The physiology of plant response to low soil temperatures is not well understood. Laboratory studies were conducted to examine the relative sensitivities of rates of leaf elongation, net photosynthesis, and transpiration and the leaf water potential of corn seedlings (Zea mays L. ‘Pride 5’) to decreasing temperature. These parameters were simultaneously monitored, as the soil temperature was decreased from 28 to 10 C at about 4 C increments. The different soil temperatures were imposed during a 10‐hour period on 14‐day‐old plants with seven exposed leaves growing at a 27.5 C air temperature, a 55% relative humidity, and a light intensity of 753 μE/m2/sec. Any decrease of the soil temperature below 28 C decreased the leaf elongation rate. This was attributed to restricted water uptake which lowered the plant water potential and to the temperature decrease of the shoot apical meristem region. Leaf elongation ceased at the plant water potential of —9 bars due to decline of leaf turgor pressure. Neither transpiration nor net photosynthesis was reduced significantly until the plant water potential reached —12 to —13 bars. Increases in both stomatal and internal resistances to CO2 diffusion coincided with the decreased net photosynthesis at low plant water potentials. Suboptimal soil temperatures affect corn seedling growth primarily by decreasing leaf elongation.

Nine‐day‐old corn (Zea mays L.) plants were grown at soil water potentials of −035 and −2.50 bars for 6 days using an osmotic‐solution semipenneable‐membrane technique. Leaf elongation, total dry matter accumulation, transpiration, soluble carbohydrate concentrations, and leaf water potentials were measured daily. When the soil water potential was decreased from −035 to −2.50 bars, leaf elongation rates decreased 44% and soluble carbohydrate concentrations increased 42%, while rates of total dry matter accumulation and transpiration decreased 26 and 24%, respectively. The increase in the soluble carbohydrate concentration was inversely related to both the rates of leaf elongation and total dry matter accumulation. The plant maintains a positive carbon balance in the leaves partly in the form of an abundant supply of soluble carbohydrates during periods of mild water stress. The sensitivity of leaf elongation rate to mild water stress appears to be an important growth determining factor.

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Lawns must be managed increasingly under less frequent or deficit irrigation. Deficit irrigation can reduce gas exchange, carbon assimilation, and physiological function in both warm- (C4) and cool- (C3) season turfgrasses, yet limited research has compared the physiological response to increasing levels of soil water deficit. The objectives of this greenhouse study were to compare three commonly used transition-zone turfgrasses—bermudagrass [Cynodon dactylon (L.) Pers.] (C4), buffalograss [Buchloe dactyloides (Nutt.) Engelm.] (C4), and tall fescue (Festuca arundinacea Schreb.) (C3)—and their ability to maintain quality and physiological function under water deficit stress. Visual turf quality, normalized difference vegetation index (NDVI), reflective canopy temperature, and gross photosynthesis were evaluated initially near field capacity (FC), and subsequent soil water deficit [48% (moderate) and 33% (severe) of plant-available water] conditions. Bermudagrass and tall fescue had similar quality ratings near FC, although the photosynthetic rate was greater for bermudagrass. Compared with other turfgrasses, bermudagrass maintained greater turf quality, NDVI, and photosynthetic rates further into water deficit stress. Tall fescue quality and photosynthetic rates declined most rapidly in both experiments as a result of the combined heat and drought stress. Buffalograss used less water compared with other species, and maintained consistent turf quality, NDVI, and photosynthetic rates under moderate and severe water deficit. These results support the notion that buffalograss and bermudagrass are better adapted than tall fescue at maintaining functional and ecosystem services with shallow soil depths in landscape situations under imposed summertime water restrictions.