Rainfall amount determines annual herb controls over soil seed bank and its similarity with vegetation in the Tengger Desert

Background Soil seed banks may offer great potential for maintaining and restoring desert ecosystems that have been degraded by climate change and anthropogenic disturbance. However, few studies have explored the year-to-year dynamics in the species composition (richness and abundance) of these desert soil seed banks. Thus, we conducted a 4-year study to assess the effects of environmental factors (meteorology and microtopography) and aboveground vegetation on the soil seed bank of the Tengger Desert, China. Results We found the seed bank was dominated by annual herb species both in species richness and abundance. More rainfall in the growing season increased the number of seeds in the soil seed bank, and quadrat micro-elevation had a negative effect on soil seed bank size. The species composition in the seed bank had significantly larger between-year similarity than that in the aboveground vegetation due to the dominance of annual herb species. For different life forms, the species composition of annual herbs showed distinctly larger temporal similarity between the aboveground vegetation and the seed bank compared with perennial herbs and shrubs. Conclusions Our findings highlight that the combined effects of environmental factors and plant life forms determine the species composition (especially the abundance) of soil seed banks in deserts. However, if degraded desert ecosystems are left to regenerate naturally, the lack of shrub and perennial herb seeds could crucially limit their restoration. Human intervention and management may have to be applied to enhance the seed abundance of perennial lifeforms in degraded deserts.

Statistical inference for seed mortality and germination with seed bank experiments

Plant population ecologists regularly study soil seed banks with seed bag burial and seed addition experiments. These experiments contribute crucial data to demographic models, but we lack standard methods to analyze them. Here, we propose statistical models to estimate seed mortality and germination with observations from these experiments. We develop these models following principles of event history analysis, and analyze their identifiability and statistical properties by algebraic methods and simulation. We demonstrate that seed bag burial, but not seed addition experiments, can be used to make inferences about age-dependent mortality and germination. When mortality and germination do not change with seed age, both experiments produce unbiased estimates but seed bag burial experiments are more precise. However, seed mortality and germination estimates may be inaccurate when the statistical model that is fit makes incorrect assumptions about the age-dependence of mortality and germination. The statistical models and simulations that we present can be adopted and modified by plant population ecologists to strengthen inferences about seed mortality and germination in the soil seed bank.

Experimental Warming Hastens Physical Dormancy Break and Germination in Tropical Fabaceae

Climate warming may threaten the germination strategies of many plants that are uniquely adapted to today’s climate. For instance, species that employ physical dormancy (PY) – the production of seeds that are impermeable to water until high temperatures break them, consequently synchronizing germination with favorable growing conditions – may find that their seeds germinate during unfavorable or potentially fatal periods if threshold temperatures are reached earlier in the year. To explore this, we subjected the seeds of five species with physical dormancy (from the genera Abrus, Bauhinia, Cassia, Albizia, and Acacia) to “mild” (+2°C) and “extreme” (+4°C) future warming scenarios and documented their germination over 2 years relative to a control treatment. Under current climatic conditions, a proportion of seeds from all five species remained dormant in the soil for 2 years. A mild warming of 2°C had little to no effect on the germination of four of the five study species. Contrastingly, an extreme warming of 4°C dramatically increased germination in all five species within the first year, indicating a reduction in their ability to persist in the soil long-term. Cassia fistula was particularly susceptible to warming, exhibiting a similar increase in germination under both mild and extreme warming relative to control. Our findings suggest that climate warming in the tropics may cause the seeds of species that rely on physical dormancy to stagger the risk of unsuccessful germination across years to leave soil seed banks prematurely – the long-term implications of which remain unknown.

Global patterns of potential future plant diversity hidden in soil seed banks

Soil seed banks represent a critical but hidden stock for potential future plant diversity on Earth. Here we compiled and analyzed a global dataset consisting of 15,698 records of species diversity and density for soil seed banks in natural plant communities worldwide to quantify their environmental determinants and global patterns. Random forest models showed that absolute latitude was an important predictor for diversity of soil seed banks. Further, climate and soil were the major determinants of seed bank diversity, while net primary productivity and soil characteristics were the main predictors of seed bank density. Moreover, global mapping revealed clear spatial patterns for soil seed banks worldwide; for instance, low densities may render currently species-rich low latitude biomes (such as tropical rain-forests) less resilient to major disturbances. Our assessment provides quantitative evidence of how environmental conditions shape the distribution of soil seed banks, which enables a more accurate prediction of the resilience and vulnerabilities of plant communities and biomes under global changes.

Seed rain and soil seed banks in Chinese fir plantations and an adjacent natural forest in southern China: implications for the regeneration of native species

The natural regeneration of native broadleaved species underneath forest monoculture plantations is important to recover ecosystem functions and to mitigate adverse environmental effects. To understand how seed rain and soil seed banks facilitate natural regeneration, we surveyed their density and composition in a monoculture Chinese fir plantation, a mixed Chinese fir–broadleaf plantation, and an adjacent natural broadleaved forest for two years in southern China. Twenty-eight species (16 families) were in seed rain, and 45 species (27 families) were in soil seed banks. Seed rain density did not differ significantly across stands; however, the number of taxa in seed rain was highest in the mixed plantation and lowest in the natural forest. Seed bank density was significantly higher in the mixed plantation than in the other stands. The Sørensen similarity indices of species composition between seed sources and aboveground vegetation were relatively low (<0.50). In addition, the seeds of native tree species common to the seed banks of the three forests indicated the adjacent natural forest was a seed source for the natural regeneration of native species in forest plantations. To augment regeneration and accelerate the rate of conversion, we recommend direct seeding or planting of desired species.

Impacts of Prosopis juliflora L. on Soil Seed Bank Flora in Amibara Rangeland of Afar Regional State, Ethiopia

Background: Prosopis juliflora L. is an evergreen exotic weedy species seriously devastating valuable rangeland resources in arid and semi-arid parts of Ethiopia. Its increasing alarming rate of invasiveness had affecting the livelihood of the pastoral communities in Amibara rangeland of Afar National Regional State. Therefore, the aim of this study was to investigate the effects of Prosopis juliflora L. on soil seed bank flora. Methods: The total of 20 soil samples were collected from five sites by measuring sample quadrats of (20 m × 20 m) area were laid out and the soil samples from each quadrant were taken from 5 sub-quadrats/m2, one from the center and four from the corners, at two depths (0-3 cm and 3-10 cm). The soil samples from the identical layers were mixed in plastic bags to form composite sample. Finally, the composite samples were transported to the Haramaya University to conduct seed germination test in the greenhouse. The soil samples were spread thinly (2 cm thickness) over sterilized soil in shallow trays (20 cm × 25 cm) placed on a bench and allowed for seed germination. Result: The total of 38 herbaceous plant species /m2 belongs to 16 families were emerged in the upper and lower layer (0-3 cm and 3-10 cm) of the soil seed bank samples. The highest values of species diversity were (3.17) in Awash-arba, (3.15) in Alaydagi, (3.04) in Kurkura within m2 area at the depth of 0-3 cm. While the least diversity values of 2.75 in Melka-Werer and 2.77 was recorded in Sarkamo. Jaccard’s coefficient similarity index was exhibited high species similarity of 55.6% in the upper soil seed bank layers (0-3 cm) in Melka-were and Sarkamo. Whereas, species similarities of 45.2% were obtained in the lower layer (3-10 cm) soil seed banks in Awash-arba and upper layer soil seed bank in Alaydagi respectively. While species similarity was decreases as 31.8% in the lower layer soil seed banks in Sarkamo and Kurkura. Increasing species richness and the diversity was also noticed in under open canopy upper layer soil seed bank samples, while decreasing richness and diversity observed in under closed canopy. This indicates that the Prosopis juliflora L. tree has high growth retarding potential on its under canopy soil seed bank flora and in the lower layer soil seed bank samples also.

Invasive species in the soil seed bank of two limestone hills in Bogor, West Java, Indonesia

Putri WU, Qayim I, Qadir A. 2021. Invasive species in the soil seed bank of two limestone hills in Bogor, West Java, Indonesia. Biodiversitas 22: 4019-4027. Study on the impact of invasive species on plant communities has been conducted mainly on the aboveground vegetation. The impact on the soil seed bank has received less attention mostly due to practical difficulties in conducting seed bank assessment. Evaluation of seed bank composition is useful in detecting invasive plant species that may have been present as buried seeds. Information on the vegetation composition in Nyungcung and Kapur hills both under and aboveground is available, but specific information on invasive species has not been discussed yet. This paper describes and analyzes the structure (composition and density) of invasive species in the soil seed bank. Eighty soil samples were taken from the study sites. The soil seed banks were analyzed using seedling emergence and seed extraction methods. 2602 and 1280 seedlings emerged from soil seed bank of Nyungcung and Kapur hills, respectively. From that number, approximately 48.96% and 68.51% of the seedlings are invasive species in the soil seed bank of Nyungcung and Kapur hills. The invasive species were dominants in the soil seed bank of the two sites. Cecropia peltata and Clidemia hirta were the most abundant invasive species in the Kapur and Nyungcung hills seed bank, respectively. Species richness and seedling density were higher in Nyungcung hills than Kapur hills, which were invaded for a relatively longer period.