Plants that connect and spread through expansive underground networks reduce biodiversity, even in soils that are thought to boost it. This could mean that such 'clonal' species — some grasses, for example — will exacerbate plant biodiversity loss in soils that have been enriched by humans.

Fertilizing soil is known to lower plant-species richness, whereas natural variations in local soil nutrient levels are thought to increase it. Alexander Eilts at the University of Minnesota in St. Paul and his colleagues manipulated nutrient levels in outdoor plots for six years. When nutrient levels varied on a small scale, clonal species dominated by reaching between areas to get more nutrients. When nutrient levels varied over larger scales, or when clonal species were absent, biodiversity was higher.

Because of their underground networks, clonal plants may lower the ability of soil nutrient heterogeneity to support a diversity of plant species.

Am. Nat. doi:10.1086/659633 (2011)