Agroforestry systems (AFS) play a major role in the sequestration of carbon (C). The objectives of this study were to quantify the organic C stocks in the above-and below-ground tree biomass and in the soil in a cattle-farming system with live fences (CFSLF) of Gliricidia sepium and to compare the levels with those of a cattle-farming system based on a grass monoculture (CFSGM). The methodology included a forest inventory in nine randomly assigned plots and the destructive sampling of G. sepium 32 trees, measuring for each tree the diameter at breast height (DBH), stem height, total tree height, branch weight, leaf weight and coarse root weight. In addition, we measured grass biomass, collected litterfall and collected soil samples at depths of 0-10, 10-20 and 20-30 cm in the plots. A logarithmic model was developed to quantify the above-and below-ground tree biomass. The soil organic matter was determined by the dry combustion method. The total carbon stored in the CFSLF was 119.82 Mg C ha -1 , with the G. sepium trees contributing 5.7 % of the total C (6.48 Mg C ha -1 ). The CFSGM stored 113.34 Mg C ha -1 . The grass biomass stored 15.32 Mg C ha -1 year -1 in the CFSGM and 15.68 Mg C ha -1 year -1 in the CFSLF, and the litterfall in the CFSLF stored 0.205 Mg C ha -1 year -1 . Despite the modest contribution of G. sepium trees to the C storage, the total carbon accumulated in the CFSLF and CFSGM was similar.

Homegardens are reservoirs of genetic resources. When native plant populations are compromised, traditional management of homegardens can be an effective means of conserving species and enhancing food security. Hylocereus undatus (dragonfruit) is a key species in homegardens but is rarely found in wild populations in the Yucatan. We analyzed management practices and genetic diversity of dragonfruit grown in homegardens in three climate regions (West, Central, and East) in the state of Yucatan, Mexico. Dragonfruit presence and reproductive phenology were documented via 2,660 surveys applied in seventeen municipalities. Eighty-nine semi-structured interviews were conducted to document dragonfruit management and use. Seventy-one specimens were collected among nine populations to characterize genetic diversity with DNA Inter Simple Sequence Repeats (ISSRs) markers. Dragonfruit was found in 12.4% of homegardens, propagated via cuttings (98%), received minimal agricultural management, and flowered and fruited in different seasons among regions. Its fruits were consumed fresh or as a beverage and different parts of the plants were used to treat dysentery, kidney stones, hair loss, and gastritis. Genetic diversity among regions was moderate (PLP [polymorphic loci] = 25.1 to 53.3%; He [expected heterozygosity] = 0.075 to 0.138), but the polymorphism information content (PIC) values were at the most 20% lower than those estimated from an ex situ germplasm collection of Hylocereus spp. A Bayesian assignment analysis identified two genetic lineages (K = 2): one in the West and East regions and another in the West and Central regions. Genetic differentiation Jaccard indexes among accessions from all homegardens were similar to those found among wild accessions from Mexico. We conclude, therefore, that homegardens in Yucatan are important in conserving the regional biocultural heritage of dragonfruit.

No abstract

Resumen. Las poblaciones naturales de Cordia dodencandra, siricote, en Yucatán se encuentran amenazadas por la sobreexplotación de su madera, apreciada por su dureza y veteado. Se requiere diseñar programas de reforestación y enriquecimiento de la vegetación en áreas perturbadas que consideren el crecimiento de esta especie en respuesta a los factores ambientales de selvas en diferentes grados de recuperación. El objetivo de este trabajo fue caracterizar las condiciones ambientales de temperatura, humedad y radiación fotosintéticamente activa en diferentes etapas sucesionales de vegetación: avanzada, media, temprana y sin vegetación, para determinar su influencia sobre el área foliar específica y el crecimiento de plantas jóvenes de siricote. En cada etapa sucesional se estableció una parcela con 60 plántulas de siricote, a distancias de 4 m entre línea de siembra y 2.7 m entre plantas. Después de 19 meses, los sitios en sucesión temprana son los más adecuados para el crecimiento de siricote. Existe una relación inversamente proporcional entre la incidencia de luz y el área foliar específica y una relación directamente proporcional entre humedad relativa y el área foliar específica. Se concluye que el siricote puede utilizarse en programas de enriquecimiento de la vegetación avanzada y para reforestar áreas en sucesión temprana.

This work aimed to evaluate domestication effects on the genetic structure of two dioecious species Brosimum alicastrum Sw. (Moraceae) and Spondias purpurea L. (Anacardiaceae), and a heterostylous one Cordia dodecandra A. DC. (Cordiaceae), growing in remnant forests and homegardens within two climatic regions of the Peninsula of Yucatan. The trees of B. alicastrum and C. dodecandra are propagated by seeds in both population types, while those of S. purpurea are propagated asexually in the homegardens. ISSRs genetic markers were amplified from foliar tissue of 18 to 21 plants per population type/region combination for each species. Genetic diversity, genetic differentiation, and genetic structure estimators were obtained and compared among species at the regional and population level. We found higher polymorphism (37.5–41), but lower private alleles (4–4.4) and similar heterozygosity (0.1–0.12) in the species with sexual reproduction compared to S. purpurea (34, 8, and 0.11, respectively). Genetic diversity in B. alicastrum populations varied with the region; in C. dodecandra, to the population type; and in S. purpurea, to both the population type and the region. Unrestricted gene flow among regions was suggested by low ΦRT in C. dodecandra and S. purpurea (−0.006 and 0.002) but not for B. alicastrum (0.1). Gene flow between populations within the regions for the sexually reproducing species was suggested by lower θII (0.005–0.07 and 0.008–0.1) estimates than those of S. purpurea (0.09 and 0.13). Even though the lowest paired FST (0.002–0.05) and ΦST (0.002–0.12) values were found between the northeastern forest and homegarden populations for the three species, the dendrogram, Bayesian assignment, and K-Means analyses suggest that the least differentiated populations are southwestern forest and homegarden populations of B. alicastrum and S. purpurea, and the southwestern forest and northeastern homegarden of C. dodecandra. The sexual reproduction, biotic interactions, and extensive management of B. alicastrum and C. dodecandra in the agroforestry and the urban systems may contribute to connectivity between wild and domesticated populations, while in S. purpurea this connectivity is interrupted by the clonal propagation of the species in the homegardens.