The Relation Between Rate of Transpiration and Rate of Absorption of Water in Plants

Abstract

shoots of course are not quantitatively comparable with those made on rooted shoots, but possibly may be useful for comparison between different species under the same conditions. Livingston and Brown (1912) reported that the leaf moisture content of a number of species showed a decrease during the day and an increase at night. Maximov and Krasnoselsky-Maximov (1924) determined the water content of leaves at various times of day and found that even in the cool, humid climate of Petrograd a considerable water deficit existed at mid-day. Both investigators interpreted their results as indicating that water was lost more rapidly than it was absorbed.'EXPERIMENTS ON PLANTS IN SOIL.-While it is comparatively easy to measure the rate of water loss, it is impossible to measure directly the rate of absorption of plants rooted in soil. However, by using auto-irrigators in the manner suggested by Transeau (1911) and later used by Livingston and Hawkins (1915), it is possible to measure the rate of absorption of the system plant-plus-soil and thus to obtain some idea of the rate of absorption during any desired period of time. Livingston and Hawkins studied the relation between rates of transpiration and absorption in Coleus, Pelarqonium, and Vicia. They found that the rate of absorption fell behind the rate of transpiration during the day, but exceeded it at night. The period of maximum absorption usually fell about two hours later than the period of maximum transpiration. The experiments to be described here were performed to determine whether or not the relations between absorption and transpiration are the same in woody, herbaceous, and succulent species. The species used were green ash (Fraxinus pennsylvanicum var. lanceolata Sarg.), yellow poplar (Liriodendron tulipijera L.), loblolly pine (Pinus taeda L.), black willow (Salix nigra Marsh.), cactus (Opuntia sp.), and sunflower (Helianthus annuus L.).The willow was grown from cuttings which were about 6 months old. The other woody species were grown from seed. The cacti were grown from single joints rooted in sand. Three months to a year before they were used, all plants were transferred to metal containers about 15 ern. in diameter and 20 cm. deep. Two plants were placed in each container on opposite sides of the centrally located auto-irrigator cone, and the containers were filled with fertile, sandy loam soil having a moisture equivalent of approximately 18 per cent. The sunflowers were grown from seed in the containers and were 6 to 8 weeks old at the time of the experiments. All plants were grown with the water level of the reservoir about 40 em. below the bottom of the containers, and no mercury barostats were used. The plants all made excellent growth. 10 THE Mos'r FUNDAMENTAL phase of plant water relations in respect to effect on growth is the internal water balance or degree of saturation of the tissues. This is determined by the relative rates of absorption and transpiration. The ratio of absorption to transpiration is therefore more important than the absol...

Diurnal Fluctuations in the Moisture Content of Some Herbaceous Plants

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DIURNAL FLUCTUATIONS in the moisture content of the leaves of many plants have been reported by numerous workers including Lloyd (1913), Shreve (1914), Miller (1917, Metzger et al (1925), and Hawkins (1927). Data from experiments reported by Kramer (1937) on changes in the moisture content of leaves confirm an observation of Miller that the maximum moisture content of the leaves of some herbaceous plants was reached during the middle of the night. It was also observed that the moisture content of the leaves of certain plants reached a peak early in the evening, declined towards 2 a.m. and then reached another peak towards sunrise.

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Cyclic Changes in Water Balance and Transpiration of Cotton Leaves in a Steady Environment

“…Fundamental to the existence of sucb a se^iuence is the lag in response of absorption behind a ri,se in transpiration, and the postulated mediation of the DPD mechanism. Such a lag in absorption has been well documented (1,2). However, demonstration of rapid changes in DPI) would be a very formidable task, since Ihis would require rapid, successive, precise measurements of DPD extending over a considerable period.…”

Effects of root restriction on growth correlations, water relations and senescence of alder seedlings

“…fourth leaf from the top LPI 3) for eight replicated seedlings. Observations were carried out during a 2-h period in the early afternoon to reduce the effects of diurnal changes in water status (Kramer 1937, Blake 1977.…”