Community Research and Development Information Service - CORDIS

Periodic Report Summary 1 - HYDROPIT (Plasticity and adaptation of hydraulic traits to overcome climate change)

Summary description of the project objectives
The increase in CO2 concentration and global scale trends of rising temperature will have progressive and cumulative effects on forested ecosystems. Some studies have also shown a clear increase in global aridity, more intense droughts and more frequent heatwaves over the past 60 years. It is largely debated whether forest trees, with long reproductive cycles, will be able to adapt in situ fast enough to outstrip the higher frequency of extreme phenomena. In this sense, the acclimation of the structure-function relations of the hydraulic system seems to play a key role to assure tree resilience. In HYDROPIT we are trying to identify which hydraulic traits involved in adaptation are likely to change in response to experimentally raised CO2 concentration, increase of temperature and drought.

Work performed since the beginning of the project
During the outgoing phase we have carried out all the sample collection, hydraulic measurements and gas exchange measurements of the three different stages we identified in the project: 1) the study of phenotypic variability in natural populations growing in contrasted climatic conditions; 2) the disentanglement between genetic and environmental effects in hydraulic traits using a common garden and 3) the assessment of acclimation in controlled or semi-controlled conditions, the first-ever full FACE (i.e. free-air CO2 enrichment), glasshouse experiment with a wide range of growing temperatures and a whole tree chamber experiment simulating a heat wave.
Furthermore, we have advanced in the comparison of classical destructive methods for the study of drought-induced embolism (formation of gas bubbles that block xylem conduits) with novel image techniques in intact plants.

Main results
In the study of natural populations our preliminary results show that the adjustment of the hydraulic system to climate dryness occurs primarily through changes in biomass partitioning and leaf level traits. Plants growing in drier environments produce less leaves and they are designed to lose less water. These trends have been confirmed in the common garden experiment where we have grown plants under two different watering treatments. In contrast, hydraulic vulnerability to drought induced embolism seems to be related to climatic variables, such as mean annual precipitation or soil moisture index, at the interspecific level but not at the intraspecific level. The low phenotypic variation in resistance to embolism compared with expected changes in water potential during severe drought events will pose serious risk in those populations inhabiting the drier limits of the distribution range of the species if they are not able to adjust the minimum water potential within a range preventing mortality.
In the study of hydraulic traits in future scenarios we have observed that leaves are more responsive than stems and branches. We have not detected any changes in xylem anatomy in trees growing under elevated CO2 at any stage of development. The study of tree hydraulic function during a heatwave revealed not significant changes in water relations, including leaf hydraulic conductivity and branch embolism.
Finally, for the first time we have analysed the vulnerability to drought-induced embolism of benchtop-dehydrated samples using flow measurements (the considered reference technique) together with microCT to compare both methods. Additionally, we have developed a quantitative procedure to improve microCT image analysis at limited resolution and accurately measure vessel lumens.

Expected final results and their potential impact and use
In HYDROPIT we will identify which hydraulic traits are likely to change in response to particular environmental conditions. Understanding basic questions about plasticity of functional traits related to water transport and water lost and their limits of adaptation is of paramount importance given current concerns about drought-induced tree mortality across the globe. There is an urgent need to determine the adaptive potential of forest trees given their importance in ecosystem functioning and their associated ecological and economic services. Indeed, underestimating rapid adaptation could lead to unnecessary recommendations such as the use of non-native (and perhaps non-adapted) genetic material for reforestation. On the contrary, overestimating adaptive potential could have detrimental consequences if populations decline massively when conditions outstrip the species recruitment.
We will assess causal links between the species distribution ranges and the environmental characteristics. From this point we will infer which will happen in the future with natural distribution and how net primary production will change. These aspects are relevant for society, biodiversity and also to decision-making in biodiversity conservation strategies and forestry companies in order to enhance integration of adaptive strategies in forest management planning.

Reported by



Life Sciences
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