Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
J Exp Bot. 2021 Jun 22;72(13):4965-4980. doi: 10.1093/jxb/erab176.
Previous studies have found that maximum quantum yield of CO2 assimilation (Φ CO2,max,app) declines in lower canopies of maize and miscanthus, a maladaptive response to self-shading. These observations were limited to single genotypes, leaving it unclear whether the maladaptive shade response is a general property of this C4 grass tribe, the Andropogoneae. We explored the generality of this maladaptation by testing the hypothesis that erect leaf forms (erectophiles), which allow more light into the lower canopy, suffer less of a decline in photosynthetic efficiency than drooping leaf (planophile) forms. On average, Φ CO2,max,app declined 27% in lower canopy leaves across 35 accessions, but the decline was over twice as great in planophiles than in erectophiles. The loss of photosynthetic efficiency involved a decoupling between electron transport and assimilation. This was not associated with increased bundle sheath leakage, based on 13C measurements. In both planophiles and erectophiles, shaded leaves had greater leaf absorptivity and lower activities of key C4 enzymes than sun leaves. The erectophile form is considered more productive because it allows a more effective distribution of light through the canopy to support photosynthesis. We show that in sorghum, it provides a second benefit, maintenance of higher Φ CO2,max,app to support efficient use of that light resource.
先前的研究发现，玉米和柳枝稷下层冠层的 CO2 同化最大量子产量（ΦCO2，max，app）下降，这是对自我遮荫的一种适应不良反应。这些观察结果仅限于单一基因型，不清楚这种 C4 草本植物——黍亚科的适应不良遮荫反应是否是普遍现象。我们通过测试以下假设来探索这种适应不良的普遍性，即直立叶形（直立叶型）允许更多的光进入下层冠层，其光合效率下降的程度比垂叶形（平展叶型）小。平均而言，35 个品种的下层冠层叶片中，ΦCO2，max，app 下降了 27%，但平展叶型的下降幅度是直立叶型的两倍多。光合效率的丧失涉及电子传递和同化的解耦。基于 13C 测量，这与鞘套泄漏增加无关。在平展叶型和直立叶型中，荫蔽叶片的叶片吸收率高于阳光叶片，而关键 C4 酶的活性低于阳光叶片。直立叶型被认为更具生产力，因为它允许更有效地通过冠层分配光来支持光合作用。我们表明，在高粱中，它提供了第二个好处，即维持更高的 ΦCO2，max，app 以支持对该光资源的有效利用。
