铬处理下超富集植物李氏禾根际溶解氧时空分布特征

植物根系泌氧能改变土壤氧化还原电位，影响重金属形态及生物有效性，是重金属污染土壤植物修复效率的重要影响因素。本文基于平面光极原位高分辨技术，在0、50、100 mg/kg等3个铬浓度下研究了铬超富集植物李氏禾根际溶解氧的时空分布特征。结果表明，李氏禾根际土壤中溶解氧浓度较高的热区集中于根系周围区域，在根尖位置溶解氧浓度较高。根际溶解氧含量显著高于非根际土壤，且距离根部越远溶解氧平均含量越低，其中100 mg/kg铬处理组李氏禾根部中心位置土壤溶解氧浓度为距离中心位置5 mm处土壤溶解氧浓度的1.45倍。在8天的拍摄周期中，对照组根部中心位置溶解氧浓度最高达77.2%，显著高于50 mg/kg铬处理组的50.2%和100 mg/kg铬处理组的42.3%。此外，3个铬浓度下李氏禾根际溶解氧浓度都呈现先升高后降低的规律，第4天达到最高值。铬处理下李氏禾根际溶解氧浓度明显下降，这可能是李氏禾为避免根际富氧环境将Cr(III)氧化为毒性更强Cr(VI)的保护性行为。

Spatio-temporal Characteristics of O2 in Rhizosphere of Hyperaccumulator Leersia hexandra Swartz Under Chromium Stress

The radial oxygen loss (ROL) of plants is a key factor affecting the phytoremediation efficiency of heavy metal contaminated soils, which can affect the soil redox potential, the speciation and bioavailability of heavy metal in the soil. In this study, the spatio-temporal characteristics of O2 in the rhizosphere of Cr hyperaccumulator Leersia hexandra Swartz were studied using pot experiments with soils spiked with different levels (0, 50, and 100 mg/kg) of Cr. The results showed the hot spots of O2 were along entire root of L. hexandra, which were relatively higher at the root tips. The O2 concentration in the rhizosphere was significantly higher than that in the bulk soil. For example, the O2 concentration at the center of the root was 1.45 times higher than that 5 mm away from the root center. Besides, the ROL became weaker when the distance from the root center became farther. During the experimental period of 8 days, the O2 concentration at the root center of L. hexandra in the control group was 77.2%, which was significantly higher than that of 50 mg/kg Cr treatment group (50.2%) and 100 mg/kg Cr treatment group (42.3%). The ROL increased first and then decreased in all the 3 groups, which reached the highest on the fourth day. The ROL was significantly inhibited by the addition of Cr in the soil, which might be the the protective behavior of L. hexandra to avoid the oxidation of Cr(III) into more toxic Cr(VI).