Soil Seed Bank Dynamics Research Articles

Factors influencing the germination, establishment and distribution of

Context Little is known of the ecology of Micromyrtus minutiflora, a threatened plant species endemic to the Cumberland subregion, New South Wales, Australia. Aims To fill ecological knowledge gaps of M. minutiflora, including habitat preferences, population size and structure, survivorship; and responses to fire and disturbance to inform appropriate management practices. Methods Surveys of distribution and abundance, regeneration mode and response to fire, survivorship, size-class analysis, greenhouse germination experiments using soil blocks; and plant tissue and soil analyses. Key results Micromyrtus minutiflora was estimated to have a population of ~4.3 × 106, an extent of occurrence of ~13 000 ha and ~1.5% area of occupancy within study areas. It is strongly associated with low tree canopy cover (few trees), dispersive clay soils and Castlereagh Scribbly Gum Woodland. In the one area studied, survivorship decreased by ~15% per annum across 14 years. However, total population numbers were stable across 3 years, indicating continuous recruitment. Size distributions were unimodal and continuous from small to large plants, consistent with recruitment matching mortality. Plants lack a lignotuber and have a high shoot:root ratio. Seedling emergence was unaffected by mechanical disturbance, but heat and smoke significantly increased germination. Conclusions This species is abundant on dispersive clays but restricted to the northern Cumberland Plain in open woodland areas. It is an obligate seeder; plants are killed by fire and can flower within 2 years of germination. Implications Understanding its soil seedbank dynamics is pertinent in determining an appropriate fire regime to maintain habitat while not directly threatening populations. Populations require regular monitoring.

Divergent successional trajectories of soil seed bank and post-fire vegetation in a semiarid oak forest: Implications for post-fire ecological restoration

Wildfires are a major disturbance in forest ecosystems around the world and may lead to changes in vegetation succession trajectories. This study examined the impact of time since wildfires on the successional gradients of the degraded Zagros semi-arid oak forest in Iran. Here, we investigated the role of soil seed bank in postfire understory vegetation successional trajectories after wildfires and how time-since-fire influenced plant recovery of this disturbed site. Three adjacent high severity burned areas with different fire histories and the same physiographic conditions were considered. In sampling, we surveyed both aboveground understory vegetation and soil seed bank in all the 96 plots taken along the transects of each area. Soil samples were also collected from each plot and physicochemical properties were analysed in the laboratory. Species composition in the seed bank showed divergent successional trajectories compared to the aboveground vegetation after wildfire. The diversity of soil seed banks followed a gradual decrease, while aboveground understory plants revealed an increasing trend of diversity over time. In addition, the physical and chemical composition of soils was significantly altered by fire. This study presents important insights into soil seed bank dynamics compared to the corresponding aboveground vegetation during postfire succession. The observed changes in diversity and vegetation composition after wildfire can give important insights to management strategies involving prescribed fire in the restoration efforts of highly disturbed semiarid oak forest.

Soil Seed Bank Dynamics of Pastures Invaded by Navua Sedge (Cyperus aromaticus) in Tropical North Queensland

Navua sedge (Cyperus aromaticus) is threatening crops, pasture species and natural ecosystems in Pacific Island countries and northern Queensland, Australia. To aid future management efforts of this exotic invasive weed, research was conducted to understand the soil seed bank dynamics of pastures invaded by Navua sedge. Six grazing properties were chosen across two landscapes, coastal and inland/upland, with areas that had Navua sedge infestations in Queensland, Australia. At each site, soil was collected from two soil depths, 0-5 and 5-10 cm, and from plots with high and low infestation levels of Navua sedge. It was observed that the soil seed bank dynamics varied significantly between these study sites. Navua sedge was the dominant species in the soil seed bank at all the sites contributing between 62% to 95% of the total seed bank, while pasture seeds occupied only 3% to 24%. Broadleaf seeds were even lower in abundance, showing between 2% to 13% of the total seed count. The abundance of Navua sedge seed present in the soil was significantly correlated with the aboveground biomass of Navua sedge (r=0.53, p=0.006), but no correlation was found with the infestation age of Navua sedge. Based on this work, it is clear that the seed bank of Navua sedge is very large and concentrated within the top 0-5 cm of the soil, with, 83% of total Navua sedge seeds being in this layer. It was also noted that, although, high infestation plots had significantly higher number of seeds than low infestation plots, more than 18,000 Navua sedge seeds/m2 were still found in the 0-5 cm soil layer of plots regarded as low infestation. We suggest that insights achieved from our soil seed bank study may be used to devise management strategies to minimise the impact of Navua sedge weed in critical grazing and agricultural areas.

Soil seed bank dynamics are regulated by bird diversity and soil moisture during alpine wetland degradation

Increased anthropogenic activities and global warming have accelerated the loss of wetlands worldwide. Given that a seed bank plays an important role in maintaining species diversity, understanding the regulatory mechanism of seed bank dynamics is crucial for using seed banks for restoration of species diversity in degraded wetlands. We collected data on biotic (i.e., aboveground vegetation, birds and rodents) and abiotic (i.e., soil environmental factors) ecosystem components as predictors along a degradation gradient in an alpine wetland and then to identify the relative importance of multiple sets of predictors in the regulating seed bank dynamics (i.e., species richness and composition). Seed bank dynamics were less responsive to environmental change than the aboveground vegetation during wetland degradation. Soil moisture and bird richness were more important than other predictors in regulating species richness and species composition of the seed bank, respectively. Our results suggest that seed banks can be used as potential resources for restoration of degraded wetlands. Birds play an important role in regulating the diversity of wetland ecosystems (seed bank is a potential diversity provider). Therefore, more attention should be paid to the protection of bird diversity in the process of conservation and restoration of degraded wetlands.

Dynamics of weedy rice soil seedbank under different control strategies in Italian rice fields: survey and model study

AbstractThe abundance of weedy rice (Oryza sativa L.) in the soil seedbank was estimated in 2011 in Italian rice (Oryza sativa L.) fields with different histories of imidazolinone-resistant Clearfield® rice varieties (CL), non-Clearfield® varieties (NCL), and planting methods. A model was used to predict weedy rice seedbank dynamics over time under different control strategies. Soil samples were taken from 50 rice fields cultivated with CL varieties consecutively for 0, 1, 2, or 3 yr, and weedy rice seedbank data were used in a model considering eight scenarios: (A) rice monoculture with CL and NCL varieties in alternate years; (B) 2 yr of CL, followed by 1 yr with NCL; (C) 3 yr of CL followed by 1 yr of NCL; (D) rice monoculture with only CL; (E) rice monoculture with only NCL; (F) 2 yr of CL followed by 1 yr of rotation with another crop (CR), and then by an additional year with NCL; (G) 1 yr of CR followed by 2 yr of CL, and then by 1 yr of NCL; (H) 2 yr of CR followed by 2 yr of CL. The weedy rice seedbank exceeded 1,000 seeds m−2 in the surveyed fields with no significant differences between rice planting methods. Highest densities were found in fields cultivated for 1 yr with CL varieties. Simulations indicated that where CL varieties were used in rice monoculture, the susceptible weedy rice seedbank was gradually reduced, producing a depletion after 17, 13, 11, and 9 yr in scenarios A, B, C, and D, respectively. The weedy rice seedbank increased in NCL monoculture (E) and declined significantly in crop rotation scenarios (F, G, H). The simulations indicated that the introduction of crop rotation is crucial for obtaining a relatively fast reduction of weedy rice seedbank and delaying the evolution of herbicide-resistant populations.

Geographic patterns of seed trait variation in an invasive species: how much can close populations differ?

Seeds play a major role in plant species persistence and expansion, and therefore they are essential when modeling species dynamics. However, homogeneity in seed traits is generally assumed, underestimating intraspecific trait variability across the geographic space, which might bias species success models. The aim of this study was to evaluate the existence and consequences of interpopulation variability in seed traits of the invasive species Carpobrotus edulis at different geographical scales. We measured seed production, morphology, vigour and longevity of nine populations of C. edulis along the Catalan coast (NE Spain) from three differentiated zones with a human presence gradient. Geographic distances between populations were contrasted against individual and multivariate trait distances to explore trait variation along the territory, evaluating the role of bioclimatic variables and human density of the different zones. The analysis revealed high interpopulation variability that was not explained by geographic distance, as regardless of the little distance between some populations (< 0.5 km), significant differences were found in several seed traits. Seed production, germination, and persistence traits showed the strongest spatial variability up to 6000% of percent trait variability between populations, leading to differentiated C. edulis soil seed bank dynamics at small distances, which may demand differentiated strategies for a cost-effective species management. Seed trait variability was influenced by human density but also bioclimatic conditions, suggesting a potential impact of increased anthropogenic pressure and climate shifts. Geographic interpopulation trait variation should be included in ecological models and will be important for assessing species responses to environmental heterogeneity and change.

Effects of long-term seed storage on germination of 13 cactus species from central Argentina

Understanding the effects of long-term seed storage on germination is important to elucidate both soil seed bank dynamics and capacity of seeds to be preserved in ex situ conservation programs. We collected seeds 13 cactus species from central Argentina and conducted the following experiments: germination of freshly collected seeds (2011) and germination of seeds stored for 3 (2014) and 7 years (2018) at ambient temperature. Seeds were germinated in a chamber at 25 °C and a 12 h light/12 h darkness photoperiod. After 3 years, germination decreased in 10 of the species, and only one species did not germinate. After 7 years, germination was null in 10 species, very low in two species and relatively high in only one. Our results suggest that most species might form a short-term persistent seed bank, but not a permanent soil seed bank. From a conservation point of view, our results suggest that seeds of cactus species from central Argentina would need other storage conditions, such as low temperatures. We propose a mechanism to explain why cactus seeds do not have a high longevity.

Vegetation and soil seedbank dynamics in Parthenium hysterophorus L. invaded subtropical grassland in Nepal

Parthenium hysterophorus L. is a noxious invasive weed and is ever expanding in its introduced range including Nepal. Understanding vegetation dynamics including soil seedbank in Parthenium invaded communities and the growth pattern of the weed itself is essential for effective management of Parthenium. We monitored growth of Parthenium (height, density, cover and soil seedbank) and species composition of associated plant species for 5-year period from 2009 in a grassland invaded by Parthenium in south-central Nepal. We found that Parthenium cover and height decreased from 2009 to 2010 and then slightly increased in 2013. Parthenium density decreased from 2009 to 2010 and then was variable until 2013. Year × grazing interactions had significant effect on Parthenium cover and density. Parthenium soil seedbank was eight times higher near the soil surface (0–5 cm) than in deep soil (5–10 cm). It increased from 2009 to 2012 but decreased in 2013. Seedbank was also affected by interactions of year × depth, depth × grazing, and year × depth × grazing. Altogether, 87 plant species were recorded in Parthenium invaded sites and their species richness decreased until 2012 but slightly increased in 2013. The composition of associated plant species was affected by animal grazing intensity, Parthenium density, cover, and their interactions. Parthenium invasion has been ever increasing in our study site and many palatable plant species are under potential threat. Thus, there is an urgent need to carry out awareness campaign, formulate proper management plans, and implement such plans properly to manage Parthenium weed in Nepal.

Physical dormancy and soil seed bank dynamics in seeds of Melilotus albus (Fabaceae)

Information on seed germination and the soil seed bank of a species is important because it contributes to a better understanding of plant reproductive strategies. Melilotus albus (Fabaceae) is considered valuable for honey production and is frequently cultivated as livestock forage. However, it is difficult to germinate M. albus seeds. The primary goal of the present study was to determine the environmental requirements for breaking seed dormancy and the dynamics of soil seed bank. The results indicate that seeds of M. albus have a water impermeable seed coat which can be penetrated by scarification or alternating wet heat and ice water cycles; however, wet heat or dry heat alone were ineffective. After receiving 30 cycles of alternating wet heat and ice water treatments, cracks formed in the lens of seeds. Under natural precipitation and temperature, > 60% of the seedlings emerged in spring. A persistent soil seed bank formed and most seeds were found in the 0–2 cm soil layer. Our findings indicate that seeds of M. albus have physical dormancy; persistence of the seed bank might spread risks associated with a specific seed cohort over multiple years.

Effect of tillage and burial depth and density of seed on viability and seedling emergence of weedy rice

Weedy rice (Oryza sativa f. spontanea) is one of the three worst paddy weeds in most rice growing areas. The unexpected heavy infestation is derived from a persistence of soil seed bank of weedy rice, which the shattered seeds chiefly feed back to. Information on soil seed bank dynamics is imperative to predict the infestation of weeds. In the present paper, the effect of rotary tillage on weedy rice seed bank structure was studied first, and a burial experiment of marked seeds was conducted to observe the overwintering survival, seed viability and seedling emergence of weedy rice. The results showed that the proportion of weedy rice seeds in deeper soil increased but seedling emergence decreased with increasing plowing depth. The viability of weedy rice seeds decreased as the burial duration time extended but more slowly in deeper soil layers. Additionally, there was no significant effect of burial density on seed viability. Moreover, the logistic model fitted well (R2≥0.95, P≤0.01) with the depressive trends of seed viability with increasing burial time under all burial depths and densities which can provide us further information about seed survival. In field experiments, number of seedling emergence significantly decreased as seed burial depth increased, conversely, proportion of seedling emergence increased as seed burial density decreased. This study has important implications for determining strategies for weedy rice management by exhausting its seed bank through the alteration of tillage practices.

A Review of the Soil Seedbank from a Weed Scientists Perspective

Despite efforts to eliminate weeds, they continue to thrive. Weed persistence is reliant upon the soil seedbank. Knowledge of the soil seedbank is continually expanding, but with the rising threat of herbicide-resistant weeds in agriculture, weed scientists have, in the past, focused their management tactics to more short-term solutions that tackle the aboveground problems, rather than long-term solutions. This article summarized the soil seedbank dynamics of weed seeds and derives management options, from a North American weed scientists’ perspective, that (i) favor the depletion of the seedbank, (ii) favor the germination of the seedbank, and (iii) reduce the possibilities of seed produced by the seedlings that germinated to return the soil. These options can potentially deter herbicide resistance and are successful in the short term for reducing field weed infestations, but are likely to take many years to affect recruitment to the weed seedbank, including recruitment of weed species with a high risk for resistance. The natural longevity of the seedbank suggests that alternative or additional weed management tactics are required to reduce the store of weed seeds in the active seedbank.

Explaining the larger seed bank of an invasive shrub in non-native versus native environments by differences in seed predation and plant size.

Large, persistent seed banks contribute to the invasiveness of non-native plants, and maternal plant size is an important contributory factor. We explored the relationships between plant vegetative size (V) and soil seed bank size (S) for the invasive shrub Ulex europaeus in its native range and in non-native populations, and identified which other factors may contribute to seed bank variation between native and invaded regions. We compared the native region (France) with two regions where Ulex is invasive, one with seed predators introduced for biological control (New Zealand) and another where seed predators are absent (La Réunion). We quantified seed bank size, plant dimensions, seed predation and soil fertility for six stands in each of the three regions. Seed banks were 9-14 times larger in the two invaded regions compared to native France. We found a positive relationship between current seed bank size and actual plant size, and that any deviation from this relationship was probably due to large differences in seed predation and/or soil fertility. We further identified three possible factors explaining larger seed banks in non-native environments: larger maternal plant size, lower activity of seed predators and higher soil fertility. In highlighting a positive relationship between maternal plant size and seed bank size, and identifying additional factors that regulate soil seed bank dynamics in non-native ranges, our data offer a number of opportunities for invasive weed control. For non-native Ulex populations specifically, management focusing on 'S' (i.e. the reduction of the seed bank by stimulating germination, or the introduction of seed predators as biological control agents) and/or on 'V' (i.e. by cutting mature stands to reduce maternal plant biomass) offers the most probable combination of effective control options.

Ecological role of physical dormancy in seeds of Oxytropis racemosa in a semiarid sandland with unpredictable rainfall

Seed dormancy and the soil seed bank are crucial to plant regeneration strategy, especially in semiarid ecosystems with unpredictable precipitation. The aim of this study was to investigate how seed dormancy is controlled by environmental factors and how it is correlated with the soil seed bank and regeneration of the perennial legume Oxytropis racemosa, a dominant perennial herb in Mu Us Sandland of semiarid China. Germination and imbibition experiments on fresh intact and scarified seeds of O. racemosa were used to identify physical dormancy (PY) in seeds of this species. Soil seed bank dynamics, timing of seedling emergence and the fate of buried seeds in the natural habitat were investigated. PY was broken by mechanical scarification or wet heat/ice water cycles but not solely by dry heat or wet heat treatment. The soil seed bank exhibited seasonal changes in the number of seeds, which was highest in September and lowest in July. Seeds buried at different sand depths gradually lost dormancy; 20–42% of the seeds remained dormant after 20 months of burial. Dormancy break occurs gradually throughout the year. Our results indicate that O. racemosa exhibits hardcoatedness heterogeneity that spreads germination of a seed cohort between seasons and years in the semiarid environment, where the amount of precipitation during the growing season is highly variable.

Ecological role of physical dormancy in seeds of Oxytropis racemosa in a semiarid sandland with unpredictable rainfall

Seed dormancy and the soil seed bank are crucial to plant regeneration strategy, especially in semiarid ecosystems with unpredictable precipitation. The aim of this study was to investigate how seed dormancy is controlled by environmental factors and how it is correlated with the soil seed bank and regeneration of the perennial legume Oxytropis racemosa, a dominant perennial herb in Mu Us Sandland of semiarid China. Germination and imbibition experiments on fresh intact and scarified seeds of O. racemosa were used to identify physical dormancy (PY) in seeds of this species. Soil seed bank dynamics, timing of seedling emergence and the fate of buried seeds in the natural habitat were investigated. PY was broken by mechanical scarification or wet heat/ice water cycles but not solely by dry heat or wet heat treatment. The soil seed bank exhibited seasonal changes in the number of seeds, which was highest in September and lowest in July. Seeds buried at different sand depths gradually lost dormancy; 20–42% of the seeds remained dormant after 20 months of burial. Dormancy break occurs gradually throughout the year. Our results indicate that O. racemosa exhibits hardcoatedness heterogeneity that spreads germination of a seed cohort between seasons and years in the semiarid environment, where the amount of precipitation during the growing season is highly variable.

PAM: Decision Support for Long-Term Palmer Amaranth (Amaranthus palmeri) Control

Palmer amaranth is the most troublesome weed problem in mid-southern US crop production. Herbicides continue to be the most commonly employed method for managing Palmer amaranth, despite the weed’s widespread resistance to them. Therefore, farmers need research and extension efforts that promote the adoption of integrated weed management (IWM) techniques. Producers, crop consultants, educators, and researchers would be more likely to deploy diversified chemical and nonchemical weed management options if they are more informed about long-term biological and economic implications via user-friendly decision-support software. Described within is a recently developed software that demonstrates the effects of Palmer amaranth management practices on soil seedbank, risk of resistance evolution, and economics over a 10-year planning horizon. Aiding this objective is a point-and-click interface that provides feedback on resistance risk, yield potential, profitability, soil seedbank dynamics, and error checking of management options.

Weed Dynamics in No-Till Rainfed Crops in Chaouia, Semi-Arid Morocco

Three on-farm research-managed trials were conducted in Settat province, Chaouia, semi-arid Morocco, from 2012-13 to 2014-15, to investigate the dynamics of germinable soil seedbank, weed density, and community composition of weeds in 3 crop rotations: continuous durum wheat, barley + pea/durum wheat/durum wheat, and canola/durum wheat/durum wheat. Initial germinable weed seedbank density estimated in September 2012, before no-till planting in November 2012 was 1890 seeds m-2. After two growing seasons, seedbank reductions were 23% in continuous durum wheat, 68% in canola/durum wheat/durum wheat, and 72% in barley + pea/durum wheat/durum wheat. In continuous durum wheat, weed densities before no-till planting were 273, 46, and 59 plants m-2 in November 2012, December 2013, and November 2014, respectively. In herbicide-free barley + pea/durum wheat/durum wheat, weed densities before no-till planting durum wheat were 128 and 42 plants m-2 in December 2013 and November 2014, respectively. In canola/durum wheat/durum wheat, weed densities before no-till planting wheat were only 20 and 25 plants m-2 in December 2013 and November 2014, respectively. This study demonstrated the combined merits of pre-plant glyphosate, herbicide use in wheat, herbicide-free barley + pea haying, and durum wheat rotation with either canola or barley + pea to manage weeds in no-till systems in semi-arid Morocco.

Ecological longevity of Polaskia chende (Cactaceae) seeds in the soil seed bank, seedling emergence and survival.

Soil seed banks are essential elements of plant population dynamics, enabling species to maintain genetic variability, withstand periods of adversity and persist over time, including for cactus species. However knowledge of the soil seed bank in cacti is scanty. In this study, over a 5-year period we studied the seed bank dynamics, seedling emergence and nurse plant facilitation of Polaskia chende, an endemic columnar cactus of central Mexico. P.chende seeds were collected for a wild population in Puebla, Mexico. Freshly collected seeds were sown at 25°C and 12-h photoperiod under white light, far-red light and darkness. The collected seeds were divided in two lots, the first was stored in the laboratory and the second was use to bury seeds in open areas and beneath a shrub canopy. Seeds were exhumed periodically over 5years. At the same time seeds were sown in open areas and beneath shrub canopies; seedling emergence and survival were recorded over different periods of time for 5years. The species forms long-term persistent soil seed banks. The timing of seedling emergence via germination in the field was regulated by interaction between light, temperature and soil moisture. Seeds entered secondary dormancy at specific times according to the expression of environmental factors, demonstrating irregular dormancy cycling. Seedling survival of P.chende was improved under Acacia constricta nurse plants. Finally, plant facilitation affected the soil seed bank dynamics as it promoted the formation of a soil seed bank, but not its persistence.

In situ germination of two tropical recalcitrant seeds and changes in activity of ROS-scavenging enzymes

Tropical recalcitrant-seeded species, which disperse seeds at different seasons, provide evidence of the role of oxidative metabolism in seed bank dynamics. Our results indicate that CAT may regulate field germination. Oxidative metabolism during viability loss in recalcitrant seeds has been previously documented, but little is known about the role of ROS-scavenging enzymes in soil seed bank dynamics, especially in recalcitrant seeds. To address this, recalcitrant-seeded species were studied, Swartzia langsdorffii and Persea wildenovii. Diaspores were kept on the soil after natural dispersion, to simulate the seed bank, and were assessed for seed water content, viability, germination and changes in catalase (CAT), superoxide dismutase (SOD) and peroxidase (PRX) activity throughout the field experiment. These parameters were tested for correlations with climatic data. S. langsdorffii start to germinate after one month in soil, with an increase after two months, when CAT activity decreased and SOD activity increased. SOD was negatively correlated with CAT, and CAT was negatively correlated with germination. However, SOD and CAT were positively correlated for P. wildenovii, whose seeds did not germinate even after four months in the soil and with high activity of ROS-scavenging enzymes throughout the period in the soil. Seeds of these species remained viable during the period in the soil with no or little changes in seed water content. ROS-scavenging enzymes respond to environmental factors, adjusting their activity to maintain seed viability. P. wildenovii seeds did not germinate in the soil due to the timing of dispersal being at the end of rainy season, when additional water supply is limited; ROS-scavenging enzymes probably play a role in seed protection during this dry period. Relationship between CAT regulation and soil seed bank dynamics is discussed.

香果树(Emmenopterys henryi)种群种子雨、种子库及 实生苗数量的海拔梯度变化

香果树为我国Ⅱ级野生保护植物,由于原生境中香果树种群的数量迅速减少,目前已濒临灭绝,种群亟待恢复。研究了武夷山不同海拔的香果树种群种子雨、种子库及其幼苗存活现状,目的是阐明不同海拔地区的香果树种群自然更新的动态过程,寻找其更新脆弱的环节及其影响因素,为香果树自然种群的恢复提供理论依据。以分布于不同海拔高度(819、980、1 140及1 301 m)的香果树母树为中心,在其周围(东、南、西、北四个方位)布设种子雨收集框和土壤种子库样方,连续观测种子雨和种子库的动态,并对不同地表覆盖物中种子萌发及幼苗数量进行观测和记录。结果表明,武夷山香果树种群种子雨持续时间近2个月,尤其是11月底至12月中旬为种子雨高峰期;随着海拔的上升,香果树种子总密度以及虫蛀种子密度均显著降低,但千粒重以及饱满种子密度则有所增加;香果树土壤种子库为瞬时种子库,其水平分布以母树南侧和西侧种子密度较大,母树北侧种子密度最小。香果树种子的垂直分布主要集中于枯落物和苔藓层;3月时香果树土壤种子库中存留的饱满种子仅占种子散布后1.80%,而1年实生苗存活率为6.18%,土壤种子库的损耗是其种群自然更新困难的主要原因;不同地表覆盖物对香果树幼苗的存活产生显著影响,枯落物及苔藓层的幼苗死亡率显著高于土壤表面。建议清理林内枯落物及苔藓,增加林内裸露土壤的面积,减小地上草本的盖度,以减少种子霉烂、虫蛀的几率,增加香果树实生苗胚根与土壤接触的几率以及改善光照条件,促进香果树自然更新。

English

Field studies were conducted from 2012-13 to 2014-15 to investigate the dynamics of germinable soil seedbank, density and community composition of weeds in crop rotations of barley (Hordeum vulgare L.) + pea (Pisum sativum L.) and bread wheat (Triticum aestivum L.) in Oued Zem, semi-arid Morocco. In September 2012, the initial seedbank in 6 fields was 2354 seeds m-². When herbicide-free barley + pea forage mixture (cut for hay) was followed by bread wheat, seedbank reductions were 35% after the two years. When bread wheat was followed by herbicide-free barley + pea forage mixture, seedbank reductions were only 5% in two years. Prior to wheat harvest, weed densities were 82, 8, and 14 plants m-² in April 2013, 2014 and 2015, respectively. Prior to haying herbicide-free barley + pea, weed densities were 76, 109 and 34 plants m-² in April 2013, 2014 and 2015, respectively. Weeds identified in bread wheat fields were 49, 36 and 40 species in 2012-13, 2013-14 and 2014-15, respectively. Weeds associated with herbicide-free barley + pea mixture were 68, 51 and 36 species in 2012-13, 2013-14 and 2014-15, respectively. The seedbank prior to planting and weed density prior to harvesting were strongly influenced by the most recent crop. Integrated weed management combining glyphosate before no-till planting, post-emergence herbicide use in bread wheat, haying barley + pea mixture, within the crop rotation (barley + pea/bread wheat) reduced weed seedbank by up to 35%, species richness by up to 47%, and weed density prior to wheat harvest or forage haying by up to 83%. Such changes suggest that integrated weed management practices in no-till system must be continued for more than 3 growing seasons to drastically reduce weed seedbanks and weed densities. Key words: Weed, seedbank, wheat, barley + pea, no-till, Morocco.