Environmental Engineering Reference
In-Depth Information
decrease of Pn was caused by non-stomatal factors under 300mM NaCl salt stress. This
conclusion could also be confirmed by the changes of CE, which reflects the efficiency of
carbon assimilation. CE of both varieties decreased significantly under high salt stress, which
indicates that the carbon assimilation is negatively influenced by salt. The higher Pn and CE
in BB52 during salt treatments proved that the BB52 has higher salt tolerance than ZH13. In
addition, the marked decrease of chlorophyll content was observed in both varieties, which
certainly contributed to the decrease of Pn. Leaf chlorophyll content is considered to be a
good indicator of photosynthetic capacity. Lower chlorophyll content would limit
photosynthetic potential and lead to a decrease in biomass and production [24]. Meanwhile,
PSII is one of the most sensitive parts to various environmental stresses and PSII structure
and function can be damaged or even failure under these stresses [25, 26]. Fv/Fm and ΦPSII
reflect the entire performance of PSII Significant decreases in the two parameters showed that
PSII were negatively affected under higher salt stress. Similar conclusion could be obtained
from the decrease of qP and the increase of NPQ. The reason is that more energy is dissipated
as heat instead of participating in photochemical reaction. The above analysis showed that the
decrease of Pn under 300mM NaCl stress was ascribed to non-stomatal factors.
Figure 5.
Changes of Na
+
content(A), K
+
content(B), Cl
-
content (C) content and K
+
/Na
+
ratio (D) in
leaves and roots in different NaCl treatments.
Salt stress usually hinders water absorption, even leads to cell dehydration and osmotic
stress. This kind of stress is also mentioned as physiological drought. In order to resist this
stress, plants reduce stomatal conductance (also contributed to the decline of Gs) firstly to
limit the transpiration rate. Meanwhile, plants accumulate several kinds of solutes which are
commonly referred to as osmoprotectants for the osmotic adjustment [27-29]. Proline is the
most important osmoprotectant, because it protects plants by stabilizing membranes, proteins
