Leguminous trees from tropical dry forest generate fertility islands in pastures

Isolated trees in several ecosystems can contribute to the accumulation of soil organic matter (SOM), carbon (C), and essential nutrients such as nitrogen (N) in soil. We investigated the potential of Lysiloma acapulcense (Kunth) Benth. and Vachellia pennatula (Schltdl. & Cham.) Seigler & Ebinger to promote SOM, organic C, and nutrient accumulation in pastures. Lysiloma acapulcense and V. pennatula accumulated similar total N (3.5 and 3.2 mg g(-1)) but more than open pasture (2.4 mg g(-1)), and total P (0.29 and 0.31 mg g(-1)) under their canopies than in open pasture (0.21 mg g(-1)). Both species influence processes that increase soil fertility but in different directions. Lysiloma acapulcense seems to accumulate higher organic carbon (100.6 mg g(-1)), SOM (17.3%), and NH4+ (10.0 mg kg(-1)) under its canopy than in open pasture (73.2 mg g(-1), 12.6%, and 6.4 mg kg(-1), respectively). V. pennatula is capable of reducing soil C:N and C:P ratios (27.6 and 285.3) compared to open pasture (31.3 and 362.7). Lysiloma acapulcense seems to maintain soil processes that promote C storage, which have as a consequence greater C and N retention, whereas V. pennatula seems to maintain soil processes that promote greater availability of P and N in soil. The species of L. acapulcense could be used to improve soil structure in a context of management of dry rangelands, whereas V. pennatula could be used to improve soil nutrient retention in the same context. Including specific tree species in dry ecosystems management could generate opportunities for diversification of soil fertility strategies.