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.

Morphological, Biochemical, and Metabolomic Strategies of the Date Palm (Phoenix dactylifera L., cv. Deglet Nour) Roots Response to Salt Stress

Numerous Tunisian arid and semi-arid regions are subjected to soil salinity. Thus, they are known for halophytes plants cultivation, including date palms. Phoenix dactylifera L., cv. ‘Deglet Nour’, is a valuable Tunisian cultivar subjected to high salinity levels. In this way, our purpose is to evaluate the response of its roots to long period exposition to increasing salt concentrations. We started by studying the effects of 4 g/L, 8 g/L, 12 g/L, and 16 g/L NaCl on the parameters of germination (Growth rate—GR, Seed Mortality Rate—SLM, Germination Mean Time—GMT, and Germination Speed—GS) of date palm seeds for a 2-month period. We found that 4 g/L NaCl did not affect the seeds germination, and, hereinafter, the parameters of germination and the radicle length decreased with the increase of NaCl concentrations and experiment time. Then, we demonstrated a high antioxidative enzymes CAT and SOD production in case of salt stress augmentation. Lastly, a metabolomic approach was carried out by LC-HRMS, followed by an untargeted and targeted analysis using the XCMS online and MZmine tools, respectively. The roots chemical composition was compared using PCA. We identified 25 secondary metabolites, divided into 3 categories. Metabolites known for their role in salt stress alleviation include δ-tocotrienol, metabolites identified in salt stress for the first time, and other unknown metabolites.

Burial Environment Drives Seed Mortality of Kochia (Bassia scoparia), Wild Oat (Avena fatua), and Volunteer Canola (Brassica napus) Irrespective of Crop Species

Models of weed population demography are critical to understanding the long-term viability of management strategies. The driving factors of weed seedbank persistence are often underrepresented in demographic models due to the cumbersome nature of seedbank research. Simplification of weed seedbank dynamics may induce substantial error in model simulations. A soil bioassay was conducted to determine whether growth of different crop species, including wheat (Triticum aestivum L.), canola (Brassica napus L.), and field pea (Pisum sativum L.), differentially impact seed mortality of kochia [Bassia scoparia (L.) A.J. Scott], wild oat (Avena fatua L.), and volunteer canola in seven burial environments in western Canada. Weed seed survival after the 7 week burial period varied widely among burial environments (from 8% to 88% when averaged among weed and crop species), whereas growth of the different crop species had negligible impact on seedbank persistence. Among environments, wild oat seed survived the greatest (79%), followed by kochia (20%), and volunteer canola (6%). Weed seed survival was associated with soil physical properties (texture) and seed microsite characteristics (temperature), but not crop species or soil chemical properties. Overall, these data support the need for greater integration of soil and environmental parameters into models of weed population demography.

Culturable Seed Microbiota of Populus trichocarpa

Plants harbor a diverse community of microbes, whose interactions with their host and each other can influence plant health and fitness. While microbiota in plant vegetative tissues has been extensively studied, less is known about members of the seed microbiota. We used culture-based surveys to identify bacteria and fungi found in the seeds of the model tree, Populus trichocarpa, collected from different sites. We found that individual P. trichocarpa seeds typically contained zero or one microbe, with common taxa including species of Cladosporium, Aureobasidium, Diaporthe, Alternaria, and Pseudomonas, a bacterium. Pseudomonas isolates were associated with seed mortality and were negatively associated with the occurrence of fungal isolates within Epicoccum, Alternaria, and Aureobasidium from the same seed. Next, we conducted an inoculation experiment with one of the isolated seed microbes, Pseudomonas syringae pv. syringae, and found that it reduced seed germination and increased seedling mortality for P. trichocarpa. Our findings highlight common fungi and bacteria in the seeds of P. trichocarpa, prompting further study of their functional consequences. Moreover, our study confirms that P. syringae pv. syringae is a seed pathogen of P. trichocarpa and is the first report that P. syringae pv. syringae is a lethal seedling pathogen of P. trichocarpa, allowing for future work on the pathogenicity of this bacterium in seedlings and potential antagonism with other seed microbes.

Fungi and insects compensate for lost vertebrate seed predation in an experimentally defaunated tropical forest

Overhunting reduces important plant-animal interactions such as vertebrate seed dispersal and seed predation, thereby altering plant regeneration and even above-ground biomass. It remains unclear, however, if non-hunted species can compensate for lost vertebrates in defaunated ecosystems. We use a nested exclusion experiment to isolate the effects of different seed enemies in a Bornean rainforest. In four of five tree species, vertebrates kill many seeds (13–66%). Nonetheless, when large mammals are excluded, seed mortality from insects and fungi fully compensates for the lost vertebrate predation, such that defaunation has no effect on seedling establishment. The switch from seed predation by generalist vertebrates to specialist insects and fungi in defaunated systems may alter Janzen–Connell effects and density-dependence in plants. Previous work using simulation models to explore how lost seed dispersal will affect tree species composition and carbon storage may require reevaluation in the context of functional redundancy within complex species interactions networks.

Plant and Seed Mortality of Fireweed Senecio madagascariensis Following Herbicide Application

Fireweed (Senecio madagascariensis Poir), is a weed of National significance and one of the worst weeds of coastal pastures in South Eastern Australia. Chemical control has been found to be effective in killing plants but there is no information on the effect of herbicides on the seeds that may be present on plants at the time of application. Consequently, a study was undertaken to determine the effect of five selective herbicides (1) on plant mortality at different life stages and (2) on the viability (as assessed by germination) of fireweeds seeds at different stages of maturity. Potted plants of the required growth stages were obtained through several collections of different sized seedlings from a field site near Brisbane. Before herbicide application, in the mature plant cohort the inflorescences were tagged according to their maturity as being either immature (IM) or intermediate (INT). Plants were sprayed with either fluroxypyr/aminopyralid (HotShot™) (A), bromoxynil (Bromicide® 200) (B), metsulfuron-methyl (Brush-Off®) (C), triclopyr/picloram/aminopyralid (Grazon™ extra) (D), triclopyr/picloram/aminopyralid (TordonTM regrowthMaster) (E) at the recommended rates with untreated control plants of the three growth stages also included for comparison. All herbicides killed fireweed seedlings and juvenile plants, but only treatments A, D and E gave high plant mortality (>80%) of mature plants. All herbicides also caused nil germination of seeds collected 30 days after spraying, except for a small percentage (8% germination) of mature seeds from Bromoxynil treated plants. These results have identified several herbicides capable of killing mature fireweed plants and minimizing replenishment of soil seed reserves.

Physiological and biochemical responses of selected cowpea (Vigna unguiculata (L.) Walp.) accessions to iron toxicity

<p>This study aimed to investigate the effect of iron toxicity in cowpea using physiological and biochemical responses of selected accessions. Fifteen accessions of cowpea were exposed to two treatments of iron using FeSO₄ solution (100 mg l^-1 and 400 mg l^-1) and distilled water at pH 6.2 as control. The results showed that there was a general reduction in germination morphology; germination percentage among the 400 mg l^-1 Fe-treated accessions. Seed mortality rates were significantly higher among the 400 mg l^-1Fe-treated accessions (&gt; 35 %). Water imbibition capacity and relative mass gained were higher for Fe-treated accessions. Furthermore, significant increase in the total sugar and percentage utilization of sugars was accompanied by an insignificant decrease in chlorophyll a, a significant decrease in chlorophyll b contents and the persistence of foliar chlorosis, among the 400 mg l^-1 Fe-treated accessions. MDA levels were significantly increased while proline remained unchanged, mean SOD activity was insignificantly increased, whereas Cat decreased among the 400 mg l^-1 Fe-treated accessions. Documentation of these observable changes in physiological and biochemical parameters will be useful in understanding the impact of elevated iron concentrations on the cultivation of cowpea accessions in soils associated with ferruginous ultisols.</p>

Fate of Weed Seeds after Impact Mill Processing in Midwestern and Mid-Atlantic United States

Harvest weed seed control (HWSC) technology such as impact mills that destroy weed seeds in seed-bearing chaff material during grain crop harvest, has been highly effective in Australian cropping systems. However, the impact mill has never been tested in soybeans and weeds common to soybean production systems in the Midwest and Mid-Atlantic US. We conducted stationary testing of Harrington Seed Destructor (HSD) impact mill and winter burial studies during 2015-2016 and 2017-2018 to determine (i) the efficacy of the impact mill to target weed seeds of seven common weeds in Midwestern and five in Mid-Atlantic US, and (ii) the fate of impact mill processed weed seeds after winter burial. The impact mill was highly effective in destroying seeds of all the species tested, with 93.5-99.8% weed seed destruction in 2015 and 85.6-100% in 2017. The weak relationships (positive or negative) between seed size and seed destruction by impact mill, and high percentage of weed seed destruction by impact mill across all seed sizes indicate that the biological or practical effect of seed size is limited. The impact mill-processed weed seeds that retained at least 50% of their original size, labeled as potentially viable seed (PVS), were buried for 90 d over winter to determine the fate of weed seeds after winter burial. At 90 d after burial (DAB), the impact mill processed PVS were significantly less viable than unprocessed control seeds, indicating that impact mill processing physically damaged the PVS and promoted seed mortality over winter. A very small fraction (< 0.4%) of the total weed seed processed by the impact mill remained viable after winter burial. The results presented here demonstrate that the impact mill is highly effective in increasing seed mortality and could potentially be used as a HWSC tactic for weed management in this region.

Density-dependent seed predation in Attalea geraensis Barb. Rodr. (Arecaceae) caused by bruchid beetles in the Brazilian Cerrado

Palms are an important component of Neotropical communities as they are often diverse and abundant. In some areas, palms occur in high density and act as limiting factor in tree recruitment by limiting tree seedling and sapling abundance. In this study, I evaluated the intensity of seed mortality caused by insects in Attalea geraensis, in a large area of preserved Cerrado (Serra do Cabral, MG, Brazil) during wet season when both A. geraensis fruits and bruchid beetles were abundant. I collected a total of 63 infructescences which had from 3 fruits and 7 seeds to 82 fruits and 251 seeds. Endocarps had from 1 to 6 seeds. Seed mortality per infructescence due to beetles (Pachymerus cardo) was intense, and increases positively and disproportionally according to seed number per infructescence. Besides that, average proportions of seeds preyed upon by insects were consistently high (> 0.83), irrespective of seed number per endocarp. Positive density-dependent seed mortality caused by specialized natural enemies has been assumed to promote species rarity, an important feature of species coexistence in Neotropical forests. Then, the intense seed mortality documented in this study suggests that seed predators may contribute to the richness and diversity of plant species in the Cerrado, the richest and most endangered savanna in the world.

Risk Analysis Of Red Tilapia Breeder In Kelompok Pembudidaya Ikan Mino Ngremboko, Ngemplak Subdistrict Sleman Regency

This study analysed the receipts, costs, and expenses received by red tilapia seed farmers, as well as the level of production risk, price risk and expenditure risk in KPI Mino Ngremboko. The basic method used in this research was a descriptive method. This research was conducted at KPI Mino Ngremboko. The selection of research locations was conducted purposively. The sampling method used was the census method. The analysis was carried out using the coefficient of variation method. Research results there were production risks, price risk, and risk of spending on red tilapia at KPI Mino Ngremboko. The sources of risk that arise were high fish seed mortality rates, increased feed prices, and limited land to increase production. Variation coefficient value (CV) of production risk, price risk, income risk were relatively low that showed the hatchery of red tilapia has a low risk. Meanwhile, the L value of price risk, production risk, and expenditure risk were positive results and the value was greater than BEP. The value shows that when the hatchery reaches the lowest point in production, price, and income, farmers still avoid losses.