接种根内球囊霉提高氮素向甘薯块根转移和再分配的机理

【目的】研究接种丛枝菌根真菌 (arbuscular mycorrhiza, AM) 对甘薯 (Ipomoea batatas L.) 的侵染率及叶片氮代谢酶活性的影响，探索甘薯氮素吸收后在植株体内的转移和分配规律，以期为全面了解菌根真菌促进氮代谢的过程提供理论依据。【方法】采用盆栽试验方法，供试菌种为一种根内球囊霉Glomus intraradices BEG141。土壤灭菌后，以不接种菌根 (–AM) 为对照，在8 kg土中接种100 g菌剂 (+AM)。于甘薯幼苗移栽后30天、60天和90天，从甘薯茎蔓顶部往下数第5片完全展开叶的叶柄与茎蔓交叉处定量注射99% (15NH₄)₂SO₄溶液，15N总施用量为199.5 μg/plant。每次注射后三天取植株样，分为茎、叶、纤维根和块根4部分，测定生物量干重、根系菌根侵染率、15N丰度、氮代谢酶活性。【结果】接种AM处理显著增加了甘薯根部真菌侵染率及泡囊丰度、根内菌丝丰度和丛枝丰度。随着移栽天数的增加，侵染率显著增加，最高达到67%。移栽后30天接种和不接种菌根真菌处理间甘薯生物量和氮素吸收量差异不显著，移栽后60天和90天，接种AM真菌处理的甘薯生物量和氮素吸收量显著高于不接种AM处理 (P < 0.05)。与CK相比，同一生育期接种AM处理显著提高了甘薯叶片谷氨酸脱氢酶 (GDH)、谷氨酰胺合成酶 (GS) 和谷氨酸合成酶 (GOGAT) 的活性，对硝酸还原酶 (NR) 活性无显著影响。双因素分析表明，接种菌根与接种后时间对提高甘薯生物量干重、氮素累积量及GDH和GS活性的正交互效应显著 (P < 0.05)。移栽后30天，接种AM处理显著提高了甘薯茎蔓和叶片15N积累量和分配率；移栽后60天，叶片中15N积累量较前一时期显著增加。接种AM处理的叶片和茎蔓中15N积累量在30 d和60 d显著高于不接种AM处理 (P < 0.05)，而在移栽后90天显著低于不接种AM处理，说明接种AM处理显著促进15N向块根的转移和分配。【结论】接种AM真菌可提高GDH、GS和GOGAT的代谢活性，促进无机氮向有机氮的转化。接种AM菌剂可促进生育前期氮素在叶片中的分配，有利于地上部的生长，而后期促进地上部积累氮素向地下部转运，进而增加甘薯块根中的干物质积累，提高甘薯的经济产量。

Inoculation of Glomus intraradices BEG141 to increase transfer and redistribution of nitrogen to tuber of sweet potato

【Objectives】Effects of inoculation with arbuscular mycorrhiza (AM) fungi on nitrogen transfer and allocation in sweet potato (Ipomoea batatas L.) were studied in this experiment, to understand the rules controlling the process of nitrogen metabolism promoted by AM fungi.【Methods】A pot experiment was conducted using sweet potato as test material. AM strain of Glomus intraradices BEG141 was prepared and inoculated into soil in concentration of 100 g strain in 8 kg of soil (+AM), taking no inoculating AM stain as control (–AM). After 30, 60 and 90 days of transplanting of seedlings, 20 μL of 99% (15NH₄)₂SO₄ solution were injected into the xylem below the top fifth open leaf, with a total 15N injection of 199.5 μg/plant. Sweet potato samples were collected three days after each 15N injection, and divided into vine, leaf, fibrogen and tuber, the dry biomass, root colonization rate, 15N abundance and N metabolism related enzyme activities were determined.【Results】The +AM treatment significantly increased the root colonization rate and the abundance of vesicle, hyphae and arbuscular of sweet potato. With the growth of sweet potato, the infection rates were increased significantly and reached up to 67%. The biomass and nitrogen uptake of sweet potato between +AM and –AM treatments were not significantly different at the 30 days, but became significant at the 60 days and 90 days. At the same growth days, the +AM treatment significantly increased the activities of GDH, GS and GOGAT in sweet potato leaves. Two-factor analysis showed that AM and growth days had significant positive interaction effects on increasing biomass dry weight, nitrogen accumulation and activities of GDH and GS (P < 0.05). At the 30 day and 60 days period, +AM treatment promoted the 15N accumulation and allocation rates in vines and leaves of sweet potato, which were significantly higher than those in –AM treatment. At the 90 days after transplanting, however, the accumulation of 15N in vines and leaves was significantly decreased compared to –AM, and the transfer and allocation of 15N to tuber roots were increased significantly by +AM.【Conclusions】Inoculation of AM fungi stimulates the activities of GDH, GOGAT and GS, which promotes the transformation of inorganic nitrogen to organic nitrogen. Infection of AM fungi improves the regulation of absorbed N. The N will be allocated into vegetative organs for the plant growth in early stage, and stimulate its transfer to underground, thus increase the accumulation of dry matter in storage organ.