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

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。

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

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 photosynthesis 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 P_n, T_r, 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, P_n, and T_r 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.