Saharan dust transport and tropical dry forests in the Yucatan peninsula: Vegetation structure, atmospheric phosphorus inputs and soil development in a tropical karst landscape.

摘要

Long-range eolian dust transport from the Sahara-Sahel region is recognized as an important source for soil development and nutrients for terrestrial ecosystems in downwind regions. Tropical forests show widespread evidence of phosphorus (P) limitation to ecosystem productivity, and long-distance dust transport may offset long-term P losses in these ecosystems. In tropical forests, the woody canopy may enhance atmospheric deposition of dust and other inputs by enhancing deposition processes. In this dissertation, the enhancement of atmospheric P inputs by the forest canopy, and the importance of long-term Saharan dust deposition in a tropical dry forest ecosystem in the central Yucatan peninsula are investigated. Forest vegetation structure was found to significantly enhance atmospheric P inputs, with mature forest canopies having four-fold greater P inputs than atmospheric bulk deposition in a deforested area. Throughfall and stemflow together convey enough P to compensate for P losses from leaching in the mature forest. Stemflow is a larger proportion of atmospheric P fluxes in secondary forests than in mature forests where the taller and more complex canopy has larger P inputs in throughfall. Saharan dust transport to the Yucatan accounts for only a quarter of annual atmospheric P inputs in bulk deposition, but is still an important source of P because of the enhancement of P inputs by the canopy, and the availability of these inputs at the beginning of the growing season. There is also clear geochemical evidence of long-term Saharan dust inputs to soils at El Refugio, Campeche. When Sr isotope ratios and trace element ratios are considered together, soils at three field sites showed the influence of Saharan dust inputs, and clear differentiation from volcanic or local limestone sources. Saharan dust is thus important for sustaining productivity of tropical dry forests and maintaining soil development in the Yucatan peninsula.