Activation of Nitrogen-Fixing Endophytes Is Associated with the Tuber Growth of Sweet Potato

Abstract

Endophytic nitrogen-xing organisms have been isolated from the aerial parts of eld-grown sweet potato (Ipomoea batatas). e 15 N dilution method, which is based on the di erences in stable nitrogen isotope ratios, is useful for measuring nitrogen xation in the eld. In this study, seedlings of two sweet potato cultivars, 'Beniazuma' and 'Benikomachi,' were transplanted into an alluvial soil that had been treated with organic improving material in advance. Whole plants were sampled every 2 or 3 weeks. A er separating plants into tuberous roots and leaves, the fresh weights of the samples were measured, and the nitrogen content and natural 15 N content of leaves were determined with an elemental analyzer and an isotope ratio mass spectrometer linked to an elemental analyzer, respectively. e contribution of nitrogen xation derived from atmospheric N 2 in sweet potato was calculated by assuming that leaves at 2 weeks a er transplanting were in a non-nitrogen-xing state. e contribution ratios of nitrogen xation by nitrogen-xing endophytes in leaves of both sweet potato cultivars increased rapidly from 35 to 61 days a er transplanting and then increased gradually to 55-57% at 90 days a er transplanting. Over the course of the sweet potato growing season, the activity of nitrogen-xing endophytes in leaves began to increase at about 47 days a er transplanting, the weight of leaves increased rapidly, and then growth of tuberous roots began a few weeks later. Our ndings indicate that nitrogen-xing endophytes will be activated under inorganic nitrogen-free sweet potato cultivation, allowing for growth of the tuberous roots.

Plant Growth Promoting Effects of Nepalese Sweet Potato Endophytes

“…Earlier reports have shown that plant-associated bacteria can improve plant growth by IAA production [10,[21][22][23] and nitrogen fixation [8]. In this study, bacterial inoculation also showed positive effects on the growth of sweet potato.…”

“…Sweet potato (Ipomoea batatas, L.) is cultivated in several countries in Asia, Africa, Europe, and America. This plant can be cultivated with little fertilization [6,7], probably due to its association with endophytes [8] and a general behavior/response of sweet potato as a plant species. For example, sweet potato endophytes Bacillus cereus, Achromobacter xylosoxidans, and Rahnella aquatilis showed superior indole-3-acetic acid (IAA) production and phosphate solubilizing abilities, which may improve the nutrient uptake, root growth, and overall plant growth [9,10].…”

Changes in Acetylene Reduction Activities and nifH Genes Associated with Field-Grown Sweet Potatoes with Different Nursery Farmers and Cultivars

“…The differences were clear after September, when carbohydrates were accumulated in the tubers. Several studies have reported that endophytic N 2 -fixation significantly contributed to the nitrogen supply of the sweet potato [1][2][3]. The ARA in September, when most samples presented the highest activity, showed no correlation with either the weight in September or the 15 N content in October, and the ARA in October showed no correlation with any parameters.…”

“…The sweet potato (Ipomoea batatas L.) is a dicotyledonous plant that belongs to the family Convolvulaceae and is a subsistence crop with huge economic importance, especially in developing countries. It is known that the sweet potato grows well in nitrogen-poor infertile soils, and it is believed that this growth ability is partially due to the functions of diazotrophic growth-promoting bacteria that contain endo-and epiphytic microorganisms of this plant [1][2][3].…”

Microbial Interactions and Activities Affecting Sago Palm Growth

“…Although the estimation of fixed N based on the acetylene-reducing activity contains some uncertainties, the amount of fixed N in a mature sago palm stand was estimated at 210 kg N/ha/y from calculation based on N-fixing activity in root (221 nM C 2 H 4 /g/day), pith (213 nM C 2 H 4 /g/day), and leaf sheath (35.4 nM C 2 H 4 /g/ day) and their mean weights per palm (68, 721, and 97 kg in root, pith, and leaf sheath, respectively) with a sago palm density in a mature forest of 923 sago palms/ ha (Toyota 2015). Yonebayashi et al (2014) estimated the amount of N fixation in sago palm using a tracer experiment. They measured δ15N values of the youngest leaves of sago palms at different stages of growth and found that δ15N values were lower with age, indicating higher N fixation with maturing.…”