Biology subjects

Hofhansl, F.

Publications and source records attributed to Hofhansl, F..

3 recordsLinked to original sources

bioRxiv2023

Competition for light can drive adverse species-composition shifts in the Amazon Forest under elevated CO2

The resilience of biodiverse forests to climate change depends on an interplay of adaptive processes operating at multiple temporal and organizational scales. These include short-term acclimation of physiological processes like photosynthesis and respiration, mid-term changes in forest structure due to competition, and long-term changes in community composition arising from competitive exclusion and genetic trait evolution. To investigate the roles of diversity and adaptation for forest resilience, we present Plant-FATE, a parsimonious eco-evolutionary vegetation model. Tested with data from a hyperdiverse Amazonian terra-firme forest, our model accurately predicts multiple emergent ecosystem properties characterizing forest structure and function. Under elevated CO2 conditions, we predict an increase in productivity, leaf area, and aboveground biomass, with the magnitude of this increase declining in nutrient-deprived soils if trees allocate more carbon to the rhizosphere to overcome nutrient limitation. Furthermore, increased aboveground productivity leads to greater competition for light and drives a shift in community composition towards fast-growing but short-lived species characterized by lower wood densities. Such a transition reduces the carbon residence time of woody biomass, dampening carbon-sink strength and potentially rendering the Amazon Forest more vulnerable to future climatic extreme events.

ecology↗

bioRxiv2022

Optimal balancing of xylem efficiency and safety explains plant vulnerability to drought

O_LIIn vast areas of the world, the growth of forests and vegetation is water-limited and plant survival depends on the ability to avoid catastrophic hydraulic failure. Therefore, it is remarkable that plants take high hydraulic risks by operating at water potentials ({psi}) that induce partial failure of the water conduits (xylem). Here we present an eco-evolutionary optimality principle for xylem conduit design that explains this phenomenon. C_LIO_LIBased on the hypothesis that conductive efficiency and safety are optimally co-adapted to the environment, we derive a simple relationship between the intrinsic tolerance to negative water potential ({psi}50) and the environmentally dependent minimum xylem{psi} . C_LIO_LIThis relationship is constrained by a physiological tradeoff between xylem conductivity and safety, which is relatively strong at the level of individual conduits although it may be weak at the whole sapwood level. The model explains observed variation in{psi} 50 both across a large number of species, and along the xylem path in two species. The larger hydraulic safety margin in gymnosperms compared to angiosperms is explained as an adaptation to the gymnosperms lower capacity to recover from conductivity loss. C_LIO_LIThe constant xylem safety factor provides a powerful principle for simplifying and improving plant and vegetation models. C_LI

plant biology↗

bioRxiv2020

Towards a unified theory of plant photosynthesis and hydraulics

The global carbon and water cycles are governed by the coupling of CO2 and water vapour exchanges through the leaves of terrestrial plants, controlled by plant adaptations to balance carbon gains and hydraulic risks. We introduce a trait-based optimality theory that unifies the treatment of stomatal responses and biochemical acclimation of plants to environments changing on multiple timescales. Tested with experimental data from 18 species, our model successfully predicts the simultaneous decline in carbon assimilation rate, stomatal conductance, and photosynthetic capacity during progressive soil drought. It also correctly predicts the dependencies of gas exchange on atmospheric vapour pressure deficit, temperature, and CO2. Model predictions are also consistent with widely observed empirical patterns, such as the distribution of hydraulic strategies. Our unified theory opens new avenues for reliably modelling the interactive effects of drying soil and rising atmospheric CO2 on global photosynthesis and transpiration.

plant biology↗