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

C B Rajashekar,Amanda Woolley,Jingwen Xu,Shannon Barry,Samuel Sumpter,Myungjin Lee,Weiqun Wang

doi:10.4236/ajps.2019.101011

Abstract

High tunnel production of horticultural food crops is becoming increasingly popular and has a significant impact on their growth, productivity and nutritional quality. The present study examines 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. 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. The results show that the high tunnel production has a significant impact on the nutritional quality relating to protein and mineral nutrients in both crops and health-promoting phytochemicals in lettuce.

Highlights

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
Lettuce varieties grown in high tunnel had higher accumulation of C, S and Zn relative to those grown in open field
We investigate the effect of high tunnel production of commonly grown vegetables such as lettuce and tomato on their nutritional quality relating to both major mineral nutrients and health-promoting phytochemicals

Summary

Introduction

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. 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. Many studies have reported that crops grown in high tunnel have reduced nutritional value, especially in relation to health-promoting phytochemicals compared to those grown in open field. Romani et al [3] showed that lettuce grown in a greenhouse which received approximately 27% less light intensity than open field had reduced concentration of many individual polyphenols as well as the total phenolic compounds. High tunnel cultivation of red raspberry resulted in reduced level of carotenoids including β-carotene, lutein and zeaxanthins in the fruits compared to open field culture [4]

Methods

Results

Conclusion