| Popis: |
Increasing global atmospheric deposition of nitrogen caused by human activities has raised nitrogen input to terrestrial ecosystem,and thus influenced carbon dioxide emissions from soil.To explore how soil respiration response to increased nitrogen input,a simulated nitrogen deposition experiment has been conducted in Cinnamomum camphora forest in subtropical China between June 2010 and January 2012.Soil respiration rate was measured twice a month under four-levels of N treatments(CK,0 g m-2a-1;LN,5 g m-2a-1;MN,15 g m-2a-1;HN,30 g m-2a-1,experimental inputs)by infrared gas analyzer techniques,and the results showed that soil respiration exhibited a strong seasonal pattern,with the highest rates found in the June(819.31 mgCO2 m-2 h-1) and the lowest rates in January(169.70 mgCO2 m-2 h-1).Nitrogen addition inhibited soil respiration significantly.Soil respiration in CK group was higher than that in any other treatment group.Annual accumulative soil respiration in LN(2.55×104 kg/hm2),MN(2.84×104 kg/hm2) and HN(2.50×104 kg/hm2) was 37.66%、30.62%、38.95%,respectively,lower than in CK(4.09× 104 kg/hm2) group,however,there was no significant difference between nitrogen treatment groups.The inhibitory effect weakened over time.From June to September in year 2010,the mean soil respiration rate of LN,MN and HN were(386.31±44.81) mgCO2 m-2 h-1、(358.25±31.55) mgCO2 m-2 h-1and(367.35±41.72) mgCO2 m-2 h-1,respectively,which were 49.63%、53.28% and 52.10% lower than that in CK group(766.87±101.60 mgCO2 m-2 h-1).During same time in year 2011,the mean soil respiration of LN,MN and HN group increased to(512.7±73.12) mgCO2 m-2 h-1,(533.02±41.80) mgCO2 m-2 h-1,(486.20±50.12) mgCO2 m-2 h-1,respectively,which were19.70%、16.51%、23.85% lower than that in CK(638.45±74.91 mgCO2 m-2 h-1).Nitrogen addition couldn′t change the diurnal soil respiration pattern,but depressed magnitude of soil respiration significantly.Soil respiration during daytime was lower than that in night,the minimums appeared in 10:00-14:00 and the maximums were in 22:00—2:00.The diurnal mean soil respiration rare in CK,LN,MN and HN treatment group was(805.86±74.95) mg CO2 m-2 h-1,(689.29±66.25) mg CO2 m-2 h-1,(778.85±73.73) mg CO2 m-2 h-1 and(609.85±65.33) mg CO2 m-2 h-1,respectively,and the mean soil respiration rate in CK group was significantly higher than that in LN and HN group(P0.01).The differences between each nitrogen addition group were significantly.Soil respiration has the similar seasonal and diurnal pattern with soil temperature at 5cm depth.No matter in seasonal scale or diurnal scale,soil respiration rates showed a positive exponential relationship with soil temperature at 5cm depth,Exponential relationships between temperature and soil respiration were highly significant in all plots.However,almost in treatment,there was no obvious effect of soil moisture on soil respiration.LN group had the largest Q10 values(2.01),which similar to CK group(1.99) and higher than MN(1.79) and HN group(1.95).These results indicated that there is a significant decline of soil respiration to N addition in subtropical Cinnamomum camphora forest. |
