Effects of Seed Size and Cache Density on the Seed Fate of Quercus wutaishanica Mediated by Rodents.

Animal-mediated seed dispersal is very important for plant population regeneration and the stability of forest ecosystems. Seed size and cache density are important factors for seed dispersal, but we still know little about seed size selection at different cache densities. Here, we conducted field experiments in a Larix principis-rupprechtii plantation in the Liupan Mountains in Ningxia province to investigate the effects of tag-marked Quercus wutaishanica seeds of different sizes and cache densities on predation and the scatter-hoarding behavior of rodents. The results showed lower proportions of intact in situ (IIS) and eaten in situ (EIS) large seeds than small seeds at all levels of cache density, with the exception of IIS seeds at a 6.25 seed·m-2 cache density. A higher proportion of small seeds were eaten after removal (EAR), but a higher proportion of large seeds were scatter-hoarded (SH) by rodents at most cache densities. Furthermore, rodents preferentially removed large seeds farther away for eating or scatter-hoarding. The IIS and EIS proportions of both large and small seeds declined, but the proportion of the two types of seeds that were EAR fluctuated, increasing with increasing cache density. Rodents preferred to increase the proportion of scatter-hoarding of large seeds with increasing cache density, whereas the proportion of scatter-hoarding of small seeds was maximized at a cache density of 6.25 seed·m-2. Both the eaten distance after removal (EDAR) and scatter-hoarded distance (SHD) increased with increasing cache density. These results suggest that large seeds are more likely to be scatter-hoarded and removed to longer distances than small ones. Rodents tended to reduce the seed proportion of EIS seeds and increased the proportion of seeds EAR and SH, and accordingly increased EDAR and SHD with increasing cache density. This study provides some scientific basis for animal-mediated seed dispersal.

Responses of soil seed banks to drought on a global scale.

The global increase in drought frequency and intensity in large areas has potentially important effects on soil seed banks (SSBs). However, a systematic evaluation of the impact of drought on SSBs at a global scale has not yet been well understood. We evaluated the effects of drought on SSBs and identified the association key drivers in the current meta-analysis. The overall effects of drought on soil seed density and richness were weak negative and positive, respectively. Drought significantly increased soil seed density by 11.94 % in forest ecosystem, whereas soil seed richness were significantly increased in vascular plants (7.39 %). Linear mixed-effect results showed that soil seed density and richness significantly reduced as increasing drought intensity. In addition, geography (altitude) has significance in controlling the lnRR of soil seed density by altering climate (mean annual precipitation, drought) and soil properties (pH, soil organic carbon, and clay content) in the structural equation model, whereas soil seed richness was controlled by geography (altitude, and latitude) via climate (mean annual precipitation). In summary, the results suggested the size of SSBs response to drought and its relationship with drought intensity in terrestrial ecosystems, it may shed light on ecosystem restoration, succession, and management using SSBs when estimating the future drought.

Molecular detection and quantification of the Striga seedbank in agricultural soils.

Striga hermonthica (Del.) Benth is a devastating parasitic weed in Sub-Saharan Africa (SSA) and its soil seedbank is the major factor contributing to its prevalence and persistence. To date, there is a little information on the Striga seedbank density in agricultural fields in SSA due to the lack of reliable detection and quantification methods. We developed a high-throughput method that combines density- and size-based separation techniques with quantitative polymerase chain reaction (qPCR)-based detection of Striga seeds in soil. The method was optimised and validated by introducing increasing numbers of Striga seeds in two physicochemically different Striga-free agricultural soils. The results showed that as little as one seed of S. hermonthica per 150 g of soil could be detected. This technique was subsequently tested on soil samples of 48 sorghum fields from different agro-ecological zones in Ethiopia to map the geospatial distribution of the Striga seedbank along a trajectory of more than 1500 km. Considerable variation in Striga seed densities was observed. Striga seeds were detectable in 75% of the field soils with densities up to 86 seeds per 150 g of soil. The Striga seed density in soil and the number of emerged Striga plants in the field showed a non-linear relationship. In conclusion, the method developed allows for accurate mapping of the Striga seedbank in physicochemically diverse SSA field soils and can be used to assess the impact of management strategies on Striga seedbank dynamics.

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

Background: Soil seed banks play a central role in vegetation dynamics and may be an important source of ecological restoration. However, the vast majority of seed bank studies examined only the uppermost soil layers (0-10 cm); hence, our knowledge on the depth distribution of seed bank and the ecological significance of deeply buried seeds is limited. The aim of our study was to examine the fine-scale vertical distribution of soil seed bank to a depth of 80 cm, which is one of the largest studied depth gradients so far. Our model systems were alkaline grasslands in East-Hungary, characterised by harsh environmental conditions, due to Solonetz soil reference group with Vertic horizon. We asked the following questions: (1) How do the seedling density and species richness of soil seed bank change along a vertical gradient and to what depth can germinable seeds be detected? (2) What is the relationship between the depth distribution of the germinable seeds and the species traits? Methods: In each of the five study sites, four soil cores (4 cm diameter) of 80 cm depth were collected with an auger for soil seed bank analysis. Each sample was divided into sixteen 5-cm segments by depth (320 segments in total). Samples were concentrated by washing over sieves and then germinated in an unheated greenhouse. Soil penetration resistance was measured in situ next to each core location (0-80 cm depth, 1-cm resolution). We tested the number and species richness of seedlings observed in the soil segments (N = 320), using negative binomial generalized linear regression models, in which sampling layer and penetration resistance were the predictor variables. We ran the models for morphological groups (graminoids/forbs), ecological groups (grassland species/weeds) and life-form categories (short-lived/perennial). We also tested whether seed shape index, seed mass, water requirement or salt tolerance of the species influence the vertical distribution of their seed bank. Results: Germinable seed density and species richness in the seed bank decreased with increasing soil depth and penetration resistance. However, we detected nine germinable seeds of six species even in the deepest soil layer. Forbs, grassland species and short-lived species occurred in large abundance in deep layers, from where graminoids, weeds and perennial species were missing. Round-shaped seeds were more abundant in deeper soil layers compared to elongated ones, but seed mass and ecological indicator values did not influence the vertical seed bank distribution. Our research draws attention to the potential ecological importance of the deeply buried seeds that may be a source of recovery after severe disturbance. As Vertisols cover 335 million hectares worldwide, these findings can be relevant for many regions and ecosystems globally. We highlight the need for similar studies in other soil and habitat types to test whether the presence of deep buried seeds is specific to soils with Vertic characteristics.

The Similarity between Species Composition of Vegetation and Soil Seed Bank of Grasslands in Inner Mongolia, China: Implications for the Asymmetric Response to Precipitation.

The asymmetric response of productivity to precipitation was recently proposed as an early warning signal for the shifts in temperate grassland function in China. It was hypothesized that the asymmetry was influenced by the increased growth of the newly emerged seedlings from the soil seed bank. Therefore, the seed density in the soil seed bank and the similarity between species composition of the vegetation and the soil seed bank should be maximized where asymmetry was maximized. However, this knowledge was still limited and unconfirmed. In this study, the desert steppe, typical steppe and the transition zone between them (with the highest asymmetry) were selected for studying the similarity index in both 2018 (dry year) and 2019 (wet year). Plant species composition was monitored in situ using an unmanned aerial vehicle. Soil seed bank samples were collected, and the seed bank density and species composition were then examined and identified in the laboratory. Results showed that: (1) The variation in vegetation species richness between the two years was the highest (41%) in the transition zone (p < 0.05), while it was only 7% and 13% for the desert steppe and typical steppe, respectively. The presence of herbaceous species mainly caused the differences in variation among three grassland types. (2) Seed density was the highest in the transition zone (114 seeds/m2 and 68 seeds/m2 in the transient and persistent soil seed bank, respectively) (p < 0.05). Additionally, herbaceous species were the main components of the soil seed bank. (3) The similarity index was the highest in the transition zone (p < 0.05), with 38%/44% and 33%/44% for the transient/persistent soil seed bank in 2018 and 2019, respectively. Our study demonstrated that variation in vegetation species composition was very similar to the composition of the seeds accumulated in the soil seed bank. These results warrant further investigation for the mechanism of asymmetric response of productivity to precipitation.

Genome-Wide Association Analysis Identifies Candidate Genes Regulating Seed Number Per Silique in Arabidopsis thaliana.

Seed weight and number ultimately determine seed yield. Arabidopsis seed number comprised of silique number and seed number per silique (SNS). Comparing seed development and weight, determinants of seed number remain largely uncharacterized. In this study, taking advantage of 107 available Arabidopsis accessions, genome-wide association analysis (GWAS) was employed to identify the candidate genes regulating SNS. GWAS-based genotype and phenotype association analysis identified 38 most significant SNPs marker sites that were mapped to specific chromosomal positions and allowed us to screen for dozens of candidate genes. One of them (PIN3) was selected for functional validation based on gene expression analysis. It is a positive regulator of Arabidopsis SNS. Although silique length of PIN3 loss of function mutant was not significantly changed, its SNS and seed density (SD) were significantly reduced as compared with the wild type. Notably, PIN3 overexpression lines driven by a placenta-specific promoter STK exhibited significantly shorter siliques, slightly reduced SNS, but significant increased SD compared with wild type, suggesting that PIN3 positively regulates SD through inducing ovule primordia initiation regardless of the placenta size. Ovule initiation determines the maximal possibility of SNS, and new genes and mechanism regulating SNS through modulating ovule initiation is worth further investigated.

A simple, non-toxic method for separating seeds based on density, and its application in isolating Arabidopsis thaliana seed oil mutants.

PREMISE: Seed oil is an economically important trait in Brassica oilseed crops. A novel method was developed to isolate Arabidopsis thaliana seeds with altered oil content. METHODS AND RESULTS: In A. thaliana, seed oil content is correlated with seed density, with high-oil seeds being less dense than wild type and tending to float in solution, and low-oil seeds being denser and tending to sink. In contrast to previous methods, which used toxic chemicals and density gradient centrifugation, different concentrations of calcium chloride (CaCl2) were employed to separate seeds without the need for centrifugation. The method was validated using known seed oil mutants, and 120,822 T-DNA mutagenized A. thaliana lines were then screened for novel seed density phenotypes. CONCLUSIONS: A number of candidate mutants, as well as new alleles of two genes known to influence seed oil biosynthesis, were successfully isolated.

Comportamento ingestivo de novilhas de corte em pastagem de sorgo forrageiro implantada com diferentes arranjos populacionais / Ingestive behavior of heifers in sorghum implanted with different population arrangements

O objetivo do presente estudo foi avaliar os efeitos da implantação de pastagem de sorgo forrageiro com diferentes arranjos populacionais no comportamento animal e na estrutura do pasto e de suas relações. Os tratamentos foram a combinação de dois espaçamentos entrelinhas e duas densidades de sementes ha-1, sendo 22 ou 44cm entrelinhas e 12 ou 24kg de sementes ha-1. Foram utilizadas 36 novilhas, com idade e peso corporal inicial de 15 meses e 262kg, respectivamente. Os tratamentos E44D24 e E22D12 apresentaram maior tempo de pastejo (469,33 e 467,78 minutos, respectivamente). Os animais do tratamento E44D24 apresentaram menor taxa de bocado (23,99 bocados minuto-1) em relação ao tratamento E22D24 (32,45 bocados minuto-1). Os animais do tratamento E44D12 apresentaram maior número de estações alimentares minuto-1 (9,21) e maior taxa de deslocamento (11,76 passos minuto-1). O espaçamento entrelinhas de plantio de 22cm aumenta o número de bocados estação-1. O aumento na densidade de sementes (24kg ha-1) e a utilização de maiores espaçamentos entrelinhas de plantio aumentam a densidade de folhas nos estratos inferior (0-30cm) e superior (acima de 60cm) do pasto. Os tratamentos E44D12 e E22D24 apresentaram maiores quantidades de colmos no estrato superior do pasto.(AU)

The objective of the study was to evaluate the effects of sorghum pasture implantation with different population arrangements in animal behavior and pasture structure and their relationships. The treatments were the combination of two row lines and two seeds per hectare densities, 22 or 44cm between rows and 12 or 24kg ha -1 of seed. 36 heifers at 15 months of age and 262kg body weight were used. The E44D24 and E22D12 treatments showed higher time of grazing (469.33 and 467.78 minutes, respectively). The animals in E44D24 treatment had lower bit rate (23.99 bites minute -1 ) compared to treatment with E22D24, a higher bit rate (32.45 bits min -1 ). The animals in E44D12 treatment presented the largest number of stations minute -1 (9.21) and higher displacement rate (11.76 steps min -1 ). The row spacing of 22cm increases the number of bits station -1 . The increase in seed density and the use of larger planting row spacing's increase the leaf density of the lower (0-30cm) and higher stratum (above 60cm) of pasture. The E44D12 and E22D24 treatment have higher amounts of stems in the upper stratum of the pasture.(AU)

Comparison of aboveground vegetation and soil seed bank composition at sites of different grazing intensity around a savanna-woodland watering point in West Africa.

Grazing removes a plant's aboveground vegetative and reproductive tissues and can modify the soil seed bank, potentially impacting the restoration of preferred species. Knowledge about aboveground vegetation and species composition of soil seed bank and the processes that contribute to vegetation recovery on and surrounding watering points subjected to grazing is lacking. Successful restoration strategies hinge on addressing these knowledge gaps. We assessed the effects of livestock grazing on aboveground vegetation and soil seed bank characteristics along a river bank and surrounding areas subject to different grazing intensities and draw implications for restoration. Plots (50 × 50 m) were established along five transects representing differing levels of grazing intensity. Soil samples were taken from three layers within each plot to determine soil properties and species composition of soil seed bank using the seedling emergence method. Heavy grazing resulted in the disappearance of perennial grasses, a reduction in species diversity and a decrease in soil nutrients with increased soil depth. Overall, the similarity between the extant aboveground vegetation and flora within the soil seed bank was low. The soil seed bank was dominated by herbaceous species and two woody species, suggesting that many woody species are not accumulating in the soil. With increasing soil depth, the seed density and richness declined. Canonical correspondence analyses (CCAs) showed that emerged seedlings from the soil seed bank were significantly influenced by soil carbon, organic matter, total nitrogen, total potassium and soil cation exchange capacity. This finding suggests that current grazing practices have a negative impact on the vegetation surrounding watering points; hence there is a need for improved grazing management strategies and vegetation restoration in these areas. The soil seed bank alone cannot restore degraded river banks; active transfer of propagules from adjacent undisturbed forest areas is essential.

Variáveis morfogênicas e estruturais de sorgo forrageiro implantado com diferentes arranjos populacionais sob pastoreio contínuo / Morphogenetic and structural variables of sorghum implanted with different population arrangements under continuous grazing

O objetivo do estudo foi avaliar os efeitos da utilização de diferentes arranjos populacionais na implantação de sorgo forrageiro nas características morfogênicas e estruturais do pasto. Os tratamentos foram 22 ou 44cm entrelinhas e 12 ou 24kg de sementes ha-1. O método de pastoreio foi contínuo. Foram utilizadas 36 novilhas, com idade e peso corporal médios de 15 meses de 262kg. As variáveis morfogênicas não foram influenciadas significativamente (P>0,05) pelos arranjos populacionais e pelos períodos de avaliação, sendo obtidos taxa de alongamento e senescência foliar de 1,43 e 1,11cm dia-1afilho-1, respectivamente, taxa de aparecimento foliar e intervalo de surgimento de folhas de 0,28 folhas dia-1afilho-1 e 3,81 dias, filocrono e duração de vida foliar de 72,99 e 351,68 graus dia, nessa ordem. As características estruturais do pasto foram influenciadas pelos períodos de avaliação. Do primeiro para o terceiro período de avaliação, foi verificada uma redução de 65,53% no número de folhas em alongamento e de 47,79% no número de folhas vivas.(AU)

The objective of the study was to evaluate the effects of using different population arrangements in the implementation of sorghum in the morphogenetic and structural characteristics of the pasture. The treatments were 22 or 44cm between rows and 12 or 24kg ha-1 of seed. The grazing method was continuous. The sample consisted of 36 heifers with an average age of 15 months and average body weight of 262kg. Morphogenic variables were not significantly influenced (P>0.05) by population arrangements and evaluation periods, elongation rate and leaf senescence of 1.43 and 1.11cm afilho-1 day-1 being obtained, respectively, and leaf appearance rate of leaf appearance leaves the range of 0.28 day-1 and 1afilho 3.81 days, phyllochron and leaf duration of life of 72.99 and 351.68 degree day, in that order. The structural characteristics of the pasture were influenced by evaluation periods. From the first to the third evaluation period, a reduction of 65.53% in the number of leaves in stretching and 47.79% in the number of living leaves was verified.(AU)

Effects of seed density and proximity to refuge habitat on seed predation rates for a rare and a common Lupinus species.

PREMISE OF THE STUDY: Biotic interactions such as seed predation can play a role in explaining patterns of abundance among plant species. The effect of seed predation will depend on how the strength of predation differs across species and environments, and on the degree to which seed loss at one life-cycle phase increases fitness at another phase. Few studies have simultaneously quantified predispersal and postdispersal predation in co-occurring rare and common congeners, despite the value of estimating both for understanding causes of rarity. METHODS: We quantified predispersal seed predation on the rare, herbaceous species Lupinus tidestromii (Fabaceae) and its common, shrubby congener L. chamissonis across multiple years in the same community. We experimentally measured postdispersal seed predation at two seed densities and locations near or far from an exotic grass housing high densities of deer mice (Peromyscus maniculatus), their primary, native seed predator. KEY RESULTS: The common L. chamissonis had the lowest predispersal seed predation of the two lupine species, potentially because of its height: its high racemes received less predation than those low to the ground. By contrast, the same species experienced higher postdispersal seed predation, and at predators traveled long distances away from refuge habitat to consume their seeds. Across both plant species, mice preferentially predated high-density seed sources. CONCLUSIONS: Our results show differences in the magnitude and direction of seed predation between the species across different life-cycle phases. We demonstrated possible roles of proximity to refuge habitat, seed density, and seed size in these patterns. Congeneric comparisons would benefit from a comprehensive framework that considers seed predation across different life-cycle phases and the environmental context of predation.

Changes in grass plant populations and temporal soil seed bank dynamics in a semi-arid African savanna: Implications for restoration.

The re-colonization or recovery of grass species after disappearance due to heavy grazing depends on the presence of persistent soil seed banks that might be accumulated over time from the aboveground vegetation. Moreover, successful plant recruitment is a function of seed production, seed germination and seedling survival, which can be mechanistically understood through studying the life cycle processes of grass species populations under field conditions. Therefore, we studied the number of germinable seeds, species richness and life-forms in the soil seed banks under light and heavy grazing conditions, and the changes in grass species populations in a semi-arid savanna of Ethiopia. Accordingly, a total of 103 species (15 perennial and 29 annual grasses, 6 legumes, 52 forbs and 1 woody species) emerged from the soil samples collected. Lightly grazed sites had a higher seed density compared with heavily grazed sites. The seed density increased over the first three months of soil sampling and decreased thereafter. Perennial grasses dominated the light grazing sites, whereas annual species dominated the heavily grazed sites, indicating that perennial grasses were replaced by annual species in the soil seed bank through grazing. The mean mortality rate from the seedling stage to adult plants was 65%. The seed-to-seedling stage was found to be the most critical transitional stage for grass survival. High seedling mortality in the aboveground vegetation and depletion of seeds in the soil seed banks as a result of sustained heavy grazing can lead to local extinction and disappearance of perennial grasses in semi-arid Ethiopian savannas.

Effects of the seasonal flooding on riparian soil seed bank in the Three Gorges Reservoir Region: a case study in Shanmu River.

INTRODUCTION: The water-level fluctuation in the Three Gorges Reservoir Region has changed dramatically as a result of the hydroelectric project for flood control and power generation. The riparian seasonal hydrological environment also has changed from summer flooding with winter drought to summer drought with winter flooding. The changes of riparian seed bank and vegetation were investigated to determine the effects of the seasonal flooding on the composition and spatial distribution of riparian soil seed bank and the similarity of seed bank to standing vegetation. CASE DESCRIPTION: We conducted intensive riparian soil sampling (525 samples) along altitude gradient in the Shanmu River, a tributary of the Yangzi River in the reservoir region of China. Seed bank density, species richness and composition of soil seed bank were examined using the seedling-emergence method. The seasonal hydrological conditions resulted in a decrease in species diversity and an increase in the distribution heterogeneity of the soil seed bank. The soil seed bank was composed of 48 species from 22 families and 40 genera. Most species were annual and perennial herbaceous Polygonaceae, Asteraceae, and Poaceae. Rumex dentatus was the predominant species accounting for 27.0 % of the total seeds. Diversity and composition of the seed bank changed along an altitude gradient and soil depth. Maximum species richness was found in the top soil layer at 165 m and 175 m above sea level. The mean overall seed density of the soil seed bank was 13,475.3 ind m(-2). Density and the number of seeds increased initially and then decreased with increased altitude. Maximum seed density (22,500.2 ind m(-2)) was found at 165 m above sea level in the intermediately flooded riverbank, with the seed number accounting for 27.8 % of the total soil seed bank. Average seed density declined significantly with soil depth. The similarity of seed bank to standing vegetation was relatively high. DISCUSSION AND EVALUATION: The environmental heterogeneity created by the wide range and seasonal flooding led to the changes in biodiversity and seed density along altitude gradient. The seasonal flooding also led to the increase in the similarity of seed bank to standing vegetation as their composition both degraded. CONCLUSIONS: The seasonal flooding due to the dam reshape the composition and spatial distribution of riparian soil seed bank and limit the vegetation to a grassland dominated by a few annuals and perennials in the Three Gorges Reservoir Region.

An effective seed protection method for planting Zostera marina (eelgrass) seeds: Implications for their large-scale restoration.

We describe an innovative method of planting Zostera marina (eelgrass) seeds in which hessian bags filled with high-silted sediments are used as a seed protecting device. Here, we evaluated the effectiveness of the method through a field seed-sowing experiment over a three year period. The suitable seed planting density required by the seeds of Z. marina in this method was also investigated. In the spring following seed distribution, seedling establishment rate of Z. marina subjected to different seed densities of 200-500seedsbag(-1) ranged from 16% to 26%. New eelgrass patches from seed were fully developed and well maintained after 2-3years following distribution. The seed planting density of 400seedsbag(-1) may be the most suitable for the establishment of new eelgrass patches. Our results demonstrate that seed-based restoration can be an effective restoration tool and the technique presented should be considered for future large-scale Z. marina restoration projects.

Efeito da semeadura em linhas cruzadas sobre a produtividade de grãos e a severidade da ferrugem asiática da soja / Effect of sowing in crossed lines on grain yield and the severity of asian soybean rust

O arranjo espacial de plantas de soja em semeadura em linhas cruzadas pode contribuir para aumentar a produtividade de grãos da cultura, justificando seu estudo experimental. Dessa forma, o objetivo deste trabalho foi de avaliar a produtividade de grãos e a severidade da ferrugem asiática na cultura da soja submetida a diferentes densidades de semeadura e adubação em linhas convencionais e cruzadas. Os tratamentos consistiram da combinação de três fatores e duas testemunhas adicionais. Para os fatores foram utilizados duas cultivares (Anta 82RR e M7211RR), duas dosagens de adubo de plantio (400 e 800 kg ha-1) e duas densidades (15 e 30 sementes por metro) em semeadura cruzada, e os dois tratamentos adicionais foram formados pela semeadura das duas cultivares em linhas não cruzadas. O delineamento experimental utilizado foi um fatorial 2 x 2 x 2 + 2, distribuídos em blocos completos casualizados com quatro repetições. A soja em linhas cruzadas apresentou maior produtividade de grãos, sendo a cultivar M7211RR superior nos dois sistemas de semeadura. A semeadura de soja cruzada é indicada com a cultivar M7211RR com 15 sementes por metro e 400 kg ha-1 de adubo. A severidade da ferrugem asiática foi maior em semeadura cruzada para as duas cultivares. Em ambos os sistemas de semeadura, a severidade foi maior nos folíolos da metade inferior das plantas da cultivar Anta 82RR. O aumento do número de sementes por metro linear, no sistema de semeadura em linhas cruzadas, reduziu a severidade da doença apenas para a cultivar M7211RR.

The spatial arrangement of soybean planted in line crossed can to increase grain yield, justifying its experimental study. Thus, the aim of this work was to evaluate the grain yield and rust severity on soybeans cultivated under different seed densities and fertilizer rates on conventional and crossed sowed lines. The treatments consisted of combination on three factors and two additional witnesses. The factors were two cultivars (Anta 82RR and M7211RR), two fertilizer rates of planting (400 e 800 kg ha-1) and two seed densities (15 e 30 seeds per meter) in the crossed sowed lines. The additional treatments were formed by the two cultivars in the conventional sowing lines. The experimental design was a randomized complete blocks in a factorial scheme 2 x 2 x 2 + 2, with four replications. The soybean cultivated in crossed sowed lines showed higher grain yield, with de M7211 cultivar higher in both sowing lines types. It was recommended the use of the cultivar M7211RR, 15 seeds per meter and 400 kg ha-1 of the fertilizer. The severity of soybean rust was higher in plants under crossed sowed lines, to both cultivars. The severity was higher in leaves located in the lower half of the cultivar Anta 82RR plants. The increase in the number of seeds per meter in the crossed sowed lines reduced the severity of the disease only to M7211RR cultivar.

Modeling the effect of density-dependent chemical interference upon seed germination.

A mathematical model is presented to estimate the effects of phytochemicals on seed germination. According to the model, phytochemicals tend to prevent germination at low seed densities. The model predicts that at high seed densities they may increase the probability of seed germination and the number of germinating seeds. Hence, the effects are reminiscent of the density-dependent effects of allelochemicals on plant growth, but the involved variables are germination probability and seedling number. The results imply that it should be possible to bypass inhibitory effects of allelopathy in certain agricultural practices and to increase the efficiency of nature conservation in several plant communities.

Modeling the effect of density-dependent chemical interference upon seed germination.

A mathematical model is presented to estimate the effects of phytochemicals on seed germination. According to the model, phytochemicals tend to prevent germination at low seed densities. The model predicts that at high seed densities they may increase the probability of seed germination and the number of germinating seeds. Hence, the effects are reminiscent of the density-dependent effects of allelochemicals on plant growth, but the involved variables are germination probability and seedling number. The results imply that it should be possible to bypass inhibitory effects of allelopathy in certain agricultural practices and to increase the efficiency of nature conservation in several plant communities.

Rodent seed predation and seedling recruitment in mesic grassland.

Seedling recruitment of two grasses (Arrhenatherum elatius and Festuca rubra) and two herbs (Centaurea nigra and Rumex acetosa) was measured in areas with and without rodents to which seeds of each species were sown at three seed densities (1000, 10,000 and 50,000 seeds m-2) in two seasons (spring and autumn 1995). Seed removal was measured for 10-day periods and the fate of seedlings was followed for 15 months after sowing. The proportion of seed removed ranged from 6 to 85% and increased with increasing seed density for each species. Rodents had no effect on seedling emergence or survival in the spring sowing. In the autumn sowing, rodents reduced seedling emergence of all four species sown at 1000 and 10,000 seeds m-2 but had no impact at 50,000 seeds m-2, presumably because of microsite limitation. We suggest the difference between spring and autumn arose because emergence was seed limited in autumn but microsite limited in spring; microsite availability was higher in autumn because a summer drought killed plants, reduced plant biomass and opened up the sward. Fifteen months after the autumn sowing, fewer A. elatius and C. nigra seedlings survived on plots exposed to rodents. This result reflected not only the reduced seedling emergence but also increased seedling mortality (seedling herbivory) in sites exposed to rodents. In contrast, F. rubra and R.acteosa showed density-dependent seedling survival which compensated for initial differences in seedling emergence, so that no effect of rodents remained after 15 months. The results suggest that rodent seed predation and seedling herbivory exert strong effects on seedling recruitment of A.elatius and C. nigra when recruitment conditions are favourable (conditions that lead to high microsite availability) and may contribute to both species being maintained at low densities in the grassland. The results also demonstrate that highly significant impacts of rodent seed predation at the seedling emergence stage can disappear by the time of plant maturation.