Studies On Roots Physiology For High Yield And High Phosphorus Efficiency Of Rice In Cold Region

Phosphorus（P）fertilizer are widely used in crops production,but only 10～30%P fertilizer can be utilized by crops in the application year.The excessive input of P fertilizer will increase production cost,waste P resource,and enhance environment risk.Reducing P fertilizer input and enhancing P fertilizer use efficiency are the key challenge for achieving high productivity and P efficiency in crops production system.Many researches have been conducted in breeding P efficient cultivars and optimizing P management strategy,however,the root characteristics of high productivity and P efficient rice and its effect mechanism have been still unclear.Our studies focused on field experiment and supplemented by rhizo-boxes experiment,and combined with investigation methods of agronomy,plant physiology and molecular biology.Firstly,thirteen cultivars released between 1958 and 2015 in Heilongjiang province were selected in this study.The plot experiment was performed on rice using three P supply levels(0,40 and 80 kg P ha^-1)to investigate the change of root characteristics due to selection for yield and its effect on P efficiency.Secondly,based on above results,the low P efficient cultivars（HJ19）and P efficient cultivars（KY131 and LJ31）were selected.Three cultivars grown in plot with six P fertilizer application rate(0、20、40、80、120 and 160 kg P ha^-1)to investigate the response of root characteristics to P supply and its relation to yield formation,and evaluate optimal soil P supply for maximum grain yield.Thirdly,LJ31 grown in rhizo-boxes with eight fertilization treatments（CK、P、K、N、PK、NK、NP and NPK）to the regulation of interactive effect between nitrogen（N）,P and potassium（K）on root growth pattern and characteristics and its effect on P efficiency.1.The change of root characteristics due to selection for yield and its effect on P efficiencyBetween 1958 and 2015,the dry matter accumulation at each growth stage,yield,harvest index（HI）gradually increased with released year,and these agronomic parameters did not exhibit significant change between varieties released after 2000.P acquisition efficiency（PAE）at each growth stage,and root dry weight and total root length at heading stage increased with released year from 1958 to 2000,after that,these parameters gradually decreased to a stable level with released year.Agronomic use efficiency（AE）,root oxidation activity（ROA）,P uptake per unit root weight and P uptake per unit root length increased with released year.P internal utilization efficiency（PIE）in the group of varieties released between 2010 and 2015sightly higher than in those of released between 1958 and 1998,and both of groups significantly higher than varieties released between 2000 and 2007.Selection of yield increased rice yield mainly due to increases in dry matter accumulation and HI.Correlation analysis indicated that dry matter accumulation exhibited highly significant positive correlations with PAE,but significant negative correlations or no correlations with PIE.The root weight,total root length and ROA showed significant positive correlations with PAE,and significant negative correlations or no correlations with PIE.These results indicate that selection for yield between sixty years in Heilongjiang province enhances rice yield mainly due to increased PAE,which was closely related to improvement of root characteristics.2.The root characteristics of different P efficiency genotypes in responses to P supply and its effect on yield formationSoil Olsen-P significantly increased as the P application level,and the response was similar between cultivars.Enhancing P fertilizer application level significantly increased dry matter accumulation,grain yield,shoot P concentration and PAE at each growth stage,but decrease PIE for triple cultivars;these agronomic parameters did not further change for three cultivars when P rate exceeded 80 kg ha^-1.We used the linear-plateau model evaluated the critical soil P supply for maximum yield of three cultivars,which ranged from 14.4 to 16.3mg kg^-1,corresponding to P fertilizer application rate with 80 kg ha^-1,and thus,80 kg P ha^-1is the optimal P fertilizer application rate under the experimental conditions.Compared to HJ19,both KY131 and LJ31 had higher dry matter accumulation,PAE and grain yield at each P supply level,and PAE for KY131 was higher than other cultivars.PIE and shoot concentration were similar between HJ19 and LJ31,and they were higher than KY131.It suggested that both KY131 and LJ31 had the higher grain yield than HJ19,primarily due to the superior PAE,not PIE.Three cultivars had the similar root response to P supply.At heading stage,when the P application rate increased up to 80 kg ha^-1,three cultivars increased the root weight,total root length and ROA,while decreased the specific root length,root acid phosphatases activity（APase）,and relative expression level of Os IPS2、Os PAP10a、Os PT2 and Os PT6;and no significant change for these parameters were obtained above this P supply level.Both KY131 and LJ31 had higher root weight,total root length and ROA than HJ19,which associated with improved PAE for KY131 and LJ31.This suggested that improved P absorption due to strong roots might be a partial mechanism for increasing grain yield in P efficient varieties.When P fertilizer application rate was less than 80 kg ha^-1,KY131 had the higher root weight and total root length,and the lower ROA,APase,and relative expression level of Os PAP10a、Os PT2 and Os PT6 compared to LJ31.It suggested that rice genotypes with similar P efficiency might be depended on different root strategies in response to change of P supply.3.Effect of N、P and K interaction on root characteristics and P efficiency of riceN、P and K interaction increased dry matter accumulation and yield of rice.enhancement of yield was mainly due to increased panicles per hill,and the spikelets per panicle,seed setting rate and 1000-grain weight were no significant difference between treatments with N.Rice yield increased by co-application of N,P and K primarily caused by increased PAE,not PIE.At elongating stage and maturity,treatment with NPK had the significantly higher PAE and lower PIE than that of treatments with N and NK.P accumulation in NPK treatment group was 1.2-fold higher than the sum of the corresponding values of N,P and K treatments groups at the elongating stage.The increased P uptake due to N,P and K interaction was closely related to improved root characteristics.NPK treatment had significantly total root length,root weight and root number,and lower specific root length than other treatments.The improved root morphological traits were caused by increases in root length,root weight and root number in 0～20 cm soil layer.The superior root physiological characteristics for NPK combination were mainly due to the higher ROA,total roots absorption area and roots active absorption area relative to other treatments.APase and the relative expression level of OSIPS2,Os PT2 and OSPT6 were similar between treatments without N,regardless of whether P was present or not;P application enhanced APase and the relative expression level of OSIPS2,Os PT2 and OSPT6,regardless of whether P was supplied or not,and these parameters were significantly higher in treatments with N and NK than other treatments without N.The results of the present study indicated that yield and P efficiency in rice increased due to N,P and K interaction were closely associated with root weight,root length and root number in 0～20 cm soil layer and ROA,total roots absorption area and roots active absorption area.