226 Singh et al.: Physiological, Growth, and Biomass Attributes Influenced by Water Stress Arboriculture & Urban Forestry 2013. 39(5): 226–230 Physiological, Growth, and Biomass Attributes in Populus deltoides L. (clones G-48 and Kranti) Influenced by Water Stress Munna Singh, Aradhna Kumari, and Krishan Kumar Verma Abstract. Six-week-old uniform cottonwood seedlings (clones G-48 and Kranti) were raised from stem cuttings and subjected under two different water regimes (full and half field capacity) up to 60 days under open field conditions. The higher and lower regulations of physiological responses were triggered in case these seedlings irrigated up to their full and half-field capacities. The enhanced A value was observed from 13–19 and 12–14 µmol m-2 s-1 ration, largely regulated by stomatal dynamics to restrict CO2 loss in maximum quantum yield of photosystem II photochemistry (Fv/ Fm) and CO2 in clones G-48 and Kranti after subjecting them under irrigation to the level of full field capacity. The withdrawal of irrigation to the level of half field capacity could reduce these values (≤50%), significantly. The decreased CO2 assimilation during drought stress was found to be correlated with decline in transpi- diffusion, which also impaired carboxylation. Upon experiencing drought, the progressive assimilation was found to be correlated with the loss in transpira- tion in both these clones. Consequently, the study reveals that irrigation to the level of half field capacity for a period of 60 days impaired agronomic traits viz., plant height, number of leaves, leaf area expansion, specific leaf area, relative water content, biomass, and harvest index, significantly. It also concludes susceptibility of clones G-48 and Kranti toward drought in relation to plant performance (i.e., CO2 assimilation, Fv/Fm, and biomass yield). Key Words. Biomass; Cottonwood; Drought; Fv/Fm; Photosynthesis; Populus deltoides L.; Transpiration. Eastern cottonwood (Populus deltoides L.) is a native of North America and was introduced in India in 1950. India became a member of the International Poplar Commission in 1965, and constituted a National Poplar Commission with an objective to cultivate cottonwood extensively due to its high productivity, possibility of co-cultivation with crops between the rows of rice in the summer or rainy season (July–September) and wheat in the winter (November–February) through inputs of irrigation and fertilizer management in India’s northern agro-climatic zones. It is one of the fast growing and commercially large-scale cultivated tree crops, getting recommended for agro-forestry these days in the foothills of northern Himalaya, especially in Himachal Pradesh, Uttarakhand, and Uttar Pradesh in India. It has also become an important agro-forestry tree species in the Indogangetic plains due to its straight stem, thin crown canopy, deciduous nature, and short-rotation with good agronomic traits (Singh 1991). The farmers have adopted its cultivation as block plantation or around field bunds, owing to its very fast growth rate (up to 48 m3 at density of 500 stems ha-1 /ha-1 yr-1 ) under short-rotation period (6–7 productivity, and biomass (Fini et al. 2009; Akcay et al. 2010; Santos et al. 2013; Fini et al. 2013). It may also induce socio- economic and environmental losses (Johari-Pireivatlou et al. 2010). The long-term effect of drought stress alters carbon allocation between plant organs due to decreased leaf area ©2013 International Society of Arboriculture years) with multiple uses of wood and high economic returns. Drought stress is an important abiotic environmental factor that limits CO2 assimilation abilities and affects plant growth, (E), stomatal conductance (gs), maximum quantum yield of PS II photochemistry (Fv/Fm), and other interrelated bio-chemical activities were found to be associated with plant performance, productivity, and biomass yield (Singh et al. 1996; Singh and Chaturvedi 1997; Singh et al. 1999; Fukuzawa et al. 2012; Fini et al. 2013). The maximum quantum yield of PS II photochem- istry and plant productivity are dependent on genotype, spe- cies, climate, soils, and plants nutrient status (Fini et al. 2013). expansion and leaf number (Chen et al. 1997; Tschaplinski et al. 1998; Xiao et al. 2005). A decrease in specific leaf area (SLA) as an indicator of density or thickness of the leaves has often been observed with a subsequent increase in water reten- tion due to an accentuation of the resistance to water transfer in the leaf (Niinemets 2001; Nautiyal et al. 2002). The loss in carbon assimilation occurs due to impaired stomatal conduc- tance (Singh et al. 1996; Maier 1998; Fukuzawa et al. 2012). The drought tolerance (i.e., an ability to maintain physiological process at declining leaf water potential) and drought avoid- ance (i.e., an ability to avoid the decline in leaf water poten- tial during drought) may extend drought resistance in plants (Levitt 1980; Poorter and Markesteijn 2008). The cotton- wood has shown temperature optima ranging from 20°C–30°C depending upon its growing seasons, was also found to be more prone for water, saline, and temperature stress in the planting year (Singh et al. 1996; Singh et al. 1999), while short-term dynamic waterlogging was found to be nearly non-vulnerable. Physi- ological responses, such as CO2 assimilation (A), transpiration
September 2013
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