PJB-2026-24
Water-Nitrogen Coupling Promotes the Growth of Piptanthus nepalensis Seedlings by Reshaping Root System Architecture to Alleviate Non-Stomatal Limitations
Han Yanying
Abstract
Water and nitrogen availability are key factors restricting vegetation restoration in the alpine ecosystems of the Qinghai-Tibet Plateau. However, the mechanisms by which woody plants adapt to variations in water and nitrogen through belowground-aboveground synergistic mechanisms remain unclear. In this study, seedlings of Piptanthus nepalensis were subjected to five water gradients and five nitrogen application levels to systematically investigate the effects of water-nitrogen coupling on root system architecture (RSA), antioxidant physiology, photosynthetic characteristics, and biomass accumulation.The results showed that:(1) Water-nitrogen interaction significantly affected seedling growth. The W3N3 treatment (40%–60% field capacity + 2 g N·plant-1) exhibited significant coupling advantages, with total biomass, root length, and net photosynthetic rate reaching peak values.(2) Appropriate water and nitrogen supply induced roots to adopt an "intensive foraging strategy." By increasing the proportion of fine roots and root surface area, this strategy improved nutrient absorption efficiency and activated the antioxidant enzyme system (SOD, POD, CAT), thereby effectively reducing membrane lipid peroxidation levels.(3) Analysis of photosynthetic mechanisms revealed that severe drought (W5) caused "metabolic collapse" in plants, characterized by sustained high intercellular CO2 concentration (Ci) and non-stomatal limitations; notably, nitrogen application could not compensate for the damage caused by this extreme water deficit. Conversely, the W3N3 treatment significantly alleviated non-stomatal limitations and extended the window of efficient carbon assimilation during the peak growth season.(4) Mantel tests and Structural Equation Modeling (SEM) confirmed that plastic changes in root morphology were the dominant factors driving aboveground physiological processes and biomass accumulation.In summary, adopting moderate water-nitrogen management (W3N3) can maximize the productivity of P. nepalensis through a "belowground-promotes-aboveground" cascade effect, making it an ideal tending strategy for vegetation restoration in alpine regions.
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