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Disentangling the relative response sensitivity of soil autotrophic (Ra) and heterotrophic respiration (Rh) to nitrogen (N) enrichment is pivotal for evaluating soil carbon (C) storage and stability in the scenario of intensified N deposition. However, the mechanisms underlying differential sensitivities of Ra and Rh and relative contribution of Rh to soil respiration (Rs) with increasing N deposition remain elusive. A manipulative field experiment with multi‐level N addition rates was conducted over 3 years (2015–2017) in an alpine meadow to explore the relative impact of N enrichment on Ra and Rh and the response of Rh/Rs ratio to the gradient of N addition. Soil respiration components had different sensitivities to N enrichment, with Ra decreasing more than Rh, leading to a higher Rh/Rs ratio as a function of increasing N addition rates. Ra and Rh decreased nonlinearly as N addition rates increased, with a critical load of 8 g N m−2 year−1 above which N enrichment significantly inhibited them. Ra and Rh were controlled by different abiotic and biotic factors, and the regulation of controlling factors on soil respiration components varied over time. N‐induced reduction in the relative abundance of forb significantly affected Ra, and this effect was mainly evident in the second and third years. Nitrogen enrichment significantly changed Rh in the third year, and the decreased Rh under high doses of N addition could be attributed to the changes in microbial biomass C, soil substrate quality and microbial composition. Our study highlights the leading role of Ra in regulating Rs responses to N enrichment and the enhancement of Rh/Rs ratio with increasing N addition. We also emphasize that N‐induced shifts in plant community composition play a vital role in regulating Ra instead of Rh. The changing drivers of Ra and Rh with time suggests that long‐term experiments with multiple levels of N addition are further needed to test the nonlinear responses and underlying mechanisms of soil respiration components in face to aggravating N deposition. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

In agriculture, winter cover crop (WCC) residues are incorporated into the soil to improve soil quality, as gradual litter decomposition can improve fertility. Decomposition rate is determined by litter quality, local soil abiotic and biotic properties. How these factors are interlinked and influenced by cropping history is, however, unclear. We grew WCC monocultures and mixtures in rotation with main crops Avena sativa (oat) and Cichorium endivia (endive) and tested how crop rotation influences WCC litter quality, abiotic and biotic soil conditions, and litter decomposition rates. To disentangle WCC litter quality effects from WCC soil legacy effects on decomposition, we tested how rotation history influences decomposition of standard substrates and explored the underlying mechanisms. In a common environment (e.g. winter fallow plots), WCC decomposition rate constants (k) correlated negatively with litter C, lignin and, surprisingly, N content, due to strong positive correlations among these traits. Plots with a history of fast‐decomposing WCCs exhibited faster decomposition of their own litters as well as of the standard substrates filter paper and rooibos tea, as compared to winter fallow plots. WCC treatments differentially affected soil microbial biomass, as well as soil organic matter and mineral nitrogen content. WCC‐induced soil changes affected decomposition rates. Depending on the main crop rotation treatment, legacy effects were attributed to biomass input of WCCs and their litter quality or changes in microbial biomass. Synthesis and applications. These results demonstrate that decomposition in cropping systems is influenced directly through crop residues, as well as through crop‐induced changes in soil biotic properties. Rotation history influences decomposition, wherein productive winter cover crops (WCC) with low lignin content decompose fast and stimulate the turnover of both own and newly added residues via their knock‐on effect on the soil microbial community. Thus, WCC have promise for sustainable carbon‐ and nutrient‐cycling management through litter feedbacks. Foreign Language In landbouw worden plantenresten van wintergroenbemesters in de bodem ondergewerkt om bodemkwaliteit te verbeteren. De afbraaksnelheid van groenbemesterstrooisel en het daarbij vrijkomen van voedingsstoffen wordt bepaald door strooiselkwaliteit en lokale abiotische en biotische bodemomstandigheden. Echter is het onduidelijk hoe al deze factoren worden beïnvloed door gewasrotatie. In een veldexperiment werden verschillende winterse groenbemesters verbouwd in monoculturen en mengsels, in rotatie met hoofdgewassen Avena sativa (haver) en Cichorium endivia (andijvie). De invloed van gewasrotatie op de kwaliteit van groenbemesterstrooisel, lokale abiotische en biotische bodemparameters en strooiselafbraaksnelheid werd getest. Om bovendien onderscheid te kunnen maken tussen effecten van strooiselkwaliteit en veranderingen in bodemomstandigheden, werden effecten van gewasrotatie ook getoetst op de afbraak van standaard substraten (filterpapier en rooibosthee). In eenzelfde omgeving, zonder specifieke groenbemestergeschiedenis (voormalig winter braak), waren afbraaksnelheden van groenbemesterstrooisels negatief gecorreleerd met concentraties van koolstof‐ (C), lignine‐, en tegen de verwachtingen in, stikstof‐ (N) in het strooisel. Dit resultaat werd verklaard door de onderlinge positieve correlaties tussen N, C en lignine. In vergelijking met voormalig winter braakvelden, toonden proefvelden met een geschiedenis van snel afbrekende groenbemesters een snellere decompositie van zowel eigen strooisels als ook van de standaard substraten. De verschillende erfeniseffecten op afbraaksnelheid konden worden gerelateerd aan de effecten van de groenbemesters op de bodem microbiële biomassa, bodem organische stof en minerale stikstofgehalten. Afhankelijk van het hoofdgewas, konden de erfeniseffecten worden toegeschreven aan de hoeveelheid plantenresten van de groenbemesters, de kwaliteit hiervan, alsmede aan veranderingen in de microbiële biomassa, maar niet aan veranderde abiotische bodemfactoren. Synthese en toepassing. Deze resultaten tonen aan dat decompositie in landbouwsystemen direct wordt beïnvloed door gewasresten en de bodem erfeniseffecten op biotische bodemomstandigheden. De volgorde van gewassen beïnvloedt afbraak, waarbij productieve groenbemesters met snel afbrekende strooisels de decompositie van nieuw materiaal stimuleren via de microbiële bodemgemeenschap en vrijgekomen stikstof. Winterse groenbemesters zijn daarom veelbelovende middelen om C‐ en N‐kringlopen duurzaam te beheren door middel van strooisel‐feedback. These results demonstrate that decomposition in cropping systems is influenced directly through crop residues, as well as through crop‐induced changes in soil biotic properties. Rotation history influences decomposition, wherein productive winter cover crops (WCC) with low lignin content decompose fast and stimulate the turnover of both own and newly added residues via their knock‐on effect on the soil microbial community. Thus, WCC have promise for sustainable carbon‐ and nutrient‐cycling management through litter feedbacks.

The abundance of species is assumed to depend on their life history traits, such as growth rate and resource specialization. However, this assumption has not been tested for bacteria. Here we investigate how abundance of soil bacteria relates to slow growth and substrate specialization (oligotrophy) vs. fast growth and substrate generalization (copiotrophy). We collected 47 saprotrophic soil bacterial isolates of differing abundances and measured their growth rate and the ability to use a variety of single carbon sources. Opposite to our expectation, there was no relationship between abundance in soil and the measured growth rate or substrate utilization profile (SUP). However, isolates with lower growth rates used fewer substrates than faster growing ones supporting the assumption that growth rate may relate to substrate specialization. Interestingly, growth rate and SUP were correlated with phytogeny, rather than with abundance in soil. Most markedly, Gammaproteobacteria on average grew significantly faster and were able to use more substrates than other bacterial classes, whereas Alphaproteobacteria were growing relatively slowly and used fewer substrates. This finding suggests that growth and substrate utilization are phylogenetically deeply conserved. We conclude that growth rate and substrate utilization of soil bacteria are not general determinants of their abundance. Future studies on explaining bacterial abundance need to determine how other factors, such as competition, prédation and abiotic factors may contribute to rarity or abundance in soil bacteria.

Soil enzymes quickly respond to the disturbances caused in environmental pollution originating from human activities. Computation of enzyme activities has been used as indexes of microbial functionality, soil fertilization, biochemical cycling of numerous components in soil, extent of contamination, and ecosystem succession. Soil enzyme activity is one of the soil biological properties used as an indicator of soil quality due to their interrelationship to soil biology, being sensitive, integrative, ease to measure, “biological fingerprints” of previous soil management, indicator of biological symmetry, fertility, and changes in biological status of soil due to pollution. Dehydrogenase (DHG) enzymes are one of the most important components of soil enzymatic assay, as they determine the correct order of all biochemical pathways in soil biogeochemical cycles. While dehydrogenase activity (DHA) is calculated utilizing the procedures INT and TTC substrate in soil at the same time, a number of authors expressed their views about the unsatisfactory results when TTC has applied as substrate. Most of the researchers have applied incubation periods of 24 h at 37 °C, but some are modified it to 6 h 37 °C with either glucose or yeast extract as electron-donating substrate. Generally, in coal mine spoil, DHG functionality seems to lower, could be owing to the damage microflora, lack of soil organic matter. Measurement of DHA is frequently used as an extent of any disturbance owing to fertilizers, heavy metals, or other soil amendment (for management) practices, or, instantaneously degree of microbial functionality of soil.

Healthy soils are essential for progressive agronomic activities. Organic fertilization positively affects agro-ecosystems by stimulating plant growth, enhancing crop productivity and fruit quality and improving soil fertility. Soil health and food security are the key elements of Organic Agriculture 3.0. Landfilling and/or open-dumping of animal wastes produced from slaughtering cause environmental pollution by releasing toxic substances, leachate and greenhouse gases. Direct application of animal carcasses to agricultural fields can adversely affect soil microbiota. Effective waste management technologies such as thermal drying, composting, vermicomposting and anaerobic digestion transform animal wastes, making them suitable for soil application by supplying soil high in organic carbon and total nitrogen. Recent agronomic practices applied recycled animal wastes as organic fertilizer in crop production. However, plants may not survive at a high fertilization rate due to the presence of labile carbon fraction in animal wastes. Therefore, dose calculation and determination of fertilizer application frequency are crucial for agronomists. Long-term animal waste-derived organic supplementation promotes copiotrophic microbial abundance due to enhanced substrate affinity, provides micronutrients to soils and protects crops from soil-borne pathogens owing to formation of plant-beneficial microbial consortia. Animal waste-derived organically fertilized soils possess higher urease and acid phosphatase activities. Furthermore, waste to fertilizer conversion is a low-energy requiring process that promotes circular bio-economy. Thus, considering the promotion of soil fertility, microbial abundance, disease protection and economic considerations application of animal-waste-derived organic fertilizer should be the mainstay for sustainable agriculture.

BackgroundLand use/cover and management practices are widely known to influence soil organic matter (SOM) quality and quantity. The present study investigated the effect of different land use, i.e., forests viz. mixed forest cover (MFC), Prosopis juliflora (Sw.) DC-dominated forest cover (PFC), and cultivated sites viz. agriculture field (AF), vegetable field (VF), respectively, on soil parameter, microbial activity, and enzymes involved in soil nutrient cycle in a semiarid region of India.ResultsThe results showed a significant reduction (P < 0.05) in soil carbon (SC), soil nitrogen (SN) content (~ 30–80%) and consequently the soil microbial biomass carbon (SMBC) (~ 70–80%), soil basal respiration (SBR), soil substrate-induced respiration (SSIR), and soil enzyme activities (β-glucosidase, acid phosphatase, and dehydrogenase) under cultivated sites in comparison with forest sites. Pearson’s correlation showed that a positive correlation of SC with SMBC, SBR, SSIR (P < 0.01), and enzymatic activities (i.e., β-glucosidase, dehydrogenase) (P < 0.05) may imply the critical role of SC in regulating microbial and enzymatic activity. Also, a positive correlation of soil moisture with urease activity (P < 0.01) was found suggesting it as a significant abiotic factor for soil biological functions. Additionally, based on the PCA analysis, we observed the clustering of SMBC/SC ratio and qCO2 nearby AF.ConclusionOur study suggests that soil microbial parameters (SMBC, SBR, SSIR, SMBC/SC, qCO2) and enzyme activity are key indicators of soil health and fertility. Land use/cover alters the SOM content and soil microbial functions. The management strategies focusing on the conservation of natural forest and minimizing the land disturbances will be effective in preventing soil carbon flux as CO2 and maintaining the SC stock.

Alley cropping systems (ACS) are regarded as a sustainable land-use alternative that provides ecosystem services, assuming that beneficial tree effects extend towards crop alleys. However, the spatial range of these effects has rarely been considered. The objective of this study was to investigate soil quality indicators at different distances from trees in three German silvo-arable ACS. We analysed soil microbial biomass C and N, ergosterol, microbial activity (enzyme activities, substrate-induced respiration rates) and their functional diversity (MicroResp™ method) in topsoils. Furthermore, fungal abundance and fungal and bacterial contribution to microbial residues (amino sugars) were determined. Tree effects on soil quality indicators were estimated for each depth, for the first time considering both, spatial dependence and abiotic factors (pH, clay content) using mixed effects models with repeated measures. Additionally, differences between soil depths were tested. Analysis combining the three ACS revealed a generalisation of effect sizes and spatial range of tree effects on soil quality indicators. Tree implementation in arable systems increased SOC, microbial biomass and activity in upper topsoils and shifted the composition of main microbial groups towards a higher fungal abundance and functional diversity. Soil quality indices decreased with increasing depth. However, in alleys, no differences between distances from trees were observed. Results demonstrate that ACS are capable to enhance soil quality mediated by microorganisms under trees within 5–8 years. Long-term studies are required to estimate whether beneficial tree effects extend towards crop alleys and deeper soil layers when systems are mature.

The Andes are predicted to warm by 3–5 °C this century with the potential to alter the processes regulating carbon (C) cycling in these tropical forest soils. This rapid warming is expected to stimulate soil microbial respiration and change plant species distributions, thereby affecting the quantity and quality of C inputs to the soil and influencing the quantity of soil‐derived CO₂ released to the atmosphere. We studied tropical lowland, premontane and montane forest soils taken from along a 3200‐m elevation gradient located in south‐east Andean Peru. We determined how soil microbial communities and abiotic soil properties differed with elevation. We then examined how these differences in microbial composition and soil abiotic properties affected soil C‐cycling processes, by amending soils with C substrates varying in complexity and measuring soil heterotrophic respiration (RH). Our results show that there were consistent patterns of change in soil biotic and abiotic properties with elevation. Microbial biomass and the abundance of fungi relative to bacteria increased significantly with elevation, and these differences in microbial community composition were strongly correlated with greater soil C content and C:N (nitrogen) ratios. We also found that RH increased with added C substrate quality and quantity and was positively related to microbial biomass and fungal abundance. Statistical modelling revealed that RH responses to changing C inputs were best predicted by soil pH and microbial community composition, with the abundance of fungi relative to bacteria, and abundance of gram‐positive relative to gram‐negative bacteria explaining much of the model variance. Synthesis. Our results show that the relative abundance of microbial functional groups is an important determinant of RH responses to changing C inputs along an extensive tropical elevation gradient in Andean Peru. Although we do not make an experimental test of the effects of climate change on soil, these results challenge the assumption that different soil microbial communities will be ‘functionally equivalent’ as climate change progresses, and they emphasize the need for better ecological metrics of soil microbial communities to help predict C cycle responses to climate change in tropical biomes.

Microplastics (MPs) correspond to plastics between 0.1 μm and 5 mm in diameter, and these can be intentionally manufactured to be microscopic or generated from the fragmentation of larger plastics. Currently, MP contamination is a complicated subject due to its accumulation in the environment. They are a novel surface and a source of nutrients in soils because MPs can serve as a substrate for the colonization of microorganisms. Its presence in soil triggers physical (stability of aggregates, soil bulk density, and water dynamics), chemical (nutrients availability, organic matter, and pH), and biological changes (microbial activity and soil fauna). All these changes alter organic matter degradation and biogeochemical cycles such as the nitrogen (N) cycle, which is a key predictor of ecological stability and management in the terrestrial ecosystem. This review aims to explore how MPs affect the N cycle in the soil, the techniques to detect it in soil, and their effects on the physicochemical and biological parameters, emphasizing the impact on the main bacterial groups, genes, and enzymes associated with the different stages of the N cycle.

Forest soil organic carbon (SOC) is one of the largest reservoirs of terrestrial carbon (C) and is a major component of the global C cycle. Yet there is still uncertainty regarding how ecosystems, and the SOC they store, will respond to changes due to anthropogenic processes. Current and future reactive nitrogen (N) deposition to forest soils may alter biogeochemical processes and shift both the quantity and quality of stored SOC. We studied SOC storage and molecular-level composition after 22 years of N additions (100 kg N ha⁻¹ y⁻¹) in a temperate deciduous forest. SOC storage in surface soils increased by 0.93 kg m⁻² due to a decline in microbial biomass (phospholipid fatty acids) and litter decomposition. N additions resulted in the selective preservation of a range of plant-derived compounds including steroids, lignin-derived, cutin-derived, and suberin-derived compounds that have anti-microbial properties or are non-preferred microbial substrates. This overall shift in SOC composition suggests limited sustainability and a decline in soil health. The reduction in microbial biomass and increase in specific SOC components demonstrate that long-term N fertilization negatively alters fundamental C cycling in forest soils. This study also demonstrates unequivocally that anthropogenic impacts on C and N cycling in forests at the molecular-level must be considered more holistically.