Recalcitrant Nutrient Research Articles

Stand development reduces soil carbon mineralization in rubber plantations through regulating microbial metabolic strategy and substrate availability

Forest age, a critical variable for land-use decision makers, is known to change soil microbial communities. However, how such changes affect microbial metabolic strategy and the associated soil C mineralization processes in different forest ages remains unknown, especially in tropical region. To address this issue, three different aged rubber plantations, namely 4-year-old (Young, YRP), 15-year-old (Mature, MRP), and 31-year-old (Old, ORP), were studied to reveal the soil mineralization characteristics. Furthermore, to understand the mechanism from the coupled perspective of decomposers and substrate availability, the microbial metabolic strategy was deciphered by 2D-COS-Biolog assay, and linked with soil microbial composition and labile-/recalcitrant- organic pools. Results showed that YRP was characterized by having more copiotrophic taxa (e.g., actinobacteria) and the largest G(-)/G(+) ratio and invertase activity. Thus, YRP exhibited a preferential utilization for carbohydrate and the largest SOC mineralization rate. In contrast, regardless of abundant labile C and N pools in MRP, the soil microbial communities were shifted to oligotrophic taxa in utilizing resistant polymer, and MRP contained abundant G(+), fungi and arbuscular mycorrhizal fungi related to aggregate formation. As a result, the soil mineralization rate in MRP was reduced by 66 % compared with YRP. However, the SOC mineralization rate was unchanged from MRP to ORP, primarily because the increased proportion of recalcitrant nutrient pool, and soil microorganism had greater priority in utilizing relatively resistant amine. The structural equation modeling revealed that the variations in mineralization were mainly regulated by soil microbial composition and metabolic strategy, and partially affected by soil C and N pools. Furthermore, random forest model indicated that soil pH, NH4-N and C/N were also the crucial factor for mineralization by affecting soil microbial communities during stand development. In summary, these findings improve our understanding in soil C budget and contribute to the C accurate management during plantation development.

Biochar is colonized by select arbuscular mycorrhizal fungi in agricultural soils

Arbuscular mycorrhizal fungi (AMF) colonize biochar in soils, yet the processes governing their colonization and growth in biochar are not well characterized. Biochar amendment improves soil health by increasing soil carbon, decreasing bulk density, and improving soil water retention, all of which can increase yield and alleviate environmental stress on crops. Biochar is often applied with nutrient addition, impacting mycorrhizal communities. To understand how mycorrhizas explore soils containing biochar, we buried packets of non-activated biochar in root exclusion mesh bags in contrasting agricultural soils. In this greenhouse experiment, with quinoa (Chenopodium quinoa) as the host plant, we tested impacts of mineral nutrient (as manure and fertilizer) and biochar addition on mycorrhizal colonization of biochar. Paraglomus appeared to dominate the biochar packets, and the community of AMF found in the biochar was a subset (12 of 18) of the virtual taxa detected in soil communities. We saw differences in AMF community composition between soils with different edaphic properties, and while nutrient addition shifted those communities, the shifts were inconsistent between soil types and did not significantly influence the observation that Paraglomus appeared to selectively colonize biochar. This observation may reflect differences in AMF traits, with Paraglomus previously identified only in soils (not in roots) pointing to predominately soil exploratory traits. Conversely, the absence of some AMF from the biochar implies either a reduced tendency to explore soils or an ability to avoid recalcitrant nutrient sources. Our results point to a selective colonization of biochar in agricultural soils.

In recognition of Mike Hedley: fate of fertiliser in soil and mobilisation of recalcitrant nutrients

In recognition of Mike Hedley: fate of fertiliser in soil and mobilisation of recalcitrant nutrients

Electro-oxidation to convert dissolved organic nitrogen and soluble non-reactive phosphorus to more readily removable and recoverable forms

Conventional wastewater treatment processes cannot effectively remove dissolved organic nitrogen (DON) and soluble non-reactive phosphorus (sNRP), which can pose regulatory compliance challenges for total nitrogen and total phosphorus discharges. Moreover, DON and sNRP are not easily recoverable for beneficial reuse as part of the waste to resource paradigm. Conversion of DON and sNRP to more readily removable dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (sRP), respectively, will help meet stringent nutrient limits and facilitate nutrient recovery. In this study, electro-oxidation (EO) was evaluated for conversion of four DON compounds to DIN and five sNRP compounds to sRP. EO was more efficient and provided higher extents of conversion of the recalcitrant nutrient fractions compared to a more traditional advanced oxidation process, UV/H2O2. Direct electron transfer was likely the dominant oxidation mechanism for EO-based DON and sNRP conversion, with DON being more recalcitrant. Among the DON compounds tested, greater availability of primary amine (C–N bonds) yielded greater conversion compared to compounds with fewer primary amine or those with secondary amine (C–N–C bond). Among the sNRP compounds tested, those with P–O–C bonds (organic sNRP) converted more readily than those with P–O–P bonds (inorganic sNRP), presumably because cleavage of the latter bond requires greater energy. Using 30 min of EO treatment, the highest DON and sNRP compound conversion was 11.7 ± 0.09% for urea and 31.1 ± 0.75% for beta-glycerol phosphate. A similar extent of EO-based conversion of DON (6.41 ± 1.5%) and sNRP (32.7 ± 3.3%) was observed in real wastewater.

Effects of residue mulching amounts on metabolic footprints based on production and respiration of soil nematodes in a long‐term no‐tillage system

AbstractResidue mulching has been adopted to improve soil organic carbon and to prevent soil erosion and degradation, which in turn promote the sustainable development of soil ecosystems. Nematode metabolic footprints provide information about the responses of nematodes to resources and also help in quantifying the contributions of nematodes to ecosystem functions and services. However, how production and respiration components of nematode metabolic footprints vary in different mulching amounts is less clear. Therefore, to explore the impact of different mulching amounts on the production and respiration of nematode trophic groups, soil samples were collected from four mulching treatments (without mulching, with 33%, 67%, and 100% mulching of the stover remaining at harvest) at the depths of 0–5 cm and 5–10 cm in a 12‐year long no‐tillage system. Our results proved that the mulching effect on the production and respiration of fungivores was significant, and the production was 71.8%, 62.7%, 71.5% higher and respiration was 67.7%, 61.9%, 70% higher in 100% mulching treatment than without mulching, 33% and 67% mulching, respectively. More basal C flowed into the fungal decomposition pathways and fungivores contributed more to soil carbon sequestration through the decomposition of recalcitrant nutrients from residue at the end of crop growth. There was higher production than respiration in bacterivores and an opposite trend was observed in fungivores. Residue mulching increased the metabolic footprints of nematode communities and carbon use efficiency of fungivores and omnivores and predators and then enhanced the potential of soil carbon sequestration through the metabolic process of different nematode trophic groups.

Mitigation of recalcitrant nutrients and organic pollutants from small- to medium-scale biological nutrient removal plant sludge by digester optimization

Digestion of biological nutrient removal (BNR) plant sludge can be challenging, particularly for small- to medium-sized wastewater treatment facilities (WWTF) which often lack the economies of scale, and/or expertise to make digestion feasible. This study compared various types of sludge digestion, sludge retention times (SRTs), and temperatures on the release of recalcitrant nutrients, digestion economics, and digester performance utilizing mixed primary and secondary sludge from a small- to medium-sized BNR facility. Mesophilic anaerobic digestion (AD), cycling aerobic/anoxic (AERO/ANOX) digestion, and sequential anaerobic/aerobic/anoxic (AD/AERO/ANOX) digestion at room and mesophilic temperatures were compared at SRTs between 5 and 20 days. AERO/ANOX digestion was very effective in treating recalcitrant forms of nitrogen and phosphorous by removing up to 87% of dissolved organic nitrogen (DON), up to 88 ± 2% of non-reactive dissolved phosphorous (NRDP). AERO/ANOX digestion also offered the lowest increase in sludge management costs versus the existing no-digestion baseline scenario. ADs removed up to 53 ± 1% of volatile solids (VS), whereas unheated AERO/ANOX digesters were less effective, removing up to 39 ± 1% of VS. Sequential AD/AERO/ANOX digesters with a mesophilic second-stage removed up to 61 ± 3% of VS but had the highest operational and capital costs. Experiments also indicated that significant amounts of orthophosphate (PO43−) may be released from digested AERO/ANOX sludge during on-site storage, with longer SRTs releasing PO43− more rapidly than shorter ones. These results are important as more WWTFs deploy BNR to meet increasingly stringent nutrient limits.

Using mass struvite precipitation to remove recalcitrant nutrients and micropollutants from anaerobic digestion dewatering centrate

The primary objective of this research was to remove recalcitrant nutrients from anaerobically digested sludge dewatering centrate. A struvite precipitation methodology is proposed where salt crystals are encouraged to ballast colloidal particles through heterogeneous nucleation and subsequent crystal growth. The secondary objective was to assess presence of micropollutants in precipitates. Four biologically unique dewatering centrates were used to test the precipitation methodology on the variety of anaerobic digester configurations that can be expected from municipal wastewater treatment plant. The effect of digestion sludge retention time (2 day, 20 day) and digestion temperature (35 °C, 55 °C) on the removal of dissolved unreactive phosphorus (P) and nitrogen (N) was monitored. Averaged across all four centrates, the precipitation methodology resulted in dissolved unreactive P and N removal of 82.4% and 66.6%, respectively. Antimicrobial contaminants (triclosan, triclocarban) were observed in the precipitates at minute concentrations (<18 ng/g-dry solids). Therefore, mass struvite precipitation can provide a means of recalcitrant nutrient treatment and reactive nutrient recovery without the micropollutant burden of biosolids land application.

The Fate of Recalcitrant Nutrients Through an Anaerobic Digester and Anammox Sidestream Treatment Process

The Fate of Recalcitrant Nutrients Through an Anaerobic Digester and Anammox Sidestream Treatment Process

Ectomycorrhizal fungal traits reflect environmental conditions along a coastal California edaphic gradient

Multispecies mutualisms, such as the association between trees and ectomycorrhizal fungi, are often shaped by environmental context. Here, we explored the functional mechanisms underlying this environmental filtering. Using a single population of Pinus muricata (Bishop pine) growing along a strong edaphic gradient, we examined how environmental stress affected ectomycorrhizal fungi. The gradient spans c. 400000 years of soil age, and reduced nutrient availability and increased water stress dwarf trees on older sites. Fungal community composition shifted with nutrient and water availability and with the stature of the P. muricata host trees. Not only did pygmy trees host a taxonomically different fungal subset as compared to nonpygmy trees, but associated fungal communities also differed in life history strategies: trees in more stressful conditions hosted fungi with more carbon-intensive foraging strategies. Our results indicate a link between environmental controls of host nutritional status and turnover in the ectomycorrhizal fungal community. The transition to more energy-intensive strategies under nutrient stress may allow for close recycling of recalcitrant nutrient pools within the root zone and facilitate transport of nutrients and water over long distances. These results highlight the value of life history data to understanding the mechanistic underpinnings of species distributions.

Release of sulphate, potassium, calcium and magnesium from spent mushroom compost under laboratory conditions

The release of sulphate-sulphur (SO4 2–-S), potassium (K), calcium (Ca) and magnesium (Mg) from soil amended with spent mushroom compost (SMC), a by-product of mushroom production, was measured for 16 weeks in an open laboratory incubation at 25°C. Rates of application were up to 80 t ha–1 moist SMC (0.84% SMC dry weight) both with and without inorganic fertilizer. The rates of nutrient application in the inorganic fertilizer were: 338 kg ha–1 N, 100 kg ha–1 of both phosphorus and K, and 114 kg ha–1 S. SMC contains 1.7% K, 6.5% Ca, 0.4% Mg and 1.2% S (of which 87% is inorganic), and has a carbon:sulphur ratio of 26. The release of SO4 2–-S was rapid, and was described using either a first or mixed order exponential equation, or (underestimated) by the CENTURY model. The release of K, Ca and Mg was initially rapid (first order) and then declined to a constant rate (zero order). Their release was also described using first/first order or first order/parabolic diffusion equations. Model parameters indicated the relative sizes of both readily releasable and recalcitrant nutrient pools. The recovery of SMC-supplied nutrients in the absence of fertilizer was 75–83% of the S, 40–45% of the K, 14–20% of the Ca and 43–66% of the Mg. When fertilizer was applied 33–45% of the S, 22–36% of the K, 12–24% of the Ca and –4 to 20% of the Mg that were supplied by the SMC and fertilizer were recovered in the leachate. The generally lower nutrient recovery when fertilizer was applied could have resulted from the incomplete recovery of fertilizer S and K, from soil fixation of applied nutrients, and from the lower pH following fertilizer application.