Effects of Relative Humidity and Root Temperature on Calcium Concentration and Tipburn Development in Lettuce

Abstract

Growth chamber studies were undertaken with a tipburn-sensitive cultivar of romaine lettuce (Lactuca sativa L. cv. Lobjoits Green Cos) grown under a photosynthetic photon flux density of 320 μmol s−1m−2 for 16 hours; light and dark temperatures were 26.0° and 12.5°C, respectively. As the relative humidity (RH) during the light period was decreased from 74% to 51%, growth was retarded, Ca concentration increased, and the onset of tipburn delayed. Decreasing RH during the dark period from 95% to 90% reduced growth and resulted in lower CA concentrations and earlier tipburn development. Further decreases from 90% to 65% caused no additional change in growth or tipburn response. Root temperatures of 23.5°, compared with 15.0°, slightly increased Ca concentration but induced earlier tipburn development. Ca concentrations were increased and tipburn delayed by humidity conditions which provided large diurnal fluctuations in water potential in the plant and which encouraged root pressure flow during the dark period. Elevated root temperatures did not provide expected increases in Ca accumulation in young leaves.

The Hidden Costs of Nighttime Warming on Yields

“…In tomato, [77] reported a decrease in calcium contents in the fruit by up to 66% as a result of relatively small increases in VPD Night , from 0.26 to 0.76 kPa. Similarly, in lettuce (Lactuca sativa), [78] reported a decrease in leaf Ca by over 33% as a result of increasing VPD Night from 0.07 to 0.15 kPa. Due to the active role of Ca-dependent protein kinases and Cabinding proteins in key yield-determining processes such as seed embryogenesis and development [79], fatty acid content and seed size [80], photoassimilate partitioning to the seed [81], and seed-fill rates [82], it could be hypothesized that high VPD Night events, particularly occurring during the reproductive phase, may depress yield potential through Ca deprivation (Figure 1).…”

Nutrient Solution Application of a Calcium-mobilizing Biostimulant Mitigates Tipburn without Decreasing Biomass of Greenhouse Hydroponic Lettuce

“…Vertical airflow fans were more effective than horizontal airflow fans at reducing tipburn severity but reduced the fresh weight of two lettuce cultivars in indoor vertical farming conditions (Kaufmann 2023). Alternatively, increasing relative humidity (90%-95%) at night increased the root pressure, which increased the Ca concentration of inner leaves, thus reducing the tipburn incidence (Collier and Tibbitts 1984).…”

“…High relative humidity during the day can increase tipburn occurrence and severity by decreasing the transpiration rate (Palzkill et al 1980), whereas low humidity at night can increase tipburn occurrence and severity by decreasing root pressure and, thus, mass flow (Vanhassel et al 2014). Lower daytime relative humidity reduces tipburn occurrence by increasing transpiration, thereby increasing Ca transport to young developing leaf tissues (Collier and Tibbitts 1984). Providing adequate airflow at the growing tip can reduce tipburn incidence by reducing boundary layer resistance around the leaf, thereby increasing the transpiration rate (Frantz et al 2004;Zhang et al 2016).…”

Preventing tipburn in chinese cabbage by high relative humidity during the night.

“…Though the quality of all tipburn-free heads seemed to be sufficient, the fact that more of the leaves declined, together with the paler green colour of the heads may have consequences for the keeping quality of heads grown at high night RH. Fur ther, attention has to be paid to achieve a lower relative humidity during daytime by ventilating on a wider scale, because this decreased growth and reduced tipburn oc currence in white cabbage (Wiebe, 1975) and lettuce (Collier & Tibbitts, 1984). However, not every decrease in growth rate does reduce tipburn occurrence.…”