Physiological and biochemical responses of alfalfa (Medicago sativa L.) to salinity stress

Authors: CORNACCHIONE, MONICA - National Institute Of Agricultural Technology(INTA); Ferreira, Jorge; Liu, Xuan; Suarez, Donald

Submitted to: Proceedings of the World Alfalfa Congress
Publication Type: Proceedings
Publication Acceptance Date: 11/10/2018
Publication Date: 11/11/2018
Citation: Cornacchione, M.V., Ferreira, J.F., Liu, X., Suarez, D.L. 2018. Physiological and biochemical responses of alfalfa (Medicago sativa L.) to salinity stress. Proceedings of the Second World of Alfalfa Congress. 179.

Interpretive Summary:

Technical Abstract: Alfalfa is the main forage in dairy cattle feed in the USA, and California is the main producer with almost 100% of the crop under irrigation. High cost of fresh water demands the use of recycled waters that may have high concentration of salts. Our group has reported alfalfa to be moderately-tolerant to salinity while maintaining its nutrient composition and antioxidant activity. In this research, we explored 15 nondormant alfalfa populations (experimental populations from INTA Argentina, and commercial cultivars from the United States), and evaluated the effect of salinity on physiological and biochemical parameters. Plants were grown in sand tanks in a greenhouse located in Riverside, CA (33°58’24’’ N, 117º19’12’’ W), and were harvested 10 times during 2011-2012. A randomized design split-plot arrangement was used with two water composition types (salts dominated by Cl- or SO42-) with five salinity levels (ECiw ranging from 0.85 to 24.5 dS m-1) as the main plot and 15 populations (P) as subplots. There were six replications (n=6 sand tanks) with three plants per population per tank (total of 2700 plants). Gas exchange, leaf area (LA), and chlorophyll content (Chl a+b, mg dm-2) were measured before the 3rd harvest at ECiw 0.85, 13 and 18.3 dS m-1. Leaf net photosynthetic rate (Pn, µmol CO2 m-2 s-1), leaf stomatal conductance (gs, mol H2O m-2 s-1), and leaf transpiration (Tr, mmol H2O m-2 s-1) were recorded using a portable Li-Cor 6400 Photosynthesis System. Chl was calculated from the equation of correlation between the concentrations of the samples collected from the same leaflet and the readings taken with a portable Minolta Chlorophyll Meter (SPAD-502). New samples were taken before the 8th harvest to estimate again the Chl and specific leaf weight (SLW) at all ECiw levels. SLW (g m-2) was estimated by the total leaf discs dry weight (g) / total discs area per m2. Shoot samples from the Cl-dominated water type were taken to analyze the hydrophilic oxygen radical absorbance capacity (ORAC, in µmoles TEg-1 DM), and total phenolics (TP, in mg GAE g-1 DM). Analysis of variance (ANOVA) and treatment comparisons were carried out using InfoStat (Di Rienzo et al, 2012). There was no difference (p>0.05) in Pn, gs, and Tr due to water salt type. There was a significant (p<0.01) interaction for ECiw x P for Pn rate. At each ECiw, there were significant differences in Pn among populations (p<0.01). Almost all populations showed a trend to increase Pn under salinity, compared to control. The gs was significantly reduced while Tr rate increased with increased salinity (ECiw p<0.05, ECiw x P p>0.05, and P p>0.05). There were significant differences for both LA and Chl content (both p<0.01) due to water salt type, showing higher LA and lower Chl when plants were irrigated with SO42- compared to Cl--dominated water. Salinity significantly reduced LA (3.84a, 2.71b, and 2.14c cm2, for control ECiw, 13, and 18 dSm-1, respectively). The ECiw x P interaction was significant at p=0.05, however the significant difference for LA among populations was observed only for control plants. There was no significant (p>0.05) ECiw x P interaction for Chl or SLW. The Chl content (consistent for both sampling dates) and SLW significantly increased as salinity increased (p<0.01).There was difference among populations (p<0.05) in Chl and SLW. Some populations maintained the highest and the lowest Chl content in both sampling dates (eg, SISA14 and Cibola at the top and SISA 1, SISA 10, and SISA 11 at the end in rank comparisons). There was no significant (p>0.05) ECiw x P interaction for ORAC or TP in Cl-dominated water. In general, according to our data, there were changes in the physiological responses of alfalfa mainly associated to the different salt levels. A highly positive correlation was found between the average of SLW and Chl (y=0.1164x +0.9496, R