杉木人工林细根寿命研究

林木细根（≤2mm）是树木水分和养分吸收的主要器官，是陆地生态系统净生产力的重要组成部分，深入理解细根生长过程及其寿命是建立全球碳及养分循环模型的关键．本试验采用微根管技术对11年生杉木（Cunninghamia lanceolata）人工林细根生长、衰老、死亡的动态过程进行了为期1年半的监测，运用Kaplan—Meier方法估计细根存活率及中值寿命（Median root longevity，MRL），生成存活曲线（Survival curve）．用对数秩检验（Log—rank test）比较不同直径、不同土层、不同季节出生的细根寿命差异程度．结果表明，细根主要出．现在雨季（3q月），以直径0～1mm的细根为主，并随观测期的延长，细根存活率下降，中值寿命为236d．直径0～1mm的细根累积存活率小于1～2mm的细根．土壤下层（20～40cm）的生存曲线在细根累积存活率达到50％以后始终高于上层（0～20cm），上下层中值寿命分别为236d和243d，这可能与土壤环境因素的垂直分布相关，下层土壤有利于延长细根寿命．不同出生时间的细根寿命不同，雨季与干季出生的细根中值寿命分别为86d和270d．

Fine Root Longevity of A Cunninghamia Lanceolata Plantation Estimated by Minirhizotrons

Fine roots （ ≤2 mm in diameter） are very important for plant in absorbing water and nutrients. The rapid turnover of the fine root system is a major pathway of carbon and nutrient flow from plant to soil in forest ecosystem. So understanding fine root growth and lifespan is a key of modeling global carbon and nutrients cycle. We studied the influence of three major factors （root diameter, depth, season） on the survivorship and longevity of fine roots of a Cunninghamia lanceolata plantation using minirhizotron technique over a year in Nanping, Fujian. Minirhizotrons provide a nondestructive and in situ method for direct and continuous observation on fine roots. We analyzed minirhizotron data using Kaplan-Meier methods within the SPSS survival analysis, and compared variations in longevity between root diameter, soil depths and seasonal root cohorts using cumulative survival rate and median root longevity of fine roots. Survival analysis of data derived from minirhizotron observations showed that, most of fine roots in 0 - 1 mm diameter were produced in rain season （3-8 month）, and the cumulative survival rate of fine roots decreased gradually with time and the MRL was 236 d. For the range of root diameters studied, the mortality of 0- 1 mm fine roots was higher than that of 1 - 2 mm. Besides, depth was also an important factor; survivorship of fine roots present at 20 - 40 cm soil depth was always higher than 0 - 20 cm in later observation time. The time of root production had little effect on overall root survivorship. The survival curves are not significantly different for rain and dry seasons, and the MRL in the two seasons were 86 d and 270 d, respectively.