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Current Virginia nitrogen (N) fertilizer recommendations do not include site-specific estimates of N supply from cover crops (CCs) or soil organic matter (SOM). Recent research successfully predicted the contribution of N from SOM and CCs to corn (Zea mays L.) in Pennsylvania. The objective of this work was to validate the biophysical model developed in Pennsylvania under Virginia conditions and to evaluate the decomposition rates of different surface-applied CC residues and the relationship between their chemical composition and decomposition rate. For the first objective, 83 N response trials were conducted in different regions of Virginia across 9 years using a randomized complete block design with four replications. The model was able to explain 47% and 15% of variability in unfertilized corn yield (RMSE = 1.6 Mg ha-1) and economical optimum N rate (EONR) (RMSE = 30 kg N ha-1) respectively. Efforts to improve the model by adding economically unresponsive sites improved the model performance to explain 45% of the variability in EONR. For the second objective, a lab incubation was performed to compare carbon (C) and N mineralization from four different CCs {Cereal Rye (CR), Hairy vetch (HV), Crimson clover (Cc) and Rapeseed (R)} on a sandy loam soil. Destructive sampling was performed at 6 different sampling dates – 3, 7, 14, 28, 56 and 112 days. ANOVA test revealed that the effects of CC species, incubation days and their interaction had a significant effect on mass decomposed, plant biochemical composition and net N mineralization. Variation in mass loss was positively related to lignin content for all the CCs while it was moderately correlated to C:N ratio for CR and R and weakly to HV and Cc. Biomass loss and N release was highest in HV followed by Cc, R and CR. Net N mineralization was highest in HV followed by R, Cc and CR amended soils.

Anticipated permafrost thaw in upcoming decades may exert significant impacts on forest soil nitrogen (N) dynamics. The rate of soil N mineralization (Nmin) plays a crucial role in determining soil N availability. Nevertheless, our understanding remains limited regarding how biotic and abiotic factors influence the Nmin of forest soil in response to permafrost thaw. In this study, we investigated the implications of permafrost thaw on Nmin within a hemiboreal forest based on a field investigation along the degree of permafrost thaw, having monitored permafrost conditions for eight years. The results indicate that permafrost thaw markedly decreased Nmin values. Furthermore, Nmin demonstrated positive associations with soil substrates (namely, soil organic carbon and soil total nitrogen), microbial biomass carbon and nitrogen, and soil moisture content. The decline in Nmin due to permafrost thaw was primarily attributed to the diminished quality and quantity of soil substrates rather than alterations in plant community composition. Collectively, our results underscore the pivotal role of soil substrate and microbial biomass in guiding forest soil N transformations in the face of climate-induced permafrost thaw.

Anticipated permafrost thaw in upcoming decades may exert significant impacts on forest soil nitrogen (N) dynamics. The rate of soil N mineralization (Nmin) plays a crucial role in determining soil N availability. Nevertheless, our understanding remains limited regarding how biotic and abiotic factors influence the Nmin of forest soil in response to permafrost thaw. In this study, we investigated the implications of permafrost thaw on Nmin within a hemiboreal forest based on a field investigation along the degree of permafrost thaw, having monitored permafrost conditions for eight years. The results indicate that permafrost thaw markedly decreased Nmin values. Furthermore, Nmin demonstrated positive associations with soil substrates (namely, soil organic carbon and soil total nitrogen), microbial biomass carbon and nitrogen, and soil moisture content. The decline in Nmin due to permafrost thaw was primarily attributed to the diminished quality and quantity of soil substrates rather than alterations in plant community composition. Collectively, our results underscore the pivotal role of soil substrate and microbial biomass in guiding forest soil N transformations in the face of climate-induced permafrost thaw.

Snow is an important driver of ecosystem processes in cold biomes. Snow accumulation determines ground temperature, light conditions, and moisture availability during winter. It also affects the growing season’s start and end, and plant access to moisture and nutrients. Here, we review the current knowledge of the snow cover’s role for vegetation, plant-animal interactions, permafrost conditions, microbial processes, and biogeochemical cycling. We also compare studies of natural snow gradients with snow experimental manipulation studies to assess time scale difference of these approaches. The number of tundra snow studies has increased considerably in recent years, yet we still lack a comprehensive overview of how altered snow conditions will affect these ecosystems. Specifically, we found a mismatch in the timing of snowmelt when comparing studies of natural snow gradients with snow manipulations. We found that snowmelt timing achieved by snow addition and snow removal manipulations (average 7.9 days advance and 5.5 days delay, respectively) were substantially lower than the temporal variation over natural spatial gradients within a given year (mean range 56 days) or among years (mean range 32 days). Differences between snow study approaches need to be accounted for when projecting snow dynamics and their impact on ecosystems in future climates.

Digging mammals displace a large amount of soil, thereby strongly altering soil ecosystem processes such as nitrogen cycling through bioturbation. Although it is well known that bears displace a large amount of soil by digging for food and denning, there is negligible empirical evidence of the effects on soil properties. In the Shiretoko World Heritage site, we investigated the effects of brown bear digging for cicada nymphs on soil properties, such as soil water content, organic and inorganic nitrogen concentrations, and nitrogen mineralization rate that are important components of soil ecosystem function and are essential for plant growth. We compared the properties of soil recently dug by brown bears with undisturbed soil in larch plantations. We found that brown bear digging decreased soil water content, organic matter, inorganic nitrogen concentration, net mineralization rates. Our results suggest that soil digging by brown bear may reduce plant growth by decreasing soil nutrient availability, thereby diminishing the net primary production of the larch plantation at the study site.

Digging mammals displace a large amount of soil, thereby strongly altering soil ecosystem processes such as nitrogen cycling through bioturbation. Although it is well known that bears displace a large amount of soil by digging for food and denning, there is negligible empirical evidence of the effects on soil properties. In the Shiretoko World Heritage site, we investigated the effects of brown bear digging for cicada nymphs on soil properties, such as soil water content, organic and inorganic nitrogen concentrations, and nitrogen mineralization rate that are important components of soil ecosystem function and are essential for plant growth. We compared the properties of soil recently dug by brown bears with undisturbed soil in larch plantations. We found that brown bear digging decreased soil water content, organic matter, inorganic nitrogen concentration, net mineralization rates. Our results suggest that soil digging by brown bear may reduce plant growth by decreasing soil nutrient availability, thereby diminishing the net primary production of the larch plantation at the study site.

Insect herbivores play important roles in shaping many ecosystem processes, but how climate change will alter the effects of insect herbivory are poorly understood. To address this knowledge gap, we quantified for the first time how insect frass and cadavers affected leaf litter decomposition rates and nutrient release along a highly constrained 4.3°C mean annual temperature (MAT) gradient in a Hawaiian montane tropical wet forest. We constructed litterbags of standardized locally sourced leaf litter, with some amended with insect frass + cadavers to produce treatments designed to simulate ambient (Control = no amendment), moderate (Amended-Low = 2 × Control level), or severe (Amended-High = 11 × Control level) insect outbreak events. Multiple sets of these litterbags were deployed across the MAT gradient, with individual litterbags collected periodically over one year to assess how rising MAT altered the effects of insect deposits on litter decomposition rates and nitrogen (N) release. Increased MAT and insect inputs additively increased litter decomposition rates and N immobilization rates, with effects being stronger for Amended-High litterbags. However, the apparent temperature sensitivity (Q10) of litter decomposition was not clearly affected by amendments. The effects of adding insect deposits in this study operated differently than the slower litter decomposition and greater N mobilization rates often observed in experiments which use chemical fertilizers (e.g., urea, ammonium nitrate). Further research is required to understand mechanistic differences between amendment types. Potential increases in outbreak-related herbivore deposits coupled with climate warming will accelerate litter decomposition and nutrient cycling rates with short-term consequences for nutrient cycling and carbon storage in tropical montane wet forests.

Insect herbivores play important roles in shaping many ecosystem processes, but how climate change will alter the effects of insect herbivory are poorly understood. To address this knowledge gap, we quantified for the first time how insect frass and cadavers affected leaf litter decomposition rates and nutrient release along a highly constrained 4.3°C mean annual temperature (MAT) gradient in a Hawaiian montane tropical wet forest. We constructed litterbags of standardized locally sourced leaf litter, with some amended with insect frass + cadavers to produce treatments designed to simulate ambient (Control = no amendment), moderate (Amended-Low = 2 × Control level), or severe (Amended-High = 11 × Control level) insect outbreak events. Multiple sets of these litterbags were deployed across the MAT gradient, with individual litterbags collected periodically over one year to assess how rising MAT altered the effects of insect deposits on litter decomposition rates and nitrogen (N) release. Increased MAT and insect inputs additively increased litter decomposition rates and N immobilization rates, with effects being stronger for Amended-High litterbags. However, the apparent temperature sensitivity (Q10) of litter decomposition was not clearly affected by amendments. The effects of adding insect deposits in this study operated differently than the slower litter decomposition and greater N mobilization rates often observed in experiments which use chemical fertilizers (e.g., urea, ammonium nitrate). Further research is required to understand mechanistic differences between amendment types. Potential increases in outbreak-related herbivore deposits coupled with climate warming will accelerate litter decomposition and nutrient cycling rates with short-term consequences for nutrient cycling and carbon storage in tropical montane wet forests.

Insect herbivores play important roles in shaping many ecosystem processes, but how climate change will alter the effects of insect herbivory are poorly understood. To address this knowledge gap, we quantified for the first time how insect frass and cadavers affected leaf litter decomposition rates and nutrient release along a highly constrained 4.3°C mean annual temperature (MAT) gradient in a Hawaiian montane tropical wet forest. We constructed litterbags of standardized locally sourced leaf litter, with some amended with insect frass + cadavers to produce treatments designed to simulate ambient (Control = no amendment), moderate (Amended-Low = 2 × Control level), or severe (Amended-High = 11 × Control level) insect outbreak events. Multiple sets of these litterbags were deployed across the MAT gradient, with individual litterbags collected periodically over one year to assess how rising MAT altered the effects of insect deposits on litter decomposition rates and nitrogen (N) release. Increased MAT and insect inputs additively increased litter decomposition rates and N immobilization rates, with effects being stronger for Amended-High litterbags. However, the apparent temperature sensitivity (Q10) of litter decomposition was not clearly affected by amendments. The effects of adding insect deposits in this study operated differently than the slower litter decomposition and greater N mobilization rates often observed in experiments which use chemical fertilizers (e.g., urea, ammonium nitrate). Further research is required to understand mechanistic differences between amendment types. Potential increases in outbreak-related herbivore deposits coupled with climate warming will accelerate litter decomposition and nutrient cycling rates with short-term consequences for nutrient cycling and carbon storage in tropical montane wet forests.

Digging mammals displace a large amount of soil, thereby strongly altering soil ecosystem processes such as nitrogen cycling through bioturbation. Although it is well known that bears displace a large amount of soil by digging for food and denning, there is negligible empirical evidence of the effects on soil properties. In the Shiretoko World Heritage site, we investigated the effects of brown bear digging for cicada nymphs on soil properties, such as soil water content, organic and inorganic nitrogen concentrations, and nitrogen mineralization rate that are important components of soil ecosystem function and are essential for plant growth. We compared the properties of soil recently dug by brown bears with undisturbed soil in larch plantations. We found that brown bear digging decreased soil water content, organic matter, inorganic nitrogen concentration, net mineralization rates. Our results suggest that soil digging by brown bear may reduce plant growth by decreasing soil nutrient availability, thereby diminishing the net primary production of the larch plantation at the study site.

Digging mammals displace a large amount of soil, thereby strongly altering soil ecosystem processes such as nitrogen cycling through bioturbation. Although it is well known that bears displace a large amount of soil by digging for food and denning, there is negligible empirical evidence of the effects on soil properties. In the Shiretoko World Heritage site, we investigated the effects of brown bear digging for cicada nymphs on soil properties, such as soil water content, organic and inorganic nitrogen concentrations, and nitrogen mineralization rate that are important components of soil ecosystem function and are essential for plant growth. We compared the properties of soil recently dug by brown bears with undisturbed soil in larch plantations. We found that brown bear digging decreased soil water content, organic matter, inorganic nitrogen concentration, net mineralization rates. Our results suggest that soil digging by brown bear may reduce plant growth by decreasing soil nutrient availability, thereby diminishing the net primary production of the larch plantation at the study site.

Insect herbivores play important roles in shaping many ecosystem processes, but how climate change will alter the effects of insect herbivory are poorly understood. To address this knowledge gap, we quantified for the first time how insect frass and cadavers affected leaf litter decomposition rates and nutrient release along a highly constrained 4.3°C mean annual temperature (MAT) gradient in a Hawaiian montane tropical wet forest. We constructed litterbags of standardized locally sourced leaf litter, with some amended with insect frass + cadavers to produce treatments designed to simulate ambient (Control = no amendment), moderate (Amended-Low = 2 × Control level), or severe (Amended-High = 11 × Control level) insect outbreak events. Multiple sets of these litterbags were deployed across the MAT gradient, with individual litterbags collected periodically over one year to assess how rising MAT altered the effects of insect deposits on litter decomposition rates and nitrogen (N) release. Increased MAT and insect inputs additively increased litter decomposition rates and N immobilization rates, with effects being stronger for Amended-High litterbags. However, the apparent temperature sensitivity (Q10) of litter decomposition was not clearly affected by amendments. The effects of adding insect deposits in this study operated differently than the slower litter decomposition and greater N mobilization rates often observed in experiments which use chemical fertilizers (e.g., urea, ammonium nitrate). Further research is required to understand mechanistic differences between amendment types. Potential increases in outbreak-related herbivore deposits coupled with climate warming will accelerate litter decomposition and nutrient cycling rates with short-term consequences for nutrient cycling and carbon storage in tropical montane wet forests.

Insect herbivores play important roles in shaping many ecosystem processes, but how climate change will alter the effects of insect herbivory are poorly understood. To address this knowledge gap, we quantified for the first time how insect frass and cadavers affected leaf litter decomposition rates and nutrient release along a highly constrained 4.3°C mean annual temperature (MAT) gradient in a Hawaiian montane tropical wet forest. We constructed litterbags of standardized locally sourced leaf litter, with some amended with insect frass + cadavers to produce treatments designed to simulate ambient (Control = no amendment), moderate (Amended-Low = 2 × Control level), or severe (Amended-High = 11 × Control level) insect outbreak events. Multiple sets of these litterbags were deployed across the MAT gradient, with individual litterbags collected periodically over one year to assess how rising MAT altered the effects of insect deposits on litter decomposition rates and nitrogen (N) release. Increased MAT and insect inputs additively increased litter decomposition rates and N immobilization rates, with effects being stronger for Amended-High litterbags. However, the apparent temperature sensitivity (Q10) of litter decomposition was not clearly affected by amendments. The effects of adding insect deposits in this study operated differently than the slower litter decomposition and greater N mobilization rates often observed in experiments which use chemical fertilizers (e.g., urea, ammonium nitrate). Further research is required to understand mechanistic differences between amendment types. Potential increases in outbreak-related herbivore deposits coupled with climate warming will accelerate litter decomposition and nutrient cycling rates with short-term consequences for nutrient cycling and carbon storage in tropical montane wet forests.

Predicting nitrogen mineralization has been the focus of many agricultural researchers for decades. This project was designed to investigate the soil properties that influence potential nitrogen mineralization in the northern Central Valley of California. A total of seventeen sites featuring annual cropping systems with a variety of common crops such as corn (Zea mays), watermelon (Citrullus lanatas), safflower (Carthamus tinctorius), sunflower (Helianthus annuus), sorghum (Sorghum bicolor), processing tomatoes (Solanum lycopersicum), and cotton (Gossypium hirsutum) were included, spanning from Colusa to Tulare Counties. We studied nitrogen mineralization using both field trials as well as laboratory incubations of undisturbed soil cores, in conjunction with continuous soil sampling of those sites every 5-6 weeks throughout the growing season to capture seasonal nitrogen turnover. Those soils were characterized and the results statistically analyzed, and a model was developed that determined particulate organic nitrogen and silt content as the best predictors of nitrogen mineralization in the undisturbed soil cores (adjusted-R2 = 0.65, P < 0.05). Over 70% of the variability in seasonal nitrogen mineralization at optimal soil moisture was described by only particulate organic nitrogen, while soil moisture was confirmed as a major controlling variable in determining nitrogen mineralization. Furthermore, even at the lowest soil moisture contents, nitrogen mineralization continued. Two separate smaller studies were also performed to determine crop residue effects on nitrogen availability. One included a field trial using seven different crop residues followed by a laboratory incubation of undisturbed soil cores, and the other included a laboratory incubation with two different residues at varying residue and soil moisture content. Seven different common crop residues (namely corn (Zea mays), watermelon (Citrullus lanatas), safflower (Carthamus tinctorius), sunflower

Context: The population increase and the demand for food generate greater demands on productivity, which stimulates the use of inorganic fertilizers as a common practice in agricultural systems, thus generating potential risks of contamination by nutrient leaching, in addition to high costs that can affect the profitability of production systems. The application of organic materials from the composting of organic substrates is a common source of fertilization in clean, organic production systems with lower costs. Method: This study evaluated the effect of fertilization with an Organic Amendment (EO) from the composting of Municipal Biowaste-BW mixed with cachaça on the mineralization of nitrogen (Nmineralized) in an acidic soil through six treatments: three controls (T1: 100% soil; T2: 100% EO; T3: 100% ureainorganic fertilization: F) and three EO( %):F( %) proportions (T4: 50-50, T5: 75-25, T6: 25-75) during an incubation period of 16 weeks. Results: Four mineralization models were applied (Stanford & Smith, Broadbent, linear, and polynomial Exponential), and it was found that T4 allowed to achieve a contribution of Nmineralized (12.546,39 mg/kg) similar to inorganic fertilization (T3: 13.931,05 mg/kg); the Broadbent (R2 >0,98) and linear (R2 >0,90) models achieved the best fit. Conclusions: This partial inorganic fertilizer replacement strategy can achieve up to 50% inorganic fertilizer replacement., Contexto: El incremento poblacional y la demanda de alimentos generan mayores demandas en la productividad, lo que estimula el uso de fertilizantes inorgánicos como una práctica habitual en los sistemas agrícolas, generando potenciales riesgos de contaminación por lixiviación de nutrientes, además de altos costos que pueden afectar la rentabilidad de los sistemas productivos. La aplicación de materiales orgánicos procedentes del compostaje de sustratos orgánicos es una fuente de fertilización común en sistemas de producción limpia, orgánica y con menores costos. Método: En este estudio se evaluó el efecto de la fertilización con una enmienda orgánica (EO) procedente del compostaje de biorresiduos de origen municipal (BOM) mezclados con cachaza, sobre la mineralización del nitrógeno (Nmineralizado) de un suelo ácido, evaluando seis tratamientos (tres controles: T1: 100% suelo; T2: 100% EO; T3: 100% urea-fertilización inorgánica: F) y 3 proporciones EO ( %): F ( %) (T4: 50-50, T5: 75-25, T6: 25-75) en un periodo de incubación de 16 semanas. Resultados: Se aplicaron los modelos de mineralización de Stanford y Smith, Broadbent, Lineal y Polinomial-Exponencial, encontrándose que T4 permitió alcanzar un aporte de Nmineralizado (12.546,39 mg/kg), el cual es un valor muy cercano al resultado obtenido por fertilización inorgánica (T3: 13.931,05 mg/kg); los modelos de Broadbent (R2 >0,98) y Lineal (R2 >0,90) alcanzaron los mejores ajustes. Conclusiones: Esta estrategia de reemplazo parcial del fertilizante inorgánico puede lograr hasta un 50% de reemplazo del fertilizante inorgánico.

Predicting nitrogen mineralization has been the focus of many agricultural researchers for decades. This project was designed to investigate the soil properties that influence potential nitrogen mineralization in the northern Central Valley of California. A total of seventeen sites featuring annual cropping systems with a variety of common crops such as corn (Zea mays), watermelon (Citrullus lanatas), safflower (Carthamus tinctorius), sunflower (Helianthus annuus), sorghum (Sorghum bicolor), processing tomatoes (Solanum lycopersicum), and cotton (Gossypium hirsutum) were included, spanning from Colusa to Tulare Counties. We studied nitrogen mineralization using both field trials as well as laboratory incubations of undisturbed soil cores, in conjunction with continuous soil sampling of those sites every 5-6 weeks throughout the growing season to capture seasonal nitrogen turnover. Those soils were characterized and the results statistically analyzed, and a model was developed that determined particulate organic nitrogen and silt content as the best predictors of nitrogen mineralization in the undisturbed soil cores (adjusted-R2 = 0.65, P < 0.05). Over 70% of the variability in seasonal nitrogen mineralization at optimal soil moisture was described by only particulate organic nitrogen, while soil moisture was confirmed as a major controlling variable in determining nitrogen mineralization. Furthermore, even at the lowest soil moisture contents, nitrogen mineralization continued. Two separate smaller studies were also performed to determine crop residue effects on nitrogen availability. One included a field trial using seven different crop residues followed by a laboratory incubation of undisturbed soil cores, and the other included a laboratory incubation with two different residues at varying residue and soil moisture content. Seven different common crop residues (namely corn (Zea mays), watermelon (Citrullus lanatas), safflower (Carthamus tinctorius), sunflower

Context: The population increase and the demand for food generate greater demands on productivity, which stimulates the use of inorganic fertilizers as a common practice in agricultural systems, thus generating potential risks of contamination by nutrient leaching, in addition to high costs that can affect the profitability of production systems. The application of organic materials from the composting of organic substrates is a common source of fertilization in clean, organic production systems with lower costs. Method: This study evaluated the effect of fertilization with an Organic Amendment (EO) from the composting of Municipal Biowaste-BW mixed with cachaça on the mineralization of nitrogen (Nmineralized) in an acidic soil through six treatments: three controls (T1: 100% soil; T2: 100% EO; T3: 100% ureainorganic fertilization: F) and three EO( %):F( %) proportions (T4: 50-50, T5: 75-25, T6: 25-75) during an incubation period of 16 weeks. Results: Four mineralization models were applied (Stanford & Smith, Broadbent, linear, and polynomial Exponential), and it was found that T4 allowed to achieve a contribution of Nmineralized (12.546,39 mg/kg) similar to inorganic fertilization (T3: 13.931,05 mg/kg); the Broadbent (R2 >0,98) and linear (R2 >0,90) models achieved the best fit. Conclusions: This partial inorganic fertilizer replacement strategy can achieve up to 50% inorganic fertilizer replacement., Contexto: El incremento poblacional y la demanda de alimentos generan mayores demandas en la productividad, lo que estimula el uso de fertilizantes inorgánicos como una práctica habitual en los sistemas agrícolas, generando potenciales riesgos de contaminación por lixiviación de nutrientes, además de altos costos que pueden afectar la rentabilidad de los sistemas productivos. La aplicación de materiales orgánicos procedentes del compostaje de sustratos orgánicos es una fuente de fertilización común en sistemas de producción limpia, orgánica y con menores costos. Método: En este estudio se evaluó el efecto de la fertilización con una enmienda orgánica (EO) procedente del compostaje de biorresiduos de origen municipal (BOM) mezclados con cachaza, sobre la mineralización del nitrógeno (Nmineralizado) de un suelo ácido, evaluando seis tratamientos (tres controles: T1: 100% suelo; T2: 100% EO; T3: 100% urea-fertilización inorgánica: F) y 3 proporciones EO ( %): F ( %) (T4: 50-50, T5: 75-25, T6: 25-75) en un periodo de incubación de 16 semanas. Resultados: Se aplicaron los modelos de mineralización de Stanford y Smith, Broadbent, Lineal y Polinomial-Exponencial, encontrándose que T4 permitió alcanzar un aporte de Nmineralizado (12.546,39 mg/kg), el cual es un valor muy cercano al resultado obtenido por fertilización inorgánica (T3: 13.931,05 mg/kg); los modelos de Broadbent (R2 >0,98) y Lineal (R2 >0,90) alcanzaron los mejores ajustes. Conclusiones: Esta estrategia de reemplazo parcial del fertilizante inorgánico puede lograr hasta un 50% de reemplazo del fertilizante inorgánico.

Mechanistic models are useful tools for understanding and taking account of the complex, dynamic processes such as carbon (C) and nitrogen (N) turnover in soil and crop growth. In this study, the EU-Rotate_N model was first calibrated with measured C and N mineralization from nine potential fertilizer resources decomposing at controlled soil temperature and moisture. The materials included seaweeds, wastes from the food industry, food waste anaerobically digested for biogas production, and animal manure. Then the model's ability to predict soil and crop data in a field trial with broccoli and potato was evaluated. Except for seaweed, up to 68% of added C and 54–86% of added N was mineralized within 60 days under controlled conditions. The organic resources fell into three groups: seaweed, high-N industrial wastes, and materials with high initial content of mineral N. EU-Rotate_N was successfully calibrated for the materials of industrial origin, whereas seaweeds, anaerobically digested food waste and sheep manure were challenging. The model satisfactorily predicted dry matter (DM) and N contents (root mean square; RMSE: 0.11–0.32) of the above-ground part of broccoli fertilized with anaerobically digested food waste, shrimp shell pellets, sheep manure and mineral fertilizers but not algal meal. After adjusting critical %N for optimum growth, potato DM and N contents were also predicted quite well (RMSE: 0.08–0.44). In conclusion, the model can be used as a learning and decision support tool when using organic materials as N fertilizer, preferably in combination with other models and information from the literature.

Aims: Microorganisms play a dichotomous role in the soil nitrogen cycle through mineralization and immobilization. We aimed to understand how nitrogen availability modifies the effect of microorganisms on plant growth. We hypothesized that soil microorganisms would increase plant biomass following amendment with a substrate rich in organic nitrogen (net mineralization), be neutral when adding inorganic nitrogen, and decrease biomass when adding organic nitrogen-limited substrate (nitrogen competition). Method: Barley (Hordeum vulgare L., cv. Evergreen) was exposed to either i) limited, organically bound nitrogen, ii) organically bound nitrogen or iii) inorganic nitrogen. In these amendments, we assessed the differences in plant biomass and physiology between plants with or without soil microbiome addition. Results: The soil microbiome reduced shoot biomass equally (12%) across all nitrogen amendments. However, nitrogen availability did modulate the effect of the soil microbiome on plant physiological parameters associated with nitrogen deficiency. Conclusions: The results indicate that the net negative effect of complex microbiomes on shoot biomass is independent of nitrogen availability. Thus, microbiome addition was deleterious to biomass even in a nutrient-stress-free environment. We suggest that strategies for improving plant growth through manipulation of microorganisms should not exclusively focus on beneficial and pathogenic microorganisms, but also include minimizing plant metabolic costs of microbiome interactions.

Mechanistic models are useful tools for understanding and taking account of the complex, dynamic processes such as carbon (C) and nitrogen (N) turnover in soil and crop growth. In this study, the EU-Rotate_N model was first calibrated with measured C and N mineralization from nine potential fertilizer resources decomposing at controlled soil temperature and moisture. The materials included seaweeds, wastes from the food industry, food waste anaerobically digested for biogas production, and animal manure. Then the model's ability to predict soil and crop data in a field trial with broccoli and potato was evaluated. Except for seaweed, up to 68% of added C and 54–86% of added N was mineralized within 60 days under controlled conditions. The organic resources fell into three groups: seaweed, high-N industrial wastes, and materials with high initial content of mineral N. EU-Rotate_N was successfully calibrated for the materials of industrial origin, whereas seaweeds, anaerobically digested food waste and sheep manure were challenging. The model satisfactorily predicted dry matter (DM) and N contents (root mean square; RMSE: 0.11–0.32) of the above-ground part of broccoli fertilized with anaerobically digested food waste, shrimp shell pellets, sheep manure and mineral fertilizers but not algal meal. After adjusting critical %N for optimum growth, potato DM and N contents were also predicted quite well (RMSE: 0.08–0.44). In conclusion, the model can be used as a learning and decision support tool when using organic materials as N fertilizer, preferably in combination with other models and information from the literature.

Intensive livestock production systems, such as cattle feedlots, play an important role in meeting the increasing global demand for animal products, driven by a growing population and increasing affluence. These intensive systems account for a significant proportion (~39%) of global atmospheric ammonia (NH3), which is released from the large amounts of manure generated. In cattle feedlots, the loss of NH3 represents about 75% of the excreted nitrogen (N) in the manure and this has important implications for environmental pollution. Consideration of management strategies to reduce this loss provides potential to obtain N enriched manures that can be used as fertilizer. A number of mitigation techniques have been shown to reduce NH3 loss from manure. These include: acidifying agents and urease inhibitors (both requiring frequent reapplication), dietary manipulation (can affect animal productivity) and manure compaction and covering (only applicable to stockpiled manure). Lignite (brown coal) has a demonstrated capacity to suppress NH3 emission from manure by 30-66% and is seen as a more effective, practical and potentially long lasting option. Lignite’s ability to effectively reduce the loss of NH3 from manure has been credited to its pH, cation exchange capacity (CEC), pH buffer capacity and labile carbon (C) content. However, we do not fully understand what the actual capacity for N retention by lignite is, or the main mechanisms by which lignite retains N, and how these are influenced by the properties of the lignite and changes in the environmental conditions when lignite is mixed with other materials (such as manure). Also, the impact of lignite on the quality of the manure during deposition, storage, processing (such as composting) and land application, has not been studied. The objectives of this study were to: (i) characterize different lignite materials for their capacity for nitrogen retention, and to understand the mechanisms of N retention; (ii) determine

The extent to which the increasingly frequent episodes of drought-induced tree decline and mortality could alter key soil biogeochemical cycles is unclear. Understanding this connection between tree decline and mortality and soils is important because forested ecosystems serve as important long-term sinks for carbon (C) and essential nutrients (e.g., nitrogen and phosphorus). In order to fill in this knowledge gap, we conducted a study on 13 sites distributed across the Spanish Iberian Peninsula where the dominant tree species was the Mediterranean evergreen Holm oak (Quercus ilex L. subsp. ballota [Desf.] Samp), a species that has shown important drought-induced crown defoliation and mortality rates in recent decades. Our study covered different climatic, soil, land-use type (forests, dehesas, and open woodlands), and crown defoliation (healthy, affected, and dead Holm oaks) gradients that characterize this species distribution within the Spanish Iberian Peninsula. Specifically, the soil C and nutrient content (nitrogen, N; phosphorus, P; magnesium, Mg), several functional parameters (heterotrophic respiration (RH); N mineralization (i.e., N ammonification, Ramm; and N nitrification, Rnit)), and relative abundances of key microbial soil functional groups (nitrifiers and ectomycorrhizal fungi (ECM)) were studied. Our results showed that aside from the potential effects associated with the climatic gradient, Holm oak decline and mortality resulted in soil stoichiometric imbalances triggered by net losses of essential oligonutrients (e.g., Mg) and the accumulation of very mobile forms of nitrogen (NO3- - N) and available phosphorus (Av P). Changes in the abundance of key microbial soil functional groups (nitrifiers and ECM) co-occurred with observed nitrate and available P accumulation. Therefore, we conclude that the potential vulnerability of soil C and nutrient stocks to ongoing changes in climate may strongly depend on tree vulnerability to climate change, its eff

In the face of global climate change there is an increasing demand for biofuel, which exerts pressure on production and thus management of biofuel plantations. The intensification of whole-tree harvest from biofuel plantations increases export of nutrients. Returning ash from biofuel combustion to the forest plantations can amend the soil nutrient status and thus facilitate sustainable forest management. However, ash affects the forest floor decomposer food web, potentially changing organic matter turnover, carbon sequestration and nitrogen availability. Our aim was to examine the response of decomposer organisms, food web structure and nitrogen mineralization function after ash application. In a coniferous forest plantation amended with 0, 3, 4.5 or 6 t ash ha− 1, we sampled in several depths of the forest floor for key organisms of the decomposer food web (fungal biomass, 0–12 cm; bacteria, protozoa, nematodes and enchytraeids, 0–3 cm and 3–6 cm; microarthropods and earthworms, 0–5 cm), 2, 14 and 26 months after ash application. We used structural equation modelling (SEM) to detangle the direct and indirect effects of ash application on organisms in the decomposer food web and on nitrogen availability. We found that ash increased the abundance of bacteria and protozoa, as well as the inorganic nitrogen pool at 0–3 cm depth, whereas the effect of ash was negligible at 3–6 cm depth. Earthworm abundance increased, whereas enchytraeid abundance decreased 2 years after ash application. The structural equation modelling showed that ash application stimulated the bacterial feeding pathway and increased nitrogen mineralization. Contrary, ash had a negative effect on fungal biomass at the first sampling, however, this effect subdued over time. Our results suggest that as the soil decomposer food web is resilient to ash application, this is a viable option for sustainable management of biofuel plantations.

The extent to which the increasingly frequent episodes of drought-induced tree decline and mortality could alter key soil biogeochemical cycles is unclear. Understanding this connection between tree decline and mortality and soils is important because forested ecosystems serve as important long-term sinks for carbon (C) and essential nutrients (e.g., nitrogen and phosphorus). In order to fill in this knowledge gap, we conducted a study on 13 sites distributed across the Spanish Iberian Peninsula where the dominant tree species was the Mediterranean evergreen Holm oak (Quercus ilex L. subsp. ballota [Desf.] Samp), a species that has shown important drought-induced crown defoliation and mortality rates in recent decades. Our study covered different climatic, soil, land-use type (forests, dehesas, and open woodlands), and crown defoliation (healthy, affected, and dead Holm oaks) gradients that characterize this species distribution within the Spanish Iberian Peninsula. Specifically, the soil C and nutrient content (nitrogen, N; phosphorus, P; magnesium, Mg), several functional parameters (heterotrophic respiration (R); N mineralization (i.e., N ammonification, R; and N nitrification, R)), and relative abundances of key microbial soil functional groups (nitrifiers and ectomycorrhizal fungi (ECM)) were studied. Our results showed that aside from the potential effects associated with the climatic gradient, Holm oak decline and mortality resulted in soil stoichiometric imbalances triggered by net losses of essential oligonutrients (e.g., Mg) and the accumulation of very mobile forms of nitrogen (NO - N) and available phosphorus (Av P). Changes in the abundance of key microbial soil functional groups (nitrifiers and ECM) co-occurred with observed nitrate and available P accumulation. Therefore, we conclude that the potential vulnerability of soil C and nutrient stocks to ongoing changes in climate may strongly depend on tree vulnerability to climate change, its effect on so

Biosolids have been used as soil conditioners and fertilizers in agriculture and mine land reclamation, but application of Exceptional Quality (EQ) biosolids to rehabilitate anthropogenic soils for urban agriculture is recent and requires greater study to ensure their appropriate use. The objectives were: 1) to quantify plant available nitrogen (PAN) of new EQ biosolids in a greenhouse bioassay; 2) to quantify PAN of EQ biosolids applied to an urban degraded subsoil via tall fescue N fertilizer equivalency, and compare field results to laboratory tests; 3) to investigate EQ biosolids and inorganic fertilizer effects on urban soil properties, vegetable yields, and potential N and phosphorus (P) loss. Biosolids evaluated were products of thermal hydrolysis plus anaerobic digestion (BLOOM), blending with woody mulch (BM) and sand/sawdust (BSS), composting (LBC), and heat-drying (OCB). Organic N mineralization of new blended biosolids products ranged between 20-25% in the greenhouse bioassay. Products BLOOM, BM, and OCB had the highest organic N mineralization as estimated by the 7-day anaerobic incubation, and this test and soil nitrate-N had the highest correlations with tall fescue N uptake (r=0.49 and r=0.505, respectively). We conducted a two-year field study with four growing seasons (fall 2016-2017 and summer 2017-2018) in an urban disturbed subsoil where EQ biosolids were applied seasonally at agronomic N rates, and yearly at reclamation rates (5x agronomic N). Cabbage yields were greater with reclamation rates (~3.0 kg m-2) and bell pepper yields were greater with BLOOM reclamation rate (~1.0 kg m-2) than with the inorganic fertilizer (1.0 kg m-2 and 0.2 kg m-2, respectively) during second year growing seasons. Soil carbon (C) accumulation (%C remaining in the soil) two years after biosolids additions ranged between 37 to 84%. Soil N availability and mineralization were limited most likely due to lack of residual soil C and N, and high clay content. Nitrogen le

Loss of nitrogen (N) from dairy manure during storage is an issue of economic, environmental, and social concern for farming communities. The lost N 1) decreases the value of manure as a fertilizer and is an economic loss because supplemental inorganic N fertilizer is purchased to meet N needs on farms; 2) produces the potential pollution for water and air systems, thereby damaging the associated ecosystems; 3) causes challenges to human health. Thus, it is vital to manage and use N in an efficient and eco-friendly manner. N mineralization is a pathway in the N cycle, which converts organic N to inorganic N that is more susceptible to loss. The objective of this study was to conduct lab-scale experiments to assess the effects of temperature, manure solids content, using manure seed and autoclave sterilization operation at the start of storage, and storage time on the N mineralization and the associated microbial community during the storage of liquid dairy manure. Manure scrapped from the barn floor of a commercial dairy farm and diluted to make experimental stocks with high (46 to 78 g/L) and low (19 to 36 g/L) total solids (TS), to simulate what is typically transported to the manure storage pit was used. The manure was incubated in the laboratory at three temperatures (10, 20, and 30°C) for two storage periods (60 and 180 days). Manure samples were taken at different storage time for analyses. The results showed that temperature and using sterilization operation at the start of storage had significant effects on N mineralization for both storage periods (p < 0.05). The highest N mineralization rate occurred at 30℃, which rate constant (k) was 0.096 week-1. While, the lowest N mineralization occurred at 10℃, and its corresponding k was 0.013 week-1. The concentrations of mineralized N (Nm) with non-sterilized (R) manure were significantly higher than that with sterilized (R0) manure (p < 0.05). Compared to that with high TS (H) manure, the concentrations of Nm wer

Biosolids have been used as soil conditioners and fertilizers in agriculture and mine land reclamation, but application of Exceptional Quality (EQ) biosolids to rehabilitate anthropogenic soils for urban agriculture is recent and requires greater study to ensure their appropriate use. The objectives were: 1) to quantify plant available nitrogen (PAN) of new EQ biosolids in a greenhouse bioassay; 2) to quantify PAN of EQ biosolids applied to an urban degraded subsoil via tall fescue N fertilizer equivalency, and compare field results to laboratory tests; 3) to investigate EQ biosolids and inorganic fertilizer effects on urban soil properties, vegetable yields, and potential N and phosphorus (P) loss. Biosolids evaluated were products of thermal hydrolysis plus anaerobic digestion (BLOOM), blending with woody mulch (BM) and sand/sawdust (BSS), composting (LBC), and heat-drying (OCB). Organic N mineralization of new blended biosolids products ranged between 20-25% in the greenhouse bioassay. Products BLOOM, BM, and OCB had the highest organic N mineralization as estimated by the 7-day anaerobic incubation, and this test and soil nitrate-N had the highest correlations with tall fescue N uptake (r=0.49 and r=0.505, respectively). We conducted a two-year field study with four growing seasons (fall 2016-2017 and summer 2017-2018) in an urban disturbed subsoil where EQ biosolids were applied seasonally at agronomic N rates, and yearly at reclamation rates (5x agronomic N). Cabbage yields were greater with reclamation rates (~3.0 kg m-2) and bell pepper yields were greater with BLOOM reclamation rate (~1.0 kg m-2) than with the inorganic fertilizer (1.0 kg m-2 and 0.2 kg m-2, respectively) during second year growing seasons. Soil carbon (C) accumulation (%C remaining in the soil) two years after biosolids additions ranged between 37 to 84%. Soil N availability and mineralization were limited most likely due to lack of residual soil C and N, and high clay content. Nitrogen le

Biosolids are rich in nutrients and organic matter, and are known to improve and maintain productive soils and stimulate plant growth. D.C. Water’s new Class A biosolids product, Bloom, was evaluated for its impact on plant and soil health. Using molecular tools, Bloom was examined for the presence of functional genes that would indicate the presence of microbes capable of improving plant growth (i.e.nitrifiers, N- fixers). Using greenhouse and laboratory experiments, we determined Bloom’s effect on plant growth, carbon and nitrogen cycling. Bloom has both nitrifying and N-fixing microbes, but their gene numbers vary depending on the stage of production. We show that plants, such as cucumber and tomato, grown in soil amended with Bloom produce more leaves and stems and have higher aboveground biomass, and soybeans produced more bean pods. Lastly, we found that N-mineralization is higher in soil amended with Bloom, even after one growing season, providing increased nutrients.

Arctic plant productivity is often limited by low soil N availability. This has been attributed to slow breakdown of N-containing polymers in litter and soil organic matter (SOM) into smaller, available units, and to shallow plant rooting constrained by permafrost and high soil moisture. Using N-15 pool dilution assays, we here quantified gross amino acid and ammonium production rates in 97 active layer samples from four sites across the Siberian Arctic. We found that amino acid production in organic layers alone exceeded literature-based estimates of maximum plant N uptake 17-fold and therefore reject the hypothesis that arctic plant N limitation results from slow SOM breakdown. High microbial N use efficiency in organic layers rather suggests strong competition of microorganisms and plants in the dominant rooting zone. Deeper horizons showed lower amino acid production rates per volume, but also lower microbial N use efficiency. Permafrost thaw together with soil drainage might facilitate deeper plant rooting and uptake of previously inaccessible subsoil N, and thereby promote plant productivity in arctic ecosystems. We conclude that changes in microbial decomposer activity, microbial N utilization and plant root density with soil depth interactively control N availability for plants in the Arctic.

Soil N availability for plants and microorganisms depends on the breakdown of soil polymers such as proteins into smaller, assimilable units by microbial extracellular enzymes. Changing climatic conditions are expected to alter protein depolymerization rates over the next decades, and thereby affect the potential for plant productivity. We here tested the effect of increased CO2 concentration, temperature, and drought frequency on gross rates of protein depolymerization, N mineralization, microbial amino acid and ammonium uptake using N-15 pool dilution assays. Soils were sampled in fall 2013 from the multifactorial climate change experiment CLIMAITE that simulates increased CO2 concentration, temperature, and drought frequency in a fully factorial design in a temperate heathland. Eight years after treatment initiation, we found no significant effect of any climate manipulation treatment, alone or in combination, on protein depolymerization rates. Nitrogen mineralization, amino acid and ammonium uptake showed no significant individual treatment effects, but significant interactive effects of warming and drought. Combined effects of all three treatments were not significant for any of the measured parameters. Our findings therefore do not suggest an accelerated release of amino acids from soil proteins in a future climate at this site that could sustain higher plant productivity.

The use of location-specific and underutilized organic residues (OR) as soil amendments in small-holder agro-ecosystems is promising. Six ORs (Leucaena leucocephala, Centrosema pubescens, Gliricidia sepium, Pueraria phaseoloides, Azadirachta indica, and Theobroma cacao) were amended to three tropical soils each at 24 mg g−1 dry soil in 120-day incubation study to estimate their nitrogen (N) mineralization and microbial biomass carbon (C) dynamics. Inorganic N contents varied among ORs, soil type and incubation days. Regardless of soil type, Gliricidia had the highest inorganic N among the studied ORs. Mineralization rate of 1.4 to 1.5 mg N kg−1 soil day−1 was observed for Lego and Tec soils, respectively, and was twice higher than Nya soil. However, Nya soil released higher inorganic N than Tec and Lego soils, implying high N mineralization efficiency in the former. Consistent soil pH increase was respectively observed for Theobroma and Pueraria treatments in all soils. Moreover, Theobroma and Pueraria amendments showed the highest soil microbial biomass C (MBC) at the end of the incubation. The assessed soil properties likely affected by the dominant edaphic factors and management influenced differences in MBC and dissolved organic carbon (DOC) while OR quality indices controlled N mineralization. Thus, we conclude that soil properties and OR type are important factors for optimal utilization of organic resources., Japan Society for the Promotion of Science, Peer Reviewed

Arctic plant productivity is often limited by low soil N availability. This has been attributed to slow breakdown of N-containing polymers in litter and soil organic matter (SOM) into smaller, available units, and to shallow plant rooting constrained by permafrost and high soil moisture. Using N-15 pool dilution assays, we here quantified gross amino acid and ammonium production rates in 97 active layer samples from four sites across the Siberian Arctic. We found that amino acid production in organic layers alone exceeded literature-based estimates of maximum plant N uptake 17-fold and therefore reject the hypothesis that arctic plant N limitation results from slow SOM breakdown. High microbial N use efficiency in organic layers rather suggests strong competition of microorganisms and plants in the dominant rooting zone. Deeper horizons showed lower amino acid production rates per volume, but also lower microbial N use efficiency. Permafrost thaw together with soil drainage might facilitate deeper plant rooting and uptake of previously inaccessible subsoil N, and thereby promote plant productivity in arctic ecosystems. We conclude that changes in microbial decomposer activity, microbial N utilization and plant root density with soil depth interactively control N availability for plants in the Arctic.

The use of location-specific and underutilized organic residues (OR) as soil amendments in small-holder agro-ecosystems is promising. Six ORs (Leucaena leucocephala, Centrosema pubescens, Gliricidia sepium, Pueraria phaseoloides, Azadirachta indica, and Theobroma cacao) were amended to three tropical soils each at 24 mg g−1 dry soil in 120-day incubation study to estimate their nitrogen (N) mineralization and microbial biomass carbon (C) dynamics. Inorganic N contents varied among ORs, soil type and incubation days. Regardless of soil type, Gliricidia had the highest inorganic N among the studied ORs. Mineralization rate of 1.4 to 1.5 mg N kg−1 soil day−1 was observed for Lego and Tec soils, respectively, and was twice higher than Nya soil. However, Nya soil released higher inorganic N than Tec and Lego soils, implying high N mineralization efficiency in the former. Consistent soil pH increase was respectively observed for Theobroma and Pueraria treatments in all soils. Moreover, Theobroma and Pueraria amendments showed the highest soil microbial biomass C (MBC) at the end of the incubation. The assessed soil properties likely affected by the dominant edaphic factors and management influenced differences in MBC and dissolved organic carbon (DOC) while OR quality indices controlled N mineralization. Thus, we conclude that soil properties and OR type are important factors for optimal utilization of organic resources., Japan Society for the Promotion of Science, Peer Reviewed

Le réchauffement climatique et l’augmentation des dépositions atmosphériques d’azote (N) associés aux activités anthropiques pourraient avoir un impact sur le cycle biogéochimique de l’N en régions boréales, ce qui pourrait avoir des conséquences sur l’écologie forestière et la croissance des arbres. En autres, ces changements environnementaux ont le potentiel d’affecter la minéralisation nette et brute de l’N, mais aucune étude n’a vérifié cette possibilité en forêt boréale via des expérimentions à plus long terme. Ainsi, l’objectif de l’expérience était d’évaluer les effets d’un réchauffement du sol et de l’augmentation des dépositions d’N sur les taux de minéralisation nette et brute de l’N des sols boréaux, et ce, après huit et neuf ans de traitements. L’étude a été conduite dans deux peuplements d’épinette noire mature situés dans le domaine bioclimatique de la sapinière à bouleau blanc du Québec. Pendant neuf ans (2008–2016), des câbles chauffants (enterrés) ont été utilisés pour augmenter la température du sol de +4 °C d’avril à juillet et une pluie artificielle a été appliquée au-dessus de la canopée de juin à septembre afin de simuler une augmentation de 50% des dépositions atmosphériques d’N. Au total, il y avait quatre traitements (c’est-à-dire 2 niveaux de température × 2 niveaux d’ajouts d’N) et chacun était répliqué trois fois à chacun des deux sites (N = 24). Durant la huitième et la neuvième année de traitements, les taux de minéralisation nette de l’N du sol (horizon F) ont été évalués régulièrement par la méthode d’incubations de sacs enfouis et les taux de minéralisation brute de l’N ont été mesurés deux fois par année à l’aide de la technique de la dilution isotopique du 15N. Les résultats ont montré que l’augmentation des dépositions d’N faisait diminuer d’en moyenne 20% les taux de minéralisation brute de l’N. Nous avons émis l’hypothèse que cela pourrait être le résultat d’une déplétion de carbone labile et/ou d’une accumulation de carbone réc

Microbial transformations of nitrogen (N) largely determine whether N is retained in ecosystems via net primary productivity or lost via gaseous emissions and leaching. The controls on soil N cycling are often studied at single locales, making it difficult to predict N cycling at regional to global scales. We hypothesized that contemporary soil properties exhibit consistent relationships with instantaneous gross N cycling rates across diverse biomes that create a continuum in these properties. We measured ex situ gross N cycling rates and soil properties at 33 study sites representing five biome classifications in California including deserts, grasslands, shrublands, forest, and wetlands. Desert soils had significantly lower total N, organic carbon (C), microbial biomass N, and soil moisture as well as higher pH than all other biomes, whereas forests and wetlands had significantly lower soil nitrate (NO3−) concentrations (P < 0.001 for all). Gross mineralization rates were best predicted by the combination of soil moisture and soil C:N ratios (R2 = 0.46), which exerted positive and negative controls, respectively. Grasslands exhibited marginally higher gross mineralization than all other biomes, whereas deserts had the lowest rates due to low soil moisture (P = 0.09). Gross nitrification rates were positively correlated to soil NO3− concentrations (R2 = 0.34) and negatively correlated to soil C:N ratios (R2 = 0.31). The negative relationship between gross nitrification and soil C:N ratios was driven by forest soils, which had significantly higher C:N ratios and lower gross nitrification than all other biomes (P < 0.05). Dissimilatory NO3− reduction to NH4+ (DNRA) occurred in soils from all biomes. The strong positive correlation between DNRA rates and soil NO3− (R2 = 0.41) suggests NO3− limitation of DNRA. Predictable patterns in gross N cycling across biomes in California suggest that contemporary soil properties are important drivers of instantaneous soil N

Microbial transformations of nitrogen (N) largely determine whether N is retained in ecosystems via net primary productivity or lost via gaseous emissions and leaching. The controls on soil N cycling are often studied at single locales, making it difficult to predict N cycling at regional to global scales. We hypothesized that contemporary soil properties exhibit consistent relationships with instantaneous gross N cycling rates across diverse biomes that create a continuum in these properties. We measured ex situ gross N cycling rates and soil properties at 33 study sites representing five biome classifications in California including deserts, grasslands, shrublands, forest, and wetlands. Desert soils had significantly lower total N, organic carbon (C), microbial biomass N, and soil moisture as well as higher pH than all other biomes, whereas forests and wetlands had significantly lower soil nitrate (NO3−) concentrations (P < 0.001 for all). Gross mineralization rates were best predicted by the combination of soil moisture and soil C:N ratios (R2 = 0.46), which exerted positive and negative controls, respectively. Grasslands exhibited marginally higher gross mineralization than all other biomes, whereas deserts had the lowest rates due to low soil moisture (P = 0.09). Gross nitrification rates were positively correlated to soil NO3− concentrations (R2 = 0.34) and negatively correlated to soil C:N ratios (R2 = 0.31). The negative relationship between gross nitrification and soil C:N ratios was driven by forest soils, which had significantly higher C:N ratios and lower gross nitrification than all other biomes (P < 0.05). Dissimilatory NO3− reduction to NH4+ (DNRA) occurred in soils from all biomes. The strong positive correlation between DNRA rates and soil NO3− (R2 = 0.41) suggests NO3− limitation of DNRA. Predictable patterns in gross N cycling across biomes in California suggest that contemporary soil properties are important drivers of instantaneous soil N

In addition to the well-studied impacts of defecation and defoliation, large herbivores also affect plant and arthropod communities through trampling, and the associated soil compaction. Soil compaction can be expected to be particularly important on wet, fine-textured soils. Therefore, we established a full factorial experiment of defoliation (monthly mowing) and soil compaction (using a rammer, annually) on a clay-rich salt marsh at the Dutch coast, aiming to disentangle the importance of these two factors. Additionally, we compared the effects on soil physical properties, plants, and arthropods to those at a nearby cattle-grazed marsh under dry and under waterlogged conditions. Soil physical conditions of the compacted plots were similar to the conditions at cattle-grazed plots, showing decreased soil aeration and increased waterlogging. Soil salinity was doubled by defoliation and quadrupled by combined defoliation and compaction. Cover of the dominant tall grass Elytrigia atherica was decreased by 80% in the defoliated plots, but cover of halophytes only increased under combined defoliation and compaction. Effects on soil micro-arthropods were most severe under waterlogging, showing a fourfold decrease in abundance and a smaller mean body size under compaction. Although the combined treatment of defoliation and trampling indeed proved most similar to the grazed marsh, large discrepancies remained for both plant and soil fauna communities, presumably because of colonization time lags. We conclude that soil compaction and defoliation differently affect plant and arthropod communities in grazed ecosystems, and that the magnitude of their effects depends on herbivore density, productivity, and soil physical properties.

The Birch effect is a pulse in soil C and N mineralization caused by the wetting of dry soils, but the role of the soil moisture increment (Delta SWC) is still poorly understood. We quantified the relationship between Delta SWC and the Birch effect, and its interactions with pre-wetting soil moisture (preSWC) and substrate supply. Two soils (clay loam and sandy loam) under a Pinus halepensis forest were subjected to rewetting in laboratory treatments combining different Delta SWC and preSWC values, with or without additional substrate (5 mg g(-1) P. halepensis needles). Respiration flush (Delta R), changes in microbial biomass C (MBC) and net N mineralization (NMIN) were measured. Overall, we found a relationship with the form: Delta R = a Delta SWC + b, where the slope (a) was significant only when pre-wetting water potential was below a threshold value in the range of -100 to -1,200 kPa. However, the threshold alone does not fully describe the role of preSWC in slope variability. Substrate addition modified the Delta SWC sensitivity of Birch effect, enhancing it in the clay loam and suppressing it in the sandy loam. The intensity of the wetting is a dominant factor regulating Birch effect, and Delta SWC is useful for its quantification.