Stomatal conductance, growth and root signaling in Betula pendula seedlings subjected to partial soil drying

Abstract

Seedlings of Betula pendula Roth were grown with their root systems separated between two soil compartments. Four treatments were imposed: (i) adequate irrigation in both compartments (WW, controls); (ii) adequate irrigation in one compartment and drought in the other compartment (WD); (iii) drought in both compartments (DD); and (iv) half of the root system severed and the remainder kept well-watered (root excision, RE). Predawn leaf water potential, stomatal conductance, soil-to-leaf specific hydraulic conductance, and root and leaf growth decreased in DD-treated seedlings, which also displayed severe leaf shedding (30% loss in leaf area). The DD treatment also resulted in increased concentrations of abscisic acid (ABA) and its glucose ester in the xylem sap of roots and shoots compared to concentrations in control seedlings (about 200 versus 20 nM). Despite the difference in xylem sap concentrations, total ABA flux to the shoots was similar in the two treatments (1-2 pmol ABA m(-2) leaf area s(-1)) as a result of reduced transpiration in the DD-treated seedlings. Compared with root growth in control plants, root growth increased in the RE-treated plants and decreased in the drying compartment of the WD treatment; however, the RE and WD treatments only slightly reduced leaf expansion, and had no detectable effects on shoot water relations or ABA concentrations of the root and shoot xylem sap. We conclude that short-term soil water depletion affecting only 50% of the root system does not cause a measurable stress response in birch shoots, despite root growth cessation in the fraction of drying soil.

Overyielding of temperate deciduous tree mixtures is maintained under throughfall reduction

“…Betula pendula followed the same pattern as Alnus glutinosa and has also been considered to be isohydric (Robson et al 2014). The decrease in root biomass in Alnus glutinosa and Betula pendula due to drought is in accordance with what is commonly observed in broad leaf species (Chiatante et al 2006;Fort et al 1998). In contrast, Fagus sylvatica in monoculture showed no tendency towards a decrease in biomass.…”

“…In the split root experiment of Fort et al (1998) fine root growth decreased over time in the dry compartment, but not the wet compartment. We were technically unable to measure root production in the gaps as the area is too small for repeated sampling.…”

“…However, results in monocultures for both seedlings and mature trees grown under experimentally altered moisture regimes, or studied along moisture gradients, are again contradictory (Meier and Leuschner 2008;Pronk et al 2002;Thomas 2000). Two general trends were shown: (i) an increase of root biomass in response to drought has mostly been observed in conifer species (Gower et al 1992;Parker and Van Lear 1996), which are known to differ in their root growth strategies from deciduous broad-leaved trees (Bauhus and Messier 1999), (ii) a decrease of root biomass occurs in European deciduous tree species in response to drought (Chiatante et al 2006;Fort et al 1998). Fagus sylvatica has, however, been found to sustain or even increase root growth in the upper soil layers during drought (Mainiero and Kazda 2006).…”

Control of stomatal aperture and carbon uptake by deficit irrigation in two grapevine cultivars

“…Increased xylem sap ABA concentration was considered as a potential cause of the observed decrease in stomatal conductance as shown in several studies (Davies et al, 2000;Stoll et al, 2000;Liu et al, 2001). However, this response can vary among species as demonstrated by Fort et al (1997Fort et al ( , 1998 working with seedlings of young oak and Betula pendula, who did not find an increase of ABA concentration in xylem sap originated in the roots under PRD conditions. A chemical signal from dehydrating roots leading to a change in apoplastic ABA content in leaves may be responsible for increased stomatal closure under PRD (Holbrook et al, 2002).…”

Deficit Irrigation and Partial Root-Zone Drying Techniques in Processing Tomato Cultivated under Mediterranean Climate Conditions

“…PRD practice has been successfully tested on a range of crops, especially tree crops, including apples [17], passion fruit [18], grapevines [19][20][21], oak [22], birch [23], and olive trees [24,25]. The results from several studies showed that crops under PRD yielded better than under DI when the same amount of water is applied, indicating higher water use efficiency (WUE) and even better fruit quality [26].…”