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Phenotypic and Physiological Changes Associated with Senescence in Stay-Green Elymus sibiricus and Germplasm
Wenhu Wang1,2, Wenhui Liu1,2, Kaiqiang Liu1,2
1Academy of Animal Science and Veterinary, Qinghai University, Xining 810016, China.
Abstract:
Early senescence of alpine pasture grass, manifested as rapid yellowing at the onset of autumn on the Qinghai-Tibet Plateau, constrains the sustainable development of grassland animal husbandry. Breeding stay-green forage germplasm is key to mitigating this problem. To identify superior stay-green germplasm and preliminarily elucidate the main drivers of senescence, we evaluated six stay-green lines of Elymus sibiricus with non-stay-green materials as controls. Fixed-site field observations were conducted for three consecutive years in Haiyan County, Qinghai Province. We quantified dynamic changes in phenotypic, photosynthetic, and physiological traits during senescence, applied mixed-effects models to identify factors associated with stay-green, and used the TOPSIS model for comprehensive evaluation. The results showed that plant height, green leaf area, chlorophyll content, net photosynthetic rate, and root activity of stay-green E. sibiricus were significantly higher than those of non-stay-green materials at all planting years, and the senescence rate was significantly slower. All traits performed optimally at the third year. Relative to HB-2, HB-4, HB-8, HB-10, HB-11, and HB-15 (stay-green E. sibiricus), plant height, green leaf area, chlorophyll content, net photosynthetic rate, and root activity of CK (non-stay-green E. sibiricus) were 0.83, 0.95, 0.79, 0.82, 0.80, and 0.78; 0.37, 0.37, 0.34, 0.35, 0.31, and 0.35; 0.82, 0.84, 0.80, 0.86, 0.82, and 0.75; 0.86, 0.86, 0.74, 0.89, 0.77, and 0.70; and 0.72, 0.74, 0.66, 0.78, 0.70, and 0.61, respectively. Mixed-effects modeling identified chlorophyll, root vitality, soluble sugars, and photosynthesis as the primary determinants of stay-green in E. sibiricus. The TOPSIS model indicated that HB-15 maintained the highest fitting degree values in years 2-4. These values were 0.69, 0.62, and 0.71, respectively. Therefore, HB-15 was the most ideal stay-green germplasm. These findings provide a theoretical basis and elite parental materials for breeding new stay-green varieties of E. sibiricus.
