Arboriculture & Urban Forestry 42(2): March 2016 sured using a Handy PEA portable fluorescence spectrometer (Hansatech Instruments Ltd., King’s Lynn, UK). Measurements were recorded up to 1 sec with a data-acquisition rate of 10 ms for the first 2 ms and of 1 ms thereaſter. The fluorescence responses were induced by a red (peak at 650 nm) light of 1500 mmol m-2 . The Performance Index (PI), one of the parameters measured by the spec- trometer, is an indicator of plant vitality. PI is an overall expression indicating the forces of redox reactions and can be used to describe the driving force of the photosynthesis occurring in leaf tissue (Strasser et al. 2004). PI has been shown to be a highly sensitive index to any form of abiotic stress and is recommended for the testing of poten- tially stressed plant stock (Strasser et al. 2000). SPAD Leaf chlorophyll content was estimated at the midpoint of the leaf next to the main leaf vein by using a handheld optical Minolta chlorophyll meter SPAD-502 (Spectrum Technologies, Inc. Plainfield, Illinois, U.S.). Calibration was ob- tained by measurement of absorbance at 663 and 645 nm in a spectrophotometer (PU8800 Pye Unicam, Portsmouth, UK) aſter extraction with 80% v/v aqueous acetone (regr. eq. y = 5.66 + 0.055x; r2 adj = 0.89, P ≤ 0.01; Lichtenthaler 1987). Photosynthetic Rates (Pn) Light-induced CO2 fixation (Pn) was measured using fully expanded leaves from near the top of the canopy (generally about four nodes down from the apex) by using an Infra-Red Gas An- alyzer (LCA-2 ADC, BioScientific Ltd., Hod- desdon, Herts, UK). The irradiance subjected to the leaves was 700 to 800 mol m-2 photosyn- thetically active radiation saturating with respect to Pn; the velocity of the airflow was 1 ml s-1 cm-2 of leaf area. Calculation of the photo- synthetic rates was carried out according to Von Caemmerer and Farquhar (1981). Two leaves per tree were selected for measurements. Statistical Analysis Treatment effects on chlorophyll fluorescence, photosynthetic rates, chlorophyll concentrations, fruit yield, and growth were determined by both 105 two- and one-way Analyses of Variance (ANOVA) as checks for normality and equal variance dis- tributions were met using an Anderson-Darling test. Differences between treatment means from non-treated controls were separated by Tukey’s Honestly Significant Difference (HSD) test at the 95% confidence level (P > 0.05) using the ‘Gen- Stat for Windows 16th edition’ statistics system (VSN International Ltd., Hemel Hempstead, UK). RESULTS Tree Growth All soil amendments reduced mortality of Pyrus communis ‘Williams’ Bon Chrétien’ aſter planting compared to non-treated controls, demonstrating all soil amendments evaluated in this study have the potential to promote transplant survival (Table 1). Likewise in both the first and second growing seasons, soil amendment with biochar, molasses pellets, and organic fertilizer individually increased tree growth in terms of fruit yield and crown vol- ume. These increases were, in most cases, sig- nificant (P < 0.05) following soil amendment with biochar and BOOST Organic but non-significant following amendment with molasses pellets. In- creases in fruit yield per tree ranged from 19.3% (slow-release molasses pellets) to 46.7% (BOOST Organic), while increases in crown canopy ranged from 14.4% (slow-release molasses pellets) to 31.1% (BOOST Organic) over non-amended soils when averaged over two growing seasons. Combination of amendments always resulted in an increased fruit yield per tree and crown canopy coverage compared to use of an amendment individually. For example, in Year 1 amendment with biochar or BOOST Organic increased fruit yield per tree from 5.8 kg (non-amended controls) to 6.6 and 6.8 kg, respectively. Soil amended with a combina- tion of biochar + BOOST Organic increased fruit yield per tree to 7.2 kg. When averaged over two growing seasons, combining products enhanced fruit yield per tree and canopy coverage by 12%– 49%. Such a response indicates that combination of amendments tested in this study induce addi- tive effects compared to application individually. Based on fruit yield per tree, positive effects were in the following order: BOOST Organic + bio- char > BOOST Organic > BOOST Organic + ©2016 International Society of Arboriculture
March 2016
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