Water-soluble organic matter in incipient podzols: accumulation in B horizons or in fibres?

To elucidate the mechanism of podzolization in its first stages we studied the fate of the water-soluble organic matter (WSOM) in incipient podzols in sandy soils by comparing the composition of the WSOM from L, F and H horizons with that in the bulk of the Bh horizons and fibres of three profiles. The WSOM appeared to consist significantly of ligno-cellulose and proteins, but these biopolymers were hardly present in the Bh horizons. The material of the fibres, however, greatly resembled the WSOM composition, thereby suggesting that in these soils most of the WSOM is transported through the B horizon and accumulates hardly changed in thin bands where the water stops moving. This implies that in the early steps of podzolization, accumulation of organic matter in the B horizon is not likely to be caused by water-soluble material.     

Change of Organic Carbon Content and Its Fractions in Black Soil under Long‐Term Application of Chemical Fertilizers and Recycled Organic Manure

Abstract

Soil organic matter (SOM) is an important indicator for soil quality and sustainable agriculture, and agricultural practices may strongly affect SOM content and chemistry. Thus, a long‐term experiment was conducted in northeast China to study the effect of chemical fertilizers and recycled organic manure on the contents of SOM along its fractions of black soil (0–20‐cm depth). Eight treatments were used: 1) control, 2) recycled organic manure (ROM), 3) nitrogen (N) alone, 4) N+ROM, 5) N+phosphorous (P), 6) N+P+ROM, 7) N+P+potassium (K), and 8) N+P+K+ROM. The results showed that from 1985 to 2002; soil total organic carbon (TOC) decreased by 6.5% over the 18 years in control (33.25 g/kg in 1985), 5.6% in ROM treatment, and 5.1% in N‐alone treatment, and 1.5% in the N+P treatment but increased by 0.3% in the N+P+K treatment. In the three treatments of chemical fertilizers together with ROM (i.e., N+ROM, N+P+ROM, and N+P+K+ROM), soil TOC content in 2002 increased by 0.3%, 1.3%, and 2.8%, respectively, when compared with control in 1985. Compared with control in 2002, light fraction organic carbon (LFOC) content increased by 23% in N+ROM treatment, 24% in N+P+ROM, and 28% in N+P+K+ROM, and readily oxidized carbon (ROC) content increased by 24% 31%, and 39%, respectively, in these three treatments. The ROC was well correlated with soil TOC. Compared with the data from 18 years ago, in all eight treatments organic carbon of soil in the humic acid fraction decreased by 5.0–13% and in fulvic acid decreased by 1.4–14%; however, with chemical fertilizers and ROM applied together, the rate of decrease was reduced. Overall, ROM is effective for increasing the content of soil TOC and thus, its different active carbon fractions in black soil would help to maintain or increase soil productivity.     

Does forest continuity matter in conservation? - A study of epiphytic lichens and bryophytes in beech forests of southern Sweden

The effects of forest continuity at local scale for red-listed and indicator species of epiphytic lichens and bryophytes were investigated in 150 Fagus sylvatica stands in southern Sweden. Stands having forest continuity (n = 106) had continuous forest cover more than 350 years, whereas stands lacking continuity (n = 44) had forest cover less than 160 years. Forest continuity was identified by comparing a sequence of historical maps with a modern survey of beech forests. In the field woody beech substrates were searched for the epiphytes of interest. A number of environmental and spatial variables were inventoried and compiled for each stand. In all 64 species (51 lichens, 13 bryophytes) were found in the stands having continuity, and 21 (14 lichens, 7 bryophytes) in the stands lacking continuity. Controlling for the different number of surveyed stands, stands having continuity had significantly more species of lichens, but not of bryophytes. In the stands lacking continuity we did not find lichens associated with the very late succession stage. The quantity of substrates, stand age and forest continuity were the three most important factors explaining species richness as well as composition of studied epiphytes. The effect of continuity was probably due to a combination of a higher substrate quality, mainly old beeches, and a longer time available for colonization. Also, we found strong positive correlations between number of indicator and red-listed epiphyte species. In short-term conservation old stands having continuity, containing suitable substrates and indicator species are target areas.     

Metabolising old soil carbon: Simply a matter of simple organic matter?

Bare fallow soils that have been deprived of fresh carbon inputs for prolonged periods contain mostly old, stable organic carbon. In order to shed light on the nature of this carbon, the functional diversity profiles (MicroResp™, Biolog™ and enzyme activity spectra) of the microbial communities of long-term bare-fallow soils were analysed and compared with those of the microbial communities from their cultivated counterparts. It was assumed that the catabolic and enzymatic profiles would reflect the type of substrates available to the microbial communities. The catabolic profiles suggested that the microbial communities in the long-term bare-fallow soil were exposed to a less diverse range of substrates and that these substrates tended to be of simpler molecular forms. Both the catabolic and enzyme activity profiles suggested that the microbial communities from the long-term bare-fallow soils were less adapted to using polymers. These results do not fit with the traditional view of old, stable carbon being composed of complex, recalcitrant polymers. Microbial communities from the long-term bare fallow soils tended to preferentially use substrates with higher nominal oxidation states of carbon relative to the substrates used by the microbial communities from the cultivated soils. This suggests that the microbial communities from the long-term bare-fallow soils were better adapted to using readily oxidizable, although energetically less rewarding, substrates. Microbial communities appear to adapt to the deprivation of fresh organic matter by using substrates that require little investment, such as enzyme production.     

Variations in the soil microbial community composition of a tropical montane forest ecosystem: Does tree species matter?

We investigated tree species effects on the soil microbial community in the tropical montane forest on Mt. Kinabalu, in Malaysian Borneo. We investigated microbial composition (lipid profile) and soil physicochemical parameters (pH, moisture, total C, N and phenolics concentration) in top 5-cm soils underneath two conifers (Dacrycarpus imbricatus and Dacrydium gracilis) and three broad-leaves (Lithocarpus clementianus, Palaquium rioence and Tristaniopsis clementis). We found that the primary difference in microbial composition was between conifer versus broad-leaves. The abundance of specific microbial biomarker lipids correlated with soil pH, total C and N. We conclude that tree species have significant impacts on the soil microbial community through their effects on soil pH, total C and N.     

Stabilization of dissolved organic matter by aluminium: a toxic effect or stabilization through precipitation?

Carbon mineralization in acidic forest soils can be retarded by large concentrations of aluminium (Al). However, it is still unclear whether Al reduces C mineralization by direct toxicity to microorganisms or by decreased bioavailability of organic matter (OM) because dissolved organic matter (DOM) is precipitated by Al. We conducted an incubation experiment (6 weeks) with two DOM solutions (40 mg C litre^?1) derived from two acidic forests and possessing large differences in composition. Aluminium was added to the solutions in realistic ranges for acidic soils (1.6–24 mg Al litre^?1) at pHs of 3.8 and 4.5, to achieve differences in Al speciation. We determined different Al species, including the potentially toxic Al³⁺, by Diffusive Gradients in Thin Films (DGT) to evaluate toxic effects on microorganisms. Precipitation of OM increased with larger amounts of added Al and higher pH, and we measured a larger fraction of dissolved ‘free’ Al at pH 3.8 than at pH 4.5. Organic matter degradation decreased significantly with Al addition, and we found more organic matter degraded at pH 3.8 than at pH 4.5 for the respective Al additions. Consequently, the observed reduction in OM degradation (i.e. stabilization) cannot be explained by toxic effects of ‘free’ Al. However, C stabilization correlated significantly with C precipitation. The pH did not influence C stabilization directly, but determined the amount of C being precipitated. Phosphorus was removed along with OM by precipitation, which possibly also affected C stabilization. We conclude that C stabilization upon Al addition did not result from toxic effects, but was caused by reduced bioavailability of OM after its precipitation. The reduction in OM degradation by 65% is of great relevance for the overall C stabilization in acidic forest soils. Increasing pH and decreasing Al concentrations upon recovery from acidic deposition should therefore not result in decreased stabilization of precipitated OM.     

Assessing the extent and causes of forest degradation in India: Where do we stand?

In India, conservation of biodiversity goes hand in hand with human welfare, as millions of people live adjacent or within protected areas and depend upon forests products. The high density and biomass requirements of these households could result in the degradation of forests and loss of biodiversity. We assessed the collection of forest products among households in five sites in the Western and Eastern Ghats of peninsular India: the Kogar region of the Central Western Ghats, the Bandipur and Sigur regions of the Nilgiri Biosphere Reserve, the Kalakad-Mundanthurai Tiger Reserve of the southern Western Ghats and Similipal Tiger Reserve of the northern Eastern Ghats, and tested whether extraction pressure on forests was associated with the proportion of agricultural households, wage labour and population density. We also examined whether data on loss of cover as stated by the State of the Forest Reports was supported by field data. The regions differed in land use: Kogar, KMTR and Similipal were primarily agricultural regions, whereas households engaged in wage labour or in running small businesses were predominant in Sigur and Bandipur. Fuel-wood was collected ubiquitously for household use in all sites, used mainly for domestic requirements and secondarily for generating income. Green leaves for making fertilizer and fodder were collected for household use and did not enter the market. Cattle manure for the global organic coffee industry was a major forest product in Bandipur and Sigur. Extraction pressure on forests was positively associated with the availability of wage labour and was negatively with the proportion of agricultural households. Data from official sources seem inadequate to measure forest degradation in protected forests. Accurate estimation of forest condition through field assessments and remote sensing, and understanding the socio-economic variables associated with forest loss and degradation are needed for the sustainable management of Indian protected areas.     

Does forest type and vegetation patchiness influence horizontal distribution of soil Collembola in two neighbouring forest sites?

The influence of forest type and heterogeneity of understory vegetation on the horizontal distribution of soil living Collembola was studied in two neighbouring mountain forest sites—a 180-year old beech forest and a 70-year old natural spruce forest. Four homogenous patches with different understory vegetation were chosen within each forest site and sampled 12 times between 1997 and 1998. A total of 56 collembolan species were identified, 51 in the beech forest and 48 in the spruce site. Twenty-three species were rare—they were recorded with low constancy and density. Although both forest sites differed in soil type, humus form and soil chemical parameters, the species composition of their collembolan communities was quite similar (77% shared species). Nevertheless, soil collembolan communities of both forest sites were clearly delimited on both qualitative (presence–absence) and quantitative (in density of individual species) levels as well as in terms of total collembolan density. Mean collembolan density reached 26 650–44 030 ind/m² in the beech patches compared to 44 470–68 050 ind/m² found in the spruce patches. Considerably higher densities of several species in one forest site may indicate more suitable habitat. In spite of similar species composition and minor differences in qualitative parameters among different vegetation patches within one forest site, there was clear variation in density of individual species, particularly between patches with and without herb vegetation. This could reflect different microclimatic conditions, additional litter supply from herbs or indirect interactions of Collembola with their roots.     

Molecular modeling of soil organic matter: Squaring the circle?

The structure of soil organic matter (SOM) and humic substances (HS) has been discussed from different viewpoints including molecular conformation, molecular aggregation, macromolecularity, supramolecular characteristics, domain mobility, and many others. Until now, the individual models appear partly contradictory, although each viewpoint provides important information on the structural and functional properties of SOM. This is most probably due to the huge heterogeneity of SOM. Therefore, the question: “How can molecular modeling help to further understand structure and functioning of soil organic matter?” needs to be addressed with care. This contribution reviews and discusses the potential of important molecular modeling approaches currently applied in soil organic matter science.Computer models are useful in giving a visualization of the general structure and of the possible effects on soil chemistry and soil physics. Computational chemistry in this context aims to estimate a lowest energy conformation for a molecule or an assembly of molecules specified by the programmer. On the basis of the calculated conformation, physicochemical characteristics like surface area, polarity and other can be estimated and information on the stability of molecular assemblies can be derived. The significance of the obtained conformation and physicochemical information strongly depends on the initial hypothesis of the molecular structure of each involved molecule. Recent computer models have been developed on the base of computer assisted structure elucidation (CASE). In this procedure, all possible isomers or a statistically representative set of isomers consistent with the experimental input data are processed.Further interesting fields of computational chemistry in soil research follow a different conception, where specific processes of interest are elucidated with the help of computational models which simplify the humic molecules with respect to the individual modeling problem. This way helps to understand the relevance of principal processes expected to occur in soil. In this context, complexes of Al with organic acids, clay mineral sorption sites, interactions of pesticides with organic functional groups or organic soil constituents as well as cross-linking of molecule segments by water molecules were modeled in targeted process-orientated models. The act of simplification is the crucial process in these kinds of models, and if the models are based on good conceptions, they allow to learn about potential SOM functioning. The transfer to more complex situations, however, needs special care and the predictive character of these models needs to be judged with care. Still, any computer model is only as good as its initial hypothesis.     

Do model choice and sample ratios separately or simultaneously influence soil organic matter prediction?

This study was performed to examine the separate and simultaneous influence of predictive models’ choice alongside sample ratios selection in soil organic matter (SOM). The research was carried out in northern Morocco, characterized by relatively cold weather and diverse geological conditions. The dataset herein used accounted for 1591 soil samples, which were randomly split into the following ratios: 10% (～150 sample ratio), 20% (～250 sample ratio), 35% (～450 sample ratio), 50% (～600 sample ratio) and 95% (～1200 sample ratio). Models herein involved were ordinary kriging (OK), regression kriging (RK), multiple linear regression (MLR), random forest (RF), quantile regression forest (QRF), Gaussian process regression (GPR) and an ensemble model. The findings in the study showed that the accuracy of SOM prediction is sensitive to both predictive models and sample ratios. OK combined with 95% sample ratio performed equally to RF in conjunction with all the sample ratios, as the latter did not show much sensitivity to sample ratios. ANOVA results revealed that RF with a ～10% sample ratio could also be optimum for predicting SOM in the study area. In conclusion, the findings herein reported could be instrumental for producing cost-effective detailed and accurate spatial estimation of SOM in other sites. Furthermore, they could serve as a baseline study for future research in the region or elsewhere. Therefore, we recommend conducting series of simulation of all possible combinations between various predictive models and sample ratios as a preliminary step in soil organic matter prediction.     

Spectroscopic Characteristics and Biodegradability of Cold and Hot Water–Extractable Soil Organic Matter under Different Land Uses in Subarctic Alaska

Cold (22 ^oC) and hot water (80 ^oC) extractions have been used to estimate labile organic carbon (C) and nitrogen (N) in soils. Sequentially extracted cold and hot water organic matter (WEOM) from 14 Alaskan soils under different land uses were characterized by ultraviolet and fluorescence spectroscopies. Compared to cold WEOM, the ultraviolet (UV) absorptivity at 254 nm and fluorescence index were significantly (P < 0.05) decreased in hot WEOM of all soils. The biodegradability, assessed in a 21-d solution incubation, of hot WEOC and WEON was significantly (P < 0.05) greater than that of cold WEOC and WEON in all soils. The biodegradability of cold or hot WEOC was correlated with the protein-like component, indicating that a protein-like fluorophore is a labile fraction in both cold and hot WEOM pools. Information derived from this work contributed to better understanding of subarctic soil WEOM properties and their biodegradability.     

Carbon decomposition of the topsoils and soil fractions under forest and pasture in the western Brazilian Amazon basin, Rondônia

The topsoils of two sites, comprising natural forest and 4- and 20-year-old pastures, respectively, were selected in Rondônia to evaluate the changes of soil organic matter due to pasture establishment. These changes were evaluated by measuring the proportions of the C and N associated with clay and silt fractions, and by the C decomposition (CD) rate of the whole topsoils and their size fractions. The topsoils studied had large proportions of C and N associated with fine fractions, especially with clay fractions. The CD rate of the silt fractions was higher than that of the clay fractions under the two forest topsoils and under the 20-year-old pasture. The CD rate of the silt fractions under forest vegetation at each site was significantly higher than that of the silt fractions under pasture vegetation at the same site. The CD of clay fractions followed the same trend as the silt fractions, showing an improvement in the stability of C associated with clay and silt fractions under pasture vegetation.     

Comparison of Soil Organic‐Matter Characteristics under the Energy Crop Giant Reed,Cropping Sequence and Natural Grass

The objective of this study was to determine, on the same pedological, topographic, and climatic conditions, the effects of a continuous giant reed cropping (GR), a cropping sequence (CS), and untilled natural grass (NG) on some soil characteristics. Selected characteristics included total soil organic carbon (TOC), light fraction carbon (LFC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC). The various humic fractions and their ratios, humification ratio (HR), humification degree (HD), and humification index (HI) were also evaluated. Results indicate that GR, characterized by low tillage intensity, showed greater values than tilled management system (CS) for all the previously mentioned properties, with the exception of the humification parameters, which were not statistically different between the two systems. Regarding the difference between GR and NG (the latter usually considered as a reference or baseline for evaluating attributes of soil quality), GR generally showed greater values for all organic parameters, with the exception of MBC and humus characteristics.     

Disappearance of spatial variability and structure in forest floors — A distinct effect of air pollution?

Small-scale spatial structure and variability are characteristic features of soils and are also of ecological importance. A few investigations show that predictability of the edaphic environment, at spatial distances relevant for the vegetative proliferation of plants, is essential for survival. The relevant scale for forest field layer vegetation would be from 0.1m to a few meters.We describe spatial variability and structure in forest humus layers by sampling 101 samples, 0.2m apart along 20m transects. pH, thickness of the humus layer and respiration at 20°C, all of which being easily measured variables with high information value, are determined. Spatial variability is expressed as 90–10 percentiles, spatial structure by geostatistical semivariograms.     

Differing N status and N retention processes of soils under old-growth lowland forest in Eastern Amazonia,Caxiuanã, Brazil

Indirect evidence of the nitrogen (N) status of tropical forests strongly suggests that in heavily weathered soils under old-growth lowland tropical forests nitrogen is in relative excess. However, within the lowland forests of the Amazon basin, there is substantial evidence that soil texture influences soil NH₄⁺ and NO₃^? concentrations and hence possibly N availability and retention in the soil. Here, we evaluate the soil N status of two heavily weathered soils which contrast in texture (sandy versus clay Oxisol). Using ¹⁵N pool dilution, we quantified gross rates of soil N cycling and retention. We also measured the δ¹⁵N signatures from the litter layer down to 50-cm depth mineral soil and calculated the overall ¹⁵N enrichment factor (ε) for each soil type. The clay soil showed high gross N mineralization and nitrification rates and a high overall ¹⁵N enrichment factor, signifying high N losses. The sandy soil had low gross rates of N cycling and ¹⁵N enrichment factor, manifesting a conservative soil N cycling. Faster turnover rates of NH₄⁺ compared to NO₃^? indicated that NH₄⁺ cycles faster through microorganisms than NO₃^?, possibly contributing to better retention of NH₄⁺ than NO₃^?. However this was opposite to abiotic retention processes, which showed higher conversion of NO₃^? to the organic N pool than NH₄⁺. Our combined results suggest that clay Oxisol in Amazonian forest have higher N availability than sandy Oxisol, which will have important consequences for changes in soil N cycling and losses when projected increase in anthropogenic N deposition will occur.     

Use of Agro‐industrial Organic Compound: Yield and Nutrient Absorption in Wheat

Abstract

This study, focusing on the cultivation of wheat, consisted of applying an organic compound to the soil for a period of 2 years. The organic compound was made from a mixture of organic residues from a jelly industry (bovine chips and sharings) and other residues from a sugar‐alcohol industry. The mixture was applied at random into the intergrowth lines in a top‐dressing process, without incorporation, and in cumulative increasing doses. In the first year, the applications ranged from 2 to 25 t ha; in the second year, the applications ranged from 8 to 75, in wheat plants. Comparing the results of the chemical treatment to the organic application, it was observed that the organic compound increased the yield of wheat during the 2 years. Furthermore, the organic compound did not contaminate the plants, such as in the absorption of nutrients by the grains, once they have presented normal patterns of nutrient concentrations.     

Wood-decaying fungi in boreal forest: are species richness and abundances influenced by small-scale spatiotemporal distribution of dead wood?

We tested whether the spatiotemporal distribution of Norway spruce (Picea abies) logs influenced species richness and abundances of wood-decaying fungi in two 2-km² boreal forest study sites in southeastern Norway. According to the random sample null-hypothesis equally large subsamples of logs should be equally efficient in sampling fungi from a regional species pool. Based on 0.25-ha plots at 1-ha grid resolution, we compared plots with high and low densities of ‘new logs’ (decay stages 1-5) and plots with ‘old logs’ (decay stages 5-8) present or absent. Based on visible sporocarps, 45 fungus species, including 15 redlisted, were identified among 4151 logs. When rarefying species accumulation curves to the same number of logs, we found no difference in species richness between old forest plots having high and low densities of new logs, or between plots where old logs were present or absent. Curves from young forest revealed fewer species than in old forest. Multiple regression analysis of six redlisted and six common species corroborated the rarefaction analysis in showing that the probability of occurrence was independent of the spatiotemporal distribution of logs for all but two common species. Aside from the fact that more dead wood harboured more wood-decaying fungi, we conclude that the spatiotemporal distribution of dead wood was of minor importance in determining species richness and abundances at the scales of <1 ha and <100 years. This suggests that wood-decaying fungi are not dispersal-limited at these scales, and it offers an optional element in forest management.     

Is the Period of 18 Years Sufficient for an Evaluation of Changes in Soil Organic Carbon under a Variety of Different Soil Management Practices?

The influence of differing soil management practices on changes seen in soil organic carbon (SOC) content of loamy Haplic Luvisol was evaluated. The field experiment included two types of soil tillage: 1. conventional tillage (CT) and 2. reduced tillage (RT) and two treatments of fertilization: 1. crop residues with nitrogen, phosphorus, and potassium (NPK) fertilizers (PR+NPK) and 2. NPK fertilizers (NPK). The results of SOC fluctuated from 9.8 to 14.5 g kg^?1 and the tillage systems employed and fertilization status did not have a statistically significant influence on SOC. The SOC content was higher in RT (12.4 ± 0.86 g kg^?1) than in CT (12.2 ± 0.90 g kg^?1). On average, there was a smaller higher value of SOC in PR+NPK (12.4 ± 1.02 g kg^?1) than in NPK (12.3 ± 0.88 g kg^?1). During a period of 18 years, reduced tillage and application of NPK fertilizers together with crop residues build up a SOC at an average speed of 7 and 16 mg kg^?1 year^?1, respectively, however conventional tillage and NPK fertilizer applications caused a SOC decline at an average speed of 104 and 40 mg kg^?1 year^?1, respectively.     

Do boundaries of soil animal and plant communities coincide? A case study of a Mediterranean forest in Russia

We studied the relationship between plant and soil animal communities by geostatistical analysis in a piedmont forest close to Novorossiysk (Southern Russia). Vegetation on the slope of a hill was an oak-ash-hornbeam forest, while the vegetation on the foot of the hill was a maple-ash-hornbeam forest. Two plots were studied each including both slope and foot habitats. On every plot samples collected formed a grid of 10 × 5 units with a 5 m distance between them. Soil macroinvertebrates were hand-sorted from the samples, and several soil parameters (soil, pebble, and litter mass, soil moisture) were measured.The analysis did not reveal coincidence between the boundaries of plant and soil animal communities on the bend of the hill. Soil animal communities of the plots were dominated by woodlice, diplopods, and insect larvae, reaching an abundance of 680–990 individuals m⁻² throughout the plots. Number of taxonomic groups per sample and overall animal abundance in the bend were the highest in both plots, whilst these parameters on the slope were the lowest. Variograms and maps of spatial distribution indicated that the boundary between soil animal communities was situated further up on the slope than the vegetation boundary. The size of the animal community was smaller than the size of plots sampled, what probably explained the lack of coincidence between the boundaries. There was a significant correlation between distribution of litter mass and parameters of soil animal communities, which was modulated by depth of soil layer and soil moisture. Soil parameters were more important for explaining boundaries between soil animal communities than plant communities in the forest considered.