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.

Keywords