Study On Soil Properties Of Chinese Fir Plantations Based On Stand Age Effect And Density Effect

With the large-scale application of high-end varieties of Chinese fir,the demand for forest soil nutrients and afforestation techniques in Chinese fir plantations has increased.Studying the mechanism of soil fertility decline in Chinese fir plantation and developing key technologies for soil fertility maintenance has become an important issue to be solved urgently.Many studies showed that stand age and stand density are important factors influencing the physical,chemical and biological properties of plantations.Investigating the stand age effect and stand density effect of soil properties of Chinese fir plantation is great significance for the scientific management of Chinese fir plantation,maintaining the soil fertility quality and ensuring the sustainable development of Chinese fir plantation.In this study,the research object was 3,6,12,18,25,32,and 49-year-old Chinese fir plantations in Shanxia Forest Farm,Subtropical Experimental Center,Chinese Academy of Forestry,Dagangshan,Fenyi County,Jiangxi Province and the initial planting densities of the1667,3333,5000,6667 and 10,000 stem?hm^-2,respectively,in Shaowu Weimin National Forest Farm in Fujian Province.The changes of soil properties of Chinese fir plantations based on forest age effect and stand density effect were studied.Soil enzyme activity was determined by spectrophotometry.The metabolic function,structure and genetic diversity of the soil microbial community were analyzed by Biolog-ECO technology,phospholipid fatty acid?PLFA?analysis and high-throughput sequencing technology,respectively.We found that at the same soil layer,soil bulk density and p H increased gradually from6-year-old to 49-year-old plantation,but the p H value of 3-year-old plantation was higher than that of 6-year-old plantation.With the increase of stand age,the contents of organic matter,total nitrogen,total phosphorus,total potassium,alkali nitrogen,available phosphorus and available potassium first decreased,then increased,and were lowest in the 12-or 18-year-old plantation.With the increase of soil depth,the soil bulk density and p H value increased gradually,and the contents of total nitrogen,total phosphorus,total potassium,alkali nitrogen,available phosphorus and available potassium decreased gradually.Soil catalase activity increased with increasing stand age,while urease,invertase,acid phosphatase and?-glucosidase activities in 12,18 and 25-year-old plantations were lower than those in 3,6,32and 49-year-old plantations.Soil enzyme activity decreased significantly with increasing soil depth.In the same soil layer,the intensity of carbon source utilization?AWCD?and the diversity index of bacteria and fungi communities all first increased and then decreased with the increase of stand age.Among all soil samples,Acidobacteria,Proteobacteria,Actinobacteria,Chloroflexi,and Firmicutes were dominant bacteria;Ascomycota,Basidiomycota,and Zygomycota were dominant fungal gates,and the relative abundance of these phyla varied with stand age and soil depth.The relative abundance of the Acidobacteria showed a trend of first increasing and then decreasing,while the relative abundance of Proteobacteria was opposite.The relative abundance of Ascomycota decreased from 6-to49-year-old plantations.At the 0-20 cm layer,when the initial planting density of Chinese fir plantation increased from 1667 to 6667 stem?hm^-2,soil p H,oxidizable organic carbon,available phosphorus and available potassium increased significantly.The activities of soil catalase,urease,invertase and acid phosphatase were lower in low-density plantations(1667 and 3333 stem?hm^-2)than in high-density plantations(5000,6667 and 10000 stem?hm^-2)and were the highest and lowest in the plantations with initial density of 3333 and 6667 stem?hm^-2,respectively.The utilization intensity of microbial community on a single carbon and six carbon sources,Shannon-Wiener diversity index,Pielou evenness index and Mc Intosh diversity index decreased from 1667 to6667 stem?hm^-2 and increased from 6667 to 10,000 stem?hm^-2.The microbial PLFA biomass in the low-density plantations was significantly higher than that in the high-density plantations.The fungal genetic diversity indices in the low-density plantations were significantly higher than those in the high-density plantations,while there were no significant differences in the bacterial genetic diversity indices between the different densities.The dominant bacterial phyla in different stand densities were Acidobacteria,Proteobacteria,Chloroflexi and Actinobacteria;the dominant fungal phyla were Ascomycota,Basidiomycota and Zygomycota.Except Ascomycota,the difference in the relative abundance of these dominant bacteria and fungal phyla between different densities was not significant.