| Phosphorus（P）,as an important soil nutrient,is one of the large elements necessary for plant growth.Lack of P is a common phenomenon in afforestation in China.In production and life,it is common to solve the problem by applying P fertilizer.However,the application of P fertilizer will lead to low soil utilization efficiency（no more than 10%）and P fertilizer into the soil are very easy to change into difficult to use immobilized P.Therefore,it is very necessary to study the biological characteristics of plants and the mechanism of P absorption.Taxodium’Zhongshanshan’is the general name of interspecific hybrids of T.distichum and T.mucronatum.It has the advantages of straight and beautiful tree shape,long green period,fast growth speed and can grow in poorly drained wetland environment.It is an excellent afforestation tree species with good ecology,landscape and economic benefits.In the afforestation of T.’Zhongshanshan’,there is also the problem of P deficiency.Soil P deficiency will lead to poor growth.In order to provide important theoretical basis and guidance for the breeding and popularization of P efficient genotypes of T.’Zhongshanshan’,the cuttings of’Zhongshanshan’118,’Zhongshanshan’302,’Zhongshanshan’406 and their parents,T.mucronatum and T.distichum,were selected as experimental materials for indoor simulated P stress hydroponic culture experiment,The morphological indexes（Total root length,Root surface area,Total root volume）,growth indexes（Biomass,Ground diameter,Plant height,Root shoot ratio）and physiological and biochemical indexes of plant roots of different genotypes of T.’Zhongshanshan’and its parents under different degrees of low P stress were measured（Photosynthesis,Enzymes,Nutrient elements,p H）,and comprehensively evaluate the low P tolerance of different genotypes and their parents by membership function method combined with weight.The results are as follows:（1）Differences in root morphology and growth traits of different genotypes of T.’Zhongshanshan’under low P stressIn the root morphological indexes,compared with CK,there was no significant difference among the three kinds of T.’Zhongshanshan’and their parents.Only under P15 treatment,the root length and root area of’Zhongshanshan’406 increased significantly by 47.21%and 50.6%compared with P5.In the growth traits,compared with CK,there were great differences among the three kinds of T.’Zhongshanshan’and their parents.The biomass of’Zhongshanshan’406 decreased significantly by 47.07%-62.34%under all low P treatments,and the biomass of T.mucronatum and’Zhongshanshan’118 decreased significantly by 75.87%and 86.38%under only P0 treatment;The ground diameter of’Zhongshanshan’302 was significantly reduced by 43.97%-88.19%under all low P treatments,and the ground diameter of’Zhongshanshan’302 was significantly increased by 295.82%under other only P15 treatment.The plant height of’Zhongshanshan’406was significantly reduced by 47.5%-67.1%under all low P treatments.The ground diameter of’Zhongshanshan’302 was significantly reduced by 46.9%and 77.6%under other P5 and P0 treatments,and the ground diameter of T.distichum,’Zhongshanshan’118 and’Zhongshanshan’302were significantly reduced by 73.6%,86.8%and 62.1%under P0 treatment.Under P0 treatment,the root shoot ratio（dry weight）and fresh weight of T.mucronatum increased significantly by50.54%-70.97%and 88.16%-100.14%;Under P10 and P0 treatments,the root shoot ratio（dry weight）of T.mucronatum increased significantly by 88.14%and 93.44%;Under P0 treatment,the root shoot ratio（fresh weight）increased significantly by 106%;Under P0 treatment,the root shoot ratio（dry weight）of’Zhongshanshan’118（fresh weight）significantly increased by242.14%and 263.88%;the root shoot ratio（fresh weight）of’Zhongshanshan’302 significantly increased by 117.66%under P0 treatment;the root shoot ratio（dry weight）of’Zhongshanshan’406 significantly increased by 60.33%and 110.34%under P15 and P0 treatments,and the root shoot ratio（fresh weight）significantly increased by 86.47%under P0treatment.Root morphology had significant correlation with aboveground P accumulation,but had no significant correlation with whole plant P accumulation and aboveground P accumulation.Plant P accumulation was significantly correlated with some of the growth indexes.Among the growth indexes,the net biomass had the closest relationship with plant P accumulation,followed by root shoot ratio（dry weight）,root shoot ratio（fresh weight）,net plant height and net ground diameter.（2）Difference of photosynthesis between different genotypes of T.’Zhongshanshan’and their parents under low P stressIn terms of chlorophyll content,compared with CK,the chlorophyll content of’Zhongshanshan’406 increased significantly,and the differences between the other two kinds of T.’Zhongshanshan’and their parents decreased significantly.Under P5 treatment,the chlorophyll a content of T.mucronatum decreased significantly by 18.55%,the chlorophyll a content of T.distichum under P15 and P10 treatments decreased significantly by 17.05%and 22.11%,the chlorophyll a content of’Zhongshanshan’302 under P15 treatment decreased significantly by19.61%,the chlorophyll a content of’Zhongshanshan’406 under P5 treatment decreased significantly by 9.34%,and the chlorophyll b content of T.mucronatum under P10 and P5treatments decreased significantly by 27.15%and 30.52%,the content of chlorophyll b of T.distichum in P15 and P10 treatments decreased significantly by 26.06%,21.23%and increased significantly by 27.65%under P0 treatment,the content of chlorophyll b in’Zhongshanshan’118decreased significantly by 19.84%-29.88%under all low P treatments,and the content of chlorophyll a in’Zhongshanshan’406 increased significantly by 13.19%under P5 treatment.Under P5 treatment,the total chlorophyll content of T.mucronatum decreased significantly by21.9%,the total chlorophyll content of T.distichum decreased significantly by 19.59%and21.86%,the total chlorophyll content of’Zhongshanshan’118 decreased significantly by 15.71%,and the total chlorophyll content of’Zhongshanshan’406 increased significantly by 10.45%.In terms of gas exchange parameters,there were great differences among the three species and their parents.Under P10 and P5 treatments,the net photosynthetic rate of T.mucronatum increased significantly by 238.38%and 351.57%respectively,T.distichum decreased significantly by 77.22%under P0 treatment,that of other low P treatments increased significantly by 81.01%-287.87%,’Zhongshanshan’118 decreased significantly by 65.44%and 62.17%under P5 and P0 treatments,and’Zhongshanshan’302 decreased significantly by 60.41%and 60.8%under P5 and P0 treatments,’Zhongshanshan’406 decreased significantly by 35.97%-62.79%under the treatments of P10,P5 and P0;Under P5 treatment,the transpiration rate of’Zhongshanshan’302 decreased significantly by 56.82%;The stomatal conductance of T.distichum increased by 141.7%under P0 treatment,and decreased by 71.15%under P5 treatment;The intercellular CO2concentration of T.mucronatum decreased significantly by 42.69%under P5treatment,T.distichum increased significantly by 44.02%under P0 treatment,other low P treatments decreased significantly by 31.52%-92.11%,’Zhongshanshan’302 increased significantly by 32.27%and 26.38%under P5 and P0 treatments;WUE of T.mucronatum increased by 476.01%under P5 treatment,T.distichum increased by 95.79%and 134.89%under P10 and P5 treatments,and decreased by 70.99%under P0 treatment,’Zhongshanshan’118decreased significantly by 52.64%and 41.45%under P5 and P0 treatments;The stomatal limit of T.mucronatum increased significantly by 402.13%under P5 treatment,T.mucronatum increased significantly by 103.51%and 170.09%under P10 and P5 treatments,and decreased significantly by 79.68%under P0 treatment,’Zhongshanshan’118 decreased significantly by 44.25%and35.03%under P5 and P0 treatments.Photosynthetic indexes had significant correlation with the whole plant P accumulation and aboveground P accumulation,but had no significant correlation with the underground P accumulation.There was no significant correlation between chlorophyll content and plant gas exchange coefficient.In addition to stomatal conductance,the correlation between net photosynthetic rate and other gas exchange coefficient indexes reached significant correlation.The correlation from large to small was water use efficiency,stomatal limit value,intercellular CO2concentration and transpiration rate.（3）Changes of Rhizosphere p H of different genotypes of T.’Zhongshanshan’and their parents under low P stressCompared with the first day（1D）,with the passage of time,except that the p H difference of Sequoia is not significant,other test materials have significant changes;Compared with the normal P supply,with the passage of time,except that the p H difference of Sequoia in 1D（first day）and 2D（second day）,other test materials have significant changes.（4）Changes of enzyme activities of different genotypes of T.’Zhongshanshan’and their parents under low P stressCompared with CK,the enzyme activities of the three species of T.’Zhongshanshan’and their parents changed greatly.The ACP activity of the aboveground part of T.distichum decreased significantly by 2.54%-12.55%under the treatments of P10,P5 and P0;The ACP activity in the underground part of T.mucronatum decreased significantly by 4.78%and 2.15%under the treatments of P15 and P0,and increased significantly by 8.35%under the treatment of P5,T.distichum decreased significantly by 4.12%-11.88%under the treatments of P10,P5 and P0,’Zhongshanshan’118 decreased significantly by 13.01%under the treatment of P15,’Zhongshanshan’302 decreased significantly by 4.54%under the treatment of P0,and’Zhongshanshan’406 decreased significantly by 9.79%under the treatment of P10;The GS activity of aboveground parts of T.mucronatum decreased significantly by 8.13%under P0treatment,the activity of GS in the aboveground part of T.distichum decreased significantly by1.7%-11.86%under P10,P5 and P0 treatments,’Zhongshanshan’302 decreased significantly by7.35%under P0 treatment and’Zhongshanshan’406 increased significantly by 9.29%under P5treatment;The activity of GS in underground part of T.mucronatum increased significantly by1.8%under P5 treatment,decreased significantly by 4.34%-7.91%under other low P treatments,T.distichum decreased significantly by 1.98%-14.4%under all low P treatments,’Zhongshanshan’118 decreased significantly by 7.05%-8.84%under P15,P10 and P5 treatments,and’Zhongshanshan’302 decreased significantly by 8.62%-14.35%under all low P treatments;The activity of NR in aboveground part of T.mucronatum increased significantly by 12.77%under P0 treatment,T.distichum decreased significantly by 1.01%and 4.44%under P10 and P0treatments,’Zhongshanshan’302 increased significantly by 15.23%under P15 treatment,’Zhongshanshan’406 decreased significantly by 5.14%and 6.46%under P15 and P10 treatments;The NR activity in the underground part of T.mucronatum decreased significantly by 1.07%and0.87%under the treatments of P15 and P5,and increased significantly by 1%and 1.93%under the treatments of P10 and P0,T.distichum decreased significantly by 0.78%-13.85%under all low P treatments,’Zhongshanshan’118 increased significantly by 4.17%under the treatment of P0,and decreased significantly by 7.59%-8.87%under other low P treatments,’Zhongshanshan’302increased significantly by 8.51%-16.88%under all low P treatments,’Zhongshanshan’406decreased significantly by 9.65%and 11.7%under P5 and P0 treatments.In terms of P and N content,except’Zhongshanshan’406,the P content of aboveground parts of other tested materials decreased significantly;The content of P in the underground part of T.mucronatum decreased significantly;The aboveground N content of’Zhongshanshan’118decreased significantly;The N content in the underground part of T.distichum increased significantly,and that of’Zhongshanshan’118 and’Zhongshanshan’406 decreased significantly.P content in aboveground part of T.mucronatum decreased significantly by 56%under P0 treatment,T.distichum decreased significantly by 48.04%-60.59%under all low P treatments,’Zhongshanshan’118 decreased significantly by 49.01%and 78.17%under P15 and P0 treatments,’Zhongshanshan’302 decreased significantly by 28.42%-55.2%under the treatments of P15,P10and P5;P content in the underground part of T.mucronatum decreased significantly by 90.79%and 91.45%under the treatments of P15 and P5;Under all low P treatments,the aboveground N content of’Zhongshanshan’118 decreased significantly by 4.22%-47.57%;N content in the underground part of’Zhongshanshan’302 increased significantly by 10.23%under P15 treatment,’Zhongshanshan’118 decreased significantly by 36.33%under P0 treatment,and’Zhongshanshan’406 decreased significantly by 17.09%-32.13%under p15,P5 and P0treatments.Under low P stress,the correlation between enzyme activity and plant N content was significant,but not P content,and there was an interaction between enzyme activities.（5）Difference of element content between different genotypes of T.’Zhongshanshan’and their parents under low P stressCompared with CK,the element contents of the three species of T.’Zhongshanshan’and their parents changed greatly.Under P0 treatment,the aboveground C content of’Zhongshanshan’406increased significantly by 115.4%;The content of C in the underground part of’Zhongshanshan’118 increased significantly by 28.99%under P5 treatment and’Zhongshanshan’302 increased significantly by 33.33%under P0 treatment;Under P0 treatment,the K content of aboveground parts of T.mucronatum and’Zhongshanshan’302 decreased significantly by 16.5%and 35.97%;Under the treatment of P10,the K content in the underground part of T.mucronatum and’Zhongshanshan’302 increased significantly by 356.57%and 398.39%;Under the treatments of P10 and P0,the Na content of aboveground parts of’Zhongshanshan’302 and’Zhongshanshan’406 decreased significantly by 55.55%,64.86%and46.67%,73.25%;The Na content in the underground part of T.mucronatum decreased significantly by 35.5%-48.36%under all low P treatments,and that of’Zhongshanshan’302increased significantly by 488.97%under P5 treatment;Under P0 treatment,the content of Mg in the aboveground part of’Zhongshanshan’406 increased significantly by 21.12%;The Mg content in the underground part of T.distichum decreased significantly by 21.17%under P0 treatment,and’Zhongshanshan’302 increased significantly by 61.19%under P10 treatment;The content of Ca in the aboveground part of T.distichum increased significantly by 34.9%under P0 treatment,and’Zhongshanshan’406 increased significantly by 39.44%under P5 treatment;The Ca content in the underground part of T.mucronatum decreased significantly by 32.47%-82.16%under all low P treatments,’Zhongshanshan’118 decreased significantly by 80.35%and 82.74%under P15and P10 treatments,and’Zhongshanshan’302 and’Zhongshanshan’406 increased significantly by622.07%and 289.39%under P5 treatment;The aboveground Zn content of T.mucronatum and T.distichum increased significantly by 208.38%and 147.19%under P0 treatment,’Zhongshanshan’118 increased significantly by 191.54%-251.58%under P15,P10 and P5treatments,’Zhongshanshan’302 increased significantly by 71.82%under P5 treatment,and’Zhongshanshan’406 increased significantly by 237.31%under P10 treatment;The content of Zn in the underground part of T.mucronatum,’Zhongshanshan’118 and’Zhongshanshan’302increased significantly by 492.93%,523.67%and 474.4%under P10 treatment,and’Zhongshanshan’406 increased significantly by 230.59%under P0 treatment;Under the treatments of P10 and P5,the Fe content in the aboveground part of’Zhongshanshan’406increased significantly by 47.53%and 53.83%;The Fe content in the underground part of T.mucronatum and’Zhongshanshan’406 increased significantly by 130.45%and 75.69%under P0treatment,T.distichum increased significantly by 70.88%and 78.88%under the treatments of P5and P0,’Zhongshanshan’118 increased significantly by 130.66%-185.2%under the treatments of P10,P5 and P0,and’Zhongshanshan’302 increased significantly by 148.14%and 278.97%under the treatments of P10 and P0;Under P0 treatment,the S content of aboveground part of T.mucronatum increased significantly by 57.96%;The content of S in the underground part of T.distichum increased significantly by 43.33%and 66.58%under P15 and P5 treatments,’Zhongshanshan’118 increased significantly by 26.39%and 39.97%under P10 and P0 treatments,’Zhongshanshan’302 increased significantly by 51.71%under P5 treatment,and’Zhongshanshan’406 decreased significantly by 38.35%under P0 treatment.The content of Na,Ca and s had significant correlation with the content of P,but the content of other elements had no significant correlation.There may be mutual influence between the contents of nutrient elements.（6）Evaluation and regression analysis of low P tolerance of different genotypes of T.’Zhongshanshan’and their parentsIt can be seen from the membership function values of different genotypes of T.’Zhongshanshan’and its parents that the ability of low P tolerance of T.mucronatum is the largest,that of’Zhongshanshan’406 is the smallest,and that of larch,’Zhongshanshan’118 and’Zhongshanshan’302 are in the middle,which shows that’Zhongshanshan’302 and’Zhongshanshan’118 have strong ability to find P and are suitable for planting in barren and low P areas.Stepwise regression analysis showed that root volume was the main factor driving the change of root foraging P ability of different genotypes T.’Zhongshanshan’and their parents,and root volume was suitable for the statistical model D=0.548 X1-0.05（X1 was the total root volume）,which could be used to further predict the root foraging P ability of different genotypes T.’Zhongshanshan’and their parents.（7）Morphological changes of roots of different genotypes of T.’Zhongshanshan’and their parents under insoluble inorganic P sourceCompared with CK,except that the total root length,total root area,net biomass and whole plant P accumulation of’Zhongshanshan’406 were significantly reduced,other reference materials had no significant difference under low P stress.Under the treatment of different insoluble P sources,the total root length,total root area and net biomass were Ca-P,Al-P and Fe-P from large to small,while the total root area and whole plant P accumulation were Ca-P,Fe-P and Al-P from large to small;Under the treatments of different insoluble P sources,the total root length,total root area,total root area,net biomass and whole plant P accumulation were Ca-P,Al-P and Fe-P;Under the treatments of different insoluble P sources,the total root length and total root area were Ca-P,Al-P and Fe-P,while the total root area,net biomass and whole plant P accumulation were Ca-P,Fe-P and Al-P;Under the treatments of different insoluble P sources,the total root length and total root area were Fe-P,Al-P and Ca-P,while the total root area,net biomass and whole plant P accumulation were Fe-P,Ca-P and Al-P;Under the treatments of different insoluble P sources,the total root length,total root area,total root area,net biomass and whole plant P accumulation of’Zhongshanshan’406 were Al-P,Fe-P and Ca-P from large to small. |
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