Nielsen K L, Eshel A, Lynch J P
Department of Horticulture, The Pennsylvania State University, University Park, PA 16802, USA.
J Exp Bot. 2001 Feb;52(355):329-39.
A common response to low phosphorus availability is increased relative biomass allocation to roots. The resulting increase in root:shoot ratio presumably enhances phosphorus acquisition, but may also reduce growth rates by diverting carbon to the production of heterotrophic rather than photosynthetic tissues. To assess the importance of increased carbon allocation to roots for the adaptation of plants to low P availability, carbon budgets were constructed for four common bean genotypes with contrasting adaptation to low phosphorus availability in the field ("phosphorus efficiency"). Solid-phase-buffered silica sand provided low (1 microM), medium (10 microM), and high (30 microM) phosphorus availability. Compared to the high phosphorus treatment, plant growth was reduced by 20% by medium phosphorus availability and by more than 90% by low phosphorus availability. Low phosphorus plants utilized a significantly larger fraction of their daytime net carbon assimilation on root respiration (c. 40%) compared to medium and high phosphorus plants (c. 20%). No significant difference was found among genotypes in this respect. Genotypes also had similar rates of P absorption per unit root weight and plant growth per unit of P absorbed. However, P-efficient genotypes allocated a larger fraction of their biomass to root growth, especially under low P conditions. Efficient genotypes had lower rates of root respiration than inefficient genotypes, which enabled them to maintain greater root biomass allocation than inefficient genotypes without increasing overall root carbon costs.
对低磷有效性的一种常见反应是相对增加根系的生物量分配。由此导致的根冠比增加可能会提高磷的获取，但也可能通过将碳转移到异养组织而非光合组织的生产中而降低生长速率。为了评估增加碳分配到根系对植物适应低磷有效性的重要性，构建了四种普通豆基因型的碳预算，这些基因型在田间对低磷有效性的适应性（“磷效率”）存在差异。固相缓冲硅砂提供了低（1微摩尔）、中（10微摩尔）和高（30微摩尔）的磷有效性。与高磷处理相比，中磷有效性使植物生长降低了20%，低磷有效性使植物生长降低了90%以上。与中磷和高磷植物（约20%）相比，低磷植物在根系呼吸中利用了其白天净碳同化的显著更大比例（约40%）。在这方面，基因型之间没有发现显著差异。基因型在单位根重的磷吸收速率和单位吸收磷的植物生长速率方面也相似。然而，磷高效基因型将其更大比例的生物量分配到根系生长，特别是在低磷条件下。高效基因型的根系呼吸速率低于低效基因型，这使得它们能够在不增加根系总碳成本的情况下，比低效基因型维持更大的根系生物量分配。
