Gas-filled root porosity in response to temporary low oxygen supply in different growth stages

Abstract

The development of gas-filled root porosity in response to temporary low oxygen supply was tested for a range of edible and ornamental crops: rice, maize, wheat, sugar beet, tomato, cucumber, sweet pepper, carnation, gerbera and rose. In a first experiment, the roots of tomato, maize and gerbera had a higher gas-filled root porosity, Ep (% v/v), when grown permanently in a non-aerated instead of aerated solution. The Ep of roots increased during two weeks when half the root system of a young plant was transferred to a non-aerated solution; in older plants this response was not seen. Carnation had a negligible gas-filled porosity in all treatments. In a second experiment, a comparison was made between high (20 kPa) and low (about 2 kPa) 02 partial pressure in a recirculating nutrient solution. Half of the root system was transferred to low O 2 at various growth stages. In most species older plants did not increase Ep on exposure to low 0 2. For tomato, sweet pepper and rose, E v was normally in the range 3-8% (v/v). Young plants of cucumber, wheat and sugar beet also had an Ep in that range, but in older plants values ranged from 1 to 3%. Transverse root sections examined by light microscopy showed, on average, 60% more intercellular spaces in the root cortex than the measurements of gas-filled porosity, probably because some gaps and spaces in the cortex were not gas-filled. This effect was most pronounced in tomato. A negative pressure in the cortex may be needed for gaps to be gas-filled. An exodermis may increase the effectiveness of gas spaces in the cortex by closing the gas channels and, by offering some resistance to water uptake, allowing a negative pressure head in the cortex which keeps gaps gas-filled. A redox dye method was developed to study the length of root which is effectively supplied with oxygen, as a function of Ep. Results indicated that for every percent Ep the root can remain aerated over at least 1 cm in a non-aerated medium under the conditions of the test.

Biology of Root Formation and Development

“…Daily: number and length of 1st order roots of each plant. Each 2nd day: (destructive) measurements of length of I st and 2nd order roots, number of 2nd order roots per 1 st order root (manually), leaf area (Licor area meter); dry weights of leaves, roots, stems, of 3 plants/stock; Day 12: diameter of I st order roots (using binoculars, at I mm from root origin), root porosity pyknometer method (Van Noordwijk and Brouwer, 1993).…”

Responses of Root Nodule Formation and Nitrogen Fixation Activity to Nitrate in a Split‐Root System in Peanut (Arachis hypogaea L.)

“…Split‐root systems have been used for studying the effect of environmental stress, such as water and oxygen stress, on plant growth (Coutts 1982, Van Noordwijk and Brouwer 1993). This experimental method has also been used to apply nitrate to half of the root systems of plant to elucidate the mechanisms of nitrate inhibition in soybean (Hinson 1975, Carrol and Gresshoff 1983, Tanaka et al.…”

Rooting characteristics of lettuce grown in irrigated sand beds

“…The increased root diameter in this zone was related with increased aerenchyma formation in the cortex (qualitatively confirmed only), which is normally an adaptation to reduced aeration (Van Noordwijk and Brouwer, 1993). The increased root diameter in this zone was related with increased aerenchyma formation in the cortex (qualitatively confirmed only), which is normally an adaptation to reduced aeration (Van Noordwijk and Brouwer, 1993).…”