Responses Of The Niche And Interspecific Association Of Peatland Bryophytes To Elevation Gradient In Changbai Mountains

Classical stress gradient hypothesis (SGH) predicts that the plant-plant interaction willshift from competition to facilitation along gradient of stress. Quite few experiments, however,with bryophytes the second biggest group of plants as study material have been done to testSGH. And it seems that SGH can not explain the hump-shaped pattern of Sphagnum richnessalong the altitude gradient in Changbai Mountains. Chosing the dominant bryophytes in fourpeatlands as experimental materials and considering the stress tolerance of species, I studiedplant interactions (including competition and interaction) type or interaction intensity variesalong the altitude gradient, by means of niche and interspecific association analysis. Mypurpose of the experimental study is test SGH in bryophytes and to explain the distributionpattern of species richness along altitude in Changbai Mountains. The main results andconclusions are as follows:(1) The temperature decreases with altitude increasing, low temperature stress exists athigh altitudes, evaporation is the maximum but the rainfall is minimal at low altitudes, so thepeat bogs are under drought stress at low altitudes.(2) Elevation and water level are the most important environmental factors that affect thedistribution of bryophytes. They not only directly affect the distribution of bryophytes, butalso influence other environment variables to indirectly influence the distribution ofbryophytes(3) According to the altitude and water level, the two environment variables can dividebryophyte into three groups: high altitude bryophyte groups, low altitude plant group inhollow, low altitude plant group on hummocks. The order of ecological niche breadth andoverlap in the three bryophyte group is: low altitude plant in hollow＞low altitude plant onhummocks＞high altitude bryophyte. Low altitude bryophyte group on hummocks and highaltitude bryophyte in group behave significantly positive association overall.(4) The ratios of significantly positive association are greater than negative associationbetween Moss between bryophytes and vascular plants. Habitat requirements are importantinfluencing factors of the associations between bryophytes and vascular plants. There will bepossitive associations among the species which have the same habitat requirements, otherwisethere will be negative associations. Most vascular plants grow on hummocks, which developpositive interactions with the species on hummocks. However, there are positive associationsbetween vascular plants and hollow species.(5) Because of the differences of habitat requirements, the ratios of significantlyinterspecific negative associations are more common than the significantly positive association. Interspecific competition is also one of the most main reasons.However, thereexist significantly positive associations among bryophytes which is in the same habitat, itsuggests generally positive interaction between bryophytes.(6) The niche breadth of dominant vascular plants and bryophytes are all narrow, andniche overlap is large. The average value of niche overlap, among bryophytes, betweenbryophytes and vascular plants, among all the dominant species all decease with the increaseof altitude.(7) We can explain interspecific interactions among the species if combining niche andinterspecific association. Positive interactions lead to large niche overlap and positiveassociation between species pairs; competitive lead to large niche overlap and negativeassociation between species pairs; when the habitats of species were different, niche overlapsbetween species pairs are small and interspecific association are negative.(8) Under drought condition, between bryophytes, especially between hollow species andhummock species, there is a strong competition which could not support SGH. However,positive interaction is displayed between bryophytes which have the same habitatrequirements.(9) With the increase of altitude and the decrease of temperature, the importance ofpositive interaction among bryophytes increases or they tend to differentiate in niche to avoidcompetition. Proportion of significant negative association between bryophytes and vascularplant species falls with altitude increase, and positive interaction is the main interaction athigh altitudes. Under the condition of low temperature, interaction between bryophytes, aswell as between bryophytes and vascular plants supports SGH.(10) Environmental stress, include non-resource and resource stress. In the non-resourcestress, positive interactions were showed. And in resource stress, if habitat needs are differentbetween species, there is a strong competition. If habitat requirements are the same, positiveinteractions were showed. And it consistented with prediction of Maestre’s (2009) SGHimprovements.(11) In the area of Changbai Mountains, the hump-shaped pattern of Sphagnum richnessalong the altitude gradient is the result of by both environmental stress and interspecificinteractions. In high altitudes, interspecific interactions mitigate the impact of environmentalstress on bryophytes. In low altitudes, however, interspecific interactions exacerbate theimpact of environmental stress on bryophytes. In Jinchuan peatland, the decrease of speciesrichness probably relates to its experience of drainage and then rehydrated.