Particulate matter air pollution may offset ozone damage to global crop production

Abstract

Abstract. Ensuring global food security requires a comprehensive understanding of environmental pressures on food production, including the impacts of air quality. Surface ozone damages plants and decreases crop production; this effect has been extensively studied. In contrast, the presence of particulate matter (PM) in the atmosphere can be beneficial to crops given that enhanced light scattering leads to a more even and efficient distribution of photons which can outweigh total incoming radiation loss. This study quantifies the impacts of ozone and PM on the global production of maize, rice, and wheat in 2010 and 2050. We show that accounting for the growing season of these crops is an important factor in determining their air pollution exposure. We find that the effect of PM can offset much, if not all, of the reduction in yield associated with ozone damage. Assuming maximum sensitivity to PM, the current (2010) global net impact of air quality on crop production varies by crop (+5.6, −3.7, and +4.5 % for maize, wheat, and rice, respectively). Future emissions scenarios indicate that attempts to improve air quality can result in a net negative effect on crop production in areas dominated by the PM effect. However, we caution that the uncertainty in this assessment is large, due to the uncertainty associated with crop response to changes in diffuse radiation; this highlights that a more detailed physiological study of this response for common cultivars is crucial.

The fertilization effect of global dimming on crop yields is not attributed to an improved light interception

“…Changes in R GR and F diff vary among different regions, and their impacts on crops may depend on crop varieties and other climatic factors. In addition, earlier studies have suggested that global dimming might also have an effect on C 4 crops like maize (Proctor et al, ; Schiferl & Heald, ; Yue & Unger, ). Whether the mechanisms we found here for wheat and rice in our study area apply to other C 3 crops or varieties grown elsewhere, or to C 4 crops merits further investigations.…”

“…When canopy is illuminated more by direct radiation, the upper leaves are easy to reach light saturation, while the leaves at the bottom may be shaded and not receive sufficient radiation for photosynthesis (Kanniah et al, 2013;Williams et al, 2014). In contrast, diffuse radiation allows the lower leaves to receive more radiation, and prevents the upper leaves from reaching light saturation (Gu et al, 2002;Mercado et al, 2009;Schiferl & Heald, 2018). This diminishing return light response shape in combination with differences in canopy light profile between CK and shading treatments contributed to our result that, for both crops, RUE increased under global dimming ( Our experiments revealed an additional, novel mechanism.…”

“…These models may assume that there is an enhanced light interception under global dimming. Some models, using nonlinear equations for describing photosynthetic light response curves (Alton, Ellis, et al, 2007;Cohan et al, 2002;Strada & Unger, 2016), indirectly recognizing the positive effect of global dimming on RUE, whereas others directly modify RUE as an empirical function of the diffuse radiation fraction (Greenwald et al, 2006;Kobayashi et al, 2005;Matsui et al, 2008;Schiferl & Heald, 2018). Whether light interception is really improved and whether the nonlinearity in photosynthetic light response curves accounts for an increased RUE under global dimming have not been examined critically.…”

Wildfire‐Smoke Aerosols Lead to Increased Light Use Efficiency Among Agricultural and Restored Wetland Land Uses in California's Central Valley

“…In addition to the effects of diffuse fraction, we assessed whether heightened [O 3 ] copollutants (Figure , bottom), often associated with wildfire (Jaffe & Wigder, ; Pfister et al, ; Yamasoe et al, ), could have caused diminished ecosystem productivity, counteracting the GEP enhancement due to increased diffuse fraction (Schiferl & Heald, ; Yue & Unger, ). Due to the distance from the fire source of our sites (>100 km) and the complex array of NOx and volatile organic carbon sources and sinks that the smoke plume passed over, attribution of O 3 can be challenging (Jaffe & Wigder, ).…”

“…Due to the lower threshold for light saturation in C 3 versus C 4 photosynthetic pathways (Ehleringer et al, 1997;Pearcy & Ehleringer, 1984), C 3 vegetation may be more sensitive to increased diffuse fraction than C 4 vegetation (Sinclair et al, 1992). Observed crop-or species-specific relationships between diffuse fraction and LUE are necessary to better constrain large-scale models (Schiferl & Heald, 2018;Sinclair et al, 1992).…”