114 cus cerris trees had higher sap flow than Q. petraea in part due to higher water storage (Tognetti et al. 1996). Both species experi- enced progressive drought stress during the day, but recovered by night, demonstrating high degree of drought tolerance. Based on seasonal reductions in root hydraulic conductance relative to leaf area, leaf water potential, and leaf relative water content, Q. cerris was considered a drought tolerant species (Nardini et al. 1999). No studies have compared the relative growth and drought resistance of Q. cerris, Q. pubescens and Q. robur, which is un- derstandable as they are not sympatric species. However, in ur- ban landscapes, these species are all candidates for planting and thus the relative growth rates and water use characteristics are concerns to both nursery producers and urban forest managers as they could be sympatric species in the context of the urban forest. Oaks are genetically diverse. Quercus robur, Q. petraea, and Q. pubescens form a genetic complex (Bruschi et al. 2000) characterized by high genetic diversity (Dumolin-Lapegue et al. 1999; Kleinschmit 1993; Petit et al. 2002). Morphologi- cal characteristics of fruits, leaves, and twigs indicated that Q. robur and Q. pubescens are divergent species, while Q. petraea and Q. pubescens form a continuum of intermediate types (Du- pouey and Badeau 1993). In contrast, genetic analysis indicated that Quercus robur and Q. petraea are less differentiated from each other than they are from Q. pubescens (Dumolin-Lepegue 1999). Genetic diversity is greater among individuals in mixed stands than among individuals from pure stands (Dumolin-Lep- egue 1999). Recent hybridization and introgression maintain the high degree of genetic diversity found within these species (Dumolin-Lepegue 1999; Bruschi et. al. 2000). Italy served as one refugium during the glaciation of Northern Europe (Kremer et al. 2002; Petit et al. 2002). Genetic analysis indicates that cur- rent Italian oak populations originated in Sicilian and Balkan refu- gia (Fineschi et al. 2002). Genetic analysis showed that Quercus cerris and Q. suber are clearly divergent from the other sections of the white oak complex (Petit el al., 2002; Curtu et al. 2004). This study was conducted to determine the inter- and intra- species variation in the growth rate, dry weight partitioning, and water use of seedlings from two sources from each of three Ital- ian oak species in order to assess the relative fitness for nurs- ery production, and survival and growth in the urban forest. Table. 1. Description of Quercus species used in the experiment. Species Q. cerris Source No. 1 2 Q. pubescens 5 6 Q. robur 7 8 Provenance Vivai Gubbio, Pupaggi di Sellano Vivaio Camaldoli, zona Cerreta Vivaio Gubbio, Bazzano Inferiore Vivaio Camaldoli, zona Cerreta Vivaio Gubbio, Pineta St. Vitale Parco cascine, Firenze Struve et al.: Relative Growth and Water Use from Seedlings MATERIALS AND METHODS Acorns were collected in fall 2006 from two sources from each of three species (Table 1) and sown the following February in 0.9 L (0.23 gal), 12 cm (4.7 in) tall, square black plastic con- tainers. In March, acorns were sown one per container in a 3:1 (by vol) peatmoss:pumice substrate supplemented with 3 kg m-3 (4.9 lb yd-3 ) 15N-2.9P-K7.12 controlled release fertilizer (15-7- 12 eight to nine month release, Osmocote, Scotts Miracle-Gro, Marysville, OH). The seedlings were spaced container-to-con- tainer and grown under 40% neutral shade cloth (black woven polypropylene fabric, Boscato Reti, Vicenza, Italy) at the Uni- versity of Florence’s Polo Scientifico campus, Sesto Fiorenti- no. In July, they were repotted into 2.1 L (0.55 gal) containers [18 cm tall, 10 cm square (7.1 and 3.9 in, respectively) black plastic] filled with the same substrate as before. They were spaced container-to-container and returned to the shade house. In September, 40 seedlings were randomly selected from each of the six sources—a total of 240 seedlings. The seedlings were moved to a glasshouse under 50% neutral shade. The plants were spaced at twice the container diameter in a randomized complete block design with one replication on each of two greenhouse benches. Air temperature, relative humidity and photosyntheti- cally active radiation (PAR, 400 to 700 nm) were record- ed every half hour using air temperature and relative hu- midity HD 9008TR (Delta Ohm, Padova, Italy) and PAR sensor LP PAR01, with sensors placed at mid-canopy height. Daily water use was calculated by first watering the sub- strate to capacity, allowing the substrate to drain for one hour and weighting the individual seedling-substrate-container units. The seedlings were re-weighed approximately 24 hours later. The seedlings were then re-watered and the weighing schedule repeat- ed for the following two days. The differences in daily weights were attributed to transpiration. The daily differences in weights were averaged to derive the average daily water use values for in- dividual seedling during the three-day water use period. At the end of the three-day water use period, all but four seed- lings from each source (these seedlings were used in another study) were destructively harvested and the following data collect- ed: plant height (cm), leaf number and area (cm2 ), and leaf, stem, and fine and coarse (root diameters of < 2 and ≥ 2 mm, respec- Description bulked seed lot collected from selected mother trees in single-species stands and pur- chased from a commercial forestry nursery Latitude 42°53’ 25”.36 N; Longitude 12°55’43”51 E; elevation: 547 m (1,777 ft). bulked seed lot collected from selected mother trees in single-species stands and pur- chased from a commercial forestry nursery Cerreta Latitude 43° 49’ 23”.55 N; Longitude 11°49’09”07 E; elevation: 500 m (1,625 ft) bulked seed lot collected from selected mother trees in mixed-species stands and pur- chased from a commercial forestry nursery Bazzano Latitude 42°46’ 45”.71 N; Longitude 12°47’08.41 E; elevation: 384 m (1,248 ft) bulked seed lot collected from selected mother trees in mixed-species stands and pur- chased from a commercial forestry nursery Amiata Latitude 42°54’ 00”.00 N; Longitude 11°37’48 E; elevation: 604 m (1963 ft) bulked seed lot collected from selected mother trees in mixed-species stands and pur- chased from a commercial forestry nursery Pineta Latitude 44°29’ 38”.62 N; Longitude 12°16’43”80 E; elevation: 3 m (10 ft). seed collected from a single tree in urban park surrounded by Q. robur trees Cascine Latitude 43°47’ 07”.61; N Longitude 11°12’50”39 E; elevation: 47 m (153 ft) ©2009 International Society of Arboriculture
May 2009
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