Parvin Shahnaj, Uddin Shihab, Tausz-Posch Sabine, Armstrong Roger, Tausz Michael
Southern Cross Plant Science, Southern Cross University, Lismore, NSW, 2480, Australia.
Charles Sturt University, Wagga Wagga, NSW, 2678, Australia.
New Phytol. 2020 Jul;227(1):132-145. doi: 10.1111/nph.16520. Epub 2020 Apr 14.
Photosynthetic stimulation by elevated [CO ] (e[CO ]) may be limited by the capacity of sink organs to use photosynthates. In many legumes, N -fixing symbionts in root nodules provide an additional sink, so that legumes may be better able to profit from e[CO ]. However, drought not only constrains photosynthesis but also the size and activity of sinks, and little is known about the interaction of e[CO ] and drought on carbon sink strength of nodules and other organs. To compare carbon sink strength, faba bean was grown under ambient (400 ppm) or elevated (700 ppm) atmospheric [CO ] and subjected to well-watered or drought treatments, and then exposed to C pulse-labelling using custom-built chambers to track the fate of new photosynthates. Drought decreased C uptake and nodule sink strength, and this effect was even greater under e[CO ], and was associated with an accumulation of amino acids in nodules. This resulted in decreased N fixation, and increased accumulation of new photosynthates ( C/sugars) in leaves, which in turn can feed back on photosynthesis. Our study suggests that nodule C sink activity is key to avoid sink limitation in legumes under e[CO ], and legumes may only be able to achieve greater C gain if nodule activity is maintained.
二氧化碳浓度升高（e[CO₂]）对光合作用的刺激作用可能会受到库器官利用光合产物能力的限制。在许多豆科植物中，根瘤中的固氮共生体提供了额外的库，因此豆科植物可能更能从e[CO₂]中获益。然而，干旱不仅会限制光合作用，还会影响库的大小和活性，而关于e[CO₂]与干旱对根瘤及其他器官碳库强度的相互作用，人们了解甚少。为了比较碳库强度，将蚕豆种植在环境大气二氧化碳浓度（400 ppm）或升高的二氧化碳浓度（700 ppm）条件下，并进行充分浇水或干旱处理，然后使用定制的气室对其进行¹⁴C脉冲标记，以追踪新光合产物的去向。干旱降低了¹⁴C的吸收和根瘤库强度，在e[CO₂]条件下这种影响更大，并且与根瘤中氨基酸的积累有关。这导致固氮作用下降，叶片中新光合产物（¹⁴C/糖类）积累增加，进而可能对光合作用产生反馈作用。我们的研究表明，根瘤碳库活性是避免豆科植物在e[CO₂]条件下出现库限制的关键，只有维持根瘤活性，豆科植物才可能实现更大的碳积累。
