Abstract
Sweetpotato can be cultivated in the reclaimed rocky soil in Sichuan Basin, China, which benefits from the release of mineral nutrients in the rocky soil by microorganisms. Shortage of nitrogen (N) in the rocky soil limits sweetpotato yield, which can be compensated through N fertilization. Whereas high N fertilization inhibits biological N fixation and induces unintended environmental consequences. However, the effect of low N fertilization on microorganism community and sweetpotato yield in the N-deficient rocky soil is still unclear. We added a low level of 1.5 g urea/m2 to a rocky soil cultivated with sweetpotato, and measured rocky soil physiological and biochemical properties, rhizosphere microbial diversity, sweetpotato physiological properties and transcriptome. When cultivating sweetpotato in the rocky soil, low N fertilization (1.5 g urea/m2) not only improved total N (TN) and available N (AN) in the rocky soil, but also increased available phosphorus (AP), available potassium (AK), and nitrogenase and urease activity. Interestingly, although low N fertilization could reduce bacterial diversity through affecting sweetpotato root exudates and rocky soil properties, the relative abundance of P and K-solubilizing bacteria, N-fixing and urease-producing bacteria increased under low N fertilization, and the relative abundance of plant pathogens decreased. Furthermore, low N fertilization increased the phytohormones, such as zeatin riboside, abscisic acid, and methyl jasmonate contents in sweetpotato root. Those increases were consistent with our transcriptome findings: the inhibition of the lignin synthesis, the promotion of the starch synthesis, and the upregulated expression of Expansin, thus resulting in promoting the formation of tuberous roots and further increasing the sweetpotato yield by half, up to 3.3 kg/m2. This study indicated that low N fertilization in the N-deficient rocky soil improved this soil quality through affecting microorganism community, and further increased sweetpotato yield under regulation of phytohormones pathway.
Highlights
Sweetpotato is the 7th most important food crop, with a global annual production of more than 1 × 1011 kg (Yang et al, 2017)
The numbers of shared operational taxonomic units (OTUs) between samples were just 82 and 5 for bacteria and fungi, respectively, while most OTUs were unique (Figure 2). These results indicated that the microorganism community varied greatly among different samples, which may be affected by sweetpotato cultivation and low N fertilization (1.5 g urea/m2)
We found that sweetpotato cultivation and low N fertilization (1.5 g urea/m2) improved the relative abundance of P and K-solubilizing bacteria such as Bradyrhizobium, Agrobacterium and Salmonella (Figure 5A) (Sharma et al, 2013)
Summary
Sweetpotato is the 7th most important food crop, with a global annual production of more than 1 × 1011 kg (Yang et al, 2017). Most of the P and K are fixed in the rocky soil, keeping them from being taken up readily by plants (Chatterjee et al, 2014). Both total nitrogen (TN) and available nitrogen (AN) are inadequate in the rocky soil due to the lack of nitrogen (N) fertilization and other exogenous N input (Zhu et al, 2008)
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