The study of spatial genetic structure (SGS) can provide an understanding of the key processes and factors involved in the maintenance of viable populations. Within plant populations SGS is mainly determined by the interplay between gene flow by seed and pollen dispersal, which are expected to be affected by species traits, biotic or abiotic interaction within the habitat. In a set of 12 populations of the subtropical understory shrub Ardisia crenata, we assessed genetic variation at 7 microsatellite loci within and among populations. Small-scale genetic structure was assessed with spatial genetic autocorrelation statistics and heterogeneity tests. We estimated gene dispersal distances based on population differentiation and on SGS. Relationships of gene dispersal with habitat characteristics were assessed with multiple regressions. The populations showed high genetic diversity (He = 0.64) within populations and rather strong genetic differentiation ( = 0.208) among populations. The population differentiation followed an isolation by distance model which suggests that populations are in gene flow-drift equilibrium. Significant spatial genetic structure was present within populations (mean Sp = 0.027). Among the habitat characters, population density and species diversity had a joint effect on SGS. Populations with low population density and high species diversity had significantly stronger SGS than plots with high population density and low species diversity, respectively. Gene dispersal estimated from population differentiation and from SGS resulted in similar values, indicating that the same processes are involved in shaping the genetic structure at both scales. We suggest that local-ranged pollen dispersal and inefficient long-distance seed dispersal, which may be affected by population density and species diversity, contributed to the genetic population structure of the species.

We established 12 plots of 30×30 m, which correspond to comparative study plots (CSPs) in the project “Biodiversity and Ecosystem Functioning of China, BEF China” (Bruehlheide et al. 2010). The plots covered the full altitudinal range of the species and different forest types. For each plot we recorded successional stage and elevation, tree density (number of woody stems, > 1 m height) as well as species diversity of all woody species (based on rarefaction analysis, Bruehlheide et al. 2010; Tab. 1). We mapped all A. crenata individuals inside the plots, determined number of A. crenata individuals per plot as population density and randomly sampled leaves from 30 individuals. Leaf samples were dried at 40°C for 48 hours and then kept dry in silica gel.

The Gutianshan National Nature Reserve (NNR) is located in the western part of Zhejiang Province (29º8'18" – 29º17'29" N, 118º2'14" – 118º11'12" E, Fig. 1). The Gutianshan NNR has an area of approximately 81 km2 and was initially established as a National Forest Reserve in 1975 and became a National Nature Reserve in 2001. The NNR comprises a large portion of broad-leaved forests of advanced successional stages (Hu & Yu 2008), which have not been managed since the beginning of the 1990ies, as well as young successional stages and conifer plantations, mainly of Cunninghamia lanceolata and Pinus massoniana. --- The vegetation is composed of different types of subtropical evergreen and mixed broad-leaved forests (Yu et al. 2001). Most of the stands are secondary forests, evidenced by maximum tree ages of 180 years, by agricultural terraces in almost all plots and by the presence of charcoal in almost all soil profiles. Around the Gutianshan NRR extensive deforestation has occurred during the Great Leap Forward in the 1950s, as in most parts of Southeast China. However, due to prevailing steep slopes, the Gutianshan area was only marginally usable for agricultural activities, and thus an exceptionally intact forest cover has been preserved. --- The climate at Gutianshan NNR is warm and temperate with a short dry season in November and December and with warm summers (Fig. 2). The climatic conditions are characteristic for the subtropics with an annual average temperature of 15.1°C, January minimum temperatures of -6.8°C, July maximum temperatures of 38.1°C and an accumulated temperature sum (≥ 5°C) of 5221.5 degree days.

the samples were collected in 2008

Ardisia crenata

Genomic DNA was extracted from leaf samples using the DNeasy Plant minikit (QIAGEN). Seven highly polymorphic microsatellite loci were used for genotyping (Hong et al. 2008). Fragment analysis was performed on an ABI PRISM 3130 with GS600-LIZ (Applied Biosystems) as internal size standard and using GeneMapper v.3.7 software for genotyping.We used Micro-Checker 2.2.3 (Van Oosterhout et al. 2004),Fstat v. 2.9.3.2 (Goudet 2001),SPAGeDi v. 1.3 (Hardy & Vekemans 2002) to analyse the data.