Effects Of Nutrient Utilization Strategies On Leaf Carbon Metabolic Temperature Response In Broad-leaved Plants At Different Altitudes In Wuyi Mountains

As the main body of terrestrial ecosystems,forest ecosystems have a profound impact on the global carbon cycle,and an in-depth understanding of the temperature response process of plant photosynthesis and respiration is crucial to predicting the carbon dynamics of forest ecosystems in the context of global change.The effectiveness of nutrients in plant leaves and the response of their utilization strategies to environmental change will have a significant impact on long-term carbon sequestration in forest ecosystems.Therefore,in order to explore the differences between leaf carbon metabolism and nutrient utilization strategies of hardwood woody plants in subtropical montane forests and their associated responses to the environment,three hardwoods at altitudes（1400,1600 and 1800 m）of Jiangxi Section of Wuyishan National Park were selected as test subjects,and the photosynthesis,respiration rate,leaf functional traits,nutrient use efficiency and resorption efficiency of broad-leaved woody plants at different altitudes were measured to improve the understanding of the response characteristics of carbon metabolism temperature,nutrient utilization strategies and their effects on carbon metabolism at different altitudes.The main findings of this study are as follows:（1）Leaf nutrient resorption efficiency of broad-leaved plants at different altitudesThe nitrogen resorption efficiency（NRE）was significantly lower than the phosphorus resorption efficiency（PRE）（34.85%,48.28%）,indicating that the resorption of phosphorus by leaves was higher than nitrogen（phosphorus restriction conditions）.and there were no significant changes in NRE and PRE with the increase of the altitude,There was a significant allometric growth relationship between NRE and PRE and nitrogen and phosphorus in senescent leaves at an altitude of 1800 m,while the relationship between NRE and PRE and senescent leaves nitrogen and phosphorus at an altitude of 1400 and 1600 m was weak.This showed that the relationship between nutrient resorption efficiency and nutrient content at different altitudes was different.（2）Characteristics of carbon metabolism temperature response of leaves of broad-leaved plants at different altitudes and seasonsThe mean photosynthetic optimum temperature(T_Opt)and optimal photosynthetic rate(A_Opt)of leaves in summer（27.52℃,6.24μmol m?2s?1）were significantly higher than those in winter（20.75℃,5.05μmol m?2s?1）,and the respiration rate at 25°C(R₂₅)（0.54μmol m?2s?1）was significantly lower than that of winter R₂₅（1.03μmol m?2s?1）（P<0.05）,the photosynthetic rate at 25°C(A₂₅),Photosynthetic heat adapts to width(T₉₀),temperature-sensitivity coefficient(Q₁₀),maximum carboxylation rate(V_cmax),electron transport rate(J_max)and its ratio(V_cmax/J_max)were not significantly different from winter.There were no significant differences in T_Opt,A_Opt,T₉₀,Q₁₀,V_cmax,J_maxand V_cmax/J_maxof same tree species at different altitudes,it shows that plants at different altitudes have similar temperature response characteristics relative to the season.（3）Leaf photosynthetic nutrient use efficiency of broad-leaved plants at different altitudes and seasonsSummer leaf nitrogen（N）,phosphorus（P）,photosynthetic nitrogen-use efficiency（PNUE）,photosynthetic phosphorus-use efficiency（PPUE）(18.10 mg·g^-1,0.91 mg·g^-1,4.60 umol g^-1s^-1,119.24 umol g^-1s^-1)were significantly higher than in winter(14.44 mg g^-1,0.76 mg g^-1,2.83 umol g^-1s^-1,54.78 umol g^-1s^-1),the specific leaf weight（LMA）(87.64 g m^-2)was significantly lower than that in winter(142.23 g m^-2)（P<0.05）.As the altitude increases,the leaf nitrogen and phosphorus increased,LMA and PPUE decreased,PNUE increased.PPUE was significantly negatively correlated with senescent leaf phosphorus,while PNUE had no trade-off relationship with senescent leaf nitrogen.（4）Relationship between leaf carbon metabolism and nutrient utilization strategies of broad-leaved plants at different altitudesSummer leaf 25℃based on biomass photosynthetic rate(A_25mass)(85.65 nmol g^-1s^-1)were significantly higher than in winter(40.44 nmol g^-1s^-1),the biomass-based dark respiration rate(R_25mass)(7.90 nmol g^-1s^-1)was not significantly different from winter(8.06 nmol g^-1s^-1).A_25massand R_25masswere significantly correlated with PNUE and PPUE,R_25masswas significantly negatively correlated with PRE,while A_25masswas not significantly correlated with NRE and PRE,indicating that photosynthetic nutrient utilization efficiency had a high impact on carbon metabolism,and PPUE and PRE had a greater impact on leaf carbon metabolism.The 1400 m and 1600 m of plant leaves adopt the resource conservation strategy,the 1800 m of plant leaves adopt the resource acquisition strategy.In summary,woody plants at different altitudes in Wuyi Mountain have similar carbon metabolism temperature response characteristics relative to the season.In phosphorus-restricted habitats,the leaf photosynthetic phosphorus-use efficiency and resorption efficiency were significantly higher than those of nitrogen,and phosphorus had a greater impact on leaf carbon metabolism.In the future,it is necessary to further study the effects of nutrient allocation and environmental factors on nutrient utilization and carbon metabolism by combining physiological factors such as plant type and cell structure with hydrothermal and other environmental factors.