Responses of Transpiration and Hydraulic Conductance to Root Temperature in Nitrogen- and Phosphorus-Deficient Cotton Seedlings

Abstract

Suboptimal N or P availability and cool temperatures all decrease apparent hydraulic conductance (L) of cotton (Gossypium hirsutum L.) roots. The interaction between nutrient status and root temperature was tested in seedlings grown in nutrient solutions. The depression of L (calculated as the ratio of transpiration rate to absolute value of leaf water potential [Ij) by nutrient stress depended strongly on root temperature, and was minimized at high temperatures. In fully nourished plants, L was high at all temperatures :200C, but it decreased greatly as root temperature approached the chilling threshold of 15°C. Decreasing temperature lowered *, first, followed by transpiration rate.In N-or P-deficient plants, L approached the value for fully nourished plants at root temperatures :30°C, but it decreased almost linearly with temperature as roots were cooled. Nutrient effects on L were mediated only by differences in transpiration, and I' was unaffected. The responses of *, and transpiration to root cooling and nutrient stress imply that if a messenger is transmitted from cooled roots to stomata, the messenger is effective only in nutrient-stressed plants.One of the earliest symptoms of growth limitation by N or P supply is a specific inhibition of leaf expansion (12,13). In cotton and some other species, N or P deficiency decreases root L' (9,12,13,18). Radin and coworkers (12, 13) presented evidence that the decreased L can limit the delivery of water to the growing leaves and thus curtail cell expansion. Both N and P stress decrease the L of individual cells in the root cortex (17), implying that the shift in root properties results from changes in properties of cell membranes.Root L is sensitive also to chilling temperatures in plants of tropical or subtropical origin such as cotton (4, 6). Experiments reported here were designed to test for interactions of nutrient status and root temperature on L. MATERIALS AND METHODSCotton seeds (Gossypium hirsutum L. cv Deltapine 70) were germinated in moist vermiculite and transferred to con-'Abbreviations and symbols: L, apparent hydraulic conductance; 'I', water potential.tinuously aerated nutrient solutions after 3 d as described earlier (13). Seedlings were grown in groups of four with their roots suspended in 16-L containers of solution. The composition of the modified half-strength Hoagland solution is reported elsewhere (16). The complete solution contained 5 mM NO3-and 0.5 mm H2PO4-; in N-and P-deficient solutions Cl-was substituted for 96% of the N or 100% of the P. After transfer to nutrient solutions, plants were grown in a growth chamber with a 14-h daylength, day/night temperatures of 30/21C, and PPFD of 450 to 500 ,mol m-2 s-' at plant height (determined with a LiCor LI-190 quantum sensor; LiCor Instruments, Lincoln, NE, USA).2 Humidity was uncontrolled, but the daytime RH remained at 45 ± 5%. Nutrient depletion and pH changes were very small at this early stage of growth, and the solutions were not renewed.One week after seedlings were transferre...

Effects of arbuscular mycorrhizal fungi and Bradyrhizobium japonicum on drought stress of soybean

“…Regardless of the moisture treatments, bacterial inoculation caused a significant enhancement in shoot N. B. japonicum may improve soybean growth in a water-stressed condition by supplying nitrogen. Radin (1990) pointed out that leaf N concentration can affect stomatal behaviour. Although mycorrhizal fungi had no significant effect on shoot N, but in nonbacterial plants it increased slightly in the presence of either fungi (Tab.…”

Mechanisms of Phosphorous Uptake Efficiency of Safflower and Sunflower Grown in Different Soils

“…There were instances, where P-deficiency decreased the hydraulic conductivity of water in the roots [66,67], and reduced the water potential of the plant, possibly by lowering the activity of the water channel proteins, aquaporins [67]. It is also possible that P-deficiency induced the closure of stomata [66], improving the water potential of these organs temporarily. The decrease in hydraulic conductivity of the root and stomatal conductance of the leaf, result in a severe reduction of leaf expansion under P-deficiency [67].…”

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