Effect Of Drainage On The Quantitative Characteristics Of Sphagnum Spore Banks In Peatlands

Spores of Sphagnum can maintain viability in soil and form spore banks,which may play an important role in maintaining the stability of population.In peatlands dominated by Sphagnum,a large number of Sphagnum spores are stored in the peat,many of which can remain viability for hundreds of years and form an extremely long-term persistent spore banks.Since the middle of last century,many peatlands around the world have been drained for agriculture,forestry and other reasons.These lead to a general water table draw-down,physicochemical characteristics change in peat and even vegetation succession.However,it is still unclear how drainage affects Sphagnum spore banks.Baijianghe Peatland in the Changbai Mountains and Tangbei Peatland in the Xiaoxingan Mountains which both have undergone drainage and were selected as my two study sites.Peat cores from three stands,near-pristine,far-from ditch and close-to ditch in both peatlands were used as experimental materials.The peat cores were cut into 2-cm-thick slices.Sphagnum spores were extracted to count spore density and test spore germinability by germination experiment for each slice.After dating and determining relationship between peat depth and age,I calculated spore accumulation rate.Physicochemical characteristics such as bulk density,ash content,p H,total carbon,total nitrogen and C/N ratio were measured layer by layer.Relationship between Sphagnum spores and burial environment was established to figure out the effect of drainage on Sphagnum spore banks.The main results are as follows:(1)Average spore density in the peat cores from near-pristine,far-from ditch and close-to ditch stands in Baijianghe Peatland was about 7,2 and 6 spores cm-3,respectively.Average spore density in the peat cores from the same three stands in Tangbei Peatland was about 14,3 and 18 spores cm-3,respectively.This suggested that the spore density of spore banks between the two peatlands were different and drainage greatly decreased spore density at far-from ditch stand.(2)The average spore accumulation rate(SAR)at the three stands in Baijiang Peatland were significantly different,near pristine stand had the highest SAR.There were also significant differences in SAR at the three stands in Tangbei Peatland,far-from ditch stand had the lowest SAR.(3)After drainage,SAR at near-pristine stand was higher than that at far-from ditch stand and close-to ditch stand in Beijinghe Peatland.In Tangbei Peatland,there was no difference in SAR between near pristine stand and far-from ditch stand,which were both lower than that at close-to ditch stand.This suggested that drainage generally inhibits SAR,but the weak drainage can increase SAR due to the emergence of high-spore producing plants.(4)After drainage,the average spore germinability at three stands in Baijianghe Peatland was 40%,30% and 74%,respectively,which meant that spore germinability was improved at close-to ditch stand.The average spore germinability at three stands in Tangbei Peatland was 42%,40% and 58%,with no difference in statistical level.This suggested that the weak intensity of drainage had little effect on spore germinability,but after 30 years of strong drainage,spores germinability was improved significantly.(5)According to estimation,in Baijianghe Peatland,spore germinability at three stands can be maintained maximumly for 414,789 and 770 years,respectively.In Tangbei Peatland it can be maintained for 2202,1548 and 1616 years,respectively.This suggested that the time spore germinability can be maintained had different responses to the change of drainage degree in the two peatlands.The method to estimate spore longevity by using the germinability has some limitation.There is a lack of spore vigor test.(6)According to the whole core,in Baijianghe Peatland,bulk density,p H,total carbon,total nitrogen and C/N ratio at three stands all were different.In Tangbei Peatland,bulk density,ash content,total carbon,total nitrogen and C/N ratio at three stands were not different.The contrasted results suggested that the drainage intensity and its effect in Baijianghe Peatland is stronger than those in Tangbei Peatland.(7)SAR and spore germinability at three stands in both peatlands were all correlated with peat physicochemical characteristics,suggesting that burial environment affected SAR and spore germinability.In summary,the drainage 30?40 years ago had an important impact on Sphagnum spore banks in the two typical peatlands.However,SAR in the two peatlands responded differently due to the difference in drainage intensity and original vegetation.Drainage generally inhibits SAR,but the weak drainage can increase SAR due to the emergence of high-spore producing plants.Drainage strongly affected physicochemical characteristics of peat via accelerating decomposition and resulted in corresponding change in spore germinability.Weak drainage had little effect on germinability of the spores buried in peatlands,but after 30 years of strong drainage,spore germinability was significantly improved,and this may reduce the persistence of spore banks and lead to a decrease of persistent regeneration potential of Sphagnum after catastrophic disturbances.