Salinity Effects on Photosynthesis and Growth in Alternanthera philoxeroides (Mart.) Griseb.

Abstract

Alternantheraphiloxeroides, alliator weed, was grown at five different NaCI concentrations to determine the effect of salinity on factors related to the net rate of CO2 uptake (Pa). Over the range of 0 to 400 millimolar NaCI, P. declined 51%. Stomatal conductance declined in parallel with P. and as a result there was no reduction in intercellular CO2 concentration and therefore no reduction in the amount of CO2 available for photosynthesis. The CO2 compensation point did not change with salt stress. Increases in leaf thickness tended to compensate slightly for the negative effects of salinity on leaf cell metabolism, at least in relation to P.. On a mesophyll cell area basis, soluble protein was relatively constant in leaves developed at 100 to 400 millimolar NaCI while total chlorophyll decreased at all salinities. Dry weight production and P. were closely correlated in alligator weed grown at different salinities. Plants produced less leaf area per unit dry weight as salinity increased, which may aid in water conservation.The PM3 of many plant species declines with increasing rhizosphere salinity (6,10,(13)(14)(15)(16)23). The decline in Pn has been attributed to salinity effects on both stomatal (6,10,14,16,23) and nonstomatal (6, 10, 15, 18, 23) controls of P,,. Although there seems to be almost general agreement that salinity effects on nonstomatal factors (i.e. metabolic parameters; 9) reduce PF, the importance to P, of observed reductions in stomatal conductance with salinity is not as clear. Declining stomatal conductance could reduce P,, by lowering the CO2 concentration in the leaf, as hypothesized for spinach ( 19). In contrast, reductions in stomatal conductance coupled to lowered potential PF, could act to maintain a relatively constant intercellular CO2 concentration (8,18,26), fitting the response of Avicennia marina developed at 50 to 500 mm NaCl and a vapor pressure deficit of 0.6 KPa (2). Further examination of stomatal effects on the amount of CO2 available for photosynthesis is necessary before generalizations can be made about the relationship of stomatal conductance to P, in salt-stressed plants.The fact that salinity changes leaf structure (12, 14-15, (11) which may be more stressful than constant salinity (5). In a previous study, water potential in alligator weed declined in response to increases in rhizosphere salinity of 50 mm NaCl/d up to a final concentration of400 mm (3). These changes in water potential were ofsufficient magnitude to maintain a water potential gradient from rhizosphere to roots and were the result of decreases in minimum tissue osmotic potential. Salinity also had a dramatic effect on cell structural properties of alligator weed as measured by the bulk elastic modulus (3).Having established that alligator weed tolerates increases in rhizosphere salinity by osmotic adjustment, we asked how this adjustment was related to carbon gain. Specifically, how does salinity affect P,, in alligator weed and what is the relationship of the P,, response to changes in ...

Effects of flooding and salinity on photosynthesis of Sagittaria lancifolia

“…Direct effects of excess salt on various plant biochernical and structural functions which can cause reductions in P, capacity have been documented by Chimikhs & Karlander (1973), Helal & Mengel (1981, and Longstreth et al (1984).…”

Population differentiation in Spartina patens: gas-exchange response to salinity

“…Similar responses to salinity have been previously documented for S. patens (Pezeshki et al 1987). Stomata1 closure in response to salinity has been reported for several species (Downton 1977, Kemp & Cunningham 1981, Longstreth et al 1984, Pearcy & Ustin 1984. The decrease in A found in response to salinity may be attributed both to stomata1 control (Downton 1977, Longstreth & Strain 1977 and to non-stomata1 (metabolic) factors ( 1979, Walker et al 1982, Longstreth et al 1984.…”

“…Pearcy & Ustin (1984) found reductions in A rates in Spartina and Scirpus species as a result of diffusional limitations and metabolic effects when soil salinity increased. Longstreth et al (1984) reported 51 O/O reduction in A for Alternanthera philoxerides plants after salt application. In the present study, recovery trends were noted for A after initial reductions, indicating some photosynthetic acclimation/adaptation to salinity conditions in both populations, but recovery appeared to be more pronounced in Ferblanc population (cf.…”

Salinity Effects on Photosynthesis in Isolated Mesophyll Cells of Cowpea Leaves

“…Several investigators concluded that chloroplasts rather than CO2 diffusion processes are the primary control of photosynthesis under different kinds of environmental stress (2,6,14). However, several recent reports have suggested that photosynthesis of plants exposed to salinity, as measured under saturating CO2 concentrations, was not greatly altered (4,5,22).…”