三江平原碟形洼地-岛状林土壤氮磷空间分布及生态化学计量特征

To better understand carbon, nitrogen, and phosphorus dynamics within small-scale gradients of tidal and vegetation interaction, 13 study sites were established along three transects (near, far, and along a tidal creek) within a salt marsh in northern Jiangsu, China, and soil samples were collected during both the growing and non-growing season; the soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents were measured. Spatiotemporal variation in SOC, TN, and TP in coastal salt marsh soils was influenced not only by the physical and chemical properties of the elements themselves, but also by the distribution of local vegetation and repetitive tidal action. Complex interactions between the vegetation and tidal flooding determined spatiotemporal patterns in SOC, TN, and TP. Compared to tidal effects, vegetation effects were more stable and persistent. The spatial distributions of SOC and TN in salt marsh soils (sediment) were relatively consistent, with both SOC and TN levels being higher in vegetated zones as compared to the mudflat. Nutrient levels were also higher further from the tidal creek, and the SOC/TN content was maximized in the S. alterniflora marsh. The TP content was higher in the tidal-creek transect versus the other two transects; among sites, the TP content was higher in the mudflat than the vegetated sites. Within the vegetated sites, the S. alterniflora marsh had the highest TP levels. Seasonal variation in SOC, TN, and TP was minimal compared to differences among vegetated sites within each transect. Differences between transects were also minimal compared to those among vegetated sites within transects. Significant spatial variation was identified in C:N:P stoichiometry across the study area; the comprehensive effects of vegetation and tidal flooding on nutrient stoichiometry in coastal salt marshes dominated by S. alterniflora in eastern China are elevation-dependent. The N/P ratio measured 0.62 ± 0.41, suggesting that plant growth in the study area may be nitrogen limited. Together, the local vegetation and repetitive tidal flooding shaped SOC, TN, and TPs in salt marsh soils, producing similar patterns in nutrient element accumulation, constraining the geochemical behavior and fate of elements, and controlling the spatiotemporal distribution of soil elements. Therefore, it is critical to consider interactions between vegetation and tidal effects, as well as the nonlinear relationship between nutrient input and ecological response in salt marsh ecosystems when managing coastal zones, supporting ecosystem functioning, and conducting ecological risk assessments.

In order to explore different forest types effects on soil chemical properties, four stand types, namely pure Cunninghamia lanceolata forest, pure Cryptomeria fortunei forest, pure Liriodendron chinense forest and Cryptomeria fortune × Phoebe zhennan mixed forest, were selected as the research objects, and the difference of soil chemical properties and the organic contents of different forest types were analyzed by variance analysis. The results showed that there were significant differences in soil pH, available potassium, total phosphorus, total potassium and total nitrogen among different forest types, but there were no significant differences in available phosphorus, alkali-hydrolyzable nitrogen, and soil organic matter. The soil pH value of the four forest stands was between 4.02 and 5.33, which was acidic, and increased with the increase of soil depth. The contents of soil organic matter, total nitrogen, total phosphorus, alkali-hydrolyzable and available phosphorus in different forests types all decreased with the increase of the soil depth. The 0~10cm total phosphorus content of soil in four different forest stands was higher than that of 10~20 cm. The soil total potassium content of pure C. lanceolata forest, pure C. fortunei forest and pure L. chinense forest all fluctuated up and down with the increase of the soil depth, while the content of C. fortune × P. zhennan mixed forest increased gradually. The contents of soil alkali-hydrolyzable nitrogen and available phosphorus in soil of four forest stands all decreased with the increase of soil depth. The soil available potassium content of pure C. lanceolata forest and pure C. fortunei forest increased first and then decreased, while that of pure L. chinense forest and C. fortune × P. zhennan mixed forest increased gradually. The average phosphorus supply intensity of the four stands at the soil layer of 0~10cm, 10~20cm, 20~40cm and 40~60cm was 2.64%, 2.71%, 2.57% and 2.61%, respectively. Soil K supply intensity of pure L. chinense forest and C. fortunei × P. zhennan mixed forest increased with the increase of soil layer, while that of pure C. fortunei forest first increased and then decreased.

By sampling in the field and analyzing the soil samples in the laboratory in 1982 and 2005 the soil fertility data were obtained. Through application of geo-statistics combined with GIS, the temporal–spatial variability of the pH, organic matter, total nitrogen, total phosphorus and total potassium in soil of Xiaojiang watershed from 1982 to 2005 were analyzed. Results showed that: (1) the pH value and total potassium in soil showed an increasing trend, but the organic matter, total nitrogen and the total phosphorus in soil declined in the past 20 years in Xiaojiang watershed, (2) the parameters fitted by semivariogram models for fertility indices changed significantly in the past 20 years and (3) the result estimated by ordinary Kriging indicated the spatial pattern of the soil fertility indices changed significantly in the past 20 years. The soil pH increased in the east and southeast, but decreased in the middle of the watershed. The organic content of the soil matter decreased in the east, southeast and southwest, but increased in the northeast and middle of the watershed. The total nitrogen content of the soil decreased in the east, but increased in the middle of watershed. The total phosphorus content of the soil decreased in the whole watershed. The total potassium content of the soil increased in the southwest and southeast, but decreased in the middle of the watershed and (4) the change of land use and soil management measures was the main driving force of variability of soil properties.

Environmental and grazing management drivers of soil condition

In order to find out the distribution of soil organic matter, total nitrogen and total phosphorus contents in gully in loess hilly region and the difference between gully and slope, 29 and 58 samples were taken from gully and slope in Yuanzegou small watershed respectively. The results showed that the contents of total nitrogen, total phosphorus and organic matter in the 0-60cm soil layer ranged 0.091~0.628g/kg, 0.402~1.388g/kg, and 0.826~6.550g/kg respectively. According to the results of the second national soil census, the total nitrogen and organic matter content in the gully are at the lower level of grade 6, the total phosphorus content is at the higher level of grade 2, and the variation coefficient ranges from 21.6% to 33.4%, which is moderate. Pearson correlation analysis shows that soil total nitrogen, total phosphorus and organic matter contents are positively correlated with slope direction and elevation, negatively correlated with slope, and weakly correlated with soil moisture content, clay content and silt content, and negatively correlated with sand content. 0-20cm, the organic matter contents in the gully was higher than that slope 7.19%; 20-40cm and 40-60cm, the organic matter content in the gully was lower than that slope 4.66% and 12.67% respectively, but there was no significant difference. 0-20cm, 20-40cm, 40-60cm, the content of total nitrogen and total phosphorus in gully were higher than that slope, and the total nitrogen content was higher 24.31%, 13.04% and 8.70% respectively, with significant difference only in 0-20cm (p<0.05); The total phosphorus content was higher 15.68%, 13.56% and 15.11% respectively, with significant differences (p<0.05).

Importance of Dalbergia sissoo for restoration of degraded land: A case study of Indian dry tropical vindhyan regions

Ecological stoichiometry is an important index that reflects the element cycle and ecosystem stability. In this study, two sites (sunny and shady slopes) and five forest ages (young stage, half-mature stage, near-mature stage, mature stage, and over-mature stage) in a Pinus tabuliformis plantation were chosen to illustrate the effects of forest ages and site conditions on the biomass and stoichiometric characteristics of leaves and soils in the temperate mountainous area of China. Except for young stage, the biomass of the leaves of P. tabuliformis on sunny slopes were higher than those on shady slopes in other forest ages, the average carbon content of the leaves in sunny slopes was higher than that in shady slope, while the average total nitrogen contents and average total phosphorus contents of the leaves showed the opposite of this. The biomass of leaves increased on sunny slopes, and increased first and then decreased in shady slopes with increasing forest ages. The contents of soil total carbon (STC) and soil total nitrogen (STN) decreased with increasing soil depth, while the soil total phosphorus (STP) and soil available phosphorus (SAP) contents displayed the opposite. In addition to SAP, the average content of STC, STN, and STP in shady slopes was higher than that in sunny slopes, and the ratio was the opposite. Except for STC: STN on shady slopes, the other ratios showed a downward trend with an increase in soil depth. Excluding the topsoil, the change trend of STC : STP and STN : STP in shady slopes and sunny slopes was consistent with forest ages. The results showed that forest ages and site conditions had significant effects on leaf biomass. The biomass of the leaves is mainly limited by nitrogen. These results have important significance in improving the refinement of local forestry management of Pinus tabuliformis plantations in the temperate mountainous area of China.

Assessing the spatial distribution of organic matter and total nitrogen in soil is essential for management and optimum utilization of fertilizers. Therefore, the present field experiment was conducted to evaluate the impact of different planting pattern arrangements on the spatial distribution of soil total nitrogen and organic matter content under a maize/soybean strip relay intercropping system. The planting was arranged in a manner such that soil sampling could be done from continuous maize/soybean relay strip intercropping (MS1), maize/soybean relay strip intercropping in rotation (MS2), traditional maize/soybean intercropping (MS3), sole maize (M), sole soybean (S), and fallow land (FL) from 2018 to 2020. The results showed significant variations for soil organic matter and total nitrogen content under different planting pattern arrangements of maize and soybean in the strip relay intercropping system. Across all systems, the highest soil organic matter (29.19 g/kg) and total nitrogen (10.19 g/kg) were recorded in MS2. In contrast, the lowest soil organic matter (1.69 g/kg) and total nitrogen (0.64 g/kg) were observed in FL. Soil organic matter and total nitrogen in MS2 increased by 186.45% and 164.06%, respectively, when compared with FL. Soil organic matter and total nitrogen in MS2 increased by 186.45% and 164.06%, respectively, when compared with FL. Furthermore, under MS2, the spatial distribution of soil organic matter was higher in both maize and soybean crop rows as compared with other cropping patterns, whereas the soil total nitrogen was higher under soybean rows as compared with maize in all other treatment. However, correlation analysis of the treatments showed variations in organic matter content. It can be concluded that different planting patterns can have varying effects on soil organic matter and total nitrogen distribution under the strip relay intercropping system. Moreover, it is recommended from this study that MS2 is a better planting pattern for the strip relay intercropping system, which can increase the spatial distribution of soil organic matter and total nitrogen, thereby improving soil fertility, C:N ratio, and crop production. This study will serve as a foundation towards the scientific usage of chemical fertilizers in agricultural sector.

Mixed planting of fir and broadleaf trees is an effective management method for improving the productivity. We investigated soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents, along with their stoichiometric ratios across 10 different combinations of Chinese fir and broadleaf species (Mytilaria laosensis, Michelia macclurei, Michelia maudiae, Cinnamomum porrectum, Castanopsis hystrix, Cinnamomum burmanni, Liquidambar formosana, Michelia chapensis, Schima superba, and Michelia odora, respectively) with the stand age of 20 yr. Additionally, we examined the activities and stoichiometric characteristics of various enzymes: β-1,4-glucosidase, β-xylosidase, cellobiohydrolase, β-1,4-N-acetylaminoglucosidase, leucine aminopeptidase, and acid phosphatase to analyze nutrient limitation status in different mixed stands. The results showed that: 1) In the 0-10 cm and 10-30 cm soil layers, the highest SOC and TN contents were found in M. macclurei, whereas in the 30-50 cm soil layer, the highest contents were observed in S. superba. The highest TP content across all three soil layers was recorded in C. burmanni. Soil SOC and TN contents of the 10 forest stands decreased with the soil depth, while TP was not affected by the soil depth. 2) The measured ranges across the 10 stand types were 4.82-32.69 g·kg-1 for SOC, 0.50-2.16 g·kg-1 for TN, and 0.24-0.55 g·kg-1 for TP, indicating nutrient deficiency. Only the stands of M. macclurei and S. superba reached national average levels for SOC and TN, while the TP content of all forest stands was below the national average. 3) The results of the enzyme quantification vector model indicated that soil microbial metabolism was jointly limited by nitrogen and phosphorus. 4) Redundancy analysis revealed that TN, available phosphorus (AP), ammonium (NH4+-N), soil water content (SWC), pH, and TP were the primary factors influencing enzyme activities. Additionally, pH, AP, TP, SWC, and the carbon-to-phosphorus (C:P) ratio emerged as key determinants of enzymatic stoichiometry. In summary, M. macclurei and S. superba were effective in promoting soil nutrient levels in mixed forests of fir and broadleaf trees, being the optimal tree species for the mixed forest renovation in the South subtropical region. Given the prevalent limitations of nitrogen and phosphorus, external nitrogen and phosphorus inputs should be considered in future management practices.

Non-point source (NPS) pollution simulation in control units can identify critical pollution source areas and make Best Management Practices (BMPs) more effective for the responsible parties. In this study, the control unit division method is introduced, and the spatial and temporal distribution characteristics of NPS pollution in the Guishui River Basin of Northern China are analyzed using the Soil Water Assessment Tool (SWAT) model. In addition, five BMP scenarios were designed for environmental and cost-benefit analyses. The results show that the loss of total nitrogen (TN) and total phosphorus (TP) is concentrated in the rainy season, and the loss of TN and TP is mainly distributed in the middle and lower reaches of the main stream of the Guishui River. This area accounts for 22.34% of the basin area. The vegetated filter strips (VFS) scenario had the best environmental benefits with average TN and TP reduction efficiencies of 63.4% and 62.6%, respectively. The Grassed Waterway was the most cost-effective scenario measure, cost-benefit (CE) values of TN and TP were 1798.13 g/€ and 601.56 g/€. Generally, research on NPS pollution using control units can more clearly identify the critical source areas of pollution than other methods, and provides technical support for watershed management decision makers.

Poyang Lake, Dongting Lake, and Taihu Lake are the largest freshwater lakes in the middle and lower reaches of the Yangtze River, China. In recent years, the eutrophication level of lakes has increased with the development of the social economy and caused many environmental and social problems. The concentrations of total nitrogen (TN) and total phosphorus (TP) are the key indicators of the degree of eutrophication, but the traditional ground monitoring methods are not capable of capturing such parameters in whole lakes with high spatial-temporal resolution. In this paper, empirical models are established and evaluated between the TN and TP and remote sensing spectral factors in the three lakes using Landsat 8 Operational Land Imager (OLI) satellite data and in-situ data. The results show that the inversion accuracy is higher than 75%. The TN and TP concentrations in the three lakes are inversed based on the Google Earth Engine (GEE) platform from 2014 to 2020 and their spatial-temporal variations are analyzed. The results show that the concentrations of TN and TP in Poyang Lake were decreased by 5.99% and 7.13% over 7 years, respectively, and the TN in Dongting Lake was decreased by 5.25% while the TP remained stable. The temporal changes in TN and TP concentrations displayed seasonal variations. A low concentration was observed in summer and high concentrations were in spring and winter. The average concentrations of TN and TP in Taihu Lake were higher than that of the other two lakes. The TP concentration was increased by 17.3% over 7 years, while the TN concentration remained almost stable. The variation in TN in Taihu Lake was the same as the growth cycle of algae, with higher value in spring and winter and lower value in summer, while the concentration of TP was lower in spring and winter and higher in summer. The spatial distribution of TN and TP concentrations in the three major lakes was significantly affected by human activities, and the concentrations of TN and TP were higher in areas near cities and agricultural activities.

Rapid urbanization has caused widespread environmental pollution in Africa, restricting sustainable development programs. Today, non-point source pollution has become a major threat to many African cities. In this study, we have classified urban land use followed by the identification of urban functional areas based on multi-source data. We have then evaluated non-point source pollution based on nitrogen and phosphorus loads at a spatial scale in Mwanza city (Tanzania). We have estimated the spatial distribution of total nitrogen (TN) and total phosphorus (TP) loads at a scale of 1 square kilometer grid. The results show that ① the built-up area of the city was identified as 28.9 km2, accounting for 6.8% of the total area of the city. The area of informal settlements was 56.9 km2, accounting for 13.4% of the total area of the city. About 90.38% of 2.41×105 kg of the total TN load and 87.23% of 4.00×104 kg of the total TP load in the city were derived from the informal settlements alone in 2020. ② The average load intensities of TN and TP in Mwanza city were 6.90 kg·hm-2·yr-1 and 1.14 kg·hm-2·yr-1, respectively. The average TN and TP intensities in Mwanza city were slightly higher than the average TN and TP load intensities in the Lake Victoria basin. However, given the high population density of the Mwanza city area, the average TN and TP intensities were found to be consistent. ③ The TN and TP pollution loads were relatively concentrated in the inner urban area, including the lower reaches of the Mirongo River basin, the eastern side of the Nyamagana Peninsula, and the lakeside area extending north and south from the peninsula, and gradually decreased toward the city’s outskirts. We propose that the identified riparian areas in our study should be prioritized as potentially key construction zones for pollution treatment plant facilities and urban renewal pilot programs for restraining the widespread informal settlements. This study contributes to the development of an innovative urban non-point source pollution control measure, which may be applicable to low-income countries in Africa and elsewhere.

Soil microbes play a critical role in the recycling of soil nutrients and soil fertility. Different crop types greatly influence the soil environment, including the carbon and nitrogen biogeochemical cycles, and the effects may be particularly important on the terraces of the Loess Plateau. In this study, the characteristics of soil physicochemical properties and microbial activity were investigated under different crop types to establish relationships among soil microbial biomass, enzyme activities, and physicochemical properties. Soils under four typical crops (potato, corn, apple, and intercropping (apple and potatoes)) grown on terraces constructed during a similar period were examined at an experimental site on the Loess Plateau, with 5-year abandoned land as the control. The activities of soil invertase, urease, and alkaline phosphatase, soil microbial biomass carbon (MBC), soil microbial biomass nitrogen (MBN), and the ratio MBC/MBN, and their relationships with soil physicochemical properties were investigated using redundancy analysis and partial redundancy analysis. (1) For soil physicochemical properties, including organic carbon, total nitrogen, total phosphorus, nitrate nitrogen, and available phosphorus, the lowest concentrations were in abandoned land and the highest contents were under apple and intercropping; (2) the activities of soil invertase were in the order intercropping > corn > apple > potato > abandoned land, whereas the activities of soil urease in apple and intercropping were more than twofold higher than those in abandoned land; (3) soil microbial biomass carbon and the ratio of MBC/MBN were highest in abandoned land, which indicated that abandoned land had a high proportion of bacterial to fungal biomass; (4) soil microbial activity was affected by the application of organic manure under terrace crop systems. The contents of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) in abandoned land were significantly lower than those under all crop types; thus, directly abandoned farmland was not favorable for soil microbial activity in the typical loess hilly-gully region. Soil TP, moisture (MS), and NO3−–N were identified as the key factors affecting soil microbial activity in the 0–20-cm soil layer, and soil TP, AP, NH4+–N, and NO3−–N were the significant factors in the 20–40-cm layer.

Reclaimed coastal areas were mostly used for agricultural purposes in the past, while land-use conversion was initiated in recent decades in eastern China. Elucidation of the effects of land-use conversion on soil properties and stoichiometry is essential for addressing climate change and ecological conservation. In this study, five land-use types in a reclaimed area were chosen to compare the differences of soil properties and stoichiometry, which comprised paddy, upland, upland-forest, forest, and vegetable garden, with a soil age of about 100 years. The results indicated that these land-use types significantly differed in soil water concentration, pH, bulk density, soil salt concentration, soil organic carbon content, total nitrogen content, and total phosphorus, as well as C:N, C:P, and N:P ratios. Positive correlations were found among soil organic carbon, total nitrogen, and total phosphorus; and among pH, bulk density, and soil salt concentration. Total phosphorus and soil organic carbon contents were the main factors shaping the topsoil among the land-use types. Contents of soil organic carbon, total nitrogen, and total phosphorus in paddy and vegetable garden soils were higher than that in upland and upland-forest soils, while bulk density, pH, and soil salt concentration showed the opposite trends. Forest soil demonstrated intermediate values for most properties. And the highest C:N occurred in the upland and vegetable garden, the highest C:P in paddy and vegetable garden, while the lowest C:N and C:P occurred in upland-forest. The highest and lowest N:P occurred in paddy and upland, respectively. The stoichiometric characteristics presented a narrow range of the ratio, and the C:N:P averaged 48:3:1 similar to the stoichiometry of average Chinese cropland soils. Rotations including legume, the use of organic fertilizers, and appropriate fertilization strategies were suggested for improving cropland management.

Base on 3 m×3 m grid in sloping cornfield with soil auger in Yingwugou Small Watershed of the Dan River Basin, a total of 39 sampling points were collected, and soil water content and nutrient content were measured in different soil depths. Meanwhile, the soil properties of different depth have been analyzed by traditional statistical and geo-statistics approaches. The results showed: the mean value of total nitrogen and soil organic carbon reduced as soil depth increased in general. But soil water content increased as the soil depth increased. The change of total phosphorus with soil depth was not obvious. The total nitrogen, soil water content, soil organic carbon and total phosphorus presented a moderate intensity variation and strong spatial dependence. In these four sampling depths, semi-variance model can simulate the precisions of total nitrogen, soil water content and total phosphorus in the spatial structures of 0 to 10 cm and 10 to 20 cm well. But the spatial structure of soil organic carbon was not good, which could not be simulated with semi-variance model. The analysis with Kriging interpolation showed that, the total nitrogen, soil water content and total phosphorus presented layered distribution in the spatial structures of 0 to 10 cm and 10 to 20 cm; when the spatial distribution changed to 10 to 20 cm from 0 to 10 cm, the average total nitrogen content reduced to 0.310 g/kg from 0.598 g/kg, while the average water content and total phosphorus increased from 12.988% to 15.439% and from 0.229 g/kg to 0.366 g/kg, respectively.