Table_2_Genetic Variation in Root Architectural Traits in Lactuca and Their Roles in Increasing Phosphorus-Use-Efficiency in Response to Low Phosphorus Availability.DOCX

Low phosphorus (P) bioavailability in the soil and concerns over global P reserves have emphasized the need to cultivate plants that acquire and use P efficiently. Root architecture adaptation to low P can be variable depending on species or even genotypes. To assess the genetic variability of root architectural traits and their responses to low P in the Lactuca genus, we examined fourteen genotypes including wild species, ancient and commercial lettuce cultivars at low (LP, 0.1 mmol. L–1) and high P (HP, 1 mmol. L–1). Plants were grown in cylindrical pots adapted for the excavation and observation of root systems, with an inert substrate. We identified substantial genetic variation in all the investigated root traits, as well as an effect of P availability on these traits, except on the diameter of thinner roots. At low P, the main responses were a decrease in taproot diameter, an increase in taproot dominance over its laterals and an increase in the inter-branch distance. Although the genotype x P treatment effect was limited to root depth, we identified a tradeoff between the capacity to maintain a thick taproot at low P and the dominance of the taproot over its laterals. Regardless of the P level, the phosphorus-use-efficiency (PUE) varied among lettuce genotypes and was significantly correlated with total root biomass regardless of the P level. As taproot depth and maximum apical diameter were the principal determinants of total root biomass, the relative increase in PUE at low P was observed in genotypes that showed the thickest apical diameters and/or those whose maximal apical diameter was not severely decreased at low P availability. This pre-eminence of the taproot in the adaptation of Lactuca genotypes to low P contrasts with other species which rely more on lateral roots to adapt to P stress.

土壤中磷（P）生物有效性偏低，加之全球磷矿储量引发的诸多担忧，使得培育高效吸收与利用磷素的植物成为迫切需求。植物根系构型对低磷环境的适应性因物种甚至基因型而异。为解析莴苣属（Lactuca）植物根系构型性状的遗传变异及其对低磷胁迫的响应，我们选取了14份基因型材料开展试验，涵盖野生种、古老栽培种与商业化生菜品种，试验设置低磷（LP，0.1 mmol·L⁻¹）与高磷（HP，1 mmol·L⁻¹）两个处理组。供试植株种植于专为根系挖掘与观测设计的圆柱形栽培容器中，基质采用惰性基质。本研究发现，除细根直径外，所有被测根系性状均存在显著的遗传变异，且磷素有效性对多数根系性状存在显著影响。在低磷条件下，莴苣属植物的主要根系响应包括：主根直径减小、主根对侧根的支配性增强，以及侧根分枝间距增大。尽管基因型×磷处理的交互效应仅体现在根深性状上，但本研究仍发现了两项能力间的权衡关系：一是在低磷环境下维持较粗主根的能力，二是主根对侧根的支配性。无论磷素供应水平如何，不同生菜基因型的磷利用效率（PUE）均存在显著差异，且其与总根系生物量呈显著正相关，这一相关性不受磷素水平影响。由于主根深度与最大顶径是总根系生物量的主要决定因子，因此在低磷条件下磷利用效率相对提升的基因型，往往具备两个特征之一：一是拥有最粗的顶径，二是在低磷环境下其最大顶径未出现显著下降。莴苣属基因型通过主根适应低磷环境的这一主导特征，与更多依赖侧根应对磷胁迫的其他植物物种形成鲜明对比。