Hot drought reduces the effects of elevated CO₂ on tree water‐use efficiency and carbon metabolism

First author: Benjamin Birami; Affiliations: Karlsruhe Institute of Technology (卡尔斯鲁厄理工学院): Garmisch‐Partenkirchen, Germany

Corresponding author: Benjamin Birami

Trees are increasingly exposed to hot droughts due to CO2‐induced climate change. However, the direct role of [CO2] in altering tree physiological responses to drought and heat stress remains ambiguous. Pinus halepensis (Aleppo pine) trees were grown from seed under ambient (421 ppm) or elevated (867 ppm) [CO2]. The 1.5‐yr‐old trees, either well watered or drought treated for 1 month, were transferred to separate gas‐exchange chambers and the temperature gradually increased from 25°C to 40°C over a 10 d period. Continuous whole‐tree shoot and root gas‐exchange measurements were supplemented by primary metabolite analysis. Elevated [CO2] reduced tree water loss, reflected in lower stomatal conductance, resulting in a higher water‐use efficiency throughout amplifying heat stress. Net carbon uptake declined strongly, driven by increases in respiration peaking earlier in the well‐watered (31–32°C) than drought (33–34°C) treatments unaffected by growth [CO2]. Further, drought altered the primary metabolome, whereas the metabolic response to [CO2] was subtle and mainly reflected in enhanced root protein stability. The impact of elevated [CO2] on tree stress responses was modest and largely vanished with progressing heat and drought. We therefore conclude that increases in atmospheric [CO2] cannot counterbalance the impacts of hot drought extremes in Aleppo pine.

由于CO₂诱导的气候变化，林木在可预见的未来将持续暴露在高温干旱的胁迫环境条件下。然而，CO2在林木响应干旱和高温胁迫所诱导的生理变化过程中的直接作用都还不清楚。阿勒坡松实生苗由种子萌发，生长在正常环境（CO2浓度421 ppm）和升高的CO2浓度环境条件下（867 ppm）。一年半的阿勒坡松幼苗连续充分浇水或干旱处理一个月，然后转移到不同的气体交换室中，并且温度从25°C开始，在10天内逐渐递增到40°C。然后，作者连续测量了这些植株的地上和地下部分的气体交换，另外也同时测量了主要代谢物。升高的CO2浓度降低了林木的水分丢失，说明植株气孔导度更低，进而在热胁迫的持续增加过程中具有更高的水分利用效率。充分浇水处理要比干旱处理的呼吸峰值来的更早，峰值也更加高，因而驱动的净碳吸收下降得非常明显，并且不受生长环境中CO2浓度的影响。此外，干旱会改变主要代谢物，而对CO2的代谢响应十分微弱，但根中的蛋白稳定性得到明显的增强。CO2浓度的升高对于林木胁迫响应的影响是中等的，并且随着高温和干旱胁迫的增强，这种影响在很大程度上会消除。因此，作者总结，大气CO2浓度的增加并不会抵消极端干旱条件对于阿勒颇松树的影响。

通讯：Benjamin Birami  (https://www.imk-ifu.kit.edu/staff_Benjamin_Birami.php)

个人简介：2014年，德国斯图加特大学，学士；2005年-至今，卡尔斯鲁厄理工学院，博士。

研究方向：可预见未来气候条件下的植物生理响应。

doi: https://doi.org/10.1111/nph.16471

Journal: New Phytologist

First Published: February 03, 2020