Soil temperature outside and inside the patches.

At a sedimentary site in an old mine site, Miscanthus sinensis formed patches, where Pinus densiflora seedlings could grow better compared with those outside the patches, indicating that M. sinensis would improve P. densiflora seedling establishment. The purpose of this study was to understand the mechanisms by which M. sinensis facilitates the survival of P. densiflora seedlings by considering the soil properties, heavy metal tolerance, and root endophytes in P. densiflora seedlings at the sedimentary site. The sedimentary site, which is a bare ground, contained high concentrations of Fe, indicating that plants should be exposed to Fe and high soil temperature stresses. Measurement of soil temperature revealed that M. sinensis suppressed sharp increases and alternation of soil temperature, resulting in reducing high soil temperature stress in P. densiflora seedlings. To adapt to the Fe stress environment, P. densiflora outside and inside the patches produced Fe detoxicants, including catechin, condensed tannin, and malic acid. Ceratobasidium bicorne and Aquapteridospora sp. were commonly isolated from P. densiflora seedlings outside and inside the patches as root endophytes, which might enhance Fe tolerance in the seedlings. Aquapteridospora sp., which is considered as a dark-septate endophyte (DSE), was also isolated from the roots of M. sinensis, suggesting that M. sinensis might play a source of a root endophyte to P. densiflora seedlings. Ceratobasidium bicorne could be classified into root endophytes showing symbiosis and weak pathogenicity to host plants. Therefore, high soil temperature stress would weaken P. densiflora seedlings, causing root endophytic C. bicorne to appear pathogenic. We suggested that P. densiflora could adapt to the Fe stress environment via producing Fe detoxicants, and M. sinensis would facilitate the establishment of P. densiflora seedlings in the sedimentary site by providing a DSE, Aquapteridospora sp., and maintaining symbiosis of C. bicorne from high soil temperature stress.在一处老矿区的沉积场地中，芒草（Miscanthus sinensis）形成了斑块状分布区域，在此区域内赤松（Pinus densiflora）幼苗的生长状况优于斑块外的个体，表明芒草可促进赤松幼苗的定植。本研究旨在阐明芒草促进赤松幼苗存活的内在机制，研究从该沉积场地中赤松幼苗的土壤理化性质、重金属耐受性以及根系内生菌三个维度展开分析。该沉积场地为裸地，土壤中铁（Fe）浓度较高，意味着生长于此的植物会面临铁胁迫与高温胁迫双重压力。土壤温度监测结果显示，芒草可抑制土壤温度的剧烈波动与骤升，从而缓解赤松幼苗所承受的高温胁迫。为适应铁胁迫环境，斑块内外的赤松幼苗均会合成铁解毒物质，包括儿茶素、缩合单宁与苹果酸。从斑块内外的赤松幼苗根系中均分离得到了双角角担菌（Ceratobasidium bicorne）与拟伞孢属菌种（Aquapteridospora sp.）这两种内生真菌，它们可能有助于提升赤松幼苗的铁胁迫耐受性。拟伞孢属菌种属于暗色有隔内生真菌（dark-septate endophyte, DSE），同时也可从芒草的根系中分离得到，这表明芒草可能为赤松幼苗提供了根系内生菌来源。双角角担菌可被归类为兼具共生性与弱致病性的根系内生真菌。因此，高温胁迫会削弱赤松幼苗的生长势，导致根系内生的双角角担菌表现出致病性。综上，赤松可通过合成铁解毒物质适应铁胁迫环境；而芒草则通过为赤松幼苗提供暗色有隔内生真菌拟伞孢属菌种，并维持双角角担菌的共生关系以缓解其高温胁迫，从而促进赤松幼苗在该沉积场地中的定植。