Forest Soil Type Research Articles

The Effects of Mixed Robinia pseudoacacia and Quercus variabilis Plantation on Soil Bacterial Community Structure and Nitrogen-Cycling Gene Abundance in the Southern Taihang Mountain Foothills.

Mixed forests often increase their stability and species richness in comparison to pure stands. However, a comprehensive understanding of the effects of mixed forests on soil properties, bacterial community diversity, and soil nitrogen cycling remains elusive. This study investigated soil samples from pure Robinia pseudoacacia stands, pure Quercus variabilis stands, and mixed stands of both species in the southern foothills of the Taihang Mountains. Utilizing high-throughput sequencing and real-time fluorescence quantitative PCR, this study analyzed the bacterial community structure and the abundance of nitrogen-cycling functional genes within soils from different stands. The results demonstrated that Proteobacteria, Acidobacteria, and Actinobacteria were the dominant bacterial groups across all three forest soil types. The mixed-forest soil exhibited a higher relative abundance of Firmicutes and Bacteroidetes, while Nitrospirae and Crenarchaeota were most abundant in the pure R. pseudoacacia stand soils. Employing FAPROTAX for predictive bacterial function analysis in various soil layers, this study found that nitrogen-cycling processes such as nitrification and denitrification were most prominent in pure R. pseudoacacia soils. Whether in surface or deeper soil layers, the abundance of AOB amoA, nirS, and nirK genes was typically highest in pure R. pseudoacacia stand soils. In conclusion, the mixed forest of R. pseudoacacia and Q. variabilis can moderate the intensity of nitrification and denitrification processes, consequently reducing soil nitrogen loss.

Lithology and elevated temperature impact phoD-harboring bacteria on soil available P enhancing in subtropical forests

Plants are generally limited by soil phosphorus (P) deficiency in forest ecosystems. Soil available P is influenced by lithology, temperature, and soil microbes. However, the interactive effects of these factors on soil P availability in subtropical forests remain unclear. To assess their impacts, we measured soil inorganic and available P fractions and the diversity, composition, and co-occurrence network of phoD-harboring bacteria in two contrasting forest soils (lithosols in karst forests and ferralsols in non-karst forests) in the subtropical regions of southwestern China across six temperature gradients. The present results showed that the complexities in composition and network and the diversity indices of phoD-harboring bacteria were higher in the karst forest soils than those in the non-karst forest soils, with marked differences in composition. In both types of forest soils, the complexities of composition and networks and the diversity indices were higher in the high-temperature regions (mean annual temperature (MAT) > 16 °C) compared to the low-temperature regions (MAT <16 °C). Soil total inorganic and available P contents were lower in the karst forest soils compared to the non-karst forest soils. Soil total available P contents were lower in the high temperature regions than those in the low temperature regions in both forest soils, whereas soil total inorganic P contents were contrary. Variance partitioning analysis showed that soil inorganic and available P fractions were predominantly explained by lithology and its interaction with soil microbes and climate. The present findings demonstrate that soil P availability in subtropical forests of southwestern China is influenced by lithology and temperature, which regulate the diversity, composition, and network connectivity of phoD-harboring bacteria. Furthermore, this study highlights the significance of controlling the composition of phoD-harboring bacteria for mitigating plant P deficiency in karst ecosystems.

Spatial patterns of biomass change across Finland in 2009–2015

Forest characteristics vary largely at the regional level and in smaller geographic areas in Finland. The amount of greenhouse gas emissions is related to changes in biomass and the soil type (e.g. upland soils vs. peatlands). In this paper, estimating and explaining spatial patterns of tree biomass change across Finland was the main interest. We analysed biomass changes on different soil and site types between the years 2009 and 2015 using the Finnish multi-source national forest inventory (MS-NFI) raster layers. MS-NFI method is based on combining information from satellite imagery, digital maps and national forest inventory (NFI) field data. Automatic segmentation was used to create silvicultural management and treatment units. An average biomass estimate of the segmented MS-NFI (MS–NFI–seg) map was 73.9 tons ha−1 compared to the national forest inventory estimate of 76.5 tons ha−1 in 2015. Forest soil type had a similar effect on average biomass in MS–NFI–seg and NFI data. Despite good regional and country-level results, segmentation narrowed the biomass distributions. Hence, biomass changes on segments can be considered only approximate values; also, those small differences in average biomass may accumulate when map layers from more than one time point are compared. A kappa of 0.44 was achieved for precision when comparing undisturbed and disturbed forest stands in the segmented Global Forest Change data (GFC-seg) and MS–NFI–seg map. Compared to NFI, 69% and 62% of disturbed areas were detected by GFC-seg and MS–NFI–seg, respectively. Spatially accurate map data of biomass changes on forest land improve the ability to suggest optimal management alternatives for any patch of land, e.g. in terms of climate change mitigation.

An Empirical Modelling and Simulation Framework for Fire Events Initiated by Vegetation and Electricity Network Interactions

Electrical infrastructure is one of the major causes of bushfire in Australia alongside arson and lightning strikes. The two main causes of electrical-infrastructure-initiated fires are asset failure and powerline vegetation interactions. In this paper, we focus on powerline–vegetation interactions that are caused by vegetation falling onto or blowing onto electrical infrastructure. Currently, there is very limited understanding of both the spatio-temporal variability of these events and their causative factors. Bridging this knowledge gap provides an opportunity for electricity utility companies to optimally allocate vegetation management resources and to understand the risk profile presented by vegetation fall-in initiated fires, thereby improving both operational planning and strategic resource allocation. To bridge this knowledge gap, we developed a statistical rare-event modelling and simulation framework based on Endeavour Energy’s fire start and incident records from the last 10 years. The modelling framework consists of nested, rare-event-corrected, conditional probability models for vegetation events and consequent ignition events that provide an overall model for vegetation-initiated ignitions. Model performance was tested on an out-of-time test set to determine the predictive utility of the models. Predictive performance was reasonable with test set AUC values of 0.79 and 0.66 for the vegetation event and ignition event models, respectively. The modelling indicates that wind speed and vegetation features are strongly associated with vegetation events, and that Forest Fire Danger Index (FFDI) and soil type are strongly associated with ignition events. The framework can be used by energy utilities to optimize resource allocation and prepare future networks for climate change.

СОДЕРЖАНИЕ УГЛЕРОДА В ПОЧВАХ И ЛЕСНОЙ ПОДСТИЛКЕ НАСАЖДЕНИЙ УФИМСКОГО ЛЕСНИЧЕСТВА

One of the important forest-climatic research areas is the study of soil carbon level in different types of forest soils with the prospect of developing effective measures to solve the problem of forest management in terms of reducing the effects of climate change. In this regard, monitoring of forest ecosystems for absorption of greenhouse gases and justification of measures to increase this capacity is relevant in carbon polygons and in the establishment of carbon farms. The assessment of carbon stock in the topsoil and structural-aggregate composition was carried out on the basis of field and laboratory studies at the site of carbon polygon No. 4 Forest (19, 20 quarters). In the course of research, the highest carbon content in the upper soil layer 0–20 cm of the studied soils in the profile of chernozem podzolized – 11.31 kg C/m2 , lower content of organic carbon in light gray forest soils – 5.26 kg C/m2 . It was revealed that the total stock of organic carbon in the upper soil layers of the carbon polygon on the territory of Dmitrievskoye forest lot is 8134.19 tons (813.42 kg C/m2 ), the greatest contribution is made by chernozem podzolnyi and dark gray forest soils. As a result of studies on the presence of nitrogen in the forest area fall, it was revealed that the linden stand contains 2.04, and birch stand – 1.43 % per 100 g of dry matter.

Effect of Platinum Nanoparticles (PtNPs) Pollution on the Biological Properties of Haplic Cambisols Eutric of the Caucasus Forests

Pollution by platinum (Pt) is an emerging threat to forest soil health. The widespread use of Pt nanoparticles (NPs) in gas neutralizers for automobile exhaust has sharply increased the amount of PtNP pollution in the environment, including forest ecosystems. Recently, territories with Pt concentrations greater than 0.3 mg/kg in soil have been discovered. This concentration is 750 times greater than the background content in the earth’s crust. Cambisols, the most prevalent forest soil type in boreal forests that determines the functioning of the entire forest ecosystem, occupy a significant share of the Earth’s soil cover, which is about 1.5 billion hectares worldwide, or 12% of the entire continental land area. This shows the importance of studying the effect of pollution on this type of soil. In this study, laboratory simulations of PtNP contamination of the Haplic Cambisols Eutric at concentrations of 0.01, 0.1, 1, 10, and 100 mg/kg were carried out. The effect of PtNPs on soil properties was assessed using the most sensitive and informative biological indicators. The total number of bacteria was studied by the methods of luminescent microscopy, catalase activity (gasometrically), dehydrogenases activity (spectrophotometrically), germination, and length of roots by the method of seedlings. It was found that at the concentrations of 0.01, 0.1, and 1 mg/kg of PtNPs, there was either no effect or a slight, statistically insignificant decrease in the biological state of Haplic Cambisols Eutric. Concentrations of 10 and 100 mg/kg of PtNPs had a toxic effect on all the studied parameters. No statistically significant stimulating effect (hormesis) of PtNPs on the biological properties of Haplic Cambisols Eutric was observed, which indicates the high toxicity of PtNPs and the importance of studying the consequences of soil and ecosystem contamination with PtNPs. However, when the content of Pt in the soil was 1 mg/kg, there was a tendency to stimulate germination, the length of radish roots, and the total number of bacteria. The toxicity of PtNPs measured by biochemical indicators (activity of catalase and dehydrogenases) starts at a concentration of 100 mg/kg for phytotoxic effects (germination and root length of radish) and 10 mg/kg for microbiological effects (total number of bacteria).

Impact of no-till technology on the fertility of degraded and low-humus soils

The transition to innovative tillage technologies is currently an effective way to preserve and increase the fertility of agricultural land. The purpose of the work is to study the impact of no-till technology on the fertility of degraded and low-humus soils in the Middle Volga region. The main research method was the monitoring of agricultural lands, where traditional (control), minimum and no-till technologies for cultivating grain crops were used as part of field crop rotations. As a result of research conducted over fifteen years on degraded leached chernozems, light gray forest and low-humus soddy-podzolic soil types, it was found that the introduction of no-till technology contributes to an increase in the number of earthworms by 36% and soil invertebrates by 42%. At the same time, the ratio of different groups of soil mesofauna also changes. In particular, an increase in the number of organized predators (ground beetles, rove beetles, spiders, geofields) capable of regulating the number of harmful species of soil animals (for example, wireworm larvae) was revealed. No-till technology has a beneficial effect on agrophysical, agrochemical indicators of fertility and biological activity of degraded and low-humus soils. The crushing of straw and its use as mulch for fifteen years made it possible to form a positive balance of organic matter and increase the content of mobile phosphorus and exchangeable potassium in the soil by an average of 20% and 15%, respectively. Improving the nutritional regime of the soil contributes to a positive impact on the quality characteristics and grain yield of winter and spring wheat, winter rye, barley and corn. With the introduction of no-till technology as the main method of crop production, grain yield increases by 3 and 6% compared to the minimum and traditional technology.

Effects of Fertilizers and Litter Treatment on Soil Nutrients in Korean Pine Plantation and its Natural Forest of Northeast China

Organic and inorganic soil fertilizer addition or removal pose significant effects on soil nutrients. As climate change and other anthropogenic factors are causing deprivation in soil nutrient profiles and altering its proper functioning, complete insight into fertilizer modification and its consequences is required for understanding the sustenance of forest ecosystems. In this regard, an experiment was conducted at Liangshui National Nature Reserve, northeast China, in which two forest soil types (i.e., Korean pine plantation and natural Korean pine forest) were evaluated for their response to external fertilizer applications and litter treatments. The litter treatments were litter application as Ck (undisturbed litter), RL (removed litter) and AL (Alter/double litter i.e., litter removed from RL was added in double litter plots), whereas the synthetic fertilizer treatments were Control (No added N and P), Low (5 g N m−2 a−1 + 5 g P m−2 a−1), Medium (15 g N m−2 a−1 + 10 g P m−2 a−1) and High (30 g N m−2 a−1 + 20 g P m−2 a−1). The outcome showed that soil organic carbon (SOC) was directly proportionate to forest litter amounts. Synthetic fertilizers affected soil total nitrogen (STN) and maximum amounts were recorded in plots with H: 30 g N m−2 a−1 + 20 g P m−2 a−1, as 3.03 ± 0.35 g kg−1 in AL. Similarly, altered litter/double was most effective in enhancing the quantity of soil total phosphorus (STP) (0.75 ± 0.04 g kg−1). Soil sampling carried out during the start and end of the experiment showed decreases in the sixth sampling of: SOC (4–23%), STN (7.5-10.8%) and STP (8.51–13.9%). A positive correlation was observed between SOC and total nitrogen; C:N ratio also increased with SOC. Principal component analysis (PCA) on captured a total of 62.1% variability, on the x-axis (35.1%) and on the y-axis (27%). It was concluded that combined application of N and P at the level of 30 g N m−2 a−1 + 20 g P m−2 a−1 under AL (Alter/double litter) treatment level improved soil total N and P content. The results clearly depicted that forest litter is an important source for building up of soil organic matter, however for attaining maximum sustenance capabilities in soil, the continuity of fertilizer application in either form is a prerequisite.

Efficacy of Liming Forest Soil in the Context of African Swine Fever Virus.

Since September 2020, Germany has experienced the first ever outbreak of African swine fever (ASF). The first known cases occurred exclusively in wild boar in forest areas in Brandenburg and Saxony; in July 2021, infected domestic pigs were also confirmed for the first time. As wild boar are considered the main reservoir for the virus in the European region, an effective interruption of this infection chain is essential. In particular, the removal and safe disposal of infected carcasses and the direct disinfection of contaminated, unpaved ground are priorities in this regard. For the disinfection, highly potent as well as environmentally compatible disinfectants must be used, which are neither influenced in their effectiveness by the soil condition nor by increased organic contamination. Thus, in this study, slaked lime, milk of lime and quicklime (1% to 10% solutions) were selected for efficacy testing against the test virus recommended by the German Veterinary Society (DVG), Modified Vaccinia Ankara virus (MVAV), and ASF virus (ASFV) in conjunction with six different forest soils from Saxony in two different soil layers (top soil and mineral soil) each. In summary, 10% of any tested lime type is able to inactivate both MVAV and ASFV under conditions of high organic load and independent of the water content of the soil. At least a 4 log reduction of the virus titer in all tested forest soil types and layers and by all applied lime types was observed. In conclusion, the high efficacy and suitability of all tested lime products against both viruses and in the presence of high organic load in forest soil can be confirmed and will help to control ASF spread.

A Study of the Distribution of Forest Density in Inner Mongolia Based on Environmental Factors

With the intensification of global climate change, exploring the impact of environmental factors on tree density can provide technical support for sustainable forest management. In this paper, the random forest parameters nTree and mtry were optimized using a particle swarm optimization algorithm. The density, average temperature, soil thickness, forest water consumption, slope, slope direction, slope position, soil type, and diameter at breast height (DBH) of the dominant tree species in Inner Mongolia were fitted using random forest regression with a satisfactory fitting effect (R2 &gt; 0.60). The results show that the average temperature, soil thickness, and forest water consumption were the main factors restricting tree density, and the influence of each factor changed depending on the stage of tree growth. Based on 2018 forest resource data of the Inner Mongolia Autonomous Region, four diameter class models were used to calculate tree density, and Kriging interpolation was used to form a density distribution grid map of the main tree species according to diameter class toward providing a theoretical basis and data support for afforestation and forest management strategies that are justified according to the available environmental resources.

The Efficacy of Disinfection on Modified Vaccinia Ankara and African Swine Fever Virus in Various Forest Soil Types.

African swine fever (ASF) has become a global threat to the pig industry and wild suids. Within Europe, including Germany, affected wild boar populations play a major role. Fencing and carcass removal in combination with the reduction in environmental contamination are key to control further spread. The handling of the ASF virus (ASFV) is restricted to high-containment conditions in Germany. According to the regulation of the German Veterinarian Society (DVG), modified vaccinia Ankara virus (MVAV) is the virus of choice to determine the efficacy of disinfection for enveloped viruses. The aim of this study was to use the MVAV as a guide to select the best possible disinfectant solution and concentration for the inactivation of ASFV in soil. Both viruses were tested simultaneously. In this study, two layers (top and mineral soil) of soil types from six different locations in Saxony, Germany, were collected. The tenacity of ASFV and MVAV were tested at various time points (0.5 to 72 h). The capabilities of different concentrations of peracetic acid and citric acid (approx. 0.1 to 2%) to inactivate the viruses in the selected soil types with spiked high protein load were examined under appropriate containment conditions. Around 2–3 Log10 (TCID50) levels of reduction in the infectivity of both ASFV and MVAV were observed in all soil types starting after two hours. For MVAV, a 4 Log10 loss was recorded after 72 h. A total of 0.1% of peracetic acid (5 L/m2) was sufficient to inactivate the viruses. A 4 log10 reduction in the infectivity of MVAV was noticed by applying 1% citric acid, while a 2 log10 decline was recorded with ASFV. In conclusion, comparing MVAV to ASFV for efficacy screening of disinfectant solutions has revealed many similarities. Peracetic acid reduced the infectivity of both viruses independently of the soil type and the existence of a high organic soiling.

Carbon stocks of soils under forest in the Komi Republic of Russia

Soils are a large reservoir of organic carbon, and plays a significant role in its accumulation and storage. The goal of this study is to provide a generalized estimate of soil organic carbon (SOC) stocks at dominant types of forest soils in the European North-East of Russia. The soil cover of the studied territory is mostly formed by Histic Retisols (HsR), Haplic Retisols (HpR) and Albic Podzols (AP). We used the results of our own SOC estimates and the ones of soil profile descriptions that were published for the region of investigation. The calculation was carried out for organic horizons and depths of 0–30, 0–50 and 0–100 cm including the organic horizon. The literature data lacks bulk density (BD) information. We calculated the mean BD value for soil horizons based on our BD determinations conducted for the studied soil groups in various parts of the region. The obtained BD values differed for separate soil groups. Relatively high BD of mineral horizons was obtained for HsR, low BD – for AP. Larger BD of organic layer for HpR is explained by accumulation of comparatively well-decomposed organic matter on the soil surface. The BD of organic layers was comparable for AP and HsR. The SOC stocks in all soil groups were characterized by a wide variation with differences between minimal and maximal values changing from 4 to 13 times. A closer spread was for HpR. The highest SOC stocks in 1 m depth were calculated for HsR with the mean value of 12.66 ± 0.13 kg m−2. The SOC content in HpR was 7.69 ± 0.12 kg m−2 and in AP – 3.80 ± 0.09 kg m−2. The organic layer share varied from 24 to 35% in SOC stocks of the 1 m profile. The depth of 0–50 cm concentrates 70–78% of SOC of the 1 m soil profile. According to the mean SOC stocks data and the area of the soil groups we estimated SOC stocks concentrated in main soil groups in the Komi Republic.

Ideas and perspectives: patterns of soil CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;, and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O fluxes along an altitudinal gradient – a pilot study from an Ecuadorian neotropical montane forest

Abstract. Tropical forest soils are an important source and sink of greenhouse gases (GHGs), with tropical montane forests, in particular, having been poorly studied. The understanding of this ecosystem function is of vital importance for future climate change research. In this study, we explored soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in four tropical forest sites located on the western flanks of the Andes in northern Ecuador. The measurements were carried out during the dry season from August to September 2018 and along an altitudinal gradient from 400 to 3010 m a.s.l. (above sea level). During this short-term campaign, our measurements showed (1) an unusual but marked increase in CO2 emissions at high altitude, possibly linked to changes in soil pH and/or root biomass, (2) a consistent atmospheric CH4 sink over all altitudes with high temporal and spatial variability, and (3) a transition from a net N2O source to sink along the altitudinal gradient. Our results provide arguments and insights for future and more detailed studies on tropical montane forests. Furthermore, they stress the relevance of using altitudinal transects as a biogeochemical open-air laboratory with a steep in situ environmental gradient over a limited spatial distance. Although short-term studies of temporal variations can improve our understanding of the mechanisms behind the production and consumption of soil GHGs, the inclusion of more rigorous sampling for forest management events, forest rotation cycles, soil type, hydrological conditions and drainage status, ground vegetation composition and cover, soil microclimate, and temporal (seasonality) and spatial (topographic positions) variability is needed in order to obtain more reliable estimates of the CO2, CH4, and N2O source/sink strength of tropical montane forests.

The Wood of Scots Pine (Pinus sylvestris L.) from Post-Agricultural Lands Has Suitable Properties for the Timber Industry

Scots pine (Pinus sylvestris L.) is a widespread species throughout Europe and at the same time is dominant in Polish forests and of key importance in the wood industry. Pine stands are subjected to numerous environmental stresses, and one of them is the different physico-chemical and biological properties of post-agricultural soils compared to forest soils, which may affect the properties of the resulting wood and its industrial suitability. The research material taken at the height of 1.3 m from tree trunks (breast height diameter, dbh) in the form of sections and discs was collected in an 80-year-old pine stand from four plots, representing former agricultural and ancient forest land, and two types of habitats: fresh coniferous forest and fresh mixed coniferous forest. The forest habitat trophy had a decisive impact on the dendrometric characteristics and properties of pine wood (density, modulus of elasticity, bending strength, and compressive strength along the tracheids). The history of soil use (post-agricultural or forestry) did not affect the analyzed pine wood properties. Regardless of the forest habitat type and soil type history, pine wood at the dbh height showed a variability of features typical of century-old cultivated stands. Individual pine trunks were characterized by significant individual variability.

Amynthas spp. impacts on seedlings and forest soils are tree species-dependent

Asian jumping worms (Amynthas spp.) are recent invaders of Upper Midwest forests. Research has highlighted the impacts of Amynthas earthworms on soil biogeochemistry and structure, and field observations suggest that Amynthas spp. decrease litter horizon depth and alter plant communities. However, the extent to which Amynthas spp. effects vary among forest types and with worm density and the mechanisms driving these effects are unknown. We conducted a 3-month tree seedling study to evaluate the effects of Amynthas spp. on tree seedling growth and a mesocosm field experiment to evaluate Amynthas spp. effects on soil carbon and nutrient cycling, soil structure, and leaf litter decomposition rates across forest types. In the seedling study, Amynthas spp. enhanced the growth of sugar maple and European buckthorn seedlings and decreased the growth of white oak seedlings. These effects were due to Amynthas spp.-induced changes in soil properties. In the mesocosm study, as Amynthas spp. density increased, carbon mineralization and carbon, nitrogen, and phosphorus availability increased in white oak forest soils and decreased in sugar maple forest soils, while decomposition rates of European buckthorn litter increased as Amynthas spp. density increased. Amynthas spp. altered soil structure similarly across all forest soil types. Taken together, our results suggest that Amynthas spp. have the potential to alter forest ecosystem dynamics via feedbacks among tree species, seedlings, and soil biogeochemistry. However, Amynthas spp. effects on tree seedlings and forest soils are largely context-dependent, and the direction and magnitude of these effects are mediated by tree species.

Dissolved organic matter characteristics in soils of tropical legume and non-legume tree plantations

Dissolved organic matter (DOM) drives many fundamental biogeochemical processes (e.g., carbon storage, nutrient cycling, and soil development) in forest soil. However, the molecular-level characteristics of DOM derived from different types of tropical forest soils are poorly understood. Here, water samples at different soil depths (0, 20, and 40 cm) from tropical legume (Acacia auriculiformis, AA) and non-legume (Eucalyptus urophylla, EU) tree plantations were analyzed using absorption and fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and solution-state 1H nuclear magnetic resonance (NMR) spectroscopy. The FT-ICR MS results indicated that DOM persisted in the soil, but its molecular composition notably shifted from low-mass (150–300 Da) and more-aromatic molecules to middle- (300–450 Da) and high-mass (>450 Da) and less-aromatic molecules with increasing soil depth. This was primarily mediated by consumption and mineral sorption of low-mass plant-derived DOM (e.g., low-mass carbohydrates and polyphenols) and further formation of larger microbial products (e.g., protein-like and lipid-like compounds). In addition, a higher abundance of microbial-derived molecules (e.g., protein-like and carboxyl-rich alicyclic molecules) was found at the legume plantation relative to the non-legume plantation, which suggests a faster microbial turnover of DOM. Also, the legume plantation had greater enrichment of middle- and high-mass and condensed aromatic-like DOM components in soils. These findings improve our understanding of the drivers that mediate the response of DOM to soil depth and tree species in tropical plantations.

Influence of Sowing Dates of Oil Flax Varieties on the Productivity at Different Seeding Rates

For the conditions of the western forest-steppe zone of Ukraine, it is important to choose the optimal sowing period, seeding rates for efficient provision of oil flax plants with nutrients and the realization of their genetic potential. When establishing the norms of seeding flaxseed, it is advisable to take into account soil fertility, precursors, weight of 1000 seeds, etc. The studies were conducted in 2016-2018 at the research field of the Institute of Agriculture of the Carpathian region of the NAAS in a five-field crop rotation on the gray forest surface-covered soil type with average fertility rates. Three sowing rates (4, 6 and 8 mln seeds / ha) of Original and Liryna flax varieties were sown, which were sown in three terms: early (at the earliest opportunity), 10 and 20 days after the early term. On survival of plants during the growing season the sowing density had a significant effect. The number of plants that have fallen during the growing season before the start of harvesting in the full ripeness phase is in the range of 9.7… 15.2 % when sown in the first and second term and 10.7…22.5 % when sown 20 days after the first possibility of entering the field (3rd sowing period). Increase of seed rate to 8 million pieces. / ha caused an increase in the rate of plant loss during the growing season. The Original variety was characterized by a higher plant survival during the growing season under the sowing periods compared to the Lirina variety. The highest seed productivity (2.57 t / ha) was obtained in the Lirina variety for sowing 6.0 million pieces / ha and sowing at the first opportunity to enter the field. Sowing in 10 and 20 days after the first term caused a decrease in the yield of the Lirina variety by 0.16-0.35 t / ha, for the Original variety - by 0.36-0.45 t / ha. The Original variety proved to be more productive with the yield of flaxseed (3.65 t / ha) compared to the Lirina variety (3.14 t / ha), provided the early sowing rate of 8.0 mln seeds / ha. The use of late sowing conditions led to a decrease of this indicator in the range of 5.3-20.0%. Delaying the sowing period from the first opportunity to enter the field for 10 and 20 days led to a decrease in the mass index of 1000 seeds for the Original and Lirina varieties by 0.1-0.2 g (at the control of 7.0 g). The highest yield of oil per hectare was provided by the Lirin variety for the first sowing period and the seeding rate of 6.0-8.0 million similar seeds / ha - 1.15-1.16 t / ha. The use of late sowing dates reduced the yield of oil by 1.7-18.4% for both varieties studied.

Effects of litter addition on the dynamics of soil humic substances during freeze-thaw events in a subalpine forest.

During soil formation, the accumulation of humic substances such as humic acid and fulvic acid is an important way to maintain soil fertility and nutrient cycling, which is regulated by soil substrate quality, litter, and environmental factors. In a laboratory incubation experiment, we exa-mined the effects of litter addition on soil humic substances accumulation in freeze-thaw environment by controlling the freeze-thaw cycles and litter additions in soils from the typical coniferous forest, mixed forest and broadleaved forest in a subalpine forest in western Sichuan. The freeze-thaw events significantly increased the content of humic substances in the coniferous forest soils but decreased those in the mixed forest soil and broadleaved forest soil. Litter addition had no significant effect on the content of soil humic substances. Freeze-thaw events increased the content of humic acid, with the net accumulation of humic acid following the order of mixed forest > coniferous forest > broad-leaved forest. Freeze-thaw events decreased the content of fulvic acid in the three forest soils during the early stage of incubation, and the degree of fulvic acid degradation was broadleaved forest > mixed forest > coniferous forest. Litter addition had no significant effect on the content of soil humic acid and fulvic acid. With prolonged incubation, the content of humic acid and fulvic acid in the three types of forest soils all declined. These results indicated that litter had effects on soil humic substances, which were related to soil substrate quality and affected by the duration of soil freeze-thaw events in winter.

Soil organic carbon density and its driving factors in forest ecosystems across a northwestern province in China

Forest soils are an important component of the global carbon cycle, as they sequester and store much more organic carbon than other terrestrial ecosystems. Thus, reliable information on the forest soil organic carbon (SOC), along with the factors that influence it, is crucial from the perspective of regional carbon budgets and climate modeling. Gansu Province in northwestern China is characterized by complex climatic gradients and diverse forest types, suggesting a large variability in the spatial distribution of SOC, yet the SOC stock in this region has not been comprehensively investigated because of insufficient soil profile data. Our study covered the entire forest area in the province via a regional-scale sampling campaign, and provided soil organic carbon density (SOCD) data obtained from 112 natural forests and 100 plantations. Influencing factors including forest type, forest stand age, soil type, litter carbon, climate, and topography were evaluated in both natural forests and plantations. The results indicated a SOC stock of 433.4 ± 13.2 Tg C and a SOCD value of 175.3 ± 33.0 Mg C ha−1 for the 0–100 cm layer at the regional scale. Specifically, the SOC stock and the forest area-weighted average SOCD in natural forests were estimated at 349.0 ± 16.5 Tg C and 207.3 ± 23.2 Mg C ha−1, which were about quadruple and double, respectively, of the values for the plantations. Regardless of natural forests and plantations, SOCD increased with both stand age class and elevation and decreased with mean annual temperature (MAT). SOCD also increased with mean annual precipitation (MAP) for natural forests with elevation <2500 m and for all plantations. The overall importance to SOCD of the explanatory variables increased with increasing soil depth in natural forests while decreased with increasing soil depth in plantations. Forest type, stand age, soil type, MAT, MAP, elevation, litter carbon, slope, and aspect explained 58 and 65% of the total variation in the SOCD at 100 cm depth in natural forests and plantations, respectively. In natural forests, the most important explanatory variable for the uppermost 30 cm was soil type, while it was MAT for the whole 100 cm; in plantations, the most prominent factors were forest type and elevation, regardless of the soil depth. These suggest that environmental changes will likely have different effects on SOCD in natural forests and plantations.

BASES OF MODERN MONITORING OF CYST NEMATODES

Identification of focal death of plants or significant deviations of uniformity and homogeneity of vegetation cover, based on the analysis of high-resolution satellite images or aerial survey by unmanned aerial vehicles, ensured the release of phytosanitary and problem phytocenoses with the aim of their primary nematological examination by traditional methods. It is established that the conventional route survey in two diagonals provides a higher probability of detecting nematode foci in the middle of the field (due to mixing and crossing routes) and less reliable – infection of the edge bands. Since the foci of cyst nematodes, especially in the initial stages of agrocenosis colonization, were more common in the edge bands, it is necessary to additionally select and analyze plant samples from all four sides of the field (envelope method) in order to increase the reliability of the diagonal examination. The probability of detection of heteroderosis foci was significantly increased when the agrocenosis was examined by the shuttle method with an interval between route lanes of 50 meters. For an objective assessment of the level of population of sod-podzolic, gray forest and other soil types with shallow bedding of the fertile layer, it is advisable to select nematological samples to a depth of 20 cm, and on chernozem to 30 cm. Cartograms of the prevalence of cyst nematodes with a detailed application of the spatial distribution of foci, their area and level of soil population are the basis for long-term planning, scientifically based choice and locally-differentiated application of various anti-nematode activities, depending on their economic payback and environmental feasibility. The long-term stay of populations within certain spatial boundaries is the main advantage of the prediction of their harmfulness and the local application of protective measures in the focal points of heteroderides that are clearly defined with the coordinate reference in comparison with actively migrating phytophages.