Abstract
Global environmental changes are leading to an increase in localized abnormally low temperatures and increasing nitrogen (N) deposition is a phenomenon recognized worldwide. Both low temperature stress (LTS) and excess N induce oxidative stress in plants, and excess N also reduces their resistance to LTS. Mosses are primitive plants that are generally more sensitive to alterations in environmental factors than vascular species. To study the combined effects of N deposition and LTS on carbon (C) and N metabolism in moss, two moss species, Pogonatum cirratum subsp. fuscatum, and Hypnum plumaeforme, exposed to various concentrations of nitrate (KNO3) or ammonium (NH4Cl), were treated with or without LTS. C/N metabolism indices were then monitored, both immediately after the stress and after a short recovery period (10 days). LTS decreased the photosystem II (PSII) performance index and inhibited non-cyclic photophosphorylation, ribulose-1,5-bisphosphate carboxylase, and glutamine synthetase activities, indicating damage to PSII and reductions in C/N assimilation in these mosses. LTS did not affect cyclic photophosphorylation, sucrose synthase, sucrose-phosphate synthase, and NADP-isocitrate dehydrogenase activities, suggesting a certain level of energy and C skeleton generation were maintained in the mosses to combat LTS; however, LTS inhibited the activity of glycolate oxidase. As predicted, N supply increased the sensitivity of the mosses to LTS, resulting in greater damage to PSII and a sharper decrease in C/N assimilation. After the recovery period, the performance of PSII and C/N metabolism, which were inhibited by LTS increased significantly, and were generally higher than those of control samples not exposed to LTS, suggesting overcompensation effects; however, N application reduced the extent of compensation effects. Both C and N metabolism exhibited stronger compensation effects in H. plumaeforme than in P. cirratum subsp. fuscatum. The difference was especially pronounced after addition of N, indicating that H. plumaeforme may be more resilient to temperature and N variation, which could explain its wider distribution in the natural environment.
Highlights
The overall trend of global climate change is warming; the accelerated melting and disappearance of Arctic Sea-Ice has led to increasing local occurrences of abnormally low temperatures (Mori et al, 2014; Overland et al, 2015)
For −Low temperature stress (LTS) samples, N application decreased performance index on absorption basis (PIabs) in both species, while it only decreased NCPSP and CPSP in H. plumaeforme, and ammonium was associated with much larger declines than nitrate
Substantial increases were observed in PIabs and NCPSP in +LTS samples, with greater increases in H. plumaeforme than in P. cirratum, with significantly higher values of these indices than those of corresponding R.−LTS samples
Summary
The overall trend of global climate change is warming; the accelerated melting and disappearance of Arctic Sea-Ice has led to increasing local occurrences of abnormally low temperatures (Mori et al, 2014; Overland et al, 2015). Low temperature stress (LTS) damages plants by inducing oxidative stress, hindering photosynthesis, and indirectly inducing osmotic stress (Nuccio et al, 1999; Allen and Ort, 2001; Beck et al, 2007). Increasing nitrogen (N) deposition is another environmental problem which attracts global attention (Stevens et al, 2004; Galloway et al, 2008; Liu et al, 2013). Excess N deposition leads to nutritional imbalance, cell membrane destruction, and oxidative stress in plants (Pearce and van der Wal, 2002; Koranda et al, 2007). Excess N deposition can reduce the resistance of plants to LTS (Fenn et al, 1998); this phenomenon merits attention, the underlying mechanisms have seldom been investigated
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