Soil Nitrogen Mineralization Rates Research Articles

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.

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

Visible and near infrared spectroscopy for predicting soil nitrogen mineralization rate: Effect of incubation period and ancillary soil properties

Soil nitrogen mineralization rate (SNMR) influences crop N uptake and nitrate leaching leading to environmental pollution. This study aims at (i) examining whether visible and near-infrared reflectance spectroscopy (vis-NIRS) can predict SNMR and (ii) investigating if incubation periods and ancillary soil attributes can improve the prediction accuracy. Total 133 soil samples collected from seven fields were incubated under aerobic conditions for 60 days with seven batches of sub-samples. Mineral N was measured at regular time intervals and soil samples were scanned using a vis-NIRS sensor (Tec5 Technology, Germany) parallelly. SNMR was determined by fitting a zero-order kinetic to the net mineralized N as a function of the incubation time. Soil total nitrogen (TN), total carbon (TC) and electrical conductivity (EC) were determined once. Partial least squares regression (PLSR) models were calibrated individually for each field both for vis-NIR spectra and its combinations with TN, TC and EC. Six out of seven batches of sub-samples were used for calibrating PLSR when remaining one batch was used for model validation, and it rotated across all seven batches. Vis-NIRS alone predicted SNMR with moderate accuracy in five of seven fields (coefficient of determination, 0.53 ≤ R2 ≥ 0.66, ratio of prediction to deviation, 1.51 ≤ RPD ≥ 1.76), while models were poor in two fields (R2 = 0.23–0.26, RPD = 1.18 – 1.20). Inclusion of soil TC, TN and/or EC was expected to improve accuracy, but improvements varied across fields (R2 = 0.23–0.79, RPD = 1.18 – 2.26). Similarly, the incubation period increased vis-NIRS prediction accuracy, but frequently occurred among 2nd to 6th batches (R2 = 0.35–0.82, RPD = 1.28 – 2.44). Even incorporating secondary properties and increasing incubation duration hardly improved predictions, improvement can be compromised since it is not significant mostly and often underperformed or remained unchanged. Considering the time and effort required to incubate and analyze soil properties, this study suggests using a vis-NIRS sensor to estimate SNMR in fresh soil conditions i.e., without incubation and incorporation of secondary properties.

Variations in the soil micro-food web structure and its relationship with soil C and N mineralization during secondary succession of subalpine forests

The soil micro-food web is an important network of belowground trophic relationships and it participates directly and indirectly in soil ecological processes. In recent decades, the roles of the soil micro-food web in regulating ecosystem functions in grasslands and agroecosystems have received much attention. However, the variations in the soil micro-food web structure and its relationship with ecosystem functions during forest secondary succession remain unclear. In this study, we investigated how forest secondary succession affected the soil micro-food web (including soil microbes and nematodes) and soil carbon and nitrogen mineralization across a successional sequence of “grasslands – shrublands – broadleaf forests – coniferous forests” in a subalpine region of southwestern China. With forest successional development, the total soil microbial biomass and the biomass of each microbial group generally increased. The significant influences of forest succession on soil nematodes were mainly reflected in several trophic groups with high colonizer-persister values (particularly bacterivore3, herbivore5 and omnivore-predator5) that are sensitive to environmental disturbance. The increases in the connectance and nematode genus richness, diversity, and maturity index indicated an increasingly stable and complex soil micro-food web with forest succession, which was closely related to soil nutrients, particularly the soil carbon contents. Additionally, we found that the soil carbon and nitrogen mineralization rates also exhibited generally increasing trends during forest succession, which had significant positive correlations with the soil micro-food web composition and structure. The path analysis results indicated that the variances in ecosystem functions induced by forest succession were significantly determined by soil nutrients and soil microbial and nematode communities. Overall, these results suggested that forest succession enriched and stabilized the soil micro-food web and promoted ecosystem functions via the increase in soil nutrients, and the soil micro-food web played an important role in regulating ecosystem functions during forest succession.

Nitrogen mineralization in grazed BSC subsoil is mediated by itself and vegetation in the Loess Plateau, China

Biological soil crust (BSC) exists widely in many kinds of grassland, its effect on soil mineralization in grazing systems has well been studied, but the impacts and threshold of grazing intensity on BSC have rarely been reported. This study focused on the dynamics of nitrogen mineralization rate in biocrust subsoils affected by grazing intensity. We studied the changes in BSC subsoil physicochemical properties and nitrogen mineralization rates under four sheep grazing intensities (i.e., 0, 2.67, 5.33, and 8.67 sheep ha−1) in seasons of spring (May–early July), summer (July–early September), and autumn (September–November). Although this moderate grazing intensity contributes to the growth and recovery of BSCs, we found that moss was more vulnerable to trampling than lichen, which means the physicochemical properties of the moss subsoil are more intense. Changes in soil physicochemical properties and nitrogen mineralization rates were significantly higher under 2.67–5.33 sheep ha−1 than other grazing intensities (Saturation phase). In addition, the structural equation model (SEM) showed that the main response path was grazing, which affected subsoil physicochemical properties through the joint mediation of BSC (25%) and vegetation (14%). Then, the further positive effect on nitrogen mineralization rate and the influence of seasonal fluctuations on the system was fully considered. We found that solar radiation and precipitation all had significant promoting effects on soil nitrogen mineralization rates, the overall seasonal fluctuation has a direct effect of 18% on the rate of nitrogen mineralization. This study revealed the effects of grazing on BSC and the results may enable a better statistical quantification of BSC functions and provide a theoretical basis to formulate grazing strategies in the grazing system of sheep in Loess Plateau even worldwide (BSC symbiosis).

Assessing long term effects of compost fertilization on soil fertility and nitrogen mineralization rate

AbstractBackgroundFertilization with organic waste compost can close the nutrient cycles between urban and rural environments. However, its effect on yield and soil fertility must be investigated.AimThis study investigated the long‐term effect of compost on soil nutrient and potentially toxic elements (PTEs) concentration, nutrient budgets, and nitrogen (N) mineralization and efficiency.MethodsAfter 21 years of annual compost application (100/400 kg N ha–1 year–1 [100BC/400BC]) alone and combined with mineral fertilization, soil was analyzed for pH, organic carbon (SOC), nutrient (total N and P, Nmin, extractable CAL‐P, CAL‐K, and Mg), and PTE (Cu, Ni, Zn) concentrations. Yields were recorded and nutrient/PTE budgets and apparent net mineralization (ANM, only 2019) were calculated.ResultsN efficiency was the highest in maize and for mineral fertilization. Compost application led to lower N efficiencies, but increased ANM, SOC, pH, and soil N, and surpluses of N, P, and all PTEs. Higher PTE concentrations were only found in 400BC for Cu. Nutrient budgets correlated with soil nutrient concentration. A surplus of 16.1 kg P ha–1 year–1 and 19.5 kg K ha–1 year–1 resulted in 1 mg kg–1 increase in CAL‐P and CAL‐K over 21 years.ConclusionCompost application supplies nutrients to crops with a minor risk of soil‐accumulation of PTEs. However, the nutrient stoichiometry provided by compost does not match crop offtakes causing imbalances. Synchronization of compost N mineralization and plant N demand does not match and limits the yield effect. In winter wheat only 65–70% of N mineralization occurred during the growth period.

The effects of ectomycorrhizal and saprotropic fungi on soil nitrogen mineralization differ from those of arbuscular and ericoid mycorrhizal fungi on the eastern Qinghai-Tibetan Plateau.

Interactions between soil fungi and soil environmental factors regulate soil nitrogen (N) mineralization rates on the eastern Qinghai-Tibetan Plateau. Some studies have also illuminated differences in soil N mineralization rate based on different mycorrhizal forests, but the associated effect of soil fungal functional guilds and soil environmental factors underlying this process are not well-understood. Three primary forests respectively dominated by Abies fargesii var. faxoniana (ectomycorrhizal, EcM), Cupressus chengiana (arbuscular mycorrhizal, AM) and Rhododendron phaeochrysum (ericoid mycorrhizal, ErM) trees were selected in this area. Meanwhile, soil net N mineralization rate, soil fungal composition and soil enzyme activity among these three mycorrhizal forests were studied. Our results showed that there were significant differences in the seasonal variation of soil net N mineralization rates among three mycorrhizal forests. Soil net N mineralization rate in the AM forest was faster. EcM fungi and saprotroph are the main functional guilds in these three mycorrhizal forests. Meanwhile, the relative abundances of soil fungal functional guilds, soil temperature and soil peroxidase activity could explain 85.0% in the difference of soil net ammonification rate among three mycorrhizal forests. In addition, soil temperature, soil water-filled pore space and soil ammonium content play a central role in controlling the differing soil net nitrification rate among three mycorrhizal forests. Our results suggest differences in soil net mineralization among different mycorrhizal forest types are driven mainly by soil net ammonification. Soil fungal functional guilds and temperature regulate the rate of soil net ammonification by modulating soil peroxidase activity.

Effects of Microplastics Addition on Soil Available Nitrogen in Farmland Soil

As microplastics (MPs) are an emerging pollution to farmland ecosystems, the research into the ecological and environmental effects of MPs need to be clarified urgently. Available nitrogen is the determining factor for productivity in most terrestrial ecosystems, especially for the farmland ecosystems with a high productivity. To explore the effects of MPs on soil available nitrogen in farmland soil, an incubation experiment was conducted by adding polyethylene MPs with different concentrations to farmland soil, which was collected from farmland in Fuqing, Fujian Province. The contents of three different nitrogen forms (nitrate, ammonium, and dissolved organic nitrogen) and soil dissolved organic carbon were measured, and the soil mineralization rate was calculated. Bacteria was quantified and bacterial community diversity indexes were measured. The results showed that the MPs addition (T1 and T2) had no significant effect on soil ammonium, nitrate and soil nitrogen mineralization rate compared to the control (p &gt; 0.05). However, a significant increase was observed in soil dissolved organic carbon and dissolved organic nitrogen content (p &lt; 0.05). It can be seen that the influence of PE MPs on the soil dissolved organic nitrogen is greater than that of inorganic nitrogen. The results of this study showed no major detrimental effects of MPs on the abundance of some bacterial families, whereas a significant change in soil bacterial evenness index was observed in T2 treatment compared to the treatment without MPs addition. In the background of current MPs pollution, the research results can provide a scientific basis for reducing nitrogen loss in soil and protecting farmland soil safety.

Effects of Spartina alterniflora invasion and subsequent mangrove restoration on soil nitrogen mineralization in Quangang, China

The Spartina alterniflora has severely invaded the coastal mangrove ecosystems in China. Here, we attempt to evaluate the invasion effect of S. alterniflora and the restoration effect of mangrove wetlands from the perspective of the nitrogen cycle characteristics. The inorganic nitrogen content, soil nitrogen mineralization, ammonification, and nitrification rate of uninvaded mudflats with those of invaded S. alterniflora site and native Kandelia obovata site at different restoration stages were compared. The results showed that the NH4+–N was the dominant form of soil inorganic nitrogen at all sites. Owing to its higher ammonification rates, the nitrogen mineralization rates at S. alterniflora site were highest in spring and summer among all sites except for mudflat. The young mangrove (1 year and 8 years) had significantly higher soil inorganic nitrogen content but lower nitrogen mineralization than the mature mangrove, indicated the short‐term response to restoration. The S. alterniflora invasion did not enhance soil nitrogen mineralization comparing with preinvaded mudflat, but it used more NH4+–N relative to K. obovata due to its higher soil nitrogen mineralization than mangrove communities in germination and growing seasons.

Effects of Tourism Trampling on Soil Nitrogen Mineralization in Quercus variabilis Blume Forests Varies with Altitudes in the Climate Transition Zone

Tourism trampling is one of the critical disturbance factors affecting forest structure and function apart from forest management activities. However, how tourism trampling affects soil nitrogen (N) mineralization rate at different altitudes in scenic forest spots is still unclear. To determine whether the responses of soil net N mineralization rate to tourism trampling varies with altitudes, we incubated soils using a field buried pipe method and analyzed soil ammonium N (NH4+-N) and nitrate N (NO3−-N) content at three altitudes (810 m, 1030 m, and 1240 m) at the Baotianman forest scenic spot in Henan Province. The results showed that tourism trampling significantly increased the soil bulk density and soil pH value but substantially reduced soil organic carbon (C) and total N content at all altitudes. Tourism trampling also resulted in a significant decrease in NO3−-N in the soil before and after incubation at all altitudes. The effects of tourism trampling on soil net N mineralization varied with latitudes, showing positive effects at 1030 m altitude (+51.4%), but negative effects at 1240 m altitude (−43.5%). For the soil net N nitrification rate, however, tourism trampling resulted in an increased rate (+141.1%) only at the 810 m altitude. Across all altitudes, soil microbial biomass C is primarily responsible for the variation in the soil net N mineralization rate. This study indicates that the effect of tourism trampling on soil net N mineralization rate varies with altitudes, which is related to the intensity of tourist disturbance and the synthetic effects of vegetation and soil microbes.

Drivers of soil respiration and nitrogen mineralization change after litter management at a subtropical Chinese sweetgum tree plantation

AbstractLeaf litter decomposition transfers elements from litter to soils that are essential for regulating nutrient cycles in plantation ecosystems, especially carbon and nitrogen. However, soil carbon and nitrogen dynamics in response to tree litter management remains insufficiently researched. We conducted a one‐year field experiment at a fast‐growing sweetgum tree plantation to evaluate the effects of leaf litter management on soil available nutrients, respiration rate and nitrogen mineralization rate. Three leaf litter treatments were applied, which were: (1) natural input (control); (2) double input and (3) non‐input. It was found that the double input treatment increased soil inorganic nitrogen and microbial biomass nitrogen, but had little effect on microbial biomass carbon, dissolved organic carbon or dissolved organic nitrogen compared with natural input. The non‐input treatment caused dissolved organic carbon to decrease compared with natural input. The respiration rate increased in the double input treatment, with a positive priming effect observed. Soil net ammonification, nitrification and mineralization rates also increased in the double input treatment in specific seasons. Meanwhile, positive linear relationships between respiration rate and all nitrogen transformation rates were observed for all treatments. Soil temperature was found to be an important prediction factor for predicting the respiration rate and mineralization as seasonal variations, but not for litter‐induced fluctuations. Soil water content and mineral nitrogen were the primary drivers of litter‐induced change to the respiration rate, whereas mineral nitrogen and microbial biomass were primary drivers of mineralization change. These results suggest that changes in soil nitrogen mineralization rate are strongly associated with the soil respiratory process, resulting in a potentially strong plant–soil feedback mechanism.

Hardwood mixtures facilitate leaf litter decomposition and soil nitrogen mineralization in conifer plantations

Productivity in conifer plantations can be increased by hardwood mixture. However, the underlying mechanisms that govern the relationship between hardwood mixture and productivity remain poorly understood, particularly with respect to nutrient cycling. We investigated how and to what extent hardwood mixtures alter nitrogen amounts in leaf litterfall, leaf litter decomposition rates, and soil nitrogen mineralization rates in an experiment that used different thinning intensities (i.e., a non-thinned “control” group with few hardwoods, a 33%-thinned “weak” group with a small amount of hardwoods, and a 67%-thinned “intensive” group with abundant hardwoods) in a conifer Cryptomeria japonica plantation (38-year old). Most of the hardwoods were 15-year old trees that have been regenerated after the first thinning. The annual leaf litterfall amount for the conifer was highest in the control group and lowest in the intensive group, whereas the reverse was true for hardwoods, although the hardwoods’ annual leaf litterfall amount was approximately half that of conifers, even in the intensive group. Consequently, the annual amount of leaf litterfall of hardwoods and conifers combined was lowest in the intensive group. However, the total amount of nitrogen in the annual leaf litterfall of hardwoods and conifers combined did not differ according to thinning intensity, because the mass-based nitrogen concentration in the leaf litterfall of hardwoods was twice that of conifers. The leaf litter decomposition rate in hardwoods was approximately three times faster than that in conifers irrespective of thinning intensity, mainly due to the lower carbon-to-nitrogen (C:N) ratio. Thus, the total amount of nitrogen in the decomposed leaves of hardwoods and conifers combined, calculated by multiplying the total amount of nitrogen in the annual leaf litterfall of hardwoods and conifers by the decomposition rate and summing the results, was highest in the intensive group. In soil from shallow depths (0–10 cm), the nitrogen mineralization rate increased in the order of control, weak, and intensive, attributable primarily to the C:N ratio, which decreased in the same order. The results indicated that increasing the hardwood content by intensive thinning significantly enhances the availability of soil inorganic nitrogen in conifer plantations, by facilitating leaf litter decomposition and soil nitrogen mineralization. These findings indicate that hardwood mixtures can increase forest productivity by enhancing nitrogen cycling.

Increased soil organic matter after 28 years of nitrogen fertilization only with plastic film mulching is controlled by maize root biomass

Nitrogen (N) fertilization and plastic film mulching (PFM) are two widely applied management practices for crop production. Both of them impact soil organic matter individually, but their interactive effects as well as the underlying mechanisms are unknown. Soils from a 28-year field experiment with maize monoculture under three levels of N fertilization (0, 135, and 270 kg N ha−1 yr−1) and with or without PFM were analyzed for soil organic C (SOC) content, total soil nitrogen (N), root biomass, enzyme activities, and SOC mineralization rates. After 28 years, N fertilization increased root biomass and consequently, SOC by 26% (averaged across the two fertilizer application rates) and total soil N by 25%. These increases, however, were only in soil with PFM, as PFM reduced N leaching and loss, as a result of a diurnal internal water cycle under the mulch. The SOC mineralization was slower with N fertilization, regardless of the PFM treatment. This trend was attributed to the 43% decrease of β-glucosidase activity (C cycle enzyme) and 51% drop of leucine aminopeptidase (N cycle) with N fertilization, as a result of a strong decrease in soil pH. In conclusion, root biomass acting as the main source of soil C, resulted in an increase of soil organic matter after 28 year of N fertilization only with PFM.

Effects of precipitation change and nitrogen addition on soil net N mineralization in a saline-alkaline grassland of Northern Shanxi Province, China.

To explore the responses of soil net nitrogen (N) mineralization rate to precipitation varia-tion and nitrogen deposition in salinized grassland, we set precipitation manipulation and nitrogen addition experiments in the typical agro-pastoral ecotone saline-alkaline grassland of Northern Shanxi Province, China. The in situ soil net N mineralization rate was determined by top-cover buried PVC cylinder from May to September in 2019. The results showed that there were seasonal dynamics in soil net N mineralization rate. Soil net N mineralization rate was not affected by increase/decrease precipitation (±50%), nitrogen addition (10 g·m-2·a-1) or the combination of nitrogen addition and increase 50% precipitation treatments. The combination of nitrogen addition and 50% reduction of precipitation significantly improved soil net nitrification rate and net N mine-ralization rate by 10.8 and 8.6 times, respectively. Soil net nitrogen mineralization rate was positively related to soil water content, and negatively related to soil pH. The effects of nitrogen addition on soil nitrogen mineralization rate were dependent on precipitation conditions. Soil water content and pH were important factors regulating soil net nitrogen mineralization rate in the saline-alkaline grassland of Northern Shanxi Province. Therefore, to roundly assess the response model of soil N mine-ralization process to global change, it is necessary to consider the interaction of precipitation changes and nitrogen addition, and the soil physical and chemical properties of salinized grassland.

Assessing the impact of soil aggregate size on mineralization of nitrogen in different soils, China

Soil aggregates play a critical role to support the development of soil nitrogen (N) pools, but the underlying mechanism by which soil aggregate size impacts N mineralization remains unclear. The objective of this study was to determine the effect of aggregate size in soil N mineralization through cultivation experiments of different type soils. The topsoil samples of ten typical profiles in different regions of China were collected, and a series of laboratory column incubation experiments were conducted to quantify the relationship between the distribution of soil aggregate size and the concentration and mass of mineral N (i.e., NH4-N and NO3-N) under N fertilizer addition. The results indicated that the weight of aggregate with different sizes was less affected by the intensity of fertilization, which was mainly influenced by the soil types. In most soils, the weight of soil aggregates of 1–0.5 mm accounted for the largest proportion of aggregates in the five categories (i.e., 5–2 mm, 2–1 mm, 1–0.5 mm, 0.5–0.25 mm, and < 0.25 mm). Moreover, the intermediate aggregates (1–0.5 mm and 0.5–0.25 mm) were detected to have the highest mineral N concentration and mass, and they were also demonstrated to be significantly (P < 0.05) correlated to the potential nitrogen mineralization (PNM) rates in most soils. Subsequently, the obtained PNM indices were classified into three levels: i.e., >65% (highly responsive), 45%–65% (moderately responsive), and < 45% (lowly responsive), and we proposed the preliminary strategies on fertilizer types, agricultural intensity, and crop selection for different soils. The outcome of this study provides new insights into the relationship between soil aggregate sizes and N mineralization abilities and will help in developing guidelines for fertilizer management.

How did the Addition of Indaziflam Affect on Carbon and Nitrogen Mineralizations in a Vineyard Soil?

Microbial activity can be affected by herbicides when they are introduced in soil. Indaziflam is a herbicide used for weed control in vineyards, apple, peach and orange orchards that inhibit cellulose biosynthesis in plants (500 g active ingredient/ l). Recommended field dose of herbicide (RD) containing Indaziflam (10 ml/ da) and its 2 (RD x2), 4 (RD x4), 8 (RD x8) and 16 (RD x16) times of RD were mixed with a loamy soil sampled from Cukurova University Faculty of Agriculture Vineyard (Adana, Turkey) in this study. These mixtures were humidified at 80% of soil field capacity and then incubated for 42 days at 28ºC for the determination of carbon and nitrogen mineralization. Effects of RD and RD x2 doses on soil carbon mineralization were similar to control and no significant difference was found between them. Higher doses of indaziflam (RD x4, RD x8 and RD x16) stimulated mineralization of soil carbon and there were found significant differences between control and these doses (P&amp;lt;0.05). All application doses of herbicide showed variability in ammonium (NH4-N) and nitrate (NO3-N) contents while there were generally found no significant differences between control and RD. In general, contents of soil NH4-N and NO3-N were increased in all applications as time passed and there were significant differences between days that were measured of these contents (P&amp;lt;0.05). Results of soil nitrogen mineralization rate were as following: 1) It was significantly decreased by only RD x2 on 11th day (P&amp;lt;0.05) 2) Higher doses of Indaziflam (RD x4, RD x8 and RD x16) significantly stimulated it on 26th day (P&amp;lt;0.05) 3) All doses of this herbicide significantly decreased it on 42nd day (P&amp;lt;0.05). In conclusion, the recommended field dose of Indaziflam had no negative effect on microorganisms that play an active role in soil carbon and nitrogen mineralization. It was suggested that higher recommended field doses of this herbicide can be used as an energy source by microorganisms in a loamy soil while these doses generally decreased production of ammonium and nitrate.

蚂蚁筑巢对西双版纳热带森林土壤有机氮矿化的影响

蚂蚁作为生态系统工程师能够调节土壤微生物及理化环境，进而对热带森林土壤有机氮矿化速率及其时间动态产生显著影响。以西双版纳白背桐热带森林群落为研究对象，采用室内需氧培养法测定土壤有机氮矿化速率，比较蚁巢和非蚁巢土壤有机氮矿化速率的时间动态，揭示蚂蚁筑巢活动引起土壤无机氮库、微生物生物量碳及化学性质改变对有机氮矿化速率时间动态的影响。结果表明：（1）蚂蚁筑巢显著影响土壤有机氮矿化速率（P<0.01），相较于非蚁巢，蚁巢土壤有机氮矿化速率提高了261%；（2）土壤有机氮矿化速率随月份推移呈明显的单峰型变化趋势，即6月最大（蚁巢1.22 mg kg^-1 d^-1、非蚁巢0.41 mg kg^-1 d^-1），12月最小（蚁巢0.82 mg kg^-1 d^-1、非蚁巢0.18 mg kg^-1 d^-1）；（3）两因素方差分析表明，不同月份及不同处理对土壤有机氮矿化速率、NH₄-N及NO₃-N产生显著影响（P<0.05），但对NO₃-N的交互作用不显著；（4）蚂蚁筑巢显著提高了无机氮库（NH₄-N与NO₃-N）、微生物生物量碳、有机质、水解氮、全氮及易氧化有机碳等土壤养分含量，而降低了土壤pH值；（5）回归分析表明，铵态氮和硝态氮对土壤有机氮矿化速率产生显著影响，分别解释87.89%、61.84%的有机氮矿化速率变化；（6）主成份分析表明NH₄-N、微生物生物量碳及有机质是影响有机氮矿化速率时间动态的主要因素，而全氮、NO₃-N、易氧化有机碳、水解氮及pH对土壤有机氮矿化速率的影响次之，且pH与土壤有机氮矿化速率呈显著负相关。总之，蚂蚁筑巢活动主要通过影响土壤NH₄-N、微生物生物量碳及有机质的状况，进而调控西双版纳热带森林土壤有机氮矿化速率的时间动态。研究结果将有助于进一步提高对土壤氮矿化生物调控机制的认识。;Ants often act as ecosystem engineers in mediating the soil microbial and physicochemical properties. This thus can exert a crucial effect on soil organic nitrogen mineralization and its temporal dynamics in tropical forest. The indoor-aerobic incubation method was used to determine soil organic nitrogen mineralization rates in Mallotus paniculatus community of Xishuangbanna tropical forest. This study aimed to compare temporal dynamics of soil organic nitrogen mineralization rates in ant nests and the reference soils. We also revealed the effects of the changes of soil inorganic nitrogen pool (i.e., NH₄-N and NO₃-N), microbial biomass carbon, and chemical properties on the temporal dynamics of organic nitrogen mineralization rates driven by the ant nesting activities. The results were as follows:(1) Ant colonization had a significant effect on soil nitrogen mineralization rates (P<0.01). The mean organic nitrogen mineralization rates were 261% higher in ant nests than in reference soils. (2) The monthly dynamics in soil organic nitrogen mineralization rates showed an obvious trend of single peak, which was the largest in June (ant nests:1.22 mg kg^-1 d^-1, reference soils:0.41 mg kg^-1 d^-1) and the smallest in December (ant nests:0.82 mg kg^-1 d^-1, reference soils:0.18 mg kg^-1 d^-1). (3) Two-way ANOVAs showed that the factors of month and treatment had significant effects on the concentrations of soil organic nitrogen mineralization rates, NH₄-N, and NO₃-N (P<0.05), but no significant interaction of them was observed on NO₃-N. (4) Ant colonization significantly increased the concentrations of soil inorganic nitrogen pool (NH₄-N and NO₃-N), microbial biomass carbon, organic matter, hydrolyzable nitrogen, total nitrogen, readily oxidizable organic carbon, but reduced the value of soil pH. (5) The regression analysis showed that ammonium and nitrate nitrogen had significant effects on soil organic nitrogen mineralization rates, accounting for 87.89% and 61.84% of the changes in soil organic nitrogen mineralization rates, respectively. 6) Principal component analysis indicated that ammonium nitrogen, microbial biomass carbon, and organic matter were the main factors affecting the temporal dynamics of soil nitrogen mineralization rates, followed by total and nitrate nitrogen, readily oxidizable organic carbon, hydrolyzable nitrogen, and pH. Soil pH was negatively correlated with soil nitrogen mineralization rates. In short, the ant colonization had a crucial role in regulating the temporal dynamics in soil organic nitrogen mineralization rates, through affecting ammonium nitrogen, microbial biomass carbon, and soil organic matter in the Xishuangbanna tropical forest. The results would be helpful to further improve our understanding of the biological regulation mechanism of soil nitrogen mineralization.

Effect of root litter addition on nitrogen mineralization rate under laboratory low‐temperature conditions in soil from a Japanese northern hardwood forest

AbstractSoil freeze–thaw can alter the soil nitrogen (N) mineralization rate by increasing root litter. However, the mechanism remains unclear. We compared the effect of adding root litter from two plant species on soil production rate and soil production rate under low‐temperature conditions in laboratory incubation. Root litter of oak (Quercus crispula) or dwarf bamboo, Sasa (Sasa nipponica) was added to soil and incubated under nonfrost and soil freeze–thaw treatments. We monitored temporal change of net/gross production rate and production rate throughout the soil frost period and the following melting period. We measured dissolved organic N (DON) in root litter leachate under the two temperature treatments. The soil N mineralization with Sasa root litter was higher than that with oak root litter in the two temperature treatments. The DON in root litter leachate of Sasa was larger than that of oak. The effect of root litter addition on net production rate was larger than that on net production rate. The higher net production rate of soil with Sasa was considered to be caused by higher DON in leachate from root litter of Sasa. The higher inducement of N mineralization of Sasa root litter than oak root litter was related to quantity of organic N in the root litter leachate.

The effect on soil nitrogen mineralization resulting from biochar and straw regulation in seasonally frozen agricultural ecosystem

To thoroughly explore the effects of different regulation measures on soil nitrogen cycling in seasonally frozen areas, four treatments, natural control (BL), biochar addition (BA), straw addition (SA) and combined of biochar and straw (CBS), were established on the Songnen Plain of Northeast China. Variations in soil moisture, temperature and urease activity were analyzed. In addition, the mineralization rate was calculated based on the changes of soil inorganic nitrogen content. Furthermore, the response functions of the soil nitrogen mineralization rate were constructed, and the response mechanism for the effect of different regulation patterns on soil nitrogen was determined. It showed that during the freezing period, straw mulch effectively inhibited the loss of soil water and heat, and hindered the reduction in soil urease activity; the average soil urease activity under the SA treatment increased by 0.390, 0.272, and 0.157 mg⋅(g−1·d−1) relative to those under the BL, BA, and CBS treatments, respectively. During the thawing period, the combined of bio char and straw had better heat preservation and water conservation, which greatly enhanced the activity of soil urease. The regulation of biochar and straw significantly affected the soil nitrogen mineralization rate its relationship with influencing factors. During the freezing period, the inorganic nitrogen content was the highest under the SA treatment. During the thawing period, the combined of biochar and straw enhanced the accumulation of soil nitrogen, and the response of the nitrogen mineralization rate to soil water, heat, and urease activity was strongest. In addition, the regulation abilities of biochar and straw decreased with increasing soil depth. These research results have important significance for understanding nitrogen transformations and efficiently guiding agricultural cleaner production.

高寒草甸退化对祁连山土壤微生物生物量和氮矿化速率的影响

高寒草甸退化对祁连山土壤微生物生物量和氮矿化速率的影响