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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.
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Abstract Metrics to quantify regulation of plant water status at the daily as opposed to the seasonal scale do not presently exist. This gap is significant since plants are hypothesised to regulate their water potential not only with respect to slowly changing soil drought but also with respect to faster changes in air vapour pressure deficit (VPD), a variable whose importance for plant physiology is expected to grow because of higher temperatures in the coming decades. We present a metric, the stringency of water potential regulation, that can be employed at the daily scale and quantifies the effects exerted on plants by the separate and combined effect of soil and atmospheric drought. We test our theory using datasets from two experiments where air temperature and VPD were experimentally manipulated. In contrast to existing metrics based on soil drought that can only be applied at the seasonal scale, our metric successfully detects the impact of atmospheric warming on the regulation of plant water status. We show that the thermodynamic effect of VPD on plant water status can be isolated and compared against that exerted by soil drought and the covariation between VPD and soil drought. Furthermore, in three of three cases, VPD accounted for more than 5 MPa of potential effect on leaf water potential. We explore the significance of our findings in the context of potential future applications of this metric from plant to ecosystem scale.more » « less
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Pfautsch, Sebastian (Ed.)Given the pressing challenges posed by climate change, it is crucial to develop a deeper understanding of the impacts of escalating drought and heat stress on terrestrial ecosystems and the vital services they offer. Soil and plant water potential play a pivotal role in governing the dynamics of water within ecosystems and exert direct control over plant function and mortality risk during periods of ecological stress. However, existing observations of water potential suffer from significant limitations, including their sporadic and discontinuous nature, inconsistent representation of relevant spatio-temporal scales and numerous methodological challenges. These limitations hinder the comprehensive and synthetic research needed to enhance our conceptual understanding and predictive models of plant function and survival under limited moisture availability. In this article, we present PSInet (PSI—for the Greek letter Ψ used to denote water potential), a novel collaborative network of researchers and data, designed to bridge the current critical information gap in water potential data. The primary objectives of PSInet are as follows. (i) Establishing the first openly accessible global database for time series of plant and soil water potential measurements, while providing important linkages with other relevant observation networks. (ii) Fostering an inclusive and diverse collaborative environment for all scientists studying water potential in various stages of their careers. (iii) Standardizing methodologies, processing and interpretation of water potential data through the engagement of a global community of scientists, facilitated by the dissemination of standardized protocols, best practices and early career training opportunities. (iv) Facilitating the use of the PSInet database for synthesizing knowledge and addressing prominent gaps in our understanding of plants’ physiological responses to various environmental stressors. The PSInet initiative is integral to meeting the fundamental research challenge of discerning which plant species will thrive and which will be vulnerable in a world undergoing rapid warming and increasing aridification.more » « less
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Frequent observations of higher mortality in larger trees than in smaller ones during droughtshave sparked an increasing interest in size-dependent drought-induced mortality. However, theunderlying physiological mechanisms are not well understood, with height-associated hydraulicconstraints often being implied as the potential mechanism driving increased droughtvulnerability. We performed a quantitative synthesis on how key traits that drive plant waterand carbon economy change with tree height within species and assessed the implications thatthe different constraints and compensations may have on the interacting mechanisms (hydraulicfailure, carbon starvation and/or biotic-agent attacks) affecting tree vulnerability to drought.While xylem tension increases with tree height, taller trees present a range of structural andfunctional adjustments, including more efficient water use and transport and greater wateruptake and storage capacity, that mitigate the path-length-associated drop in water potential.These adaptations allow taller trees to withstand episodic water stress. Conclusive evidence forheight-dependent increased vulnerability to hydraulic failure and carbon starvation, and theircoupling to defence mechanisms and pest and pathogen dynamics, is still lacking. Furtherresearch is needed, particularly at the intraspecific level, to ascertain the specific conditions andthresholds above which height hinders tree survival under drought.more » « less
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The exchange of multiple greenhouse gases (i.e., CO2 </sub>and CH4</sub>) between tree stems and the atmosphere represents a knowledge gap in the global carbon cycle. Stem CO2</sub> and CH4</sub> fluxes vary across time and space and is unclear which are their individual or shared drivers. This dataset contains information of CO2</sub> and CH4</sub> fluxes at different stem heights combining manual (biweekly; n=678) and automated (hourly; n>38,000) measurements in a temperate upland forest.</div>This study was performed in an upland forested area at the St. Jones Reserve [39°5’20”N, 75°26’21”W], a component of the Delaware National Estuarine Research Reserve (DNERR).</div></div>The dominant vegetation species are bitternut hickory (Carya cordiformis</i>), eastern red cedar (Juniperus virginiana</i> L.), American holly (Ilex opaca</i> (Ashe)), sweet gum (Liquidambar styraciflua</i> L.) and black gum (Nyssa sylvatica</i> (Marshall)), with an overall tree density of 678 stems ha-1</sup> and mean diameter at breast height (DBH) of 25.7±13.9 cm (mean±sd). We studied bitternut hickory, which is one of the most important species in the study site, accounting for 24.9% of the total basal area.</div></div>For code </div>more » « less
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Abstract Tundra and boreal ecosystems encompass the northern circumpolar permafrost region and are experiencing rapid environmental change with important implications for the global carbon (C) budget. We analysed multi-decadal time series containing 302 annual estimates of carbon dioxide (CO2) flux across 70 permafrost and non-permafrost ecosystems, and 672 estimates of summer CO2flux across 181 ecosystems. We find an increase in the annual CO2sink across non-permafrost ecosystems but not permafrost ecosystems, despite similar increases in summer uptake. Thus, recent non-growing-season CO2losses have substantially impacted the CO2balance of permafrost ecosystems. Furthermore, analysis of interannual variability reveals warmer summers amplify the C cycle (increase productivity and respiration) at putatively nitrogen-limited sites and at sites less reliant on summer precipitation for water use. Our findings suggest that water and nutrient availability will be important predictors of the C-cycle response of these ecosystems to future warming.more » « less
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Abstract Tree stems exchange CO2, CH4and N2O with the atmosphere but the magnitudes, patterns and drivers of these greenhouse gas (GHG) fluxes remain poorly understood. Our understanding mainly comes from static-manual measurements, which provide limited information on the temporal variability and magnitude of these fluxes. We measured hourly CO2, CH4and N2O fluxes at two stem heights and adjacent soils within an upland temperate forest. We analyzed diurnal and seasonal variability of fluxes and biophysical drivers (i.e., temperature, soil moisture, sap flux). Tree stems were a net source of CO2(3.80 ± 0.18 µmol m−2s−1; mean ± 95% CI) and CH4(0.37 ± 0.18 nmol m−2s−1), but a sink for N2O (−0.016 ± 0.008 nmol m−2s−1). Time series analysis showed diurnal temporal correlations between these gases with temperature or sap flux for certain days. CO2and CH4showed a clear seasonal pattern explained by temperature, soil water content and sap flux. Relationships between stem, soil fluxes and their drivers suggest that CH4for stem emissions could be partially produced belowground. High-frequency measurements demonstrate that: a) tree stems exchange GHGs with the atmosphere at multiple time scales; and b) are needed to better estimate fluxes magnitudes and understand underlying mechanisms of GHG stem emissions.more » « less
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null (Ed.)Abstract. Evaporation (E) and transpiration (T) respond differentlyto ongoing changes in climate, atmospheric composition, and land use. It isdifficult to partition ecosystem-scale evapotranspiration (ET) measurementsinto E and T, which makes it difficult to validate satellite data and landsurface models. Here, we review current progress in partitioning E and T andprovide a prospectus for how to improve theory and observations goingforward. Recent advancements in analytical techniques create newopportunities for partitioning E and T at the ecosystem scale, but theirassumptions have yet to be fully tested. For example, many approaches topartition E and T rely on the notion that plant canopy conductance andecosystem water use efficiency exhibit optimal responses to atmosphericvapor pressure deficit (D). We use observations from 240 eddy covariance fluxtowers to demonstrate that optimal ecosystem response to D is a reasonableassumption, in agreement with recent studies, but more analysis is necessaryto determine the conditions for which this assumption holds. Anothercritical assumption for many partitioning approaches is that ET can beapproximated as T during ideal transpiring conditions, which has beenchallenged by observational studies. We demonstrate that T can exceed 95 %of ET from certain ecosystems, but other ecosystems do not appear to reachthis value, which suggests that this assumption is ecosystem-dependent withimplications for partitioning. It is important to further improve approachesfor partitioning E and T, yet few multi-method comparisons have beenundertaken to date. Advances in our understanding of carbon–water couplingat the stomatal, leaf, and canopy level open new perspectives on how toquantify T via its strong coupling with photosynthesis. Photosynthesis can beconstrained at the ecosystem and global scales with emerging data sourcesincluding solar-induced fluorescence, carbonyl sulfide flux measurements,thermography, and more. Such comparisons would improve our mechanisticunderstanding of ecosystem water fluxes and provide the observationsnecessary to validate remote sensing algorithms and land surface models tounderstand the changing global water cycle.more » « less
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