| Soil respiration is an important part of the carbon cycle in ecosystem and has important influence on atmospheric CO2 concentration,climate change and global carbon cycle.Wuyi Mountain,the second largest danxia landform area in China,has unique geological features and ecological environment.There were many studies on soil respiration in woodland of different forest types in Wuyi Mountain,but there are few reports on soil respiration in economic plant and Pinus massoniana.In this paper,it intended to choose the danxia landform area of Wuyi Mountain as research area.It took different woodland use of Wuyi Mountain(Castanea henryi forest,Tea garden,Pinus massoniana forest)as research object,in contrast to the bare land.From september 2016 to august 2017,we measured variation of soil respiration,investigated the vegetation and got soil samples.By determining the hydrothermal factors,soil nutrients,soil microbial carbon and nitrogen,we analyzed dynamic characteristics of soil respiration under different forest land use in Wuyi Mountain,and explored the rules of soil respiration and its influencing factors.In order to provide some theoretical basis and reference value for the ecological environment,carbon cycle,effective utilization of land and sustainable development in danxia landform area of Wuyi Mountain.(1)The daily variation and seasonal variation of soil respiration under different forest use in Wuyi MountainCompared with the bare land,the trend of soil respiratory in the Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)were similar to that of bare land.The daily variation of soil respiration showed unimodal trend.From 6:00 to 18:00,the trend of first increase and then decrease was shown,and the highest value appeared at 12:00 or 14:00,and the lowest value appeared at 6:00 or 18:00.The seasonal variation of soil respiration was the highest in summer,followed by spring and autumn,and the lowest in winter.The mean difference of soil respiration between seven different woodlands was relatively small.But the respiration rate of the bare soil was significantly less than that of the soil under different woodland use in different seasons and different points.Soil respiration daily average and seasonal average of Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a),Pinus massoniana forest(10 a,20 a,30 a)were higher than bare land.Among them,Seasonal variation of soil respiration in Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a),Pinus massoniana forest(10 a 20 a 30 a)was 1.628-3.031μmol·m-2·s-1,1.455～4.676 μmol·m-2·s-1,2.034～6.177 μmol·m-2·s-1,respectively.Seasonal variation of soil respiration in bare land was 1.166～2.059 μmol·m-2·s-1.Compared with the bare land,the difference in forest land(Castanea henryi forest,Tea garden,Pinus massoniana forest)were relatively small.(2)The effects of different woodland use methods on soil respiration in Wuyi MountainCompared with the bare land,soil respiration average of the four seasons show Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a),Pinus massoniana forest(10 a,20 a,30 a)of seven kinds of forest land were higher than bare land,and have significant difference.Among them,the average of the four seasons of soil respiration in 7 woodlands were 2.230,2.761,3.070,2.578,3.004,3.437,and 4.106 μmol·m-2·s-1,respectively.They were 1.47,1.82,2.02,1.69,1.98,2.26,and 2.7 times of bare land.In the different forest land use mode,the soil respiration of same forest age(10 a)woodland,the four-season average of soil respiration showed 10 a Tea garden(3.070 μmol·m-2·s-1)>10 a Pinus massoniana forest(3.004μmol·m-2·s-1)>10 a Castanea henryi forest(2.230 μmol·m-2·s-1),and 10 a Tea garden,10 a Pinus massoniana forest and 10 a Castanea henryi forest showed significantly different(p<0.05).In the same land use mode,the four seasons average of soil respiration in Tea garden(5 a,10 a,20 a)were 2.761,3.070 and 2.578 μmol·m-2·s-1,respectively.Tea garden(10 a)>Tea garden(5 a)>Tea garden(20 a).The average of the four seasons of soil respiration in Pinus massoniana forest(10 a,20 a,30 a)were respectively 3.004,3.437 and 4.106 μmol·m-2·s-1,Pinus massoniana forest(30 a)>Pinus massoniana forest(20 a)>Pinus massoniana forest(10 a).But the seasonal variation trend of soil respiration in different forest age of Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)were consistency,all showed the highest summer,followed by spring and autumm and lowest in winter.(3)The changes of hydro thermal factors and their effects on soil respiration under different woodland use methods in Wuyi MountainThe daily variation of near-surface temperature and soil temperature was basically consistent with the daily variation of soil respiration.From 6:00 to 18:00,the trend of first increased and then decreased was shown,and the highest value appeared at 12:00 or 14:00,and the lowest value appeared at 6:00 or 18:00.The daily variation of soil moisture was not obvious.Compared with the bare land,the variation trend of water heat factor was basically consistent with that of bare land.The seasonal changes of near-surface temperature,soil temperature and soil moisture showed summer>spring>autumn>winter.Compared with the bare land,Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a),Pinus massoniana forest(10 a,20 a,30 a)of soil respiration and soil temperature,the surface temperature showed a significant correlation at the 0.05 level,But soil respiration and soil moisture were not significantly correlated at the 0.05 level.The fitting coefficient between the soil respiration of each woodland and its nearsurface temperature was between 0.586～0.968,and the fitting coefficient of soil temperature was between 0.584-0.969.The fitting coefficient of soil moisture was 0.101～0.934.The fitting coefficient between soil respiration of bare land and near-surface temperature was 0.569～0.877,and the fitting coefficient of soil temperature was 0.454～0.915,and the fitting coefficient of soil moisture was 0.179～0.619.As a whole,soil respiration was affected by near-surface temperature and soil temperature,which is less affected by soil moisture.The fitting coefficient of double factor composite model(Soil respiration and soil temperature,soil moisture)showed mostly were higher than fitting coefficient of single factor model(soil respiration and near-surface temperature or soil temperature or soil moisture).Compared with the bare land,the Q10 values of soil respiration and near-surface temperature of 7 woodland soil were 1.127～1.954,and the Q10 value of soil respiration and soil temperature was 1.174～2.435.The Q10 value of soil respiration and near-surface temperature of 7 bare land soil was 1.094～1.284,and the Q10 value of soil respiration and soil temperature 1.162～1.616.On the whole,soil respiration and soil temperature sensitivity Q10 were higher than that of soil respiration and near surface temperature sensitivity Q10.Soil respiration was more affected by temperature,especially in soil temperature.On the whole,the soil respiration in different woodlands of Wuyi Mountain were greatly influenced by the hydrothermal factors(soil temperature and soil humidity synthesis),and the influence of temperature(near ground temperature or soil temperature)were relatively large,which were less affected by soil moisture.(4)The changes of soil nutrient content and their effects on soil respiration under different woodland use methods in Wuyi MountainCompared with the bare land,the vertical profile variation trend of soil nutrient in Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)were consistent with that of bare land.The content of soil carbon,nitrogen and hydrolyzed nitrogen showed a decrease with the increase of soil layer,which was 0～10 cm>10-20 cm>20～30 cm;Soil total phosphorus,effective phosphorus,total potassium,and available potassium content in different soil layers were not obvious.Compared with the bare land,the seasonal variation trend of the soil nutrients in the Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)were similar to that of bare land.The content of soil carbon,hydrolyzed nitrogen and nitrogen showed higher in spring,summer and autumn,and lower in winter.The content of total phosphorus,potassium,available phosphorus and available potassium in soil showed that the spring and summer were higher,and the autumn and winter were lower.Compared with the bare land,the average of the four seasons values of carbon,nitrogen and hydrolyzed nitrogen in forest soil,such as Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a),Pinus massoniana forest(10 a,20 a,30 a)were significantly higher than that of bare land,and most of the woodland and bare land showed significant difference(p<0.05).Among them,the average soil carbon content were bare land of 1.90,2.28,1.52,2.16,1.33,3.28,2.88 times respectively;the average soil nitrogen content were bare land were 1.90,2.19,1.76,2.05,1.28,2.03 and 1.63 times of the bare land respectively;the average soil hydrolysis nitrogen content were bare land were 2.60,3.48,2.23,3.88,1.34,4.20 and 3.59 times respectively.The average of the four seasons of total phosphorus and available phosphorus in the soil showed that Tea garden(5 a,10 a,20 a)were higher,Castanea henryi forest(10 a)and Pinus massoniana forest(10 a,20 a,30 a)were second,bare land was minimum.However,the four seasons of the total potassium content of the soil showed that the forests of Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)were all lower than the bare land.Under different forest land use,the average of the four seasons of available potassium content in forest land soil,Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a),were not much different from that of bare land.There were also small differences between the uses of different forest land.There were a significant correlation between the soil respiration of the Castanea forest(10 a)and the total potassium and the available potassium in soil(p<0.05).The soil respiration of the Tea garden(5 a,10 a,20 a)had significant correlation with total phosphorus,effective phosphorus,total potassium and available potassium(p<0.05)).There was significant correlation between soil respiration and hydrolyzed nitrogen,total phosphorus,effective phosphorus,total potassium,and available potassium(p<0.05)in the soil respiration of the Pinus massoniana forest(10 a,20 a,30 a).Soil respiration of bare land was significantly correlated with soil carbon and available potassium(p<0.05).Overall,soil respiration showed significant correlation with soil carbon,hydrolyzed nitrogen,total phosphorus,available phosphorus,total potassium,and available potassium in the whole year(p<0.05).Comprehensive,Wuyi Mountain danxia landform area soil respiration were greatly influenced by soil nutrient,soil carbon element was its important influence factors.And Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)also were affected by soil phosphorus and potassium.Soil nutrient content of bare land was lower.There was no significant correlation between soil respiration and soil nitrogen,phosphorus and other elements in bare soil.It was shown that different woodland uses changed soil structure,nitrogen,phosphorus and other nutrient sources and sinks,effectively improving the soil respiration rate of woodland.(5)The changes of soil microbial carbon and nitrogen content and their effects on soil respiration under different woodland utilization methodsCompared to the bare ground,the vertical profile variation trend of soil microbial carbon and nitrogen in Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)were consistent with that of bare land.The content of soil microbial carbon and nitrogen showed a decrease with the increase of soil layer,which was 0～10 cm>10～20 cm>20～30 cm.Compared to the bare ground,the seasonal variation trend of the soil microbial carbon and nitrogen in the Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)were similar to that of bare land.Soil microbial carbon content showed the highest summer,followed by spring and autumn lowest winter,and significant difference(p<0.05).Soil microbial nitrogen content showed the highest summer,followed by autumn and winter,lowest spring,and significant difference(p<0.05).Compared to the bare ground,the season average of soil microbial carbon and nitrogen content of Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana.forest(10 a,20 a,30 a)were higher than bare land,and there were significant differences(p<0.05).Among them,soil microbial carbon content of the four seasons average in Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)were 325.86,292.81,324.64,352.78,436.50,511.69,548.17 mg·kg-1,they were bare land of 8.36,7.52,8.33,9.06,11.20,13.13 and 14.07 times,respectively.The four seasons average of soil microbial carbon content in seven kinds of forest land were 31.97,40.87,45.63,55.74,39.75,45.78,52.26 mg.kg-1,respectively.And they were 1.97,2.51,2.81,3.43,2.45,2.82 and 3.22 times as much as the bare land,respectively.Castanea henryi forest(10 a),Tea garden(5 a,10 a,20 a)and Pinus massoniana forest(10 a,20 a,30 a)of forest soil respiration and soil microbial carbon or nitrogen average showed that there were significant difference(p<0.05)among them.There was significant difference between the soil respiration in the bare land and the soil microbial nitrogen content(p<0.05).Soil respiration showed significant difference with soil microbial carbon and nitrogen in the whole year(p<0.01).On the whole,soil respiration under different woodland use in Wuyi Mountain was significantly affected by soil microbial carbon and nitrogen content(p<0.05). |
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