Ozone exposure, nitrogen addition and moderate drought dynamically interact to affect isoprene emission in poplar

摘要

Ozone (O_3) pollution can induce changes in plant growth and metabolism, and in turn, affects isoprene emission (ISO), but the extent of these effects may be modified by co-occurring soil water and nitrogen (N) availability. To date, however, much less is known about the combined effects of two of these factors on isoprene emission from plants. We investigated for the first time the combined effects of O_3 exposure (CF, charcoal-filtered air; EO_3, non-filtered air plus 40 ppb of O_3), N addition (NO, no additional N; N50, 50 kg ha~(-1) year~(-1) of N) and moderate drought (WW, well-watered; WR, 40% of WW irrigation) on photosynthetic carbon assimilation and ISO emission in hybrid poplar at both leaf- and plant-level over time. Consistent with leaf-level photosynthesis (Pn_(leaf)) and ISO (ISO_(leaf)) responses, plant-level ISO (ISO_(plant)) responses to O_3, N addition and moderate drought were more marked after long exposure (September) than short exposure duration (July). EO_3 significantly decreased ISO_(leaf) and Pn_(leaf), while WR and N50 significantly increased them. Although O_3 and water interacted significantly to affect Pn_(leaf) over the exposure duration, neither N50 nor WR mitigated the negative effects of EO_3 on ISO_(leaf). When ISO was scaled up to the plant level, the WR-induced increase in ISO_(leaf) under EO_3 was offset by a reduction in total leaf area. By contrast, effects of EO_3 on ISO_(leaf) were not changed by N addition. Our results highlight that the dynamic effects on ISO emission change over the exposure duration depending on involved co-occurring factors and evaluation scales.