Ruiz-Vera Ursula M, De Souza Amanda P, Long Stephen P, Ort Donald R
Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-ChampaignUrbana, IL, United States.
Department of Plant Biology, University of Illinois at Urbana-ChampaignUrbana, IL, United States.
Front Plant Sci. 2017 Jun 9;8:998. doi: 10.3389/fpls.2017.00998. eCollection 2017.
Down-regulation of photosynthesis is among the most common responses observed in C plants grown under elevated atmospheric CO concentration ([CO]). Down-regulation is often attributed to an insufficient capacity of sink organs to use or store the increased carbohydrate production that results from the stimulation of photosynthesis by elevated [CO]. Down-regulation can be accentuated by inadequate nitrogen (N) supply, which may limit sink development. While there is strong evidence for down-regulation of photosynthesis at elevated [CO] in enclosure studies most often involving potted plants, there is little evidence for this when [CO] is elevated fully under open-air field treatment conditions. To assess the importance of sink strength on the down-regulation of photosynthesis and on the potential of N to mitigate this down-regulation under agriculturally relevant field conditions, two tobacco cultivars ( L. cv. Petit Havana; cv. Mammoth) of strongly contrasting ability to produce the major sink of this crop, leaves, were grown under ambient and elevated [CO] and with two different N additions in a free air [CO] (FACE) facility. Photosynthetic down-regulation at elevated [CO] reached only 9% in cv. Mammoth late in the season likely reflecting sustained sink strength of the rapidly growing plant whereas down-regulation in cv. Petit Havana reached 25%. Increased N supply partially mitigated down-regulation of photosynthesis in cv. Petit Havana and this mitigation was dependent on plant developmental stage. Overall, these field results were consistent with the hypothesis that sustained sink strength, that is the ability to utilize photosynthate, and adequate N supply will allow C crops in the field to maintain enhanced photosynthesis and therefore productivity as [CO] continues to rise.
在大气CO₂浓度（[CO₂]）升高条件下生长的C₃植物中，光合作用下调是最常见的反应之一。下调通常归因于库器官利用或储存因[CO₂]升高刺激光合作用而增加的碳水化合物产量的能力不足。氮（N）供应不足会加剧下调，这可能会限制库的发育。虽然在大多数涉及盆栽植物的封闭研究中有强有力的证据表明[CO₂]升高会导致光合作用下调，但在露天田间处理条件下[CO₂]完全升高时，几乎没有证据支持这一点。为了评估在农业相关田间条件下，库强度对光合作用下调以及N缓解这种下调潜力的重要性，在自由空气CO₂浓度增高（FACE）设施中，种植了两种烟草品种（烟草品种 Petit Havana；品种 Mammoth），它们产生该作物主要库（叶片）的能力差异很大，并在环境[CO₂]和升高的[CO₂]条件下添加了两种不同的N。在生长季后期，品种Mammoth在[CO₂]升高时的光合作用下调仅达到9%，这可能反映了快速生长植物持续的库强度，而品种Petit Havana的下调达到了25%。增加N供应部分缓解了品种Petit Havana光合作用的下调，这种缓解取决于植物发育阶段。总体而言，这些田间结果与以下假设一致：持续的库强度，即利用光合产物的能力，以及充足的N供应将使田间的C₃作物在[CO₂]持续升高时保持增强的光合作用，从而维持生产力。
