不同强度盐胁迫下AM真菌对羊草生长的影响

不同浓度NaCl盐处理下,AM真菌对羊草(Leymus chinensis)的侵染能力和对植物生长的影响,从植物形态和离子含量角度探讨了AM真菌提高羊草耐盐性的作用机理。结果表明,在高盐胁迫下,AM真菌显著降低了盐胁迫效应,提高了羊草生物量,菌根效应明显。菌根化羊草的根茎比显著增加,并且N、P浓度较高,Na~+和Cl~-离子浓度较低,表明AM真菌即促进羊草对营养元素的吸收,又减少了离子毒害。菌根化羊草的Ca~(2+)和K~+离子浓度,以及P/Na~+和K~+/Na~+比高于非菌根化羊草,表明AM真菌可通过调节渗透势以避免或减缓盐胁迫造成的生理缺水。随着盐胁迫的增加,菌根化羊草对磷的依赖性逐渐转换为对钾的依赖性。研究结果有助于揭示AM真菌提高植物耐盐能力的作用机理,并对应用菌根技术修复盐化草地具有理论指导意义。

The effect of the arbuscular mycorrhizal fungi on the growth of Leymus chinensis under saline stress of different intensities

Arbuscular mycorrhizal fungi (AMF) could improve the tolerance of plants under saline stress. However, the degree of this improvement might differ relative to salt stress intensity. We conducted an experiment to explore the ability of AMF to colonize Leymus chinensis roots and evaluate the effect of AMF inoculation on the growth of plants under four NaCl concentrations (0, 1, 2, and 3 g NaCl/kg soil). The mechanism behind the saline tolerance of mycorrhizal L. chinensis plants was also discussed in terms of their root:shoot ratio and ionic content. The inoculants used in this study were Glomus mosseae and G. geosporum, two dominant species found in highly saline-alkaline natural grasslands. Sixteen pots of inoculated L. chinensis seedlings were randomly subjected to one of four NaCl treatments, as were sixteen pots of non-inoculated plants of the same species. The plants were harvested and measured after 75 d of growth. The results show that under high saline stress, the AMF significantly decreased the strength of the salinity response and increased plant biomass. The mycorrhizal growth response under high saline stress was significantly positive, which indicated that the AMF-plant symbiotic relationship is important to plants under salt stress. However, the colonization rate and infection intensity of AMF in L. chinensis roots both decreased as salt stress increased. The ability of AMF to improve plant growth might decrease, and one-sided or mutually harmful negative effects might occur when salt stress becomes worse, because of the increasing intensity of the competition between AMF and plants. The AMF significantly increased the root:shoot ratio in each NaCl treatment. More photosynthetic product was allocated to the roots of mycorrhizal plants than those of non-mycorrhizal plants, which increased both the water and nutrient absorption, and transportation capacity of the AMF-plant symbiont. The re-allocation of resources between roots and shoots might be one of the primary strategies used by mycorrhizal plants to increase their fitness under harsh environmental conditions. The higher N and P concentrations observed in mycorrhizal plants also support the idea that AMF help L. chinensis absorb and utilize more nutrients under saline stress. The concentrations of Na⁺ and Cl^- were both lower in mycorrhizal plants than in non-mycorrhizal plants, decreasing the ionic content of inoculated plants. Ca²⁺ and P/Na⁺ concentrations were higher in mycorrhizal plants under low saline stress, while the K⁺ and K⁺/Na⁺ concentrations were higher in mycorrhizal plants under high saline stress, indicating that the mycorrhiza could reduce the physiological drought response of plants under saline stress by adjusting their osmotic potential via absorbing other ions and/or increasing ionic ratios such as K⁺/Na⁺. The results also showed that the saline tolerance of mycorrhizal plants was increased by the mycorrhizal P response under lower saline stress, and by the mycorrhizal K response under high saline stress. This study has improved the understanding of the mechanism underlying the improved saline tolerance of mycorrhizal plants, and provides some guidelines for using AMF technology to restore saline-degraded grasslands.