From waste to worth: valorizing lawn waste into carbon dots for saline agricultural enhancement

Soil salinity is a major constraint on plant establishment and ecosystem restoration in degraded landscapes. This study presents a circular-economy strategy for converting lawn waste into carbon dots (LW-CDs). Hydrothermally synthesized LW-CDs (∼6.4 nm) improve bermudagrass growth and salt tolerance as a high-value bioproduct. At 160 mg/L, LW-CDs significantly promoted plant growth under non-saline conditions, as indicated by improved growth performance, increased chlorophyll content and transcriptional enrichment of photosynthesis and carbon metabolism pathways. Under salinity, seed pretreatment and mature-stage exogenous application induced distinct but complementary protective responses. Seed pretreatment produced a low-ROS state, characterized by reduced MDA accumulation, selective SOD/CAT activition, and transcriptional repression of several oxidative and metabolic pathways together with enrichment of repair-related signatures. Conversely, exogenous application supported mature plants under salt exposure by increasing chlorophyll content, broadly enhancing POD/SOD/CAT activities, and up-regulating glutathione-metabolism-related transcript. Cross-scenario transcriptome comparison further identified shared expression modules related to proteostasis and vacuolar trafficking. The recurrent induction of EIL1A, further suggests a putative ethylene-associated transcriptional node linking LW-CDs treatment with growth-stress response coordination. These findings demonstrate that lawn-waste-derived LW-CDs can modulate bermudagrass growth and salt-stress responses through application-stage-specific mechanisms, providing a waste-to-worth route for developing sustainable inputs for saline-land restoration.