Arboriculture & Urban Forestry 35(5): September 2009 Arboriculture & Urban Forestry 2009. 35(5): 241–251 241 Withholding Irrigation During the Establishment Phase Affected Growth and Physiology of Norway Maple (Acer platanoides) and Linden (Tilia spp.) Alessio Fini, Francesco Ferrini, Piero Frangi, Gabriele Amoroso, and Riccardo Piatti Abstract. The aim of this work was to investigate the drought tolerance of different Tilia species and of different cultivars of Acer platanoides grown during the establishment phase, and to evaluate irrigation effect on their growth and physiology. In winter 2004–2005, 168 trees [8–10 cm (3–4 in) circumference] of Tilia platyphyllos, T. cordata, T. × europaea, T. tomentosa, Acer platanoides ‘Summershade’, A. platanoides ‘Debo- rah’, and A. platanoides ‘Emerald Queen’ were planted in the field. Eighty-four plants were irrigated with a drip irrigation system (4 l/h) and eighty-four were not. Height, trunk diameter, and shoot elongation were measured at the end of the growing season in 2005, 2006, and 2007. Leaf gas exchange and chlorophyll fluorescence were measured monthly during the 2006 and 2007 growing seasons. Leaf greenness index content was measured in 2006 and 2007. Results indicate that T. tomentosa and T. cordata are more drought tolerant during establishment than T. platyphyl- los, while Acer platanoides ‘Summershade’ is less drought tolerant during establishment than the cultivars ‘Emerald Queen’ and ‘Deborah’. Key Words. Acer platanoides; Chlorophyll Fluorescence; Drought Avoidance; Leaf Gas Exchange; Tilia spp.; Water Stress. Global environmental conditions have changed during the last century and based on current trends, temperature will rise by about 1°–3.5°C (1.8°–6.3°F) over the next 70 years, and rain- fall will also be affected by a decrease in the frequency and an increase in intensity of rainy events (UNEP/IUC 1999). Water limitation may prove to be a critical constraint to primary pro- ductivity of plants under future scenarios of more arid climates due to climate change (Fisher et al. 2001). When referred to shade trees planted in the urban environment and peri-urban forests and recreational areas, plant productivity may correspond with the ability of single plants or plant communities to provide benefits to the inhabitants. Healthy, long-lived trees provide environmen- tal, ecological, economic, social, cultural, and aesthetic benefits to the community (Akbari 2002; Brack 2002; Fini and Ferrini 2007; Nowak et al. 2007; Elmendorf 2008; Escobedo et al. 2008). Mortality rate in the urban environment is usually very high and ranges from 10% to 50% with water stress playing a major role, especially where pavements, soil compaction, and small planting pits prevent infiltration into the root zone (Kaushal and Aussenac 1989; Miller and Miller 1991; Whitlow et al. 1992; Pauleit et al. 2002). This threat is very dangerous in the first years after planting, when mortality can be 50% in the first year, and up to 34% in the second (Gilbertson and Bradshaw 1985; Nowak et al. 1990). Irri- gation is an important factor to increase plant survival and quality during the establishment phase, but landscape water consumption is highly visible and provides a prime target for water restrictions and subsequent regulation (Scheiber et al. 2007). Despite the need of saving water, water restrictions during landscape estab- lishment can be detrimental to plants which have not had enough time to develop a sufficient root system to compensate for evapo- transpirational losses (Montague et al. 2000). One way to increase water efficiency is to irrigate trees until they are fully established and then terminate irrigation unless there are periods of extreme drought. Establishment time can be estimated by comparing leaf gas exchange and growth rates of newly planted stressed (nonir- rigated) and unstressed (irrigated) trees (Scheiber et al. 2007). Another strategy to reduce drought-related transplant losses is to plant species/cultivars that show a certain degree of drought tolerance during the establishment phase. Even within a ge- nus or a species, great differences in water needs for establish- ment can be found among species/cultivars. A previous work ranked drought tolerance of Fraxinus genotypes on the basis of drought-induced changes in chlorophyll fluorescence, chlo- rophyll content, and carbon assimilation (Percival et al. 2006). Few studies have assessed drought tolerance among maples and lindens: most were performed on container-grown plants (Abrams and Kubiske 1990; Zwack et al. 1998; Fini et al. 2008) and none of them addressed drought tolerance during the es- tablishment phase. This is very surprising because maples and lindens are widely-used species for the urban environment in Italy and Europe. Four linden species are commonly used for urban forestry: 1) T. cordata Mill., a native European species widespread from Spain to Northern Greece to Southern Finland which forms climax forest in plain and mountain areas up to 1500 m (0.93 mi) above sea level; 2) T. platyphyllos Scop., a native European species which grows widely from Northern Spain to Caucasus and to Southern Sweden and forms climax forest pref- erentially in mountain areas, up to 1600 m (1 mile) above sea level; 3) T. × europaea (syn. T. × vulgaris) L. is the natural hybrid between T. cordata and T. platyphyllos; 4) T. tomentosa Moench, a native of Southern Europe and Asia. Norway maple (Acer pla- tanoides L.), and Sycamore maple (Acer pseudoplatanus L.) are the most commonly used maple species in European and Ital- ian towns. A previous study found that A. platanoides is more ©2009 International Society of Arboriculture
September 2009
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