Peek Michael S, Leffler A Joshua, Hipps Larry, Ivans Sasha, Ryel Ronald J, Caldwell Martyn M
Department of Forest, Range and Wildlife Sciences and the Ecology Center, Utah State University, Logan, UT 84322, USA.
Tree Physiol. 2006 Nov;26(11):1469-76. doi: 10.1093/treephys/26.11.1469.
Juniper species are noted for long-lived foliage, low and persistent gas exchange activity and drought tolerance. Because leaves and roots of the same species are thought to be similar in structure and life history, we hypothesized that Juniperus osteosperma (Torr.) Little (Utah juniper) fine roots would reflect the persistent aboveground foliage characteristic of this species. We monitored fine roots, less than 1 mm in diameter, by minirhizotron imaging to a depth of 150 cm over two growing seasons from April 2002 to December 2003. We measured fine root numbers, lengths and diameters, and noted the time of birth and death of root segments. We correlated our root data with soil water potential measured by thermocouple psychrometry and ecosystem evapotranspiration measured by ecosystem eddy flux. Median fine root lifespan, determined by the Kaplan-Meier product-limit method, was about one year, much less than foliage lifespan estimates of more than five years. Yet, roots of juniper live much longer than those of other Great Basin species. The median survivorship of shallow and deep roots was 144 and 448 days, respectively. Production of new roots was observed during periods of favorable soil water potential and there was a seasonal progression of increased new roots and root length during the warm season toward lower soil depths with root loss in the upper soil layers. This was also reflected in water extraction which progressed to greater soil depths later in the warm season. Aboveground, rates of ecosystem evapotranspiration decreased with decreasing soil water potentials in a similar manner in both 2002 and 2003, reflecting the relocation of roots to available water at depth. Juniper exhibited a flexible root depth distribution throughout the 20 months of this study, indicating the potential to respond to shifting soil water resources despite long fine root lifespans.
刺柏属植物以其长寿的叶片、低且持久的气体交换活动以及耐旱性而闻名。由于同一物种的叶片和根系在结构和生活史方面被认为相似，我们推测刺柏（Juniperus osteosperma (Torr.) Little，犹他刺柏）的细根会反映出该物种地上叶片持久的特征。从2002年4月至2003年12月的两个生长季节里，我们通过微根窗成像技术监测了直径小于1毫米的细根，深度达150厘米。我们测量了细根的数量、长度和直径，并记录了根段的出生和死亡时间。我们将根系数据与通过热电偶湿度计测量的土壤水势以及通过生态系统涡度通量测量的生态系统蒸散量进行了关联。通过Kaplan-Meier乘积限界法确定的细根寿命中位数约为一年，远低于超过五年的叶片寿命估计值。然而，刺柏的根系寿命比其他大盆地物种的根系长得多。浅根和深根的存活中位数分别为144天和448天。在土壤水势适宜的时期观察到有新根产生，并且在温暖季节，随着新根数量和根长度的增加，根系呈现出季节性向下层土壤延伸的趋势，而上层土壤层的根系则有损失。这也反映在水分提取上，在温暖季节后期水分提取向更深层土壤发展。在地上部分，2002年和2003年生态系统蒸散速率均随着土壤水势的降低以相似的方式下降，这反映了根系向深层可利用水分的迁移。在这项研究的20个月中，刺柏表现出灵活的根系深度分布，表明尽管细根寿命较长，但它仍有潜力对不断变化的土壤水资源做出响应。
