感染内生真菌的羽茅对大针茅的化感作用

以羽茅(Achnatherum sibiricum)为材料,采用室内生物测定法研究感染不同内生真菌的羽茅浸提液对大针茅(Stipa grandis)种子萌发和幼苗生长的化感作用,并采用气相色谱-质谱(GC-MS)联用技术对羽茅浸提液中的化学成分进行分析。结果表明:(1)内生真菌感染可缓解宿主羽茅对群落优势种大针茅的化感作用;(2)内生真菌感染对宿主羽茅化感作用的影响与内生真菌种类有关,具体表现为相比于未染菌羽茅,感染Epichloё gansuensis可显著缓解宿主羽茅对大针茅的抑制作用,而感染Neotyphodium sibiricum、Neotyphodium gansuensis有缓解羽茅对大针茅化感作用的趋势,但未达到显著影响;(3)羽茅浸提液中含有2,4-二叔丁基苯酚、邻苯二甲酸、邻苯二甲酸二丁酯和硬脂酸甲酯等潜在化感物质,这4种物质相对含量的差异可能是不同内生真菌感染状态的羽茅产生不同化感效应的主要原因;(4)对羽茅浸提液中4种潜在化感物质的化感作用进行验证实验,结果表明,2,4-二叔丁基苯酚对大针茅的化感作用基本表现为低浓度无影响,高浓度抑制,邻苯二甲酸二丁酯的化感作用表现为"低促高抑"的效应趋势,而邻苯二甲酸和硬脂酸甲酯对大针茅均表现出"剂量效应"的化感作用趋势,即4种潜在化感物质在高浓度时均可显著抑制大针茅的种子萌发和幼苗生长。

Allelopathic effect of endophyte-infected Achnatherum sibiricum on Stipa grandis

Endophytes are commonly defined as fungi that colonize internal tissues of plants for all or part of their life cycle. The largest plant family hosting endophytes is Poaceae. Enhanced competitive ability of endophyte-infected grasses has been well documented, including improved shoot and root growth, and greater resistance to biotic and abiotic stresses. However, the role of endophytes on the allelopathic effect of host grass is less studied. Achnatherum sibiricum is a perennial sparse bunchgrass, which always occurs as an accompanying species, and is typically highly infected by fungal endophytes. A. sibiricum can be infected by three endophytic fungi, Neotyphodium sibiricum (Ns), Neotyphodium gansuensis (Ng), and Epichloë gansuensis (Eg). Early studies of A. sibiricum-endophyte symbiota suggested that endophyte infection could improve the growth and stress tolerance of A. sibiricum, allowing the host grass to adapt to stressful or even extreme environmental conditions. However, few studies have examined effects of endophyte infection on allelopathic performance of A. sibiricum. In our study, we selected the natural grass Stipa grandis, a dominant species in a native community of A. sibiricum, as our research subject. The allelopathic effect of water aqueous extracts of A. sibiricum with different endophyte infection levels on seed germination and seedling growth of S. grandis was tested in petri dishes in the laboratory. GC-MS were used to identify chemical components of aqueous extracts of A. sibiricum. The results were as follows:(1) Uninfected A. sibiricum elicited the strongest inhibitory effect on the germination and seedling growth of S. grandis. Endophyte infection could alleviate allelopathic effect of A. sibiricum on the target species. (2) The allelopathic effect of A. sibiricum was related to the endophyte species. Compared with endophyte-free A. sibiricum, Eg infection significantly alleviated the allelopathic effect of A. sibiricum, whereas Ns and Ng infection tended to alleviate the allelopathic potential of the host grass, although the difference was not significant. (3) Four allelochemicals in water aqueous extracts of A. sibiricum were identified via GC-MS, including 2,4-di-tert-butylphenol, phthalic acid, dibutyl phthalate, and methyl stearate. The relative difference in the amounts of these four allelochemicals may account for different allelopathic responses of A. sibiricum. (4) The allelopathic effect of the four potential allelochemicals was validated. The results showed that 2,4-di-tert-butylphenol had no significant effect on S. grandis at lower concentration, but was inhibitory at higher concentration, as compared to the control. Dibutyl phthalate showed a "low-promotion and high-inhibition effect", whereas phthalic acid and methyl stearate showed a "dose effect" on S. grandis. Therefore, the four potential allelochemicals could inhibit seed germination and seedling growth of S. grandis at higher concentrations.