Sari Palmroth | Duke University (original) (raw)
Uploads
Papers by Sari Palmroth
Canopy water and carbon exchange rates are controlled by leaf-level adjustment of stomatal apertu... more Canopy water and carbon exchange rates are controlled by leaf-level adjustment of stomatal aperture and photosynthetic capacity. Both leaf-level stomatal conductance and the leaf photosynthetic machinery respond nonlinearly to soil water availability, atmospheric CO2 concentration, and other environmental variables. Here we propose and test a canopy-scale coupled soil-vegetation-atmosphere model based on leaf-level optimality principles to describe leaf interactions with the immediate microclimate. Building on previous work, we assume that stomatal conductance is optimized so as to maximize the leaf-level net carbon gain, interpreted as photosynthesis minus the costs associated with water losses through leaf transpiration. This optimality principle is shown to describe a wealth of available leaf-level gas exchange data under different soil water availabilities and atmospheric conditions. The leaf-level optimality model is scaled up to the canopy-level by accounting for light and wind speed profiles within the canopy, as well as including a new model of soil-to-leaf water flow. The coupled model is applied to study the responses of a grassland ecosystem to different rainfall patterns and atmospheric CO2 concentrations.
Tree physiology, Jan 15, 2015
Manipulating tree belowground carbon (C) transport enables investigation of the ecological and ph... more Manipulating tree belowground carbon (C) transport enables investigation of the ecological and physiological roles of tree roots and their associated mycorrhizal fungi, as well as a range of other soil organisms and processes. Girdling remains the most reliable method for manipulating this flux and it has been used in numerous studies. However, girdling is destructive and irreversible. Belowground C transport is mediated by phloem tissue, pressurized through the high osmotic potential resulting from its high content of soluble sugars. We speculated that phloem transport may be reversibly blocked through the application of an external pressure on tree stems. Thus, we here introduce a technique based on compression of the phloem, which interrupts belowground flow of assimilates, but allows trees to recover when the external pressure is removed. Metal clamps were wrapped around the stems and tightened to achieve a pressure theoretically sufficient to collapse the phloem tissue, thereby...
Forest Ecology and Management, 2015
Water Resources Research, 2014
ABSTRACT Plant hydraulic traits have been conjectured to be coordinated, thereby providing plants... more ABSTRACT Plant hydraulic traits have been conjectured to be coordinated, thereby providing plants with a balanced hydraulic system that protects them from cavitation while allowing an efficient transport of water necessary for photosynthesis. In particular, observations suggest correlations between the water potentials at which xylem cavitation impairs water movement and the one at stomatal closure, and between maximum xylem and stomatal conductances, begging the question as to whether such coordination emerges as an optimal water-use strategy under unpredictable rainfall. Here, mean transpiration is used as a proxy for long-term plant fitness and its variations as a function of the water potentials at 50% loss of stem conductivity due to cavitation and at 90% stomatal closure are explored. It is shown that coordination between these hydraulic traits is necessary to maximize , with rainfall patterns altering the optimal range of trait values. In contrast, coordination between ecosystem-level conductances appears not necessary to maximize . The optimal trait ranges are wider under drier than under mesic conditions, indicating that in semi-arid systems different water use strategies may be equally successful. Comparison with observations across species from a range of ecosystems confirms model predictions, indicating that the coordinated functioning of plant organs might indeed emerge from an optimal response to rainfall variability.
New Phytologist, 2013
Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water tr... more Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water transport and hence carbon uptake by leaves. While more negative xylem water potentials provide a larger driving force for water transport, they also cause cavitation that limits hydraulic conductivity. An optimum balance between driving force and cavitation occurs at intermediate water potentials, thus defining the maximum transpiration rate the xylem can sustain (denoted as E(max)). The presence of this maximum raises the question as to whether plants regulate transpiration through stomata to function near E(max). To address this question, we calculated E(max) across plant functional types and climates using a hydraulic model and a global database of plant hydraulic traits. The predicted E(max) compared well with measured peak transpiration across plant sizes and growth conditions (R = 0.86, P < 0.001) and was relatively conserved among plant types (for a given plant size), while increasing across climates following the atmospheric evaporative demand. The fact that E(max) was roughly conserved across plant types and scales with the product of xylem saturated conductivity and water potential at 50% cavitation was used here to explain the safety-efficiency trade-off in plant xylem. Stomatal conductance allows maximum transpiration rates despite partial cavitation in the xylem thereby suggesting coordination between stomatal regulation and xylem hydraulic characteristics.
Geophysical Research Letters, 1997
Number size distribution of ambient submicron and ultrafine aerosol particles have been measured ... more Number size distribution of ambient submicron and ultrafine aerosol particles have been measured on a continuous basis (every 10 minutes) for three quarters of the year 1996, at a forest site in Southern Finland. Continuous monitoring offers additional insight over the ...
Canopy water and carbon exchange rates are controlled by leaf-level adjustment of stomatal apertu... more Canopy water and carbon exchange rates are controlled by leaf-level adjustment of stomatal aperture and photosynthetic capacity. Both leaf-level stomatal conductance and the leaf photosynthetic machinery respond nonlinearly to soil water availability, atmospheric CO2 concentration, and other environmental variables. Here we propose and test a canopy-scale coupled soil-vegetation-atmosphere model based on leaf-level optimality principles to describe leaf interactions with the immediate microclimate. Building on previous work, we assume that stomatal conductance is optimized so as to maximize the leaf-level net carbon gain, interpreted as photosynthesis minus the costs associated with water losses through leaf transpiration. This optimality principle is shown to describe a wealth of available leaf-level gas exchange data under different soil water availabilities and atmospheric conditions. The leaf-level optimality model is scaled up to the canopy-level by accounting for light and wind speed profiles within the canopy, as well as including a new model of soil-to-leaf water flow. The coupled model is applied to study the responses of a grassland ecosystem to different rainfall patterns and atmospheric CO2 concentrations.
Tree physiology, Jan 15, 2015
Manipulating tree belowground carbon (C) transport enables investigation of the ecological and ph... more Manipulating tree belowground carbon (C) transport enables investigation of the ecological and physiological roles of tree roots and their associated mycorrhizal fungi, as well as a range of other soil organisms and processes. Girdling remains the most reliable method for manipulating this flux and it has been used in numerous studies. However, girdling is destructive and irreversible. Belowground C transport is mediated by phloem tissue, pressurized through the high osmotic potential resulting from its high content of soluble sugars. We speculated that phloem transport may be reversibly blocked through the application of an external pressure on tree stems. Thus, we here introduce a technique based on compression of the phloem, which interrupts belowground flow of assimilates, but allows trees to recover when the external pressure is removed. Metal clamps were wrapped around the stems and tightened to achieve a pressure theoretically sufficient to collapse the phloem tissue, thereby...
Forest Ecology and Management, 2015
Water Resources Research, 2014
ABSTRACT Plant hydraulic traits have been conjectured to be coordinated, thereby providing plants... more ABSTRACT Plant hydraulic traits have been conjectured to be coordinated, thereby providing plants with a balanced hydraulic system that protects them from cavitation while allowing an efficient transport of water necessary for photosynthesis. In particular, observations suggest correlations between the water potentials at which xylem cavitation impairs water movement and the one at stomatal closure, and between maximum xylem and stomatal conductances, begging the question as to whether such coordination emerges as an optimal water-use strategy under unpredictable rainfall. Here, mean transpiration is used as a proxy for long-term plant fitness and its variations as a function of the water potentials at 50% loss of stem conductivity due to cavitation and at 90% stomatal closure are explored. It is shown that coordination between these hydraulic traits is necessary to maximize , with rainfall patterns altering the optimal range of trait values. In contrast, coordination between ecosystem-level conductances appears not necessary to maximize . The optimal trait ranges are wider under drier than under mesic conditions, indicating that in semi-arid systems different water use strategies may be equally successful. Comparison with observations across species from a range of ecosystems confirms model predictions, indicating that the coordinated functioning of plant organs might indeed emerge from an optimal response to rainfall variability.
New Phytologist, 2013
Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water tr... more Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water transport and hence carbon uptake by leaves. While more negative xylem water potentials provide a larger driving force for water transport, they also cause cavitation that limits hydraulic conductivity. An optimum balance between driving force and cavitation occurs at intermediate water potentials, thus defining the maximum transpiration rate the xylem can sustain (denoted as E(max)). The presence of this maximum raises the question as to whether plants regulate transpiration through stomata to function near E(max). To address this question, we calculated E(max) across plant functional types and climates using a hydraulic model and a global database of plant hydraulic traits. The predicted E(max) compared well with measured peak transpiration across plant sizes and growth conditions (R = 0.86, P < 0.001) and was relatively conserved among plant types (for a given plant size), while increasing across climates following the atmospheric evaporative demand. The fact that E(max) was roughly conserved across plant types and scales with the product of xylem saturated conductivity and water potential at 50% cavitation was used here to explain the safety-efficiency trade-off in plant xylem. Stomatal conductance allows maximum transpiration rates despite partial cavitation in the xylem thereby suggesting coordination between stomatal regulation and xylem hydraulic characteristics.
Geophysical Research Letters, 1997
Number size distribution of ambient submicron and ultrafine aerosol particles have been measured ... more Number size distribution of ambient submicron and ultrafine aerosol particles have been measured on a continuous basis (every 10 minutes) for three quarters of the year 1996, at a forest site in Southern Finland. Continuous monitoring offers additional insight over the ...