| Fine roots are the central part of material and energy exchange between plant and soil,and play an important role in global carbon cycle.Observation and research on fine root production and turnover are of great significance for improving forest ecosystem productivity and guiding plantation management.Meanwhile,the biomass,production and turnover of fine root were different in different stages of stand development.In this study,we used the soil core method,excavation method and minirhizotron technique to collect fine root samples and to observe the fine root dynamics of young(3year,8year),middle-aged(16year),near mature(21year,25year),mature(26year,29year,32year)and over mature(101year)Cunninghamia Lanceolata plantations in Huitong National Forest Ecosystem Research Station,Hunan province,China.We compared the fine root biomass and the heterogeneity morphology of different stand ages,meanwhile,we discussed the temporal and spatial patterns of fine root standing crop,production,and mortality between different plantations based on the minirhizotron technique.The main research results are as follows:(1)The total and live fine root biomass showed a trend of first increasing,then decreasing and then increasing with the stand age,and dead fine root biomass showed a trend of first decreasing and then increasing with the age of the plantation.Biomass of live and dead fine root was significantly different among different stand ages(P<0.05).The total biomass of young forest,middle-aged forest,near mature forest,mature forest and over mature forest were 171.28g·m-2,194.97g·m-2,177.80g·m-2,148.68g·m-2,199.57g·m-2,respectively.The live fine root biomass were 138.16g·m-2,167.15g·m-2,158.53g·m-2,128.59g·m-2,183.00g·m-2.The dead fine root biomass were 35.23g·m-2,29.08g·m-2,19.93g·m-2,22.44g·m-2,23.39g·m-2.(2)The biomass of fine root decreased with the increase of soil depth.With the increase of stand age,the fine roots have a tendency to grow deeper into the soil.The total biomass of fine root in the 0-15cm soil layer of young forest accounts for 48.19%of the 0-60cm total biomass,which is significantly higher than that of other stand ages.With the increase of stand age,the fine root has an obvious tendency to grow deeper into the soil.With the gradual maturity of stand development,the fine root biomass was mainly concentrated in the soil layer of 0-30cm.(3)The specific root length(SRL)and specific fine root surface area(SRA)of Chinese fir plantation decreased first and then increased,and then decreased or became stable with the increase of stand age.The average diameter of fine roots of different stand ages increased with the increase of root orders,while the specific root length and specific surface area decreased accordingly.The average diameter of grade 1,2 and 3 roots in Chinese fir plantation was less than 1mm.In addition,The diameter of grade 1 and 2 roots may be the same,but their specific root length and specific surface area are obviously different.(4)From the observation period of fine root standing crop of each stand age of the seasonal dynamics,the fine root standing crop of minirhizotron in Chinese fir plantation was still in the accumulation stage.Production of fine roots was low in July and death was high in July,so the fine root standing crop decreased in July.With the increase of stand age,the vertical distribution of the fine root standing crop tended to be distributed in the deeper soil layer,and the fine root standing crop of each stand age first increased and then decreased with the depth of soil layer,which may be caused by the underestimation of the fine root standing crop of minirhizotron in surface soil,which was more obvious with the increase of stand age.(5)During the observation period,the total production of fine roots in the whole soil profile of young forest,middle-aged forest,near mature forest,mature forest and over mature forest was 216.34g·m-2,111.85g·m-2,286.78g·m-2,91.36g·m-2,180.09g·m-2,and the total mortality was 53.47g·m-2,42.78g·m-2,98.78g·m-2,37.01 g·m-2,29.33g·m-2,respectively.The total production of fine root of all stand ages was greater than the amount of mortality,so the total fine root standing crop of minirhizotron was still in the accumulation stage.The production and mortality of fine root were concentrated in the soil layer of 0-45cm,and the increase of the mortality of fine root occurred after the production peak of fine root.(6)The fine root production turnover and mortality turnover both showed a trend of increasing first and then decreasing with the increase of stand ages and the maximum production and mortality turnover both appeared in the near-mature forest.The mortality turnover of fine roots showed a trend of decrease with the increase of soil depth.Except mature forest,other forests showed the lowest mortality turnover of fine root in soil layer of 45-60cm.During the observation period,the turnover rate of fine root production in young forest,middle-aged forest,near mature forest,mature forest and over mature forest were 0.604 a-1,0.462 a-1,0.651 a-1,0.554 a-1,0.468 a-1,and turnover rate of fine root mortality were 0.210 a-1,0.228 a-1,0.372 a-1,0.278 a-1,0.069 a-1,respectively. |
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