Abstract
Root systems play a pivotal role in water and nutrient uptake from soil. Lateral root (LR) growth is promoted to compensate for inhibited main root growth. Compensatory LR growth contributes to maintaining total root length (TRL) and hence water and nutrient uptake in compacted soils. However, it remains unclear how shoot and root phenotypic traits change during the compensatory growth and whether there are genotypic variations in compensatory root growth. This study analyzed shoot and root morphological traits of 20 rice genotypes, which includes mutants with altered root morphology, during the vegetative stage using a semihydroponic phenotyping system. The phenotyping experiment detected large variation in root and shoot traits among the 20 genotypes. Morphological changes induced by root cutting were analyzed in six selected genotypes with contrasting root system architecture. Root cutting significantly affected root distribution along vertical sections and among diameter classes. After root cutting, more roots distributed at shallower depth and thicker LRs developed. Furthermore, genotypes with deeper root growth without root cutting allocated more compensatory roots to deeper sections even after root cutting than the genotypes with shallower rooting. Due to the compensatory LR growth, root cutting did not significantly affect TRL, root dry weight (RDW), or shoot dry weight (SDW). To analyze the interaction between crown root (CR) number and compensatory root growth, we removed half of the newly emerged CRs in two genotypes. TRL of YRL38 increased at depth with CR number manipulation (CRM) regardless of root tip excision, which was attributed to an increase in specific root length (SRL), despite no change in RDW. Taken together, the tested rice genotypes exhibited compensatory root growth by changing root distribution at depth and in diameter classes. Reducing CR number promoted root development and compensatory growth by improving the efficiency of root development [root length (RL) per resource investment].
Highlights
Root system architecture (RSA) is the shape and distribution of a root system in soil (Rogers and Benfey, 2015)
Results of Crown Root Number Manipulation Crown root number was reduced by removing 50% of newly emerged crown root (CR) (CRM) in Taichung 65 and YRL38 to analyze the relationships between CR number and the degree of compensatory root growth
Effect of Crown Root Number Manipulation on Shoot and Root Growth Combined With Root Cutting Treatment Based on a three-way analysis of variance (ANOVA), phenotypic variations between with and without CR number manipulation (CRM) were detected for maximum root depth (MRD), SCRN, RD, SRL, and leaf number (LN) (Table 6 and Supplementary Table S8)
Summary
Root system architecture (RSA) is the shape and distribution of a root system in soil (Rogers and Benfey, 2015). It has an important role in plant anchorage, soil water and nutrient uptake, and plant growth and yield. LRs are produced postembryonically from seminal and CRs (main roots) and play a major role in water and nutrient uptake as they occupy ∼ 90% of the TRL (Yamauchi et al, 1987). The production of L-type LRs is important for expanding the root system due to their ability to produce higher-order LRs. Plastic development of LRs plays an important role for the adaptation to soil water fluctuation in rice (Suralta et al, 2018; Lucob-Agustin et al, 2021)
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