Centre for Ecosystem Management, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA, 6027, Australia.
Oecologia. 2012 Dec;170(4):909-16. doi: 10.1007/s00442-012-2381-1. Epub 2012 Jun 13.
While seasonal redistribution of fine root biomass in response to fluctuations in groundwater level is often inferred in phreatophytic plants, few studies have observed the in situ growth dynamics of deep roots relative to those near the surface. We investigated the root growth dynamics of two Banksia species accessing a seasonally dynamic water table and hypothesized that root growth phenology varied with depth, i.e. root growth closest to the water table would be influenced by water table dynamics rather than surface micro-climate. Root in-growth bags were used to observe the dynamics of root growth at different soil depths and above-ground growth was also assessed to identify whole-plant growth phenology. Root growth at shallow depths was found to be in synchrony with above-ground growth phenophases, following increases in ambient temperature and soil water content. In contrast, root growth at depth was either constant or suppressed by saturation. Root growth above the water table and within the capillary fringe occurred in all seasons, corresponding with consistent water availability and aerobic conditions. However, at the water table, a seasonal cycle of root elongation with drawdown in summer followed by trimming in response to water table rise and saturation in winter, was observed. The ability to grow roots year-round at the capillary fringe and redistribute fine root biomass in response to groundwater drawdown is considered critical in allowing phreatophytes, in seasonally water-limited environments, to maintain access to groundwater throughout the year.
虽然人们通常推断，在依赖地下水的植物中，细根生物量会随地下水位波动而季节性重新分配，但很少有研究观察到深根相对于近地表根的原位生长动态。我们研究了两种 Banksia 物种的根系生长动态，这些物种的根系可接触到季节性动态地下水位，并假设根生长物候学随深度而变化，即最接近地下水位的根生长将受到地下水位动态而非地表微气候的影响。我们使用根内生长袋来观察不同土壤深度的根生长动态，同时还评估了地上部分的生长情况，以确定整株植物的生长物候学。浅层根的生长与地上部分的生长物候相同步，随着环境温度和土壤含水量的增加而增加。相比之下，深层根的生长要么保持不变，要么因饱和而受到抑制。地下水位以上和毛管带内的根生长发生在所有季节，与持续的水分供应和有氧条件相对应。然而，在地下水位处，夏季地下水位下降导致根伸长的季节性循环，随后在冬季由于地下水位上升和饱和而进行修剪。在季节性缺水环境中，能够在毛管带全年生长根系并响应地下水位下降重新分配细根生物量，被认为是允许依赖地下水的植物全年都能接触到地下水的关键。
