**2.3 Chlorophyll a fast fluorescence and JIP test**

Chlorophyll fast fluorescence transient was measured by a Plant Efficiency Analyzer (Hansatech, UK), according to methods of Strasser et al. (1995) and Sun et al. (2009a). All the leaves were immediately exposed to a saturating light pulse (3000 mmol·m-2·s-1 PFD) for 1 s after dark adapted for 20min. Each transient obtained from the dark-adapted samples was analyzed according to the JIP-test (Srivastava et al., 1997; Li et al., 2005; Sun et al., 2009a).
