Responses of PSII photochemical parameter to a snowfall event in early growing season in Artemisia ordosica

ObjectiveThe aim is to examine the impact of a snow event in the early growing season on photosynthetically physiological status of a typical shrub, and to understand photosynthetically physiological mechanism to acclimate to the snow stress.

MethodWe monitored the variations in chlorophyll fluorescence and calculated energy partitioning parameters continuously in situ by a multi-channel monitoring fluorometry during a snow event which covered a period of prior- and post-snowing days, in relation to environmental factors.

ResultActual photosynthetic quantum yield (Φ_PSII) was lowest on snow day. The daytime mean value of Φ_PSII on snow day was 40% and 33% lower than that of prior and post snow. Regulatory energy dissipation (Φ_NPQ) and non-photochemical quenching (NPQ) were highest on snow day, with daytime mean value of Φ_NPQ being 95% and 48% higher than that of prior and post snow, respectively. The daytime mean value of NPQ on snow day was 94% and 76% higher than that of prior and post snow. Maximal quantum yield of PSII photochemistry (F_v/F_m) was 0.69 on snow day, smaller than that of prior snow, and smaller than stress line of 0.73. F_v/F_m recovered back within 3−4 days. There were opposite response trends at PAR threshold of 900 μmol/（m²·s）and at air temperature of 10 ℃, indicating different controlling environmental factors around the thresholds. Water availability was always one of the most common limitations during the stress recovery.

ConclusionThere was a stress for Artemisia ordosica during the snow event. The stress was mainly induced by the synergy of low temperature and high radiation. A. ordosica acclimated to the stress by mechanism of increasing ratio of regulatory thermal energy dissipation of energy partitioning in PSII reaction center. The 3−4 days were needed for A. ordosica to recover from the snow stress. The recovery period could be shortened by condition of low radiation, moderate high temperature and high moisture.