Raw data pot experiment Musanga cecropioides

Tropical forests in central Africa are under increasing pressure due to slash-and-burn agriculture and charcoal production. Earlier studies have shown that this land-use system is depleting soil nutrients, which might in turn be essential to sustain primary productivity and hence forest regrowth. To explore which nutrients potentially limit tree growth, we conducted a full factorial pot trial using Musanga cecropioides, a keystone pioneer species that plays a critical role in forest or fallow establishment following agricultural abandonment in the Congo basin. Nutrient treatments involved the addition of nitrogen (N), phosphorus (P), and a combined cation treatment (calcium, magnesium, and potassium) and their combinations.

Our results demonstrated that the addition of nutrient cations with and without N or P increased tree growth over the course of one year, with the final tree diameter increasing up to 76 % and tree height up to 122 %, compared to treatments without nutrient cations. Particularly strong growth responses were observed during the first 14 weeks of the experiment, where cation addition resulted in an up to 97 % increased diameter growth rate and up to 103 % increased height growth rate. In contrast, adding N and P with or without cations generally had a small negative effect on growth. Analyses of stable carbon and oxygen isotopes on foliar α-cellulose suggest that cation addition increased the photosynthetic activity as intrinsic water-use efficiency (iWUE) did not change significantly, while stomatal conductance increased.

These findings further underscore the critical role of cations in the natural regeneration of forests in central Africa, supporting their inclusion in future research focused on secondary forest recovery, old-growth forests, and sustainable agricultural intensification.