Maize yield under a changing climate: The hidden role of vapor pressure deficit

TL;DR

This study reveals that vapor pressure deficit (VPD) independently and significantly reduces maize yield under climate change, with effects comparable to temperature and CO2, emphasizing the need to consider VPD in crop projections.

Contribution

It provides a mechanistic analysis separating VPD effects from temperature, highlighting VPD's critical role in crop yield decline under climate change.

Findings

VPD increases have a greater negative impact on maize yield than warming alone.

Elevated CO2 partially mitigates yield loss through water savings, especially in drier conditions.

VPD affects yield via water stress responses, distinct from temperature effects.

Abstract

Temperatures over the next century are expected to rise to levels detrimental to crop growth and yield. As the atmosphere warms without additional water vapor input, vapor pressure deficit (VPD) increases as well. Increased temperatures and accompanied elevated VPD levels can both lead to negative impacts on crop yield. The independent importance of VPD, however, is often neglected or conflated with that from temperature due to a tight correlation between the two climate factors. We used a coupled process-based crop (MAIZSIM) and soil (2DSOIL) model to gain a mechanistic understanding of the independent roles temperature and VPD play in crop yield projections, as well as their interactions with rising CO2 levels and changing precipitation patterns. We found that by separating out the VPD effect from rising temperatures, VPD increases had a greater negative impact on yield compared to that from warming. The negative impact of these two factors varied with precipitation levels and influenced yield through separate mechanisms. Warmer temperatures caused yield loss mainly through shortening the growing season, while elevated VPD increased water loss and triggered several water stress responses such as reduced photosynthetic rates, lowered leaf area development, and shortened growing season length. Elevated CO2 concentrations partially alleviated yield loss under warming or increased VPD conditions through water savings, but the impact level varied with precipitation levels and was most pronounced under drier conditions. These results demonstrate the key role VPD plays in crop growth and yield, displaying a magnitude of impact comparative to temperature and CO2. A mechanistic understanding of the function of VPD and its relation with other climate factors and management practices is critical to improving crop yield projections under a changing climate.