Effects of continuous rainout deficit on growth and yield of spring wheat in the semi-arid region of the Loess Plateau, China

In northern China, wheat is the primary staple crop, cultivated extensively in arid and semiarid regions where drought poses a significant challenge to production. Understanding wheat's response to drought stress and its recovery mechanisms is crucial for ensuring future yield stability. To address this, we have conducted a field experiment manipulating rainfall on spring wheat in the semi-arid rain-fed agricultural area of the Loess Plateau in China. We induced drought stress at various growth stages of spring wheat by completely excluding rainfall using rain-out shelters. We measured and compared several eco-physical characteristics of wheat growth, including height, chlorophyll content, chlorophyll fluorescence parameters, biomass, and grain yield. The results showed that normal growth and development of spring wheat could be obviously influenced by continuous water stress given at vegetative stages. Drought stress can shorten the growth period of spring wheat. Specifically, during periods of drought, the heading and flowering stages are delayed the earlier the drought occurs, while the maturation stage advances. If the drought persists during the grain filling stage without recovery in precipitation, it significantly reduces the thousandgrain weight, consequently leading to decreased yield. Additionally, the ongoing drought process resulted in a decrease in leaf moisture, chlorophyll content, and chlorophyll fluorescence. Dry matter accumulation rate in the organ allocation of plants, pre-reproductive concentrated in the leaves, late reproduction concentrated in the panicle, and stem throughout dry matter accumulation rate decreased. These changes in plant physiology and allocation of resources lead to considerable differences in plant morphology, particularly in terms of plant height. After the natural precipitation was restored, the leaf water, chlorophyll content, and chlorophyll fluorescence rapidly returned to normal levels, and the morphological changes did not recover significantly under severe stress. The experimental data collected from two seasons strongly indicates that chlorophyll fluorescence parameters can identify crop water stress. The study highlights the ability of plants to function during drought and recover immediately after rehydration during the vegetative growth period is important in determining the final yield of wheat. Chlorophyll fluorescence parameters can identify crop water stress. We believe that this work lays the foundation for research on crop drought-related mechanisms and provide opportunities for the management of high-yield crop production.