Deficit irrigation during the vegetative stage improves tomato growth and yield by optimizing root architecture and delaying root senescence

Root systems exhibit significant structural and functional plasticity in response to changes in soil conditions, yet the dynamic properties and coordinated effects with aboveground parts remain understudied. This study investigated the effects of regulated deficit irrigation (RDI) with two irrigation levels: full irrigation (W, 90 % field capacity) and deficit irrigation (D, 1/2 full irrigation). These levels were applied during three tomato growth stages-vegetative, fruit development, and fruit ripening-resulting in five irrigation treatments: DDD, WWW, DWD, DWW, and WWD. Results showed that over two consecutive years of trials, compared with full irrigation (WWW), deficit irrigation during the vegetative stage (DWW) maintained equivalent yield in 2023 while achieving a 9.4 % yield increase in 2024, while enhancing irrigation water use efficiency (IWUE) by 14.5 % and 16.7 %. DWW significantly promoted both fine and coarse roots development and optimized root distribution, particularly in deeper soil layers. It also increased root activity and lifespan, especially at the 20–40 cm depth, where the cumulative loss of dead roots was reduced by 21.6 % and 31.9 %. Overall, DWW enhanced yield and IWUE by optimizing root architecture and distribution while delaying root senescence progression. These findings revealed the temporal dynamics and critical point for root senescence, highlighting the critical role of optimizing root architecture and distribution in improving IWUE and productivity in greenhouse tomato cultivation.