In spite of the agricultural importance of potato (Solanum tuberosum L.), most plant physiology studies have not accounted for the effect of the interaction between elevated carbon dioxide concentration ([CO2]) and other consequences of climate change on WUE. In 2010, a first controlled environment chamber experiment (E1) was performed with two treatments: one control at a [CO2] exposure level of 380 ppm and the other at elevated [CO2] first to 700 ppm and subsequently to 1000 ppm. Plants grown at elevated [CO2] levels of 700 and 1000 ppm showed a consistent significant increase in leaf level photosynthetic water use efficiency (pWUE) by stimulation in net photosynthesis rate (62 and 43% increase of An) with coincident decline in both stomatal conductance (21 and 43% decrease of gs) and leaf transpiration rate (19 and 40% decrease of E) resulting in pWUE increments of 89 and 147%. Furthermore, the ratio of leaf intercellular [CO2] to ambient air [CO2] (Ci/Ca) remained unchanged among treatments. In 2011, a second experiment was performed (E2), where two treatments comprised [CO2] levels of 380 ppm (control) and elevated of 1000 ppm. The plants were subjected to three temperature levels (14, 21 and 280C). This procedure provided for investigation of WUE dependence of temperature at different [CO2]. At leaf-level, a consistent increase in pWUE of 28% across the three temperature levels was observed, caused by a significant stimulation in net photosynthesis rate (16%), and a significant decreased stomatal conductance (25%) with a simultaneous drop in transpiration rate although not significant. The ratio Ci/Ca was in contrast to the first experiment significantly higher in plants grown at elevated [CO2]. Despite this photosynthetic acclimation, concurrent stimulation of aboveground and belowground biomass accumulation was observed at elevated [CO2], resulting in higher harvest indices and irrigation WUE (45%), not significantly different from the increase of pWUE. Out of four cultivars investigated, the largest increase in irrigation WUE was found in the cultivar Ballerina, which also showed a six time increase in tuber yield, perhaps indicating less overall inhibition of photosynthesis by sugar accumulation. At all temperature levels WUE was significantly larger at high [CO2]. This was the result of increased net photosynthesis rate (at low temperature), decreased transpiration rate and stomatal conductance (high temperature) or a combination of those two responses (moderate temperature). The results signify that beneficial effects of potato plant cultivation at elevated [CO2] comprise increased WUE at various temperature levels, but due to acclimation of photosynthesis the increase was smaller during prolonged than stepwise exposure. The experiment also showed that, in the conditions of climate change, associated higher T could decrease the response of photosynthesis to higher [CO2] and higher vapor pressure deficit will decrease the gain in WUE.
Agricultural and Forest Meteorology, 2014, Vol 187, p. 36-45
potato; carbon dioxide; water use efficiency; Photosynthesis; Stomatal conductance; transpiration