Endophytic N2 fixation in sweet potato: responses to N, P, and K inputs and visualization of 15N2 utilizing bacterial cells via Raman spectroscopy

Abstract

Fertilizer-N strongly limits non-leguminous crop yields; however, sweet potato (Ipomoea batatas) is an exception, likely due to its ability to acquire atmospheric N2 via endophytic diazotrophs. Using Raman spectroscopy, we found that in 15N2-fed sweet potato, some endophytic bacteria contained 15N, providing direct evidence of N2 fixation in planta. To assess N2-fixing capability, pot experiments were conducted by varying N, P, and K fertilizer inputs. Sweet potato showed higher N content than the non-N2-fixing Ipomoea aquatica; additionally, it showed increased N content which was 1.4-fold higher than the fertilizer-N input. Its δ15N values were closer to those of N2-fixing soybean, with an estimated 11–56% of plant N derived from N2. The estimated amount of fixed-N in sweet potato was negligible without fertilizer-N; however, a gradual accumulation leading to an immediate saturation was observed with increasing fertilizer-N. During this state, increasing P supply linearly enhanced the capability, reaching 13 g N m−2, comparable to that of legumes. However, K inputs affected neither N2 fixation nor growth owing to strong K acquisition from the soil even without fertilizer-K. Our results indicate extensive N2 fixation in sweet potato, depending on its nutritional status, particularly P; resonance Raman spectroscopy facilitates the visualization of active N2-fixing bacteria on a single-cell scale.

Accelerate Senescence Reversed CO2‐Fertilization Effect under Elevated CO2 in Potato: A Weak Relationship with Nitrogen Acquisition

“…After sprouting, seedlings with intact roots were carefully separated from tubers to eliminate the nutrient effects of the tuber. Seedlings were then transferred to nursery plates filled with andosol (the same soil used by Ueda and Yano (2023), composed of 29% sand, 55% silt and 16% clay; pH 5.7; total C 89 g kg −1 , total N 7.2 g kg −1 ) and grown in growth chambers under the same conditions as described above. Separation stress was not taken into account because all seedlings were treated under the same conditions and acclimatized in soil before the experimental treatments.…”

“…At this growth rate, CO 2 concentrations will rise to approximately 600 and 840 ppm by 2100 and 2200, respectively. Regardless of global warming, elevated CO 2 (eCO 2 ) can effectively promote plant growth, known as the CO 2 -fertilization effect, especially in C 3 plants (Kimball 2016;Poorter et al 2022;van der Kooi et al 2016;Zhang et al 2021). The most recent study suggests that CO 2 levels by 2100 could potentially increase plant biomass by 12 ± 3% above current levels, with the magnitude depending on soil nutrient conditions, particularly nitrogen (N) (Terrer et al 2019).…”

"Effects of Different Fertilizers on the Yield and Yield Attributing Parameters of Sweet Potato (Ipomoea Batatas L.) in the Eastern Midhill of Nepal"

“…In Nepal, it is a neglected and underutilized crop species that can thrive well in the terai and mid-hills (Joshi,et al [3]). The presence of endophytic bacteria is responsible for fixing nitrogen in sweet potatoes (Ueda & Yano [4]). It can give a good yield even in marginal land most probably due to its ability to fix atmospheric nitrogen.…”