The Effect of Water Deficit and Interspecific Competition on Selected Physiological Parameters of Spring Barley and Italian Ryegrass

M. JASTRZĘBSKA, M. K. KOSTRZEWSKA, M. WANIC and K. TREDER
University of Warmia and Mazuryin Olsztyn, Department of Agricultural Systems, 10-727 Olsztyn, Poland

Abstract

JASTRZĘBSKA, M., M. K. KOSTRZEWSKA, M. WANIC and K. TREDER, 2015. The effect of water deficit and interspecific competition on selected physiological parameters of spring barley and Italian ryegrass. Bulg. J. Agric. Sci., 21: 78–88

Stomatal conductance, transpiration and photosynthetic rates of spring barley and Italian ryegrass plants subjected and not subjected to interspecific competition at different water supply levels were compared in a pot experiment. The experimental factors were: water supply – optimal for the analyzed species and reduced by 50%, sowing regime – single species sowing (pure-sown barley, pure-sown ryegrass) and mixed species sowing (barley mixed-sown with ryegrass, ryegrass mixed-sown with barley). Gas exchange was analyzed during five BBC H growth stages for pure-sown barley under optimal soil moisture conditions: leaf development (10-13), tillering (22-25), stem elongation (33-37), heading (52-22) and ripening (87-91). The measurements for barley were completed at the heading stage. The photosynthesis/transpiration ratio was used to determine water use efficiency (WUE) in plants.
Water deficit generally decreased stomatal conductance, transpiration and photosynthetic rates of spring barley and Italian ryegrass. In water-deficient treatments, ryegrass was characterized by higher water use efficiency throughout the growing period, and spring barley – only during the tillering stage. Interspecific competition had little effect on stomatal conductance and transpiration rates of both species as well as the photosynthetic rate of barley, but it increased the photosynthetic rate of ryegrass. Under optimal soil moisture conditions, interspecific competition reduced stomatal conductance and increased photosynthetic rate in ryegrass. Water stress alone and in combination with interspecific competition produced similar results. A combination of water deficit and interspecific competition lowered the photosynthetic rate of spring barley, in particular at the tillering stage. In treatments with optimal water conditions, ryegrass mixed-sown with spring barley was characterized by higher WUE than puresown ryegrass. Water stress increased WUE of ryegrass in all sowing regimes. Spring barley from water-deficient treatments was generally characterized by higher WUE in pure-sown stands, in particular at the tillering stage. Competition from ryegrass did not induce significant changes in WUE of barley plants in water-deficient or optimal water treatments.

Key words: stomatal conductance; transpiration; photosynthesis; water use efficiency; undersowing
Abbreviations: GS – stomatal conductance; E – transpiration rate; A – CO2 assimilation rate, photosynthetic rate;WUE –water use efficiency; HW – optimal water supply for the analyzed species (higher dose); LW – water supply reduced by 50% (lower dose); BP – pure-sown barley; BM – barley mixed-sown with ryegrass; RP – pure-sown ryegrass; RM – ryegrass mixed-sown with barley

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