Early Stress Resilience in Turfgrass: Comparative Germination and Seedling Responses of Lolium perenne L. and Poa pratensis L. Under Osmotic and Salt Stress

Abstract

Seed germination and early seedling development represent critical stages for turfgrass establishment under increasingly frequent drought and salinity constraints. This study evaluated the germination performance of three cultivars of Lolium perenne L. and three cultivars of Poa pratensis L. exposed to iso-osmotic drought stress simulated with polyethylene glycol (PEG) and salt stress induced by NaCl. Germination percentage, mean germination time, germination index, seedling vigor index, and radicle and plumule elongation were quantified, and post-stress recovery tests assessed the reversibility of stress effects. Osmotic restriction imposed by PEG caused stronger inhibition of germination and seedling growth than NaCl at equivalent water potentials. L. perenne showed higher overall tolerance, maintaining faster emergence and greater seedling vigor across treatments, while P. pratensis was more sensitive but exhibited substantial germination recovery after stress removal. Cultivar-dependent variation was evident in both species, and multivariate analyses consistently differentiated tolerant and sensitive genotypes. The contrasting germination strategies, with rapid activation in L. perenne and delayed, recovery-oriented germination in P. pratensis, highlight species-specific adaptive responses to water and salt stress. These findings provide a physiological basis for selecting resilient turfgrass cultivars suited to drought- and salinity-prone environments, contributing to sustainable turfgrass establishment and management.

1. Introduction

Grasses (family Poaceae) are among the most widespread and ecologically important plant groups, occupying nearly every terrestrial biome. Morphologically characterized by cylindrical culms, basal sheaths, and spikelet-type inflorescences, they display remarkable adaptability to contrasting environments [1,2]. This ecological plasticity explains their dominance in natural grasslands and their pivotal role in soil stabilization, erosion control, and landscape restoration [3,4]. Their rapid germination and early growth enable efficient ground coverage, reducing wind and water erosion while promoting water infiltration and nutrient retention through dense fibrous root systems [5,6].

Beyond their ecological significance, grasses also hold great economic and aesthetic value in urban and peri-urban landscapes. The expansion of cities and the increasing emphasis on sustainable green infrastructure have reinforced the importance of turfgrass in lawns, recreational areas, and urban parks [7,8,9,10]. Turfgrasses contribute to environmental quality by regulating the urban microclimate, reducing dust and noise, and controlling runoff [11,12]. Their low maintenance cost and high resilience under anthropogenic stress make them essential elements of green urban systems and ecological restoration projects [13,14].

However, turfgrass species are continuously exposed to biotic and abiotic constraints due to their perennial nature and the environmental variability characteristic of open landscapes. Drought, salinity, heat, cold, and waterlogging are among the most severe abiotic stressors, often impairing germination, seedling development, and photosynthetic processes [15,16,17,18]. Because germination and early seedling establishment are the most sensitive developmental stages, understanding the physiological responses of turfgrass species to these stresses is essential for improving establishment success and management under changing climatic conditions [19,20].

Within the Poaceae, the genera Lolium and Poa are of particular relevance to temperate-region turf systems. Lolium includes approximately ten accepted species, primarily native to Europe, Asia, and North Africa, many of which have been introduced globally [21]. Lolium perenne L. (perennial ryegrass) is especially valued for its rapid establishment, fine texture, and high visual quality, making it a dominant choice for sports fields, lawns, and temporary grasslands [22,23]. However, its relatively shallow root system could limit performance in prolonged drought and saline conditions [24,25]. By contrast, the genus Poa includes more than 500 species with broad ecological amplitude [26]. Among them, Poa pratensis L. (Kentucky bluegrass) is a key cool-season turfgrass due to its rhizomatous growth, cold tolerance, and persistence under soil compaction [27,28]. Its slower establishment rate compared with L. perenne is offset by its long-term durability and capacity for vegetative self-repair [29,30]. Even though clear differences exist among turfgrass species and cultivars regarding seed morphology, the relationship between morphological traits and germination vigor is often weak [31,32]. Nevertheless, identifying and selecting genotypes with rapid germination could facilitate a faster and more uniform turf establishment [33].

The successful establishment of turfgrass species depends largely on the ability of seeds to germinate and seedlings to develop under water and salt stress [34,35]. Salinity and drought are among the most widespread abiotic constraints limiting turf performance, particularly in urban areas where irrigation water may contain high salt levels [36,37]. Both stressors affect osmotic balance, enzymatic activity, and hormone regulation during germination, leading to delayed or reduced emergence and weaker seedling growth [17,20,38]. Consequently, identifying cultivars that maintain germination and early vigor under adverse conditions is a prerequisite for sustainable turf management and ecological resilience [39].

In favorable climatic regions, including Romania, L. perenne and P. pratensis are widely used for landscaping lawns, sports fields and urban green spaces [40,41]. Although salinization patterns vary across regions, chloride-based salinity is the most widespread form reported in urban, peri-urban and irrigated soils in Central and Eastern Europe, including Romania. Therefore, NaCl was selected as the representative salt for simulating salinity stress in this study. Selecting appropriate cultivars with improved tolerance to drought and salinity can substantially reduce irrigation and maintenance costs while preserving aesthetic and functional quality [42]. Understanding their early responses to osmotic and salt stress provides essential information for both practical turf management and breeding programs targeting stress adaptation [34,35,43].

Given their complementary ecological and functional traits, rapid establishment and visual quality in L. perenne versus persistence and self-repair in P. pratensis, these species represent an ideal model for comparative evaluation under abiotic stress. This study, therefore, aimed to assess the germination and early seedling responses of selected cultivars of L. perenne and P. pratensis under simulated drought (PEG-induced osmotic stress) and salt stress (NaCl) conditions. The specific objectives were to (i) quantify the effects of iso-osmotic drought and salt treatments on germination parameters and seedling vigor, (ii) compare species- and cultivar-specific tolerance patterns, and (iii) identify the most resilient cultivars suitable for turfgrass establishment and restoration under saline or drought-prone conditions.

Overall, these comparative evaluations are relevant not only for identifying tolerant cultivars but also for understanding the ecological strategies underlying germination behavior under stress. In germination ecology, two contrasting adaptive patterns are commonly recognized: a ‘risk strategy’, characterized by rapid germination even under suboptimal conditions, and an ‘avoidance strategy’, in which seeds delay germination during stress and resume growth once conditions improve. These concepts provide a useful framework for interpreting potential species-specific responses in turfgrasses and support the rationale of this study.

2. Materials and Methods

2.1. Experimental Design and Plant Material

The experiment was conducted to evaluate the germination behavior and early seedling performance of six turfgrass cultivars, three belonging to Lolium perenne L. and three to Poa pratensis L., under controlled osmotic and salinity stress conditions.

The selected L. perenne cultivars (‘Allstarter’, ‘Columbine’, and ‘Esquire’) and P. pratensis cultivars (‘Dakisha’, ‘Sombrero’, and ‘Conni’) are adequate for high-quality turf applications, including sports fields, ornamental lawns, and public green spaces. The six cultivars were selected because they are widely commercialized and commonly used in professional turf mixtures in Central and Southern Europe. They represent contrasting germination behaviors and stress-adaptation profiles documented by breeders and suppliers, making them suitable for evaluating intraspecific variability under drought and salinity. Seed lots were obtained from certified commercial distributors, in original sealed packages, ensuring cultivar authenticity and viability.

2.2. Germination Tests Under Osmotic and Salinity Stress

Germination tests were performed using sterilized Petri dishes (90 mm diameter), each containing 25 seeds placed on two layers of filter paper moistened with 5 mL of the respective treatment solution. Petri dishes and forceps were sterilized by immersion in 70% ethanol for 10 min and air-dried under a laminar flow hood. Seeds were not surface-sterilized, consistent with ISTA recommendations for turfgrass species. The dishes were sealed with Parafilm to prevent evaporation and incubated under controlled laboratory conditions (25 ± 1 °C, 12 h photoperiod).

Osmotic stress was simulated using polyethylene glycol (PEG 6000) at water potentials of −0.22, −0.44, and −0.88 MPa, calculated according to the equation proposed by Ben-Gal et al. [44]. Salt stress was induced with sodium chloride (NaCl) solutions at 50, 100, and 200 mM, corresponding approximately to the osmotic potentials of the PEG treatments, while also imposing ionic stress due to Na⁺ and Cl⁻ accumulation. Distilled water served as the control treatment.

Each cultivar × treatment combination was replicated four times (n = 4), with 25 seeds per replicate. Germination was monitored daily, and a seed was considered germinated when the radicle reached a length of at least 2 mm. Although ISTA [45] and AOSA [46] standards recommend 14 days for L. perenne and 21 days for P. pratensis, in this study, germination dynamics were evaluated over a standardized 21-day period for both species to ensure consistency and comparability among treatments [47]. This duration is widely used in stress-germination research when multiple species and cultivars are assessed under identical conditions, allowing a synchronized evaluation of germination progress and stress effects [47].

The following parameters were recorded to quantify germination dynamics and seed vigor, according to standard procedures [46,48,49].

Germination Percentage (G%)—proportion of seeds that germinated during the test period.

Mean Germination Time (MGT)—average time for germination [50].

Germination Index (GI)—a weighted index integrating germination speed and success [51]:

$$GI=\sum {\displaystyle \frac{G}{T}}$$

(1)

where G is the number of seeds germinated on day T.

Speed of Emergence (SE)—measure of germination rate [52]:

$$SE=\left({\displaystyle \frac{Number of seeds germinated on the first day}{Number of seeds germinated on the last day}}\right)\times 100$$

(2)

First Day of Germination (FDG) and Last Day of Germination (LDG)—used to calculate Total Spread of Germination (TSG = LDG − FDG)—an indicator of germination synchrony.

Seedling Vigor Index (SVI)—integrating germination percentage and mean seedling length [53]:

$$SVI={\displaystyle \frac{Seedling length\times G\%}{100}}$$

(3)

Radicle length and plumule length were measured after 21 days using Digimizer software (MedCalc Software Ltd., Ostend, Belgium) from digital images taken under standardized lighting. The measurements provided an accurate assessment of root–shoot balance and seedling vigor under stress.

2.3. Germination Recovery Assessment

To evaluate post-stress recovery capacity, non-germinated seeds from each treatment were rinsed with distilled water and transferred to new Petri dishes containing only distilled water under optimal germination conditions. Recovery was monitored daily for 21 days, and germinated seeds were recorded as a percentage of the total number of previously ungerminated seeds. This test differentiated between temporary metabolic inhibition and irreversible loss of viability, providing an additional indicator of stress resilience [54].

2.4. Statistical Analysis

All germination parameters expressed as percentages (germination percentage, proportion of normal seedlings) were arcsine square-root transformed prior to analysis to stabilize variances and improve normality. For seedling type data, statistical analysis focused on the proportion of normal seedlings (Category A) in each Petri dish, used as an integrative indicator of germination quality. The remaining abnormal categories (B–G) were reported descriptively to illustrate the pattern of developmental anomalies under stress.

Although PEG and NaCl treatments were applied within the same experimental framework, the two stressors differ in their physiological modes of action (PEG induces mainly osmotic restriction, whereas NaCl combines osmotic and ionic effects). Because the purpose of the study was to characterize tolerance patterns to each stress type independently, statistical analyses were conducted separately for osmotic stress (PEG) and for salt stress (NaCl). This approach avoids conflating the effects of two mechanistically distinct stressors and allows clearer interpretation of cultivar responses.

For the assessment of seedling type (normal vs. abnormal), data from all stress treatments were pooled, as the objective of this analysis was to describe the overall morphological impact of stress regardless of its origin. In contrast, all analyses of germination dynamics and vigor-related indices (G%, MGT, GI, SVI, radicle and plumule length) were performed separately for osmotic and salt stress.

For each species, the transformed proportion of normal seedlings was analyzed using a two-way ANOVA, with cultivar (three levels) and treatment (Control vs. Stress) as fixed factors, including the Cultivar × Treatment interaction. For osmotic stress, the “Stress” category represented the mean response across all PEG treatments; for salt stress, it represented the mean response across all NaCl treatments. When significant effects were detected (p < 0.05), post hoc comparisons between control and stress within each cultivar were performed using Duncan’s Multiple Range Test. Values are reported as mean ± standard deviation (SD). Statistical analyses were conducted using Statgraphics Centurion XVII (Statgraphics Technologies, Inc., The Plains, VA, USA) and IBM SPSS Statistics 26 (IBM Corp., Armonk, NY, USA).

To explore relationships among germination and seedling variables and to identify key traits associated with stress tolerance, multivariate analysis was performed using standardized mean values. Principal Component Analysis (PCA) and dendrograms using PAST software, version 4.17 [55] were used to visualize cultivar differentiation under stress and to identify variables contributing most strongly to variation in tolerance responses [56].

3. Results

3.1. Effects of Salt and Osmotic Stress on Germination and Seedling Traits

In both species, germination progressed steadily over the first 10–14 days, with marked differences among treatments. Under control conditions, all cultivars exhibited rapid and uniform germination, reaching the highest final percentages. Increasing salinity and osmotic stress progressively reduced both the rate and extent of germination. In Lolium perenne, mild stress (50 mM NaCl or −0.22 MPa PEG) caused only slight delays, whereas moderate and severe stress levels substantially slowed daily emergence and reduced final germination (Figure 1). Among the cultivars, ‘Allstarter’ maintained comparatively higher germination under intermediate stress, suggesting greater initial tolerance.

Poa pratensis was more sensitive overall, showing pronounced reductions in daily germination even at moderate stress intensities. Severe PEG (−0.88 MPa) and high salinity (200 mM NaCl) nearly inhibited germination in some cultivars, with ‘Conni’ showing the strongest decline (Figure 2). Despite these differences, the general trend in both grasses indicated a clear dose-dependent inhibition of germination, with osmotic and saline stress affecting both the speed and synchronization of seedling emergence.

Germinants obtained were categorized as either normal or abnormal seedlings (Figure 3). The evaluation of seedling development under controlled and stress conditions revealed distinct responses between the two species and their respective cultivars. The detailed distribution of normal and abnormal seedlings, averaged across all stress treatments, is presented in

Table 1. Percentage of normal and abnormal seedlings in Lolium perenne L. and Poa pratensis L. cultivars under control and stress conditions. Values represent averages across the experiment: control (distilled water), osmotic and saline stress treatments. Statistical analysis was performed on the proportion of normal seedlings (Category A).

Species/ Cultivar	Treatment	Normal and Abnormal Seedlings Category (%) 1
		A 2	B	C	D	E	F	G
L. perenne
Allstarter	Control	96.5 ± 2.8 a	0.0	0.5	2.2	0.0	0.0	0.8
	Osmotic stress	88.3 ± 3.1 b	0.0	1.2	9.7	0.0	0.0	0.8
	Saline stress	95.3 ± 2.7 a	0.0	0.9	3.1	0.0	0.0	0.8
Columbine	Control	92.9 ± 3.4 a	0.0	0.4	6.8	0.0	0.0	0.0
	Osmotic stress	89.3 ± 3.9 b	0.0	0.4	8.6	0.0	0.0	1.7
	Saline stress	92.0 ± 3.0 a	0.0	2.2	5.5	0.0	0.0	0.4
Esquire	Control	95.4 ± 2.8 a	0.0	0.0	4.3	0.0	0.0	0.3
	Osmotic stress	85.9 ± 4.1 b	0.0	0.1	10.1	0.0	0.0	3.9
	Saline stress	91.3 ± 2.7 ab	0.0	0.8	2.4	0.0	0.0	5.4
P. pratensis
Dakisha	Control	84.0 ± 4.1 a	0.0	3.7	12.3	0.0	0.0	0.0
	Osmotic stress	79.6 ± 4.4 b	0.0	0.3	20.1	0.0	0.0	0.0
	Saline stress	80.7 ± 3.7 b	0.0	5.6	13.7	0.0	0.0	0.0
Sombrero	Control	80.4 ± 4.3 a	0.0	1.4	18.2	0.0	0.0	0.0
	Osmotic stress	80.2 ± 4.5 a	0.0	2.8	17.0	0.0	0.0	0.0
	Saline stress	79.7 ± 4.7 a	0.0	2.1	18.2	0.0	0.0	0.0
Conni	Control	84.1 ± 3.6 a	0.0	2.0	13.9	0.0	0.0	0.0
	Osmotic stress	77.5 ± 4.8 c	0.0	4.2	13.3	0.0	0.0	5.0
	Saline stress	80.7 ± 3.3 b	0.0	1.8	17.5	0.0	0.0	0.1

¹ (A) Normal seedlings: well-developed plumule and root system; (B) Abnormal seedlings: weakly developed (overall); (C) Abnormal seedlings: without roots; (D) Abnormal seedlings: single or weak primary root; (E) Abnormal seedlings: weak plumule; (F) Abnormal seedlings: plumule shorter than half the coleoptile length; (G) Abnormal seedlings: weak plumule and poorly developed roots. ² For normal seedlings, the values are mean ± SD. Within each cultivar, means followed by different letters differ significantly between control, osmotic and salt stress treatments (p < 0.05, two-way ANOVA followed by Duncan’s Multiple Range Test, applied to the arcsine-transformed proportion of normal seedlings). Abnormal seedling categories (B–G) are presented descriptively.

.

Following the definitions by Rao et al. [57] regarding normal and abnormal seedlings derived from germinated seeds, the results reveal clear species- and cultivar-dependent effects of osmotic and salt stress on seedling quality. In L. perenne, the proportion of normal seedlings was very high under control conditions (92.9–96.5%) and declined mainly under osmotic stress, with the most notable reductions in ‘Esquire’ (85.9%) and ‘Allstarter’ (88.3%). Salt stress had a limited effect, and both ‘Allstarter’ and ‘Columbine’ maintained values close to their controls. Stress-induced abnormalities occurred predominantly in category D (weak or single primary root), while category G increased especially in ‘Esquire’.

In P. pratensis, the proportion of normal seedlings under control conditions was lower than in L. perenne (80.4–84.1%), and stress effects were generally more pronounced. The largest reductions under osmotic stress were recorded in ‘Conni’ (77.5%) and ‘Dakisha’ (79.6%). By contrast, ‘Sombrero’ showed nearly identical values across treatments (80.4% control; 80.2% osmotic; 79.7% saline), indicating minimal sensitivity at this stage. Abnormalities were dominated by categories C (seedlings without roots) and D, with ‘Conni’ also displaying an increase in category G under osmotic stress.

Overall, L. perenne maintained higher proportions of normal seedlings and fewer severe abnormalities under both stress types, whereas P. pratensis exhibited greater morphological impairment. These patterns indicate a stronger early-stage tolerance in L. perenne and a higher susceptibility of P. pratensis during germination and initial seedling development.

3.2. Species-Specific Responses

3.2.1. Lolium perenne L.

Germination percentage in L. perenne showed a gradual and cultivar-dependent decline as osmotic and salt stress intensified (Figure 4). Under optimal conditions, all cultivars exceeded 90% germination, confirming their high intrinsic viability. PEG treatments caused the strongest inhibition, with marked reductions already at −0.44 MPa and particularly at −0.88 MPa, where germination dropped sharply in all cultivars. By contrast, NaCl produced a milder decline, and even at 200 mM, ‘Allstarter’ and ‘Esquire’ maintained over 70% germination. Among cultivars, ‘Allstarter’ consistently displayed the highest tolerance across treatments, whereas ‘Columbine’ and especially ‘Esquire’ showed more pronounced declines under severe osmotic restriction.

Mean germination time increased progressively as stress intensity rose, revealing a clear delay in germination across all L. perenne cultivars (Figure 5). PEG produced the most pronounced effects, with MGT nearly doubling at −0.88 MPa, compared with the control, particularly in ‘Esquire’, which showed the slowest germination under all osmotic treatments. Salt stress led to more moderate increases in germination time, and at 50–100 mM NaCl, values remained close to those recorded in optimal conditions. Among the cultivars, ‘Allstarter’ maintained the shortest germination times under both stress types, indicating a greater capacity to initiate germination rapidly despite reduced water availability or elevated salinity.

Radicle elongation in L. perenne was strongly restricted by both osmotic and saline treatments, with the magnitude of inhibition increasing proportionally to stress severity (Figure 6). The PEG solutions produced the sharpest declines, particularly at −0.88 MPa, where radicle growth was markedly reduced in all cultivars. Salt exposure resulted in more gradual decreases in root length, especially at 50 and 100 mM NaCl, where seedlings still maintained appreciable elongation. Among the analyzed cultivars, ‘Allstarter’ consistently retained the longest radicles under all stress intensities, whereas ‘Esquire’ showed the highest sensitivity, exhibiting substantial reductions even under moderate PEG levels.

Plumule growth responded similarly to radicle elongation, showing a progressive reduction as stress levels intensified (Figure 7). PEG treatments had the strongest impact, particularly at −0.88 MPa, where plumule development was substantially curtailed in all cultivars. Salinity produced milder decreases, and seedlings exposed to 50 or 100 mM NaCl often maintained plumules of comparable length to the control. Of the three cultivars, ‘Allstarter’ displayed the most stable shoot elongation under both osmotic and saline conditions, whereas ‘Esquire’ again proved the most susceptible, exhibiting pronounced reductions even under moderate stress.

3.2.2. Poa pratensis L.

Germination responses in P. pratensis declined markedly under increasing stress intensity, with the strongest inhibition recorded under PEG treatments (Figure 8). Even the mildest osmotic restriction (−0.22 MPa) reduced germination noticeably in all three cultivars, and at −0.88 MPa, germination was almost completely suppressed, except for ‘Conni’, which retained a small but detectable capacity to germinate. In contrast, salinity produced a more moderate decline: at 200 mM NaCl, both ‘Sombrero’ and ‘Conni’ maintained relatively high germination levels, whereas ‘Dakisha’ showed the steepest reductions across all treatments. These patterns highlight the higher sensitivity of P. pratensis to osmotic limitation compared with salt stress, and underline the superior resilience of the cultivar ‘Conni’.

Mean germination time increased progressively in P. pratensis as stress intensity rose, reflecting a clear delay in seed activation and radicle emergence under both osmotic and saline conditions (Figure 9). PEG treatments produced the strongest effects, particularly at −0.44 and −0.88 MPa, where germination was substantially postponed in all three cultivars. ‘Dakisha’ exhibited the longest germination times under severe osmotic stress, whereas ‘Conni’ maintained the shortest delays across treatments, consistent with its generally higher tolerance. Salinity caused a more moderate increase in MGT, and at 50–100 mM NaCl, germination proceeded relatively close to control dynamics. Overall, the results indicate that water deficit imposed by PEG disrupts germination timing more strongly than salt stress and that ‘Conni’ retains a comparatively rapid germination pattern even under unfavorable conditions.

Radicle elongation in P. pratensis was strongly inhibited by both osmotic and salt stress, with the degree of reduction closely following the severity of the treatments (Figure 10). PEG had the most pronounced impact: even at −0.22 MPa, root growth declined noticeably, and at −0.88 MPa, radicle development was almost completely arrested in all cultivars except ‘Conni’, which retained minimal elongation. Salinity caused a more gradual reduction in root length, and seedlings exposed to 50 or 100 mM NaCl still produced measurable radicles, particularly in ‘Sombrero’ and ‘Conni’. Across all treatments, ‘Conni’ consistently exhibited the longest radicles, whereas ‘Dakisha’ proved the most sensitive, showing sharp decreases in root growth under both stress types. These results emphasize the high vulnerability of early root development to osmotic restriction and the comparatively stronger adaptability of ‘Conni’.

Plumule elongation in P. pratensis declined progressively with increasing stress intensity, mirroring the strong inhibitory effects observed on radicle growth (Figure 11). Osmotic restriction exerted the most severe impact: at −0.44 MPa PEG, shoot development was already markedly reduced, and at −0.88 MPa, no substantial plumule formation occurred in any cultivar except ‘Conni’, which maintained a minimal but detectable elongation. Salt treatments produced a more moderate response, and seedlings of ‘Sombrero’ and ‘Conni’ exposed to 50 or 100 mM NaCl retained considerably longer plumules compared with those under PEG. Across all treatments, ‘Conni’ consistently showed the greatest shoot elongation, whereas ‘Dakisha’ was the most affected. Overall, these patterns confirm the high sensitivity of early shoot growth to limited water availability and highlight the relatively stronger resilience of ‘Conni’ under both osmotic and saline stress.

3.3. Germination Indices Under Osmotic and Salt Stress

A comprehensive summary of the main germination indices considered in this study is provided in the tables in Appendix A, which complement and extend the patterns already illustrated in the figures.

Table A1. Main germination indices of three cultivars of L. perenne (‘Allstarter’—C1, ‘Columbine’—C2, and ‘Esquire’—C3) under control (T1) and increasing levels of osmotic stress (T2–T4), respectively. PEG treatments: T2 = −0.22 MPa, T3 = −0.44 MPa, T4 = −0.88 MPa.

No	Cultivar/ Treatment	GI	SE	FDG	LDG	TSG	SVI
Effect of the interaction between cultivar and treatment
1	C1T1	4.0 a	20.6 c	4.0 d	17.3 c	13.3 a	74.1 a
2	C1T2	2.8 b	32.1 b	6.0 cd	18.3 b	12.3 a	64.9 a
3	C1T3	2.9 b	54.6 a	5.0 d	16.0 d	11.0 ab	38.8 c
4	C1T4	1.3 d	8.4 d	11.0 b	19.3 a	8.3 b	24.7 d
5	C2T1	2.9 b	11.1 d	4.3 d	17.0 c	12.8 a	68.8 a
6	C2T2	2.0 c	25.2 bc	6.0 cd	18.5 b	12.5 a	55.6 b
7	C2T3	1.6 d	17.5 c	5.8 cd	18.5 b	12.8 a	25.1 d
8	C2T4	0.8 e	9.4 d	11.3 b	19.8 a	8.5 b	15.1 e
9	C3T1	2.6 b	9.4 d	5.0 d	19.5 a	14.5 a	77.2 a
10	C3T2	2.1 c	6.1 d	6.3 cd	18.8 ab	12.5 a	68.9 a
11	C3T3	1.6 d	20.9 c	7.5 c	20.0 a	12.5 a	31.3 cd
12	C3T4	0.5 e	14.5 dc	15.3 a	20.0 a	4.8 c	8.6 e
Effect of cultivar
1	Allstart	2.7 A	28.9 A	6.5 B	17.7 B	11.2 A	50.6 A
2	Columbine	1.8 AB	15.8 B	6.8 B	18.4 AB	11.6 A	41.1 B
3	Esquire	1.7 B	12.7 B	8.5 A	19.6 A	11.1 A	46.5 AB
Effect of treatment
1	Control	3.1 A	13.7 B	4.4 C	17.9 B	13.5 A	73.4 A
2	−0.22 MPa	2.3 B	21.1 AB	6.1 B	18.2 AB	12.4 A	63.1 B
3	−0.44 MPa	2.0 C	31.0 A	6.1 B	18.5 AB	12.1 A	31.7 C
4	−0.88 MPa	0.8 D	10.7 B	12.5 A	19.7 A	7.2 B	16.1 D

GI—Germination Index; SE—Speed of Emergence; FDG—First Day of Germination; LDG—Last Day of Germination; TSG—Total Spread of Germination; SVI—Seedling Vigor Index. Different letters indicate significant differences among treatments for interactions C × T, cultivar C and treatment T (Duncan’s MRT, p < 0.05).

shows that osmotic stress progressively reduced all major germination indices in the three L. perenne cultivars. The most severe PEG treatment (−0.88 MPa) caused substantial declines in GI and SVI and clear delays in germination timing (higher FDG and LDG). Although all cultivars followed a similar trend, ‘Allstarter’ maintained relatively better performance at moderate stress levels, whereas ‘Esquire’ was more sensitive, especially in terms of germination spread. Significant cultivar × treatment interactions confirm differential cultivar susceptibility.

As presented in

Table A2. Main germination indices of three cultivars of L. perenne (‘Allstarter’—C1, ‘Columbine’—C2, and ‘Esquire’—C3) under control (T1) and increasing levels of salt stress (T2–T4), respectively. NaCl treatments: T2 = 50 mM, T3 = 100 mM, T4 = 200 mM.

No	Cultivar/ Treatment	GI	SE	FDG	LDG	TSG	SVI
Effect of the interaction between cultivar and treatment
1	C1T1	4.0 a	20.6 a	4.0 e	17.3 a	13.3 ab	74.1 a
2	C1T2	2.7 b	30.6 ab	5.3 cd	12.0 a	6.8 d	58.4 bc
3	C1T3	2.8 b	23.7 b	4.8 d	20.0 b	15.3 a	62.3 b
4	C1T4	2.7 bc	50.9 a	7.0 b	16.5 a	9.5 c	44.9 d
5	C2T1	2.9 b	11.1 b	4.3 de	17.0 a	12.8 ab	68.8 ab
6	C2T2	2.3 bc	18.2 b	6.0 c	17.0 a	11.0 bc	63.6 b
7	C2T3	2.6 b	16.6 b	5.0 d	19.3 a	14.3 a	55.8 c
8	C2T4	1.8 d	23.4 b	7.0 b	17.3 a	10.3 c	28.2 e
9	C3T1	2.6 b	9.4 b	5.0 d	19.5 a	14.5 a	77.2 a
10	C3T2	2.0 b-d	12.7 b	6.5 bc	18.8 a	12.3 b	69.2 ab
11	C3T3	2.3 c	14.2 b	5.3 d	20.0 a	14.8 a	53.0 c
12	C3T4	1.4 e	18.7 b	8.0 a	19.0 a	11.0 bc	26.3 e
Effect of cultivar
1	Allstart	3.0 A	31.3 A	5.3 B	16.44 A	11.2 A	59.9 A
2	Columbine	2.4 AB	17.3 A	5.6 B	17.63 A	12.1 A	54.1 A
3	Esquire	2.1 AB	13.5 A	6.2 A	19.31 A	13.1 A	56.4 A
Effect of treatment
1	Control	3.1 A	13.7 B	4.4 D	17.92 AB	15.5 A	73.4 A
2	50 mM	2.3 C	20.5 AB	5.0 C	15.92 B	10.0 B	63.7 B
3	100 mM	2.5 D	17.8 B	5.9 B	19.75 A	14.8 A	57.0 B
4	200 mM	2.0 B	31.0 A	7.3 A	17.58 AB	10.3 B	33.1 C

GI—Germination Index; SE—Speed of Emergence; FDG—First Day of Germination; LDG—Last Day of Germination; TSG—Total Spread of Germination; SVI—Seedling Vigor Index. Different letters indicate significant differences among treatments for interactions C × T, cultivar C and treatment T (Duncan’s MRT, p < 0.05).

, salinity also reduced germination performance, with 200 mM NaCl resulting in the strongest inhibition of GI, SE and SVI. Delays in FDG were evident under high salinity, indicating slower germination initiation. Differences among cultivars were smaller than under PEG stress, but ‘Allstarter’ generally showed slightly higher vigor at moderate salinity, while ‘Esquire’ displayed more delayed germination at the highest concentration. The significant interaction effects indicate cultivar-specific responses to increasing NaCl levels.

Table A3. Main germination indices of three cultivars of P. pratensis (‘Dakisha’—C1, ‘Sombrero’—C2, and ‘Conni’—C3) under control (T1) and increasing levels of osmotic stress (T2–T4), respectively. PEG treatments: T2 = −0.22 MPa, T3 = −0.44 MPa, T4 = −0.88 MPa.

No	Cultivar/ Treatment	GI	SE	FDG	LDG	TSG	SVI
Effect of the interaction between cultivar and treatment
1	C1T1	1.9 c	19.3 c	6.5 e	16.0 a	9.5 a	26.6 b
2	C1T2	1.0 f	15.4 d	10.5 c	19.0 a	8.5 a	13.8 c
3	C1T3	0.1 h	73.0 a	16.3 b	20.0 a	3.8 c	0.8 e
4	C1T4	0.0 i	0.0 g	0.0 f	0.0 c	0.0 d	0.1 e
5	C2T1	2.2 b	8.1 f	6.0 e	11.8 b	5.8 c	24.1 b
6	C2T2	1.6 d	13.5 e	8.0 d	17.5 a	9.5 a	13.4 c
7	C2T3	0.5 g	27.0 b	11.0 c	19.0 a	8.0 b	4.5 d
8	C2T4	0.0 i	0.0 g	0.0 f	0.0 c	0.0 d	0.1 e
9	C3T1	2.6 a	26.5 b	6.5 e	16.8 a	10.3 a	38.1 a
10	C3T2	1.3 e	15.2 d	11.0 c	18.8 a	7.8 b	20.6 b
11	C3T3	0.6 g	26.3 b	11.5 c	18.5 a	7.0 b	5.1 d
12	C3T4	0.1 h	77.8 a	19.5 a	20.0 a	0.5 d	0.1 e
Effect of cultivar
1	Dakisha	0.7 B	26.9 B	8.3 B	13.8 B	5.4 B	10.3 B
2	Sombrero	1.1 A	12.1 C	6.3 C	12.1 B	5.8 B	10.5 B
3	Conni	1.1 A	36.4 A	12.1 A	18.5 A	6.4 A	16.0 A
Effect of treatment
1	Control	2.2 A	17.9 C	6.3 C	14.8 B	8.5 A	29.6 A
2	−0.22 MPa	1.3 B	14.7 D	9.8 B	18.4 A	8.6 A	15.9 B
3	−0.44 MPa	0.4 C	42.1 A	12.9 A	19.2 A	6.3 B	3.4 C
4	−0.88 MPa	0.0 C	25.9 B	6.5 C	6.7 C	0.2 C	0.1 D

GI—Germination Index; SE—Speed of Emergence; FDG—First Day of Germination; LDG—Last Day of Germination; TSG—Total Spread of Germination; SVI—Seedling Vigor Index. Different letters indicate significant differences among treatments for interactions C × T, cultivar C and treatment T (Duncan’s MRT, p < 0.05).

demonstrates that P. pratensis seeds were strongly inhibited by PEG-induced osmotic stress, with GI and SVI approaching zero at −0.44 and −0.88 MPa for all cultivars. Germination was markedly delayed (higher FDG and LDG), particularly in ‘Dakisha’ and ‘Conni’. Under moderate stress, ‘Conni’ preserved slightly higher vigor, while ‘Dakisha’ showed the sharpest decline. The significant treatment and interaction effects illustrate the severe physiological constraints imposed by osmotic drought.

Table A4. Main germination indices of three cultivars of P. pratensis (‘Dakisha’—C1, ‘Sombrero’—C2, and ‘Conni’—C3) under control (T1) and increasing levels of salt stress (T2–T4), respectively. NaCl treatments: T2 = 50 mM, T3 = 100 mM, T4 = 200 mM.

No	Cultivar/ Treatment	GI	SE	FDG	LDG	TSG	SVI
Effect of the interaction between cultivar and treatment
1	C1T1	1.9 bc	19.3 b	6.5 d	16.0 ab	9.5 bc	26.6 b
2	C1T2	1.3 d	18.2 b	10.0 c	17.5 a	7.5 d	13.4 c
3	C1T3	0.6 e	22.9 b	9.3 c	19.8 a	10.5 b	10.3 c
4	C1T4	0.1 ef	83.3 a	18.0 a	18.5 a	0.5 h	0.3 e
5	C2T1	2.2 b	8.1 b	6.0 d	11.8 b	5.8 f	24.1 b
6	C2T2	1.7 c	15.9 b	8.0 dc	16.8 a	8.8 c	25.9 b
7	C2T3	1.5 cd	12.4 b	8.5 dc	19.8 a	11.3 a	13.8 c
8	C2T4	0.8 e	18.5 b	13.3 b	19.8 a	6.5 e	4.8 d
9	C3T1	2.6 a	26.5 b	6.5 d	16.8 a	10.3 b	38.1 a
10	C3T2	1.6 cd	21.0 b	10.0 c	16.0 ab	6.0 ef	25.3 b
11	C3T3	1.3 d	11.6 b	9.8 c	19.5 a	9.8 b	14.2 c
12	C3T4	0.5 e	15.8 b	16.0 a	20.0 a	4.0 g	3.8 d
Effect of cultivar
1	Dakisha	1.0 B	35.9 A	10.9 A	17.9 A	7.0 A	12.6 B
2	Sombrero	1.5 A	13.7 BC	8.9 A	17.0 A	8.1 A	17.1 AB
3	Conni	1.5 A	18.7 B	10.6 A	18.1 A	7.5 A	20.3 A
Effect of treatment
1	Control	2.2 A	17.9 B	6.3 C	14.8 B	8.5 AB	29.6 A
2	50 mM	1.5 B	18.4 B	9.3 B	16.8 B	7.4 C	21.5 B
3	100 mM	1.1 C	15.6 B	9.2 B	19.7 A	10.5 A	12.7 C
4	200 mM	0.4 D	39.2 A	15.8 A	19.4 A	3.7 D	2.9 D

GI—Germination Index; SE—Speed of Emergence; FDG—First Day of Germination; LDG—Last Day of Germination; TSG—Total Spread of Germination; SVI—Seedling Vigor Index. Different letters indicate significant differences among treatments for interactions C × T, cultivar C and treatment T (Duncan’s MRT, p < 0.05).

indicates that salinity produced a gradual reduction in germination indices in all P. pratensis cultivars. High salinity (200 mM) led to clear inhibition of GI and SVI and increased FDG, reflecting delayed germination. Although cultivars performed similarly under control conditions, ‘Conni’ retained somewhat higher vigor at moderate salinity, whereas ‘Dakisha’ was more negatively affected at the strongest treatment. Significant cultivar × treatment interactions confirm differentiated tolerance levels.

3.4. Multivariate Analysis

Principal Component Analysis (PCA) confirmed the variability among cultivars and their responses to osmotic and salt stress. For L. perenne, the first two components accounted for 82.28% of total variance (Figure 12). PC1 (63.51%) was positively associated with germination percentage, plumule and radicle length, germination index (GI), and seedling vigor index (SVI), and negatively correlated with mean germination time (MGT) and first day of germination (FDG). PC2 (18.77%) was mainly related to LDG and TSG. Along PC1, treatments with PEG clustered on the negative side, whereas control and low-salt treatments were positioned on the positive side, indicating distinct responses between osmotic and salt stress. Among cultivars, ‘Allstarter’ grouped positively along PC1, showing higher vigor and faster germination, whereas ‘Esquire’ clustered negatively, reflecting stress susceptibility. ‘Columbine’ occupied an intermediate position.

In P. pratensis, the two principal components of PCA explained 89.12% of total variance (Figure 13). PC1 (76.88%) correlated positively with GI, SVI, germination percentage, and plumule and radicle length, and negatively with MGT and FDG, whereas PC2 (12.24%) was associated with TSG and LDG. Control and low-stress treatments were located on the positive side of PC1, whereas PEG and high NaCl concentrations shifted toward the negative axis. ‘Conni’ consistently occupied the positive side of PC1, indicating superior performance, while ‘Dakisha’ appeared at the negative end, confirming its sensitivity. ‘Sombrero’ showed an intermediate response.

In both species, PC1 represented a general ‘germination vigor and stress tolerance’ axis, strongly associated with high germination percentage, GI, SVI, radicle and plumule length, and low MGT. PC2 represented a ‘germination synchrony’ axis, mainly driven by LDG and TSG. Thus, variation along PC1 primarily reflected tolerance intensity, whereas PC2 captured differences in timing and uniformity of germination among cultivars.

PCA clearly separated cultivars according to their germination performance and stress resilience. In both species, variation along PC1 was driven mainly by indices integrating germination rate and seedling vigor, emphasizing their relevance as indicators of early stress tolerance.

The UPGMA dendrogram for L. perenne (Figure 14a) reveals two well-defined clusters, separating control and low-stress treatments from the more intense PEG and NaCl levels. Cultivars group primarily according to stress intensity rather than genotype, indicating that germination-related traits respond strongly and consistently to increasing osmotic and saline constraints.

In P. pratensis, the hierarchical clustering (Figure 14b) similarly distinguishes high-stress treatments as a distinct group, with control, 50 mM NaCl and −0.22 MPa PEG treatments forming a separate cluster. Compared with L. perenne, cultivar-specific patterns are slightly more pronounced, yet stress severity remains the dominant factor shaping the clustering structure.

3.5. Recovery of Germination

Recovery tests demonstrated contrasting post-stress behaviors between species (

Table 2. Percentages of recovery of germination in the analyzed cultivars of Lolium perenne L. and Poa pratensis L.

Treatment	L. perenne			P. pratensis
	Allstarter	Columbine	Esquire	Dakisha	Sombrero	Conni
Control	0	0	0	0	0	0
50 mM	0	0	0	21.21 a	5.56 b	0
−0.22 MPa	16.67 a	0	11.11 b	41.25 ab	14.29 b	13.33 bc
100 mM	0	4.17 a	0	30.30 ab	9.52 b	4.17 c
−0.44 MPa	8.33 a	7.88 a	11.11 b	60.51 a	47.55 ab	28.03 bc
200 mM	0	0	20.83 b	52.95 ab	38.97 ab	23.81 bc
−0.88 MPa	31.67 a	32.74 a	60.19 a	56.67 ab	77.78 a	70.77 a

Note: Different letters indicate statistically significant differences between treatments within each cultivar (Duncan’s MRT, p < 0.05).

). In L. perenne, germination recovery was generally low. Only ‘Esquire’ showed a moderate increase in germination after exposure to −0.88 MPa PEG, whereas ‘Allstarter’ and ‘Columbine’ exhibited negligible recovery. This limited response likely reflects the high initial germination during stress, leaving few viable ungerminated seeds for recovery.

In P. pratensis, recovery was more pronounced, particularly after severe PEG treatments. All cultivars resumed germination once transferred to optimal conditions, with the highest recovery percentages observed in ‘Conni’ (≈70%) and ‘Dakisha’ (≈57%) following −0.88 MPa PEG. Recovery after salt stress was lower but still evident, suggesting that osmotic inhibition was largely reversible. These findings indicate that P. pratensis exhibits a more effective avoidance strategy, maintaining seed viability during stress and germinating rapidly upon rehydration.

Overall, osmotic stress imposed by PEG had stronger inhibitory effects on germination and seedling growth than NaCl-induced salt stress at equivalent osmotic potentials. L. perenne maintained higher germination percentages and vigor indices under both stress conditions, while P. pratensis displayed greater sensitivity but stronger post-stress recovery. Among cultivars, ‘Allstarter’ (L. perenne) and ‘Conni’ (P. pratensis) showed the highest tolerance, whereas ‘Esquire’ and ‘Dakisha’ were the most affected. PCA results supported these findings, highlighting consistent separation of tolerant and sensitive genotypes based on germination dynamics and vigor traits.

4. Discussion

Abiotic stressors such as drought and salinity are major constraints affecting seed germination and early seedling establishment in turfgrass systems. Their impact is particularly relevant in urban environments and semi-arid regions, where irregular precipitation and low-quality irrigation water frequently generate osmotic imbalance and ionic toxicity [4,7]. In this study, the responses of Lolium perenne and Poa pratensis were evaluated separately under osmotic stress induced by PEG and salinity induced by NaCl, allowing a clear distinction between the physiological pathways affected by reduced water availability and those influenced by ionic accumulation. The results reveal substantial interspecific and genotypic variability, emphasizing the importance of early-stage stress responses for successful turfgrass establishment.

4.1. Comparative Impact of Osmotic and Salt Stress

Under PEG-induced osmotic stress, germination and seedling vigor decreased progressively as water potential in the germination medium declined. Because PEG molecules reduce external water availability without entering cells, they primarily limit imbibition and slow the biochemical activation required for radicle protrusion [17,58]. These effects account for the longer mean germination times and delayed initiation of germination observed in both species, consistent with general patterns documented under drought-related germination inhibition in cool-season grasses [20,38].

Under NaCl, germination was influenced by the combined effects of osmotic restriction and ionic stress. As NaCl concentration increased, germination proceeded more slowly at first, followed by stronger inhibition at higher concentrations as Na⁺ and Cl⁻ accumulated sufficiently to affect cellular metabolism and membrane function [59]. The gradual onset of ionic effects explains the more moderate reductions in germination speed under mild salinity and the stronger inhibition observed under high salt levels. Together, these patterns reflect the distinct temporal and physiological modes of action through which osmotic and saline stress influence seed germination.

4.2. Species-Specific Responses

The two turfgrass species displayed markedly different sensitivities to osmotic and saline stress. L. perenne maintained higher germination percentages, shorter germination times, and greater seedling vigor across treatments, reflecting a rapid activation of metabolic processes that support early establishment even under unfavorable conditions [2,22]. This germination strategy enables efficient ground coverage in managed systems where irrigation or moisture input can mitigate subsequent stress.

By contrast, P. pratensis showed stronger inhibition of germination under reduced water availability and elevated salinity, with substantial declines recorded even at moderate stress levels. However, many seeds of this species remained viable during stress and germinated rapidly when transferred to favorable conditions, indicating the presence of a dormancy-like response that postpones germination until water availability improves [35,60]. This adaptive behavior resembles an avoidance strategy, minimizing the risk of seedling mortality during periods of acute water deficit.

Both species exhibited reductions in the proportion of normal seedlings under stress, but the magnitude differed. L. perenne seedlings retained more balanced root–shoot development, whereas P. pratensis displayed a higher frequency of stress-related abnormalities, particularly involving underdeveloped root systems. These differences indicate distinct structural sensitivities during early development and support the overall patterns observed in germination and vigor parameters.

4.3. Genotypic Variation and Cultivar Performance

Within each species, cultivars differed substantially in their tolerance to osmotic and saline stress. In L. perenne, the cultivar ‘Allstarter’ consistently showed the most stable performance, maintaining higher germination, shorter germination times, and greater seedling vigor across stress levels. ‘Columbine’ displayed intermediate responses, while ‘Esquire’ was more sensitive, exhibiting greater delays in germination and reduced vigor. These cultivar-specific differences underline the presence of distinct physiological capacities for coping with reduced water availability and ion accumulation.

In P. pratensis, ‘Conni’ maintained detectable germination even under severe PEG stress and displayed the highest recovery upon rehydration, indicating a strong ability to preserve seed viability under adverse conditions. ‘Sombrero’ exhibited moderate tolerance, while ‘Dakisha’ showed the highest sensitivity across germination parameters. The performance differences among cultivars demonstrate that early-stage responses to stress are strongly genotype-dependent and can be effectively characterized using germination indices and seedling growth traits.

Multivariate analysis reinforced these patterns by grouping cultivars according to the combined behavior of germination percentage, germination timing, seedling growth, and vigor-related indices. The parameters contributing most strongly to variation among genotypes were those reflecting both the rate and the structural quality of early seedling development, confirming their relevance for evaluating early-stage stress tolerance.

4.4. Germination Dynamics and Physiological Interpretation

The progressive reduction in germination and seedling development under both osmotic and saline stress reflects limitations on water uptake, hormonal regulation, and tissue expansion. Radicle elongation was more strongly inhibited than plumule elongation, indicating a higher sensitivity of root tissues to reduced water potential [15,16]. Because root growth depends directly on water-driven cell expansion, osmotic restriction imposed by PEG rapidly constrained radicle development.

The decline in germination synchrony suggests that only physiologically robust seeds germinated under stressful conditions, while others remained inactive. Although this mechanism may enhance survival in natural ecosystems, it can reduce uniformity of establishment in turf systems, where even and rapid emergence is essential for achieving consistent surface coverage and aesthetic quality [61].

Hormonal adjustments also contribute to the observed delays in germination. Osmotic stress is associated with elevated abscisic acid and reduced gibberellin activity, slowing the transition from dormancy to active growth [62]. The rapid initiation of germination during recovery tests indicates that these hormonal effects were reversible and that viability remained intact under stress, particularly in P. pratensis.

4.5. Post-Stress Recovery and Adaptive Strategies

Recovery assays demonstrated clear differences in post-stress behavior. In L. perenne, recovery was limited because most viable seeds germinated during stress exposure, leaving fewer dormant but viable seeds available to resume germination afterward. In contrast, P. pratensis exhibited substantial recovery, especially after severe osmotic restriction, indicating an ability to maintain viability even under conditions that temporarily suppress germination. These contrasting responses reflect distinct germination strategies: rapid activation and establishment in L. perenne versus a more conservative strategy in P. pratensis, where germination is postponed until conditions improve [63,64,65].

Both strategies offer ecological advantages under specific environmental contexts. Rapid germination supports early soil stabilization and fast establishment when moisture is sufficient, whereas delayed germination reduces the risk of seedling failure during periods of acute drought. In turfgrass management, these differences imply that the timing of sowing and irrigation should be tailored to species and cultivar-specific germination behavior.

4.6. Practical Implications for Turfgrass Selection and Management

The contrasting responses of L. perenne and P. pratensis to osmotic and saline stress highlight the importance of matching species and cultivars with site-specific environmental conditions. L. perenne is better suited for situations requiring rapid establishment, such as sports fields or temporary ground cover, particularly where irrigation or moisture input is available. P. pratensis, with its greater recovery capacity and long-term durability, is more appropriate for parks, residential lawns, and restoration projects in areas exposed to intermittent drought or salinity.

Germination indices such as germination percentage, mean germination time, germination index, and seedling vigor index proved effective in characterizing early-stage stress responses. These metrics enable rapid screening of cultivars in breeding programs aimed at improving establishment under water-limited or saline conditions [33,64,66]. Seed priming techniques, including osmopriming and halopriming, may further enhance germination performance by improving osmotic adjustment and increasing uniformity of emergence [67,68,69,70].

4.7. Broader Ecological and Agronomic Context

Improving the stress resilience of turfgrass species contributes to the sustainability of urban green spaces and supports ecosystem services such as soil stabilization, erosion control, microclimate regulation, and carbon sequestration [8,71,72,73,74]. Combining species with complementary traits, for example, rapidly germinating grasses with those that offer long-term persistence, may enhance overall stand resilience and performance. Functional complementarity among cultivars or species can improve stability under variable environmental conditions, supporting long-term ecological and ornamental functions [61].

5. Conclusions

This study demonstrated that osmotic stress induced by polyethylene glycol (PEG) exerted a stronger inhibitory effect on germination and early seedling development than salinity at equivalent osmotic potentials. Among the six evaluated turfgrass cultivars, Lolium perenne showed overall higher tolerance than Poa pratensis, maintaining greater germination percentages, faster emergence, and superior vigor indices under both PEG and NaCl treatments. Clear genotypic differences were also evident within each species. In L. perenne, ‘Allstarter’ displayed the most stable performance, combining high germination capacity with comparatively sustained radicle and plumule growth under stress. In P. pratensis, ‘Conni’ showed the strongest resilience, being the only cultivar capable of germinating even under severe osmotic restriction and exhibiting the highest post-stress recovery. Multivariate analyses supported these cultivar-dependent patterns, with germination index and seedling vigor index emerging as reliable indicators of early stress tolerance.

The contrasting adaptive strategies observed, rapid germination in L. perenne versus delayed germination and stronger recovery capacity in P. pratensis, reflect distinct ecological approaches to coping with adverse conditions. Rapidly germinating cultivars are advantageous in systems requiring quick establishment under intermittent moisture availability, whereas cultivars capable of postponing germination and resuming growth after stress may perform better in drought- or salinity-prone environments. Overall, the results provide a physiological and practical framework for selecting turfgrass cultivars with improved establishment and resilience under challenging environmental conditions, contributing to more sustainable turfgrass management and breeding programs focused on early-stage stress tolerance.