BREEDING,CULTIVARS,ROOTSTOCKS, AND GERMPLASM RESOURCES HORTSCIENCE 41(6):1373–1376. 2006. Woolverton et al., 1984, 1989) that build up within energy-efficient buildings, often reaching concentrations of five to seven times Diurnal CO2 Assimilation Patterns that of outdoor city air (Brown, 1997; Brown et al., 1994). Over 300 volatile organic in Nine Species of CAM-Type compounds have been detected as indoor contaminants in addition to dust and inor- Succulent Plants ganic gases (American Conference of Gov- ernment and Industrial Hygienists, 1994). Sang Deok Lee and Soon Jae Kim Volatile pollutants originating from inani- Cactus Research Institute, Gyeonggi ARES, Goyang 411-809, Korea mate objects (e.g., formaldehyde from car- pet) within the dwelling are continuously Seung Il Jung and Ki-Cheol Son1 released; however, most indoor plants are Department of Environmental Science, Konkuk University, Seoul 143-701, C3 or C4 species, which do not have their Korea stomata open at night. CAM plants, in con- trast, absorb CO2 and other gases during the Stanley J. Kays night and therefore could potentially reduce Department of Horticultural Science, The University of Georgia, Athens, the ambient concentration of these com- GA 30602-7273 pounds during that period. For example, Spathiphyllum wallisii Hort. (C3) and Gym- Additional index words. indoor environment, volatile organic compounds nocalycium baldianum Speg. (CAM) have comparable CO exchange rates per unit Ô Õ 2 Abstract.CO2 assimilation rate of Crassula hybrid Himaturi , a succulent ornamental surface area during the day (C3) vs. night species with the crassulacean acid metabolism (CAM) photosynthetic pathway, was (CAM) (Son, 2004); thus, each would have affected by light intensity (50, 100, 300 mmolÁm–2Ás–1), photoperiod (16/8, 8/16 h day/ a comparable effect on repressing the buildup ° night), and temperature (30/25, 25/20 C day/night). Maximum assimilation of CO2 of CO2 and possibly other gases. The utili- occurred at 300 mmolÁm–2Ás–1 of diurnal irradiance, 16/8 h day/night photoperiod, and zation of CAM species in interiorscapes, in ° a day/night temperature of 30/25 C. Diurnal CO2 assimilation patterns of nine succulent addition to traditional C3 or C4 species, ornamental CAM species were evaluated (300 mmolÁm–2Ás–1, 35/25 °C day/night and a therefore, could more effectively improve 16/8-h day/night photoperiod) for CO2 fixation. Of the nine ornamentals, Crassula indoor air quality and the well-being of Ô Õ Himaturi had the highest and Echeveria derembergii the lowest maximum CO2 people within the environment. absorption rate (13.0 vs 2.4 mmolÁkg–1Ás–1), total nighttime (179.3 vs 13.4 mmolÁkg–1), As a result of the number and importance Á –1 and 24 h total (200.6 vs 19.0 mmol kg ) absorption. Based on the CO2 assimilation of ornamental CAM species in international patterns, the nine ornamentals were separated into two groups: 1) full CAM (Faucaria trade, their potential value in modulating tigrina, Gasteria gracilis var. minima, Haworthia cymbiformis, and Haworthia fasciata); indoor air quality, and the very limited and 2) weakly CAM (Adromischus clarifolius, Crassula hybrids ÔMoonglowÕ and amount of information currently available ÔHimaturiÕ, E. derembergii, and Haworthia retusa). on them, our objective was to assess the CO2 assimilation patterns and a cross-section of CO2 absorption characteristics of nine Of the three primary photosynthetic car- as well as many cacti and succulents, some succulent ornamentals under uniform condi- bon fixation pathways [C3,C4, and crassula- of which are important ornamental crops tions characterizing their CAM response. cean acid metabolism (CAM)], CAM species (Anderson, 2001). Considering the relatively are unique in that their stomata are closed large number of CAM species, there have Materials and Methods during the day, an adaptive advantage mini- been relatively few detailed photosynthetic mizing water loss in hot, dry environments. studies when contrasted with C3 and C4 Nine succulent CAM ornamentals were CAM plants fix carbon during the night when species. evaluated: Adromischus clavifolius Lem., their stomata are open rather than during the The pattern of CO2 assimilation in CAM Crassula hybrids ÔHimaturiÕ and ÔMoonglowÕ, day like in C3 and C4 species. Carbon dioxide species can be strongly modulated by envi- Echeveria derembergii J.A. Purpus, Fauca- is fixed through the action of phosphoenol- ronmental conditions such as light inten- ria tigrina Schwant., Gasteria gracilis Baker pyruvate carboxylase, forming oxaloacetate sity, day and night temperature, daylength var. minima, Haworthia cymbiformis (Haw.) from phosphoenolpyruvate. During the day (Brulfert et al., 1982; Grams and Thiel, 2002; Duv., Haworthia fasciata (Willd.) Haw., and when the stomata are closed, malate formed Kaplan et al., 1976a, 1976b; Lee et al., 2003a; Haworthia retusa (L.) Haw., each of which from oxaloacetate is decarboxylated and Neales and Hew, 1975; Ota et al., 1991), are popular, commercially available plants in the CO2 refixed through the reductive pen- water status, and mineral nutrition (Mattos South Korea. One-year-old, vegetatively tose phosphate cycle (Borland et al., 2000; and Lu¨ttge, 2001; Ota, 1987). Although there propagated plants grown under normal glass- Markovska, 1999; Mazen, 2000). Therefore, are differences among the species, CAM house conditions (800–1000 mmolÁm–2Ás–1, both the C3 and C4 cycles are operative and plants tended to assimilate more CO2 when irrigated two to three times/wk) were used. found within the same cells. grown under high light intensity (Kaplan Individual plants were transplanted into 11- Only 6% of higher plants are CAM et al., 1976a, 1976b), extended daylengths cm-diameter · 18-cm-tall pots containing species (i.e., 16,000) (Winter and Smith, (Gregory et al., 1954), and at a nighttime a medium of coarse sand (1–3 mm-dia) and 1996), which are distributed across five temperature range between 10–22 °C pig manure compost (1:1) and acclimatized taxonomic classes, 33 families, and 328 (Drennan and Nobel, 2000). For example, $1 mo in a controlled-environment room –2 –1 genera (Smith and Winter, 1996). Included the maximum CO2 assimilation rate in cactus maintained at 200 mmolÁm Ás diurnal irra- within these are members of the Crassulaceae was at a 16/8-h day/night (D/N) photoperiod, diance, 23–25 °C temperature, 40% to 60% 30/20 °C (D/N) temperature, and at an RH, and 16/8 h (day/night) photoperiod along irradiance of 300 mmolÁm–2Ás–1 (Lee et al., with 300 mL of top irrigation per 2 wk. Received for publication 27 Feb. 2006. Accepted 2003b). As a result of the unique morphology of for publication 24 Apr. 2006. This research was In addition to their ornamental value, the plants that made leaf chambers not funded by a grant from Konkuk University. interest in the use of CAM plants in interior- a viable option, CO2 exchange was measured 1To whom reprint requests should be addressed; scapes arises in part from their potential for using five constructed gas-tight cylindrical e-mail [email protected]. removing volatile air pollutants (Son, 2004; acrylic chambers (200 mm · 120-mm HORTSCIENCE VOL. 41(6) OCTOBER 2006 1373 diameter) designed to hold a single plant. Air (mLÁL–1), F = air flow rate (mLÁmin–1), T = tions for each species. Several million orna- was metered into the chambers at 600 temperature (°C), and g = dry weight of the mental cactus plants are sold each year as mLÁmin–1 from a cylinder containing 480 aerial plant parts (g). Rate was subsequently indoor plants in Korea. These are typically –1 –1 –1 mLÁL CO2 and exited through an exhaust converted to mmol CO2Ákg Ás . Dry weights placed on windowsills with light intensities line. The differential in CO2 concentration were determined after oven drying at 105 °C comparable to the irradiation level used. To was automatically determined using an IR for 8 h followed by 80 °C for 72 h. maximize day/night differences, the day tem- CO2 analyzer (MC-DA CO2 Analyzer Unit, The CO2 assimilation measurement sys- perature was increased to 35 °C (i.e., 35/25 Koito, Japan). Carbon dioxide assimilation tem allowed monitoring five chambers simul- °C). The maximum CO2 absorption rate, CO2 was determined for 12 minÁh–1 for each taneously (Lee et al., 2003b), four with plants absorption during the day (16 h) and night chamber using solenoid switching values and the fifth containing a control pot with (8 h) periods, and total CO2 absorption during controlled by a CO2-monitoring software media alone (i.e., above- and below-ground 24 h and the average day and night absorption system (VisiDaq Tool; Advantech, Seoul, plant parts removed). The small amount of rates for each ornamental was determined. Korea). The chambers were held in a con- CO2 uptake by the control chamber was Data were analyzed by analysis of variance trolled-environment room; chamber temper- subtracted from the plant-assimilation rates. using standard software (SAS Institute, Cary, ature was modulated by altering the room Four replicates of each species were mea- N.C.) with the means separated using temperature. All plants were irrigated 1 d sured; to minimize the effect of outliers and Duncan’s test. before CO2 measurement. to maintain a uniform sample size, the three Photosynthetic rate was initially calcu- most representative plants were averaged for lated for ÔHimaturiÕ using leaf surface area the illustrations. To ascertain the effect of Results and Discussion with the leaf area determined using a Li-COR irradiance, photoperiod,