Ozone Pollution, Nitrogen Addition, and Drought Stress Interact to Affect Non-structural Carbohydrates in the Leaves and Fine Roots of Poplar

Abstract

Ground-level ozone (O3) pollution frequently co-occurs with drought and nitrogen (N) deposition during the growing season. It is important to understand how the carbon dynamics of plants respond to O3 pollution in drier and N-enriched environments. Here we present the patterns of non-structural carbohydrates and its components (soluble sugar and starch) in the leaves and fine roots in poplar clone 546 (Populus deltoides cv. '55/56'×P. deltoides cv. 'Imperial') for one growing season at two O3 concentrations (control, charcoal-filtered air, and elevated O3, non-filtered air+40 nmol·mol-1 of O3), two watering regimes (well-watered and reduced watering at 40% of well-watered irrigation), and two soil nitrogen addition treatments[no addition and the addition of 50 kg·(hm2·a)-1]. The results showed that O3 stress significantly increased the content of soluble sugar in leaves and starch in fine roots but decreased the content of starch and total non-structural carbohydrate (NSC) in leaves. Drought stress significantly reduced the content of starch and total NSC in leaves but increased the contents of soluble sugar and total NSC in fine roots. Nitrogen addition had no significant effect on NSC and its components in leaves and fine roots. NSC and its components in leaves and fine roots were positively correlated with photosynthetic rate and biomass. With an increase in the number of environmental stress factors, NSC in leaves showed a significant downward trend while NSC in fine roots showed a significant upward trend. The study demonstrates that environmental stress can promote the transformation of starch into soluble sugars in plant leaves and the transfer of NSC from leaves to roots for storage, which may be a coping strategy for plants exposed to environmental stress.