Relationship between Mineral Nitrogen Influx and Transpiration in Radish and Tomato

Abstract

Net ammonium and nitrate influx were independent of transpiration rate for intact seedlings of both a wild species of radish (Raphanus raphanistrum) and a wilty tomato mutant (Lycopersicon escwdkatum Mill. cv RR facca).Studies on the influence of water movement upon root ion fluxes have led to conflicting results (6, 10, 14). Jensen The night before the experiment, an intact plant was transferred to a measurement system in which the shoots and roots were enclosed in separate, but contiguous, cuvettes (3). Photosynthesis and transpiration were calculated from the changes in CO2 and H20 concentration of the gas passing through the shoot cuvette. Ion selective electrodes monitored the differences in ammonium and nitrate concentration of the nutrient solution entering and leaving the root cuvette and net influx estimated from these differences times the flow rate (2).All experiments were performed at 26C leaf temperature, 20C root temperature, 300 to 320 gbar ambient CO2 concentration, and 450 imol quantum m 2 s-' to the shoot. The incoming nutrient solution contained 1 mM Na2SO4 to adjust ionic strength, 0.1 mm CaSO4 to provide adequate amounts ofcalcium for membrane integrity, 0.5 mm KH2PO4 to avoid phosphate deficiencies, and varying amounts of NH4C1 and KNO3. The solution for radish contained 20 or 200 uM KNO3 and 20 Mm NH4Cl. The ammonium concentration was kept low because radish is susceptible to ammonium toxicity (9). The solution for tomato contained 200 or 1000 ,M of both NH4Cl and KN03.Humidity around the shoot was adjusted according to the following protocol: vapor pressure deficit was (a) started at a moderate level, (b) increased to a high level, (c) returned to the initial moderate level, (d) decreased to a very low level, and (e) time permitting, returned to the initial level. After each of these step changes in humidity, constant conditions were maintained for 1 to 2 h until steady state CO2, water, and nutrient fluxes were observed. The gas analyzer, humidity sensors, and electrodes were rezeroed after two or three consecutive measurements. All data were related to the leaf area and root dry weight obtained at the end of the experiment. RESULTSDaily changes in net ion influx did not correlate with changes of the water flux for either radish or tomato. While transpiration varied between 0.2 and 8.7 mmol m-2 s-', photosynthesis and net ammonium influx remained relatively constant; net nitrate influx increased steadily during the day for radish and remained relatively constant for tomato at a low supply or varied inconsistently with transpiration at a high supply (Fig. 1)

Acclimation to High CO2 in Monoecious Cucumbers

“…Lower stomatal conductances in CO2 enriched plants may reduce transpiration sufficiently to affect nutrient uptake as suggested by Madsen ( 18) for tomatoes. This linkage between transpiration and nutrient uptake is not important at natural soil fertility levels (29), but at high nutrient levels such as those we used, low transpiration may be a factor in reducing nutrient uptake (28).…”

Oxygen and Carbon Dioxide Fluxes from Barley Shoots Depend on Nitrate Assimilation

“…This plant was then transferred to a measurement system in which the roots and the shoot were enclosed by separate, but contiguous, cuvettes (24). To allow for recovery from any transplant shock, the plant was maintained in the dark for at least 8 h before experimental data were taken.…”

The biology of Canadian weeds. 132. Raphanus raphanistrum L.

“…In a greenhouse study of a California population of wild radish seedlings, Schulze and Bloom (1984) found that net ammonium (NH 2 ) and nitrate ion (NO 3 ) accumulation in the roots were independent of water movement into the plant, as would be expected in a nitrophilic species. In R. sativus × R. raphanistrum wild hybrid plants grown under continuous high NO 3 supply, NO 3 accumulation was greatest in the older leaves and petioles, and ca.…”

“…Wild radish as well as wild radish × R. sativus hybrid populations are considered to be nitrophiles, i.e., able to rapidly accumulate large amounts of free nitrate in the vegetative stage (Schulze and Bloom 1984;Schulze et al 1985). In a greenhouse study of a California population of wild radish seedlings, Schulze and Bloom (1984) found that net ammonium (NH 2 ) and nitrate ion (NO 3 ) accumulation in the roots were independent of water movement into the plant, as would be expected in a nitrophilic species.…”