Abstract
Low atmospheric relative humidity (RH) accompanied by elevated air temperature and decreased precipitation are environmental challenges that wheat production will face in future decades. These changes to the atmosphere are causing increases in air vapor pressure deficit (VPD) and low soil water availability during certain periods of the wheat-growing season. The main objective of this study was to analyze the physiological, metabolic, and transcriptional response of carbon (C) and nitrogen (N) metabolism of wheat (Triticum durum cv. Sula) to increases in VPD and soil water stress conditions, either alone or in combination. Plants were first grown in well-watered conditions and near-ambient temperature and RH in temperature-gradient greenhouses until anthesis, and they were then subjected to two different water regimes well-watered (WW) and water-stressed (WS), i.e., watered at 50% of the control for one week, followed by two VPD levels (low, 1.01/0.36 KPa and high, 2.27/0.62 KPa; day/night) for five additional days. Both VPD and soil water content had an important impact on water status and the plant physiological apparatus. While high VPD and water stress-induced stomatal closure affected photosynthetic rates, in the case of plants watered at 50%, high VPD also caused a direct impairment of the RuBisCO large subunit, RuBisCO activase and the electron transport rate. Regarding N metabolism, the gene expression, nitrite reductase (NIR) and transport levels detected in young leaves, as well as determinations of the δ15N and amino acid profiles (arginine, leucine, tryptophan, aspartic acid, and serine) indicated activation of N metabolism and final transport of nitrate to leaves and photosynthesizing cells. On the other hand, under low VPD conditions, a positive effect was only observed on gene expression related to the final step of nitrate supply to photosynthesizing cells, whereas the amount of 15N supplied to the roots that reached the leaves decreased. Such an effect would suggest an impaired N remobilization from other organs to young leaves under water stress conditions and low VPD.
Highlights
Increased temperature, elevated CO2 concentrations, and reduced rainfall are the main characteristics of future climate projections
This impaired photosynthesis caused by vapor pressure deficit (VPD) was accompanied by stomatal closure in well-watered plants alone, whereas no significant change was observed under water stress conditions for both VPD levels (Figure 2b)
The results indicated that a high VPD in well-irrigated plants impacted many of the C metabolism components and activated some other N metabolism aspects in the durum wheat flag leaf
Summary
Increased temperature, elevated CO2 concentrations, and reduced rainfall are the main characteristics of future climate projections. Increases in air temperature are accompanied by decreases in atmospheric relative humidity (RH), leading to changes in evaporative demand, known as vapor pressure deficit (VPD). Lobel and coworkers [3] identified the hidden effect of VPD in decreasing corn yield in recent decades, and their model simulations suggest even more severe reductions in the future in the corn belt in the United States. These are just a few examples of how VPD drives global ecosystems and plant photosynthesis
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