Biology subjects

Juillard, T.

Publications and source records attributed to Juillard, T..

3 recordsLinked to original sources

bioRxiv2025

Decoupling of stomatal conductance from net assimilation at high temperature as a mechanism to increase transpiration

O_LIPhotosynthetic assimilation (Anet) and stomatal conductance (gs) are usually strongly coupled, but this relationship is decreased or even lost at high temperatures (Tair). The contributions of environmental drivers (Tair, vapour pressure deficit (VPD), and soil moisture) in interaction with the physiological mechanisms behind this process are still unclear. C_LIO_LIWe exposed saplings of three temperate and tropical species to rising Tair (20 to 40{degrees}C) at low (1.2 to 1.9 kPa) and increasing VPD (1.1 to 5.6 kPa), and at stable Tair (35{degrees}C) to increasing VPD (1.4 to 4.3 kPa) under well-watered or chronic soil drought conditions ([≤]10 %). Anet, gs, and transpiration (E) in the light and the dark and leaf thermoregulation were tracked throughout the experiment. C_LIO_LIWhen VPD remained low, gs continued to increase while Anet decreased at Tair > 35{degrees}C, leading to stomatal decoupling. In contrast, under rising VPD, trees maintained the coupling between Anet and gs at high Tair. C_LIO_LIWhile a decoupling of Anet and gs only occurred when VPD was low, Anet and E decoupled under both VPD regimes at high Tair. C_LIO_LIOur results indicate that, since gs and VPD collectively drive E, stomatal decoupling is needed to increase E when VPD is not sufficiently high. C_LI

plant biology↗

bioRxiv2025

Root vulnerability to embolism and lack of physiological recovery limit the competitive ability of an invasive palm

O_LIClimate change and invasive species both threaten forest ecosystems. While exacerbated droughts drive tree mortality, species invasion alters forest composition. Invasive plants may be more vulnerable to drought due to acquisitive traits and low embolism resistance, but their potentially superior recovery capacity raises key uncertainties in predicting future species distributions. C_LIO_LIWe compared the drought resistance and recovery of an invasive palm (Trachycarpus fortunei) with two native species (Ilex aquifolium & Tilia cordata) from the Southern Alps. Saplings were exposed to increasing intensities of drought-induced xylem embolism, then rewatered for 45 days. Among others, we tracked net assimilation (Anet), stomatal conductance (gs), and leaf water potential ({Psi}leaf) before and after the drought, and modeled the time to hydraulic failure in leaves, stems, and roots. C_LIO_LIWhile the invasive palm had exceptionally drought-tolerant leaves, its roots were the most drought-sensitive among all species. The palm maintained positive gas exchange until {Psi}leaf of -4 MPa, as some native species; however, it failed to recover from the most severe drought, with simulations showing root embolism preceding leaf failure, unlike native species. C_LIO_LIInvasive plants may match or exceed natives drought resistance, but their inability to recover from extreme droughts could limit their future spread. C_LI

ecology↗

bioRxiv2025

Thermal acclimation fails to confer a carbon budget advantage to invasive species over natives

Both native and invasive plants can adjust photosynthesis and respiration when exposed to warmer temperatures. However, it is uncertain if invasive plants are more plastic and exhibit higher acclimation to rising temperatures than native ones, a trait that could contribute to their invasive behavior in novel environments. We compared the capacity of a highly invasive palm in central Europe (Trachycarpus fortunei) and two native co-occurring species (Ilex aquifolium and Tilia cordata) to acclimate photosynthesis and respiration to air temperature changes using a two-year-long transplant experiment across Europe (mean temperatures ranging from 8.4 to 21.8{degrees}C). We measured the optimal temperature of photosynthesis (Topt), the assimilation at optimal temperature (Aopt), the thermal breath of photosynthesis (T80), the respiration at 25{degrees}C (R25), the temperature sensitivity of respiration (Q10), and simulated the whole-plant carbon budget. For all species, Topt, Aopt, and T80 increased with warming, while R25 decreased in the native species and Q10 decreased in the invasive species only. Consequently, acclimation enhanced the carbon budget of the invasive and native plants in the warm and hot sites. The invasive palm had a similar or lower acclimation capacity than other species and a lower but constant carbon budget across the European temperature gradient. Our work reveals that not all invasive plants exhibit greater photosynthetic plasticity than native ones, suggesting that temperature-driven enhancement of their carbon budget may play a limited role in future invasion processes.

plant biology↗