Přednášky: Giulia Vico a Stefano Manzoni

Giulia Vico, Swedish University of Agriculture, Uppsala
Acclimation of leaf net carbon gain under fluctuating and increasing temperatures

Plants are able to adjust their physiological activity to fluctuations and long-term changes in their growing environment. Nevertheless, projected increases in temperature will occur with unprecedented speed. Will global warming exceed the acclimation capacity of leaves, thus reducing net CO2 assimilation? Such a reduction in net CO2 assimilation rate (Anet) in response to warming may lower ecosystems’ net primary productivity, with global impacts on the carbon cycling. Here we combine data on net photosynthetic thermal acclimation to short- and long-term changes in temperature with a probabilistic description of leaf temperature variability. We study the effects of mean leaf temperature and its variability on average Anet and the frequency of occurrence of sub-optimal thermal conditions and how acclimation capacity may affect them.

Stefano Manzoni, Stockholm University, Sweden
Eco-hydrological optimality of plant function Merging hydrological and ecological theories from sub-daily to evolutionary scales

The carbon (C) uptake of terrestrial ecosystems is tightly linked to water losses by transpiration, due to the exchange of both water and CO2 through leaf stomata. Water can thus be interpreted as a resource that is consumed to acquire C needed for plant growth. This inherent coupling requires plants to manage available water in such a way as to avoid the occurrence of water stress, while preserving C uptake. Accordingly, it has been hypothesized that plants optimally regulate transpiration to maximize photosynthesis. This optimization problem can be addressed at different time scales – at the sub-daily scale to assess the role of rapidly changing atmospheric conditions; at the dry down scale to predict the effect of soil moisture dynamics; at evolutionary time scales to investigate the effects of hydro-climatic variability on plant fitness. Here we present a hierarchy of optimization models that span sub-daily to evolutionary time scales to yield analytical expressions linking photosynthesis, transpiration, and environmental and climatic drivers. Based on the model results, we define broad plant water use strategies and characterize their success in a changing environment. In some cases, different strategies are found to yield similar long-term plant fitness levels as long as plant hydraulic traits are coordinated, thus explaining why species with widely variable eco-physiological traits may coexist under the same climatic conditions.