Effect of precipitation change on the photosynthetic performance of Phragmites australis under elevated temperature conditions

Background: As a fundamental metabolism, leaf photosynthesis not only provides necessary energy for plant survival and growth but also plays an important role in global carbon fixation. However, photosynthesis is highly susceptible to environmental stresses and can be significantly influenced by future climate change. Methods: In this study, we examined the photosynthetic responses of Phragmites australis (P. australis) to three precipitation treatments (control, decreased 30%, and increased 30%) under two thermal regimes (ambient temperature and +4 degrees C) in environment-controlled chambers. Results: Our results showed that the net CO2 assimilation rate (P-n), maximal rate of Rubisco (V-cmax), maximal rate of ribulose-bisphosphate (RuBP) regeneration (J(ma)(x)) and chlorophyll (Chl) content were enhanced under increased precipitation condition, but were declined drastically under the condition of water deficit. The increased precipitation had no significant effect on malondialdehyde (MDA) content (p > 0.05), but water deficit drastically enhanced the MDA content by 10.1%. Meanwhile, a high temperature inhibited the positive effects of increased precipitation, aggravated the adverse effects of drought. The combination of high temperature and water deficit had more detrimental effect on P. australis than a single factor. Moreover, non-stomatal limitation caused by precipitation change played a major role in determining carbon assimilation rate. Under ambient temperature, Chl content had close relationship with P-n (R-2 = 0.86, p < 0.01). Under high temperature, P-n was ralated to MDA content (R-2 = 0.81, p < 0.01). High temperature disrupted the balance between V-cmax and J(max) (the ratio of J(max) to V-cmax decreased from 1.88 to 1.12) which resulted in a negative effect on the photosynthesis of P. australis. Furthermore, by the analysis of Chl fluorescence, we found that the xanthophyll cycle-mediated thermal dissipation played a major role in PSII photoprotection, resulting in no significant change on actual PSII quantum yield (Phi(PSII)) under both changing precipitation and high temperature conditions. Conclusions: Our results highlight the significant role of precipitation change in regulating the photosynthetic performance of P. australis under elevated temperature conditions, which may exacerbate the drought-induced primary productivity reduction of P. australis under future climate scenarios.