Academic literature on the topic 'Alkaline soil tolerance'

Saline or alkaline soils present a strong stress on plants that together may be even more deleterious than alone. Australia's soils are old and contain large, sometimes overlapping, areas of high salt and alkalinity. Acacia and other Australian plant lineages have evolved in this stressful soil environment and present an opportunity to understand the evolution of salt and alkalinity tolerance. We investigate this evolution by predicting the average soil salinity and pH for 503 Acacia species and mapping the response onto a maximum-likelihood phylogeny. We find that salinity and alkalinity tolerance have evolved repeatedly and often together over 25 Ma of the Acacia radiation in Australia. Geographically restricted species are often tolerant of extreme conditions. Distantly related species are sympatric in the most extreme soil environments, suggesting lack of niche saturation. There is strong evidence that many Acacia have distributions affected by salinity and alkalinity and that preference is lineage specific.

Collection site soil pH may be a useful predictor of tolerance in Lupznus angustifolzus to chlorosis induced by alkaline soils. We examined a range of genotypes from the Mediterranean region for their tolerance of an alkaline sandy clay loam (pH 8.8) from Merredin, Western Australia. Fifteen wild L. angustifolius lines, collected on a variety of soils that ranged in pH from 4.2 to 9.0, were compared with cultivars of L. angustifolzus and known alkaline-tolerant (L. cosentinii) and alkaline-sensitive (L. luteus) lupin species. Five-week-old seedlings varied greatly in chlorosis on the alkaline soil, from almost no chlorosis (as in L. cosentinzi cv Erregulla) to severely chlorotic (L. angustifolius line MJS176 from Spain). No lines were chlorotic after acid amelioration of the soil. Chlorosis score in wild L. angustifolius was not significantly correlated with soil pH at the collection site and was not associated with a particular soil texture, but there was a significant correlation between altitude of collection sites and chlorosis scores. Chlorosis-sensitive lines were from higher altitudes, had lower root and shoot fresh weight, were lower in Fe, Mn and K and were higher in Zn, P, and S in new growth than resistant lines. Chlorosis-sensitive lines also had the largest increases in fresh weight of roots and shoots in response to soil acidification. Genotypes with better root growth and therefore lower chlorosis symptoms on alkaline soil did not necessarily have the strongest root growth on acid ameliorated soil. Soil pH at the collection site in the Mediterranean region was not a reliable predictor of chlorosis in L. angustifolius induced by an alkaline fine-textured soil in Western Australia, although significant variation in tolerance to this soil was found within the species.

Cowpea or Southernpea [Vigna unguiculata (L.) Walp.] is an important legume crop used as a feed for livestock, as a green vegetable, and for consumption of its dry beans, which provide 22% to 25% protein. The crop is very sensitive to alkaline soil conditions. When grown at soil pH of 7.5 or higher, cowpea develops severe leaf chlorosis caused by deficiencies of iron (Fe), zinc (Zn), and manganese (Mn) resulting in stunted plant growth and yield reduction. We evaluated in replicated field experiments at St. Croix, U.S. Virgin Islands, and Juana Díaz, Puerto Rico, 24 PIs and two commercial cultivars, some of which have shown some tolerance to alkaline soils in unreplicated, seed regeneration plots of the U.S. cowpea collection. Alkaline soil conditions at St. Croix were too severe resulting in average yield of genotypes at this location being significantly lower and 77% less than that at Juana Díaz. Nevertheless, some genotypes performed well at both locations. For example, PIs 222756, 214354, 163142, 582605, 582840, 255766, 582610, 582614, 582576, 582809, and 349674 yielded in the upper half of the group at both locations. Accession PI 163142 ranked third in grain yield production at both locations and outyielded the iron-chlorosis-resistant controls at St. Croix. These genotypes deserve further attention as potential sources of alkaline soil tolerance.

Subsoil physicochemical constraints such as primary salinity and high boron (B) can significantly reduce grain yields across wide areas of Australia. Financially viable amelioration options are limited for cropping systems on these soils, which has raised interest in ‘genetic solutions’. Increasing the tolerance of crops to high salinity and boron that typically co-exist within alkaline soils offers the potential for substantial yield benefits. To assess the contribution that genetic variation can make to crop yield, closely related genotypes differing in B and/or Na+ tolerance of bread and durum wheat, barley, and lentil were compared by growing the different lines in intact soil cores of 2 Calcarosol profiles differing in level of subsoil constraints (‘hostile’/’benign’). The hostile profile had salinity increasing to EC1 : 5 ~1.2 dS/m and B ~18 mg/kg to 0.60 m, whereas in the benign soil EC1 : 5 did not exceed ~0.6 dS/m and B ~11 mg/kg. Grain yields were significantly less on the hostile soil than the benign soil for barley (34%), bread wheat (20%), durum wheat (31%), and lentil (38%). Accumulation of B in shoots was significantly lower on the hostile soil across all crop species, indicating high sodium within the soil was associated with inhibited uptake of B in plants. In contrast, accumulation of Na+ was greater for all cereal crops in the hostile soil compared with the benign soil. Lentil plants with reputed sodium tolerance (CIPAL415) produced a significant yield benefit on both the benign and hostile soil over the commercial line, Nugget. The lentil line with combined Na+ and B tolerance (02-355L*03Hs005) also produced an additional yield increase over CIPAL415 on the hostile soil; however, yield was equivalent on the benign soil. For durum wheat, 2 genotypes differing in Na+ tolerance, containing either the Nax1 or Nax2 genes, accumulated less sodium in the straw than the parent cv. Tamaroi within the hostile soil; however, this did not translate to a yield advantage. For barley, there was no difference in either grain yield or B uptake in either the grain or straw between the B-tolerance line 03_007D_087 and its parent cv. Buloke. Similarly, there was no difference in either grain yield or B uptake between the bread wheat Schomburgk and its B-tolerant near-isogenic line BT-Schomburgk. This study suggests that of the cereal lines tested, there was no obvious benefit in lines with potentially improved tolerance for a single, specific subsoil constraint on alkaline soils where multiple potential constraints exist. In contrast, in lentils, incorporating tolerance to Na+ and B did show promise for increased adaptation to soils with subsoil constraints.

Muscadine (Muscadinia rotundifolia) grapes have been used in grape variety and rootstock development due to their inherent pest and disease resistance, but little is known about their alkaline soil tolerance. In this study, Muscadine varieties, commercialrootstock and interspecific hybrid grape (Vitis spp.) cultivars were evaluated for alkaline soil tolerance under field conditions to determine the potential suitability of muscadines for rootstock development. Thirty-one muscadine and eleven interspecific hybridgrape cultivars were grown in a moderately alkaline soil (pH = 8.1) over a three-year period. Alkaline soil tolerance wasdetermined by relative vine vigour (shoot length), vine nutrient status (whole leaf tissue testing) and visual chlorosis. Additional data were collected on the timing of budbreak. Overall, the muscadines studied expressed low vigour and had greater chlorosissymptoms than the interspecific hybrid rootstocks (Paulsen 1103, Millardet et de Grasset 101-14, Millardet et de Grasset 420A,Ruggeri 140, Schwarzmann, and Matador). These parameters were not correlated with the concentration in any specific nutrient, although nutrient deficiencies (nitrogen, copper) and excesses (calcium, boron) were observed in the muscadine varieties.Overall, the muscadine grapes expressed poor alkaline soil tolerance compared to interspecific hybrid grape rootstocks (1103P, 101-14 MGt., 140Ru, Schwarzmann, 420A, and Matador), even the ones having poor alkaline soil tolerance (101-14 MGt., Schwarzmann) and own-rooted cultivars (Black Spanish, Blanc Du Bois, Dunstan’s Dream and Victoria Red). Nevertheless, some variability in chlorosis symptoms and nutrition was observed across the muscadine group, suggesting some interests to select Muscadine hybrid rootstocks less sensitive to iron chlorosis.

AbstractSoil alkalinity imposes important limitations to lupin productivity; however, little attention has been paid to investigate the effects of soil alkalinity on plant growth and development. Many lupins are sensitive to alkaline soils, but Lupinus albus material from Egypt was found to have tolerance to limed soils. The aim of this study was to compare the growth response of two cultivars of L.albus L. – an Egyptian cultivar, P27734, and an Australian cultivar, Kiev Mutant, to different soil pH levels and to understand the physiological mechanisms underlying agronomic alkalinity tolerance of P27734. Plants were grown under three pH levels (5.1, 6.7, and 7.8) in a temperature-controlled glasshouse. For both cultivars, the greatest dry mass production and carboxylate exudation from roots were observed at alkaline pH. The better performance of the Egyptian cultivar at high pH was entirely accounted for by its greater seed weight. From a physiological perspective, the Australian cultivar was as alkaline-tolerant as the Egyptian cultivar. These findings highlight the agronomic importance of seed weight for sowing, and both cultivars can be used in alkaline soils.

This study evaluated a diverse range of oak (Quercus) hybrids for tolerance to alkaline soils, which is a common site condition in urban landscapes that often limits the growth and longevity of many tree species. Different oak hybrids display varying severities of iron-deficiency induced leaf chlorosis when grown in a highly alkaline medium. Severity of leaf chlorosis was found to vary between different maternal parent species, with the results suggesting that hybrids with the maternal parents Q. macrocarpa (bur oak), possibly Q. muehlenbergii (chinkapin oak), and Q. ‘Ooti’ (ooti oak), are more likely to maintain healthy green leaf color when growing in a highly alkaline medium. These findings suggest that breeders interested in developing oak hybrids that are both cold-hardy and tolerant of alkaline soils should utilize these species in their crosses, and avoid Q. bicolor (swamp white oak), hybrids of which were generally found to be intolerant of alkaline soil. This study is one phase of a long-term project underway at Cornell University's Urban Horticulture Institute to select superior urban-tolerant cultivars of oak hybrids for future introduction into the horticulture industry.

Wolfberry (Lycium barbarum L.) is an important economic crop widely grown in China. The effects of salt-alkaline stress on metabolites accumulation in the salt-tolerant Ningqi1 wolfberry fruits were evaluated across 12 salt-alkaline stress gradients. The soil pH, Na+, K+, Ca2+, Mg2+, and HCO3− contents decreased at a gradient across the salt-alkaline stress gradients. Based on the widely-targeted metabolomics approach, we identified 457 diverse metabolites, 53% of which were affected by salt-alkaline stress. Remarkably, soil salt-alkaline stress enhanced metabolites accumulation in wolfberry fruits. Amino acids, alkaloids, organic acids, and polyphenols contents increased proportionally across the salt-alkaline stress gradients. In contrast, nucleic acids, lipids, hydroxycinnamoyl derivatives, organic acids and derivatives and vitamins were significantly reduced by high salt-alkaline stress. A total of 13 salt-responsive metabolites represent potential biomarkers for salt-alkaline stress tolerance in wolfberry. Specifically, we found that constant reductions of lipids and chlorogenic acids; up-regulation of abscisic acid and accumulation of polyamines are essential mechanisms for salt-alkaline stress tolerance in Ningqi1. Overall, we provide for the first time some extensive metabolic insights into salt-alkaline stress tolerance and key metabolite biomarkers which may be useful for improving wolfberry tolerance to salt-alkaline stress.

Narrow-leafed lupin (Lupinus angustifolius L.) grows poorly on alkaline soils, whereas white lupin (Lupinus albus L.) grows relatively well. This study aimed at examining genotypic variations of white lupins grown in limed acid and alkaline soils in the glasshouse and to test whether the glasshouse findings correlated with those observed in the field. Twelve white lupin genotypes were tested for their tolerance of limed and alkaline soils in the glasshouse. In limed soils compared with the control soil, genotypic variation in shoot growth ranged from 58 to 80%, root weight from 49 to 72%, and leaf chlorophyll concentration from 47 to 96%. In the alkaline soil, shoot weight ranged from 75 to 110%, root weight from 39 to 63%, and chlorophyll concentration from 58 to 94% of the control. However, iron chlorosis did not negatively correlate with shoot growth of the genotypes on the limed or alkaline soils. The results suggest that iron chlorosis may not be used as a sole indicator for selecting tolerant albus lupins for alkaline soils. Nineteen lines including those used in the glasshouse were compared in the field for their ability to grow on an alkaline clay. Large genotypic variation in early shoot growth was also found; shoot weight on the alkaline soil relative to an acid soil ranged from 38 to 85%. However, growth performance of the white lupin genotypes in response to the alkaline soil did not correlate with those in the glasshouse, indicating that factors other than soil alkalinity might also be important for the growth of albus lupin. Screening techniques to identify tolerant genotypes for alkaline soils need to be further developed.

Current indices of saline-alkaline (SA) tolerance are mainly based on the traditional growth and physiological indices for salinity tolerance and likely affect the accuracy of alfalfa tolerance predictions. We determined whether the inclusion of soil alkalinity-affected indices, particularly Ca2+, Mg2+, and their ratios to Na+ in plants, based on the traditional method could improve the prediction accuracy of SA tolerance in alfalfa, determine important indices for SA tolerance, and identify suitable alfalfa cultivars in alkaline salt-affected soils. Fifty alfalfa cultivars were evaluated for their SA tolerance under SA and non-SA field conditions. The SA-tolerance coefficient (SATC) for each investigated index of the alfalfa shoot was calculated as the ratio of SA to non-SA field conditions, and the contribution of SATC under different growth and physiological indices to SA tolerance was quantified based on the inclusion/exclusion of special alkalinity-affected indices. The traditional method, excluding the special alkalinity-affected indices, explained nearly all of the variation in alfalfa SA tolerance, and the most important predictor was the SATC of stem length. The new method, which included these special alkalinity-affected indices, had similar explanatory power but instead identified the SATC of shoot Ca2+/Na+ ratio, followed by that of stem length, as key markers for the field evaluation of SA tolerance. Ca2+, Mg2+, and their ratios to Na+ hold promise for enhancing the robustness of SA-tolerance predictions in alfalfa. These results encourage further investigation into the involvement of Ca2+ in such predictions in other plant species and soil types under more alkaline salt-affected conditions.

The optimum soil pH for most cultivated plants ranges from pH 6 to 8. This range provides optimal nutrient availability and minimal effects of toxic ions. Soils with pH below 5.5 (acid) and above 8 (alkaline) pose challenges for plant growth and development due to ion toxicities and lack of nutrient availability or nutrient imbalances. Roots of some species such as Triticum aestivum (wheat) exude organic anions such as malate under acidic conditions, providing tolerance against free Al3+ which is highly toxic to roots. In wheat the transporter responsible for this exudation is the Aluminium Activated Malate Transporter (TaALMT1). This thesis examines the role of the TaALMT1 transporter in extreme pH stress tolerance. Plant ALMTs are anion channels named after the first characterized member from wheat roots (TaALMT1). However, most ALMTs are not activated by Al3+, but all those so far investigated are regulated by gamma-aminobutyric acid (GABA). Gamma-aminobutyric acid (GABA) regulation of anion flux through ALMT proteins requires a specific amino acid motif in ALMTs that shares similarity with a GABA-binding site in mammalian GABAA receptors. In wheat root apices a negative correlation between activation of TaALMT1 and endogenous GABA concentrations ([GABA]i) was previously identified. This is explored here further in both wheat root apices and in heterologous expression systems using inhibitors that are reported to change [GABA]i: amino-oxyacetate (AOA) – a glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) inhibitor, and vigabatrin – a GABA transaminase (GABA-T) inhibitor. It is demonstrated that activation of TaALMT1 reduces [GABA]i because TaALMT1 facilitates GABA efflux. Though TaALMT1 is activated by Al3+ the released GABA does not complex Al3+. TaALMT1 also facilitates GABA transport into cells, demonstrated by a yeast complementation assay and via 14CGABA uptake into TaALMT1-expressing Xenopus laevis oocytes; found to be a general feature of all ALMTs examined. Mutation of the GABA ‘motif’ (TaALMT1F213C) prevented both GABA influx and efflux in yeast and Xenopus laevis oocytes, and resulted in no correlation between malate efflux and [GABA]i. It is concluded that ALMTs are likely to act as both GABA and anion transporters in planta. GABA and malate appear to interact with ALMTs in a complex manner to regulate each other’s transport, suggestive of a role for ALMTs in communicating metabolic status. One of the potential roles for GABA is as a pH regulator. Being a zwitterion its exudation into acidic or alkaline solutions will tend to bring pH towards neutrality. Previous field studies have suggested that TaALMT1 in wheat may also confer tolerance to alkaline soil. Soil alkalinity reduces yield and is a major problem worldwide, but very little is known about the physiological mechanisms that allow some plants to tolerate alkaline conditions. Along with its role in Al3+ tolerance at low pH, TaALMT1 is also activated by external anions at alkaline pH. Therefore it was hypothesized that TaALMT1 provides alkaline soil tolerance by exuding malate and GABA facilitating acidification of the rhizosphere. To test this hypothesis, a series of experiments were carried out using wheat NILs; ET8 (Al+3 tolerant, high expression of TaALMT1) and ES8 (Al+3 sensitive, low expression of TaALMT1) and Xenopus laevis oocytes expressing TaALMT1. Under alkaline conditions, root biomass was significantly higher in the ET8 plants compared to ES8 plants and was inhibited by the application of GABA. Shoot gas exchange also differed between NILs but continuous GABA application to roots interfered with shoot gas exchange. In alkaline conditions, a higher concentration of both malate and GABA was found in root exudates from root apices and whole seedling roots with high TaALMT1 expression which appears to decrease the rhizosphere pH more so in ET8 compared with ES8. Xenopus laevis oocytes expressing TaALMT1 also acidified an alkaline media more rapidly than controls corresponding to higher GABA efflux. TaALMT1 expression did not change under alkaline conditions but key genes involved in GABA turnover changed in accord with a high rate of GABA synthesis in ET8. It is concluded that TaALMT1 plays a role in alkaline soil tolerance by exuding malate and GABA, possibly coupled to proton efflux, facilitating rhizosphere acidification. To further explore the role of TaALMT1 in alkaline soil tolerance, transgenic Golden Promise barley plants expressing TaALMT1 (TaALMT1-GP) were treated with pH 6 and pH 9 nutrient solutions over 5 weeks of growth. There was no significant effect of TaALMT1 expression on shoot and root growth relative to GP wildtype in alkaline conditions. However, root fresh mass was more sensitive to pH for TaALMT1-GP with a significantly larger root fresh mass at pH 9 compared with pH 6. GABA application significantly reduced both root and shoot growth independently of TaALMT1 expression. Malate and GABA efflux was higher in TaALMT1-GP plants than for GP plants at pH 9, however, the opposite was the case at pH 6. GABA application affected malate efflux with different effects between TaALMT-GP and GP. Malate efflux from root apices over 1 h was not significantly different between TaALMT1-GP and GP and both genotypes increased malate efflux at high pH. However, GABA efflux was significantly higher in TaALMT1-GP than GP at pH 9 in buffered solution. It is concluded that the expression of TaALMT1 may be interfering with the endogenous systems that allow barely to tolerate alkaline soils and that future experiments will require the use of null segregants as the appropriate controls rather than wildtype (GP) background. Preliminary experiments were also undertaken to test the effects of externally applied sodium aluminate, calcium, GABA and muscimol, and selected hormones using wheat (ET8 and ES8 NILs) and Barley (TaALMT1-GP and GP, aluminate only) at alkaline pH. Sodium aluminate treatment significantly increased malate and GABA efflux above the already elevated level at pH 9 in plants with high expression of TaALMT1, suggestive of TaALMT1 involvement. Root growth was also higher in response to sodium aluminate in both ET8 and TaALMT1-GP compared with ES8 and GP respectively. Elevated external calcium significantly increased Al3+-activated malate efflux in ET8 compared with ES8 with an optimum at 3 mM CaCl2. In response to external jasmonic acid (JA) and brassinosteroid (BR) at pH 4.5, ET8 showed a higher Al3+activated malate efflux compared to ES8. However, in contrast to malate, GABA efflux was significantly reduced by BR and JA compared with the Al3+ treatment alone. Root growth was significantly reduced in response to JA plus Al3+ compared with Al3+ alone. However, BR plus Al3+ significantly enhanced root growth compared to Al3+ treatment alone. Overall, it is concluded that: 1) TaALMT1 is not only regulated by GABA but also mediates its transport, which is a general feature of ALMTs. 2) TaALMT1 plays a role in alkaline soil tolerance by exuding malate and GABA and facilitating rhizosphere acidification. 3) External application of high concentrations of GABA (10 mM) to roots results in inhibited root growth and alters leaf gas exchange possibly by interactions with other ALMTs. In addition, the following preliminary conclusions are subject to carrying out experiments with TaALMT1 expressed in heterologous systems: 1) TaALMT1 might be calcium sensitive. 2) TaALMT1 may play a role in aluminium tolerance in alkaline conditions. 3) There may be complicated hormonal control over TaALMT1 activity and selectivity.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2018

Soil reaction is the amount of acids (acidity) or bases (alkalinity) present in a soil and is indicated by a term called “pH”. By definition, pH is the logarithm of the reciprocal of the hydrogen ion (H+) concentration, or When a number has a smaller superscript number with it, the number is raised to that power which is called the “logarithm.” Raising a number to a power means multiplying that number by itself the number of times indicated by the superscript. . . . Examples: 102 means 10 x 10 = 100; 103 means 10 x 10 x 10 = 1,000. The logarithm (log) is 2 for the first example and 3 for the second. . . . Logarithms are used as these are more convenient in expressing the amount of hydrogen ions present. Under neutral solutions the pH is 7.0. Any pH that is less than 7 is acid and any pH above is alkaline. When changing from a pH of 7 to a pH of 6, the H ion concentration increases ten times, and when going from a pH of 7 to a pH of 5, the H ion concentration increases 100 times because pH uses a geometric scale and not an arithmetic scale. Thus, pH changes by steps of ten times the next adjacent number. The logarithmic scale used for pH is the same type, but opposite in direction, as that used to measure earthquakes. For each larger number of earthquake, the severity increases ten times; for each smaller number of pH, the acidity increases ten times. Some plants can tolerate very low pH (4.5) and others can withstand a pH of 8.3, but the optimum range for growth of most plants and microbes is between 6 and 7. Availability of most nutrients is affected by pH changes. Charts have been constructed to show this relationship. On these charts the pH at which most nutrients are readily available is from 6 to 7. At extremes of pH, availability of nutrients to plants often is reduced considerably.