Long‐term responses of Melilotus segetalis to salinity. I. Growth and partitioning

Abstract

Annual sweetclover plants [Melilotus segetalis (Brot) Ser.] were grown for a complete life cycle with and without saline (NaCl treatment of CE=15 dS m−1). Growth and partitioning analyses were performed. Sequential harvests (every 15 d) during the life cycle, and separation of plant material into roots, stems, petioles, leaves and reproductive structures were carried out Salt treatment reduced growth during the early and middle stages of the life of the plant, but did not significantly affect RGR in the reproductive phase. The root–shoot allometric coefficient of salinized plants in the generative phase decreased more than in control plants. We suggest that salinity‐induced growth reduction in M. segetalis was primarily a result of a lower unit leaf rate (ULR) despite an increased leaf area ratio (LAR). Earlier flowering, higher biomass allocation to shoot and greater reproductive investment, but similar relative growth rate (RGR), were some of the main characteristics of salt‐stressed plants compared to controls during the reproductive phase, these apparently being associated with increased sink strength caused by developing flowers and fruits.

Growth and Physiological Responses ofPhaseolusSpecies to Salinity Stress

“…Results confirm that decreases on RGR for salt-sensitive genotypes were related to ULR (r 2 = 0.95), indicating that the reduced growth in these species under high salinity was primarily as a result of a decline in leaf photosynthetic rate, as indicated by the lower stomatal conductance (r 2 = 0.62). These results support those reported by Romero and Marañón [17] and Bayuelo-Jiménez et al [23], where the ULR was also found to be highly correlated with RGR for salt-stressed barley and beans, respectively.…”

“…Salinity affected the potassium accumulation in the vegetative phase, probably by significantly reducing the absorption of potassium in roots ( Table 1). The K + concentration fell continuously in roots and stems of salt-stressed species, while the leaves had similar concentrations to those in control plants at the medium salt stress levels, suggesting a compensation over time, probably by translocation of K + from roots and stems to leaves [17], a sustained acquisition despite appreciable overall Na + uptake [23], and/or a high K + selectivity and/or K + /Na + exchange across the plasmalemma of the root epidermis [6,9,10]. The ability to withdraw Na + and to retranslocate K + seems crucial for salt tolerance [10,11].…”

“…A decrease in potassium accumulation in salt-stressed plants appears to be one of the most widespread responses associated with reduced growth [17,44]. Salinity affected the potassium accumulation in the vegetative phase, probably by significantly reducing the absorption of potassium in roots ( Table 1).…”

“…RGR is determined by two factors, the unit leaf rate (ULR), which is an index of plant photosynthetic-assimilatory capacity per leaf area unit, and leaf area ratio (LAR), which is the amount of leaf area per total plant weight [16]. In some species, salinity mainly affects the leaf elongation and hence the development of photosynthetic surface area (LAR) [17] and photosynthetic capacity in others [18]. Salinity reduction of LAR could be caused by a decrease in SLA (the amount of leaf area per unit leaf weight) and/or a decrease in the proportion of dry matter allocated to the leaf tissue (leaf weight ratio) (LWR) [16].…”

Physiological responses of plants to salinity: A review

“…For example, Maas and Grieve (1990) and Grieve et al (1994) reported that salt stress (140 mol m -3 NaCl) accelerated development of the wheat shoot apex on the main stem by as much as 18 d and decreased the time to initiation of reproductive structures. They, along with others (e.g., sweet clover [Romero and Maranon 1994a]), also reported a shorter time to flowering. Accelerated phenological development may not necessarily be a common response among all plant species, as demonstrated by Rawson (1986), who reported no change in phenology of barley in response to NaCl up to 150 mol m -3 .…”