| Soil bacterium play an important role in soil nutrient cycling. For an in-depth understanding of the forest soil ecosystem mechanism, the research of changings of soil bacterial community is needed to be known. Soil bacterial diversity is an important factor affecting the plantation ecosystem stability, and it can reflect the level of the continued operation of artificial forests. High soil bacterial diversity plantation ecosystem is generally stable, resistive to natural disasters and other human interference activity. Forest gap as one of the driving factors of forest interference, affects soil bacterial diversity in maintaining and updating of the forest ecosystem. Pinus massoniana can adapt drought or poor of soil, have a strong ability to adapt the forest soil ecosystem, is one of the main plantation tree species in upper Yangtze river low hilly land for the formation of the forest from returning farmland, due to long-term taking the pure specie of forest management pattern, the forest productivity and ecological function droped. In a view of the ecological status of Pinus massoniana plantation in the region, we cut the Pinus massoniana to form different sized forest gap disturbance artificially, then to study the soil bacterial community diversity and soil environmental factors in the forest after gaps’formation, through this study, we expect to find the reference for nearly natural transformation with Pinus massoniana plantations of inefficient, improving the stability and productivity of plantations, it is significative to improve the ecological service function and sustainable management methods of plantations. This study abroad started since October 2013, In order to study the soil bacterial community, we chose seven gap size of a Pinus massoniana plantation (G1-100 m2, G2-225 m2, G3-400 m2, G4-625 m2, G5-900 m2, G6-1225 m2, G7-1600 m2) in the hilly area of the upper reaches of Yangtze River of 41 years mature Pinus massoniana plantation, based on DGGE technique, we studied the gaps and forest edge on soil bacterial diversity, and selected 7 samples which were collected from August 2014 to study soil bacterial communities deeply by high-throughput sequencing. The results showed that:(1) The daily average temperature of forest gap and gap edge had consistent trends, it changed largely in summer and autumn. There was similarity trends at the same months of year 2013 and 2014, the highest temperature followed by august. The soil water content had basically the same change trend from G1-G7 to US, all of them rose first, and then fall overall, but it was lower of 2013 than that of 2014 in spring, and there was no significant difference of soil moisture between forest gaps and the corresponding edges.(2) The analysis of DGGE profiles indicated that there were lots of bands in each lane (sample), and the bacteria taxa were abundant both in forest gaps and gap edges at different sampling time. Our results indicated that the soil bacterial community structure and diversity indices were changed after the formation of forest gaps. Changes in bacterial Patrick index was significant higher, Mainly for G6, G7 and medium gaps, little gaps. The Patrick index was lower in autumn, winter and summer than that in spring for G6; Significant changes of Shannon index were found betweenG3, G6 and G7 in autumn, and Shannon index of US was lower than that of gaps and gap edges in spring and summer; Pielou index wasn’t significantly improved in every sampling time; The Simpson index of G6 was significant higher than G2, G3 and G4 in summer, and it was the highest than other gaps, There was significant difference between EG2 and EG4, but no significant difference found between EG at other seasons.(3) Correlation analysis of soil physical and chemical properties and environmental factors with bacterial diversity indexs revealed that:there was significant correlation between water content and diversity indexs (S, H, Eh), and there was a significant negative correlation between water content and dominance index, there was a significant positive correlation between water content and the other index. Except the soil water content, other physical and chemical properties had no significant correlation with diversity index.(4) There were 16668 OTUs found in this study, and at the least of 99.82% could reach the phylum level,19.16% could reach the genus level. The soil bacteria taxa of the phylum level (>0.5%) mainly included:Proteobacteria, Chloroflexi, Acidobacteria, Actinobacteria, Bacteroidetes, Crenarchaeota, Planctomycetes, Firmicutes, Verrucomicrobia, Spirochaetes, Gemmatimonadetes, Cyanobacteria, WPS-2, Armatimonadetes; The soil bacteria taxa of the genus level (>0.5%) mainly included:Rhodoplanes, Gallionella, Candidatus Nitrososphaera, Candidatus Solibacter, Treponema, Burkholderia, Candidatus Koribacter, FFCH10602, Flavobacterium, Ruminococcus, Methylomonas, Lactococcus, Planctomyces, DA101, Pseudomonas, Sphingomonas.(5) The formation of gaps could enrich soil bacterial community diversity, and there were significant effect between gaps and the number of soil bacterial 16S rDNA. Combined effect of gap size and sampling date had extremely significant effects of the number of soil bacterial, and the same as gap size and sampling point to the number of soil bacterial. The numbers of soil bacterial community in gaps were higher than that of forest edge and forest understory in the winter. |
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