Hultine K R, Williams D G, Burgess S S O, Keefer T O
School of Renewable Natural Resources, University of Arizona, Tucson, AZ 85721, USA.
Oecologia. 2003 Apr;135(2):167-75. doi: 10.1007/s00442-002-1165-4. Epub 2003 Feb 14.
We measured sap flow in taproots, lateral roots and stems within a single individual in each of three co-occurring tree species in a Chihuahuan desert arroyo to assess the seasonality and magnitude of hydraulic redistribution. Nocturnal reverse flow (hydraulic redistribution) was detected in shallow lateral roots of Fraxinus velutina and Juglans major during periods when surface soils were dry. Reverse flow in the Fraxinus lateral root ranged from near zero to 120 g h(-1), and was inversely correlated with nighttime vapor pressure deficit (D), suggesting that nighttime transpiration may have inhibited hydraulic redistribution. Reverse flow in the Juglans lateral root ranged from near zero to 18 g h(-1). There was no relationship between reverse flow and nighttime D in the Juglans lateral root, despite a weak positive relationship between nighttime D and rates of basipetal flow (flow towards the stem) in the taproot. Reverse flow in Fraxinus and Juglans ceased when surface soils were wetted by monsoon rains and flooding. We found no reverse flow or seasonal variation in root sap flow in Celtis reticulata. However, basipetal sap flow in Celtis roots continued throughout most of the evening, even during periods when D was near zero, and commenced in the morning more than two hours after the onset of sap flow in the main stem. Patterns of nocturnal root sap flow in Celtis may have been facilitated by the diurnal withdrawal from, and refilling of above ground storage compartments (i.e. above ground diurnal storage capacity), which may have prevented hydraulic redistribution. Species differences in nocturnal root function may have significant impacts on ecosystem hydrological fluxes, and should be considered when scaling fluxes to catchment, landscape, and regional levels.
我们在奇瓦瓦沙漠峡谷中三种共生树种的每一个个体内，测量了主根、侧根和茎中的液流，以评估水力再分配的季节性和幅度。在表层土壤干燥的时期，在绒毛白蜡和大核桃树的浅侧根中检测到夜间反向流动（水力再分配）。绒毛白蜡侧根中的反向流动范围从接近零到120克/小时，并且与夜间水汽压差（D）呈负相关，这表明夜间蒸腾作用可能抑制了水力再分配。大核桃树侧根中的反向流动范围从接近零到18克/小时。尽管夜间D与主根中向基流动（流向茎的流动）速率之间存在微弱的正相关关系，但大核桃树侧根中的反向流动与夜间D之间没有关系。当表层土壤被季风雨和洪水浸湿时，绒毛白蜡和大核桃树中的反向流动停止。我们在网脉朴的根液流中未发现反向流动或季节性变化。然而，网脉朴根中的向基液流在整个晚上的大部分时间都持续存在，即使在D接近零的时期也是如此，并且在主干液流开始后两个多小时的早晨开始。网脉朴夜间根液流的模式可能受到地上储存隔室的昼夜排空和再填充（即地上昼夜储存能力）的促进，这可能阻止了水力再分配。夜间根系功能的物种差异可能对生态系统水文通量产生重大影响，在将通量尺度扩展到集水区、景观和区域水平时应予以考虑。
