Growth responses of Salix gracilistyla cuttings to a range of substrate moisture and oxygen availability

Abstract

The objective of this study is to determine the effects of substrate moisture and oxygen availability on growth traits of Salix gracilistyla Miquel, which colonizes gravel bars along rivers, the shoot growth schedule, biomass production, and resource allocation were examined under greenhouse conditions. We used four treatments representing a range of substrate moisture and oxygen availability: drought (D), flooding with standing water (FS), flooding with running water (FR), and control without drought or flooding (C). Cuttings in D stopped flushing and had low biomass production, reduced total leaf mass, and small leaves. Under anaerobic conditions, cuttings in FS stopped flushing and had low biomass production, small root biomass, low biomass allocation to roots, shallow roots, high biomass allocation to hypertrophied lenticels, and a few small, thick leaves. Under aerobic conditions, cuttings in FR showed continuous branch elongation and flushing, large biomass production, and large leaf biomass, similar to cuttings in C, in addition to low allocation to hypertrophied lenticels and many large leaves. The growth of cuttings was not inhibited by flooding of the roots throughout the experiment unless the conditions were anaerobic. Thus, cuttings respond to water stress under low moisture conditions by reducing the transpiration area and respond to flooding under low oxygen conditions by high allocation to hypertrophied lenticels and reduced transpiration area. Plasticity in the shoot growth schedule, biomass production, and resource allocation according to moisture conditions and the ability to develop hypertrophied lenticels upon flooding allow S. gracilistyla to colonize sites in which both desiccation and flooding occur.

Stress responses in Salix gracilistyla cuttings subjected to repetitive alternate flooding and drought

“…This is because under longer flooding, root biomass and root ratio are inhibited (Table 3). Root growth of S. gracilistyla cuttings is also inhibited by each hypoxic flooding or drought event (Nakai et al 2009). S. gracilistyla will not increase drought tolerance, as water absorption ability increases under conditions of longer flooding between droughts, and may suffer dehydration during the following drought.…”

Time is on our side: the importance of considering a recovery period when assessing flooding tolerance in plants

“…This is a reasonable simplification for a relative short period of growth during the vegetative growth young plants ('classical approach' for plant growth analysis, see Poorter 1989). Second, plant biomass is used as the main variable in determining flooding stress-tolerance, as it integrates all ecophysiological processes leading to growth (Nakai et al 2009;Li et al 2011), while 'stress' is defined as any environmental factor that restricts growth (sensu Grime 1989). Third, it is assumed that the use of reserve carbohydrates is essential in defining growth during (and importantly after) flooding.…”

“…In this way, plants maximize the leaf area exposed above water, ensuring the capture of oxygen by leaves ) and facilitating root aeration (Colmer 2003). As a result of such preferential allocation of carbon to shoots-and the discontinuance of root growth-there is an increase in the shoot-to-root biomass ratio in flooded plants (Nakai et al 2009;L ie ta l .2011), which, additionally, can be seen as a reduction and an increase in the mass fraction of roots and shoots, respectively, according to Poorter et al (2012). In some cases, the magnitude of this effect can be diminished partially-but not counterbalanced-as a result of the formation porous adventitious roots (see Malik et al 2002), which help plants to alleviate the adverse effect of anaerobiosis by functionally replacing the original root system during flooding.…”

“…The former method requires consecutive plant harvests during recovery (a larger number of plants will be required). At each harvest, measurements of root number, length, depth, and root branching, besides root mass, are recommended in order to evaluate more specific changes linked to the functioning of roots (see Nakai et al 2009;Li et al 2011). The second method monitors root system recovery using minirhizotrons, which are transparent plexiglass tubes inserted into the soil to provide a snapshot view of roots growing past an angled tube.…”

100-N Area Strontium-90 Treatability Demonstration Project: Phytoextraction Along the 100-N Columbia River Riparian Zone ? Field Treatability Study

“…Li et al (2006) reported that partial flooding (intermittent) enhances root aerenchyma formation while reducing the root to shoot ratio while drought has the opposite effect in black willow. Nakai et al (2009) showed significant differences such as increased stem xylem vessel diameter and resistance to xylem cavitation with periodic water stress (flooding and drought) in various willow clones. These show a high degree of plasticity on the part of willows to respond to wide variations of water availability in their environment.…”