Data from: Micronutrients may influence the efficacy of ectomycorrhizas to support tree seedlings in a lowland African rain forest

In the lowland rain forest of SW Cameroon, a field experiment tested whether ectomycorrhizal hyphal connections might affect the growth and survival of seedlings of a principal tree species, Microberlinia bisulcata, close to its adults. Nursery‐raised seedlings were planted into fine‐, medium‐, and coarse‐mesh root bags, and as no‐bag controls, in replicate subplots. The bags prevented fungal hyphae, and fine‐ and medium‐sized roots, respectively, entering from the outside forest floor root mat. Harvests were taken after 1 and 2 yr, with non‐destructive recording in between. Seedlings grew in typically low‐light locations. Survivorship did not differ between treatments (33%), but seedlings grew significantly better in terms of stem dry mass by harvest 2 in the medium‐mesh compared with other treatments. Treatment 1 to 3 seedlings had stem masses 25, 44, and 5% higher than controls, respectively. Using a method of differences across treatments, the positive effect of ectomycorrhizas on growth was 13.6%, while the negative effect of root competition (RCM) was 31.2% (net outcome = 17.6%). Adjustment was made to account for root penetration damaging some mesh bags. Differences in growth in replicate subplots were, however, much larger than those for treatments. Elemental analysis of seedling plant parts showed few differences between treatments, but phosphorus was high in stems, aluminum and iron were very high in roots, and copper was deficiently low in leaves. Soil analyses revealed very low copper levels, suggesting with the seedling results that this element was critically limiting for seedlings. Ectomycorrhizas are probably important for copper uptake (as for phosphorus), so roots may have been competing for this element. Because seedlings were growing in the shade and the soil was inhibitory to roots, they could not form network connections enough to positively out‐balance root competition. The efficacy of ectomycorrhizal networks for at least seedling establishment in this forest is low. harvest1Dry masses of leaves, stems and roots (‘DM_leaf’, ‘DM_stem’ and ‘DM_root’) of M. bisulcata seedlings from the forest experiment using mesh bags at harvest H1. ‘LS’ is the Latin-square subplot, ‘trmt’ is treatment (1 to 4 being with 0.5, 35 and 250 µm mesh, and no mesh, respectively), ‘col’ and ‘row’ are the column and row numbers of each LS layout, and ‘tag’ the seedling identifier. Survivorship is shown as ‘ad’ (0 – died, 1 – alive). Total plant mass (‘DM_total’) is shown where leaves were present to harvest. Covariates (‘cov_’) ‘rootpen1’ and ‘rootpen2’ are the coarse and fine scales scorings for external root penetration of the bags, and ‘height1’ and ‘height2’ (cm), and ‘leafnr’ (leaf number), the starting size variables (see Methods of publication).harvest2Dry masses of leaves, stems and roots (‘DM_leaf’, ‘DM_stem’ and ‘DM_root’) of M. bisulcata seedlings from the forest experiment using mesh bags at harvest H2. Explanation of the variables and coding is the same as for 'harvest1.xls'.nutrientsConcentrations of nutrients in the plant parts (L – leaf, R – root, S – stem) of M. bisulcata seedlings (survivors) from the forest experiment using mesh bags. N, P, Ca, K and Mg are in mg/g, and Al, Fe, Mn, Cu and Zn are in mg/100g, dry mass. Harvests are H1 and H2; LS is the Latin-square subplot, and trmt is treatment (1 to 4 being 0.5, 35 and 250 µm mesh, and no mesh, respectively). Means per harvest and plant part are shown as the bars under ‘LS’ in the panels of Figs 3 and 4 of the publication.