Spinach plants favor the absorption of K+ over Na+ regardless of salinity, and may benefit from Na+ when K+ is deficient in the soil

Authors: Ferreira, Jorge; FILHO, JAIME - University Of California; Liu, Xuan; Sandhu, Devinder

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2020
Publication Date: 4/15/2020
Citation: Ferreira, J.F., Filho, J.B., Liu, X., Sandhu, D. 2020. Spinach plants favor the absorption of K+ over Na+ regardless of salinity, and may benefit from Na+ when K+ is deficient in the soil. Plants. 9(4). https://doi.org/10.3390/plants9040507.
DOI: https://doi.org/10.3390/plants9040507

Interpretive Summary: With the availability of fresh water for irrigation decreasing in many regions, recycled waters are increasingly viewed as an alternative, although their relatively high salinity (salt content) may reduce crop yields. We studied the impact of irrigation water salinity on two spinach cultivars, investigating interactions between salts and fertilization levels on the growth of ‘Raccoon’ and ‘Gazelle’ spinach. The results showed that, at moderate salinity levels, spinach plants can benefit from sodium salts in irrigation water for growth when potassium fertilization is low, and that ‘Gazelle’ is less affected by salts than ‘Raccoon’. Thus, recycled waters of low to moderate salinity are a viable alternative for spinach production in semiarid regions. Also, results indicate that spinach plants can grow with much less potassium fertilization than usually recommended. This study will benefit spinach growers in semiarid regions and researchers interested in understanding the relationship between salts and minerals in plants. Our results may help increase profits for farmers who chose to use recycled water and reduce potassium fertilizer inputs for spinach cultivation.

Technical Abstract: Two spinach (Spinacea oleracea L.) cultivars were evaluated for their response to deficient (0.25 mmolcL-1 or 0.25K) and sufficient (5.0 mmolcL-1 or 5.0K) potassium (K) levels combined with salinities of 5, 30, 60, 90 and 120 mmolcL-1 NaCl. Plants substituted K for Na proportionally with salinity within each K dose. Plants favored K+ over Na+ , regardless of salinity, accumulating significantly less Na at 5.0K than at 0.25K. Salinity had no effect on N,P, and K shoot accumulation, suggesting that spinach plants can maintain NPK homeostasis even at low soil K. Ca and Mg decreased with salinity, but plants showed no deficiency. There was no NA+ to K+ or Cl- to NO3- competition, and shoot biomass decrease was attributed to excessive NaCl accumulation. Overall, ‘Raccoon’ and ‘Gazelle’ biomasses were similar regardless K dose but ‘Raccoon’ outproduced ‘Gazelle’ at 5.0K at the highest salinity levels, indicating that ‘Raccoon’ may outperform ‘Gazelle’ at higher NaCL concentrations. At low K, Na may be required by ‘Raccoon’, but not ‘Gazelle’. This study suggested that spinach can be cultivated with recycled waters of moderate salinity and less potassium than recommended, leading to savings on crop input and decreasing crop environmental footprint.