Shallower Root Spatial Distribution Induced by Phosphorus Deficiency Contributes to Topsoil Foraging and Low Phosphorus Adaption in Sugarcane (Saccharum officinarum L.).

Ke Yi,Xiaofeng Li,Guizhi Ling,Shu Yang,Zunkang Zhao,Ying Liu,Xinlian Tang,Diwen Chen

doi:10.3389/fpls.2021.797635

Abstract

Low phosphorus (P) availability in acid soils is one of the main limiting factors in sugarcane (Saccharum officinarum L.) production. Reconstruction of the root system architecture (RSA) is a vital mechanism for crop low P adaption, while the RSA of sugarcane has not been studied in detail because of its complex root system. In this study, reconstruction of the RSA and its relationship with P acquisition were investigated in a P-efficient sugarcane genotype ROC22 (R22) and two P-inefficient genotypes Yunzhe 03-103 (YZ) and Japan 2 (JP). An efficient dynamic observation room was developed to monitor the spatiotemporal alternation of sugarcane root length density (RLD) and root distribution in soil with heterogeneous P locations. The sugarcane RSA was reconstructed under P deficiency, and R22 had an earlier response than YZ and JP and presented an obvious feature of root shallowness. Compared with the normal P condition, the shallow RLD was increased by 112% in R22 under P deficiency while decreased by 26% in YZ and not modified in JP. Meanwhile, R22 exhibited a shallower root distribution than YZ and JP under P deficiency, supported by 51 and 24% greater shallow RLD, and 96 and 67% greater shallow root weight, respectively. The ratio of shallow RLD to total RLD in R22 was 91% greater than YZ, and the ratio of shallow root weight to total root weight in R22 was greater than that of YZ and JP by 94 and 30%, respectively. As a result, R22 had a higher shoot P accumulation than YZ and JP, which thereby increased the relative leaf sheath inorganic P concentration (RLPC) by 47 and 56%, relative shoot biomass (RSB) by 36 and 33%, and relative cane weight (RCW) by 31 and 36%, compared with YZ and JP under P deficiency, respectively. We verified the reliability and efficiency of a dynamic observation room and demonstrated that a shallower root distribution contributed to improving topsoil foraging, P acquisition, and low P adaption under P deficiency in sugarcane. Therefore, a shallower root distribution merits consideration as an evaluation trait for breeding P efficient sugarcane genotypes and genetic improvement.

Highlights

The availability of phosphorus (P), one of the three major essential elements, profoundly affects plant metabolism and growth
We investigated the root system architecture (RSA) using three genotypes associated with distinct root characteristics grown hydroponically and found significant genotypic differences in the root adaptation strategy to P deficiency
The findings demonstrate that a shallower root distribution facilitates P acquisition from topsoil in sugarcane

Summary

Introduction

The availability of phosphorus (P), one of the three major essential elements, profoundly affects plant metabolism and growth. Plants have evolved a suite of adaptive mechanisms in response to low P stress, including the enhancement of the expression of Pi transporters, the induction of secretion of root exudates, such as organic acids and acid phosphatase, and the reconstruction of the root system architecture (RSA) including root morphology, growth angle, and spatial distribution (Péret et al, 2014). A previous study reported that the shallower root distribution of Arabidopsis was caused by a reduction of primary root length and an increase in lateral roots under limited P conditions (Williamson et al, 2001). Low P stress stimulated the growth of primary roots, inhibited the formation of lateral roots, and increased root depth in maize (Li et al, 2012). The diversity of RSA under low P stress indicates that RSA plasticity depends on external environmental and internal genetic factors

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Conclusion