菌豆共生体对豆类植物受根部半寄生植物危害的缓解效应及生理机制

Root hemiparasitic plants often impair the growth performance of their host plants. Some root hemiparasites are notorious weeds in farmland or grassland ecosystems. Suppression of growth caused by parasitism of root hemiparasitic plants varies greatly among different host plants. This opens up the possibility of working out a way to management of these hemiparasitic weeds. A number of studies have shown that root hemiparasitic plants lead to significant biomass reduction in their grass hosts, but have a much weaker effect on growth of their legume hosts. However, underlying mechanisms remain unknown. When conducting eco-physiological studies on root hemiparasitic plants of the genus Pedicularis L., we found that fungal symbionts significantly alleviated growth suppression of the parasitized legume hosts. We hypothesize that microbial symbionts of the legume hosts may enhance the tolerance of a legume host to infestation of root hemiparasites by alleviating nutrient stress. In the proposed research, we aim to study the effects and relevant physiological mechanisms of microbial symbionts (nitrogen-fixing bacteria and arbuscular mycorrhizal fungi) of legumes on alleviation of growth suppression in legume hosts parasitized by two root hemiparasitic Pedicularis species that differ in nutrient requirements. This research will be the first attempt to unravel the mechanisms of alleviation of parasitized legume hosts from their microbial symbionts’ perspective. Knowledge obtained will open a new perspective for development of new biocontrol strategies in the management of parasitic weeds, and provide a reference for understanding the function of symbiotic microorganism on regulating the relationship between hemiparasitic plants and host plants.

根部半寄生植物常削弱寄主长势，部分种类是农田或草地生态系统中的恶性杂草。不同寄主在受根部半寄生植物侵染时，生长受抑程度存在较大差异，这为探寻防控这些寄生性杂草的方法提供了可能。研究表明，相对于禾草类寄主，豆类寄主在受到根部半寄生植物侵染后生物量的下降水平明显较低。然而，相关机理仍是未解之谜。我们在开展马先蒿属根部半寄生植物生理生态学研究时，发现豆类寄主的共生微生物可以缓解因马先蒿寄生而导致的生长受抑现象，推测这些微生物可以通过缓解寄主的养分压力而增强其对寄生危害的耐受性。本研究拟以两种养分需求不同的马先蒿为对象，通过人工接种，分析豆类寄主的共生微生物（固氮细菌和丛枝菌根真菌）在缓解豆类寄主受寄生危害中的作用，并解析相关生理机制。该项目首次尝试从共生微生物角度探讨豆类寄主耐受寄生危害的机制，可为寄生性杂草的防控提供新思路，并为探究微生物对寄生植物与寄主关系的调控作用提供参考和借鉴。

根部半寄生植物可以通过吸器摄取寄主植物的大量养分和水分，从而抑制寄主植物的生长。不少种类已经成为影响农业生产和生态系统稳定的恶性杂草。研究表明，与禾本科植物相比，豆科植物表现出较高的寄生耐受性。然而，相关机理仍是未解之谜。本项目利用盆栽试验，考察了豆科植物的共生菌AMF和根瘤菌及其互作在缓解两种豆科牧草白三叶和紫花苜蓿受大王马先蒿和三色马先蒿寄生抑制中发挥的作用并解析了相关机制。结果显示，大王马先蒿和三色马先蒿寄生可以显著抑制白三叶根系的生长的与吸收能力，从而导致其地上部分生长受到抑制。接种根瘤菌对缓解豆科寄主植物受两种马先蒿寄生抑制影响不大。接种AMF或者同时接种AMF和根瘤菌可以显著提高被寄生白三叶的根系生长，提高根系吸收能力，促进白三叶对N、P等养分的吸收，从而提高寄主白三叶对马先蒿的寄生耐受性。双接种条件下，受大王马先蒿寄生的白三叶的生长和养分状况显著高于单接种AMF条件下的结果。而单接种AMF对提高白三叶对三色马先蒿寄生耐受性最为有效。大王马先蒿寄生可通过抑制紫花苜蓿根系的生长和对P的吸收而显著抑制紫花苜蓿的生长；而三色马先蒿寄生对其生长无显著影响。接种根瘤菌或AMF对缓解紫花苜蓿受两种马先蒿寄生抑制影响亦不大。同时接种AMF和根瘤菌可以显著提高被大王马先蒿寄生紫花苜蓿的根系生长，提高根系吸收能力，促进其对N、P等养分的吸收，从而提高自身对马先蒿的寄生耐受性。而双接种对被三色马先蒿寄生的紫花苜蓿生长的促进作用均不明显。综上所述，AMF及其与根瘤菌的互作在缓解豆科植物受马先蒿寄生抑制中发挥着重要的作用，但缓解程度因寄主植物种类和马先蒿种类不同而异。该项目首次分析了共生微生物在缓解豆科寄主受根部半寄生植物寄生抑制中的作用机制，该研究结果不但为深入探究微生物对寄生植物与寄主关系的调控作用提供参考和借鉴，还为寄生性杂草的防控提供新思路。