Biosystems Department; Risø DTU, Roskilde, Denmark.
J Exp Bot. 2011 Aug;62(12):4253-66. doi: 10.1093/jxb/err133. Epub 2011 May 16.
Global change factors affect plant carbon uptake in concert. In order to investigate the response directions and potential interactive effects, and to understand the underlying mechanisms, multifactor experiments are needed. The focus of this study was on the photosynthetic response to elevated CO(2) [CO2; free air CO(2) enrichment (FACE)], drought (D; water-excluding curtains), and night-time warming (T; infrared-reflective curtains) in a temperate heath. A/C(i) curves were measured, allowing analysis of light-saturated net photosynthesis (P(n)), light- and CO(2)-saturated net photosynthesis (P(max)), stomatal conductance (g(s)), the maximal rate of Rubisco carboxylation (V(cmax)), and the maximal rate of ribulose bisphosphate (RuBP) regeneration (J(max)) along with leaf δ(13)C, and carbon and nitrogen concentration on a monthly basis in the grass Deschampsia flexuosa. Seasonal drought reduced P(n) via g(s), but severe (experimental) drought decreased P(n) via a reduction in photosynthetic capacity (P(max), J(max), and V(cmax)). The effects were completely reversed by rewetting and stimulated P(n) via photosynthetic capacity stimulation. Warming increased early and late season P(n) via higher P(max) and J(max). Elevated CO(2) did not decrease g(s), but stimulated P(n) via increased C(i). The T×CO2 synergistically increased plant carbon uptake via photosynthetic capacity up-regulation in early season and by better access to water after rewetting. The effects of the combination of drought and elevated CO(2) depended on soil water availability, with additive effects when the soil water content was low and D×CO2 synergistic stimulation of P(n) after rewetting. The photosynthetic responses appeared to be highly influenced by growth pattern. The grass has opportunistic water consumption, and a biphasic growth pattern allowing for leaf dieback at low soil water availability followed by rapid re-growth of active leaves when rewetted and possibly a large resource allocation capability mediated by the rhizome. This growth characteristic allowed for the photosynthetic capacity up-regulations that mediated the T×CO2 and D×CO2 synergistic effects on photosynthesis. These are clearly advantageous characteristics when exposed to climate changes. In conclusion, after 1 year of experimentation, the limitations by low soil water availability and stimulation in early and late season by warming clearly structure and interact with the photosynthetic response to elevated CO(2) in this grassland species.
全球变化因素共同影响植物的碳吸收。为了研究响应方向和潜在的相互作用，并了解潜在机制，需要进行多因素实验。本研究的重点是在温带石南荒地中，对升高的 CO2（CO2；自由空气 CO2 富集（FACE））、干旱（D；挡水帘）和夜间增温（T；红外线反射帘）的光合作用响应。测量了 A/C(i) 曲线，从而可以分析光饱和净光合作用（P(n)）、光和 CO2 饱和净光合作用（P(max)）、气孔导度（g(s)）、Rubisco 羧化的最大速率（V(cmax)）、核酮糖二磷酸（RuBP）再生的最大速率（J(max)）以及每月叶片 δ(13)C、草类 Deschampsia flexuosa 的碳和氮浓度。季节性干旱通过 g(s)降低了 P(n)，但严重（实验）干旱通过降低光合能力（P(max)、J(max)和 V(cmax)）降低了 P(n)。重新润湿完全逆转了这些影响，并通过刺激光合能力来刺激 P(n)。增温通过提高 P(max)和 J(max)，增加了早季和晚季的 P(n)。升高的 CO2 没有降低 g(s)，但通过增加 C(i)刺激了 P(n)。T×CO2 通过早季调节光合能力和重新润湿后更好地利用水协同增加植物碳吸收。干旱和升高的 CO2 的组合效应取决于土壤水分的可用性，当土壤水分含量较低时，二者具有累加效应，而在重新润湿后 D×CO2 协同刺激 P(n)。光合作用的响应似乎受到生长模式的强烈影响。该草具有机会性的水分消耗和双相生长模式，当土壤水分含量较低时允许叶片凋落，然后在重新润湿后迅速重新生长活性叶片，并且可能通过根茎介导具有较大的资源分配能力。这种生长特性允许光合能力的上调，从而介导 T×CO2 和 D×CO2 对光合作用的协同作用。当暴露于气候变化时，这些显然是有利的特征。总之，经过 1 年的实验，土壤水分含量低的限制以及增温和早季的刺激，明显构成并相互作用，影响了该草本物种对升高的 CO2 的光合作用响应。
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