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

Bin‐Yang Liu,Chun‐Yi Lei,Yi‐Shun Zhang,Wei‐Qiu Liu,Jian‐Hua Jin,Yi‐Yun Guan,Shan Li

doi:10.1002/ece3.2521

Bin‐Yang Liu, Chun‐Yi Lei + Show 5 more

Open Access

https://doi.org/10.1002/ece3.2521

Copy DOI

Abstract

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 (KNO 3) or ammonium (NH 4Cl) 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.

Highlights

Atmospheric nitrogen (N) deposition has risen sharply during recent decades and is expected to increase further in the near future (Fang, Gundersen, Mo, & Zhu, 2008; Galloway et al, 2008; Liu et al, 2013; Steven, Dise, Mountford, & Gowing, 2004)
To improve knowledge of these phenomena, we have investigated primary metabolism, secondary metabolism, and hormone regulation responses of Pogonatum cirratum subsp. fuscatum and Hypnum plumaeforme to drought and subsequent short-term recovery under varied nitrate (KNO3) or ammonium (NH4Cl) exposure treatments
We found that water stress decreased PN contents generally, but increased NPN and Free amino acids (FAAs) contents of the mosses, especially under low-to-moderate N supply conditions, indicating that endogenous proteolysis activity was stimulated by oxidative stress (Palma et al, 2002)

Summary

| INTRODUCTION

Atmospheric nitrogen (N) deposition has risen sharply during recent decades and is expected to increase further in the near future (Fang, Gundersen, Mo, & Zhu, 2008; Galloway et al, 2008; Liu et al, 2013; Steven, Dise, Mountford, & Gowing, 2004). Various studies have shown that excess N and drought can induce oxidative or osmotic stresses in plants and affect both their primary and secondary metabolism (Bauer et al, 2004; Fresneau, Ghashghaie, & Cornic, 2007; Guo, Schinner, Sattelmacher, & Hansen, 2005; Irigoyen, Einerich, & Sánchez-Díaz,1992; Liu et al, 2015a; Pearce, Woodin, & Van der Wal, 2003). We have previously reported results pertaining to secondary metabolism, including acclimation characters of the mosses to drought stress and interspecific differences in responses of their phenylpropanoid metabolism to water deficit (Liu et al, 2015a). We explored responses of the mosses’ carbon and nitrogen metabolism process and interactions between associated metabolic pathways to combined water deficit and N application treatments, compensation effect in them following water deficit, and the physiological mechanism involved

| MATERIALS AND METHODS

| DISCUSSION

Findings

| CONCLUSION