Abstract
(1) Background: Plant roots respond to nutrients through root architecture that is regulated by hormones. Strong inter-specific variation in root architecture has been well documented, but physiological mechanisms that may control the variation have not. (2) Methods: We examined correlations between root architecture and hormones to seek clues on mechanisms behind root foraging behavior. In the green house at Beijing Normal University, hydroponic culture experiments were used to examine the root responses of four species—Callistephus chinensis, Solidago canadensis, Ailanthus altissima, Oryza sativa—to two nitrogen types (NO3− or NH4+), three nitrogen concentrations (low, medium, and high concentrations of 0.2, 1, and 18 mM, respectively) and two ways of nitrogen application (stable vs. variable). The plants were harvested after 36 days to measure root mass, 1st order root length, seminal root length for O. sativa, density of the 1st order laterals, seminal root number for O. sativa, the inter-node length of the 1st order laterals, and root hormone contents of indole-3-acetic acid, abscisic acid, and cytokinins (zeatin + zeatinriboside). (3) Results: Species differed significantly in their root architecture responses to nitrogen treatments. They also differed significantly in hormone responses to the nitrogen treatments. Additionally, the correlations between root architecture and hormone responses were quite variable across the species. Each hormone had highly species-specific relationships with root responses. (4) Conclusions: Our finding implies that a particular root foraging behavior is probably not controlled by the same biochemical pathway in all species.
Highlights
Soil resources are heterogeneously distributed in space and time at various scales, and with differences in concentration that individual plants sense and respond to [1,2]
We examined the relationships between and among patterns of nutrient supply, root hormones, and Root architecture (RA) features in four plant species with various ecological strategies: Callistephus chinensis (Chinese aster), an annual/biannual herb, Ailanthus altissima (Tree of Heaven), a deciduous hardwood tree, Oryza sativa, a monocot gramineous species, and Solidago canadensis (Canadian goldenrod), a perennial herb
Seedlings were transplanted into water tanks for nitrogen treatments when they grew to the following sizes: six leaves present for C. chinensis, eight leaves for S. canadensis, 10 cm tall for A. altissima, and presence of second leaf stage for O. sativa
Summary
Soil resources are heterogeneously distributed in space and time at various scales, and with differences in concentration that individual plants sense and respond to [1,2]. Root foraging plasticity has been defined as phenotypical changes of roots under the influences of soil variation [6,7,8], and the changes have been classified as morphological, physiological, demographic, and mycorrhizal plasticity [9,10,11]. Through these types of plasticity, plants are able to efficiently acquire resources in heterogeneous resource environments [5,12]. Most studies of root foraging behavior have focused on morphological plasticity, i.e., the changes in root proliferation and architecture features in resource patchy soils [11,13].
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