Gas Exchange, Root Morphology and Nutrients in Maize Plants Inoculated with Azospirillum brasilense Cultivated Under Two Water Conditions

HIGHLIGHTS Azospirillum brasilense stimulates root growth in maize under water deficit. Maize inoculated with A. brasilense shows greater photosynthesis under drought conditions. Under water deficit, maize plants inoculated with A. brasilense showed greater water use efficiency (WUE).

Abstract The objective of this study was to evaluate the gas exchange, root morphology and nutrient concentration in maize plants inoculated with A. brasilense under two water conditions. The experiments were carried out in a greenhouse, one under irrigation and the other under water deficit. The treatments consisted of four A. brasilense inoculants (control (without inoculation), Az1 (CMS 7 + 26), Az2 (CMS 11 + 26) and Az3 (CMS 26 +42). At the V6 plant stage, water stress was imposed on maize plants for 15 days. The phytotechnical characteristics, gas exchange, root morphology, root dry matter and macronutrient analysis were evaluated after 15 days of water deficit imposition. The water deficit caused a reduction in the development of maize plants. The presence of A. brasilense Az1 under the same condition yielded higher photosynthesis, carboxylation efficiency, water use efficiency, and greater soil exploration with increased length, surface area and root volume of plants. Inoculation by A. brasilense increased root system volume by an average of 40 and 47% under irrigation and water deficit, respectively, when compared to non-inoculated plants. The inoculant Az1 attenuated the deleterious effects caused by drought and yielded the best growth of the root system, resulting in the tolerance of maize plants to water deficit.

Proposal of a New Estimation Method of Colonization Rate of Arbuscular Mycorrhizal Fungi in the Roots of Chengiopanax sciadophylloides

This study proposed a rapid method to quantify the colonization rate of arbuscular mycorrhizal fungi (AMF) in plant roots. The method involved the use of an image analysis software (WinRHIZO Pro). The colonization rate is defined as the ratio of the fungal body to the plant root area in a micrograph. Three seedlings of Chengiopanax sciadophylloides, a woody species that accumulates radiocesium, were collected from a secondary forest in the Yamakiya district of Kawamata, Fukushima Prefecture during May–September 2014. The colonization of AMF structures was examined under a light microscope, and the percentage of colonization was determined using the WinRHIZO method. The superiority of the new method was verified by comparing with a modified grid-line intersect method. The colonization of AMF was confirmed in all the seedlings, and a significant coefficient of determination (R² = 0.94) was found with both the methods. The results suggested that the WinRHIZO method is reliable for estimating the colonization of AMF in C. sciadophylloides.