Investigating the response of soil nitrogen cycling to grass invasion

peer reviewedIn heathlands, high mineral N input causes replacement of Calluna vulgaris, the dominant plant, by fast-growing grasses such as Molinia caerulea. The vegetation shift signifies altered litter quality from low- to high-quality litter due to differences in lignin content. Litter quality usually affects decomposition processes, which can, in turn, alter nutrient cycling. Therefore, the change in plant dominance in this ecosystem possibly alters soil carbon and nutrient cycles, and consequently, ecosystem services (e.g. biodiversity conservation, groundwater recharge, …). We hypothesise that, because of its higher litter quality, nutrient turnover becomes faster with grass encroachment. We tested this hypothesis in a field set-up consisting of 14 plots presenting a gradient of increasing grass dominance (from 0% to 100%). We measured nine soil parameters and assessed possible associations between grass dominance and the soil parameters using multivariate analysis and linear mixed models. We found that grass dominance significantly impacted net N mineralisation and the root biomass. Our results showed very low net N mineralisation rates (0.09 ± 0.04 mg N (kg soil)−1 day−1) and relative nitrification rates (1.99 ± 0.62%). At high grass levels, acid phosphatase activity was significantly lower than at lower grass percentages. These results show that grass encroachment has a minimal impact on heathland soil biochemistry at this point. Still, we consider that it may take many years to translate a change in litter quality and dynamics into a change in soil functioning

The SlZRT1 Gene Encodes a Plasma Membrane-Located ZIP (Zrt-, Irt-Like Protein) Transporter in the Ectomycorrhizal Fungus Suillus luteus.

Zinc (Zn) is an essential micronutrient but may become toxic when present in excess. In Zn-contaminated environments, trees can be protected from Zn toxicity by their root-associated micro-organisms, in particular ectomycorrhizal fungi. The mechanisms of cellular Zn homeostasis in ectomycorrhizal fungi and their contribution to the host tree's Zn status are however not yet fully understood. The aim of this study was to identify and characterize transporters involved in Zn uptake in the ectomycorrhizal fungus Suillus luteus, a cosmopolitan pine mycobiont. Zn uptake in fungi is known to be predominantly governed by members of the ZIP (Zrt/IrtT-like protein) family of Zn transporters. Four ZIP transporter encoding genes were identified in the S. luteus genome. By in silico and phylogenetic analysis, one of these proteins, SlZRT1, was predicted to be a plasma membrane located Zn importer. Heterologous expression in yeast confirmed the predicted function and localization of the protein. A gene expression analysis via RT-qPCR was performed in S. luteus to establish whether SlZRT1 expression is affected by external Zn concentrations. SlZRT1 transcripts accumulated almost immediately, though transiently upon growth in the absence of Zn. Exposure to elevated concentrations of Zn resulted in a significant reduction of SlZRT1 transcripts within the first hour after initiation of the exposure. Altogether, the data support a role as cellular Zn importer for SlZRT1 and indicate a key role in cellular Zn uptake of S. luteus. Further research is needed to understand the eventual contribution of SlZRT1 to the Zn status of the host plant

Towards more predictive and interdisciplinary climate change ecosystem experiments

We thank the Flemish government (through Hercules Stichting big infrastructure and the Fund for Scientific Research Flanders project G0H4117N) and LSM (Limburg Sterk Merk, project 271) for providing funds to build the UHasselt Ecotron; Hasselt University for both funding and policy support (project BOF12BR01 and Methusalem project 08M03VGRJ); and the ecotron research committee for comments on the experimental design. We also thank Regional Landscape Kempen and Maasland for its collaboration and support. N.W., S.L., A.N. and I.V. are funded by Research Foundation-Flanders (FWO).Peer reviewedPostprin