AUTHOR=Jin Chuan , Zha Tianshan , Bourque Charles P.-A. , Jia Xin , Tian Yun , Liu Peng , Li Xinhao , Liu Xinyue , Guo Xiaonan , Xu Mingze , Kang Xiaoyu , Guo Zifan , Wang Ning 

TITLE=Temporal heterogeneity in photosystem II photochemistry in Artemisia ordosica under a fluctuating desert environment

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.1057943

DOI=10.3389/fpls.2022.1057943

ISSN=1664-462X

ABSTRACT=<p>Acclimation strategies in xerophytic plants to stressed environmental conditions vary with temporal scales. Our understanding of environmentally-induced variation in photosystem II (PSII) processes as a function of temporal scales is limited, as most studies have thus far been based on short-term, laboratory-controlled experiments. In a study of PSII processes, we acquired near-continuous, field-based measurements of PSII-energy partitioning in a dominant desert-shrub species, namely <italic>Artemisia ordosica</italic>, over a six-year period from 2012–2017. Continuous-wavelet transformation (CWT) and wavelet coherence analyses (WTC) were employed to examine the role of environmental variables in controlling the variation in the three main PSII-energy allocation pathways, i.e., photochemical efficiency and regulated and non-regulated thermal dissipation, i.e., <italic>Φ</italic><sub>PSII</sub>, <italic>Φ</italic><sub>NPQ</sub>, and <italic>Φ</italic><sub>NO</sub>, respectively, across a time-frequency domain from hours to years. Convergent cross mapping (CCM) was subsequently used to isolate cause-and-effect interactions in PSII-energy partitioning response. The CWT method revealed that the three PSII-energy allocation pathways all had distinct daily periodicities, oscillating abruptly at intermediate timescales from days to weeks. On a diurnal scale, WTC revealed that all three pathways were influenced by photosynthetically active radiation (<italic>PAR</italic>), air temperature (<italic>T</italic><sub>a</sub>), and vapor pressure deficit (<italic>VPD</italic>). By comparing associated time lags for the three forms of energy partitioning at diurnal scales, revealed that the sensitivity of response was more acutely influenced by <italic>PAR</italic>, declining thereafter with the other environmental variables, such that the order of influence was greatest for <italic>T</italic><sub>a</sub>, followed by <italic>VPD</italic>, and then soil water content (<italic>SWC)</italic>. PSII-energy partitioning on a seasonal scale, in contrast, displayed greater variability among the different environmental variables, e.g., <italic>Φ</italic><sub>PSII</sub> and <italic>Φ</italic><sub>NO</sub> being more predisposed to changes in <italic>T</italic><sub>a</sub>, and <italic>Φ</italic><sub>NPQ</sub> to changes in <italic>VPD</italic>. CCM confirmed the causal relationship between pairings of PSII-energy allocation pathways, according to shrub phenology. <italic>A. ordosica</italic> is shown to have an innate ability to (i) repair damaged PSII-photochemical apparatus (maximum quantum yield of PSII photochemistry, with <italic>F</italic><sub>v</sub>/<italic>F</italic><sub>m</sub> &gt; 0.78), and (ii) acclimatize to excessive <italic>PAR</italic>, dry-air conditions, and prolonged drought. <italic>A. ordosica</italic> is relatively sensitive to extreme temperature and exhibits photoinhibition.</p>