Ouyang Y, Shinde D, Ma L Q
Department of Water Resources, St. Johns River Water Management District, P.O. Box 1429, Palatka, FL 32178-1429, USA.
J Environ Qual. 2005 Aug 9;34(5):1490-6. doi: 10.2134/jeq2004.0471. Print 2005 Sep-Oct.
Knowledge of water movement in the plant-xylem system and contaminant bioavailability in the soil environment is crucial to evaluate the success of phytoremediation practices. This study investigated the removal of 2,4,6-trinitrotoluene (TNT) from a contaminated sandy soil by a single poplar (Populus fastigiata) tree through the examinations of temporal variations of xylem water potential, root water uptake, and soil TNT bioavailability. A mathematical model, CTSPAC (Coupled Transport of water, heat, and solutes in the Soil-Plant-Atmosphere Continuum), was modified for the purpose of this study. The model was calibrated using laboratory measurements before its application. Our simulations show that the xylem water potential was high in the roots and low in the leaves with a potential head difference of 3.55 cm H2O, which created a driving force for water flow and chemical transport upward from the roots through the stem to the leaves. The daily average root water uptake rate was 25 cm3 h(-1) when an equilibrium condition was reached after 24 h. Our simulations further reveal that no TNT was found in the stem and leaves and only about 1% of total TNT mass was observed in the roots due to the rapid biodegradation and transformation of TNT into its daughter products. About 13% of the soil TNT was removed by the poplar tree, resulting mainly from root uptake since TNT is a recalcitrant compound. In general, the soil TNT bioavailability decreased with time due to the depletion of soil solution TNT by the poplar tree. A constant bioavailability (i.e., 3.1 x 10(-6)) was obtained in 14 d in which the soil TNT concentration was about 10 mg L(-1). Our study suggests that CTSPAC is a useful model to simulate phytoremediation of TNT-contaminated sites.
了解植物木质部系统中的水分运动以及土壤环境中污染物的生物可利用性对于评估植物修复实践的成功与否至关重要。本研究通过考察木质部水势、根系水分吸收和土壤中2,4,6-三硝基甲苯（TNT）生物可利用性的时间变化，研究了单一杨树（速生杨）对污染沙质土壤中TNT的去除情况。为了本研究的目的，对数学模型CTSPAC（土壤-植物-大气连续体中水分、热量和溶质的耦合传输）进行了修改。在应用该模型之前，利用实验室测量数据对其进行了校准。我们的模拟结果表明，根部的木质部水势较高，而叶片中的水势较低，水头差为3.55 cm H2O，这为水分从根部向上通过茎干流向叶片以及化学物质的运输创造了驱动力。当24小时后达到平衡状态时，根系每日平均吸水量为25 cm3 h(-1)。我们的模拟进一步揭示，在茎干和叶片中未发现TNT，由于TNT迅速生物降解并转化为其衍生物，根部仅观察到约1%的总TNT质量。杨树去除了约13%的土壤TNT，这主要是由于根系吸收，因为TNT是一种难降解的化合物。一般来说，由于杨树消耗了土壤溶液中的TNT，土壤中TNT的生物可利用性随时间降低。在14天内获得了恒定的生物可利用性（即3.1×10(-6)），此时土壤TNT浓度约为10 mg L(-1)。我们的研究表明，CTSPAC是模拟TNT污染场地植物修复的有用模型。
