Characteristics Of Mound-pit Microsites At Different Age Classes And The Analysis On Their Soil Physical And Chemical Properties In Picea Koraiensis-abies Nephrolepis Forest Of Xiaoxing'an Mountains,Northeast China

Picea koraiensis-Abies nephrolepis forest is the climax community in the valley of Xiaoxing'an Mountains,which occupies an important position in the temperate coniferous forest vegetation types in Northeast China.Due to the mound-pit microsites formed by uprooted trees,increased the complexity of the forest,improved the light,temperature,moisture and other environmental conditions in gaps,promoted the regeneration ability of surrounding trees and grasses in the forest community at the same time,gaps have an effect on Picea koraiensis-Abies nephrolepis updates.Therefore,the mound-pit microsites formed by uprootd trees play an important role in maintaining the diversity of forest species and the landscape pattern.In this study,the mound-pit microsites formed by uprooted trees in Picea koraiensis-Abies nephrolepis forest of Xiaoxing'an Mountains as the research object.In September 2015,the characteristics of the mound-pit microsites were investigated,soil samples were taken at 0-15 and 15-30 cm depths from all mocrosites including mound top,pit bottom,edge of downed trees and closed canopy(as control).To determine the formation age of mound-pit microsites by growth release and decay degree of downed trees,The differences of soil physical and chemical properties and stoichiometry ratios of soil C,N,P were compared among different microsites position and at different ages.The results show that:(1)The microsites located in gaps and non-gaps,the maximum variation of the DBH IS Abies nephrolepis in gaps,the DBH of Picea koraiensis and Abies nephrolepis in gaps is relatively larger than in non-gaps.The Picea asperata and Abies nephrolepis have appeared different intensity of growth release in the period from 2000 to 2010 year,the release events of Picea asperata and Abies nephrolepis in gpas were more than those of in non-gaps.There was a strong consistency of the ring width between Picea asperata and Abies nephrolepis in gap-edge trees at the same age level mound-pit microsites,whereas the relative difference of the ring width was found among different age classes mound-pit microsites.The age of class I mound-pit microsites formed about in 2012-2013 year,the age of class II mound-pit microsites was formed two in 2010,average one each year from 2006-2008 year,the age of class III mound-pit microsites was formed two in 2005,one in 2004 and two in 2003.(2)The number of uprooted trees is Picea koraiensis,Abies nephrolepis,Pinus koraiensis and Betula platyphylla in turns.The order of average DBH of uprooted trees in three age classes mound-pit microsites is class III(40.8 cm)>class II(33.4 cm)>class I(30.0 cm).The maxmum average volume of mound and pit are class I(0.609 m~3)and class III(0.690 m~3),respectively,the minimum average volume of mound and pit are class II(0.481 m~3)and class I(0.363 m~3).The maximum value of length and width of mound and pit appears in the age of class III.There was a positive significant correlation between the DBH and the mound length,the DBH and the pit length,the pit volume with the mound length in age classes I mound-pit microsites.In age classes II and III mound-pit microsites,the average pit volume was positive significant correlated with the mound length and pit width,the mound length and pit width were significantly positively correlated.The survey results show that the larger the DBH of the uptooted trees,the larger the characteristic parameters of the corrresponding mounds and pits,indicating that the DBH of uptooted trees is related to the size of the mound and pit.(3)Soil bulk density increased significantly with soil depths increase,the soil capillary porosity,total porosity,saturated moisture capacity and capillary water holding were all significantly decreased gradually with soil depths increase.The maximum soil bulk density appeared at the pit bottom and the microsites of age class I,Soil bulk of pit bottom at the same age class was significantly higher than the other microsites and closed canopy,there was no significant difference in the bulk density at pit bottom among microsites at different age classes.The minimum values of capillary porosity,total porosity,saturated moisture capacity and capillary water holding were appear at the pit bottom and age class III microsites exceppt the maximum value of the capillary porosity appears at the age class I microsites.Among three factors such as age classes,microsites positions and soil depths,in general,the microsites positions and soil depths have a significant effect on soil physical properties(P<0.05),the effect on parts of indicators is extremely significant(P<0.01).(4)The soil pH was significantly increased with soil depth increase.The soil total C,total N,total P,available P and available K were all significantly decreased with soil depth increase.The maximum of soil total C,total N appeared at the closed canopy,while the minimum appared at pit bottom.The contents of total P and available K in the mound top were higher than those in the other microsite positions,the available P content in the mound-pit microsites was higher than that of the close canopy.The maximum values of soil pH,total C,total P and available K were appeared in age class III mound-pit microsite.The maximum values of total N and available P were appeared in age class I mound-pit microsite.Among three factors such as age classes,microsites positions and soil depths,in general,the microsites positions and soil depths have a significant effect on soil chemical properties(P<0.05),the effect on parts of indicators is extremely significant(P<0.01),while not significantly affected by microsite positions.Therefore,the soil chemical properties show their differences in different age classes,different microsite positions,different soil depths.(5)The coefficient of variation of soil total C,total N,total P,C/N,C/P and N/P ranged from 0.2-0.5 in microsites in Picea koraiensis-Abies nephrolepis forest,which belongs to medium variation.The values of soil C/N,C/P and N/P were decreased with the soil depth increase in different age classes microsites.There was no significant difference in soil C/N among different age classes microsites and different microsite positions.In the upper soil layer,soil C/P of the same age class mound,age class II and III microsites at the same position was significantly less than that of closed canopy.The change of soil N/P in different microsite positions is irregular relatively,the order of soil N/P is Class I>Class II>Class III at the same microsite positions in different age classes.There was a significant positive correlation between soil total C and total N,total C and total P,total N and total P.There was a significant positive correlation between soil total N and C/P,total P and C/N.Soil total C was negatively correlated with soil N/P.