MINERAL-CONTENT OF LEAVES FROM TREES GROWING ON SERPENTINE SOILS UNDER CONTRASTING RAINFALL REGIMES IN PUERTO-RICO

The interactions between water and soil nutrient availability in deter mining leaf nutritional composition and structural features were inves tigated in forests on serpentine in Maricao and Susua (Puerto Rico). T hese forests grow under contrasting rainfall regimes: Maricao is a wet forest located at altitudes above 500 m and receiving more than 2500 mm rainfall, while Susua is a humid forest located well below 500 m, w ith less than 1500 mm rainfall and a well defined dry season. Dominant tree species and soils were analysed for N, P, K, Ca, Mg and Ni. Soil s can be differentiated according to their K content (higher in Marica o) and P contents (higher in Susua). Mature leaves of both forests hav e sclerophyllous characteristics as judged from the Specific Leaf Area s (<80 cm(2) g(-1)) and low P contents. Leaf area development is stron gly correlated with leaf N and P contents in both forests, but Maricao samples appear to be more limited by P availability, In concordance w ith soil values, the Susua leaf sample set has significantly higher co ntents of P, but lower contents of K when compared with the Maricao sa mple set. Analyses of soluble K, Ca, and Mg reveal strong physiologica l selectivity in the absorption of these cations. K/Ca and Ca/Mg ratio s are markedly higher in the soluble leaf extracts than in the soil ex tracts. It seems that restriction to vegetation development in the ser pentine areas investigated are more related to nutritional deficiencie s and not to high contents of either Mg or Ni in the upper soil layers . Only two strong Ni accumulators were found, Cassine xylocarpa (1.2 m u mol Ni g(-1) dry mass or 70 mu g g(-1)) from Susua, and Chionanthus domingensis (12.2 mu mol g(-1), or about 700 mu g g(-1)) from Maricao. These species are not restricted to serpentine areas in Puerto Rico.