The impact of nitrogen deposition on photobiont-mycobiont balance of epiphytic lichens in subtropical forests of central China.

Ming Wang,Raozhen Jia,Chuanhua Wang

doi:10.1002/ece3.5803

Abstract

Excessive nitrogen (N) deposition can impact lichen diversity in forest ecosystems, and this is a particular situation in China. Here, we examined the N uptake, assimilation, and the impact of excessive N deposition on the symbiotic balance of dominant epiphytic lichens in the subtropical forests in the Mts. Shennongjia of central China. The results show that lichen species took up, assimilated and utilized more ammonium than nitrate in a species‐specific way, following the increase of N availability. The photobiont of the lichens decreased with the increase of N concentration following an initial increase, while the mycobiont response to the N addition was not apparent. Considerable variation in response to excessive N deposition exists among the lichen species. Usnea longissima could regulate its N uptake, resulting in a stable photobiont‐mycobiont ratio among N treatments. In contrast, the photobiont‐mycobiont ratio of other four lichens increased initially but decreased when N concentration exceeded a certain level, and N stress may have broken the balance between photobiont and mycobiont of these lichens. Our results suggest that most epiphytic lichens in subtropical forest of central China could uptake and assimilate more ammonium than nitrate and that the balance between photobiont and mycobiont of many epiphytic lichens might change with the increasing N deposition load, which could impact the lichen diversity of this forest ecosystem.

Highlights

Long‐term exposure to excessive nitrogen (N) from the atmosphere has been reported to result in a range of impacts on forest ecosys‐ tems (Aber et al, 2003)
By using five dominant epiphytic lichens in this region, we addressed the following questions: (a) Do epiphytic lichens in the sub‐ tropical mountains of the central China selectively uptake and assim‐ ilate ammonium and nitrate? (b) Does nitrogen addition influence the photobiont and mycobiont balance of lichen species? and whether different species reacts differently, with a species‐specific way, if that is the case? Our findings will help to understand the mechanism of N stress on lichen diversity, and provide experimental evidence on the effects of increased nitrate on lichen diversity
We found that N addition has significantly increased N utilization, especially taken up more ammonium by all the five epiphytic lichen species (Figure 1), which is consistent with the results reported by Palmqvist & Dahlman (2006)

Summary

| INTRODUCTION

Evidence exists that N improves the photosynthetic capacity of photo‐ bionts, and subsequently promotes the growth of several lichen species (Palmqvist & Dahlman, 2006) Such mixed response indi‐ cates that N deposition could impact the growth and survival of the lichens in a species‐specific way. We hypothesized that the epiphytic lichens in sub‐ tropical mountains of central China would uptake and utilize more ammonium than nitrate, which may subsequently break the balance between photobionts and mycobionts of the lichens in a species‐spe‐ cific way. Our findings will help to understand the mechanism of N stress on lichen diversity, and provide experimental evidence on the effects of increased nitrate on lichen diversity

| MATERIALS AND METHODS

| DISCUSSION

| CONCLUSIONS

Findings

CONFLICT OF INTEREST