The Coupling Relationships Between Fine Roots And Soil Moisture And Organic Carbon Of Artificial Vegetations In Loess Region Of Western Shanxi Province

Vegetation restoration is the main measure to reduce soil erosion and improve the ecological environment in loess region of western Shanxi Province,China.Five artificial vegetation types?Medicago sativa,Robinia pseudoacacia,Platycladus orientalis,and Juglans regia?were selected from the study region,with long-term cropland as the control.Analyzed the distribution of soil moisture content?SMC?,soil organic carbon?SOC?and active component under 0-500 cm soil layer,constructed and verified the vertical profile model of vegetation soil moisture.Analyzed the distribution of fine root,constructed the vertical profile model of vegetation root indexes.Based on this,discussed the relationship between fine roots,SMC and SOC,comprehensive evaluation of the contribution of fine roots of artificial vegetation to SMC and SOC.The main conclusions of this papers is as follows:?1?The distribution of SMC differed across different artificial vegetation types,and the soil moisture deficit effect has been generated in the deep layers.The distribution of SMC in the region was divided into two layers of shallow?0-70 cm?and deep?70-500 cm?;the latter was subdivided into precipitation infiltration layer?70-160cm?,transition layer?160-280 cm?,and relatively stable layer?280-500 cm?.The average SMC in deep layers of the five artificial vegetation was 12.01%.Compared with cropland,the total soil moisture storage?SMS?deficit of Medicago sativa,Robinia pseudoacacia,Platycladus orientalis,and Juglans regia was 170.83 mm,448.25 mm,161.94 mm and357.61 mm,and the depth of soil moisture deficit?SMD?with Medicago sativa and Platycladus orientalis reached more than 3 m,and Robinia pseudoacacia and Juglans regia reached 5 m.The vertical profile soil moisture model SMC=a(e^-kh-1)+b(1-e^-k1h)+d reflected the vertical variation of soil moisture in agricultural land Robinia pseudoacacia and Juglans regia well?R²>0.60,p<0.05?,but was not suitable for Medicago sativa and Platycladus orientalis?R²<0.60,p>0.05?.?2?The distribution of soil organic carbon and its active components and their accumulation effects differed across different artificial vegetation types.The shallow layers soil organic carbon?SOC?was 5.29-12.44 g·kg^-1,accounting for about 23%-41%in the whole soil layer of five artificial vegetation.The shallow layers soil organic carbon density?SOCD?was 0.60-2.42 kg·m^-2,accounting for about 14%-24%in the whole soil layer of five artificial vegetation.Compared with the control,the SOCA of Medicago sativa,Platycladus orientalis and Juglans regia was generally positive accumulation effect,and the Robinia pseudoacacia was negative deficit effect.In soil surface,both of the content of dissolve organic carbon?DOC?and SOC was highest,and the forest was significantly higher than grass and cropland,the difference was only in 0-20 cm layers.The characteristics of UV spectrum and fluorescence spectrum indicated that the aromatization index?AI?and humification index?HIX?of each plot significantly differed only in individual soil layer,so the effect of artificial vegetation restoration on soil structure was slow.The easily oxidized organic carbon?EOC?in the shallow layers of the five artificial vegetations was 2.46-2.70 g·kg^-1,accounting for 14.5%-40.2%of the total soil organic carbon.The significant difference was only in the shallow layers of each plot.?3?The distribution of fine root indexes differed across different artificial vegetation types.The fine roots of five artificial vegetations were mainly distributed in the shallow layer.and the fine root indexes,root length density?FRLD?and fine root mass density?FRMD?,for example,was exponentially distributed in the vertical profile,and the root surface area density?FRAD?was distributed in a cubic polynomial,accounting for 25.9%-34.3%,34.2%-41.7%and 18.2%-27.1%of the whole soil layer.The phenomenon of fine root aggregation is obvious,and the density of fine roots of the other four artificial vegetations was significantly higher than cropland.The distribution of the percent of root cumulative biomass?Y?was consistent with the exponential model Y=1-?^h,with strong correlation.The root weakening coefficient???in deep layer was higher than that in shallow layer of all vegetations?p<0.05?.?4?The coupling relationships between fine roots,SMC and SOC among artificial vegetations at different levels was different.The contribution of fine roots of artificial vegetations to SMC and SOC differed in different soil layers.In shallow layer,fine roots were significantly correlated with SMC and SOCD.In deep layers,fine roots were significantly correlated with SOCD,and SMC was only significantly correlated with Juglans regia.Stepwise regression analysis further showed that the multiple linear regression equations of fine roots and SMC of Robinia pseudoacacia and Juglans regia reached a significant level?p<0.05?,with the strong coupling.The regression equations of fine roots and SOC among five vegetations were significant,all of them had the strong coupling?p<0.05?.The relevancy of fine roots of artificial vegetation with SMC and SOCD lied different to vegetation types.The fine root in deep layers significantly differed among three forests,and it has caused the distribution differences of SMC and SOCD.In overall,the deep root of the Robinia pseudoacacia has caused SMD effect,and was bad to SOCD accumulation.