Spatial and temporal patterns of root distribution in developing stands of four woody crop species grown with drip irrigation and fertilization |
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Authors: | Mark Coleman |
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Institution: | (1) Southern Research Station, USDA Forest Service, Savannah River, 241 Gateway Drive, Aiken, SC 29803, USA |
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Abstract: | In forest trees, roots mediate such significant carbon fluxes as primary production and soil CO2 efflux. Despite the central role of roots in these critical processes, information on root distribution during stand establishment
is limited, yet must be described to accurately predict how various forest types, which are growing with a range of resource
limitations, might respond to environmental change. This study reports root length density and biomass development in young
stands of eastern cottonwood (Populus deltoidies Bartr.) and American sycamore (Platanus occidentalis L.) that have narrow, high resource site requirements, and compares them with sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.), which have more robust site requirements. Fine roots (<1 mm), medium roots (1 to 5 mm) and coarse roots (>5 mm) were
sampled to determine spatial distribution in response to fertilizer and irrigation treatments delivered through drip irrigation
tubes. Root length density and biomass were predominately controlled by stand development, depth and proximity to drip tubes.
After accounting for this spatial and temporal variation, there was a significant increase in RLD with fertilization and irrigation
for all genotypes. The response to fertilization was greater than that of irrigation. Both fine and coarse roots responded
positively to resources delivered through the drip tube, indicating a whole-root-system response to resource enrichment and
not just a feeder root response. The plastic response to drip tube water and nutrient enrichment demonstrate the capability
of root systems to respond to supply heterogeneity by increasing acquisition surface. Fine-root biomass, root density and
specific root length were greater for broadleaved species than pine. Roots of all genotypes explored the rooting volume within
2 years, but this occurred faster and to higher root length densities in broadleaved species, indicating they had greater
initial opportunity for resource acquisition than pine. Sweetgum’s root characteristics and its response to resource availability
were similar to the other broadleaved species, despite its functional resemblance to pine regarding robust site requirements.
It was concluded that genotypes, irrigation and fertilization significantly influenced tree root system development, which
varied spatially in response to resource-supply heterogeneity created by drip tubes. Knowledge of spatial and temporal patterns
of root distribution in these stands will be used to interpret nutrient acquisition and soil respiration measurements.
The US Government has the right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.
Mention of a commercial or proprietary product does not constitute endorsement or recommendation by the USDA Forest Service. |
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Keywords: | Functional groups Root length density Soil heterogeneity Stand development Vertical root distribution Woody crops |
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