Siological processes, among which is xanthophyll cycle activity controlling the diurnal changes of PRI, as well as the other may be the pigment pool size dominating the seasonal variations of PRI. PRI0 and sunlit PRI in our final results shared really related temporal variation patterns across time scales. The seasonal variation patterns of PRI0 and sunlit PRI were constant across years (Figure six), which implied that the size in the pigment pool was affected by seasonal variations of environmental components [38], in specific for PAR. This really is constant having a prior study displaying that PRI was radiation-dominated with additional effects from high VPD [42]. The common seasonal variations of subtropical mangrove forests have larger and decrease PAR in summer time andRemote Sens. 2021, 13,12 ofwinter, respectively [42], major to comparable seasonal variations of two elements of PRI. On the annual scale, the PRI0 and sunlit PRI showed a important decline because of drought anxiety but seasonal PRI didn’t show any response. The seasonal PRI reflected the day-to-day maximum depression the canopy suffered from, or the maximum in the xanthophyll cycle. In comparison together with the facultative element, the Nelfinavir Biological Activity response with the constitutive element of PRI was additional sensitive to environmental stresses such as drought tension. For that reason, we confirmed that in subtropical mangrove forests, the pigment pool size may be the key bring about in the long-term variations of PRI with extra contribution in the xanthophyll cycle, which agrees with lots of earlier research [36,54]. The high correlation coefficients in between PRI and carbon fluxes at the diurnal scale verified the capacity of PRI to track the carbon dynamics at brief time scales. The slightly greater correlation coefficient among PRI and carbon fluxes in 2020 additional implied that drought tension could also exert an influence around the each day short-term xanthophyll cycle, but the influence was not as considerable because the long-term variations of pigment pool size. Furthermore, it really is shown that the temporal variation patterns of PRI and carbon fluxes have been really similar at both seasonal and annual time scales (Figure three). Zhu et al. [42] reported that PRI was an IACS-010759 supplier excellent indicator of photosynthetic capacity at quick time scales, displaying excellent correlations amongst carbon fluxes and PRI. Our benefits additional confirmed that at a longer time scale, PRI was also in a position to track the response of carbon fluxes to environmental stresses including drought tension. Around the seasonal scale, the relationship in between PRI and carbon fluxes was superior when mangroves experienced drought strain, which was consistent with earlier findings that the PRI-carbon connection was greater below enhanced VPD or water anxiety [30,37,56]. Thus, we conclude that the connection between PRI and carbon fluxes performs improved under drought stress in mangrove forests. The RF analyses indicated that PRI was mainly correlated with lagged GPP and advanced VPD. All round, the decreasing PRI values following larger VPD and reduced rainfall did serve as an early indicator of the declines of carbon uptake. PRI variations were mostly brought on by pigment pool size plus the response to changing environmental things were fairly more quickly than the response of carbon dynamics. The partnership involving PRI0 and carbon fluxes pretty much mimicked the PRI-carbon connection, indicating that constitutive pigment pool size played a vital part in driving the seasonal variations of carbon fluxes, specially un.
