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The inoculants of arbuscular mycorrhizal fungi (AMF) propagated by the in vitro culture system is important in scientific research; however, the long-term storage reduces the spore germination rate. The propagules of AMF consist of three components, including spores, hyphae and colonized root fragments. It is well known that cold storage can improve the germination rate of AMF spores, with limited investigations on the germination of other propagules. In this study, AMF inoculants were stored at 25°C or at 4°C (cold storage) to investigate the effect of cold storage on the propagule viability of the AMF Rhizophagus irregularis DAOM197198. The germination rate of propagules (spores, hyphae, root fragments) and their colonization ability were determined at 3 and 6 months after storage. The results showed that the spore germination rate remained unchanged after storage for 0 and 1 month at 25°C, but decreased rapidly after storage for 3 months. Furthermore, we investigated the hyphal germination rate for the first time. The germination rates of spores, hyphae and root fragments were significantly higher under cold storage compared to those at 25°C. Additionally, we classified the germ tubes of hypha into two types: long-type (L-type) and short type (S-type). The germination rate and the proportion of L-type germ tubes of hyphae significantly increased with cold storage time, which was conducive to colonization. The results of mycorrhizal colonization confirmed that cold storage significantly increased the colonization of hypha compared with 25°C treatment. Cold storage may break the dormancy of AMF propagules and activate related enzymes to promote the germination and colonization of propagules, which needs further investigation. [ABSTRACT FROM AUTHOR]

Drought stress poses increasingly serious threats to agricultural production in the era of global climate change. Arbuscular mycorrhizal (AM) fungi are well-recognized biostimulants promoting plant tolerance to drought stress. Lipids are indispensable for AM fungal colonization, however, the involvement of lipid metabolism in the drought tolerance conferred by AM fungi is largely unknown. In this study, we inoculated Poncirus trifoliata (L.) with Rhizophagus irregularis DAOM197198 under no drought stress, medium drought stress and severe drought stress, with non-inoculation under respective treatments as control. Results indicated that AM fungal inoculation significantly promoted the drought tolerance of P. trifoliata (L.), with the effect size decreasing along with drought severity. Moreover, the effect size was significantly related to arbuscule abundance. Fatty acid profiling showed that the arbuscule abundance was determined by the AM-specific phospholipids (PLs), whose biosynthesis and delivery were inhibited by drought stress as revealed by qRT-PCR of FatM , RAM1 and STR / STR2. More interestingly, AM fungal inoculation increased the lipid allocation to total PLs and the unsaturation rate of total neutral lipids (NLs), probably indicating the involvement of non-AM-specific lipids in the increased drought tolerance. Taken together, our results demonstrate that lipid metabolism in AM mediates the increased drought tolerance conferred by AM fungal inoculation, with AM-specific and non-AM-specific lipids functioning therein in different ways. [ABSTRACT FROM AUTHOR]

Background: Phosphate mobilising bacteria (PMB), such as phoD- and pqqC-harbouring bacteria, play a crucial role in mobilising insoluble phosphorus (P) in soil through the secretion of alkaline phosphatase and organic acids., Objectives: To evaluate the succession pattern of PMB communities in response to different insoluble P sources., Methods: Five P source treatments, including the addition of KH 2 PO 4 (PDP), FePO 4 (FEP), Ca 3 (PO 4 ) 2 (TCP), lecithin (LEC), and a negative control, were established in the soil in a microcosmic system. Subsequently, phoD- and pqqC-harbouring bacterial communities were investigated by sequential sampling and high-throughput sequencing. In addition, PMB strains were isolated from these five treatments, and their phosphate mobilising activity was further analysed., Results: The effect of the insoluble organic P source (LEC) on the succession of PMB communities consistently exceeded that of insoluble inorganic P (Pi) sources (FEP and TCP). A successively enhanced succession and a successively diminishing succession were observed in PMB communities in FEP and TCP, respectively. Furthermore, the soil AP content significantly increased with incubation time in LEC and FEP. Most of the variation in phoD- and pqqC-harbouring bacterial communities was explained by all P fractions, respectively, while Fe-P and stable organic P fractions determined the PMB communities. Insoluble Pi sources, particularly FEP, tended to enrich more high-performance PMB strains for Fe-P., Conclusion: This study firstly reveals the dynamic response of PMB communities to different insoluble P sources at the community level in a short time scale and identifies key PMB taxa that respond to different insoluble P sources, particularly Fe-P. It is also the first to provide community evidence and a feasible method for obtaining high-performance PMB strains for Fe-P in subtropical acidic red soils through directed enrichment culture., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)