AM真菌在不同氮磷营养水平下对三色马先蒿吸器形成的影响研究

Haustoria are exclusive organs of parasitic plants responsible for host attachment and nutrient transfer. Initiation and proper differentiation of haustoria is essential to successful plant parasitism. Investigations have been focused on inducing effects of host plants on initiation and differentiation of haustoria. Little is known about effects of other factors on haustorium formation in parasitic plants. Recently we found that inoculation with arbuscular mycorrhizal (AM) fungi strongly suppressed haustorium initiation and differentiation in root-hemiparasitic Pedicularis tricolor, which is the first report so far regarding repressive effects of a living organism on haustorium formation in parasitic plants. Being able to form AM association with AM fungi as well as to grow and produce haustoria in the absence of a host plant, P. tricolor is an ideal plant system for studying direct influence of AM fungi on haustorium formation in root parasitic plants. To gain a better knowledge of the repressive effects of AM fungi on haustorium formation and relevant regulation processes, we aim to study the effects of different AM fungal species on haustorium formation in P. tricolor under greenhouse conditions, using six AM fungal species isolated from habitat soil of the hemiparasite. In addition, we will test the influence of AM fungal inoculation on haustorium formation in P. tricolor under different nitrogen (N) and phosphorus (P) conditions, by supplying different levels of N, P, and N:P ratios. Knowledge gained will open a new perspective for a better understanding of regulation of haustorium formation in root parasitic plants, and may provide clues for development of new biocontrol strategies in the management of parasitic weeds.

吸器是寄生植物的特征器官及其从寄主获取养分的唯一通道。吸器的数量和分化水平直接影响寄生关系的建立。先前关于吸器发生仅限于对源自寄主诱导信号的研究，而对其它因素的影响则知之甚少。我们近期发现，接种丛枝菌根（AM）真菌可抑制根部半寄生植物三色马先蒿的吸器形成。这是迄今发现的首例对寄生植物吸器发生有直接抑制效应的生物现象。三色马先蒿可与AM真菌建立共生关系，且可在无寄主条件下生长并产生吸器，是研究AM真菌直接影响根寄生植物吸器形成过程的理想材料。为进一步阐释AM真菌对吸器形成的抑制现象及相关调控，本项目拟以6种AM真菌为接种材料，通过温室控制条件下的菌种回接实验，分析不同AM真菌种类对三色马先蒿吸器形成的影响；并通过设置不同氮、磷水平及氮磷配比，研究不同氮磷营养水平下AM真菌对三色马先蒿吸器形成的影响。该研究可为了解根寄生植物的吸器发生和调控过程提供新视角，并为根寄生杂草的生物防治提供新思路。

本研究通过人工控制条件的栽培试验，利用模式AM真菌菌株及从马先蒿生境土中分离的AM真菌，在不同氮磷供应水平和不同植物组合条件下接种，分析了氮磷供应水平和AM真菌种类对三色马先蒿及另外两种与之存在养分需求差异的马先蒿吸器形成的影响。结果显示，接种AM真菌对三种马先蒿的吸器发生和生长发育均有一定程度的影响。在马先蒿独立生长时，不同AM真菌种类对三色马先蒿自发性吸器的数量影响存在一定种间差异，根内球囊霉对三色马先蒿吸器发生的抑制作用更为明显。与单纯接种AM真菌孢子相比，接种包含扩繁土壤、根段、菌丝及孢子的混合接种物对三色马先蒿吸器发生的抑制效果更明显。当寄生于寄主植物时，马先蒿的吸器发生受AM真菌种类的影响不显著，但寄主植物对养分供应及接种AM真菌的生长反应，对马先蒿生长发育和吸器数量有较大影响。在多数AM真菌－植物组合中，栽培基质中氮磷供应水平对马先蒿生物量积累和根系发育有明显影响，氮磷供应比例显著影响AM真菌对马先蒿吸器发生的抑制效应。除AM真菌和栽培基质养分状况外，马先蒿及寄主植物的苗龄、移栽时与寄主植物的距离对马先蒿吸器数量均有显著影响。除利用土壤栽培试验开展研究外，我们还初步建立了三种马先蒿的毛根转化体系和皿内吸器诱导体系，为进一步探讨吸器形成过程中细胞和分子水平的调控机理奠定了基础。