Gas exchange characteristics and their influencing factors for halophytic plant communities on west coast of Bohai Sea

Water–salt stress and nutrient limitation may affect leaf economic spectrum of halophytes and confuse our understanding on plant physiological principles in a changing world. In this study, three halophytic plant communities of Phragmites australis, Suaeda salsa, and Tamarix chinensis, were selected in two sites (sites 1 and 2) on the west coast of Bohai Sea. The net photosynthetic rate (P(n)), transpiration rate (T(r)), stomatal conductance (G(s)), leaf vapor pressure deficit (VPD(leaf)) and their influencing factors were studied to test the possible carbon assimilation strategies of the halophytes. P. australis had higher P(n), T(r), and G(s) than S. salsa and T. chinensis in both sites. Similar trends were found for leaf P and photosynthetic N and P efficiency (PNUE and PPUE, respectively) in one or both sites. By contrast, the leaf dry mass per area (LMA) increased in the order of P. australis < S. salsa < T. chinensis in both sites. For identical species in different sites, P(n), leaf P, and PNUE were lower but T(r), VPD(leaf), leaf N, leaf N:P, and PPUE were higher in site 1 than in site 2 for one or more halophytes. Although soil physicochemical properties in different sites explained several variations among the halophytes, two-way ANOVA indicated that the species can explain most of the leaf traits compared with the site. LMA also had significant nonlinear relationships with P(n), T(r), G(s), and VPD(leaf). PNUE and PPUE showed positive correlation with P(n) in both sites, but they decreased in the power-law function with increasing LMA. Overall, the redundancy analysis showed that the gas exchange capacity of the halophytic plant communities was significantly affected by PPUE (60.0% of explanation), PNUE (57.1%), LMA (35.0%), leaf P (22.0%), and soil N (15.8%).