Ecophysiology of Endangered Plant Species Saussurea esthonica: Effect of Mineral Nutrient Availability and Soil Moisture

Abstract

Saussurea esthonica is an endangered plant species typical for wet inland habitats such as calcareous fens. Due to its limited population size and distribution, non-invasive sampling of is important in the research of S. esthonica. The aim of the present study was to assess the effect of mineral nutrient availability and substrate moisture on the growth, physiological status, and mineral nutrition of S. esthonica. The non-destructive measurement of physiological parameters was performed in native habitats during three vegetative seasons, followed by two experiments in controlled conditions. Soil at the two Estonian sites had a relatively larger similarity in the composition of plant-available mineral nutrients in comparison to the two Latvian sites. The chlorophyll a fluorescence parameter Performance Index correlated with the total precipitation in the respective month before measurement, but no significant relationship with other environmental variables was found. For mineral nutrient experiments, plants were grown in four substrates with different mineral nutrient composition, resembling that of soil at different S. esthonica sites. Plant growth and physiological indices were significantly affected by the mineral composition of the substrate. Differences in leaf and root mineral nutrient concentrations of S. esthonica plants in part reflected differences in substrate mineral concentration. To evaluate the effect of soil moisture on growth and photosynthesis-associated parameters of S. esthonica, plants were cultivated in “Pope+” substrate at four different moisture treatments (dry, normal, wet, and waterlodged). The most intense growth of S. esthonica plants was evident in waterlodged conditions, which decreased with a decrease in soil moisture. The biomass of leaves increased by 106% and that of the roots increased by 72% as soil moisture increased from dry to normal. For waterlodged plants, leaf biomass increased by 263% and root biomass increased by 566%, in comparison to that for plants cultivated in dry substrate. Substrate drying had a more negative effect on the growth of S. esthonica plants in comparison to that of waterlodging, and this can be directly linked to prevalent hydrological conditions of an alkaline fen habitat native to the species. Therefore, the preservation of the natural water regime in natural habitats is critical to the conservation of the species.

Comparison of Growth and Physiological Effects of Soil Moisture Regime on Plantago maritima Plants from Geographically Isolated Sites on the Eastern Coast of the Baltic Sea

“…However, as the optimum growth of P. maritima plants was at 50–75% soil moisture and the highest values of the Performance Index Total were at 25% soil moisture, this indicates that this parameter cannot be used as the sole indicator of the physiological status of plants. A similar discrepancy between fluorescence indicators and biomass production under the influence of various factors, including soil moisture, has also been shown in other studies [ 48 ]. From a physiological point of view, it has been argued that photosynthesis and the expansive growth of plants under different water availability situations are independently controlled [ 30 ].…”

“…Another characteristic species of salinity- and flooding-affected coastal habitats, Trifolium fragiferum , showed signs of metabolic disturbance even after several weeks of flooding, such as leaf chlorosis, accompanied by a severe reduction in plant growth [ 47 ]. Saussurea esthonica plants, typical for calcareous fens, had maximum growth and development in waterlogged conditions but showed symptoms of metabolic disorder in the form of purple regions between main leaf veins (after four weeks of waterlogging) and chlorotic lesions (after six weeks of waterlogging) [ 48 ].…”

Coastal Wetland Species Rumex hydrolapathum: Tolerance against Flooding, Salinity, and Heavy Metals for Its Potential Use in Phytoremediation and Environmental Restoration Technologies

“…It has been shown previously that the chlorophyll a fluorescence parameter Performance Index Total is an extremely sensitive indicator for suboptimal changes in environmental conditions [33]. With respect to soil moisture, for alkaline fen species Saussurea esthonica plants with optimum growth in high soil moisture conditions, increased substrate moisture resulted in a significantly increased Performance Index [28]. Usually chlorophyll a fluorescence parameters decrease in salt-sensitive plants as a result of NaCl treatment, as shown for Eruca sativa [34], Boehmeria nivea [35], and Medicago truncatula [36].…”

“…It is usually expected that plant species native to permanently wet habitats will have higher tolerance against soil waterlogging than soil drying when cultivated in controlled conditions. For example, Saussurea esthonica, a rare species of Compositae found only in wet inland alkaline fen habitats, showed the most intense growth in waterlogged soil [28]. Also, in natural conditions of dune slacks, experimentally assessed tolerance of waterlogging and submergence for different species results in particular zonation patterns of these species [29].…”