Elevated [CO₂] effects on crops: Advances in understanding acclimation, nitrogen dynamics and interactions with drought and other organisms

Abstract

Future rapid increases in atmospheric CO 2 concentration [CO 2 ] are expected, with values likely to reach~550 ppm by mid-century. This implies that every terrestrial plant will be exposed to nearly 40% more of one of the key resources determining plant growth. In this review we highlight selected areas of plant interactions with elevated [CO 2 ] (e[CO 2 ]), where recently published experiments challenge long-held, simplified views. Focusing on crops, especially in more extreme and variable growing conditions, we highlight uncertainties associated with four specific areas. (1) While it is long known that photosynthesis can acclimate to e[CO 2 ], such acclimation is not consistently observed in field experiments. The influence of sink-source relations and nitrogen (N) limitation on acclimation is investigated and current knowledge about whether stomatal function or mesophyll conductance (g m ) acclimate independently is summarised.(2) We show how the response of N uptake to e[CO 2 ] is highly variable, even for one cultivar grown within the same field site, and how decreases in N concentrations ([N]) are observed consistently. Potential mechanisms contributing to [N] decreases under e[CO 2 ] are discussed and proposed solutions are addressed. (3) Based on recent results from crop field experiments in highly variable, non-irrigated, waterlimited environments, we challenge the previous opinion that the relative CO 2 effect is larger under drier environmental conditions. (4) Finally, we summarise how changes in growth and nutrient concentrations due to e[CO 2 ] will influence relationships between crops and weeds, herbivores and pathogens in agricultural systems.

30 years of free‐air carbon dioxide enrichment (FACE): What have we learned about future crop productivity and its potential for adaptation?

“…Sorghum only showed greater yields at elevated [CO 2 ] under dry conditions (Ottman et al., 2001). These early experiments provided evidence for the hypothesis that under drought, the benefits of elevated [CO 2 ] would be greater because lower stomatal conductance and canopy evapotranspiration would benefit soil water content, such that crops could sustain growth in a drought cycle for a longer period of time (Kimball, 2016; Leakey et al., 2009; Tausz‐Posch et al., 2019). With more CO 2 x water treatments in recent FACE experiments, Figure 2 shows a different picture for C 3 crops, with an apparently similar average response to elevated [CO 2 ] with and without water deficit.…”

Early vigour in wheat: Could it lead to more severe terminal drought stress under elevated atmospheric [CO2] and semi‐arid conditions?

“…We hypothesized there might be a three-way interaction between Hartog Janz SB062 Spitfire SsrT65 Yitpi 1.0 1.1 1.2 1.3 1.4 1.5 SIMPLACE importance of radiation intercepted as illustrated by the models is in sharp contrast with the current literature: among environmental factors hypothesized to influence the response to e[CO 2 ], the scientific focus has rather been on investigating water and nutrient availabilities, sometimes with varying temperatures (see e.g. recent reviews by Kimball, 2016;Tausz-Posch et al, 2020;van der Kooi et al, 2016) while differences in radiation intercepted are not typically among the primary factors being considered. A notable connection, however, is the work by Shimono (2011) and Shimono et al (2014Shimono et al ( , 2019 who suggested using the response to low-density planting (in rice) as a surrogate for grain yield response to e[CO 2 ], although they also argue that the two responses would likely occur through different physiological mechanisms (Shimono et al, 2019).…”

“…However, there are also recent reports that seem to indicate the contrary (Gray et al, 2016) or that there are no consistent differences (van der Kooi, Reich, Löw, De Kok, & Tausz, 2016), leading some to suggest the response to e[CO 2 ] might depend on the timing of the drought experienced by the crop (Bourgault et al, 2017). The relationships between timing and extent of drought and trade-offs between biomass stimulation and leaf level water use efficiency gains have been shown to be especially important in highly variable, semi-arid or Mediterranean field conditions (Tausz-Posch, Tausz, & Bourgault, 2020).…”

Carbon sink strength of nodules but not other organs modulates photosynthesis of faba bean (Vicia faba) grown under elevated [CO2] and different water supply

“…Photosynthetic acclimation is related to limited sink strength (Ainsworth et al , 2004; Tausz‐Posch et al , 2020). Sinks are the organs/tissues that consume photosynthates, and their ability to acquire and utilize photosynthates is termed sink strength (Farrer, 1993).…”