Prelimilary Study On Physiological Mechanisms Of Soil Acidification Affected Nitrogen Utilization Efficiency Of Early Rice

Soil acidification is a form of soil degradation. Acid rain and environmental pollution cause soil acidification increased progressively. Rice is the main food crop, the soil acidification has been a serious threat to the rice high yield, high quality, efficient and safe production because of the increase acidification area of southern paddy fields of our country. This research emphasis on germination test and field trials to select3types of early rice that response to acid, then with the nitrogen test to divide into3response types according to their sensitivity to acidification, At the same time, we studied the soil acidification influence on physiological characteristics and nitrogen utilization efficiency of the nitrogen sensitive early rice varieties through field experiments. We tried to explore the nitrogen utilization efficiency effect mechanism of soil acidification to early rice varieties. The results are as follows:1. Compared with the acid sensibility of thirty early rice varieties (combinations) through indoor germination and field experiments. We preliminarily conformed that the Xiangzaoxian44and German111A/974were acidic dull varieties and Xiangzaoxian45, Luliangyou211, Luliangyou611, Tyou705, lingliangyou396and Lingliangyou104were acidic sensitive varieties, other varieties were material acidic intermediate (more sensitive) varieties.2. Nitrogen experiment of acid sensitive early rice varieties was conducted, the tested varieties were divided into three types of nitrogen sensitive types according to the increasing extent of yield and the correlation of nitrogen rate and yield. Lingliangyou104and Luliangyou611belonged to nitrogen sensitive varieties, Lingliangyou396and Luliangyou211belonged to nitrogen non-sensitive varieties, while Xiangzaoxian45and Tyou707belonged to nitrogen medium-sensitive type (more sensitive) varieties.3. The effect of soil acidification on nitrogen utilization efficiency was not consistent among three types of nitrogen sensitive varieties. In the acid condition, the nitrogen accumulation and nitrogen harvest index of three kinds of nitrogen sensitive varieties were decreased highly significantly, nitrogen physiological efficiency decreased significantly. As for nitrogen utilization efficiency, only the nitrogen sensitive varieties showed significant decrease trend, while nitrogen non-sensitive varieties showed unobvious. 4. The soil acidification had an effect on the root volume, dry weight and nitrogen content, but different nitrogen sensitive varieties showed difference. The root volume, dry weight and nitrogen content of the sensitive nitrogen varieties all showed significant and highly significant decrease trend. As for nitrogen medium-sensitive varieties, only the root volume showed significant decrease trend. While as for nitrogen non-sensitive varieties, root volume, dry weight and nitrogen content were not decreased significantly.5. The soil acidification had an effect on the root physiological characteristics, and different nitrogen sensitive varieties showed difference. As for the total root absorption area and active absorption area, the nitrogen sensitive varieties showed highly significant decrease trend, the nitrogen medium-sensitive varieties generally showed significant decrease trend, while the nitrogen non-sensitive varieties only showed significant decrease trend in total root absorption area, and its active absorption area decreased unobvious. The root SOD and POD activity of nitrogen sensitive and medium varieties generally showed significant increase trend. Only the root SOD activity of nitrogen non-sensitive varieties showed significant increase ttrend, while the POD activity changed unclear.6. The soil acidification had an effect on the early rice leaves physiological characteristics, and different nitrogen sensitive varieties showed difference. The leaf area index and net photosynthetic rate of the sensitive and nitrogen medium varieties decreased significantly. While the nitrogen non-sensitive varieties decreased unobvious. The stomatal conductance, transpiration rate, chlorophyll content, carotenoid content and the soluble protein content in leaves of three kinds of varieties showed significant decrease trend. Their intercellular CO2concentration showed significantly increase trend. The POD activity in leaves of sensitive-and medium-varieties increased significantly, while the nitrogen non-sensitive varieties changed unobviously.7. Correlation analysis showed that the correlation between all indexes of nitrogen utilization efficiency of early rice and leaf chlorophyll content, leaf area index, net photosynthetic rate, stomatal conductance, intercellular CO2concentration and transpiration rate was significantly positive. The root absorption area and active absorption area showed a significant positive correlation with the nitrogen utilization efficiency. The root volume and nitrogen physiological efficiency showed a highly significant positive correlation. The root shoot ratio and nitrogen harvest index and nitrogen accumulation showed significant positive correlation. All of these illustrated that the soil acidification influenced the nitrogen utilization efficiency mainly by influencing photosynthetic characteristics in early rice.