150 Sax and Bassuk: Tree Growth and Gas Exchange Response of Ficus benjamina 'Evergreen' trees growing in unamended soils with lower AWHC. Leaf water potential declined at similar rates for trees in both soil treatments, indicating that even though S&D soils held more accumulative water, this did not buffer the effect of soil water deficit for S&D trees. It is difficult to determine the exact mechanism that caused S&D trees to respond equally to water deficit conditions in terms of gas exchange as unamended trees, but the differences in leaf area and plant growth between treatments is a likely explanatory factor. Future studies could be conducted to determine if plants of the same size and leaf area resist drought effects in soils with increased AWHC. This could be explored by conducting a similar experiment, but implementing a water deficit treatment after a signifi- cantly shorter plant establishment period or by prun- ing trees to have equal number of leaves and woody biomass. If the trees were a similar size and leaf area during water deficit, then the increased accumulative water held in S&D soils might lead to improved gas exchange rates for trees. Even though trees growing in S&D soils did not have an increased ability to buf- fer the effects of water deficit, the enhanced growth showed promising results for tree development in restored urbanized soils. Further investigation is required to test the S&D method outside of the controlled greenhouse and growth chamber environment. Limitations to this study include the collection of soils directly from the landscape instead of creating a uniform experimental S&D soil. As a result, the soils data presented here represents field conditions at the time of sampling and should be considered as observational. Undis- turbed soil cores were used in this study as a means of collecting samples in as close to field conditions as possible. While effective at maintaining soil struc- ture, this method also created an artificial soil envi- ronment including the negative space between core walls and the soil. Likewise, due to the size and archi- tecture of the PVC tubes, roots were confined to a maximum soil depth of 15 cm (5.9 in). As a result, growing trees in these undisturbed cores limits infer- ence for direct comparison to trees growing under field conditions. Future studies can add to this body of knowledge by either creating S&D conditions in containers for use in a greenhouse and growth cham- ber study, or by creating urbanized soils and conduct- ing S&D restoration under field conditions. CONCLUSION The S&D technique of soil remediation improved biomass growth on Ficus benjamina ‘Evergreen’ in remediated urban soils grown in greenhouse and growth chamber conditions. The tree growth biomass indicators were positively correlated with decreased soil bulk density and increased organic matter. Increases in soil’s accumulative water holding capac- ity did not significantly resist the effects of water defi- cit on plants growing in S&D remediated soil as indicated by gas exchange measurements and leaf water potentials. Gas exchange measures, transpira- tion, and stomatal conductance displayed similar water deficit response patterns for Ficus benjamina ‘Evergreen’ in both soil treatments. Increased plant size and leaf area of trees grown in S&D soils likely explain this observation with larger plants using soil water at similar rates to smaller trees in unamended soils. Results suggest that consideration of both total soil volume and soil quality (bulk density, OM, AWHC) are important to achieve desired tree growth in confined spaces. For trees growing in confined spaces, the use of low bulk density soils could result in larger trees with greater leaf surface area. This study adds to the developing body of knowledge that promotes compost as an urban soil amendment and method to remediate compaction. The S&D tech- nique provides a tool for land managers that can be easily implemented using available technology and locally and sustainably sourced amendment material. LITERATURE CITED Alliaume, F., W. Rossing, M. García, K. Giller, and S. Dogliotti. 2013. Changes in Soil Quality and Plant Available Water Capacity Following Systems Re-design on Commercial Vegetable Farms. Euro- pean Journal of Agronomy 46: 10-19. Alameda, D., and R. Villar. 2012. Linking root traits to plant physiology and growth in Fraxinus angus- tifolia Vahl. seedlings under soil compaction con- ditions. Environmental and Experimental Botany 79: 49-57. Améglio, T., P. Archer, M. Cohen, C. Valancogne, F.A. Daudet, S. Dayau, and P. Cruiziat. 1999. Sig- nificance and limits in the use of predawn leaf water potential for tree irrigation. Plant and Soil 207(2): 155-167. Arndt, S., S. Clifford, W. Wanek, H. Jones, and M. Popp. 2001. Physiological and morphological ©2019 International Society of Arboriculture
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