Plant community assembly at small scales: Spatial vs. environmental factors in a European grassland

Abstract

24Dispersal limitation and environmental conditions are crucial drivers of plant species 25 distribution and establishment. As these factors operate at different spatial scales, we asked: Do 26 the environmental factors known to determine community assembly at broad scales operate at 27 fine scales (few meters)? How much do these factors account for community variation at fine 28 scales? In which way do biotic and abiotic interactions drive changes in species composition? 29We surveyed the plant community within a dry grassland along a very steep gradient of soil 30 characteristics like pH and nutrients. We used a spatially explicit sampling design, based on 31 three replicated macroplots of 15x15, 12x12 and 12x12 meters in extent. Soil samples were 32 taken to quantify several soil properties (carbon, nitrogen, plant available phosphorus, pH, 33water content and dehydrogenase activity as a proxy for overall microbial activity). We 34 performed variance partitioning to assess the effect of these variables on plant composition and 35 statistically controlled for spatial autocorrelation via eigenvector mapping. We also applied null 36 model analysis to test for non-random patterns in species co-occurrence using randomization 37 schemes that account for patterns expected under species interactions. 38At a fine spatial scale, environmental factors explained 18% of variation when controlling for 39 spatial autocorrelation in the distribution of plant species, whereas purely spatial processes 40 accounted for 14% variation. Null model analysis showed that species spatially segregated in a 41 non-random way and these spatial patterns could be due to a combination of environmental 42 filtering and biotic interactions. Our grassland study suggests that environmental factors found 43 to be directly relevant in broad scale studies are present also at small scales, but are 44 supplemented by spatial processes and more direct interactions like competition.

Effect of different root endophytic fungi on plant community structure in experimental microcosms

“…ex J. Presl & C. Presl., Armeria elongata Hoff., and Rumex acetosella L. (Horn et al, 2015), which have been frequently reported for dry grasslands in north eastern Germany (Hensen, 1997).…”

“…Our experimental microcosms were designed to recreate conditions found in a natural grassland located near the town of Mallnow, Lebus (Brandenburg, Germany, 52°127.77′N, 14°129.349′E) (referred as the "Mallnow Grassland" throughout this study). Specifically, this study is based on the vegetation occurring in a 15 × 15 m plot within this grassland that was used in previous studies in our laboratory (Horn, Caruso, Verbruggen, Rillig, & Hempel, 2014;Horn et al, 2015). Within the plot, there is a strong gradient in soil texture from loamy to sandy soil along a hillside.…”

Non-random co-occurrence of native and exotic plant species in Mediterranean grasslands

“…Other studies have used null models to detect patterns of plant species assembly in invasion processes, particularly comparing between invaded and uninvaded areas along environmental gradients (Cornwell and Ackerly, 2009;Jansen et al, 2011;Santoro et al, 2012;Horn et al, 2015). However, as far as we know, no previous research has focused on the spatial patterns of a whole community of plant species that undertook transcontinental naturalization by comparing species assembly between the source area and the invaded region.…”

Assessing soil ecosystem processes – biodiversity relationships in a nature reserve in Central Europe

“…Other than occasional grazing, implemented for conservation purposes, disturbance levels in the reserve are low. We focused our harvests on three hills that exhibited gradients in soil texture (the top of the hills were sandy-loamy whereas downhill the soil was sandy -see Horn et al 2015) with pronounced implications on plant composition and nutrient availability. On each of the three hills we marked three square macroplots with sides that varied from 12 to 15m.…”