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The form of inorganic N in soil is governed by N transformations, but the relationship between the soil N transformation dynamics and the N uptake by plants is unclear. The effect of liming and nitrification inhibitor on crop N uptake efficiency (NUE) and N loss due to altered soil N processes was investigated using a 15 N tracing approach. Crops with different N uptake strategies (sweet potato (Dioscorea esculenta L.); an ammonium-N preferring plant and pakchoi (Brassica chinensis L.); a nitrate–N preferring plant) were grown in two agricultural soils with different pH values with or without lime and nitrification inhibitor (3,4-dimethylpyrazole phosphate, DMPP). We monitored the effects of 15 N-nitrate or 15 N-ammonium on the plant biomass and NUE, residual soil N, leachate, and emitted gas. The NUE of pakchoi in acidic soil was greater with nitrate than with ammonium; however, when lime was applied, the NUE of pakchoi increased significantly compared to ammonium alone. The NUE of pakchoi was not affected by N source in the alkaline soil, but application of DMPP together with ammonium significantly reduced NUE of pakchoi compared to ammonium alone. The N source had no effect on the NUE of sweet potato in acidic or alkaline soils, while NUE increased significantly after application of lime and ammonium (31.3%) and with application of DMPP (32.4%) compared to ammonium alone (30% in acidic soil and 23% in alkaline soil). Pakchoi NUE was significantly (p

Soil microbes are the key to revealing the mechanisms driving variation in soil biogeochemical processes. In recent decades, forests in Southeast China have been widely transformed into tea plantations due to the drivers of economic benefits. However, the changes in the soil microbial community and their potential function during the transition from a typical forest ecosystem to tea plantations remain poorly understood. This study investigated the soil microbial community in tea plantation soils with different planting ages, i.e., 6, 12, 23 and 35 years, and in an adjacent woodland control. We discovered that tea planting significantly increased soil bacterial richness (ACE and Chao1) and decreased fungal richness, the diversity of bacteria (Simpson and Shannon) show a trend of initially decreasing and then increasing while there was no significant effect on fungal diversity. After tea planting, the relative abundances of Actinobacteria and Proteobacteria increased by 180.9%–386.6% and 62.3%–97.5%, respectively; the relative abundances of Acidobacteria decreased by 11.4%–66.8%. However, the fungal phyla were not significantly different among different aged tea plantations and woodlands. FAPROTAX and FUNGuild revealed that the transition of natural woodland to tea plantations significantly increased the relative abundances of aerobic_chemoheterotrophy (14.66%–22.69%), chemoheterotrophy (34.36%–37.04%), ureolysis (0.68%–1.35%) and pathogenic fungi (26.17%–37.02%). db-RDA proved that the bacterial community structure was more strongly related to soil pH and available nitrogen (AN), while the main determinants of the fungal community composition were soil pH and soil organic matter (SOM). These findings indicate that tea planting has a strong effect on the soil microbial community and potential function. The change in soil pH during tea planting was the most important factor affecting the soil microbial community, while soil bacteria were more sensitive to tea planting than fungi.

In complex watersheds with multiple types of waterbodies, the effect of river damming on the distribution pattern of heavy metals in sediments and their potential ecological risks are inconsistent, leading to an inability to accurately manage heavy metal pollution. The aim of this study was to reveal the driving mechanisms of hydropower reservoirs on the distribution of heavy metals in sediments and their ecological risks. Characterization of the spatial distribution patterns of Cd, Cr, Cu, Ni, Pb, and Zn and evaluation of their ecological risks in surface sediments were conducted to explore the role of dam construction and operation in modulating heavy metal pollution in the Jiulong River Basin (JRB) using sequentially extracted European Community Bureau of Reference (BCR) extraction scheme, geo-accumulation index (Igeo), and potential ecological risk (RI). The results showed that hotspot patchiness pattern of sediment heavy metal contents highly matched the reservoir distribution but not for the non-dammed south river of the JRB. Ecological risk assessment demonstrated the RI of sediment heavy metals in the reservoir was markedly higher than those in the mainstream and its tributary (p < 0.05), and the potential ecological risks were dominated by Cd, followed by Pb in the sediments of three waterbodies (reservoir, mainstream, tributary). Moreover, BCR heavy metal fractionation showed bioavailability of heavy metals in Xipi Reservoir sediments was much greater than that in downstream reservoir sediments. The reason for this phenomenon was mainly attributed to the elongation of hydraulic residence time (HRT) in this reservoir, which promoted suspended solid sorting by grain size and consequent deposition, facilitating adsorption of finer sediments, with more bioavailable heavy metals falling onto the upper sediment layer in the reservoir. In brief, dam construction and operation reinforced the accumulation of heavy metals and aggravated potential ecological risks in reservoir surface sediments. These findings deepen current understanding of the driving mechanism of reservoirs for sediment heavy metal pollution and confer the probability to precisely control sediment heavy metal pollution for management practices in the multitype waterbody catchment.

Nitrogen (N) is an important nutrient for re-vegetation during ecosystem restoration, but the effects of cover restoration on soil N transformations are not fully understood. This study was conducted to investigate N transformations in soils with different cover restoration ages in Eastern China. Soil samples were collected from four degraded and subsequently restored lands with restoration ages of 7, 17, 23, and 35 years along with an adjacent control of degraded land. A 15N tracing technique was used to quantify gross N transformation rates. Compared with degraded land, soil organic carbon (SOC) and total N (TN) increased by 1.60–3.97 and 2.49–5.36 times in restoration land. Cover restoration increased ammonium and nitrate immobilization, and dissimilatory nitrate reduction to ammonium (DNRA) by 0.56–0.96, 0.34–2.10, and 0.79–3.45 times, respectively, indicating that restoration was beneficial for N retention. There were positive correlations between SOC content and ammonium and nitrate immobilization and DNRA, indicating that the increase in soil N retention capacity may be ascribed to increasing SOC concentrations. The stimulating effect of SOC on ammonium immobilization was greater than its effect on organic N mineralization, so while SOC and TN increased, inorganic N supply did not increase. Autotrophic and heterotrophic nitrification increased with increasing SOC and TN concentrations. Notably, heterotrophic nitrification was an important source of NO3−−N production, accounting for 47–67% of NO3−−N production among all restoration ages. The capacity of N retention was improved by cover restoration, leading to an increase in soil organic carbon and total N over time, but inorganic N supply capacity did not change with cover restoration age.

Aquatic vegetation serves an important structuring function in shallow freshwater ecosystems. Although increasing evidence indicates that sediment-associated phosphorus (P) is mobilized by aquatic macrophytes under P-deficient conditions, the influence of the holistic growth period of rooted macrophytes on transfer mechanism and bioavailability of sediment P around rhizosphere at millimeter scale remains unclear. In this present study, a 120-day batch intact sediment microcosm simulation was implemented to explore the effect of the whole Phragmites australis growth period on the stability and exchange of sediment P across critical micro-interfaces in lacustrine ecosystems. High-resolution dialysis peeper (HR-Peeper) was used to investigate the variations of pore water P in sediments around the P. australis rhizosphere and Zr-oxide diffusive gradients in thin-film (DGT) sampler was used to capture changes in the two-dimensional (2D) images of labile P over the whole growth period. Phosphorus fractionation showed a general decrease of total phosphorus (TP) and calcium-bound P (Ca-P), whereas an increase in iron-adsorbed P (Fe-P), loosely bound P (LS-P), and organic P (Org-P) was observed on day 120 compared to the values on day 0. Notably, the Ca-P content decreased by approximately 77%, while the Fe-P content increased by approximately 400%. Highly synchronous rises in P release flux and in the morphological characteristics of P. australis were the exponential function of incubation time. High-resolution data demonstrated that concentrations of soluble reactive P (SRP) and labile P concentrations in pore water were prominently enhanced by P. australis growth. Meanwhile, a top-down root-shaped patchy distribution pattern of labile P in the pore water was obviously stimulated over time. The reason for this phenomenon could be ascribed to remobilization of sediment mineral P by root organic exudates, as well as Fe-coupled accumulation of labile P due to oxygenation of Fe2+ followed by the formation of Fe plaques on the root surface within the more oxic rhizosphere. The annual growth period of P. australis could persistently enhance the mobility of sediment P, converting it from a more inert status to a redox-sensitive species. Our findings highlight that remobilization of sediment-associated P by P. australis accounts for a significant portion of the P cycle in eutrophic lake ecosystems.

Water-level regime alteration-associated redox fluctuation plays a primary role in governing exchange and transformation of nitrogen (N) in water-level fluctuation zones (WLFZs), while few understanding of how hydrological regimes under reservoir operation affected N cycling across the sediment-water interface (SWI), giving rise to uncertainties in reservoir N nutrient management. Batch microcosm simulation experiments with intact sediment cores from WLFZs of the Three Gorges Reservoir (TGR) were conducted for 24 days to identify holistic flooding-drying process mechanism on N-cycling patterns. Our results showed a distinct transition of N-cycling mode across the SWI, shifting from biological denitrogen loss dominated in initial period of flooding to enhance endogenous N retention. A dramatic source-sink switch of nitrous oxide (N2O) occurred in the first 1.5 days during the flooding period. However, combined accelerating migration of NH4+-N from sediment to overlying water, and subsequently enhanced transformation of NH4+-N to NO3−-N formed from flooding to drying rotation, thereby increasing N loading to overlying water. The reason for this investigation could be attributed to intensive N loss through coupled nitrification and denitrification in oxic-anoxic microenvironments after flooding. With oxygen replenishment from atmosphere during drying phase, persistent ammonification of organic N in sediments provided sufficient source of NH4+-N for the formation of NO3−-N fraction in a more oxic overlying water. Therefore, water-level regime alteration by reservoir operation was capable of weakening N removal from water body and lengthening internal N turnover time across redox-variable SWI. These findings elucidate new understanding of holistic hydrological regime mechanisms on N cycling across SWI and provide insight to biogenic N nutrient management for improving the green credentials of hydroelectric reservoir.

To improve crop yielding, a large amount of fungicides is continuously applied during the agricultural management, while the effects of fungicides residues on microbial processing of N in soil need further study. In the present study, two broad spectrum fungicides, chlorothalonil and carbendazim, were applied at the rates of 5, 10, and 50 mg of active ingredient (A.I.) per kg of dry soil combined with urea with 200 mg of N per kg of dry soil under laboratory conditions. The results showed that chlorothalonil obviously retarded the hydrolysis of urea, whereas carbendazim accelerated it in 4 days after the treatments (P < 0.05). Chlorothalonil reduced denitrification, nitrification, and N2O production (P < 0.05), but not for carbendazim. Further analysis on N-associated microbial communities showed chlorothalonil reduced nitrosomonas populations at the rates of 10 and 50 mg of A.I. per kg and autotrophic nitrifying bacterial populations at three application rates (P < 0.05), but Carbendazim decreased nitrosomonas populations only at the rate of 50 mg of A.I. per kg and also autotrophic nitrifying bacterial populations at three rates and heterotrophic nitrifying bacterial populations at the rates of 10 and 50 mg of A.I. per kg. The reasons for this difference were ascribed to arrest urea hydrolysis and impediment of denitrification and nitrification processes by chlorothalonil. In conclusion, to improve crop yielding, chlorothalonil might be more beneficial to conserve soil N by improving soil N fertility, compared with carbendazim.

The production and consumption pathways of nitrate (NO 3 − -N) are key factors for NO 3 − -N retention capacity ( NR ) in soils, especially in subtropical regions with high precipitation. This study was designed to examine the effect of land-use type on NO 3 − -N production and consumption pathways, in acidic soils in a subtropical region. Soils were collected from 5 differing land-use types: shrubland (SB), a eucalyptus plantation (ET), a sweet potato farm (SP), a citrus orchard (CO) and a mixed-vegetable farm (VE), in southeast China. In our study, SB was considered a natural system, ET was considered an artificial plantation system, and SP, CO and VE were considered agricultural systems. An incubation experiment was conducted with two 15 N tracing treatments, and a numerical modeling method was applied to the experimental data to quantify gross N transformation rates. The results showed that 76% and 69% of NO 3 − -N was produced by heterotrophic nitrification ( O Nrec ) in SB and ET respectively. Whereas, O Nrec was negligible in SP, CO and VE, with >99% of NO 3 − -N produced by autotrophic nitrification. Dissimilatory NO 3 − -N reduction to NH 4 + -N (DNRA) had an important role in soil NO 3 − -N consumption in SB and ET, with >90% of NO 3 − -N produced in SB being simultaneously consumed via DNRA. However, DNRA was unimportant in SP, CO and VE. Nitrate immobilization and denitrification ( I NO3 ) was negligible for all land-use types. Soil NR under different land-use types was in the order SB > ET > SP ≈ CO ≈ VE. Although N fertilizer was applied at low rates, for only the following two years after planting eucalyptus saplings, the NR in ET was significantly lower than in SB (natural system). Nitrate retention capacity was negatively correlated with soil organic carbon (SOC) and total nitrogen (TN) concentrations, and positively correlated soil C:N and C: NO 3 − -N ratios. The lower NR in SP, CO and VE may therefore be due to higher SOC and TN concentrations and lower C:N and C:NO 3 − -N ratios in those soils relative to SB and ET soils. Our observations imply that O Nrec and DNRA play an important role in soil NO 3 − -N production and consumption in SB and ET land-uses, but not in agricultural land-use (SP, CO and VE), within the subtropical region of China studied. These findings could contribute to a theoretical and practical framework for managing NO 3 − -N in subtropical acidic soils.

Soils are major sources and sinks of nitrous oxide (N

To boost grain yield, land use conversion and herbicide application are commonly considered two primary anthropogenic interventions to microbe-mediated nitrogen (N) cycling of soils. However, the coupling effects of land use and herbicide acetochlor application on soil N cycle are still poorly understood although separate role had been extensively investigated. A 31-day laboratory batch experiment on bacterial communities associated with N metabolism in soil collected from various land use types were carried out under acetochlor application using classic dilution plating method. The results showed soil characteristic changes induced by land-use strongly influenced soil bacterial communities, and pH, nitrate (NO3−-N) contents were the best predictors for nitrifying bacteria (p

The connection between moisture and nitrogen (N) transformation in soils is key to understanding N losses, particularly nitrate (NO3−) losses, and also provides a theoretical framework for appropriate water management in agricultural systems. Thus, we designed this study to provide a process-based background for management decision. We collected soil samples from the long-term field experiment in subtropical China, which was designed to examine tobacco and rice rotations under a subtropical monsoon climate. The field experiment was established in 2008 with four treatments: (1) no fertilization as control; (2) N, phosphorus (P), and potassium (K) fertilizers applied at recommended rates; (3) N fertilizers applied at rates 50% higher than the recommended amounts and P and K fertilizers applied at recommended rates; and (4) N, P, and K fertilizers applied at recommended rates with straw incorporated (NPKS). Soil samples were collected during the unsaturated tobacco-cropping season and saturated rice-cropping season and were incubated at 60% water holding capacity and under saturated conditions, respectively. Two 15N tracing treatments (15NH4NO3 and NH415NO3) and a numerical modeling method were used to quantify N transformations and gross N dynamics. Autotrophic nitrification was stimulated by N fertilizer both under unsaturated and saturated conditions. The rate of NO3− consumption (via immobilization and denitrification) increased under the NPKS treatment under saturated conditions. Secondly, the rates of processes associated with ammonium (NH4+) cycling, including mineralization of organic N, NH4+ immobilization, and dissimilatory NO3− reduction to NH4+, were all increased under saturated conditions relative to unsaturated conditions, except for autotrophic nitrification. Consequently, NO3−-N and NH4+-N concentrations were significantly lower under saturated conditions relative to unsaturated conditions, which resulted in reduced risks of N losses via runoff or leaching. Our results suggest that under saturated conditions, there is a soil N conservation mechanism which alleviates the potential risk of N losses by runoff or leaching.

The gaseous losses of fertilizer nitrogen (N) applied to agroecosystems are a major contributor to a host of environmental problems, inefficient production systems, and decreased N-use efficiency. These losses lead to the wastage of resources, increasing the greenhouse effect and harming human health. The red soil hilly region of Southeast China houses the biggest orchard area of the world, and nitrogen fertilizers are usually heavily applied to the orchard systems in China. Therefore, this study aimed to measure the gaseous losses of the fertilizer N by ammonia (NH3) volatilization and denitrification losses using the venting method and acetylene inhibition method respectively, and to assess the potential environmental risk of NH3 and nitrous oxide (N2O) emission from this orchard system based on the recent orchard management practices. An experiment was conducted in an Ougan citrus (Citrus reticulata Blanco ‘Suavissima’) orchard in the red soil hilly region of Southeast China. Three fertilizatio...

To elucidate the inhibitory effects of different herbicides on soil nitrification, eight widely used herbicides, i.e., acetochlor, atrazine, dicamba, isoproturon, paraquat, puma, tribenuron-methyl, and 2,4-dichlorophenoxyacetic acid butyl ester (2,4-Dbe), which represent different chemical taxonomy were selected. Our results indicated that herbicide 2,4-Dbe displayed the best inhibitory effect on nitrification, followed by puma and tribenuron-methyl, whereas the remaining five herbicides exhibited less effect when 10 mg of active ingredient (A.I.) of every herbicide per kg of soil was applied in vegetable-planting soil. The inhibition appeared when 5–100 mg of A.I. 2,4-Dbe was employed, which was enhanced with an increment in its dose in both vegetable-planting and fluvo-aquic soils. However, the inhibitory effect of 10 mg of A. I. 2,4-Dbe exhibited obvious differences in these two types of soils, where the duration of inhibition was shorter as it only continued about a week in fluvo-aquic and calcic cambisols soils with strong nitrification activity but poorer effect as compared to 10 mg of dicyandiamide (DCD). In contrast, the duration of inhibition exceeded 2 months in dryland red and shajiang black soils with a weak nitrification activity which was equivalent to DCD. In addition, comparing with five nitrification inhibitors, 10 mg of 2,4-Dbe had better inhibition than the substituted pyrimidine (AM) and sulfocarbamide (SU), but was equivalent to DCD, nitrapirin, and 3,4-dimethylpyrazole phosphate (DMPP) at their recommended application rates in dryland red soil. These obtained data clearly indicated that 2,4-Dbe could play a stronger role as a nitrification inhibitor in soils.

The effectiveness of rice-straw incorporation to alleviate environmental deterioration and increase soil fertility is widely accepted, whereas, the effect of this management on stimulating soil nitrogen (N) transformation is not fully understood. This study was conducted to investigate the effect of rice-straw incorporation on soil N transformation. An incubation experiment was conducted with rice-straw incorporated at rates of 0 (RS0), 1.67 (RS1), 3.33 (RS2) and 6.67 g kg−1 soil (RS3). Tracing experiments with 15NH4NO3 and NH415NO3 was conducted in the first (Week 1) and tenth week (Week 10) after straw incorporation, and a numerical model was used to calculate gross rates of N transformations. Incorporation of rice-straw increased gross rates of soil organic N mineralization, ammonium (NH4+) and nitrate (NO3−) immobilization and oxidized organic-N to NO3−, by 0.2–1.7 times, 4.6–11.6 times, 20.4–74.9 times and 6.2–20.3 times, respectively. However, the stimulation of soil N transformation via rice-straw incorporation was insignificant by week 10. Over the incubation period, the stimulation of soil inorganic N production pathways (organic N mineralization and oxidized organic-N to NO3−) via rice-straw incorporation was less than on consumption pathways (NH4+ and NO3− immobilization), leading to soil inorganic N supply capacity decreasing with straw incorporation rates. Dissimilatory NO3− reduction to NH4+ was stimulated by rice-straw incorporation, as observed in both the first and tenth week. Compared with RS0, autotrophic nitrification decreased by 14%, 25% and 46% in RS1, RS2 and RS3, respectively, but this effect disappeared by week 10. However, nitrification capacity (NC, the ratio of autotrophic nitrification rate to total mineralization rate) was constrained following rice-straw incorporation both in the first and tenth weeks. Decreasing autotrophic nitrification was the most important factor contributing to decreased NO3− content with straw incorporation, followed by increasing NO3− immobilization. The gross rate of autotrophic nitrification was negatively correlated with NH4+immobilization, indicating that autotrophic nitrification inhibition may be attributed to increased NH4+ immobilization. Therefore, based on the observations of this study, rice-straw incorporation is recommended for reducing nitrification capacity and reducing risks of N losses in subtropical acid soil.

Ecosystem degradation is one of the most pressing environmental problems in the world. Re-vegetation is the major method in land restoration, playing an important role in improving soil quality and biodiversity. Bacteria constitute a vital part of terrestrial ecosystems; however, the relationship between bacteria and restoration of degraded land is not well understood. In this study, we investigated how restoration of degraded land impacts soil physicochemical properties and soil bacterial communities 7, 17, 23 and 35 years after re-vegetation, along with an adjacent control of degraded land. Results showed increases in OTUs, Chao1 and Shannon indices by 54.7%–69.7%, 55.6%–66.0% and 13.5%–17.8% after restoration, with Proteobacteria, Acidobacteria, Chloroflexi and Actinobacteria being the dominant phyla in the study area. Bacterial diversity increased, more strongly during the initial 7 years, but continuous until 35 years. There were positive correlation between the number of OTUs, the Chao1 and Shannon indices and soil nutrients, indicating that improved nutrient contents after restoration was an important driver of bacterial richness and diversity. Vegetation restoration increased the relative abundance of Alphaproteobacteria by 55.9%–118%, especially the genus Bradyrhizobium, which doubled. The relative abundance of Nitrospira (a nitrite-oxidizing bacterial group) was very low (

To investigate the fate of urea nitrogen (N) applied to vegetable fields, three N rates, N0 (0 kg N/ha), N1(225 or 240 kg N/ha) and N2 (450 or 480 kg N/ha) were applied to a rotation system. Nitrogen fertilizer recovery (NFR), N residue in soil, and N losses were measured in situ. Higher N application rates resulted in lower NFR, and increased N residues in soil and losses. The NFR, Chinese cabbage, and eggplant were different in the N1 and N2 groups (P

The change in land-use from woodland to crop production leads to increased nitrous oxide (N

To know constraint forces of joints in static equilibrium is one of the important bases for mechanical design. As a 3 degree-of-freedom (dof) in-parallel manipulator, 3-RPS is has found wide applications. Static characteristics of 3-RPS are presented in this paper taking gravity into account. With constructed static equilibrium equations of 3-RPS, constraint forces of passive joints applied on each link have been obtained. Static analysis shows that each link is subjected to push/pull, bending and twisting torque in general. In particular, when centre of mass (CM) of link is on line through centres of joints fixed on platform and base respectively, or when gravity is omitted, each link will not bear twisting moment. Finally an example is provided to demonstrate static characteristics of 3-RPS. (5 pages)

Static analysis of a translational 3-UPU parallel mechanism (PM) based on the principle of virtual work is presented in this paper. The translational 3-UPU PM is constituted with a fixed base and a movable platform connected by three identical UPU type limbs, where U and P stand for universal and prismatic joint respectively. Given configuration of PM and force applied to platform, actuating forces in prismatic joints of each limb to keep the PM in static equilibrium can be obtained with formula put forward in this paper. To decide actuating forces, gravity force of platform and three limbs are taken into account and each limb is dissected into three parts: piston, cylinder and oil between the piston and the cylinder. There is difference between actuating forces decided with the method presented in this paper and the ones calculated by using Jacobian matrix. It is thought that the method presented in this paper is more accurate than that of Jacobian method. Based on formula in this paper, static simulation of 3-UPU PM used in compensating platform in deep-ocean mineral mining is worked out finally.

The change in land-use from woodland to crop production leads to increased nitrous oxide (N2O)emissions. An understanding of the main N2O sources in soils under a particular land can be a useful tool in developing mitigation strategies. To better understand the effect of land-use on N2O emissions, soils were collected from 5 different land-uses in southeast China: shrub land (SB), eucalyptus plantation (ET), sweet potato farmland (SP), citrus orchard (CO) and vegetable growing farmland (VE). A stable isotope experiment was conducted incubating soils from the different land use types at 60% water holding capacity (WHC), using 15NH4NO3 and NH4 15NO3 to determine the dominant N2O production pathway for the different land-uses. The average N2O emission rates for VE, CO and SP were 5.30, 4.23 and 3.36 mgN kg1 dry soil d1, greater than for SB and ET at 0.98 and 1.10 mgN kg1 dry soil d1, respectively. N2O production was dominated by heterotrophic nitrification for SB and ET, accounting for 51 and 50% of N2O emissions, respectively. However, heterotrophic nitrification was negligible (