| The resistance of plant from the metal pollution has always been the hot spot in Pollute Ecology for many years. The root system acts an important role in the metal resistance. This article, took Houttuynia cordata Thunbs gathered from Ya'an city(Y) and the Meishan city(M) as materials, studied injury effects, rhizosphere physiology effects, ecology effects of lead on Houttuynia cordata Thunb under lead stress through hydroponics and the earth experiment. The article also studied accumulation characteristics of lead by Houttuynia cordata Thunb. And the mechanism that Houttuynia cordata Thunb adapt to lead stress environment was also been discussed. The main results are as follows:1. Lead treatment seriously suppressed the growth of overground part of two Houttuynia cordata Thunbs which gathered from two places. But lead stimulated the growth of root systems of two Houttuynia cordata Thunbs when lead was at low concentration. Root-length reduced When the lead density surpassed 250 mg/kg. Root tolerance index of the Houttuynia cordata Thunbs Y was higher than that of M, that explained the resistance of Houttuynia cordata Thunbs Y to lead was higher than that of M.2. The Chlorophyll content of leaves of the Houttuynia cordata Thunbs Y reduced after increased at first, and then elevated again. While the Chlorophyll content of leaves of the Houttuynia cordata Thunbs M reduced along with the lead density increased. Lead can stimulate root activity of Houttuynia cordata Thunb. The effects of lead on Root Activity of two Houttuynia cordata Thunbs under different lead treatment was similar, which reduced after increased at first. The lead sensitivity of root system of the Houttuynia cordata Thunbs M was higher than that of Y, which Root Activity change scope was also wilder than Y.3. The pH of Houttuynia cordata Thunbs rhizosphere environment decreased obviously under lead stress, which explained that lead created the rhizosphere environment of Houttuynia cordata Thunbs acidified. Along with the time passage, the pH of Houttuynia cordata Thunbs rhizosphere environment rose, which explained that root systems of two Houttuynia cordata Thunbs suppressed acidization in rhizosphere environment. The higher lead density was, the weaker suppression function of Houttuynia cordata Thunb root system was. As time passed, ion concentration in the rhizosphere environment reduced at first, then increased, afterwards reduced. The types, quantities of organic acid exuded from root systems of two Houttuynia cordata Thunbs increased obviously after lead processing. Along with lead density increased, the tartaric acid that exuded from root systems all obviously increased, the maximum achieved 5.05 and 3.71 times of that of contrast. Lots of malic acid was exuded by root systems while it was not examined in the contrast treatment. It presented to be drop tendency along with the lead density increased. Amino acid that exuded from root systems increased along with lead density increased, which achieved 3.92 and 3.12 times of that of contrast when lead density was 600 mg/kg. The soluble sugar increased at first, which dropped when lead density increased. And it achieved 2.88 and 3.74 times of that of contrasts when lead density was 200 mg/kg.4. Activity of POD in leaves of Houttuynia casdata thumb Y was higher than that of M. And the tendencies of them presented in different lead density treatments were also different. Along with the lead density increased, activity of POD in leaves of Houttuynia casdata thumb Y increased first, latter dropped, which achieved maximum when lead density was 400 mg/kg. While Activity of POD in leaves of Houttuynia casdata thumb M presented trend of escalation, which achieved maximum when lead density was 600 mg/kg. Activity of CAT in leaves of two Houttuynia casdata thumbs increased first, latter dropped along with the lead density increased. Activity of CAT in leaves of Houttuynia casdata thumb Y achieved maximum when lead density was 200 mg/kg, while M when 100 mg/kg. Along with the lead density increased, activity of CAT in leaves of two Houttuynia casdata thumbs decreased when lead density exceeded that density.5. Microbial Biomass Carbon in rhizosphere soil and non-rhizosphere soil of Houttuynia cordata Thunbs which gathered from two places increased first, latter dropped, then increased again along with the lead density increased. And the difference of them became small.6. The higher lead processing density was, the higher lead content in roots, stems, and leaves of Houttuynia casdata thumbs was, which were connected. Lead distribution in Houttuynia casdata thumbs presented roots>stems>leaves. Lead content of roots and stem increased obviously along with the lead density increased. Lead content of leaves was relatively lower. The lead is mainly fixed in roots by plant.
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