Gypsum endemics accumulate excess nutrients in leaves as a potential constitutive strategy to grow in grazed extreme soils

Abstract

Extreme soils often have mineral nutrient imbalances compared to plant nutritional requirements and co‐occur in open areas where grazers thrive. Thus, plants must respond to both constraints, which can affect nutrient concentrations in all plant organs. Gypsum soil provides an excellent model system to study adaptations to extreme soils under current grazing practices as it harbours two groups of plant species that differ in their tolerance to gypsum soils and foliar composition. However, nutrient concentrations in organs other than leaves, and their individual responses to simulated herbivory, are still unknown in gypsum plants. We studied plant biomass, root mass ratio and nutrient partitioning among different organs (leaves, stems, coarse roots, fine roots) in five gypsum endemics and five generalists cultivated in gypsum and calcareous soils and subjected to different levels of simulated browsing. Gypsum endemics tended to have higher elemental concentration in leaves, stems and coarse roots than generalist species in both soil types, whereas both groups tended to show similar high concentrations in fine roots. This behaviour was especially clear with sulphur (S), which is found in excess in gypsum soils, and which endemics accumulated in leaves as sulphate (>50% of S). Moreover, plants subjected to clipping, regardless of their affinity to gypsum, were unable to compensate for biomass losses and showed similar elemental composition to unclipped plants. The accumulation of excess mineral nutrients by endemic species in aboveground organs may be a constitutive nutritional strategy in extreme soils and is potentially playing an anti‐herbivore role in grazed gypsum outcrops.

A Data-driven Approach for Generating Leaf Tissue Nutrient Interpretation Ranges for Greenhouse Lettuce

“…Each element was modeled independently and outliers that were extremely excessive (greater than what is biologically feasible or a significant break in the population) of any other samples were removed before further analysis. Data were analyzed by fitting Normal, Gamma, and Weibull distributions (Cera et al 2022;Mhango et al 2021;Slaton et al 2021;Weibull 1951). Corresponding P values were calculated based on the Shapiro-Wilk test for normality for the Normal and Gamma distributions, and the Kolmogorov-Smirnov test was used for the Weibull distribution.…”

“…Most data tend to be skewed, which makes the Normal distribution curve less suitable. Two models that account for possible skewness in distribution curves are Gamma and Weibull (Cera et al 2022;Mhango et al 2021;Slaton et al 2021;Weibull 1951). The evaluation of all three models is necessary to determine the one that most accurately depicts the data.…”

Nutritional strategy underlying plant specialization to gypsum soils

“…Accordingly, gypsophiles display higher foliar S and Mg (and marginally higher Ca) and lower K concentrations than gypsovags ( Palacio et al 2007 , 2022 ). The increased accumulation of S and Mg of gypsophiles also occurs in stems and coarse roots, although both groups show similar concentrations in fine roots ( Cera et al 2022 a ). Gypsophiles are hence leaf accumulators, whereas generalist gypsovag species seem to exclude S, Mg and Ca uptake at the fine root level, as an avoidance strategy to gypsum.…”

“…As Ca and S accumulators ( Merlo et al 2019 ), gypsophiles primarily store S as sulphate in leaves ( Cera et al 2022 a ). Sulphate appears to be stored in the vacuole ( Abdallah et al 2010 ) in a saturated solution with Ca, and not in calcium sulphate crystals, as described in other papers (i.e.…”

“…Thus, these species have pre-adaptive physiological mechanisms to tolerate excess Ca in their cells ( White and Broadley 2003 ). However, they produced less biomass when growing on gypsum than on calcareous soil (without gypsum) in a common garden experiment, while gypsophiles produced similar biomass ( Cera et al 2022 a ). Hence, it seems that adaptations to establish and survive on limestone and marble soils should convey preadaptation to establish, survive and complete the life cycle on gypsum soils ( Cera et al 2021 b ), but not to achieve optimal performance.…”