Carbon dioxide in the tomato plant microenvironment

Abstract

Paper and polyethylene mulches have proven effective in causing increased growth and yields of several field-grown vegetable crops. These increases cannot always be attributed entirely to temperature and moisture differences resulting from mulching. This indicates that another environmental factor, perhaps CO2, could be partially responsible. Carbon dioxide enrichment has met with great success in greenhouses. A slight CO2 enrichment effect could result from the trapping of diffusing CO2 by a mulch and its subsequent release directly around plants growing outdoors. The relationship among polyethylene-coated black paper mulch, CO2 in the plant microenvironment, and subsequent plant growth and yield was studied. Spring Giant Hybrid tomato seedlings were transplanted into mulched and unmulched beds in the field. Similar soil moisture levels were maintained through separate drip irrigation systems for mulched and unmulched plots. Temperatures were monitored relative to both treatments and found not significantly different at a 5 cm depth in the soil or at a 30 cm height in the canopy. Gas samples were collected from within the plant canopy at 3-hour intervals over two 24-hour periods. The CO2 concentration at the base of the plants (1 cm) was greater in the mulched plots in both the light and the dark while the CO2 level over the entire 34 cm profile was greater above the mulch in the dark. Carbon dioxide levels in the soil under the mulch and between the mulch and soil surface were greater relative to the bare soil. Plant tis sue dry weights were greater by 18% in the mulched plots. Total marketable fruit yield per plant was increased 36% and a 23% increase in weight per fruit was noted in the mulched plots. The increased plant growth and fruit yields were attributed to elevated levels of CO2 occurring in the mulched plant microenvironment.