Two lucerne (Medicago sativa) varieties, an anecdotally waterlogging-intolerant old New Zealand variety, Grasslands Wairau, and a reputedly waterlogging-tolerant new variety, Pioneer 54Q53, were subjected to waterlogging stress and a range of physiological and agronomic measurements performed. Waterlogging stress was characterized by measurement of soil oxygen depletion and soil carbon dioxide accumulation. Both varieties exhibited strong responses to waterlogging stress, including reduction in leaf soluble protein concentration, photosynthetic rate and tap root weight, but also exhibited differences in response, notably a decrease in carboxylation efficiency and in the steady-state quantum yield of electron flow through PSII (FPSII) in Wairau, but not in Pioneer. Implications for understanding of waterlogging effects on photosynthesis, and for field management of lucerne on wet soils are discussed.

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The relationship between soil texture and the degree of apple replant disease (ARD) was analyzed from the perspective of the microbial community structure and diversity within the rhizosphere soil of Malus hupehensis Rehd. seedlings. Three different textured soils were taken from different apple orchards in Laizhou, Yantai. The soils were divided into two parts, one was kept in replanted conditions, and the other was fumigated with methyl bromide to act as a high standard control. The strength of ARD occurrence was examined by measuring fresh and dry weight suppression (%) of the M. hupehensis seedlings. Differences in the fungal community structure (especially in Fusarium) among the three soil texture types were analyzed using high-throughput sequencing. The results showed that replanted loam clay soil had the highest fungal diversity, followed by sandy loam soil and finally loam soil. The richness of fungi between soil textures, however, was not significantly different. At the genus level, the relative abundance of Fusarium was 1.96%, 0.78%, and 10.89% in replanted sandy loam, replanted loam soil, and replanted loam clay soil, respectively. Moreover, the gene copy number of Fusarium oxysporum, Fusarium solani, and the inhibition rate of fresh weight of M. hupehensis seedlings were the same in the three soil textures. The plant height, photosynthesis (net) (Pn), and stomatal conductance (gS) of the M. hupehensis seedlings were significantly less in the replanted soil compared with the control treatments, with the overall difference being greatest in replanted loam clay soil, followed by replanted sandy loam and then replanted loam soil.