Responses to Mg/Ca balance in an Iranian serpentine endemic plant, Cleome heratensis (Capparaceae) and a related non-serpentine species, C. foliolosa

Abstract

A soil Ca/Mg quotient greater than unity is generally considered necessary for normal plant growth but some serpentine plants are adapted to much lower Ca/Mg quotients, resulting from a major cation imbalance in their substrata. In order to investigate the growth and tolerance responses of serpentine and non-serpentine species to varied Ca/Mg quotients, controlled nutrient solution experiments were performed using an a newly reported Iranian endemic serpentine plant, Cleome heratensis Bunge et Bien. Ex Boiss. and a related non-serpentine species Cleome foliolosa DC. and a Eurasian Ni-hyperaccumulating species Alyssum murale Waldst. and Kit. Seedlings were grown in modified Hoagland's solutions with varying Ca and Mg concentrations (0.2-2.5 and 0.5-10 mM, respectively) in a fully factorial randomised block design. The yields of the two serpentine plants increased significantly as Mg concentrations in the nutrient solution were increased from 0.5 to 4 mM but decreased in the 10 mM Mg treatment. For C. foliolosa yields decreased significantly from 0.5 to 10 mM Mg, indicating the sensitivity of this non-serpentine plant, and the relative tolerance of the serpentine plants to extremely high levels of Mg. Shoot and root Mg and Ca concentrations in C. heratensis and A. murale were higher than those in C. foliolosa in the low and moderate Mg treatments, supporting the view that many serpentine plants have a relatively high requirement for Mg. Maximum Mg concentrations were found in the roots of C. heratensis. Yields of C. heratensis and A. murale did not change significantly as Ca levels in nutrient solution increased from 0.2 to 2.5 mM Ca, However the yield of C. foliolosa increased significantly from 0.2 to 1.5 mM Ca, indicating sensitivity in this non-serpentine plant and tolerance of the two serpentine plants to low levels of Ca correlated with tissue Ca concentrations, probably because of a greater ability for Ca uptake at low-Ca availability. Calcium deficiency in the low-Ca treatments could be a reason for reduced yield in the non-serpentine plants.

Evidence for Cross-Tolerance to Nutrient Deficiency in Three Disjunct Populations of Arabidopsis lyrata ssp. lyrata in Response to Substrate Calcium to Magnesium Ratio

“…There are particularly low levels of diversity at these loci in the serpentine populations, which is consistent with strong purifying selection against gene flow at these loci with important function in Ca ion transport in the extreme serpentine environment [42], [60]. Maintaining as high of an internal Ca to Mg ratio as possible is favorable to plant function [2]–[3] and could be particularly advantageous in serpentine soils where Ca concentrations are limiting and Mg concentration may be toxic [35], [39]–[40]. Since seeds were field collected, maternal effects could also have played a role in the differences among populations that we observed, particularly the differences in seed germination and early seedling growth [70].…”

“…The first group of seeds (Dover) was collected from plants growing on the Perry Preserve in the Dover Plains region of New York (41.4351° N, 73.3345° W), on calcareous limestone sand with high levels of Ca and low levels of Mg [46]–[47]. The second group of seeds (Pilot) was collected from a serpentine soil from the Pilot Serpentine Barrens of Maryland and Pennsylvania (39.4214° N, 76.1123° W), which is characterized by high levels of Mg and low levels of Ca and the presence of heavy metals such as nickel and chromium [2]–[3]. The third group of seeds (Jug Bay) was collected from the Jug Bay Wetlands Sanctuary population [48] (38.7847° N, 76.7017° W), which grows on a sandy loam soil without extreme Ca or Mg concentrations.…”

“…In addition, some plants may have as yet unknown tolerance mechanisms that counteract the toxic effects of high Mg without the need for Mg exclusion [24]. Other species have increased or more efficient Ca uptake [2]–[3], [7], [9], [15], [22], [25]. Due to this diverse array of responses to Ca to Mg ratio, it is difficult to make generalizations about plant adaptations to variations in soil Ca and Mg content [26].…”

MCA1 and MCA2 That Mediate Ca2+ Uptake Have Distinct and Overlapping Roles in Arabidopsis

“…In this context, it is possible that the phenotype of the mca1-null mca2-null mutant is due to the deficiency of Ca 2+ influx to the cytoplasm, resulting in low Ca :Mg 2+ ratios, which is thought to be a main reason for the growth defect in serpentine soils derived from the weathering of ultramafic rocks and characterized by the presence of excessive Mg, high levels of heavy metals, and low levels of important plant nutrients, including Ca. Studies of serpentinetolerant and serpentine-intolerant plant species suggested that the adaptation to serpentine soils is mediated by unknown genetic elements (Brady et al, 2005;Asemaneh et al, 2007). To explore elements involved in tolerance to soil with low Ca 2+ :Mg 2+ ratios, a genetic approach using Arabidopsis has been performed and has isolated the cax1 mutant described above (Bradshaw, 2005).…”

Inducing Ni sensitivity in the Ni hyperaccumulator plant Alyssum inflatum Nyárády (Brassicaceae) by transforming with CAX1, a vacuolar membrane calcium transporter

“…Plants growing on serpentine soils have a range of strategies to deal with the disproportionately low soil Ca:Mg ratio (Palm et al 2012;Palm and Van Volkenburgh 2014). For example, some plants have a requirement for and tolerance of high Mg (Main 1981;Johnston and Proctor 1984;Asemaneh et al 2007) while others have an enhanced ability for Ca uptake (Rajakaruna et al 2003;Ghasemi and Ghaderian 2009;Veatch Blohm et al 2013) or the ability to exclude Mg (O'Dell and Claassen 2006;Sambatti and Rice 2007), enabling them to survive the relatively high Mg concentrations typical of serpentine soils. The discovery of genes responsible for maintenance of plant Ca:Mg homeostasis (Li et al 2001;Cheng et al 2003;Turner et al 2008Turner et al , 2010Tang et al 2015) is now making it possible to explore the genetic basis for tolerance of low soil Ca:Mg, a key factor associated with serpentine tolerance.…”