Effects of elevated ozone and water deficit on poplar saplings: Changes in carbon and nitrogen stocks and their allocation to different organs

Abstract

Ozone (O3) pollution and drought are frequent in summer, which adversely affects plant growth. In this study, we investigated the interactive effects of O3 and water deficit on growth parameters, and carbon (C) and nitrogen (N) stocks and their allocation to different organs in poplar saplings in the summer of 2017. The saplings were subjected singularly and in combination to two chronic O3 treatments (charcoal-filtered air [CF] and ambient air + 40 ppb of O3 [E-O3]) and two watering regimens (well-watered [WW] and reduced watering [RW]). The results showed that both O3 and drought inhibited poplar growth, whereas the effects of drought were greater than those of O3. Moreover, drought stress protected the saplings from O3 damage, suggesting that some previous studies on well-watered plants might have overestimated the damage caused by O3. Inconsistent with the general trend, RW significantly increased the light-saturated rate of CO2 assimilation (Asat) in this study, whereas it reduced the total leaf area. E-O3 significantly increased the N concentration and reduced the C/N ratio of each organ as well as the total C stock (CStotal), while it did not significantly affect the total N stock (NStotal). Drought significantly increased the C and N concentrations and reduced the C/N ratio in most organs, and significantly reduced the C stock of each organ, CStotal, and NStotal. CStotal was positively correlated with the total leaf area and the photosynthetic rate of the whole plants (Aplant). However, there was no significant relationship between CStotal and Asat, suggesting that Aplant can better reflect the growth of the whole plant than Asat. In addition, NStotal was positively correlated with the root biomass. Both O3 and drought had no significant effect on the ratio between the root and shoot N stocks, and there were also no interactive effects of O3 and drought on most C and N parameters. These findings will facilitate better understandings of C and N metabolisms future environment with higher O3 and more frequent droughts.