Physiological responses of two moss species to the combined stress of water deficit and elevated N deposition (II): Carbon and nitrogen metabolism

• Published in: Ecology and evolution Vol. 6; no. 21; pp. 7596 - 7609
• Main Authors: Liu, Bin‐yang, Lei, Chun‐yi, Jin, Jian‐hua, Guan, Yi‐yun, Li, Shan, Zhang, Yi‐shun, Liu, Wei‐qiu
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.11.2016; John Wiley and Sons Inc; Wiley
• Subjects: Ammonium; Ammonium chloride; Assimilation; Bryophyta; Carbon; carbon metabolism; Combined stress; compensation effect; Deposition; Drought; Extreme drought; Glutamate dehydrogenase; Glutamate-ammonia ligase; Glutamine; Hypnum; Interspecific; Metabolism; moss; Mosses; Nitrogen; nitrogen assimilation; Nitrogen metabolism; Original Research; Osmotic stress; Photorespiration; Physiological responses; Pogonatum; Proline; Rehydration; stress; Water deficit; Water shortages; Water stress; China; moss; stress; drought; nitrogen; compensation effect; carbon metabolism; nitrogen assimilation
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.2521

Nitrogen (N) deposition levels and frequencies of extreme drought events are increasing globally. In efforts to improve understanding of plants' responses to associated stresses, we have investigated responses of mosses to drought under elevated nitrogen conditions. More specifically, we exposed Pogonatum cirratum subsp. fuscatum and Hypnum plumaeforme to various nitrate (KNO3) or ammonium (NH4Cl) treatments, with and without water deficit stress and monitored indices related to carbon (C) and N metabolism both immediately after the stress and after a short recovery period. The results show that N application stimulated both C and N assimilation activities, including ribulose‐1,5‐bisphosphate carboxylase, glutamine synthetase/glutamate synthase (GS/GOGAT), and glutamate dehydrogenase (GDH) activities, while water deficit inhibited C and N assimilation. The mosses could resist stress caused by excess N and water deficit by increasing their photorespiration activity and proline (Pro) contents. However, N supply increased their sensitivity to water stress, causing sharper reductions in C and N assimilation rates, and further increases in photorespiration and Pro contents, indicating more serious oxidative or osmotic stress in the mosses. In addition, there were interspecific differences in N assimilation pathways, as the GS/GOGAT and GDH pathways were the preferentially used ammonium assimilation pathways in P. cirratum and H. plumaeforme when stressed, respectively. After rehydration, both mosses exhibited overcompensation effects for most C and N assimilation activities, but when supplied with N, the activities were generally restored to previous levels (or less), indicating that N supply reduced their ability to recover from water deficit stress. In conclusion, mosses can tolerate a certain degree of water deficit stress and possess some resilience to environmental fluctuations, but elevated N deposition reduces their tolerance and ability to recover. Although N application generally caused various physiological stresses to the mosses, N application did stimulate carbon and nitrogen assimilation in them; Water deficit inhibited both C and N metabolisms; however, mosses showed over compensatory growth after rehydration; and N application exacerbated the negative effects of water deficit and hindered the recovery of the mosses from the damage caused by the water deficit.