| Root activity is an important indicator of plant response to environmental conditions. High iron content (Fe-plaques) frequently form on roots of wetland plants, reflecting the adaptation of wetland plants to submersion, facilitates nutrient uptake and prevents uptake of phytotoxins. In this study, root activity and the growth of adventitious roots of Typha latifolia and Iris pseudacorus in solution culture experiments were determined to investigate the response of wetland plant roots to iron plaque induced on the root surface. Typha latifolia and Iris pseudacorus (each 60 plants) were cultivated in Hoagland nutrient solution for one week. After adventitious roots of Typha latifolia and Iris pseudacorus emerged, the existing root was removed and the plants were cultivated in the Hoagland solution for an additional three weeks at a pH of 5.5. Thirty-five plants with similar shoot height and root length were transferred to seven plastic buckets with a solution pH of 5.0 and different Fe2+ (FeSO4•7H2O) concentrations (0, 10, 20, 60, 100, 150, 200 mg/L）to induce iron plague formation. The buckets were covered with black polyethylene bags and filled with N2 gas. After five days, two plants were removed from solution to determine root activity. One week later, the fresh weight and activity of the adventitious roots of both species in all treatment groups were measured. Adventitious root growth of Typha latifolia was inhibited by Fe2+ concentrations of less than 100 mg/L, but was promoted at concentrations over 100 mg/L. At higher Fe2+ concentrations, the root activity of Typha latifolia decreased and there was a large difference 〔9.70 μg/(g.h)〕between maximum and minimum values. However, the influence of Fe plague on the adventitious root growth of Iris pseudacorus was not significant in all treatments, and the root activity of Iris pseudacorus ranged from 2.36 μg/(g.h) to 5.48 μg/(g.h) with little variation among treatments. There was a significant negative relationship between the root activity of Typha latifolia and the amount of iron plaque (r = -0.861). Root activity also decreased in Iris pseudacorus with the amount of iron plaque, but the correlation was not significant (r = -0.735). The adventitious root activity of Typha latifolia increased initially and then decreased with amount of iron plaque. The highest activity of new adventitious root occurred in the 20 mg/L Fe2+ treatment, higher than that of the control group by a factor of 1.55. The activity of new adventitious root of Iris pseudacorus showed a similar pattern, but the maximum value occurred at 10 mg/L of Fe2+. Our results indicate that iron plaque on the root surface of wetland plants decreases root activity, but promotes the growth of adventitious roots and the activity of the new roots increases at low concentrations of Fe2+, but declines at high concentrations. This research provides a reference for studies related to the effects of Fe plaque on the absorption and utilization of elements in wetland plants. |
