Effects Of Habitat Fragmentation On Bryophytes Richness And Genetic Diversity In Thousand-Island Lake Region, Zhejiang

Habitat fragmentation, the reduction of continuous habitat into several smaller spatially isolated remnants, is a significant threat to the maintenance of biodiversity in natural ecosystems. The Thousand-Island Lake possesses an ideal condition to study the effects of fragmented habitat. We studied the effects of habitat fragmentation on bryophytes richness in the southeastern sub-region of the Thousand-Island Lake. In addition, two common species were chosen, H. plumaeforme and P. inflexum, to compare genetic diversity within and among populations by using inter-simple sequence repeat (ISSR) markers and DNA sequence variation. The results are as follows:1) Based on the investigation of bryophytes in the southeastern sub-region of Thousand-Island Lake, there are 129 species belonging to 71 genera and 37 families, of these,15 species of liverworts belonging to 12 genera in 10 families,114 species of mosses belonging to 59 genera in 27 families.3 species (Bryum dichotomum Hedw.; Glyphomitrium humillimum (Mitt.) Cardot; Lindbergia brachyptera (Mitt.) Kindb.) were new to Zhejiang Province. The bryoflora of Thousand-Island Lake was characterized by East Asia elements representing 39.45% of the entire species, followed by North Temperate elements and Tropical Asia elements accounting for 20.18% and 18.35% respectively.2) It was indicated that the distribution of 58 bryophyte species was affected by island area size. These species which were sensitive to environment only distributed in the large (>50 hm2) or medium-sized (10-50 hm2) islands and were in danger of extinction risk.3) The relationship between island area size and bryophyte richness was a positive correlation. When the island area increased to a certain degree, habitat types that island included were similar to these of around areas and species richness would to be saturated.4) Based on ISSR molecular marker,14 of 100 primers produced 111 loci in H. plumaeforme. Of these loci,98 (88.29%) were polymorphic, HT=0.2581, Hs= 0.1714,SI=0.4065, Nm=0.9889, -rd=0.0223, GST=0.3358; 12 primers were selected for P. inflexum,117 loci were generated,114 loci were polymorphic, PPB was 97.44%, higher than the value in H. plumaeforme (88.29%). At the species level, HT=0.2832, Hs=0.2120, SI=0.4296, Nm=1.4879,-rd=0.00683, GST=0.2515. The results using ISSR markers showed relatively higher levels of genetic diversity in P. inflexum which mainly reproduces sexually. Genetic variation was mainly attributed to within populations in both of the two mosses. Coefficient of gene differentiation index was low both in H. plumaeforme and P. inflexum, Nm could resist negative effects of genetic drift. Results for the Mantel test analyzing data from all populations indicated a positive correlation (r-0.3342, P=0.0180< 0.05) between genetic distance and geographic distance in P. inflexum, while no correlation was detected in H. plumaeforme (r=0.1099, P=0.1760).5) DNA sequence data showed that chloroplast regions (atpB-rbcL and rps4) had relatively more informative sites in H. plumaeforme, however, there was no sufficient divergence among H. plumaeforme populations. AtpB-rbcL sequence included one nucleotide substitution,10 deletions and rps4 had only one variable site. Five cpDNA haplotypes were detected based on atpB-rbcL and rps4. Only chloroplast rps4 and nuclear Leafy regions were used for P. inflexum populations, there were 3 variable sites in rps4 and 26 in Leafy respectively. Nine haplotypes were detected based on rps4 and Leafy regions. Their haplotypes differ by only limited SNPs from each other, indicating there has been minimal divergence between the island and lakeside populations.