Abstract
Restoration of native vegetation and fuelwood production are important environmental pending goals for Mexico, where years of wrong management practices resulted in ecosystemic degradation and fuelwood scarcity. In degraded areas, native rhizobial strains are often undetectable, therefore, the restoration of natural vegetation associated with an effective nodulation of the leguminous trees is mostly appropriate. Sinorhizobium americanum is a native nitrogen-fixing bacteria isolated from nodules of the native Acacia species in the region. Acacia farnesiana is a multipurpose leguminous shrub from Mexican seasonally dry tropical forests (SDTF). In this study we analyzed the effect of inoculation with S. americanum on A. farnesiana growth in a greenhouse and in a very degraded area and compared with non-inoculated seedlings. In a greenhouse, we measured the biomass dry weight of different parts of the plant, using destructive sampling after 15, 20, 30, 45 and 120 days of growth. We also calculated the relative growth rate (RGR) and the resources allocation (root/shoot weight ratio and root length/root dry weight) of seedlings. In a degraded area we measured the seedling length and survival and calculated the RGR. In the greenhouse and in the degraded area, the inoculation positively affected the growth of seedlings. However in the greenhouse, the inoculation did not have effect on resource allocation patterns. Therefore, the inoculation with Sinorhizobium americanum could improve the A. farnesiana growth and the re-establishment of important plant-soil interactions in degraded areas, being a recommendable technique for land restoration and the improvement of fuelwood production.
Highlights
Tropical regions worldwide suffer increasing pressure due to anthropogenic disturbances of their natural ecosystems
Native rhizobium are often undetectable in eroded soils where native legumes have been cleared (THRALL et al, 2001) and so can become a handicap for plant establishment since microorganisms represent the major component of soil biomass and their activities have a key roll in nutrient cycling, affecting nutrients availability (COLEMAN et al, 1983)
The field studies were conducted in Rio Tembembe Ecological Restoration Station (RTERS), in the Tembembe river basin cliff, in the northwestern region of Morelos state in Mexico (18° 54’ 34” N and 99° 20’ 23” W)
Summary
Tropical regions worldwide suffer increasing pressure due to anthropogenic disturbances of their natural ecosystems. Mexico presented the third highest average annual deforestation by area of primary forests, 2000-2005 (395,000 ha), among tropical countries (FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS - FAO, 2005). In a more local scale, in the Tembembe river basin, in the Morelos state, the degradation of the seasonally dry tropical forest environment and mainly of its soils is evident, reaching 80% of erosion rates (GOMEZ-GARZÓN, 2002). In the area of study, Galindo-Escamilla (2006) found a high soil bulk density, flooding events and a low microbiological activity. At this location, primary vegetation has been substituted or diminished because it is the only source of firewood, foliage and fruit for the local inhabitants (DORADO, 1983). The restoration of native vegetation and an effective nodulation of the leguminous trees could have a productive and ecological advantage
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