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

Abstract

The aim of the present study was to evaluate the morphological and physiological responses of P. maritima plants from five geographically isolated sites growing in habitats with different conditions to different substrate moisture levels in controlled conditions. Plants were produced from seed and cultivated in a greenhouse at four relatively constant soil moisture regimes: at 25, 50, and 75% soil water content and in soil flooded 3 cm above the surface (80% F). The two morphological traits that varied most strikingly among P. maritima accessions were the number of flower stalks and the number of leaves. Only plants from two accessions uniformly produced generative structures, and allocation to flowering was suppressed by both low moisture and flooding. Optimum shoot biomass accumulation for all accessions was at 50 and 75% soil moisture. The Performance Index Total was the most sensitive among the measured photosynthesis-related parameters, and it tended to decrease with an increase in soil water content for all P. maritima accessions. The initial hypothesis-that plants from relatively dry habitats will have a higher tolerance against low soil water levels, but plants from relatively wet habitats will have a higher tolerance against waterlogged or flooded soil-was not proven. The existence of three ecotypes of P. maritima within the five accessions from geographically isolated subpopulations on the eastern coast of the Baltic Sea at the level of morphological responses to soil water content can be proposed. P. maritima plants can be characterized as extremely tolerant to soil waterlogging and highly tolerant to soil flooding and low soil water content.

Keywords: Plantago maritima; chlorophyll; chlorophyll a fluorescence; coastal habitats; ion accumulation; osmotic adjustment; soil flooding; soil water content; waterlogging.

Figure 1

Map of the eastern Baltic Sea region indicating sites for collection of different accessions of Plantago maritima in Estonia. Kihnu, Hiiumaa, and Saaremaa are Estonian islands.

Figure 2

Effects of soil moisture and flooding (F) on the number of flower stalks of Plantago maritima plants from different accessions. Data are means ± SE from five replicates. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 3

Effects of soil moisture and flooding (F) on the number of leaves of Plantago maritima plants from different accessions. Data are means ± SE from five replicates. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 4

Effects of soil moisture and flooding (F) on the dry mass of shoots of Plantago maritima plants from different accessions. Data are means ± SE from five replicates. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 5

Effects of soil moisture and flooding (F) on the dry mass of roots of Plantago maritima plants from different accessions. Data are means ± SE from five replicates. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 6

Effects of soil moisture and flooding (F) on water content in middle leaves of Plantago maritima plants from different accessions. Data are means ± SE from five replicates. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 7

Effects of soil moisture and flooding (F) on water content in old leaves of Plantago maritima plants from different accessions. Data are means ± SE from five replicates. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 8

Generated heat map and cluster analysis of the effect of soil moisture and flooding on morphological parameters in Plantago maritima plants from different accessions. Hierarchical clusters were generated via the average linkage method with correlation distance; color scale shows relative intensity of normalized parameter values. DM, dry mass; FS, flower stalks; H₂O, water content; L, leaves; ML, middle leaves; n, number; OL, old leaves; R, roots. The numbers 25, 50, 75, and 80 indicate soil water content (%).

Figure 9

Effects of soil moisture and flooding (F) on chlorophyll concentration in middle leaves of Plantago maritima plants from different accessions. Data are means ± SE from five replicates, with two measurements each. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 10

Effects of soil moisture and flooding (F) on chlorophyll a fluorescence parameter F_v/F_m in middle leaves of Plantago maritima plants from different accessions. Data are means ± SE from five replicates, with two measurements each. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 11

Effects of soil moisture and flooding (F) on chlorophyll a fluorescence parameter F_v/F₀ in middle leaves of Plantago maritima plants from different accessions. Data are means ± SE from five replicates, with two measurements each. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.

Figure 12

Effects of soil moisture and flooding (F) on chlorophyll a fluorescence parameter Performance Index Total in middle leaves of Plantago maritima plants from different accessions. Data are means ± SE from five replicates, with two measurements each. Different letters indicate statistically significant differences according to the Tukey HSD test (p < 0.05) within the particular accession.