| Chinese fir is one of the most important fast-growing timber species in southern China.Due to the impact of poor planting measures such as higher density planting,short cycle rotation and multiple generations of continuous planting,most of the Chinese fir plantations face many problems such as decreased productivity.Reducing the management density of Chinese fir plantation,promoting the restoration of undergrowth vegetation of Chinese fir plantation and extending the rotation period of Chinese fir plantation are effective ways to solve the decline of productivity of Chinese fir plantation.This paper takes 100 years old Chinese fir plantation in Ancaoxia,Wangtai Town,Nanping City,Fujian Province as the research object and analyzes the growth,timber assortment structure and undergrowth vegetation diversity of Chinese fir plantation in different terrains,by measuring the soil physical properties,chemical properties,phenolic acid substance content,microbial composition and diversity of old Chinese fir plantations in different terrains,and further analyzes the correlation between soil physical properties,chemical properties,phenolic acid substance content,microbial diversity and undergrowth vegetation diversity,the research results provide theoretical reference basis for the restoration of degraded ecosystem of Chinese fir plantation,the long-term productivitymaintenance of Chinese fir plantation and the accurate improvement of the quality of Chinese fir plantation.The main research results are as follows:(1)There were differences in the growth and timber assortment structure of the old Chinese fir plantations in different terrains.The average tree height and average breast diameter were the largest in the foothills,the smallest in the northwest,and the opposite in the stand volume.The growth index of each stand was significantly different under different topographic conditions(P<0.05).The timber assortment structure is characterized by large-size timber in the foothills,and the highest yield and yield of the middle-size and small-size timber in the northwest slope.The difference in the yield of large-size timber with different topography is not significant,but the yield difference is significant(P<0.05).In general,the growth of old Chinese fir plantations is good,and the main species are large-size timber.(2)The undergrowth vegetation of old Chinese fir plantation is rich.There are 83 species of plants belonging to 51 families and 70 genera.There are 49 species in the southwest slope,belonging to 37 families and43 genera;there are 46 species in the northwest slope,belonging to 36 families and 41 genera;there are 45 species in the mountain recess,belonging to 32 families and 39 genera;there are 16 species in the foothills,belonging to 14 families and 16 genera.The number ofvegetation types in the southwest slope,northwest slope and mountain recess is similar and significantly larger than the foothills.(3)The Shannon-Wiener index and species richness index of the old Chinese fir plantation shrub layer are all northwest slope>southwest slope>mountain recess>foothills.Simpson dominance index is northwest slope>mountain recess>southwest slope>foothills,Pielou evenness index is mountain recess>northwest slope>southwest slope>foothills;The Shannon-Wiener index,Simpson dominance index and Pielou evenness index of the herb layer are all northwest slope>southwest slope>mountain recess>foothills,and the species richness index is northwest slope>mountain recess>southwest slope>foothills.The diversity indexes of undergrowth vegetation in the foothills were significantly different from those in the other three types(P<0.05).In general,the vegetation diversity of old Chinese fir plantations is shrub layer>herb layer.(4)The soil physical and chemical properties of old Chinese fir plantations in different terrains are different.The soil physical properties of southwest slope,northwest slope and mountain valley are better than that of mountainous land.The soil organic matter,total N and available K content were the highest in the southwest slope,and the soil active aluminum content was the highest in the northwest slope.The content of available P in the soil of the mountain recess was the highest,and thecontent of total P and total K in the soil of the foothills was the highest.In general,the soil nutrient content of the old Chinese fir plantation is higher,indicating that the extension of the main cutting period can maintain the soil fertility of Chinese fir plantation.(5)A total of 15 phenolic acids were identified in the old Chinese fir plantation soil,and 4 species were identified in the positive ion mode.The higher content was Cis-2,3-dihydroxy-2,3-dihydro-p-cumate,Vanillic acid.And the two phenolic acids have different tendency in different soil layers,and the soil layer in the southwest slope,the northwest slope and the foothills increases significantly with the soil layer,while the mountain recess decreases sharply with the soil layer.Eleven species were identified in the negative ion mode,and the higher content was Monoisobutyl phthalic acid,Amurensisin,and Butylparaben.The Monoisobutyl phthalic acid changed in different soil layers.The trend is relatively large,with a significant increase in the soil layer on the southwest slope and the northwest slope,and a sharp decline in the mountain recess with the deepening of the soil layer.(6)Eight kinds of bacteria and four fungi were identified in the old Chinese fir plantation soil.Actinobacteria and Proteobacteria were the main dominant bacteria of bacteria,and Ascomycota was the main dominant bacteria of fungi.The microbial diversity of soils in different terrains was different.The parameters of Chao1 and Ace were the largestin the foothills and the smallest in the northwest.The Chao1 and Ace indices of the fungi were opposite.The Shannon index of the bacteria showed the largest in the southwest slope and the smallest in the mountain recess.The Shannon index is the same;the Simpson index of bacteria is the largest in the northwest slope and the smallest in the foothills.The Simpson index of the fungus is the largest in the northwest slope and the smallest in the mountain recess.(7)Correlation analysis showed that there were significant corre-lations between undergrowth vegetation diversity,soil physicochem-ical properties,phenolic acid content and microbial diversity in old Chinese fir plantations with different topography.Undergrowth ve-getation diversity index and soil bulk density,total P,The total K and pH values were significantly negatively correlated;with orga-nic matter,total N,exchangeable Al,acid soluble inorganic Al,humic acid Al,Cis-2,3-dihydroxy-2,3-dihydro-p-cumate,Monoisobutyl phthalic acid,3-hydroxy-5-methoxy-6-prenylstilbene-2-carboxylic acid,2-O-protocatechuoylalphitolic acid,Armillaribin,5,5’-dehydrodivan illate,Lunularic acid,Amurensisin,Cannabidiolic acid,bacterial Shannon index and fungal Shannon index were significantly positive correlated. |
