Department of Biology, University of Pennsylvania, Philadelphia, PA 19104;
Department of Biology, University of Pennsylvania, Philadelphia, PA 19104.
Proc Natl Acad Sci U S A. 2018 Nov 20;115(47):12057-12062. doi: 10.1073/pnas.1718988115. Epub 2018 Nov 6.
CO, temperature, water availability, and light intensity were all potential selective pressures that determined the competitive advantage and expansion of the C photosynthetic carbon-concentrating mechanism over the last ∼30 My. To tease apart how selective pressures varied along the ecological trajectory of C expansion and dominance, we coupled hydraulics to photosynthesis models while optimizing photosynthesis over stomatal resistance and leaf/fine-root allocation. We further examined the importance of nitrogen reallocation from the dark to the light reactions. We show here that the primary selective pressures favoring C dominance changed through the course of C evolution. The higher stomatal resistance and leaf-to-root ratios enabled by C led to an advantage without any initial difference in hydraulic properties. We further predict a reorganization of the hydraulic system leading to higher turgor-loss points and possibly lower hydraulic conductance. Selection on nitrogen reallocation varied with CO concentration. Through paleoclimate model simulations, we find that water limitation was the primary driver for a C advantage, with atmospheric CO as high as 600 ppm, thus confirming molecular-based estimates for C evolution in the Oligocene. Under these high-CO conditions, nitrogen reallocation was necessary. Low CO and high light, but not nitrogen reallocation, were the primary drivers for the mid- to late-Miocene global expansion of C We also predicted the timing and spatial distribution for origins of C ecological dominance. The predicted origins are broadly consistent with prior estimates, but expand upon them to include a center of origin in northwest Africa and a Miocene-long origin in Australia.
CO、温度、水分可用性和光强度都是潜在的选择压力，它们决定了 C 光合作用碳浓缩机制在过去约 3000 万年中的竞争优势和扩张。为了梳理选择压力如何沿着 C 扩张和优势的生态轨迹变化，我们将水力学与光合作用模型相结合，同时优化光合作用对气孔阻力和叶/细根分配的影响。我们进一步研究了氮从暗反应向光反应重新分配的重要性。我们在这里表明，有利于 C 优势的主要选择压力在 C 进化过程中发生了变化。C 所具有的较高的气孔阻力和叶根比使其具有优势，而无需在水力特性上有任何初始差异。我们进一步预测了水力系统的重组，导致更高的膨压损失点和可能更低的水力传导率。氮重新分配的选择随着 CO 浓度的变化而变化。通过古气候模型模拟，我们发现水限制是 C 优势的主要驱动因素，大气 CO 浓度高达 600ppm，从而证实了分子基估计的始新世 C 进化。在这些高 CO 条件下，氮重新分配是必要的。低 CO 和高光，而不是氮重新分配，是中到晚中新世 C 全球扩张的主要驱动因素。我们还预测了 C 生态优势起源的时间和空间分布。预测的起源与先前的估计大致一致，但扩展了它们，包括在西北非的起源中心和澳大利亚的中新世起源。
