Tree health: Making trees more resilient to stress through sulphur Collaborative project researches improved immune defence of forest trees

Plant biologists at Technische Universität Braunschweig are investigating the health of oak and beech trees in the face of global climate change. The aim is to develop ways of improving the trees’ natural immune defences based on sulphur. The scientists will not only study the plants in the laboratory, but will also carry out large-scale experiments in the real forest laboratory. The Institute of Plant Biology at TU Braunschweig, the Julius Kühn Institute, the Niedersachsen State Forests and a local industrial partner have joined forces for the project. The Federal Ministry of Food and Agriculture is funding the research with around 1.1 million euros.

During the period of industrialisation until well after the middle of the last century, the concentration of sulphur dioxide in the atmosphere rose to levels that were harmful to plants, mainly as a result of the use of fossil fuels. The water-soluble gas led to the death of forests in exposed locations – known as ‘acid rain’. With the introduction of desulphurisation plants and the use of desulphurised diesel, this anthropogenic environmental impact has been reduced to almost zero – a great success of human activity for nature.

Sulphur is not only a poison to plants, it is also an essential macronutrient in well-defined amounts. In an undisturbed ecosystem, many nutrients are kept in a constant cycle. This is not the case in a human-used environment. In agriculture, much of the biomass is removed from this cycle at least once a year. This removal irretrievably removes macro- and micro-elements from the cycle, which in agriculture are returned through regular fertilisation. To maintain soil fertility in the long term, this imbalance has been redressed in agriculture since the late 1980s through targeted sulphur fertilisation. Without external sulphur inputs, crops are much more susceptible to disease, as sulphur is contained in many molecules involved in pathogen defence or stress management.

Since 2012, the Institute of Plant Biology (AG Hänsch) at TU Braunschweig has been studying antimicrobial plant defensins (PDFs) in trees – small proteins consisting of 48 to 54 amino acids that serve as a defence against microbial pathogens. PDFs are characterised by a high proportion of the sulphur-containing amino acid cysteine, which forms four disulphide bridges, giving the molecule a characteristic and extremely stable structure. The mechanism of action of PDFs is extremely diverse and helps against stressors as diverse as fungal or bacterial infections, insect damage, drought stress and heavy metal contamination. In addition to defensins, a number of other sulphur-containing substances are important for plant health.

At the Julius Kühn Institute (JKI), the German Federal Research Centre for Cultivated Plants, the importance of sulphur for plant health in agriculture was extensively investigated in the mid-1990s and described by the acronym SiR for ‘sulphur-induced resistance’. The SiR phenomenon now seems to have arrived in our native forests. The time lag is easy to explain – tree growth is much slower and biomass is removed at much greater intervals. The effects are the same: the vitality of individual trees declines, their susceptibility to biotic and abiotic stresses increases, and they may even die. This raises an exciting scientific question for the working groups in the joint project: Can a targeted application of sulphur help our forests, which are already significantly affected by global climate change, to improve their tolerance and resistance to various stressors?

Project data:

The joint project “Improving the resilience of native tree species to climate change-induced stress by using sulphur-induced resistance/tolerance” (duration 01.05.2024 to 30.04.2027) involves the Institute of Plant Biology (Prof. Robert Hänsch) at TU Braunschweig, the JKI Institutes of Crop and Soil Science (Prof. Elke Bloem) and Forest Protection (Prof. Henrik Hartmann), the Niedersachsen State Forests and a local fertiliser manufacturer. The project is funded by the German Federal Ministry of Food and Agriculture (BMEL) with around €1.1 million, administered by the Agency for Renewable Resources (FNR).