Vertical distribution of soil seed bank and the ecological importance of deeply buried seeds in alkaline grasslands

Diversity and composition of vegetation and soil seed banks after sand dune restoration by oil mulching and plantations

Soil seed bank (SSB) is valuable reserves of seeds hidden in the soil and are especially important for the preservation and establishment of vegetation under adverse environmental conditions. However, there is a lack of knowledge on the effects of restoration measures on SSB, especially in arid ecosystems. Here, we assess the impacts of oil mulching (1 and 3 years after mulching) and plantations (15-year-old) on the diversity and composition of SSB and aboveground vegetation (AGV) in comparison with those in non-restored areas (i.e., control). Based on the results, species richness was poor in the studied area (36 species belonging to 16 families), with a lower contribution of SSB than of AGV (11 and 34 species, respectively). The largest number of exclusive species was observed in the planted treatment for both SSB and AGV (4 and 5 species, respectively), while the lowest was found in the 1-yr mulching treatment. The mean comparison of the diversity indices revealed that the highest values occurred in the plantation and 3-yr-mulching plots. The seed density in the plantation area was significantly greater (4145 ± 694 seeds/m2) than that in the other areas (3-yr-mulching > 1-yr-mulching > control treatments (145 ± 53, 65 ± 28, and 43 ± 22, respectively). The results of the DCA showed that the plantation treatment was completely separated from the other treatments in terms of the plant composition of the AGV, and the treatment closest to that area was 3-yr mulching, which indicates the positive effect of time since mulching on plant composition. The results of this study suggest that there is a trade-off between the short-term and medium-term effects of oil mulching, such that in the early years, oil mulching has a negative effect on the AGV and SSB, but its positive effects increase with time since mulching. It can be concluded that mulching, along with afforestation, creates a favorable microclimate and improves the diversity and composition of AGV and SSB.

Response of the germinable soil seed bank of temperate Leymus chinensis meadows to mowing regimes

Mowing is a primary practice in temperate L. chinensis meadows, which are severely degraded due to frequent mowing, overgrazing, and other factors, necessitating restoration and sustainable management. The natural recovery of these grasslands hinges on their germinable soil seed banks, which form the basis for future productivity. Thus, germinable soil seed banks are critical for restoring overexploited meadows. In this study, we conducted germination experiments on 135 soil samples from various depths to comprehensively analyze the germinable seed bank under different mowing regimes. The main results were as follows: (1) the germinable soil seed bank density decreased significantly with a mowing event per year (C1), and the number of perennial grass seeds and upper grass seeds also decreased under the mowing event per year; (2) the size of the germinable soil seed bank increased under the other mowing regimes (control area without mowing or grazing, CK; mowing event every 2 years, C2; mowing event every 3 years, C3; and mowing event every six years, C6) relative to that under once-a-year mowing. With increasing soil depth, the number of germinable soil seeds decreased significantly. Most of the seeds in the germinable soil seed banks were distributed in the 0-2 cm soil layer, accounting for approximately 80% of the total, and at depths of 5-10 cm, the number of seeds of upper grasses was greater than that of perennial grasses. (3). During the mowing event each year, the seed bank of germinable soil seeds significantly decreased. Mowing every 2 years provides a one-year interval for natural vegetation growth, allowing for greater retention of seeds in the germinable soil seed bank. Mowing every 6 years significantly reduces the disturbance frequency, providing ample time for plant reproduction and resulting in the accumulation of germinable seeds in the soil.

Grassland restoration on linear landscape elements - comparing the effects of topsoil removal and topsoil transfer

Artificial linear landscape elements, including roads, pipelines, and drainage channels, are main sources of global habitat fragmentation. Restoration of natural habitats on unused linear landscape elements can increase habitat quality and connectivity without interfering with agricultural or industrial development. Despite that topsoil removal and transfer are widely applied methods in restoration projects, up to our knowledge these were previously not compared in the same study system. To address this knowledge gap, we compared spontaneous vegetation recovery after the elimination of positive (embankments) and negative landscape scars (drainage channels) in lowland alkaline landscapes in South Hungary. The novelty of our study is that we compared the fine-scale and landscape-scale results of both methods. At the fine scale, we monitored the spontaneous vegetation development on the created open surfaces in the first, second and fourth year after restoration in 160 permanent plots per year. For characterizing the habitat changes on the landscape scale, we prepared habitat maps and assigned naturalness scores to each patch before and after the restoration activities. Both restoration methods resulted in a rapid vegetation recovery at the fine scale, progressing toward the reference state. In the topsoil removal treatment, a large part of the soil seed bank was removed; therefore, the colonization of the bare surface was a slower process. Seeds of halophytes, including the endemic and protected Suaeda pannonica, were probably present in the deeper soil layers, and these species became established in the restored surfaces, despite being absent in the surrounding vegetation. For restoring vegetation cover, topsoil transfer was a more rapid option; however, vegetation closure and competition by generalist species and weeds hampered the establishment of target species. The removal of the landscape scars by both methods made the sites accessible for grazing. At the landscape scale, the two methods had different effects: there was a slight increase in the habitat naturalness in the topsoil removal site, and a slight decrease in the topsoil transfer site because of weed encroachment. Spreading an upper layer of nutrient-poor soil with low amounts of weed seeds, direct propagule transfer, and targeted grazing regimes could enhance restoration success.

Responses of soil seed bank and its above-ground vegetation to various reclamation patterns

Coastal land reclamation has become a primary strategy for alleviating conflicts between human development and land resource utilization. However, anthropogenic activities associated with land reclamation inevitably result in significant changes to coastal wetland ecosystems. Previous studies have mainly focused on the ecological consequences of land reclamation on above-ground vegetation, while overlooking the distinctions between different reclamation patterns and the critical role of soil seed bank in maintaining ecosystem stability. In this study, the responses of soil seed bank and vegetation to various reclamation patterns, as well as the factors influencing changes in seed bank characteristics, were analyzed in a natural coastal wetland (NCW), a reclaimed wetland with sea embankments constructed on native wetland (SEW), and another reclaimed wetland formed through land reclamation from the sea (LRW). These findings suggest that seed banks and their vegetation adopt different adaptation strategies under various reclamation patterns. In the NCW, the proportion of non-halophytes (1.39%), diversity, and density of the seed bank were at their lowest levels, whereas the species compositions derived from the seed bank and vegetation were very similar (similarity coefficient = 0.67). Conversely, the seed bank in the SEW demonstrated the highest species diversity, which differed significantly from the species composition of its above-ground vegetation (similarity coefficient = 0.21). However, the highest proportion of non-halophytes (36.60%), vegetation diversity, and seed bank density occurred in LRW. Furthermore, differences in seed bank characteristics under different reclamation patterns may be related to changes in soil salinity and plant reproductive strategies after reclamation. Adjusting reclamation patterns and restoring soil properties could potentially optimize the types of local plant species and their distribution in reclaimed areas.

Dormancy, germination, and associated seed ecological traits of 25 Fabaceae species from northern India

Fabaceae produce seeds with water-impermeable seed coats, i.e., physical dormancy (PY). We hypothesized that the proportion of PY seeds will increase with the dryness of the habitat, and some key seed ecological traits will be strongly associated with different levels of PY. Fresh seed of 25 Fabaceae species collected in northern India were used for imbibition and germination experiments to determine the proportion of seeds with PY and of nondormant (ND) seeds compared to their Sri Lankan congeners. Seed coat:seed mass ratio (SCR), 1000 seed weight, seed shape index (SSI), embryo type and median germination time of ND seeds were determined. Four imbibition and germination patterns were identified among seeds of the studied species. Seeds collected from Indian populations had a higher proportion of PY seeds than those of Sri Lankan populations. We identified a type of embryo called 'spatulate axile' that had not been identified before among the studied species. Species with ND seeds had a lower SCR and a higher SSI than those with PY. Our hypothesis was confirmed since populations from drier habitats in India produce a higher proportion of PY seeds than those from Sri Lanka. A low SCR ensures minimal resistance to germinating seeds, while seeds with a high SSI have a lower tendency to incorporate into the soil seed bank. Thus, these seed traits aid the fast germination of ND seeds, often dispersed just before the rainy season.

Effects of different grassland utilization methods on the germinable soil seed bank of the Hulunbuir meadow steppe

Seed banks are crucial regenerative resources for aboveground vegetation. The pattern of their changes holds immense significance in understanding alterations in the belowground seed bank. This understanding is pivotal for uncovering both short-term and long-term shifts in plant communities. Additionally, it contributes to the restoration of grassland ecosystems. To better protect grassland biodiversity and provide a theoretical basis for the restoration of degraded grasslands, in this study, the germination characteristics of soil seed banks in free-grazed, enclosed and mown areas were compared, and the results were combined with those of previous studies for a comprehensive analysis. The density of soil seed bank and perennial forage soil seed bank were significantly affected by different grassland utilization and soil depths. Grazing and enclosure grassland utilization methods increased the content of the soil seed bank, and mowing reduced the content of the seed bank. The soil seed bank density of perennial grasses accounted for the highest proportion under grazing, followed by mowing, and its lowest proportion was observed in the enclosures. Grazing not only facilitated the germination of the perennial grass seed bank but also substantially augmented its content. Mowing inhibited the germination of the upper growth grasses seed bank, which was particularly significant in the 0-2 cm soil layer under grazing. The content of the upper growth grasses seed bank affected the total seed bank to a certain extent, mainly in the 5-10 cm layer. The general correlations among the perennial grasses, upper growth grasses and soil germination seed bank resulted in 84.58% information extraction, and this information has practical significance for grassland ecological restoration.

Seed Bank Community under Different-Intensity Agrophytocenoses on Hilly Terrain in Lithuania

On the summit of a hill with a lack of humidity, and in usually stronger eroded midslope parts, crops thin out. Changing ecological conditions change the soil seed bank as well. The aim of this study was to examine changes in the seed bank size and number of species and the influence of seed surface characteristics on their spread in different-intensity agrophytocenoses under hilly relief conditions. This study included different parts of the hill (summit, midslope and footslope) in Lithuania. The southern exposition slope's soil was slightly eroded Eutric Retisol (loamic). In spring and autumn, the seed bank was investigated at depths of 0-5 and 5-15 cm. Irrespective of the season, in the soil of permanent grassland, the seed number was 6.8 and 3.4 times smaller compared to those of cereal-grass crop rotation and crop rotation with black fallow. The highest number of seed species was determined in the footslope of the hill. Seeds with rough surfaces dominated on all parts of the hill, but the highest amount (on the average 69.6%) was determined on the summit of the hill. In autumn, a strong correlation was found between the total seed number and soil microbial carbon biomass (r = 0.841-0.922).