Rapid emergence and high-quality seedlings are an important basis for achieving high yields and high-quality grains in wheat production. It is not clear how long-term straw incorporation affects the emergence and quality of wheat seedlings in lime concretion black soil. Based on a 12-year long-term fixed-site experimental field, a three-year field experiment with wheat-maize rotation was conducted on the Huang-Huai-Hai Plain of China in 2020-2023 to assess the effect of straw incorporation on seedling emergence and seedling quality of wheat. The treatments comprised no-tillage wheat straw mulching and conventional tillage with maize straw return (T1), conventional tillage with maize straw return only (T2), and without straw incorporation (CK). The results showed that seedling emergence time (SET) and seedling emergence peak day (SEPD) in the T1 and T2 treatments were delayed compared with those of the CK. The SET was delayed (by 0.3-2.0 d), and the seedling emergence speed (SES) decreased (by 5.88%-25.01%), whereas the differences in emergence rate were not significant. The T1 and T2 treatments led to increases in leaf area, number of tillers per plant, and number of secondary roots at the six-leaf stage compared with those of the CK. Principal component analysis revealed that the first principal component that affected wheat seedling growth was dominated by the leaf area index and the net assimilation rate, whereas the leaf weight ratio mainly contributed to the second principal component. Straw incorporation delayed the wheat SET and the SEPD, and reduced the SES in the seedling emergence stage, but increased the leaf area, number of tillers per plant, and number of secondary roots in the seedling establishment stage, thereby promoting the development of strong seedlings. This study provides theoretical support for the efficient utilization of straw resources and the improvement of the quality of wheat seedlings on the Huang-Huai-Hai Plain.

With the intensification of climate change, spring low-temperature stress (SLTS) leads to floret degeneration and a decrease in grain number. This study investigated the physiological mechanisms underlying SLTS-induced floret degeneration using two wheat varieties with contrasting cold sensitivity. SLTS caused yellowing and shrinkage of floret primordia, increasing floret degeneration and fertile floret abortion, ultimately reducing grains per spike by 12.2%–26.1%. SLTS disrupted nutrient supply, impairing dry matter accumulation in young spikes. At 0–15 d after low-temperature stress (DALTS), SLTS caused a brief increase in the sugar content of young spikes (0–3 DALTS), followed by a rapid decrease (6–15 DALTS), while the total nitrogen content keeps decreasing. SLTS altered key enzyme activities, enhancing sucrose synthase and sucrose phosphate synthase but suppressing nitrate reductase and glutamine synthetase. Transcriptomic analysis revealed that SLTS perturbed starch and sucrose metabolism, carbon and nitrogen metabolism, and amino sugar pathways, altering soluble sugars, sucrose, fructose, and protein levels. SLTS disrupted carbon–nitrogen metabolic homeostasis, thereby reducing the number of fertile florets and ultimately leading to a decrease in grain number per spike. These findings enhance understanding of SLTS impacts on wheat floret development and provide insights for improving low-temperature tolerance and yield stability in wheat.