高寒山区地形序列土壤有机碳和无机碳垂直分布特征及其影响因素

地形、生物气候条件具有明显差异的青藏高原约占我国陆地面积的五分之一,开展该地区土壤有机碳和无机碳分布特征的研究对于理解青藏高原土壤碳循环过程与陆地碳库的精确预测以及应对全球气候变化具有重要意义。研究选取位于祁连山中段的阴、阳坡地形序列土壤,分析了不同坡向间以及同一坡向内随海拔高度变化土壤有机碳和无机碳的垂直分布特征及其影响因素。结果表明:阴、阳坡有机碳含量均随土壤深度增加而下降,但阳坡下降的速率(66%~91%)明显高于阴坡(31%~77%);阴坡土壤中碳酸钙基本淋失,通体无机碳含量较低(5.0 g kg-1),阳坡B层土壤无机碳含量是A层的2倍,表现为明显富集。阴坡和阳坡1 m土体总碳密度相当(分别为16.1~33.9 kg m-2和11.8~32.8 kg m-2),其中,阴坡以有机碳为主(占总碳密度的82%~99%),而阳坡有机碳和无机碳密度变化均较大(分别占总碳密度的27%~81%和19%~73%)。因此,坡向是影响高寒山区土壤碳垂直分布和组成的重要因素。此外,降雨量和植被类型对地形序列土壤有机碳和无机碳含量的空间变异也具有重要影响:降雨量每增加1 mm,表层(0~20 cm)土壤有机碳含量增加0.4 g kg-1,而淀积层(40~80 cm)土壤无机碳含量下降0.2 g kg-1;植被类型在一定程度上影响了土壤有机碳的富集程度。本研究揭示了青藏高寒山区土壤碳循环及其碳库预测应充分考虑微地形对坡面尺度下土壤碳垂直分布、碳库组成和空间变异的影响。     

Phosphorus mineralization in subarctic agricultural and forest soils

Summary Potential P and C mineralization rates were determined in a 12-week laboratory incubation study on subarctic forest and agricultural soil samples with and without N fertilizer added. There was no significant difference in net inorganic P produced between N fertilized and unfertilized soils. The forest soil surface horizons had the highest net inorganic P mineralized, 32 mg P kg^-1 soil for the Oie and 17 mg P kg^-1 soil for the Oa. In the cropped soils net inorganic P immobilization started after 4 weeks and lasted through 12 weeks of incubation. Cumulative CO₂–C evolution rates differed significantly among soils, and between fertilizer treatments, with the N-fertilized soils evolving lower rates of CO₂–C than the unfertilized soils. Soils from the surface horizons in the forest evolved the highest rates of CO₂–C (127.6 and 89.4 mg g^-1 soil for the Oie and Oa horizons, respectively) followed by the cleared uncropped soil (42.8 mg g^-1 soil C), and the cropped soils (25.4 and 29.0 mg g^-1 soil C). In vitro soil respiration rates, or potential soil organic matter decomposition rates, decreased with increasing time after clearing and in accord with the degree of disturbance. Only soils with high potential C mineralization rates and high organic P to total P ratios, mineralized P by the end of the study. Mineralizable P appeared to be associated with readily mineralizable organic C.     

Stock, turnover time and accumulation of organic matter in bulk and density fractions of a Podzol soil

Temperate forest soils store large amounts of organic matter and are considered as net sinks for atmospheric carbon dioxide. Information about the sink strength and the turnover time of soil organic carbon (SOC) is required to assess the potential response of soils to climate change. Here we report on stocks, turnover times (TT) and accumulation of SOC in bulk soil and density fractions from genetic horizons of a Podzol in the Fichtelgebirge, Germany. Stocks of SOC, total nitrogen and exchangeable cations determined in nine quantitative soil pits strongly varied with stone content and thickness of horizons in both the organic layer and the mineral soil. On the basis of radiocarbon signatures, mean turnover times of 4, 9 and 133 years, respectively, were calculated for Oi, Oe and Oa horizons from three soil pits, using a non-steady-state model. The Oa horizons accumulated 4–8 g C m⁻² year⁻¹ whereas the Oi and Oe horizons were close to steady-state during the past decade. Free particulate organic matter (FPOM) was the most abundant fraction in the Oa and EA horizons with TT of 70–480 years. In the B horizons, mineral associated organic matter (MAOM) dominated with over 40% of total SOC and had TT of 390–2170 years. In contrast to other horizons, MAOM in the Bsh and Bs horizon had generally faster TT than occluded particulate organic matter (OPOM), possibly because of sorption of dissolved organic carbon by iron and aluminium oxides/hydroxides. Our results suggest that organic horizons with relatively short turnover times could be particularly vulnerable to changes in climate or other disturbances.     

The coarse‐soil fraction is the main living space of fungal hyphae in the BhBs horizon of a Podzol

In acidified forest soils, the coarse‐soil fraction is a potential nutrient source. Plant nutrient uptake from the coarse‐soil fraction is aided by ectomycorrhiza. Similarly, (recalcitrant) organic matter (OM) is an important nutrient source largely made plant‐available through (symbiotic) microorganisms, especially in the topsoil. We hypothesized that in a podzol profile, fungal hyphae would concentrate in nutrient hotspots, either OM or the coarse‐soil fraction. Absolute hyphal length, base saturation, and organic‐C content of a Podzol profile were determined in the fine‐earth and coarse‐soil fractions. In the fine‐earth fraction, hyphae were attracted by the organic‐C content and relative high base saturation. In the coarse‐soil fraction of the BhBs horizon, the absolute hyphal length exceeded the hyphal length in the fine earth by factor 3, yet C content and base saturation were lowest. We could not determine to what fungi the hyphae belonged. Most likely ectomycorrhiza, ericoid mycorrhiza and saprotrophic fungi dominate the upper soil layers of this profile and all utilize OM for nutrition. In the deeper mineral horizons and especially in the coarse‐soil fraction, ectomycorrhiza are better adapted than other fungi to harvest nutrients from inorganic sources. Additionally, favorable physical properties may explain the high amount of fungal hyphae in the coarse‐soil fraction of the BhBs horizon. Both the coarse‐soil fraction and deeper mineral soil horizons may play a more active role in microbial nutrient cycling than previously assumed.     

Mechanisms controlling the mobility of dissolved organic matter, aluminium and iron in podzol B horizons

The processes governing the (im)mobilization of Al, Fe and dissolved organic matter (DOM) in podzols are still subject to debate. In this study we investigated the mechanisms of (im)mobilization of Al, Fe and organic matter in the upper and lower B horizons of two podzols from the Netherlands that are in different stages of development. We equilibrated batches of soil material from each horizon with DOM solutions obtained from the Oh horizon of the corresponding soil profiles. We determined the amount of (im)mobilized Al, Fe and DOM after addition of Al and Fe at pH 4.0 and 4.5 and initial dissolved organic carbon (DOC) concentrations of 10 mg C litre^?1 or 30 mg C litre^?1, respectively. At the combination of pH and DOC concentrations most realistic for the field situation, organic matter was retained in all horizons, the most being retained in the lower B horizon of the well‐developed soil and the least in the upper B horizon of the younger profile. Organic matter solubility seemed to be controlled mainly by precipitation as organo‐metal complexes and/or by adsorption on freshly precipitated solid Al‐ and Fe‐phases. In the lower B horizons, at pH 4.5, solubility of Al and Fe appeared to be controlled mainly by the equilibrium with secondary solid Al‐ and Fe‐phases. In the upper B horizons, the solubility of Al was controlled by adsorption processes, while Fe still precipitated as inorganic complexes as well as organic complexes in spite of the prevailing more acidic pH. Combined with a previous study of eluvial horizons from the same profiles, the results confirm the important role of organic matter in the transport of Al and Fe to create illuvial B horizons initially and subsequently deepening and differentiating them into Bh and Bs horizons.     

The total concentration and fractional composition of the aluminum compounds in soil solutions from peaty-podzolic-gleyic soils developed on binary deposits

The total concentration and fractional composition of aluminum compounds were determined in soil solutions obtained using vacuum lysimeters from the main genetic horizons of peaty-podzolic-gleyic soils developed on binary deposits. The total concentration of aluminum in the brooks draining the area with a predominance of these soils was also estimated. The total aluminum concentration in the soil solutions reached the maximum values (0.079–0.092 mmol/l) in the Eih horizon and generally decreased down the profile. The aluminum in the soil solutions occurred in the form of monomeric inorganic and organic compounds and complexes with high-molecular-weight organic acids. The proportion of inorganic monomeric aluminum compounds in the solutions from the peaty-podzolic-gleyic soils increased compared to that in the podzolic soils; no aluminosilicate compounds were found. Aluminum arrived to the brooks draining the areas with the predominant peaty-podzolic-gleyic soils mainly from the above-moraine horizons, including the Eih, E, and Ecn. It was supposed that the removal of aluminum from these soils exceeded that from the podzolic soils.     

Tracing Pb Pollution Penetration in Temperate Podzols

We combine high‐resolution soil sampling with lead (Pb) analyses (concentrations and stable isotopes) in two temperate podzols, together with previous data obtained with selective Al and Fe dissolution techniques. We aim to assess how atmospheric Pb is incorporated into the soils during pedogenesis. Partial least squares modelling for Pb concentrations shows that the podzolization process has the largest effect on Pb concentration (80·3% of the variance). The proportion of inorganic secondary compounds, the input of fresh organic matter from the soil surface and the relative abundance of Fe versus Al are responsible for a small part of the Pb concentration variance. Lead isotopic composition (²⁰⁶Pb/²⁰⁷Pb ratios) depends on soil organic matter content either fresh/poorly humified (57·3% of the variance) or humified (24·7% of the variance). The Pb linked to inorganic compounds and the overall podzolization process play a minor role in isotopic signature (5·3 and 3·7% of the variance respectively). Soil pH appears to be the controlling variable of the different transport and retention mechanisms. The relatively low isotopic ratios observed in spodic horizons result from geogenic Pb released through the preferential dissolution of the isotopically distinct most weatherable minerals of the parent material in the eluvial horizons, which undergoes downward mobilization. An accurate knowledge of soil reactive components and formation mechanisms is essential to a correct diagnose of the scope of Pb pollution and a more effective design of remediation strategies. Copyright © 2017 John Wiley & Sons, Ltd.     

Microbial properties of soils as affected by cropping and nutrient management practices in several long-term manurial experiments in the semi-arid tropics of India

Microorganisms play a critical role in nutrient transformation, soil health and for sustaining the productivity of soils. Effects of long-term cropping, fertilization, manuring and their integration on microbial community were studied in soil samples from five long-term fertilizer experiments under various rainfed production systems in the semi-arid tropics (SAT) of India. Microbial population counts were analyzed by dilution plating and were in turn compared with different parameters such as soil treatments, soil type, soil microbial biomass C, soil organic C, rainfall and soil pH. The counts were high in treatments where combinations of organic and inorganic fertilizers were applied compared to control. Vertisols showed larger organic carbon levels than Alfisols. Fungal population was higher in acidic soils and in treatments under continuous inorganic fertilization treatments whereas a high number of bacteria were found in integrated use of organic and inorganic fertilizers. At most of the locations soil organic C and microbial biomass C showed significant positive (p ≤ 0.05) correlation with microbial populations. Thus, results suggest that even under arid and semi-arid tropical conditions, regular addition of nutrients in an integrated manner could improve soil organic carbon and microbial population counts. For each production system, better carbon sequestration management practices were identified.     

Labile, recalcitrant, and inert organic matter in Mediterranean forest soils

The biochemical quality of soil organic matter (SOM) was studied in various profiles under Quercus rotundifolia Lam. stands on calcareous parent material. Special attention was paid to the question of how biochemical quality is affected by position within the soil profile (upper versus lower horizons). The following global SOM characteristics were investigated: (a) overall recalcitrance, using hydrolysis with either hydrochloric or sulphuric acid; (b) hydrolyzable carbohydrates and polyphenolics; (c) extractability by hot water and quality of the extract; and (d) abundance of inert forms of SOM: charcoal and soot-graphite. The recalcitrance of soil organic carbon (OC) decreases with depth, following the order: H horizons>A horizons>B horizons. In contrast, the recalcitrance of nitrogen is roughly maintained with depth. The ratio carbohydrate C to total OC increases from H to B horizons, due to the increasing importance of cellulosic polysaccharides in B horizons, whereas other carbohydrates are maintained throughout the soil profile at a relatively constant level, 12-15% of the total OC in the horizon. Whereas the quality of the hydrolyzable carbon (measured by the carbohydrate to polyphenolic C ratio) decreases with depth from H to B horizons, the quality of the hot-water extractable organic matter is much higher in B horizons than in A or H horizons. The relative importance of both charcoal and soot-graphitic C and N tends to increase with depth. The ratio black/total is usually higher for N than for C, a result that suggests that inert SOM may represent a relevant compartment in the nitrogen cycle. Overall, our data suggest that in Mediterranean forest soils the organic matter in B horizons could be less stable than often thought.     

Aluminum compounds in soil solutions and their migration in podzolic soils on two-layered deposits

The fractional composition of aluminum compounds was studied in soil solutions obtained using vacuum lysimeters from loamy podzolic soils on two-layered deposits. The concentration of aluminum was estimated in brooks and a river draining the area with a predominance of these soils. In soil solutions, the concentration of aluminum was experimentally determined in the following compounds: (1) organic and inorganic monomers, (2) stable complexes with HAs and FAs together with polymers, and (3) the most stable complexes with HAs and FAs together with fine-crystalline and colloidal compounds. The total Al concentration in soil solutions from forest litter was 0.111–0.175 mmol/l and decreased with depth to 0.05 mmol/l and lower in solutions from the IIBD horizons. More than 90% of the Al in the solutions was bound into complexes with organic ligands. Some amount of Al in solution could occur in aluminosilicate sols. The translocation of Al complexes from the litter through the AE horizon to the podzolic horizon was accompanied by an increase in the ratio between the Al concentration in fraction 2 and the C concentration in the solution. The concentrations of Al_tot in the surface waters varied in the range from 0.015 to 0.030 mmol/l. Most of the Al came to the surface waters from the litter and AE horizons and partially from the podzolic horizon due to the lateral runoff along the waterproof IIBD horizon. Approximate calculations showed that the recent annual removal of Al from the AE and E horizons with the lateral runoff was 7 to 560 mg (3–21 mmol) from 1 m².     

Speciation and mobilization of aluminium and cadmium in podzols and cambisols of S. Sweden

Processes governing the mobilization of Al and Cd in podzols and cambisols of S. Sweden having different tree layer vegetation (Picea abies, Fagus sylvatica, or Betula pendula) were investigated. Speciation of Al and Cd in soil solutions were performed by a column cation exchange procedure (cf. Driscoll, 1984) in combination with thermodynamic calculations. Podzols in spruce and beech stands were characterized by a high release of organic compounds from the O/Ah horizons, resulting in a high organic complexation of Al (c. 93%) in the soil solution from the E horizon (15 cm lysimeters). Organic complexes were mainly adsorbed/precipitated in the upper Bh horizon and the overall transport of Al at 50 cm depth was governed by a pH dependent dissolution of a solid-phase Al pool. In the cambisols, inorganic Al forms were predominant at both 15 and 50 cm depth, and Al solubility was closely related to solution pH. Secondary minerals like synthetic gibbsite, jurbanite, kaolinite or imogolite could generally not explain measured solution Al³⁺ activities. Results instead indicated that the relatively large organically bound solid-phase Al pools present in both soil types could do so. The column fractionation procedure could be used only qualitatively for Cd, but results strongly indicated that Cd-organo complexes contributed significantly to the overall mobilization of Cd in the podzol E horizons. In all other soil solutions, Cd²⁺ was the predominant species. Both solid-phase and solution chemistry suggests that ion exchange processes controlled the Cd²⁺ activities in these solutions. All reactive solidphase Cd was extractable by NH₄Cl and Cd²⁺ activities could in most cases effectively be modeled by the use of ion exchange equations. Solubilized Al³⁺ efficiently competed for exchange sites and played an important role for the Cd mobilization in these soils.     

水氮互作对设施菜田土壤氮素形态组成以及细菌群落结构的影响

利用室内模拟培养试验,研究了不同水氮互作条件对设施菜田土壤氮素形态组成和细菌群落结构的影响。主因素为2种土壤水分条件:70%田间持水量和100%田间持水量;副因素为5种氮素添加形态:不施氮肥、纯无机氮、纯有机氮、2/3无机氮 + 1/3有机氮和1/3无机氮 + 2/3有机氮。结果表明:水氮互作效应对土壤无机氮含量和土壤细菌群落Shannon和Simpson指数的影响显著（P < 0.05）。高含水量条件下,土壤无机氮含量显著降低（P < 0.05）,但土壤细菌群落的Shannon,Ace和Chao1指数极显著升高（P < 0.01）,并且随着土壤含水量升高,Aeromonas和Flavobacterium菌属的相对丰度增加;培养30 d后,添加有机氮处理的土壤有机氮含量显著高于添加无机氮处理,添加有机氮使Cellvibrio和Devosia菌属相对丰度上升。可见,设施菜田施用有机氮肥尽管短期内不利于土壤速效氮的积累,但在适宜的水分条件下,土壤优势菌群发生了较大改变,部分固碳功能菌群丰度增加,有利于稳定土壤碳氮循环。试验结果为进一步研究设施菜田水氮管理介导的土壤碳氮循环功能菌群变化的环境驱动机制提供了一定科学依据。     

Effect of long-term N fertilization on soil organic C and total N in continuous wheat under conventional tillage in Oklahoma

Fertilizer nitrogen (N) can impact on soil total N and organic carbon (C). The effects of long-term nitrogen (N) applications in continuous winter wheat (Triticum aestivum L.) production systems on total N and organic C in soils has not been studied previously. Deep soil cores were taken from four long-term winter continuous wheat experiments in Oklahoma, on silt loam and clay loam soils, to evaluate differences in total N and C as affected by more than 23 years of annual N applications. When N was applied at rates ≥90 kg ha⁻¹, surface soil (0–30 cm) organic C was either equal to that of the check (no N applied) or slightly greater. Total soil N (0–30 cm) increased at the high N rates at all locations. However, at two locations, total soil N decreased at low N rates, indicating the presence of priming (increased net mineralization of organic N pools when low rates of fertilizer N are applied). At these two same sites, soil–plant inorganic N buffering (amount of N that could be applied in excess of that needed for maximum yield without resulting in increased soil profile inorganic N accumulation) was greater compared to the other two sites where no evidence of priming was found. In general, C:N ratios increased at the low rates of applied N and then decreased to levels below that found in check plots at high N rates (≥134 kg N ha⁻¹ yr⁻¹). Combined surface (0–30 cm) soil analyses of total N and organic C were useful in detecting where priming had taken place and where soil–plant inorganic N buffering was expected to be high in these long-term N fertilization experiments. Predictability of the priming effect combined with soil–plant inorganic N buffering should assist us in establishing environmentally safe N rates. Soil organic C increased when N was applied at rates in excess of that required for maximum yield.     

Potentially Mobile Lead Fractions in Montane Organic-Rich Soil Horizons

Anthropogenic emissions during the 20th century resulted in global lead (Pb) contamination of soils. Recent studies have demonstrated that the organic horizons of temperate montane Spodosols in the northeastern United States retain Pb on timescales of 50 to 150 years. The precise mechanism(s) of this strong Pb partitioning to organic-rich soil material remain elusive, but a detailed understanding of Pb retention by organic layers and mineral topsoils is critical for predicting the fate of pollutants deposited on ecosystems. Here we use selective extractions to quantify potentially mobile pools of Pb in the surface horizons of relatively remote montane Spodosols from New Hampshire and Vermont. Using 10 consecutive rinses of water, we extracted a total of 1 to 5% of the carbon, and 4 to 12% of the Pb. Dialysis equilibration experiments demonstrate that this Pb is >5,000 molecular weight, and not truly dissolved as Pb²⁺. When soil was extracted with a single rinse of 0.02 M HCl (pH 1.7), 5 to 11% of the Pb was mobilized. However, hydroxylamine hydrochloride in 0.02 M HCl (a reducing agent) extracted 30 to 40% of the Pb. Repeated rinses with sodium hydroxide and sodium pyrophosphate, which target organic matter but may extract other soil phases removed 16 to 75% and 60 to 100% of the Pb, respectively. We show that significant Fe, Pb, and Al can be released from soils under reducing conditions, and that this fraction can be underestimated if sodium pyrophosphate is used in a previous step for leaching the organic-metal phase, as is typically done in sequential extraction schemes. Our results indicate that inorganic phases play an important role in determining Pb mobility and bioavailability, even in surface soil horizons dominated by organic matter.     

Phosphorus forms and enzymatic hydrolyzability of organic phosphorus in soils after 30 years of organic and conventional farming

Lower P‐input levels in organic than conventional farming can decrease soil total and available P, which can potentially be resupplied from soil organic P. We studied the effect of 30 y of conventional and organic farming on soil P forms, focussing especially on organic P. Soil samples (0–20 cm) were taken in a field experiment with a nonfertilized control, two organic systems receiving P inputs as animal manure, and two conventional systems receiving only mineral P or mineral P and manure. Soils were analyzed for total, inorganic, organic, and microbial P, by sequential P fractionation and by enzyme additions to alkaline soil extracts. Samples taken prior to starting the experiment were also analyzed. Average annual P balances ranged from –20 to +5 kg ha^–1. For systems with a negative balance, labile and moderately labile inorganic P fractions decreased, while organic and stable inorganic P fractions were hardly affected. Similar quantities and proportions of organic P extracted with NaOH‐EDTA were hydrolyzed in all soils after addition of an acid phosphatase, a nuclease, and a phytase, and enzyme‐stable organic P was also similar among soils. Thus, neither sequential fractionation nor enzyme addition to alkaline soil extracts showed an effect of the type of applied P (manure vs. mineral) on organic P, suggesting that organic P from manure has largely been mineralized. Thus far, we have no indication that the greater microbial activity of the organic systems resulted in a use of stable P forms.     

MODELLING LEACHING OF INORGANIC Hg(II) IN A SCANDINAVIAN IRON-HUMUS PODZOL - VALIDATION AND LONG-TERM LEACHING UNDER VARIOUS DEPOSITION RATES

Increasing mercury contents are reported from freshwater systems and fish in northern Europe and North America. Mercury input from soils is a major source with the leaching being affected by increased atmospheric mercury deposition compared to pre-industrial times and by other environmental conditions such as acid rain. The results of a mathematical model-calculation of vertical inorganic Hg(II) leaching in a Scandinavian iron-humus podzol under different atmospheric input rates of mercury are presented. Leaching under background rain conditions was calculated to be considerably stronger than under acid rain conditions. Increasing fractions of deposited soluble or solute atmospheric mercury were leached from the O _f(h)-horizon with decreasing soil content of soluble mercury under acid rain conditions; this effect was less pronounced under background rain conditions. The steady state concentrations of soluble mercury of the upper soil horizons were calculated and compared with the actual concentrations of total (= soluble + insoluble mercury) and extractable (= estimate of soluble) mercury measured in these horizons. The results indicate that even if the deposition of airborne mercury to soil is strongly reduced, the total mercury content of the soil decreases only slowly. It may take decades or even centuries before a new steady state concentration of total mercury is established in the soil. The decrease of the mercury concentration in the O _f(h)-horizon is probably largely dependent on the turnover of organic matter, binding most of the deposited airborne mercury in an insoluble form. Hence, present day mercury leaching is likely to be dominated by mercury deposited during former times and temporarily retained in an insoluble form in the organic matter.     

Soil phosphorus fractions after 111 years of animal manure and fertilizer applications

Accumulated soil P in agricultural soils is a major source of soluble and particulate forms of P entering water resources and degrading water quality. However, few research sites are currently available to evaluate the long-term effects of different cropping systems and fertility practices on soil inorganic and organic P accumulation. The objectives of this study were: (1) to compare the forms and quantity of different inorganic and organic soil P fractions in plots on Sanborn Field, which has been cultivated for 111 years; and (2) to assess the use of standard soil test P extractants for determining changes in soil P dynamics over time. A modified sequential P extraction procedure was used to separate labile and stable inorganic and organic P pools from surface soils collected on Sanborn Field in 1915, 1938, 1962, and 1999 from plots in continuous corn, continuous wheat, continuous timothy, and a corn-wheat-clover rotation amended with either manufactured fertilizers, horse or dairy manure or receiving no fertilization since 1888. Additional samples were collected from a native grass prairie site of a similar soil series to estimate soil characteristics at Sanborn Field before initial cultivation in 1888. Observed accumulation of Bray-1 P among fertilizer and manure treatments was attributed to over-application of P due to unrealistically high yield goals for each cropping system. Long-term cultivation of Sanborn Field increased soil bulk density and lowered soil pH and total organic C compared with native prairie. Fertilization either by addition of manufactured fertilizer or manure significantly increased inorganic resin-P and inorganic NaOH-extractable P. Applications of animal manure also significantly increased most organic P fractions compared with the unfertilized treatment. The native prairie had a larger proportion of total P in organic forms compared with cultivated plots, especially in organic NaOH-extractable P, but no significant decreases in either residual or total P were observed due to cultivation. This study confirms that soil P availability in cropping systems that are amended with predominantly organic P amendments may differ from conventional cropping systems relying on manufactured P fertilizers. However, no direct evidence was found to support the hypothesis that any individual inorganic or organic soil P fraction has a better relationship than conventional soil test P extractants with plant P uptake under contrasting organic and conventional fertility practices.     

Microbial community composition shapes enzyme patterns in topsoil and subsoil horizons along a latitudinal transect in Western Siberia

Soil horizons below 30 cm depth contain about 60% of the organic carbon stored in soils. Although insight into the physical and chemical stabilization of soil organic matter (SOM) and into microbial community composition in these horizons is being gained, information on microbial functions of subsoil microbial communities and on associated microbially-mediated processes remains sparse. To identify possible controls on enzyme patterns, we correlated enzyme patterns with biotic and abiotic soil parameters, as well as with microbial community composition, estimated using phospholipid fatty acid profiles. Enzyme patterns (i.e. distance-matrixes calculated from these enzyme activities) were calculated from the activities of six extracellular enzymes (cellobiohydrolase, leucine-amino-peptidase, N-acetylglucosaminidase, chitotriosidase, phosphatase and phenoloxidase), which had been measured in soil samples from organic topsoil horizons, mineral topsoil horizons, and mineral subsoil horizons from seven ecosystems along a 1500 km latitudinal transect in Western Siberia. We found that hydrolytic enzyme activities decreased rapidly with depth, whereas oxidative enzyme activities in mineral horizons were as high as, or higher than in organic topsoil horizons. Enzyme patterns varied more strongly between ecosystems in mineral subsoil horizons than in organic topsoils. The enzyme patterns in topsoil horizons were correlated with SOM content (i.e., C and N content) and microbial community composition. In contrast, the enzyme patterns in mineral subsoil horizons were related to water content, soil pH and microbial community composition. The lack of correlation between enzyme patterns and SOM quantity in the mineral subsoils suggests that SOM chemistry, spatial separation or physical stabilization of SOM rather than SOM content might determine substrate availability for enzymatic breakdown. The correlation of microbial community composition and enzyme patterns in all horizons, suggests that microbial community composition shapes enzyme patterns and might act as a modifier for the usual dependency of decomposition rates on SOM content or C/N ratios.     

Physicochemical and Microbiological Characteristics of Tundra Soils on the Rybachii Peninsula

The Rybachii Peninsula is composed of Proterozoic sedimentary rocks and differs sharply from the rest of the Kola Peninsula in its geological structure, topographic forms, and parent rocks. It is dominated by Al–Fe-humus soils formed on moraines with an admixture of local rock fragments, including slates. Organic horizons of tundra soils in the peninsula are less acid than those on granitoids of adjacent mainland of the Kola Peninsula. The content of exchangeable calcium in the organic horizons varies from 17.4 to 68.0 cmolc/kg, and the content of water-soluble carbon reaches 400 mg/100 g amounting to 1–2% of the total soil organic matter content. The total number of bacteria in the organic horizons of tundra soils varies from 3.5 × 10⁹ to 4.8 × 10⁹ cells/g; and bacterial biomass varies from 0.14 to 0.19 mg/g. The length of fungal mycelium and its biomass in the organic horizons are significant (>1000 m/g soil). The biomass of fungal mycelium in the organic horizons exceeds the bacterial biomass by seven times in podzols (Albic Podzols) and by ten times in podbur (Entic Podzol), dry-peat soil (Folic Histosol), and low-moor peat soil (Sapric Histosol).