Amorphous Silica and Drought Stress Mitigation: Unraveling Phenological Dynamics, Carbon-Water Balance, and Crop Resilience

Amorphous silica (ASi) is increasingly recognized for its potential to improve plant resilience to abiotic stress, especially drought. However, because drought affects crop physiology as well as its carbon and water cycling differently depending on when drought occurs during plant development, the effects of ASi across key phenological stages remain poorly understood. In a greenhouse experiment, we investigated whether ASi as a soil amendment mitigates drought stress in spring barley (Hordeum vulgare L., variety: Planet) during three key phenological stages: stem elongation, flowering, and grain filling. A factorial design was used, combining two levels of ASi (0 as control and 1 g per 100 g of dry soil) with four water regimes: a well-watered reference and drought imposed during stem elongation, flowering, or grain filling. Carbon and water flux dynamics were monitored throughout the experiment by measuring CO ₂ exchange and evapotranspiration using an automated soil-plant-atmosphere enclosure system, while soil water dynamics were tracked continuously with TOMST sensors. Plant responses to drought were assessed by daily measurements of stomatal conductance, leaf water potential, abscisic acid, and soil matric potential during drought. At the end of the growing period, biomass and grain yield were determined. ASi increased soil water retention over time and reduced drought-induced stress across growth stages. Drought effects were strongest during flowering and grain filling, whereas plants exposed to drought at stem elongation recovered fully and showed no yield reduction, irrespective of their ASi treatment. In contrast, drought during reproductive stages caused early senescence, poor recovery, and strong yield loss in control plants. These effects were substantially reduced by ASi, which maintained higher leaf water potential, stomatal conductance, evapotranspiration, and CO ₂ uptake, while reducing abscisic acid accumulation. ASi also improved post-drought recovery and largely preserved yield under reproductive-stage drought. These results show that ASi can mitigate drought effects, especially during drought-sensitive reproductive stages, by helping sustain plant function during water shortages and delaying the onset of physiological stress.