Golnazalsadat Mirfenderesgi

Species‐specific transpiration responses to intermediate disturbance in a northern hardwood forest

Intermediate disturbances shape forest structure and composition, which may in turn alter carbon, nitrogen, and water cycling. We used a large-scale experiment in a forest in northern lower Michigan where we prescribed an intermediate disturbance by stem girdling all canopy-dominant early successional trees to simulate an accelerated age-related senescence associated with natural succession. Using 3 years of eddy covariance and sap flux measurements in the disturbed area and an adjacent control plot, we analyzed disturbance-induced changes to plot level and species-specific transpiration and stomatal conductance. We found transpiration to be ~15% lower in disturbed plots than in unmanipulated control plots. However, species-specific responses to changes in microclimate varied. While red oak and white pine showed increases in stomatal conductance during postdisturbance (62.5 and 132.2%, respectively), red maple reduced stomatal conductance by 36.8%. We used the hysteresis between sap flux and vapor pressure deficit to quantify diurnal hydraulic stress incurred by each species in both plots. Red oak, a ring porous anisohydric species, demonstrated the largest mean relative hysteresis, while red maple, bigtooth aspen, and paper birch, all diffuse porous species, had the lowest relative hysteresis. We employed the Penman-Monteith model for LE to demonstrate that these species-specific responses to disturbance are not well captured using current modeling strategies and that accounting for changes to leaf area index and plot microclimate are insufficient to fully describe the effects of disturbance on transpiration.

Tree level hydrodynamic approach for resolving aboveground water storage and stomatal conductance and modeling the effects of tree hydraulic strategy

The finite difference ecosystem-scale tree crown hydrodynamics model version 2 (FETCH2) is a tree-scale hydrodynamic model of transpiration. The FETCH2 model employs a finite difference numerical methodology and a simplified single-beam conduit system to explicitly resolve xylem water potentials throughout the vertical extent of a tree. Empirical equations relate water potential within the stem to stomatal conductance of the leaves at each height throughout the crown. While highly simplified, this approach brings additional realism to the simulation of transpiration by linking stomatal responses to stem water potential rather than directly to soil moisture, as is currently the case in the majority of land surface models. FETCH2 accounts for plant hydraulic traits, such as the degree of anisohydric/isohydric response of stomata, maximal xylem conductivity, vertical distribution of leaf area, and maximal and minimal xylem water content. We used FETCH2 along with sap flow and eddy covariance data sets collected from a mixed plot of two genera (oak/pine) in Silas Little Experimental Forest, NJ, USA, to conduct an analysis of the intergeneric variation of hydraulic strategies and their effects on diurnal and seasonal transpiration dynamics. We define these strategies through the parameters that describe the genus level transpiration and xylem conductivity responses to changes in stem water potential. Our evaluation revealed that FETCH2 considerably improved the simulation of ecosystem transpiration and latent heat flux in comparison to more conventional models. A virtual experiment showed that the model was able to capture the effect of hydraulic strategies such as isohydric/anisohydric behavior on stomatal conductance under different soil-water availability conditions.

Trait-based representation of hydrological functional properties of plants in weather and ecosystem models

Land surface models and dynamic global vegetation models typically represent vegetation through coarse plant functional type groupings based on leaf form, phenology, and bioclimatic limits. Although these groupings were both feasible and functional for early model generations, in light of the pace at which our knowledge of functional ecology, ecosystem demographics, and vegetation-climate feedbacks has advanced and the ever growing demand for enhanced model performance, these groupings have become antiquated and are identified as a key source of model uncertainty. The newest wave of model development is centered on shifting the vegetation paradigm away from plant functional types (PFTs) and towards flexible trait-based representations. These models seek to improve errors in ecosystem fluxes that result from information loss due to over-aggregation of dissimilar species into the same functional class. We advocate the importance of the inclusion of plant hydraulic trait representation within the new paradigm through a framework of the whole-plant hydraulic strategy. Plant hydraulic strategy is known to play a critical role in the regulation of stomatal conductance and thus transpiration and latent heat flux. It is typical that coexisting plants employ opposing hydraulic strategies, and therefore have disparate patterns of water acquisition and use. Hydraulic traits are deterministic of drought resilience, response to disturbance, and other demographic processes. The addition of plant hydraulic properties in models may not only improve the simulation of carbon and water fluxes but also vegetation population distributions.

Evaporation and CO2 fluxes in a coastal reef: an eddy covariance approach

ABSTRACT Introduction: We conducted season-long observations of evaporation and carbon flux at the Gulf of Aqaba coast, northern Red Sea. We used the eddy-covariance method with a two-tower setup to measure evaporation rates over land and sea and the advection between them. Using a three-dimensional mass balance approach, we calculated total evaporation as the sum of two main components in our site: horizontal advection and turbulent vertical flux, with half-hourly change of water vapor storage and horizontal flux divergence found to be negligible. Outcomes: Average evaporation rates were 11.4 [mm/day] from April through May (early summer) and 10.5 [mm/day] from June through August (summer). The coastal reef was a CO2 sink over the period of measurements, significantly higher in June through August than in April through May. The main environmental drivers of CO2 flux were humidity, water temperature, sensible heat flux, and wind speed. Discussion: The rates of evaporation near the shore were considerably higher than values reported in other studies typically used to represent the mean for the whole Gulf area. We found that evaporation rates computed by common bulk models approximate the mean values of evaporation but have poor representativeness of the intra-daily temporal variation of evaporation. There was a significant correlation between CO2 flux and evaporation attributed to common environmental drivers of gas diffusion, turbulent fluxes, and horizontal transport. Conclusion: We conclude that observations of fluxes in coastal waters need to use at least a two-tower system to account for the effect of horizontal advection on the total flux.

Hydrodynamic trait coordination and cost-benefit trade-offs throughout the isohydric-anisohydric continuum in trees: Hydrodynamic Trait Coordination and Cost-Benefit Trade-offs in Trees

Department of Civil, Environmental, and Geodetic Engineering, The Ohio State University, Columbus, Ohio Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas Correspondence Mirfenderesgi Golnazalsadat, Department of Civil, Environmental, and Geodetic Engineering, The Ohio State University, Columbus, OH. Email: mirfenderesgi.1@osu.edu Funding information U.S. Department of Energys Office of Science, Ameriflux Management Program under Flux Core Site, Grant/Award Number: 7096915; National Science Foundation Hydrological Science, Grant/Award Number: 1521238