Fine Root Production, Mortality And Turnover Of Two Kinds Of Origin Of Eucalyptus Grandis Plantation

Fine roots can absorb water and nutrients from soil, which are the most active organs for forest trees. Its growth and death have an important impact on forest net primary productivity and nutrient cycling (NPP). Despite the fine root biomass accounted for only 3%-30% of the total biomass of stand, there is need to maintain the fine root turnover consume 10%-75% of net primary productivity. The fine root turnover is mainly a process of fine-root growth and death. Fixed carbohydrates and N can be break down into the soil through fine root growth and death. Research on its production, mortality and turnover dynamics of forest ecosystems is important for nutrient cycling processes and underground C allocation pattern. Therefore, this study selected Eucalyptus grandis stands which originated from 4-year-old seedlings and tissue culture plantlets, used typical sampling method to set experimental plots and selected criteria wood. Forest fine root production and death in the same position were observed for one year by using Minithizotron technology. Fine roots’diameter, length, root orders and other data were measured and analyzed by using WinRHZOTRON MF 2012 software image. The effects of soil environment on fine root production, mortality and turnover were studied combining with the effectiveness of soil resources. The results were showed as follows:(1) Fine root length production and fine root numbers which originated from two different seedlings were reached the peak in August and June respectively, while the amount of root and root length mortality reached the peak in September. The average production per year of fine roots length and quantities which originated from tissue culture plantlets were 1.16 and 1.24 times than that of seedlings. The average mortality per year of root length and quantities originated from tissue culture plantlets were 1.19 and 1.30 times than that of seedlings. Growth trends of fine root number and length were slightly different, that is, growth spurt of root quantities was June, while August for root length. Two kinds of origins’production of fine root length and quantities were higher than that of mortality (p> 0.05).(2)Fine root production (peaked in August) and mortality (Peaked in September) of different diameters and sequences showed obviously seasonal dynamics. With the root diameter increased, the production and mortality of fine roots reduced. The highest production and mortality were the class which diameters belonged to 0-0.3 mm (due to previous studies, Eucalyptus fine roots diameter were divided into 3 classes, that is, 0-0.3mm,0.3-0.6 and 0.6-1 mm), and which were significantly higher than that of other two diameter classes (p<0.05). With the sequence levels increased, production and mortality decreased. The highest production and mortality were the root in level 1 (there was not so much 2 and 3-level roots, almost haven’t 4 and 5-level roots, so this study classified root in 2 and above 2 as senior root), which was significantly higher than that of senior roots (p<0.05). Fine root production and mortality of each diameter classes and sequences which originated tissue culture plantlets were higher than that of seedlings, but the differences were not significant (p> 0.05). The influences of diameter and sequence on root production and mortality were significant (p<0.05).(3) With the increasing of soil depth, fine root diameter increased while the root number reduced. Fine root production and mortality in soil layer 0-15 cm were significantly higher than that in soil layer 15-30 cm and 30-45 cm (p<0.05). Fine root production and mortality of 15-30 cm were higher than that in 30-45 cm, but the differences were not significant (p> 0.05). When the stands originated from tissue culture plantlets, fine root production and mortality in 0-15cm were significantly higher than that of seedlings, while the other two soil layers showed non-significant (p> 0.05) experiences. Soil depth showed significant difference effects on production and mortality (p<0.05).(4) During two originated Eucalyptus grandis samples, fine root turnover originated from tissue culture plantlets (1.85a-1) was higher than that of seedlings (1.66a-1). With the enlargement of the diameter, the turnover rate decreased. Fine root turnover rate of 0-0.3 mm was significantly higher than that in 0.3-0.6 mm and 0.6-1 mm(p<0.05); 0-0.3mm diameter tissue culture fine root turnover was significantly higher than that of seedlings (p <0.05), while the other two diameter grades showed non-significant differences (p> 0.05). With the root sequences increased, turnover rate reduced. Turnover rate of root level 1 was significantly higher than that of the senior roots (p<0.05). Root turnover rates of tissue culture plantlets were higher than that of the seedlings, but the difference were non-significant (p> 0.05). With the deepening of the soil, the turnover rate reduced, fine root turnover rate of 0-15cm soil layer was significantly higher than that in 15-30cm and 30-45cm soil layers. The effects of different soil depth on fine root turnover rates showed significantly different (p<0.05).Overall, fine root production, mortality and turnover, which originated different sprout and grown in the same site conditions, showed the same variation trends. But these measured fine root characteristics, which originated from tissue culture plantlets, are higher than that of seedlings. Genetic characteristics of two Eucalyptus grandis origins are identical, which resulted in the same variation traits. However, different origins of Eucalyptus grandis showed different adaptability to soil environment, when put them in the same environment conditions, tissue culture plantlets showed higher production, mortality, C utilization, soil nutrients return and soil fertility maintaining. Therefore, Eucalyptus grandis originated from tissue culture plantlets can produce greater ecological and economic benefits in this study area.