Light compensation points of biocrusts under two water conditions (SW and E-NRW) and different temperature gradients.
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For R/Pg (Fig. 3a), it exponentially declined with light intensity, but as temperature increased, the differences among biocrusts gradually decreased and became more similar, especially when light intensity was higher than 25 μmol m-2 s-1. At 3 μmol m-2 s-1, R/Pg of AC1 was lowest, followed by AC2, then LCs and MC. At 5 μmol m-2 s-1 of light intensiy, R/Pg of two ACs were still lowest, that of MC was highest; but under -2.5~5 °C, the order of two lichen crusts was LC1 < LC2, under 7.5~10 °C, LC2 < LC1. Under 10 μmol m-2 s-1 light, R/Pg of LC2 was highest from -2.5~7.5 °C, LC1 was second-highest from 2.5~7.5 °C, MC was second-highest at -2.5 °C. At 10 °C, the sequence was LC1 > LC2 > MC.
The ratios of dark respiration to gross photosynthesis (R/Pg) for biocrusts at different range of Led Tube intensity (3~400 μmol m-2 s-1) and temperature gradients (-2.5~10 °C) under SW and E-NRW.
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R, Pn, LCPs, Pg and R/Pg under E-NRW
R of all biocrusts under E-NRW also increased with temperature (Fig. 4), the sequence from high to low was MC > LC2 > LC1 > AC2 > AC1. For Pn and LCPs, both increased with temperature, but Pn (except LC1 was never detected) had no significant differences (P > 0.05) between temperature gradient of 2.5 °C. At the same temperature, LCP in AC1 was lowest, in turn followed by AC2, LC2 and MC (Fig. 2b). Under light intensity lower than LCPs, the time window of positive Pn and the increasing amplitude with decreasing temperature manifested in the order: AC1 > AC2 > LC2 (LC2 slightly above MC). But the order reversed under higher light intensity, the increasing amplitude with rising temperature was in the order of AC1 > AC2 > LC2 ≈ MC. The pattern of Pg was similar to that of SW except for LC1 (Fig. 4), Pg also increased with light intensity and temperature, and the increasing amplitude was also highest in ACs, and then in turn was LCs and MC (Fig. 4a). The magnitude under the same temperature and light intensity from highest to the lowest was MC, LC2, AC2, and AC1. When light intensities were higher than 25 μmol m-2 s-1, the warming of 2.5 °C in ACs also resulted in quite different Pg.