Wells Christina E, Glenn D Michael, Eissenstat David M
Intercollege Graduate Program in Plant Physiology, The Pennsylvania State University, University Park, Pennsylvania 16802 USA;
Am J Bot. 2002 Jan;89(1):79-87. doi: 10.3732/ajb.89.1.79.
Previous studies suggest that younger roots are more vulnerable to mortality than older roots. We analyzed minirhizotron data using a mixed-age, proportional hazards regression approach to determine whether the risk of mortality (or "hazard") was higher for younger roots than for older roots in a West Virginia peach orchard. While root age apparently had a strong effect on the hazard when considered alone, this effect was largely due to different rates of mortality among roots of different orders, diameters, and depths. Roots with dependent laterals (higher order roots) had a lower hazard than first-order roots in 1996 and 1997. Greater root diameter was also associated with a decreased hazard in both 1996 and 1997. In both years, there was a significant decrease in the hazard with depth. When considered alone, age appeared to be a strong predictor of risk: a 1-d increase in initial root age was associated with a 1.26-2.62% decrease in the hazard. However, when diameter, order, and depth were incorporated into the model, the effect of root age disappeared or was greatly reduced. Baseline hazard function plots revealed that the timing of high-risk periods was generally related to seasonal factors rather than individual root age.
先前的研究表明，较年轻的根系比老根系更容易死亡。我们使用混合年龄的比例风险回归方法分析了微根管数据，以确定在西弗吉尼亚州的一个桃园中，较年轻的根系是否比较老的根系具有更高的死亡风险（或“风险率”）。单独考虑时，根系年龄显然对风险率有很大影响，但这种影响很大程度上是由于不同等级、直径和深度的根系死亡率不同。1996年和1997年，带有从属侧根的根系（高阶根系）的风险率低于一级根系。较大的根直径在1996年和1997年也与较低的风险率相关。在这两年中，风险率都随着深度的增加而显著降低。单独考虑时，年龄似乎是风险的一个有力预测指标：初始根系年龄每增加1天，风险率就会降低1.26%至2.62%。然而，当将直径、等级和深度纳入模型时，根系年龄的影响就消失或大大降低了。基线风险函数图显示，高风险期的时间通常与季节因素有关，而不是与单个根系年龄有关。
