Sphagnum outcompetes feathermosses in their photosynthetic adaptation to postharvest black spruce forests

Abstract

Mosses dominate the understory of black spruce forest, and changes in moss community composition and functional traits may influence many important ecosystem processes, particularly paludification due to accumulation of peat (mainly Sphagnum). To understand performance and fitness of ground-cover mosses in early forest succession following clearcutting, we investigated photosynthetic traits in Sphagnum and three feathermoss species (i.e., Hylocomium, Ptilium, and Pleurozium) coexisting in mature stands and decade-old black spruce harvest blocks. The results showed that all of these mosses have a significantly higher light saturation point at the harvested plots than the forested plots. Feathermosses at the harvested plots all underwent a reduction in quantum efficiency, chlorophyll b content, and chlorophylls:carotenoids ratio related to photoinhibition, particularly Pleurozium, which experienced a significant decrease in maximum net photosynthesis. In contrast, Sphagnum showed a significant increase in maximum gross photosynthesis, dark respiration, and the ratio of chlorophyll a:b at the harvested plots compared with the forested plots. The distinctive responses of moss photosynthetic traits indicate the potential proliferation of Sphagnum and decrease of feathermosses, and thus consequent peat accumulation. Our results emphasize the importance of the photosynthetic traits of moss as indicators of postharvest conditions for enhancing understory vegetation management to maintain and improve productivity of black spruce.

Partial Harvest in Paludified Black Spruce Stand: Short-Term Effects on Water Table and Variation in Stem Diameter

“…These results do not mean that we can ignore the potential negative effects of silvicultural treatments on water table depth and stem diameter fluctuations. The potential negative effects can be expect over a longer horizon such as: water table can rise and enhance sphagna growth decreasing the stand productivity [17,22]. Indeed, we noted a marginal effect of canopy openness on variation in stem diameter.…”

“…In this stand type, we posit that an additional problem is water table rise following harvest, which can induce tree mortality [20,21]. Over longer periods following harvest, the water table can rise further in the absence of fire when sphagnum growth increases with the formation of canopy openings [17,22]. On thick organic soils, the perched water table rises between 2.6 and 22 cm following silvicultural treatments, such as clearcutting and pre-commercial thinning [23][24][25][26].…”

Current Perspective Concerning the Potential Value of Chloroplast Lipidome in Assessing Moss Response to Abiotic Stress During Boreal Forest Regeneration

“…Clearcutting is a common harvesting practice for regeneration of boreal forest stands (Zhu et al, 2019). Clearcutting is considered a major anthropogenic disturbance and accounts for approximately 80% of boreal forests harvested annually in Canada (Youngblood and Titus, 1996).…”

“…Mosses are important parts of many ecosystems, specifically in boreal forests where they play an important role in regulating conditions such as soil climate, nitrogen (N) assimilation, forest regeneration, and C cycling in ecosystems (Zhu et al, 2019). In fact, mosses contribute significantly to aboveground vegetative biomass, which affect ecosystem processes such as C cycling (Lindo and Gonzalez, 2010).…”

“…In a study by Zhu et al (2019) the effects of clearcutting on moss species in harvested and forested plots were evaluated. The feathermosses Hylocomium and Pleurozium had the highest P nmax , Sphagnum had the lowest, and Ptilium was intermediate in forested plots (Zhu et al, 2019). Whereas in harvested plots, Sphagnum had the highest P nmax and Pleurozium had the lowest.…”