Arboriculture & Urban Forestry 38(1): January 2012 HydES-treated red maples (which averaged -1.47 MPa for both PPS- and BRS-grown seedlings) was higher (less negative) than it was in droughted, EcoS-treated seedlings (which aver- aged -2.14 MPa across both production types) (Table 4). And, while seedlings of both species had higher (less negative) wa- ter potentials when grown in humectant-treated substrate, only those grown in HydES-treated media were significantly higher than the untreated controls (Table 4). In comparing xylem water potential measurements between species (red maple versus river birch) and between production types (PPS versus BRS maples), no significant treatment differences were observed (Table 3). From the results of these studies with HydES and EcoS, the Xylem Water Potential Based on the leaf gas exchange measurements reported, it was not unexpected that xylem water potential (Ψx ) in droughted, 11 Ciardi, J.A., C.S. Vavrina, and M.D. Orzolek. 1998. Evaluation of tomato transplant production methods for improving establishment rates. HortScience 33:229–232. Ferrini F., and F.P. Nicese. 2002. Response of English oak (Quercus robur L.) trees to biostimulants application in the urban environment. Journal of Arboriculture 28:70–75. Fraser, G.A., and G.C. Percival. 2003. The influence of biostimulants on growth and vitality of three urban tree species following transplant- ing. Arboricultural Journal 27:43–57. Hanson, R.P. 1999. Solution for plant root watering. United States patent 5,865,869. Hasse D.L., and R. Rose. 1993. Soil moisture stress induces transplant shock in stored and unstored 2+0 Douglas-fir seedlings of varying root volumes. Forest Science 39:275–294. following conclusions were drawn: 1) the moisture content of humectant-treated substrate was consistently higher throughout a progressive drying cycle than it was in untreated substrate; 2) foliar growth was unaffected by humectant treatment, but fine root growth was less extensive for seedlings grown in humectant- treated substrate, a finding attributed to more available soil mois- ture in the treated media; 3) plant-water stress was lower in hu- mectant-treated maples than it was in untreated (control) plants, and physiological activity (fluorescence and net photosynthesis) was consistently higher in both HydES-treated and untreated seedlings than it was in EcoS-treated plants; 4) for the species in- cluded in these studies, root growth of humectant-treated red ma- ple (fine-rooted) outperformed root growth of humectant-treated yellow poplar (coarse-rooted); 5) between the two production types, root growth of bare-root seedlings was generally greater than the root growth of peat plug seedlings of the same species. Acknowledgments. This project was car- ried out with financial support from the TREE Fund’s Hyland Johns research grant program (06-HJ-06). Jupp, A.P., and E.I. Newman. 1987. Morphological and anatomical effects of severe drought on roots of Lolium perenne L. New Phytolo- gist 105:393–402. Kramer, P.J., and J.S. Boyer. 1995. Water Relations of Plants and Soils. Academic Press, New York City, New York, U.S. Larson, P.R., and J.G. Isebrands. 1971. The plastochron index as applied to developmental studies of cottonwood. Canadian Journal of Forest Research 1:1–11. Marzouk, H., P. Baur, and J. Schonherr. 1998. Relative solubilities of bifenox and 1-naphthylacetic acid (NAA) in plant cuticles and in selected pure or aqueous glycol additives. Pesticide Science 53:278–284. Matsumoto, S., S. Suzuki, H. Tomita, and T. Shigematsu. 1992. Effects of humectants on pesticide uptake through plant leaf surfaces, pp. 261– 271. In: C.L. Foy (Ed.). Adjuvants for Agrichemicals. CRC Press, Boca Raton, Florida, U.S. Maxwell, K., and G.N. Johnson. 2000. Chlorophyll fluorescence - a practical guide. Journal of Experimental Botany 51:659–668. Monterusso, M.A., D.B. Rowe, and C.L. Rugh. 2005. Establishment and persistence of Sedum spp. and native taxa for green roof applications. HortScience 40:391–396. Ramsey, R.J.L., G.R. Stephenson, and J.C. Hall. 2005. A review of the effects of humidity, humectants and surfactant composition on the absorption and efficacy of highly water-soluble herbicides. Pesticide Biochemistry and Physiology 82:162–175. LITERATURE CITED Abbey, T., and T. Rathier. 2005. Effects of mycorrhizal fungi, biostimu- lants and water absorbing polymers on the growth and survival of four landscape plant species. Journal of Environmental Horticulture 23:108–111. Arena, M.J. 2001. Evaluation of Hydretain 2X on container grown trees. Clemson Univ. Extension Service. Barrett, J. 1991. New media-applied humectant can improve plants’ drought resistance. Greenhouse Manager 10:123. Berlyn, G.P., and S. Sivaramakrishnan. 1996. The use of organic biostim- ulants to reduce fertilizer use, increase stress resistance, and promote growth, pp. 106–112. In: T.D. Landis and D.B. South (Eds.). National Proceedings, 1996 Forest and Conservation Nursery Association Meeting. Gen. Tech. Rep. PNW-GTR-389. Dept. of Agriculture, For- est Service, Pacific Northwest Research Station, Portland, OR. Bolhar-Nordenkampf, H.R., S.P. Long, N.R. Baker, G. Oquist, U. Schreiber, and E.G. Lechner. 1989. Chlorophyll fluorescence as a probe of the photosynthetic competence of leaves in the field: A review of current instrumentation. Functional Ecology 3:497–514. Ramsey, R.J.L., G.R. Stephenson, and J.C. Hull. 2006. Effects of humec- tants on the uptake and efficiency of glufosinate in wild oat (Avena fatua) plants and isolated cuticles under dry conditions. Weed Sci- ence 54:205–211. Richardson, A.D., M. Aikens, G.P. Berlyn, and P. Marshall. 2004. Drought stress and paper birch (Betula papyrifera) seedlings: Effects of an organic biostimulant on plant health and stress tolerance, and detection of stress effects with instrument-based, noninvasive meth- ods. Journal of Arboriculture 30:52–60. Roberts, B.R. 2006. Compost-containing substrates and their effect on post-transplant growth of containerized tree seedlings. Arboriculture & Urban Forestry 32:289–296. Roberts, B.R., and R.S. Linder. 2010. Humectants as post-plant soil amendments: Effects on the wilting cycle of drought-stressed, contain- er-grown tree seedlings. Arboriculture & Urban Forestry 36:275–280. Ruan, X., D. Li, Q. Xu, H. Mao, G. Li, Y. Gong, T. Kuang, and N. Zhao. 2002. Phosphatidylcholine-induced reactivation of photosystem II membranes penetrated with Triton X-100. Journal of Photochemistry and Photobiology B: Biology 87:109–115. Sagaram, M., and J.K. Burns. 2009. Leaf chlorophyll fluorescence pa- rameters and Huanglongbing. Journal of the American Society for Horticultural Science 134:194–201. ©2012 International Society of Arboriculture
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