Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2010
Publication Date: 6/28/2010
Publication URL: http://www.ars.usda.gov/SP2UserFiles/Place/53102000/pdf_pubs/P2303.pdf
Citation: Grieve, C.M., Poss, J.A., Grattan, S.R., Suarez, D.L., Smith, T.E. 2010. The Combined Effects of Salinity and Excess Boron on Mineral Ion Relations in Broccoli. Scientia Horticultureae. 125(3)179:187. Interpretive Summary: The mineral ion, boron, is an essential nutrient for plants. However, the optimum concentration range for plant available-B is very narrow; too little will result in B deficiency, too much in B toxicity. Toxic levels of B often occur in saline areas such as the San Joaquin Valley of California (SJV). To answer questions that have arisen concerning effects the combined stress factors have on crop yield in the Valley, broccoli was planted in greenhouse sand tanks irrigated with saline waters containing B. The experimental design was 3 salinity levels (low, medium and high) and 3 B concentrations (low, medium, and high). This report, the third in a series describing the interactive effects of salinity and excess B on broccoli, presents treatment effects on leaf morphology, distribution of B in leaf tissues, partitioning of mineral ions in leaves of different ages, and mineral ion relations. When salinity was low and B was high, the first true leaves, as well as subsequent leaves, were cupped upwards. The reason for this abnormality which was observed only in this particular treatment was not determined and deserves further investigation. Boron taken up by the plant was distributed to the leaves in a characteristic manner: very high in the blade margins, moderately high in the rest of blade tissue, and least in the petioles. With the exception of phosphorus (which was partitioned to the broccoli head), all of the other major ions were accumulated in the lower leaves on the broccoli stem. Examination of ion relations revealed the positive effect of salinity on B uptake and accumulation in the leaves: leaf-B was reduced in the presence of salinity. This finding provides a potential explanation of the results given in earlier papers: the combined effects of salinity and B were less detrimental to broccoli growth and yield than one would expect by the two stress factors acting individually. The results of this comprehensive research will allow growers to develop improved management strategies for crops produced in the SJV.
Technical Abstract: Two plant stress factors, salinity and high levels of boron, often co-occur in natural and agricultural environments. Many investigations have been conducted to document the influence of the combined stresses on crop growth and yield. Only limited information, however, is available concerning the combined effects of the two stresses on mineral ion uptake and partitioning to shoot organs and tissues. Data for this study were obtained from an experiment conducted in greenhouse sand cultures with two water types: (1) a chloride-dominated system, and (2) sulfate-dominated waters characteristic of those present in the San Joaquin Valley of California. Each saline composition treatment was tested at three salinity levels (2, 12, 18 dS m-1) and three B concentrations (0.046, 1.11, 2.22 mM; 0.5, 12, 24 mg L-1). The gradient in B distribution in individual leaves sampled midseason was steep, with less boron accumulating in petioles than in the blades. The highest B concentrations (> 100 mmol B kg -1 dry weight) were found in leaf margins of plants grown in the low salinity-high boron treatments. These leaves were cupped upward, an unusual visual symptom characteristic of B toxicity. At final harvest, concentrations of B, Ca, Mg, Na, K, and Cl were highest in the oldest leaves on the broccoli shoots, decreasing acropetally to the heads. Total-P, however, was highest in broccoli heads, decreasing in the older tissues. Leaf-B accumulation was more closely related to salinity rather than to the concentration of Cl in the irrigation waters. Analysis of variance indicated that substrate B had little effect on Cl accumulation in salt-stressed broccoli leaves regardless of water type. No clear cut relationships were evident that would explain the reciprocal effects of B and Cl on crop yields.