Effect of drought on C cycling: which roles play lignin and lipids?

Drought events are predicted to occur more frequently and for a longer duration due to climate change. Especially, severe droughts most likely increase in Central Europe during the summer season, when commonly plants actively grow. Due to this drought C uptake by plants and its translocation towards soil can be expected to decrease. Thus, this has a strong influence on the plant driven sequestration of C in soil and also drought might promote C loss in the soil. Furthermore, it remains questionable, if the plant-soil system can adapt to drought to further resist to severe droughts.

Strong effects of drought were described for the regulation of lipid formation in plants including fatty acids as part of cell membranes and alkanes as part of the wax layer, whereas so far no information is available, if lipid incorporation into soils and lipid turnover therein is also influenced by drought. For another part of plant tissues like lignin a response on drought cannot be expected as lignin formation is not directly connected to the regulation of the stomata and the wax formation. However, as influences of drought on lignin and lipid cycling in the plant-soil system remain largely unknown, but they are part of intermediate stable C pool in soil, it should be known, whether drought might improve their mineralisation or storage in soils.

In this proposal, we will determine CO2 uptake by plants, translocation of C from plants to soil and soil C fluxes of two different plant communities (grass and heath) that are exposed to a severe drought of 14 weeks under field conditions. Additionally, plots are differentiated that were previously exposed to annual drought or control conditions. C cycling is investigated under field conditions by help of a triple 13CO2 pulse labeling experiment and subsequent analyses of the isotope label in plant and soil samples. The whole experiment was performed under rainout shelters installed on the Bayreuth EVENT I experiment in summer 2011. Further, a laboratory experiment will be conducted, where under controlled conditions only soil moisture is regulated to drought and control conditions, respectively and via a continuous 13CO2 labeling C cycling in the plant-soil system is determined. All samples from the EVENT I experiment and the laboratory experiment will be analysed for their d13C isotopic values to trace the bulk C fluxes. In addition to the bulk C, lipids including fatty acids, alkanes and alcohols and lignin monomers will be monitored for the whole sample set to determine the regulation of lipid and lignin formation in plants under drought and especially to investigate the incorporation and mineralisation of bulk C and at a molecular level for lipids and lignin during the drought. This research will serve the following central goals: 1. Determine effect of increasing drought on C uptake by plants and bulk C, lipid and lignin translocation towards soil. 2. Assess the effect of severe drought on bulk C, lipid and lignin storage and mineralisation in soil. Such information is strongly required to understand the effects of severe drought on C cylcing in the plant-soil system as such conditions are predicted to occur more frequently under future climatic conditions.    

Figure 1: picture of the setup