Effects of nitrogen and phosphorus imbalance on photosynthetic traits of poplar Oxford clone under ozone pollution
2018
Zhang, Lu | Hoshika, Yasutomo | Carrari, Elisa | Cotrozzi, Lorenzo | Pellegrini, Elisa | Paoletti, Elena
Ozone (O₃) pollution and the availability of nitrogen (N) and phosphorus (P) in the soil both affect plant photosynthesis and chlorophyll (Chl) content, but the interaction of O₃ and nutrition is unclear. We postulated that the nutritional condition changes plant photosynthetic responses to O₃. An O₃-sensitive poplar clone (Oxford) was subject to two N levels (N0, 0 kg N ha⁻ ¹; N80, 80 kg N ha⁻ ¹), two P levels (P0, 0 kg P ha⁻ ¹; P80, 80 kg P ha⁻ ¹) and three levels of O₃ exposure (ambient concentration, AA; 1.5 × AA; 2.0 × AA) over a growing season in an O₃ free air controlled exposure (FACE) facility. The daily change of leaf gas exchange and dark respiration (Rd) were investigated at mid-summer (August). Chl a fluorescence was measured three times in July, August and September. At the end of the growing season, Chl content was measured. It was found that Chl content, the maximum quantum yield (Fᵥ/Fₘ), Chl a fluorescence performance index (PI) and gas exchange were negatively affected by elevated O₃. Phosphorus may mitigate the O₃-induced reduction of the ratio of photosynthesis to stomatal conductance, while it exacerbated the O₃-induced loss of Fᵥ/Fₘ. Nitrogen alleviated negative effects of O₃ on Fᵥ/Fₘ and PI in July. Ozone-induced loss of net photosynthetic rate was mitigated by N in medium O₃ exposure (1.5 × AA). However, such a mitigation effect was not observed in the higher O₃ level (2.0 × AA). Nitrogen addition exacerbated O₃-induced increase of Rd suggesting an increased respiratory carbon loss in the presence of O₃ and N. This may result in a further reduction of the net carbon gain for poplars exposed to O₃.
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