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Seeds M (seed + m)
Selected AbstractsSize traits and site conditions determine changes in seed bank structure caused by grazing exclusion in semiarid annual plant communitiesECOGRAPHY, Issue 1 2006Yagil Osem 1. Contrasting patterns of change in the seed bank of natural grasslands are frequently found in response to grazing by domestic herbivores. Here, we studied the hypotheses that a) patterns of change in seed bank density and composition in response to grazing depend on spatial variation in resource availability and productivity, and b) that variation among species in patterns of seed bank response to grazing is linked to differences in species size traits (i.e. size of plant, dispersal unit and seed). 2. Effects of sheep grazing exclusion on the seed bank were followed during five years in a semiarid Mediterranean annual plant community in Israel. Seed bank density and composition were measured in autumn, before the rainy season, inside and outside fenced exclosures in four neighboring topographic sites differing in vegetation characteristics, soil resources and primary productivity: Wadi (dry stream terraces, high productive site), Hilltop, South- and North-facing slopes (less productive sites). 3. Topographic sites differed in seed density (range ca 2500,18000 seed m,2) and in seed bank response to grazing exclusion. Fencing increased seed density by 78, 51 and 18% in the Wadi, South- and North-facing slopes, respectively, but had no effect in the Hilltop. At the species level, grazing exclusion interacted with site conditions in determining species seed bank density, with larger or opposite changes in the high productive Wadi compared to the other less productive sites. 4. Changes in seed bank structure after grazing exclusion were strongly related to species size traits. Grazing exclusion favored species with large size traits in all sites, while seed density of tiny species decreased strongly in the high productive Wadi. Species with medium and small size traits showed lesser or no responses. 5. The size of plants, dispersal units and seeds were strongly correlated to each other, thus confounding the evaluation of the relative importance of each trait in the response of species to grazing and site conditions. We propose that the relative importance of plant size vs seed size in the response to grazing changes with productivity level. [source] Growth and Yield Response of Facultative Wheat to Winter Sowing, Freezing Sowing and Spring Sowing at Different Seeding RatesJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2006A. Ozturk Abstract Growth and yield of wheat are affected by environmental conditions and can be regulated by sowing time and seeding rate. In this study, three sowing times [winter sowing (first week of September), freezing sowing (last week of October) and spring sowing (last week of April)] at seven seeding rates (325, 375, 425, 475, 525, 575 and 625 seeds m,2) were investigated during the 2002,03 and 2003,04 seasons, in Erzurum (Turkey) dryland conditions, using Kirik facultative wheat. A split-plot design was used, with sowing times as main plots and seeding rates randomized as subplots. There was a significant year × sowing time interaction for grain yield and kernels per spike. Winter-sown wheat produced a significantly higher leaf area index, leaf area duration, spikes per square metre, kernel weight and grain yield than freezing- and spring-sown wheat. The optimum time of sowing was winter for the facultative cv. Kirik. Grain yields at freezing and spring sowing were low, which was largely the result of hastened crop development and high temperatures during and after anthesis. Increasing seeding rate up to 525 seeds m,2 increased the spikes per square metre at harvest, resulting in increased grain yield. Seeding rate, however, was not as important as sowing time in maximizing grain yield. Changes in spikes per square metre were the major contributors to the grain-yield differences observed among sowing times and seeding rates. Yield increases from higher seeding rates were greater at freezing and spring sowing. We recommended that a seeding rate of 525 seeds m,2 be chosen for winter sowing, and 575 seeds m,2 for freezing and spring sowing. [source] Field Pea Seeding Management for Semi-arid Mediterranean ConditionsJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2004A. M. Tawaha Abstract The effects of seeding rate (30, 60 and 90 seeds m,2), seeding date (14 January, 28 January and 12 February), seed weight (0.18 and 0.25 g seed,1), seeding depth (3 and 6 cm), and phosphorus fertilization rate (17.5, 35.0 and 52.5 kg P ha,1) and placement method (banded or broadcasted) on field pea (Pisum sativum L.) development and seed yields were investigated in irrigated field experiments conducted in northern Jordan in 2000 and 2001. Results and treatment responses were consistent in both years. Seeding rate, seeding date, seed weight and rate and method of phosphorus fertilization had significant effects on most traits measured; planting depth however did not affect any of the traits. Generally a positive correlation was observed between each factor and seed yield and yield components, with the exception of a negative correlation between seeding rate and yield components, and seeding date and yield and yield components. Increase in seeding rate from 30 to 90 seeds m,2, and increase in P fertilization from 17.5 to 52.5 kg ha,1 alone increased seed yields by 50 and 41 %, respectively. Each delay of 2 weeks for seeding from mid-January resulted in reductions of 12 % in seed yields. Overall, the results revealed that a combination of early seeding (14 January), of large seeds at an high seeding rate (90 seeds m,2), with P fertilizer banding (52.5 kg P ha,1) maximize field pea yields in irrigated fields in semi-arid Mediterranean environments. With such management pea seed yields can be as high as 2800 kg ha,1. [source] Effect of Different Crop Densities of Winter Wheat on Recovery of Nitrogen in Crop and Soil within the Growth PeriodJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 3 2001K. Blankenau Previous experiments have shown that, at harvest of winter wheat, recovery of fertilizer N applied in early spring [tillering, Zadok's growth stage (GS) 25] is lower than that of N applied later in the growth period. This can be explained by losses and immobilization of N, which might be higher between GS 25 and stem elongation (GS 31). It was hypothesized that a higher crop density (i.e. more plants per unit area) results in an increased uptake of fertilizer N applied at GS 25, so that less fertilizer N is subject to losses and immobilization. Different crop densities of winter wheat at GS 25 were established by sowing densities of 100 seeds m,2 (Slow), 375 seeds m,2 (Scfp= common farming practice) and 650 seeds m,2 (Shigh) in autumn. The effect of sowing density on crop N uptake and apparent fertilizer N recovery (aFNrec = N in fertilized treatments , N in unfertilized treatments) in crops and soil mineral N (Nmin), as well as on lost and immobilized N (i.e. non-recovered N = N rate , aFNrec), was investigated for two periods after N application at GS 25 [i.e. from GS 25 to 15 days later (GS 25 + 15d), and from GS 25 + 15d to GS 31] and in a third period between GS 31 and harvest (i.e. after second and third N applications). Fertilizer N rates varied at GS 25 (0, 43 and 103 kg N ha,1), GS 31 (0 and 30 kg N ha,1) and ear emergence (0, 30 and 60 kg ha,1). At GS 25 + 15d, non-recovered N was highest (up to 33 kg N ha,1 and up to 74 kg N ha,1 at N rates of 43 and 103 kg N ha,1, respectively) due to low crop N uptake after the first N dressing. Non-recovered N was not affected by sowing density. Re-mineralization during later growth stages indicated that non-recovered N had been immobilized. N uptake rates from the second and third N applications were lowest for Slow, so non-recovered N at harvest was highest for Slow. Although non-recovered N was similar for Scfp and Shigh, the highest grain yields were found at Scfp and N dressings of 43 + 30 + 60 kg N ha,1. This combination of sowing density and N rates was the closest to common farming practice. Grain yields were lower for Shigh than for Scfp, presumably due to high competition between plants for nutrients and water. In conclusion, reducing or increasing sowing density compared to Scfp did not reduce immobilization (and losses) of fertilizer N and did not result in increased fertilizer N use efficiency or grain yields. Einfluß unterschiedlicher pflanzendichten von Winterweizen auf die Wiederfindung von Stickstoff in Pflanze und Boden während der Vegetationsperiode Aus Wintergetreideversuchen ist bekannt, daß zur Ernte die Wiederfindung von Düngerstickstoff aus der Andüngung (Bestockung, [GS-Skala nach Zadok] GS 25) im Aufwuchs und in mineralischer Form im Boden (Nmin) niedriger ist als die von Düngerstickstoff der Schosser-und Ährengaben. Dies kann auf höhere Verluste bzw. eine höhere Immobilisation von Düngerstickstoff zwischen GS 25 und Schoßbeginn zurückgeführt werden, da hier die N-Aufnahme der Pflanzen im Vergleich zu späteren Wachstumsstadien gering ist. Daraus wurde abgeleitet, daß eine Erhöhung der Pflanzendichte zu einer erhöhten Aufnahme von früh gedüngtem N führen könnte, so daß weniger Dünger-N für Verlust- und Immobilisationsprozesse im Boden verbleibt. Unterschiedliche Pflanzendichten wurden durch unterschiedliche Aussaatstärken im Herbst erreicht (Slow= 100 Körner m,2, Scfp [herkömmliche Praxis]= 375 Körner m,2, Shigh= 650 Körner m,2). In der folgenden Vegetationsperiode wurde der Einfluß der verschiedenen Aussaatstärken auf die N-Aufnahme, die apparente Wiederfindung von Dünger-N (aFNrec = N in gedüngten , N in ungedüngten Prüfgliedern) in Pflanzen und Nmin, sowie auf potentielle Verluste und Immobilisation von Dünger-N (N-Defizit = N-Düngung , aFNrec) für zwei Phasen im Zeitraum zwischen der ersten N-Gabe (GS 25) und der Schossergabe zu GS 31 (d. h. zwischen GS 25 und 15 Tagen später [GS 25 + 15d] und von GS 25 + 15d bis GS 31), sowie zwischen GS 31 und der Ernte (d. h. nach der zweiten und dritten N-Gabe) untersucht. Die N-Düngung variierte zu den Terminen GS 25 (0, 43, 103 kg N ha,1), GS 31 (0, 30 kg N ha,1) und zum Ährenschieben (0, 30, 60 kg N ha,1). Unabhängig von der Aussaatstärke war das N-Defizit zum Termin GS 25 + 15d am höchsten (bis zu 33 kg N ha,1 und 74 kg N ha,1 bei einer N-Düngung von 43 bzw. 103 kg N ha,1), da die N-Aufnahme durch die Pflanzen während der Bestockungsphase am geringsten war. Das N-Defizit zeigt vornehmlich immobilisierten N an, da zu späteren Terminen eine Re-Mobilisation von N auftrat. Zwischen GS 31 und der Ernte wurden für die Aussaatstärke Slow die geringsten Aufnahmeraten von Düngerstickstoff aus der Schosser- und Ährengabe errechnet, so daß für Slow die höchsten N-Defizitmengen ermittelt wurden. Obwohl die N-Defizitmengen für Scfp und Shigh annähernd gleich waren, wurden bei N-Düngung von 43 + 30 + 60 kg N ha,1 für Scfp die höchsten Kornerträge erzielt. Diese Kombination von Aussaatstärke und N-Düngung kann als praxisüblich bezeichnet werden. Für Shigh wurden vermutlich niedrigere Kornerträge erzielt, weil die Konkurrenz um Nährstoffe und Wasser zwischen den Pflanzen aufgrund der hohen Pflanzendichte am intensivsten war. Die Ergebnisse lassen den Schluß zu, daß eine Verringerung oder Erhöhung der Pflanzendichte über entsprechende Aussaatstärken nicht zu einer Reduktion der Dünger-N-Immobilisation (oder von N-Verlusten) führt und demnach auch nicht die Dünger-N-Ausnutzung durch die Bestände erhöht wird. [source] Disruption of an exotic mutualism can improve management of an invasive plant: varroa mite, honeybees and biological control of Scotch broom Cytisus scoparius in New ZealandJOURNAL OF APPLIED ECOLOGY, Issue 2 2010Quentin Paynter Summary 1.,A seed-feeding biocontrol agent Bruchidius villosus was released in New Zealand (NZ) to control the invasive European shrub, broom Cytisus scoparius, in 1988 but it was subsequently considered unable to destroy sufficient seed to suppress broom populations. We hypothesized that an invasive mite Varroa destructor, which has caused honeybee decline in NZ, may cause pollinator limitation, so that the additional impact of B. villosus might now reach thresholds for population suppression. 2.,We performed manipulative pollination treatments and broad-scale surveys of pollination, seed rain and seed destruction by B. villosus to investigate how pollinator limitation and biocontrol interact throughout the NZ range of broom. 3.,The effect of reduced pollination in combination with seed-destruction was explored using a population model parameterized for NZ populations. 4.,Broom seed rain ranged from 59 to 21 416 seeds m,2 from 2004 to 2008, and was closely correlated with visitation frequency of honeybees and bumblebees. Infestation of broom seeds by B. villosus is expected to eventually reach 73% (the average rate observed at the localities adjacent to early release sites). 5.,The model demonstrated that 73% seed destruction, combined with an absence of honeybee pollination, could cause broom extinction at many sites and, where broom persists, reduce the intensity of treatment required to control broom by conventional means. 6.,Nevertheless, seed rain was predicted to be sufficient to maintain broom invasions over many sites in NZ, even in the presence of the varroa mite and B. villosus, largely due to the continued presence of commercial beehives that are treated for varroa mite infestation. 7.,Synthesis and applications. Reduced pollination through absence of honeybees can reduce broom seed set to levels at which biocontrol can be more effective. To capitalize on the impact of the varroa mite on feral honeybees, improved management of commercial beehives (for example, withdrawal of licences for beekeepers to locate hives on Department of Conservation land) could be used as part of a successful integrated broom management programme at many sites in NZ. [source] Seed limitation in a Panamanian forestJOURNAL OF ECOLOGY, Issue 5 2005JENS-CHRISTIAN SVENNING Summary 1The role of seed limitation in tropical forests remains uncertain owing to the scarcity of experimental evidence. We performed seed addition experiments to assess seed limitation for 32 shade-tolerant tropical forest species and monitored the natural seed rain of 25 of these species for 17 years. 2One, two or five seeds were sown into 0.0079-m2 plots for large- (n = 5 species), medium- (n = 5) and small-seeded species (n = 22), respectively. The experiment was replicated at 69 sites, placed in groups of three at 23 locations. Seedling establishment was evaluated after 1 and 2 years in paired seed addition and control plots. Natural seedling emergence and understorey plant density were also measured. 3Median natural seed rain was 0.31 seeds m,2 year,1 per focal species. 4Seed addition enhanced seedling establishment in 31 and 26 of the 32 species after 1 and 2 years, respectively. Mean number of focal species' seedlings after 2 years was 0.002 seedlings in control plots and 0.12, 0.37 and 0.60 seedlings in seed addition plots for large-, medium- and small-seeded species, respectively. 5A 25 seeds added treatment increased seedling establishment by , 2.0-fold over the five seeds added treatment after 2 years. 6Community-wide recruitment and understorey plant density were strongly seed-limited. The natural density of understorey plants averaged 12 plants m,2 and was significantly less than for seedlings of the single focal species in plots with , 2 seeds added 2 years earlier. 7The number of established seedlings per seed added was independent of seed size. 8Treatment (adding zero or five seeds), species identity and location all affected seedling establishment for the 11 small-seeded species represented at all sites, with treatment and its interactions accounting for 86% of the explained variation. 9Our results suggest that seed limitation plays a dominant role in seedling recruitment and understorey plant community assembly in tropical forests. Although strong seed limitation may set the stage for species-neutral community assembly, the species differences in seedling establishment rate and its spatial variation demonstrate an important role for species-specific processes. [source] Post-dispersal predation of Taraxacum officinale (dandelion) seedJOURNAL OF ECOLOGY, Issue 2 2005ALOIS HONEK Summary 1The importance of predation in determining the fate of post-dispersal dandelion (Taraxacum officinale) seed was investigated. Flowering, seed dispersal, seedling establishment, seed predation and seed predator abundance were recorded in 2002 and 2003, at two sites. Number of flowers were counted in 1-m2 plots, wind-borne seeds were collected in water traps, invertebrate seed predation was estimated from the rate of removal of dandelion seeds exposed on the ground and invertebrate activity density was determined by using pitfall traps. The censuses were made at 2- to 3-day intervals. 2Seed dispersal occurred 10 days after flowering. Although some seeds were blown away, 3.7,24.2 × 103 seeds m,2 fell to the ground. Four weeks after the peak in seed dispersal 0.7,3.1% of these seeds germinated. Three weeks later only 11,13% of the dispersed seed remained on the ground and most of these were damaged, the remainder presumably having been removed by predators. 3Predation of exposed seeds was low before seed dispersal but increased after its onset, in parallel with increases in the number of seeds present on the ground and in the activity density of adults of a seed-consuming carabid, Amara montivaga. 4In cafeteria experiments in which the seeds of 28 perennial and annual herbs were provided A. montivaga consumed the most dandelion seeds, followed by nine other Amara species. In no-choice experiments, under field conditions, A. montivaga consumed six seeds day,1. 5Post-dispersal predation, mainly due to aggregation of a single ground beetle species, was more important than that which occurred prior to dispersal. Although predators destroyed c. 97% of the seeds, the effect on dandelion population biology is likely to be small. 6Post-dispersal seed predation may nevertheless be important in other species, as aggregates of large invertebrate predators can consume large quantities of seed. [source] Resource distribution and the trade-off between seed number and seed weight: a comparison across crop speciesANNALS OF APPLIED BIOLOGY, Issue 1 2010B.L. Gambín In grain crops, total sink capacity is usually analysed in terms of two components, seed number and individual seed weight. Seed number and potential individual seed weight are established at a similar timing, around the flowering period, and seed weight at maturity is highly correlated with the potential established earlier. It is known that, within a species, available resources during the seed set period are distributed between both yield components, resulting in a trade-off between seed number and seed weight. Here we tested if this concept could apply for interspecific comparisons, where combinations of numbers and size across species could be related to the total available resources being either allocated to more seed or larger potential individual seed weight during the seed set period. Based on this, species differences in seed weight should be related to resource availability per seed around the period when seed number is determined. Resource availability per seed was estimated as the rate of increase in aboveground biomass per seed around the period of seed set. Data from 15 crop species differing in plant growth, seed number, seed weight and seed composition were analysed from available literature. Because species differed in seed composition, seed weight was analysed following an energy requirement approach. There was an interspecific trade-off relationship between seed number per unit of land area and seed weight (r = 0.92; F(1, 13) = 32.9; n = 15; P < 0.001). Seed weight of different species was positively correlated (r = 0.90; F(1, 13) = 52.9; n = 15; P < 0.001) with resource availability per seed around the seed set period. This correlation included contrasting species like quinoa (Chenopodium quinoa; ,100000 seeds m,2, ,4 mg equivalent-glucose seed,1) or peanut (Arachis hypogaea; ,800 seeds m,2, ,1000 mg equivalent-glucose seed,1). Seed number and individual seed weight combinations across species were related and could be explained considering resource availability when plants are adjusting their seed number to the growth environment and seeds are establishing their storage capacity. Available resources around the seed set period are proportionally allocated to produce either many small seeds or few larger seeds depending on the particular species. [source] Seed production in fens and fen meadows along a disturbance gradientAPPLIED VEGETATION SCIENCE, Issue 3 2009A. Klimkowska Abstract Question: The seed production in several wetland communities across Europe was investigated and differences in seed output in relation to disturbance intensity were tested. The relationship between the vegetation composition and the seed production profile was examined and the results are discussed in relation to restoration. Location: Poland, Germany and the Netherlands. Methods: The seed production in various plant communities was estimated, based on field counts. In addition, records from available databases were used for missing data. Multivariate methods were used to characterize the vegetation and seed production. Communities were grouped according to level of disturbance and tested for differences in seed production. Similarity between vegetation composition and seed profile was examined using the Sørensen index and Spearman correlation coefficient. Results: It was found that the seed production of the studied communities is large, variable and in general increasing with disturbance intensity. The estimated median seed production was ca. 24 × 103 seeds m,2 in fens, 167 × 103 in fen meadows and 556 × 103 seeds m,2 in degraded meadows. The majority of seeds was produced by just a few species. The similarity between the vegetation composition and the seed production profile was low (similarity 52%, correlation coefficient 0.42, P<0.05) and slightly increased with disturbance intensity. Conclusions: Increased disturbance enhances seed production at the community level. The composition of the vegetation is a poor predictor of the seed output. It is estimated that the number of seeds transferred with hay is much lower than the seed production in fens and fen meadows. [source] | |||||||||||||