| Better knowledge of root distribution and characteristics of plants would be important in field water and nutrient management.Switchgrass(Panicum virgatum L.)is a perennial tussock grass with high production and great ecological adaptation,often used as biofule crop,high-quality forage as well as for water and soil conservation.Root biomass and characteristics above and between rows were investigated for switchgrass after 6-7 years plantation,which was grown on a terrace under three different row spacings of 20 cm,40 cm and 60 cm in loess hilly-gully region of China.Results showed that:1.Fine roots(d?1 mm)were the dominant component in the root system of switchgrass and the fraction of fine root biomass in row spacing of 40 cm exhibited the highest value among these three row spacings: in April,the proportion of fine root biomass in 20 cm,40 cm and 60 cm was 90%,88% and 83%,respectively;while in October there were 77%,83% and 79%,respectively.2.More than 70% of root biomass distributed in the upper 0-40 cm soil layer in all three row spacings,of which row spacing of 40 cm exhibited higher root biomass in the upper as well as deeper soil depth: Fine root biomass in 0-40 cm soil layer in narrower row spacing of 20 cm and 40 cm were significantly higher than that in 60 cm,but it was lower in spacing of 20 cm than that in 40 cm and 60 cm in the deeper soil profile,which suggested that spacing of 20 cm limited the root growth in the deeper soil;horizontally,fine root biomass at and between rows increased with increasing row spacing,suggesting that wider row spacing was of benefit to root extension.The thick root depth increased with the increasing row spacing,which provided fine roots in wider row spacing with easy access to soil resources in deeper soil.3.More than 70% of the fine root length was attributed to roots ?0.5mm in diameter and this fraction was the highest in row spacing of 40 cm which produced roots with smaller root average diameter,higher fine root biomass,root length density,root surface area,specific root length and specific root area in both shallower and deeper soil depths: In 0-20 cm soil layer,averaged root length density and surface area were the highest in row spacing of 40 cm,and specific root length as well as specific surface area increased with increasing row spacing.In the soil depth down below 20 cm,mean root length density,root surface area,specific root length and specific root area were lower in spacing of 20 cm.The root average root diameter throughout the whole soil profile was significantly the highest in spacing of 20 cm.4.In October,average root length density,specific root length and specific surface area were higher in all row spacings than April,while root biomass was lower in spacing of 40 cm and 60 cm: Root length density of 0.1-0.3 mm in diameter increased and 0.8-1.0 mm decreased significantly in October(p<0.05),resulting in the reduction in the FRB.And thick root biomass increased in row spacing of 20 cm and 40 cm.5.Row spacing of 20 cm improved above-ground biomass accumulation and soil water use efficiency significantly.In summary,wider row spacing were beneficial for root growth of individual and downward extension,but root biomass accumulation and utilization of soil resource in the upper soil would decline if row spacing was too large.We concluded that row spacing of 40 cm produced higher fine root biomass,root length density,surface area,specific root length,specific root area and more roots with smaller root diameters,which is more beneficial for the water and nutrient acquisition,but spacing of 20 cm improved above-ground biomass accumulation and water use efficiency significantly. |
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