Search

Forests face considerable pressure from climate change, while demand of provided ecosystem services is high. Managing and planting forests need well informed decisions by practitioners, to fulfill the goal of sustainability. In Germany, informed decisions are derived from forest site evaluation maps, integrating biogeoecolocigal conditions (climate, soil water, nutrients). Here, we focus on mapping of nutrients in the federal state Hesse, Germany. For Hesse, a forest site map exists, which indicates a soil nutrient regime (SNR) index (classes very poor, poor, medium, rich, very rich). Site mapping was done in the field by experts, considering ground vegetation and soil morphology. Guidelines exist for choosing management options (i.e. suitable species composition, harvest restrictions, etc.), but if spatial information is not accurate, management decisions will be misguided.Three major challenges regarding the currently available site information exist: (1) the spatial proportion of “medium” sites is exceptionally high (65% of mapped forest area) and while there is differentiation between parent materials, topography is neglected. (2) Whereas 80% of Hesse’s forests were mapped, there is need to fill the gaps. (3) The existing SNR index does not take analytical measurements of soil nutrients into account. Objectives were (1) to refine and expand the existing map of SNR by (2) including soil chemical properties from the second National Forest Soil Inventory (NFSI), (3) which have to be regionalised beforehand.Stocks of Ca, Mg and K, base saturation, effective cation exchange capacity (90cm depth and organic layer), and C/N ratio (organic layer or 0-5 cm) of 380 profiles from the NFSI were chosen to characterise the SNR. Regionalisation was performed with generalised additive models (GAM) by using environmental relationships of the target variables with variables of climate, vegetation, parent material and soil properties (soil map 1:50,000). Ten-fold cross validation revealed R² values from 0.54 to 0.79, with low relative root mean square deviation (5 to 17%) and slopes not significantly different from 1. From the six successfully modelled target variables, we inferred a single SNR for each soil map polygon. This was challenging, because variables provided contrasting information regarding the SNR. We addressed this by using the Soil Inference Engine (SIE), which bases on fuzzy logic. Each variable received an optimality value for each SNR class. Using an expert-driven weighting system a SNR membership was inferred, whereas highest membership defined the SNR class. The result was highly sensitive towards parent material and topography. For instance, acidic parent material had lower SNR classes compared to base rich parent material. Within a given parent material, ridges where judged less nutrient rich compared to planes and topographic positions, where material is accumulated.The results provide a much more differentiated and complete map for SNR, which mirror actual expectations of nutrient distribution across Hesse’s landscape units. The approach is transparent and inter-subjectively reproducible. The new map will be used to guide reforestation activities in Hesse after the severe forest disturbances by recent climatic extremes (e.g. drought, storms) and the approach can be transferred to other regions.

Crop residue addition is a way to increase soil organic matter (SOM) level in croplands. However, organic matter input and SOM stocks are not linearly related. Consequently, adding high amounts of residues, such as straw, may increase SOM to only a small extent, and an alternative use of the residues may be justified. The objective of this study was to test how the level and type (above- or belowground) of residue addition affect SOM stabilization. We hypothesise that (1) root residues will be mineralised slower than leaf and stalk residues, (2) soil aggregate formation will increase with high additions, and (3) wheat residue addition will induce positive priming, with the magnitude depending on the residue level and type. Homogeneously 13C-labelled wheat residues (leaves, stalks, roots) were added to a silt-loam soil at levels of 1.40 and 5.04 g DM kg− 1 and CO2 release and δ13C signature were measured over 64 days at 20 °C. Water-stable macroaggregates (> 250 μm), microaggregates (53–250 μm) and silt plus clay size fractions (

Crop residues and manure are important sources of carbon (C) for soil organic matter (SOM) formation. Crop residue return increases by nitrogen (N) fertilization because of higher plant productivity, but this often results only in minor increases of SOM. In our study, we show how N fertilization and organic C additions affected SOM and its fractions within a 32-year-long field-experiment at Puch, Germany. Five organic additions, no-addition (control), manure, slurry, straw and straw + slurry, were combined with three mineral N fertilization rates (no, medium and high fertilization), which resulted in 1·17–4·86 Mg C-input ha-1 y-1. Topsoil (0–25 cm) SOM content increased with N fertilization, mainly because of the C in free light fraction (f-LF). In contrast, subsoil (25–60 cm) SOM decreased with N fertilization, probably because of roots' relocation in Ap horizon with N fertilization at the surface. Despite high inputs, straw contributed little to f-LF but prevented C losses from the mineral-associated SOM fraction (ρ > 1·6 g cm-3) with N fertilization, which was observed without straw addition. Above (straw) and belowground (roots) residues had opposite effects on SOM fractions. Root C retained longer in the light-fractions and was responsible for SOM increase with N fertilization. Straw decomposed rapidly (from f-LF) and fueled the mineral-associated SOM fraction. We conclude that SOM content and composition depended not only on residue quantity, which can be managed by the additions and N fertilization, but also on the quality of organics. This should be considered for maintaining the SOM level, C sequestration, and soil fertility. Copyright © 2016 John Wiley & Sons, Ltd.

The management of forests needs well informed decisions by stakeholders to fulfil the goals of sustainability, stability, and productivity. Decisions are guided by forest site maps. The forest site map of Hesse, Germany, consists of six soil nutrient index (SNI) classes (poor, moderate-weak, moderate, moderate-good, rich, carbonatic). Three major challenges regarding the currently available site information exist: (i) the spatial proportion of “moderate” sites is exceptionally high (65% of mapped forest area) and while there is differentiation between parent materials, topography is neglected. (ii) As 80% of Hesse's forests were mapped, there is demand to fill the gaps without site information. (iii) The existing SNI does not take soil analysis into account, which is required to detect finer differences in morphologically similar soil profiles. Objectives were to regionalize soil chemical variables and derive a more differentiated SNI for Hesse's forest soils with complete forest coverage. Stocks of intermediately available Ca, Mg, and K, base saturation, effective cation exchange capacity, and C/N ratio of 380 profiles from the National Forest Soil Inventory were used to characterize the SNI. Regionalization of soil chemical variables was successfully performed (R2 values from 0.54 to 0.79, root mean square deviation 5 to 17%) using generalized additive models. SNI classes were inferred by fuzzy logic for dealing with soil chemical variables. The results were highly sensitive towards parent material and topography. The modelled SNI map provides a much more differentiated and complete map for Hesse, Germany, which mirror actual expectations across landscape units. The approach is transparent and inter-subjectively reproducible. The new map will be used to guide the management and reforestation of sites, which were damaged by biotic or abiotic threats due to recent climatic extreme events.

It is still open to question which method is the best for quantifying organic carbon (OC) and inorganic carbon (IC) in soils containing dolomite. The aims of this study were (1) to compare the accuracy of a novel thermal gradient (ThG), the classical calcimeter (CALC) and the loss-on-ignition (LOI) methods on a reference sample set with known proportions of OC present as soil organic matter (SOM) and IC present as dolomite and (2) to compare the results of the different methods on a set of soil samples with different dolomite and SOM contents. The CALC and LOI methods rely on separate quantification or removal of IC by acid or heat, whereas IC and OC can be quantified in a single run by the ThG analysis. The ThG method was the most accurate method for the reference sample set, especially when dolomite contents were high. On the soil sample set, the ThG and CALC methods performed equally well, but only when two outliers were eliminated. The LOI method was not satisfactory for either sample set. Overall, ThG was the most reliable method for measuring IC and OC in dolomite-containing samples over a wide range of concentrations, but the more widely used CALC method was also acceptable.

Grasslands are very important regionally and globally because they store large amounts of carbon (C) and nitrogen (N) and provide food for grazing animals. Intensive degradation of alpine grasslands in recent decades has mainly impacted the upper root-mat/soil horizon, with severe consequences for nutrient uptake in these nutrient-limited ecosystems. We used 15N labeling to identify the role of individual soil layers for N-uptake by Kobresia pygmaea—the dominating plant in the degraded Tibetan pasture ecosystems. We hypothesized a very efficient N-uptake corresponding mainly to the vertical distribution of living roots (topsoil > subsoil). We assume that K. pygmaea develops a very dense root-mat, which has to be maintained by small aboveground biomass, to enable this efficient N-uptake. Consequently, a higher N-investment into roots compared to shoots was hypothesized. The 15N recovery in whole plants (~70%) indicated very efficient N-uptake from the upper injection depths (0–5 cm). The highest 15N amounts were recovered in root biomass, whereby 15N recovery in roots strongly decreased with depth. In contrast, 15N recovery in shoots was generally low (~18%) and independent of the 15N injection depth. This clearly shows that the low N demand of Kobresia shoots can be easily covered by N-uptake from any depth. Less living root biomass in lower versus upper soil was compensated by a higher specific activity of roots for N-uptake. The 15N allocation into roots was on average 1.7 times higher than that into shoots, which agreed well with the very high R/S ratio. Increasing root biomass is an efficient strategy of K. pygmaea to compete for belowground resources at depths and periods with available resources. This implies high C-costs to maintain root biomass (~6.0 kg DM m−2), which must be covered by a very low amount of photosynthetically active shoots (0.3 kg DM m−2). It also suggests that Kobresia grasslands react extremely sensitively toward changes in climate and management that disrupt this above-/belowground trade-off mechanism.

SUMMARYAgroforestry systems (AFS) can serve to decrease ecosystem carbon (C) losses caused by deforestation and inadequate soil management. Because of their shade tolerance, cacao plants are suitable to be grown in AFS, since they can be combined with other kinds of trees and shrubs. The potential for C sequestration in cacao farming systems depends on various factors, such as management practices, stand structure and plantation age. We compared conventionally and organically managed cacao monoculture systems (MCS) and AFS in Sara Ana (Bolivia) with respect to C stocks in plant biomass and to amounts of litterfall and pruning residues. The total aboveground C stocks of the AFS (26 Mg C ha−1) considerably exceeded those of the MCS (~7 Mg C ha−1), although the biomass of cacao trees was greater in the MCS compared to the AFS. Due to higher tree density, annual litterfall in the AFS (2.2 Mg C ha−1 year−1) substantially exceeded that in the MCS (1.2 Mg C ha−1 year−1). The amounts of C in pruning residues (2.6 Mg C ha−1 year−1 in MCS to 4.3 Mg C ha−1 year−1 in AFS) was more than twice those in the litterfall. Annual nitrogen (N) inputs to the soil through pruning residues of cacao and N-fixing trees were up to 10 times higher than the N inputs through external fertiliser application. We conclude that appropriate management of cacao AFS, involving the pruning of leguminous trees, will lead to increases in biomass, litter quantity and quality as well as soil C and N stocks. Thus, we recommend stimulating the expansion of well-managed AFS to improve soil fertility and enhance C sequestration in soils.

Crop residue quality and quantity have contrasting effects on soil organic matter (SOM) decomposition, but the mechanisms explaining such priming effect (PE) are still elusive. To reveal the role of residue quality and quantity in SOM priming, we applied two rates (5.4–10.8 g kg−1) of 13C-labeled wheat residues (separately: leaves, stems, roots) to soil and incubated for 120 days. To distinguish PE mechanisms, labeled C was traced in CO2 efflux and in microbial biomass and enzyme activities (involved in C, N, and P cycles) were measured during the incubation period. Regardless of residue type, PE intensity declined with increasing C additions. Roots were least mineralized but caused up to 60% higher PE compared to leaves or stems. During intensive residue mineralization (first 2–3 weeks), the low or negative PE resulted from pool substitution. Thereafter (15–60 days), a large decline in microbial biomass along with increased enzyme activity suggested that microbial necromass served as SOM primer. Finally, incorporation of SOM-derived C into remaining microbial biomass corresponded to increased enzyme activity, which is indicative of SOM cometabolism. Both PE and enzyme activities were primarily correlated with residue-metabolizing soil microorganisms. A unifying model demonstrated that PE was a function of residue mineralization, with thresholds for strong PE increase of up to 20% root, 44% stem, and 51% leaf mineralization. Thus, root mineralization has the lowest threshold for a strong PE increase. Our study emphasizes the role of residue-feeding microorganisms as active players in the PE, which are mediated by quality and quantity of crop residue additions.

It has been demonstrated before that growing pea (Pisum sativum L.) plants reduce the decomposition of 15N labeled maize residues. This reduction was especially strong in pots planted with the mycorrhizal wild-type Frisson (myc+) in comparison with the non-mycorrhizal mutant P2 (myc−). The aim of the present experiment was to assess the contribution of AMF and saprotrophic microorganisms to the formation of aggregates and accumulation of C and N as occluded light fraction organic matter in the soil of this pot experiment. In the myc+ treatment of the size class

The best method for determining soil organic carbon (SOC) in carbonate-containing samples is still open to debate. The objective of this work was to evaluate a thermal gradient method (ThG), which can determine simultaneously inorganic carbon (SIC) and SOC in a wide range of soil samples. The determination of SOC by ThG (SOCThG) was compared to the following widespread standard methods: (1) acidification (ACI) as pretreatment and subsequent dry combustion (SOCACI) and (2) volumetric quantification of SIC by a calcimeter (CALC) and subtraction of the total carbon content as determined by dry combustion (SOCCALC). Precision (F test) and bias (t test) were tested on a subset of seven samples (n = 3). Comparison of the ThG and CALC methods was performed by regression analysis (n = 76) on samples representing a wide range of SOC (5.5 to 212.0 g kg−1) and SIC (0 to 59.2 g kg−1) contents. Tests on the replicated subset showed that the precision of ThG was not significantly different from ACI or CALC (F values

Terrestrial herbs are important elements of tropical forests; however, there is a lack of research on their diversity patterns and how they respond to different intensities of forest-use. The aim of this study was to analyze the diversity of herbaceous angiosperms along gradients of elevation (50 m to 3500 m) and forest-use intensity on the eastern slopes of the Cofre de Perote, Veracruz, Mexico. We recorded the occurrence of all herbaceous angiosperm species within 120 plots of 20 m x 20 m each. The plots were located at eight study locations separated by ~500 m in elevation and within three different habitats that differ in forest-use intensity: old-growth, degraded, and secondary forest. We analyzed species richness and floristic composition of herb communities among different elevations and habitats. Of the 264 plant species recorded, 31 are endemic to Mexico. Both α- and γ-diversity display a hump-shaped relation to elevation peaking at 2500 m and 3000 m, respectively. The relative contribution of between-habitat β-diversity to γ-diversity also showed a unimodal hump whereas within-habitat β-diversity declined with elevation. Forest-use intensity did not affect α-diversity, but β-diversity was high between old-growth and secondary forests. Overall, γ-diversity peaked at 2500 m (72 species), driven mainly by high within- and among-habitat β-diversity. We infer that this belt is highly sensitive to anthropogenic disturbance and forest-use intensification. At 3100 m, high γ-diversity (50 species) was driven by high α- and within-habitat β-diversity. There, losing a specific forest area might be compensated if similar assemblages occur in nearby areas. The high β-diversity and endemism suggest that mixes of different habitats are needed to sustain high γ-richness of terrestrial herbs along this elevational gradient., Open-Access-Publikationsfonds 2017

What would current ecosystems be like without the impact of mankind? This question, which is critical for ecosystem management, has long remained unanswered due to a lack of present-day data from truly undisturbed ecosystems. Using mountaineering techniques, we accessed pristine relict ecosystems in the Peruvian Andes to provide this baseline data and compared it with the surrounding accessible and disturbed landscape. We show that natural ecosystems and human impact in the high Andes are radically different from preconceived ideas. Vegetation of these ‘lost worlds’ was dominated by plant species previously unknown to science that have become extinct in nearby human-affected ecosystems. Furthermore, natural vegetation had greater plant biomass with potentially as much as ten times more forest, but lower plant diversity. Contrary to our expectations, soils showed relatively little degradation when compared within a vegetation type, but differed mainly between forest and grassland ecosystems. At the landscape level, a presumed large-scale forest reduction resulted in a nowadays more acidic soilscape with higher carbon storage, partly ameliorating carbon loss through deforestation. Human impact in the high Andes, thus, had mixed effects on biodiversity, while soils and carbon stocks would have been mainly indirectly affected through a suggested large-scale vegetation change. Fil: Sylvester, Steven P.. Universitat Zurich; Suiza. Philipps-Universität Marburg; Alemania Fil: Heitkamp, Felix. Universität Göttingen; Alemania Fil: Sylvester, Mitsy D. P. V.. Universitat Zurich; Suiza. Universidad Nacional del San Antonio Abad del Cusco; Perú Fil: Jungkunst, Hermann F.. Universität Koblenz-Landau; Alemania Fil: Sipman, Harrie J. M.. Freie Universität Berlin; Alemania Fil: Toivonen, Johanna M.. University of Turku; Finlandia Fil: Gonzales Inca, Carlos A.. University of Turku; Finlandia Fil: Ospina Gonzalez, Juan Camilo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; Argentina Fil: Kessler, Michael. Universitat Zurich; Suiza

Annual changes in stocks of soil organic carbon may be detected by measurement of heterotrophic respiration, but field studies of heterotrophic respiration in long-term fertilization experiments on sandy soils are scarce. Our objectives were to: (1)investigate the influence of fertilizer type on mineralization of soil organic carbon and crop residue, and (2) show how fertilization treatments affect the annual C balance (net ecosystem carbon balance, NECB; negative values indicate a CO2-source) in the sandy soil of the Darmstadt experiment. Treatments were long-term mineral fertilization with cereal straw incorporation (MSI) and application of rotted farmyard manure (FYM), both treatments receiving 14 g N m−2 year−1. This study used δ13C natural abundance after introduction of a C4 crop to distinguish between different sources of respiration. Mineralization derived from C3 sources was similar for MSI and FYM treatments (∼270 g C m−2 year−1). The rate of residue mineralization in MSI treatments was higher, ...

Effects of fertilisation and cropland management on soil organic carbon (SOC) dynamics can be assessed best in long-term experiments. Using data from the long-term fertilisation experiment in Puch, Germany (part of the series “Internationale Organische Stickstoff Dauerversuche”, IOSDV), we tested the performance of the Rothamsted Carbon Model 26.3 (RothC). The objectives of this work were: (i) quantify the C-input and the efficiency of SOC stabilisation, (ii) test the performance of different input estimates on predictive power of the RothC and (iii) test implementations of residue quality and C-saturation on model predictions. The experiment is a full-factorial strip design, the factors being “organic amendment” and “level of N-fertiliser”. Each treatment was replicated three times. The crop rotation is silage maize–winter wheat–winter barley. Five levels of the factor “organic amendment” were considered: (i) CON: no organic amendment; (ii) SLU: slurry application (on average 0.8 Mg C ha− 1 year− 1); (iii) FYM: application of farmyard manure (30 to 40 Mg ha− 1 fresh mass every third year to maize, on average 1.0 Mg C ha− 1 year− 1); (iv) STR: straw incorporation after harvest of wheat and barley (depending on straw yield on average 0.7 to 2.2 Mg C ha− 1 year− 1); (v) STSL: slurry application plus straw incorporation (on average 1.1 to 2.4 Mg C ha− 1 year− 1). All treatments (including CON) were combined with five different levels of N-fertilisation (N0 to N4), whereas N0 was nil N application and N4 averaged 177 kg N ha− 1 year− 1. N-rates increased gradually and differed depending on the crop. Starting values for SOC stocks (Mg ha− 1) were measured in 1983 as a mean among N-rates for organic amendment treatments (CON: 42; SLU: 39.8; FYM: 40.5; STR 39.8; STSL: 40.5). SOC stocks (0–25 cm) in 2004 (35.5 to 46.6 Mg C ha− 1) were in the order STSL > FYM = SLU > STR = CON (p ≤ 0.001). However, slightly different starting values indicated a higher loss of SOC after 21 years in the CON (11–14%) compared to the STR treatments (1–10%). Effect of N-rate was not significant. The observed relation between change of SOC and C-input was quadratic (YO = − 13.4 + 7.5x − 0.9x2; R2 = 0.74, p ≤ 0.001), which contrasted the linear relationship predicted by RothC (YP = − 12.9 + 5.5x; R2 = 0.97, p ≤ 0.0001). Serious deviation between observed and predicted relationship occurred above C-inputs of 2.5 Mg C ha− 1 year− 1. Mechanistic explanation (e.g. C-saturation or increased mineralisation by N-fertilisation) for the observation needs further exploration, but implication on regional estimates for C-accumulation for different cropland management scenarios is obvious: potential gain in SOC storage by increasing C-inputs may be overestimated, at least under conditions of the Puch site. Independent model predictions (i.e. no parameter adjustment and independent estimation and measurement of C-input) were successful for treatments without straw incorporation (CON, SLU, FYM). Using a regression between crop yields and crop residue input yielded better results than using a constant belowground-to-aboveground biomass ratio. SOC stocks of treatments STR and STSL were seriously overestimated by the model. Using a higher decomposability of crop residue improved result only marginally and required the change of a standard parameter. Using a simple implementation of C-saturation improved predictions for STR and STSL but failed to simulate dynamics in all other treatments. Overall, our results showed that it is important to recognise that relation between SOC change and C-input is not necessarily linear. However, the RothC model predicted SOC dynamics well at lower input levels. Observation that a regression equation for input estimation is superior to a constant biomass ratio for modelling purposes has to be tested further. An implementation of residue quality or saturation capacity in the RothC model may be promising for a better mechanistic understanding of SOC dynamics. However, this requires careful calibration and will increase the number of parameters to be fitted.

One aim of organic and biodynamic agriculture is to improve soil fertility. Our objectives are to (1) explain previously reported differences in the soil organic matter levels between soils receiving farmyard manure (FYM) with or without biodynamic preparations (BD), (2) quantify the effect of three levels of FYM applications on microbial biomass and soil organic matter (SOM) pools with different stability, and (3) relate SOM pools to crop yields in a long-term experiment on a sandy soil at Darmstadt, Germany. Soils of the BD-FYM treatments had significantly higher Corg contents compared to soils of the FYM treatments. However, soil fractionation indicated that there was a greater storage of Corg in the intermediate and passive pools of the BD-FYM treatments, and the temporal course of Corg contents suggested a slow convergence of Corg stocks between FYM and BD-FYM with time. Thus, the observed differences between BD-FYM and FYM treatments were likely to have existed since the beginning of the experiment. Contents of labile C (70–114 g [kg Corg],−1 turnover time 462 days) and labile N (35–49 g [kg N t ]−1, turnover time of 153 days) were strongly related to the application rate and also to crop yields. Yield of potatoes, winter rye, and clover significantly increased in proportion to the application rate of FYM, while BD had no effect. Overall, the study showed that increasing rates of FYM increased C and N availability independent of the use of BD. Nevertheless, efficiency of C sequestration in a more stable form (intermediate pool) decreased with increasing rate.

The application of density fractionation is an established technique, but studies on short-term dynamics of labile soil fractions are scarce. Objectives were (1) to quantify the long-term and short-term dynamics of soil C and N in light fraction (LFOC, LFON, ρ ≤ 2.0 g cm- 3 ) and microbial biomass C (C mic ) in a sandy Cambisol as affected by 28 y of different fertilization and (2) to determine the incorporation of C 4 -C into these labile fractions during one growing season of amaranth. The treatments were: straw incorporation plus application of mineral fertilizer (MSI) and application of farmyard manure (FYM) each at high (MSI H , FYM H , 140-150kg N ha -1 y -1 ) and low (MSI L , FYM L , 50-60 kg N ha- 1 y -1 ) rates at four field replicates. For all three sampling dates in 2008 (March, May, and September), stocks of LFOC, LFON and C mic decreased in the order FYM H > FYM L > MSI H , MSI L . However, statistical significance varied markedly among the sampling dates, e.g., with LFOC being significantly different (p≤ 0.05) in the order given above (sampling date in March), significantly different depending on the fertilizer type (May), or non-significant (September). The high proportion of LFOC on the stocks of soil organic C (45% to 55%) indicated the low capacity of soil-organic-matter stabilization on mineral surfaces in the sandy Cambisol. The incorporation of C 4 -C in the LFOC during one growing season of amaranth was small in all four treatments with C 4 -LFOC ranging from 2.1 % to 3.0% of total LFOC in March 2009, and apparent turnover times of C 3 -derived LFOC ranged from 21 to 32 y for the sandy soils studied. Overall, our study indicates that stocks of LFOC and LFON in a sandy arable soil are temporarily too variable to obtain robust significant treatment effects of fertilizer type and rate at common agricultural practices within a season, despite the use of bulked six individual cores per plot, a common number of field replicates of four, and a length of treatments (28 y) in the order of the turnover time (21-32 y) of C 3 -derived LFOC.

Type and rate of fertilizers influence the level of soil organic carbon (Corg) and total nitrogen (Nt) markedly, but the effect on partitioning of C and N into different pools is open to question. Objectives were to investigate the impact of fertilizer type and rate on labile, intermediate and passive C and N pools in a sandy Cambisol at Darmstadt, Germany, after 27 years of different fertilization treatments. The six treatments were: straw incorporation plus application of mineral fertilizer (MSI) and application of farmyard manure (FYM) each at high (140–150 kg N ha−1 year−1), medium (100 kg N ha−1 year−1) and low (50–60 kg N ha−1 year−1) rates. Soil microbial biomass C (Cmic) and N (Nmic) and C and net N mineralization (266 days incubation at 10°C and 50% waterfilled pore space) were determined. Soils (0–25 cm) of MSI treatments had significantly (p ≤ 0.05) lower Cmic stocks (308–361 kg ha−1) than soils of FYM treatments (404–520 kg ha−1). Differences in Nmic stocks were less pronounced. After 266 days, mineralized C (1130–1820 kg ha−1) and N (90–125 kg ha−1) had significantly increased with fertilizer rate. The application of an exponential two-pool model showed that very labile pools (turnover times: 17 and 9 days for C and N, respectively) were small (1.3–1.8% of Corg and 0.5–1.0% of Nt) and not influenced by type or rate of fertilizer. Stocks of the modeled labile C and N pools (turnover times: 462 and 153 days for C and N, respectively) were not influenced by the type of fertilizer but depended significantly on the application rate and ranged from 7 to 13% of Corg and from 4 to 5% of Nt. In contrast, the size of the calculated intermediate C pool was greater for the FYM treatments, and depended significantly on the interaction of fertilizer type and rate. The intermediate N pool was unaffected by fertilizer type or rate. Passive C and N pools, as experimentally revealed by oxidation with disodium peroxodisulfate (Na2S2O8), were independent of the treatments. Overall, labile and intermediate pools were affected differently by the fertilizer type and the application rate.

Decline of heathlands in Central Europe raises the question of successful restoration of degraded heathlands. We examined the impact of different restoration techniques on soil microbial biomass carbon (Cmic) and nitrogen (Nmic) and enzyme activity on an abandoned military training site in the Luneburger Heaths. The aim was to determine which technique resulted in typical heathland soil conditions. The training site was in use for about 50 years. Vegetation and soils were degraded in large areas. Restoration actions were: (1) spreading of heath plaggen (sods, containing the organic layer and a few centimetres mineral soil), (2) spreading of heath plaggen and grass seeds (Festuca filiformis Pourr.), (3) spreading of F. filiformis-seeds and (4) succession (episodical tree removal). Ten years after restoration, we measured pH, bulk density, abundance of roots, soil organic carbon (SOC), nitrogen (Nt), phosphorus (Pt), Cmic, Nmic and acid phosphatase activity (AcP) in the first 10 cm of the mineral soil. Four restoration treatments were compared with one reference site. The reference site is heathland located near the training site, where no military actions took place. At all disturbed sites, bulk density and pH proved to be higher than on the reference site. Relative to the reference site, SOC storage reached from 37 to 91 per cent, regeneration of Nt was slightly lower. In contrast to the advanced development of SOC and Nt, the regeneration of Cmic and Nmic was much lower (15–44 per cent). The succession site showed a low pool of SOC, Nt, Cmic and Nmic, but microbial ratios indicated a less disturbed C- and N-cycle. AcP pronounced differences in nutrient demand between disturbed sites and reference. On this base, recommendations for restoration management were given. Copyright © 2008 John Wiley & Sons, Ltd.

Deforestation and fragmentation are threats to the conservation of species and have consequences for ecosystem functions. The focus of this study was to elucidate forest cover change in the period of 1993 to 2014. Our study area is in the central region of Veracruz, Mexico. Land cover and land use classes for the Years 1993, 2000, and 2014 were derived from Landsat images applying supervised classification. Then, we quantified the net change in forest area, the loss of original forest area, and evaluated forest fragmentation using landscape metrics. Our results showed that the area covered by remnant forests decreased 57%. The annual net forest cover change rate for 1993 to 2000 was −0.44%; since then forest cover increased at a rate of 0.11% from 2000 to 2014. The decreasing total edge density and the mean proximity index during the entire period of the study indicate decreasing irregularity in the shape of remnant forest patches and a slight decrease of vulnerability to edge effects. Forest patches augm...

Human activity affects properties and development of ecosystems across the globe, to such a degree that it is now challenging to get baseline values for undisturbed ecosystems. This is especially true for soil development, which is potentially affected by land-use history and holds a legacy of past human interventions. Therefore, it is still largely unknown for most ecozones how soil would have developed ‘naturally’. Here, we show undisturbed soil development, i.e. the processes of weathering and accumulation of soil organic matter (SOM), by comparing pristine with grazed sites in the high Andes (4500 m) of southern Peru. We located study plots on a large ledge (0.2 km2) that is only accessible with mountaineering equipment. Plots with pristine vegetation were compared to rangeland plots that were presumably under relatively constant grazing management for at least four millennia. Vegetation change, induced by grazing management, led to lower vegetation cover of the soil, thereby increasing soil surface temperatures and soil acidification. Both factors increased weathering in rangeland soils. Formation of pedogenic oxides with high surface area explained preservation of SOM, with positive feedback to acidification. Higher contents of pyrophosphate extractable Fe and Al oxides indicated the importance of organo-mineral associations for SOM stabilization on rangeland sites, which are likely responsible for a higher degree of humification. This higher degree of humification induced melanization (darker colour) of the rangeland soils which, together with sparse vegetation cover, also feeds back to soil temperature. With this work, we present a conceptual framework of positive feedback links between human-induced vegetation change, soil development and accumulation of SOM, which is only possible due to the unique baseline values of a pristine ecosystem. Using ‘inaccessibility’ as a tool to quantify human impact in future interdisciplinary studies may push research forward on evaluating anthropogenic impact on Earth’s ecosystems.

In the context of “recarbonization”, it is important to know where the soil C stocks are located and how much of these are prone to emission to the atmosphere. While it may appear to be a trivial question considering available global estimates and maps, yet there is a strong need to emphasize that erroneous estimates are made in assessing the global soil C stocks. Without doubt, peatlands hold the single most important soil C stock at the global scale, and these soils are mostly located in the northern latitudes between 50°N and 70°N. However, there are additional wetlands or other ecosystems which also hold potentially relevant amounts of soil C stocks. From the soil science perspective, it implies that there are other hydromorphic soils, besides Histosols and potentially other soil types, also containing relevant amounts of soil C stock. Differences in scientific approaches, which include terminology, definitions, depth to which soil C is considered, and bulk density, etc., lead to different estimates of soil C stocks. Recent estimates indicate that peatlands cover only 3% of the global land surface but contain 40% of the soil C stocks to 1-m depth. Consequently, only small differences in the estimate of the land coverage lead to great differences in the soil C stock estimates. Typically peatlands, wetlands and other ecosystems rich in soil C, cover only small parts of the landscapes, and yet are not easily accounted for by any inventory or mapping attempts. With estimates presented in this chapter, hydromorphic soils, aside Histosols, add 10% soil C stock to the estimates of peatland’s Histosols. Additionally, non hydromorphic Podzols add another 10% to the soil C stock. Above all, soils from the steppe biome must also be considered. The soil C stock of Cryosols (frozen soil C not separated from peatlands) contain as much as 1,500 Pg C, which is as much C as the total stock estimated in world soils to 1-m depth. Thus, coordinated and substantial efforts are needed to improve the mapping of ecosystems, particularly of those which are rich in soil C stocks. One option is to improve remote sensing techniques for wetlands. These efforts must be undertaken quickly because soil C stocks are being depleted not only by the positive feedback with the climate system but also directly by land use change. The conversion of peatlands to agricultural and forestry uses is not sustainable because of the depletion C stocks, and especially not for conversion of peatlands for “biofuels” production.

Climate change is evident and increases of carbon dioxide concentration (CO2), temperature and extreme weather events are predicted. To predict the effects of such changes on carbon (C) cycling, the processes and mechanisms determining the magnitude of C storage and fluxes must be well understood. The biggest challenge is nowadays to quantify belowground components of the C-cycle. Soil respiration accounts for ∼70% of total annual ecosystem respiration. However, the CO2 flux from soil originates from several sources, such as root respiration, rhizomicrobial respiration, mineralization of litter and mineralization of soil organic matter (SOM). Increasing atmospheric CO2 concentrations will generally increase plant growth, thus C-input to soil. This higher C-input will be accompanied by higher SOM mineralization due to warming. However, mineralization of more stable pools may be affected more by warming compared to mineralization of labile pools. The importance of cropland management is demonstrated in a model scenario. Crop residue incorporation increased C-storage in the soil markedly. However, under the assumption of a higher temperature sensitivity of mineralization of stable C-pools the net-sink of C under recommended management practice is severely reduced. Precise predictions are hampered due to the lack of quantitative, mechanistic knowledge. It is discussed that a more interdisciplinary scientific approach will increase the speed in generating urgently needed understanding of belowground processes of C-cycling.