Growth, Photosynthetic Performance, and Water Relations of Weeds under Salt Stress

Soil salinization is a major environmental problem that limits agricultural productivity, particularly in semiarid regions. Although the effects of salinity on crops are well documented, little is known about the response of weeds to this stress. Thus, the objective of this study was to evaluate the effect of salt stress on the growth and physiological traits of the weeds Amaranthus hybridus, Portulaca oleracea, Macroptilium lathyroides, Digitaria horizontalis, and Eleusine indica. The experiment was conducted in a randomized block design, with three replications, considering one plant per experimental plot. The species were subjected to five salinity levels in the irrigation water: 0.5 (control), 4.0, 8.0, 12.0, and 16.0 dS m–1. Growth variables (height, stem diameter, number of leaves, leaf area, root length, and dry mass) and physiological parameters (chlorophyll content, net photosynthetic rate, transpiration rate, stomatal conductance, and water-use efficiencies) were measured. The results showed significant differences between the species regarding the response to salt stress. P. oleracea stood out for presenting greater tolerance, maintaining high values in morphophysiological variables, with only ∼30% reduction in biomass at 2.0 dS m–1 and ∼70% at 16.0 dS m–1. In contrast, A. hybridus and M. lathyroides showed marked reductions in height (above 70%) and shoot biomass (up to 90%) at the highest salinities, while D. horizontalis and E. indica exhibited intermediate reductions of 40–76%. These results indicate that salinity affects the growth and physiological functioning of the species in a differentiated way, evidencing variations in the adaptive potential among the weeds evaluated.