Sublethal effects of herbicides on the biomass and seed production of terrestrial non-crop plant species,influenced by environment,development stage and assessment date

Guidelines provided by the OECD and EPPO allow the use of single-species tests performed in greenhouses to assess the risk of herbicides to non-target terrestrial plant communities in the field. The present study was undertaken to investigate the use of greenhouse data to determine effects of herbicides with a different mode of action on the biomass, seed production and emergence of field-grown plants. In addition, a single species approach was compared with a mixed species approach. Effects on the biomass of greenhouse and field-grown plants were found to be related at different effect levels, indicating that it might be possible to translate results from greenhouse studies to field situations. However, the use of single-species tests may not be valid. The response of a single plant species to sublethal herbicide dosages differed to the response of the same species grown in a mixture with other species.     

The effect of glyphosate on the growth and competitive effect of perennial grass species in semi-natural grasslands

Biodiversity within European semi-natural biotopes in agro-ecosystem is declining, and herbicide drift from neighbouring fields is considered as an important factor for the decline. The aim of the present study was to investigate whether the growth and competitive interactions in a model system of two perennial grass species, Festuca ovina and Agrostis capillaris, are affected by sub-lethal doses of glyphosate in field margins. In a glasshouse experiment with ample nitrogen, the interspecific competitive interactions were found to be significantly affected by glyphosate; the competitive effect of F. ovina on A. capillaris increased and the competitive effect of A. capillaris on F. ovina decreased with increasing doses of glyphosate. Furthermore, the importance of interspecific competition increased with the glyphosate dose. The results of the study of competitive interactions are in agreement with the observed plant community dynamics at the field site where F. ovina was found to be more dominant in plots treated with a relatively high dose of glyphosate. Importantly, the effects of glyphosate on the plant community dynamics critically depended on the effect of glyphosate on the plant competitive interactions. The study concludes that the current practice in the environmental risk assessment of non-target effects of herbicides, where single species are tested in the greenhouse, may be inadequate for assessing the effect of herbicides in semi-natural plant communities. The presented methods can be used for assessing the importance of competitive interactions for the sensitivity of non-target plants to herbicides in risk assessment.     

Sources of variability in plant toxicity testing

Published literature is investigated regarding the response of plants to various substances to determine the sensitivity of agricultural plants versus other species, the similarity of effects seen at different taxonomic levels, sensitivity of plants growing outdoors versus in a greenhouse, and the sensitivity of different measurement endpoints. We find that agricultural species are not consistently more or less sensitive to the herbicides tested than non-crop species. Genus and family taxonomic groupings may show similar responses among species, but this similarity quickly decreases as the comparison progress between orders and classes. Results from field and greenhouse studies are less in agreement between studies than data from the other topics. Shoot length will be affected at concentrations lower than for other vegetative endpoints for most species tested for inorganic substances, but for organic substances root and shoot mass were more sensitive. Overall, there is no one species or endpoint that is consistently the most sensitive for all species or all chemicals in all soils, and differences in bioavailability among compounds may confound comparison of test results. Therefore, species sensitivity distributions, adjusted for bioavailability when possible, should be considered in order to better evaluate effects to non-target terrestrial plants.     

Enhanced phytoremediation of arsenic contaminated land

In an attempt to clean up arsenic (As) contaminated soil, the effects of phosphorus (P) fertilizer and rhizosphere microbes on arsenic accumulation by the silverback fern, Pityrogramma calomelanos, were investigated in both greenhouse and field experiments. Field experiments were conducted in Ron Phibun District, an As-contaminated area in Thailand. Soil (136-269 microg As g(-1)) was collected there and used in the greenhouse experiment. Rhizosphere microbes (bacteria and fungi) were isolated from roots of P. calomelanos growing in Ron Phibun District. The results showed that P-fertilizer significantly increased plant biomass and As accumulation of the experimental P. calomelanos. Rhizobacteria increased significantly the biomass and As content of the test plants. Thus, P-fertilizer and rhizosphere bacteria enhanced As-phytoextraction. In contrast, rhizofungi reduced significantly As concentration in plants but increased plant biomass. Therefore, rhizosphere fungi exerted their effects on phytostabilization.     

Effects on hawthorn the year after simulated spray drift

This paper describes the effect of a herbicide applied at levels consistent with off target movement on hawthorn the year following exposure. In the experiment, metsulfuron-methyl was applied in five dosages to individual trees in seven different hawthorn hedgerows. Spraying was conducted both at the bud stage and at the early flowering. Five endpoints (i.e. leaves, buds, flowers, green berries and mature berries) were sampled and counted. All were significantly reduced with increasing exposure. Present day risk assessment of effects on non-target plants is therefore likely to overlook significant effects on perennial non-target plants in the spray drift zone due to the focus on results from short-term laboratory test studies. The significance of the present study is underlined by the fact that the effects observed were significant, even though other influential factors such as herbivory and differential pollination were not eliminated and that experiments were conducted in multiple locations.     

Dose-response studies with the antiozonant ethylenediurea (EDU), applied as a soil drench to two growth substrates, on greenhouse-grown varieties of Phaseolus vulgaris L

To study plant growth and yield effects of the antiozonant ethylenediurea (EDU), which is frequently used for ozone crop loss assessments, dose-response studies were carried out with potted bean plants under greenhouse conditions in winter and spring. Two cultivars of Phaseolus vulgaris L., differing in sensitivity to ozone (O(3)), were grown in unfiltered air on a sandy loam rich in organic matter and on a vermiculite-clay mixture. Four treatments of EDU at concentrations from 300 to 800 mg liter(-1) were given as a soil drench during plant development. Foliar symptoms of EDU phytoxicity were observed at all doses, and plant biomass, particularly pod dry weight, was considerably reduced to increasing doses of EDU. Primary and first trifoliate leaf weight in EDU-treated plants increased as did the number of buds, indicating an extension of vegetative growth and a delay of reproductive processes. 'BBL 290' beans, which are O(3)-sensitive, were injured by EDU more than the O(3)-tolerant 'BBL 274'. The phytotoxic effects of EDU were more pronounced in the synthetic growth substrate than in field soil. In a second experiment, EDU was applied in concentrations from 100 to 400 mg liter(-1) to 'BBL 290' plants, exposed to filtered air or simulated levels of O(3) pollution. In field soil, plant growth and biomass partitioning in filtered air was only slightly altered by EDU, although leaf injury due to EDU occurred. In the vermiculite-clay mix, the biomass of most plant organs, particularly that of roots, was linearly reduced with increasing EDU doses. O(3) did not cause any alteration in plant biomass in field soil-grown and EDU-treated plants. Ozone leaf injury, which affected 67% of primary leaf area in non-treated plants, was completely suppressed by EDU doses as low as 100 mg liter(-1). This indicates that low concentrations of EDU, which do not affect plant growth in field soil, provide sufficient protection from O(3) injury. The need for careful EDU dose-response studies prior to field assessments is emphasized.     

Growth rate effects, responses of antioxidant enzymes and metabolic fate of the herbicide Propanil in the aquatic plant Lemna minor

Propanil (3,4-dichloropropionanilide) is a selective contact pesticide, recommended for post-emergence use in rice. This herbicide may end up in surface waters and present potential risk for aquatic vascular plants. Therefore, its toxicity was evaluated on Lemna minor L., an aquatic plant regularly used for toxicological studies, during time- and concentration-dependent exposure. Toxicity assessments were based on inhibition of growth of L. minor cultures after 24 days. The obtained results showed that the growth of Lemna was affected by the herbicide. The responses of the guaiacol peroxidase (G-POD) and glutathione S-transferase (GST) involved in the xenobiotic metabolism and antioxidative system were also investigated following Propanil exposure. Our results showed that Propanil has not induced enzymatic antioxidative defenses of L. minor. Both 3,4-dichloroaniline (3,4-DCA) and 3,4-dichloroacetanilide are the major metabolites in this plant. On the contrary, only 3,4-DCA was found in culture media after 4 days. Probably, the enzymatic hydrolysis by acyl acylamidase and the acetylation by acetyl-CoA are the major pathways for these transformation products, respectively. The results of this study showed that the selected aquatic plant has the potential to accumulate and metabolize rice herbicide, like Propanil. Based on these toxicity data this herbicide should impair the establishment of non-target aquatic plants.     

Effect of airborne bromoxynil-octanoate and metribuzin on non-target plants

The present study was conducted to determine the effects of airborne herbicides on the photosynthesis and growth of non-target plants. Sunflowers at different growth stages were used as test plants and exposed for 24 h in a wind tunnel to a range of concentrations of bromoxynil-octanoate and metribuzin. The quantum yield (phiPSII) and the dry weight were used as response parameters. Results indicate that young sunflower plants are affected by sublethal concentrations of both herbicides, whereas metribuzin proved to be more phytotoxic. Bromoxynil-octanoate and metribuzin concentrations > 0.265 and >0.135 microg/m(3) impair the photosynthetic activity of exposed leaves and concentrations >0.780 and >0.641 microg/m(3) of leaves developed after exposure. Effects on dry weight indicate that younger plants were more susceptible, whereby the response to metribuzin proved to be more dependent on growth stage. Based on these results and considering herbicide concentrations in ambient air, there is a reasonable probability that non-target plants are temporarily at risk of being affected.     

Ecological recovery of vegetation on a coke-factory soil: role of plant antioxidant enzymes and possible implications in site restoration

The present paper investigated the short-term colonization by plants of a highly degraded soil in field conditions. The objectives were to identify, through phytosociological analysis, the plant species able to grow on such polluted areas and to characterize pollutant effects at different biological levels through analyses of plant oxidative status, plant growth or community indexes of richness and biodiversity. Our results showed that among the plants present in the uncontaminated surrounding area, only few species were able to colonize the polluted soil. These species were typical of the first years of grassland successions. Ecological indexes proved that the polluted soil vegetation presented a lower degree of species richness and biodiversity than the control area. These discrepancies were partly explained by pollutant phytotoxicity. Indeed, for several species including Erigeron canadensis and Oenothera biennis, we observed toxic effects of the polluted soil on plant height and biomass. Moreover, at the cellular level, changes in antioxidant enzyme activities (SOD, CAT, APX, GPX and GRD) and lipid peroxidation level (MDA) were observed. Such biochemical changes seemed to play an important role on plant sensitivity/tolerance to pollutants and thus to render them more or less competitive for colonization of such disturbed areas.     

Effects of planting system design on the toxicological sensitivity of Myriophyllum spicatum and Elodea canadensis to atrazine

The triazine herbicide atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-trazine) was selected as a chemical stressor in an investigation of how toxicological responses of individually grown macrophytes reflect those of plants grown in more natural model populations and two-species communities. Phytotoxicity of the compound to Myriophyllumspicatum L. and Elodeacanadensis Michx. was assessed under semi-natural field conditions using 12000l outdoor microcosms. Exposure concentrations of 25, 50, 100, 250mugl(-1) plus controls (n=3) were evaluated, selected to fall within a range of concentrations known to produce a toxic response in the tested macrophytes, and effective concentrations required to cause a decrease in biomass endpoints by 10%, 25%, and 50% were estimated. The sensitivities of aquatic plants to atrazine did not differ substantially between planting systems, and few interactions between the effects of the planting method and atrazine effects on macrophyte biomass were detected using a two-way ANOVA. A lack of significant differences in biomass and relative growth rate measures between plants grown under the various test systems also indicated that interactions between and among species did not influence growth of plants in the model population and communities. Under these test conditions, the use of the "cone-tainer" method provided estimates of toxicity consistent with those from plants grown in assemblages, and potential interactions between plants were not found to modify the response of macrophytes to atrazine.     

Effect of fertilizer on the growth of radish plants exposed to simulated acidic rain containing different sulfate to nitrate ratios

Two successive experiments were performed in the greenhouse to test the hypothesis that plant response to the amounts and ratios of sulfuric and nitric acids in rain is affected by the amount of fertilizer added to the growing medium. Radish plants, grown with different levels of N?P?K fertilizer, were given ten 1-h exposures over a 3-week period to simulate acidic rain at pH values from 2.6 to 5.0 and sulfate to nitrate mass ratios from 0.3 to 7.5. Increased acidity of simulated rain reduced plant growth, with a greater depression of hypocotyl mass than shoot mass. The reverse growth response occurred with increased supply of fertilizer: plant biomass rose with a larger increase in shoot mass than hypocotyl mass. In one experiment, plants that received a greater supply of fertilizer exhibited more obvious reductions in growth of hoots at the higher levels of acidity of simulated rain. There were no significant effects of sulfate to nitrate ratios in simulated rain on plant growth, nor any effect of this ratio on the response of shoots and hypocotyls to acidity of simulated rain. Addition of fertilizer had no effect on plant response to sulfate to nitrate ratios. These results do not support the hypothesis that nutrient-deficient plants are either more or less responsive to sulfate and nitrate in rain than plants grown with optimal supplies of nutrients. They support previous results indicating no effects of sulfate to nitrate ratio in simulated acidic rain on plant growth. The results also suggest that the greatest risk of harmful effects on vegetation may come from the combination of high sulfate and high acidity in rainfall.     

Stress reactions in Vitis vinifera L. following soil application of the herbicide flumioxazin

In order to evaluate the stress effects of flumioxazin (fmx) on grapevine, a non-target plant (Vitis vinifera L.), physiological parameters such as carbohydrate content, water status or nitrogenous metabolites were investigated on fruiting cuttings and plants grown in vineyard. In the leaves of cuttings, the soil-applied herbicide induced stress manifestations including a decrease of the dry weight percentage and the soluble carbohydrate content during the first week after treatment. Thereafter, a decrease of the osmotic potential was observed, as well as a decrease of total protein content and a parallel accumulation of free amino acids, including proline. Altogether, these results suggest that soil-applied fmx induced a stress in grapevines, leading to leaf proteolysis. However, this stress was partially recovered 3 weeks after herbicide application, suggesting that the cuttings were capable to adapt to the fmx exposure. In the vineyard, the flumioxazin effects were still significant 5 months after the treatment, particularly in the CH cv. They included a decrease of the leaf dry weight percentage and soluble carbohydrate content, as well as an increase of the osmotic potential. The decrease of leaf soluble carbohydrates may have dramatic consequences for the berry growth and the reserve constitution. Moreover, treated plants were characterized by a decrease of the free amino acid content and an accumulation of ammonium, while the protein level did not significantly increase, suggesting a degradation of amino acids. The alteration of carbon and nitrogen status after herbicide treatment may affect the grapevine vigour in a long term.     

The Greenhouse effect: impacts of ultraviolet-B (UV-B) radiation, carbon dioxide (CO2), and ozone (O3) on vegetation

There is a fast growing and an extremely serious international scientific, public and political concern regarding man's influence on the global climate. The decrease in stratospheric ozone (O3) and the consequent possible increase in ultraviolet-B (UV-B) is a critical issue. In addition, tropospheric concentrations of 'greenhouse gases' such as carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) are increasing. These phenomena, coupled with man's use of chlorofluorocarbons (CFCs), chlorocarbons (CCs), and organo-bromines (OBs) are considered to result in the modification of the earth's O3 column and altered interactions between the stratosphere and the troposphere. A result of such interactions could be the global warming. As opposed to these processes, tropospheric O3 concentrations appear to be increasing in some parts of the world (e.g. North America). Such tropospheric increases in O3 and particulate matter may offset any predicted increases in UV-B at those locations. Presently most general circulation models (GCMs) used to predict climate change are one- or two-dimensional models. Application of satisfactory three-dimensional models is limited by the available computer power. Recent studies on radiative cloud forcing show that clouds may have an excess cooling effect to compensate for a doubling of global CO2 concentrations. There is a great deal of geographic patchiness or variability in climate. Use of global level average values fails to account for this variability. For example, in North America: 1. there may be a decrease in the stratospheric O3 column (1-3%); however, there appears to be an increase in tropospheric O3 concentrations (1-2%/year) to compensate up to 20-30% loss in the total O3 column; 2. there appears to be an increase in tropospheric CO2, N2O and CH4 at the rate of roughly 0.8%, 0.3% and 1-2%, respectively, per year; 3. there is a decrease in erythemal UV-B; and 4. there is a cooling of tropospheric air temperature due to radiative cloud forcing. The effects of UV-B, CO2 and O3 on plants have been studied under growth chamber, greenhouse and field conditions. Few studies, if any, have examined the joint effects of more than one variable on plant response. There are methodological problems associated with many of these experiments. Thus, while results obtained from these studies can assist in our understanding, they must be viewed with caution in the context of the real world and predictions into the future. Biomass responses of plants to enhanced UV-B can be negative (adverse effect); positive (stimulatory effect) or no effect (tolerant). Sensitivity rankings have been developed for both crop and tree species. However, such rankings for UV-B do not consider dose-response curves. There are inconsistencies between the results obtained under controlled conditions versus field observations. Some of these inconsistencies appear due to the differences in responses between cultivars and varieties of a given plant species; and differences in the experimental methodology and protocol used. Nevertheless, based on the available literature, listings of sensitive crop and native plant species to UV-B are provided. Historically, plant biologists have studied the effects of CO2 on plants for many decades. Experiments have been performed under growth chamber, greenhouse and field conditions. Evidence is presented for various plant species in the form of relative yield increases due to CO2 enrichment. Sensitivity rankings (biomass response) are agein provided for crops and native plant species. However, most publications on the numerical analysis of cause-effect relationships do not consider sensitivity analysis of the mode used. Ozone is considered to be the most phytotoxic regional scale air pollutant. In the pre-occupation of loss in the O3 column, any increases in tropospheric O3 concentrations may be undermined relative to vegetation effects. As with the other stress factors, the effects of O3 have been studied both under controlled and field conditions. Thboth under controlled and field conditions. The numerical explanation of cause-effect relationships of O3 is a much debated subject at the present time. Much of the controversy is directed toward the definition of the highly stochastic, O3 exposure dynamics in time and space. Nevertheless, sensitivity rankings (biomass response) are provided for crops and native vegetation. The joint effects of UV-B, CO2 and O3 are poorly understood. Based on the literature of plant response to individual stress factors and chemical and physical climatology of North America, we conclude that nine different crops may be sensitive to the joint effects: three grain and six vegetable crops (sorghum, oat, rice, pea, bean, potato, lettuce, cucumber and tomato). In North America, we consider Ponderosa and loblolly pines as vulnerable among tree species. This conclusion should be moderated by the fact that there are few, if any, data on hardwood species. In conclusion there is much concern for global climate change and its possible effects on vegetation. While this is necessary, such a concern and any predictions must be tempered by the lack of sufficient knowledge. Experiments must be designed on an integrated and realistic basis to answer the question more definitively. This would require very close co-operation and communication among scientists from multiple disciplines. Decision makers must realize this need.     

Detached leaf culture: viability to evaluate 2,4-D toxicity symptoms in cotton apex leaves

To study the viability of detached leaf culture technique, studies were carried out with detached leaves from cotton apex (true trilobed leaves). The prepared leaves were sprayed with 2,4-D amine and ester, at rates of 10, 30, 70, and 100% of the recommended doses. Detached leaves without herbicide spray were used as controls. Simultaneously, a greenhouse experiment was conducted with the same treatments as used for the detached leaves experiment. Toxicity was measured through a 0-to-5 grading according to the percentage of affected leaf area in the detached leaves experiment or examining the affected rate of whole plant as indicated in the greenhouse. Results showed that the ester form of the herbicide induced earlier and more severe toxicity symptoms in detached leaves and greenhouse grown plants. Positive and significant correlations (p < 0.001) were found between toxicity results obtained at 7 and 14 days after application in detached leaves and greenhouse plants (r = 0.97 and 0.92, respectively). Negative, significant correlations (p < 0.005) were found between the toxicity levels found at 7 and 14 days after application in detached leaves and dry matter of cotton plants grown in the greenhouse (r= - 0.92 and -0.92, respectively).     

Plant protection products: assessing the risk for terrestrial plants

The fundamental data requirements for the authorization of plant protection products and the inclusion of active ingredients in Annex I of Council Directive 91/414/EEC (Council Directive of 15 July 1991 referring to placing plant protection products on the market (91/414/EEC). Official Journal of European Communities L 230, 19 August 1991) are described in the Annexes II and III of this Directive. Definite instructions with regard to preconditions for implementation and methodology (guidelines) concerning investigations with terrestrial plants are deficient. In addition to that, the uniform principles for the registration of plant protection products in the Member States described in Annex VI of the directive do not include any criteria concerning the risk assessment for non-target plants. However, plant protection products often show effects on non-target plants which need to be assessed as a requirement for the authorisation of the product. Hence, the German Federal Environmental Agency has developed a tiered approach to assess the effects of plant protection products on non-terrestrial plants. The risk is assessed using the effect-concentration evaluated in ecotoxicological tests and the environmental concentration predicted by validated exposure models. To protect non-target plants in terrestrial ecosystems assessment factors need to be considered. In the future, the risk for terrestrial plants needs to be addressed, also with regard to the revision of the Annexes of Directive 91/414/EEC.     

Analysis of the effects of rotational larviciding on aquatic fauna of two Guinean rivers: the case of permethrin.

Within the Onchocerciasis Control Programme about 50,000 km of west African rivers have been regularly sprayed with larvicides to control the vector of dermal filariasis caused by Onchocerca volvulus. Since the beginning of the programme invertebrates and fish data were collected to monitor adverse effects on non-target organisms. The regular series of biological and hydrological data collected in two Guinean rivers were analysed to evaluate the effects of rotational larviciding with particular attention to permethrin, as preliminary acute toxicology tests and semi-field experiments suggest it has stronger effects on non-target fauna in respect to other larvicides. Invertebrates and fish variations in biomass and species richness are seasonal and flow-related and the results presented here do not support any evidence of specific effects of permethrin application on the biological targets monitored. Larvicide applications influence community structures, putting pressure on some taxonomic groups, causing, for example, the rarefaction of some taxa. In spite of the above results, the scarcity of some invertebrate systematic units does not result in a significant reduction of total invertebrate density because of the corresponding increase in other systematic units. In nature the studied aquatic communities would rarely be in equilibrium because of frequent natural stresses, such as drought and spate events, the biological variations discussed are to be considered ecologically acceptable.     

Effects of inoculation of plant growth-promoting rhizobacteria on metal uptake by Brassica juncea

A greenhouse study was carried out with Brassica juncea to critically evaluate effects of bacterial inoculation on the uptake of heavy metals from Pb-Zn mine tailings by plants. Application of plant growth-promoting rhizobacteria, including nitrogen-fixing bacteria and phosphate and potassium solubilizers, might play an important role in the further development of phytoremediation techniques. The presence of these beneficial bacteria stimulated plant growth and protected the plant from metal toxicity. Inoculation with rhizobacteria had little influence on the metal concentrations in plant tissues, but produced a much larger above-ground biomass and altered metal bioavailability in the soil. As a consequence, higher efficiency of phytoextraction was obtained compared with control treatments.     

The herbicide paraquat induces alterations in the elemental and biochemical composition of non-target microalgal species

Huge quantities of pesticides are dispersed in the environment, affecting non-target organisms. Since paraquat affects the photosynthetic process, the biochemical composition of affected species should be altered. The effect of paraquat on Chlamydomonas moewusii, a freshwater non-target species, was studied. After 48 h of herbicide exposure, growth rate, dry weight, and chlorophyll a and protein content were affected by paraquat concentrations above 0.05 μM. C/N ratio was also affected due to a decrease in nitrogen content in the dry biomass, while the carbon content remained constant for all paraquat concentrations assayed. Enzymes involved in nitrogen assimilation were affected by paraquat, being nitrate reductase activity more sensitive to paraquat than nitrite reductase. Based on the results obtained in the present study, paraquat exerts adverse effects upon a common freshwater green microalga, thus the application of this herbicide for weed control must be carried out very carefully, so that any disturbance affecting algae will have severe repercussions on higher trophic levels and on the elemental biogeochemical cycles.     

Two Decades of Experimental Manipulations of Heaths and Forest Understory in the Subarctic

Current atmospheric warming due to increase of greenhouse gases will have severe consequences for the structure and functioning of arctic ecosystems with changes that, in turn, may feed back on the global-scale composition of the atmosphere. During more than two decades, environmental controls on biological and biogeochemical processes and possible atmospheric feedbacks have been intensely investigated at Abisko, Sweden, by long-term ecosystem manipulations. The research has addressed questions like environmental regulation of plant and microbial community structure and biomass, carbon and nutrient pools and element cycling, including exchange of greenhouse gases and volatile organic compounds, with focus on fundamental processes in the interface between plants, soil and root-associated and free-living soil microorganisms. The ultimate goal has been to infer from these multi-decadal experiments how subarctic and arctic ecosystems will respond to likely environmental changes in the future. Here we give an overview of some of the experiments and main results.     

Two decades of experimental manipulations of heaths and forest understory in the subarctic

Current atmospheric warming due to increase of greenhouse gases will have severe consequences for the structure and functioning of arctic ecosystems with changes that, in turn, may feed back on the global-scale composition of the atmosphere. During more than two decades, environmental controls on biological and biogeochemical processes and possible atmospheric feedbacks have been intensely investigated at Abisko, Sweden, by long-term ecosystem manipulations. The research has addressed questions like environmental regulation of plant and microbial community structure and biomass, carbon and nutrient pools and element cycling, including exchange of greenhouse gases and volatile organic compounds, with focus on fundamental processes in the interface between plants, soil and root-associated and free-living soil microorganisms. The ultimate goal has been to infer from these multi-decadal experiments how subarctic and arctic ecosystems will respond to likely environmental changes in the future. Here we give an overview of some of the experiments and main results.