Effect Of Forest Gaps And Epiphytes On Fallen Log Humification In A Minjiang Fir Forest

Fallen log is an important ecological factor in forest ecosystems.As a carrier of materials circulation and nutrient sources,fallen log also provides a suitable habitat for epiphytic flora and fauna,microorganisms.The slower humification process of fallen log has a positive significance for promoting biodiversity and maintaining soil fertility.The structure of fallen log is complex,and the different compositional features of heartwood,sapwood and bark will inevitably affect the humification process of fallen log.At the same time,epiphytes have a significant impact on the decomposition of fallen log,and the response of fallen log humification to the epiphytes is unclear.The formation of fallen wood will be accompanied by the emergence of forest gaps.The effects of hydrothermal condition of the gradient changes from the gaps center to under closed canopies on fallen log humification has been lacking of research.Therefore,the fallen log in alpine forest Minjiang fir(Abies faxoniana)primary forest was selected in the eastern Tibet Plateau and western Sichuan.In order to study effects of structure characteristics of fallen log and epiphytes on humifiaction of fallen log,and response of humification of fallen log to forest gaps.The results show:There were remarkable differences in the process of humification between different structures of fallen log.Humic substances,humic acid and fulvic acid content and humic acid/fulvic acid generically showed: bark> heartwood> sapwood,?logK and E4/E6 of humic substances generically showed: sapwood> heartwood>bark.This indicated that the fallen log structure will significantly affect the humification process,and the humification process of the fallen log itself is heterogeneous.With the increase of decay classes,the humic substances,humic acid,fulvic acid contents,and humic acid/fulvic acid of heartwood and sapwood showed an increasing tendency,and the highest content in IV decay class of heartwood.The humic substances and humic acid contents and humic acid/fulvic acid showed the tendency of first decrease and then increase,the content of fulvic acid of bark showed the tendency of first increased and then decreased,the ?logK and E4/E6 of humic substances showed an increasing trend with the increasing of decay classed of bark.Epiphytes had no significantly effected on the humic substances and humic acid content of heartwood in the early stage of humification process.Epiphytes causedhigher content humic substances,humic acid and fulvic acid on the upper sapwood of fallen log compared with the removal of epiphytes in the early stage of humification process,whereas in the later stage of humification.In the growth period(August),higher humic acid content in lower sapwood of epiphytes removal than epiphytes retain.higher humic substances and humic acid content,humic acid/fulvic acid in bark of epiphytes retain than epiphytes removal in the II decay class.The epiphytes had significantly effects on the ?logK and E4/E6 of humic substances of heartwood and sapwood of the fallen log,but there was no obvious regularity,and the epiphytes had no significantly effect on the ?logK and E4/E6 of humic substances the fallen log bark.This showed that the epiphyte had the dual effect of promoting and inhibiting on humification process of fallen log,which mainly depended on the structure of the fallen log,the season,and decay classes of fallen log.From the above,the sapwood was more susceptible to epiphytes,the impact of epiphytes on fallen log was more effective in the growing period than snow cover period,and the fallen log was more susceptible to epiphytes in later stage of humification.Forest gaps had a significantly effect on the humification process of fallen log.The specific performance was as follows: In the early stage of humification process,the humic acid and fulvic acid,and humic acid/fulvic of heartwood and sapwood acid within limits.The humic substances,humic acid and fulvic acid contents of heartwood at IV decay class showed: gap edge,closed canopy > gap center.The humic substances,humic acid and fulvic acid content of heardwood in V decay class at the gap center was higher in the growth period(August)and lower in the snow cover period(February).At the same time,no obvious regularity of ?logK and E4/E6 of humic substances of heartwood and sapwood with forest gaps,the forest gap had no significantly effect on E4/E6 of humic substances of bark.This results showed that the effect of forest gaps on the humification process of fallen would will increase with the increase of decay class of fallen log,but the humification of bark had a weak response to forest gaps.In addition,the humic substances,humic acid content,and humic acid/fulvic acid of heartwood and sapwood were significantly negatively correlated with the pH of heartwood and sapwood.The correlation between air temperature,water content of fallen log and humus content had a difference with forest gaps.This suggest that environmental factors have restrictions on the humification process of fallen log in different environments.In summary,the humification process of fallen log in Minjiang fir(Abies faxoniana)forests affected through many factors.With the increase of decay classes,the humification rates of heartwood,sapwood and bark were various,which was different from the humification process of litter.In addition,the epiphytes had a negative influence on humification process of fallen log,and this effect would change with decay class of fallen log.At the later stage of humification process,the impact forest gaps on humification of heartwood and sapwood had enhanced.However,the humification process of the bark might be mainly affected by means of its own components.From above results,we provided the basic data for understanding the function of fallen log in forest ecosystem,and it also further indicated the important role of humification of fallen log in promoting nutrient cycling and maintaining soil fertility.