| Climate change has become a fact in the world. Global warming was triggered by the increasement of CO2 concentration and other greenhouse gas in atmosphere.The frequency of extreme precipitation events and patterns of regional preticipation were changed by general circulation of atmosphere which was caused by global warming.As the main ecosystem in terrain,forest play an significant role in global carbon cycle and mitigation of climate change.To accurately predict the feedbacks between global warming and terrestrial ecosystem,soil warming and throughfall reduction were used to explore the long-term response of forest soil carbon pool and the regulation mechanism of biotic and abiotic factors. Warm-temperate oak(Quercus aliena var. acuteserrata) forest soil was taken as the subject,a randomized complete block design with infrared radiation heater and throughfall reduction was conducted in our field experiment. To analyze the response and mechanism of lasting soil waming and throughfall reduction on soil carbon flux, Li-8100 system was used to measure soil respiration,and PLFAs and 96 micro-plate were used to elucidate the microbial community structure and function.The main results are as follows:(1) In trench plots:soil temperature at 5cm was significantly changed by infrared heater, soil temperature was increased by 1.54 ℃ and 1.12 ℃ under warming(W) and warming+throughfall reduction(W+D) treatments compared to control treatment(C);soil moisture was significantly decreased under W+D treatment,and soil moisture was a little decline under W and D treatments,but not significant. In untrench plots: soil temperature at 5cm was significantly changed by infrared heater, soil temperature was increased by 1.33℃ and 0.99℃ under W and W+D treatments compared to C treatment;but there is no significant effect of treatments on soil moisture.(2)Soil organic carbon(SOC) was significantly decreased under soil warming and throughfall reduction treatments. There is no effect of root on SOC and dissolved organic carbon(DOC), but the inorganicn nitrogen content was significantly influenced by different treatments.In trench plots, ammonium nitrogen content(NH4+)was increased by 29.00% and 42.36% under warming treatment in growth and ungrowth season, and nitrate nitrogen content(NO3-)was increased by 129.65% and 74.68% under throughfall reduction treatment in growth and ungrowth season.Compared to untrench plot, NH4+ was decreased but NO3- was increased: NH4+ was decreased by 38.08% and 16.07% in C and W+D treatments,while NO3-was sigcificantly increased by 180.86%、351.22% and 208.37% except for control treatment in growth season. NH4+ was significantly decreased by 39.58% under control treatment, while NO3- was sigcificantly increased by 168.05%、178.29%、303.22% and 522.51% under all treatments.The study indicated that soil carbon pool was significantly affect by climate change,and root was important in regualting soil nitrogen forms under climate change context.(3)As the main factor,which regulate soil respiration(Rs), soil temperature at 5cm could explain 82.3%~88.5% of the temporal variation of Rs.Except for soil temperature, soil moisture at 5cm could explain 6.6%~9.1% of the temporal variation of Rs under D,W and W+D treatments. Further analysis showed that: the same with soil temperature, soil moisture was the main factor in regulating Rs in drought period, soil temperature and moisture at 5cm could explain 78.3% and 37.1% of the temporal variation of Rs.The acclimation of Rs occurred after 3 years observation, the coincident response of the quality(total nitrogen,dissolved organic carbon,fine root biomass) and quantity(ratio of soil organic carbon to total nitrogen)of soil substrate was the main reason to elucidate the phenomenon. The acclimation of Rs will not lead to the lasting change of soil carbon pool under climate change context, and feedbacks between soil carbon flux and climate change will be mitigeted.(4)The same with Rs, soil temperature at 5cm was the main factor in regulating soil respiration components. Soil temperature at 5cm could explain 79.0%~87.4% of the temporal variation of soil heterotrophic respiration(Rh),and soil moisture at 5cm could explain 11.6%~31.1% of the temporal variation of Rh. Soil temperature at 5cm could explain 36.3%~52.0% of the temporal variation of soil autotrophic respiration(Ra),and soil moisture at 5cm could explain 7.2%~9.6% of the temporal variation of Ra.Soil moisture has the dual function in regulating Rh and Ra.The potimal soil moisture of Rh and Ra was about 25% and 18%(cm3/cm3). The dependence of Rh(R2=0.329) to soil moisture is higher than that of Ra(R2=0.174)in our analysis.Though soil temperature and moisture were changed under different treatments, Rh and Ra did not show significant variations.The microbial community structure,substrate supply and underground biomass were vital reasons to explain the phenomenon.(5)The response of temperature sensitivity(Q10) of Rh and Ra to soil warming and throughfall reduction was not consistent. Q10 of Rs, Rh and Ra was 3.05~3.25, 2.54~2.79,4.25~5.97. The result of variance analysis indicated that Q10 of Rh was significantly increased under W and D treatments,but the Q10 of Rs and Ra was unchanges.Further analysis showed that soil temperature and moisture plays an important role in regulating Q10,and microbe and the physiological metabolic activity of root may be the necessary reasons.(6)The response of soil microbial PLFAs to soil warming and throughfall reduction in growth and ungrowth season was not significant,but the ratio of gram positive bacteria to gram negative bacteria was significantly changed under treatments. The principal component analysis in growth season showed that Axis1 could explain 53.0% of microbial community structure variation,and Axis2 could explain 29.2%.The reason was that: the abundance of fungi and arbuscular mycorrhizal fungi under D treatment was relative higher than left treatments,while the abundance of bacteria under W+D was lower than that under W and D treatments. The principal component analysis in ungrowth season showed that Axis1 could explain 73.4% of microbial community structure variation,and Axis2 could explain 11.6%. The reason was that: the abundance of arbuscular mycorrhizal fungi under C treatment was relative higher. Redundancy analysis showed that soil moisture was the main reason to elucidate microbial community structure variation in growth season,while soil substrate availability was the main reason in ungrowth season.The effect of time on soil enzyme activity was not significant,but the specific response of microbial function to biotic and abiotic factors was the main reason to explain the variation of soil enzyme activity. |
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