Improved Seedling Emergence Research Articles

Role of mucilage in improving seedling emergence of Ocimum basilicum L. exposed to salinity stress

The seeds of many desert plants have an extraneous mucilage layer that can raise water holding capability of seeds under stressful environments. The purpose of this study was to investigate the role of mucilage in improving the salinity resistance of Ocimum basilicum L. The treatments include salinity (0, 5, 10, 15 and 20 dS/m) and seed type (with and without mucilage) with three replications. Results showed that all studied traits were significantly (p < 0.01) effected by salinity stress. Seed type had a significant effect (p < 0.01) on the germination rate and root and shoot length, whereas this factor did not significantly affect other traits. Except for seed germination, other variables were significantly affected by salinity and seed type interaction. With increasing salinity stress, germination and seedling growth of both seed types were significantly decreased; however, seeds with mucilage were less affected by salinity stress than those without mucilage.

Effects of precipitation variation and trampling disturbance on seedling emergence of annual plants in a semi-arid grassland

Precipitation change and grazing are the main factors influencing vegetation structure and dynamics in semi-arid grassland. However, the effects of precipitation variation and livestock trampling on the seedling emergence patterns of plants remain largely unknown. In this study, an experiment with four gradients of trampling (no-trampling, light, moderate, and heavy) and three precipitation treatments (ambient precipitation, +30% precipitation, and −30% precipitation) was conducted to assess the effects of trampling disturbance and precipitation variation on seedling emergence of annual plants. The results showed that an increase in precipitation significantly improved total seedling emergence by 3.5–3.6 times and seedling density of grasses by more than 4.1 times under trampling conditions, while significantly improving total seedling emergence and density of forbs under no-trampling conditions. Moreover, +30% precipitation significantly improved the seedling proportion of grasses under light, moderate, and heavy trampling, while decreasing the seedling proportion of forbs. Seedling emergence of forbs was more sensitive to trampling disturbance, and seedling emergence of grasses was more sensitive to precipitation changes, especially under trampling conditions. Light and moderate trampling with a +30% precipitation increase promoted seedling emergence of grasses, and no trampling with a +30% precipitation increase improved seedling emergence of forbs. Thus, targeted grazing management measures should be implemented for plant communities dominated by either grasses or forbs under changing precipitation conditions.

Bromelain crude extract to improve the emergence and growth of pepper seedlings

Pepper (Capsicum annuum L.) is one of the most consumed horticultural products worldwide. However, pepper seeds have slow and asynchronous germination. Organic agriculture encourages using natural substances for the pre-germinative treatment of seeds. The objective of the present work was to evaluate the effect of priming sweet pepper seeds with bromelain crude extract (obtained from pineapple stem residues) on subsequent seedling emergence and growth. The effects of the proteolytic activity of the extract (0, 3.16, 6.25, 12.25, and 25.0 totalU), imbibition time (0, 3, 6, 9, 12, and 15 h), and imbibition temperature (15, 25, 35 and 45 ℃) on seedling emergence and growth were assessed. The significantly best emergence, based on a range of indicators (emergence percentage: E, time to 50% emergence: TE50, emergence index: EI, mean emergence rate: MER, mean emergence time: MET, and synchronization index: SI), was obtained when the seeds were treated for three h at 35°C with a 6.25 totalU bromelain crude extract. Seeds subjected to this treatment combination also yielded the most vigorous seedlings (number of true leaves, length and thickness of the stems, fresh mass, dry mass, leaf area) . In conclusion, pre-germinative treatment with bromelain crude extract of 6.25 totalU proteolytic activity for three h at 35°C improved seedling emergence and growth in sweet pepper seedlings relative to untreated seed. This result offers an organic priming alternative for seeds of sweet pepper.

Native bacteria and cyanobacteria can influence seedling emergence and growth of native plants used in dryland restoration

Abstract Seed‐based ecosystem restoration has huge potential to restore degraded drylands. However, fewer than 10% of directly sown seeds transition to established seedlings. One of the potential factors restricting plant establishment in degraded soils is the low abundance and diversity of native soil micro‐organisms. In this study, we investigated whether returning indigenous bacteria and cyanobacteria consortia to degraded dryland soils improved seedling emergence, survival and growth of native plants. We inoculated ‘culturable whole soil’ native heterotrophic bacteria and biocrust cyanobacteria individually and as a mixed inoculant into extruded pellets containing Acacia inaequilatera (Fabaceae) and Triodia epactia (Poaceae) seeds. The pellets were planted in an active minefield for 28 weeks and seedling emergence and total biomass of plants were determined. Cyanobacteria and bacteria inoculants increased the emergence of A. inaequilatera by 55% and 48%, respectively. Seedling emergence in T. epactia was increased by 20% by cyanobacteria but was not increased by bacteria. The only effect of inoculation on seedling survival or mass per surviving seedling in either species was an 11% reduction of the growth of T. epactia seedlings that were inoculated with cyanobacteria. Synthesis and applications: Our results suggest that the benefit of micro‐organisms on plant establishment is both species specific and life stage specific, with particularly strong benefits in the early stages of recruitment. Our experiment was conducted under shade and with additional water, so a worthwhile future direction would be to quantify the effect of inoculation under unmodified field conditions. It would also be worthwhile monitoring the outcomes for longer than 28 weeks. Since seedling emergence is one of the critical challenges in dryland restoration, our study provides direct evidence in the use of native micro‐organisms to potentially improve seedling emergence in seed‐based dryland restoration.

Effect of bio-seed priming and nano zinc oxide foliar application on quality and productivity of finger millet + greengram intercropping system

A critical stage of the plant's life cycle is germination and insufficient seedling emergence contributes to the lower productivity of finger millet. Priming improves seedling emergence, reduces stand establishment time, and improves seedling germination. There is a need to develop a new technology like Nanotechnology that can precisely detect and deliver the right amount of nutrients or other inputs to safe crops for the environment and maximising productivity. A field experiment was conducted during Kharif season to evaluate the response of effective farming practice for sole finger millet + greengram intercropping system under rainfed conditions to varied levels of bio-seed priming and foliar application of nanoparticles on crop growth and productivity. The results of the experiment revealed that finger millet (Eleusine coracana) intercropped with greengram (Vigna radiata) (2:1) had a significant level (&lt;0.05) increase in growth and yield parameter of finger millet compared to sole finger millet. Application of Prosopis juliflora leaf extract 1 per cent alone + Foliar ZnO nanoparticle @ 500 ppm showed a significant level (&lt;0.05) increase in growth and yield parameter like grain yield (3238.84 kg ha-1), finger millet equivalent yield (FMEY) (3483.84 kg ha-1) and straw yield (7393.83 kg ha-1) compared to Pogamia pinnata leaf extract 1% alone + Foliar ZnO nanoparticle @ 500 ppm. The present study mainly focussed on cropping system, bio seed priming, and foliar application of nano zinc oxide utilized during rainfed conditions to increase uniform germination, drought resistance and improve crop yield along with nutrient content in seeds.

Seed coat mucilages: Structural, functional/bioactive properties, and genetic information.

Seed coat mucilages are mainly polysaccharides covering the outer layer of the seeds to facilitate seed hydration and germination, thereby improving seedling emergence and reducing seedling mortality. Four types of polysaccharides are found in mucilages including xylan, pectin, glucomannan, and cellulose. Recently, mucilages from flaxseed, yellow mustard seed, chia seed, and so on, have been used extensively in the areas of food, pharmaceutical, and cosmetics contributing to stability, texture, and appearance. This review, for the first time, addresses the similarities and differences in physicochemical properties, molecular structure, and functional/bioactive properties of mucilages among different sources; highlights their structure and function relationships; and systematically summarizes the related genetic information, aiming with the intent to explore the potential functions thereby extending their future industrial applications.

Field-Deployed Extruded Seed Pellets Show Promise for Perennial Grass Establishment in Arid Zone Mine Rehabilitation

Current methods of mine rehabilitation in the arid zone have a high failure rate at seedling emergence largely due to limited availability of topsoil and low water-holding capacity of alternative growth substrates such as mining overburden and tailings. Further, seedlings have consistently failed to emerge from seeds sown on the soil surface using traditional broadcasting methods. Seed pellets, formed by extruding soil mixtures and seeds into pellets, can potentially increase soil water uptake through enhanced soil-seed contact and thereby improve seedling emergence. We tested an extruded seed pelleting method in a three-factor field experiment (i.e., different pellet-soil mixtures, organic amendments, and simulated rainfall regimes) in north-western Australia. Given the observed lack of seedling emergence from broadcast seeds, the aims of the experiment were to assess: (i) the use of pellets to promote native seedling emergence and establishment and; (ii) the soil physico-chemical and microbiological changes that occur with this method of rehabilitation. The effects of pellet-soil mixtures, organic amendment, and rainfall regime on seedling emergence and survival of three native plant species suggest trade-offs among responses. Pellets made with a 1:1 blend of topsoil and a loamy-sand waste material had the highest seedling emergence, while 100% topsoil pellets had lower emergence probably because of hardsetting. Triodia pungens (a native grass) survived to the end of the experiment while Indigofera monophylla and Acacia inaequilatera (native shrubs) emerged but did not survive. Adding an organic amendment in the extruded pellet inhibited Triodia seedling emergence but increased soil microbial activity. Overall, extruded pellets made from a 1:1 blend showed promise for the establishment of Triodia seeds and beneficially, incorporates mine waste overburden and lesser amounts of topsoil. Further research is needed to improve pelleting production and to test the applicability of the method at scale, for different species and other ecosystem types.

Dormancy breaking in Teramnus labialis (L.f.) Spreng seeds through liquid nitrogen exposure is based on the modification of the hilar region, cuticle, and macrosclereid

Teramnus labialis (L.f.) Spreng is a legume that plays an important role in mixed agroecosystems, due to its use as animal feed and its role in restoring soil nitrogen levels. However, its wide-scale use in agriculture and revegetation efforts is limited due to its physically dormant seeds. In our previous study on the effects of seed cryopreservation on seedling vigor in this species, our preliminary findings (using scanning electron microscopy) indicated that liquid nitrogen (LN) disrupted the seed coat in this species and led to improved seedling emergence. In our present study, we use light microscopy to investigate whether LN exposure influences the structure/integrity of the hilar region, cuticle, and macrosclereid in relation to seed imbibitional rate and germination. In terms of thickness, statistically significant differences between treated and control seeds were not observed in the cuticle, macrosclereid, osteosclereid or the counter-packed cell layer. Contrastingly, the percentage of seeds with the hilar region open reached 45% in seeds treated with LN but only 10% in the control seeds. Additionally, 85% of seeds immersed in LN showed cracks and breaks in the cuticle and macrosclereid, which were not present in the control. Seed exposure to LN improved seed imbibition rate and germination significantly relative to control seeds/seedlings. Cryo-stored seeds showed a 5.6 fold-increase in imbibition rate, and 2.6 fold-increase in germination. The results validate the use of LN exposure for breaking physical dormancy in seeds of other legumes that display seed anatomy similar to T. labialis.

Treatment of bell pepper (Capsicum annuum L.) seeds with chitosan increases chitinase and glucanase activities and enhances emergence in a standard cold test

Pepper (Capsicum annuum), as a warm-season crop, germinates poorly under wet and cold soils due in part to seed fungal diseases. The objective of this study was to test whether seed treatment with chitosan improved low temperature germination by increasing chitinase and glucanase activities. Pepper seeds were imbibed in 0.01, 0.05, 0.1, 0.3, and 0.5 % chitosan solutions, 1 % acetic acid, 1 % Benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazole] fungicide, or hydroprimed in distilled water for comparison with dry-untreated seeds. After treatment, all seeds were slowly dried back to their original moisture content and evaluated for germination percentage, mean time to germination (MTG), seedling growth in a warm germination test and for seedling emergence in a standard cold test. Chitinase and glucanase activities were also measured for seeds after treatment and for germinating seedlings. Seeds treated with chitosan or hydroprimed germinated faster with decreased MTG compared to untreated seeds germinated at 25 °C and produced longer seedlings with greater fresh weights. Treatment of seeds with chitosan significantly improved final germination percentage by 8% in the second lab experiments (≥90 %). Seed treatment with chitosan or hydropriming improved seedling emergence in the cold test by 29 %. Seed treatment with chitosan increased chitinase and glucanase activities in both seeds and seedlings compared to untreated seeds. In conclusion, treatment of pepper seeds with chitosan improved seed germination under wet and cold conditions, which might be due to the induction of systemic acquired resistance in seeds by increasing chitinase and glucanase activities. Greater chitinase and glucanase activities in chitosan-treated seeds might protect seedlings from fungal diseases under cold conditions.

Hydro-Priming Effects on Seed Germination and Field Performance of Faba Bean in Spring Sowing

Seed priming has been used to advance germination and stand in several crops, but relevant research on faba bean (Vicia faba L.) is scarce. Laboratory and field trials were carried out for two years to study the effect of hydro-priming on faba bean germination and field performance in spring sowing. In laboratory trials, the effects of hydro-priming for 0, 8, 16, 24, 36, and 48 h on final germination percentage, germination speed, Timson’s germination index, mean germination time, mean daily germination, synchronization index, and seedling vigor index were studied. All hydro-priming treatments improved germination parameters of faba bean seeds, except for final germination percentage and mean daily germination compared with non-primed seeds. Averaged over priming duration treatments, hydro-priming improved germination speed by 16.2%, germination synchrony by 20.7%, and seedling vigor index by 13.4%. All hydro-priming durations improved germination synchrony, while hydro-priming for 8, 16, and 24 h provided the highest values of germination speed (2.56, 2.58, and 2.37 seeds day−1, respectively). Hydro-priming for 8 and 16 h provided the lowest values of mean germination time (5.81 and 5.96 days, respectively). In field trials, hydro-priming periods of 0, 8, 16, and 24 h were compared. On average, seed hydro-priming did not affect significantly seedling emergence 14 days after sowing in the first year, but significantly improved seedling emergence by 34.4% in the second year. No significant effect of seed hydro-priming was noted in the number of plants at 28 and 35 days after sowing. Seed priming for 8 h resulted in higher fresh weight at anthesis by 22.3% and 8.6% in the first and the second year, respectively, than the non-primed control. Similarly, seed priming for 8 h provided higher seed yield by 12.0% in the first year and by 5.9% in the second year compared with non-primed control. Overall, seed hydro-priming accelerated faba bean germination and seedling emergence, but the magnitude of the response was associated with the environment and was more evident under limited soil moisture after sowing, whereas the beneficial effect of priming was masked when rainfall followed sowing. Similarly, the beneficial effect of priming on seed yield was more pronounced with limited soil moisture after anthesis.

Impacts of bracteole removal and seeding rate on seedling emergence of halophyte shrubs: implications for rangeland rehabilitation in arid environments

Direct seeding techniques often result in unsatisfactory outcomes in rangeland rehabilitation, primarily because of low seedling emergence and poor establishment. Seed processing techniques aimed at improving seedling emergence have gained interest by pasture managers. The purpose of this study was to investigate the combined effects of bracteole removal and seeding rate on seedling emergence in seven halophytic species: Atriplex halimus, A. canescens, A. leucoclada, A. nummularia, A. lentiformis, Salsola vermiculata and Haloxylon aphyllum under semi-arid conditions in Tel Hadya (Syria). Each of these species was evaluated for seedling emergence under two seed treatments (bracteoles removed and non-removed bracteoles) with three seeding rates (10, 30 and 60 seeds per pot), in a completely randomised block design. The results showed a positive effect of seed treatment on seedling emergence for all studied species. The native A. halimus had the highest emergence percentages whereas the introduced A. mummularia, had the lowest. However, there were no significant effects of seeding rates on seedling emergence. These results showed that bracteole removal could improve germination and seedling emergence, and potentially increase the rate of establishment of the species studied. Therefore, when implementing rangeland rehabilitation projects, bracteole removal needs to be considered. The native S. vermiculata should be recommended for direct seeding in the West Asia and North Africa region given its high seedling emergence, known high palatability, nutritive value, and high auto-regeneration performance.

Damping-off caused by Pythium sylvaticum on soybeans subjected to periods of cold stress is reduced by seed treatments

Soybean damping-off caused by Pythium spp. is frequently associated with the occurrence of cold weather fronts soon after spring planting. In this study, we evaluated the efficacy of a commercial seed treatment with metalaxyl and ethaboxam on emergence during various simulated cold stress conditions. A growth chamber experiment utilized a five-way factorial design with two cold stress temperatures (4ºC and 10ºC), two cold stress timings (initiated 24 and 96 h after planting), three durations of cold stress (24, 48 and 96 h), and two levels of seed treatment (INTEGO SUITETM and untreated). Cups planted with soybean seeds IA 2094 were inoculated with P. sylvaticum or not inoculated. Cups were incubated at 18ºC and evaluated 21 days after planting. Seedling emergence was reduced when the pathogen was present compared with the non-inoculated controls. In untreated seed, cold stress duration reduced seedling emergence, but no differences in emergence were detected in response to either initiation of cold stress or cold stress temperature. The seed treatment improved seedling emergence, reduced root rot severity and increased shoot weight. There was no significant effect of seed treatment on root weight. Data from this study confirm that cold stress soon after planting can increase the risk of reduced crop stands in Iowa and suggest that seed treatment with metalaxyl and ethaboxam protects seedlings when cold conditions are expected soon after planting.

Seed mucilage interacts with soil microbial community and physiochemical processes to affect seedling emergence on desert sand dunes.

Seedling emergence is a critical stage in the establishment of desert plants. Soil microbes participate in plant growth and development, but information is lacking with regard to the role of microbes on seedling emergence. We applied the biocides (captan and streptomycin) to assess how seed mucilage interacts with soil microbial community and physiochemical processes to affect seedling emergence of Artemisia sphaerocephala on the desert sand dune. Fungal and bacterial community composition and diversity and fungal-bacterial interactions were changed by both captan and streptomycin. Mucilage increased soil enzyme activities and fungal-bacterial interactions. Highest seedling emergence occurred under streptomycin and mucilage treatment. Members of the phyla Firmicutes and Glomeromycota were the keystone species that improved A.sphaerocephala seedling emergence, by increasing resistance of young seedlings to drought and pathogen. Seed mucilage directly improved seedling emergence and indirectly interacted with the soil microbial community through strengthening fungal-bacterial interactions and providing favourable environment for soil enzymes to affect seedling emergence. Our study provides a comprehensive understanding of the regulatory mechanisms by which soil microbial community and seed mucilage interactively promote successful establishment of populations of desert plants on the barren and stressful sand dune.

Rice (Oryza sativa L.) germplasm with better seedling emergence under direct sowing in flooded paddy field

AbstractDirect sowing of rice in a flooded paddy field is a beneficial cultivation practice for water use and labour efficiency, compared to the transplanted cultivation. However, a drastic reduction in seedling emergence under flooded paddy fields is a serious constraint especially when the seeds fell at deeper soil layers. Suitable rice germplasm for the direct sowing in flooded paddy fields could ensure the success of this cultivation practice. Instead of laborious field-based screening systems, a pot-based screening method was adopted for simplicity and efficient evaluation of seedling emergence of a subset of world rice germplasm (n = 75) at different sowing depths. As a result, two rice genotypes, ‘Vary Futsi’ (landrace from Madagascar, non-glutinous, subspecies Indica) and ‘Dahonggu’ (landrace from China, non-glutinous, subspecies Indica), with consistently better seedling emergence were identified from a wide range of rice germplasm. These genotypes could serve as excellent parents for the breeding program in developing new rice cultivars with the improved seedling emergence in flooded paddy fields. There were no significant differences in the seedling emergence rate in flooded paddy conditions among the groups from various agro-geographical regions.

Fludioxonil + Mefenoxam Seed Treatment Improves Edamame Seedling Emergence

Poor crop establishment is a major problem in edamame (Glycine max), a specialty type of soybean produced in locations throughout the United States. The objective of this research was to quantify the extent to which seed treatment with fludioxonil + mefenoxam improves seedling emergence of edamame. Emergence characteristics of fludioxonil + mefenoxam-treated and nontreated seed of 30 cultivars were characterized in field conditions over 2 years. Edamame cultivars used in the study exhibited poor field emergence in a previous study despite high germinability. Seed treatment with fludioxonil + mefenoxam at 2.5 and 3.75 g/100 kg seed, respectively, improved crop emergence 33% to 47% more than the nontreated control. The emergence rate (days to 50% emergence) was improved the most by the seed treatment for several cultivars that were generally slow to emerge. Crop establishment is essential for further development of domestic edamame production. Seed treatment with fludioxonil + mefenoxam, at the rate currently registered for use on grain-type soybean, offers one approach to help vegetable growers improve edamame seedling emergence.

Influence of soil pathogens on early regeneration success of tropical trees varies between forest edge and interior.

Soil fungi are key mediators of negative density-dependent mortality in seeds and seedlings, and the ability to withstand pathogens in the shaded understory of closed-canopy forests could reinforce light gradient partitioning by tree species. For four species of tropical rainforest trees-two shade-tolerant and two shade-intolerant-we conducted a field experiment to examine the interactive effects of fungal pathogens, light, and seed density on germination and early seedling establishment. In a fully factorial design, seeds were sown into 1m2 plots containing soil collected from underneath conspecific adult trees, with plots assigned to forest edge (high light) or shaded understory, high or low density, and fungicide or no fungicide application. We monitored total seed germination and final seedling survival over 15weeks. Shade-intolerant species were strongly constrained by light; their seedlings survived only at the edge. Fungicide application significantly improved seedling emergence and/or survival for three of the four focal species. There were no significant interactions between fungicide and seed density, suggesting that pathogen spread with increased aggregation of seeds and seedlings did not contribute to pathogen-mediated mortality. Two species experienced significant edge-fungicide interactions, but fungicide effects in edge vs. interior forest varied with species and recruitment stage. Our results suggest that changes to plant-pathogen interactions could affect plant recruitment in human-impacted forests subject to fragmentation and edge-effects.

Seed priming improves seedling emergence and reduces oxidative stress in Nigella sativa under soil moisture stress

ABSTRACTNigella sativa seeds have multiple industrial and pharmaceutical uses for the diseases treatment such as bronchitis, rheumatism, high blood pressure, cough, eczema, inflammation, and influenza. Although semi-arid areas are suitable for production of annual medicinal plants because they receive favorable amounts of solar radiations, the establishment of these plants' seedling requires frequent irrigations because their seeds are small and the climate is hot at the time of planting. When the irrigation sources are limited, poor establishment and inadequate production will result. Therefore, in order to improve nitrogen (N) in N. sativa seedling establishment, different effects of seed priming treatments were evaluated under drought stress. Different levels of soil moisture (irrigation after 11, 22, 33, and 44 mm of evaporation as no water stress, mild water stress, moderate water stress, and severe water stress, respectively) and seed priming treatments [no priming, potassium nitrate (KNO3), zinc sulfate (ZnSO4), polyethylene glycol 6000, and gibberellic acid (GA)] were evaluated as the main plot and subplot factors, respectively. The results showed that under mild water stress condition, seed priming significantly increased proline content and the highest percentage of emergence was obtained with ZnSO4. Furthermore, the highest amount of soluble protein was observed in the KNO3 treatment and the catalase enzyme content increased in all priming treatments, except polyethylene glycol treatment. Under moderate water stress condition, the KNO3 treatment raised the rate and percentage of emergence and the seedling length. However, under severe water stress condition, the highest percentage of emergence was achieved by GA and ZnSO4 treatments. Moreover, hydropriming and GA produced the highest proline content and seedling dry weight. Under moderate and severe water stress conditions, the hydropriming and ZnSO4 treatments showed a significant increase in catalase activity. It can be concluded that priming of N. sativa seeds with ZnSO4 and GA can alleviate drought stress in the early stages of seedling growth by increasing the antioxidants in the seedlings. Farmers in semi-arid regions can prime N. sativa seeds with these compounds before planting to increase production of this valuable medicinal plant and reduce water consumption.

Small vegetation gaps increase reseeded yellow-flowered alfalfa performance and production in native grasslands

Reseeding yellow-flowered alfalfa (YFA) in degraded grasslands may require a vegetation-free microsite for germination and subsequent establishment. This study aimed to examine the role of microclimates of different-sized vegetation gaps on seedling performance and adult plant production of YFA. Field microsites were established in the meadow steppe of Hulunber, Inner Mongolia, China. Seedling performance, plant production, the microclimate within vegetation gaps, and soil nutrients (plant-available N, P, and K, total N concentration) were assessed at the end of each growing season from 2013 to 2015. Our results indicate light availability, and topsoil temperature of each gap were significantly increased as gap size increased, while topsoil moisture and air relative moisture were decreased in larger gaps. Small gaps (diameter ≤10cm) improved seedling emergence, survival, biomass, and root nodulation, as compared with seedling performance associated with the larger gaps, presumably in response to increased shade and moisture. Additionally, large gaps (>20 or >40cm) were characterized by significantly lower plant-available P, total N concentrations, plant-available K, and soil pH. However, root exclusion treatments did not improve overall seedling performance, plant production, or soil properties, as compared to corresponding microsites with root presence, regardless of gap size. Our results suggest that reseeding YFA into grasslands where disturbance, such as light grazing, has resulted in small gaps will be more effective than in highly degraded grasslands.

Increasing the germination envelope under water stress improves seedling emergence in two dominant grass species across different pulse rainfall events

Summary Demographic recruitment processes, such as seed germination and seedling emergence, are critical transitional phases to the re‐establishment of degraded plant populations, but often fail due to rainfall not supporting plant requirements. Using species from the widespread arid Australian perennial grass genus Triodia, we investigated the interactions of seeds in different dormancy states and their functional germination envelope in response to water stress after simulated pulse rainfall events. Seed dormancy was alleviated in Triodia species to varying degrees by wet/dry cycling or by removing floret structures from seeds. The seeds were then exposed to different rainfall frequency and quantity events mimicking the 25th, median, 75th and 95th percentile rainfall events found in natural habitats for the study species in the north‐west Australian arid zone. Under 95th percentile rainfall conditions recruitment was highest, but still limited to 35% germination and 10% emergence of cleaned seeds (i.e. the least dormant state evaluated). This was related to the functional germination envelope as indicated by more negative base water potential thresholds (Ψb50) for cleaned seeds (≥ −0·33 MPa) compared to intact florets (≥ −0·26 MPa). As a result, the maximum cumulative time where soil water potentials were optimal for germination (Ψsoil ≥ Ψb50) was 1·6–2·6 times longer for cleaned seeds in large frequent rainfall events when compared to intact florets. Furthermore, seed dormancy, that usually prolongs seed survival, was linked to a short‐term reduction in seed viability, which may further reduce recruitment rates. Synthesis and applications. Our findings indicate that large frequent rainfall events raised soil water potentials above critical thresholds for germination and are important for successful plant establishment. If recruitment bottlenecks are a result of seed dormancy and variable rainfall for arid grass species, then this study shows benefits for alleviating seed dormancy prior to seeding in restoration sites, as this increases the environmental envelope for germination.

Abiotic barriers limit tree invasion but do not hamper native shrub recruitment in invaded stands

The interplay between the invasion of alien plant species and re-colonization of native plant species is important for conservation. Sandy coastal plains (called restinga in Brazil) were used as a model system to explore the abiotic barriers that potentially limit the initial establishment of alien and native woody plants in invaded and non-invaded areas. The study tested the influence of light availability, soil type and litter layer on recruitment of a wind-dispersed alien tree (Casuarina equisetifolia) and two bird-dispersed native shrubs under a Casuarina stand and in the preserved restinga. The effect of soil type and the physical and allelopathic effects of Casuarina litter on seedling emergence of the three species were also evaluated under greenhouse conditions. Low dispersal associated with low seedling emergence and zero survival of young plants (mainly due to microhabitat conditions) apparently prevents the spread of Casuarina in the preserved restinga. The main cause of low recruitment of native species in the Casuarina stand was the physical barrier of the litter. However, if seeds overcome this physical barrier, the presence of litter improves seedling emergence and survival of young plants, mainly because the litter increases soil moisture. Sowing seeds below litter and planting young plants of native shrubs on litter can improve the re-colonization of native plants in invaded areas. In conclusion, Casuarina invasion on sandy coastal plains is strongly limited by abiotic barriers, but anthropogenic disturbances are altering the key processes that naturally make the restinga resistant to invasion.