丛枝菌根真菌对枳根净离子流及锌污染下枳苗矿质营养的影响

Abstract

盆栽实验研究了不同施Zn水平(0、300 mg/kg和600 mg/kg)下,接种丛枝菌根真菌<em>Glomus intraradices</em>对枳苗生长、Zn、Cu、P、K、Ca、Mg分布的影响,并采用非损伤微测技术测定分析了菌根化与非菌根化枳根净Ca²⁺、H⁺、NO₃^-离子流动态。结果表明:(1)在不同施Zn水平下,接种菌根真菌显著提高了枳苗地上部及根部鲜重;随着施Zn水平的提高,菌根侵染率呈降低趋势,枳苗地上部与根部Zn含量呈增加趋势,且接种株根部Zn含量显著高于未接种株。(2)接种株未施Zn处理的地上部Cu、P、K、Mg和根部Cu含量、施600 mg/kg Zn处理的根部Cu及施300 mg/kg Zn处理的根部P含量均显著高于对照,而菌根真菌侵染对枳苗Ca含量并无显著性影响。(3)接种株未施Zn处理的根部距根尖端0 μm和600 μm处净Ca²⁺流出速率、600 μm处净H⁺流入速率、2400 μm处净NO₃^-流入速率均显著高于未接种株。;We investigated the effects of arbuscular mycorrhizal fungus inoculation on net ion flux in the roots of trifoliate orange (<em>Poncirus trifoliata</em> (L.) Raf.) and mineral nutrition in seedlings under zinc contamination. A pot experiment was conducted to study plant growth as well as the distribution of zinc, copper, phosphorus, potassium, calcium, and magnesium in trifoliate orange seedlings inoculated by the arbuscular mycorrhizal fungus, <em>Glomus intraradices</em>, under greenhouse conditions. Plants were grown in yellow soil:quartz sand (9∶1, v/v) medium and were irrigated with solutions containing three different zinc concentrations (0, 300 and 600 mg/kg), which corresponded to control, medium and high zinc contamination treatments, respectively. Meanwhile, a non-invasive micro-test technique was used to determine the net fluxes of Ca²⁺, H⁺ and NO₃^- along mycorrhizal and non-mycorrhizal roots of trifoliate orange seedlings grown in medium with no zinc added. Arbuscular mycorrhizal colonization significantly increased the fresh weight of shoots and roots exposed to different zinc levels. With increasing zinc concentrations, the mycorrhizal colonization percentage decreased, while the zinc levels in the shoots and roots progressively increased. Zinc concentrations in the roots were significantly higher in arbuscular mycorrhizal seedlings than in non-arbuscular mycorrhizal seedlings. The shoot/root ratios of the zinc translocation coefficient gradually decreased in arbuscular mycorrhizal seedlings with increasing zinc concentrations. This indicated that at medium or high levels of zinc contamination, a lot of zinc was immobilized in roots through the establishment of mycorrhizae. Therefore, phytotoxicity might be alleviated. Copper, phosphorus, potassium, and magnesium concentrations in shoots of plants grown in medium with no added zinc were significantly higher in arbuscular mycorrhizal seedlings than those in non-arbuscular mycorrhizal seedlings. Similarly, copper concentrations in the roots of plants in medium with 600 mg/kg of added zinc and phosphorus concentrations in roots of plants in medium with 300 mg/kg added zinc were higher in arbuscular mycorrhizal seedlings. Arbuscular mycorrhizal colonization had no significant effects on calcium concentrations in seedlings. Copper and phosphorus concentrations gradually decreased in both arbuscular mycorrhizal and non-arbuscular mycorrhizal seedlings with increasing zinc levels, which demonstrated that zinc levels in seedlings are negatively correlated with copper or phosphorus. With no added zinc, phosphorus, potassium, magnesium and copper uptake was promoted by arbuscular mycorrhizal fungus infection. Under zinc contamination, phosphorus, and copper uptake was still accelerated by mycorrhizal colonization. Thus, the effects of mycorrhizal colonization were not only related to the degree of zinc pollution, but were also correlated with the species of fungi and host plants. Additionally, net Ca²⁺ efflux at 0 μm and 600 μm, net H⁺ influx at 600 μm, and net NO₃^- influx at 2400 μm from the root tip of arbuscular mycorrhizal seedlings in medium with no added zinc were significantly higher than those of non-arbuscular mycorrhizal seedlings. These results suggest that mycorrhizal symbiosis activates Ca²⁺-ATPase, Ca²⁺/H⁺ antiporters and NO₃^-/H⁺ symporters in root plasma membranes. Nutrient uptake and stimulation of growth are mediated by arbuscular mycorrhizal fungi. Furthermore, the variations detected in arbuscular mycorrhizal roots for Ca²⁺, H⁺ and NO₃^- fluxes point to a significant involvement of the fungus.