Increasing Soil Depth Research Articles

Elevational distribution patterns and drivers factors of fungal community diversity at different soil depths in the Abies georgei var. smithii forests on Sygera Mountains, southeastern Tibet, China.

Soil fungal communities play a crucial role in maintaining the ecological functions of alpine forest soil ecosystems. However, it is currently unclear how the distribution patterns of fungal communities in different soil layers of alpine forests will change along the elevational gradients. Therefore, Illumina MiSeq sequencing technology was employed to investigate fungal communities in three soil layers (0-10, 10-20, and 20-30 cm) along an elevational gradient (3500 m to 4300 m) at Sygera Mountains, located in Bayi District, Nyingchi City, Tibet. The results indicated that: 1) Soil depth had a greater impact on fungal diversity than elevation, demonstrating a significant reduction in fungal diversity with increased soil depth but showing no significant difference with elevation changes in all soil layers. Within the 0-10 cm soil layer, both Basidiomycota and Ascomycota co-dominate the microbial community. However, as the soil depth increases to 10-20 and 20-30 cm soil layers, the Basidiomycota predominantly dominates. 2) Deterministic processes were dominant in the assembly mechanism of the 0-10 cm fungal community and remained unchanged with increasing elevation. By contrast, the assembly mechanisms of the 10-20 and 20-30 cm fungal communities shifted from deterministic to stochastic processes as elevation increased. 3) The network complexity of the 0-10 cm fungal community gradually increased with elevation, while that of the 10-20 and 20-30 cm fungal communities exhibited a decreasing trend. Compared to the 0-10 cm soil layer, more changes in the relative abundance of fungal biomarkers occurred in the 10-20 and 20-30 cm soil layers, indicating that the fungal communities at these depths are more sensitive to climate changes. Among the key factors driving these alterations, soil temperature and moisture soil water content stood out as pivotal in shaping the assembly mechanisms and network complexity of fungal communities. This study contributes to the understanding of soil fungal community patterns and drivers along elevational gradients in alpine ecosystems and provides important scientific evidence for predicting the functional responses of soil microbial ecosystems in alpine forests.

Effects of coal mine waste dump on soil seed bank and vegetation distribution pattern

Long-term occupation of coal gangue dumping sites (CGDS) may destroy ecological environment of nearby area. However, how the CGDS affects the distribution pattern of soil seed banks and vegetation in the nearby area is not clear. In this study, we investigated soil seed bank and vegetation at different distances from the second CGDS of Yangchangwan in Ningdong mining area, Lingwu, Ningxia. The results showed that soil seed bank was mainly distributed in 0-10 cm layer and decreased with increasing soil depth. Species richness of soil seed bank and vegetation first increased and then tended to be stable with increasing distance to the CGDS. The influence range of CGDS on soil seed banks was 300-500 m and was 100-300 m on aboveground vegetation. The CGDS did not affect the vertical distribution pattern of soil seed bank, but significantly affected the horizontal distribution pattern of soil seed banks and aboveground vegetation. The key area of vegetation restoration around the CGDS was between 100 m and 300 m.

Long-term conservation tillage changes the diversity, assembly and network stability of the diazotrophic community

Diazotrophs make important contributions to nitrogen (N) inputs in agricultural ecosystems. However, strong evidence on the effects of conservation tillage (CT) on the coexistence and assembly of diazotrophic communities and related mechanisms is lacking. Here, we studied the impacts of long-term CT on the coexistence and assembly patterns of diazotrophic communities. Compared to traditional tillage (CK), CT significantly reduced both the N fixation rate (0–10 cm) and the alpha diversity of the diazotrophic community while increasing the density of the diazotrophic and overall bacterial communities. CT also reduced the competitive relationships within the diazotrophic community and enhanced network stability. Furthermore, diazotroph assembly was dominated by deterministic processes (68.63%) under CK, and stochastic processes (58.82%) under CT. Soil depth and total N (TN) were identified as crucial predictors shaping the assembly processes of diazotrophic communities under different tillage practices. The relative influence of stochastic processes on the diazotrophic community under CT varied more significantly with increasing soil depth. Overall, tillage practices and soil depth had significant influences on the coexistence and assembly processes of the soil diazotrophic community. Moreover, long-term CT may impact the selection of N fixation agents and the specific taxa associated with N fixers. Our results indicated that in CT systems, relatively sufficient nutrient availability leads to a reduction in interspecies competition, an increase in network stability, and a greater influence of stochastic processes on community assembly. These findings may help us better understand biological N fixation in sustainable agricultural systems.

The changes in soil organic carbon stock and quality across a subalpine forest successional series

Soil organic carbon (SOC) affects the function of terrestrial ecosystem and plays a vital role in global carbon cycle. Yet, large uncertainty still existed regarding the changes in SOC stock and quality with forest succession. Here, the stock and quality of SOC at 1-m soil profile were investigated across a subalpine forest series, including shrub, deciduous broad-leaved forest, broadleaf-conifer mixed forest, middle-age coniferous forest and mature coniferous forest, which located at southeast of Tibetan Plateau. The results showed that SOC stock ranged from 9.8 to 29.9 ​kg⋅m−2, and exhibited a hump-shaped response pattern across the forest successional series. The highest and lowest SOC stock was observed in the mixed forest and shrub forest, respectively. The SOC stock had no significant relationships with soil temperature and litter stock, but was positively correlated with wood debris stock. Meanwhile, the average percentages of polysaccharides, lignins, aromatics and aliphatics based on FTIR spectroscopy were 79.89%, 0.94%, 18.87% and 0.29%, respectively. Furthermore, the percentage of polysaccharides exhibited an increasing pattern across the forest successional series except for the sudden decreasing in the mixed forest, while the proportions of lignins, aromatics and aliphatics exhibited a decreasing pattern across the forest successional series except for the sudden increasing in the mixed forest. Consequently, the humification indices (HIs) were highest in the mixed forest compared to the other four successional stages, which means that the SOC quality in mixed forest was worse than other successional stages. In addition, the SOC stock, recalcitrant fractions and HIs decreased with increasing soil depth, while the polysaccharides exhibited an increasing pattern. These findings demonstrate that the mixed forest had higher SOC stock and worse SOC quality than other successional stages. The high proportion of SOC stock (66% at depth of 20–100 ​cm) and better SOC quality (lower HIs) indicate that deep soil have tremendous potential to store SOC and needs more attention under global change.

Variations in soil physico-chemical properties, soil stocks, and soil stoichiometry under different soil layers, the major forest region Liupan Mountains of Northwest China.

Liupan Mountains are an important region in China in the context of forest cover and vegetation due to huge afforestation and plantation practices, which brought changes in soil physio-chemical properties, soil stocks, and soil stoichiometries are rarely been understood. The study aims to explore the distribution of soil nutrients at 1-m soil depth in the plantation forest region. The soil samples at five depth increments (0-20, 20-40, 40-60, 60-80, and 80-100 cm) were collected and analyzed for different soil physio-chemical characteristics. The results showed a significant variation in soil bulk density (BD), soil porosity, pH, cation exchange capacity (CEC), and electric conductivity (EC) values. More soil BD (1.41 g cm-3) and pH (6.97) were noticed in the deep soil layer (80-100 cm), while the highest values of porosity (60.6%), EC (0.09 mS cm-1), and CEC (32.9 c mol kg-1) were reflected in the uppermost soil layer (0-20 cm). Similarly, the highest contents of soil organic carbon (SOC), total phosphorus (TP), available phosphorus (AP), total nitrogen (TN), and available potassium (AK) were calculated in the surface soil layer (0-20 cm). With increasing soil depth increment a decreasing trend in the SOC and other nutrient concentration were found, whereas the soil total potassium (TK) produced a negative correlation with soil layer depth. The entire results produced the distribution of SOCs and TNs (stocks) at various soil depths in forestland patterns were 0→20cm > 20→40cm > 40→60cm ≥ 60→80cm ≥ 80→100 cm. Furthermore, the stoichiometric ratios of C, N, and P, the C/P, and N/P ratios showed maximum values (66.49 and 5.46) in 0-20 cm and lowest values (23.78 and 1.91) in 80-100 cm soil layer depth. Though the C/N ratio was statistically similar across the whole soil profile (0-100 cm). These results highlighted that the soil depth increments might largely be attributed to fluctuations in soil physio-chemical properties, soil stocks, and soil stoichiometries. Further study is needed to draw more conclusions on nutrient dynamics, soil stocks, and soil stoichiometry in these forests.

Soil Microbial and Enzymatic Properties in Luvisols as Affected by Different Types of Agricultural Land-Use Systems and Soil Depth

Determination of the microbial and enzymatic properties in soil is primarily concentrated on the surface layers of the soil profiles; however, it is well known that the transformation of soil organic matter also occurs in the deeper horizons of the soil profile. The aim of this study was to assess any changes in specific sets of enzyme activities and their associated physicochemical properties as affected by two different agricultural land-use systems and soil depth. Changes in the studied properties were determined across four Luvisol profiles in two agricultural land uses (arable land and vineyards). The enzyme activities associated with the transformation of C, N and P were analyzed. Additionally, the activity of some oxidoreductases and the fluorescein diacetate hydrolysis (FDAH) rate were also determined. Moreover, the content of the various forms of soil carbon, nitrogen, phosphorus (including microbial biomass C, N and P) and some other properties (pH, clay and silt content) were assessed. Agricultural land use significantly affected the microbial biomass content and as well as the studied enzyme activities. Most of the studied enzymes exhibited a higher activity in the grapevine (GV) profiles, which was followed by the winter wheat (WW) profiles; however, the largest variability occurred for the urease activity. There was no clear differentiation between the two studied land uses for the activity of nitrate reductase, dehydrogenases, acid phosphatase, or endo- and exo-cellulase. Irrespective of the plant being cultivated, the soil variables decreased significantly with increasing soil depth, wherein the greatest changes were observed between the surface and sub-surface soil horizons (I–II). The activity of some enzymes (e.g., the urease activity in WW profiles) decreased gradually across the soil profiles, while others were located almost solely within the surface layers (e.g., the nitrate reductase activity in the GV profiles as well as invertase in the WW profiles). The α-glucosidase activity did not exhibit any statistically significant changes along the analyzed profiles. The activity of phenol oxidase and peroxidase also revealed different trends along the studied profiles compared to the other enzymes and did not decrease gradually with depth. The microbial biomass of the C, N and P content was generally the highest in the upper horizons and gradually decreased with depth, wherein the largest decrease was observed between the surface and sub-surface horizon. The studied enzyme activities were more dependent on the soil carbon content compared to the other soil properties. And thus, in the C-rich horizons (C > 4 g kg) for the surface and subsurface layers the enzyme activities were highly correlated with TOC, DOC and MBC content as compared to the deeper, C-low horizons (C < 4 g kg). By examining how the microbial and enzymatic properties change across the soil profiles, it is possible to gain valuable insight into the long-term biogeochemical processes that are involved in soil fertility and in the health of agricultural ecosystems.

Microbial carbon and nitrogen limitation in Larix gmelinii forests along an altitudinal gradient: Evidence from ecoenzymatic stoichiometry and vector analysis

Mountain ecosystems have obvious variations in environmental factors at small spatial scales and thus provide a natural platform for investigating climate change. To investigate the characteristics of extracellular enzymes and microbial metabolic limitations in the hostile environmental conditions of cold temperate mountain ecosystems, soil physicochemical properties and enzyme activities were measured in the 0–10 cm and 10–20 cm soil layers of Larix gmelinii forests at elevations of 830 m, 950 m, 1100 m, and 1300 m. Our results showed that altitude and soil depth had a significant effect on 1,4-β-glucosidase, 1,4-β-N-acetyl-glucosaminidase, leucine aminopeptidase, and acid phosphatase activities. Extracellular enzyme activities decreased with increasing altitude and soil depth. The stoichiometric ratio of soil C-, N-, and P-acquiring enzymes after logarithmic transformation was 1:1.27:0.72 across all altitudes and soil depths. The metabolism of the microorganisms was mainly limited by C and N, and a high C limitation was observed at higher-altitude sites. With increased soil depth, the N limitation gradually weakened. Moreover, soil bulk density and pH were the main factors affecting extracellular enzyme activities and microbial nutrient constraints. Our study revealed that the carbon and nitrogen limitation of soil microbes was induced by the variation in soil factors in a cold temperate mountain forest ecosystem. This finding provides important insights into the mechanism of microbial metabolic limitation in the face of climate change.

Seed Bank Distribution of Kongwa Weed (Astripomoea Hyoscyamoides) for Different Land Use Types in Kongwa District, Tanzania

Weed invasion poses significant challenges to agriculture and ecosystems, leading to substantial economic losses globally. Astripomoea hyoscyamoides Vatke Verdc. commonly known as Kongwa weed, is a highly invasive species causing a severe infestation in the Kongwa district, Tanzania. This study investigated the seed bank distribution of Kongwa weed across different land use types, specifically arable land, fallow land, and range land in the Kongwa district. Soil samples were collected from chamae, chigwingwili, chimotolo, machenje, msunjulile, ndalibo, nyerere, and sejeli villages, representing range, arable, and fallow land, at different soil depths (0-5 cm, 5-10 cm, 10-15 cm, and 15-20 cm). The results showed significant variations in Kongwa weed seed density among villages, with Msunjulile exhibiting the highest density across all land use types (1.92 seeds/m2 in arable, 6.67 seeds/m2 in fallow, and 9.83 seeds/m2 in range land). In comparison, Chigwingwili displayed the lowest density (0.33 seeds/m2 in arable land) The study revealed a decline in seed density with increased soil depth, with the topsoil (0-5 cm) showing the highest seed density. Also, range land exhibited the highest seed density, while arable and fallow land were comparable. Generally, kongwa weed seeds are observed to be higher in range land with a depth of 0–5 cm, particularly in areas near ranch areas. Implementing control measures, especially before the flowering stage, is crucial to mitigating the kongwa weed invasion. Further research on seed germination patterns is recommended to enhance weed management strategies.

Multi-Scale Periodic Variations in Soil Moisture in the Desert Steppe Environment of Inner Mongolia, China

Uncovering the complex periodic variations in soil moisture can provide a significant reference for climate prediction and hydrological process simulation. We used wavelet analysis to quantify and identify the multi-scale periodic variations of soil moisture in the desert steppe of Inner Mongolia from 2009 to 2019 and analyzed the differences between the multi-scale periodic changes in soil moisture at the bottom (BS) and upper slope (US). The results show that the interannual variability in soil moisture at the BS and US has a significant upward trend. Moreover, the amount and volatility decrease with the increase in soil depth in the range of 0–30 cm, and the soil moisture at the BS is 26.4% higher than the US. The soil moisture has periodic changes of 0.5a, 1a, 2a, 3a and 3.5a in the desert steppe environment of Inner Mongolia. The periodic structure and intensity of different slope positions are greatly different. Soil moisture at the US has more complex multi-scale periodic changes, and the periodic oscillations of 3.5a, 3a, and 1a are dominant. The periodic oscillations of 0.5a and 1a are dominant at the BS. At the BS, the intensity of periodic oscillation of 1a after January 2015 has weakened. The weakening of soil moisture by temperature, rainfall and soil temperature caused the change in the multiple time-scale periodic oscillation of soil moisture.

Assessment of heavy metal distribution and bioaccumulation in soil and plants near coal mining areas: implications for environmental pollution and health risks.

Monitoring heavy metals (HMs) across source distance and depth distribution near coal mining sites is essential for preventing environmental pollution and health risks. This study investigated the distribution of selected HMs, cadmium (Cd2+), chromium (Cr2+), copper (Cu2+), manganese (Mn2+), nickel (Ni2+), lead (Pb2+), and zinc (Zn2+), in soil samples collected from ten sites (S-1-S-10) at two different depths (0-15 and 15-30 cm) and distances of 50, 100, and 200 m from a mining source. Additionally, three plant species, Prosopis spp., Justicia spp., and wheat, were collected to assess HM bioavailability and leaf accumulation. Coal mine activities' impact on soil properties and their HM associations were also explored. Results reveal HM concentrations except for Cr2+ exceeding World Health Organization (WHO) limits. In surface soil, Cd2+ (58%), Cu2+ (93%), Mn2+ (68%), Ni2+ (80%), Pb2+ (35%), and Zn2+ (88%) surpassed permissible limits. Subsurface soil also exhibited elevated Cd2+ (53%), Cu2+ (83%), Mn2+ (60%), Ni2+ (80%), Pb2+ (35%), and Zn2+ (77%). Plant species displayed varying HM levels, exceeding permissible limits, with average concentrations of 1.4, 1.34, 1.42, 4.1, 2.74, 2.0, and 1.98 mg kg-1 for Cd2+, Pb2+, Cr2+, Cu2+, Mn2+, Ni2+, and Zn2+, respectively. Bioaccumulation factors were highest in wheat, Prosopis spp., and Justicia spp. Source distance and depth distribution significantly influenced soil pH, electrical conductivity (EC), and soil organic carbon (SOC). Soil pH and EC increased with an increase in soil depth, while SOC decreased. Pearson correlation analysis revealed varying relationships between soil properties and HMs, showing a considerably negative correlation. Concentrations of HMs decreased with increasing depth and distance from mining activities, validated by regression analysis. Findings suggest crops from these soils may pose health risks for consumption.

Study on the seismic characteristics of piers considering site conditions and hydrodynamic effect

Sea-crossing bridges face complex site environments compared to onshore bridges, with the marine environment significantly influencing seismic responses. Despite this, current seismic design for these bridges relies on onshore earthquake records. Therefore, investigating the impact of seawater layers and site conditions on sea-crossing bridge seismic performance is crucial. This paper investigates the influence of characteristics of offshore ground motion, site conditions, and hydrodynamic effect on the seismic performance of piers. Initially, based on the validated finite element model, 5 offshore and onshore strong ground motion records from K-NET were selected for assessing the seismic performance of piers. Subsequently, the effects of the water depth and site conditions on the seismic responses of piers were investigated. Finally, the effects of the section size, section shape, and boundary conditions on the piers were investigated. The result shows that the seismic response of piers under offshore ground motion exceeds that under onshore ground motion. In addition, the seismic response of the pier increases with greater water depth, while they exhibit a slight decrease with increasing soil depth. Notably, the larger the section size, result in higher the hydrodynamic pressure, and square piers experience greater hydrodynamic pressure compared to circular piers.

Ecotoxicity of heavy metals in soil around long-term e-waste recycling sites in Tema and Ashaiman areas of Ghana.

The effect of e-waste recycling activities on the prevalence of metals (Cd, Cu, Hg, Ni, Pb, and Zn) and a metalloid (As) in soil was assessed for four e-waste sites in Ghana. Samples of top- and subsoil were collected from dismantling and burning sections, and the prevalence and the distribution of selected metals were determined using atomic absorption spectroscopy. The concentrations of the metals analyzed were above the background concentrations except for Cd, which was detected at a comparable level to the background levels. Levels of Cu and Pb increased with increasing soil depth. Cd, Zn, As, and Ni levels decreased with increasing soil depth. However, Hg levels showed no recognizable trend in its distribution relative to soil depth. The pollution indices evaluated revealed deterioration of the soil quality at the e-waste sites. Pollution indices are used to categorize soil pollution levels based on cut-off values. Geo-accumulation indices suggested that the soil was very highly polluted with Pb, highly polluted with Cu, and moderately polluted with As, Hg, Cd, and Zn. The enrichment factor values indicated that soil from the studied sites was very highly enriched with Pb (i.e., EF of 9.60 to 63.14; median being 28.51) and significantly enriched with Cu and Hg (i.e., EF of 3.09 to 21.86; median 7.72 for Cu and EF of 1.48 to 25.5; median 10.57 for Hg). The contamination factor analysis revealed very high contamination of soils with Pb. The metals Cu, Zn, As, Ni, Cd, and Hg exhibited moderate to considerable contamination. This study is part of the continuous effort to assist policymakers with scientific information needed to influence policy decisions on environmental management in Ghana.

Niche-specific modulation of long-chain n-alkanes degrading bacterial community and their functionality in forest habitats across the leaf litter-soil compartments

Long-chain n-alkanes are vital constituents of plant-derived wax, however, their limited reactivity, life cycle in terms of biodegradation, and ecological impacts are not lucid in a niche-specific manner. Here, we provide an insight into the bacterial community and their functional variations associated with long-chain n-alkanes degradation across leaf litter-soil compartments in three rainforest habitats aiming to elucidate the microbial modulation linked to the long-chain n-alkanes concentration and composition. The ravine habitat showed significantly higher long-chain n-alkanes concentration, bacterial diversity and functional genes than the windward and leeward habitats. Among the statistically significant genera (p < 0.05) Intrasporangium, Virgisporangium, Micromonospora, and Planomicrobium were more abundant in the ravine habitat than in the other two habitats. Interestingly, three statistically significant genera including Sphingobium, Tepidisphaera, and Methylobacterium showed a decrease abundance with increasing soil depths compared to their abundance in leaf litter. The correlation analysis revealed that Rhizobium, Pseudorhodoferax, Micromonospora, Dongia, Actinoplanes, Bdellovibrio, Ohtaekwangia, Planctomicrobium, Opitutus, Actinokineospora, Novosphingobium, and Methylobacterium were significantly in a positive relationship with alkB gene and most of the long-chain n-alkanes (C27 to C34). The ordination analysis further unveiled a strong association among the long-chain n-alkanes concentration, potential degraders and alkB gene within the ravine habitat. Additionally, we observed a decreasing trend in the abundance of bacterial taxa and related functional genes with decreasing the long-chain n-alkane concentration, suggesting n-alkane specific taxa modulation. Fundamentally, this study provides niche-specific evidence that the concentration of long-chain n-alkanes could contribute to a shift in bacterial diversity, abundance and function in forest habitats.

Large-Scale Freezing and Thawing Model Experiment and Analysis of Water–Heat Coupling Processes in Agricultural Soils in Cold Regions

Heilongjiang Province, the largest commercial grain base in China, experiences significant challenges due to the environmental effects on its soil. The freezing and thawing cycle in this region leads to the transport of water and heat, as well as the exchange and transfer of energy. Consequently, this exacerbates the flooding disaster in spring and severely hampers farming activities such as plowing and sowing. To gain a better understanding of the freezing and thawing mechanisms of farmland soil in cold regions and prevent spring flooding disasters, this study focuses on Heilongjiang Province as a representative area in northeast China. The research specifically investigates the frozen and thawed soil of farmland, using a large-scale low-temperature laboratory to simulate both artificial and natural climate conditions in the cold zone. By employing the similarity principle of geotechnical model testing, the study aims to efficiently simulate the engineering prototypes and replicate the process of large-span and long-time low temperatures. The investigation primarily focuses on the evolution laws of key parameters, such as the temperature field and moisture field of farmland soil during the freeze–thaw cycle. The findings demonstrate that the cooling process of soil can be categorized into three stages: rapid cooling, slow cooling, and freezing stabilization. As the soil depth increases, the variability of the soil temperature gradually diminishes. During the melting stage, the soil’s water content exhibits a gradual increase as the temperature rises. The range of water content variation during thawing at depths of 30 cm, 40 cm, 50 cm, and 80 cm is 0.12% to 0.52%, 0.47% to 1.08%, 0.46% to 1.96%, and 0.8% to 3.23%, respectively. To analyze the hydrothermal coupling process of farmland soil during the freeze–thaw cycle, a theoretical model of hydrothermal coupling was developed based on principles of mass conservation, energy conservation, Darcy’s law of unsaturated soil water flow, and heat conduction theory. Mathematical transformations were applied after defining the relative degree of saturation and solid–liquid ratio as field functions with respect to the relative degree of saturation and temperature. The simulated temperature and moisture fields align well with the measured data, indicating that the water–heat coupling model established in this study holds significant theoretical and practical value for accurately predicting soil temperature and moisture content during the spring sowing period, as well as for efficiently and effectively utilizing frozen soil resources in cold regions.

Spatial temperature distribution and ground thermal storage in the plastic greenhouse: An experimental and modeling study

The precise regulation of the indoor thermal environment in plastic greenhouses is impacted by the spatial distribution of indoor air temperature and soil temperature fluctuations. This study used a scaled-down model to take the preliminary experiment to demonstrate the dynamic spatial temperature variation in a plastic greenhouse. Then, by considering the dynamic change in solar orientation, a transient model of a real-size plastic greenhouse coupling soil and indoor microenvironment was developed, validated, and then applied to investigate the spatial temperature distribution in the plastic greenhouse. In addition, a method for measuring the soil capability for effective thermal conversion was proposed. Results showed that the indoor air temperature varied significantly with height. The temperature difference between the air near the roof surface and the air within the building peaked at 13.3 °C at 12:00 and was just 2 °C at 9:00. The soil temperature increased, and soil temperature peaks delayed sequentially with the soil depths. The daily fluctuation of soil temperature decreased with increasing soil depth, and the temperature remained stable at the depth of 0.45 m. In addition, with an effective heat conversion rate of 40.3 %, the soil regulated the indoor thermal environment as a heat source. This paper provides a reference for the indoor thermal environment regulation of plastic greenhouses for the purpose of saving energy in agricultural production.

Changes in soil quality under long‐term rice‐crayfish farming in the Dongting Lake Plain, China

AbstractRice‐crayfish (RC) integrated cultivation, as a sustainable agricultural system, could significantly improve soil fertility. However, the soil quality under the long‐term RC farming system is still unclear. To examine the effects of RC cultivation on soil quality in paddy fields, this study utilized an integrated soil quality index (SQI) for examining the soil quality at different soil profiles (0–10, 10–20, and 20–30 cm depth) in rice monoculture (RM) and RC farming systems (after 1, 6, 10, and 15 years) scattered in Nanxian County, Hunan Province, China. The minimum datasets for evaluating soil quality were assembled using the soil pH, bulk density, total nitrogen, microbial biomass carbon, microbial biomass nitrogen, and β‐d‐glucosidase. The findings demonstrated that soil quality was greatly impacted by RC farming, which improved with the increase of years under RC management. The soil quality of 10‐ and 15‐year RC farming systems were significantly higher than RM system. Besides, soil quality declined with increasing soil depth. The SQI value, which may be used as an indicator to assess the soil quality of RC systems, was dominated by total nitrogen, which contributed 27.60% to the SQI value. On the whole, long‐term RC farming affected the soil quality of paddy fields through management methods including non‐rice season flooding, feeding, and no tillage. Through this study, it was found that MDS and SQI composed of appropriate physical, chemical, and biological indicators could more objectively analyze the soil quality of long‐term RC system and provide guidance for sustainable development of RC farming.

Responsive characteristics of soil water regimes to rainfall events in a boreal larch forest in China: Dynamic processes and decoupling effects

Investigating the soil water dynamics in relation to rainfall events is of great importance for enhancing our understanding of eco-hydrological processes and improving soil hydrological models. However, the lack of long-term, in-situ observational data and the neglect of soil moisture decoupling have hindered the study of dynamic responses in soil water regimes to rainfall events in China’s boreal forests with permafrost. This study utilized soil water content monitoring and rainfall observational data from the Xing’an larch (Larix gmenilii) forest in Northeast China during the growing seasons of 2015–2021 to evaluate the dynamic response of soil water regimes to rainfall events. The results show a significant increase in the decoupling strength between soil water and rainfall with increasing soil depth. The thresholds of rainfall amount (RA), duration (RD), and intensity (RI) for triggering soil wetting events also increased. Soil water dynamic processes exhibited inconsistent and complex patterns in response to the hierarchical effects of RA, RD, and RI along the vertical soil profile. However, the dominant controls on soil water dynamic responses to RA, RD, and RI varied depending on specific response metrics, such as the accumulated soil water content increments (ASMI), duration time (DT), and the mean slope of the soil wetting curve (Sm). Interestingly, the dominant factor for affecting response time (RT) changed from RI to RD as soil depths increased. Importantly, the decoupling of soil moisture led to a substantial reduction in the responsiveness of these metrics of subsurface soil water to rainfall, and the role of the decoupling effect diminished with increasing soil depths. These findings highlight the complexity of the dynamic response of soil water to rainfall events and provide new insights into the relationship between soil water dynamics and rainfall features through the introduction of the decoupling of soil moisture in boreal forests.

Responses of Soil Respiration to the Interactive Effects of Warming and Drought in Alfalfa Grassland on the Loess Plateau

Elevated temperature and frequent drought events under global climate change may seriously affect soil respiration. However, the underlying mechanism of the effects of warming and drought on soil respiration is not fully understood in the context of the Loess Plateau. This study examined the response of soil respiration (Rs) to multiple factors, including warming (W), drought (P), and their interaction (WP), in the semi-arid grassland of the Loess Plateau in Northwest China. The research period was from May to November 2022, with an open-top heating box used for warming and a rain shelter used for drought. The results showed the following: (1) Rs ranged from 1.67 μmol m−2 s−1 to 4.77 μmol m−2 s−1, with an average of 3.36 ± 0.07 μmol m−2 s−1. The cumulative soil carbon flux ranged from 500.97 g C·m−2 to 566.97 g C·m−2, and the average cumulative soil respiration was 535.28 ± 35.44 g C·m−2. (2) Warming increased Rs by 5.04 ± 3.11%, but drought inhibited Rs by 3.40 ± 3.14%, and the interaction between warming and drought significantly reduced soil respiration by 11.27 ± 3.89%. (3) The content of particulate organic carbon (POC), dissolved organic carbon (DOC), soil organic carbon (SOC), and readily oxidized carbon (ROC) decreased with the increased soil depth. ROC after W and WP treatments was significantly higher than that of the control, and POC after P treatment was significantly higher than CK (p &lt; 0.05). (4) The seasonal variation of soil respiration was positively correlated with soil temperature, soil water content, plant height, and leaf area index (p &lt; 0.05), but the response rules differed during different regeneration periods. Soil water content; soil water content and leaf area index; and soil water content, soil temperature, and leaf area index were the factors that regulated the variation in soil respiration in the first, second, and third regeneration periods, respectively. These results clearly showed the limiting effect of drought stress on the coupling between temperature and soil respiration, especially in semi-arid regions. Collectively, the variations in soil respiration under warming, drought, and their interactions were further regulated by different biotic and abiotic factors. Considering future warming, when coupled with increased drought, our findings indicate the importance of considering the interactive effects of climate change on soil respiration and its components in arid and semi-arid regions over the next decade.

Varied Macro- and Micronutrient Fertilization Rates Impact Root Growth and Distribution and Fruit Yield of Huanglongbing-affected Valencia Orange Trees

Candidatus Liberibacter asiaticus (CLas), which causes huanglongbing (HLB) in citrus trees, has a great impact on tree root health, fruit development, and juice quality. HLB-affected trees have a fibrous root density loss of ∼30% to 80%, resulting in the limited capacity of citrus trees to uptake nutrients. Therefore, this study was conducted for 3 years to 1) assess the temporal changes in root density as a result of varied fertilization, 2) determine dynamics of HLB with regard to root growth and distribution as a result of varied fertilization for Valencia orange trees, and 3) evaluate the impact of varied fertilization rate and method of fertilization on fruit yield for HLB-affected trees. Macronutrients and micronutrients were applied at varying fertilization rates (0×, 1×, 2×, and 4×, of University of Florida guidelines). Root scans were done using minirhizotrons at 0 to 19.1 cm, 19.1 to 40.7 cm, 38.2 to 59.8 cm, and 57.3 to 78.9 cm soil depths. Results obtained from the study showed that root growth and distribution were greater in 0 to 19.1 cm than 19.1 to 40.7 cm to 57.3 to 78.9 cm soil depths. Thus, root growth decreased (P &lt; 0.0004) with increasing soil depth due to variation in nutrient availability for tree uptake. Increased nutrient availability at occurrence of physiological processes in citrus trees also influenced root growth and distribution, resulting in root growth flushes in the months of Nov to early Feb and Jul to early Aug. Fruit yield was significantly different between treatments in 2 of the 4 years of the study (P = 0.001 and P = 0.003), and largely ascribed to soil fertilization of micronutrients compared with foliar. Therefore, at higher fertilization rates, particularly via soil application, nutrient availability was increased, thus promoting root growth and distribution and fruit yield in HLB-affected orange trees.

Reforestation regulated soil bacterial community structure along vertical profiles in the Loess Plateau

IntroductionReforestation is a widely used strategy for ecological restoration in areas facing ecological degradation. Soil bacteria regulate many functional processes in terrestrial ecosystems; however, how they respond to reforestation processes in surface and deep soils remains unclear.MethodsArtificial Robinia pseudoacacia plantation with different stand ages (8, 22, and 32 years) in a typical fallow forest on the Loess Plateau was selected to explore the differential response of soil bacterial community to reforestation in different soil depths (surface 0–200 cm, middle 200–500 cm, and deep 500-100 cm). Soil bacterial diversity, community composition and the co-occurrence patterns, as well as the functions were analyzed.Results and discussionThe results showed that alpha diversity and the presence of biomarkers (keynote species) decreased with the increasing soil depth, with a sharp reduction in family-level biomarker numbers in 500–1,000 cm depth, while reforestation had a positive impact on bacterial alpha diversity and biomarkers. Reforestation induced a more loosely connected bacterial community, as evidenced by an increase of 9.38, 22.87, and 37.26% in the average path length of the co-occurrence network in all three soil layers, compared to farmland. In addition, reforestation reduced the hierarchy and complexity but increased the modularity of the co-occurrence network in top and deep soil layers. Reforestation also led to enrichment in the relative abundance of functional pathways in all soil layers. This study sheds light on the strategies employed by deep soil bacteria in response to reforestation and underscores the significant potential of deep soil bacteria in terrestrial ecosystems, particularly in the context of human-induced environmental changes.