1121 HORTSCIENCE V OL. 39(5) AUGUST 2004 Chlorophyll Fluorescence and Needle Chlorophyll Concentration of Fir (Abies sp.) Seedlings in Response to pH B.M. Cregg Department of Horticulture, Michigan State University, East Lansing, MI 48824, and Department of Forestry, Michigan State University, East Lansing, MI 48824 M.W. Duck, C.M. Rios, and D.B. Rowe Department of Horticulture, Michigan State University, East Lansing, MI 48824 M.R. Koelling Department of Forestry, Michigan State University, East Lansing, MI 48824 Additional index words. conifers, chlorosis, liming, Christmas trees Abstract. We assessed variable chlorophyll fluorescence (F v /F m ) and needle chlorophyll concentration of seedlings of Maccedonia fir (Abies borisii regis Mattfeld), subalpine fir [A. lasiocarpa (Hooker) Nuttall] , Sakhalin fir [A. sachalinensis (Schmidt) Mast.], Siberian fir [A. sibirica (Lebed.)], and Veitch fir (A. veitchii Lindl.) grown under varying soil me- dia pH. Soil media pH was modified using liquid flowable dolomitic limestone, resulting in five pH levels (3.4, 4.0, 5.4, 6.0, and 6.8). Increasing media pH significantly reduced F v /F m and needle chlorophyll concentration in all of the species tested. The effect of pH on photochemistry was due to depressed nutrient uptake of P, Mn, B, and Cu. Because photosynthetic quantum yield may be related to deficiencies of several elements affected by pH, F v /F m may serve as a criterion to select for improved pH tolerance. Among the species examined, A. veitchii and A. lasiocarpa were most tolerant of increased pH based on F v /F m and needle chlorophyll concentration. HORTSCIENCE 39(5):1121–1125. 2004. Received for publication 16 Sept. 2002. Accepted for publication 5 June 2003. Evergreen conifers are an important com- ponent of landscapes in the upper Midwest. Conifers fulfill an important design function by providing year-round color, form, and texture in landscapes as well as providing cover for wildlife. However, horticulturists are recognizing that many of the principal conifers planted in the central United States are becoming overplanted and suffer from an increasing number of pest problems. For example, Scots pine (Pinus sylvestris L.), a mainstay of landscape and Christmas tree industries, is affected by at least 40 different insects and diseases (McCullough, personal communication). Eastern white pine (Pinus strobus L.), Austrian pine (Pinus nigra Ar- nold), and Douglas-fir [Pseudotsuga menziesii (Mirbel) Franco] likewise are often overplanted and are hosts to a variety of pests (Dix et al., 1986; Riffle and Peterson, 1986). True firs (Abies sp. Miller) include a number of species that may add diversity to the conifers available for landscape planting. The genus Abies includes 50 to 60 species of trees native to North and Central America, Europe, Asia, and North Africa (Farjon and Rushforth, 1989; Liu, 1971). Most species of true firs occur in cool, moist habitats in northern latitudes or at high elevation in lower latitudes. Several firs such as grand fir [Abies grandis (Douglas ex D. Don) Lindley], pacific silver fir (Abies amabilis Douglas ex J. Forbes), and noble fir (Abies procera Rehder) are large trees that are important commercial forest species in the Pacific Northwest. However, true firs have a number of characteristics that make them excellent ornamentals and Christmas trees. Firs grow straight and have a highly symmetrical growth habit. Firs also have a wide range of needle colors and lengths that can add year-round interest and variety to the landscape. While many firs are fast growers in their native environment, most are slower growing off-site. In the upper Midwest, the use of true firs in landscapes is limited by their fairly exacting site requirements. In general, most Abies grow best on sites with good drainage, adequate moisture, and low soil pH. For example, Fraser fir [Abies fraseri (Pursh) Poiret] is native to mountainous sites with extremely acid soils; the A horizon pH is ≈3.5, and the B horizon pH 3.8 to 4.2 (Beck 1990). Concolor fir [A. concolor (Gord. & Glen.) Hildebr.] and Canaan fir, in contrast, may grow on sites with considerably higher pH (Brown, 2000; Laacke, 1990), indicating that Abies sp. vary in their pH tolerance. However, most information on the pH tolerance of firs is based on observational studies of soils in forest stands. Little direct comparative data on the relative pH tolerance of firs have been reported. Increasing soil pH may induce chlorosis in plants due to reduced uptake of one or more nutrients, particularly phosphorus, manganese, boron, and copper (Lucas and Davis, 1961). All of these nutrients are involved, either directly or indirectly, in photosynthetic processes. There- fore, understanding the effect of increasing soil pH on photosynthetic function may provide an opportunity for identifying species or geno- types that are adapted to relatively alkaline conditions. The efficiency with which photo- system II captures light energy may be rapidly and nondestructively estimated as the ratio of variable to maximal chlorophyll fluorescence (F v /F m ) (Bjorkman and Demming, 1987). Because the function of the photosynthetic system is related to foliar nutrition, variable chlorophyll fluorescence may provide a rapid means to identify physiological response of plants to nutrient imbalances (Laing et al., 2000; Val et al., 1995). The objectives of the present study were to 1) compare the response of five diverse species of true firs (Abies sp.) to varying soil pH, and 2) determine the utility of chlorophyll fluorescence as a tool to quantify this response. Materials and Methods The study was conducted in a glass green- house at the Michigan State Univ. Plant Science greenhouse complex. We planted plug +2 or 2–2 seedlings of five Abies sp. (Table 1) in 8-L containers filled with a mixture of 3 sphagnum moss : 1 perlite (by volumev). The number of transplants per species varied from 20 to 35, depending on availability. Seedlings were irrigated as needed with a nutrient solution of well water (EC = 0.65 mS·cm –1 and 105, 35, and 23 mg·L –1 Ca, Mg, and S, respectively) acidified with H 2 SO 4 to a titratable alkalinity 130 mg·L –1 CaSO 3 and water-soluble fertilizer providing 125N–12P–125K–13Ca mg·L –1 plus 1.0Fe–0.5Mn–0.5Zn–0.5Cu–0.1B–0.1Mo mg·L –1 (MSU Special, Greencare Fertilizers, Chicago). Greenhouse photoperiod was ex- tended to 16 h using high-pressure sodium lamps. Greenhouse temperature was main- tained at 20 °C. Seedlings from each species were assigned Table 1. Abies species studied in this trial. Scientific Common Geographic name names origin Abies lasiocarpa (Hooker) Nuttall Subalpine fir W. North America Abies veitchii Lindl. Veitch fir, Japan: Honshu Veitch silver fir Abies sachalinensis (Schmidt) Mast. Sakhalin fir Russia (Sakhalin, S. Kuril Islands), Japan Abies sibirica Ledeb. Siberian fir Russia E. from Volga River and S of 67°40´ latitude; Turkestan; Mongolia; China Abies borisii regis Mattfeld King Boris fir, Bulgaria, N. Greece, Albania, and , Bulgarian fir, the former Yugoslavia Macedonian fir