Changes in gas exchange characteristics and water use efficiency of mangroves in response to salinity and vapour pressure deficit

Abstract

Measurements were made of the photosynthetic gas exchange properties and water use efficiency of 19 species of mangrove in 9 estuaries with different salinity and climatic regimes in north eastern Australia and Papua New Guinea. Stomatal conductance and CO assimilation rates differed significantly between species at the same locality, with the salt-secreting species, Avicennia marina, consistently having the highest CO assimilation rates and stomatal conductances. Proportional changes in stomatal conductance and CO assimilation rate resulted in constant and similar intercellular CO concentrations for leaves exposed to photon flux densities above 800 μmol·m·s in all species at a particular locality. In consequence, all species at the same locality had similar water use efficiencies. There were, however, significant differences in gas exchange properties between different localities. Stomatal conductance and CO assimilation rate both decreased with increasing salinity and with increasing leaf to air vapour pressure deficit (VPD). Furthermore, the slope of the relationship between assimilation rate and stomatal conductance increased, while intercellular CO concentration decreased, with increasing salinity and with decreasing ambient relative humidity. It is concluded from these results that the water use efficiency of mangroves increases with increasing environmental stress, in this case aridity, thereby maximising photosynthetic carbon fixation while minimising water loss.

Estimating leaf area index and photosynthetic production in canopies of the mangrove Rhizophora apiculata

“…The approach taken in this study was to integrate measu.rements of the instantaneous rates of net photosynthesis of leaves at different levels in the canopy from top to bottom throughout the day. The highest instantaneous rate of net photosynthesis of about 25 pm01 CO2 m-2 leaf S-', and the overall average rate of photosynthesis of 9 pm01 CO, m-2 leaf S-' for the whole canopy, are similar to those reported by Gong et al (1992) for Rhizophora apiculata in the Matang mangrove forest, and by Clough & Sim (1989) and Cheeseman et al (1991) for mangrove forests in areas of moderate salinity, moderate to high rainfall and persistent cloud cover in Papua New Guinea and northeastern Australia. Under less favourable conditions, usually associated with edaphlc or climatic aridity due to high salinity, low soil-water content or exposure to persistently high solar radiation, rates of net canopy photosynthesis may be substantially lower; in such cases, the average rate of net canopy photosynthesis may be only 4 to 5 pm01 CO2 m-2 leaf S-' (Moore et al 1972, 1973, Clough & Sim 1989, Smith et al 1989, Lin & Sternberg 1992.…”

“…Measurements of net photosynthesis were made with a Li-Cor LI-6200 portable photosynthesis system, fitted with a custommade leaf chamber (Clough & Sim 1989). Repeated measurements were made on tagged leaves at varlous levels from the top to the bottom of the canopy throughout the day, over a period of several days.…”

Annual cyclicity in high‐resolution stable carbon and oxygen isotope ratios in the wood of the mangrove tree Rhizophora mucronata

“…Maximum and minimum c i values were set to 200 and 100 p.p.m., respectively, which is the range reported in literature for several mangrove species over a wide range of salinities (e.g. Ball & Farquhar 1984;Andrews & Muller 1985), however, lower and higher values have also been reported (Clough & Sim 1989;Mwangi Theuri, Kinyamario & Van Speybroeck 1999). Since a linear relationship between precipitation, salinity and c i can be debated, a second set of monthly c i values was constructed by including a time-lag between increase in salinity and reduction of rainfall, as well as by including a buffering for short-term rainfall events, such as those occurring during the short rainy season (OctoberNovember, see Materials and Methods).…”

Gas Exchange Analysis for Estimating Net CO2Fixation Capacity of Mangrove (Rhizophora stylosa) Forest in the Mouth of River Fukido, Ishigaki Island, Japan

“…Our results may be caused by some environmental stress. It was noted that photosynthetic rates of mangroves decreased under less favorable conditions, usually associated with high salinity (Sobrado, 1999), low soilwater content (Smith et al, 1989;Lin and Sternberg, 1992), or exposure to continuous high solar radiation (Clough and Sim, 1989).…”