Severe drought-influenced composition and δ13C of plant and soil n-alkanes in model temperate grassland and heathland ecosystems

Abstract

Drought events are predicted to increase under future climate change. In temperate ecosystems, plants are capable of resisting drought due to their hydrophobic wax layer, in which n-alkanes are important constituents. In soils, plant-derived n-alkanes are comparatively resistant to degradation. To improve understanding of the significance of n-alkanes in plant-soil systems during a severe drought period (104 days), we investigated bulk organic carbon (Corg) concentration, total lipid extract (TLE) concentration, and n-alkane molecular ratios such as average chain length (ACL), carbon preference index (CPI) and chain length ratios of different n-alkane compounds, in addition to the compound-specific isotope composition (δ13C) of n-alkanes in model temperate grassland and heathland plant-soil systems. Although plant communities of two (heathland) and four (grassland) species were available, only one representative species per biome was accessible for the current study.Heathland plants and soil revealed significantly higher concentrations of Corg and TLE compared with grassland. TLE and alkane composition responded quickly during the first drought phase (0–40 days). This indicates that plants were actively utilizing C and produced more n-alkanes in order to withstand drought, which was confirmed by increased (2–3‰) δ13C values for n-alkanes in shoot biomass. However, during later drought phases all the parameters remained constant for plants and soils. This suggests limited change in biosynthesis and cycling of plant lipids such as n-alkanes during intense drought. Surprisingly, during the first drought phase, increased ACL and CPI values in soil demonstrated a rapid input of plant-derived long chain n-alkanes to soil, which was not expected due to the decadal residence time of alkanes in soil. The study enabled tracing of plant metabolic response in terms of alkane biosynthesis under different phases of drought and rapid cycling of alkanes in the plant-soil system.