Study On CO₂ And CH₄ Fluxes From Soil-plant Systems Of Alpine Grassland Under Different Degrees Of Degradation In The Source Area Of Yellow River

In this paper, the fluxes of carbon dioxide and methan(eCO2,CH4)were measured at the same time with static enclosed chamber/GC technique through the experiment in five represent sample sites in the alpine meadow ecosystem in the source area of Yellow River . Five different representative grassland types were heavily degraded, lightly degraded, moderately degraded, non-degraded alpine meadow and artificial grassland. The air temperature, soil temperature (0cm, 5cm, 10cm),soil water content and biomass were measured parellel with the geses flux measurement. According to the results of experiment, we analyzed the characteristics and the possible effects of different environmental factors on diurnal variation and seasonal variation of CO2 and CH4 in different grassland. The main conclusions are as follows:1. the diurnal variation of CO2 flux of different degrees degraded alpine meadowThe fluxes of CO2 from different degrees degraded alpine meadow were mostly positive during the field measurements, which indicate that the alpine meadow emits CO2 to atmosphere basically. The daily continues measurements showed that the flux of CO2 emission in daytime was higher than that of nighttime. The maximal emission flux occured at 11:00~13:00 a.m., and the minimal flux occured at 4:00~7:00 in the morning. The increasing period of CO2 emission appeared from 7:00 to 15:00 and the decreasing period appeared from 15:00 to 7:00 of the following day. The maximum of CO2 emission flux in the heavily degraded, lightly degraded, moderately degraded, non-degraded alpine meadow and artificial grassland are respectively 327.34±2.38 mgm-2h-1, 304.21±4.12 mgm-2h-1, 299.56±3.02 mgm-2h-1 , 309.28±0.28 mgm-2h-1 and 369.23±2.36mgm-2h-1.The minimum of them are respectively 109.93±3.09 mgm-2h-1, 101.16±3.17 mgm-2h-1, 92.21±2.69mgm-2h-1, 97.12±5.86mgm-2h-1 and 119.31±4.75mgm-2h-1.2. the seasonal dynamic of CO2 flux of different degrees degraded alpine meadowSeasonal dynamic of the CO2 emission rate was pretty remarkable,and the trend of five different representative grassland types were consistent. The fluxes of CO2 from different degraded alpine meadow and grassland were mostly positive during the plant growing seasons. CO2 fluxes in heavily degraded meadow and artificial grassland were significantly different from moderately degraded meadow, and the CO2 fluxes in heavily degraded meadow were not significantly different from non-degraded meadow. CO2 emission rate higher in the heavily degraded alpine meadow than in the moderately degraded alpine meadow during the plant growing seasons.Ruderal is the dominant species and poison grass is secondary in heavily degraded meadow and Grass or Cyperaceae is only a few. Whole coverage of the heavily degraded alpine meadow is more than that of the moderately degraded alpine meadow although the heavily degraded alpine meadow germinates late and the moderately degraded alpine meadow germinates early.Whole coverage is 40%~60% in the heavily degraded alpine meadow and it is 20%~30% in the moderately degraded alpine meadow.3. the diurnal variation of CH4 flux of different degrees degraded alpine meadowThe fluxes of CH4 in different degrees degraded alpine meadow were mostly negative, this means that the alpine meadow sink CH4 from atmosphere. The diurnal variation of CH4 flux is complicated, the maximal sink was occurred at night. The minimal absorption flux was happened at 9:00～11:00 a.m.. There was no significant relationship between the diurnal variation of CH4 absorption and temperature.4. the seasonal dynamic of CH4 flux of different degrees degraded alpine meadowThere was an different seasonal variation in different alpine meadow.The seasonal dynamic of CH4 flux in moderately degraded and lightly degraded alpine meadow is not significant.There was an obvious seasonal variation in non-degraded alpine meadow,heavily degraded alpine meadow and artificial grassland.The CH4 fluxes were higher in summer and lower in autumn and spring.The CH4 fluxes were significantly correlated with the air temperature and soil temperature, and they were also significantly correlated with soil water in different alpine meadow.CH4 fluxes in different degrees degraded alpine meadow were not significantly .5. the analysis of CO2 flux in different degrees degraded alpine meadowThe result of analysis of variance about CO2 fluxes in different types of meadow are displayed as follows. For the the original meadow, the order of CO2 emission fluxes was artificial grassland>heavily degraded meadow>non-degradedmeadow>lightly degraded meadow>moderately degraded meadow. CO2 fluxes in heavily degraded meadow and artificial grassland were significantly different from moderately degraded meadow, and the CO2 fluxes in heavily degraded meadow were not significantly different from non-degraded meadow.For the reaped meadow treatment, the order of CO2 emission fluxes was non-degraded meadow> lightly degraded meadow > moderately degraded meadow>heavily degraded meadow> artificial grassland. For the soil treatment, the order of CO2 emission fluxes was non-degraded meadow >lightly degraded meadow>artificial grassland> moderately degraded meadow>heavily degraded meadow.6. relationships between CO2 flux and temperature,soil moisture in different degrees degraded alpine meadowThe correlativity of CO2 flux and temperature in different degrees degraded alpine meadow are displayed as follows. For the the original meadow, the correlativity order of CO2 flux and temperature was heavily degraded meadow > moderately degraded meadow > lightly degraded meadow >non-degradedmeadow>artificial grassland. The correlativity are respectively 0.9179, 0.9169, 0.8818, 0.8511 and 0.6774. For the the reaped meadow, the correlativity order of CO2 flux and temperature was lightly degraded meadow>moderately degraded meadow>heavily degraded meadow>artificial grassland>non-degradedmeadow. The correlativity are respectively 0.9488, 0.9377, 0.9287, 0.7455 and 0.73821. For the the soil treatment, the correlativity order of CO2 flux and temperature was moderately degraded meadow > lightly degraded meadow > heavily degraded meadow >non-degradedmeadow>artificial grassland. The correlativity are respectively 0.9546, 0.95, 0.9473, 0.7757 and 0.7706 .The diurnal variation and the seasonal variation were both significantly correlated with the air temperature and soil temperature (0cm,5cm,10cm).Whereas having a weak correlation with the soil moisture. In the five sample sites, the effect of soil moisture to CO2 flux in the heavily degraded meadow (Black soil patch)was more significant than the other four sample sites.7. relationships between CO2 flux and biomass in different degrees degraded alpine meadowCO2 fluxes increased with the green biomass and aboveground biomass in different types of meadow. Exponential functions could be used to describe relationship between CO2 fluxes and biomass. There was a significant correlation relationship between CO2 fluxes and green biomass. However, there was weak relationship between CO2 fluxes and aboveground biomass. CO2 fluxes decreased with the increase of standing dead biomass in different types of meadow. Relationships between CO2 fluxes and standing dead biomass could be described by exponential equations in different types of meadow. There was weak relationship between CO2 fluxes and standing dead biomass in heavily degraded meadow. There was a significant correlation relationship between CO2 fluxes and standing dead biomass in non-degraded meadow.Exponential functions could be used to describe relationships between CO2 fluxes and underground biomass in different types of meadow. CO2 fluxes increased with the 10~20cm underground biomass, but the upward trend is not same in different types of meadow. 8. relationships between CH4 flux and biomass in different degrees degraded alpine meadowCH4 absorption flux increased with the green biomass in different types of meadow. Exponential functions could be used to describe relationship between CH4 absorbable fluxes and biomass, but there was a weak relationship between them. CH4 absorbable fluxes decreased with the increase of standing dead biomass in different types of meadow. Exponential functions could be used to describe relationship between CH4 absortion fluxes and standing dead biomass in non-degraded meadow,moderately degraded meadow, lightly degraded meadow and artificial grassland. Logarithmic functions could be used to describe relationship between CH4 fluxes and standing dead biomass in heavily degraded meadow because of CH4 emission flux sometimes. CH4 absortion fluxes increased or decreased with the underground biomass in different types of meadow.