Characteristics Of Soil Carbon,Nitrogen And Phosphorus Stoichiometry Under Different Forest Types And Site Conditions In The Maoershan Region,Northeastern China

Exploring the stoichiometry of soil carbon(C),nitrogen(N)and phosphorus(P)is important for soil carbon sequestration and nutrient cycling processes.Five forest types under different site conditions but identical climate was selected,which included two plantations(i.e.,Pinus koraiensis and Larix gmelinii)and three broadleaved forests(Quercus mongolica stand,Populus davidiana and Betula platyphylla stand,and hardwood stand).The contents and densities of the soil C,N and P in these stands were quantified in order to examine their vertical changes and stoichiometry along the soil profiles.In order to exclud the influence of forest type,we selected larch plantations alone the hillside,and quantified the stoichiometry of soil,soil microbial and soil extracellular enzyme,moisture content and soil pH in order to figure out the main factors and the underlying mechanism of the changes in different soil conditions.Then,the plantation biomass,fine root biomass,soil N,P densities were quantified in order to explore the mechanism of how soil nutrient affect the biomass of larch plantations.The results of the first part showed that(1)the contents and densities of soil C,N and P differed significantly among the five forest types;the contents and densities of soil C and N at both O-and A-horizons in the hardwood stand were significantly greater than those in the rest stands.(2)The contents of C and N decreased with soil depth in all stands;however,the content of P decreased significantly with soil depth only in the broadleaved stands.(3)The soil C:N ratio at A-horizon,N:P ratios at O-horizon,the C:P ratios at A-and B-horizon differed significantly among all the stands.(4)Both slopes and intercepts of the relationship between soil C and N did not differ significantly among the five forest types,with a common slope of 11.7 and intercept of-8.0.However,significant N-P and C-P relationships existed only in the broadleaved stands.The results of second part showed that(1)There were significant positive correlation between soil stoichiometric,except soil C:N,and moisture content.(2)There were no significant relationships between soil stoichiometry and microbial stoichiometry,but significant positive correlation between soil C,N,P contents,N:P and enzyme stoichiometry,reciprocally.(3)There was no significant relationship between the biomass of larch plantations and soil P density,but a significant negative correlation with soil N density,and a significant positive correlation with the ratio of larch fine root biomass to total fine root biomass.Our results indicated that the C-N coupling relationship tended to converge,while the N-P and C-P coupling relationships tended to diverge among these temperate forests.Moisture content is the main factor of the changes of soil stoichiometric expect soil C:N.The interaction of soil nutrient and interspecific competition resulted in the change of the relationship between larch plantation biomass and soil nutrient.By measuring the soil stoichiometry in different forest types and site conditions,revealed a part of mechanism of its changes and explored the relationship between soil stoichiometry and productivity of plantation,provided basic data and suggestions for plantation management.