Abstract
There is little direct evidence for effects of soil heterogeneity and root plasticity on the competitive interactions among plants. In this study, we experimentally examined the impacts of temporal nutrient heterogeneity on root growth and interactions between two plant species with very different rooting strategies: Liquidambar styraciflua (sweet gum), which shows high root plasticity in response to soil nutrient heterogeneity, and Pinus taeda (loblolly pine), a species with less plastic roots. Seedlings of the two species were grown in sandboxes in inter‐ and intraspecific combinations. Nutrients were applied in a patch either in a stable (slow‐release) or in a variable (pulse) manner. Plant aboveground biomass, fine root mass, root allocation between nutrient patch and outside the patch, and root vertical distribution were measured. L. styraciflua grew more aboveground (40% and 27% in stable and variable nutrient treatment, respectively) and fine roots (41% and 8% in stable and variable nutrient treatment, respectively) when competing with P. taeda than when competing with a conspecific individual, but the growth of P. taeda was not changed by competition from L. styraciflua. Temporal variation in patch nutrient level had little effect on the species’ competitive interactions. The more flexible L. styraciflua changed its vertical distribution of fine roots in response to competition from P. taeda, growing more roots in deeper soil layers compared to its roots in conspecific competition, leading to niche differentiation between the species, while the fine root distribution of P. taeda remained unchanged across all treatments. Synthesis. L. styraciflua showed greater flexibility in root growth by changing its root vertical distribution and occupying space of not occupied by P. taeda. This flexibility gave L. styraciflua an advantage in interspecific competition.
Highlights
Heterogeneous distribution of soil resources at different spatiotemporal scales is ubiquitous in nature (Farley & Fitter, 1999; Fitter, 1994; Jackson & Caldwell, 1993; Ryel, Caldwell, & Manwaring, 1996)
Our results indicate that L. styraciflua performed better in competition with P. taeda, with the aboveground biomass of L. styraciflua increased by 42% and 27% in interspecific competition in the stable and variable nutrient treatments, respectively, compared to that in intraspecific competition (Figure 2a)
Our results showed that L. styraciflua had an advantage in terms of aboveground biomass when competing with P. taeda, possibly through the former’s higher root mass, which could give the species more access to nutrients in the soil
Summary
Heterogeneous distribution of soil resources (i.e., nutrient elements and water) at different spatiotemporal scales is ubiquitous in nature (Farley & Fitter, 1999; Fitter, 1994; Jackson & Caldwell, 1993; Ryel, Caldwell, & Manwaring, 1996). Plants often respond to soil resource heterogeneity through plasticity in root growth This plasticity consists of morphological changes in root architecture and selective placement. Studies on the effects of soil heterogeneity on root morphology have shown that some species exhibit much stronger selective root placement than other species. The former are called “precise foragers” and the latter, which grow roots less selectively within their rooting zones, are called “scalers,” and they represent two alternative strategies for root foraging (Campbell, Grime, & Mackey, 1991). Studies have shown that dominant species usually employ a low- precision but high-scale foraging strategy to maximize root foraging area, whereas subordinate species show greater precision (Mommer et al, 2011; Rajaniemi, 2007; Ravenek et al, 2016)
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