| With the contradiction between the supply and demand of water and fertilizer increasing,the study of local irrigation and fertilization has been paid more and more attention.Many studies have been done on the growth and physiological responses of crops under partial resupply,especially under partial rewatering.However,few studies have been conducted to consider the stress status of early crops.In agricultural production,irrigation or fertilization is often carried out by crops after a certain time of water or nutrient stress.Therefore,in order to develop water and nutrient stress adaptation potential and provide a theoretical basis for improve water resource management level,research of function of previous stress time on partial resupply of water and nitrogen on crop root growth and absorption need to be carried out.Therefore,Maize seedling was prepared using split-root hydroponic technique,with PEG 6000 simulating water stress,setting different nitrogen supply for nitrogen stress level,the test was divided into two stages.In the previous stress stage,-0.4MPa water stress or 1mM nitrogen stress were subjected to maize seedling root.With the time of 0,1,3,6d previous stress,then partial resupply,the 1/2 root zone with normal supply,labeled with 15 N Ca(15NO3)2 as nitrogen source,The other 1/2 root zone supplied with normal level,with no labeled Ca(NO3)2.Then monitor the crop growth status of absorption of root water and nitrogen dynamically,at the resumption time of 0,0.25,0.5,1,3,5,7 and 9 d,exploring the dynamic changes of root growth and absorption function after partial re supply.At the same time,the changes of root anatomical structure were observed,investigating the internal relationship between root structure and root absorption function.The main results are as follows:(1)Study on root water uptake showed that the rewatering root hydraulic conductance increase rapidly at 0.25 d,0.5d,3d and 5d respectively,with the previous stress time of 0d,1d,3d and 6d.both sides of the root zone total hydraulic conductance、unit root length and area hydraulic conductance conductivity showed significant difference at the resupply time of 0.5d,1d,3d,7d、 0.5d,3d,5d,7d and 0.5d,5d,5d,7d,rewatering zone was significantly higher than that of stress zone,showed that the longer previous stress time the slower hydraulic conductance recovery.After water or nitrogen previous stress,the resupply root zone hydraulic conductance increase rapidly at 0.5d,1d,3d and 5d respectively.Both sides of the root zone unit root length and area hydraulic conductance showed significant difference at the resupply time of 3d,5d,5d,5d、3d,3d,3d,5d and 0.5d,5d,5d,7d.Thus the time of resupply zone increase obviously and significant difference between two roots delayed with the increase of the previous stress time.The partial resupply can restore leaf water status.The leaf water content with presvious tress 0d keeps the same with CK;Water previous stress 1d,3d,6d,the leaf water content keeps close to CK respectively at the partial resupply of 3d,7d,7d.Nitrogen previous stress level at the resupply time of 3d,7d,and 9d reached CK.The longer previous stress time,the slower rate of recovery.(2)Study on the nitrogen absorption of the root zone using 15 N isotope tracer technique showed that maize seedlings subjected to-0.4 MPa,1mM of water or nitrogen stress,rewatering root zone nitrogen uptake rate showed that the previous stress time of 0d and 1d was significantly greater than CK at the partial resupply time of 0d and 5d;The nitrogen uptake rate of previous stress 3d at the partial resupply time of 5d reached CK;The nitrogen uptake rate of previous stress 6d always lower than CK.The nitrogen absorption rate of nitrogen supply side,after the previous stress 0d and 1d was significantly greater than CK;Previous stress 3d reached CK after resupply 1d;Previous stress 6d higher than CK after resupply 1d.Stress side showed that water and nitrogen previous stress 0d,stress sides less than CK after the resupply time of 1d and 5d.The previous stress 1d,3d,6d,always less than CK significantly.The duration of stress time significantly affect the recovery of nitrogen uptake in resupply roots,and the difference in nitrogen uptake between the two roots was delayed with the increase of previous stress.The nitrogen content and nitrogen accumulation of both roots of water stress 0,1,3 and 6d showed significant differences at partial rewatering time of 9,5,1,5d and 9,9,1,and 1d,respectively.After nitrogen stress,the nitrogen content and nitrogen accumulation of both roots showed significant differences in the resupply time of 5d,5d,9d,9d,and 1d,5d,5d and 5d.(3)Study on the root growth response showed that root length,root area and root dry weight of previous stress 0d has no significant difference with CK after resupply,both root length and root dry weight had significant difference at resupply time of 1d and 5d,the root area had no significant differences.The root length,root dry weight and root area with previous stress 1d,3d,6d,showed significant difference at 1d,1d,3d、3d,3d,5d and 1d,3d,7d.The root length and root growth rate with previous stress 0d were significantly greater than the stress side at the resupply time of 0.5d and 3d.The root length and root growth rate,with previous stress 1d,3d,6d,had significant difference on both sides of the root,except the root area at 0.25~0.5d with previous stress 1d had no significant difference.After partial resupply of nitrogen stress,the two sides of the root length and root area of the average growth rate in 5~9d had no significant difference and root dry weight average growth rate of no significant difference in 5~7d with previous stress 0d;root area and root dry weight growth rate at resupply time of 0.25~0.5d and 1~3d,had no significant difference with previous stress 1D.Other time and previous stress on both sides of the root of 3D and 6D were significantly greater than the supply side.With previous stress time prolonged,the resupply root growth restore degree reduce and recovery time delay.(4)The anatomical structure of maize roots showed that the diameter of roots and tubes were significantly smaller than that of CK,and the proportion of cortex thickness to root diameter was significantly higher than that of CK after water 、nitrogen stress 6d.The difference was that water stress had no significant effect on cortical thickness,while nitrogen stress 、water and nitrogen stress increased the cortical thickness.The diameter of roots and tubes recovered quickly and even more than CK at the resupply time of 1d,then tended to be stable,it is larger than resupply 0d;the thickness of cortex accounted for the proportion of root diameter in 1~5d was significantly lower than resupply 0d.After water resupply,the thickness had no significant difference with CK,cortical thickness proportion less than stress side significantly at resupply 5d.After nitrogen resupply,the thickness of cortex reached CK level at the recovery of 9d;The thickness of cortex less than CK at the recovery of 9d The restored supply side showed recovery and adaptation.The continued stress side of diameter of root tube less than CK significantly,except nitrogen stress resupply at 1d had not difference significantly,the thickness of cortex and the root diameter ratio accounted for stress continues to increase. |
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