drought - irrigation; root lignin/N ratio; pyrosequencing; 13CO2 pulse-labelling; lignin monomers; decomposing fungi and bacteria; Pinus sylvestris
Hartmann Martin, Brunner Ivano, Hagedorn Frank, Bardgett Richard D., Stierli Beat, Herzog Claude, Chen Xiamei, Zingg Andreas, Graf-Pannatier Elisabeth, Rigling Andreas, Frey Beat (2017), A decade of irrigation transforms the soil microbiome of a semi-arid pine forest, in Molecular Ecology
, 26(4), 1190-1206.
Brunner Ivano, Herzog Claude, Dawes Melissa A., Arend Matthias, Sperisen Christoph (2015), How tree roots respond to drought, in Frontiers in Plant Science
, 6, 547-16.
Herzog Claude, Steffen Jan, Graf Pannatier Elisabeth, Hajdas Irka, Brunner Ivano (2014), Nine Years of Irrigation Cause Vegetation and Fine Root Shifts in a Water-Limited Pine Forest, in PLoS ONE
, 9(5), e96321-11.
Temperature in Switzerland has risen by 1.6°C over the last 100 years. Thus, an extraordinarily high tree mortality of Scots pine has been observed in the southern regions of Switzerland, and below 1100 m a.s.l. mortality of Scots pine has exceeded the 1% level which is significantly higher than the 0.4% of managed forests in Switzerland. From the literature there are indications that roots react with increased lignin contents due to drought. Thus, with an elevated lignin/N ratio, the decomposability of the roots might be hampered, which subsequently would influence belowground C and nutrients dynamics in the forest soils.In this project, we focus on the responses of the roots and the root litter decomposition to drought and non-drought (irrigated) conditions. The experimental setup at ‘Pfynwald’ in the Valais, after a decade of an irrigation treatment, offers the unique opportunity to investigate the consequences of drought / irrigation to the roots of Scots pines. The combination of the element concentrations with the longevity of the roots allows the investigation of the impact of the treatments on the belowground C and nutrient fluxes. We hypothesise that roots, growing under drought conditions, have altered lignin/N ratios, which directly affects the decomposability of the root litter. In order to address this question, litterbag experiments will be conducted in the ‘Pfynwald’ over two years with root litter from both, the control and the irrigated treatment. By measuring the change of the lignin monomers, obtained after a CuO oxidation, the fate of the lignin shall be followed in dependence on time and water availability. The application of the new technology 454-pyrosequencing on the root litter further allows the identification of the bacterial and fungal key players in the decomposition. A second experimental setup in the greenhouse, applying a 13CO2 pulse label to young Scots pine trees under a drought and a non-drought (irrigated) treatment, further enables the observation of the incorporation of the 13C-label into the lignin monomers under various conditions. And finally, a decomposition study using the 13C-labelled roots carrying the 13C-labelled lignin monomers and using two different types of fungi, a white-rot and a brown-rot fungus, allows the analysis of the different decomposition stages and the changes of the lignin monomers over time. This project brings novel insights into tree roots and their contribution to the C and nutrient cycling of forest soils. We will use for the first time different types of roots and characterise its decomposition with the use of lignin ‘fingerprints’ in connection with their decomposing microorganisms. It is expected that environmental conditions will further change and that extreme climatic events will affect belowground C and nutrient dynamics in forests. With linking these investigations to a forest site in a climatic dry region in Switzerland, the effects of altered soil water conditions on the root quality and its consequences to the soil ecosystem (biodiversity) can be estimated directly in the field. Such an improved understanding is necessary in order to assess accurately the consequences of climatic change and to suggest management options if necessary.