Effects of intraspecific competition on growth and photosynthesis of Atriplex prostrata

We investigated the effect of intraspecific competition on growth parameters and photosynthesis of the salt marsh species Atriplex prostrata Boucher in order to distinguish the effects of density-dependent growth inhibition from salt stress. High plant density caused a reduction of 30% in height, 82% in stem dry mass, 80% in leaf dry mass, and 95% in root dry mass. High density also induced a pronounced 72% reduction in leaf area, 29% decrease in length of mature internodes and 50% decline in net photosynthetic rate. The alteration of net photosynthesis paralleled growth inhibition, decreasing from 7.6 ± 0.9 μmol CO2 m−2 s−1 at low density to 3.5 ± 0.4 μmol CO2 m−2 s−1 at high density, indicating growth inhibition caused by intraspecific competition is mainly due to a decline in net photosynthesis rate. Plants grown at high density also exhibited a reduction in stomatal conductance from 0.7 ± 0.1 mol H2O m−2 s−1 at low density to 0.3 ± 0.1 mol H2O m−2 s−1 at high density and a reduction in transpiration rate from 6.0 ± 0.3 mmol H2O m−2 s−1 at low density to 4.3 ± 0.3 mmol H2O m−2 s−1 at high density. Biomass production was inhibited by an increase in plant density, which reduced the rate of photosynthesis, stomatal conductance and leaf area of plants.