Tropospheric ozone pollution reduces the yield of African crops

Abstract

Northern, Southern and Equatorial Africa have been identified as among the regions most at risk from very high ozone concentrations. Whereas we know that many crop cultivars from Europe, north America and Asia are sensitive to ozone, almost nothing is known about the sensitivity of staple food crops in Africa to the pollutant. In this study cultivars of the African staple food crops, Triticum aestivum (wheat), Eleusine coracana (finger millet), Pennisetum glaucum (pearl millet) and Phaseolus vulgaris (bean) were exposed to an episodic ozone regime in solardomes in order to assess whether African crops are sensitive to ozone pollution. Extensive visible leaf injury due to ozone was shown for many cultivars, indicating high sensitivity to ozone. Reductions in total yield and 1,000‐grain weight were found for T. aestivum and P. vulgaris, whereas there was no effect on yield for E. coracana and P. glaucum. There were differences in sensitivity to ozone for different cultivars of an individual crop, indicating that there could be possibilities for either cultivar selection or selective crop breeding to reduce sensitivity of these crops to ozone.

Evidence of Ozone-Induced Visible Foliar Injury in Hong Kong Using Phaseolus Vulgaris as a Bioindicator

“…The resistant genotype can recover by producing some new leaves from week eight and it reduces the percentage of leaves that are larger than 25% injury. This result is consistent with the studies by [20], which also showed that higher O 3 exposure led to higher occurrence of O 3 injury in P. vulgaris.…”

“…The standard deviation and difference significance level are displayed in Tables 1 and 2. For the visible leaf injury data, we followed the statistical methodology performed by Hayes et al (2019) [20], who tested if the proportion of leaves per injury category varied with the genotype of the bean. We used the "multinom" function in the "nnet" package in R [45,46] to perform a multinomial logistic regression models on the relationship between leaf injury and genotype.…”

“…This phenomenon implies that when plants are exposed to a drought and O 3 stress at the same time, they continue to lose water through transpiration, resulting in desiccation [18]. The sensitivity of photosynthetic and stomatal biology to O 3 varies greatly between species and with the age of individuals [19,20].…”

Can Reduced Irrigation Mitigate Ozone Impacts on an Ozone-Sensitive African Wheat Variety?

“…Further research at a range of O 3 concentrations during the whole growing season is needed to develop robust O 3 flux-yield relationship and assess whether mitigation of adverse impacts of O 3 on wheat yield at reduced irrigation can simply be explained by a reduction in the phytotoxic O 3 dose [46]. Developing such a flux–yield relationship for the Kenyan wheat variety Korongo, a very O 3 -sensitive variety [43], would also allow comparison of the O 3 -sensitivity of an African wheat variety to those from other continents. Preferably, further research with Korongo should be conducted under Kenyan growth conditions as Korongo might perform differently under local conditions compared to the environmental conditions at the UK study site.…”

“…We hypothesised that reduced irrigation will reduce g s and therefore the accumulated uptake of O 3 , resulting in a delay in an O 3 -induced decline in flag leaf photosynthesis and an improved yield compared to full irrigation. An O 3 -sensitive African variety of wheat [43] was exposed to low (daylight mean O 3 concentration of 25 ppb, with peak concentrations aimed at 30 ppb) and high O 3 (daylight mean O 3 concentration of 45 ppb, with peak concentrations aimed at 80 ppb) for five days a week in hemi-spherical glasshouses for four weeks during flowering and grain fill. The high O 3 treatment represents surface peak O 3 concentrations observed in South Africa during periods of biomass burning [10].…”