Study On Soil Organic Carbon(SOC) Pool Under Different Vegetation Types

Soil organic carbon(SOC) is closely related to global climate change. Mu Us desert is one of the areas where desertification take place frequently. Over the years, the construction and restoration of vegetation by the local, coupled with the development of natural vegetation, formatting the vegetation patterns today; In order to clarify the impact of change and development of vegetation on SOC sequestration in the area, we measured 9 vegetation types of Mu Us Desert from late August to early September 2009, including shifting sandy land, Artemisia ordosica community on semi-fixed sandy land, Artemisia ordosica community on fixed sandy land, Salix psammophyla community, Caragana intermedia community, Salix matsudana community, Achnatherum splendens community, Iris lactea var.chinensis community and farm land. Soil SOC content, active organic carbon(SAOC) content, total nitrogen content, and other soil properties (soil bulk weight, soil moisture, pH value, Soil particle size distribution) were measured under every vegetation type, and vegetation surveys were also conducted. In addition, we collected the data of changes of vegetation area from 1988 to 2002. The results showed as follows:(1) In Mu Us Desert, SOC contents or SOC densities were different under different vegetation types. The order of SOC content in 0-80cm soil layer was:Iris lactea var.chinensis community(22.33g/kg)>Achnatherum splendens community(9.05g/kg)>Salix matsudana community(6.72g/kg)>Artemisia ordosica community on fixed sandy land(4.31g/kg)>Salix psammophyla community(3.20g/kg)>Artemisia ordosica community on semi-fixed sandy land(2.54g/kg)>farm land (1.76g/kg)>Caragana intermedia community(1.58g/kg)>shifting sandy land(1.24g/kg); The order of SOC density in 0-80cm soil layer was:Iris lactea var.chinensis community(27.49kg/m2)>Achnatherum splendens community(12.18kg/m2)> Salix matsudana community(8.09kg/m2)>Artemisia ordosica community on fixed sandy land(5.24kg/m2)>Salix psammophyla community(4.00kg/m2)>Artemisia ordosica community on semi-fixed sandy land(3.14kg/m2)>farm land(2.23kg/m2)>Caragana intermedia commun-ity(1.93kg/m2)>shifting sandy land(1.55kg/m2)。The SOC contents under Artemisia ordosica community(fixed sandy land), Salix matsudana community, Achnatherum splendens community, Iris lactea var.chinensis community and farm land had a significant accumulation, while the SOC contents under shifting sandy land, Artemisia ordosica community(semi-fixed sandy land), Caragana intermedia community and Salix psammophyla community decreased with the soil layer deepen. SOC density and SOC content of each vegetation type had a similar vertical distribution pattern in the soil profile.Among the several dune vegetations, Artemisia ordosica community and Salix psammophyla community had a better effect on SOC sequestration.(2) The SOC storage was 411.15×105t of 0-80cm soil layer in Mu Us desert, SOC density was 3.55kg/m2. The order of SOC storage under diifferent vegetation types was: Artemisia ordosica community(fixed sandy land)(164.48×105t)>wetland(86.04×105t)shifting sandy land(58.70×105t)>Caragana intermedia community(28.61×105t)>Artemisia ordosica community(semifixed sandy land)(26.74×105t)>farm land(25.77×105t)> Salix psammophyla community(14.82×105t)> Salix matsudana community (5.99×105t).From 1988 to 2002, the areas of shifting sandy land, Artemisia ordosica community(semi-fixed sandy land) and wetland were reduced, and the percentages of SOC storage reduced were 22.41%,25.31% and 9.15% accordingly. The areas of other vegetation types were increased at the same time and the SOC storage were increased too. Among the different vegetation types, the SOC storage of Salix matsudana community increased with the maximum rate for 130.38% and of Artemisia ordosica community (fixed sandy land) got the largest increase of 37.09×105t. From 1988 to 2002, the SOC storage of Mu Us desert was increased of 22.61×105t, the rate of which was 5.82%.(3) Different vegetation types had different SOC contents. In Mu Us desert, the main impact factors on SOC content were soil fine paticles and soil moisture, and the former had a greater influence. Three of the regression model was:Y=35.209X1+0.621X2-2.540(X1 stand for soil moisture, X2 stand for soil fine paticles, R=0.950**). Soil fine paticles or soil water moisture had significant effect on SOC respectively.In addition, there are positive correlation between C/N and SOC content. Aboveground biomass and litter also had a certain impact on SOC content.(4) The order of SAOC content in 0-80cm soil layer under different vegetation types was: Iris lactea var.chinensis community(7.19g/kg)>Achnatherum splendens community(2.19g/kg) >Salix matsudana community(1.78g/kg)>Artemisia ordosica community (fixed sandy land) (1.49g/kg)>Salix psammophyla community(1.10g/kg)>Artemisia ordosica community (semifixed sandy land)(0.81g/kg)>farm land(0.40g/kg)>Caragana intermedia community (0.38g/kg)shifting sandy land(0.21g/kg). The order of SAOC density in 0-80cm soil layer under different vegetation types was:Iris lactea var.chinensis community(8.84kg/m2)> Achnatherum splendens community(2.90kg/m2)>Salix matsudana community(2.16kg/m2)> Artemisia ordosica community(fixed sandy land)(1.80kg/m2)>Salix psammophyla community (1.37kg/m2)>Artemisia ordosica community(semi-fixed sandy land)(1.00kg/m2)>farm land (0.51kg/m2)>Caragana intermedia community(0.47kg/m2)>shifting sandy land (0.27kg/m2).The order of the SAOC/SOC ratio under different vegetation types was:Artemisia ordosica community(fixed sandy land)(36.78%)>Iris lactea var.chinensis community (36.62%)>Salix matsudana community(34.93%)> Salix psammophyla community(32.35%) >Artemisia ordosica community(semi-fixed sandy land)(32.26%)>Achnatherum splendens community (29.31%)>farm land(24.30%)>Caragana intermedia community(24.25%)> shifting sandy land(17.45%).SAOC storage in Mu Us desert was 114.53×105t, accounting for 28.06% of SOC reserves. The order of SAOC storage under different vegetation types was:Artemisia ordosica community(fixed sandy land) (56.65×105t)>wetland(20.46×105t)>shifting sandy land (10.13×105t)>Artemisia ordosica community(semi-fixed sandy land) (8.49×105t)>Caragana intermedia community(6.94×105t)> farm land(5.17×105t)>Salix psammophyla community (5.09×105t)>Salix matsudana community(1.60×105t).(5) The order of the total nitrogen content in 0-80cm soil layer under different vegetation types was:Iris lactea var.chinensis community (3.631g/kg)>Salix matsudana community (1.218g/kg)>Artemisia ordosica community(fixed sandy land)(1.032g/kg)>Achnatherum splendens community(1.026g/kg)>Salix psammophyla community(0.849g/kg)>Artermisia ordosica community (semi-fixed sandy land)(0.628g/kg)>Caragana intermedia community (0.382g/kg)>farm land(0.366g/kg)>shifting sandy land(0.287g/kg).The order of C/N ratio in 0-80cm soil layer under different vegetation types was: Achnatherum splendens community(9.33)>Iris lactea var.chinensis community(6.64)>Salix matsudana community(5.20)>farm land(4.94)>Salix psammophyla community(4.75)>shifting sandy land(4.37)>Caragana intermedia community(4.21)>Artemisia ordosica community (fixed sandy land)(4.09)>Artemisia ordosica community(semi-fixed sandy land) (4.05).