Responses Of Two Rice Varieties To Stress Of Dryland Soil Being Reclaimed Into Paddy Soil And Arsenic Stress

Rice is one of the most important food crops in China. In recent years, panicle malformation disease have occurred in the fields of dryland being reclaimed into paddy in the middle and lower reaches of the Yangtze river region,with symptoms of blank spikelets, distorted lemma and palea like crescent-shape, heads remaining upright at maturity, which is called Hanqingli disease in China and straighthead at abroad. Currently, the causes and mechanisms of the disease are still unknown, and some scholars believe that it may be related to arsenic stress. So it has a great significance to systematically study of soil properties change and rice growth in dryland being changed into paddy condition, as well as the response of different straighthead-resistant rice varieties to arsenic stress for investigating the etiology and prevention of straighthead. In this paper, with the rice panicle malformation disease sensitive variety Fengliangyouxiang NO.1and resistant variety Zhennuo chosen as the test materials, the rice growth and development, changes of antioxidant systems and photosynthesis, mineral nutrient content, as well as uptake and migration of arsenic were studied, and at the same time, the soil physicochemical properties and arsenic speciation, as well as the different responses of the two rice varieties to stress of dryland being changed into paddy and arsenic stress were investigated, aiming to provide the scientific basis for prevention and control of panicle malformation disease. The main findings are as follows:1. When cotton soil being reclaimed into paddy soil, the soil redox potential was significantly higher than that of the old paddy soil and adding straw into the cotton soil could effectively reduce the redox potential. Compared with the old paddy soil, the effective iron content in cotton soil decreased significantly, and the effective copper content increased markedly. Compared with rice plants in old paddy soil, Fe content of two rice varieties seedling plants in cotton soil being reclaimed into paddy soil decreased significantly, but Cu and Zn content increased significantly. The growth of rice seedlings cultivated in cotton soil changed into paddy soil also was stunted presenting with low biomass as well as yellow and weak leaves as symptoms of iron deficiency and copper excess. Adding straw into cotton soil being reclaimed into paddy soil could increase chlorophyll content and effectively ameliorate the iron deficiency symptom and copper excess symptom. In addition, the shoots and roots arsenic content of seedlings in cotton soil being changed into paddy soil were significantly lower than those of in old paddy soil. Adding straw into the cotton soil being changed into paddy soil could significantly increase the arsenic content of roots and leaves. Straighthead-sensitive rice cultivar Fengliangyouxiang NO.1seedlings had a greater capacity of arsenic uptake and accumulation.than straighthead-resistant rice cultivar Zhennuo seedlings.2. The treatment of cotton soil being changed into paddy soil made the two rice varieties yield and panicle length be significantly lower than that of old paddy soil treatment (p<0.05), and adding straw into the cotton soil could effectively improve the yield of rice cultivar Zhennuo, but have no significant effect on rice cultivar Fengliangyouxiang NO.1yield. Meanwhile, when cotton soil was changed into paddy soil, the nonspecific adsorption of arsenic content in cotton soil, and the iron as well as manganese content in iron plaque of rice roots were all higher than that of the old paddy soil, but arsenic content in iron plaque of rice roots was significantly lower than that of the old paddy soil. The arsenic content in rice roots iron plaque of rice cultivar Zhennui was significantly lower than that of rice cultivar Fengliangyouxiang NO.1. Adding straw made the cotton soilbeing reclaimed into paddy soil more suitable for the rice growth. Under the condition of dryland being changed into paddy, rice cultivar Fengliangyouxiang NO.1had a greater uptake capacity of arsenic than rice cultivar Zhennuo, and adding straw promoted arsenic accumulation in Fengliangyouxiang NO.1shoots.3.≥50mg/kg arsenic treatment inhibited the growth of rice with short and small seedlings, reducing tillers and lowering chlorophyll content, and increasinglipid peroxide MDA content. It also significantly decreased photosynthesis of sword leaf in booting stage and delayed rice reproductive growth as well as inhibited rice normal heading, and eventually led to yield reduction. With increasing the level of arsenic treatment, the ratios of several forms of arsenic content in soil, including non-specifically sorbed arsenic which was easily absorbed by plants and specifically sorbed arsenic which was easily released as well as arsenic of amorphous and poorly-crystalline hydrous oxides of Fe and Al., to total arsenic content in soil increased. Under≥50mg/kg arsenic treatment conditions, total arsenic in rhizosphere soil of the rice cultivar Fengliangyouxiang NO.1was higher than that of non-rhizosphere soil, which was inverse to that of the rice cultivar Zhennuo. The arsenic content in Zhennuo roots iron plaque were significantly lower than that in Fengliangyouxiang NO.1. Under low arsenic treatment conditions(≤25mg/kg As), Zhennuo had a weaker capacity of arsenic uptake and accumulation than Fengliangyouxiang NO.1, and its stems, leaves and husk had significantly lower arsenic content than those of Fengliangyouxiang NO.1. With increasing concentration of arsenic, Zhennuo could reduce arsenic stress to its plant growth especially reproductive growth, through inhibiting arsenic transporting to the shoots and reproductive organs under50mg/kg As condition. In higher arsenic contamination conditions (75mg/kg As), Zhennuo had a greater capacity of transpoting arsenic to leaves, which made the arsenic content in its roots remain at a lower level.