Effects of root medium pH on water transport in paper birch (Betula papyrifera) seedlings in relation to root temperature and abscisic acid treatments

Department of Renewable Resources, 4-42 Earth Sciences Bldg., University of Alberta, Edmonton, AB T6G 2E3, Canada.
Tree Physiology (Impact Factor: 3.66). 11/2004; 24(10):1173-80. DOI: 10.1093/treephys/24.10.1173
Source: PubMed


We investigated the effects of root medium pH on water transport in whole-plant and detached roots of paper birch (Betula papyrifera Marsh.). Exposure of seedling roots to pH 4 and 8 significantly decreased root hydraulic conductivity (Lp) and stomatal conductance (gs), compared with pH 6. When roots of solution-culture-grown (pH 6) seedlings were transferred to pH 4 or 8, their steady-state water flow (Qv) declined within minutes, followed by a decline in gs. The root oxygen uptake rates were not significantly affected by the pH treatments. Treatment of roots with mercuric chloride resulted in a large decrease in Qv at pH 6; the extent of this decrease was similar to that brought about by pH 4 and 8. Lowering root temperature from 21 to 4 degrees C decreased Qv irrespective of medium pH. Low root temperatures did not offset the effects of medium pH 4 on Qv and the roots in this treatment had a high activation energy for water flow. Conversely, roots exposed to pH 8 had a low activation energy, similar to that at pH 6. When 2 micro M abscisic acid, (+/-)-cis-trans-ABA, was added to the root medium, Qv increased in roots that were incubated at pH 6. It also increased slightly in roots incubated at pH 4, but not at pH 8. The increase at pH 4 and 6 was temperature-dependent, occurring at 21 degrees C, but not 4 degrees C. We suggest that the pH treatments are responsible for altering root water flow properties through their effects on the activity of water channels. These results support the concept that ABA effects on water channels are modulated by other, possibly metabolic- and pH-dependent factors.

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    • "The decreases in dry weights at high pH were accompanied by the decreases in total chlorophyll concentrations, chlorophyll a:b ratios, and reductions in E and Pn, which are commonly affected in plants by high pH (Zhang et al., 2013). Many of the observed effects of high pH on plant growth and physiological processes could be caused by the reductions in plant water transport triggered by the inhibitory effects of high pH on root aquaporin activity (Tournaire-Roux et al., 2003; Kamaluddin and Zwiazek, 2004) and the reduced root system size (Tang et al., 1993a; Zhang et al., 2013). "
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    ABSTRACT: Plants growing in calcareous soils are exposed to high pH and elevated calcium levels which may reduce growth and produce high mortality in sensitive plants. In this study, we examined the hypotheses that in the high pH-sensitive jack pine (Pinus banksiana) seedlings, elevated root zone pH would reduce the ability of seedlings to control Ca uptake and the increase in Ca tissue concentrations would further aggravate the detrimental effects of high pH. We conducted two separate experiments to (i) investigate growth and physiological responses of jack pine (P. banksiana) seedlings to root zone pH ranging from 6 to 9, and (ii) examine the effects of 0.25 mM, 1 mM, 5 mM, and 10 mM Ca on physiological responses and nutrient uptake in jack pine seedlings exposed to the root zone pH of 6.5, 7.5, and 8.5 in nutrient solution culture. High root zone pH and high Ca concentrations significantly reduced growth, net photosynthesis, transpiration rates, needle chlorophyll concentrations, and root cortex cell lengths in seedlings. High root zone pH also decreased needle Ca and B concentrations, but the examined concentrations of Ca in nutrient solution had little effect on the needle composition of the examined essential elements including Fe, P, K, Cu, B, Mn, and Zn. We concluded that poor growth of conifer trees reported for calcareous soils is likely due to impaired root growth and the effects on gas exchange, likely caused by the reduced water uptake at high pH and elevated Ca levels.
    Full-text · Article · Nov 2014 · Environmental and Experimental Botany
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    • "It is also conceivable that pH may have differently affected root water uptake and root hydraulic conductivity in the different plants. Since root water transport is largely controlled by the cell-to-cell pathway involving aquaporins (Aroca et al. 2006; Lee et al. 2010), and aquaporins are sensitive to changes in pH (Tournaire- Roux et al. 2003; Kamaluddin and Zwiazek 2004; Tornroth-Horsefield et al. 2006; Siemens and Zwiazek 2011), a reduction in the aquaporin-mediated water transport in pH-sensitive plants could have an immediate impact on plant water balance. "
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    ABSTRACT: Background and aims Soil pH is among the major environmental factors affecting plant growth. Although the optimum range of soil pH for growth and the tolerance of pH extremes widely vary among plant species, the pH tolerance mechanisms in plants are still poorly understood. In this study, possible mechanisms were examined to explain the differences in tolerance of boreal plants to root zone pH. Methods In the controlled-environment solution culture experiments, we compared growth, physiological parameters and tissue nutrient concentrations in aspen, white spruce and tamarack seedlings that were subjected to 8 weeks of root zone pH treatments ranging from 5.0 to 9.0. Results The pH treatments had little effect on dry weights and net photosynthesis in white spruce seedlings despite reductions in transpiration rates at higher pH levels. In aspen and tamarack, both the growth and physiological parameters significantly decreased at pH higher than 6.0. The chlorosis of young tissues in aspen and tamarack was associated with the reductions in foliar concentrations of several of the examined essential nutrients including Fe and Mn. Although the plants varied in their ability to deliver essential nutrients to growing leaves, there was no direct correlation between tissue nutrient concentrations, chlorophyll concentrations and plant growth. The results also demonstrated strong inhibition of transpiration rates by high pH. Conclusions The results suggest that high root zone pH can upset water balance in pH sensitive species including aspen. Although the uptake and assimilation of essential elements such as Fe and Mn contribute to plant tolerance of high soil pH, we did not observe a direct relationship between growth and foliar nutrient concentrations to account for the observed differences in growth.
    Full-text · Article · Dec 2013 · Plant and Soil
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    • "The Q R of five plants per group was measured according to the hydrostatic pressure method (Kamaluddin and Zwiazek, 2004). Entire root systems were immersed in a beaker filled with measuring solution (20 mM KCl, 1 mM CaCl 2 ) and placed in a pressure chamber. "
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    ABSTRACT: Isohydric plants tend to maintain a water potential homeostasis primarily by controlling water loss via stomatal conductance. However, there is accumulating evidence that plants can also modulate water uptake in a dynamic manner. The dynamics of water uptake are influenced by aquaporin-mediated changes in root hydraulics. Most studies in this area have been conducted on herbaceous plants, and less is known about responses of woody plants. Here a study was conducted to determine how roots of hybrid poplar plants (Populus trichocarpa×deltoides) respond to a step change in transpirational demand. The main objective was to measure the expression of selected aquaporin genes and to assess how transcriptional responses correspond to changes in root water flow (Q R) and other parameters of water relations. A subset of plants was grown in shade and was subsequently exposed to a 5-fold increase in light level. Another group of plants was grown at ~95% relative humidity (RH) and was then subjected to lower RH while the light level remained unchanged. Both plant groups experienced a transient drop in stem water potentials. At 28h after the increase in transpirational demand, water potentials recovered. This recovery was associated with changes in the expression of PIP1 and PIP2 subfamily genes and an increase in Q R. Stomata of plants growing at high RH were larger and showed incomplete closure after application of abscisic acid. Since stomatal conductance remained high and unchanged in these plants, it is suggested that the recovery in water potential in these plants was largely driven by the increase in Q R.
    Full-text · Article · Apr 2013 · Journal of Experimental Botany
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