J.A. Poss

Wheat response to interactive effects of boron and salinity

Abstract In semiarid regions with irrigated agriculture, excess boron (B) often occurs in association with moderate to high salinity. However, little information is available on plant uptake of B under saline conditions. This greenhouse study was conducted to determine the interactive effects of salinity and varying concentrations of boron on growth, yield and ion relations of wheat (Triticum aestivum L., cv. ‘Yecora Rojo). Plants were grown in sand cultures that were irrigated four times daily with modified Hoaglands nutrient solution. Sixteen treatments were initiated 4 d after planting in a completely randomized factorial experiment with 4 salinity levels (electrical conductivities of the irrigation waters=1.5, 4, 8, and 12 dS m−1) and 4 B concentrations (1, 5, 10, and 15 mg L−1). Salinizing salts were NaCl and CaCl2 (2:1 molar basis). Symptoms of B toxicity were closely correlated with B concentration in the leaves and injury became severe when leaf‐B exceeded 400 mg kg−1. At each concentration of external B, shoot‐B was least under nonsaline conditions and increased significantly as salinity increased. Shoot‐calcium (Ca) concentration increased with increasing salinity, but was unaffected by applied B. Shoot‐magnesium (Mg), and potassium (‐K) decreased significantly in response to increases in salinity and substrate B. Salinity and B as well as their combined effects significantly reduced wheat biomass production, yield components, and final grain yield.

Evaluation of salt tolerance in rice genotypes by physiological characters

AbstractThe use of physiological characters as selection criteria in salt tolerance breeding requires the identification of the contribution each individual character makes to salt tolerance. Rice genotypes were evaluated for salt tolerance in terms of grain yield and physiological characters. Plants of twelve genotypes were grown in sand tanks in a greenhouse and irrigated with Yoshida nutrient solution. Sodium chloride and calcium chloride (5:1 molar ratio) were added at two concentrations to give moderate (4.5 dS m-1) and high (8.3 dS m-1) salinity treatments. One set of plants was harvested at 635 °Cċd (accumulative thermal time) after planting to determine LAI and mineral ion concentrations. Another set of plants was allowed to grow to maturity. High genotypic diversity for LAI and shoot ion contents was observed. LAI contributed the most to the variation of the grain yield under salt stress. Significantncorrelations between LAI and yield components in both salt-tolerant and-sensitive genotypes further confirmed the significant contribution of LAI to grain yield. K-Na selectivity increased with increasing salinity. Conversely, Na-Ca selectivity decreased with increasing salinity. Significant correlations were identified between grain yield and both Na-Ca and K-Na selectivity. Highly significant (p<0.001) correlations were identified between Na-Ca selectivity and the rankings among genotypes for grain yield. Thus, Na-Ca selectivity could be one salt tolerance component and an useful selection criterion in screening for salt tolerance.

Biomass accumulation and potential nutritive value of some forages irrigated with saline-sodic drainage water

A controlled study using a sand-tank system was conducted to evaluate 10 forage species (bermudagrass, ‘Salado’ and ‘SW 9720’ alfalfa, ‘Duncan’ and ‘Polo’ Paspalum, ‘big’ and ‘narrow leaf’ trefoil, kikuyugrass, Jose tall wheatgrass, and alkali sacaton). Forages were irrigated with sodium-sulfate dominated synthetic drainage waters with an electrical conductivity of either 15 or 25 dS/m. Forage yield was significantly reduced by the higher (25 dS/m) salinity level of irrigation water compared to the lower (15 dS/m) level. There was wide variation in the sensitivity of forage species to levels of salinity in irrigation water as reflected by biomass accumulation. With the exception of bermudagrass, which increased accumulation at the higher level of salinity, and big trefoil, which failed to establish at the higher level of salinity, ranking of forages according to the percent reduction in biomass accumulation due to the higher level of salinity of irrigation water was: Salado alfalfa (54%) = SW 9720 alfalfa (52%) > Duncan Paspalum (41%) > narrow leaf trefoil (30%) > alkali sacaton (24%) > Polo Paspalum (16%) > Jose tall wheatgrass (11%) = kikuyugrass (11%). Bermudagrass and Duncan Paspalum were judged to be the best species in terms of forage yield and nutritive quality. Kikuyugrass, which had the third highest biomass accumulation, was judged to be unacceptable due to its poor nutritional quality. Although narrow leaf trefoil had a relatively high nutritional quality, its biomass accumulation potential was judged to be unacceptably low. Alfalfa cultivar’s biomass accumulations were the most sensitive to the higher level of salinity, among forages that survived at the higher salinity level, although actual accumulations at the higher salinity were high relative to other forages. Increased salinity influenced several forage quality parameters, including organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), and in vitro gas production, generally leading to higher nutritional quality at the higher salinity level, although their significance varied amongst species and cuttings.

Lesquerella growth and selenium uptake affected by saline irrigation water composition

Abstract A greenhouse study was conducted to determine the effects of waters differing in salt composition on growth and selenium (Se) accumulation by lesquerella (Lesquerella fendleri Gray S. Wats.). Plants were established by direct seeding into sand cultures and irrigated with solutions containing either (a) Cl− as the dominant anion or (b) a mixture of salts of SO42− and Cl−. Four treatments of each salinity type were imposed. Electrical conductivities of the irrigation waters were 1.7, 4, 8, and 13 dS m−1. Two months after salinization, Se (l mg l−1, 12.7 μM) was added to all solutions as Na2SeO4. Shoot growth was significantly reduced by increasing Cl-salinity. Regardless of salinity type, concentrations of Ca2+, Mg2+, Cl−, total-S, and Se were higher in the leaves than the stems, whereas K+ and Na+ were higher in the stem. Leaf-Se concentrations were not significantly affected by Cl-based irrigation waters, averaging 503 mg Se kg−1 dry wt across salinity levels, whereas leaf-Se decreased consistently and significantly from 218 to 13 mg kg−1 as mixed salt salinity increased. The dramatic reduction in Se was attributed to SO42−:SeO42− competition during plant uptake. The strong Se-accumulating ability of lesquerella suggests that the crop should be further evaluated as a potentially valuable phytoremediator of Se-contaminated soils and waters of low to moderate salinity in areas where the dominant anion in the substrate is Cl−.

pH dependent salinity-boron interactions impact yield, biomass, evapotranspiration and boron uptake in broccoli ( Brassica oleracea L.)

AimsSoil pH is known to influence many important biochemical processes in plants and soils, however its role in salinity—boron interactions affecting plant growth and ion relations has not been examined. The purpose of this research was to evaluate the interactive effects of salinity, boron and soil solution pH on broccoli (Brassica oleracea L.) growth, yield, consumptive water use and shoot-boron accumulation.MethodsA greenhouse experiment was conducted using a sand tank system where salinity-B-pH treatment solutions were supplemented with a complete nutrient solution. Sulfate-dominated irrigation waters, characteristic of groundwater in California’s San Joaquin valley (SJV), were tested at EC levels of 2, 5, 8, 11 and 14xa0dSu2009m−1. Each salinity treatment consisted of two boron treatments (0.5 and 21xa0mgu2009L−1) and each of those treatments was tested under slightly basic (pHu20098.0) and slightly acidic (pHu20096.0) conditions.ResultsResults included multiple salinity-boron-pH interactions affecting shoot biomass, head yield and consumptive water use. Broccoli fresh head yields were significantly reduced by salinity and boron, but the degree of yield reductions was influenced by pH. Relative head yields were substantially reduced in treatments with high pH and high B, particularly under low and high salinity where head yields were decreased by 89xa0% and 96xa0%, respectively, relative to those at low salinity and low boron. Intermediate levels of salinity were far less damaging. Increased salinity and boron reduced evapotranspiration (ET) and there were no salinity-boron associated interactions on ET. However, increased salinity and boron concentrations increased water use efficiency (shoot biomass/cumulative volume ET). Shoot B concentration increased with increased boron and was greater at pHu20096 as compared to pHu20098. Shoot boron concentration decreased with increasing salinity at both pH levels but particularly at the high substrate boron concentration.ConclusionsIt is likely that different mechanisms, yet unknown, are responsible for severe head-yield reductions at low and high salinity in the presence of high boron under alkaline conditions. We found that boron in the shoot did not accumulate by a simple passive process. Rather as boron increased from 0.5 to 21xa0mgu2009L−1, there was a restrictive mechanism where total shoot boron (mg plant−1) was reduced by 10 to 40 times the amount potentially supplied to the shoot by passive transport via mass flow perhaps involving complex interactions with membrane channels and B exporters. Total shoot boron concentration was a poor indicator of plant growth response.

Irrigation Method Affects Selenium Accumulation in Forage Brassica Species

Abstract A greenhouse study was conducted in sand cultures to compare the effects of saline irrigation waters applied by two different methods, flooding and above‐canopy sprinkling, on selenium (Se) accumulation by the forage brassicas, kale (Brassica oleracea L., cv. “Premier”) and turnip (B. rapa L., cv. “Forage Star”). The composition of the irrigation water was designed to simulate saline (7 dS m−1) drainage effluent commonly encountered in the San Joaquin Valley of California, and being evaluated for reuse by irrigation of salt tolerant crops. The experimental design was a randomized complete block with two irrigation methods, two plant species (kale and turnip), four Se concentrations (0.25, 0.50, 1.0, and 2.0 mg L−1 Se–SeO4 2−), and three replications. Kale was generally a more efficient Se accumulator than turnip. Shoot Se concentrations in kale and turnip increased with increasing Se in the irrigation waters regardless of irrigation method. Selenium was readily taken up by the leaves of the sprinkled plants to give shoot‐Se concentrations that were two‐ to three‐fold higher than in plants of the same cultivar grown under flood irrigation. Both kale and turnip can accumulate Se to concentrations that would be toxic to animals if exclusively fed this material. These Se‐enriched forages may be useful as an additive to Se‐deficient fodders in order to meet the nutritional requirements of livestock. The potential for phytoremediation of Se contaminated soils or waters is greatly enhanced by sprinkler irrigation via the mechanism of foliar absorption of Se. This enhanced uptake is especially important in the presence of elevated sulfate concentrations, which normally reduce Se uptake by plants.

Characterization of leaf boron injury in salt-stressed Eucalyptus by image analysis

Symptoms of boron toxicity (i.e., necrosis of leaf tips and margins) have been observed on eucalyptus trees in the San Joaquin Valley of California where the trees are being tested for their effectiveness at reducing the volume of agricultural drainage effluents. In a controlled, outdoor sand-tank study, Eucalyptus camaldulensis Dehn., Clone 4544 trees were grown and irrigated with combinations of salinity and B to determine their influence on tree growth and water use. Irrigation water quality treatments were prepared to simulate the Na-sulfate salinity, high B nature of these drainage effluents. Electrical conductivities (ECiw) of the waters ranged from 2 to 28 dS m-1 and B concentrations ranging from 1 to 30 mg L-1. As an integral component of this study , we developed a method to quantify and correlate foliar damage with leaf B concentrations. By scanning both injured and uninjured leaves into computer files and processing with image analysis, we were able to simultaneously correlate salinity stress with its overall effect on leaf area as well as to quantify the relative fraction of leaf area affected by specific-ion (i.e., B) injury. Leaf area was unaffected by B stress but was reduced by salinity only in the younger leaves. Boron injury was correlated with increasing irrigation water B only in older leaves. The relative injured area (RIA) of the older leaves was related to the B concentrations of leaves from trees grown at various salinities . A regression equation was developed from injury data obtained from trees grown under boron and salinity stress for 223 days (r2=0.90). From this relationship, we were able to estimate leaf boron concentrations from injury symptoms in leaves selected at random from main trunk branches of trees grown for 333 days under the same stress conditions. The results suggest that this method may have potential as an effective tool for monitoring the response to toxic levels of boron in eucalyptus, once B toxicity has been established by analytical means. The RIA appears to be mitigated by increased salinity of the irrigation water and is consistent with the general reduction in leaf B by salinity. The interactive effects of boron and salinity on foliar injury depends on the physiological age of the leaf.