Photosynthetic Characteristics of Five Hardwood Species in a Mixed Stand’

In 1998, photosyWhesis (Pn) was measunxl on ch&barfc oak, green ash. swemp chestnut oak, swatgum, and wa@r hickory in a mixed stand established in Febfuaty 1994. Baclcld on the apparent quantum yield Obtained from light response u~rves. cherrybark oak had the lowest Pn in August whetus crwsctbgum. 9men esh and w&r hickory we18 squally act&a in Pn. Daily August Pn of swaa@um and grean ash pa&cad be&m 10 am and dacmasad sharply thamaftar. Be~3and5pm,~umandgresnaahPnMm,about40~oftheir~Pn.DailySeptembsrPndidnot show such sharp decreesin the afternoon for any species. Swset9um hsd lhe hbhest chlorophyll level and the laVJO8t specific laaf wight in August. The ability of cherrybark oak and swamp chastnut oak to maintain laaves with adequate chlorophyll contents contributed to their act&e Pn in mi&December. INTRODUCTlQN Multiple species coniferous stands are generally unsuccessful tecause a tingle species usually becomes dominant in ths stand due to differences in seedling growth rates. Stands with multiple hardwood species characteristically coexist in the forest with species distributions ranging from random to clumped. These mixed species stands can be invaluable for providing forest products and for providing food for wildlife. One wmmon and central aspect of tr88 physiology is that survival and growth of transplanted seedling stocks are dependent upon the availability and metabolism of sucrose (Sung and others lQQ4,1995, IQQSa, b). For most plants, the product of photosynthesis (Pn) is translocated in the form of sucrose to all carbon sinks such as stems and roots for growth and storage (Shimya and others 1962). We report the photosynthetic characteristics of fiv8 hardwood species in a mixed stand 4 years after establishment. Details on the establishment of this five-hardwood species study and results of sun&al and growth of individual species are reported by Kormanik and other (this proceedings). MATERIAL8 AND ME77lODS All seedlings in this study w8r8 grown at the Georgia Forestry Commission’s Flint River Nursery (Montezuma, GA) using a single hardwood nursery protocol developed by Kormanik and others (1994). Prior to sowing, soil levels of Ca, K, P, Mg, Cu, Zn, and 6 w8r8 adjusted to 500,80,80, 50.2,8, and 1.2 ppm, respectMy. Nitrogen was applied as NH,NO, at an annual rate equivalent to 1322 kg per ha. Seedling bed density for all species was 54-57 per n?. In February 1994, two hundred 1-O seedlings from 88ch of the five hardwood specitierrybark oak (CBO, Quercus p8gOda Raf.), green ash (GA, Fmxinus pennsyfvanba Marsh.), swamp chestnut oak (SCO, 9. michauxli Nutt.), sweetgum (SG, Uquidemb8f sfymu7lua L.), and water hickory (WH, C&rye aqua&e Nutt.)--were selected from the top 50 percent of the crops based on fin&order latsral root number, root collar diameter, and height (Kormanik and others, this proceedings). These seedlings w8r8 randomly planted at a 3.3 x 3.3 m spadng on a cleared 2.5ha site at the National Environmental Research Park (Savannah River Natural Resource Management and R8S88Kh htbte, New Ellenton, SC). Soil series on this sit8 is mainly Rembert sandy loam with Homsv&le fine sandy loam, N8eS8S loamy sand, Norfolk loamy sand, Ailey sand, and Albany loamy sand in some areas. Fertilization and vegetation control on this stand is reported in detail by Kormanik and others (this proceedings). In 1998, three areas within the stand w8r8 systematically Selected so that f&8 species w8r8 located within a radius of IO m of each other. These areas w8r8 at least 30 m apart. One tree from each spedes wes tagged within each ama. In August 1998, Pn light response cu1v8s ~r8 determined from 880h tagged free in th8 thr88 areas Using a portable open-system infra+8d gas analyzer (LICor 6400) equipped with an internal red-blue light source and a CO, mixer. M8asur8ments w8r8 mad8 between 8 am and 11 am (Eastern Standard Time) on one fully expanded, attached &if from th8 outside canopy of 88Ch t@g8d tr88. The same leaf was measured ow a tinge of different levels of photosynthetic photon flux density (PPFD, 400 700 nm) levels. During Pn measurements, selected PPFD levels w8r8 us8d randomly with a 3to Smin adjustment period between measurements. The reference chamber CO2 Was set at 350 ppm for all measurements. lndivkfual values of Pn obtained fmm three CBO, three SCO, two GA, two SG, and two WH were pooled to construct a light response curve for each species using the mod81 of Long and HBllgren (1993):