Comparative responses of legume vs. non-legume tropical trees to biochar additions

Nitrogen-fixing plants in the legume family (Fabaceae) may show particularly large positive responses to biochar additions due to their capacity to potentially compensate for reduced N in biochar-amended soils. Prior studies also suggest that biochar may have specific developmental effects on legumes, including increased root nodulation and altered morphology. We examined the growth and morphometric responses of legume and non-legume tropical trees to biochar additions in a common garden pot trial experiment. Four legume species ( Acacia auriculiformis , A. mangium , Delonix regia , and Pterocarpus santalinus ) and four non-legumes ( Eucalyptus alba , Melia azedarach, Swietenia macrophylla , and Syzygium cumini ) were compared in terms of sapling responses to additions of a wood-feedstock biochar applied at 10 and 20 t/ha. Overall, strong positive effects of biochar additions on sapling performance were observed, with an average increase of 30% in total biomass and a notable increase in height relative to diameter growth. Species showed pronounced differences in responses, with strong interactive effects of species and biochar treatments on growth metrics. Legume species showed an average increase somewhat greater than non-legumes; however, responses were variable among species, with the two Acacia species showing the largest responses, resulting in a non-significant pattern. A literature-based meta-analysis of tropical and subtropical trees likewise suggests greater biochar responses in legumes, but the analysis also falls short of statistical significance. In addition, experimental results indicate large interactive effects of species and biochar on soil pH and other soil properties. Large growth responses of certain taxa of legumes (and other taxa) to biochar, and pronounced species-specific effects on soil properties, may reflect evolved responses to fire disturbance that can be leveraged in the context of forest restoration and enhanced carbon sequestration in degraded tropical landscapes.