Biology subjects

Muller, J. D.

Publications and source records attributed to Muller, J. D..

3 recordsLinked to original sources

bioRxiv2022

In-situ energy budget of needle-leaves reveals shift from evaporative to 'air cooling' under drought

O_LIThe modulation of the leaf energy budget and the balance between its sensible heat (H) and latent heat (LE) fluxes is vital for vegetation functioning and survival, as it is linked to maintaining leaf temperature below the thermal threshold, an increasingly important mechanism under a drying and warming climate, when evaporative cooling is suppressed. C_LIO_LICombining measurements and theoretical estimates using a new methodology, we obtained rare and comprehensive energy budgets of leaves on twigs under field conditions in droughted and non-droughted plots of a semi-arid pine forest with low and high evapotranspiration rates, respectively. C_LIO_LIAn examination of all components of the needle-leaf energy budget indicated that under the same radiative load, leaf cooling shifts from nearly equal contributions to H and LE in non-droughted trees to almost exclusively H in droughted ones while maintaining a similar leaf temperature. C_LIO_LIThis LE-to-H shift in leaves of droughted trees highlights the efficiency of the air cooling mechanism in maintaining temperature, which can enhance the resilience of trees to drying conditions. Additionally, leaf energy budgets are a fundamental tool to help understand leaf cooling and aerodynamic resistance under field conditions, and to improve modelling of ecosystem activity and its effect on the climate system. C_LI

plant biology↗

bioRxiv2021

Dual reference method for high precision infrared measurement of leaf surface temperature under field conditions

O_LITemperature is a key control over biological activities from the cellular to the ecosystem scales. However, direct, high precision measurements of surface temperature of small objects such as leaves under field conditions with large variations in ambient conditions remain rare. Contact methods such as thermocouples are prone to large errors. The use of non-contact remote sensing methods such as thermal infrared measurements provides an ideal solution, but their accuracy has been low (in the order of ~2 {degrees}C) due to necessity for corrections for material emissivity and fluctuations in background radiation (Lbg). C_LIO_LIA novel dual-reference method was developed to increase the accuracy of infrared needle-leaf surface temperature measurements in the field. It accounts for variations in Lbg and corrects for the systematic camera offset using two reference plates. C_LIO_LIWe accurately captured surface temperature and leaf-to-air temperature differences of needle-leaves in a forest ecosystem with large diurnal and seasonal temperature fluctuations with an uncertainty of {+/-}0.23 and {+/-}0.25 {degrees}C, respectively. C_LIO_LIRoutine high precision leaf temperature measurements even under harsh field conditions, such as demonstrated here, opens the way for investigating a wide range of leaf-scale processes and its dynamics. C_LI

plant biology↗

bioRxiv2021

Evidence for efficient non-evaporative leaf-to-air heat dissipation in a pine forest under drought conditions

O_LIDrier climates predicted for many regions can result in reduced evaporative cooling leading to leaf heat stress and enhanced mortality. To what extent non-evaporative cooling can contribute to plant resilience to the increasingly stressful conditions is poorly known at present. C_LIO_LIUsing a novel, high accuracy infrared system for continuous measurements of leaf temperature in mature trees under field conditions, we assessed leaf-to-air temperature differences {Delta}Tleaf-air of pine needles during drought. C_LIO_LIOn mid-summer days, {Delta}Tleaf-air remained <1.5 {degrees}C, both in trees exposed to summer drought, and in those provided with a supplement irrigation having a 10x higher transpiration rate. The non-evaporative cooling in the drought-exposed trees must be facilitated by low resistance to heat transfer generating large H. {Delta}Tleaf-air was weakly related to variations in the radiation load and mean wind speed in the lower part of the canopy, but highly dependent on canopy structure and within-canopy turbulence that enhanced the sensible heat flux H. C_LIO_LINon-evaporative cooling is demonstrated as an effective cooling mechanism in needle-leaf trees, which can be a critical factor in forest resistance to drying climates. The generation of a large H at the leaf scale provides a basis for the development of the previously identified canopy-scale convector effect. C_LI

physiology↗