Differential Responses And Adaptive Strategies Of Dioecious Populus Cathayana To Different Phosphorus,water Resources And Their Interactions

After long-term evolution of dioecious plants,the reproductive costs between genders are significantly different,which leads to sexual dimorphism in response to resources.Phosphorus（P）and water play key roles in plants growth.However,it is not clear how soil P availability,distribution,water content and their combinations affect the growth dynamics of dioecious plants.Populus cathayana is a typical dioecious plant.In this paper,the effects of P and water and their interaction on dioecious P.cathayana were studied systematically,and two greenhouse control experiments were designed.In the first experiment,three soil P supply levels(0,50,200 mg kg^-1)and two types of soil P supply distribution（homogeneous and heterogeneous distribution）were set up,in order to explore the effects of soil P supply level and distribution on the growth dynamics and P acquisition strategies of dioecious P.cathayana;in the second experiment,two water treatments（WW:maximum field capacity 75%;WD:maximum field capacity 15%）and two soil P supply levels(0,200 mg kg^-1)were set to reveal the sex-specific differences of P.cathayana in response to drought,P deficiency and their interaction.The main results are as follows:（1）Different responses of dioecious P.cathayana to soil P availability and distributionFemales had a greater total root length,specific root length（SRL）,biomass accumulation and foliar P concentration under high P supply.Under P deficiency,males had a smaller root system than females but a greater exudation of soil acid phosphatase,and a higher colonization rate and arbuscular mycorrhizal hyphal biomass,suggesting a better capacity to mine P and a stronger association with arbuscular mycorrhizal fungi to forage P.Heterogeneous P distribution enhanced growth and root length density in females.Female root proliferation in P-rich patches was associated with increased foliar P assimilation.Increased P availability by localized P application did not enhance the biomass accumulation and the morphological plasticity of roots in males,but increased hyphal biomass.（2）Different responses of dioecious P.cathayana exposed to drought and low phosphorus stressDrought and P deficiency caused a greater negative impact on female growth than on male growth.P application ameliorated more negative effect of drought on the shoot dry matter accumulation and P concentration in male leaves,while less effects were observed in females.The concentration of citrate in the rhizosphere of males was higher under drought combined with P application than under adequate water availability,and the increase was greater in males than in females.Males also showed a higher abundance of main soil microbial groups,including bacteria,actinomycetes,arbuscular mycorrhizal fungi（AMF）,and Gram+and Gram-bacteria in the rhizosphere,resulting in a more resistant microhabitat.In contrast,the abundance of bacteria and AMF was less in the rhizosphere of females exposed to stress conditions,while saprophytic fungi increased significantly.P enhanced more drought resistance in stress-resistant males but less in females under relatively severe drought stress.Increased drought resistance by P in males might be associated with greater plasticity in rhizosphere processes when compared with females.