| Carbon efflux in grassland is an important component in the carbon cycling of the terrestrial ecosystem,and attracts more and more attention.With field investigation and laboratory tests,a study was conducted in a fenced grassland（F,fenced for 9 years）and a grazed grassland（G）from Mar,2014 to Feb,2015 on the Loess Plateau,aiming to investigate the effects of enclosure on vegetation carbon pool,soil carbon pool,carbon exchange in the grassland ecosystem and to discuss the carbon sequestration potential in both F and G,so as to provide valuable information for evaluating the current situation of carbon pool in the grassland ecosystem in this region.The main results are as follows:1、With the static chamber method,soil respiration（SR）rate,net ecosystem carbon dioxide（CO2）exchange（NEE）,ecosystem respiration rate（ER）were measured,while the corresponding controlling factors were investigated from Mar,2014 to Feb,2015.The results showed that SR,ER and NEE in F were significantly higher than those in G（P<0.05）on most occasions in the growing season.SR,ER and NEE in both F and G were mainly controlled by soil temperature in the growing and non-growing season,while the Q10values in F and G were 1.0007 and 1.0011,respectively.Moreover,ER in F and G were also significantly affected by the photosynthetic active radiation（P<0.05）.Compared to the single factor equation,a two-factor regression equation with soil temperature and soil moisture could better simulate ER in G,as well as SR and NEE in F and G.ER in F could be better simulated by a three-factor regression equation with soil temperature,soil moisture and photosynthetic active radiation.2、The annual accumulation of SR were 170.98 g C·m-2 and 117.10 g C·m-2in F and G,respectively,while that in F was 46.1%higher than that in G.The annual accumulation of ER in F was 356.19 g C·m-2,which was 58.3%higher than that in G(225.07 g C·m-2).The annual accumulation of NEE in F and G were-58.59 g C·m-2and-40.99 g C·m-2,respectively.Both of F and G act as carbon sink in 2014.It indicated that the grazing intensity in grazed grassland was moderate,which contributes to carbon sequestration in the grassland in this region.3、Enclosure significantly increased soil organic carbon（SOC）content in 0-20cm and 30-50 cm soil layers in grassland,while no significant differences were found in the other soil layers.SOC storages in 0-5 cm and 30-50 cm soil layers in F were significantly higher than that in G（P<0.05）,but opposite trends were found in the20-30 cm soil layer and there was no significant differences in other soil layers between the two sites.SOC storage in 0-100 cm soil layers in F was significantly higher than that in G（P<0.05）,while soil total nitrogen content in 0-100 cm soil layer did not change significantly after enclosure.In addition to 5-10 cm soil layer,soil bulk density in 0-50 cm soil layers in G was significantly higher than that in F（P<0.05）.4、The total above-ground biomass in F was 183.49 g m-2,which was 123.60%higher than that in G(82.06 g m-2).There was no significant difference in the below-ground biomass in 0-50 cm soil layer between F and G(F:452.62 g m-2;G:421.33 g m-2).The below-ground biomasses were mainly distributed in 0-20 cm soil layers,which accounted for 84.36%and 84.73%of the total below-ground biomass in F and G,respectively.The root/shoot ratio was 5.28 in G,which was significantly higher than that in F（2.47,P<0.05）.In addition to litter,C contents in the different vegetation components in F were significantly higher than those in G（P<0.05）.The litter decomposition constants were 0.31 and 0.39 for F and G respectively and the time required for 95%of the litter decomposition were 9.79 and 7.85 years,respectively,indicating a higher litter decomposition rates in G than that in F.5、The ecosystem C storages was 6929.06 g C m-2 in F,which wass 25.57%higher than that in G(5518.27 g C m-2).The carbon storages in soil accounted for96.62%and 96.92%of that in total ecosystem in F and G,respectively. |
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