| Grassland is an important part of terrestrial ecosystem,and the root morphology and biomass are important parameters in the study of grassland ecosystem.It is of great significance to study the variation in the root morphology and biomass along the environmental gradient for the local vegetation construction and restoration.In this study,we selected ten sites from east to west in the Loess Plateau,which covered the main grassland types,including forest grassland,typical grassland and desert grassland.At each site,the roots of grassland plant were sampled to 0 cm to 50 cm soil depth at eight experimental plots(1m×1 m)by using roots cores.Root morphological trait(including total root length and total root surface area)and biomass of each soil depth were determined.We aimed to analyze the variation of root morphological traits(including total root length and total root surface area)and biomass along the environmental gradient in the Loess Plateau and their influence factors.The results showed that:(1)The total root length was significantly different among three grassland types(P<0.05),and the root length of forest steppe was significantly higher than that of typical steppe and desert steppe.The root length of the three grassland types was mainly distributed in the surface soil(0-10 cm),and the root length of the forest steppe was most distributed in the surface soil,and the root length of deep layer(10-50 cm)of desert steppe accounted for more of the total root length of desert steppe.With the increase of longitude,the root length of grassland in the Loess Plateau showed a gradually increasing geographical pattern,and more roots appeared in the shallow soil.Root length had significant positive correlation with climate and soil factors(P<0.01).The ratio of shallow root length to deep root length(i.e.,shallow-deep ratio of length)was positively correlated with average annual precipitation(MAP)and soil total nitrogen content(TN)(P<0.01),and negatively correlated with soil p H(P<0.01).Environmental factors explained 37.2%-48.94% of the variation in root length of grassland in the Loess Plateau,and climate factors explained the most variation(5.2%-18.46%)of root length.The interaction of climate factors and soil factors could explain 18.25%-37.03% of variability.(2)The total root surface area was significantly different among three grassland types(P<0.01),and the root surface area of forest steppe was significantly higher than those of typical steppe and desert steppe.The root surface area of the three grassland types mainly concentrated in the surface soil,and the root surface area of forest steppe and typical steppe was more in the surface soil,and the root surface area of deep desert steppe accounted for more in the total root surface area of desert steppe.With the increase of longitude,the root surface area of grassland in the Loess Plateau showed a gradually increasing geographical pattern,and more roots appeared in the shallow soil.Root surface area had significant positive correlation with climate and soil factors(P<0.01).The ratio of shallow root surface area to deep root surface area(i.e.,shallow-deep ratio of surface area)was significantly positively correlated with MAP and TN(P<0.01),and negatively correlated with soil p H(P<0.01).Environmental factors explained 39.07%-52.24% of the variation in the root surface area of grassland in the Loess Plateau,and climate factors accounted for the most variation(9.36%-23.17%).The interaction of climate factors and soil factors could explain 23.28%-35.44% of the variability.(3)The root biomass of three grassland types in the Loess Plateau was significantly different(P<0.05),with the root biomass of forest grassland being the largest and that of typical grassland being the smallest.All of the root biomass vertical distribution of the three different grassland types in the Loess Plateau were “T” type,and the surface soil accounted for more than 55% of total root biomass.Moreover,more proportion of the root biomass of the desert grassland was distributed on the surface soil.As the longitude increased,the grassland root biomass of the Loess Plateau decreased first,and then increased.However,the ratio of the root biomass of shallow soil layer to the root biomass of deep soil layer(i.e.,shallow-deep ratio of biomass)did not show an obvious longitudinal pattern.The change in total root biomass was affected positively by the mean annual temperature(MAT)(P<0.01).But the root biomass of deep soil layer was affected by both climate and soil nutrient content(P<0.01),and the shallow-deep ratio of biomass was influenced negatively by the total soil phosphorus(TP)of the average and deep soil layer(P<0.05).Climate and soil factors could explain 5.12—39.36% of the variation in root biomass,among the independent effects,climate factors had the largest explanatory degree to root biomass,which could reach 2.77%—9.12%. |
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