Response Of The Reproductive Characteristics Of Sphagnum To Environmental Changes In The Changbai Mountains

Reproductive process is the base for plant populations to persist and develop.In different environments,plants form specific features of resource allocation and reproductive strategies.As the dominant species of peatlands,Sphagnum play an important role in global carbon cycle.Although reproductive ecology research of Sphagnum has made great progress in spore production,spore rain,spore-release mechanism and persistent spore bank,there are still rather few studies on the sporophyte production and reproduction phenology,and effect of environmental change on reproductive strategy selection in Sphagnum has not been reported yet.In this study,three dioecious bryophytes,Sphagnum fallax Klinggr.,S.magellanicum Brid.and S.fuscum(Schimp.)Klinggr.in Dongfanghong Peatland and one monoecious bryophyte S.capillifolium(Ehrh.)Hedw in Hani Peatland of the Changbai Mountains,northeastern China,were selected as study species.I studied the effect of environmental change on sexual reproduction ratio,sporophyte production,reproduction phenology and reproduction strategies by combining field investigation and a laboratory experiment.I aimed to better understand the mechanism of bryophytes to adapt to environmental change,reveal the ecological mechanism of growth and reproduction,and contribute to the development of peatland bryophyte reproduction ecology.The main results and conclusions are as follows:(1)Sexual reproduction ratio of S.fallax and S.magellanicum increased with water level.It showed a reverse relation with total cover in great quadrats in S.fallax.It increased with Na concentration and dwarf shrub cover in small quadrats in S.fuscum.These mean that water level and vascular plant cover are important factors affecting the sexual reproduction ratio of Sphagnum.(2)Sporophyte production of S.fallax and S.magellanicum increased with water level or total coverage in small quadrats.It increased with dwarf shrub cover in small quadrats and Na concentration in S.fuscum.The formation of sporophyte was more sensitive to summer drought.Decrease in water level resulted in sporophyte production decrease in S.fallax and S.magellanicum,but no effect on hummock species S.fuscum that with superior water transport ability was found.Cover increase of vascular plants probably decreases the water evaporation of bryophyte surface to guarante constant water supply to promote the sporophyte production in the three Sphagnum species.(3)In the laboratory experiment,the capsules of S.capillifolium changed their color from pale yellow to dark brown,and changed their morphology from oval to spherical,and their capsule diameter and seta length gradually increased.In addition,light intensity increase was favor in the increase of capsule diameter and seta length and especially when the water level was higher.The possible reasons are that long stea increased the height of sporophytes,and large capsules are able to produce greater pressure inside.Both of these make spores released higher,increase air turbulence intensity,which can facilitate spores to spread further and expand their potential populations.(4)Both water level increase and canopy density decrease in small quadrats increased capsule cracking rate of S.fallax and S.magellanicum.Decrease in both herb cover in large quadrat and sodium concentration promoted capsule cracking rate in S.fuscum.Laboratory tests showed that the increase of both water level and light intensity led to greater capsule cracking rate and earlier spore release about 4.0 d and 4.8d of S.capillifolium.Sphagnum generally had a low sporophyte and spore production per unit area compared with many other bryophytes.More capsule cracking will increase the proportion of spores released.Advancing reproductive phenology can reduce the abortive risk of spores by avoiding detrimental environmental conditions such as drought.(5)The height increment of three Sphagnum species(S.fallax,S.magellanicum and S.fuscum)in the field decreased with the increase of the number of branches and capsules in one shoot.Laboratory control experiments showed that under the condtion of higher water level,height increment of reproductive and vegetative shoots of S.capillifolium were higher,and reproductive shoots were significantly lower than vegetative ones.After capsules dehisced,reproductive shoots were able to accelerate height increment to be higher than capsules gradually and eventually shaded them.This means that asexual reproduction,namely branching and sexual reproduction,namely sporophyte production lead to decrease of material and energy investment in height increment.(6)There was a negative correlation between capsule diameter and capsule number per shoot in three Sphagnum species(S.fallax,S.magellanicum and S.fuscum).This suggests that resource availability for gametophytes is limited and resource limitation forces bryophytes to make a reasonable choice between capsule quantity and capsule quality in the process of sporophyte production.Spore number and spore diameter were positively correlated with diameter per capsule in the three species.Spore number and capsule diameter were negatively correlated when size difference of capsule was eliminated.This suggests that there is a strong resource trading-off between the reproductive traits.In addition,both spore number and spore diameter in S.magellanicum was greater than S.fallax and S.fuscum,indicating that larger plants have more resources to allocate to the production of sporophytes.(7)Asexual reproduction is the main reproduction means in the three Sphagnum species(S.fallax,S.magellanicum and S.fuscum)and sexual reproduction ratio is low by the shoots with one capsule in the sexual reproduction shoots.This suggest that greater demand for resource investment limits sexual reproduction.Furthermore,asexual: sexual reproduction ratio decrease with branch number per shoot and capsule number.Proportion of the shoots with both asexual and sexual reproduction decrease with increase of capsule number per shoot.When a shoot with more than three capsules,the proportion of shoots with branches in S.magellanicum and no shoots produced branches in S.fallax.When the number of capsules was greater than one of S.fuscum,branch was none.This clearly shows that sexual reproduction limits asexual reproduction.(8)Sexual reproduction of plants requires substantial resource investment.Excellent environmental conditions can guarantee resource availability and enhance the chance of sexual reproduction in Sphagnum.My study suggests that the increase of both water level and vascular plant cover(herb cover in small quadrats for S.fallax,total cover in small quadrats for S.magellanicum)the bryophytes increase resources investment to reproduction and they probably tend to prefer producing offspring by sexual reproduction.In S.fuscum,increase of density and dwarf shrub cover in small quadrat are in favor of sexual reproduction probably by virtue of shortening the distance between males and females and enhancing humidity.It seems that S.fuscum was more likely to propogate by sexual reproduction.In short,my study shows that environmental change in peatlands affects reproduction pattern selection in Sphagnum.