| This study focuses on three different altitudinal gradients(1750m/2050m/2350m)of plantation and natural Larix principis-rupprechtii stands in different ages(10-90a)on Guandishan Mountain.The distribution pattern of carbon,nitrogen and phosphorus elements was analyzed by using ecological stoichiometry methed.Main research contents were: The C N P stoichiometry characteristics of each component of the Larix principis-rupprechtii forest ecosystem;the coupling relationship among plant-litter-soil continuum element stoichiometry characteristics;The purpose of this study was to explain the response of different components of Larix principis-rupprechtii forest ecosystem to the changes in altitude and forest age,nutrient cycling among different components,growth restriction and elements resorption of Larix principis-rupprechtii,and to further reveal the ecological strategies of Larix principis-rupprechtii in response to the change of environmental factors and nutrient restriction under the background of global climate change.In order to provide scientific theoretical support for nutrition control,tending optimization and rational management of Larix principis-rupprechtii forest in this region.The results revealed that:(1)Origins,elevation and age have different effects on Larix principis-rupprechtii C N P stoichiometry characteristics and ratios.Growth,resorption rate and physical and chemical properties of Larix principis-rupprechtii forest show different patterns with the change of altitude and age.This changes better indicate the nutritional status of forest ecosystems and the response to changes in environmental factors.(2)The physical and chemical properties of soil and C:N:P stoichiometry in the study area showed that the level of C N P content was generally low,especially for soil phosphorus,there are differences between plantations and natural forests,and the content of carbon,nitrogen and phosphorus in plantations was higher than that in natural forests.soil physical and chemical indexes show a typical vertical distribution pattern in 0-30 cm soil layer,which accords with the general conclusion.Soil available nutrients showed a variety of elevation and forest age patterns,among which the response of nitrogen was not sensitive to the change of altitude,but more sensitive to the change of forest age.The soil TOC,TN,C:N,N:P of the two origin stands increased with altitude,while the C:N decreased.Compared with the natural forest,the soil of plantations showed greater variation with elevation;Soil TOC,TN increased and soil TP decreases first and then increases with forest age.The soil TP content minimum appeared in 30-40 a plantations and 40-50 a in natural forests respectively.To some extent,this reflects the difference between the two origins in the rapid growth period of Larix principis-rupprechtii forest.The rapid growth period of plantation was earlier and reaching a peak at 30-40 a,while the natural forest appears at 40-50 a of forest age.(3)The C N P contents and stoichiometry characteristics of different organs and litter in Larix principis-rupprechtii showed that the trend of plantations was basically the same as the natural forests,while the variation range of plantations was significantly higher than that of natural forests,and the response to elevation change was more sensitive.The C:N and N:P ratios of fine roots of natural forest and plantations also showed the same trend to the change of elevation,and the TP and C:N of fine roots in natural forest were higher.The response of the fine roots in plantations to altitude changes also showed a higher sensitivity.Changes in litter C N P contents and stoichiometry ratios with altitude and forest age were consistent with the changing trend in the leaf.The TOC and TN contents in plantations were lower than that in natural forests,and the variation range was larger in plantations.The TOC content in natural forest branches increased with the forest age,while the TN and TP contents did not change significantly.On the whole,the leaf TP content in natural forest was higher than plantations,while TN,C:P and N:P were lower in natural forest.The leaf N:P ratios minimum appeared in 30-40 a plantations and 40-50 a in natural forests respectively.It was consistent with the soil TP nutrient characterization,which confirmed that the most vigorous growing age of plantation and natural forest was 30-40 years and 40-50 years respectively.(4)Carbon,nitrogen and phosphorus contents and stoichiometric ratios of each component of leaf-litter-soil continuum in Larix principis-rupprechtii forest ecosystem were closely related.The nutrient content of litter was positively correlated with mature leaves.Soil nutrients were partly derived from the return of litter and there was a close relationship between soil and litter.Leaf nutrients are mainly derived from soil,and the element stoichiometric characteristics of leaves can feed back the soil nutrient status.This relationship between the aboveground and underground components is the main driving mechanism of nutrient circulation in forest ecosystem.(5)The average annual radial growth of Larix principis-rupprechtii in both origins showed a downward trend with altitude and forest age,and the DBHi in plantation was higher than that in natural forest.Among them,the DBHi of plantation showed the highest in middle altitude.A total order of element resorption rate of Larix principis-rupprechtii was: PRE>NRE>C-loss.The C-loss,NRE and PRE of two origins of Larix principis-rupprechtii showed a decreasing trend with altitude,and showed a trend of diversity with the forest age sequence.The C-loss of plantation and the NRE of natural forest all decreased with forest age.The PRE in plantation is higher than natural forest,but C-loss and NRE are lower.The C-loss,NRE and PRE of two origins of Larix principis-rupprechtii are more sensitive to changes in altitude gradient than changes in forest age.There was a significant linear positive correlation between DBHi and C-loss,and a negative correlation with NRE.There was a significant positive correlation between DBHi and leaf P content,and a negative correlation between DBHi and leaf C:P and N:P ratios.There was a significant positive correlation between DBHi and root P content,and a negative correlation between DBHi and root C content and N:P ratios.(6)According to the results,the stoichiometric characteristics,resorption rate and stand growth of different components of Larix principis-rupprechtii ecosystem showed different changes in altitudinal gradients and forest age sequence.Compared two origins of Larix principis-rupprechtii stand,we found that there were differences in response to nutrient restriction and conservation strategies between them.Plantations engaged a highly conservative strategy by enhancing nutrient resorption efficiencies;however,natural forests employed positive strategies for improving the soil nutrient-status and utilization efficiencies. |
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