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Plant functional traits hold the potential to greatly improve the understanding and prediction of climate impacts on ecosystems and carbon cycle feedback to climate change. Traits are commonly used to place species along a global conservative-acquisitive trade-off, yet how and if functional traits and conservative-acquisitive trade-offs scale up to mediate community and ecosystem fluxes is largely unknown. Here, we combine functional trait datasets and multibiome datasets of forest water and carbon fluxes at the species, community, and ecosystem-levels to quantify the scaling of the tradeoff between maximum flux and sensitivity to vapor pressure deficit. We find a strong conservative-acquisitive trade-off at the species scale, which weakens modestly at the community scale and largely disappears at the ecosystem scale. Functional traits, particularly plant water transport (hydraulic) traits, are strongly associated with the key dimensions of the conservative-acquisitive trade-off at community and ecosystem scales, highlighting that trait composition appears to influence community and ecosystem flux dynamics. Our findings provide a foundation for improving carbon cycle models by revealing i) that plant hydraulic traits are most strongly associated with community-and ecosystem scale flux dynamics and ii) community assembly dynamics likely need to be considered explicitly, as they give rise to ecosystem-level flux dynamics that differ substantially from trade-offs identified at the species-level. [ABSTRACT FROM AUTHOR]

The article emphasizes the importance of establishing a solid scientific foundation for nature-based climate solutions (NbCS) in the United States. While NbCS have gained support, their implementation has outpaced scientific understanding. The article highlights challenges in evaluating and monitoring NbCS, such as a lack of data and standardized protocols. The authors propose a hierarchical system of networks, open data sharing, and improved monitoring approaches to develop robust and credible NbCS programs. They also suggest prioritizing measurements from various sources, including eddy covariance flux towers, soil and biomass inventories, and satellite data. By investing in data collection and research, the US can reduce risks and develop a scientific basis for NbCS. [Extracted from the article]

The response of forests to climate change depends in part on whether the photosynthetic benefit from increased atmospheric CO2 (ΔCa = future minus historic CO2) compensates for increased physiological stresses from higher temperature (ΔT). We predicted the outcome of these competing responses by using optimization theory and a mechanistic model of tree water transport and photosynthesis. We simulated current and future productivity, stress, and mortality in mature monospecific stands with soil, species, and climate sampled from 20 continental US locations. We modeled stands with and without acclimation to ΔCa and ΔT, where acclimated forests adjusted leaf area, photosynthetic capacity, and stand density to maximize productivity while avoiding stress. Without acclimation, the ΔCa-driven boost in net primary productivity (NPP) was compromised by ΔT-driven stress and mortality associated with vascular failure. With acclimation, the ΔCa-driven boost in NPP and stand biomass (C storage) was accentuated for cooler futures but negated for warmer futures by a ΔT-driven reduction in NPP and biomass. Thus, hotter futures reduced forest biomass through either mortality or acclimation. Forest outcomes depended on whether projected climatic ΔCa/ΔT ratios were above or below physiological thresholds that neutralized the negative impacts of warming. Critically, if forests do not acclimate, the ΔCa/ΔT must be above ca. 89 ppm⋅°C-1 to avoid chronic stress, a threshold met by 55% of climate projections. If forests do acclimate, the ΔCa/ΔT must rise above ca. 67 ppm⋅°C-1 for NPP and biomass to increase, a lower threshold met by 71% of projections. [ABSTRACT FROM AUTHOR]

Forests play a major role in the global carbon cycle. Previous studies on the capacity of forests to sequester atmospheric CO2 have mostly focused on carbon uptake, but the roles of carbon turnover time and its spatiotemporal changes remain poorly understood. Here, we used long-term inventory data (1955 to 2018) from 695 mature forest plots to quantify temporal trends in living vegetation carbon turnover time across tropical, temperate, and cold climate zones, and compared plot data to 8 Earth system models (ESMs). Long-term plots consistently showed decreases in living vegetation carbon turnover time, likely driven by increased tree mortality across all major climate zones. Changes in living vegetation carbon turnover time were negatively correlated with CO2 enrichment in both forest plot data and ESM simulations. However, plot-based correlations between living vegetation carbon turnover time and climate drivers such as precipitation and temperature diverged from those of ESM simulations. Our analyses suggest that forest carbon sinks are likely to be constrained by a decrease in living vegetation carbon turnover time, and accurate projections of forest carbon sink dynamics will require an improved representation of tree mortality processes and their sensitivity to climate in ESMs. [ABSTRACT FROM AUTHOR]

The response of forests to climate change depends in part on whether the photosynthetic benefit from increased atmospheric CO 2 (∆C a = future minus historic CO 2 ) compensates for increased physiological stresses from higher temperature (∆T). We predicted the outcome of these competing responses by using optimization theory and a mechanistic model of tree water transport and photosynthesis. We simulated current and future productivity, stress, and mortality in mature monospecific stands with soil, species, and climate sampled from 20 continental US locations. We modeled stands with and without acclimation to ∆C a and ∆T, where acclimated forests adjusted leaf area, photosynthetic capacity, and stand density to maximize productivity while avoiding stress. Without acclimation, the ∆C a -driven boost in net primary productivity (NPP) was compromised by ∆T-driven stress and mortality associated with vascular failure. With acclimation, the ∆C a -driven boost in NPP and stand biomass (C storage) was accentuated for cooler futures but negated for warmer futures by a ∆T-driven reduction in NPP and biomass. Thus, hotter futures reduced forest biomass through either mortality or acclimation. Forest outcomes depended on whether projected climatic ∆C a /∆T ratios were above or below physiological thresholds that neutralized the negative impacts of warming. Critically, if forests do not acclimate, the ∆C a /∆T must be above ca 89 ppm⋅°C -1 to avoid chronic stress, a threshold met by 55% of climate projections. If forests do acclimate, the ∆C a /∆T must rise above ca 67 ppm⋅°C -1 for NPP and biomass to increase, a lower threshold met by 71% of projections., Competing Interests: The authors declare no competing interest.