Abstract
Alfalfa,one of the uppermost leguminous grasses in the world,is widely cultivated in arid-semiarid areas of the loess plateau. Because the content of water-soluble boron (B) is less than 0.5 mg kg–1 in 56% soil in loess plateau and alfalfa is a highly sensitive crop to B,it is necessary to supply adequate B for perennial alfalfa growth. Previous studies showed that physiological characteristics of crops were influenced by B through its effect on the structure of chloroplast,promoting the transportation of sugar and adjusting the balance between moisture and nutrient,then indirectly on the oxidation and reduction process of photo-synthesis and respiration of crops. Until now,most studies have concentrated on the effects of B on yield and quality of alfalfa,few reports on the impact of B on photosynthetic characteristics of alfalfa were available. This study focused on the effects of different B fertilizer levels on the photosynthesis and translocation of soluble carbohydrate by spraying B on the leaves surface of alfalfa grown in B deficient soil,and investigated the high-yield technology of applying B fertilizer in alfalfa. The results showed that photosynthesis and translocation of soluble carbohydrate between source and sink were differently influenced by spraying five concentrations of B fertilizer with different times (1,2,or 3 times) at reviving,branching and early flower bud stages. Significant influences were observed on the increase of Pn,Tr,and chlorophyll content by 39%,30%,and 70%,respectively,in the treatment of spaying three times of 0.3% borax solution compared with the control. Leaf area increased by 37% and soluble carbohydrate concentration in leaves decreased by 50% in the treatment of spraying three times of 0.2% borax solution. B content,Pn,and Tr in leaf were significantly increased by 51%,33%,and 25%,respectively in the treatment of spraying two times of 0.4% borax solution compared with the control. However,B intoxication might occur,along with the decrease of photosynthesis capacity and retardness of growth by spraying 0.5% borax solution 1–3 times.
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