Arboriculture & Urban Forestry 39(5): September 2013 Besides food and fiber requirements, timber and wood are also needed by the human societies globally these days. The forest cover of India is ~21.05%, which is lower compared to developed nations. Thus, keeping the large-scale utilities of cottonwood in view, the current study is focused on extending its cultivation areas in other nearby agro-climatic zones, which often experience less rain showers, and could not sustain adequate moisture content in the soil. These sites are also influenced by dry air (lower rela- tive humidity) and higher temperature (35°C–45 °C). Hence, the aim was to reveal growth and developmental attributes in cotton- wood influenced by irrigation levels (i.e., up to full and half field capacities) to correlate plant performance and productivity or bio- mass yield integrated with sustainability of agro-socio economy. MATERIALS AND METHODS Plant and Growth Conditions Cottonwood is a temperate in origin and may grow well upon maintaining soil moisture content. The experiment was con- ducted at the Department of Plant Physiology, College of Basic Science and Humanities (CBSH), G.B. Pant Univer- sity of Agriculture and Technology, Pantnagar, Uttarakhand (India). Cottonwood clones [i.e., G 48 and Kranti (stem cuttings)] were purchased from WIMCO seedlings (Pvt.) Ltd. Bagwala (Kashipur Road), Rudrapur, Udham Singh Nagar (Uttarakhand). These clones are highly preferred by the farmers for large-scale plantation- cultivation. The cuttings, having uniform diameter and length (18–20 cm), were planted in poly-bags (2 kg) to allow sprouting for four weeks. Afterwards these seedlings were transplanted in earthen pots (30 cm diameter, 30 cm depth) filled with fertile soil (silty clay loam, pH 7.1, organic carbon- 0.86% and N, P, K-245, 35.5 and 172 kg ha-1 ) for a period of two weeks to allow their establishment. Uniformly grown cot- tonwood seedlings were chosen for subjecting them under two irrigation water regimes (i.e., up to full and half field capacities). Thus, two soil moisture levels were maintained through precise application of water in earthen pots. The control set of plants were irrigated to the level of full field capacity (l L day-1 ), while half field capacity (0.5 L day-1) was maintained to impose water stress over growing seedlings throughout and up to a period of 60 days. These pots were covered by plastic to prevent the intrusion of rain water. The growth, physiological and biomass responses of these seedlings were measured at specific time intervals, as indicated. Field Capacity The field capacity was calculated by applying the formula for volume of frustum of right circular cone. It was also calculated by recording incremental diameter of the container at different heights [i.e., 0 (base), 5, 10, 15, 20, 25, and 30 cm (from bot- tom to top)]. These calculation methods have provided the con- tainer’s volume, which was nearly the same [i.e., 12.4 cm3 (12.4 L)]. The moist soil from an agricultural field was extracted and placed in these containers (earthen pots) up to the height of 20 cm only. The field capacity of these containers was calculated as: (i) The volume of water required for saturating filled soil in the containers = 1475 ml. (ii) The volume of water drained out after 24 hours from the containers = 475 ml. 227 (iii) The volume of water retained after removal of gravitational water = 1000 ml Photosynthetic and Chlorophyll Fluorescence Measurement Photosynthetic measurements were made by using CIRAS-1, IRGA, portable photosynthesis system (PP system, Amesbury, Massachusetts, U.S.). The completely expanded leaves (6th– 8th position) were used for the observations under natural sunlight (~1500 µmol m-2 s-1 ) between 8:00–10:00 a.m. to avoid high temperature and low humidity. The maximum quantum yield of PS II photochemistry was obtained through chloro- phyll a fluorescence on the same leaf for which CO2 assimila- tion was evaluated. The measurements of maximum quantum yield of PS II photochemistry (Fv/Fm) were determined, after the leaves were adapted to the dark (30 min) by using Plant Efficiency Analyzer (Handy PEA, Hansatech, King Lynn, UK). Growth Parameters At the end of the experiment (60 days after treatment), plant height and number of leaves were monitored followed by a destructive harvest. Ten seedlings of each clone (G-48 and Kranti) from control and treatment were randomly sampled. Leaf area was measured using a Leaf Area Meter (CI-203-CID, U.S.). Spe- cific leaf area of the whole plant (SLA) (cm2 g-1 ) was calculated according to Beadle (1993). The relative leaf water content (RWC) was determined as 100 × (FM-DM)/(TM-DM), where FM is a fresh mass, TM is turgid mass after re-hydrating the leaves (24 hours, 25°C, dark), and DM is dry mass after oven drying the leaves (68°C, 48 hours). Dry weight was obtained by weighing the plant material after drying to achieve the constant dry mass. The harvest index was calculated according to Michael et al. (1988) by harvesting at least 10 seedlings from each set of the treatment. Data management and statistical analysis were performed using SPSS software (SPSS, Chicago, Illinois, U.S.). Means were expressed with their standard error (±SE) and compared by ANOVA. All statistical tests were considered significant at P ≤ 0.05. RESULTS The influence of two different irrigation regimes was assessed on CO2 assimilation (A), transpiration (E), and maximum quan- tum yield of PS II photochemistry (Fv/Fm) in cottonwood clones (i.e., G-48 and Kranti). The expression of higher and lower lev- els of physiological responses occurred when these plants were irrigated up to their full and half field capacities, respectively. A temporal up-regulation for A occurred in these clones in case irrigated up to full field capacity. Accordingly, upon maintaining irrigation up to field capacity to 60 days, clones G-48 and Kranti expressed progressively enhanced A values from 13 to 19 µmol m-2 s-1 and 12 to 14 µmol m-2 s-1 of irrigation to half field capacity in these clones viz. G-48 and Kranti resulted in significant decline in A from 13 to 6 µmol m-2 and 12 to 5 µmol m-2s-1 , respectively. However, withdrawal s-1 , respectively (Figure 1A, a). The transpira- tion (E) was found to be almost identical for both clones (~3 µmol m-2 s-1 irrigation up to half field capacity reduced to the level of ~1 µmol m-2 ) upon irrigating them up to field capacity, while providing s-1 water use efficiency) were found always higher than the con- (Figure 1B, b). The improved PN ©2013 International Society of Arboriculture /E trends (intrinsic ,
September 2013
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