Hyphal growth in ingrowth mesh bags in Fagus sylvatica, Quercus petraea and Pinus pinaster stands in France

•Hyphal ingrowth was studied in Quercus, Fagus and Pinus stands in France.•Ingrowth bags filled with sand were deployed for one to three months.•Hyphal production was lower in autumn than in summer or spring (Fagus, Quercus).•Ingrowth was low in Pinus in all seasons, and lowest in the winter season.•Soil moisture appears the most likely candidate explaining these differences.

Our objective was to quantify the production of ectomycorrhizal (ECM) hyphae throughout the growing season. For this purpose, we used ingrowth mesh bags (30 μm mesh filled with 40 g sand) in top soils of Fagus sylvatica, Quercus petraea and Pinus pinaster forests in France. Installations were done at three or four different growth phases at each site and mesh bags were retrieved after one to three months. Ingrowing ECM hyphae measured 250–2257 mm bag−1 on average after one to three months. Specific hyphal length was 14.6–42.9 km g−1 of hyphal mass and differed among sites. Hyphal colonization was generally greater after three months than after one month regardless of season or species. Ingrowth was lower in autumn relative to the growth in summer (Fagus) or in spring and summer (Quercus). In Pinus, growth in winter was lower than in other seasons. These differences in ingrowth may relate to differences in seasonal carbon allocation, but may also result from differences between soils and/or climate such as the prolonged summer drought, affecting in particular the Pinus site.