| Phosphorus(P)is an essential element for the growth of trees.However,the available P is extremely deficient and highly heterogeneous in the acid soil,due to the strong chemical fixation of P in the south of China.While it could be easily lead to forest growth was inhibited.In the long course of evolution,some plants could use a variety of adaptation strategies to increase the chance of completing the life cycle under low P stress.Chinese fir(Cunninghamia lanceolata)is one of elite timber species in South China,but the deficiency of available P in soil has become an important factor which leads to the decline of the yield of Chinese fir.Previous researches showed that it is effective for maintaining the production of Chinere fir plantation to screen out the elite genotype with high P efficiency,and verified that there was significant difference of root plasticity among different genotypes.This showed that the heterogenous P stress induced significantly the phased morpholofical strategy of Chinese fir to forage P.Endogenous hormone is the regulator of plant metabolism and closely related with the morphological adaptability of plant and response to stress.Therefore,it is one of effective ways to reveal the inherent mechanism of Chinese fir to adapt to the low P environment,through the study of the endogenous hormones of the root of Chinese fir in different P patches;moreover,the staged response of endogenous hormone content in roots may be closely related to the growth characteristics of Chinese fir in the initiation of response strategies of low P stressTo reveal the above relationship,objected with two half-sib families seedlings of Chinese fir(No.25,No.32)with significantly different P use efficiency,we designed three different P treatment(P0-0,supply with no P in compartment ? and ?;P0-1,supply with no P in compartment ?and with normal P in compartment ?;P1-1,supply with normal P in compartment ? and ?)in the indoor sand culture,and determined the content of four kinds endogeneous hormones(cytokinin,gibberellin,auxin and abscisic acid)in the needles,stem,and roots in different compartments each 20 days during the experimental course.To further reveal the intrinsic regulation mechanism on the response strategies of Chinese fir families with high P use efficiency in heterogeneous P supply environment,the correlation of endogenous hormones,growth and biomass allocation in the seedlings of different Chinese fir families was analyzed under the condition of heterogeneous P supply,according to the changed characteristics of the tested seedling height and ground diameter increment,root:shoot ratio,and the root length,root surface area,root average diameter and root volume increment and biomass,separately,in the two compartments.Main results were as follows:(1)There was difference in the changes of the contents of four kinds endogenous hormones in Chinese fir(No.25)with high P use efficiency under different P heterogeneous supply treatments.Compared with the normal P supply treatment(P1-1),the content of GA and auxin in needles and stems increased in the treatments of P0-1 and P0-0,while the content of ABA in the needles decreased in the later experimental stage.For the two root compartments in the heterogeneous P supply treatment(P0-1),the content of auxin and ABA of root increased with the stress time extended in compartment I,compared with the treatments of P1-1 and P0-0,while the content of gibberellin increased only in the early stage of stress.In contrast,the content of gibberellin and auxin of root in the compartment II always were less than that in P1-1 treatment.(2)There was significantly difference in the changes of the contents of four kinds endogenous hormones in Chinese fir(No.32)with low P use efficiency under different P heterogeneous supply treatments.Compared with the normal P supply treatment(P1-1)and without P supply treatment(Po-o),the content of cytokinin and auxin in needles increased in the P0-1 treatment during the middle experimental stage,while the GA content decreased and the ABA increased with the experimental stage extending.Compared with the P0-0 treatment,the content of cytokinin,GA,and auxin in needles decreased markedly,but ABA increased in the latest test stage.Moreover,the ABA content in both of two root compartments was separately higher than the P1-1 treatment,whereas the cytokinin and GA contents in root compartment ? were higher than the P1-1 treatment during the middle and latest test stages.(3)There was a certain correlation between the content of endogenous hormones and growth characteristics of Chinese fir(No.25)with high P use efficiency.In the different heterogeneous P supply treatments,there were significantly negative correlations between cytokinin content in the two root compartments,separately,with root biomass in compartment ? and ?,the total root biomass,the increments of root length,root surface area and root volume.The root growth deceased with the ABA content increasing,but the biomass accumulation of needles,stems and roots increased significantly.There were significant negative correlations between GA content in the seedling shoot,separately,with the increments of root length,root surface area and root volume in root compartment ?,? or the total.The GA content decreased with the ABA content increasing.(4)The changes of endogenous hormone content and growth characteristics of Chinese fir(No.32)with low P use efficiency also showed some correlation.Under the heterogeneous P supply treatment,the auxin in roots could enhance the growth of root length,root surface area,root volume and biomass accumulation in needles and stems,but not for the ABA,resulting in the decrease of root shoot ratio.There were significantly negative correlations between GA content in the shoot with seedling ground diameter,root length,root surface area,root volume,the biomass of different organs,and root:shoot ratio separately,while there no significant correlation between the increase of ABA content and seedling growth. |
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