| The current research was conducted to elucidate the carbon storage and soil available nutrient characters of several monoculture artificial grasslands in loess plateau, based on a long-term fixed-point monitoring experiment at the Lanzhou Scientific and Experimental Field Station of Ministry of Agriculture. The four monoculture artificial grasslands are alfalfa(Medicago sativa L.), sainfoin(Onobrychis viciaefolia Scop.), wheatgrass(Agropyron cristatum Gaertn.)and Kentucky Kentucky bluegrass(Poa crymophila Keng.). The abandoned land was selected as control. The following parameters were monitored and determined, vegetation carbon density, litter carbon density, 0-100 cm layer underground biomass carbon density, soil carbon density, ecosystem carbon density, carbon sequestration rate, and soil available N, available P, available K, available Fe, available Mn, available Cu and available Zn in 0-100 cm layer. The results showed scientific reference and strategies for grassland management and utilization of monoculture artificial grassland carbon storage and soil available nutrients in the loess plateau of China.The main results were as follows:1. The total biomass carbon density of 4-year alfalfa grassland was the highest(18635.8 kg C·hm-2). The soil carbon density of 5-year alfalfa grassland ecosystem was the highest(101.96t·hm-2), which accounts for 80.6%-90.5% of ecosystem carbon density. With the increase of growth year, the soil available N, available P in the 0-100 cm layer decreased in alfalfa grassland, and the soil available K in 0-60 cm layer, soil available Fe in 0-20 cm layer, soil available Mn in 0-30 cm layer, soil available Cu in 0-70 cm layer, soil available Zn in 0-60 cm layer decreased significantly(P<0.05).The contents of soil available N, available P and available K in 0-100 cm layer, available Fe in 0-50 cm layer, available Mn and available Cu in 0-70 cm and available Zn in 0-90 cm layer were decreased with the increase of soil depth.2. The total biomass carbon density of 3-year sainfoin grassland was the highest, 16454.5 kg C·hm-2. And the aboveground biomass carbon density in 3-year sainfoin grassland accounted for 31.6%-56.3% of the total biomass carbon density. The 3-year Sainfoin grassland had the highest carbon density, 104.68 t·hm-2. In sainfoin grassland ecosystem, the soil carbon density accounted for 84.3%~94.4% of ecosystem carbon density. The contents of soil available N in 0-30 cm layer, soil available P and soil available Mn in 0-70 cm layer, soil available K in 0-50 cm layer, soil available Cu in 0-40 cm layer and soil available Zn in 0-100 cm layer decreased with the increase of soil depth. With the increase of growth year, from the first to fifth year, the available N content in sainfoin grassland increased, and decreased in the 5th year. And the content of soil available P and available K in sainfoin grassland decreased significantly(P<0.05). The contents of soil available Fe and Mn in 0-70 cm layer, soil available Cu and Zn in 0-100 cm layer increased with the increase of sainfoin growth year.3. The total biomass carbon density of 4-year wheatgrass grassland was the highest, 7310.7kg C·hm. The carbon density of 4-year wheatgrass grassland was the highest, 66.18t·hm-2, and the soil carbon density accounted for 88.1%~97.2% of ecosystem carbon density. The contents of soil available N in 0-60 cm layer, available P in 0-100 cm layer, available K in 0-50 cm layer, available Fe in 0-50 cm layer, available Mn and available Cu in 0-60 cm layer, available Zn in 0-70 cm decreased with the increase of soil depth in different growing years’ wheatgrass grassland. The soil available N decreased with the increase of wheatgrass growth year. In 0-30 cm layer, the soil available P in the same soil layers increased with the increase of growth period. In 0-50 cm layer, the soil available K reduced from the first to third growing year, but in the fourth year and fifth year increased significantly. With the increase of growth year, the contents of soil available Fe in 0-50 cm layer, soil available Mn in 0-30 cm layer, soil available Cu in 0-60 cm layer, soil available Zn in 0-30 cm layer decreased.4. The total biomass of 4-year Kentucky bluegrass grassland was the highest, with the carbon density of 6553.0 kg C·hm-2. The underground biomass carbon density accounts for 45.1%~62.0% of the total biomass carbon density in 4-year Kentucky bluegrass grassland. The highest carbon density(66.3t·hm-2) was found in the fourth year. The soil carbon density accounted for 90.1%-98.5% of the ecosystem carbon density. The soil available N in 0-60 cm layer, available P in 0-70 cm layer, available K in 0-50 cm layer, available Fe in 0-100 cm layer, available Mn in 0-70 cm layer, available Cu and Zn in 0-60 cm layer decreased with the increase of soil depth in different growth year’s Kentucky bluegrass grassland. With the increase of growth year, the soil available N in 0-60 cm layer, available P and available K in 0-50 cm soil layer were significantly increased(P<0.05). The available Fe in 0-30 cm layer, available Mn in 0-40 cm layer, available Cu and Zn in 0-10 cm layer increased with the increase of Kentucky bluegrass growth year.5. The total biomass carbon density in the 1-year abandoned grassland was the highest, 969.4 kg C·hm-2. The ecosystem carbon density in the abandoned grassland increased with the increase of abandon year, and was significantly different with the others(P<0.05). The ecosystem carbon density in the 5-year abandon grassland was 49.0t·hm-2. The ecosystem carbon density accounted for 92.3%-98.3% of the abandoned land soil carbon density. The soil available N, available P and available K, available Fe and Mn in different land abandon years decreased with the increase of soil depth. In 0-40 cm soil, the available Cu and available Zn declined with the increase of soil depth. The soil available N and available K in 0-50 cm layer, available P in 0-30 cm layer, available Fe and Zn in 0-30 cm layer, available Mn and Cu in 0-50 cm layer increased with the increase of land abandon year.6. The average carbon sequestration rate in different5-year monoculture artificial grassland ecosystem from higto low was: alfalfa grassland(13.04t·hm-2·a-1)>sainfoin grassland(10.87t·hm-2·a-1)>Kentucky bluegrass grasslan(5.17t·hm-2·a-1) > wheatgrass grassland(4.79t·hm-2·a-1)>abandoned land(2.46t·hm-2·a-1). The soil availablN in different monoculture artificial grassland was significantly higher than that in the abandoned grassland. Amonthem, from the first to the fifth year, the soil available N in alfalfa grassland and sainfoin grassland was significantlhigher than in wheatgrass grassland and Kentucky bluegrass grassland(P<0.05).With the increase of growth yearthe soil available P and available K in wheatgrass grassland, Kentucky bluegrass grassland and the abandonegrassland increased. And the reduction was observed for soil available P and available K in sainfoin grassland analfalfa grassland, soil available Cu, available Fe, available Mn, available Zn in different monoculture artificiagrassland. However, the alfalfa and sainfoin showed a greater reducing rate than wheatgrass and Kentucky bluegrassThe soil available Fe, available Mn, available Cu, available Zn in the abandoned grassland slightly increased with thgrowth year.The current research can provide basic data and reliable reference for the calculation of grassland carbon storage and carbon sequestration mechanism, as well as provide theoretical support for sustainable development and ecological environmental construction of artificial grassland in the Loess Plateau. |
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