Abstract
In this study, effects of nitrogen (N) availability on growth, survival of Ramalina calicaris var. japonica, and whether it respond nitrogen stress in an integrated physiological way was evaluated. Thalli growth and propagule survival, thalli N and phosphorus (P) content, and activity of phosphomonoesterase (PME) of R. calicaris var. japonica were determined in a field experiment. Its differentiate adsorption in ammonia and nitrate, the activity of glutamine synthetase (GSA) and nitrate reductase (NRA) also were investigated in a series of indoor experiments. The results showed that N deposition significantly decreased the growth and survival of this lichen, and the N sensitivity threshold was suggested at 6.0 kg N⋅ha-1⋅y-1. When the N deposition increased from 8.59 kg N⋅ha-1⋅y-1 to 14.24, 20.49, 32.99 and 57.99 kg N⋅ha-1⋅y-1, the growth rates of lichen thalli decreased by 26.47, 39.01, 52.18 and 60.3%, respectively; Whereas the survival rate of the lichen propagules decreased from 92.8% of control (0.0 kg N⋅ha-1⋅y-1) to 10.7% of 50.0 kg N⋅ha-1⋅y-1, when they were treated with 0.00, 6.25, 12.5, 25.0, and 50.0 kg N⋅ha-1⋅y-1 deposition. Compared with an adequate adsorption of ammonium N, no nitrate adsorption occurred when thalli was submerged in solution lower than 0.4 mM. Our results also suggested that thalli total nitrogen, N:P ratio increased with N availability, and the activity of PME was significantly correlated with thalli total nitrogen. These all indicated that phosphorus limitation occurred when R. calicaris var. japonica treated with higher nitrogen deposition. Compared with slightly effects of NRA, GSA of R. calicaris var. japonica responded nitrogen availability significantly; In addition, GSA and NRA negatively correlated with thalli growth rate and propagule survival significantly. These results indicated that nitrogen stress do decrease growth and survival of R. calicaris var. japonica, and lichen would be impacted by excess nitrogen in a integrated, not a fragmentary way, including nitrogen uptake, assimilation, even nutrient balance of nitrogen and phosphorous.
Highlights
Lichens mainly acquire mineral nutrients, including nitrogen (N) and phosphorus (P), directly from the atmosphere and rainfall via thalli surface, so they have evolved into a class of organisms sensitive to environmental pollution (Pearson and Skye, 1965; Galloway et al, 2004)
The results showed that the growth of R. calicaris var. japonica decreased when N deposition increased
Under N deposition of 8.59∼57.99 kg N ha−1.y−1, the growth rate of R. calicaris var. japonica declined from 52.8% to 20.97% (57.99 kg N ha−1.y−1)
Summary
Lichens mainly acquire mineral nutrients, including nitrogen (N) and phosphorus (P), directly from the atmosphere and rainfall via thalli surface, so they have evolved into a class of organisms sensitive to environmental pollution (Pearson and Skye, 1965; Galloway et al, 2004). A randomized sampling demonstrated absence of significant eutrophication in the area, but provided, along one of the main roads crossing the area, records of species like Xanthomendoza ulophyllodes and Phaeophyscia ciliata, that are characteristic for dust deposition and nutrient rich bark (Munzi et al, 2015). In this region, the wet N deposition in 2015 was 7.99 kg·ha−1·y−1 (Yang et al, 2018), which greatly exceeded the nitrogen deposition threshold of N-sensitive lichens of 3.2 kg·ha−1·y−1 (Fenn et al, 2008)
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