Papers by Jean-christophe Domec
Acta horticulturae, May 1, 2013
Over the last decade, it has become increasingly apparent that the properties of the root-to-leaf... more Over the last decade, it has become increasingly apparent that the properties of the root-to-leaf hydraulic pathway in trees can quickly acclimate over short timescales. In this context, the term hydraulic architecture takes on a broader meaning, making it essential to understand how static and, above all, dynamic hydraulic properties are integrated at the organismal level. Here we discuss some key processes operating in roots, stems and leaves that act in a coordinated manner to stabilize plant hydraulic function under both non-extreme and extreme conditions such as prolonged drought. Hydraulic redistribution (HR) is often manifested as reverse flow of water in shallow roots via transport of water from deeper soil layers. By partially uncoupling root water potential from that of the surrounding dry soil and slowing the rate of soil drying, HR serves to mitigate seasonal drought-induced hydraulic dysfunction in roots and to maintain nutrient uptake, thereby extending their lifespan. Stems of many species show a high capacity for refilling of embolized xylem conduits. This is an important component of their apparent hydraulic safety margins that is likely to be related to xylem structural features that confer resistance to tension-induced embolism. Hydraulic capacitance in stems contributes to hydraulic safety margins by dampening fluctuations in xylem tension that might otherwise result in excessive embolism. Embolism-induced loss of stem xylem conductivity can be partially compensated by rapid increases in the ionic concentration of xylem sap in remaining functional conduits. In many species, leaves lose and recover a substantial fraction of their hydraulic conductance daily, suggestive of a hydraulic circuit breaker function that promotes stomatal closure to avoid excessive embolism in stems upstream. The functioning of these homeostatic processes is likely to be influenced by the drier climates that are predicted for much of the globe.
Plant Cell and Environment, Oct 6, 2011
Co-occurring species often have different strategies for tolerating daily cycles of water stress.... more Co-occurring species often have different strategies for tolerating daily cycles of water stress. One underlying parameter that can link together the suite of traits that enables a given strategy is wood density. Here we compare hydraulic traits of two pioneer species from a tropical forest in Panama that differ in wood density: Miconia argentea and Anacardium excelsum. As hypothesized, the higher wood density of Miconia was associated with smaller diameter vessels and fibres, more water stress-resistant leaves and stems, and roughly half the capacitance of the lower wood density Anacardium. However, the scaling of hydraulic parameters such as the increases in leaf area and measures of hydraulic conductivity with stem diameter was remarkably similar between the two species. The collection of traits exhibited by Miconia allowed it to tolerate more water stress than Anacardium, which relied more heavily on its capacitance to buffer daily water potential fluctuations. This work demonstrates the importance of examining a range of hydraulic traits throughout the plant and highlights the spectrum of possible strategies for coping with daily and seasonal water stress cycles.
Oecologia, Mar 29, 2011
Plant hydraulic architecture (PHA) has been linked to water transport sufficiency, photosynthetic... more Plant hydraulic architecture (PHA) has been linked to water transport sufficiency, photosynthetic rates, growth form and attendant carbon allocation. Despite its influence on traits central to conferring an overall competitive advantage in a given environment, few studies have examined whether key aspects of PHA are indicative of successional stage, especially within mature individuals. While it is well established that wood density (WD) tends to be lower in early versus late successional tree species, and that WD can influence other aspects of PHA, the interaction of WD, successional stage and the consequent implications for PHA have not been sufficiently explored. Here, we studied differences in PHA at the scales of wood anatomy to whole-tree hydraulic conductance in species in early versus late successional Panamanian tropical forests. Although the trunk WD was indistinguishable between the successional groups, the branch WD was lower in the early successional species. Across all species, WD correlated negatively with vessel diameter and positively with vessel packing density. The ratio of branch:trunk vessel diameter, branch sap flux and whole-tree leaf-specific conductance scaled negatively with branch WD across species. Pioneer species showed greater sap flux in branches than in trunks and a greater leaf-specific hydraulic conductance, suggesting that pioneer species can move greater quantities of water at a given tension gradient. In combination with the greater water storage capacitance associated with lower WD, these results suggest these pioneer species can save on the carbon expenditure needed to build safer xylem and instead allow more carbon to be allocated to rapid growth.
Plant Cell and Environment, Jan 29, 2018
From 2011 to 2013, Texas experienced its worst drought in recorded history. This event provided a... more From 2011 to 2013, Texas experienced its worst drought in recorded history. This event provided a unique natural experiment to assess species-specific responses to extreme drought and mortality of four co-occurring woody species: Quercus fusiformis, Diospyros texana, Prosopis glandulosa, and Juniperus ashei. We examined hypothesized mechanisms that could promote these species' diverse mortality patterns using postdrought measurements on surviving trees coupled to retrospective process modelling. The species exhibited a wide range of gas exchange responses, hydraulic strategies, and mortality rates. Multiple proposed indices of mortality mechanisms were inconsistent with the observed mortality patterns across species, including measures of the degree of iso/anisohydry, photosynthesis, carbohydrate depletion, and hydraulic safety margins. Large losses of spring and summer whole-tree conductance (driven by belowground losses of conductance) and shallower rooting depths were associated with species that exhibited greater mortality. Based on this retrospective analysis, we suggest that species more vulnerable to drought were more likely to have succumbed to hydraulic failure belowground.
Oecologia, Feb 6, 2008
Stomatal regulation of transpiration constrains leaf water potential ('¥ L) within species-specif... more Stomatal regulation of transpiration constrains leaf water potential ('¥ L) within species-specific ranges that presumably avoid excessive tension and embolism in the stem xylem upstream. However, the hydraulic resistance of leaves can be highly variable over short time scales, uncoupling tension in the xylem of leaves from that in the stems to which they are attached. We evaluated a suite of leaf and stem functional traits governing water relations in individuals of 11 lowland tropical forest tree species to determine the manner in which the traits were coordinated with stem xylem vulnerability to embolism. Stomatal regulation of '¥ L was associated with minimum values of water potential in branches ('¥ br) whose functional significance was similar across species. Minimum values of '¥br coincided with the Communicated by Manuel Lerdau.
Agricultural and Forest Meteorology, May 1, 2019
Monitoring drought in real-time using minimal field data is a challenge for ecosystem management ... more Monitoring drought in real-time using minimal field data is a challenge for ecosystem management and conservation. Most methods require extensive data collection and in-situ calibration and accuracy is difficult to evaluate. Here, we demonstrated how the space-borne canopy "thermal stress", defined as surface-air temperature difference, provides a reliable surrogate for drought-induced water stress in vegetation. Using physics-based relationships that accommodate uncertainties, we showed how changes in canopy water flux from ground-based measurements relate to both the surface energy balance and remotely-sensed thermal stress. Field measurements of evapotranspiration in the southeastern and northwestern US verify this approach based on sensitivity of evapotranspiration to thermal stress in a large range of atmospheric and climate conditions. We found that a 1 °C change in the thermal stress is comparable to 1-1.2 mm day -1 of evapotranspiration, depending on site and climate conditions. We quantified temporal and spatial sensitivity of evapotranspiration to the thermal stress and showed that it has the strongest relationship with evapotranspiration during warm and dry seasons, when monitoring drought is essential. Using only air and surface temperatures, we predicted the inter-annual anomaly in thermal stress across the contiguous United States over the course of 15 years and compared it with conventional drought indices. Among drought metrics that were considered in this study, the thermal stress had the highest correlation values. Our sensitivity results demonstrated that the thermal stress is a particularly strong indicator of water-use in warm seasons and regions. This simple metric can be used at varying time-scales to monitor surface evapotranspiration and drought in large spatial extents in near real-time.
Remote Sensing of Environment, May 1, 2018
Interactions between climate and ecosystem properties that control phenological responses to clim... more Interactions between climate and ecosystem properties that control phenological responses to climate warming and drought are poorly understood. To determine contributions from these interactions, we used space-borne remotely sensed vegetation indices to monitor leaf development across climate gradients and ecoregions in the southeastern United States. We quantified how air temperature, drought severity, and canopy thermal stress contribute to changes in leaf flushing from mountainous to coastal plain regions by developing a hierarchical state-space Bayesian model. We synthesized daily field climate data with daily vegetation indices and canopy surface temperature during spring green-up season at 59 sites in the southeastern United States between 2001 and 2012. Our results demonstrated strong interaction effects between ecosystem properties and climate variables across ecoregions. We found spring green-up is faster in the mountains, while coastal forests express a larger sensitivity to inter-annual temperature anomalies. Despite our detection of a decreasing trend in sensitivity to warming with temperature in all regions, we identified an ecosystem interaction: Deciduous dominated forests are less sensitive to warming than are those with fewer deciduous trees, likely due to the continuous presence of leaves in evergreen species throughout the season. Mountainous forest green-up is more susceptible to intensifying drought and moisture deficit, while coastal areas are relatively resilient. We found that with increasing canopy thermal stress, defined as canopy-air temperature difference, leaf development slows following dry years, and accelerates following wet years.
Authorea (Authorea), Oct 17, 2021
The coordination of plant leaf water potential (Ψ L ) regulation and xylem vulnerability to embol... more The coordination of plant leaf water potential (Ψ L ) regulation and xylem vulnerability to embolism is fundamental for understanding the tradeoffs between carbon uptake and risk of hydraulic damage. There is a general consensus that trees with vulnerable xylem more conservatively regulate Ψ L than plants with resistant xylem. We evaluated if this paradigm applied to three important eastern US temperate tree species, Quercus alba L., Acer saccharum Marsh. and Liriodendron tulipifera L., by synthesizing 1600 Ψ L observations, 122 xylem embolism curves and xylem anatomical measurements across 10 forests spanning pronounced hydroclimatological gradients and ages. We found that, unexpectedly, the species with the most vulnerable xylem (Q. alba) regulated Ψ L less strictly than the other species. This relationship was found across all sites, such that coordination among traits was largely unaffected by climate and stand age. Quercus species are perceived to be among the most drought tolerant temperate US forest species; however, our results suggest their relatively loose Ψ L regulation in response to hydrologic stress occurs with a substantial hydraulic cost that may expose them to novel risks in a more drought-prone future.
Authorea (Authorea), Apr 29, 2021
Quantifying the spatial variability of species-specific tree transpiration across hillslopes is i... more Quantifying the spatial variability of species-specific tree transpiration across hillslopes is important for estimating watershed-scale evapotranspiration (ET) and predicting spatial drought effects on vegetation. The objectives of this study are to (1) assess sap flux density (J s ) and tree-level transpiration (T s ) across three contrasting zones a (riparian buffer, mid-hillslope and upland-hillslope, (2) determine how species-specific J s responds to vapour pressure deficit (VPD) and ( ) estimate watershed-level transpiration (T w ) using T s derived from each zone. During 2015 and 2016, we measured J s in eight tree species in the three topographic zones in a small 12-ha forested watershed in the Piedmont region of central North Carolina. In the dry year of 2015, loblolly pine (Pinus taeda), Virginia pine (Pinus virginiana) and sweetgum (Liquidambar styraciflua) J s rates were significantly higher in the riparian buffer when compared to the other two zones. In contrast, J s rates in tulip poplar (Liriodendron tulipifera) and red maple (Acer rubrum) were significantly lower in the buffer than in the mid-hillslope. Daily T s varied by zone and ranged from 10 to 93 L/day in the dry year and from 9 to 122 L/day in the wet year (2016). J s responded nonlinearly to VPD in all species and zones. Annual T w was 447, 377 and 340 mm based on scaled-J s data for the buffer, mid-hillslope and uplandhillslope, respectively. We conclude that large spatial variability in J s and scaled T w was driven by differences in soil moisture at each zone and forest composition. Consequently, spatial heterogeneity of vegetation and soil moisture must be considered when accurately quantifying watershed level ET.
Journal of Experimental Botany, Mar 19, 2021
The influence of aquaporin (AQP) activity on plant water movement remains unclear, especially in ... more The influence of aquaporin (AQP) activity on plant water movement remains unclear, especially in plants subject to unfavorable conditions. We applied a multitiered approach at a range of plant scales to (i) characterize the resistances controlling water transport under drought, flooding, and flooding plus salinity conditions; (ii) quantify the respective effects of AQP activity and xylem structure on root (K root ), stem (K stem ), and leaf (K leaf ) conductances; and (iii) evaluate the impact of AQP-regulated transport capacity on gas exchange. We found that drought, flooding, and flooding plus salinity reduced K root and root AQP activity in Pinus taeda, whereas K root of the flood-tolerant Taxodium distichum did not decline under flooding. The extent of the AQP control of transport efficiency varied among organs and species, ranging from 35-55% in K root to 10-30% in K stem and K leaf . In response to treatments, AQP-mediated inhibition of K root rather than changes in xylem acclimation controlled the fluctuations in K root . The reduction in stomatal conductance and its sensitivity to vapor pressure deficit were direct responses to decreased whole-plant conductance triggered by lower K root and larger resistance belowground. Our results provide new mechanistic and functional insights on plant hydraulics that are essential to quantifying the influences of future stress on ecosystem function.
Beyond Carbon Flux Partitioning: Inferring the Dynamic Non-structural Carbon Storage and Carbon Allocation at the Canopy Scale from Continuous Fluxes
AGU Fall Meeting Abstracts, Dec 1, 2020
Change of Tree-ring δ13C, δ18O and Water Use Efficiency of Loblolly Pine in Southeastern US in Response to Drought
Change of intrinsic Water Use Efficiency of Loblolly Pine in Southeastern US in Response to Drought and Fertilization
Methane Fluxes and Drivers in a Coastal Freshwater Forested Wetland: From the Soil to the Canopy
Trait generality in two temperate forest regions: Do community weighted trait responses to environment translate between continents?
Water and Energy Balances of Loblolly Pine Plantation Forests during a Full Stand Rotation
Ecosystem Level Methane Dynamics in a Southern Forest Wetland
Regional Estimates of Drought-Induced Tree Canopy Loss across Texas
Acta Horticulturae, 2013
Over the last decade, it has become increasingly apparent that the properties of the root-to-leaf... more Over the last decade, it has become increasingly apparent that the properties of the root-to-leaf hydraulic pathway in trees can quickly acclimate over short timescales. In this context, the term hydraulic architecture takes on a broader meaning, making it essential to understand how static and, above all, dynamic hydraulic properties are integrated at the organismal level. Here we discuss some key processes operating in roots, stems and leaves that act in a coordinated manner to stabilize plant hydraulic function under both non-extreme and extreme conditions such as prolonged drought. Hydraulic redistribution (HR) is often manifested as reverse flow of water in shallow roots via transport of water from deeper soil layers. By partially uncoupling root water potential from that of the surrounding dry soil and slowing the rate of soil drying, HR serves to mitigate seasonal drought-induced hydraulic dysfunction in roots and to maintain nutrient uptake, thereby extending their lifespan. Stems of many species show a high capacity for refilling of embolized xylem conduits. This is an important component of their apparent hydraulic safety margins that is likely to be related to xylem structural features that confer resistance to tension-induced embolism. Hydraulic capacitance in stems contributes to hydraulic safety margins by dampening fluctuations in xylem tension that might otherwise result in excessive embolism. Embolism-induced loss of stem xylem conductivity can be partially compensated by rapid increases in the ionic concentration of xylem sap in remaining functional conduits. In many species, leaves lose and recover a substantial fraction of their hydraulic conductance daily, suggestive of a hydraulic circuit breaker function that promotes stomatal closure to avoid excessive embolism in stems upstream. The functioning of these homeostatic processes is likely to be influenced by the drier climates that are predicted for much of the globe.
Wood anatomical traits shape a xylem segment's hydraulic efficiency and resistance to embolism sp... more Wood anatomical traits shape a xylem segment's hydraulic efficiency and resistance to embolism spread due to declining water potential. It has been known for decades that variations in conduit connectivity play a role in altering xylem hydraulics. However, evaluating the precise effect of conduit connectivity has been elusive. The objective here is to establish an analytical linkage between conduit connectivity and grouping and tissue-scale hydraulics. It is hypothesized that an increase in conduit connectivity brings improved resistance to embolism spread due to increased hydraulic pathway redundancy. However, an increase in conduit connectivity could also reduce resistance due to increased speed of embolism spread with respect to pressure. We elaborate on this trade-off using graph theory, percolation theory and computational modeling of xylem. The results are validated using anatomical measurements of Acer branch xylem. Considering only species with vessels, increases in connectivity improve resistance to embolism spread without negatively affecting hydraulic conductivity. The often measured grouping index fails to capture the totality of the effect of conduit connectivity on xylem hydraulics. Variations in xylem network characteristics, such as conduit connectivity, might explain why hypothesized trends among woody species, such as the 'safety-efficiency' trade-off hypothesis, are weaker than expected.
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Papers by Jean-christophe Domec