Nitrogen Mineralization Rates Research Articles

Long-Term Soil Warming Drives Different Belowground Responses in Arbuscular Mycorrhizal and Ectomycorrhizal Trees.

The ability of trees to acquire soil nutrients under future climate conditions will influence forest composition and function in a warmer world. Rarely are multiple belowground carbon allocation pathways measured simultaneously in large global change experiments, restricting our understanding of how trees may shift their allocation of resources to different nutrient acquisition mechanisms under future climates. Leveraging a 20-year soil warming experiment, we show that ectomycorrhizal (EM) trees reduce mycorrhizal colonization and root exudation while increasing fine root biomass, while arbuscular mycorrhizal (AM) trees largely maintained their belowground carbon allocation patterns in warmer soils. We suggest that AM trees may be better adapted to thrive under global warming due to higher rates of nitrogen mineralization in warmer soils and the ability of their mycorrhizal symbiont to acquire mineralized inorganic nutrients, whereas EM trees may need to alter their belowground carbon allocation patterns to remain competitive as global temperatures rise.

The impact of agricultural land use on the linkages between soil microbial communities and agroecosystem functioning is depth-dependent

Soil carbon (C) and nitrogen (N) mineralization rates are critical indicators of ecosystem functioning in agricultural land. However, the effects of agricultural land use on the interactions between soil C and N mineralization at different soil depths, especially in tropical regions, are poorly understood. Here, a longan orchard (LO) was converted to a conventional tea plantation (CTP) and an organic tea plantation (OTP) in the tropical region of China, and the responses of fungal and bacterial communities to these changes were assessed. The characteristics of the microbial communities, enzyme activities, and N and C mineralization rates were evaluated in response to the changes in land use. It was found that LO and OTP had faster N and C mineralization rates than CTP in surface soil. However, in subsurface soil, LO and OTP showed a faster C mineralization rate and a slower N mineralization rate than CTP. Structural equation modeling revealed that pH and C/N were the most crucial factors affecting N and C mineralization rates in surface soil. In contrast,soil bacterial and fungal community structures were the principal drivers of both the C and N mineralization in subsurface soil. Although soil C and net N mineralization were positively correlated in surface soil, this was not seen in subsurface soil. Collectively, this study demonstrated that differential drivers and their effects on the interactions between soil C and N mineralization at different soil depths should be considered for more accurate prediction of soil C and N dynamics under land-use changes.

Effects of Microplastics on Soil N2O Emission and Nitrogen Transformations from Tropical Agricultural Soils

A widespread concern had been there regarding soil ecological and environmental problems caused by microplastic pollution in agricultural soils. A controlled laboratory incubation experiment was performed to examine the effects of different types of microplastics on soil properties, N2O emissions, and nitrogen （N） transformations in tropical arable soils from a pepper-corn cropping system in Hainan Province. Three treatments were done： soil without microplastics （CK） and soil amended with 5% of polyethylene （PE） or with 5% of polybutylene adipate co-terephthalate （PBAT）. The results showed that both types of microplastic addition increased soil pH, soil organic carbon （SOC）, and dissolved organic carbon （DOC） contents, with stronger treatment effects observed for PBAT than those for the PE treatment. In addition, the PE and PBAT treatments increased soil ammonium nitrogen （NH4+-N） contents by 66.07% and 119.65% and decreased nitrate nitrogen （NO3--N） contents by 8.56% and 29.68%, respectively. Compared to those in the CK treatment, the addition of PBAT significantly increased soil N2O emissions by 254.92% （P < 0.05）, whereas that of PE produced no significant effects. Furthermore, both the PE and PBAT treatments increased soil net nitrogen mineralization rate （NMR） and decreased soil net nitrification rate （NNR）, with more obvious treatment effects observed in PBAT than in the PE treatment. PBAT addition increased the abundance of ureC, while PE had no significant effects. Microplastic addition reduced the abundance of nitrifying gene abundances （AOA-amoA, AOB-amoA, and nxrA）, with more obvious treatment effects found in the PBAT treatment. Further, PBAT addition significantly increased the gene abundances of nirK, nirS, nosZ, and fungal nirK （P < 0.05）, whereas the addition of PE had no significant effect on those gene abundances. Soil N2O emissions had positive relationships with NH4+-N intensity, pH, DOC, SOC, and nirS abundance. In conclusion, biodegradable microplastics addition produced stronger influences on soil properties and N transformations than the non-biodegradable one in tropical arable soils and aggravated soil N2O emissions mainly by promoting denitrification.

Seasonal variability and seagrass traits affect methane fluxes in a subtropical meadow

Abstract Plant traits which vary both within and between species often drive biogeochemical cycling. Understanding the relative role of within‐ and between‐species trait variability in driving carbon cycling is essential to scaling site measurements to global carbon budgets. In seagrass meadows, carbon and nitrogen mineralization rates and associated greenhouse gas emissions are highly variable, impeding our ability to reliably predict whether meadows are net carbon sinks. Evaluating the influence of within‐ and between‐species trait variability on greenhouse gas fluxes will improve our understanding of local‐scale drivers of greenhouse gas production and consumption in seagrass meadows. To test the effects of plant traits on dissolved greenhouse gas fluxes, we performed mesocosm incubations with live, intact seagrass plants. We compared methane (CH4) and nitrous oxide (N2O) fluxes under dark and light conditions from sediments dominated by Halodule wrightii and Thalassia testudinum across dormant, early and peak growing seasons in a subtropical meadow along the west coast of peninsular Florida. We also measured oxygen (O2) fluxes to interpret greenhouse gas fluxes within the context of community metabolism. We measured several seagrass traits, such as above‐ and below‐ground biomass and leaf and root area and assessed their impact as well as the impact of species identity on dissolved gas fluxes. We found that abiotic factors linked to metabolism (i.e. light and temperature) influenced greenhouse gas fluxes across seasons. In addition to light conditions and sampling month, plant size (a composite trait variable) was a significant predictor of O2 consumption and CH4 production under dark conditions, and better predicted fluxes than individual plant traits. CH4 production was slightly higher in H. wrightii‐dominated sediments, but species identity was less important than plant size in driving CH4 production. N2O fluxes were low and not influenced by plant traits or species identity. Synthesis: Our results indicate that within‐species more so than between‐species trait variability drives the direction and magnitude of CH4 fluxes in seagrass meadows. We identified a trade‐off where seagrass biomass is often associated with enhanced sediment carbon storage, but in our study, plant size promoted CH4 production, potentially offsetting the benefits of long‐term storage.

The latest status of nitrogen saturation on Kureha Hill, Toyama, Japan, based on 20‐year observations

AbstractExcessive anthropogenic nitrogen fixation alters the nitrogen cycle and increases nitrogen deposition, leading to nitrogen saturation, which in turns leads to forest decline and nitrate leaching into stream waters. Kureha Hill in Toyama Prefecture, Japan, is considered to be in nitrogen saturation, since many streams have contained high concentrations of nitrate for more than 20 years. In this study, the latest status of nitrogen saturation was verified by comparing most recent data with 20 years observational data, focusing on various indicators of nitrogen saturation, such as stream water quality, nitrogen budget of the watershed, and soil nitrification and mineralization potential. Both the nitrogen deposition on the Hyakumakidani watershed on Kureha Hill and the amount of nitrate leaching to the stream tended to decrease. The reduction in nitrate leaching could be attributed to the reduction in nitrogen deposition and other factors, such as nitrogen pools in the soil. Despite the recent decline in nitrate concentration of the Hyakumakidani stream, the pH level has remained unchanged. This may be due to decreased concentrations of sulfate and acid neutralizing capacity (ANC). The C/N ratio of the soil ranged from 12 to 18 from 2000 to 2023, which was lower than the nitrogen saturation threshold of 25. The net nitrification rate and net mineralization rate showed no significant changes between 2002 and 2023, indicating that the potential to produce nitrate has been unchanged. Similar values in net nitrification and net nitrogen mineralization rates reflected that the Hyakumakidani watershed remained in Stage‐3 nitrogen saturation.

Visible-to-near-infrared spectroscopy for prediction of soil nitrogen mineralization after sample stratification by textural homogeneity criteria

On-time and accurate estimation of the soil nitrogen mineralization rate (SNMR) is critical for nitrogen (N) management and protecting the environment. This study evaluated the performance of a visible-to-near-infrared reflectance (vis-NIR) spectroscopy for predicting SNMR for four texture groups. A total of 62 topsoil samples were collected from 17 management zones distributed over four fields and incubated with seven destructive sampling events. Samples were analysed for total mineral N (NH4++NO3–) content and scanned using a vis-NIR sensor simultaneously at each of the seven-sampling times. Four partial least squares regression models were calibrated and validated for four textural groups (groups- 1– 4) identified over the United State Department of Agriculture (USDA) texture triangle. Prediction accuracies indicated that vis-NIR sensor was moderately to highly accurate for predicting SNMR, while observing variable accuracies across texture groups. The highest accuracy was obtained for group 1 (sandy-loam; coefficient of determination, R2 = 0.90; root mean square error, RMSE = 0.04 mg N kg−1 soil day−1), successively followed by group 2 (mostly loam; R2 = 0.80, RMSE = 0.05 mg N kg−1 soil day−1) group 4 (mostly silt; R2 = 0.66, RMSE = 0.08 mg N kg−1 soil day−1), and group 3 (silt-loam; R2 = 0.44, RMSE = 0.08 mg N kg−1 soil day−1). Variable importance in projection score revealed that the key spectral bands to predict SNMR were in 2150 – 2260 nm and 2470 – 2480 nm, resembling the key bands associated with soil organic compounds and clay minerals. In-advance texture information required for soil stratification is regarded a limitation of the proposed approach. In conclusion, vis-NIR holds potential for a rapid estimation of SNMR when samples are stratified into similar texture groups in advance, however, confirmatory research will be needed to validate the current findings for soils from different origin and under different management.

Effects of Incubation Temperature and Sludge Addition on Soil Organic Carbon and Nitrogen Mineralization Characteristics in Degraded Grassland Soil

Elucidating the characteristics and underlying mechanisms of soil organic carbon (SOC) and nitrogen mineralization in the context of sludge addition is vital for enhancing soil quality and augmenting the carbon sink capacity of soil. This study examined the chemical properties, enzyme dynamics, and organic carbon and nitrogen mineralization processes of soil from degraded grasslands on the Loess Plateau at various incubation temperatures (5, 15, 25, and 35 °C) and sludge addition rates (0%, 5.0%, 10.0%, and 20.0%) through a laboratory incubation experiment. The results showed that incubation temperature, sludge addition, and their interactive effects significantly altered the soil enzyme C:N, C:P, and N:P stoichiometries. The cumulative mineralization rates of SOC and nitrogen increased significantly with increasing incubation temperature and sludge addition rate. Principal component analysis revealed a significant linear correlation between cumulative SOC and nitrogen mineralization. Random forest analysis indicated that β-1,4-Glucosidase (BG), β-1,4-N-acetyglucosaminidase (NAG), cellobiohydrolase (CBH), ammonium nitrogen (NO3−), enzyme C:P ratio, alkaline phosphatase (ALP), and incubation temperature were crucial determinants of cumulative SOC mineralization. Structural equation modeling demonstrated that sludge addition, NO3−, NAG, ALP, and enzyme C:P positively impacted SOC mineralization, whereas dissolved organic carbon and BG had negative impacts. Conversely, incubation temperature negatively affected soil nitrogen mineralization, whereas NO3−, available phosphorus, and ALP contributed positively. Sludge addition and temperature indirectly modulated soil net nitrogen mineralization by altering soil chemical properties and enzyme activities. These findings underscore the role of SOC and nitrogen mineralization as indicators for evaluating soil nutrient retention capabilities.

Grazing stabilized carbon and nitrogen pools by reducing carbon and net nitrogen mineralization after soil nutrients were added

Nutrient addition and grazing exclusion are effective methods to restore carbon and nitrogen pools in degraded grassland. However, how the combination of nutrient addition and grazing exclusion affect carbon and nitrogen pools through carbon and net nitrogen mineralization is unknown. A 56-day incubation study examined the effect of no additive (control — CK) and, the addition of sucrose (S), urea (U), sucrose + urea (SU), and yak dung (D) to the soil of grazed and fenced alpine grassland on carbon and net nitrogen mineralization. The 15N-tracer technique was used to determine nitrogen utilization by soil microorganisms. Nutrient addition with grazing exclusion increased soil organic carbon, microbial biomass carbon (MBC), inorganic nitrogen, and dissolved organic nitrogen (DON), and promoted carbon and net nitrogen mineralization in early incubation. The 15N recovery rate in soil was 4.5 to 21.7 % and decreased with time. Grazing exclusion altered the drivers of the carbon and net nitrogen mineralization rates, and increased carbon and net nitrogen mineralization rates by enhancing MBC and DON. The results indicated that nutrient addition: (1) decreased soil carbon and nitrogen stability by increasing nutrient availability and enhancing carbon and net nitrogen mineralization rates; and (2) in combination with grazing exclusion promoted carbon and net nitrogen mineralization. Consequently, soil carbon and net nitrogen mineralization depended on nutrient availability, and grazing stabilized soil carbon and nitrogen pools by reducing carbon and net nitrogen mineralization. The results could provide a theoretical basis for alpine grassland management.

Quantitative importance of subsoil nitrogen cycling processes in Andosols and Cambisols under temperate forests

Nitrogen availability often limits plant growth in forest ecosystems. Plants, including trees, utilize soil inorganic nitrogen transformed via nitrogen cycling processes, including mineralization and nitrification. While most plant fine roots are distributed in surface soil layers, plants take up nitrogen even from subsurface soil layers in addition to the surface soil layers, especially under high nutrient competition. However, there is still limited knowledge about nitrogen cycles within deeper soil layers. In this study, we investigated the vertical profiles (0–60 cm) of the net nitrogen mineralization and nitrification rates at four Japanese forest sites with two different soil types (Andosols and Cambisols). The partial least square path modeling (PLS-PM) was used to determine factors affecting nitrogen cycling processes. The net nitrogen mineralization and nitrification rates per unit soil weight were considerably higher in the surface soil layer than in the deeper soil layers in Andosols but not in Cambisols. PLS-PM analysis showed that microbial biomass and soil organic matter quantities were the important factors influencing the net nitrogen mineralization and nitrification rates, indicating that a similar mechanism, which drives the spatial variations of nitrogen cycling processes in the surface soil layer, predominantly regulates the vertical variations of the processes. Moreover, it was estimated that the net nitrogen mineralization rate could be comparable at all soil types and depths when the rate was expressed per unit soil volume. Therefore, subsoil layers could be a quantitatively important source of plant-available nitrogen in Andosols and Cambisols.

Tree species richness improves soil net nitrogen mineralization rates in a young biodiversity-ecosystem function experiment

Forest ecosystems are facing declining plant species diversity. However, the effects of reduced tree species diversity on soil nutrient supply and tree productivity remain poorly understood. We conducted a biodiversity-ecosystem function experiment with a range of subtropical tree species richness (1, 4, 8, 16, and 32) to investigate the impacts of tree species diversity on soil net nitrogen (N) mineralization rates and its regulation on tree productivity in a young subtropical forest experiment. Our findings indicate a log-linear trend between soil net N mineralization rates and tree species richness, potentially suggesting an improvement in soil N supply capacity with greater species richness. Leaf N content, soil water content and peroxidase enzyme activity were identified as primary positive predictors influencing soil net N mineralization rates. In monoculture forests, soil net N mineralization rates were negatively correlated with litter production and tree basal area, while no such correlation was observed in mixed forests. This implies that soil net N mineralization rates play a critical role in tree productivity for monoculture forests. Together, these results provide strong evidence that the rate of decrease in soil nutrient supply capacity potential accelerates with the loss of tree species diversity in young tree communities, and highlights the importance of increasing tree species diversity to mitigate nutrient limitations. Therefore, preserving tree species diversity is crucial for the future functionality of ecosystems amidst global biodiversity loss.

Long-term impact of wildfire on soil physical, chemical and biological properties within a pine forest

AbstractAnthropogenic fires pose a serious threat to many terrestrial ecosystems because they can cause loss of biodiversity and carbon stocks in the biosphere. Specifically, wildfires impacting natural conservation areas such as European Natura 2000 sites (N2K) are of particular concern. The main study objective was to evaluate the long-term effects of wildfires on the organic layer and some physical, chemical and biological properties of the underlying soil mineral layer, linked to soil quality. Here, we studied two coastal Mediterranean Aleppo pine stands within an N2K site differing for the fires’ years of occurrence, the time between fires (TBF) and the time since last fire (TSLF) throughout 24 years. Furthermore, in each stand, differences in fire frequency (FF) were considered by selecting three sites—double-fire, single-fire and control (unburnt). Our results show the absence of the O-layer in double-fire sites, indicating a loss of this organic carbon (if compared to control) pool of 204 g m−2 in R2F and 139 g m−2 in M2F. Despite this loss being offset by the Corg increase in soil mineral layer, the disappearance of O-layer may compromise the ecosystem services provided by soil. In each stand, long-term fire effects were evident at both single-fire and double-fire sites for some chemical as well as biological soil properties and depended on TSLF. Increased rates of nitrogen mineralization and nitrification were found at all burned sites, persisting up to 24 years post-fire. Soil quality indicators data highlighted the recovery handicap of the microbial community within the considered period. Since our outcomes showed wildfires enduring consequences, mainly relating to TSLF and FF, on different organic and mineral soil properties, we advocate employing prompt strategies to mitigate recurring fires.

Insight into the generation of toxic by-products during UV/H2O2 degradation of carbamazepine: Mechanisms, N-transformation and toxicity

Carbamazepine (CBZ) is a widely used anticonvulsant drug that has been detected in aquatic environments. This study investigated the toxicity of its by-products (CBZ-BPs), which may surpass CBZ. Unlike the previous studies, this study offered a more systematic approach to identifying toxic BPs and inferring degradation pathways. Furthermore, quadrupole time-of-flight (QTOF) and density functional theory (DFT) calculations were employed to analyze CBZ-BP structures and degradation pathways. Evaluation of total organic carbon (TOC) and total nitrogen (TN) mineralization rates, revealed carbon (C) greater susceptibility to mineralization compared with nitrogen (N). Furthermore, three rules were established for CBZ decarbonization and N removal during degradation, observing the transformation of aromatic compounds into aliphatic hydrocarbons and stable N-containing organic matter over time. Five potentially highly toxic BPs were screened from 14 identified BPs, with toxicity predictions guiding the selection of commercial standards for quantification and true toxicity testing. Additionally, BP207 emerged as the most toxic, supported by the predictive toxicity accumulation model (PTAM). Notably, highly toxic BPs feature an acridine structure, indicating its significant contribution to toxicity. These findings offered valuable insights into the degradation mechanisms of emerging contaminants and the biosafety of aquatic environments during deep oxidation.

A theory for context-dependent effects of mammalian trampling on ecosystem nitrogen cycling.

Large mammalian herbivores substantially impact ecosystem functioning. As their populations are dramatically altered globally, disentangling their consumptive and non-consumptive effects is critical to advance mechanistic understanding and improve prediction of effects over ecosystem and Earth-system spatial extents. Mathematical models have played an important role in clarifying potential mechanisms of herbivore zoogeochemistry, based mostly on their consumptive effects as primary consumers and recyclers of organic and inorganic matter via defecation and urination. Trampling is a ubiquitous effect among walking vertebrates, but the consequences and potential mechanisms of trampling in diverse environments remain poorly understood. We derive a novel mathematical model of large mammalian herbivore effects on ecosystem nitrogen cycling, focusing on how trampling and environmental context impact soil processes. We model herbivore trampling with a linear positive or negative additive effect on soil-mediated nitrogen cycling processes. Combining analytical and numerical analyses, we find trampling by large mammalian herbivores is likely to decrease nitrogen mineralisation rate across diverse environments, such as temperate grassland and boreal forest. These effects are mediated by multiple potential mechanisms, including trampling-induced changes to detritivore biomass and functioning (e.g. rate of organic matter consumption). We also uncover scenarios where trampling can increase nitrogen mineralisation rate, contingent on the environment-specific relative sensitivity of detritivore mineral-nitrogen release and detritivore mortality, to trampling. In contrast to some consumptive mechanisms, our results suggest the pace of soil nitrogen cycling prior to trampling has little influence over the direction of the trampling net effect on nitrogen mineralisation, but that net effects may be greater in slow-cycling systems (e.g. boreal forests) than in fast-cycling systems (e.g. grasslands). Our model clarifies the potential consequences of previously overlooked mechanisms of zoogeochemistry that are common to all terrestrial biomes. Our results provide empirically testable predictions to guide future progress in empirical and theoretical studies of herbivore effects in diverse environmental contexts. Resolving ecological contingencies around animal consumptive and non-consumptive effects will improve whole-ecosystem management efforts such as restoration and rewilding.

Retention time and organic loading rate as anaerobic co-digestion key-factors for better digestate valorization practices: C and N dynamics in soils

The growing use of anaerobic co-digestion (AcoD) in processing organic waste has led to a significant digestate production. To effectively recycle digestate back into soils, it is crucial to understand how operational variables in the AcoD process influence the conversion of organic matter (OM). To address this, a combination of biochemical fractionation and various soil incubation tests were employed to assess the stability of OM in digestates generated from anaerobic continuous reactors fed with a food waste-hay mixture and operating at different hydraulic retention times (HRT) and organic loading rates (OLR). This study revealed that digester performance and operating parameters impacted carbon dynamics in soils. A decrease in the carbon mineralization in soils when increasing the HRT was reported (48 ± 4 % for 70 days compared to 59 ± 1 % for 42 days). Specific HRT and OLR values were found to be linked to carbon accessibility and complexity, confirming that longer HRT lead to higher OM removal and increased complexity in soluble OM, despite minor discrepancies in relative carbon distribution. Furthermore, comparable rates of nitrogen mineralization in soils were observed for all digestates, consistent with the accessibility of nitrogen from the particulate OM. Nevertheless, AcoD converted substrates with the potential to immobilize nitrogen in soils into fast-acting fertilizers. In summary, this study underscores the importance of controlling the AcoD performances to evaluate the suitability of digestates for sustainable agricultural practices.

Divergent regulating modes of greenhouse gas emissions at different soil layers under altered precipitation regime

How soil microbial communities regulate greenhouse gas (GHG) emissions as precipitation events are “repackaged” from many small events to a few larger events has received significant attention. Previous studies have quantified the net fluxes of GHG across the soil/atmosphere interface; however, they have not investigated GHG fluxes in soil profiles under altered precipitation regimes. This study investigated the joint regulation of topsoil and subsoil microorganisms on GHG emissions under changes in precipitation regime in an alpine meadow. Severely altered precipitation regimes have led to changes in NO3–, DOC, and soil moisture among different soil layers, which can be attributed to a combination of substrate migration and changes in carbon and nitrogen mineralization rates. Topsoil microorganisms exhibit high sensitivity to severe changes in the precipitation regime, which can affect their biomass, microbial composition, and metabolic activities. In contrast, the activity of subsoil microorganisms remains relatively stable. This was likely due to the heterogeneity of dominant regulators across soil layers. Under the severely altered precipitation regime, carbon dioxide (CO2) emissions significantly decreased by approximately 11.08%. This decrease was primarily due to a reduction in microbial respiration in the topsoil. The decrease in both topsoil and subsoil methane (CH4) uptake likely caused the inhibition of the CH4 sink from the surface (by approximately 11.60%). While a 1.75-fold increase in nitrous oxide (N2O) emissions under the severe changes in the precipitation regime might be primarily related to the increase in subsoil N2O emissions caused by the increasing abundance of subsoil denitrifiers, as well as the addition of subsoil nitrate content and soil moisture. This study revealed the divergent modes of microbial communities at different soil layers regulating GHG fluxes, which could guide the improvement of ecological models predicting GHG emissions in response to altered precipitation regimes.

Dynamics of nitrogen mineralization and fine root decomposition in sub-tropical Shorea robusta Gaertner f. forests of Central Himalaya, India

This study aimed to examine the effects of spatial and temporal variability in edaphic, and climatic attributeson soil net nitrogen mineralization rate, and to understand the pattern of fine root decomposition of dominant and co-dominant tree species, and its influence on the nutrient cycling in forest ecosystems. Study was carried out at four different sites in sub-tropical forest ecosystems of Shorea robusta, in foothills of Central Himalayan region, India. Co-dominant tree species at four sites were Mallotus philippensis (site A), Glochidion velutinum (site B), Holarrhena pubescens (site C), and Tectona grandis (site D). Buried bag technique was used for nitrogen mineralization, while fine root decomposition was determined using fine root mesh bags. Seasonal variation, soil depth, soil characteristics, and site variability, all significantly (p < 0.05) affected nitrogen mineralization rates. Fine root decomposition was significantly affected by nutrient concentration of fine roots. Total mineral nitrogen was maximum at site D (16.24 ± 0.96 μg g−1 soil), while minimum at site C (10.10 ± 0.84 μg g−1 soil). Maximum nitrogen mineralization (13.18 ± 0.18 μg g−1 month−1) was recorded during summer season at site D, while the minimum nitrogen mineralization (3.20 ± 0.46 μg g−1 month−1) was recorded during rainy season at site C. Inorganic-N and net nitrogen mineralization was relatively higher in 0–20 cm soil layer than 20–40 cm and 40–60 cm soil layer. The fine roots showed 70.61–74.82 % weight loss on completion of 365 days of decomposition process. Maximum fine root decomposition was observed in the G. velutinum, and minimum in T. grandis. A significant positive correlation (p < 0.05) was observed between root nitrogen and carbon content, and decomposition rates per month. This study concluded that the spatial and temporal variability in soil nitrogen mineralization rates and fine root decomposition optimises nutrient cycling in forest ecosystems, which can contribute to the development of sustainable forest management practices.

Drivers of plant diversity, community composition, functional traits, and soil processes along an alpine gradient in the central Chilean Andes.

High alpine regions are threatened but understudied ecosystems that harbor diverse endemic species, making them an important biome for testing the role of environmental factors in driving functional trait-mediated community assembly processes. We tested the hypothesis that plant community assembly along a climatic and elevation gradient is influenced by shifts in habitat suitability, which drive plant functional, phylogenetic, and spectral diversity. In a high mountain system (2400-3500 m) Región Metropolitana in the central Chilean Andes (33°S, 70°W). We surveyed vegetation and spectroscopic reflectance (400-2400 nm) to quantify taxonomic, phylogenetic, functional, and spectral diversity at five sites from 2400 to 3500 m elevation. We characterized soil attributes and processes by measuring water content, carbon and nitrogen, and net nitrogen mineralization rates. At high elevation, colder temperatures reduced available soil nitrogen, while at warmer, lower elevations, soil moisture was lower. Metrics of taxonomic, functional, and spectral alpha diversity peaked at mid-elevations, while phylogenetic species richness was highest at low elevation. Leaf nitrogen increased with elevation at the community level and within individual species, consistent with global patterns of increasing leaf nitrogen with colder temperatures. The increase in leaf nitrogen, coupled with shifts in taxonomic and functional diversity associated with turnover in lineages, indicate that the ability to acquire and retain nitrogen in colder temperatures may be important in plant community assembly in this range. Such environmental filters have important implications for forecasting shifts in alpine plant communities under a warming climate.

Temperature sensitivity of soil net nitrogen mineralization rates across different grassland types

Temperature sensitivity of soil net nitrogen mineralization rates across different grassland types

Responses of soil nitrogen and carbon mineralization rates to fertilization and crop rotation

Responses of soil nitrogen and carbon mineralization rates to fertilization and crop rotation

Towards a mechanistic understanding of animal-ecosystem interactions.

Research Highlight: Ferraro, K. M., Welker, L., Ward, E. B., Schmitz, O. J., & Bradford, M. A. (2023). Plant mycorrhizal associations mediate the zoogeochemical effects of calving subsidies by a forest ungulate. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.14002. Animals play large roles in ecosystem elemental cycling but predicting effects in diverse contexts remains a substantial challenge. Fundamental to progress is (1) identifying mechanisms by which animals impact nutrient distribution and cycling, and (2) disentangling how environmental context mediates the operation of alternative mechanisms. In an elegant field experiment, Ferraro etal. (2023) provide the first detailed exploration of the impact of nutrient inputs from mammalian parturition on soil functioning and the stoichiometry of plant tissues. The authors find that nitrogen from experimental additions of ungulate parturition material (natal fluids) is rapidly incorporated into microsite soil organic pools and plant tissues. They also find that soil processes (soil microbial biomass, rates of carbon mineralization, nitrogen mineralization and nitrification) and the nitrogen content of plant tissues above- and belowground are increased by addition of parturition material. Notably, the authors identify that increases in some soil processes and plant tissue nitrogen are weaker in microsites dominated by ericoid mycorrhizal plants than those dominated by ectomycorrhizal plants. These findings demonstrate that parturition depositions, a ubiquitous but overlooked mechanism of mammalian impacts on ecosystems, impact ecosystem processes and plant tissue stoichiometry. Furthermore, plant-fungal associations are a predictive axis of context dependency mediating zoogeochemical effects at fine scales. Ferraro etal.'s (2023) novel approach simultaneously advances mechanistic understanding of animal-ecosystem interactions at fine scales and facilitates prediction of ungulate effects on nutrient availability at landscape extents.