Interactive impact of potassium and arbuscular mycorrhizal fungi on the root morphology and nutrient uptake of sweet potato (Ipomoea batatas L.)

Abstract

Sweet potato is a typical "potassium (K)-favoring" food crop and strongly dependent on arbuscular mycorrhizal fungi (AMF). Recent studies show the importance of K and AMF to morphology optimization and nutrient uptake regulation of sweet potato; meanwhile, the interaction exists between K and K use efficiency (KIUE) in sweet potato. To date, only a few studies have shown that AMF can improve plant K nutrition, and whether the benefits conferred by AMF on plant are related to K remains unclear. In this study, low-KIUE genotype "N1" and high-KIUE genotype "Xu28" were used as experimental sweet potato; Funneliformis mosseae (FM) and Claroideoglomus etunicatum (CE) were used as experimental AMF. In a pot experiment, plants "N1" and "Xu28" were inoculated with FM or CE, and applied with or without K fertilizer to uncover the effects of K application and AMF inoculation on the root morphology and nutrient absorption of sweet potato during their growing period. Results demonstrated that AMF inoculation-improved root morphology of sweet potato highly relied on K application. With K application, AMF inoculation significantly increased root tip number of "N1" in the swelling stage and optimized multiple root morphological indexes (total root length, root surface area, root volume, root diameter, root branch number, and root tip number) of "Xu28" and CE had the best optimization effect on the root morphology of "Xu28". In addition, CE inoculation significantly promoted root dry matter accumulation of "Xu28" in the swelling and harvesting stages, coordinated aerial part and root growth of "Xu28", reduced the dry matter to leaf and petiole, and was beneficial to dry matter allocation to the root under conditions of K supply. Another promising finding was that CE inoculation could limit K allocation to the aboveground and promote root K accumulation of "Xu28" under the condition with K application. The above results lead to the conclusion that K and CE displayed a synergistic effect on root development and K acquisition of high-KIUE "Xu28". This study could provide a theoretical basis for more scientific application of AMF in sweet potato cultivation and will help further clarify the outcomes of plant-K-AMF interactions.

Keywords: arbuscular mycorrhizal fungi; nutrient uptake; potassium; root morphology; sweet potato; tuberous root yield.

FIGURE 1

Microscopic visualization of arbuscular mycorrhizal fungi structures in root of sweet potato at seeding stage. “N1” and “Xu28” indicate “sweet potato “N1”” and “sweet potato “Xu28””, respectively. “FM” and “CE” indicate “Funneliformis mosseae” and “Claroideoglomus etunicatum”, respectively. Red arrows indicate different arbuscular mycorrhizal fungi (AMF) structures. Ih, intraradical hyphae; V, vesicle.

FIGURE 2

The effects of arbuscular mycorrhizal fungi inoculation on tuberous root yield of sweet potato. Different lowercase letters indicate significant differences between different groups (P < 0.05). Asterisks denote significant differences after arbuscular mycorrhizal fungi (AMF) inoculation (t-test; *P < 0.05), while “ns” indicates nonsignificant difference.

FIGURE 3

Two-way ANOVA for the effects potassium (K) and F. mosseae (FM) or C. etunicatum (CE) inoculation on root morphological traits of sweet potato. Asterisks denote significant differences (t-test; *P < 0.05; **P < 0.01).

FIGURE 4

The effects of potassium application and arbuscular mycorrhizal fungi (AMF) inoculation on the root morphology of N1 (A) and Xu28 (B). For different groups, asterisks denote significant differences after AMF inoculation (t-test; *P < 0.05; **P < 0.01).

FIGURE 5

The effects of potassium application and arbuscular mycorrhizal fungi (AMF) inoculation on dry matter accumulation of root (A), stem (B), petiole (C), and leaf (D) of sweet potato. For different groups, asterisks denote significant differences after AMF inoculation (t-test; *P < 0.05; **P < 0.01).

FIGURE 6

The effects of potassium application and arbuscular mycorrhizal fungi inoculation on dry matter proportion of different organs of sweet potato. For each growth stage, different lowercase letters indicate significant differences between different groups (P < 0.05). For different groups, asterisks denote significant differences after arbuscular mycorrhizal fungi (AMF) inoculation (t-test; *P < 0.05).

FIGURE 7

The effects of potassium application and arbuscular mycorrhizal fungi inoculation on K concentration (A) and K accumulation (B) of sweet potato. For each growth stage, different lowercase letters indicate significant differences between different groups (P < 0.05). For different groups, asterisks denote significant differences after arbuscular mycorrhizal fungi (AMF) inoculation (t-test; *P < 0.05; **P < 0.01), while “ns” indicates nonsignificant difference.

FIGURE 8

Pearson’s correlation coefficients between root morphological index, root dry matter, root K concentration, and root K accumulation of N1 (A) and Xu28 (B). Relationship between root K concentration or root dry matter and root K accumulation of N1 (C) and Xu28 (D). Asterisks denote significant differences (*P < 0.05). The value of R and P given in each figure to exhibit the significant level (P < 0.05, significant; P ≥ 0.05, nonsignificant).

FIGURE 9

Conceptual diagram depicting the synergistic effect of K and arbuscular mycorrhizal fungi (AMF) on root development and K acquisition of high K use efficiency genotype “Xu28”.