石漠化地区桑根围AMF多样性及AMF在桑树间传递干旱信号机制

Drought is the main factor affecting the growth of plants and the restoration of vegetation in rocky desertification area. Mulberry is a rare economic crop in rocky desertification area and its growth depends on the arbuscular mycorrhizal fungi (AMF). But it is not clear how the AMF community affects the mulberry, and whether mulberry could perceive drought stress signals effectively generated by the adjacent mulberry trees through the AMF mycelium network, and made timely response to drought. This project will systematically evaluate the community composition of AMF in the rhizosphere of mulberry, and the response mechanism of mycorrhizal mulberry to drought stress. After the mycelium bridge was established between two mulberry plants with Funneliformis mosseae, the donor mulberry was treated with drought stress and 2H2O. Then the change of receptor/donor mulberry root structure, photosynthetic capacity, antioxidant enzyme activity and osmotic regulator was explored, as well as the relevance with expression changes of transcription factors and signal transduction key genes. The moisture transfer way was detected though mycelium bridge between donor mulberry and receptor mulberry. Mechanism of mulberry sensing drought stress signals and enhancing drought resistance through mycelium bridge was explained at the levels of morphology, physiology, biochemistry and molecular. The research results provide theoretical and practical basis for ecological restoration of rocky desertification vegetation by using AMF and promoting the income growth of mulberry and sericulture.

干旱是影响石漠化植物生长和植被恢复的主要因子。桑树作为喀斯特生境中少有的适生经济作物，其生长主要依赖于根际重要的土壤丛枝菌根真菌（AMF），但AMF群落组成对桑树影响如何，桑树是否通过AMF菌丝网络传递而感知邻近植株干旱胁迫信号及时启动干旱抵御机制尚不清楚。本项目就此对喀斯特桑树根际AMF的群落组成及菌根桑对干旱胁迫的响应进行研究。利用优势菌种摩西球囊霉菌在桑树植株间建立菌根菌丝桥，对供体桑进行干旱胁迫和2H2O同位素处理，探索受体/供体桑根系结构、光合能力、抗氧化酶活性、渗透调节物质变化，与抗旱相关转录因子和信号转导关键基因表达变化的相关性，通过在供体桑和受体桑间建立的菌根菌丝桥来检测水分传递的途径。从根系形态结构、生理生化和分子水平上解析桑树通过菌根菌丝桥感知干旱胁迫信号和增强抗旱能力的机制。研究结果为利用丛枝菌根真菌进行石漠化植被生态修复，促进农民栽桑养蚕创收增益提供理论与实践依据。

干旱是限制石漠化地区植物生长的主要因素，桑树作为喀斯特生境中少有的适生经济作物，对土壤丛枝菌根真菌（AMF）具有较高的依赖性。桑树根际AMF的群落组成及菌根桑对干旱胁迫的响应机制还需进一步研究。本研究主要进展如下：.（1）在石漠化地区采集6个不同桑树主栽品种（白油桑、川桑98-1号、强桑1号、丰田5号、红芽桑、云桑1号）根系和根际土壤，菌根侵染率测定发现6个供试桑树品种根系均能与AMF形成共生关系，桑树根系菌丝侵染率约为30~50%，泡囊侵染率为15~30%，丛枝侵染率为10~15%。Illumina MiSeq高通量测序显示桑根际土壤中存在丰富的AMF真菌资源，主要是Ambispora、Archaeospora、Claroideoglomus、Gigaspora、Glomus、Paraglomus和Scutellospora，其中Glomus和Paraglomus分别占比61%和35%，为优势菌属。不同品种桑园土壤中Glomus和Paraglomus相对丰度和AMF多样性均显著不同。.（2）品种是土壤AMF群落的主要影响因子，单个土壤因子对AMF群落的影响不显著，但土壤因子间的相互作用会显著影响土壤AMF群落，其中有效磷、速效钾、有机碳和总球囊霉素相关土壤蛋白是主要的影响因素。随着有效磷含量的增加，AMF多样性会显著降低；有机碳和总球囊霉素相关土壤蛋白含量的增多会降低土壤AMF丰度；速效钾对AMF丰度呈不显著直接正影响，对AMF多样性呈不显著间接负影响。.（3）利用优势菌种摩西球囊霉接种桑树，对菌根桑进行干旱胁迫处理，发现在土壤干旱胁迫情况下，根系活力增强，叶片中叶绿素ａ、叶绿素ｂ、叶绿素ａ＋ｂ和类胡萝卜素含量、光合速率、气孔导度、蒸腾速率值显著下降，桑叶渗透调节物质（脯氨酸、可溶性糖、可溶性蛋白）、叶片酶系统活力（SOD，POD，CAT）和四个转录因子（Mntrihelix、Mnb ZIP、MnMYB和MnERF）基因表达量均显著增加，且接种桑相应测量指标始终显著高于非接种桑对照。因此菌根桑耐旱生理生化的可能机制为：接种AMF增强桑苗根系的活力，满足根系的水分和营养物质的吸收与运输，提高叶片保护酶活性，提高光合效率，增加叶片渗透物质含量，诱导抗旱基因表达，从而促进桑苗生长，干旱胁迫能力得到增强。