Evidence for Significant, Genotype-Dependent Nocturnal Transpiration across Maize NAM Parents.

There is accumulating evidence that nocturnal transpiration rate (TRN) in crops is significant and potentially involved in drought tolerance as we have recently shown in wheat. Because nocturnal water loss could aggravate soil moisture deficit, particularly in semi-arid or arid environments, lowering TRN might save enough water to protect from crop failure under severe drought conditions. So far, there was no evidence documenting the magnitude and the extent of variation in TRN in maize. In this investigation we used a high-resolution gravimetric phenotyping system that we have developed to track at a high temporal resolution nocturnal water use at a resolution of 1/100 of a gram. We used the system to examine time courses of TRN among a group of 25 nested association mapping (NAM) maize parents provided by the maize genetics cooperation stock center. The phenotyping system was deployed in three controlled chambers in order to enable us to track TRN independently from potentially confounding environmental variables such as light, temperature and vapor pressure deficit. Plants were grown for 4 weeks under the naturally fluctuating conditions of the greenhouse and then transferred to the growth chamber for a night of measurement. Based on a set of 3 independent experiments, average TRN was found to be non-null for a vast majority of the studied genotypes, with a significant genotype-dependent variability (P<0.0001). Further, the analysis of the TRN kinetics revealed the existence of a genotype-dependent pattern in TRN time courses (P<0.0001). The reported TRN values were not correlated with the slopes of daytime TR response to increasing VPD, specific leaf areas or leaf dry weights suggesting that breeding for lower TRN might be achieved without tradeoffs in terms of daytime water use and CO2 fixation.