and respiration in P. massoniana seedlings was limited under well‐watered conditions. However, drought increased the capacity for thermal acclimation in the warmer‐wetter provenance compared to the cooler‐drier provenance, suggesting that P. massoniana seedlings from warmer‐wetter areas may cope better with future warm and dry environments.

Climate change-induced drought and heatwave events (hotter droughts) are causing mass plant dieback events globally. Recently, Uluru-Kata Tjuta National Park (UKTNP) in central Australia experienced a widespread plant dieback (mortality) event. Anangu (Traditional Owners) are concerned about the resulting negative impacts to ecosystems and wish to understand more about the underlying causes of mass plant death. With a focus on ecologically and culturally significant species chosen by Anangu, we measured morphological and physiological traits to characterize differences in physiological strategy underpinning the patterns of dieback observed at UKTNP. Maintenance of leaf relative water content (RWC) was the leaf trait that best predicted dieback severity, with all species that had low levels of dieback exhibiting drought-avoidance strategies where RWC was maintained between spring and summer. Most species with moderate and high levels of dieback exhibited drought-tolerance strategies, evidenced by large declines in seasonal RWC and higher wood densities. However, two small shrub species with high dieback severity may have died due to failure of different physiological mechanisms—one of hydraulic failure via drought tolerance and one of carbon limitation via drought avoidance—highlighting the importance of considering species-specific trait combinations to understand drivers of mortality. Understanding the drivers of dieback will help to support Anangu-led land stewardship and conserve the natural and cultural values of this important landscape. Pitjantjatjara Kuwari, punu munu ukiri tjuta piltiringanyi manta winkingka panya ailurungka munu kuli pulkangka. Mungatu, Uluru-Kata Tjuta National Parkangka, ailuru pulkangku piltira wiyanu punu munu ukiri tjuta Anangu tjutaku. Nganana mukuringanyi nintiringkutjaku nyaa nguru punu munu ukiri tjuta wiyaringu, ka punu kutjupa tjuta palyatu ngaranyi. Nganana kulini punu munu ukiri wankatu ngaranyi panya kapi ngarinyi nyarlpingka. Tjingurula kulini punu pilti tjutangku putu kapi Kanyini nyarlpingka. Tjinguru kapi putu pakani nyarlpinguru. Pukara munu kaliny-kalinypa tjuta wiyaringu ailurungka. Tjinguru pukarangku kapi kawalanu aturu ungu. Tjinguru kaliny-kalinypangku mai munu tjuratja kawalanu aturu ungu. Nyangatjalanya nintini panya punu wiyaringanyi nyanga paluru tjanalanguru, punu kutjupa tjuta tjinguru wiyaringanyi kutjupa kutjupanguru. Nganana tjungu warkarira nintiringkutjaku panya ailurungku ngura nganampa piltini. Nyanga palulanguru nganana ngura nganampa wirura atunmangkuntjaku.

Climate change-induced drought and heatwave events (hotter droughts) are causing mass plant dieback events globally. Recently, Uluru-Kata Tjuta National Park (UKTNP) in central Australia saw a widespread plant dieback (mortality) event, resulting in negative impacts to the ecosystems and concern and a desire to understand more about the underlying causes of mass plant death from Anangu (Traditional Owners). We measured morphological and physiological traits that were hypothesised to drive physiological mechanisms underpinning the patterns of dieback observed at UKTNP in culturally important species chosen by Anangu. Maintenance of leaf relative water content (RWC) was the leaf trait that best predicted dieback severity, with all low dieback severity species exhibiting drought-avoidance strategies, where RWC was maintained between spring and summer. Most moderate and high dieback severity species exhibited drought-tolerance strategies, evidenced by large declines in seasonal RWC compensated by higher wood densities. However, two small shrub species with high dieback severity likely died due to failure of different physiological mechanisms - one of hydraulic failure and one of carbon starvation - highlighting the importance of considering species-specific trait combinations to understand drivers of mortality. Hotter drought events in central Australia are likely to impact not only plant communities, but Anangu culture.

Extreme drought events are predicted to increase with climate change, yet their impacts on ecosystem carbon dynamics under warming and elevated carbon dioxide (eCO ₂ ) remain unclear. In a peatland experiment with five warming treatments each under ambient carbon dioxide (aCO ₂ ) and eCO ₂ (+500 parts per million), a 2-month extreme drought in 2021 reduced net ecosystem productivity by 444.0 ± 65.8 and 736.6 ± 57.8 grams of carbon per square meter at +9°C under aCO ₂ and eCO ₂ , respectively—228.6 ± 56.8% and 381.9 ± 83.4% of the reduction at +0°C under aCO ₂ . This exacerbation was driven by warming-induced water table decline, prolonged low water tables, and CO ₂ -enhanced substrate availability through increased plant carbon inputs. Findings indicate that future climate will greatly amplify carbon loss during extreme drought, reinforcing positive carbon-climate feedbacks.