Nutrient Economy Research Articles

Long-Term Amendment with Sewage Sludge: Effects on Nutrient Value and Trace-Metal Content in Different Parts of Maize Plants

Agricultural soils play a key role in the achievement of a circular nutrient economy. The use of sewage sludges as fertilizers is important for such an achievement, assisting in the maintenance of soil health and nutritional crop value. This study was established, after 23 years of a fertilization experiment, in calcareous soil under a maize monoculture. The treatments included mineral fertilization as a control (MIN, 225 kg N ha−1) and two sludge treatments, where doses followed a threshold sludge nitrogen criterion (SNC, 170 kg org-N ha−1) or a threshold soil phosphorus criterion (SPC; when the soil Olsen-P value exceeded 40–60 kg P ha−1, the sludge application was stopped). A detailed study was performed on Cd, Cu, F, Mn, Pb, and Zn soil extractable with diethylenetriaminepentaacetic acid (DTPA), as well as the nutrient and heavy metal concentration of different fractions of the maize plant (grain, cob, and the rest of the plant). Extractions were also quantified. No biomass-yield differences were observed in the different parts of the maize plant in the year of sampling. Sludges increased the soil DTPA extraction of Cd, Cu, Fe, and Zn and diminished Mn extraction, without differences in extractable Pb. The SNC, when compared with MIN, showed increased P cob concentrations, and in grain, it showed increased Fe, Cr, and Co concentrations. The SPC figures of the studied parameters were, in general, between both treatments (MIN and SNC), although Cr extractions in grain diminished vs. SNC. Based on the results, the SPC can be recommended as it also avoids excessive available-P build up.

Sustainability of Organic Fertilizers Use in Dryland Mediterranean Agriculture

Organic fertilization is a key issue in European Union (EU) regulations, particularly in the context of promoting a circular nutrient economy, maintaining soil quality, and sequestering carbon to face climate change. In a rainfed system in Northeastern Spain, an experiment was set up (split-plot design). It included five pre-sowing N fertilization treatments: control, mineral, pig slurry, and composted sewage sludge (two rates). The average N rates were 0, 30, 141, 176, and 351 kg N ha−1, respectively. They were combined with mineral N topdressings (0, 50, and 100 kg N ha−1). Three crops were grown: barley (nine years), wheat (three years), and rapeseed (one year). In the driest years (c. 350 mm rainfall), the yields averaged 2.5, 2.0, and 1.9 Mg ha−1, respectively. The maximum yields were for barley (6.5 Mg ha−1) and wheat (5.5 Mg ha−1). The avoidance of a significant increase in soil residual NO3−-N, plus the control of soil build up of available P, micronutrients, and Cd, defines the fertilization strategies. (i) With a previous spring drought season, no fertilization is needed in the following year, if devoted to winter cereals. (ii) In rainier seasons, pig slurry or composted sewage sludge (lowest rate) applied at sowing is sufficient; however, 50 kg of mineral-N ha−1 at the topdressing can be applied. The study found that pig slurry favors K, Mg, Cu, and Zn availability, while composted sewage sludge enhances Fe availability. Although it is possible to reduce N inputs from organic fertilizers, organic C build-up will be constrained.

Coordination of water use strategies and leaf economic traits in coexisting exotic and native woody species from evergreen and deciduous broadleaf forests

The leaf economics spectrum (LES) describes the covariation of traits relevant for carbon and nutrient economy in different plant species. However, much less is known about the correlation of LES with leaf water economy, not only because some woody species do not follow the rules, but also because they are rarely tested on the widespread, non-native, fast-growing trees. We hypothesized that fast-growing exotic species that spread on the fast side of the LES coordinate their water-use strategies (WUS) to maintain rapid growth, and that the pattern of coordination differs between evergreen and deciduous forests. Using 4 exotic and 4 native species from evergreen and deciduous broadleaf forests in China, we measured 17 traits of LES and WUS and analyzed their functional roles in different species groups. Our results suggest that LES plays a more important role in the coexistence of species within a community, while WUS contributes more to the distribution of species across different regions. The multidimensional coordination of LES and WUS could better explain the growth and distribution of different plant species and shed light on the coexistence of species from different forest types, especially fast-growing woody exotics.

Life cycle assessment of nutrient recovery strategies from domestic wastewaters to quantify environmental performance and identification of trade-offs

Increase in anthropogenic activities proliferated the consumption of resources such as phosphorus; and increase the adverse environmental impacts especially eutrophication on water resources such as lakes. Nutrient recovery from domestic wastewaters to produce a fertiliser has been explored to address these challenges in the context of a sustainable circular nutrient economy. Life cycle assessment (LCA) was performed to holistically assess the impacts of integrating a nutrient recovery system on wastewater and water resource management using Laguna de Bay, Philippines as the geographical boundary. The inventory was developed based on the results of the emerging nutrient recovery reactor operations and the application of the recovered fertiliser on the agricultural crops. The LCA results for the proposed scenario showed environmental benefits of about 83.6% freshwater eutrophication, 102.5% terrestrial ecotoxicity, 26.9% water consumption, 100.7% mineral resource scarcity, while the global warming potential is 95.4% higher than the baseline scenario. Results imply policy review for septage management, system optimisation, and evaluation of alternative methods of wastewater management, in terms of life cycle thinking and sustainability across the globe.

Biogeochemical effects of a forest understory plant invasion depend more on dissimilar nutrient economies than invader biomass

There is increasing need to better understand how and why invasion impacts on biogeochemical cycling differ across heterogeneous landscapes. One hypothesis predicts invader impacts are greatest, where the invader is most abundant (the mass ratio hypothesis; MRH). Alternatively, invader impacts may be greatest in communities, where the nutrient acquisition strategies of the invader are most dissimilar from those of native species (the nutrient economy dissimilarity hypothesis; NEDH). We tested whether the impact of an invasive grass, Microstegium vimineum, on soil biogeochemistry could be better explained by MRH, NEDH, or both. Invaded and reference study plots were established at 3 locations (Indiana, North Carolina, and Georgia) that varied in the relative abundance of arbuscular mycorrhizal (AM) versus ectomycorrhizal (ECM) associated overstory trees (across a nutrient economy gradient), reflecting gradients in biotic nutrient acquisition strategies and edaphic factors. At 2 locations, we found a proxy for NEDH explained invader effects on soil conditions and the net effect of M. vimineum was to homogenize soil properties across the nutrient economy gradient toward conditions consistent with AM-dominated stands. At the third location, both ECM-dominance (NEDH) and invader biomass (MRH) predicted differences in soil moisture, pH, and nitrification rates with may be related to the high N availability and intermediate acidity at this location. Collectively, these results suggest the biogeochemical consequences of M. vimineum depend, in part, on preinvasion soil nutrient economies. Where preinvasion conditions are known, we provide a scalable and predictive approach to determine where impacts on biogeochemical cycling of C and N may be greatest.

Evolutionary and ecological forces shape nutrient strategies of mycorrhizal woody plants.

The associations of arbuscular mycorrhizal (AM) or ectomycorrhiza (EcM) fungi with plants have sequentially evolved and significantly contributed to enhancing plant nutrition. Nonetheless, how evolutionary and ecological forces drive nutrient acquisition strategies of AM and EcM woody plants remains poorly understood. Our global analysis of woody species revealed that, over divergence time, AM woody plants evolved faster nitrogen mineralization rates without changes in nitrogen resorption. However, EcM woody plants exhibited an increase in nitrogen mineralization but a decrease in nitrogen resorption, indicating a shift towards a more inorganic nutrient economy. Despite this alteration, when evaluating present-day woody species, AM woody plants still display faster nitrogen mineralization and lower nitrogen resorption than EcM woody plants. This inorganic nutrient economy allows AM woody plants to thrive in warm environments with a faster litter decomposition rate. Our findings indicate that the global pattern of nutrient acquisition strategies in mycorrhizal plants is shaped by the interplay between phylogeny and climate.

Steps to circularity: Impact of resource recovery and urban agriculture in Seattle and Tacoma, Washington

Capturing the value in urban residuals (food scraps and wastewater) is a critical component of urban sustainability and a circular nutrient economy. Food production in urban areas has also been recognized as an important component of urban health. Data from two cities (Seattle and Tacoma, WA) with active resource recovery and community garden programs were used to quantify nutrient recovery and food production potential. Yield data from growth trials conducted using soil amendments produced from locally generated organic residuals were used to model yields in existing urban agriculture programs. Our survey showed much lower than expected volume of food scraps from both residential and multifamily housing for both cities. Nutrient generation rates from food scraps were estimated as 0.55–0.67 kg N and 0.09–0.11 kg P capita−1 yr−1. Recovery rates for Seattle with an established food scrap collection program were 0.21 kg N and 0.006 kg P capita−1 yr−1. Nutrient recovery from wastewater biosolids was higher; 1–1.67 kg N and 0.23–0.76 kg P capita−1 yr−1. Data on effluent quantity and nutrient concentrations from these programs suggests that effluent has a high potential for nutrient recovery (4.03–5 kg N and 0.3–0.5 kg P capita yr−1). Yield was modeled for kale (brassica oleracea) considering the number of people that could be fed per hectare for one year using a 67 g portion by comparing yields from synthetic fertilizer and residuals-based amendments in both high and low quality urban soils. The Tacoma biosolids potting soil yielded enough for 310 and 736 people ha−1 yr−1 for the high and low quality soils, respectively. The modeled food/yard compost produced from the food scraps yielded sufficient kale for 148 to 353 people ha−1 yr−1. Relative yield from fertilizer for the low and high quality soils was 15 and 263 people ha−1yr−1, respectively. Considering yield, enough biosolids are produced to meet 6.7–29.2% of the vegetable needs of each city. These results suggest that significant nutrients can be recovered using existing infrastructure. With enhanced nutrient capture from wastewater effluent, sufficient nutrients could be recovered to meet the N and P needs for food crops for the residents of each city.

Extent of intraspecific trait variability in ecologically central and marginal populations of a dominant alpine plant across European mountains.

Studying trait variability and restricted gene flow between populations of species can reveal species dynamics. Peripheral populations commonly exhibit lower genetic diversity and trait variability due to isolation and ecological marginality, unlike central populations experiencing gene flow and optimal conditions. This study focused on Carex curvula, the dominant species in alpine acidic meadows of European mountain regions. The species is sparser in dry areas such as the Pyrenees and Balkans, compared to the Central-Eastern Alps and Carpathians. We hypothesized that distinct population groups could be identified based on their mean functional trait values and their correlation with the environment; we predicted that ecologically marginal populations would have stronger trait correlations, lower within-population trait variability (intraspecific trait variability, ITV) and lower genetic diversity than populations of optimal habitats. Sampling was conducted in 34 populations that spanned the entire distribution range of C. curvula. We used hierarchical clustering to identify emergent functional groups of populations, defined by combinations of multiple traits associated with nutrient economy and drought tolerance (e.g. specific leaf area, anatomy). We contrasted the geographical distribution of these groups in relation to environment and genetic structure. We compared pairwise trait relationships, within-population trait variation (ITV) and neutral genetic diversity between groups. Our study identified emergent functional groups of populations. Those in the southernmost ranges, specifically the Pyrenees and Balkan region, showed drought-tolerant trait syndromes and correlated with indicators of limited water availability. While we noted a decline in population genetic diversity, we did not observe any significant changes in ITV in ecologically marginal (peripheral) populations. Our research exemplifies the relationship between ecological marginality and geographical peripherality, which in this case study is linked to genetic depauperation but not to reduced ITV. Understanding these relationships is crucial for understanding the biogeographical factors shaping trait variation.

Impacts of organic matter amendments on urban soil carbon and soil quality: A meta-analysis

Organic matter amendment application is an important avenue of beneficial waste diversion and is used to improve soil quality in agricultural and urban settings. In urban regions, amendments are used to support local food production, maintain vegetation for landscaping and recreational use, and reclaim disturbed soils. Urban regions generate large quantities of wasted organic resources for potential application aiding in creating a circular nutrient economy. There is a growing interest in understanding the effects of amendments such as compost, biosolids, and biochar on soil properties in agricultural settings. Gaps remain, however, in assessing their effects in urban land uses. We conducted a literature review to assess the effects of compost, biochar, and biosolids on soil carbon and soil quality of urban soils managed for gardening, landscaping, recreation, and reclamation. Application of organic matter amendments led to an average increase of 3.6 units of soil organic matter% (SOM%). Compost and biochar improved SOM% the most, by 3.1 and 6.5 units of SOM%, respectively. Biosolids resulted in the smallest increase in SOM% but had greater nutrient benefits than other amendments. Parameters related to chemical and physical soil quality improved with the application of amendments. Gaps in the literature remain, such as assessing urban gardens, soil to depths greater than 30 cm, and the persistence of SOM in amended soils. This meta-analysis proposes that organic matter amendments are a powerful means to improve soil quality in urban regions, provide vital cobenefits to surrounding communities, and increase soil carbon storage.

Integrating decadal and century-scale root development with longer-term soil development to understand terrestrial nutrient cycling

Nearly 50 y ago, Walker and Syers hypothesized that sources of most terrestrial nutrients shift in dominance from mineral- to organic matter-derived over millennia as soils weather. We investigated how overlaying this soil development framework with vegetation dynamics that can feed back to soil development on relatively short timescales offers insight into ecosystem functioning. To test the hypothesis that forest nutrient economies mediate the nutritional importance of organic matter as mineral weathering proceeds, we paired litterfall decay experiments with soil mineralogical data from diverse forests across the Critical Zone (CZ) Observatory Network, USA. Our findings suggest that dominant sources of tree P may shift from organic matter-bound stocks to minerals as roots expand during the transition from mid to late stages of forest growth and encounter deeper soils that have experienced a lesser degree of weathering. Thus, plants may develop nutritional strategies that do not necessarily rely most heavily on the dominant P form present in an ecosystem, typically driven by stage of soil development, but rather on root proliferation over time, which governs the ability of plants to mine soil volumes at a diversity of depths. Ecosystem P nutrition therefore depends strongly on the interaction between dominant P form and root system growth, particularly as it reflects past land use for both plants and soils. We use these findings to produce a novel framework of vegetative nutrient economics that highlights how root system growth and land use change can influence nutrient transformations and bioavailability, and soil development, across Earth’s critical zones.

Nutrients in a circular economy: Role of urine separation and treatment

The increasing global population, over the last few decades, brought about the rise in synthetic fertiliser market prices along with explosive agricultural demand. Source separation of urine can be one of the most effective solutions for nutrient recovery as a fertiliser, transforming the conventional linear economy into a circular economy. The urine diversion from wastewater can improve conventional wastewater treatment plants to be energy-efficient and cost-effective, as a considerable quantity of nutrients in wastewater is derived from urine. The stabilisation and sanitisation of source separated urine have been studied earlier by applying physical, biological, chemical, and electrochemical treatment processes. Further processes such as evaporation, freeze-thawing, and membrane processes have been investigated to recover as well as concentrate nutrients as a urine-derived fertiliser. As such, this review discusses the urine diversion and collection systems as well as previous technologies for the urine treatment and nutrient recovery. In addition, the industrial research hub funded by Australian Research Council (ARC) which focuses on the Nutrients in a Circular Economy (NiCE) is introduced in this paper. The ARC NiCE hub aims to achieve four themes, including urine collection, processing, fertiliser optimisation, and fertiliser end-use, moving towards a closed circular nutrient economy.

Imprint of tree species mycorrhizal association on microbial‐mediated enzyme activity and stoichiometry

Abstract Understanding the effects of tree species and their mycorrhizal association on soil processes is critical for predicting the ecosystem consequences of species shifts owing to global change and forest management decisions. While it is well established that forests dominated by different mycorrhizal types can vary in how they cycle carbon (C), nitrogen (N) and phosphorus (P), the degree to which these patterns are driven by microbial‐mediated enzyme activity (EA) and ecoenzymatic stoichiometry (ES) remains elusive. Here, we synthesized the effects of mycorrhizal association on seven soil enzymes involved in microbial C, N and P acquisition and ES using data from 56 peer‐reviewed papers. We found that relative to soil in ectomycorrhizal (EcM) trees, soil in arbuscular mycorrhizal (AM) trees exhibited greater activity of some C acquisition enzymes (e.g. beta‐glucosidase; BG) and higher ecoenzymatic ratios of BG/NAG (N‐acetyl‐glucosaminidase) and BG/AP (acid phosphatase). These results supported that AM trees had rapid C and nutrient turnover rates, inorganic nutrient economics and high soil microbial C limitation. We also found evidence for an organic nutrient economy and greater soil microbial demand for nutrients in EcM trees compared to AM trees. In addition, the effect of mycorrhizal association on the activity of certain soil enzymes and enzymatic stoichiometry (i.e. BG and BG/NAG ratio) appeared to be associated with the differences in soil pH, phylogenetic group (i.e. conifers and broadleaves) and leaf habit (i.e. evergreen and deciduous) between AM and EcM trees. The results from the global meta‐analysis suggested that soil EA and ES appear to play critical roles in shaping the differences in the nutrient economy between AM and EcM tree species, but leaf morphology and soil conditions should be considered in evaluations of soil processes in forests of different mycorrhizal associations. Given that most of the studies in the database were from the temperate and subtropical regions, further research in other biomes is needed to elucidate the underlying mechanisms driving the mycorrhizal effect at the global scale. Read the free Plain Language Summary for this article on the Journal blog.

A ‘Get‐Save‐Return’ process continuum runs on phosphorus economy among subtropical tree species

Abstract Plants allocate nutrients to new leaves via making a cost–benefit trade‐off between root nutrient absorption (‘get’) and leaf nutrient resorption (‘save’). This active trade‐off in nutrient acquisition pathways may cause a passive trade‐off between resorption and decomposition (‘return’). However, whether these nutrient‐associated processes are linked and form a ‘get‐save‐return’ (GSR) continuum, and its linkages with the above‐ground leaf economics spectrum (LES) and the below‐ground mycorrhizal association remain unclear. Here, we present the first empirical evidence of a direct link among multiple nutrient‐associated processes and tested this continuum hypothesis by synchronously integrating root nutrient absorption, leaf nutrient resorption and leaf litter decomposition of 15 co‐occurring tree species hosting either arbuscular mycorrhizal or ectomycorrhizal fungi in subtropical forests of China. Across species, there was an active trade‐off between phosphorus (P) absorption and resorption, which further caused a passive trade‐off between P resorption and leaf litter decomposition, indicating that the GSR continuum exists and runs on P economy. However, these processes associated with nitrogen economy were not well linked. Interestingly, the loading scores of species on the LES were positively correlated with root P absorption, negatively with leaf P resorption and positively with leaf litter decomposition. These linkages indicate that species running in the ‘fast lane’ had greater root P absorption, lower leaf P resorption and faster leaf litter decomposition than species running in the ‘slow lane’, and that the process‐based GSR continuum follows the trait‐based ‘fast‐slow’ LES. Furthermore, the continuum on P economy emerged evidently in the ectomycorrhizal tree species rather than in the arbuscular mycorrhizal tree species, indicating critical control of mycorrhizal association over the continuum. Synthesis. Overall, these results demonstrate the existence of the GSR continuum on tree P economy, which conforms to the economics spectrum theory but varies with mycorrhizal association type. Our findings provide a process‐based framework for mechanistic understanding of the whole plant nutrient economy and ecosystem nutrient cycling, and facilitate improved predictions of biogeochemical models.

CO2 concentration and water availability alter the organic acid composition of root exudates in native Australian species

PurposeRoot exudation of organic acids (OAs) facilitates plant P uptake from soil, playing a key role in rhizosphere nutrient availability. However, OA exudation responses to CO2 concentrations and water availability remain largely untested.MethodsWe examined the effects of CO2 and water on OA exudates in three Australian woodland species: Eucalyptus tereticornis, Hakea sericea and Microlaena stipoides. Seedlings were grown in a glasshouse in low P soil, exposed to CO2 (400 ppm [aCO2] or 540 ppm [eCO2]) and water treatments (100% water holding capacity [high-watered] or 25–50% water holding capacity [low-watered]). After six weeks, we collected OAs from rhizosphere soil (OArhizo) and trap solutions in which washed roots were immersed (OAexuded).ResultsFor E. tereticornis, the treatments changed OArhizo composition, driven by increased malic acid in plants exposed to eCO2 and increased oxalic acid in low-watered plants. For H. sericea, low-watered plants had higher OAexuded per plant (+ 116%) and lower OArhizo per unit root mass (–77%) associated with larger root mass but fewer cluster roots. For M. stipoides, eCO2 increased OAexuded per plant (+ 107%) and per unit root mass (+ 160%), while low-watered plants had higher citric and lower malic acids for OArhizo and OAexuded: changes in OA amounts and composition driven by malic acid were positively associated with soil P availability under eCO2.ConclusionWe conclude that eCO2 and altered water availability shifted OAs in root exudates, modifying plant–soil interactions and the associated carbon and nutrient economy.

The circular nutrient economy of terrestrial ecosystems and the consequences for rock weathering

Earth’s biosphere is thought to exert a substantial influence on regolith evolution and chemical weathering rates. However, ecosystems are also highly efficient at retaining and recycling nutrients. Thus, when the ecological demand for rock-derived nutrients (e.g., P, Ca, K) exceeds the rates of regolith supply, ecological retention and recycling strategies can minimize nutrient limitations. To evaluate the balance between nutrient recycling and new nutrient input, we combined a plant model that drives growth according to foliar P levels with a weathering model that includes regolith rejuvenation via erosion and export via chemical weathering according to water flow, regolith thickness, mineral dissolution rates, secondary minerals, and nutrient storage in organic and mineral phases. We find that plant growth is strongly dependent on the total regolith nutrient inventory, resulting in a strong correlation between plant productivity and erosion. Increased water export or decreased regolith thickness diminish the total inventory of nutrient corresponding to lower rates of recycling and lower plant growth. In contrast, purported biogenic drivers of weathering, such as enhanced mineral dissolution, only support higher growth rates at high erosion rates. At erosion rates typical of the global land surface, more rapid mineral dissolution combined with enhanced formation of secondary minerals, depletes the inventory of mineral P, resulting in no benefit for plant growth. We also find that the increased chemical weathering export does not scale directly with plant growth. For example, accelerated mineral weathering does increase chemical weathering export but not potential plant growth. Conversely, thicker regolith is associated with a small increase in weathering export, but a large increase in potential plant growth. Collectively, when plant growth is coupled to regolith weathering our calculations suggest that plant productivity is not directly correlated with silicate weathering fluxes, and that biotic drivers of silicate weathering may only be effective at high erosion rates not typical at the Earth’s surface.

Advancing circular nutrient economy to achieve benefits beyond nutrient loss reduction in the Mississippi/Atchafalaya River basin

Advancing circular nutrient economy to achieve benefits beyond nutrient loss reduction in the Mississippi/Atchafalaya River basin

A test of the mycorrhizal-associated nutrient economy framework in two types of tropical rainforests under nutrient enrichments

Shifts in tree species and their mycorrhizal associations driven by global change play key roles in biogeochemical cycles. In this paper, we proposed a framework of the mycorrhizal-associated nutrient economy (MANE), and tested it using nutrient addition experiments conducted in two tropical rainforests. We selected two tropical rainforests dominated by arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees, and established eighteen 20 ​m ​× ​20 ​m plots in each rainforest. Six nitrogen (N) and phosphorus (P) addition treatments were randomly distributed in each rainforest with three replicates. We examined the differences in soil carbon (C) and nutrient cycling, plant and litter productivity between the two rainforests and their responses to 10-year inorganic N and P additions. We also quantified the P pools of plants, roots, litter, soil and microbes in the two rainforests. Overall, distinct MANE frameworks were applicable for tropical rainforests, in which soil C, N and P were cycled primarily in an inorganic form in the AM-dominated rainforest, whereas they were cycled in an organic form in the ECM-dominated rainforest. Notably, the effects of mycorrhizal types on soil P cycling were stronger than those on C and N cycling. The intensified N and P deposition benefited the growth of AM-dominated rainforests instead of ECM-dominated rainforests. Our findings underpin the key role of mycorrhizal types in regulating biogeochemical processes, and have important implications for predicting the ecological consequences of global changes.

Tree species traits and mycorrhizal association shape soil microbial communities via litter quality and species mediated soil properties

Soils harbor a vast diversity of soil microbiota, which play a crucial role in key ecosystem processes such as litter transformation and mineralization, but how complex plant-soil interactions shape the diversity and composition of soil microbiota remains elusive. We performed amplicon sequencing of DNA isolated from mineral topsoil of six common European trees planted in multi-site common garden monoculture stands of broadleaved maple and ash associated with arbuscular mycorrhiza (AM), broadleaved beech, lime and oak associated with ectomycorrhizal fungi (ECM) and coniferous spruce associated with ECM. The main aim of this study was to evaluate the effects of tree species identity, traits and mycorrhizal associations on diversity, community structure, cohesion, and shift in the relative abundance of taxonomic and functional groups of soil bacteria, fungi and nematodes. Our results revealed that soils beneath broadleaved trees hosted higher OTU richness of bacteria, fungi, and nematodes than under Norway spruce. Broadleaved tree species associated with AM fungi showed higher cohesion of bacterial and fungal communities than broadleaved trees associated with ECM fungi, but the cohesion of nematode communities was higher under trees associated with ECM fungi than under trees associated with AM fungi. Copiotrophic bacteria, fungal saprotrophs and bacterivorous nematodes were associated with ash, maple and lime having high soil pH, and high litter decomposition indices, while oligotrophic bacteria, ectomycorrhizal fungi and fungivorous nematodes were associated with beech, oak and Norway spruce that had low soil pH and low litter decomposition indices. Tree species associated with AM fungi had a high proportion of copiotrophic bacteria and saprotrophic fungi while trees associated with ECM fungi showed a high relative abundance of oligotrophic bacteria, ECM fungi and fungivorous nematodes. The different abundances of these functional groups support the more inorganic nutrient economy of AM tree species vs the more organic dominated nutrient economy of ECM tree species. The bacterial community was indirectly affected by litter quality via soil properties, while the fungal community was directly affected by litter quality and tree species. The functional groups of nematodes mirrored the communities of bacteria and fungi, thereby indicating the main and active groups of the tree species-specific microbial communities. Our study suggested that tree species identity, traits, and mycorrhizal association substantially shape microbial communities via a direct effect of litter chemistry as well as via litter-mediated soil properties.

Tree regeneration response to a shifting soil nutrient economy depends on mycorrhizal association and age

Atmospheric nitrogen (N) deposition has led to an increase in N cycling and N availability. This increase in inorganic N is likely to impact forest ecosystems, although the responses remain uncertain. Most tree species are associated with one of two mycorrhiza types – arbuscular mycorrhizae (AM) or ectomycorrhiza (ECM). Due to functional differences in their ability to access soil nutrients, we might expect that increased N cycling and availability of inorganic N would benefit AM associated species, with negative or neutral impact for ECM associated species. This study addresses how the abundance of the regeneration layer responds to those shifting soil conditions, based on their mycorrhizal association. We used a long-term experiment located in a temperate deciduous forest, where the native acidic soils are low in nutrients. Soil treatments began in 2009, by adding lime and/or phosphate to raise pH and increase the availability of N and P. All trees ≥ 6.0 cm in 2010 were tagged and have been monitored with annual censuses. To quantity the density of the regeneration layer, seedlings and saplings were recorded in the control and limed plots in 2019. Trees that had recruited into the canopy (DBH ≥ 6.0 cm) were measured in 2020 in all treatment plots. Seedlings older than one year responded to the treatments as predicted, as AM seedlings increased by 42 % in the lime treatment (1.53 ± 0.38 individuals per m2 in control, to 2.17 ± 0.56 in lime) and ECM seedlings decreased by 49 % in response to liming (0.61 ± 0.14 individuals per m2 in control, to 0.31 ± 0.04 in lime). AM saplings also responded positively to liming, increasing 254 % from control to lime (from 0.013 ± 0.003 to 0.046 ± 0.018 individuals per m2), while ECM sapling abundance was neutral (0.063 ± 0.015 individuals per m2 in control, and 0.054 ± 0.009 in lime). The highest number of ECM recruits was found in the control plots (34.4 %), followed by phosphate (25.8 %), lime + phosphate (21.5 %), then lime (18.3 %). For AM associated tree species, the number of trees recruiting into the canopy was substantially higher in the phosphate treatment (39.4 %), with lower numbers in the other three treatments (26.8 % in control, 19.7 % in lime, and 14.1 % in lime + phosphate). Overall, we found a positive regeneration response in AM associated species to increasing nutrient availability which has important consequences for species composition in forests experiencing chronic N deposition.

Farmers’ Knowledge, Attitude and Perception towards Uptake and Utilization of Treated Human Excreta as Organic Fertilizer in Imenti South, Meru County

Universal access to safe and adequate sanitation for everyone remains a global challenge as over 35% of the total global populations have no access to adequate sanitation. This call for action and a paradigm shift from the sanitation conventional approach systems to onsite sanitation approach to ensure complete sanitation value chain and safeguard circular nutrient economy. This study explores small scale farmers’ knowledge, attitude, perception and practices on the uptake and utilization of treated human excreta as organic fertilizer. Data was collected from 96 respondents comprising of the farming household heads using both stratified and purposive sampling techniques across the six wards of Imenti South Sub-County using questionnaires. The study showed that education level and religion significantly influence on the level of utilization (p<0.05), while gender, occupation and farming duration had no significance level (p>0.05) on the utilization of treated human excreta. Half (50%) of the respondents agreed that increase in knowledge, positive attitudes and perceptions on treated human excreta improved on their application of treated human excreta as organic fertilizer. However, negative attitudes and health risk perceptions were the main limiting factors to utilization of treated human excreta. The type of sanitation technology used also influenced on the uptake and utilization of treated human excreta where by improved sanitation practices increased usage and application of human excreta as organic fertilizer by 52%. Therefore, there is a need for frequent open dialogues around the benefits and risks of treated human excreta utilization as organic fertilizer to increase farmers’ knowledge on it proper application. Further, it is important to understand the nature and direction of attitudinal influence dimensions and characteristics of farmers for mainstreaming circular economy interventions.