Species-genetic diversity correlations (SGDCs) could have important implications for the planning of biodiversity conservation. Previous studies on parallel effects of environment on biodiversity resulted in positive SGDC. However, negative SGDCs are observed less often, and the drivers of negative SGDCs are rarely discussed in the literature on empirical studies. The relationships between the distributions of plants and soil properties have long attracted the interests of ecologists. However, relatively little is known about the effect of soil properties on the genetic diversity of a population of focal species.

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to test whether the tree diversity of a community and the genetic diversity of a common tree species were correlated. They also asked what the possible drivers of the SGDC pattern were in those species-diverse communities.

The researchers established 15 plots (40 m x 40 m) within a 20-ha forest dynamics plot (FDP) in the Xishuangbanna tropical seasonal rainforest. They surveyed the tree diversity of the community, evaluated the genetic diversity of a common tree species Beilschmiedia roxburghiana (Lauraceae) using microsatellite DNA markers. They then measured the environmental properties (soil nutrients and topography) of each plot.

They found that the soil properties were highly variable across the 15 plots. A negative correlation was found between the tree diversity and the genetic diversity of B. roxburghiana. With the structural equation modeling (SEM) analysis, a hierarchical effect among the environmental properties, tree diversity and genetic diversity of B. roxburghiana within the plots was identified. The increase in tree diversity within a plot was directly affected by the elevated soil pH and available phosphorus, whereas the increase in species diversity directly depleted the genetic diversity of B. roxburghiana. The SEM analysis also revealed that the variation in soil pH was a direct consequence of the topographic variation and that soil pH determined the availability of phosphorus.

Based on SEM analysis, the environmental characteristics (soil pH and phosphorus availability) effected tree diversity within the community and ultimately led to the negative SGDC.

The study entitled “Soil properties drive a negative correlation between species diversity and genetic diversity in a tropical seasonal rainforest” has been published in Scientific Reports.