臭氧升高栾树和白皮松光合生理响应机制

Mechanisms of photosynthetic physiological responses of Koelreuteria paniculata and Pinus bungeana under elevated ozone conditions

工业化和快速城市化进程导致城市树木暴露于高浓度地表臭氧(O_(3))和氮(N)沉降的环境。以两种北京常见的城市园林绿化树种栾树(Koelreuteria paniculata)和白皮松(Pinus bungeana)为研究对象,采用臭氧开顶式气室(OTC)和15N同位素示踪法,研究了2022年5月—9月3种臭氧浓度NF(自然环境臭氧浓度)、NF40(NF+40 nmol/mol O_(3))和NF60(NF+60 nmol/mol O_(3))环境下两种树苗的生理生长特性,特别是生长季末期植物叶片氮吸收的响应机制。研究结果表明:(1)高浓度O_(3)显著抑制栾树和白皮松叶片饱和光合速率、气孔导度、叶绿素含量、类胡萝卜素含量和生物量累积,但增加了叶片N含量。(2)生长季末期栾树与白皮松叶片N元素的吸收策略不同,栾树的新叶比老叶吸收更多的N,同时N可能从老叶转移到新叶;白皮松则将N更多地储存在老叶中以维持叶片常绿,而不是将N转移到新叶中。(3)在生长季结束前一周,不论施N与否O_(3)浓度升高均会显著增加叶片的衰老比率,O_(3)浓度越高栾树叶片衰老比率越高,而施N处理可降低由于O_(3)升高导致叶片衰老的比率,越接近生长季结束O_(3)增加栾树叶片衰老和施N缓解叶片衰老的变化规律越显著。由此可见,在研究城市树种应对O_(3)浓度升高和N沉降的环境变化时,不仅要考虑不同功能型如落叶和常绿树种的差异,同时也应关注落叶植物的不同生长时期,特别是生长季末期的变化。

Industrialization and rapid urbanization have led to the exposure of urban tree species during their growing seasons under high concentrations of surface ozone(O_(3))and nitrogen(N)deposition conditions.To understand the combined effects of elevated O_(3)and N deposition on urban trees,two common urban tree species in Beijing,Koelreuteria paniculata and Pinus bungeana,were selected as experimental materials from May to September 2022.We utilized open-top chambers(OTCs)and the 15N isotope tracing method to investigate the variations in the photosynthetic physiology and leaf N distribution of the two tree species under three different O_(3)exposure concentrations:NF(ambient O_(3)concentration),NF40(NF+40 nmol/mol O_(3)),and NF60(NF+60 nmol/mol O_(3)).The results showed that:(1)At the end of the growing season,both K.paniculata and P.bungeana exhibited significant inhibition of leaf light-saturated photosynthetic rate(Asat),stomatal conductance(gs),chlorophyll content(Chl a+b),carotenoid content(Car),and biomass by elevated O_(3)concentrations.However,there was an increase in leaf N content andδ15N abundance.(2)K.paniculata and P.bungeana adopted different strategies for N absorption at the end of the growing season.K.paniculata absorbed more N in new leaves compared to old leaves,and nitrogen might be transferred from old leaves to new leaves before old leaves fall down to the ground.In contrast,P.bungeana stored relatively more N in old leaves to maintain evergreen foliage rather than transfer it to the new leaves.(3)During one week before the growing season finished,the elevated O_(3)accelerated leaves senescence of K.paniculata whether N addition or not,and with the O_(3)concentration increased the senescence rate increased.However,N addition could alleviate the negative effect of elevated O_(3).This pattern was shown much more clearly when the growing season nearly finished.When simulating the response of urban tree species to the increased O_(3)concentrations and N deposition,it is essential to consider differences in functional types,such as deciduous and evergreen species,as well as the growth period of plants,especially during the late growing season.