Arboriculture & Urban Forestry 38(4): July 2012 Arboriculture & Urban Forestry 2012. 38(4): 151–159 151 Characterization of Physical, Gaseous, and Hydrologic Properties of Compacted Subsoil and its Effects on Growth and Transpiration of Two Maples Grown Under Greenhouse Conditions Barbara A. Fair, James D. Metzger, and James Vent Abstract. City foresters and horticulturists often seek trees suited for urban conditions. Two maples often used were selected to assess response to compacted soil: ‘Armstrong’ Freeman maple and ‘Brandywine’ red maple. Soil physical parameters were assessed to determine effects of high density on movement of gas and water. Rigid-walled lysimeters constructed from polyvinyl chloride pipe were filled with clay subsoil compacted to 1.64 g·cm-3 and 1.78 g·cm-3 (MODEARTE-density) soil were 5–18 times higher than atmospheric concentrations, while O2 (HIGH-density). Compaction decreased total porosity and saturated hydraulic conductivity. In addition, CO2 played no real role in plant growth response to compaction. Trees growing in MODERATE-density soils had higher transpiration rates than trees growing in HIGH-density soils, although differences decreased over time. A high soil density did not affect caliper growth, but did reduce annual height growth, leaf area and dry weight, and stem dry weight, but responses varied over time and between species. Root dry weight and volume were unaffected by compaction, but root:shoot ratio was higher for trees growing in HIGH-density soils, which is expected as aboveground biomass is typically reduced by soil compaction. Key Words. Acer × freemanii ‘Armstrong’; Acer rubrum ‘Brandywine’; Bulk Density; Lysimeter; Saturated Hydraulic Conductivity; Soil Compac- tion; Transpiration; Urban Forestry. concentrations were similar to atmospheric levels despite density. O2 concentrations in compacted concentration Research consistently indicates soil compaction and aboveground and belowground woody plant biomass are negatively correlated, but plant response varies depending on intensity of compaction, soil water content, soil texture, and species (Alberty et al. 1984; Pan and Bassuk 1985; Day et al. 2000). Alberty et al. (1984) found no decrease in shoot and root dry weights due to high-bulk- density sandy loam and loam soils for red-osier dogwood (Cornus sericea L.); however, there was significant reduction in growth of early forsythia (Forsythia ovata Nakai) in the same soils. Pan and Bassuk (1985) found root growth of tree-of-heaven (Ailanthus altissima Swingle) was restricted more in a sandy loam soil with a bulk density of 1.64 g·cm-3 than in mason sand (very fine aggre- gates) with a bulk density of 1.67 g·cm-3. Researchers have reported aboveground growth was affected more than root growth (Alber- ty et al. 1984; Masle and Passioura 1987; Cook et al. 1996; Mon- tagu et al. 2001), although higher soil water content may alleviate some effects of compaction (Buttery et al. 1998; Day et al. 2000). Urban soils pose many obstacles for sustained tree growth, including compaction, poor drainage, and poor physical proper- ties. Accordingly, city foresters and landscape architects often select a bottomland species, for example sycamore (Platanus occidentalis L.), because of its demonstrated durability in city sites (Arnold 1980). Bottomland species may be successful be- cause they are adapted to prolonged wet conditions, or they may centrations of ethylene. High ethylene can lead to the produc- tion of “ethylene” roots, which are short, thick and considerably branched (Kays et al. 1974; Morgan et al. 1993). Arborists have been taught that insufficient O2 in compacted soil is the primary restraint on tree growth. This may occur when soil is wet, but the relationship between oxygen and compaction is more com- plex. Recent studies indicate O2 concentration is not limited; ylene content, physical properties, and the differential growth and transpiration of Acer × freemanii ‘Armstrong’ and Acer rubrum ‘Brandywine’ growing in these soils. To determine soil physi- cal property changes, researchers measured saturated hydrau- lic conductivity, aeration, and soil gas concentrations (particu- larly O2 rather, diffusion rates are weakly correlated with high densities (Boone and Veen 1994; Day et al. 1995; Murphy et al. 2000). Therefore, the following research was conducted to compare moderately and highly compacted soil with respect to O2 ) that may change in response to increased soil density. and eth- be adapted to fluctuating conditions of wet and dry. Day et al. (2000) found silver maple (Acer saccharinum L.) was better able to penetrate wet high-density soils and performed better than flowering dogwood (Cornus florida L.). Flowering dogwood, an upland species, was not tolerant of wet or compacted soil condi- tions. Jackson (1997) found that in a high-density soil with low levels of O2 and poor drainage, some species produced high con- ©2012 International Society of Arboriculture
July 2012
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