Growth and Physiological Response of Fraser Fir [Abies fraseri (Pursh) Poir.] Seedlings to Water Stress: Seasonal and Diurnal Variations in Photosynthetic Pigments and Carbohydrate Concentration

Abstract

<jats:p>Four-year-old seedlings of <jats:italic>Abies fraseri</jats:italic> [(Pursh) Poir] (fraser fir) were grown in semicontrolled conditions in hoop houses with five watering regimes (0.00, 0.62, 1.25, 2.50, and 3.70 cm/week) with the goal of determining the seasonal variation in the physiological response to drought stress. Drought stress was monitored by measuring predawn (Ψpd) and midday (Ψmd) potentials in a subset of plants from each treatment. Physiological variables monitored were chlorophyll fluorescence (<jats:italic>F</jats:italic><jats:sub>v</jats:sub>/<jats:italic>F</jats:italic><jats:sub>m</jats:sub>), Chl a, Chl b, total carotenes, and total carbohydrate concentrations. Morphological characteristics including height growth, root collar diameter, and terminal shoot growth were also measured. Predawn stem water potential values were generally higher (–0.8 to –1.9 Mpa) than midday values (–1.3 to –2.9 Mpa). Irrigation consistently increased Ψpd and Ψmd compared with non-irrigated treatments. Photosynthetic pigments (Chl a, Chl b, and carotenes) decreased midseason (14 July) and increased toward the end of the season (25 Aug.) in predawn and midday measurements. There was a significant effect (<jats:italic>P</jats:italic> &lt; 0.05) of drought stress on photosynthetic pigment concentrations in predawn and midday samples in the late-season measurements (25 Aug.). These results were accompanied with a similar significant difference in <jats:italic>F</jats:italic><jats:sub>v</jats:sub>/<jats:italic>F</jats:italic><jats:sub>m</jats:sub> between non-irrigated and irrigated trees. We concluded that significant effects observed on photosynthetic pigment concentrations in some of the treatments did not affect carbohydrate concentrations. Exposure of <jats:italic>A. fraseri</jats:italic> to water stress did not cause a reduction in supply of metabolic carbohydrates; consequently, the decline and mortality in water-stressed plants can only be the result of hydraulic failure caused by xylem cavitation leading to cessation of water flow in tissues, desiccation, and cellular death. Further studies are needed to confirm these preliminary conclusions.</jats:p>

Drought stress responses of seedlings of two oak species (Quercus cerris and Quercus robur)

“…In both species, total soluble sugar content, which was quite high at the beginning of the drought experiment, declined in the first month (24 July) of the drought experiment. This decrease was probably related to seedling growth, which is in agreement with Kulac et al (2012). In the first month of the drought experiment (24 July), drought stress did not significantly affect total soluble sugar content.…”

Relative contributions of hydraulic dysfunction and carbohydrate depletion during tree mortality caused by drought

“…Recently, three hypotheses have been proposed concerning the mechanisms of drought-related tree mortality: hydraulic failure, carbon starvation and biotic attack ( McDowell et al 2008 ). Many studies have supported these hypotheses ( Galvez et al 2011 ; Kulac et al 2012 ; Plaut et al 2012 ; Barigah et al 2013 ; Mitchell et al 2013 , 2014 ; Klein et al 2014 ; Sevanto et al 2014 ). Two physiological responses to drought are defined as follows ( Pangle et al 2015 ): (i) hydraulic failure—low water potential due to decreased soil water content or increased transpiration rate impeding long-distance water transport and causing cavitation embolism or dehydration; (ii) carbon starvation—stomatal closure and restricted carbon translocation, uptake and assimilation during prolonged drought.…”

“…Hydraulic failure is a major cause of woody plant mortality during drought ( Choat 2013 ). Carbon starvation is relatively slow and may occur in the late stages of prolonged drought ( McDowell 2011 ; Kulac et al 2012 ; Klein et al 2014 ). Drought alters carbon allocation and partitioning among organs or tissues above- or below-ground.…”

Effects of Some Hormone Applications on Germination and Morphological Characters of Endangered Plant Species Lilium artvinense L. Seeds

“…Such advancement of the ornamental plants market made the researchers to be interested in various issues such as defining the distribution areas [24,25], protection [26][27][28][29][30], cultivation [31,32], resistance to stress factors [33,34], various applications [11,35,36], genetic variability [16,[37][38][39][40], their relationship with the environment [41][42][43][44], raising awareness about plants and legal dimension of the issue [45][46][47], thus resulting in various works on these issues. In addition to these, a large number of reports were conducted on especially the generative [48][49][50][51][52][53][54][55] and vegetative cultivation methods, and the studies are still going on [56]. However, it is of particular importance to define new species, variations, forms, cultivars or hybrids that can be launched especially to the ornamental plants market, as all plants are of high economic importance.…”