Abstract
Arbuscular mycorrhizal fungi (AMF) are present in paddy fields, where they suffer from periodic soil flooding and sometimes shading stress, but their interaction with rice plants in these environments is not yet fully explained. Based on two greenhouse experiments, we examined rice-growth response to AMF under different flooding and/or shading regimes to survey the regulatory effects of flooding on the mycorrhizal responses of rice plants under different light conditions. AMF had positive or neutral effects on the growth and yields of both tested rice varieties under non-flooding conditions but suppressed them under all flooding and/or shading regimes, emphasizing the high importance of flooding and shading conditions in determining the mycorrhizal effects. Further analyses indicated that flooding and shading both reduced the AMF colonization and extraradical hyphal density (EHD), implying a possible reduction of carbon investment from rice to AMF. The expression profiles of mycorrhizal P pathway marker genes (GintPT and OsPT11) suggested the P delivery from AMF to rice roots under all flooding and shading conditions. Nevertheless, flooding and shading both decreased the mycorrhizal P benefit of rice plants, as indicated by the significant decrease of mycorrhizal P responses (MPRs), contributing to the negative mycorrhizal effects on rice production. The expression profiles of rice defense marker genes OsPR1 and OsPBZ1 suggested that regardless of mycorrhizal growth responses (MGRs), AMF colonization triggered the basal defense response, especially under shading conditions, implying the multifaceted functions of AMF symbiosis and their effects on rice performance. In conclusion, this study found that flooding and shading both modulated the outcome of AMF symbiosis for rice plants, partially by influencing the mycorrhizal P benefit. This finding has important implications for AMF application in rice production.
Highlights
Arbuscular mycorrhizal fungi (AMF, subphylum Glomeromycotina; Spatafora et al, 2016) originated ca. 450 million years ago and today form a symbiosis with most vascular plant species, including many important crops
We investigated the following two questions: (i) How does the mycorrhizal growth responses (MGRs) of rice plants respond to flooding regimes? and (ii) Does the effect of flooding on MGR vary at different plant C levels [as assessed by the application of shading to suppress plant photosynthetic activity (Yang et al, 2019)]? The rice-growth response to AMF symbiosis was recorded in Exp. 1 using two rice varieties at two rice growth stages under three different flooding intensities
Before being subjected to different flooding treatments, rice plants were cultivated for 30 days under non-flooding conditions in which the soil surface was wet but not water-logged, to ensure successful AMF colonization in rice roots based on results from our pilot experiment and other studies (e.g., Solaiman and Hirata, 1997)
Summary
Arbuscular mycorrhizal fungi (AMF, subphylum Glomeromycotina; Spatafora et al, 2016) originated ca. 450 million years ago and today form a symbiosis with most vascular plant species, including many important crops. 450 million years ago and today form a symbiosis with most vascular plant species, including many important crops. They have significant ecological functions in the movement of mineral nutrients (such as P and N) and water between soil and plants. Arbuscular mycorrhizal fungi can improve plants’ biotic resistance (soil-borne fungal and bacterial pathogens, nematodes, or root-chewing insects) (Rivero et al, 2018; Campo et al, 2020; but see Cosme et al, 2011; Bernaola et al, 2018b) and increase their tolerance under abiotic stress, including shading stress, drought, high salinity, and heavy metal contamination (Amir et al, 2019; Li et al, 2019), partly through triggering basal resistance in host plants (Cornejo et al, 2017). Considering the importance of developing disease-resistant crops and reducing fertilizer usage in modern agricultural production, knowledge of nutrient assimilation and disease resistance is of vital importance for plant breeding
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