158 height), balled and burlapped (size of the root ball was approxi- mately 30 cm [12 in] in diameter) Aesculus × carnea (red horsechestnut) and Tilia × europaea (european linden) trees were planted in an experimental plot located at the Fondazione Minoprio (Como) (45°44N, 9°04E). Planting holes were two times the width and one-and-a-half times the depth of the root ball to ensure a greater volume of loose soil within the planting hole. The sides of the planting pit were scarified with a shovel. Before planting, some soil mixed with peat (50% in volume) was placed at the bottom of the planting hole. At planting, care was taken that the root flare was not positioned below the soil level. All trees with almost identical size characteristics were obtained from the same nursery and planted at the same time. Trees were planted in a randomized block design with three blocks and four plants per block (12 plants per each treatment, 36 plants per species) and provided supplemental irrigation. Treat- ments included: • Mulching with coarse compost derived from green material left after sifting (coarse compost) (layer 5 to 8 cm [2 to 3 in]); • Mulching with pine bark (layer 5 to 8 cm [2 to 3 in]); and • Control (weeding by herbicide). In 2004, no data were collected with the exception of plant height and trunk diameter at the end of the growing season. In 2005 and 2006, the following parameters were measured: 1) Plant height and trunk diameter (determined on each plant at the end of each growing season; plant diameter was also measured in 2007); 2) Shoot length (determined on 20 shoots/plant at the end of the growing season; shoot length was also measured in 2007); 3) Leaf gas exchange (instantaneous net photosynthesis [Pn], transpiration rate [E], water use efficiency [WUE, calcu- lated by dividing Pn by E], stomatal conductance [gs], and internal CO2 concentration [ci]; measured eight times in 2005 and five times in 2006); and 4) Chlorophyll fluorescence (measured four times in 2005 and three times in 2006). Leaf gas exchange was measured during the whole growing season using the CIRAS-2 portable infrared gas analyzer (PP Systems, Hertfordshire, U.K.). The readings were taken between Ferrini et al.: Mulching of Ornamental Trees 8:00 A.M. and 1:00 P.M., which was presumed to be the diurnal period when photosynthetic rates would be maximal, in sunny days under fixed CO2 concentration (360 ppm) and saturating irradiance (1300 mol/m−2/s−1 provided by a built-in red light- emitting diode radiation source) on six plant per each thesis on five fully expanded leaves from the outer part of the crown and at different heights per plant per treatment. Chlorophyll fluores- cence was measured on the same plants by using a HandyPEA portable fluorescence spectrometer (Hansatech Instruments Ltd., King’s Lynn, U.K.) four times from mid-May through the end of July (Percival 2005). Fluorescence values were obtained by plac- ing leaves in darkness for 30 min by attaching light-exclusion clips to the leaf surface of whole trees. Upon the application of a saturating flash (3,000 mol/m−2/s−1 for 1 sec), fluorescence raises from the ground state value (Fo) to its maximum value, Fm. In this condition, QA, the first electron acceptor of photo- system II (PSII), is fully reduced. This allows the determination of the maximal or potential photochemical efficiency or optimal quantum yield of PSII given by Fv/Fm (Fm−Fo)/Fm where Fm is the maximum value. Fv/Fm is considered a quantitative measure of the maximal or potential photochemical efficiency or optimal quantum yield of PSII. In healthy leaves, this value is always above 0.75 to 0.8, independent of the plant species stud- ied. A lower value indicates that a proportion of PSII reaction centers are damaged, a phenomenon called photoinhibition, of- ten observed in plants under stress conditions (Maxwell and Johnson 2000; Krause and Weis 1991; Percival 2005; Lazár 2006). Statistical Analyses All data were subjected to one-way analysis of variance using SPSS statistical package for Windows (SPSS Inc., Chicago, IL, U.S.). Difference between means of investigated parameters were tested with Duncan’s multiple range test (P 0.05). Data on leaf gas exchange and on chlorophyll fluorescence have been processed per single sampling date, merged together, and pro- cessed again to obtain the average value on an annual basis. RESULTS AND DISCUSSION Tables 1 and 2 summarize growth data for both species. In horsechestnut, height increment was higher in trees mulched with compost only in the first year, whereas no difference emerged either in the second year or considering the total height increment (Table 1). Similarly, trunk diameter was positively Table 1. Effect of soil management techniques on and plant height (cm), trunk diameter (cm), and shoot length of Aesculus × carnea.z Parameter Height increment (cm) Total height increment (cm) Diameter increment (mm) Total diameter increment (mm) Shoot length (cm) Data are reported as means and subjected to analysis of variance. Different letters within the same row indicate statistical differences at P 0.05 (*) or P 0.01 (**) using Duncan test. NS nonsignificant. z ©2008 International Society of Arboriculture Year 2004–2005 2005–2006 2004–2006 2004–2005 2005–2006 2006–2007 2004–2007 2005 2006 2007 Pine bark 3.28 ab 32.95 36.23 11.89 b 15.23 14.45 41.57 b 9.57 b 47.37 54.72 b Compost 5.76 a 38.81 44.57 18.11 a 17.24 15.81 51.16 a 13.94 a 46.98 62.6 a Control 1.54 b 33.75 35.29 12.69 b 16.3 13.91 42.9 b 13.72 a 45.34 55.34 b P * NS NS * NS NS ** ** NS **
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