| In Yinbei region of Ningxia,two energy crops(lowland variety Alamo and highland variety Pathfinder)were used as materials,and three p fertilizer rates of 0,30 and 90 kg/hm2 were set in the field.A total of 6 treatment combinations were tested,which were represented as A0,P0,A30,P30,A90 and P90,respectively.To study the effects of different treatments on the growth characteristics of switchgrass,soil physical and chemical characteristics and organic carbon characteristics,CBBL gene versatility,and carbon sequestration effect of saline-alkali land-switchgrass ecosystem.Explore saline-alkali land under the condition of potassium nitrogen fixed with plant growth and photosynthetic physiological characteristics on response law of p,p application of switchgrass rhizosphere environment and different saline-alkali soil salinity,effect of organic carbon dynamic regulation,p application of saline-alkali land,switchgrass ecosystem carbon sequestration effect mechanism of action,in order to determine the appropriate of phosphorus fertilizer,It provides theoretical basis for soil modification and carbon sequestration and energy crop production in yinbei saline and alkaline land of Ningxia.The main results are as follows:1.Under the condition of nitrogen and potassium fixed combined application,phosphorus application in saline-alkali land is beneficial to the growth and development of switchgrass.Compared with A0,A30 and A90 treatments increased plant height by 20.37 cm and 34.88 cm on average,tiller number by 37 and 33 on average,and shoot dry matter accumulation by 72.15%and 144.92%on average from green to mature stage.Compared with P0 treatment,P30 and P90 treatments increased plant height by 14.54cm and 23.33cm on average,tiller number by 34 and 17 on average,and shoot dry matter accumulation by 44.37%and 124.54%on average.It can be seen that the application of phosphorus makes switchgrass grow better.At the same time,p application increased the net photosynthetic rate and relative chlorophyll content of switchgrass leaves,but the transpiration rate decreased with the increase of P application.2.Phosphorus application improves soil salinization in 1m soil layer.In the same soil layer,soil pH and total salinity decreased gradually with the increase of P application.Compared with A0,soil pH and total salinity decreased by 2.62%and 8.65%on average under A30 and A90 treatments,and 8.97%and 44.03%on average under A30 and A90 treatments.Compared with P0 treatment,soil pH value and total soil salt content under P30 and P90 treatments decreased by 1.68%and 4.43%on average,24.15%and 38.73%on average.3.Phosphorus application can improve rhizosphere soil fertility level of switchgrass.Under the experimental conditions,the soil enzyme activity of different varieties of switch grass at different growth stages showed that the soil sucrase activity,urease activity and alkaline phosphatase activity increased by 37%and 82%,35%and 65%,and 2%and 16%on average under A30 and A90 treatments compared with A0 treatments.Cellulase activity increased by 92.7%and 168.82%on average.Compared with P0 treatment,soil sucrase activity,urease activity,alkaline phosphatase activity and cellulase activity under P30 and P90 treatments were increased by 9%and 33%,19%and 52%,9%and 15%respectively,and 20.51%and 45.1%respectively,on average.4.Phosphorus application significantly improved the conversion ability of soil organic carbon,and increased the content of light and reconstituted organic carbon and easily oxidized organic carbon in soil.In the vertical direction,the content of carbon components in the surface layer was the highest,and gradually decreased with the deepening of soil layer.During the whole growth period of switchgrass,the content of soil reconstituted organic carbon decreased under no AND low P treatments,but increased significantly under high P treatments,that is,the increment of reconstituted organic carbon increased with the increase of P application level,while the content of light organic carbon and easily oxidized organic carbon increased with the increase of P application level.A0 and A30 treatments decreased by 73.65%and 40.05%on average,A90 treatments increased by 194.95%on average,P0 and P30 treatments decreased by 58.69%and 36.24%on average,and P90 treatments increased by 109.76%on average.Compared with A0 treatment,the content of light group organic carbon in soil under A30 and A90 treatments increased by 94.59%and 441%on average,and the content of easily oxidized organic carbon increased by 26.2%and 50.9%on average.Compared with P0 treatment,the content of light group organic carbon under P30 and P90 treatments increased by 197%and 663%on average.The average increase of easily oxidized organic carbon was 35.4%and 159.77%.5.Planting switchgrass in saline-alkali land can enrich the diversity of soil carbon sequestration microbial community a and increase the number of soil carbon sequestration microbial species.Under the experimental conditions,the α richness index of each treatment was higher than that of the nearby blank wasteland,while the a diversity index had no significant difference.These results indicated that planting switchgrass in saline-alkali land could improve the richness of soil microbial community,but the diversity of soil microbial community did not change significantly.The number of ASV/OUT species in each treatment was significantly higher than that in the nearby blank wasteland.With the increase of phosphorus application level,the number of characteristic OUT of each treatment was increased,and A0 treatment was the most.Compared with A0 treatment,the number of characteristic OTU of A30 and A90 treatment was 511 and 514,respectively,and the number of characteristic OTU of P30 and P90 treatment was 415 and 451,respectively.The relative abundance statistics of species at phylum level showed that Proteobacteria were the dominant phyla in each treatment under this test condition.The relative abundance of A0,A30 and A90 were 57.77%,61.59%and 55.8%,respectively.The relative abundance of P0,P30 and P90 were 56.1%,34.59%and 61.91%,respectively,which were all higher than that of blank wasteland nearby.6.Phosphorus application significantly increased the carbon sequestration of switchgrasssoil ecosystem in saline-alkali land.The carbon sequestration in aboveground and underground parts of switch grass was obviously accumulated with the increase of P application level.Compared with A0,aboveground carbon sequestration in A30 and A90 increased 87.53%and 148.5%on average,and underground carbon sequestration in A30 and A90 increased 84.58%and 176.82%on average.Compared with P0 treatment,the aboveground part of P30 and P90 treatment increased by 47.72%and 119.98%on average,and the underground part increased by 21.18%and 81.65%on average.For the soil carbon sequestration in 1m soil layer,there was obvious surface aggregation,and the soil organic carbon density decreased gradually with the deepening of soil layer.On the whole,soil profile organic carbon density(SOCi)increased synergically with the increase of P application,and the increase was particularly significant under high P treatment.Compared with A0 treatment,soil carbon sequestration in A30 and A90 treatments increased by 33.89%and 60.96%on average.Compared with P0 treatment,P30 and P90 treatments increased by 5.5%and 6.69%on average.For the ecosystem of saline-alkali land and switchgrass,the effect of phosphorus application on carbon sequestration was obvious,and there was a significant positive correlation between them.Compared with A0,A30 and A90 treatments increased the carbon sequestration by 29.09%and 66.72%on average.Compared with P0 treatment,P30 and P90 treatment increased by 10.9%and 19.45%on average. |
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