Abstract Salinity is a growing threat to urban green spaces, as it affects plant health and urban ecosystem services. Dichondra repens is a ground cover species used extensively in the landscape. This study evaluates the effect of humic acid (HA) on D. repens under salinity stress, addressing a gap in species-specific research. A factorial experiment was conducted using a completely randomized design with four salinity levels (0, 4, 7 and 10 dS/m) and four HA concentrations (0, 250, 500 and 1000 ppm) during two months after transplanting. Results showed that salinity led to a decrease in some traits. Shoot dry and fresh weight at 10 dS/m decreased 43 and 42% compared with 0 dS/m, respectively. HA generally enhanced growth traits, especially under moderate salinity (4 and 7 dS/m), with 250 and 500 ppm proving optimal for shoot fresh and dry weight. HA also benefitted root fresh weight across various salinity levels. Proline content peaked at 10 dS/m with 250 ppm HA, while chlorophyll content responded positively to 250 ppm HA under non-saline conditions. However, HA did not reduce the electrolyte leakage except at 250 and 500 ppm with 10 dS/m salinity and non-saline conditions, respectively. A high HA concentration (1000 ppm) exhibited an antagonistic effect on growth traits, including shoot weight (fresh and dry), root length, root fresh weight and also proline accumulation at the highest salinity level (10 dS/m); however, at this concentration (10 dS/m), this effect was not recorded for physiological and other biochemical traits. These findings suggest that HA, particularly at 250 ppm, can alleviate salinity stress in D. repens, enhancing its potential for use in saline-affected urban landscapes. Further research should be conducted on the effects of HA on dichondra in conjunction with salinity at different growth stages. Such research would further contribute to the broader goals of urban sustainability and climate-resilient green infrastructure. Significance of the study What is already known on this subject? Previous studies have highlighted the significance of humic acid (HA) application in various plants, including ornamental plants used in green spaces. HA has been shown to exert a positive effect in mitigating the detrimental impacts of stresses, such as salinity stress, thereby enhancing the growth characteristics and aesthetic qualities of plants in landscaping environments. What are the new findings? To date, no study has examined the effects of salinity stress on this important ornamental and ground cover plant. The present study investigates the impact of salinity stress on dichondra plants combined with the application of HA. It was determined that salinity stress adversely affects the morphological, physiological and biochemical traits of dichondra during the seedling stage and thereafter. HA application effectively mitigated the harmful effects of salinity stress. Additionally, the concentration of HA used proved to be critically important, as higher concentrations exhibited antagonistic effects on specific traits. What are the expected impacts on horticulture? According to the water scarcity crisis and the necessity to use saline and low-quality water in green spaces in some regions of the world, and also the widespread use of dichondra as a ground cover plant, the results of this study can be valuable for producers and cultivators in urban green spaces. The application of HA was found to alleviate the detrimental effects of salinity stress in Dichondra , offering a practical approach to improve plant performance under such challenging conditions.
Bazaz et al. (Wed,) studied this question.