Effects of Soil Nutrient Heterogeneity and Earthworms on Aboveground Biomass of Experimental Plant Communities

Soil nutrients are commonly heterogeneously distributed and earthworms are one of the most common soil organisms.While effects of both soil nutrient heterogeneity and earthworms have been well studied,their interactive effect on plant community productivity has rarely been tested.In a greenhouse experiment,we constructed experimental plant communities by sowing seed mixtures of four grasses,two legumes and two forbs in either a heterogeneous soil consisting of low and high nutrient soil patches or a homogeneous soil where the low and high nutrient soil patches were evenly mixed.The earthworm Eisenia fetida was either added to these soils or not.Aboveground biomass of the whole communities,grasses and legumes did not differ between the homogeneous and heterogeneous soils or between the soils with and without earthworms.However,soil nutrient heterogeneity reduced aboveground biomass of forbs,and such an effect did not interact with earthworms.In response to soil heterogeneity and earthworms,biomass ratio of the three functional groups showed similar patterns as that of their biomass.At the patch level,aboveground biomass of the whole community,grasses and legumes were greater in the high than in the low nutrient soil patches within the heterogeneous soil.A similar pattern was found for the forbs,but this was only true in the absence of earthworms.Our results suggest that soil nutrient heterogeneity and earthworms may not influence aboveground biomass of plant communities,despite the fact that they may modify the growth of certain plant functional groups within the community.

Soil heterogeneity affects ramet placement of Hydrocotyle vulgaris

Aims Soil heterogeneity is common in natural habitats.It may trigger for-aging responses(placing more ramets and/or roots in nutrient-rich patches than in nutrient-poor patches)and further affect the growth of plants.However,the impact of soil heterogeneity on competitive interactions has been little tested.Methods We conducted a greenhouse experiment to investigate the effects of soil heterogeneity on intraspecific competition with a stolonif-erous herb Hydrocotyle vulgaris.We grew one(without com-petition)or nine ramets(with competition)of H.vulgaris under a homogeneous environment and two heterogeneous environ-ments differing in patch size(large or small patches).In the het-erogeneous treatment,the soil consisted of the same number of nutrient-rich and nutrient-poor patches arranged in a chessboard manner,and in the homogeneous treatment,the soil was an even mixture of the same amount of the nutrient-rich and the nutrient-poor soil.Important Findings Irrespective of intraspecific competition,H.vulgaris showed for-aging responses to soil heterogeneity in the large patch treatment,e.g.it produced significantly more biomass,ramets,aboveground mass and root mass in the nutrient-rich patches than in the nutrient-poor patches.In the small patch treatment,foraging responses were observed when intraspecific competition was present,but responses were not observed when there was no competition.However,we find a significant effect of soil heterogeneity on neither overall growth nor competitive intensity of H.vulgaris.Our results suggest that foraging responses to soil heterogeneity may not necessarily be adaptive and intraspecific competition may not be influenced by soil heterogeneity.