Nitrogen and drought effects on the tree-soil interaction of ECM and AM temperate trees
Soil Sciences
Final Report Abstract
The main components of anthropogenic global change will affect the C sink strength and biogeochemistry of the terrestrial vegetation. In this project I analyzed the influence of summer drought and of shifts in the mycorrhizal association type on carbon (C) sequestration and nutrient cycling in temperate deciduous forests. Specifically, I (i) classified important root functions of temperate trees according to the mycorrhizal type, (ii) investigated biogeochemical cycles in the rhizosphere of mature arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees, (iii) identified functional classifications for adult trees, and (iv) tested the translation of the leaf economics spectrum into a root economics spectrum for temperate tree species. To address these four research topics a combination of observational field studies, drought experiments, and literature syntheses was conducted. My results show that the type of mycorrhizal association is a crucial mediator of the metabolomic richness of root exudates and explains a significant part of the variation in exudate-rhizosoil feedbacks. Reduced metabolomic richness of root exudates in ECM trees exerted positive feedback with rhizosoil functions, with the consequence that the nitrogen (N) cycle was faster in ECM than in AM rhizosoil. Since ECM trees were less efficient in inorganic N uptake than AM trees this may support the greater need for limiting N resources. With soil drought, ECM trees increased the amount of photosynthates invested into root exudation whereas their biomass production did not respond, which seems to indicate an adaptive increase of root exudation in dry soil. At the same time, ECM root lifespan decreased with soil drought and fine root turnover and the associated input of root-borne C increased. This drought strategy of ECM trees to increase the production of tender, short-lived roots with high turnover can increase resource uptake efficiencies and hydraulic conductivity in dry soil, but it also significantly impacts on soil C cycling, as a consequence of both increased root C turnover and increased root C exudation. In my investigation of functional leaf and fine root traits of mature, sympatric tree species of Central Europe, I identified branching of lower order roots as a leading root trait of the plant economics spectrum of temperate trees, which was independent from phylogeny, but related to the mycorrhizal association type and belowground resource exploitation. Conspicuously, root branching influenced not only belowground but also aboveground functional traits and resource exploitation strategies in temperate trees. It seemed that root branching as a key functional trait has the potential to describe the ecological strategy of trees across different temperate environments. In conclusion, the mycorrhizal type can be a key grouping for global predictions of C and N cycles of temperate forests in trait-based forest vegetation and biogeochemistry models that warrants further investigations across other ecosystems and climates.
Publications
- (2017) Root branching is a leading root trait of the plant economics spectrum in temperate trees. Frontiers in Plant Science 8:315
Liese R, Alings K, Meier IC
(See online at https://doi.org/10.3389/fpls.2017.00315) - (2018) The mycorrhizal type governs root exudation and N uptake of temperate tree species. Tree Physiology 38:83-95
Liese R, Lübbe T, Albers NW, Meier IC
(See online at https://doi.org/10.1093/treephys/tpx131)
