The capacity of Jamaican mine spoils, agricultural and forest soils to nodulateMyrica cerifera, Leucaena leucocephalaandCasuarina cunninghamiana

Abstract

Soils from seven sites on the island of Jamaica were assayed for the symbiotic diazotrophsFrankiaandRhizobiumusing serial dilutions. Most probable number and least squares regression methods were used to estimate each soil's capacity to nodulate nativeMyrica cerifera, exoticLeucaena leucocephalaand exoticCasuarina cunninghamiana. The sample sites included a montane forest, a slash‐and‐burn agricultural site, reclaimed bauxite mining areas, abandoned sugar cane fields, and a garden plot. None of the host plants used in the bioassay were present on the sites sampled except for scatteredL.leucocephalaon one site.Frankiacapable of nodulatingM. cerifera, which is native to Jamaican highlands, occurred at all sites sampled. NoC. cunninghamiana‐infective Frankiawas detected in soils sampled. Only soils from one site on the tropical coastal plain harbored rhizobia able to nodulateL. leucocephala(37 nodulation units cm−3 of soil). A subset of nodulatedM. ceriferaandL. leucocephalareduced acetylene to ethylene indicating nitrogenase activity. The slash‐and‐burn agricultural site, which was situated at an elevation of 200 m and possessed both high natural fertility and high soil moisture‐supplying capacity, had significantly greaterMyricainfectious capacity (1 000 nodulation units cm−3of soil) than the other sites (7−207 nodulation units cm−3of soil). A planned, paired comparison revealed that a recently cultivated sugar cane field and a recently reclaimed bauxite mining site together had significantly lessMyrica‐infectiveFrankia(4 nodulation units cm−3of soil) than a corresponding pair of sites consisting of a sugar cane field abandoned for 25 years and a bauxite mining site reclaimed 20 years before sampling (118 nodulation units cm−3of soil). Results indicate that Myrica‐infectiveFrankiais widespread in Jamaica, that the number ofMyrica‐infective Frankiaunits vary from site to site in accordance with soil type and soil history, that Jamaican sites sampled lack soilFrankiapopulations capable of nodulating a casuarina host, that rhizobial symbionts capable of nodulatingL. leucocephalamay be geographically restricted to lowlands in Jamaica, and that the occurrence ofFrankiain these soils is independent of host plant presence.