Prof. Dr. Arthur Gessler

Research area

Basic research:

Advancing the understanding of the stable isotope signals in plants and ecosystems.

Stable isotopes are increasingly used to reconstruct past climatic and other environmental conditions as well as plants’ reactions towards environmental drivers from biological archives such as tree rings. We seek to increase the understanding of isotope fractionation and exchange processes in plants that affect the δ13C and δ18O isotopic composition of plant metabolites and organs. Our group was amongst the first to apply complex oxygen isotope enrichment models to understand the impact of air humidity and transpiration on the leaf water isotopic composition in the field and how this information is transferred to organic compounds  and combined in-depth analysis of CO2 and water movement in the leaf with isotope studies . Moreover, we strongly improved our understanding on the short-term dynamics of water uptake by applying novel isotope-laser based technologies and how the isotope signal of source water is directly and indirectly affecting the tree ring archive isotopic signal. In addition, our and collaborators have been intensively working on compound and positions specific isotope signals in order to disentangle central metabolic pathways and shifts in their commitment as depending on internal and external drivers .

Functional diversity in forest ecosystems across forest types and scales

We intensively assess  Biodiversity-Ecosysystem functioning (BEF) relations in forests. One of the main findings, which is highly important on the background of a changing climate, was that tree diversity does not always improve resistance of forest ecosystems to drought . Within a study network of 160 forest stands across Europe, we found that mixed species forests are less exposed to drought stress in some regions only and that environmental context plays an important role for BEF. This has also practical implications as managing forest ecosystems for high tree species diversity does not necessarily assure improved resistance to the more severe and frequent drought events predicted for the future. Moreover, we could show that species identity and the physiological characteristics of species in a mixed forest needs to be considered to improve climate-smart forest management . These major results where included into synthetic analyses of forest multifunctionality on different scales (landscape to European level).

Carbon, water nutrient relations in plants and ecosystems.

We are also working  in the field of carbon (C) nutrient and water relations of trees and ecosystems. Source-sink relationships and their the control of C sequestration are in important topic in the face of climate change. We need to understand which plant processes control C uptake and storage in the ecosystem and to predict how changing climatic conditions affect these processes. My group and collaborators could show that in a beech ecosystem plant C uptake is controlled during drought and after drought release by the activity and thus C demand of the non-photosynthetic sink tissues . Moreover, we could show that depending on the previous drought history, photosynthetic activity of trees reacted differently to light and temperature cues, implying environmental memory effects . On a shorter time scale, we were able could show that the circadian clock strongly affects the reaction of respiration, transpiration and photosynthesis towards environmental drivers and propose this internal regulation to be included into vegetation models .