| By using open-path eddy covariance system and micro-climate instruments in the Mao bamboo forest ecosystem of subtropical in China since2011. The variations of NEE, RE and GEE were studied by analyzing the flux datasets of the Mao bamboo forest ecosystem. But the energy flux and analysis of the Mao bamboo forest ecosystem reported in the literature at home and abroad is very few, in subtropical regions to establish long-term continuous observation of the flux tower, enhancing the research is highly requirement. The study contributed to the research of carbon cycle of the Mao bamboo forest ecosystem and the understanding of carbon sink of forests in China especially the Mao bamboo forest ecosystem. The results indicated:(1) The monthly accumulation of the NEE was always negative, indicating that forest is a carbon sink for all the time. The minimum and maximum appeared in November (-23.49gC·m2·month-1) and June (-99.33gC·m-2·month-1)2011, respectively, the seasonal change showed a bimodal shape. Monthly mean flux during daytime varied significantly from-0.303g CO2·m-2·s-1to-0.596g CO2·m-2·s-1. The minimum and maximum appeared in January and September2011, respectively. NEE in positive and negative conversion point time had obvious seasonal characteristics. Ecosystem respiration peaked in summer, the nadir in winter. The estimated NEE was-668.40gC·m-2·a-1the RE was932.55gC·m-2·a-1and the GEE was-1600.95gC·m-2·a-1, the NEE was41.8%of GEE. The bamboo has strong solid carbon ability and enriched observation and research in subtropical forest ecosystem.(2) As an important index to evaluate the reliability of eddy covariance measurements, energy balance analysis has been widely accepted by the community. Using two methods of OLR (Ordinary least spuares) and EBR (Energy balance ratio), energy imbalance characteristics of the Mao bamboo forest ecosystem were systematically analyzed compared in the paper. The results showed that:the yearly net radiation of the Mao bamboo forest ecosystem was2628.00MJ·m-2, and the sensitive flux heat, latent heat flux, and soil heat flux were576.80MJ-m’2,1666.77MJ·m-2, and-7.52MJ·m"2, respectively. The results suggest that soil of Mao bamboo forest was a heat source. The energy balance components had obvious seasonal pattern, diurnal variations of energy balance components existed on expected single peaks. The sensible and latent heat fluxes almost have22.0%and63.4%of the net radiation, respectively, indicating that latent heat flux was the main form of energy loss in this forest ecosystem. Monthly variation of the Bowen ratio is slight, and fluctuated from0.07to1.77, the yearly enrgy balance closure of the Mao bamboo forest ecosystem was0.85, and the mean monthly averge was0.84, yet energy imclosure of15%still existed for the energy balance of Mao bamboo forest ecosystem.(3) Especially in South China. Soil heat fluxes and meteorological factors of the Mao bamboo forest ecosystems in Anji were monitored with soil heat flux plates (HFP01) and a meteorological monitoring system. Presently, few works are available on soil heat fluxes in bamboo ecosystems, but soil heat flux is an important part of ecosystem energy flow. Soil heat flux varied seasonally with monthly mean flux differing sharply between months, and diurnally, displaying an "S" curve, with one peak and one valley. On an annual scale, soil is the source of heat, providing-7.52MJ·m-2a year and contributing,-0.289%to the total net radiation of a year. The maximum positive value appeared in July and the maximum negative one in January.(4) The temperature of the canopy and NEE of Mao bamboo forest ecosystem is variate as quadratic polynomial in the time scale of half hour and monthly. When the temperature is15℃, quadratic polynomial reach the peak, means NEE is the negative maximum. Annual RE had an exponential relationship with soil temperature, equation was y=0.034e0059x,R2=0.403. Regression relationship analysis of different temporal scales and different soil depths shows that on a monthly scale, soil heat flux was best related to the soil temperature at5cm in soil depth, showing a relationship at the extremely significant level, while on a daily scale, soil heat flux was in an extremely significant relationship with soil water content at5cm in soil depth, but the correlation coefficient was not so high. The monthly mean of soil heat fluxes was extremely significantly related with net radiation on a monthly scale and even at a half-an-hour scale, showing no temporal retardation phenomenon. |
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