| In this study, the effects of arbuscular mycorrhizal fungi (AMF) on the growth andbioenergy traits of Populus×canadensis (a hybrid of P. nigra×P. deltoids)‘Neva’ in thepresence and absence of other soil microorganisms were investigated. In order to reflect thefunctions of AMF comprehensively, microbial community structure, glomalin content and soilorganic carbon content in the rhizosphere of the poplar influenced by AMF were alsoobserved. We also determined the effects of AMF on the growth, photosynthesis, chlorophyllfluorescence, anatomical properties of stoma and xylem, osmotic adjustment, antioxidationand the expression of aquaporins gene of poplar. The main points are as follows:1. Effects of AMF on the biomass and bioenergy traits of poplarThe effects of Rhizophagus irregularis and Glomus versiforme on the growth,root-absorbing area, chlorophyll content, gas exchange, total organic carbon (TOC) content,gross calorie value (GCV), lignin and cellulose content of Populus×canadensis ‘Neva’ insterilized and unsterilized soil were investigated. The results showed that under two differentsoil conditions, AM symbiosis increased the height (by55.1%~119.2%), ground diameter (by13.8%~26.7%), dry weight (by33.2%~77.5%), root-absorbing area (total absorbing areaincreased by21.7%~64.1%, active absorbing area increased by28.3%~84.4%), chlorophyllcontent (by9.6%~13.1%), net photosynthetic rate (by18.1%~41.6%), TOC content (by3.2%~34.8%), GCV (by3.0%~5.4%) and lignin content (by3.1%~14.6%) of poplar seedlings,while had small effect on cellulose content. The AM effectiveness in sterilized soil hadadvantages over that in unsterilized soil, and the effect of R. irregularis was greater than G.versiforme in sterilized soil, but lower in unsterilized soil.2. Effects of AMF on the microbial community structure, glomalin content and organic carboncontent in the rhizosphere of poplarChanges of microbial community structure, glomalin content and organic carbon contentin the rhizosphere of poplar influenced by AMF were observed. The results showed that thefungal and bacterial community structures, easily extractable glomalin (EE-GRSP), totalglomalin (T-GRSP) and soil organic carbon were significantly affected by R. irregularis andG. versiforme, respectively. R. irregularis increased the diversity and richness of the bacterial community, increased the evenness of the fungal community. G. versiforme increased thediversity and richness of the bacterial community but decreased the diversity and richness ofthe fungal community, increased the evenness of the bacterial community. Both of the twoAMF improved the EE-GRSP, T-GRSP and soil organic carbon content, G. versiformeincreased by311.9%,27.9%and16.3%respectively and R. irregularis increased by110.2%,13.3%and12.3%separately, while the extent increased by G. versiforme was higher than R.irregularis. AMF can change the microbial community structure, and increase the storage ofsoil carbon.3. Effects of AMF on the growth, photosynthesis, anatomical properties of stoma and xylemof poplar under droughtEffects of R. irregularis colonization on the growth, photosynthesis, chlorophyllfluorescence, anatomical properties of stoma and xylem of poplar were investigated underdrought. The results showed that mycorrhizal plant had higher Fv/Fm (5.2%), ΦPSII (4.9%),qP (11.4%) and qN (14.2%) under drought stressed condition. This indicated that AMsymbiosis could enhance the efficiency of excitation energy captured by chloroplasts, andincrease the photochemical capacity of PSII in light-adapted leaves and promote the energycycling between the reaction centre and the chloroplast pool. Mycorrhizal plants also hadhigher net photosynthetic rate (54.9%) to accumulate more biomass and reduce the losscaused by drought. Compared with the well watered condition, the effect of AMF on vesselfunction was greater under drought stressed condition, while on stoma function was lowerunder drought stressed condition. This might be beneficial for plants to maintain water.4. Effects of AMF on the osmotic adjustment and antioxidation of poplar under droughtEffects of R. irregularis colonization on the osmotic adjustment and antioxidation ofpoplar were investigated under drought. We found that the malondialdehyde (MDA) contentwas increased when plants suffered drought, which indicated that oxidative damage of poplarseedlings was induced by drought. The MDA contents of poplars decreased by26.8%~34.3%when they were inoculated with AMF. This demonstrated that AMF alleviated the damagecaused by drought. The leaf proline content had no significant difference between mycorrhizalplant and non-mycorrhizal plant under well watered condition, while under drought stressedcondition, the leaf proline content of mycorrhizal plant was lower (13.5%) thannon-mycorrhizal plant, even if the drought markedly increased the proline content. Thisindicated that mycorrhizal plant had higher drought tolerance because mycorrhizal plant wasless influenced by drought. AMF can improve the cell osmotic potential and maintain thewater content in cells by increasing the content of soluble protein. The activity of superoxidedismutase (SOD) and peroxidase (POD) in mycorrhizal poplar leaves was24.2%and36.6% higher than that in non-mycorrhizal leaves under well watered condition. When poplarssuffered drought, the activity of SOD and POD in non-mycorrhizal poplar leaves wereincreased by31.8%and89.8%respectively, while only POD activity was just increased by47.0%in mycorrhizal poplar leaves, and the extent was less than that in non-mycorrhizalpoplar leaves. This indicated that the oxidative damage caused by drought was higher innon-mycorrhizal poplars, forcing them to enhance their antioxidant enzymes activities toscavenge the reactive oxygen species induced by drought.5. Effects of AMF on the expression of aquaporins gene of poplar under droughtThe expression of aquaporin PIP family genes PIP1-1、PIP1-2、PIP1-3、PIP1-4、PIP1-5、PIP2-1、PIP2-2、PIP2-3affected by R. irregularis under drought was tested using qRT-PCRtechnology, and the relative water content, water use efficiency were also observed to reflectthe water status influenced by AMF. We found that AM symbiosis up-regulated the expressionof PIP1-1(1.10times), PIP1-2(0.39times), PIP1-3(2.43times), PIP1-4(1.69times),PIP1-5(9.68times), PIP2-3(1.99times), down-regulated the expression of PIP2-1(0.42times), PIP2-2(0.27times) under drought stressed condition. The relative water content andwater use effeiciency were increased10.2%and19.3%by AMF. This indicated that differentaquaporins genes have different functions in the water transportation of a plant. AMF mayregulate the water usage of the host via regulating the expression of different aquaporinsgenes. |
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