Variability Of Soil Nutrients Research Articles

Spatial distributions of soil nutrients affected by land use, topography and their interactions, in the Loess Plateau of China

Soil nutrient availability and their spatial distributions are strongly related to land use and landscape morphology. This study aims to address the knowledge gap regarding the interaction between these factors and the underlying mechanisms. We selected five land uses (grassland with Artemisia gmelinii, woodland with Robinia pseudoacacia, shrubland with Caragana korshinskii and Hippophae rhamnoides, and apple orchard with Malus pumila) and nine slope positions across hillslopes in the Loess Plateau, China, to investigate their combined effects on the contents and stocks of soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP). Parametric and non-parametric statistical tests were conducted to determine the significant differences in the means or the medians of the soil nutrient variables. Results showed that the SOC and TN contents of shrubland with Caragana korshinskii were statistically significantly greater than those of the grassland (p < 0.05). SOC and TN contents generally decreased from the upper slope to the middle slope, and to the foot slope for the grassland, woodland and shrublands, and on the contrary, an increasing trend from the upper slope, to the middle slope, and to the foot slope was identified for the apple orchard. This study highlights that land use, slope position and their interaction have significant effects on the spatial distributions of soil nutrients. It provides essential empirical evidence for the identification of the optimal vegetation type and slope positions in land management and vegetation restoration activities.

Soil differentiation and soil comprehensive evaluation of in wild and cultivated Fritillaria pallidiflora Schrenk

Few studies have focused on the growth, soil quality and sustainability of medicinal plants under different soil conditions. In this study, the spatial heterogeneity of soil physical and chemical properties, the diversity of rhizosphere soil microbial community structure, and the characteristics of growth of the wild and cultivated medicinal plant, Siberian fritillary (Fritillaria pallidiflora Schrek) were analyzed, and the soil quality and ecosystem sustainability were comprehensively evaluated. The results showed that there was significant spatial variability of soil nutrients in the different habitats. Nitrate nitrogen (NO3-N) was strongly variable, while those of the soil organic carbon (SOC) and available phosphorus (AP) were moderately variable. There was little variability among the soil available potassium (AK), electrical conductivity (EC), pH and ammonium nitrogen (NH4-N). Inverse Distance Weighting spatial interpolation showed that SOC, NO3-N, NH4-H and EC were highly distributed in the southeastern part of the wild area, and the soil was more acidic in the original habitat than in the planting habitat. There was little AK and AP in the native habitat, and there was a high content in the planting habitat. Simultaneously, the soil microbial communities of the two soils also differed. The wild-type soil showed a “fungal” type, while the planted soil showed a “bacterial” type. Pathogenic bacteria were among the primary microflora in the planting area. In general, it is difficult to maintain the sustainable development and geo-herbalism of F. pallidiflora in today's cultivation mode because of the significant differences in soil nature, spatial heterogeneity and microbial community structure for the growth of F. pallidiflora. Therefore, future planting should focus on transforming it from intensive to mountain forest planting. This is highly significant for improving the planting efficiency of F. pallidiflora, protecting their geo-herbalism and germplasm resources, and maintaining the stability and sustainable development of the ecosystem.

Effects of Cinnamomum camphora coppice planting on soil fertility, microbial community structure and enzyme activity in subtropical China.

Cinnamomum camphora (C. camphora) is a broad-leaved evergreen tree cultivated in subtropical China. Currently, the use of C. camphora clonal cuttings for coppice management has become popular. However, the effects of C. camphora coppice planting on soil abiotic and biotic variances remained unclear. In this study, we collected soil from three points in the seven-year C. camphora coppice planting land: under the tree canopy (P15), between trees (P50), and abandoned land (Control) to investigate the effects of C. camphora coppice planting on soil fertility, microbial community structure and enzyme activity. The results revealed that C. camphora coppice planting significantly increased soil fertility in the point under the tree canopy (P15) and point between trees (P50), and P15 had more significant effects than P50. Meanwhile, in P15 and P50, soil bacterial, fungal alpha-diversity were improved and microbial community structures were also changed. And the changes of soil organic carbon and total nitrogen promote the transformation of soil bacterial, fungal community structures, respectively. In addition, C. camphora coppice planting significantly (p < 0.05) increased soil urease (UE), polyphenol oxidase, and peroxidase activities, while significantly decreased soil ACP activity. This study demonstrated that the C. camphora coppice planting could improve soil fertility in subtropical China, which promoted the transformation of soil microbial community from oligotrophs (K-strategist) to copiotrophs (r-strategist). Thus, this work can provide a theoretical basis for soil nutrient variation and productive management of C. camphora coppice plantation in subtropical China.

INFLUENCE OF INVASIVE PLANT SPECIES ON SOIL PROPERTIES IN TROPICAL RIPARIAN ZONES

Riparian zones are highly productive biodiversity-rich transition areas. However, the invasion of exotic plant species depletes diversity and productivity, a severe global environmental concern as they alter ecosystem services. The analysis of spatio-temporal variations of soil nutrients in an invasive plant-impacted riparian zone is significant. This study was conducted in the riparian zones of a tropical river basin, Vamanapuram river basin (VRB), Southern Western Ghats, India, to analyse soil samples (total n= 60) from invaded (VR) and uninvaded (Control) areas for pH, Electrical Conductivity (EC), Organic Carbon (OC), available nitrogen (AN), available phosphorus (AP), and available potassium (AK). In general, comparing the invaded and control sites, changes were noticed in almost all the above physico-chemical parameters (except OC) at a significant level with high values in invaded soil sites mainly due to invasion. However, more studies are needed to differentiate the impacts within the system for a better understanding of invasive plant-soil interactions.

Changes in Rhizosphere Soil Nutrients, Enzyme Activities, and Microbial Communities at Different Stages of Industrial Hemp Development

Determining the nutrient requirements of industrial hemp to increase the yield requires quantifying variations in soil nutrients and enzyme activities in different growth stages, along with relevant soil microbial response. This study investigated the effects of different growth stages of industrial hemp on rhizosphere soil nutrients, enzyme activities, and microbial communities. The results showed that with the increase in the growth stages, the pH and available phosphorus (AP) decreased, while the soil organic matter (SOM), available nitrogen (AN), and available potassium (AK) increased substantially, indicating that the demand for nutrients of industrial hemp was constantly changing. Proteobacteria, Acidobacteria, Ascomycota, and Basidiomycota were found to be the keystone taxa to adapt to the nutrient requirements of industrial hemp at different growth stages by regulating soil enzyme activity. Furthermore, using the redundancy analysis and Spearman’s correlation analysis, we found that microbial taxonomic composition was related to the variations in AN, AP, and pH. In general, we emphasized that the interaction between industrial hemp and soil is closely related to the growth stage, which increases plant adaptability and growth because of the change of soil microorganisms.

Diagnosis of the Spatial Variability of Soil Nutrients and Economics of Precision Management in Degraded Pastures

Most Brazilian pastures are in some stage of degradation, either by the reduction of soil fertility or inadequate management. The objective of this study was to diagnose the stage of pasture degradation and the diagnosis and management of the spatial variability of available phosphorus (P) and potassium (K+). A total of 100 soil samples were collected at a depth of 0–20 cm for available P and K+ contents determination. Geostatistical analyses of the obtained data were carried out to produce maps of the spatial distribution of available P and K+, using kriging, and allow the recommendation of fertilizers doses. The cost/benefit ratio of fertilizer recommendation and application was evaluated at fixed and variable rates. The different stages of pasture degradation were directly related to the reduction of soil fertility, as well as to the adopted management. The variability of soil available P and K+ presented spatial dependence, and the pattern of distribution resulted in the stage of the pasture degradation. The diagnosis of the level of pasture degradation associated with the use of geostatistical techniques under a precision agriculture perspective favors the efficient use of fertilizers, as well as correct decision-making and cost reduction regarding soil management.

Nutrient Transformation in Different Land Use Systems

Land use is an emerging socio-economic activity wherein a region of one major specific purpose utility may be converted into another land for general purpose utility. Land use and management practices influence soil nutrients related to soil processes, such as erosion, oxidation, mineralization and leaching, consequently modifying the transport and redistribution processes. Deforestation is widespread in the tropics, and future changes in land use may have an impact on soil nutrient conversions. Understanding how the ecosystem operates and estimating the effects of future land use change on soil properties require characterising the spatial variability of soil nutrients in relation to site properties such as climate, land use, topography, and other variables.

Seasonal Variations of Fine Root Dynamics in Rubber-Flemingia macrophylla Intercropping System in Southwestern China.

Intercropping cover crops with trees enhance land productivity and improves the soil’s physio-chemical properties while reducing the negative environmental impact. However, there is a lack of quantitative information on the relationships between fine root biomass and available soil nutrients, e.g., nitrogen (N), phosphorus (P), and potassium (K), especially in the rubber-Flemingia macrophylla intercropping system. Therefore, this study was initiated to explore the seasonal variation in fine root biomass and available soil nutrients at different stand ages (12, 15, and 24 years) and management systems, i.e., rubber monoculture (mono) and rubber-Flemingia macrophylla intercropping. In this study, we sampled 900 soil cores over five seasonal intervals, representing one year of biomass. The results showed that the total fine root biomass was greater in 12-year-old rubber monoculture; the same trend was observed in soil nutrients P and K. Furthermore, total fine root biomass had a significant positive correlation with available N (p < 0.001) in rubber monoculture and intercropping systems. Thus, it suggests that fine root growth and accumulation is a function of available soil nutrients. Our results indicate that fine root biomass and soil nutrients (P and K) may be determined by the functional characteristics of dominant tree species rather than collective mixed-species intercropping and are closely linked to forest stand type, topographic and edaphic factors. However, further investigations are needed to understand interspecific and complementary interactions between intercrop species under the rubber-Flemingia macrophylla intercropping system.

Evaluation of soil nutrient characteristics in Tianshan Mountains, North-western China

• Soil nutrient index method was used to gain a comprehensive insight of soil nutrient characteristics of Tianshan Mountains. • The average soil nutrient indices of the western area were higher than those of the eastern area. • All nutrients except the total salts decreased with increasing depth. • The differentiations of soil nutrients and variation patterns were attributed to the vegetation type and coverage, altitude, and more importantly, to human activity. Soil nutrients are the basic properties and essential characteristics of the soil. Study of areal variability of soil nutrients is an important fundamental work for regional planning, environmental protection, and regionally sustainable development. Dynamic changes in soil nutrients are affected by factors such as soil type, fertilization, farming, irrigation, altitude, and climate. This study takes the Tianshan Mountains, located in the central region of Xinjiang, China, as this region is not only a hub for agriculture, industry, transportation, and tourism, but also it is crucial as a forest-grassland transition zone. Through field sampling, laboratory analysis and supported by statistical analysis, we investigated the soil nutrient characteristics and the soil nutrient index to gain a spatial image of soil nutrient status in Tianshan followed by the discussion of those influencing factors. We selected suitable locations along the forest-grassland transition zone to excavate pits of 40 cm × 40 cm in area and 100 cm in depth. A total of 133 soil samples were collected from 0–5 cm, 5–20 cm, and 20–40 cm in pairs (woodland, grassland). Five soil nutrients (soil organic matter (SOM), available nitrogen (AN), available phosphorus (AP), available potassium (AK) and total salts were selected for experimental, multivariate statistical, correlation and soil nutrient index analyses. The results show that (1) the average soil nutrient indices of the western area (M-T and K-B sites) were 0.5 and 0.24, respectively, higher than 0.2 of the eastern area (B-A site); (2) in soil layers of different depths of these three locations, all nutrients except the total salts (SOM, AN, AP, and AK) decreased with the increase in depth; (3) more fertile soils distribute in the western area (M-T and K-B sites) than in others of the Tianshan Mountains, showing higher soil nutrient contents and nutrient indices, abundant vegetation with greater diversity, higher vegetation coverage (80%-90%), and higher altitude. It can be concluded that the differentiation of soil nutrient index between western and eastern section of Tianshan were attributed to theirs’ vegetation type and coverage, altitude, and more importantly, human activity. .

Drivers of nutrient content and spatial variability of soil multifunctionality in the topsoil of Kyrgyzstan

Soil nutrient status is a crucial measure of soil fertility, which not only coordinates and provides the nutrients necessary for plant growth, but also stimulates the decomposition of soil humus and biogeochemical cycles. Therefore, understanding the distribution characteristics of soil nutrients in the Kyrgyzstan, while exploring the drivers of their variability, is important for understanding ecological processes and the distribution of soil resources. Simultaneously, the study of the spatial distribution of soil multifunctionality and its drivers across Kyrgyzstan can better elucidate the functions of the entire ecosystem, assist in optimizing the allocation of resources and serve as a reference material for the scientific and rational management of the country’s soil ecosystems. In this paper, We have used field sampling data from Kyrgyzstan, to examined the geographic variability and distribution of soil nutrients and soil multifunctionality within different soil depths, as well as the drivers in the country, using a combination of factor analysis and structural equation modeling (SEM). Findings indicated: (1)The topsoil of Kyrgyzstan (0–30 cm) stores 4.24 ± 0.59 Pg of SOC, 0.33 ± 0.06 Pg of total nitrogen (TN), 0.31 ± 0.03 Pg of total phosphorus (TP), and 5.12 ± 1.84 Pg of total potassium (TK). The nutrient reserves of various land-cover categories vary greatly across the nation, with grasslands accounting for the largest reserves (40%) but urban areas allocating the smallest proportion (0.3%). (2): the analysis revealed that using the linear or nonlinear fitting equations, the majority of soil nutrients exhibited a strong correlation with each other and also environmental parameters; (3): in Kyrgyzstan, soil multifunctionality varied substantially from –0.63 to 2.30 across regions. (4): according to the SEM results, NPP, wind speed (VS), MAP, longitude (Lon), SWC, and pH directly affected soil multifunctionality. In addition, several indirect effects of ST, MAT, Sard, and latitude (Lat) on soil multifunctionality were observed. Lon, map, SWC, and pH also had various direct and indirect impacts on soil multifunctionality. The findings of this study shed light on the functions of the entire soil ecosystem in the Kyrgyz Republic that help better predict the effects of environmental changes on ecosystem multifunctionality in drylands and provide a scientific basis for rational utilization of soil resources, efficient management of dryland soils, and prevention of land productivity decline in the country.

Niche differentiation along multiple functional‐trait dimensions contributes to high local diversity of Euphorbiaceae in a tropical tree assemblage

AbstractUnderstanding the mechanisms that drive community assembly in species‐rich tropical forest remains a fundamental challenge in ecology. Here, we integrated multivariate functional trait dimensions, phylogeny and metabolomics to test fundamental predictions concerning the role of differentiation with respect to abiotic and biotic niche axes in the maintenance of high local diversity of woody plants in the Euphorbiaceae.We measured 40 functional traits related to resource acquisition, photosynthetic capacity, hydraulic efficiency and secondary‐metabolite profiles generated using untargeted metabolomics in all 26 Euphorbiaceae species in a 20‐ha forest dynamics plot in tropical southwestern China. We examined the correlation structure of 40 traits using a trait networking approach. We coupled these traits with variation in soil nutrients, light environment, soil water content and herbivore pressure within the plot to assess niche differentiation in space. We compared phylogenetic signal among multivariate trait dimensions and secondary metabolites to assess niche differentiation in evolutionary time.Network analysis revealed that a small number of traits with high network centrality reflected variation in ecological strategy among the Euphorbiaceae. Using these high‐centrality traits, we observed significant functional turnover along environmental gradients defined by light, soil moisture, soil nutrients and leaf herbivory, respectively. Most resource utilization traits showed significant phylogenetic signal, whereas almost all defensive traits lacked phylogenetic signal, including species similarity with respect to plant secondary metabolites.Synthesis. Our results suggest that resource‐utilization traits and the habitat associations play a significant role in the niche segregation of co‐occurring woody plants in the Euphorbiaceae. Secondary metabolites, however, may enhance diversity at a finer spatial scale by allowing closely related species with similar functional traits to partition biotic niche space within shared habitats in tropical rainforest.

Groundwater depth alters soil nutrient concentrations in different environments in an arid desert

Soil nutrients are vital for plant growth and survival and present a crucial role in terrestrial function and productivity. However, little is known about the effect mechanism of groundwater table on soil nutrients in an arid desert ecological system. This study investigated the impacts of groundwater depth on the concentrations of soil organic carbon (C), available nitrogen (N), phosphorus (P), and potassium (K) at shallow groundwater depths (0.4, 0.8, 1.2, 1.8, and 2.2 m) and field deep groundwater depths (2.5, 4.5, and 11.0 m) in a desert-oasis ecotone in Central Asia in 2015 and 2016. Soil nitrate-N, inorganic-N, soil available P, and K concentrations were significantly affected by shallow and field deep groundwater. Groundwater depths did not alter soil ammonium-N concentration. Soil organic C concentration was influenced by field deep groundwater depth. Structural equation model showed that groundwater depth directly affected soil nitrate-N and K concentrations and indirectly altered the soil inorganic-N, soil organic C and available P concentrations in shallow groundwater. Moreover, groundwater depth directly influenced soil nitrate-N and soil organic C, available P and K concentrations and indirectly affected soil inorganic-N concentration in deep groundwater. Hence, groundwater depth should be considered one of the most critical environmental factors affecting soil nutrient variation in an arid desert. This study provides new insights into the soil nutrient variation under a declining groundwater depth in a hyper-arid ecosystem.

The Process of Soil Nutrient Stabilization in Micro-Patches in Alpine Kobresia Meadows

Micro-patches are the basic unit of grazing ecosystems; the characteristics of these micro-patches are relatively stable in species under different grazing intensities in the same vegetation, but obviously different in terms of the distribution pattern. This leads to differentiation of plant community numerical characteristics under different grazing intensities. Understanding the driving force of soil nutrient variation in micro-patches under grazing disturbances will help us comprehend the regulation strategy and adaptation mechanisms of the ecosystem against over-disturbance. We designed four scales: spatial (three typical micro-patches), temporal serial (6 years), a degradation succession process (four key degradation stages), and recovery treatment (three treatments: the original grazing intensity based on herder preferences, half of the original grazing intensity, and zero grazing). The soil nutrient characteristics used to estimate stabilization were the typical soil total nutrient content (soil organic matter [SOM], total nitrogen [TN], total carbon [TC], inorganic carbon [IC], total phosphorus [STP], total potassium [TK], and pH), and available soil nutrients (NH4+, NO3−, phosphorous [avP], and potassium [avK]). Variations in the SOM, TC, IC, TN, STP, avK, and NO3− levels in the main root distribution layers (0–20 cm) on the spatial scale were 69.8–79.7%, 61.4–80.35%, 49.8–79.58%, 60.52–76.34%, 46.44–89.89%, 45.5–71.36%, and 59.21–65.38%, respectively, which accounted for the largest variation in the four scales, based on multivariable analysis. The variations in the avP and NH4+ content of the main root distribution layers (0–20 cm) at the temporal scale were 46.42–67.93% and 48.11–64.55%, respectively, which accounted for the greatest variation in the four scales, based on a multivariable analysis. Upon comparing the degradation succession stages and recovery treatment in each stage, we found that the variation in avP, avK, STP, TN, TC, SOM, TC, and TN content was greater at the degradation succession scale than at the recovery treatment scale. The soil nutrient content of the micro-patches exhibited the smallest decrease in the Gramineae-Kobresia transformation (G-KP) micro-patch, followed by the Gramineae micro-patches (G) and Kobresia micro-patches (KP). The number of G micro-patches decreased with increasing grazing intensity whereas the number of KP micro-patches increased. When the number of KP micro-patches increased to a certain degree, the number of G-KP micro-patches then increased as well. G-KP micro-patches, characterized by cracking in the mattic epipedon in alpine meadows, increased with the grazing intensity increasing in a certain degree in K. pygmaea meadows with mattic epipedon cracking (CP); the latter buffered the nutrient variation and maintained the soil nutrients’ relative stability in the ecosystem. Thus, CP formed the buffer stage for maintaining self-stabilization during a regime shift and was considered the withstanding stage during the alpine Kobresia meadow degradation process.

Small but mighty: Impacts of rodent‐herbivore structures on carbon and nutrient cycling in arctic tundra

Abstract Understanding arctic ecosystem function is key to understanding future global carbon (C) and nutrient cycling processes. However, small mammal herbivores can have effects on ecosystems as structure builders and these effects have been underrepresented in the understanding of arctic systems. We examined the impact of small mammal structures (hay piles, runways, latrines) on soils and plants in three arctic tundra regions near Utqiaġvik, Toolik Lake, and Nome, Alaska. Our aims were to (1) examine how vole and lemming structures influence plant and soil nutrient pools and microbial processes, (2) determine if structure effects were similar across tundra system types, and (3) understand how changes in the abundance and cover of these structures during different phases of small mammal multi‐annual population cycles might influence biogeochemical cycling. In general, small mammal structures increased nitrogen (N) availability in soils, although effects varied by study region. Across study regions, hay piles were relatively uncommon (lowest % cover) but increased multiple soil N and P pools, C‐ and N‐acquiring enzyme activities, and leaf phosphorus (P) concentrations, with the specific nutrient variables and size of the effects varying by study region. Latrines had the second highest cover and influenced multiple C, N and P pools, but their effects were mainly observed within a single region. Lastly, runways had the highest % cover of all activity types but increased the fewest number of soil nutrient variables. We conclude that by influencing soil nutrient availability and biogeochemical cycling, small mammal structures can influence bottom‐up regulation of ecosystem function, particularly during the high phase of the small mammal population cycle. Future changes in these population cycles might alter the role of small mammals in the Arctic and have lasting effects on system processes. Read the free Plain Language Summary for this article on the Journal blog

Understory Plant Abundance Is More Important than Species Richness in Explaining Soil Nutrient Variation Following Afforestation on the Eastern Loess Plateau, China

Afforestation plays an important role in controlling soil erosion and nutrient loss on the Loess Plateau in China. However, previous studies on soil nutrient changes have mainly focused on the effects of tree species, whereas little is known about how changes in shrubs and herbs caused by afforestation drive soil nutrient changes. In this study, we examined the variation characteristics of understory vegetation and soil nutrients for different vegetation types. The results showed that compared to abandoned farmland, plantations significantly increased soil organic carbon and total nitrogen but had no significant effect on total phosphorus. Robinia pseudoacacia L. forests were more effective than Pinus tabuliformis Carr. forests in increasing soil nutrient content. In addition, herbaceous vegetation in the R. pseudoacacia forest better explained the soil nutrient variation, and herb abundance was the best explanatory variable; however, shrub vegetation contributed more to soil nutrient variation in the P. tabuliformis forest, and shrub abundance contributed the most. Accordingly, we determined that understory plant abundance, rather than species richness, may be the most important factor driving soil nutrient changes. Specifically, herb abundance in the R. pseudoacacia forest may drive soil nutrient changes mainly by regulating herb biomass and litter biomass. By contrast, shrub abundance in the P. tabuliformis forest indirectly affected soil organic carbon mainly by altering shrub biomass. Furthermore, although the phylogenetic relationships had less effect on soil nutrients than species composition, they also made important contributions. Therefore, the phylogenetic relationships should also be considered in addition to species composition when assessing the impact of vegetation on soil properties in the future.

English

Studying the spatial and temporal variability of soil micronutrients and their effects on plant growth is important for implementing precision-farming and/or economizing fertilizer management. The present investigation was done through soil sampling (0&ndash;20 cm depth) from three locations in central Ethiopia. The tools employed include, descriptive and/or classical statistics. The concentrations of available copper ranged from 1.38&ndash;3.20 mg/kg with narrower range in season-I, than season-II. Manganese ranged from 5.00 &ndash; 65.00 mg/kg, indicating its significant uneven distribution over the years and locations. The concentrations of iron ranged from 1.80 &ndash; 8.20 mg/kg. Narrower ranges were observed for zinc, boron and molybdenum. From the influencing factors analysis, soil pH was the major factor negatively influenced the availability of the evaluated micronutrients, except molybdenum. Organic carbon was the major positive contributor to sulfur, nitrogen, manganese, zinc, and boron availability. Considering the widely varied wheat yields due to the variations in soil nutrients, more positive relationship was established for the grain than total biomass yield indicating more partitioning of plant nutrients into grains. Overall, the dynamics of soil nutrients, particularly the micronutrients and their influences on wheat yield were described and the results could provide practical bases for sustaining crop production in precision-agriculture. Key words: Soil micronutrients, spatial and temporal variability, geostatistics, regression, correlation.

Sensitive indicators of soil nutrients from reservoir effects in the hot-dry valleys of China

The construction of giant reservoirs can affect the hydroclimatic cycles and related soil nutrient recycling. The current understanding of variations in soil nutrients driven by reservoir impoundment is limited because soil often reacts slowly to changes and the impoundment effects can be masked by various factors, making detection difficult. The soils in the hot-dry valleys suffer from a savanna-like hot and dry climate, making it an ideal area for studying the effect of reservoir impoundment on the soil. Here we collected 138 soil samples in April and November along the cascading reservoirs located in the hot-dry valleys of China, including Xiangjiaba, Xiluodu, Baihetan, and Wudongde reservoirs. Results showed that (1) the reservoir impoundment does alter the soil nutrients. The contribution of the impoundment to the variation of soil nutrients was 3.82% in April and 6.44% in November. (2) Compared to April, a relatively dry and cold November is preferred for revealing the reservoir impact on soil nutrients in the hot-dry valleys. (3) Available nitrogen and available phosphorus, followed by soil organic matter, are potential sensitive indicators that can be used to reflect the reservoir impoundment effects. Additionally, pH may be a potential indicator, particularly in the head reservoir area. It is important to note that the effect of reservoir impoundment on soil nutrients is easily masked. This study encourages dam operating agencies, policymakers, and researchers to regard reservoirs as integral parts of the forcings that modify soil nutrients and is an essential step in gaining an insight into the impact of hydropower development on surrounding terrestrial ecosystem services related to soil nutrients.

Nitrogen addition altered the plant-arbuscular mycorrhizal fungi network through reducing redundant interactions in an alpine meadow

Interactions between plants and arbuscular mycorrhizal fungi (AMF) are pivotal in linking belowground soil nutrients with plant-derived carbon in terrestrial ecosystems. However, little is known about the effect of variation in soil nutrients (i.e., nitrogen enrichment) on the structure and phylogenetic characteristics of the mutualistic network. With a 7-year nitrogen addition experiment in an alpine meadow, we built networks for 20 plant species that all occur along the nitrogen addition gradient and their AMF by sequencing 314 root samples. We investigated the responses of association degree (i.e., the number of links of plant or AMF species), network connectance, nestedness, modularity and specialization to different concentrations of nitrogen addition. Phylogenetic signal was calculated to evaluate if the phylogenetically closely related plant species or AMF taxa share similar symbiosis partners. We found that nitrogen addition significantly reduced the plant and AMF association degree, with the generalist (with high association degree) and abundant AMF taxa in nature significantly decreasing association degree and relative abundance (sequencing reads). Therefore, the network connectance and nestedness decreased, but modularity increased with nitrogen addition. Phylogenetic signal of plants (i.e., phylogenetically related plants had similar AMF partners) was always stronger than that of AMF, but the signal vanished with nitrogen addition. The shifted soil properties after nitrogen addition, especially pH, played an important role in regulating the network structures. Our results discover a non-random plant-AMF network shaped by both phylogeny and soil environments in an alpine meadow, and suggest that global nitrogen addition may result in a non-random loss or switch of plant-fungal associations, changes in network structures and phylogenetic relationships, which may have ramification to nutrient exchange and symbiotic performance.

Delineation of nutrient management zones for precise fertilizer management in wheat crop using geo‐statistical techniques

AbstractUnderstanding the variability in crop yield in relation to the spatial variations in soil properties can help to more efficiently apply agricultural inputs on a site‐specific basis. This study was designed to characterize and quantify the spatial variation in soil properties and wheat yield and to delineate prescription maps for site‐specific fertilization. A wheat field was selected at the research farm of the University of Agriculture, Faisalabad, Pakistan, and a grid pattern (30 m * 30 m) was established at the experimental sites to collect soil and crop yield samples at two sampling depths (0–15 &amp; 15–30 cm). The soil samples were analysed for soil nitrogen (N), phosphorus (P), potassium (K), pH, electrical conductivity (EC), soil organic matter (SOM) and saturation (S) at both sampling depths. The locations of the sampling points and field boundary were marked with a GPS receiver. Results of classical, geo‐statistical and interpolated maps revealed significant spatial variability in soil properties and crop yield, demanding for site‐specific nutrient management. The cluster analysis was performed to group the soil and yield data into five productivity zones termed as ‘very low’, ‘low’, ‘medium’, ‘high’ and ‘very high’ without prior knowledge of productivity potential with the internal homogeneity and external heterogeneity at a similarity level of greater than 70%. Results of correlation matrix suggested significant relationships among the crop yield and the soil properties. Results of means comparison in different productivity zones indicated that the crop yield and soil properties were significantly different in developed management zones except ‘low’ and ‘very low’ zones. Significant variation of soil nutrients in very low‐to‐very high productivity zones at both sampling depths suggested that the soil nutrients in combination with soil pH and organic matter can be used to develop prescription maps for site‐specific fertilization. Furthermore, the results of this study emphasize the need to predict soil and crop variables using sensors, in future studies, to delineate prescription maps, as soil sampling and analysis is expansive and time consuming. Site‐specific fertilization based on soil and crop needs can improve economic and environmental efficiency.

How the development of barren land into orchards affects soil ecosystem in Tibet, China

Fruit production is an important strategy for alleviating poverty on the Tibetan Plateau and leads to the conversion of natural barren land into orchards. This study aimed to understand how the conversion of barren land to peach (Prunus persica) orchards affects soil nutrients, heavy metals, and fungal communities in the 0–40 cm profile (at 20 cm intervals) in an experiment including three treatments, barren land (BL), peach orchards planting for 4 years (Y4), and peach orchards planting for 10 years (Y10). Results of the experiment showed that compared with BL, Y4 reduced the availability of some macronutrients (N and K) and micronutrients (Fe and Mn) due to the exclusive application of chemical fertilizer at the seedling stage. Conversely, Y10, which included six years of green cultivation management, using a combination of sheep manure and chemical fertilizer as well as alfalfa (Medicago sativa Linn) intercropping, effectively improved soil macronutrients, but did not enhance the availability of Fe and Mn. Although the investigated heavy metals (As, Hg, Pb, Cr, and Cd) in both the Y4 and Y10 soils were found to pose a low risk to food safety and soil environment, Hg, Cr, and As tended to accumulate in the subsoil (20–40 cm). Furthermore, the variations in the fungal community composition and functional groups were mainly driven by the interaction effects of macronutrients, micronutrients, and heavy metals, but their independent contribution to specific key functional groups cannot be overlooked. For example, Y4 and Y10 decreased the relative abundance of soil saprotrophic and lichenized fungi, mainly due to the loss of micronutrients (Fe and Mn). However, as a result of macronutrient input and dung saprotrophic fungi enrichment, orchard soils promoted the growth of pathogens that play critical roles in fungal co-occurrence networks. These findings indicate that supplementation with N or K fertilizer or manure at the seedling stage and fertilizers rich in Fe and Mn throughout the growth period would be beneficial to the balance of soil nutrients and provide insights into linking the variations in soil nutrients and heavy metals to the function of the fungal community during the conversion of barren land to orchards in alpine soil ecosystems. The risks posed by heavy metal accumulation and fungal pathogen enrichment should be actively prevented.