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Agriculture (Species: Strawberry) -- Summary

Nearly all agricultural plants benefit from increases in the air's CO2 content and strawberry (Fragaria x ananassa) is no exception. The Plant Growth Database of CO2 Science, for example, presents 30 individual experimental results from peer-reviewed studies, demonstrating the fact that elevated CO2 enhances rates of photosynthesis and biomass production in this important agricultural species (see http://www.co2science.org/data/plant_growth/dry/f/fragariaa.php and http://www.co2science.org/data/plant_growth/photo/f/fragariaa.php). In this summary we highlight the work of some of these studies, plus other work that illustrates yet other important benefits strawberries will reap as the air's CO2 content rises in the years and decades to come.

We begin with the study of Deng and Woodward (1998), who grew strawberries in controlled glasshouses exposed to atmospheric CO2 concentrations of 390 and 560 ppm for nearly three months. In addition, the strawberries were supplied with fertilizers containing three levels of nitrogen so that the pair of researchers could study the direct and interactive effects of elevated CO2 and nitrogen supply on strawberry growth.

Results indicated that elevated CO2 increased rates of net photosynthesis and total plant dry weight at all nitrogen levels. In addition, the extra CO2 provided enough sugar and physical mass to support significantly greater numbers of flowers and fruits than in the plants grown at 390 ppm CO2. This effect consequently led to total fresh fruit weights that were 42 and 17% greater in CO2-enriched plants that received the highest and lowest nitrogen levels, respectively. Further, elevated CO2 increased the nitrogen-use efficiency of these plants by 23 and 17%, respectively.

Such findings suggest that, as the amount of CO2 in the atmosphere increases, strawberry plants will exhibit increased rates of photosynthesis, regardless of soil nitrogen fertility. Additionally, the increased supply of carbohydrates provided by this phenomenon will likely be utilized by the plants to increase their size and numbers of flowers and fruits. Ultimately, these effects will lead to increased yields, which should be very important to commercial strawberry growers and home gardeners.

Working in the field, Bunce (2001) grew strawberry plants in open-top chambers at three levels of atmospheric CO2 (350, 650, and 950 ppm) over a period of two years in an effort to study the effects of elevated CO2 on photosynthesis in this important agricultural crop. Measurements were made on a weekly basis to evaluate the temperature dependence of photosynthetic stimulation resulting from the two levels of atmospheric CO2 enrichment.

Surprisingly, elevated CO2 increased photosynthetic rates to an even greater extent than predicted by kinetic models based on the characteristics of the enzyme rubisco at all temperatures. Although photosynthetic acclimation was apparent in two-thirds of the measurements made during the course of the experiment, plants grown at 650 and 950 ppm CO2 still exhibited average photosynthetic rates that were 77 and 106% greater, respectively, than those displayed by control plants exposed to ambient air. In addition, when soil water potentials were measured during several "dry summer days," as the author described them, an increasingly greater amount of soil moisture was indicated for each step increase in the air's CO2 concentration. Thus, as the CO2 concentration of the atmosphere increases, strawberry plants will likely exhibit enhanced rates of photosynthesis, regardless of seasonal air temperature, which should lead to increased biomass and fruit production. In addition, strawberry plants should fare better under conditions of water stress than they do now.

Bushway and Pritts (2002) studied the effects of atmospheric CO2 enrichment on the early spring photosynthesis and growth of over-wintering strawberry plants. The plants were grown in controlled environmental chambers receiving ambient (375 ppm) and elevated (700 to 1,000 ppm) atmospheric CO2 concentrations for about six weeks until new blooms began to form on the plants, after which they were moved to a common greenhouse receiving ambient CO2 concentrations.

Elevated CO2 stimulated rates of photosynthesis in leaves of the over-wintering strawberry plants by more than 50%. This phenomenon led to significantly greater amounts of starch in key plant organs when new spring growth began. Indeed, plants grown in elevated CO2 had two-, three- and four-times the amount of starch in their crowns, leaves and roots, respectively, than their ambiently-grown counterparts. In addition, plants grown in elevated CO2 flowered and fruited an average of four and seven days earlier than plants grown in ambient air, respectively. Finally, yield per plant was increased by 62% due to atmospheric CO2 enrichment.

Based upon these several findings, it would appear that over-wintering strawberry plants will exhibit enhanced rates of photosynthesis and starch production as the air's CO2 content increases, which will support more rapid and extensive growth in the spring. Such increases in carbohydrate availability at this critical time should allow strawberry plants in a CO2-enriched world to produce greater numbers of fruit per plant, thus increasing marketable berry yields.

Wang and Bunce (2004) grew strawberry plants out-of-doors in open-top chambers maintained at three different CO2 concentrations. The plants were grown from rooted runners transplanted into field plots until the plants reached maturity and their fruit were harvested at the commercially ripe stage, after which the fruit were analyzed for a number of parameters that contribute to their flavor and aroma. In doing so the authors determined that plants grown in air enriched with an extra 300 ppm CO2 produced 17.6% more dry matter per fruit than the plants grown in ambient air, while plants grown in air enriched with an extra 600 ppm CO2 produced 38.5% more dry matter per fruit than the plants grown in ambient air.

Wang and Bunce also found that the ambient + 300 ppm CO2 plants contained 12% more total sugars (which enhance flavor) per gram dry weight of fruit than the ambient-treatment plants, while the ambient + 600 ppm plants contained 20% more total sugars per gram dry weight of fruit than the ambient-treatment plants. In addition, the ambient + 300 ppm CO2 plants contained 8.4% less total organic acids (which promote sourness) per gram dry weight of fruit than the ambient-treatment plants, while the ambient +600 ppm plants contained 17.4% less total organic acids per gram dry weight of fruit than the ambient-treatment plants. It was also observed that the elevated levels of atmospheric CO2 significantly increased the fruit concentrations of several aroma-enhancing compounds, leaving the two scientists to conclude their paper by saying "the results of this study indicate that enhancing CO2 concentration in the growing atmosphere would probably improve fruit quality by increasing fruit dry weight, sugar and aroma concentration and decreasing acid content."

Probing into yet other benefits of atmospheric CO2 enrichment on strawberries, Wang et al. (2003) evaluated the effects of elevated CO2 on strawberry fruit antioxidant activity and flavonoid content. More specifically, the three scientists grew strawberry plants in open-top chambers maintained at either ambient atmospheric CO2 concentration, ambient + 300 ppm CO2, or ambient + 600 ppm CO2, for a period of 28 months, harvesting the fruit "at the commercially ripe stage" and analyzing it for a number of different antioxidant properties and flavonol contents.

Before reporting what they found, however, Wang et al. provide some background by noting that "strawberries are good sources of natural antioxidants (Heinonen et al., 1998)." They further report that "in addition to the usual nutrients, such as vitamins and minerals, strawberries are also rich in anthocyanins, flavonoids, and phenolic acids," and that "strawberries have shown a remarkably high scavenging activity toward chemically generated radicals, thus making them effective in inhibiting oxidation of human low-density lipoproteins (Heinonen et al., 1998)." In this regard, they note that previous studies (Wang and Jiao, 2000; Wang and Lin, 2000) "have shown that strawberries have high oxygen radical absorbance activity against peroxyl radicals, superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen." In their experiment, therefore, they were essentially seeking to see if atmospheric CO2 enrichment could make a good thing even better.

In discussing their findings, the scientists report, first of all, that strawberries had higher concentrations of ascorbic acid (AsA) and glutathione (GSH) "when grown under enriched CO2 environments." In going from ambient to +300 ppm and +600 ppm CO2, for example, AsA concentrations increased by 10 and 13%, respectively, while GSH concentrations increased by 3 and 171%, respectively. They also learned that "an enriched CO2 environment resulted in an increase in phenolic acid, flavonol, and anthocyanin contents of fruit." For nine different flavonoids, for example, there was a mean concentration increase of 55 &plsmns; 23% in going from the ambient atmospheric CO2 concentration to +300 ppm CO2, and a mean concentration increase of 112 &plsmns; 35% in going from ambient to +600 ppm CO2. In addition, they report that the "high flavonol content was associated with high antioxidant activity." As for the significance of these findings, Wang et al. note that "anthocyanins have been reported to help reduce damage caused by free radical activity, such as low-density lipoprotein oxidation, platelet aggregation, and endothelium-dependent vasodilation of arteries (Heinonen et al., 1998; Rice-Evans and Miller, 1996)."

In summarizing their findings, Wang et al. say "strawberry fruit contain flavonoids with potent antioxidant properties, and under CO2 enrichment conditions, increased the[ir] AsA, GSH, phenolic acid, flavonol, and anthocyanin concentrations," further noting that "plants grown under CO2 enrichment conditions also had higher oxygen radical absorbance activity against [many types of oxygen] radicals in the fruit." These findings, coupled with those of Wang and Zheng (2001), which show that warmer temperatures (particularly warmer nighttime temperatures) also enhance the phenolic content and antioxidant activities in strawberries, bode well for strawberry growth under model scenarios of future climate and atmospheric CO2 concentrations.

The results of the several studies presented above are extremely encouraging. As the air's CO2 content continues to rise, strawberry plants will likely exhibit enhanced rates of photosynthesis and biomass production, which should lead to greater fruit yields in this economically important agricultural crop. They will also likely benefit in other ways, including the production of more flowers and fruit that will develop more quickly. Starch content, phenolics, and antioxidants will all be enhanced and strawberry plants will be better able to cope with water stress, nitrogen stress, and the stress of oxidation. And multiple reviews posted on our CO2 Science website indicate these benefits are realized in many, many other crops, endowing humanity with a highly optimistic future. It is therefore a shame when government organizations such as the United Nations Intergovernmental Panel on Climate Change or the U.S. Environmental Protection Agency fail to sufficiently acknowledge such benefits and instead forge ahead with efforts that would mute them when they should be promoting them.

References
Bunce, J.A. 2001. Seasonal patterns of photosynthetic response and acclimation to elevated carbon dioxide in field-grown strawberry. Photosynthesis Research 68: 237-245.

Bushway, L.J. and Pritts, M.P. 2002. Enhancing early spring microclimate to increase carbon resources and productivity in June-bearing strawberry. Journal of the American Society for Horticultural Science 127: 415-422.

Deng, X. and Woodward, F.I. 1998. The growth and yield responses of Fragaria ananassa to elevated CO2 and N supply. Annals of Botany 81: 67-71.

Heinonen, I.M., Meyer, A.S. and Frankel, E.N. 1998. Antioxidant activity of berry phenolics on human low-density lipoprotein and liposome oxidation. Journal of Agricultural and Food Chemistry 46: 4107-4112.

Rice-Evans, C.A. and Miller, N.J. 1996. Antioxidant activities of flavonoids as bioactive components of food. Biochemical Society Transactions 24: 790-795.

Wang, S.Y. and Bunce, J.A. 2004. Elevated carbon dioxide affects fruit flavor in field-grown strawberries (Fragaria x ananassa Duch). Journal of the Science of Food and Agriculture 84: 1464-1468.

Wang, S.Y., Bunce, J.A. and Maas, J.L. 2003. Elevated carbon dioxide increases contents of antioxidant compounds in field-grown strawberries. Journal of Agricultural and Food Chemistry 51: 4315-4320.

Wang, S.Y. and Jiao, H. 2000. Scavenging capacity of berry crops on superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen. Journal of Agricultural and Food Chemistry 48: 5677-5684.

Wang, S.Y. and Lin, H.S. 2000. Antioxidant activity in fruit and leaves of blackberry, raspberry, and strawberry is affected by cultivar and maturity. Journal of Agricultural and Food Chemistry 48: 140-146.

Wang, S.Y. and Zheng, W. 2001. Effect of plant growth temperature on antioxidant capacity in strawberry. Journal of Agricultural and Food Chemistry 49: 4977-4982.

Last updated 5 February 2015