The PPE team presented several new results at the GfÖ annual meeting in Vienna

GfÖ annual meeting in Vienna

The 48th Annual Meeting of the Ecological Society of Germany, Austria and Switzerland took place in Vienna during the week of September 10th.

 

SESSION 25-O1 THURSDAY 16:30

Above- and belowground processes shaping tree resilience to drought

Matthias Arend1, Arthur Gessler2, Frank Hagedorn2, Jobin Joseph2, Ellen Pflug2, Christoph Sperisen2

1University of Basel, Basel, CH, matthias.arend@clutterunibas.ch
2Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, CH

Drought is a major environmental threat to plants, causing severe limitations at different scales of plant organization and function. The ability to resist the drought impact and recover after drought release determines the overall response of plants to this environmental threat, which is fundamental to the recent concept of plant and ecosystem resilience. While past studies provide a large body of information on drought-induced limitations of plant growth and function, little is known about processes counteracting these limitations during drought and after drought release. Using a set of lab and model ecosystem experiments, in combination with molecular and eco-physiological approaches, we studied the above- and belowground responses of young beech, oak and poplar trees to cycles of soil water shortage and rewetting or to osmotically imposed steady-state drought. In these experiments, we show not only the well-known limitations which trees experience under drought conditions, but also the mechanisms that trees may activate in roots and leaves to minimize the adverse effect of drought on plant water relations and molecular function and compensate for the loss of photosynthetic carbon gain. The obtained response patterns also suggest a close coupling of root and leaf function after drought release, in that increasing root metabolic activity triggers the subsequent recovery and stimulation of photosynthetic activity in leaf organs. From this observation, we propose that the maintenance and recovery of root function play a key role in tree resilience to drought. 

 

SESSION 25-O4 THURSDAY 17:15

Carbon starvation of epiphytic orchids from tropical cloud forests at warm temperatures

Günter Hoch1, Tiffany Fioroni1, Helna Römer1, Inayat Olmedo1, Ansgar Kahmen1

1University of Basel, Basel, CH, guenter.hoch@clutterunibas.ch

Because of the annually stable climate at tropical cloud forests, plants that are specialized to this ecosystem are often very sensitive to climate change. Especially, epiphytic orchids are considered to be extremely sensitive to the anticipated future rise in temperature. Within two experiments, we investigated the consequences of increasing temperatures on the CO2 gas-exchange and the carbon reserve household in different species of the two orchid genera Masdevallia and Dracula. 10 different species from each genera, were subjected to three different temperature treatments in phytotrons: i) a constant temperature treatment, ii) a slow temperature ramp (+0.75 °C every 14 days), and iii) a fast temperature ramp (+1.5 °C every 14 days). Plant status, leaf gas- exchange was and non-structural carbohydrates (NSC) concentrations were analyzed regularly throughout the experiment. In all investigated species, net-photosynthesis declined strongly at daytime temperatures above 29 °C, and became negative at daytime temperatures between 32 and 34 °C. Because leaf respiration increased only moderately in this temperature range, the observed fast decrease of net-gas exchange was likely caused by a decline of the photosynthetic reaction. Closer analyses of light-response and A/Ci curves of photosynthesis suggested a malfunctioning of the photosynthetic dark reaction. The decline of photosynthesis was accompanied by a fast depletion of leaf starch reserves and plant death, giving strong experimental evidence for carbon starvation. Such an extreme sensitivity against warm temperatures is surprising, but new in situ measurements at the natural habitat of these orchids confirmed the extremely constant temperatures throughout the year, with maximum temperature peaks well below 30 °C. The exceptionally high vulnerability of the photosynthetic apparatus of Masdevallia and Dracula orchids already at mild heat stress confirms that these epiphytes will be highly endangered by climate warming.

 

 

SESSION 34-O1 WEDNESDAY 10:00

The isotope composition of water in the stems of trees does not necessarily equal the isotope composition of the trees source water

Eligio Amicabile1, Sarah Newberry1, Ansgar Kahmen1

1University of Basel, Basel, CH, ansgar.kahmen@clutterunibas.ch

The isotope composition of water in the stems of trees carries important information. This information can be used to estimate the origin of source water of trees and it serves as starting point for the interpretation of the oxygen and hydrogen isotope composition of plant organic compounds. These applications rest on the belief that the water extracted from the stems of trees is identical in its isotopic composition to the trees source water. Recently, there have, however, been indications that this assumption might not be true. In a series of greenhouse experiments, we tested if isotope fractionation occurs (i) during the water uptake by the root and (ii) during the upward transport of water in the xylem of trees. We used 1–2 m tall saplings from seven different temperate tree species in our experiments. We found that indeed no fractionation occurred during the uptake of water by the roots. However, we found clear indications that both hydrogen and oxygen in stem water become slightly enriched in 2H (5 ‰ m-1) and 18O (0.6 ‰ m-1) with progressive upward flow of water in the stems. This enrichment could be the result of stem evaporation or because of the exchange of xylem water with enriched phloem water. We also found that water directly extracted from the conducting tissue (i.e. the xylem) was depleted in 2H by up to –15 ‰ compared to parenchyma and whole stem water. For oxygen, we did not observe such differences among different stem tissues. We speculate that the exchange of 2H depleted metabolic water between xylem and parenchyma cells caused this depletion. Our study has important implications for interpreting the isotope composition of stem water. It shows that stem water does not necessarily equal the isotope composition of source water and that these deviations need to be considered in the interpretation of stem water isotope data of trees. 

 

SESSION 34-O6 WEDNESDAY 11:15

Effect of organic farming on soil hydraulic properties and plant water relations

Marie-Louise Schärer1, Lars Dietrich1, Dominika Kundel2, Andreas Fliessbach2, Paul Mäder2, Ansgar Kahmen1

1University of Basel, Basel, CH, marie-louise.schaerer@clutterstud.unibas.ch 2Research Institute of Organic Agriculture, Frick, CH 

Conventional high-input farming systems in Europe are often regarded as unsustainable with severe environmental impacts on biodiversity, soils, water and climate. Low-input approaches, typically referred to as organic farming practices, have been proposed as alternative farming systems with reduced environmental impact. The DOK trial is the world’s oldest long-term field trial, in which organic and conventional farming systems are being compared since 1978. This experiment has shown that organic farming practices can, among many other effects, dramatically improve major structural properties of the soil, such as aggregate and percolation stability (Mäder et al. 2002 Science). What remains unclear is, whether these changes in structural soil properties also influence ecohydrological properties of organically managed farming systems and potentially improve the water relations of organically grown crops. We therefore investigated if soil hydraulic properties (i.e. matrix potential, infiltration rates, soil moisture and water holding capacity) and consequently plant water relations (i.e. midday water potentials, stomatal conductance and stable C and O isotope ratios) are affected by forty years of organic farming. We performed our investigations for almost two years on the two crop species winter wheat and soy bean. Against our expectations, organic management practices did not significantly affect soil hydraulic properties nor plant water relations under ambient climatic conditions. In future work, we will address if these patterns prevail also under extreme drought conditions.