喷施硼肥对紫花苜蓿光合作用及可溶性糖源库间运转的影响

Effects of Different Levels of Boron Fertilizer on Alfalfa Photosynthesis and Source-Sink Translocation of Soluble Carbohydrate in Alfalfa

通过叶面喷施不同次数、不同浓度硼肥,研究其对缺硼土壤条件下紫花苜蓿光合作用及可溶性糖运转的影响,探讨苜蓿吸收硼的规律及高产施硼技术。结果表明,从返青期开始,连续在分枝期和现蕾初期累计喷施1次、2次或3次5个浓度的硼砂,均不同程度影响紫花苜蓿光合特性和可溶性糖源库间的运转。喷施3次0.3%(W/W)的硼砂对提高叶片中硼(B)含量、光合速率(Pn)、蒸腾速率(Tr)和叶绿素含量(Chl)作用最显著,较对照提高幅度分别为75%、39%、30%和70%,喷施3次0.2%(W/W)的硼砂对增大叶面积效果最佳,较对照增加37%,并可有效降低叶片可溶性糖含量(50%);一次或多次喷施0.5%(W/W)的硼砂会导致硼中毒现象,抑制光合作用,植株生长受阻。

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.