Accumulation of Mineral Nutrients and Phytochemicals in Lettuce and Tomato Grown in High Tunnel and Open Field

High tunnels are passive protective structures that markedly alter the microclimate, soil characteristics and intensity and quality of light received by crops, which can impact both plant growth and its nutritional quality. High tunnel production of horticultural crops is increasingly becoming popular in the US because it can extend the growing season and lead to aesthetically better looking produce with greater consumer preference.

The present study examined the effect of high tunnel production of lettuce (Lactuca sativa cv. “Two Star” and “New Red Fire”) and tomato (Solanum lycopersicum cv. “Celebrity” and “Mountain Fresh”) on their nutritional quality relating to major nutrients and health-promoting phytochemicals. Daily weather data with regard to mean, maximum and minimum temperatures, precipitation, and solar radiation (data not presented) were collected during the growing season from the weather station located near the test plots. The statistical differences in nutrients and phenolic compounds between open field and high tunnel were determined using ANOVA (SAS 9.4, Cary, NC and XLSTAT, Addinsoft, New York, NY) and the means were compared using Tukey’s method at p ≤ 0.05 and p ≤ 0.01.

The results showed that high tunnel environment increased the concentration of N (protein) in both lettuce and tomato relative to the open field cultivation. The accumulation pattern of mineral nutrients in high tunnel was similar in green-leaf and red-leaf lettuce varieties. Lettuce varieties grown in high tunnel had higher accumulation of C, S and Zn relative to those grown in open field. However, high tunnel environment suppressed the accumulation of many micronutrients such as Mg, Fe, Cu and Mn in both lettuce varieties but not in tomato. For example, accumulation of Fe was reduced by more than 80% in “Two Star” and by more than 55% in “New Red Fire” under high tunnel. It also suppressed the levels of many health-promoting phenolic compounds such as chlorogenic acid, chicoric acid, rutin and kaempferol in green-leaf lettuce and gallic acid in red-leaf lettuce. High tunnel environment improved the soil nutrient status but reduced the radiation levels (PAR, UV-A and UV-B) received by the crops.

In conclusion, high tunnel environment had significant impact on the accumulations of major nutrients and health-promoting phytochemicals in both lettuce and tomato cultivars.

Article by Amanda Woolley, et al, from Kansas State University, Manhattan, KS, USA.

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Image by Clinton Felsted, from Flickr-cc.