Differences in vertical root distributions are often assumed to create resource uptake trade‐offs that determine plant growth and coexistence. Yet, most plant roots are in shallow soils, and data linking root distributions with resource uptake and plant abundances remain elusive. Here we used a tracer experiment to describe the vertical distribution of absorptive roots of dominant species in a shrub–steppe ecosystem. To describe how these different rooting distributions affected water uptake in wet and dry soils across a growing season, we used a soil water movement model. Root traits were then correlated with plant landscape abundances. Deeper root distributions extracted more soil water, had larger unique hydrological niches and were more abundant on the landscape. Though most (>50%) root biomass and tracer uptake occurred in shallow soils (0–32 cm), the depth of 50% of tracer uptake varied from 11 to 32 cm across species and species with deeper rooting distributions were more abundant on the landscape (
Trees partition biomass in response to resource limitation and physiological activity. It is presumed that these strategies evolved to optimize some measure of fitness. If the optimization criterion can be specified, then allometry can be modeled from first principles without prescribed parameterization. We present the Tree Hydraulics and Optimal Resource Partitioning (THORP) model, which optimizes allometry by estimating allocation fractions to organs as proportional to their ratio of marginal gain to marginal cost, where gain is net canopy photosynthesis rate, and costs are senescence rates. Root total biomass and profile shape are predicted simultaneously by a unified optimization. Optimal partitioning is solved by a numerically efficient analytical solution. THORP’s predictions agree with reported tree biomass partitioning in response to size, water limitations, elevated CO2and pruning. Roots were sensitive to soil moisture profiles and grew down to the groundwater table when present. Groundwater buffered against water stress regardless of meteorology, stabilizing allometry and root profiles as deep as Much of plant allometry can be explained by hydraulic considerations. However, nutrient limitations cannot be fully ignored. Rooting mass and profiles were synchronized with hydrological conditions and groundwater even at considerable depths, illustrating that the below ground shapes whole‐tree allometry.
- NSF-PAR ID:
- 10385401
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 230
- Issue:
- 6
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 2226-2245
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract R 2 = .95). The water flow model revealed that deeper rooting distributions should extract more soil water (i.e. a range of 60–113 mm of soil water) because shallow roots were often in dry soils. These potential water uptake values were tightly correlated with species’ abundances on the landscape (R 2 = .90). Finally, each species’ rooting distribution demonstrated a depth and time at which it could extract more soil water than any other rooting distribution, and the size of these unique hydrological niches indices was also well correlated with species’ abundances (R 2 = .89).Synthesis . Our results demonstrate not only a correlation between root distributions and species abundance, but also the mechanism through which differences in rooting distributions can determine resource uptake and niche partitioning, even when most roots are found in shallow soils. -
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