| Fine roots(＜2mm in diameter) are important for the water and nutrient uptake of trees.They have also been regarded as short-lived and the most important component contributing tobelowground carbon flux and nutrient circle in forest ecosystems. With the development of thestudy on global carbon cycle, fine roots have attracted considerable attention. Three GorgesReservoir Area of the Yangtze River, whose environment has been greatly influenced by theThree Gorges project, is fragile and sensitive to the climate change. In this study, PinusMassoniana plantation in Three Gorges Reservoir Area was selected. Through the sequentialsoil cores and buried bags, the root spatial distribution and seasonal dynamics were analyzed,and then fine root production and turnover of Pinus massoniana plantation in Three GorgesReservoir Area were estimated. The aim of this study was to provide the theoretical basis forindicating carbon storage and cirulation of below-ground ecosystem and understanding theenvironmental effects on vegetation in Three Gorges Reservoir Area.In July,2010, the spatial distribution of root(0-10mm)biomass of Pinus Massonianaplantation of three different stand ages (middle-age, premature and mature, respectively) inThree Gorges Reservoir Area was studied. Soil cores with10cm diameter were taken atdifferent horizontal distances (0.5,1.0,1.5and2.0m) from the stem and were separated into5sections,0-10,10-20,20-30,30-40and40-60cm. Then, sequential soil cores and buried bagswere used to measure the fine root production and turnover of middle-age Pinus massonianaplantation in Three Gorges Reservoir Area from March to December,2011. The fine rootbiomass was investigated in the1.0m horizontal distance from the stem. Both the biomasssampling and buried bags recycling were carried out every other month. The results showedthat:1. The total biomass of＜10mm root was4.72,2.94and2.40t/hm~2in middle-age,pre-mature and mature forest, respectively, and differences were statistically significant (P＜0.05). However, the fine root biomass (＜2mm) declined with the increase of forest age from 0.68t/hm~2in middle-age forest to0.52t/hm~2in mature forest with no significant difference (P＞0.05).2. Fine root biomass (＜2mm) was mainly concentrated on the upper soil and decreasedwith the increase of soil depth. Among which,47.92%-72.15%of fine roots were observed in0-20cm soil layer, while the major of2-10mm roots were existed in the20-60cm deep soil. Allof fine root biomass of different age forests reached the highest values at1.0m horizontaldistance from the stem.3. The seasonal changes of fine root biomass of Pinus Massoniana plantation in ThreeGorges Reservoir Area varied with diameter, in which, the dynamic of＜1mm fine root wasmore obvious. As for living fine root, the larger amount of＜1mm root appeared in the initialstage of sampling than that in the latter. And the biomass of＜1mm fine root reached themaximum value in March with significantly higher than that of other months (P＜0.05), whilethere was no significant difference among the biomass in each sampling period (P＞0.05). Andin terms of dead fine root, the roots of two different diameters followed the similar patternwhich the maximum root biomass appeared in the initial stage of sampling, and the minimumvalue existed in September.4. According to the analysis of the effect of environmental factors on fine root growth, wefound the influences of soil nutrient and water content on fine root were more significant thanthat of the temperature of soil and air and precipitation. Except for soil moisture, the effects ofenvironmental factors on the root growth of0-20cm soil depth were more obvious than that of20-60cm soil depth. The multiple correlation coefficients showed that the79%-95.8%of fineroot dynamics could be explained by the seasonal changes of soil nutrient availability andmoisture.5. The root decomposition characteristics of Pinus massoniana plantation in Three GorgesReservoir Area showed a bi-phase pattern, being decomposed faster in prophase and slower inanaphase. The decomposition rate differed from the root diameter. During the initial stages ofdecomposition, the percent of＜1mm root mass losing was very higher than that of1-2mmroot. However, after122days, the differences between them were small. Through the nonlinear exponential model, the decomposition coefficients of＜1mm and1-2mm root were0.7513,0.7177, respectively. The correlation analysis indicated that the mass loss rate of fine root wassignificantly correlated with the initial P, C/N and C/P concentration (P＜0.05). As for theenvironmental factors, the decomposition rate was mainly controlled by the soil condition,among which, the effects of soil organic carbon and available nitrogen on root dynamic weresignificantly (P＜0.05).6. Great differences were observed in estimating the fine root production and turnover rateby three different calculation methods, with the highest values by compartmental-flow method,followed by adding increments and maximum-minimum method calculations. According tocompartmental-flow method, the fine root annual production and turnover were1.04t/(hm2．a),1.05/a. The annual production of two diameter classes were0.58t/(hm2．a),0.46t/(hm2．a), respectively, and the turnover of <1mm fine root with0.69/a was larger than that of1-2mm root with0.69/a. The fine root annual production and turnover of Pinus Massonianaplantation showed the obviously vertical distribution, i.e., the values decreased with theincrease of soil depth. |
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