Interaction between Light Intensity and NaCl Salinity and Their Effects on Growth, CO₂ Assimilation, and Photosynthate Conversion in Young Broad Beans

Abstract

MATERIALS AND METHODS Seedlings of Viiafaba were grown for four weeks at two different light intensities (55 and 105 watts per square meter) in a saline (50 millimlar NaCI) and nonsaline nutrient solution. NaCi salinity depressed growth and restricted protein formation, CO2 assimilation, and especially the incorporation of photosynthates into the lipid fraction. Conversion of photosynthates in leaves was much more affected by salinity than was photosynthate turnover in roots. The detrimental effect of NaCi salinity on growth, protein formation, and CO2 assimilation was greater under low than under high light conditions. Plants of the high light intensity treatment were more capable of excluding Na+ and Cl and accumulating nutrient cation species (Ca2 , K+, Mg2e) than plants grown under low light intensity. It is suggested that the improved ionic status provided better conditions for protein synthesis, CO2 assimilation, and especially for the conversion of photosynthates into lipids.Saline conditions depress the growth rate of many plant species. Salinity also influences various biochemical processes such as the assimilation of N, protein synthesis, and CO2 assimilation (1, 4, 14, 15, During the first week of cultivation the solution was diluted to fifth and in the second week to half strength. In addition to these nutrients, NaCl also was added at two concentrations: I mM, control treatment; and 50 mm, salinization treatment. A concentration of 1 mm NaCl was chosen for the control treatment, because under field conditions some Na+ and Cl-always is present in the soil solution. Such a low NaCl level has no salinity effect. Plants in both of these treatments were exposed to two light intensities: 55 w/m2 and 105 w/m2. The experiment thus consisted of a 2 x 2 factorial design. Each treatment comprised four 5 x 1 pots with five plants per pot. NaCl was added gradually after the first week ofgrowth. On each day 10 mmol NaCl/l was introduced into the nutrient solution until the final level of 50 mm. The pH of the nutrient solutions ranged from 5.2 to 5.8. The nutrient solutions were continuously aerated and were completely renewed every fourth day. The plants were grown in growth chambers supplying the following environmental conditions: 14 h light, day temperature 24 C, night temperature 14 C, air humidity 70%.Twenty-seven days after germination one plant was harvested from each pot (four replications per treatment) and divided into leaves, stems, and roots. These were weighed, cut, and then subdivided. One subsample was oven-dried for the determination of the dry matter content. In this subsample the minerals were analyzed. In the other subsample the N fractions were analyzed according to a technique described by Helal et al. (4). As the effect of salinity on the N fractions did not differ much for leaves, stems, and roots, the N contents were recalculated on a total plant matter basis (Table II). The effect of salinity on the mineral content was especially evident in the leaves and for this reason only ...

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).…”

Influence of salinity stress on growth parameters, photosynthetic activity and cytological studies of Zea mays, L. plant using hydrogel polymer

“…Salinity treatments progressively reduced photosynthesis and this was coincident with a decline in leaf chloroplast pigments (chlorophyll a, chlorophyll b and carotenoids). Other workers have concluded that salinity affected the rate of photosynthesis reflecting changes in pigment composition (Ahmed, et al, 1980;Helal and Mengel, 1981;and Berlin, et al, 1982). Photosynthetic activity decreased with increase in salinity concentrations in pure sand soil (SS) but increased with sand/hydrogel polymer (SS/HP) (v/v) (Fig.…”

SALT LOADING DOES NOT CONTROL CO2 EXCHANGE IN RAMALINA MENZIESII TAYL.

“…The effects of salinity on photosynthetic rates appear to be extremely variable, ranging from a stimulation of COg uptake (Passera & Albuzio, 1978) to a reduction (Helal & Mengel, 1981;Malloch, Bamidele & Scott, 1985;Yeo, Caporn & Flowers, 1985;Flowers et al, 1985). This is probably because the salt is distributed unevenly among the different cell compartments and the extracellular spaces, so that average tissue salt loads do not accurately refiect salt concentrations at the sites of photosynthetic activity.…”