Effect of Water Deficit on Gas Exchange, Osmotic Solutes, Leaf Abscission, and Growth of Four Birch Genotypes (Betula L.) Under a Controlled Environment

Abstract

<jats:p>Water was withheld from 2-year-old seedlings or rooted cuttings of four birch genotypes (<jats:italic>Betula alleghaniensis</jats:italic> Britton, <jats:italic>B. davurica</jats:italic> Pall., <jats:italic>B. nigra</jats:italic> L. ‘Cully’, and <jats:italic>B. papyrifera</jats:italic> Marsh.) until the combined weight of the container and plant decreased below 40% of its original value to induce plant predawn water potential between −1.5 MPa and −2.1 MPa, after which plants were supplied with a requisite amount of water to reach 40% of its original value for 5 weeks under controlled conditions to investigate changes in gas exchange, osmotic solutes, leaf abscission, and growth compared with well-watered (WW) plants. Observations indicated that three of the four genotypes (except <jats:italic>B. papyrifera</jats:italic>) expressed three stages of photosynthetic response during water deficit: 1) a stress stage, 2) an acclimation stage, and 3) an adapted (or tolerance) stage. The stages were characterized by decreasing, increasing, and stabilized Pn<jats:sub>ws/ww</jats:sub> (net photosynthesis presented as a ratio of water-deficit stressed (WS) plants to WW plants), respectively. A strong relationship between Pn and <jats:italic>g</jats:italic> <jats:sub>S</jats:sub> observed in the WS plants of the four genotypes, suggested inhibition of Pn by stomatal closure. After exposure to water deficit for 5 weeks, Pn<jats:sub>ws/ww</jats:sub> recovered to 70% of the initial value for <jats:italic>B. alleghaniensis</jats:italic> and <jats:italic>B. nigra</jats:italic> ‘Cully’ and 98% for <jats:italic>B. davurica</jats:italic> and <jats:italic>B. papyrifera</jats:italic>. WS plants had higher foliar concentrations of chlorophyll a and b (nmol/g) and potassium (%) than the WW plants. Increased levels of polyols (mg/g) were detected only in the WS plants of <jats:italic>B. allegahaniensis</jats:italic>. Increased levels of carbohydrates or organic acid under water deficit were not detected. A significant increase in leaf abscission in the WS plants of <jats:italic>B. papyrifera</jats:italic> compared with the other genotypes could be a morphological adaptation to water deficit conditions and facilitate recovery of Pn<jats:sub>ws/ww</jats:sub> during the acclimation stage.</jats:p>

An overview of models of stomatal conductance at the leaf level

“…2006); (2) a decrease of the number of leaves on new shoots (Gomez‐Del‐Campo et al . 2003) and abscission of existing leaves (Gu et al . 2007); (3) an increase in the root‐to‐shoot ratio (Assuero et al .…”

“…In response to environmental stresses, modifications of the morphology of the plant were reported. It was observed that drought results in: (1) a decrease in the specific leaf area that leads in turn to a decrease of the evaporative surface (Assuero et al 2002;Gomez-Del-Campo et al 2003;Al-Khalifah et al 2006); (2) a decrease of the number of leaves on new shoots (Gomez-Del-Campo et al 2003) and abscission of existing leaves (Gu et al 2007); (3) an increase in the root-to-shoot ratio (Assuero et al 2002); and (4) modifications in vessel anatomy that favour small diameter vessels (Al-Khalifah et al 2006). These adaptive strategies buffer the effects of water stress on gs and, for that reason, should be integrated into models.…”

Nutrient and water availability alter belowground patterns of biomass allocation, carbon partitioning, and ectomycorrhizal abundance in Betula nigra

“…Birch species can acquire water from soils of low soil moisture content (Fort et al 1998). Furthermore, river birch has been shown to acclimate to water deficit, thereby limiting the effects of water deficit on photosynthesis (Gu et al 2007). The reduction in total leaf area in the (W-) treatment may have been due, in part, to premature leaf abscission, which was observed during warm summer weather.…”

“…Abscission of foliage is considered a drought avoidance adaptation of river birch (http://www.dnr. state.oh.us/Home/trees/) that reduces transpirational losses (Fort et al 1998;Gu et al 2007). Even in response to moderate drought stress, we observed a reduction of root phenolics in the low water treatment.…”

“…River birch is an ectomycorrhizal species adapted to flood plains that grows well in high clay soils, and is sensitive to water deficit (Ranney et al 1991;Gilman and Watson 1993;Gu et al 2007). Specifically, we tested the following predictions of allocation theory: (1) percent root biomass and total nonstructural carbohydrate content will decrease as nutrient availability increases; (2) root secondary metabolite levels and concentrations will be highest at intermediate levels of nutrient availability; (3) EMF abundance will decrease with as nutrient availability increases; and (4) as nutrient availability increases, drought stress tolerance will decrease.…”