The application of biochar or silicate rock powder as soil amendments combines carbon dioxide removal with soil improvement. However, their combined short-term effects on nutrient dynamics and microbial activity are poorly understood. Therefore, we combined wood biochar and basanite powder via co-application and via copyrolysis of biomass and basanite to rock-enhanced biochar in a nine-week semi-field-based lysimeter experiment with cabbage turnip (Brassica oleracea var. gongylodes L.). We measured carbon (C), nitrogen (N), available phosphorous (P), mineral N, dissolved organic C (DOC), microbial biomass C (Cmic), soil pH, and electric conductivity (EC). We examined extracellular enzyme kinetics of ss-glucosidase (BG), chitinase (CH), leucineaminopeptidase (LAP), and acid phosphatase (AP) related to C, N, and P cycles. From potential enzyme activity (Vmax) of BG, LAP, and AP we calculated extracellular enzyme stoichiometry (EES), vector angle and length to assess nutrient limitations. In combined applications, the influence of biochar was dominant. The application of biochar-containing amendments (biochar, co-application, co-pyrolyzed rock-enhanced biochar) to our sandy topsoil significantly increased C, P, DOC, Cmic, pH, and EC. Co-application even exceeded single biochar in increasing N, pH, and EC. Single biochar application resulted in the highest short-term P availability, while combined applications potentially result in a long-term P supply. While LAP's Vmax increased following biochar-containing amendment application, Vmax of the other enzymes decreased. Although AP showed the highest Vmax, indicating a P limitation, the enzyme patterns and EES suggest an increased N demand and a shift from P-limited towards a more balanced microbial nutrient demand following biochar-containing amendment application.

Droughts increasingly threaten crop productivity in nutrient-depleted tropical soils. We investigated how water limitation influences rhizomicrobial traits (microbial biomass and functional community composition, enzyme activities) and nitrogen (N) uptake in three sorghum genotypes Makueni local (Mkl), Gadam (Gd), and IESH 22012 (IESH) under well-watered and drought conditions. Depth-specific (0-30 and 30-60 cm) 15N labelling traced N uptake at flowering and grain-filling. Drought reduced grain N content across all genotypes but shoot N only in IESH. Gd enhanced 15N recovery in grains via post-anthesis uptake from both depths under drought, whereas Mkl and IESH rather reallocated N within the plants towards the grain. Compared to well-watered conditions, rhizosphere chitinase activity declined in Mkl under drought, while leucine aminopeptidase (LAP) activity remained unchanged. Under drought, microbial biomass decreased at flowering but recovered at grain-filling, coinciding with enhanced arbuscular mycorrhiza fungi (AMF) colonisation. At grain-filling, AMF associations with specific bacterial taxa aligned with grain N recovery, N-utilisation efficiency, and LAP activity, displaying complementary roles within the plant-AMF-bacterial functional consortia in sustaining N acquisition. Overall, N acquisition in sorghum shifted in a genotype-specific manner from reliance on microbial activity under well-watered conditions to selective AMF-bacterial partnership at grain-filling under drought. These responses highlight the significant role of rhizosphere functional dynamics in sorghum N nutrition during reproductive stages under concomitant drought and nutrient limitation.

Agricultural soils in semi-arid sub-Saharan Africa are often low in soil organic carbon (SOC) and nitrogen (N), making them vulnerable to degradation and threatening food security of smallholder farmers. Conservation agriculture practices such as mulching are promoted as climate-resilient strategies to improve soil fertility, but it remains unclear whether these practices improve soil biogeochemical properties in semi-arid regions. We conducted a greenhouse experiment that simulated a cowpea (Vigna unguiculata) growth period, a regional key crop, under water optimum and stress conditions using sandy soil from the Omusati region in Namibia. Effects of different mulches (wheat straw, wood chips, 1:1 mixture), inoculation with a locally adapted Bradyrhizobium and water conditions on soil biogeochemical properties, including SOC, N, microbial biomass and enzyme kinetics (β-glucosidase, chitinase, leucine-aminopeptidase) were investigated. We showed that mulching had limited short-term effects on SOC and N. Inoculation with rhizobia increased soil N, lowered C:N ratios and reduced N-related enzyme activities, demonstrating its potential to mitigate N limitation. Water stress decreased enzyme activities by 64

Drylands store most of the global soil inorganic carbon (SIC), yet the extent to which this pool interacts with contemporary carbon (C) cycling remains poorly understood. To test whether SIC behaves primarily as an inert geological reservoir or instead bears a modern carbon imprint, we quantified SIC content and radiocarbon (∆14C) at 42 dryland sites spanning broad aridity gradients across Eurasia. We also evaluated the climatic, edaphic, and biotic factors associated with variation in ∆14C-SIC. Across all sites, topsoil SIC (~0-10 cm) was strongly depleted in 14C but consistently enriched relative to 14C-dead carbonates, indicating that it contains a measurable component derived from modern carbon inputs. In the Chinese drylands, ∆14C-SIC declined with increasing aridity, consistent with weaker modern carbon exchange under drier conditions and a greater contribution of inherited or 14C-depleted carbonate carbon. Soil pH and ∆14C of soil organic carbon were the strongest predictors of ∆14C-SIC, suggesting that carbonate dissolution-reprecipitation and the age of carbon entering soil CO2 play key roles in determining SIC origins. At a subset of nine Chinese sites, ∆14C-SIC declined sharply with depth and approached 14C-dead values in subsoils, indicating little influence of modern carbon in deeper carbonate pools. The presence of mixed 14C-depleted and modern 14C signatures in SIC potentially complicates the use of SIC isotopic signatures as proxies of environmental conditions. Together, our results indicate that dryland topsoil SIC commonly carries a measurable modern carbon signature that is tightly linked to contemporary carbon cycling. This coupling weakens with increasing aridity and soil depth, suggesting that environmental change in drylands may reshape one of the planet's largest carbon pools not only through changes in SIC stocks, but also through shifts in carbonate radiocarbon signatures and sources.

The pivotal role of the soil microbiome in global biogeochemical cycles is undisputed. The subsequent demand for simplified quantitative descriptions of its functions in modelling approaches resulted in transferring the pure-culture based microbial yield concept into microbial carbon use efficiency (CUE) – a “one-number” approach to partition C input to soils and to describe the physiological efficiency of the microbiome.The holy grail lost its sanctity once our challenges to reliably determine it became evident. The method comparison of Geyer et al. (2019) identified which critical assumptions underly the contrasting outcomes in CUEs derived from these methods. Our own data just underline this: While substrate-based CUE has a temporal and substrate dependency, 18O-based and metabolic CUE remain often unaffected by substrate addition but cover, with either DNA-replication or anabolic precursor-based upscaling of biomass C formation contrasting physiological processes of microbial cells.Such divergent findings highlight that despite decades of research, current methods do not allow an unambiguous quantification of microbial substrate use in soils, owing to two overlapping methodological challenges: 1) Neither extracting microbial biomass nor predicting it from de-novo formed DNA can deliver a reliable quantitative estimation of the newly formed microbial biomass carbon; and 2) Whatever we add as substrate to soils does not reflect what microbes use for growth under native conditions. Our progress in quantitatively covering an increasing number of cellular pools (e.g. also considering cell walls and membranes), the increased consideration of storage, and first concepts on how to integrate secreted extracellular carbon offer perspectives to tackle the first of the two challenges. However, experimentally representing the incredible diversity of organic molecules accessible to microbes for consumption in soils is yet rather avoided, although Lehmann et al (2020) postulated compound diversity as a central factor determining the fate of carbon in soils. Comparing incubations with individual compounds to those of complex monomer mixture revealed that the microbial use of an individual compounds is significantly affected by the presence or absence of other compounds, i.e. the molecular diversity in soil solution. This can readily be explained by viewing microbes through the lens of their metabolic capacities, which impose fundamental constraints on their functioning. Formation of microbial biomass requires a defined ratio of precursor building blocks, which are products of distinct pathways of the basic carbon metabolism. De-novo production requires expression and formation of all pathway-related enzymes, while direct precursor uptake from soil solution allows for “saving” this energy. Therefore, we postulate that monomer diversity would positively affect microbial efficiency. This may be contrasting for polymer diversity, where extracellular enzyme costs exceed those of intracellular de-novo formation and thus a low diversity may be bioenergetically favorable. Thus, substrate diversity-efficiency relationships may centrally underlie deviations between our current CUE approaches. We recommend microbial ecologists to whenever possible replace CUE by the actual processes of interest, i.e. the ecophysiological response and subsequent changes in microbial pools (metabolome, growth) and fluxes (fluxome). This would provide parameters allowing for quantitative upscaling to pools and fluxes required for higher scale soil system models.

Despite increasing climatic stress, grassland management is intensifying globally to enhance productivity. However, how increased biomass removal and associated shifts in plant composition and plant–microbe feedbacks regulate ecosystem functioning, particularly in nutrient-poor tropical grasslands, remains poorly understood. We hypothesised that increasing biomass removal structures plant communities and their rhizomicrobiome from resource-conservative towards resource-acquisitive dominated systems, and that both low and high management intensities induce unfavourable feedbacks between nutrient cycling and resource allocation, constraining soil microbial activity, plant productivity, and drought resilience. In a native managed tropical grassland, four aboveground biomass removal frequencies (1×, 2×, 3×, and 6× cutting annually) were applied in the field. Intact soil core mesocosms were exposed to drought stress in a split-plot completely randomised design (CRD), and combined with 13CO2 pulse labelling. We assessed plant biomass yield, 13CO2 assimilation and belowground C allocation, arbuscular mycorrhizal fungi (AMF) colonisation, extracellular enzyme activities, and rhizosphere microbial community structure and function. Increased cutting frequency shifted vegetation from resource-conservative, “slow” strategists to more acquisitive, “fast” strategists, accompanied by a transition from oligotrophic, fungi-dominated to copiotrophic, bacteria-dominated rhizosphere communities. Drought reduced total 13C assimilation and biomass production but enhanced allocation of assimilates to symbiotic and stress-alleviating microbes, particularly AMF. Overall, our results demonstrate that biomass removal regulates plant–soil–microbe interactions underpinning ecosystem resilience and productivity under drought, highlighting the importance of optimising management intensity in tropical grasslands under climate change.

Abstract Reliable predictions of dryland carbon fluxes require understanding the persistence and turnover of soil organic carbon (SOC). We measure radiocarbon to quantify the age of SOC and CO2 released from soil respiration at 97 dryland sites across six continents. Here we show that bulk SOC contains little C fixed in the past 60 years, while respired CO2 originates from both bomb-derived recent C and millennia-old C, challenging the idea that old C is chemically or physically protected. Radiocarbon suggests mean ages of ~2100 years for bulk SOC and ~520 years for respired CO2, the latter far older than machine-learning (<50 years) or Earth system models predict. Aridity, net primary productivity, and SOC content are dominant predictors for radiocarbon signatures, with abrupt shifts to older C beyond an aridity threshold of ~0.87. Our findings underscore the need to incorporate the vulnerability of older carbon into models and land management strategies.

Perennial cropping systems hold great potential to enhance soil organic carbon (SOC) stocks and contribute to climate change mitigation. However, the effects of perennial crops on SOC fractions with different stabilities remain poorly understood. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) are considered to have different formation mechanisms and different stabilities. Plant- and microbial-derived carbon (C) are the main origins of SOC, yet their relative contributions to POC and MAOC remain unclear. Here, based on an 11-year experiment, we compared two perennial cropping systems (festulolium and grass-clover) with an annual cropping system (maize), to investigate their effects on soil POC and MAOC, and quantify the contribution of plant- and microbial-derived C to these two soil C fractions using lignin phenols and amino sugars as biomarkers. The soil of the two perennials had higher POC and MAOC than maize at 0-20 cm soil depth, with higher proportions of POC in SOC. The higher POC of the two perennials was linked to their significantly higher fungal and bacterial necromass C in POC. Total microbial necromass C accounted for only 29% of POC and 36% of MAOC at 0-20 cm across all systems, suggesting that plant-derived C dominates these two C pools. However, no significant differences were detected in the lignin phenols content in POC and MAOC at 0-20 cm. Our results challenge the conventional assumption that microbial necromass C dominates MAOC, highlighting the role of plant-derived C in POC and MAOC, which could have a greater influence on soil C sequestration in climates with low mean annual temperature than previously assumed. Given that only two biomarkers were used, interpretations should not be extrapolated beyond their analytical scope.

The physical colocation of decomposers and substrates has been proposed as being a determining factor of microbial metabolism in soil, which is also greatly modulated by environmental temperature. Moreover, spatial heterogeneity of insoluble substrates is hypothesized to favor the fungal energy channel, as fungi have a well-developed capacity to translocate resources within their mycelia thus overcoming local resource limitation. Here, the effects of warming, substrate spatial heterogeneity, and fungal translocation on microbial metabolism as indicated by substrate-derived CO2 emission, heat production, and calorespirometric ratio (CR, the ratio of heat production to CO2 emission) were tested, using cylinders with four compartments that either prevent or allow diffusion between compartments.With increasing spatial heterogeneity, the CO2 emission rate generally declined under ambient temperature. The emission rate was slightly higher when diffusion was not allowed across the compartments, except the second half of incubation in the most heterogeneous treatment (100-0-0-0%). In warming environment, the CO2 emission rates were stimulated, but with diminished effect of spatial heterogeneity. The heat release in the most heterogeneous treatment was lower than the most homogenous (25-25-25-25%) and intermediate heterogeneous (50-0-50-0%) treatments. Under warming condition, the peaks of heat release were heightened, and the peak of the most heterogeneous treatment was brought forward. The heat release was higher when diffusion was not allowed across the compartments under ambient temperature, but insignificant difference among treatments were detected under warming environment. CR decreased rapidly in the first half of incubation, and remained stable during the rest . The difference in CR was mainly detected in the first half of incubation, with CR declining with the decrease of spatial heterogeneity.Overall, our findings provide detailed information about microbial metabolism in response to substrate spatial heterogeneity and warming climate, and suggest that the degree of substrate spatial heterogeneity is an important boundary condition shaping the energy use channel in this soil compartment.

The intricate interaction between human activities and the repercussions of climate change has made urban ecosystem health and biodiversity—both vital to human survival and well-being—particularly vulnerable. Recent research has spotlighted the frequently underestimated but crucial role that interactions between plant roots and several biotic and abiotic components of soil play in affecting urban biodiversity and ecosystem dynamics.We conducted a controlled experiment to investigate this relatively obscure aspect of the urban environment. The experiment has been done with young plantlets of Quercus cerris and three urban soils collected from distinct sites in the city of Campobasso (Italy). We selected three sites in the city to clearly show a specific gradient of urbanization and vegetation fragmentation. Q. cerris young plants were grown in the rhizoboxes packed with three urban soils for two weeks to evaluate the impact of soil-plant interactions on the possible enzymes’ release by the roots and root-harboring microorganisms. The spatial distribution of three enzymes, namely acid phosphatase (P-cycle), β-glucosidase (C-cycle), and leucine aminopeptidase (N-cycle), was mapped and detected in each soil region (i.e., bulk soil and rhizosphere longitudinal surface) using a 2-D soil zymography technique.The zymogram analysis revealed that the enzyme activities in soils differed spatially along the urbanization gradient, with the more urbanized soil having the highest levels of enzymatic activity and hotspot presence.The root activity toward the exudation correlated with the highest enzymatic activity, that futrther lead to more intensive turnover of soil organic matter in soil. This could be linked to the exudation of roots to regulate plant growth in unfavorable conditions or to the rhizodeposition of substrates to change soil composition. Further in-depth analyses of the physical and chemical properties of the soil, along with the profiling and characterization of the microbial community composition, are currently underway in order to obtain a better understanding of the role of root enzymatic activities and their consequences on the biogeochemical processes in urban soils.

Analysing root traits to identify below ground acquisition mechanisms and relating them to above ground traits, such as leaf phenology, can improve the understanding and design of resource use efficiency in drought resilient agroforestry systems. Shade trees play a key role in regulating above and below ground resource use dynamics in agroforestry systems. Specific shade tree functional traits such as leaf phenological development, crown architecture and leaf traits such as specific leaf area and nitrogen content have been related to shade tree impact on productivity, ecosystems service provision and drought resilience of agroforestry systems. Understanding the influence of many different shade tree species on resource use and the productivity outcome resulting from their interaction with cocoa plants have, so far, mainly focused on aboveground traits. Yet, there is an urgent need to put adequate emphasis to the equally important belowground processes, root systems, and root-rhizosphere interactions. Root trait research is significantly limited in tropical communities, constraining understanding of belowground processes and interactions within complex systems such as agroforestry. There is lack of understanding of strategies in belowground resource acquisition among functional groups of shade tree species. In this study, two key roots traits, i.e. fine root length density and fine root diameter of 13 common shade trees species belonging to 6 functional (leaf phenology) groups and cocoa were evaluated under farmer field conditions. Fine root samples were acquired for 4 replicates of each shade tree species through extensive root coring up to 60 cm depth and at three horizontal shade tree impact zones (inner, mid and outer). Scanned sorted shade tree and cocoa plant root images were analysed with WINRHIZO. All cocoa plants irrespective of their associated shade tree functional group exhibited resource acquisitive (non-conservative) fine root traits, i.e. with higher root length density and smaller diameter. Similarly, shade trees in the ‘brevi deciduous during dry season’ functional group exhibited the notable paradox of leaf flushing during dry season characterized by higher, leaf area-related, water uptake in the dry season exhibited non-conservative root traits. Evergreen and complete deciduous functional groups showed a conservative root trait showing lower fine root length density and larger diameter. Shade trees with conservative root traits are therefore considered complementary to the cocoa plant acquisitive traits, thereby enhancing belowground resource use efficiency and drought resilience in cocoa agroforestry systems.

Little is known about the path of root-derived carbon (C) into soil microbial communities in response to arbuscular mycorrhizal fungi (AMF) and nitrogen (N) fertilization. A mycorrhiza defective mutant of tomato (reduced mycorrhizal colonization: rmc) and its mycorrhizal wild type progenitor (MYC) were used to control for the formation of AMF. 16-week continuous 13CO2 labeling was performed to quantify the photosynthetic C allocation in active microorganisms via 13C profiles of neutral (NLFAs) and phospholipid fatty acids (PLFAs). The 13C incorporation into fungal biomarker (the sum of PLFA 16:1ω5c, NLFA 16:1ω5c, PLFA 18:2ω6,9) increased with time over 16 weeks, and 4.62

Nutrient and water limitations contribute to yield losses in semi-arid regions. Therefore, crop rotations incorporating nitrogen-fixing legumes and drought-tolerant sorghum varieties offer a strategy to improve the utilization of scarce soil resources. Under semi-arid, field-like conditions, sorghum crop rotations with either cowpea pre-crop or fallow, including two early and three late maturing genotypes, were tested to identify stress adaptation traits of sorghum to water and phosphorus limitations. Morphological and physiological parameters were evaluated on a single-plant basis. Lower soil P content significantly delayed flowering compared to higher P levels. However, improved P availability arising from pre-crop residues reduced this effect. Mycorrhizal infection rates and root-to-shoot ratios were positively correlated with panicle N and P content at anthesis under low P conditions. Although drought significantly impacted yield, early maturing genotypes with the highest reduction in shoot biomass and reduced water use before flowering, could sustain yield production. Early-maturing genotypes characterized by high root-to-shoot ratios, rapid AMF establishment, and reduced water use before flowering exhibit a strong potential for maintaining yield and biomass production on nutrient-poor soils in semi-arid regions. Such genotypes conserve water before flowering and thus can alleviate post-flowering water stress, ensuring adequate P uptake despite low soil P availability.

Phosphorus (P) acquisition in forest ecosystems relies on litter cycling, but foliar P concentrations in beech forests are decreasing. This highlights the urgency to understand how soil microbes adapt to P limitations caused by environmental shifts. In this study, a novel approach combining 33P-wick labeling to trace litter-P recycling with a microbial dilution approach was used to study microbial P cycling associated with microbial biodiversity loss. Sterilized soils, re-inoculated with different dilutions of their native microbial communities were incubated with 33P-labeled beech litter for four weeks. The kinetics of acid phosphatase and the flux of 33P into different soil pools were determined. Carbon (C), nitrogen (N), and P, in soil microbial biomass and in extractable pools (e.g., Presin) were measured. The acid phosphatase activity decreased by 75-92 % with the dilution increase from 10-4 to 10-6 at the P-rich site, indicating a functional loss of P mobilization. The overall acid phosphatase activity was 1-fold higher at the P-deficient site than at the P-rich site, suggesting a high functional redundancy of microbial P mobilization. The recoveries of litter-derived 33P in soil microbial biomass (SMB) and in Presin were 5-fold and 2fold higher for the P-deficient site than for the P-rich site throughout all dilutions, suggesting that the recycling of litter-P by SMB in the P-deficient soil is highly redundant as an intermediate reservoir. Our study confirms that the high functional redundancy of microbial P acquisition at a P-deficient forest site can maintain pivotal microbial acquisition processes for P uptake.

Metabolic flux analysis is an integrated experimental and computational approach for quantitative understanding of biochemical reaction networks with particular relevance in systems biology. Mass and energy flows through soil microbial metabolism are subject to the laws of thermodynamics. Carbon (C) allocation through central metabolic pathways (e.g. glycolysis, pentose phosphate, and Entner-Doudoroff) can be reconstructed by 13C-labelling coupled to metabolic flux analysis (13C-MFA) by tracing specific C atoms from within substrate molecules into metabolic products such as carbon dioxide (CO2) or fatty acids. However, mass flow calculated via 13C-MFA alone cannot fully characterise microbial carbon use. Here, we took the novel approach of coupling MFA with microcalorimetry, to also take bioenergetic constraints into account. We coupled energetics and mass flow on a metabolic level by selecting optimal sets of isotopomer tracers. Fifteen position-specific or uniformly 13C-labelled isotopomers - four alanine, seven glucose, and four glutamic acid ones – were added to a Luvisol (in total 4 folds of the microbial biomass C), and we analyzed substrate-derived 13CO2 fluxes as well as heat dissipation via isothermal microcalorimetry. Our results demonstrate that the temporal dynamics of catabolic CO2 release resembles that of the heat dissipation, i.e. peak respiration and peak heat dissipation were reached approximately 18 h after substrate addition, irrespective of whether the substance entered the central metabolic pathway at the monosaccharide level (glucose), at the pyruvate level (alanine) or in the citric acid cycle (glutamic acid). This indicates that heat dissipation in the initial growth period was strongly dominated by catabolic processes. However, whereas 13CO2 release leveled off during the 36 hours of incubation, the heat dissipation remained above its original level, suggesting that anabolic processes increasingly contribute to the heat dissipation in the later phases of incubation. Glucose isotopomer utilization indicated dominance of the pentose phosphate and Entner Douderoff pathways over glycolysis, suggesting a high activity of fast-growing organisms with considerable C allocation to anabolism. The dominance of this anabolic C use in the later stage of the incubation was confirmed by the isotopomer utilization of alanine and glutamic acid. This study shows that the heat dissipation of growing microbial communities under high C supply is closely linked to their catabolic CO2 release, whereas slow, potentially recycling-based growth after resource depletion releases energy more via anabolic reactions. We furthermore demonstrated that coupled MFA and calorespirometry provides a powerful tool to differentiate among metabolic contributions to the energy use of soil microbial communities in different growth phases.

Understanding nitrogen (N) retention mechanisms in pristine humid temperate rainforest soils is critical for effective ecosystem management and nutrient conservation. The potential abiotic transformation of nitrite (NO2−) into organic N forms in the absence of microbial activity in these ecosystems remains largely unexplored, despite its role in mitigating N leaching. This study focuses on the abiotic incorporation of nitrite (NO2−) into dissolved organic nitrogen (DON) under anoxic conditions, a mechanistic step not directly evaluated in previous research, which employed 15N-labelled nitrate (NO3−). To address this gap, we used 15N-labelled NO2− at 5 and 15 mg L−1 in a lab incubation study under anoxic conditions to trace the contribution of abiotic nitrite transformation to organic N formation in organic matter-rich soils from temperate rainforests developed on both volcanic and non-volcanic parent materials. The added 15N declined rapidly after 15 min by 52% and 60% in both soil solutions, while it started to form labelled DON, increasing by 11% and 34%, after five days of incubation, with the highest accumulation at 15 mg L−1 of 15N-NO2−. These results show that up to 77% of the added 15N-NO2− can be abiotically incorporated into the DON of unpolluted old-growth temperate rainforest, whether developed on volcanic or non-volcanic soils. Nitrogen input has a stronger effect than soil parent material from which the soils originate. This reveals the natural resilience of unpolluted temperate rainforests to N loss, with implications for long-term ecosystem stability and nutrient cycling.

Wildfires strongly alter soil properties, which in turn affect ecosystem recovery over extended periods, though long-term impacts are less certain. This study investigated a 14-year post-fire chronosequence in Chile's mediterranean and temperate humid forests, revealing ecosystem-specific soil properties and nutrient recovery mechanisms. By analysing sites at successional stages, the chronosequence approach assessed temporal changes and ecosystem recovery, revealing long-term wildfire effects on soil dynamics and nutrients recovery. Wildfires raised soil bulk density to 0.9 g cm- 3 in humid temperate and 1.2 g cm-3 in mediterranean ecosystems. Mediterranean soils experienced greater compaction from organic matter loss, soil aggregate destruction, ash-clogged pores, and topsoil erosion. Soil texture shifts were ecosystem-dependent: mediterranean soils increased 10-12 % in clay and silt through ash redistribution and aggregation, while temperate soils saw sand content rise by 0.74 % and 0.32 % yearly at 0-5 and 5-10 cm depths from thermal disaggregation and erosion. Ground vegetation recovers quickly, but physical soil properties like bulk density require over 14 years to return to pre-fire conditions. In humid temperate forests, ash input initially increased soil pH (4.8 to 5.8), reducing acidity, mitigating aluminium toxicity, while increasing nutrient availability. Base cation stocks increased in mediterranean woodlands (e.g., Ca: up to 0.41 Mg ha- 1 y- 1) due to ash retention, lower leaching, and ash infiltration into subsoil. Nutrient stocks in humid forests recovered slowly (Ca: 0.087-0.13 Mg ha- 1 y- 1) due to rainfall-driven leaching and low subsoil reserves. Carbon and N losses were restricted to the litter horizon in temperate forests, recovering via fire-resistant tree inputs, whereas mediterranean soils suffered severe C and N depletion from vegetation loss, erosion, and low N fixation. Fire effects and recovery are ecosystem-specific, shaped by landscape, geology, hydrology, and vegetation resilience. Understanding how fire regimes affect soil and nutrient recovery is vital for improving projections in fire-prone regions.

Hotspots are characterized by an increased availability of nutritional elements compared to the surrounding bulk soil, which enhances microbial activity. However, the shifts in nutrient stoichiometry, when hotspot formation is initiated by a non-microbial organic matter source (rhizodeposits, litter, feces & mucus, percolating dissolved organic matter), are highly hotspot-specific. This results in contrasting microbial dynamics in the rhizo-hyphosphere, the detritusphere, the drilosphere and further biopores of soil animals, and in preferential flow pathways. Experiments and models of microbial growth-death dynamics have recently improved our understanding of how element stoichiometry shapes element allocation in microbial metabolism. This holds specifically true for to the two contrasting pathways of microbial growth – intracellular element storage versus the investment of C, nutrients and energy in replicative microbial growth. Both growth modes involve synthesis of organic polymers – either storage or structural cellular polymers. However, the nature of these two types of polymers is highly contrasting with regards to their elemental but also their molecular diversity, such that the two growth modes generate distinct differences in the molecular compositon of the cellular biomass. We can therefore expect that the stoichiometric differences of nutrient hotspots will drive differences in the molecular diversity of the microbial biomass, and so ultimately the successively accumulating necromass. Whereas controlled incubation experiments demonstrate how element allocation to storage and replicative growth depends on nutrient stoichiometry, we lack an understanding of how growth modes are distributed among hotspots in situ. Besides developing this conceptual understanding, we aim to shed light on the implications of differences in cell physiology among hotspots, which includes i) the turnover rate of microbial biomass due to contrasting resistance to stress (e.g. starvation), ii) the molecular composition of the microbial cells and iii) the resulting chemical properties and molecular diversity of necromass. These factors strongly influence the formation rates, qualities and persistence of necromass-derived soil organic matter arising in these hotspots. Furthermore, the accrual of organic matter shapes microbial resource availability, including element stoichiometry, in the hotspot, as well as the physico-chemical microbial habitat properties. In consequence, a feedback loop between microbial growth- and turnover-based organic matter formation and the initial processes, that trigger the hotspot formation elaborates. Thus, although hotspot formation is always initiated by non-microbial organic matter input, the characteristics of the established soil hotspots are ultimately linked to the microbial necromass’ molecular and elemental diversity, which is the direct product of the hotspots’ microbial metabolism and growth mode. This study aims to relate the nutrient enriching processes (rhizodeposits, litter, feces & mucus, percolating DOM) and soil-intrinsic feedbacks to the dominant microbial growth modes and resulting properties of the organic matter in soil hotspots.

Biochar (BC) application to soil is a method of long-term carbon (C) sequestration in croplands. Along with contribution to climate change mitigation, agronomic benefits of biochar are widely accepted. Amelioration and nutritive benefits of biochar are mainly attributed to high applications rates, which may not be viable for farmers. We suggest a new approach: band application, which implements biochar in modern intensive crop rotations and optimizes both C and nutrients cycles (i.e. phosphorus (P)).As maize is globally one of the most widely planted crops, corncobs (CC) may be utilized for BC production. Corncob biochar (CC BC) may be implemented into the farming practice as suspension with liquid phosphorus solution jointly applied in band in the close proximity to seeds.We conducted an incubation experiment to evaluate the short-term effects (within 32 days) of corncob biochar and inorganic P application on P availability and microbial activity in a loamy Luvisol.Corncobs were pyrolyzed to biochar (350oC; 0.2-0.3oC s-1), grinded (

Interest in managing agroecosystems for improving soil health has driven the application of conservation practices, such as reduced tillage. However, our understanding remains limited regarding changes in soil organic carbon (SOC), microbial resource limitations, and soil ecosystem multifunctionality across the soil profile (not just in the upper layers) following long-term reduced tillage as compared to conventional tillage. This study aimed to compare the impacts of reduced tillage (RT) and conventional tillage (CT) on SOC storage, soil enzyme activities, and ecosystem functionality in a 90 cm soil profile. Soil cores were collected from four different soil depths (0-10, 10-30, 30-50, 50-90 cm) in a 55-year field experiment (crop rotation primarily featured cereals) in central Germany comparing RT (rotary harrow, 5-8 cm depth) and CT (mouldboard plough, 25 cm depth). Results showed that RT increases SOC content by 24 % at 0-10 cm depth but decreases SOC content by 22 % at 10-30 cm depth relative to CT. The enhanced SOC content under RT further improved soil ecosystem multifunctionality by a factor of 2.8 at 0-10 cm compared to CT. Notably, higher available nitrogen (N) content increased vector length at 0-10 cm depth under RT, related to the higher production and release of C-acquisition enzymes. In contrast, the higher exudation of N-acquiring enzymes found at 10-50 cm depth indicated N limitation for microorganisms under RT. At this depth, CT alleviated microbial N limitation. Moreover, RT lowered SOC stock by 24 % compared to CT at 10-30 cm, resulting in an 11 % decrease in SOC across the entire 0-90 cm soil profile. In conclusion, while reduced tillage improved soil ecosystem functionality in the 0-10 cm, it may not enhance SOC sequestration, highlighting the importance of considering the whole soil profile when comparing the SOC sequestration potential of different tillage practices.