Differences in oxalate–carbonate pathway of Brosimum alicastrum in karst homegarden and forest soils

Abstract

The oxalate-carbonate pathway (OCP) allows atmospheric carbon dioxide (CO 2 atm) sequestration through deposition of CaCO 3 in soils. The participation of Brosimum alicastrum Sw. (Moracea) in the OCP has been demonstrated in traditional Maya agroforesty systems (homegardens) in Yucatan, Mexico, but remains unstudied in wild vegetation. To compare the OCP role of B. alicastrum trees associated to homegardens and forest, the calcium oxalate (CaC 2 O 4 ) content of leaves, bark, roots, and adjacent soil of 40 trees was measured, as well as the abundance of soil and rizospheric oxalothropic bacteria. The highest CaC 2 O 4 contents were present in leaves (45.37 g kg -1 ) and adjacent soil (576.93 mg kg -1 ) of wild trees. Oxalotrophic bacteria abundance was higher in the rhizospheric soil associated to wild trees. Soil CaC 2 O 4 content was positively correlated to soil Ca (r s = .911; p < .01) and CaCO 3 (r s = .885; p < .01) contents in wild trees and negatively correlated to soil redox potential (r s = -.625; p = .02). The CaC 2 O 4 contents and oxalotrophic bacteria abundance in soils indicate an active participation of B. alicastrum trees in the OCP in both systems, allowing the capture of CO 2 atm. The lower potential to sequester CO 2 in homegardens is mainly due to the use of the B. alicastrum as forage, which prevents the addition of litter to soil. If trees in homegardens were not defoliated, the amount of CO 2 atm captured by B. alicastrum in these systems would be greater than those in forest because the tree density in homegardens can be up to 18 times greater than in forest. INTRODUCTIONThe increase in greenhouse gas emissions and their concentration in the atmosphere is one of the main environmental challenges today. As one of the principal greenhouse gases, car-Abbreviations: OCP, oxalate-carbonate pathway.