| Plant population genetic variation under diverse habitats, in other words, effects of habitats on population genetic variation, is the main research topics of landscape genetics. Spatial pattern of population is normally investigated first, then interactions between the spatial pattern and habitat are analyzed, and processes of these interactions are demonstrated. The population dynamics and spatial distribution pattern, gene flow, spatial and temporal genetic structure and habitat heterogeneity are the core issues in the population genetics. In the present study, spatial pattern of habitat factors, population quantity dynamics and spatial pattern, seed and pollen dispersal, spatial genetic structure and their interactions were studied in eight B.alnoides patches in an ecotone of two types of soils originated from limestone and granite in Guangxi Autonomous Regime. This can provide a systematic case study for landscape genetics, and the findings will theoretically contribute to genetic improvement, orchard establishment, natural forest management and plantaion forestry of B. alnoides. The main results are as follows:1. There was fine scale spatial pattern in the variation of topsoil moisture content, soil thickness and litter thickness. Positive spatial autocorrelations were detected at the scales of 0-14 m, 0-17 m and 0-20 m for above three habitat factors, respectively, while no or positive spatial autocorrelation for the other scales. Topsoil moisture content showed positive correlations with soil thickness and litter thickness at the scale of 7-18 m and 0-3 m, respectively, while no or negative correlation at other scales.2. Population age structure and dynamics differed in all patches. The proportion of individuals within each patch decreased with increase of age class. According to the proportions of young trees(age class 1 to 2), middle-aged trees(age class 3 to 7), old trees(age class 8 to 12), four B. alnoides populations in Patches LJ, YC, XX, LJYC belonged to expanding population, and that in Population BY to stable population, and three populations in Patches BYD, NGS, TS to declining population. Static life table analysis showed that the Qx and Kx tended to decrease first, then increased and finally decreased as increasing of age class, and their maximum values occurred at age class 7 or age class 9. It was indicated from the survival curves of population that Patches LJ and LJYC belonged to Deevey-III type, YC and XX to Deevey-IItype, and BY, BYD, NGS and TS to Deevey-I type.3. B. alnoides populations demonstrated clustering distribution pattern within majority of patches at different development stages, which were 0-11 m, 0-20 m, 0-16 m, 0-15 m, 4-8 m, 0-1 m, 0-7 m in Patches LJ, YC, XX, BY, BYD, LJYC and TS, respectively, while in Patch NGS, it did random. Compared to saplings and adults, seedlings were clusterred at small scale. There existed association between spatial patterns of B. alnoides population and three habitat factors. Spatial distribution pattern showed positive correlation between population and topsoil moisture content and soil thickness at the scale of 0-2 m and 0-5 m, respectively, while negative correlation between population and litter thickness. Spatial pattern of seedlings demonstrated strong correlation with three habitat factors at fine scale rather than saplings and adults,4. The seed rain lasted 83 and 60 days at stand and individual level, respectively. Three stages of seed dispersal including the starting, fastigium and subsiding stages lasted 11, 32 and 40 days at stand level, while 9, 25 and 26 days at individual level. The seeds dispersed at the fastigium stage occupied 83.1% and 68.7% of all seeds collected during the whole experimental period at the stand and individual levels, respectively. The seed rain density by day was higher than that at night, and the highest seed rain density by day occurred at 12:00-16:00. At the individual level, the seed rain density decreased with increase of distance from the mother tree, and 79.6 % of seeds were collected within 0-30 m around the mother tree. At the stand level, 81.2 % of seed were collected within 0-45 m around the forest edge. The seed rain densities were significantly different between directions(P<0.01), which was affected by wind direction. And the seed rain density was also positively significantly affected by the wind speed(P<0.05).5. At landscape level, the minimum distance of pollen dispersal was 1.6 m at BY patch, and the maximum was 2098.9 m from patch YC to NGS. Mating events occurred with high frequencies at the scale of 0-200 m. Compared to the individuals outside of patch, the mother trees received much more pollens from the individuals inside of patch. The main pollens in the whole studied landscape were from Patch YC at direction of northeast.6. There existed strong spatial genetic structure in most patches of B. alnoides with different scales. The scales were 0-10 m, 0-70 m, 0-70 m, 0-40 m, 0-40 m in Population LJ, YC, XX, BY, BYD, respectively. No spatial autocorrelation was detected at whole scale in Patches NGS, LJYC, TS, this was maybe caused by less individuals sampled. In most populations, the seedlings had strong spatial genetic structure at small scale rather than the saplings and adults. The strong spatial genetic structure of B. alnoides population at fine scale might result from heterogeneous microhabitat, pollen and seed dispersal mode, clustering distribution of individuals and manmade disturbances. |
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