Contrasting Strategies of Nitrogen Absorption and Utilization in Alfalfa Plants Under Different Water Stress
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ORIGINAL PAPER
Contrasting Strategies of Nitrogen Absorption and Utilization in Alfalfa Plants Under Different Water Stress Limin Gao 1 & Jing Su 1 & Qian Tian 1 & Yixin Shen 1 Received: 18 December 2019 / Accepted: 11 March 2020 # Sociedad Chilena de la Ciencia del Suelo 2020
Abstract Drought and flooding stress are among the challenges to improving alfalfa yields. Nitrogen (N) is a major element required for plant growth and has a key role in stress tolerance. However, the role of N in mediating alfalfa growth under drought and flooding stress remains unknown. Pot experiments with three different soil water contents (30, 70, and 110% of the field water capacity, i.e., W-30%, W-70%, and W-110%) and three nitrogen application rates (0, 30, and 60 mg kg−1 soil, i.e., N-0, N-30, and N-60) were conducted to determine the strategies of alfalfa response to drought and flooding stress in relation to N absorption and utilization. Regardless of the N rate, alfalfa biomass was restricted in both W-30% and W-110% treatments compared with W-70% treatment. Root biomass proportion and root length were elevated in W-30%, but not in W-110% plants. The sugar content response to water stress was concordant with the biomass response. N accumulation in W-30% plants was significantly higher than in W-110% plants under N-30 and N-60. The photosynthetic rate, photosynthetic N use efficiency, and leaf photosynthetic N proportion were elevated in W-110% treatments compared with W-30% treatments. Increased root sugar allocation and N absorption under drought stress sustained alfalfa growth, while an enhanced leaf photosynthetic N in flooded plants offset reduced N accumulation and contributed to an elevated net photosynthesis rate. Keywords Alfalfa . Drought . Flooding . Nitrogen
1 Introduction Alfalfa is an important perennial forage legume for dairy production systems worldwide due to its outstanding economic value and desirable agricultural traits (Bouton 2012). Because of its importance for livestock and nutritional security, extensive efforts have been made to increase alfalfa production. However, efforts to improve yields have encountered severe challenges due to a range of biotic and abiotic stresses. Among the stresses, drought and flooding are thought to be the main factors restricting agricultural crop yields because they have negative effects on photosynthesis, protein content, leaf expansion, and respiration (Chaves et al. 2003; Liao and Lin Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42729-020-00230-0) contains supplementary material, which is available to authorized users. * Yixin Shen [email protected] 1
College of Agro-grassland Science, Nanjing Agricultural University, Weigang 1, Nanjing 210095, China
2001). Drought is a result of inadequate water supply from either rainfall or groundwater. The deep penetrating, strongly developed roots of adult alfalfa plants confer good drought tolerance, but the negative impacts of water deficit on early seedling growth substantia
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