Soil Nitrogen Availability Research Articles

Clay soil amendment suppressed microbial enzymatic activities while increasing nitrogen availability in sandy soils

AbstractConservation management practices often produced positive but limited desirable outcomes in US Southeast sandy soils, likely due to their intrinsically low clay contents that constrain the soil's capacity to preserve organic carbon (C) and nutrients. In the field, we tested the effectiveness of a novel approach, that is, clay soil amendment, to improve sandy soils. In October 2017, clay‐rich soils (25% clay) were spread at 25 metric tons ha−1 and tilled onto a sandy soil (1.9% clay) in the field, which was further mixed by light tillage at 0‐ to 15‐cm depth, followed by planting winter cover crop mixtures (cereal rye, crimson clover, and winter pea). The crop rotation was cotton and corn with cover crop mixtures planted in the winter fallow season. Soils (0–15 cm) were collected in August 2021 and subjected to physio‐biochemical analyses. Clay amendment increased soil clay content to 3.4%, which improved nitrogen (N) availability by 51% but inhibited the activities of C (β‐d‐cellubiosidase [CB]; β‐xylosidase [BX]; N‐acetyl‐β‐glucosaminidase [NAG]) and N (leucine aminopeptidase [LAP]) cycling enzymes, resulting in up to 78% reduction in microbial respiration. A follow‐up kinetic study on BG and LAP enzymes suggested that clay addition can have different impacts on enzymes with diverse biological origins through distinct mechanisms. Clay addition can potentially improve sandy soils by stabilizing the organic inputs in soils. However, more research is required to understand its long‐term impacts making this approach practical.

Effect of Zinc and Silica Solubilizing Microbial Consortia on Soil and Plant Nutrient Status in Paddy

Effect of zinc and silica solubilizing bacteria and their consortia on paddy was studied under pot culture conditions at Agricultural Research Station, Janagamaheswarapuram, Andhra Pradesh, India. Thirteen treatments were assessed for availability of nutrients viz., Nitrogen, Phosphorus, Potassium, Zinc and Silica in soil and concentration of Nitrogen, Phosphorus and Potassium in plant at 45, 90 and 120 days after sowing (DAS). Significantly highest nitrogen (189.3, 249.4 and 239.7 kg ha-1), available phosphorus (34.6, 61.8 and 38.5 kg ha-1), potassium (214.2, 347.9 and 232.1 kg ha-1), zinc (0.78, 0.99 and 0.86 ppm) and silica (60.1, 90.8 and 78.4 ppm) were recorded in T13 (RDF + ZnKJJ-4 & ZnPGG-1 + SiKPP-1 & SiPYY-3) at 45, 90 and 120DAS. In plant, nitrogen (0.79, 0.99 and 0.89 %), phosphorus (0.37, 0.58 and 0.49 %) and potassium (1.78, 2.18 and 1.89 %) were significantly highest in T13. There was increase in available nutrient content upto 90 DAS which then decreased at 120DAS. It is inferred that consortia of two zinc solubilizing and two silica solubilizing microorganisms (T13) is useful for increased availability of Nitrogen, Phosphorus, Potassium, Zinc and Silica in soil and increased uptake of NPK by rice plant.

Effects of defoliation on root traits, nitrogen fixation, soil nitrogen availability, soil enzyme activities and soil bacterial communities of forage legumes

Effects of defoliation on root traits, nitrogen fixation, soil nitrogen availability, soil enzyme activities and soil bacterial communities of forage legumes

Response of soil microbial diversity and functionality to snow removal in a cool-temperate forest

Climate-induced changes in thinning snowpack can greatly impact soil freeze-thaw patterns and water supply. These effects may influence the soil microbial diversity and the key ecological functions mediated by microorganisms, thereby altering the cycling of nutrient in the ecosystem. A snow-exclusion experiment to explore the effects of snow removal on soil microbial diversity and functionality in Larix gmelinii forest. Control (natural snowfall), SR (complete snow removal) and SR-SR (complete snow removal, with snow returned for water supplementation at the end of winter) were represented three experimental treatments. The results showed that: snow removal resulted in more severe soil frost in winter. Soil nitrogen availability was higher in the snow removal plots compared to control plots in freeze-thaw period. Fungal diversity was not affected by snow removal, neither the α diversity of bacteria. However, snow removal did alter the bacterial community structure. These changes of the above did not persist into the growing season. SR-SR significantly reduced soil multifunctionality during freeze-thaw period, whereas SR did not. However, SR and SR-SR resulted in significantly higher soil multifunctionality than was observed in control during early growing season. Additionally, a widespread increase in the abundance of nitrogen cycling genes was observed in the SR and SR-SR plots during the freeze-thaw period and the early growing season, respectively. Snow removal significantly affected soil multifunctionality, which can be explained by changes in the microbial biomass, bacterial community structure and network complexity. Furthermore, snow removal significantly altered soil water content, temperature, and dissolved carbon, nitrogen. dbRDA and random forest analysis showed that soil water content, temperature, and total nitrogen as drivers of soil microbial community structure and multifunctionality. This study highlights that snow removal altered soil nitrogen availability, microbial community diversity, and multifunctionality during freeze-thaw period. However, these changes did not result in cross-seasonal legacy effects.

Global needs for nitrogen fertilizer to improve wheat yield under climate change.

Increasing global food demand will require more food production1 without further exceeding the planetary boundaries2 while simultaneously adapting to climate change3. We used an ensemble of wheat simulation models with improved sink and source traits from the highest-yielding wheat genotypes4 to quantify potential yield gains and associated nitrogen requirements. This was explored for current and climate change scenarios across representative sites of major world wheat producing regions. The improved sink and source traits increased yield by 16% with current nitrogen fertilizer applications under both current climate and mid-century climate change scenarios. To achieve the full yield potential-a 52% increase in global average yield under a mid-century high warming climate scenario (RCP8.5), fertilizer use would need to increase fourfold over current use, which would unavoidably lead to higher environmental impacts from wheat production. Our results show the need to improve soil nitrogen availability and nitrogen use efficiency, along with yield potential.

Differential Responses of Bacterial and Fungal Community Structure in Soil to Nitrogen Deposition in Two Planted Forests in Southwest China in Relation to pH

Increased nitrogen deposition profoundly impacts ecosystem nutrient cycling and poses a significant ecological challenge. Soil microorganisms are vital for carbon and nutrient cycling in ecosystems; however, the response of soil microbial communities in subtropical planted coniferous forests to nitrogen deposition remains poorly understood. This study carried out a four-year nitrogen addition experiment in the subtropical montane forests of central Yunnan to explore the microbial community dynamics and the primary regulatory factors in two coniferous forests (P. yunnanensis Franch. and P. armandii Franch.) under prolonged nitrogen addition. We observed that nitrogen addition elicited different responses in soil bacterial and fungal communities between the two forest types. In P. yunnanensis Franch. plantations, nitrogen supplementation notably reduced soil bacterial α-diversity but increased fungal diversity. In contrast, P. armandii Franch. forests showed the opposite trends, indicating stand-specific differences. Nitrogen addition also led to significant changes in soil nutrient dynamics, increasing soil pH in P. yunnanensis Franch. forests and decreasing it in P. armandii Franch. forests. These changes in soil nutrients significantly affected the diversity, community structure, and network interactions of soil microbial communities, with distinct responses noted between stands. Specifically, nitrogen addition significantly influenced the β-diversity of fungal communities more than that of bacterial communities. It also reduced the complexity of bacterial interspecies interactions in P. yunnanensis Franch. forests while enhancing it in P. armandii Franch. forests. Conversely, low levels of nitrogen addition improved the stability of fungal networks in both forest types. Using random forest and structural equation modeling, soil pH, NH4+-N, and total nitrogen (TN) were identified as key factors regulating bacterial and fungal communities after nitrogen addition. The varied soil nutrient conditions led to different responses in microbial diversity to nitrogen deposition, with nitrogen treatments primarily shaping microbial communities through changes in soil pH and nitrogen availability. This study provides essential insights into the scientific and sustainable management of subtropical plantation forest ecosystems.

Biocrusts enhance soil nitrogen mineralization and nitrification under experimental warming in a dryland ecosystem

Nitrogen (N) transformation is essential for soil nitrogen availability and plant growth in drylands, but climate warming may be altering the dynamics of this process. Biological soil crusts (biocrusts) are soil surface communities dominated by cyanobacteria, lichens, and mosses that perform many vital functions in dryland ecosystems. However, their role in regulating soil N transformations under climate warming is uncertain. To explore this, we conducted a one-year field warming experiment in the Tengger Desert of northwestern China to investigate whether and how biocrusts modulate the effects of warming on N transformations, microbial biomass and enzyme activity in the soil underneath them. We found increases in microbial biomass carbon and nitrogen, soil nitrate reductase and urease activities, and net nitrification and mineralization rates in the soil below the biocrusts in response to warming. Our results suggest that biocrusts, acting as a “living skin,” significantly enhance the soil's organic matter and total nitrogen content. Thus, the resultant soil “hot zones” formed by the nutrient increases, help to sustain microbial activity and to mitigate the negative effects of warming on the soil environment. This nutrient enhancement is closely related to microbial biomass and enzyme activity, which are key contributors to N transformation in drylands. Therefore, our study highlights the regulatory role of biocrusts in soil N transformation, emphasizing the necessity to consider their effects to more accurately predict the impact of warming on N cycling in dryland ecosystems.

Minimal impact of nitrogen addition on bacterial and fungal communities during fungal necromass decomposition in a subalpine coniferous plantation

Fungal necromass is a vital source of stable carbon and available nitrogen in soils, especially in coniferous forests that are extensively colonized by ectomycorrhizal fungi. Here, we examined changes in the necromass microbial community during a 20-week incubation experiment in a subalpine coniferous plantation. We also explored how the necromass microbial community responded to simulated nitrogen deposition, a global change factor that substantially affects nitrogen-limited coniferous forests. The results showed that necromass microbial community was more dominated by copiotrophic bacteria with high community average rRNA operon copy number (3.1–6.4) and fast-growing fungi (moulds and yeasts) than surrounding soils. Ectomycorrhizal fungi also constituted a significant portion of the fungal community during the fast decay stage (first 5 weeks) of necromass decomposition, indicating that fungal necromass may serve as a nitrogen source for the nitrogen-limited trees. The shifts in microbial functional compositions (e.g., decreased proportions of copiotrophic bacteria) as decomposition progressed were partly due to alterations in substrate chemistry (i.e., the levels of aliphatic compounds including soluble carbohydrate, amorphous glucan polymers, and crystalline glucans and chitin). In contrast, nitrogen addition had limited influences on microbial diversity and composition, likely due to the nitrogen-rich nature of the fungal necromass. Overall, our findings reinforce the existence of a specific and dynamic core necrobiome in fungal necromass and enhance our understanding of how fungal necrobiome responds to environmental changes.

Effect of Adding NPK-Chitosan Fertilizer and Organic Matter on phosphorus and potassium content of Corn (Zea mays L.)

A field experiment was conducted at the College of Agriculture, University of Basrah's research station in Garmat Ali during 2022 agricultural season. The study aimed to investigate the impact of three types of fertilizers (commercial NPK as a control and two types of prepared NPK-Chitosan organic fertilizers) at four addition levels (0, 1, 1.5, and 2 ton ha-1) and two levels of organic matter (0% and 2.5%) on the availability of nitrogen and potassium in loam sandy soil and yield of corn (Zea mays L.). The results indicated a significant effect of fertilizer type on increasing Phosphorus and Potassium Content of corn plant. The highest values of Phosphorus and Potassium Content for corn were 6.15 and 47.07 gm kg-1 respectively for the added fertilizer type. The NPK-Chitosan fertilizer in a 1:3 coating ratio achieved the, 3.62 and 31.01 kg ha-1, respectively, followed by the treatment of NPK-Chitosan fertilizer with a 1:3 mixing ratio and a fertilizer level of 2 tons/ha, which yielded The results showed a significant effect of fertilizer level on increasing Phosphorus and Potassium Content of the corn plants. Phosphorus and Potassium Content increased with higher levels of added fertilizer. The level 2 achieved the highest values of Phosphorus and Potassium Content for the vegetative part corn plants, reaching 2 tons per hectare.4.22 and 37.91 gm kg-1, and with a significant difference from level 1 and 1.5 tons per hectare, level 2 also outperformed level 0 tons per hectare (the control treatment). Similarly, the organic matter showed a significant effect the results indicated a significant interaction between the type and level of fertilizer, as well as the level of added organic matter to the soil, on Phosphorus and Potassium Content of the yellow corn plants. The NPK-Chitosan fertilizer with a 1:3 coating ratio added at the level of 2 tons per hectare outperformed the other treatments, yielding the highest phosphour contentand grain yield.

Responses of soil aggregation and aggregate‐associated nitrogen to straw return in China: Evidence from a meta‐analysis and a pot experiment

AbstractEnhancing soil structure and soil nitrogen availability is the key to sustainable agricultural development in global cropping systems. Straw return can affect soil aggregation, but the results of recent studies on the influence of straw return on soil aggregation are not consistent, and the distribution and availability of straw‐derived nitrogen in soils are still unclear. Here, a meta‐analysis of the effects of straw return on soil aggregation was conducted based on 57 studies published in China over the past 10 years. Moreover, combined with a pot experiment, the distribution and transfer characteristics of the two main wheat (Triticum aestivum L.)‐preceding crops, corn (Zea mays L.) and soybean (Glycine max L.) straw‐derived nitrogen in the soils were studied by using the 15N‐tracer method in the main wheat‐producing areas of China. 15N‐labeled straw was introduced into soils in pots at rates of 0.3% and 0.5% of the soil dry mass and incubated 60%–70% of the field water capacity throughout the entire growth period of wheat (220 days). A meta‐analysis revealed that straw return significantly improved the mass ratio of large macro‐aggregates (LM%) and small macro‐aggregates (SM%) but significantly decreased the mass ratio of micro‐aggregates (MI%) and silt plus clay‐size particles (CS%), with mean effect sizes of 36.27%, 9.06%, −8.26%, and −21.32%, respectively. The mean weight diameter (MWD) and geometric mean diameter (GMD) also increased by 21.48% and 15.64%, respectively. Compared with SM%, LM% made a greater contribution to the stability of soil aggregates. Moreover, only LM% showed a significant positive correlation with the corresponding aggregate‐associated nitrogen content, which was an important reason for the improvement in soil nitrogen availability after straw return. The positive effect of straw return on soil aggregation was greatest when the soil pH was close to 6.5–7.5, the average annual temperature was greater than 15°C, and the average annual rainfall was close to 800–1000 mm. The results of the pot experiment revealed that the proportions of straw‐derived nitrogen in >2 mm aggregates were 1.21–1.28, 1.50–2.23, and 1.34–1.74 times greater than those in 0.25–2, 0.053–0.25, and <0.053 mm aggregates, respectively. Moreover, the proportion of straw‐derived nitrogen content of aggregates of different particle sizes showed that the proportion of straw used to reach 0.5% of the soil dry weight was greater than 0.3%, which was 1.09–1.66 times greater, and that of soybean straw was significantly greater than that of corn straw, which was 1.50–2.28 times greater. At application rates of 60 g pot−1 and 100 g pot−1 straw, the absorption of soybean straw‐derived nitrogen by wheat was 1.83 and 2.15 times greater than that of corn straw‐derived nitrogen, respectively. In conclusion, straw return effectively improved soil aggregate stability and nitrogen availability, which was closely related to the increase in soil LM%. Soybean straw can stabilize soil aggregates better than corn straw, and its straw‐derived nitrogen is an important nitrogen source for subsequent wheat crops.

Evaluation of saline water effects on use efficiency and soil nutrient availability of maize (Zea mays L.) under drip fertigation

A field experiment was conducted during the rabi season of 2022-23 at the Saline Water Scheme, Agricultural College Farm, Bapatla. The study’s objective was to evaluate the effects of saline water on nutrient use efficiency and soil nutrient availability in maize under drip fertigation. The experiment consisted of eight treatments and four replications, arranged in a randomized block design. Irrigation with the best available water along with the application of a recommended dose of fertilizer (240-80-80 NPK kg ha-1) recorded the highest uptake of N (88.2 and 62.4 kg ha-1), P (21.2 and 16.20 kg ha-1), and K (25.4 and 126.7 kg ha-1) in grain and stover of maize, respectively, which were at par with the alternate use of fresh water with saline water of 2 dS m-1. Nutrient use efficiencies, i.e., agronomic efficiency (7.4, 18.4, and 18.4 kg kg-1), physiological efficiency (85.2, 225.3, and 159.4 kg kg-1), apparent recovery efficiency (22.5, 17.0 and 48.7 %) and utilization efficiency (15.7, 39.1 and 39.1 kg kg-1) of N, P, and K, respectively, were also observed to be the highest under irrigation with the best available water along with a recommended dose of fertilizer application. Soil pH remained unaffected with saline water irrigation, whereas the EC of the soil was the highest under irrigation with saline water of 4 dS m-1 without the application of fertilizers. Soil-available nitrogen, phosphorous, and potassium were most elevated under irrigation with the best available water, with values of 152.5, 36.3, and 352.8 kg ha-1 respectively. The lowest values of nutrient uptake, nutrient use efficiencies, and soil available nutrients were recorded under irrigation with a water salinity of 4 dS m-1 without applying fertilizers. The use of a cyclical approach in utilizing both freshwater and saline water has demonstrated its effectiveness in mitigating the adverse effects of salts, resulting in enhanced efficiency in nutrient utilization and greater accessibility of soil nutrients.

Effects of Nitrate Assimilation in Leaves and Roots on Biomass Allocation and Drought Stress Responses in Poplar Seedlings

Knowledge of tree biomass allocation is fundamental for estimating forest acclimation and carbon stock for global changes in the future. Optimal partitioning theory (OPT) and allometric partitioning theory (APT) are two major patterns of biomass allocation, and occurrences have been tested on taxonomical, ontogenetic, geographic and environmental scales, showing conflicting results and unclear ecophysiological mechanisms. Here, we examine the biomass allocation patterns of two young poplar (Populus) clones varying greatly in drought resistance under different soil water and nitrogen availabilities and the major physiological processes involved in biomass partitioning. We found that Biyu, a drought-sensitive hybrid poplar clone, had significant relations among biomass of leaf, stem and root, showing allometric partitioning. Xiaoye, a drought-tolerant poplar clone native to semi-arid areas, on the contrary, showed tightly regulated biomass allocation following optimal partitioning theory. Biyu had higher nitrate reductase activity in the fine roots, while Xiaoye had higher nitrate reductase activity in the leaves. Biochemical analyses and measurements of fluorescence and gas exchange showed that Xiaoye maintained more stable chloroplast membranes and photosystem electron flow, showing higher water use efficiency and a higher resistance to drought. A nitrogen addition could improve leaf photosynthesis and growth both in Biyu and Xiaoye seedlings under drought conditions. We concluded that the two poplar clones showed different biomass allocation patterns and suggest that the site of nitrate assimilation may play a role in biomass partitioning under varying water and nitrogen availabilities.

Soil-Microbial CNP Content and Ecological Stoichiometry Characteristics of Typical Broad-Leaved Tree Communities in Fanjing Mountain in Spring

This study aims to investigate the impact of diverse forest stand types and soil depths on soil ecological stoichiometry characteristics, shedding light on nutrient limitations and cycling patterns within the mid-subtropical forest ecosystem in southwest China during spring. The research focused on four representative forest stands situated in Fanjing Mountain: Castanopsis fargesii (C. fargesii), Cyclobalanopsis multiervis (C. multiervis), Cyclobalanopsis argyrotricha (C. argyrotricha), and Rhododendron argyrophyllum Franch (R. argyrophyllum). Sample plots were established in these forest types, and soil samples were collected from the 0–20 cm and 20–40 cm soil layers in March, spring of 2023. Various soil parameters, including pH, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), soil microbial biomass carbon (MBC), soil microbial nitrogen (MBN), and soil microbial phosphorus (MBP) were measured, and their stoichiometric ratios were calculated. The findings of the study were as follows: (1) In the 0–20 cm soil layer, C. argyrotricha exhibited the highest soil organic carbon, followed by C. fargesii, C. multiervis, and R. argyrophyllum with the lowest content. No significant differences in soil organic carbon were observed among the four forests in the 20–40 cm soil layer. Additionally, C. argyrotricha displayed a significantly higher soil C:N ratio compared to other forest types in different soil layers. In the typical broad-leaved forest area of Fanjing Mountain, the TP was classified as deficient. (2) In the 0–20 cm soil layer, the MBC of C. fargesii surpassed C. multiervis, C. argyrotricha, and R. argyrophyllum by 26.59%, 42.92%, and 24.67%, respectively. There were no significant differences in soil MBC:MBP ratio and MBN:MBP ratio, regardless of forest species and soil depths. The low availability of soil nitrogen in different forest stand types in Fanjing Mountain strongly limits soil microorganism biomass. (3) The correlation between SOC, TN, TP, and their stoichiometric ratios varied across different soil layers. Therefore, in managing the Fanjing Mountain forest area, attention should be paid to supplementing N and P in the soil.

Species-specific responses of C and N allocation to N addition: evidence from dual 13C and 15N labeling in three tree species

Soil nitrogen (N) availability affects plant carbon (C) utilization. However, it is unclear how various tree functional types respond to N addition in terms of C assimilation, allocation, and storage. Here, a microcosm experiment with dual 13C and 15N labeling was conducted to study the effects of N addition (i.e., control, 0 g N kg−1; moderate N addition, 1.68 g N kg−1; and high N addition, 3.36 g N kg−1 soil) on morphological traits, on changes in nonstructural carbohydrates (NSC) in different organs, as well as on C and N uptake and allocation in three European temperate forest tree species (i.e., Acer pseudoplatanus, Picea abies and Abies alba). Our results demonstrated that root N uptake rates of the three tree species increased by N addition. In A. pseudoplatanus, N uptake by roots, N allocation to aboveground organs, and aboveground biomass allocation significantly improved by moderate and high N addition. In A. alba, only the high N addition treatment considerably raised aboveground N and C allocation. In contrast, biomass as well as C and N allocation between above and belowground tissues were not altered by N addition in P. abies. Meanwhile, NSC content as well as C and N coupling (represented by the ratio of relative 13C and 15N allocation rates in organs) were affected by N addition in A. pseudoplantanus and P. abies but not in A. alba. Overall, A. pseudoplatanus displayed the highest sensitivity to N addition and the highest N requirement among the three species, while P. abies had a lower N demand than A. alba. Our findings highlight that the responses of C and N allocation to soil N availability are species-specific and vary with the amount of N addition.

Legume rhizodeposition promotes nitrogen fixation by soil microbiota under crop diversification

Biological nitrogen fixation by free-living bacteria and rhizobial symbiosis with legumes plays a key role in sustainable crop production. Here, we study how different crop combinations influence the interaction between peanut plants and their rhizosphere microbiota via metabolite deposition and functional responses of free-living and symbiotic nitrogen-fixing bacteria. Based on a long-term (8 year) diversified cropping field experiment, we find that peanut co-cultured with maize and oilseed rape lead to specific changes in peanut rhizosphere metabolite profiles and bacterial functions and nodulation. Flavonoids and coumarins accumulate due to the activation of phenylpropanoid biosynthesis pathways in peanuts. These changes enhance the growth and nitrogen fixation activity of free-living bacterial isolates, and root nodulation by symbiotic Bradyrhizobium isolates. Peanut plant root metabolites interact with Bradyrhizobium isolates contributing to initiate nodulation. Our findings demonstrate that tailored intercropping could be used to improve soil nitrogen availability through changes in the rhizosphere microbiome and its functions.

Nitrogen addition alleviates the adverse effects of drought on plant productivity in a temperate steppe.

Drought and nitrogen enrichment could profoundly affect the productivity of semiarid ecosystems. However, how ecosystem productivity will respond to different drought scenarios, especially with a concurrent increase in nitrogen availability, is still poorly understood. Using data from a 4-year field experiment conducted in a semiarid temperate steppe, we explored the responses of aboveground net primary productivity (ANPP) to different drought scenarios and nitrogen addition, and the underlying mechanisms linking soil properties, plant species richness, functional diversity (community-weighted means of plant traits, functional dispersion) and phylogenetic diversity (net relatedness index) to ANPP. Our results showed that completely excluding precipitation in June (1-month intense drought) and reducing half the precipitation amount from June to August (season-long chronic drought) both significantly reduced ANPP, with the latter having a more negative impact on ANPP. However, reducing half of the precipitation frequency from June to August (precipitation redistribution) had no significant effect on ANPP. Nitrogen addition increased ANPP irrespective of drought scenarios. ANPP was primarily determined by soil moisture and nitrogen availability by regulating the community-weighted means of plant height, rather than other aspects of plant diversity. Our findings suggest that precipitation amount is more important than precipitation redistribution in influencing the productivity of temperate steppe, and nitrogen supply could alleviate the adverse impacts of drought on grassland productivity. Our study advances the mechanistic understanding of how the temperate grassland responds to drought stress, and implies that management strategies to protect tall species in the community would be beneficial for maintaining the productivity and carbon sequestration of grassland ecosystems under climate drought.

Soil erosion alters the composition of soil nitrogen and induces nitrogen immobilization along a sloping agricultural landscape

AbstractSoil erosion transports and redistributes sediment across the landscape, altering soil organic carbon (SOC) and nitrogen (N) availability and stocks. However, the effect of erosion on soil N remains largely unclear. In this study, SOC, soil total N (TN), mineral N ( and ), dissolved organic N (DON) and total dissolved N (TDN) were evaluated in 100‐cm soil profiles in different sites (including the non‐erosion flat site, erosional site and depositional site) to examine the responses of the concentration and composition of soil N to different erosional intensity. Additionally, N mineralization and microbial biomass nitrogen (MBN) were determined to evaluate the bioavailability of soil N. Our results showed that erosion depleted TN in the erosional sites while enriching it in the depositional site throughout the soil profile. The erosion, rather than the deposition, altered the composition of dissolved N, with TDN (DON and mineral N) dominating deeper soil profiles (40–100 cm, accounting for 18%–50% of TN). The wide soil C:N ratio in the erosional site altered microbial metabolism to mine N to maintain their growth rather than mineralizing organic matter into soil bioavailable forms. This was supported by the net N mineralization (Nm), which exhibited a significant negative correlation with MBN and soil C:N ratio. The imbalanced loss of SOC and TN caused by the erosion induces soil N limitations. Collectively, our results suggested that erosion decreased TN concentrations and altered the composition of dissolved N, inducing N immobilization and decreasing soil bioavailable N.

Inhibitory effects of Pseudomonas sp. W112 on cadmium accumulation in wheat grains: Reduced the bioavailability in soil and enhanced the interception by plant organs

Microorganisms play an important role in heavy metal bioremediation and soil fertility. The effects of soil inoculation with Pseudomonas sp. W112 on Cd accumulation in wheat were investigated by analyzing the transport, subcellular distribution and speciation of Cd in the soil and plants. Pseudomonas sp. W112 application significantly decreased Cd content in the roots, internode and grains by 10.2%, 29.5% and 33.0%, respectively, and decreased Cd transfer from the basal nodes to internodes by 63.5%. Treatment with strain W112 decreased the inorganic and water-soluble Cd content in the roots and increased the proportion of residual Cd in both the roots and basal nodes. At the subcellular level, the Cd content in the root cell wall and basal node cytosol increased by 19.6% and 61.8%, respectively, indicating that strain W112 improved the ability of the root cell wall and basal node cytosol to fix Cd. In the rhizosphere soil, strain W112 effectively colonized and significantly decreased the exchangeable Cd, carbonate-bound Cd and iron-manganese oxide-bound Cd content by 43.5%, 27.3% and 17.6%, respectively, while it increased the proportion of residual Cd by up to 65.2%. Moreover, a 3.1% and 23.5% increase in the pH and inorganic nitrogen content in the rhizosphere soil, respectively, was recorded. Similarly, soil bacterial community sequencing revealed that inoculating with strain W112 increased the abundance of Pseudomonas, Thauera and Azoarcus, which are associated with inorganic nitrogen metabolism, and decreased that of Acidobacteria, which is indicative of soil alkalinization. Hence, root application of Pseudomonas sp. W112 improved soil nitrogen availability and inhibited Cd accumulation in the wheat grains in a two-stage process: by reducing the Cd availability in the rhizosphere soil and by improving Cd interception and fixation in the wheat roots and basal nodes. Pseudomonas sp. W112 may be a suitable bioremediation agent for restoring Cd-contaminated wheat fields.

Effects of Different Ecological Restoration Pattern on Soil Organic Nitrogen Components in Alpine Sandy Land

Ecological restoration can improve soil fertility and have a significant impact on the soil nitrogen cycle. Nitrogen (N) is an essential nutrient element for plant growth and development, and also an important factor limiting soil productivity. As an important part of soil nitrogen, the composition and proportion of soil organic nitrogen components can directly or indirectly affect the difficulty of soil organic nitrogen mineralization and nitrogen availability, and then affect soil fertility. However, the current studies on soil nitrogen under ecological restoration mainly focus on nitrogen accumulation and nitrogen mineralization, while there are relatively few studies on changes in soil organic nitrogen components, especially in alpine regions. Therefore, in this study, three restoration pattern of mixed forage (MG), single shrub (SA) and shrub combination (SG) that have been restored continuously for 15 years in northwest Sichuan, China, were taken as the research object, and natural sandy land (CK) without manual intervention was taken as the control. Through field sampling and laboratory analysis, the characteristics of the soil nitrogen content and its proportion to soil total nitrogen (TN) under ecological restoration in alpine sandy land in northwest Sichuan, China, were investigated, and the correlation between the nitrogen content and soil physicochemical properties was analyzed. The results showed that the three ecological restoration patterns significantly increased the contents of acylated ammonium nitrogen (AMMN), acid-lyzed amino sugar nitrogen (ASN), acid-lyzed amino acid nitrogen (AAN), acid-lyzed unknown nitrogen (HUN), acid-lyzed total nitrogen (AHN) and non-acid-lyzed nitrogen (NHN) in soil, and the change trend was consistent with that of soil TN. Ecological restoration improved soil nitrogen mineralization and storage capacity by increasing the proportion of AAN, HUN and NHN to soil TN, and the effect was most obvious in the MG pattern 20–40 cm and SG pattern 40–60 cm soil layers. In general, except ASN, the soil nitrogen content was positively correlated with the soil TN, soil water content (SWC) and soil organic carbon (SOC), and negatively correlated with the soil bulk density (BD) and pH. The results of this study will help us to understand the supply capacity of soil nitrogen under ecological restoration and provide a scientific basis for the selection of an ecological restoration mode and the improvement of the restoration effect and efficiency in alpine sandy land.

Soil C:N impacts on soil biological health and consequences on weed control in soybean and corn systems

Abstract Nitrogen availability has an important influence on agricultural weed growth, because many weeds in annual cropping systems are more competitive in high-nitrogen soils. A potential method to control nitrogen availability is through soil carbon amendments, which stimulate soil microbial growth and immobilize nitrogen. Additionally, carbon amendments may alter soil microbial community composition, increase soil biological functioning, and improve soil health. In a 2-yr field experiment in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.], we implemented five amendment treatments to test their ability to alter weed and crop growth through soil nitrogen availability and soil biological functioning. The treatments included: an untreated control, an unamended weed-free control, rye hay adding 3,560 kg C ha−1 and 3,350 kg C ha−1 in 2020 and 2021, respectively, sawdust adding 5,030 kg C ha−1 and 4,350 kg C ha−1 in 2020 and 2021, respectively, and a rye hay and sawdust combined treatment adding 8,590 kg C ha−1 and 7,700 kg C ha−1 in 2020 and 2021, respectively. Each treatment was replicated five times in corn and six times in soybean. Each season, we explored correlations between crop and weed biomass and weed community composition and nitrogen immobilization measured through soil respiration and nitrogen availability. We also explored changes to the soil microbial community composition and soil health as a secondary result of the carbon amendment treatments. Nitrogen availability was lowest in plots treated with the highest C:N amendment. Increasing carbon improved soil health metrics, but the microbial community composition was most affected by the rye hay treatment. Amendments with high C:N reduced weed growth in both soybean and corn plots but only selected for specific weed communities in soybean, leading to improved soybean competitiveness against weeds. In corn, crop growth and weed community composition remained consistent across amendment treatments. Targeted nitrogen immobilization may improve leguminous crop competition in some weed communities as part of an integrated weed management program.