Arable Weed Species Research Articles

Major field margin vegetation types in France and their relationships with climate, agricultural landscapes and management intensity

ABSTRACT Arable field margins are an important semi-natural habitat providing multiple functions in agroecosystems. Despite three decades of research, analyses of species assemblage and functional traits are lacking. Leveraging a national monitoring network in metropolitan France, we aim to provide a comprehensive taxonomic and functional synthesis of field margin flora, outline main field margin types and explore their associations with management practices, climate, and agricultural landscapes. We analysed data from 532 field margins surveyed between 2013 and 2017, using both uni- and multivariate analyses. Field margins exhibited great diversity with 711 distinct taxa (12% of all flora in mainland France) at the national scale and an average of 16 species per 10 m2 locally. While field margins contained few species of conservation value, they offered a refuge for many declining species as well as rare arable weed species. We identified seven main field margin types, each linked to distinct conditions of climate, soil, landscape and agricultural practices. Mediterranean field margins notably differed from all others. In the main cluster, vineyard margins also stood out as distinct from annual crop margins. Additionally, field margins in landscapes with a high proportion of grassland differed from those within intensively cultivated field crop plains in conventional agriculture. Overall, our study highlights the high botanical diversity of field margins and their interest for plant conservation in agricultural landscapes. Promoting the installation and/or maintenance of field margins through agri-environmental schemes should thus favour biodiversity conservation and associated ecosystem provision.

Seed germination of common and endangered arable weed species is differently affected by the herbicide metazachlor and its transformation products

AbstractHigh inputs of herbicides have caused the decline of arable weed species, which formerly evolved under less intensively managed crop lands. Arable weed species have adapted their germination strategies to respond to unfavourable periods. However, species considered endangered have more specific germination requirements. The herbicide metazachlor (MZ), in its formulated form Butisan®, is used for the control of annual and dicotyledonous weeds and degrades in the soil into two major transformation products (TPs): metazachlor oxalic acid (MZ‐OA) and metazachlor ethane sulphonic acid (MZ‐ESA). These TPs are often found in higher concentrations compared to MZ. We tested the effect of MZ and its TP on seed germination of four common and three endangered arable weed species present in Central Europe by setting up multi‐factorial climate chamber experimental designs. We chose concentrations imitating field conditions and according to previously reported fraction occurrences in the topsoil. We assessed germination by measuring germination percentage, mean germination time and synchrony of germination. All germination variables were affected with increasing concentrations of MZ. Both, common and endangered species showed a decrease in germination percentage under the highest concentration of MZ. MZ and MZ‐OA increased the synchronicity of endangered species, while both TPs decreased mean germination time of endangered species. Common species showed less significant differences when compared to the control and also had a less synchronised and longer germination time compared to endangered species. The observed response of common species to both MZ and TPs may be convenient in the face of short term unfavourable environmental conditions, such as those found in intensively managed arable lands. Our results highlight that the species‐specific response of arable weeds to herbicides will further increase the dominance of common over rare arable weed species.

Iconic Arable Weeds: The Significance of Corn Poppy (Papaver rhoeas), Cornflower (Centaurea cyanus), and Field Larkspur (Delphinium consolida) in Hungarian Ethnobotanical and Cultural Heritage

There are an increasing number of initiatives that recognize arable weed species as an important component of agricultural biodiversity. Such initiatives often focus on declining species that were once abundant and are still well known, but the ethnographic relevance of such species receives little recognition. We carried out an extensive literature review on the medicinal, ornamental, and cultural applications of three selected species, Papaver rhoeas, Centaurea cyanus, and Delphinium consolida, in the relevant Hungarian literature published between 1578 and 2021. We found a great diversity of medicinal usages. While P. rhoeas stands out with its sedative influence, D. consolida was mainly employed to stop bleeding, and C. cyanus was most frequently used to cure eye inflammation. The buds of P. rhoeas were sporadically eaten and its petals were used as a food dye. All species fulfilled ornamental purposes, either as garden plants or gathered in the wild for bouquets. They were essential elements of harvest festivals and religious festivities, particularly in Corpus Christi processions. P. rhoeas was also a part of several children's games. These wildflowers were regularly depicted in traditional Hungarian folk art. In poetry, P. rhoeas was used as a symbol of burning love or impermanence; C. cyanus was frequently associated with tenderness and faithfulness; while D. consolida regularly emerged as a nostalgic remembrance of the disappearing rural lifestyle. These plants were also used as patriotic symbols in illustrations for faithfulness, loyalty, or homesickness. Our results highlight the deep and prevalent embeddedness of the three iconic weed species studied in the folk culture of the Carpathian Basin. The ethnobotanical and cultural embeddedness of arable weed species should also be considered when efforts and instruments for the conservation of arable weed communities are designed.

Cytochrome P450 CYP709C56 metabolizing mesosulfuron-methyl confers herbicide resistance in Alopecurus aequalis.

Multiple herbicide resistance in diverse weed species endowed by enhanced herbicide detoxification or degradation is rapidly growing into a great threat to herbicide sustainability and global food safety. Although metabolic resistance is frequently documented in the economically damaging arable weed species shortawn foxtail (Alopecurus aequalis Sobol.), relevant molecular knowledge has been lacking. Previously, we identified a field population of A. aequalis (R) that had evolved metabolic resistance to the commonly used acetolactate synthase (ALS)-inhibiting herbicide mesosulfuron-methyl. RNA sequencing was used to discover potential herbicide metabolism-related genes, and four cytochrome P450s (CYP709C56, CYP71R18, CYP94C117, and CYP94E14) were identified with higher expressions in the R vs. susceptible (S) plants. Here the full-length P450 complementary DNA transcripts were each cloned with identical sequences between the S and R plants. Transgenic Arabidopsis overexpressing CYP709C56 became resistant to the sulfonylurea herbicide mesosulfuron-methyl and the triazolo-pyrimidine herbicide pyroxsulam. This resistance profile generally but does not completely in accordance with what is evident in the R A. aequalis. Transgenic lines exhibited enhanced capacity for detoxifying mesosulfuron-methyl into O-demethylated metabolite, which is in line with the detection of O-demethylated herbicide metabolite in vitro in transformed yeast. Structural modeling predicted that mesosulfuron-methyl binds to CYP709C56 involving amino acid residues Thr-328, Thr-500, Asn-129, Gln-392, Phe-238, and Phe-242 for achieving O-demethylation. Constitutive expression of CYP709C56 was highly correlated with the metabolic mesosulfuron-methyl resistance in A. aequalis. These results indicate that CYP709C56 degrades mesosulfuron-methyl and its up-regulated expression in A. aequalis confers resistance to mesosulfuron-methyl.

Farming Intensity Affects Soil Seedbank Composition and Spontaneous Vegetation of Arable Weeds

Former studies carried out in the 2000s in the Lahn-Dill region located in the middle-east of the German state Hesse stated a depletion of arable weeds on the field scale and more diverse weed flora on the landscape scale. Current study, having started in 2018, aims to contribute to a better understanding of the interactions between arable weed species diversity, farming intensity, grown crops and landscape area. Moreover, the potential of organic farming methods for conservation and promotion the arable weed diversity is aimed to be assessed with the study. In total, 42 fields in two landscape regions were sampled—six seedbank samples were collected from each field; additionally, data on spontaneous arable weed flora were recorded each spring from 2019 to 2021; emerged aboveground weeds were identified in the fields and their coverage was documented. Four factors were considered in the field trial: Farming practice, landscape area, soil depth and the current crop. Effects of these factors on arable weed species diversity were calculated with a Generalized Linear Model (GLM), resulting in significant effects of the management system, the area and the current crop. Among the four organic farming systems that were sampled, the time period of organic growing had a significant effect on weed seed numbers in the soil with an increase in seed numbers. Average seedbank species numbers were around twice as high in organic farming systems (18 species) compared to conventional managed fields (nine species). Evidence of an ongoing species decline in the region on the landscape scale could be detected by comparison with a former study. Especially rare and endangered weed species are a concern due to seedbank and current vegetation depletion tendencies.

Cyhalofop-butyl resistance conferred by a novel Trp-2027-Leu mutation of acetyl-CoA carboxylase and enhanced metabolism in Leptochloa chinensis.

Chinese sprangletop (Leptochloa chinensis (L.) Nees) is an invasive grass weed severely infesting rice fields across China. In October 2020, a suspected resistant Leptochloa chinensis population HFFD3 that survived the acetyl-CoA carboxylase (ACCase)-inhibiting herbicide cyhalofop-butyl applied at its field-recommended rate was collected from a rice field in Feidong County, Anhui Province, China. This study aimed to determine the resistance profile of HFFD3 to ACCase inhibitors and to investigate its mechanisms of resistance to cyhalofop-butyl. Single-dose testing confirmed that HFFD3 had evolved resistance to cyhalofop-butyl. Two loci encoding plastidic ACCase were each amplified from the susceptible (S) and resistant (R, HFFD3) individual plants. Target gene sequencing and derived cleaved amplified polymorphic sequence assay revealed all the R plants carried a Trp-2027-Leu substitution in their ACCase1,2 copies. Dose-response bioassays revealed that HFFD3 was highly resistant to cyhalofop-butyl and exhibited cross-resistance to metamifop, fenoxaprop-P-ethyl, quizalofop-P-ethyl, and clethodim. Pre-treatment with piperonyl butoxide and 4-chloro-7-nitrobenzoxadiazole considerably reversed the resistance of the R plants to cyhalofop-butyl, by 23% and 43%, respectively. Liquid chromatography-tandem mass spectrometry analysis suggested the metabolic rates of cyhalofop-butyl were significantly faster in the R than in the S plants. This study confirmed the first case of an arable weed species featuring cross-resistance to ACCase-inhibiting herbicides due to a novel Trp-2027-Leu mutation of ACCase. Target gene mutation and cytochrome P450s- and glutathione-S-transferases-involved enhanced metabolism may have simultaneously participated in the resistance of HFFD3 population to cyhalofop-butyl.

Genetic Variability of Acetolactate Synthase (ALS) Sequence in Centaurea cyanus Plants Resistant and Susceptible to Tribenuron-Methyl

Centaurea cyanus, belonging to the Asteraceae family, is an arable weed species encountered mainly in fields with cereals, sugar beet, and maize. The high genetic variability of C. cyanus has been recently reported; however, little is known about its sequence variability in the context of its herbicide resistance. C. cyanus resistance was found mainly against acetolactate synthase (ALS) inhibitors, but no ALS sequence information concerning the herbicide resistance mechanism has been published yet. The aim of this study was to determine the ALS sequences for biotypes susceptible and resistant to tribenuron-methyl in order to identify mutations that may be associated with the resistance emergence. DNA isolation from susceptible and resistant plants was followed by PCR amplification and ALS sequencing. As a result, different lengths of DNA products were obtained. Moreover, both nucleotide and amino acid sequence analysis revealed high sequence variability within one plant as well as between plants from the same biotype. In a few resistant plants, four changes in the amino acid sequence were identified in comparison to those in the susceptible ones. However, these preliminary studies require further investigation toward confirming the significance of these mutations in herbicide resistance development. This study provides preliminary information contributing to the research on the C. cyanus target-site resistance mechanism.

Populations of arable weed species show intra-specific variability in germination base temperature but not in early growth rate.

Key plant traits affecting growth performance can differ among and within species, influencing competitive plant community dynamics. We determined the intra-specific variability of germination base temperature among 13 arable weed species and the seedlings' early post-emergence relative growth rate among 21 species in climate chamber and green house experiments. Intra-specific variability was quantified with two seed populations (originating from contrasting climate in Germany & France) for the germination base temperature of 6 species and for the early growth rate of 16 species. Inter-specific variability for both traits was always higher than intra-specific variability. Within a given species, we found that germination base temperatures were higher in seeds stemming from colder climate populations. Seedling relative growth rates did not differ between seed populations. Models simulating weed growth should reflect these differences in germination traits among populations, especially when they are used for weed community assembly studies in a local to regional extent.

Species composition, richness, and diversity of weed communities of winter arable land in relation to geo-environmental factors: a gradient analysis in mainland Italy

The interest in knowledge of the weed communities of arable land is growing worldwide. Italy is one of the countries in Europe that is the most biodiverse, geographically and environmentally heterogeneous, and rich in arable weed species. Thus, in this study, the geo-environmental factors influencing the floristic composition, the species richness, and the Shannon diversity of weed communities of Italian winter arable crops were investigated along a gradient across mainland Italy. Original data were collected in the spring of 2018 in 106 winter cereal and legume arable fields from one fixed area plot per field. Environmental and geographic data were retrieved for each plot, including latitude, longitude, elevation, soil texture, soil pH, continentality, temperature, and precipitation. The effect of crop type was also tested. Latitude was the main driver of floristic differentiation between the studied plant communities, followed by precipitation, temperature, continentality, elevation, and longitude. Soil features and crop type had no significant effects. Higher values of species richness and Shannon diversity were found in southern areas and at higher elevations. Significant explanatory variables accounted for 11.55% of the total variation in species composition of the surveyed communities. The results are discussed and compared with those of similar studies in other Eurasian countries.

Reduced crop sowing density improves performance of rare arable weed species more effectively than reduced fertilisation

AbstractCharacteristic arable weed species of dryland cereal fields have undergone significant declines, due to agricultural intensification, to the point that some of them are considered rare. Crop edges host higher abundances of arable weed species, therefore they may act as a refuge for the conservation of these rare arable species. Using mesocosms, we experimentally tested how conditions at field edges (i.e. lower sowing densities and less intensive fertiliser applications) operate on the growth (biomass and height) and reproduction (reproductive biomass and flower onset) of six rare arable species. We found the rare arable species achieved lower biomass when growing with wheat compared with growing alone, and biomass of most of species was lower under high wheat sowing density than under low sowing density. In contrast, fertiliser application affected only two of the six arable species tested, especially when they were growing alone. Although the time to flowering was not affected by the conditions tested, reproductive biomass showed the same trends as overall biomass. These results indicate that conservation of rare arable species must primarily consider reductions in crop competition to increase their biomass and reproductive ability.

A comparison of dicamba absorption, translocation and metabolism in Chenopodium album populations resistant and susceptible to dicamba

Chenopodium album is a troublesome arable weed species which has evolved resistance to dicamba in New Zealand. The objective of this work was to investigate the patterns of absorption, translocation and metabolism of dicamba in resistant and susceptible C. album populations. No significant differences in absorption by the two populations were measured, with over 80% of applied herbicide entering the plants of both populations during the 5 days after application. The 14C from dicamba was also readily translocated out of the treated leaf, with this occurring more rapidly in resistant plants than susceptible plants. The majority of the 14C from dicamba was translocated into untreated leaves in both populations. However, by 5 days after application, 18.4% of the absorbed 14C from dicamba was found in stem material for susceptible plants, compared with only 5.1% for resistant plants. No dicamba metabolism was detected for either population. Based on the results of this study, the mechanism of resistance to dicamba in C. album could not be adequately explained by differential patterns of absorption, translocation or metabolism, but the mechanism appears to differ from previously published cases of dicamba resistance.

Arable weed species associated with soil tillage systems under Mediterranean conditions

AbstractTillage soil erosion is seen as a great problem in the Mediterranean region and is worsened by the climatic conditions. Previous studies have shown a decrease in biodiversity in arable lands across Europe. Weeds are a major component of biodiversity within agro‐ecosystems, but few studies have aimed to associate weed species with soil tillage intensity. We performed an analysis to test the potential short‐term effects of different tillage systems on weed species under our study conditions. The emerged weed data were measured, comparing a conventional tillage system with conservational tillage systems (minimum tillage and no tillage) in 2 cropping systems (monoculture wheat and a rotation scheme of barley–legume–wheat–fallow). Compared with the tilled soil, higher weed density and weed species richness were observed in the conservation tillage plots. The weed density and weed species richness in the monoculture system were higher compared with those in the crop rotation system. We used classification and regression trees to analyze the relationship between the soil tillage systems and the weed community, taking into account the climatic conditions. The results indicate that different soil tillage systems produced tree models: Silene vulgaris (L.) was associated with the MT system and high and irregularly distributed rainfall; Hypecoum imberbe Sm. and Hypecoum procumbens (L.) were linked to MT plots with low and well‐distributed precipitation rates; and Cardaria draba (L.) was present all years independently of climatic conditions but was never found in the NT system, so its presence could be regarded as an indicator of tillage intensity.

The influence of farming on weed flora in the Gäu region of Southwestern Germany with an emphasis on rare arable weed species

Durch hoch entwickelte Unkrautbekampfungsmasnahmen werden Unkrauter effektiv unterdruckt, was im gleichen Zuge zu einer Veranderung der Zusammensetzung der Unkrautflora sowie dem Ruckgang von selteneren Arten fuhrt. Um dieser Entwicklung entgegenzuwirken und Arten zu schutzen, werden Flachen mit seltenen Arten unter Naturschutz-Vertrag genommen, jedoch meist nur zeitlich begrenzt. Wir kartierten 2016 in der Gau-Region Baden-Wurttembergs die Unkrautflora konventioneller (K) und okologischer (O) Getreideflachen sowie fruherer (E) und aktueller (V) Schutzacker. Die Unkrautartenzahlen waren zwischen O (24 – 38 Arten) und V (26 – 43 Arten) sowie zwischen C (7 – 17 Arten) und E (13 – 15 Arten) sehr ahnlich. Die Zusammensetzung der Unkrautflora variierte betrachtlich zwischen den untersuchten Flachen. Mithilfe einer Kanonischen Korrespondenzanalyse (CCA) war es moglich, 23 % dieser Variation durch die Parameter Aussaatstarke und Stickstoffdungung zu erklaren. Trotzdem zeigten einige Arten wie Alopecurus myosuroides, Geranium dissectum, Papaver rhoeas, Poa trivialis und Veronica persica eine hohe Stetigkeit in allen untersuchten Flachen. Seltene und gefahrdete Unkrautarten wie Papaver argemone, Consolida regalis, Ranunculus arvensis und Galium tricornutum waren nur in aktuellen Vertragsflachen vorhanden und traten gelegentlich in E oder O auf. Dies weist auf einen Ruckgang der Artenvielfalt hin, sobald die Vertrage fur diese Acker auslaufen. Die Unkrautflora nahert sich dann kontinuierlich der Florenzusammensetzung von konventionellen Flachen an. Um einen dauerhaften Erhalt der seltenen Arten zu garantieren, sollten deshalb neue Entwurfe zum Artenschutz entwickelt und umgesetzt werden.

Cucurbit chlorotic yellows virus: Insights Into Its Natural Host Range, Genetic Variability, and Transmission Parameters.

Cucurbit chlorotic yellows virus (CCYV) (genus Crinivirus, family Closteroviridae) is implicated in cucurbit yellows disease (CYV), causing typical interveinal yellowing symptoms in leaves, and is transmitted by Bemisia tabaci Mediterranean (MED) and Middle East-Asia Minor 1 (MEAM1). Due to its recent report in cucurbit crops in Greece, field surveys were conducted during 2011-2016 to determine the presence of the virus in symptomatic cucurbits and alternative hosts among arable weed species. Results indicated the restricted spread of the virus and identified 13 weed species as CCYV hosts for the first time. Sequence analysis of the RNA-dependent RNA polymerase (RNA1) coat and minor coat proteins (RNA2) revealed very low genetic diversity (<0.1%) among the Greek isolates. Transmission experiments were also conducted using B. tabaci MED with retention determined at four days, whereas transmission efficiency was positively correlated with the number of adults used, features linked to the virus semipersistent mode of transmission.

Dramatic decline in the Swiss arable flora since the 1920s

Arable weeds are among those groups of plants that are most threatened in Europe due to management intensification and efficient cleaning of crop seeds in modern agriculture. Plant species loss in arable fields had been assessed in many European countries about 30 years ago, and has gained renewed interest during the last few years. A rich historical data set on plots where arable weeds had historically been recorded in Switzerland enabled the study of changes in arable weed species since the 1920s onward. In total, 232 locations with historical plots were revisited. There, we recorded all plant species and their abundances on 100m2 plots. Across all plots the average number of species per plot declined dramatically by more than 60% during the last 90 years. Most species decreased in frequency, but common species stayed more frequent, while rare species − often characteristic weeds of traditionally managed crop fields − decreased in frequency or even disappeared. Plant groups with increasing species numbers and frequency were mostly neophytes, grasses and species with high nutrient demand. The above mentioned decline in species number and frequency of rare and characteristic weed species suggests that more effective conservation measures than hitherto taken are needed to ensure their preservation.

Species but not genotype diversity strongly impacts the establishment of rare colonisers

Summary Understanding species coexistence and regulation of biodiversity are major research challenges, yet there is no consensus on the effects of diversity on diversity, including their mediation through plant–plant interactions. We examined how the diversity of recipient communities impacted on the establishment of colonising species. We ran a greenhouse‐based community experiment, creating artificial arable crop communities with varying levels of barley genotype and weed species diversity, analysed with structural equation modelling of responses across trophic levels. Colonising arable weed species establishment was significantly reduced when the recipient communities’ weed species richness, but not barley genotype richness, increased. Recipient plant communities with higher species richness occupied more total niche space and showed stronger competition with colonising species. In contrast, recipient plant communities with higher genotype richness, even though they had slightly greater niche space occupancy, had no significant effects on the colonisation of additional species. Responses were species specific: colonising common weed species establishment was less affected by the recipient plant communities than that of colonising rare weed species. Strong responses of colonising rare species were related to the abiotic rather than the biotic environment created by the recipient communities. The stronger response of colonising rare species suggests greater niche overlap with and competitive inferiority to the recipient plant community, whereas the relative independence of colonising common species indicates less niche overlap and/or competitive equality or superiority. We observed a negative species diversity effect on colonising species, with the effect size increasing with increasing rarity of the colonising species. This differential responsiveness of colonising rare and common arable weed species to the presence of and diversity in the recipient arable plant communities may be crucial in understanding rarity and may result from differential evolutionary pathways in response to interactions.

Resurveying hedgerows in Northern Germany: Plant community shifts over the past 50 years

Resurveying is a powerful approach to investigate responses of plant species communities to a changing environment. We present a resurvey of hedgerows from the “Knick” landscape of eastern Schleswig-Holstein, Germany. The original survey was done by H. E. Weber in 1967 and new data from totally 51 semi-permanent plots was sampled in 2015. Hedgerows are a key near-natural habitat that can harbour a great biodiversity in otherwise agriculturally intensified landscapes.Our study reveals a distinct shift in the herbaceous species composition of the hedgerows over the past five decades. To understand the reasons for these changes, we compared the mean Ellenberg indicator values (EIVs) and measured pH values, as well as hedge shape parameters of the hedgerows between the recent and the original study. The main driver behind the change in species composition appeared to be the increase in nutrient supply. The hedge shape changed as well, indicating an altered hedgerow management. Interestingly, we found a contradictory relationship between measured pH values and mean EIVs for reaction: while the former showed a decrease over time, the latter suggested an increase.Species richness decreased in some groups (shrubs and herbaceous forest species) but increased in others (grass species and arable weed species), with an overall decline in species richness. An analysis of the species' changes in frequency in relation to their EIVs showed that species with higher nitrogen and temperature scores were more likely to have increased.

Impacts of short-term germination delay on fitness of the annual weed Agrostemma githago (L.)

AbstractTime of seedling emergence is an important step in the life cycle of annual plants because it may determine subsequent performance and success. Timing of emergence is especially critical to plant performance in habitats like arable fields which are subject to frequent disturbances. Within-season variation in timing of germination in the range of only a few days is typical for many arable weeds. However, since it is unclear whether such small deviations in germination date translate into fitness differences in the course of the life cycle, the aim of this paper was to quantify the effects of short germination delays on plant performance. We conducted two generalized randomized block experiments in an unheated greenhouse to study the impact of delayed germination (1, 2, 3 and 7 d) with and without competition, respectively, on the fitness of the arable weed species Agrostemma githago (L.). We expected that delayed germination significantly reduces fitness in terms of several life-history traits, and that the decrease of fitness is higher in the presence of competition. Under realistic conditions with competition through barley, Agrostemma plants with delayed germination of 7 d produced 54% fewer shoots, 57% less biomass, 52% fewer flowers, 36% lighter seeds and were 23% shorter as compared to control plants without delayed germination. Without additional stress through competition with barley this pattern was less pronounced. Thus, in the situation of interspecific competition, early emerging seedlings have biologically significant fitness advantages over later emerging seedlings of the same species.

Positive diversity effects on productivity in mixtures of arable weed species as related to density–size relationships

Positive diversity effects on productivity in mixtures of arable weed species as related to density–size relationships

Perturbation Experiments in Community Plant Species during Recovery from Agricultural Abandonment in a Semi-Arid Region of Central-Western Spain

Background: Can high diversity mixtures of later succession plant species be able to suppress early successional (arable weed) species than low diversity species mixtures? Can the removal of plant functional groups have important consequences on the sys-tem stability? Location: The study area was located at 850 m a.s.l., fifteen kilometers (15 km) to the west of Salamanca city, Spain, in a dehesa-like woodland. Methods: The field experiment was installed in Spring 1996 (May). The plots represented former agricultural lands cropped with (a rotation of) monocultures and abandoned right at the beginning of the experiment after the last crop was harvested in 1995. Before in-stalling plots, the fields were harrowed and equalized. The treatments (NC-natural colonization, LD-low diversity seed mixture and HD-high diversity seed mixture) were randomly allocated to the plots in each block. The experiment was organised accord-ing to a block design with five replicate blocks. Within each block, four plots measur-ing 10 × 10 m were marked out and each of the three treatments was randomly as-signed to one plot. All plots were separated by 2 m walkways. Results: The competitive ability of the sown species in different mixtures in LD, valued on the basis of their performance in HD, is a good predictor of their ability to suppress the weed crops spe-cies. This was also corroborated by the high relationship between the efficiency of the sown species in both treatments of species mixture (R2 = 0.51, F (1, 33) = 34.56, P