Abstract
As the demand for drought hardy tree seedlings rises alongside global temperatures, there is a need to optimize nursery drought preconditioning methods to improve field performance of planted seedlings. This perspective article advocates for a more holistic approach to drought preconditioning research that considers the moderating role of plant developmental stage on the effects of drought preconditioning. We identify discrepancies in past studies of root growth potential (RGP) responses to drought preconditioning and highlight studies that suggest such discrepancies may result from inconsistencies among studies in the timing of drought preconditioning implementation. We then illustrate our perspective by presenting original research from an aeroponic RGP trial of 1st-year western larch (Larix occidentalis Nutt.) seedlings exposed to three soil moisture contents for 6months. We evaluated whether drought preconditioning could be used to increase the ratio of root: foliar tissue mass or enhance seedling physiological vigor during a subsequent growth period. Drought preconditioning was found to increase the ratio of root: foliar tissue mass and enhance seedling physiological vigor. Specifically, soil moisture content related negatively with new root biomass, positively with new foliar biomass, and negatively with the length and number of new roots (p<0.001). Meanwhile, the mass of lateral root production following drought preconditioning, but prior to aeroponic growth, correlated weakly to the mass, count, and length of new roots produced during aeroponic growth. We propose that evaluating the importance of the timing of drought preconditioning treatments constitutes an important research frontier in plant science.
Highlights
Aridity in western North America threatens the survival of planted and natural tree seedlings (Vilagrosa et al, 2003; Minott and Kolb, 2020)
Long-Duration Drought Preconditioning of L. occidentalis perspective article, we advocate for consistent, holistic approaches for conducting and evaluating the effects of drought preconditioning on tree seedlings, and we present results from a root growth potential (RGP) trial following drought preconditioning of western larch (Larix occidentalis Nutt.) seedlings
The first research question was supported in that water limitation during long-term drought preconditioning increased the ratio of new root tissue to new foliar tissue mass (χ2 = 184.13, p = 2.2e−16; Table 1A; Figure 1A)
Summary
Aridity in western North America threatens the survival of planted and natural tree seedlings (Vilagrosa et al, 2003; Minott and Kolb, 2020). Assessments of RGP (a measure of plant physiological vigor that evaluates new root production after a short period of growth under optimal growth conditions in a controlled environment; Folk and Grossnickle, 1997) following drought preconditioning rapidly reveals whether water limitation treatments promote desirable belowground plant traits (Villar-Salvador et al, 2013). In a unique multispecies comparison of three conifer species exposed to a treatment of varying water limitation intensities initiated after approximately 5 months after seed sowing and lasting 2.5 months, the RGP of white spruce [Picea glauca (Moench) Voss] increased with water limitation, but RGP of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and lodgepole pine (Pinus contorta Dougl.) was not affected (Driessche, 1992). In a study of Pinus pinea L. exposed to 3 months of water limitation using three watering levels initiated 4 months after seed sowing, Villar-Salvador et al (2013) found that RGP decreased with the intensity of water limitation
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