Effects Of Root System Architecture On Nitrogen And Phosphorus Absorption And Utilization Efficiency In Alfafa

This study was conducted in a pot experiment to assess the effects of soil moisture on root growth characteristics in alfalfa(Medicago sativa L.),and nutrient use efficiency under different root system morphology.Two cultivars(Sadie-7 and Icon)were grown with lower(deficiency),appropriate(CK),or higher(waterlogging)soil moisture treatment for 20 days,then water application of each pot was returned to CK level.Nitrogen or phosphorus use efficiency of the plants was determined by application of nitrogen(urea)or phosphorus(superphosphate)at the end of soil moisture treatment.The results showed that:1.The root growth was significantly different(P<0.05)under 3 soil moisture conditions.Taproot elongation was significantly inhibited by water logging.The diameter,surface area and volume of root system were lower than CK.The taproot length was significantly higher in lower soil moisture condition than that in CK.2.After water stress removed,the recovery growth of root system from water logging pre-treatment was the poorest,recovery ability of lateral root growth(mass growth or relative growth rate of lateral roots and root tips)of the plants pre-treated by water logging was lower than CK.But the taproot of plants pre-treated by waterlogging recovered fast.The taproot growth was siginificantly higher in plot pre-treated by lower soil moisture then pre-treated by water logging.However,its root growth was still lower then in CK.3.When water stess was removed,nitrogen and phosphorus were at the same time applicated.The recovery growth of roots system from water logging and low soil moisture both was accelerated.The root recovery growth of two varieties was almost sames.The taproot growth and lateral root growth of plants applied fertilizer were both higher than the plot did not apply the fertilizer.Taproot growth of plants from water logging treatment was significantly higher then in pre-treatment of CK and soil moisture(P<0.05).However,the lateral root growth was still significantly lower then CK(P<0.05).Taproot growth of plants growth with low soil moisture had no significantly diffierence with CK,and the lateral root growth was higher then water logging but lower then CK.4.The results showed that the uitilization efficiency was significantly different(P<0.05)under different nutrition condition.Under low nitrogen(0.336 g/pot)and moderate nitrogen(1.008 g/pot)condition,The absorbtion efficiency of plants grown with water logging was significantly lower then CK and low soil moisture,but at high nitrogen level(2.019 g/pot),The absorbtion efficiency of plants grown with water logging had no difference with low moisture(P>0.05).Under low phosphorus(1.51 g/pot)condition,The absorbtion efficiency of plants grown with water logging was significantly lower then CK(P<0.05).Uder high phosphorus(7.54 g/pot)condition,The utilization efficiency of plants grown with water logging had no difference with CK(P>0.05).The relative growth rate and absolute growth rate of alfalfa roots had significant differnnt(P<0.05).Except root activity,There was a positively correlation between lateral roots,root tips and nitrogen uptake efficiency,nitrogen utilization efficiency,phosphorus uptake efficiency,phosphorus utilization efficiency,the relative and absolute growth rate.The results suggested that it is needed to avoid water logging and increase fertiliser application properly,to compensate for the decrease of sbsorption capacity of root system in the southern china.