细柄阿丁枫和米槠细根寿命影响因素

采用微根管技术对福建建瓯万木林自然保护区细柄阿丁枫(ALG)和米槠(CAC)细根进行了连续2 a的观测。估计细根寿命采用Kaplan-Meier方法,用对数秩检验(log-rank test)比较单一因素(细根直径、序级、出生年份、出生季节、土层以及邻近细根数量)对细根寿命的影响。同时采用Cox比例风险回归分析方法,分析上述因素对细根存活的影响程度。结果表明:细柄阿丁枫细根平均寿命和中值寿命分别为(286±8)d和(184±9)d,而米槠的则分别为(261±10)d和(212±8)d。仅考虑单一因素时,出生季节、径级、序级以及邻近细根数量对细柄阿丁枫和米槠细根寿命皆有极显著影响(P<0.01);出生年份对米槠细根寿命有极显著影响(P<0.01),但对细柄阿丁枫细根寿命的影响无统计学意义(P>0.05);土层深度对细柄阿丁枫细根寿命有极显著影响(P<0.01),而对米槠细根寿命的影响无统计学意义(P>0.05)。Cox比例风险回归分析则表明出生年份对二者细根寿命的影响皆无统计学意义(P>0.05),影响因素按照影响程度大小排列均依次是序级、出生季节、细根直径、邻近细根数量,而土层对细柄阿丁枫细根寿命的影响最弱,对米槠细根寿命的影响无统计学意义(P>0.05)。

Fine root longevity and controlling factors in subtropical Altingia grlilipes and Castanopsis carlesii forests

Fine roots production and turnover is a significant component of the carbon cycle in forest ecosystems. Fine root survivorship was monitored by minirhizotrons during two successive years in two subtropical evergreen broadleaved forests (Altingia grlilipes, ALG; and, Castanopsis carlesii, CAC) in Wanmulin Natural Reserve, Jian-ou, Fujian province. Root longevity was estimated by the Kaplan-Meier method and differences among single factors, including fine root diameter (d<0.3 mm, 0.3<d<0.6 mm, 0.6<d<1 mm), order (first order, higher order), year of birth (2007, 2008), season of birth (spring, summer, autumn, winter), soil depth(0<D<20 cm, 20<D<40 cm), and number of neighbor root (N <5, 5< N <10, 10 < N), were tested by the Log-rank test. Cox proportional hazards regression analysis was also applied to assess the relative effects of these factors on root survivorship. Mean and median fine root longevity of ALG were (286±8) d and (184±9) d, respectively, while CAC's were (261±10) d and (212±8) d. When considering the individual factor alone, root longevity were significantly affected by season of birth, root diameter, order, and number of neighbor root (P<0.01 for all cases) in both two forests; year of birth had significant effect only in CAC (P<0.01) and soil depth had significant effect only in ALG (P<0.01). Mean fine root longevity of ALG in summer was (204±14) d, which was respectively lower than in spring (290±11) d, autumn (307±13) d and winter (263±25) d. Mean fine root longevity of CAC in summer and winter were (164±20) d and (156±16) d, respectively, which were significantly lower than in spring (269±15) d and autumn (346±17) d. With the increase of fine root diameter, median fine root longevity increased significantly in ALG (P<0.01); while in CAC, median fine root longevity increased from d<0.3 mm diameter to 0.3<d<0.6 mm diameter, and showed little change with further increase in diameter (P>0.05). With the increase of root order, mean fine root longevity of ALG and CAC were increased significantly (P<0.01). Mean fine root of ALG's first order and higher order were (267±8) d and (559±32) d, respectively, While CAC's were (247±10) d and (425±41) d. The number of fine root in ALG and CAC was decreased with root order increased. With the addition of number of neighbor root, mean fine root longevity of ALG and CAC were increased significantly (P<0.01). Furthermore, mean fine root longevity of ALG in 0<N<5, 5<N<10 and 10<N was (226±9) d, (309±15) d and (467±21) d, respectively. While CAC's was (246±11) d, (290±25) d and (438±45) d. Cox proportional hazards regression showed that in both two forests year of birth had no significant effects on root longevity (P>0.05). According to the size of impact on root longevity, these factors can be ranked as: root order, season of birth, root diameter, and number of neighbor root. Soil depth had the weakest effect in ALG while had no effect in CAC (P>0.05).