| In this trial the characteristics of carbon cycle for seven-year-old citrus orchard ecosystem were studied with long-term observation in Fuzhou, China, and the effects of human management such as grass intercroption, tillage on soil respiration were investigated. The main results indicated that:(1) Carbon storage of seven-year-old citrus orchard ecosystem was 158.282 t·hm-2, and soil (0-100 cm) carbon storage was 151.734 t·hm-2, occuping on 95.86% of total carbon storage in citrus orchard ecosystem, vegetation carbon reserves was 6.548 t·hm-2, accounting for 4.14%. Nitrogen reserves of seven-year-old citrus orchards ecosystem was 14.602 t·hm-2, and soil (0-100 cm) of nitrogen reserves was 14.399 t·hm-2, accounting for 98.61%, vegetation nitrogen reserves was 0.203 t·hm-2, accounting for 1.39%.(2) The net primary productivity(NPP) of seven-year-old citrus orchard ecosystem was 4.722 t·hm-2·a-1, and the biomass increment of the fruit tree was 1.104 t·hm-2·a-1, accounting for 23.28% of NPP. The biomass of harvested fruit and annual litterfall was 1.936 t·hm-2·a-1 and 1.682 t·hm-2·a-1, accounting for 41% and 35.62% of NPP, respectively.(3) Annual litterfall of seven-year-old citrus orchard ecosystem was 1682.48 kg·hm-2, of which carbon and nitrogen fluxes to soil were 704.56 kg·hm-2·a-1 and 43.72 kg·hm-2·a-1, respectively. the litterfall had a double peak curve change in one year ,and the peaks lied in March and July, respectively. The litter decomposition rate was higher at first, and then decreased gradually. There was only 23.3% of litterfall remained after ten months. During the decomposition of leaf litter, carbon concentration rapidly decreased from 41.74% to 20.96% in the previous five months.(4) There were significantly monthly and daily dynamics of soil respiration in citrus orchard ecosystem. The maximum flux occurred in July and the minimum flux occurred in January in one year. Soil respiration had certain spatial heterogeneity in the plant scale in the citrus orchard ecosystem. In September, soil respiration rate on 130 cm distance from the fruit trees was 25.918% to 41.194% of that on 20cm distance, .being the average of 33.259%. There were extremely significant exponential correlations between total soil respiration, soil heterotrophic respiration, root respiration and soil temperature in 10cm depth (p<0.01). Soil temperature in 10cm depth explained 68.6%, 62.9% and 69.3% of changes of total soil respiration, soil heterotrophic respiration, root respiration, respectively. Their Q10 values were 2.54, 2.17 and 2.65 respectively. And root respiration was more sensitive to soil temperature than soil heterotrophic respiration.(5) Tillage significantly made soil respiration rate increase in citrus orchard ecosystem. Soil respiration increased by 49% in the field experiment. Although soil respiration increased by 26.24% by incroping grass in orchard, but carbon storage of the ecosystem also increased by 3400.0 kg·hm-2.
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