在低于环境水平的二氧化碳浓度下，植物水分状况的降低限制了C3和C4谷类作物野生祖先的植物生产力。
Reduced plant water status under sub-ambient pCO2 limits plant productivity in the wild progenitors of C3 and C4 cereals.
作者信息
Cunniff Jennifer, Charles Michael, Jones Glynis, Osborne Colin P
机构信息
Department of Animal and Plant Sciences, Alfred Denny Building, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
Institute of Archaeology, 36 Beaumont St, Oxford OX1 2PG, UK.
出版信息
Ann Bot. 2016 Nov;118(6):1163-1173. doi: 10.1093/aob/mcw165. Epub 2016 Aug 29.
BACKGROUND AND AIMS
The reduction of plant productivity by low atmospheric CO partial pressure (pCO) during the last glacial period is proposed as a limiting factor for the establishment of agriculture. Supporting this hypothesis, previous work has shown that glacial pCO limits biomass in the wild progenitors of C and C founder crops, in part due to the direct effects of glacial pCO on photosynthesis. Here, we investigate the indirect role of pCO mediated via water status, hypothesizing that faster soil water depletion at glacial (18 Pa) compared to post-glacial (27 Pa) pCO, due to greater stomatal conductance, feeds back to limit photosynthesis during drying cycles.
METHODS
We grew four wild progenitors of C and C crops at glacial and post-glacial pCO and investigated physiological changes in gas exchange, canopy transpiration, soil water content and water potential between regular watering events. Growth parameters including leaf area were measured.
KEY RESULTS
Initial transpiration rates were higher at glacial pCO due to greater stomatal conductance. However, stomatal conductance declined more rapidly over the soil drying cycle in glacial pCO and was associated with decreased intercellular pCO and lower photosynthesis. Soil water content was similar between pCO levels as larger leaf areas at post-glacial pCO offset the slower depletion of water. Instead the feedback could be linked to reduced plant water status. Particularly in the C plants, soil-leaf water potential gradients were greater at 18 Pa compared with 27 Pa pCO, suggesting an increased ratio of leaf evaporative demand to supply.
CONCLUSIONS
Reduced plant water status appeared to cause a negative feedback on stomatal aperture in plants at glacial pCO, thereby reducing photosynthesis. The effects were stronger in C species, providing a mechanism for reduced biomass at 18 Pa. These results have added significance when set against the drier climate of the glacial period.
背景与目的
末次冰期期间低大气二氧化碳分压（pCO）导致植物生产力下降，这被认为是农业起源的一个限制因素。支持这一假说的是，先前的研究表明，冰期pCO限制了C4和C3作物野生祖先的生物量，部分原因是冰期pCO对光合作用的直接影响。在此，我们研究了通过水分状况介导的pCO的间接作用，假设由于气孔导度更大，与冰后期（27 Pa）pCO相比，冰期（18 Pa）pCO下土壤水分消耗更快，这在干燥周期中反馈限制了光合作用。
方法
我们在冰期和冰后期pCO条件下种植了四种C4和C3作物的野生祖先，并研究了定期浇水事件之间气体交换、冠层蒸腾、土壤含水量和水势的生理变化。测量了包括叶面积在内的生长参数。
主要结果
由于气孔导度更大，冰期pCO下的初始蒸腾速率更高。然而，在土壤干燥周期中，冰期pCO下的气孔导度下降得更快，这与细胞间pCO降低和光合作用减弱有关。不同pCO水平下的土壤含水量相似，因为冰后期pCO下较大的叶面积抵消了水分消耗较慢的影响。相反，这种反馈可能与植物水分状况降低有关。特别是在C3植物中，与27 Pa pCO相比，18 Pa时土壤-叶片水势梯度更大，这表明叶片蒸发需求与供应的比率增加。
结论
植物水分状况降低似乎对冰期pCO下植物的气孔开度产生了负反馈，从而降低了光合作用。这些影响在C3物种中更强，为18 Pa时生物量降低提供了一种机制。相对于冰期更干燥的气候，这些结果具有额外的意义。
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