闽楠人工林细根寿命及其影响因素

采用微根管技术对闽楠(Phoebe bournei (Hemsl.) Yang)人工林细根生长动态进行了连续2a的观测,通过Kaplan-Meier方法估计细根寿命,使用对数秩检验(Log-rank test)比较单一因素(细根直径、序级、出生季节和土层)对细根寿命的影响；并分析细根化学性质对细根寿命的影响.结果表明:出生季节极显著影响闽楠细根寿命(P＜0.01),细根主要在春季出生(82.36％),夏季出生的细根平均寿命和中值寿命皆最长,分别为(218±23)d和(175±65)d；土层对闽楠细根寿命的影响不显著(P＞0.05),下层(20-40 cm)细根平均寿命为(126±4)d高于表层(0-20cm)的(116±5)d；细根平均寿命随直径增大而极显著增大(P＜0.01),0-0.3 mm的细根平均寿命为(109±4)d,0.3-0.6 mm的为(123±5)d,0.6-1 mm的为(139±11)d,1-2 mm的为(185±25)d.随着径级增大,闽楠细根碳含量极显著增大(P＜0.01),氮含量极显著减小(P＜0.01),碳氮比极显著增大(P＜0.01),磷含量极显著减小(P＜0.01).细根平均寿命随序级增大亦显著增大(P＜0.05),其中一级根平均寿命和中值寿命分别为(120±4)d和(89±1)d,高级根的则为(137±7)d和(123±1)d.以上结果表明闽楠细根寿命受到细根形态结构(直径和序级)、出生季节以及细根化学性质的影响.

Fine root longevity and controlling factors in a Phoebe Bournei plantation

Fine roots (<2mm), as the most dynamic component of root system, play an important role in energy flow and nutrient cycling in the forest ecosystems, which send enormous carbon belowground through root turnover. Fine root survivorship in a plantation of Phoebe bournei (Hemsl.) Yang in Xihou, Wangtai, Fujian province, was monitored by the minirhizotron method for two consecutive years. Fine root longevity was estimated by the Kaplan-Meier method and differences among single factors, including root diameter (<0.3mm, 0.3-0.6mm, 0.6-1mm, 1-2mm), root order (first order, higher order), season of birth (spring, summer, autumn and winter), and soil depth (<20cm, 20-40cm), were tested by the Log-rank test. The chemical properties of different root diameter (<0.3mm, 0.3-0.6mm, 0.6-1mm, 1-2mm) were also determined. The objective of this study was to understand whether the more rapidly the fine roots grow, the shorter their lifespans. The mean and median root lifespans of Phoebe bournei (Hemsl.) Yang were (121±3)d and (89±1)d, respectively. Root growth was highly dynamic during the year, with 82.36% of new roots born in spring. Fine root longevity was significantly affected by the season of birth (P<0.01); the mean and median lifespans were (218±23)d and (175±65)d for roots born in summer, (121±3)d and (89±1)d for those born in spring, and (93±3)d and (46±6)d for those born in autumn and winter, respectively. While soil depth had no significant effect on the median fine-root longevity ((89±3)d amd (89±2)d respectively in the lower and upper soil layer) (P>0.05), mean root lifespan in the lower layer ((126±4)d) was higher than that in the upper layer ((116±5)d). Mean root lifespan increased significantly with root diameter (P<0.01); the mean root lifespan was (109±4)d, (123±5)d, (139±11)d and (185±25)d, and the median root lifespan was (89±0)d, (89±1)d, (123±13)d and (130±13)d, respectively, for root diameter classes of <0.3mm, 0.3-0.6mm, 0.6-1mm and 1-2mm. Root lifespan was significantly affected by root order (P<0.05). Mean root lifespan and median root lifespan of the first root order were (120±4)d and (89±1)d, respectively, while those of the higher order were (137±7)d and (123±1)d, respectively. The root carbon content ranged from 455.2g/kg to 475.6g/kg and the root C/N ratio rangeed from 20.04 to 42.62, both increased significantly with root diameter (P<0.01). Whereas, both the nitrogen (from 11.16 g/kg to 22.71 g/kg) and phosphorus content (from 0.38 g/kg to 0.97g/kg) were decreased significantly with root diameter (P<0.01). It is evidenced from the above that the smaller the root diameter, the higher the root physiological activity, and the shorter the root lifespan. It's concluded that the fine-root longevity of the Phoebe bournei (Hemsl.) plantation was affected by the morphological (root diameter and root order) and chemical traits, and the season of birth.