Short-term Greenhouse Experiments Research Articles

Vegetative growth drives the negative effects of an invasive species on resident community diversity and is not limited by plant-soil feedbacks: A temporal assessment.

Many pathways of invasion have been posited, but ecologists lack an experimental framework to identify which mechanisms are dominant in a given invasion scenario. Plant-soil feedbacks (PSFs) are one such mechanism that tend to initially facilitate, but over time attenuate, invasive species' impacts on plant diversity and ecosystem function. PSFs are typically measured under greenhouse conditions and are often assumed to have significant effects under field conditions that change over time. However, direct tests of PSFs effects in natural settings and their change over time are rare. Here we compare the role of PSFs with the effects of biomass in limiting the dominance of an invasive species and impacts on resident species diversity. We characterized the effects of the invader Bromus inermis (Leyss.) on native plant communities over time and measured changes in its conspecific PSFs and vegetative growth to understand their integrated effects on community diversity. To do so, we combined data from a 6-year field study documenting the rate and impacts of invasion with a short-term greenhouse experiment quantifying PSF as a function of time since invasion in the field. We found that the nature and strength of B. inermis PSFs did not change over time and were not mediated by soil microbial communities. Though PSFs impacted B. inermis reproduction, they did not sufficiently limit vegetative growth to diminish the negative impacts of B. inermis biomass on native species. B. inermis experienced the full strength of its negative PSFs immediately upon invasion, but they were ineffective at reducing B. inermis vigor to facilitate the recovery of the native plant community. We recommend that conservation efforts focus on limiting B. inermis vegetative growth to facilitate community recovery.

Synthesis of plant-soil feedback effects on eastern North American tree species: implications for climate-adaptive forestry

Climate change represents an existential threat to many forest ecosystems because tree populations are often adapted to local climate means and variability. If tree populations cannot migrate or adapt, they risk becoming increasingly maladapted with climate change. This emerging mismatch underscores the need for climate adaptive management techniques, such as assisted migration of tree species, to help mitigate climate change impacts on forest ecosystems. Although biotic and abiotic factors are known to constrain tree establishment success, the extent to which they may determine the success of assisted migration plantings is poorly understood. Thus, defining the extent to which trees affect—and in turn are affected by local soil environments and microbial communities (i.e., plant-soil feedbacks; hereafter PSFs) remains important for guiding effective climate-adaptive forest management. Our objectives were to synthesize the current state of knowledge about the direction and magnitude of PSF effects on temperate tree species of eastern North America, and to identify key hypotheses important for guiding future research. To accomplish these goals, we conducted a meta-analysis of 26 peer-reviewed publications that addressed our criteria. Our compiled database included 61 tree species and was composed primarily of short-term greenhouse experiments that studied PSF effects by manipulating the soil biota in three ways: (1) soil was previously inoculated by a conspecific or heterospecific tree species (i.e., home vs. away), (2) soil was live or sterilized, or (3) soil was untreated or treated with fungicide. We found that PSF had significant effects on tree growth, with the direction and magnitude of PSF strongly dependent on tree mycorrhizal guild. Arbuscular mycorrhizal tree species grown in live or home soils grew 13–33% less than those in sterile or away soils, while ectomycorrhizal tree species grew 11–44% more in live or home than sterile or away soils. PSF effects were associated with several plant functional traits, including specific leaf area, tissue nitrogen, and specific root length. We provide suggestions on incorporating PSFs into assisted migration trials and outline key knowledge gaps for future research. Our synthesis of context-dependent effects of PSFs on tree performance will help inform management decisions involving assisted migration.

Substrate composition impacts long-term vegetation development on blue-green roofs: Insights from an experimental roof and greenhouse study

Green roofs provide ecosystem services and can promote biodiversity in urban areas. Blue-green roofs have an additional water storage compartment under the substrate to reduce roof water runoff, thereby also reducing drought stress which is beneficial for green roof vegetation. In order to study which blue-green roof design supports the highest plant diversity, we assessed the effect of different substrates and seed mixtures on vegetation development in a short-term greenhouse experiment and long-term blue-green roof experiment. A ten-week full-factorial greenhouse experiment was performed for six substrate composition and four seed mixture treatments. On an experimental blue-green roof, we annually surveyed plants from 2013 to 2021 in nine different treatments (five replicates each), that varied in substrate composition, substrate depth and seed mixture that was initially applied. Two treatments resembled conventional non-green roofs (100% gravel) and conventional extensive Sedum green roofs. The results of the greenhouse experiment showed that seed mixture is more important than substrate composition in shaping the initial species richness and species composition. However, on the experimental roof the substrate composition was an important determinant of species richness and species composition long-term. Plant species richness on the experimental roof was lowest in the gravel treatment (resembling conventional non-green roofs), and highest in treatments where locally collected soil was used, likely due to additional species that appeared from the seed bank present in the transplanted soil. Soil was never completely covered with vegetation on unfertilized substrates that contained 20% or less dense and organic materials. Plant species richness on conventional Sedum roof substrate was higher on the experimental blue-green roof compared to an adjacent non-blue roof, highlighting that blue-green roofs can promote biodiversity more than conventional green roofs. For future construction of blue-green roofs in our region, we recommend the addition of 30% locally collected soil to a 6 cm deep lightweight substrate to maximize long-term plant cover and plant species richness.

Changes of soil-rhizosphere microbiota after organic amendment application in a Hordeum vulgare L. short-term greenhouse experiment

AimsIn order to counteract the enduring decreases in the quality of agricultural land, mechanistic studies for a more sustainable agricultural crop production were performed. They aimed to assess the effects of organic amendments in combination with mineral fertilizer on soil-rhizosphere microbiota and their influence on soil health and plant performance.MethodsIn a short-term greenhouse experiment, the effects of pelletized spent mushroom substrate, with different combinations of biochar and mineral fertilizer, on agricultural soil and performance of Hordeum vulgare L were scrutinized. To evaluate improved soil quality, different soil biological and chemical properties, microbial activity, bacterial diversity and plant performance were assessed.ResultsPlant performance increased across all fertilizer combinations. Bacterial β-diversity changed from the initial to the final sampling, pointing at a strong influence of plant development on the rhizosphere with increasing abundances of Acidobacteria and decreasing abundances of Actinobacteria, Chloroflexi, and Bacteroidetes. Microbial activity (FDA), potential enzyme activity and metabolic diversity of the microbial community (BIOLOG) were not affected by the amendments, whereas bacterial community structure changed on family level, indicating functional redundancy. Treatments containing biochar and the highest amount of mineral fertilizer (B_MF140) caused the strongest changes, which were most pronounced for the families Xanthobacteraceae, Mycobacteriaceae, and Haliangiaceae.ConclusionApplying organic amendments improved plant performance and maintained soil health, contributing to more sustainable crop production. Nevertheless, long-term field studies are recommended to verify the findings of this short-term experiment.

Linking plant traits to multiple soil functions in semi-arid ecosystems

Understanding the role plant species play on ecosystems is fundamental for restoration programs, particularly in semi-arid areas because land-use intensification combined with critical droughts has resulted in widespread desertification. Here, we evaluate 15 species of native trees for restoring degraded areas in the Brazilian semi-arid region on the basis of the suitability of their functional traits to ecosystem multifunctionality. To do so, we performed a short-term greenhouse experiment using saplings to estimate the importance of above- and below-ground traits in modulating soil and water quality. Above-ground traits yielded stronger effects on soil and water quality than below-ground traits. Above-ground biomass held the strongest positive effect on ecosystem multifunctionality, being the most beneficial attribute for the soil functions assessed. Thus, plants holding high biomass production should be preferentially selected for restoration in semi-arid regions.

Matching seedling size to planting conditions: interactive response with soil moisture

Seedling size is a very important issue when producing plants for restoration projects. Scientific evidence on the appropriate size for drylands is contradictory. Thus, the aim of this study was to evaluate the effect of seedling size during first establishment by conducting a short term greenhouse experiment with Pinus canariensis containerized seedlings. A selection of large (mean height: 33.7 cm) and small (14.3 cm) one-year-old seedlings were planted in pots under two volumetric water content regimes: dry (7%) and wet (15%). Midday shoot water potential was measured in two periods: 10 (prior to root protrusion) and 30 (once the roots had protruded from the plug) days after planting. The length of protruding roots was measured after 30 days. One month after planting, the large seedlings under the dry regime produced more new roots than the small seedlings, but also showed the highest midday water potential values. Therefore, the greater root growth of the former did not offset the higher transpiration demand when planted in dry soils. These results suggest that under uncertainty about the soil humidity levels of dry areas, using small seedlings can improve their short-term survival after planting.

Foliar Roundup application has minor effects on the compositional and functional diversity of soil microorganisms in a short-term greenhouse experiment

The herbicide Roundup (and glyphosate, its active ingredient) is extensively used for weed control on a worldwide scale. It is absorbed after foliar application and quickly translocated inside the plant. In this study, we investigated the effects of Roundup speed, a commercial glyphosate formulation, on the structural composition (dominance of microbial groups, phospholipid fatty acid analysis - PLFA) and functional diversity (use of carbon sources, Multiple Substrate Induced Respiration - MSIR) of soil microorganisms. We specifically aimed at understanding the potential impact of biotic interactions on herbicide effects and included plants, earthworms, and endomycorrhizal fungi in the experimental setup. For this, we grew clover (Trifolium repens) in the greenhouse and added mycorrhizal inoculum (Glomus mosseae) and earthworms (Lumbricus terrestris) to the pots. Two weeks after foliar Roundup application and subsequent plant death, the pots were destructively sampled. The application resulted in a significant increase of microbial respiration (SIR) by approximately 30%. A multivariate analysis of the MSIR data exhibited small but significant differences between the microbial communities of treated and untreated pots, while no significant difference was apparent for the PLFA data. Bacterial PLFAs generally decreased following herbicide application, while mycorrhizal and fungal PLFAs were not affected. We did not find a consistent difference between the fatty acid markers of gram negative and gram positive bacteria. For all investigated parameters, there were highly significant differences between the upper (0–5 cm depth) and lower (5–10 cm) soil layers. The fact that rooting density differed by a factor of 3.5 between the two layers indicated that herbicide effects were especially pronounced in the clover rhizosphere and were likely due to changes in root exudate composition. We found significant, though very small, interactions between Roundup and other experimental factors (especially mycorrhizal inoculum).

Live long and prosper: plant-soil feedback, lifespan, and landscape abundance covary.

Plant soil feedbacks (PSFs) are thought to be important to plant growth and species coexistence, but most support for these hypotheses is derived from short-term greenhouse experiments. Here we use a seven-year, common garden experiment to measure PSFs for seven native and six nonnative species common to the western United States. We use these long-term, field-based estimates to test correlations between PSF and plant landscape abundance, species origin, functional type, and lifespan. To assess potential PSF mechanisms, we also measured soil microbial community composition, root biomass, nitrogen cycling, bulk density, penetration resistance, and shear strength. Plant abundance on the landscape and plant lifespan were positively correlated with PSFs, though this effect was due to the relationships for native plants. PSFs were correlated with indices of soil microbial community composition. Soil nutrient and physical traits and root biomass differed among species but were not correlated with PSF. While results must be taken with caution because only 13 species were examined, these species represent most of the dominant plant species in the system. Results suggest that native plant abundance is associated with the ability of long-lived plants to create positive plant-soil microbe interactions, while short-lived nonnative plants maintain dominance by avoiding soil-borne antagonists, increasing nitrogen cycling and dedicating resources to aboveground growth and reproduction rather than to belowground growth. Broadly, results suggest that PSFs are correlated with a suite of traits that determine plant abundance.

Beyond Focal Pests: Impact of a Neonicotinoid Seed Treatment and Resistant Soybean Lines on a Non-Target Arthropod.

Integrated pest management (IPM) tactics may effectively control focal pests, but it is also important to test the compatibility of different tactics, and consider non-target organisms. We investigated the effects of a neonicotinoid seed treatment and Rag resistance genes used for soybean aphid (Aphis glycines Matsumura) control on reproduction of a non-target herbivore (twospotted spider mite, Tetranychus urticae Koch) in short-term greenhouse experiments. We also examined interactions between spider mites and a specialist phytoseiid mite [Ambylseius fallacis (Garman)] and assessed the effects of a co-occurring opportunistic omnivore [Frankliniella occidentalis (Pergande)] by including thrips density as a covariate. There were no interactive or main effects of the presence of Rag genes on the densities of any of the arthropods. Overall, effects of the seed treatment on spider mite densities varied, with no difference when mites were confined in clip cages, and higher populations on seed-treated plants when on whole plants. Predatory mites had a consistent negative impact on spider mites, and densities of A. fallacis immatures were similar between seed treated and non-seed treated plants. However, the relationship between spider mite and thrips densities was different between these two plant types, but only in the clip cage experiment lacking predatory mites. This research highlights the importance of considering how IPM tactics might affect non-target organisms.

The Potential Benefits and Limitations of Corn Cob and Sewage Sludge Biochars in an Infertile Oxisol

The thermal conversion of sewage sludge to biochar offers a promising alternative use for a hazardous waste material with potential benefits to agricultural productivity and soil quality. Three short-term greenhouse experiments were conducted to evaluate the effect of corn cob (CC) and sewage sludge (SS) biochars, with their anaerobically treated counterparts, on soil properties and plant growth in an infertile Oxisol. The anaerobically treated SS biochar showed the greatest concentration of bioavailable essential nutrients, but treatment only resulted in increased yields for the SS biochar in the first crop in the absence of added fertilizer. Both CC and SS biochars in combination with fertilizer doubled plant growth compared to the control in the first crop cycle, produced no significant effect in the second cycle, and more than tripled plant growth for the SS biochars in the third cycle. High ash content with high nutrient contributions (especially P) and a persistent liming effect explain the benefits of the SS biochars to plant growth. The SS biochar showed promise in mitigating the negative effects of soil Mn toxicity. Sewage sludge biochars reduced Cd bioavailability and had no significant effect on the bioavailability of other potentially toxic metals compared to the control.

Comparative evaluation of commercial rhizobial inoculants of soybean

Inoculation of soybean seeds with root-nodule bacteria results in a significant increase in nodulation and yield. Two commercial rhizobial inoculants available on the South African market were tested for their efficacy under standardised conditions in a short-term greenhouse experiment. The rhizobial inoculants used were: (1) Plant Health Products mix (PHP), a wet formulation containing Trichoderma harzianum Eco-T® [strain KD] and Bradyrhizobium japonicum [strain WB74] and (2) ‘Product X’, a commercial dry tri-formulation containing Trichoderma spp. and three Bradyrhizobium strains. Seeds treated with the PHP mix yielded plants with significantly greater chlorophyll content (P<0.01), percent nitrogen (P = 0.001), and nodule occupancy (P<0.01) when compared with plants that had been treated with Product X. Correlation analysis indicated that 99% of the variation in nitrogen content levels was predicted by chlorophyll content meter readings. The use of the registered PHP product was shown to be the more efficient and reliable rhizobial inoculant for the improved growth and development of soybean.

Effect of European Chafer Larvae (Coleoptera: Scarabaeidae) on Winter Wheat and Role of Neonicotinoid Seed Treatments in Their Management.

A critical density of four third-instar larvae per 900 cm2 for European chafer, Rhizotrogus (Amphimallon) majalis (Razoumowsky), in winter wheat, Triticum aestivum L., was derived from small-plot greenhouse and field experiments conducted under favorable crop growing conditions at several Ontario and Michigan locations from 2001-2003. On average, plant weight was decreased by 14% and plant stand by 11% between zero and four larvae per 900 cm2. In a commercial field under moisture stress, a yield loss of 35% occurred at a density of two third-instars per 900 cm2. In short-term greenhouse experiments, density-dependent mortality was evident, whereas low larval recovery in field experiments indicates a high level of overwintering mortality, regardless of larval density. Winter wheat seed treatments of neonicotinoid insecticides, clothianidin, imidacloprid, and thiamethoxam provided protection from damage by larvae, but the level of protection was inconsistent between greenhouse and field small plots, and there was no apparent difference in protection amongst active ingredients or between application rates. There was little evidence of larval mortality owing to seed treatment, which supports the suggestion that neonicotinoid insecticides protect seedlings from loss by a nonlethal mechanism. Overall, we estimate that a low rate of neonicotinoid insecticide used at larval densities just less than the critical density will mitigate winter wheat losses by 85%.

Yield-scaled greenhouse gas emissions from flood irrigated rice under long-term conventional tillage and no-till systems in a Humid Subtropical climate

Soils under flooded rice (Oryza sativa L.) production are one of the major anthropogenic source of CH4 emissions, an important greenhouse gas (GHG) with a 25-times larger global warming potential (GWP) than CO2. No-till systems (NT) systems may be a viable alternative to mitigate GHG emissions in comparison to conventional tillage (CT). The objectives of this study were to evaluate on a field scale the long-term effects of CT and NT systems on soil CH4 and N2O emissions, rice yields and yield-scaled emissions during five growing seasons (GS) in Southern Brazil. In addition, a short-term greenhouse experiment was conducted to isolate the effect of winter crop [ryegrass (Lolium multiflorum L.)] biomass incorporation on soil CH4 efflux. Averaged across years, the NT system resulted in 21% lower seasonal CH4 emissions than the CT system, at 408 and 517kg CH4ha−1 GS−1, respectively. No significant effect of tillage system on N2O emissions was observed. Methane emission was responsible for 96.5% of partial GWP (pGWP=CH4×25+N2O×298), stressing the importance of this GHG for developing low GHGs rice systems. No significant effect of tillage system on rice grain yields (average of 7.8Mgha−1GS−1) was detected. Consequently, the NT system resulted in 23% lower yield-scaled pGWP, at 1.35 and 1.76kg CO2eqkg−1 grain for NT and CT treatments, respectively. According to the greenhouse study, the incorporation of ryegrass biomass into the soil resulted in 2.8 times larger cumulative CH4 emission than the surface application of biomass, at 347.4 and 125.5g CH4m−2, respectively, due to higher dissolved organic carbon (DOC) concentration and reduced soil environment in subsurface soil layers. Our results indicate that biomass incorporation is the main cause of higher CH4 emissions from conventionally tilled soil and that NT system is a viable alternative to reduce yield-scaled GHG emissions from flooded rice fields.

Intermediate herbivory intensity of an aboveground pest promotes soil labile resources and microbial biomass via modifying rice growth

The importance of aboveground herbivores for modifying belowground ecosystems has prompted numerous studies; however, studies can be biased by context dependent conditions which lead to extremely inconsistent results. So far, the impacts of herbivory intensity by important rice pests on rice paddy soil ecosystems are lacking. The aim of this study was to test the hypothesis that intermediate herbivory intensity of the brown planthopper (Nilaparvata lugens Stal) could promote soil labile resources and microbial biomass, while high intensity would show a reverse pattern, by mediating rice plant growth. This study will also help the development of integrative pest management. Four hopper infestation density treatments (0, 4, 8 and 12 nymphs per rice plant) and two infestation duration treatments (9 and 15 days after N. lugens infestation, DAI 9 and DAI 15) were established in a glasshouse experiment. Soil and plant were sampled destructively from four replicates and analysed for soil labile resources availability, soil microbial biomass and plant performance, respectively. The infestation density significantly affected both shoot and root mass of rice (P < 0.05), soil dissolved organic carbon (DOC) and nitrogen (DON), and microbial biomass carbon (MBC) and nitrogen (MBN), and the effects were further enhanced by prolonged infestation duration. Compared to the control (CK) without N. lugens, plant dry mass, DOC, DON, MBC and MBN increased under low (LD) and moderate hopper densities (MD) but decreased under high density (HD) on DAI 9. Moreover, the LD treatment exerted the most promotional effects on DAI 15. Rice root to shoot ratio generally increased in treatments subjected to herbivory. The labile resources and microbial biomass showed close relationships with both shoot and root mass across treatments, in particular with root mass on DAI 15. Such a trend indicated that the shift of photosynthate allocation to belowground contributed to changes of soil resource availability and microbial biomass. Intermediate herbivory intensity showed positive effects on rice seedling performance and, further, promoted soil labile resource availability and microbial biomass. The importance of extrapolating temporal and spatial scale, i.e. from the short-term greenhouse experiment to an entire rice growing season in the field, was highlighted.

The mechanism on rhizosphere phosphorus activation of two wheat genotypes with different phosphorus efficiency

A short-term greenhouse experiment was carried out with two phosphorus (P) levels of purple soil to investigate P availability and associated processes in the rhizosphere of two different P-efficiency wheat genotypes using a thin slicing technique. Two genotypes with different P efficiencies were grown in a root-compartment experiment under low P (P 10: 10 P mg/kg) and high P (P 100: 100 P mg/kg) treatments. Results show that readily extracted forms of soil inorganic P were depleted by the two wheat genotypes, depletion zones extended further adjacent to 4 to 6 mm. Enhanced depletion of sodium hydroxide extractable organic P apparent in the rhizosphere of high P-efficient wheat cultivar 10098 compared with low P inefficient wheat cultivar 10026 was related to the presence of greater concentrations of microbial biomass and higher soil acid phosphatase and phosphodiesterase enzyme activities. These results confirm that microorganisms and soil enzymic activities played important roles in the mineralization of soil organic P, particularly under high P-efficient wheat cultivar 10098. These results suggest that improving P efficiency based on the character of P efficiency acquisition in Pefficient genotype would be a potential approach for maintaining wheat yield potential in soils with low P bioavailability.

Potential for Phytoremediation of Polychlorinated Biphenyl-(PCB)-Contaminated Soil

Weathered soils contaminated with commercial-grade Aroclor 1260 from three sites in Canada were used to investigate the polychlorinated biphenyl (PCB) phytoextraction potential of nine plant species (Festuca arundinacea, Glycine max, Medicago sativa, Phalaris arundinacea, Lolium multiflorum, Carex normalis, and three varieties of Cucurbita pepo ssp. pepo) under controlled greenhouse conditions. The soils used varied in PCB concentration (90–4200 μg/g) and total organic content (0.06–2.02%). Greenhouse experiments controlled for PCB volatilization through the use of a vented enclosure and by isolating the contaminated soils with parafilm. After 8 wks, PCB concentrations of 47–6700 μg/g were observed in root tissues. Although PCB concentrations in shoot tissues were lower (<1–470 μg/g), the absolute amounts of PCBs observed in shoot tissue were significant (1.7–290 μg) once shoot biomass was accounted for. Congener signatures indicated that tetra-to hexa-chlorobiphenyls contributed the largest proportions to shoot tissues, but hepta-to nona-chorobiphenyls were also present in measurable amounts. Overall, the results indicate that varieties of C. pepo were more effective at extracting PCBs from soil than other plants screened. The evidence suggests that this was mainly due to root uptake of PCBs and tranlocation to the shoots, rather than volatilization of PCBs from soil. All plants screened showed signs of stress in the most highly contaminated soil (4200 μg/g), but not in the two lower PCB contaminated soils (250 and 90 μg/g, respectively). No detectable decreases in soil PCB concentrations were observed in these short-term greenhouse experiments, but the results suggest that this may be achievable through multiple plantings.