Seed density significantly affects species richness and composition in experimental plant communities.

Zuzana Münzbergová

doi:10.1371/journal.pone.0046704

Abstract

Studies on the importance of seed arrival for community richness and composition have not considered the number of seeds arriving and its effect on species richness and composition of natural communities is thus unknown. A series of experimental dry grassland communities were established. All communities were composed of the same 44 species in exactly the same proportions on two substrates using three different seed densities.The results showed that seed density had an effect on species richness only at the beginning of the experiment. In contrast, the effects on species composition persisted across the entire study period. The results do not support the prediction that due to higher competition for light in nutrient-rich soil, species richness will be the highest in the treatment with the lowest seed density. However, the prevalence of small plants in the lowest seed density supported the expectation that low seed density guarantees low competition under high soil nutrients. In the nutrient-poor soil, species richness was the highest at the medium seed density, indicating that species richness reflects the balance between competition and limitations caused by the availability of propagules or their ability to establish themselves. This medium seed density treatment also contained the smallest plants.The results demonstrate that future seed addition experiments need to consider the amount of seed added so that it reflects the amount of seed that is naturally found in the field. Differences in seed density, mimicking different intensity of the seed rain may also explain differences in the composition of natural communities that cannot be attributed to habitat conditions. The results also have important implications for studies regarding the consequences of habitat fragmentation suggesting that increasing fragmentation may change species compositions not only due to different dispersal abilities but also due to differential response of plants to overall seed density.

Highlights

Dispersal is considered one of the key processes affecting the richness and composition of natural communities, e.g. [1], [2], [3], [4]
The results of these studies generally show that seed arrival increases local species richness in a wide range of communities, and the increase in species richness is more pronounced in more disturbed communities [3]
Seed rain intensity had no significant effect on total aboveground biomass (Table 1A; 2A)

Summary

Introduction

Dispersal is considered one of the key processes affecting the richness and composition of natural communities, e.g. [1], [2], [3], [4]. The importance of seed arrival is usually studied by seed addition experiments in which changes in community and composition are tracked following the addition of seeds of different species, e.g. [11], [12], [13], [14], [15], reviewed by Myers & Harms [3] The results of these studies generally show that seed arrival increases local species richness in a wide range of communities, and the increase in species richness is more pronounced in more disturbed communities [3]. The second is that there is little information available on the intensity of the natural seed rain, so the number of seeds added to the communities probably far exceeds the number that arrives naturally

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