Plant Interactions In Heavy Metal-Contaminated Soils

Interaction among plants under various environmental stresses are the hotspots to ecology. Many studies have focused on plant interactions under drought stress or salt stress, but little is known about plant interactions under heavy metal stress. In this study, we used Kummerowia striata as a neighbour and the crops (maize or tobacco) as target plants to investigate plant interactions under single or combined heavy metal pollution stress. All the expriments are carried out by root compartments in greenhouse. Main results obtained from these experiments are as follows:1. Total plant biomass of tobacco and maize decreased when neighbour plant Kummerowia striata existed both under single or combined heavy metal pollution stress. So plant interactions between tobacco (maize) and K. striata is negative, and K. striata is the competitor. The competition became weaker when AMF existed in the soil. In addition, there was more competition in below-ground than that in above-ground of plants.2. The ratio of root/shoot of tobacco increased significantly when the neighbour plant K. striata existed, indicating that K. striata could alleviate the harmful effects of heavy metal on target plants. However, the ratio of root/shoot of maize did not change significantly with the presence of K. striata.3. The relative interaction index (RⅡ) of tobacco with 0.45μm aperture millipore filtration barrier is-0.062 under the combined heavy mental stress, implying that the exchange of root exudates between plants had inhibitory effects on tobacco growth. But under lead or cadmium heavy mental stress, plant interaction between maize and K. striata with 0.45μm aperture millipore filtration barrier changed from competition to facilitation along with the stress increasing.4. RⅡof tobacco with 25μm aperture millipore filtration barrier is 0.023 under the combined heavy mental stress, implying that hyphe between tobacco and K. striata was beneficial to tobacco growth. Biomass of tobacco is significantly higher in non-sterilized soil than that in sterilized soil, indicating that AMF is the key factor ti the growth of tobacco. The results of maize are in good agreement with that found in tobacco under single heavy mental stress, except for the moderate stress of lead.5. Compared to no heavy mental stress, the competition between maize and K. striata under single pollution stress of lead became weaker. But no significant differences were observed under with and without cadmium pollution stress.6. Absolute value of total RⅡincreased with the increasing stress under single heavy metal stress, implying that competition was enhanced.