Over three million hectares of salt-affected soils characterized with high salinity and sodicity caused serious land degradation in Songnen Plain, northeast China. Soil salinity–sodicity heterogeneous distribution under microtopography is usually influenced by several environmental factors. The side direction movement of soil water driven by water from depression is the key factor that aggravates the soil salinization under microtopography in dry condition. In this study, the differences in surface soil salinity–sodicity (0–10 cm) between dry year and wet year were compared, and the relationship between soil salinity–sodicity and environment factors such as ground elevation, surface ponding time, surface ponding depth, and soil moisture at four soil layers (0–10, 10–30, 30–60, and 60–100 cm) were analyzed using redundancy analysis (RDA) and simple correlation analysis (Pearson analysis) for two different hydrological years. Analyzed soil salinity–sodicity parameters include soluble ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, CO₃²⁻, HCO₃⁻, Cl⁻ and SO₄²⁻), salt content (SC), electrical conductivity (EC), sodium adsorption ratio (SAR), and pH. Results showed that values of SAR, Cl⁻, and SO₄²⁻ were significantly higher in dry year than in wet year, while Ca²⁺, Mg²⁺, K⁺, and HCO₃⁻ showed the opposite results. Values of Na⁺, CO₃²⁻, and EC were significantly higher at higher ground elevation gradient (20–40 cm) in dry year than wet year. Redundancy analysis indicated that spatial distributions and variations of salinity and sodicity in surface soil layer were related with environmental factors of ponding depth, ponding time and ground elevation in wet year, and they were related with ground elevation, ponding depth, ponding time, and soil moisture at 30–60 and 60–100 cm soil layer in dry year. Ponding depth and ground elevation rank first and second as the influential factors of the spatial distribution and variation of soil salinity–sodicity in wet year. However in dry year, primary and secondary influential factors are ground elevation and soil moisture at 60–100 cm soil layer.

Introduction: Soil salinity–alkalinity has emerged as a global problem affecting many ecosystems, including grassland. Plants evolve into different ecotypes to adapt to various environments. Leymus chinensis widely distributed in the eastern Eurasian steppe, has evolved into two main ecotypes: yellow–green(YG) and gray–green (GG). Studies on the adaption mechanisms of both ecotypes in response to saline–alkaline stress are limited.Methods: In this study, the growth and physiological traits of ecotypes YG and GG in soils with different salinity–alkalinity levels—severe saline–alkaline soil (SS), moderate saline–alkaline soil (MS), and light saline–alkaline soil (LS)—were studied. After exposure to saline–alkaline stress for 15 months, the L. chinensis ecotypes exhibited significant differences in the growth characteristics.Results: The specific leaf area, individual tiller biomass, net photosynthetic rate, and potassium content of the two ecotypes under MS conditions were significantly higher than or similar to those under LS conditions. This indicates that L. chinensis showed a certain degree of tolerance to saline–alkaline environments under MS conditions. Saline–alkaline stress increased the tillers by 56% in GG and reduced them by 26% in YG, and did not alter the SLA and the number of individual tiller leaves of GG but reduced that of YG. Moreover, with increasing levels of saline–alkaline stress, ecotype GG exhibited an increase in net photosynthetic rate (Pn), while ecotype YG showed insignificant changes. Under SS, GG exhibited higher Pn and chlorophyll content than YG. Additionally, with the increase in the saline–alkaline stress level, the Na⁺ content increased, but GG exhibited a significantly lower Na⁺ content than YG. Conversely, the K⁺ and Ca²⁺ contents and the K⁺/Na⁺ and Ca²⁺/Na⁺ ratios decreased, but GG exhibited higher values than YG.Discussion: GG reduced Na⁺ by absorption by increasing tillers. Additionally, GG absorbed more K⁺ and Ca²⁺ ions, thereby maintaining higher K⁺/Na⁺ and Ca²⁺/Na⁺ ratios than YG under saline–alkaline stress. These adaptive strategies enable ecotype GG to grow and maintain normal physiological functions under high saline–alkaline stress. The findings of this study hold practical significance for enhancing the economic and ecological value of saline–alkaline grasslands.

Variations in the degree of seed dormancy expressed among conspecific populations provide a basis for improving understanding of the mechanisms controlling species persistence, especially in fire-prone ecosystems. We investigated seed germination of 12 Anigozanthos flavidus populations in response to various fire-related cues that included exposure to karrikinolide, glyceronitrile and smoke water at five temperatures, and the effects of heat shock and its interaction with glyceronitrile. Seeds from populations with deep-degree dormancy (DD) and light-degree dormancy (LD) were subjected to 0–8 months of after-ripening, and the viability of the ungerminated seeds was tested. The degree of seed dormancy and responses to fire-related cues were highly variable among populations. Glyceronitrile and smoke water significantly improved germination in 12 and 8 populations respectively. Heat significantly enhanced germination in all populations, but was less effective when combined with glyceronitrile. After-ripening for 3 months increased germination, whereas ≥4 months led to secondary dormancy or loss of viability. Loss of viability was greater for DD than for LD seeds. Interpopulation variations in the degree of seed dormancy, seed germination requirements for fire-related cues and germination viability in response to after-ripening in A. flavidus contribute to persistence in the variable and unpredictable Mediterranean environment.

Seed dormancy status regulates the response of seeds to environmental cues that can trigger germination. Anigozanthos flavidus (Haemodoraceae) produces seeds with morphophysiological dormancy (MPD) that are known to germinate in response to smoke, but embryo growth dynamics and germination traits in response to temperatures and after-ripening have not been well characterized. Seeds of A. flavidus, after-ripened for 28 months at 15 °C/15 % relative humidity, were incubated on water agar, water agar containing 1 μM karrikinolide (KAR₁) or 50 μM glyceronitrile at 5, 10, 15, 20, 25, 20/10 and 25/15 °C for 28 days. After incubation at 5, 10 and 25 °C for 28 days, seeds were transferred to 15 °C for another 28 days. Embryo growth dynamics were tested at 5, 10, 15 and 25 °C. Results demonstrated that fresh seeds of A. flavidus had MPD and the physiological dormancy (PD) component could be broken by either glyceronitrile or dry after-ripening. After-ripened seeds germinated to ≥80 % at 15–20 °C while no additional benefit of germination was observed in the presence of the KAR₁ or glyceronitrile. Embryo length significantly increased at 10 °C, and only slightly increased at 5 °C, while growth did not occur at 25 °C. When un-germinated seeds were moved from 5–10 °C to 15 °C for a further 28 days, germination increased from 0 to >80 % in significantly less time indicating that cold stratification may play a key role in the germination process during winter and early spring in A. flavidus. The lower germination (<50 %) of seeds moved from 25 to 15 °C was produced by the induction of secondary dormancy. Induction of secondary dormancy in seeds exposed to warm stratification, a first report for Anigozanthos species, suggests that cycling of PD may be an important mechanism of controlling germination timing in the field.