Biology subjects

Harkes, P.

Publications and source records attributed to Harkes, P..

3 recordsLinked to original sources

bioRxiv2020

Characterization of the habitat- and season-independent increase in fungal biomass induced by the invasive giant goldenrod and its impact on the fungivorous nematode community

Outside its native range, the invasive plant species giant goldenrod (Solidago gigantea) has been shown to increase belowground fungal biomass. This non-obvious effect is poorly characterized; we dont know whether it is plant developmental stage-dependent, which fractions of the fungal community are affected, and whether it is reflected in the next trophic level. To address the questions, fungal assemblages in soil samples collected from invaded and non-invaded plots in two soil types were compared. Whereas ergosterol as a marker for fungal biomass demonstrated a significant increase in fungal biomass, specific qPCR assays did not point at a quantitative shift. MiSeq-based characterization of the belowground effects of giant goldenrod revealed a local increase of mainly Cladosporiaceae and Glomeraceae. This asymmetric boost in the fungal community was reflected in a specific shift in the fungivorous nematode community. Our findings provide insight in the potential impact of invasive plants on local fungal communities.

molecular biology↗

bioRxiv2020

Effect of nitrogen on fungal growth efficiency

The contribution of fungi to carbon (C) and nitrogen (N) cycling is related to their growth efficiency (amount of biomass produced per unit of substrate utilized). The concentration and availability of N influences the activity and growth efficiency of saprotrophic fungi. When N is scarce in soils, fungi have to invest more energy to obtain soil N, which could result in lower growth efficiencies. Yet, the effect of N on growth efficiencies of individual species of fungi in soil has not been studied extensively. In this study we investigated the influence of different concentrations of mineral N on the growth efficiency of two common soil fungi, Trichoderma harzanium and Mucor hiemalis in a soil-like environment. We hypothesized that a higher N availability will coincide with higher biomass production and growth efficiency. To test this, we measured fungal biomass production as well as the respiration fluxes in sand microcosms amended with cellobiose and mineral N at different C:N ratios. We found that for both fungal species lower C:N ratios resulted in the highest biomass production as well as the highest growth efficiency. This may imply that when N is applied concurrently with a degradable C source, a higher amount of N will be temporarily immobilized into fungal biomass.

ecology↗

bioRxiv2019

Mapping of long-term impact of conventional and organic soil management on resident and active fractions of rhizosphere communities of barley (Hordeum vulgare)

Soil biota plays an essential role in ecosystem services such as carbon fixation, nitrogen and phosphorous cycling, and disease suppressiveness. Conventional soil management with large inputs of mineral fertilizers and pesticides have a significant impact on primary decomposer communities (bacteria and fungi), as well as on protists and metazoa, representatives of the next trophic level. Organic soil management is thought to contribute to a more diverse and stable soil food web. However, information to pinpoint this supposed beneficial effect is sparse and fragmented. Keeping in mind that a substantial fraction of the soil biota is dormant, we set out to map both the resident and the active the bacterial, fungal, protozoan and metazoan communities under various soil management regimes in two distinct soil types with barley as main crop. For all four organismal groups, the contrast between resident (rDNA-based) and active (rRNA-based) was the most important explanatory variable explaining 22%, 14%, 21% and 25% of the variance among bacterial, fungal, protozoan, and metazoan communities. Less prominent were the effects of soil management and soil type, however significant as well for all four organismal groups. LEfSe was used to identify indicator taxa for both the contrasts between resident and active communities, and the effects of soil management. Our results suggest that - next to DNA-based community characterisation - mapping of the active microbial community could provide essential insights in the effects of variables such as crop and soil management on the soil living community.

ecology↗