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Organic production is growing globally following a rising demand. Other than EU-regulations, the USDA regulations (North America), allow soilless cultivation as organic when specific requirements are accomplished, for instance the use of fertilisers from organic source. However, the small volume of growing medium in soilless cultivation can be a limitation. At first, because a certain microbiological activity should be established in the root environment to enable mineralisation of the organic fertilisers. Secondly, the buffer capacity of the system is limited. As a result, the release of plant available N is often lower compared to the crop demand, and it limits the growth. In addition, this has a negative effect on the efficiency of the system, for instance in terms of water or energy use. NO3 is the preferred form for available N. Recently, the use of natural NO3 has been discussed as a possibility to feed the plants in organic soilless productions with readily available N. Natural NO3 is formed in nature during thunderstorms when the lightings fix the N of the air into the water. The natural process of lightning have been mimicked in an industrial process and there is a technology that reproduce the same process and fix N into water in the form of HNO3. The resulting N enriched water is called plasma activated water (PAW). This paper describes the results of a comparison study between a standard soilless organic cultivation with one that used PAW as a source of NO3. We investigated and pointed out the benefits in terms of water, fertilisers and energy use. The results showed a rising water, fertilisers and energy use efficiency with PAW, mainly due to the higher production and a longer period of using a closed-loop irrigation system. In addition to these results, the technical equipment needed to implement this technology into a current organic soilless system is also discussed.

Root-associated fungi could play a role in determining both the positive relationship between plant diversity and productivity in experimental grasslands, and its strengthening over time. This hypothesis assumes that specialized pathogenic and mutualistic fungal communities gradually assemble over time, enhancing plant growth more in species-rich than in species-poor plots. To test this hypothesis, we used high-throughput amplicon sequencing to characterize root-associated fungal communities in experimental grasslands of 1 and 15 years of age with varying levels of plant species richness. Specifically, we tested whether the relationship between fungal communities and plant richness and productivity becomes stronger with the age of the experimental plots. Our results showed that fungal diversity increased with plant diversity, but this relationship weakened rather than strengthened over the two time points. Contrastingly, fungal community composition showed increasing associations with plant diversity over time, suggesting a gradual build-up of specific fungal assemblages. Analyses of different fungal guilds showed that these changes were particularly marked in pathogenic fungi, whose shifts in relative abundance are consistent with the pathogen dilution hypothesis in diverse plant communities. Our results suggest that root-associated fungal pathogens play more specific roles in determining the diversity–productivity relationship than other root-associated plant symbionts.

Availability of rain water is lower than the total water requirement for several crops, while the use of ground water is under discussion. This creates the need to either find alternative water sources, or decrease the required amount of water. This project investigated with model calculations the options to produce year-round tomatoes without the use of additional water, by decreasing transpiration, regain of transpiration water, or by using water collected by energy production via hydrogen. An increased size rain water basin up to 3000 m3/ha strongly decreases the required amount of additional water. Reflection of sun-light at higher irradiation strength than 600 W/m2 and increasing relative humidity (measures from Het Nieuwe Telen) decrease the water requirement. Measures to regain transpired water (balanced ventilation, active dehumidification and closed greenhouse) also lead to a decreased requirement for additional water. A completely closed greenhouse does not require additional water, but the energy demand for dehumidification increases. Investments in these technologies are only financially interesting when also the picture for energy is right. Hydrogen as fuel has potential, but production of water from this energy source is a by-catch and should not be the main reason for investment., De beschikbaarheid van hemelwater is voor een aantal gewassen minder dan de totale waterbehoefte van het gewas, terwijl er druk ligt op het gebruik van grondwater. Hierdoor moet men op zoek naar alternatieve waterbronnen, of de watervraag moet verlaagd worden. In dit project is met behulp van modelberekeningen onderzocht of het mogelijk is jaarrond tomaten te telen zonder gebruik te maken van aanvullend water, door het beperken van verdamping, het terugwinnen van verdampingswater of gebruik van water afkomstig van de productie van energie via waterstof. Een groter hemelwaterbassin tot 3000 m3/ha verlaagt de behoefte aan aanvullend water sterk. Schermen vanaf een instraling van 600 W/m2 en aanhouden van hogere RV (maatregelen uit Het Nieuwe Telen) beperken de vraag naar water. Maatregelen om verdampingswater terug te winnen (balansventilatie, actieve ontvochtiging en gesloten kas) leiden ook tot een verlaging van het gebruik van aanvullend water. Bij een volledig gesloten kas is geen aanvullend water nodig, maar neemt het energiegebruik voor ontvochtiging fors toe. Investeringen hierin zijn financieel alleen interessant als ook het plaatje voor energie klopt. Waterstof als brandstof heeft potentie, maar de productie van water hieruit moet worden gezien als bijvangst en niet als hoofdreden voor toepassing van deze technologie.

After a revision of standardised water in 2021 when a couple of active components of crop protection agents in standardised water were replaced, after a first test with purification equipment and a follow-up test it showed that one of the new components from standardised Water did not break down as good as the other components. Therefore, an additional test is executed to the degradability of all allowed substances in greenhouse horticulture, by advanced oxidation (H2O2 + UV). Three active components from standardised water have been used in the test as a reference. A number of active substances shows to be less degradable with this technology, with a purification efficacy of <95%., Na herziening van het Standaard Water in 2021 waarbij een aantal werkzame stoffen van gewasbeschermingsmiddelen in het standaard water zijn vervangen, is na een eerste test met een zuiveringstechniek, en ook na herhaling van het onderzoek, gebleken dat één van de nieuwe stoffen uit het Standaard Water minder goed afbreekt. Daarom is een aanvullend verkennend onderzoek uitgevoerd naar de afbreekbaarheid van alle in de glastuinbouw toegelaten werkzame stoffen, door geavanceerde oxidatie (H2O2 + UV). Als referentie zijn drie werkzame stoffen uit standaard water in de tests meegenomen. Een aantal stoffen blijkt met deze techniek minder goed af te breken, met een zuiveringsrendement <95%.

In 2021 heeft een herziening van het Standaard Water plaatsgevonden. Hierbij zijn 5 gewasbeschermingsmiddelen die inmiddels niet meer toegelaten zijn vervangen door 5 andere gewasbeschermingsmiddelen en is Standaard Water Versie 3.0 samengesteld. De samenstelling van het Standaard Water is vastgelegd in het ‘Meetprotocol voor het testen van het zuiveringsrendement van zuiveringsinstallaties glastuinbouw’, Versie 4 maart 2021. In een hierop volgend onderzoek met deze nieuwe samenstelling van het Standaard Water, ten behoeve van een goedkeuring door de BZG voor een installatie gebaseerd op geavanceerde oxidatie (H2O2 + UV), kwam naar voren dat één van de nieuw toegevoegde werkzame stoffen (flonicamid) veel minder goed wordt afgebroken dan de andere stoffen (±40%). Dit roept de vraag op of er meer stoffen in het middelenpakket van toegelaten werkzame stoffen voor de glastuinbouw zijn, die door goedgekeurde zuiveringstechniek minder goed worden verwijderd. Naar aanleiding hiervan is voor de technologie waarvan de meeste goedkeuringen zijn behaald (geavanceerde oxidatie op basis van H2O2 + UV) een test uitgevoerd met een installatie die in de BZG-toets een zuiveringsrendement van net 95% haalde. Uit deze test bleek dat verschillende stoffen inderdaad moeilijker afbreekbaar zijn dan de stoffen in Standaard Water. Om dit nog verder te valideren en oorzaken voor de minder goede afbraak vast te stellen is een nieuw onderzoek opgezet met een andere installatie met dezelfde technologie. Deze installatie haalde tijdens de beoordelingstoets voor alle stoffen uit het Standaard Water nagenoeg 100% zuiveringsrendement. -- Doel van het uitgevoerde verkennende onderzoek was dan ook: Vaststellen van welke van de in de glastuinbouw toegelaten werkzame stoffen minder goed wordenverwijderd en in welk mate, met de best scorende zuiveringstechniek op basis van H2O2 en UV.

Plant–soil feedback (PSF) and diversity–productivity relationships are important research fields to study drivers and consequences of changes in plant biodiversity. While studies suggest that positive plant diversity–productivity relationships can be explained by variation in PSF in diverse plant communities, key questions on their temporal relationships remain. Here, we discuss three processes that change PSF over time in diverse plant communities, and their effects on temporal dynamics of diversity–productivity relationships: spatial redistribution and changes in dominance of plant species; phenotypic shifts in plant traits; and dilution of soil pathogens and increase in soil mutualists. Disentangling these processes in plant diversity experiments will yield new insights into how plant diversity–productivity relationships change over time.

The allowance for use of imidacloprid, iprodione and pymetrozine in Dutch greenhouse horticulture is not prolonged, therefore these active ingredients are no longer suitable for use Standardised Water. Seven potential active ingredients (fludioxonil, cyprodinil, penconazool, metalaxyl-M, flonicamid, flupyradifuron en acetamiprid) are selected to replace these three active ingredients and are tested for stability under influence of addition of sodium sulphite and analyzability in the Standardised Water matrix. All seven new active ingredients showed well analyzable and stable. Two active ingredients from current Standardised Water (spinosad and fenvalerate) showed not well analysable/not stable. It is advised to also replace these by two new active ingredients., De toelating van imidacloprid, iprodion en pymetrozine is verlopen voor de Nederlandse glastuinbouw, waardoor deze middelen niet meer gebruikt kunnen worden in het Standaard Water. Zeven potentiële werkzame stoffen (fludioxonil, cyprodinil, penconazool, metalaxyl-M, flonicamid, flupyradifuron en acetamiprid) zijn geselecteerd ter vervanging van deze drie werkzame stoffen en zijn getest op stabiliteit in Standaard Water en onder invloed van toevoeging van natriumsulfiet, en analyseerbaarheid in de matrix van Standaard Water. Alle zeven geselecteerde werkzame stoffen bleken goed te analyseren en stabiel. Twee werkzame stoffen uit het huidige Standaard Water (spinosad en fenvaleraat) blijken niet goed analyseerbaar/niet stabiel. Daarom wordt geadviseerd ook deze stoffen te vervangen door twee nieuwe stoffen.

Climate change will increase the likelihood and severity of droughts into the future. Although diversity may buffer plant communities against the negative effects of drought, the mechanisms underlying this pattern remain unclear. Higher-diversity plant communities may have a higher likelihood of including more drought-resistant species that can compensate for drought-sensitive species (“insurance effects”). Alternatively, higher-diversity communities may alter environmental conditions and improve performance of even drought-sensitive species. Here we planted nonleguminous forbs and grasses into monocultures and four- and eight-species mixtures, and measured species and plot productivity every year from 2000 to 2010. We found that six of our eight species were suppressed when growing in monoculture during dry years. These same species were unaffected by drought when growing in higher-diversity mixtures. Because of this poor performance in monoculture (not insurance effects), the biodiversity productivity relationship was strongest during the driest years. If biodiversity ameliorates hot/dry conditions and therefore improves performance of drought-sensitive species during periods of low rainfall, this may mean biodiversity can be used as a tool to protect individual species from drought conditions.

Plant economics run on carbon and nutrients instead of money. Leaf strategies aboveground span an economic spectrum from “live fast and die young” to “slow and steady,” but the economy defined by root strategies belowground remains unclear. Here, we take a holistic view of the belowground economy and show that root-mycorrhizal collaboration can short circuit a one-dimensional economic spectrum, providing an entire space of economic possibilities.Root trait data from 1810 species across the globe confirm a classical fast-slow “conservation” gradient but show that most variation is explained by an orthogonal “collaboration” gradient, ranging from “do-it-yourself”resource uptake to “outsourcing” of resource uptake to mycorrhizal fungi. This broadened “root economics space”provides a solid foundation for predictive understanding of belowground responses to changing environmental conditions.

Locally, plant species richness supports many ecosystem functions. Yet, the mechanisms driving these often‐positive biodiversity–ecosystem functioning relationships are not well understood. Spatial resource partitioning across vertical resource gradients is one of the main hypothesized causes for enhanced ecosystem functioning in more biodiverse grasslands. Spatial resource partitioning occurs if species differ in where they acquire resources and can happen both above‐ and belowground. However, studies investigating spatial resource partitioning in grasslands provide inconsistent evidence. We present the results of a meta‐analysis of 21 data sets from experimental species‐richness gradients in grasslands. We test the hypothesis that increasing spatial resource partitioning along vertical resource gradients enhances ecosystem functioning in diverse grassland plant communities above‐ and belowground. To test this hypothesis, we asked three questions. (1) Does species richness enhance biomass production or community resource uptake across sites? (2) Is there evidence of spatial resource partitioning as indicated by resource tracer uptake and biomass allocation above‐ and belowground? (3) Is evidence of spatial resource partitioning correlated with increased biomass production or community resource uptake? Although plant species richness enhanced community nitrogen and potassium uptake and biomass production above‐ and belowground, we found that plant communities did not meet our criteria for spatial resource partitioning, though they did invest in significantly more aboveground biomass in higher canopy layers in mixture relative to monoculture. Furthermore, the extent of spatial resource partitioning across studies was not positively correlated with either biomass production or community resource uptake. Our results suggest that spatial resource partitioning across vertical resource gradients alone does not offer a general explanation for enhanced ecosystem functioning

Dutch greenhouse horticulture is putting much effort into implementing measures to reduce emission of nutrients and plant protection products to surface water. This report shows results of analyses of cleaning waterproduced during crop interchange of substrate grown crops, water flows currently not included in legislationon nitrogen emission and obligated purification of discharge water. Water for cleaning the inside of windows,irrigation pipelines and cultivation gutters/tables is evaluated. Measurements show that discharge of these waterflows to surface water can cause exceedance of surface water quality standards. Therefore, best practices aredescribed to prevent emission of nutrients and plant protection products with these water flows. First step is to adapt the cultivation system or cleaning strategy in such a way that collection of the water is possible. This creates an option for reuse or treatment of the water. Second step is close consideration of the use of cleaningor disinfection agents, as some of these products can cause damage to the new crop. If reuse is undesirable,it is advisable to purify the water before discharge for the removal of plant protection agents, by using a BZG approved installation, as this significantly decreases the emission of plant protection products., De Nederlandse glastuinbouw werkt hard aan het terugdringen van de emissie van meststoffen en gewasbeschermingsmiddelen naar oppervlaktewater. In het voorliggende rapport worden resultaten getoondvan analyses van vrijkomend water tijdens de teeltwisseling van substraatteelten, waterstromen die buitende zuiveringsplicht en emissienormen stikstof vallen. Het gaat hierbij onder andere om het reinigingswatervan de binnenzijde van het kasdek, irrigatieleidingen en teeltgoten/teelttafels. De metingen tonen aan dat de waterstromen bij lozing op het oppervlaktewater kunnen zorgen voor overschrijdingen van de normen voor oppervlaktewater. Daarom zijn best practices beschreven voor het voorkomen van emissie van deze waterstromen. De eerste stap om het water te kunnen hergebruiken is het zodanig aanpassen van het teeltsysteem of de reinigingsstrategie dat het vrijkomende water kan worden opgevangen. De tweede stap is kritisch kijken naar de gebruikte reinigings- of ontsmettingsproducten, omdat sommige producten schadekunnen geven aan het nieuwe gewas. Indien hergebruik toch niet wenselijk is, is het advies de waterstromen tezuiveren voor lozing met een BZG-goedgekeurde installatie, zodat de emissie van gewasbeschermingsmiddelen voor het grootste deel voorkomen wordt.

The importance of wild pollinators compared to conventional agricultural management is undervalued, suggests the PhD thesis of Thijs Fijen of Wageningen University. A study in commercial leek seed production fields shows that wild pollinators contribute as much to crop yield as plant quality. Honeybees, placed next to flowering leek fields specifically for pollination, do not contribute much to crop yield. Experimental work confirmed these findings: a 50% reduction in pollination leads to much larger reductions in seed yield than similar reductions in fertilizer applications or irrigation. Surprisingly, a 50% reduction in fertilisation resulted in equally high, or higher crop yields. These results may explain the international trend that crop yields of insect-pollinated crops increase less fast as those of wind-pollinated crops. The research of Fijen furthermore shows that both crop pollination and pollinator biodiversity in agricultural landscapes can be promoted by better protection of semi-natural habitats such as flower-rich road sides and nature areas.

Competition for freshwater resources, and legal restrictions on discharge of agrochemicals (plant protection products and fertilisers) increase pressure on agricultural practice to improve water-use-efficiency of crop production globally. Zero-discharge greenhouse crop production can be an effective solution to both problems. Preliminary results of experiments with cucumber and sweet pepper on stone wool substrate in two greenhouse compartments showed that productivity did not differ in zero-discharge growing compared to standard growing strategies. In this paper we present the final evaluation of the sweet pepper trial (December 2014-November 2015). In the reference compartment a total amount of 465 m3 ha-1 year-1 (169.3 kg N) was discharged. In the zero-discharge compartment there was no discharge during cropping. The nutrient composition of irrigation and drain water was analysed weekly (compared to two-weekly in reference) and nutrient stock composition was changed accordingly. Drain water was filtered with a flatbed filter (no rinsing water) and upon changes in fertigation, the new fertigation solution was first distributed throughout the entire irrigation system by a circulation pump, before application. An irrigation strategy was developed for the end of the cropping season, aiming to drain substrate slabs and to empty drain tanks as much as possible and reduce the amount of remaining nutrients in the slabs, without compromising productivity. Water-use-efficiency of the zero-liquid discharge strategy could be optimised by steering towards more generative crop growth.

Evidence suggests that biodiversity supports ecosystem functioning. Yet, the mechanisms driving this relationship remain unclear. Complementarity is one common explanation for these positive biodiversity–ecosystem functioning relationships. Yet, complementarity is often indirectly quantified as overperformance in mixture relative to monoculture (e.g., ‘complementarity effect’). This overperformance is then attributed to the intuitive idea of complementarity or, more specifically, to species resource partitioning. Locally, however, several unassociated causes may drive this overperformance. Here, we differentiate complementarity into three types of species differences that may cause enhanced ecosystem functioning in more diverse ecosystems: (i) resource partitioning, (ii) abiotic facilitation, and (iii) biotic feedbacks. We argue that disentangling these three causes is crucial for predicting the response of ecosystems to future biodiversity loss.

A substantial body of evidence has demonstrated that biodiversity stabilizes ecosystem functioning over time in grassland ecosystems. However, the relative importance of different facets of biodiversity underlying the diversity–stability relationship remains unclear. Here we use data from 39 grassland biodiversity experiments and structural equation modelling to investigate the roles of species richness, phylogenetic diversity and both the diversity and community-weighted mean of functional traits representing the ‘fast–slow’ leaf economics spectrum in driving the diversity–stability relationship. We found that high species richness and phylogenetic diversity stabilize biomass production via enhanced asynchrony in the performance of co-occurring species. Contrary to expectations, low phylogenetic diversity enhances ecosystem stability directly, albeit weakly. While the diversity of fast–slow functional traits has a weak effect on ecosystem stability, communities dominated by slow species enhance ecosystem stability by increasing mean biomass production relative to the standard deviation of biomass over time. Our in-depth, integrative assessment of factors influencing the diversity–stability relationship demonstrates a more multicausal relationship than has been previously acknowledged.

The more plant species grow together, the higher the yield. Higher plant species richness may also increase drought resistance, i.e. yield preservation during droughts. However, the mechanisms underlying these positive biodiversity effects are still debated. I this thesis, I investigated whether diversity in root characteristics or ‘traits’, such as rooting depth, can explain increased yield, or ‘overyielding’, and drought resistance in grassland plant communities. My results show that, although diversity in roots traits could not explain overyielding, root traits – and deep rooting in particular – were important: communities with deep-rooting species performed better than expected. Further, overyielding of deep-rooting species in diverse communities increased when growing with shallow-rooting neighbours, supporting the importance of rooting depth diversity. This research shows that rooting strategies play an important role in the positive effect of plant diversity on yield production. We found no evidence that plant species richness or root trait diversity increased drought resistance, perhaps due to extremeness of the drought treatment. On the contrary, drought decreased overyielding. Future biodiversity research at different drought intensity levels may further increase our insights on how biodiversity affect the drought resistance of our grasslands.

Background Plant diversity influences ecosystem functioning. A positive relation between plant diversity and productivity above- and belowground has been established. Aboveground, this effect has been shown to be due to complementarity effects, interactions between species in a mixture that lead species to, on average, produce more biomass than expected based on their productivity in monoculture. The mechanisms underlying complementarity effects and the positive diversity-productivity relation are predicted to lie belowground, e.g. resource partitioning and/or facilitation. The relation between plant diversity and decomposition is less clear, and research on the diversity-decomposition relation belowground is limited. This is an important gap in biodiversity knowledge, as the decomposition of plant litter is the major source of nutrients and carbon in terrestrial ecosystems, and most plant litter in grasslands is belowground. Methods This thesis explored the effect of plant diversity on belowground productivity and decomposition. Belowground complementarity effects were quantified in the Jena Trait Based Experiment, and the diversity of or plasticity in species-specific vertical root distribution as underlying mechanism was tested. The plant diversity- root decomposition relation was quantified in the Jena Experiment and the Jena Trait Based Experiment. The role of root traits and the soil environment as mediating factors were tested. Major findings Plant diversity had a positive effect on root biomass production, and this relation was attributed to complementarity effects. The diversity in species-specific vertical root distribution did not explain complementarity effects, and thus, is not likely a major mechanism underlying the diversity-productivity relation. Species altered their vertical root distribution in response to inter-specific neighbours. The direction of this change differed between functional groups: grasses became shallower in mixture, forbs became d

There is consensus that plant species richness enhances plant productivity within natural grasslands, but the underlying drivers remain debated. Recently, differential accumulation of soil-borne fungal pathogens across the plant diversity gradient has been proposed as a cause of this pattern. However, the below-ground environment has generally been treated as a 'black box' in biodiversity experiments, leaving these fungi unidentified. Using next generation sequencing and pathogenicity assays, we analysed the community composition of root-associated fungi from a biodiversity experiment to examine if evidence exists for host specificity and negative density dependence in the interplay between soil-borne fungi, plant diversity and productivity. Plant species were colonised by distinct (pathogenic) fungal communities and isolated fungal species showed negative, species-specific effects on plant growth. Moreover, 57% of the pathogenic fungal operational taxonomic units (OTUs) recorded in plant monocultures were not detected in eight plant species plots, suggesting a loss of pathogenic OTUs with plant diversity. Our work provides strong evidence for host specificity and negative density-dependent effects of root-associated fungi on plant species in grasslands. Our work substantiates the hypothesis that fungal root pathogens are an important driver of biodiversity-ecosystem functioning relationships.

Biodiversity-ecosystem functioning (BEF) studies typically show that species richness enhances community biomass, but the underlying mechanisms remain debated. Here, we combine metrics from BEF research that distinguish the contribution of dominant species (selection effects, SE) from those due to positive interactions such as resource partitioning (complementarity effects, CE) with a functional trait approach in an attempt to reveal the functional characteristics of species that drive community biomass in species mixtures. In a biodiversity experiment with 16 plant species in monocultures, 4-species and 16-species mixtures, we used aboveground biomass to determine the relative contributions of CE and SE to biomass production in mixtures in the second, dry year of the experiment. We also measured root traits (specific root length, root length density, root tissue density and the deep root fraction) of each species in monocultures and linked the calculated community weighted mean (CWM) trait values and trait diversity of mixtures to CE and SE. In the second year of the experiment, community biomass, CE and SE increased compared to the first year. The contribution of SE to this positive effect was greater than that of CE. The increased contribution of SE was associated with root traits: SE increased most in communities with high abundance of species with deep, thick and dense roots. In contrast, changes in CE were not related to trait diversity or CWM trait values. Together, these results suggest that increased positive effects of species richness on community biomass in a dry year were mainly driven by increased dominance of deep-rooting species, supporting the insurance hypothesis of biodiversity. Positive CE indicates that other positive interactions did occur, but we did not find evidence that belowground resource partitioning or facilitation via root traits was important for community productivity in our biodiversity experiment.

Contains fulltext : 168951.pdf (publisher's version ) (Closed access)

Contains fulltext : 176862.pdf (publisher's version ) (Closed access), Plant diversity influences many ecosystem functions including root decomposition. However, due to the presence of multiple pathways via which plant diversity may affect root decomposition, our mechanistic understanding of their relationships is limited. In a grassland biodiversity experiment, we simultaneously assessed the effects of three pathways—root litter quality, soil biota, and soil abiotic conditions—on the relationships between plant diversity (in terms of species richness and the presence/absence of grasses and legumes) and root decomposition using structural equation modeling. Our final structural equation model explained 70% of the variation in root mass loss. However, different measures of plant diversity included in our model operated via different pathways to alter root mass loss. Plant species richness had a negative effect on root mass loss. This was partially due to increased Oribatida abundance, but was weakened by enhanced root potassium (K) concentration in more diverse mixtures. Equally, grass presence negatively affected root mass loss. This effect of grasses was mostly mediated via increased root lignin concentration and supported via increased Oribatida abundance and decreased root K concentration. In contrast, legume presence showed a net positive effect on root mass loss via decreased root lignin concentration and increased root magnesium concentration, both of which led to enhanced root mass loss. Overall, the different measures of plant diversity had contrasting effects on root decomposition. Furthermore, we found that root chemistry and soil biota but not root morphology or soil abiotic conditions mediated these effects of plant diversity on root decomposition.

© 2017 The Author(s). In peatland ecosystems, plant communities mediate a globally significant carbon store. The effects of global environmental change on plant assemblages are expected to be a factor in determining how ecosystem functions such as carbon uptake will respond. Using vegetation data from 56 Sphagnum-dominated peat bogs across Europe, we show that in these ecosystems plant species aggregate into two major clusters that are each defined by shared response to environmental conditions. Across environmental gradients, we find significant taxonomic turnover in both clusters. However, functional identity and functional redundancy of the community as a whole remain unchanged. This strongly suggests that in peat bogs, species turnover across environmental gradients is restricted to functionally similar species. Our results demonstrate that plant taxonomic and functional turnover are decoupled, which may allow these peat bogs to maintain ecosystem functioning when subject to future environmental change.

The effects of biodiversity on ecosystem functioning generally increase over time, but the underlying processes remain unclear. Using 26 long-term grassland and forest experimental ecosystems, we demonstrate that biodiversity–ecosystem functioning relationships strengthen mainly by greater increases in functioning in high-diversity communities in grasslands and forests. In grasslands, biodiversity effects also strengthen due to decreases in functioning in low-diversity communities. Contrasting trends across grasslands are associated with differences in soil characteristics.

To apply to the Dutch generic obligation to purify discharge water, each horticultural company needs to treat it’s discharge water with a technology that removes 95% of plant protection products. This report shows the process that growers need to go through to make a good choice for a purification technology: mapping of water flows, decrease the amount of discharge water, determine the strategy to apply to the generic obligation and make a choice for a purification technology. For a cucumber production company and a company that combines vegetable plant propagation and growth of potted plants this process is followed. A design for a purification system is developed and built for a semi-practice scale cucumber and sweet pepper production system. In the semi-practice scale and the cucumber production company, an ozone installation (Agrozone) is chosen, either to disinfect drain water and eventually purify discharge water. At the propagation company, an Opticlear Diamond (WaterIQ) is chosen to disinfect the drain water and eventually purify discharge water. For both installations the purification efficacy is measured. In the second part of the project the practical format for the generic obligation for discharge water purification is elaborated., Om te kunnen voldoen aan de generieke zuiveringsplicht, moet ieder glastuinbouwbedrijf zijn lozingswater behandelen met een techniek die ten minste 95% van de gewasbeschermingsmiddelen uit het water verwijdert. In dit rapport is het proces weergegeven dat telers moeten doorlopen om een goede keuze te kunnen maken voor een zuiveringstechniek: waterstromen in kaart brengen, hoeveelheid lozingswater verlagen, strategie bepalen om te voldoen aan de zuiveringsplicht en een keuze maken voor een bepaald type zuiveringstechniek. Voor een komkommerbedrijf en een gecombineerd bedrijf met opkweek groenteplanten en op- en afkweek van potplanten is dit proces doorlopen. Voor een semi-praktijk situatie is een ontwerp gemaakt van een systeem om het lozingswater op een efficiënte manier te zuiveren. In de semi-praktijksituatie en bij het komkommerbedrijf is gekozen voor een installatie op basis van ozon (Agrozone), zowel om drainwater te ontsmetten als lozingswater te zuiveren. Bij de plantenkwekerij is gekozen voor een Opticlear Diamond (WaterIQ), ook om drainwater te ontsmetten en indien nodig lozingswater te zuiveren. Voor beide installaties is in (semi)praktijksituatie het zuiveringsrendement gemeten. In het tweede deel van het project is de uitvoeringsvorm van de zuiveringsplicht uitgewerkt

Species-rich plant communities are more productive than species-poor plant communities but the reasons behind this relationship are currently unclear. We characterised the fungal communities associated with plant roots from the Wageningen biodiversity experiment to explore the effect of plant species identity, abundance and diversity on root associated fungal communities. Briefly, the Wageningen biodiversity experiment consisted of plant communities comprised of the following plant species: Agrostis capillaris L., Anthoxanthum odoratum L., Festuca rubra L., and Holcus lanatus L., Centaurea jacea L., Leucanthemum vulgare Lamk., Plantago lanceolata L., and Rumex acetosa,.These were grown either in monocultures or 2,4 or 8 plant species mixtures. 3cm diameter soil cores were taken from this experiment in 2010 and divided into two depth increments: (0-5, 20-35 cm). Roots from each depth were washed and their fungal communities characterised using 454 GS FLX pyrosequencing of amplicon libraries of the internal transcribed spacer (ITS1) region using primers ITS1F (Gardes & Bruns 1993) and ITS2 (White et al. 1990), Species-rich plant communities are more productive than species-poor plant communities but the reasons behind this relationship are currently unclear. We characterised the fungal communities associated with plant roots from the Wageningen biodiversity experiment to explore the effect of plant species identity, abundance and diversity on root associated fungal communities. Briefly, the Wageningen biodiversity experiment consisted of plant communities comprised of the following plant species: Agrostis capillaris L., Anthoxanthum odoratum L., Festuca rubra L., and Holcus lanatus L., Centaurea jacea L., Leucanthemum vulgare Lamk., Plantago lanceolata L., and Rumex acetosa,.These were grown either in monocultures or 2,4 or 8 plant species mixtures. 3cm diameter soil cores were taken from this experiment in 2010 and divided into two depth increments: (0-5, 20-35 cm). Roots from each depth were washed and their fungal communities characterised using 454 GS FLX pyrosequencing of amplicon libraries of the internal transcribed spacer (ITS1) region using primers ITS1F (Gardes & Bruns 1993) and ITS2 (White et al. 1990)

1. Belowground resource partitioning is often proposed as the underlying mechanism for the positive relationship between plant species richness and productivity. For example, if species have different root distributions, a mixture of plant species may be able to use the available resources more completely than the individual species in a monoculture. However, there is little experimental evidence for differentiation in vertical root distributions among species and its contribution to biodiversity effects. 2. We determined species-specific root standing biomass over depth using molecular techniques (real time-qPCR) in a large grassland biodiversity experiment (1-8 plant species mixtures), in two years. Species-specific root biomass data were used to disentangle the effects of positive interactions between species (complementarity effects) and effects due to dominance of productive species (selection effects) on root biomass in mixtures. In a next step, these biodiversity effects were linked to the diversity of rooting depths and the averaged rooting depth of the community. 3. Root biomass increased with species richness. This was mainly due to positive interactions (the complementarity effect), which increased with species richness belowground. In contrast, the selection effect decreased with species richness. Although there was considerable variation in vertical root distribution between species in monocultures, the diversity of rooting strategies did not explain the complementarity effect. Rather, the abundance of deep-rooting species in mixtures (i.e. high community weighted mean) was significantly related to the complementarity effect. Comparing the ‘predicted’ root distribution (based on monocultures) to the actual distribution in mixtures, we found that mixtures rooted deeper than expected, but this did not better explain the complementarity effect. 4. Synthesis: This study demonstrates that vertical root distributions of species provide only subtle evidence fo

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Plant diversity enhances many ecosystem functions, including root biomass production, which drives soil carbon input. Although root decomposition accounts for a large proportion of carbon input for soil, little is known about plant diversity effect on this process. Plant diversity may affect root decomposition in two non-exclusive ways: by providing roots of different substrate quality (e.g. root chemistry) and/or by altering the soil environment (e.g. microclimate).To disentangle these two pathways, we conducted three decomposition experiments using a litter-bag approach in a grassland biodiversity experiment. We hypothesized that: (i) plant species richness negatively affects substrate quality (indicated by increased C:N ratios), which we tested by decomposing roots collected from each experimental plot in one common plot; (ii) plant species richness positively affects soil environment (indicated by increased soil water content), which we tested by decomposing standardized roots in all experimental plots; (iii) the overall effect of plant species richness on root decomposition, due to the contrast between quality and environmental effects, is neutral, which we tested by decomposing community roots in their ‘home’ plots.Plant species richness negatively affected root decomposition in all three experiments. The negative effect of plant species richness on substrate quality was largely explained by increased root C:N ratios along the diversity gradient. Functional group presence explained more variance in substrate quality than species richness. Here, the presence of grasses negatively affected substrate quality and root C:N ratios, while the presence of legumes and small herbs had positive effects. Plant species richness had a negative effect on soil environment despite its positive effect on soil water content which is known to stimulate decomposition. We argue that – instead of soil water content – a combined effect of soil temperature and seasonality might drive

Global change drivers are rapidly altering resource availability and biodiversity. While there is consensus that greater biodiversity increases the functioning of ecosystems, the extent to which biodiversity buffers ecosystem productivity in response to changes in resource availability remains unclear. We use data from 16 grassland experiments across North America and Europe that manipulated plant species richness and one of two essential resources—soil nutrients or water—to assess the direction and strength of the interaction between plant diversity and resource alteration on above-ground productivity and net biodiversity, complementarity, and selection effects. Despite strong increases in productivity with nutrient addition and decreases in productivity with drought, we found that resource alterations did not alter biodiversity–ecosystem functioning relationships. Our results suggest that these relationships are largely determined by increases in complementarity effects along plant species richness gradients. Although nutrient addition reduced complementarity effects at high diversity, this appears to be due to high biomass in monocultures under nutrient enrichment. Our results indicate that diversity and the complementarity of species are important regulators of grassland ecosystem productivity, regardless of changes in other drivers of ecosystem function.

The search for a root economics spectrum (RES) has been sparked by recent interest in trait-based plant ecology. By analogy with the one-dimensional leaf economics spectrum (LES), fine-root traits are hypothesised to match leaf traits which are coordinated along one axis from resource acquisitive to conservative traits. However, our literature review and meta-level analysis reveal no consistent evidence of an RES mirroring an LES. Instead the RES appears to be multidimensional. We discuss three fundamental differences contributing to the discrepancy between these spectra. First, root traits are simultaneously constrained by various environmental drivers not necessarily related to resource uptake. Second, above- and belowground traits cannot be considered analogues, because they function differently and might not be related to resource uptake in a similar manner. Third, mycorrhizal interactions may offset selection for an RES. Understanding and explaining the belowground mechanisms and trade-offs that drive variation in root traits, resource acquisition and plant performance across species, thus requires a fundamentally different approach than applied aboveground. We therefore call for studies that can functionally incorporate the root traits involved in resource uptake, the complex soil environment and the various soil resource uptake mechanisms – particularly the mycorrhizal pathway – in a multidimensional root trait framework.

AimsShrub expansion is common in the tundra biome and has been linked to climate warming. However, the underlying mechanisms are still not fully understood. This study aimed to investigate the seasonal and vertical rooting patterns of different plant functional types, which is important for predicting tundra vegetation dynamics.MethodsWe harvested root samples by soil coring and investigated seasonal changes in root biomass and vertical root distribution across a vegetation gradient, focusing on the differences between graminoids and dwarf shrubs, at a northeastern Siberian tundra.ResultsGraminoid fine root biomass increased significantly during the growing season, whereas that of shrubs was already high at the beginning and did not change later on. Shrubs had a much shallower rooting pattern than graminoids. Also, shrub roots did not respond to increases in permafrost thawing depth over the growing season, whereas graminoids grew fine roots in deeper, recently thawed soil layers during the growing season.ConclusionsOur results show that shrubs are predominantly shallow-rooted and grow roots earlier than graminoids, which allows shrubs to take advantage of the nutrient pulse after snowmelt in the early growing season. In contrast, the deep-rooted graminoids can access the nutrients in deeper soil and may profit from increasing permafrost thawing depth. The outcome of the competitive interactions between graminoids and shrubs in tundra may depend on the balance between the benefits associated with earlier root growth and deeper root distribution, respectively. The shrub expansion with climate warming observed in recent decades suggests that earlier root growth in the upper soil layer may be more important than increased rooting depth later in the growing season.

Climatewarming is known to increase the aboveground productivity of tundra ecosystems.Recently, belowground biomass is receiving more attention, but the effects of climate warming onbelowground productivity remain unclear. Enhanced understanding of the belowground componentof the tundra is important in the context of climate warming, sincemost carbon is sequesteredbelowground in these ecosystems. In this study we synthesized published tundra belowgroundbiomass data from36 field studies spanning amean annual temperature (MAT) gradient from−20 °C to 0 °C across the tundra biome, and determined the relationships between different plantbiomass pools andMAT. Our results show that the plant community biomass–temperaturerelationships are significantly different between above and belowground. Aboveground biomassclearly increased withMAT, whereas total belowground biomass and fine root biomass did not showa significant increase over the broadMATgradient. Our results suggest that biomass allocation oftundra vegetation shifts towards aboveground in warmer conditions,which could impact on thecarbon cycling in tundra ecosystems through altered litter input and distribution in the soil, aswellas possible changes in root turnover.

This data set contains mass loss of community roots decomposing in the common plot in the Jena experiment in 2014. The Metadata contains the Dataset ID in the Jena Experiment database and detailed information of column: 'plotcode' is plot ID in the Jena Experiment; 'bag_ID' is the ID for litter bags within each decomposition experiment; 'root_type' is the type of roots in the litter bags where plot coded for community roots, lolium coded for standardized roots; 'site' is the location of where decomposition happened; 'sector' is the subplots in common plot; 'mass_initial' is root mass in the litter bags before buried in the field and handling loss is seduced already; 'mass_remain' is root mass in the litter bags at each retrieval; 'date_in' is the exact dates when the litter bags were buried. In the form of DD-MM-YY; 'date_out' is the exact dates when the litter bags were retrieved. In the form of DD-MM-YY; 'actual_decomptime' is the exact days litter bags were in the field; 'massloss' is actual mass loss =100 - mass_remain/mass_initial*100; 'std_decomptime' is standardized days litter bags were in the field; 'std_massloss' is stadardized mass loss = massloss/actual_decomp.time*std_decomp.time.

1.Climate warming is faster in the Arctic than the global average. Nutrient availability in the tundra soil is expected to increase by climate warming through 1) accelerated nutrient mobilization in the surface soil layers, and 2) increased thawing depths during the growing season which increases accessibility of nutrients in the deeper soil layers. Both processes may initiate shifts in tundra vegetation composition. It is important to understand the effects of these two processes on tundra plant functional types. 2.We manipulated soil thawing depth and nutrient availability at a Northeast-Siberian tundra site to investigate their effects on above and belowground responses of four plant functional types (grasses, sedges, deciduous shrubs and evergreen shrubs). Seasonal thawing was accelerated with heating cables at ~15 cm depth without warming the surface soil, whereas nutrient availability was increased in the surface soil by adding slow-release NPK fertilizer at ~5 cm depth. A combination of these two treatments was also included. This is the first field experiment specifically investigating the effects of accelerated thawing in tundra ecosystems. 3.Deep soil heating increased the aboveground biomass of sedges, the deepest-rooted plant functional type in our study, but did not affect biomass of the other plant functional types. In contrast, fertilization increased aboveground biomass of the two dwarf shrub functional types, which both had very shallow root systems. Grasses showed the strongest response to fertilization, both above and belowground. Grasses were deep-rooted, and they showed the highest plasticity in terms of vertical root distribution, as grass root distribution shifted to deep and surface soil in response to deep soil heating and surface soil fertilization, respectively. 4.Synthesis - Our results indicate that increased thawing depth can only benefit deep-rooted sedges, while the shallow-rooted dwarf shrubs as well as flexible-rooted grasses take a