Ecological study on the relationship between plant biodiversity and soil fertility in a mature tropical forest, Costa Rica Beaudoin Nadeau, Martin
The relationship between plant biodiversity and soil chemical fertility has been widely investigated in temperate forests and agroecosystems, but there is lack of information about the correlation between these two variables in tropical forests. In this study, the relationship between plant biodiversity and soil chemical fertility was analyzed in a mature tropical forest in Costa Rica. Soil samples were collected in 9 sampling plots (5 m by 25 m) in order to identify the concentration level of P, K, Ca, Mg, Fe, Zn, Mn, and Cu, the soil fertility index, the CEC, and the C/N ratio. Furthermore, species richness, Shannon-Wiener and Simpson’s species diversity, structural richness, and structural diversity were determined for each of the 9 sampling plots. Simple linear regression analysis was used to determine if there was a significant relationship between any of the different variables of plant biodiversity and soil chemical fertility. Tree species richness was inversely related to concentration levels of K, Ca, and P, CEC, and soil fertility index. These results agree with the few studies that were done in tropical ecosystems. Higher tree species richness tended to be found in sites with lower soil fertility. Shannon-Wiener tree species diversity was positively correlated to C/N ratio. This is a new discovery and it seems that there is less N stored in organic matter compared to C in sites with higher species diversity. Herb structural richness was positively related to soil fertility index and P concentration. The herb community may be able to grow taller in soil with higher P content and soil fertility leading to higher structural richness because P is the main soil factor limiting growth in tropical ecosystems. There was a positive relationship between herb structural diversity and Mn concentration in the soil. Therefore, structural diversity is not affected much by soil fertility. No relationship was found among any of the other variables. This study gives important insights on the ecological relationship between plant biodiversity and soil chemical fertility in primary tropical forest stands.
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