中文摘要：

细根分解是陆地生态系统C和养分循环的重要环节。以往的细根分解研究以埋袋法的应用为主。然而,由于埋袋法对分解材料的干扰以及对分解环境的改变使其很难揭示原位环境下根系的自然分解过程。该研究应用微根管（Minirhizotron）技术连续3年对水曲柳（Fraxinus mandshurica）和兴安落叶松（Larixgmelinii）细根的分解过程进行原位监测,运用Kaplan-Meier方法估算细根分解的保存率及分解期中位值（即50%细根完全分解的时间,Medianroot decomposition time）,做分解曲线,用对数秩检验（Log-ranktest）方法分析不同树种、直径、根序及土层对细根保存率的影响。结果表明,伴随时间延长,细根的保存率逐渐下降,兴安落叶松细根保存率的下降显著快于水曲柳（p〈0.001）,两树种分解期中位值分别为（82±7）d和（317±28）d;不同直径等级（≤0.3、0.3～0.6、〉0.6mm）细根的分解速率不同,两树种最长分解期中位值均出现在最细直径（≤0.3mm）根中;高级根分解速率显著低于一级根（p〈0.05）;土壤上层分解速度快,随着土壤深度增加细根分解速率减小。微根管技术为了解细根自然分解过程提供了有效途径。

英文摘要：

Aims Fine root decomposition is a major pathway of carbon and nutrient cycling in terrestrial ecosystems. Litterbag studies change the environmental conditions of root decay, so we employed a minirhizotron technique. Our objectives were to： 1） compare fine-root decomposition time and rate be- tween ash （Fraxinus mandshurica） and larch （Larix gmelinii） in the same site, 2） analyze the effect of root diameter and root order on fme root decomposition and 3） investigate patterns of fine root decom- position in different soil depths. Methods In October 2003, we established three 20 m × 30 m plots in each plantation, and randomly installed six minirhizotron tubes. From April 2004 to October 2006, video images were collected at ap- proximately two-week intervals during the growing season. The interval from date of root death to dis- appearance was defined as decomposition time. Video images were digitized via RooTracker software （NC, USA）. Kaplan-Meier method in survival analysis was used to generate cumulative remaining rate and median root decomposition time （MRDT）, and factors of tree species, diameter, root order and soil depth were compared by logrank test. Important findings Cumulative remaining rate of fine-roots in both species decreased gradually with time, with the decrease significantly faster for larch than ash （p〈0.001）. MRDT of larch was （82±7） d compared with （317±28） d for ash. The MRDT of both species differed in three diameter classes （≤0.3, 0.3-0.6 and 〉0.6 mm）. The finest roots （≤0.3 mm） of both ash and larch decayed slower than the other two diameter classes; however, only the MRDT of ash decreased systematically with increasing root diameter. With increasing root order, the cumulative remaining rate of both species increased significantly （p〈0.05）, resulting in a delay time of 82 d and 58 d of MRDT for higher order compared with first order in larch and ash roots, respectively. The fine-root cumulative remaining rate of both species showe