The Effects Of Arsenic And Glyphosate Combined Pollution On Rice Growth And Its Mechanism

Rice(Oryza satival. L) is one of primary cereal crops in China. It can uptake and accumulate more arsenic than other cereal crops. The enrichment of As in rice can not only result in the decrease of rice production, but also cause health risks for human and livestock. Glyphosate is one of most extentively used herbicides at present. Glyphosate residue in the soil and its harm to crops has been a hot focus in agriculture. In order to understand how heavy metals and residual herbicide combined pollution take effects on rice cultivation, it’s necessary to investigate the growth and development of rice under the condition of arsenic and glyphosate combined pollution, The effects of single and combined pollution of arsenic and glyphosate on rice growth and development were studied by investigating the seed germination, plant growth,and carbon metabolism of seedlings, yield components, accumulation of mineral elements and arsenic in rice treated with different concentrations of arsenic and glyphosate alone and combined, aiming to provide a reference for the toxicity of heavy metals and herbicide combined pollution on rice. The main results are as follows.1. The influence of arsenic(0-20mg/L) and glyphosate(0-20mg/L) with single and combined treatment on rice seed germination were studied. It showed that As and glyphosate significantly inhibited the germination of rice, reduced the germination rate and vigor of rice seed, shortened the length of roots and germs, and suppressed amylase activity and storage transport rate. The inhibiting effect of As was more powerful than glyphosate in rice seed germination rate and radicle growth; on the contrary, germ suffered greater inhibition when exposed to glyphosate. Glyphosate and arsenic combined pollution had a synergistic inhibition effect, resulting in reducing rice germination rate, root length, shoot length growth and the activity of amylase further.2. The effects of arsenic(0-5mg/L) and glyphosate(0-5mg/L) alone and combined treatment on the biomass, antioxidant system, carbon metabolism and arsenic uptkae of rice seedling were investigated by a solution culture experiment. The results showed that: Arsenic and glyphosate significantly inhibited the growth of rice seedlings, reduced rice plant height, chlorophyll SPAD value, the shoots and roots fresh weight and root vitality. Arsenic stress also cut down the ability of rice seedlings antioxidant defenses, leading to the increase of MDA content. However, low level of glyphosate treatment enhanced the ability of rice resistance to oxidative stress and decreased MDA content; and high level of glyphosate treatment was the opposite. Arsenic and glyphosate treatment had no significant interactive effect on rice MDA content. 1mg/LAs treatment reduced, but 5mg/L As increased soluble sugar and sucrose content in rice shoots. Except the low concentration(1mg/L) reduced the sucrose content, glyphosate alone treatment significantly improved soluble sugar and sucrose content in rice stems and leaves. Arsenic and glyphosate had no significant influence on rice SPS enzyme activity, but high concentration of arsenic and glyphosate significantly increased the activity of SS. Arsenic and glyphosate had so remarkably interaction effect that strikingly increased the soluble sugar content and reduced the SPS enzyme activity. High concentration of glyphosate(5mg/L) decreased As content in rice leaves and roots. Under the conditions of 1mg/L As and 5mg/L As treatment, the arsenic content in roots and shoots of 5mg/L glyphosate were 55.1%, 89.6%(roots) and 77.5%, 84.3%(shoots) of those of no glyphosate, respectively.3. The process of plant growth period, yield, mineral nutrient content and the uptake and accumulation of arsenic in rice under the condition of arsenic(0-5mg/L) and glyphosate(0-5mg/L) with single and combined treatment were investigated by a pot experiment. The results indicated that As and glyphosate notably inhibited the growth of rice, reduced plant height and chlorophyll SPAD value, and delayed the growth periods of rice. Rice yields were reduced by arsenic stress, and combined As and glyphosate tretment led to rice yields much less than single treatment. Arsenic had a significant inhibiting influence on N、P、K content, and arsenic and glyphosate combined together existed synergetic effect, in declining N、P、K content in rice of tillering period. Arsenic significantly improved Fe and Mn content, but decreased Cu and Zn content in rice of mature period. Conversly, glyphosate treatment significantly decreased Fe and Mn content, but increased Zn content of brown rice husk, stem and leaf in mature period. Arsenic and glyphosate combined pollution existed significant interaction on Fe, Mn, Cu and Zn content of rice in mature period. Arsenic significantly improved arsenic content in rice. Glyphosate promoted the uptake of arsenic in rice of tillering period, but had no significant effect on As content of rice in heading period and mature period..