Improving Cacao Based Reforestation through Whole Soil Microbial Inoculation

Abstract

Deforestation is one of the greatest greenhouse gas sources, releasing more greenhouse gas than all the world’s cars, trucks and trains combined. Since deforestation rates are highest in the tropics reforestation efforts in this region are greatly needed. In particular, regenerative agroforestry would not only increase tree cover but also provide farmers with a livelihood outside of the agriculture associated with deforestation. Regenerative Agroforestry creates a matrix that is valuable to wildlife and the people who most depend on the land to survive. In Ecuador, where my study took place, Cacao is a native tree valuable to smallholder farmers, but depending on the variety and conditions, may or may not be ideal for reforestation. A technique that could improve reforestation efforts is inoculation with mycorrhizal fungus taken from a nearby intact ecosystems. Therefore, in this study I ask: 1) do whole soil inoculants taken from nearby secondary forest increase arbuscular mycorrhizal fungi (AMF) in planted cacao trees? 2) Does percent canopy cover and cacao cultivar influence the beneficial effects of whole soil inoculants on plant growth? And, 3) Is the level of AMF in plant roots associated with plant growth? My results suggests that whole-soil inoculations did increase AMF colonization in cacao seedlings in terms of easily extractible glomalin-related soil protein and relative quantity AMF DNA but not total glomalin-related soil protein and percent root length colonization. Data from 480 cacao seedlings over 1 year suggests whole soil inoculations resulted in an increase in seedling growth. In addition soil inoculations resulted in a decrease in herbivory in both cacao cultivars at 2 months. Furthermore, full sun had a negative effect on cacao growth (a predicted 79% decrease) which was reversed when whole soil inoculations were used resulting in higher predicted growth under full sun. Given the low costs, I recommend introducing nearby intact forest soil for ongoing reforestation efforts in order to combat climate change with carbon sequestration and increase small holder farmer's adaptation to a changing climate with regenerative agroforestry.