Drivers of spatial variability in urban plant and soil isotopic composition in the Los Angeles basin

Aims

Plant litter decomposition plays an important role in the storage of soil organic matter in terrestrial ecosystems. Conversion of native vegetation to agricultural lands and subsequent land abandonment can lead to shifts in canopy structure, and consequently influence decomposition dynamics by alterations in soil temperature and moisture conditions, solar radiation exposure, and soil erosion patterns. This study was conducted to assess which parameters were more closely related to short-term decomposition dynamics of two predominant Mediterranean leaf litter types.

Methods

Using the litterbag technique, we incubated leaf litter of Pinus halepensis and Rosmarinus officinalis in two Mediterranean land-uses with different degree of vegetation cover (open forest, abandoned agricultural field).

Results

Fresh local litter lost between 20 and 55% of its initial mass throughout the 20-month incubation period. Rosemary litter decomposed faster than pine litter, showing net N immobilization in the early stages of decomposition, in contrast to the net N release exhibited by pine litter. Parameters related to litter quality (N content or C:N) or land-use/site conditions (ash content, an index of soil deposition on litter) were found to explain the cross-site variability in mass loss rates for rosemary and Aleppo pine litter, respectively.

Conclusions

The results from this study suggest that decomposition drivers may differ depending on litter type in this Mediterranean ecosystem. While rosemary litter was degraded mainly by microbial activity, decomposition of pine litter was likely driven primarily by abiotic processes like soil erosion.     

Soil properties and C dynamics in abandoned and cultivated farmlands in a semi-arid ecosystem

Background and Aims

Land abandonment might be an alternative management for restoring soil conditions and C from prolonged cultivation and agricultural practices. In the present study, the influence of 18–22?years of land abandonment on soil properties, C dynamics and microbial biomass was evaluated in closely situated wheat and alfalfa farmlands, and abandoned lands on calcareous soils, Central Iran.

Methods

Soil properties of the 0–15 and 15–30?cm depths from abandoned lands were compared to those from conventionally cultivated lands (i.e., continuous wheat–fallow and alfalfa–wheat rotation) common in calcareous soils of Central Zagros Mountains.

Results

Soil bulk density in the 0–15 and 15–30?cm layers decreased significantly while total porosity increased significantly in abandoned lands. Generally, soil aggregate stability tended to increase within the abandoned fields owing to increased water-stable macro-aggregates. Soil organic C (OC) contents (g kg^?1) and pools (Mg ha^?1) in the 0–15?cm soil layer increased significantly in abandoned lands compared with cultivated lands, with no effect in the 15–30?cm soil layer after 18–22?years of land abandonment, suggesting the restoration of C is pronounced in the upper 0–15?cm soil depth . The total C accumulation in abandoned lands was 7.0?Mg?C?ha^?1 for the entire sampling depth (0–30?cm) over the 18–22?years of land abandonment, which was 26% greater relative to cultivated lands. Carbon mineralization (Cmin) followed a trend similar to organic C, whereas C turnover (Cmin/OC ratio) was slightly greater in wheat fields. However, soil microbial biomass C (MBC) did not vary considerably among the three land uses.

Conclusions

In brief, improvements, albeit slowly, in soil properties of the top layer with the cessation of cultivation indicated that land abandonment may result in enhanced soil C sequestration, and would maintain fertility and productivity of the farmlands of semi-arid climates.     

Origin of mound-field landscapes: a multi-proxy approach combining contemporary vegetation, carbon stable isotopes and phytoliths

Background and aims

Seasonally flooded South American savannas harbor different kinds of mound-field landscapes of largely unknown origin. A recent study used soil carbon-isotope depth profiles and other proxies to infer vegetation history in murundu landscapes in Brazil. Results suggested that differential erosion, not building-up processes (e.g., termite mounds), produced mounds. We tested this approach to inferring mound origin in a mound-field landscape in French Guiana.

Methods

We examined carbon-isotope depth profiles of soil organic matter, phytolith profiles and contemporary vegetation composition in mounds and inter-mounds.

Results

Relative abundance of C3 and C4 plants across habitats was very different from that in murundu landscapes; C3 plants were better represented in inter-mounds than on mounds. Habitat differences in C3/C4 distribution were subtler than in murundu landscapes, limiting inference of vegetation history based on carbon isotopes. Still, carbon-isotope and phytolith depth profiles gave similar pictures of vegetation history, both favoring a building-up hypothesis, corroborating other evidence that these mounds are vestiges of ancient agricultural raised fields.

Conclusions

Carbon-isotope depth profiles are unlikely to be adequate for deciphering origin of mound-field landscapes from vegetation history in seasonally flooded savannas. Including data on current vegetation and phytoliths makes inferences more robust.     

Carbon allocation in Larrea tridentata plant-soil systems as affected by elevated soil moisture and N availability

Background and Aims

Global change will likely express itself in southwestern United States arid lands through changes in amounts and timing of precipitation in response to elevated CO₂ concentrations. In addition, increased nitrogen (N) deposition may occur due to increased urban development. This study addressed the effects of water and N availability on C allocation in arid land soil-plant systems.

Methods

Columns filled with Mojave Desert topsoil containing Larrea tridentata seedlings with two treatment levels each of N and soil moisture were labeled by exposure to ¹³C-enriched CO₂.

Results

Increased soil moisture increased plant biomass, total ¹³C uptake, ¹³C levels in leaves, soil organic matter, and soil respiration, decreased relative C allocation to stems but increased allocation to soil organic matter. Increased soil N availability increased N uptake but decreased C allocation to soil respiration presumably due to decreased substrate supply for microbes. There was no detectable label in carbonate C, suggesting that this pool does not significantly contribute to ecosystem C fluxes.

Conclusions

Our study indicates that increased water availability causes increased C uptake with increased C allocation to soil organic matter in Larrea tridentata-dominated communities while increased N deposition will have a minimal impact on C sequestration.     

Biogeochemical cycling of soil phosphorus during natural revegetation of Pinus sylvestris on disused sand quarries in Northwestern Russia

Background and aims

Quarrying causes severe degradation of soils and vegetation that can be recovered partially when the quarries are abandoned and re-colonised by plants. To understand the recovery of soil functionality and nutrient cycling, we studied the development of soil phosphorus pools during Scots pine (Pinus sylvestris) revegetation in a disused sand quarry in Northwestern Russia.

Methods

Sites that had been developing for different times since abandonment were compared to the parent sand and an adjacent undisturbed forest. Phosphorus speciation in genetic horizons of soil profiles was determined by sequential fractionation and solution phosphorus-31 nuclear magnetic resonance spectroscopy.

Results

Rapid transformations in soil properties occurred in 40 years, with a marked decline in pH and an accumulation of organic matter. Phosphorus transformations were shaped by geochemical processes, with a rapid release of inorganic phosphorus from primary minerals and accumulation of organic phosphorus to concentrations exceeding those found in the undisturbed site. Adsorbed and/or precipitated phosphorus increased rapidly, despite few reactive mineral colloidal surfaces.

Conclusions

Natural succession of Scots pine in post-mining landscapes promotes ecosystem restoration through the rapid re-establishment of the biogeochemical cycles of organic matter and phosphorus. This study provides an important example of biogeochemical phosphorus cycling during the initial stages of pedogenesis.     

Linkages between grazing history and herbivore exclusion on decomposition rates in mineral soils of subalpine grasslands

Background & aims

Herbivore-driven changes to soil properties can influence the decomposition rate of organic material and therefore soil carbon cycling within grassland ecosystems. We investigated how aboveground foraging mammalian and invertebrate herbivores affect mineral soil decomposition rates and associated soil properties in two subalpine vegetation types (short-grass and tall-grass) with different grazing histories.

Methods

Using exclosures with differing mesh sizes, we progressively excluded large, medium and small mammals and invertebrates from the two vegetation types in the Swiss National Park (SNP). Mineral soil decomposition rates were assessed using the cotton cloth (standard substrate) method between May and September 2010.

Results

Decomposition displayed strong spatio-temporal variability, best explained by soil temperature. Exclusion of large mammals increased decomposition rates, but further exclusion reduced decomposition rates again in the lightly grazed (tall-grass) vegetation. No difference among treatments was found in the heavily grazed (short-grass) vegetation. Heavily grazed areas had higher decomposition rates than the lightly grazed areas because of higher soil temperatures. Microbial biomass carbon and soil C:N ratio were also linked to spatio-temporal decomposition patterns, but not to grazing history.

Conclusions

Despite altering some of the environmental controls of decomposition, cellulose decomposition rates in the SNP’s subalpine grasslands appear to be mostly resistant to short-term herbivore exclusion.     

Mechanical properties and soil stability affected by fertilizer treatments for an Ultisol in subtropical China

Background and aims

Soil mechanical properties are crucial for plant growth, soil erosion, tillage and traffic. The soil mechanical properties and stability of an Ultisol were determined in a 13-year fertilization experiment in subtropical China. The effect of organic matter on soil structure was also evaluated.

Methods

The treatments include: unfertilized, mineral fertilized, mineral mixed with straw, and animal manure. Bulk soil strengths (shear strength and penetration resistance) were tested in field. Aggregate strengths (penetration resistance and tensile strength), water stability, organic carbon (OC), hot-water-extractable carbohydrate (HWEC) and some related factors were determined in laboratory.

Results

Fertilizer increases aggregate penetration resistance, tensile strength, water stability and organic matter content in cultivated horizon (0–15 cm depth), especially at the 0–5 cm layer. OC and HWEC showed significantly regression relationships with aggregate water stability, porosity and water repellency for the whole soil profile (0–40 cm). Aggregate strengths also increased with OC and HWEC in cultivated horizon.

Conclusions

Animal manure is most effective in improving soil structure while aggregate water stability is the most sensitive index of fertilizer management. Soil organic matter is a strong determinant of soil structure. Both OC and HWEC are good indicators of surface aggregate strengths and stability, and thus, soil quality in this region.     

Long-term effects of organic amendments on the recovery of plant and soil microbial communities following disturbance in the Canadian boreal forest

Background and Aims

Ecosystem recovery following disturbance requires the reestablishment of key soil biogeochemical processes. This long-term 7 year study describes effects of organic material, moisture, and vegetation on soil microbial community development in the Athabasca Oil Sands Region of Western Canada.

Methods

Phospholipid fatty acid analysis was used to characterize and compare soil microbial community composition and development on reclaimed and natural forest sites. Additionally, we conducted a laboratory moisture manipulation experiment.

Results

The use of forest floor material as an organic amendment resulted in a greater percent cover of upland vegetation and placed the soil microbial community on a faster trajectory towards ecosystem recovery than did the use of a peat amendment. The soil microbial composition within the reclaimed sites exhibited a greater response to changes in moisture than did the soil microbial communities from natural sites.

Conclusion

Our research shows that the use of native organic amendment (forest floor) on reclaimed sites, and the associated establishment of native vegetation promote the development of soil microbial communities more similar to those found on natural forest sites. Additionally, soil microbial communities from natural sites may be more resistant to changes in soil moisture than those found on reclaimed sites.     

Differentiation of some Venezuelan blackwater rivers based upon physico-chemical properties of their humic substances

The dissolved humic substances of seven Venezuelan blackwater rivers, belonging to different tropical biogeographical regions, were analyzed. Fractionation using Sephadex gel together with an analysis of their fluorescence, absorbance and infrared spectral properties, showed differences between their humic substances. These differences were related to their biological sources and humification environment. Statistical analysis of the properties of these humic substances allowed us to separate the rivers into three groups. These groups were directly related to the geological features and vegetation of the terrestrial ecosystems into which they drain:

1. The Autana, Atabapo, Chola, Negro which belong to the Amazon basin on the Guayana Shield, each with typical blackwater riverine forest.
2. The Caroni, belonging to the Orinoco basin on the Guayana Shield and with tropical humid forest and rainforest.
3. The Morichal Largo which draines the Mesa Formation from the eastern Llanos and has gallery forest of Mauritia flexuosa.

     

Biological nitrification inhibition in sorghum: the role of sorgoleone production

Aims

Organically-certified orchard floor management was assessed for its ability to improve soil fertility and biological activity and apple orchard performance.

Methods

‘Ambrosia’/B9 apple was maintained for the first six growing seasons with four orchard floor treatments, including 1) annual compost application; 2) in-row application of mown alfalfa grown between the rows; 3) bark mulch plus in-row application of mown hay; and 4) black plastic mulch.

Results

Soil collected from 0 to 10 cm indicated high soil organic matter and exchangeable K were measurable for all treatments by the second year. After 6 years, highest organic matter, total-, particulate- and mineral–C were associated with soil beneath the bark mulch treatment which also had most vigorous trees, decreased leaf N and elevated leaf P and K. Addition of alfalfa and bark mulch were equally effective at maintaining high exchangeable K and soil phosphatase enzymes, high total and particulate-N by the fourth year.

Conclusions

Despite measurable improvements in soil properties among treatments, fruit yield and quality were minimally affected by management implying no limitations to adoption of any of the assessed strategies.     

The activities of soil and root acid phosphatase in the nine tropical rain forests that differ in phosphorus availability on Mount Kinabalu, Borneo

Background and aims

Tropical rain forests on deeply weathered soils are increasingly thought to be limited by phosphorus (P), where plants and associated organisms would demonstrate adaptations to efficiently recycle P using acid phosphatase from organic matter. The activities of soil and root acid phosphatase were investigated in nine tropical rain forests that demonstrated a 20-fold difference in the soil organic P pool on Mt. Kinabalu, Borneo.

Methods

Acid phosphatase activity was measured at pH6.0 using p-nitrophenyl phosphate as substrate.

Results

The specific phosphatase activity of tree roots on a soil-surface-area basis was significantly positively related with P-use efficiency of above-ground productivity, suggesting a physiological linkage between above and below-ground systems in the adaptation to P deficiency. The phosphatase activities of soils and roots were significantly negatively correlated with the pool size of soil organic P fractions, suggesting that demand for P determines phosphatase activities.

Conclusions

It is suggested that tree roots and soil microbes develop more active phosphatases in response to the chronic shortage of soil P, which forms the basis for an important functional role for the efficient acquisition of P from soil organic matter.     

Successional changes in the soil microbial community along a vegetation development sequence in a subalpine volcanic desert on Mount Fuji, Japan

Aims

To study the relationship between vegetation development and changes in the soil microbial community during primary succession in a volcanic desert, we examined successional changes in microbial respiration, biomass, and community structure in a volcanic desert on Mount Fuji, Japan.

Methods

Soil samples were collected from six successional stages, including isolated island-like plant communities. We measured microbial respiration and performed phospholipid fatty acid (PLFA) analysis, denaturing gradient gel electrophoresis (DGGE) analysis, and community-level physiological profile (CLPP) analysis using Biolog microplates.

Results

Microbial biomass (total PLFA content) increased during plant succession and was positively correlated with soil properties including soil water and soil organic matter (SOM) contents. The microbial respiration rate per unit biomass decreased during succession. Nonmetric multidimensional scaling based on the PLFA, DGGE, and CLPP analyses showed a substantial shift in microbial community structure as a result of initial colonization by the pioneer herb Polygonum cuspidatum and subsequent colonization by Larix kaempferi into central areas of island-like communities. These shifts in microbial community structure probably reflect differences in SOM quality.

Conclusions

Microbial succession in the volcanic desert of Mt. Fuji was initially strongly affected by colonization of the pioneer herbaceous plant (P. cuspidatum) associated with substantial changes in the soil environment. Subsequent changes in vegetation, including the invasion of shrubs such as L. kaempferi, also affected the microbial community structure.     

Soil substrate utilization pattern and relation of functional evenness of plant groups and soil microbial community in five low mountain NATURA 2000

Background and aims

Species rich, semi-natural grassland systems provide several ecosystem functions. The goal was to assess how aboveground composition and evenness affects soil substrate utilization pattern and soil microbial functional evenness.

Methods

At five German NATURA 2000 grassland sites, the interactions of plant functional groups (graminoids, forbs and legumes) and belowground microbial functional evenness were investigated in relation to soil properties and sampling date. Functional evenness of soil microorganisms was measured with high spatial resolution by community level physiological profiling (CLPP) using multi-SIR (substrate-induced respiration) at three sampling dates during the vegetation period. Evenness indices were used to compare plant functional group diversity and soil microbial functional diversity.

Results

All sites differed in the consistently high soil microbial functional evenness, which was strongly predicted by soil pH, but not by plant functional groups or aboveground plant dry matter production. However, soil microbial functional evenness was particularly decreased by an increasing legume proportion and showed seasonal changes, probably driven by shifts in resource availability and soil water content.

Conclusions

Our results suggest that changes in soil chemical properties or in a single key plant functional group may have stronger effects on soil microbial functional evenness than changes in plant functional group evenness.     

Nitrogen deposition and soil carbon content affect nitrogen mineralization during primary succession in acid inland drift sand vegetation

Background and aims

Two inland dunes in the Netherlands receiving low (24) and high (41 kg N ha^?1 yr^?1) nitrogen (N) deposition were compared for N dynamics and microbial activity to investigate the potential effect of N on succession rate of the vegetation and loss of pioneer habitats.

Methods

Primary succession stages were sampled, including bare sand, and vegetation dominated by Polytrichum piliferum, Campylopus introflexus, lichens and grasses respectively, representing a series of vegetation types in undisturbed drift sand sites with succession starting on bare sand containing virtually no organic matter. Microbial characteristics and potential N mineralization were analysed in a laboratory experiment.

Results

Organic matter accumulated during succession, resulting in a lower pH and in higher microbial biomass (bacteria and fungi), respiration and net N mineralization. The increase in respiration and N mineralization was largely due to the development of an ectorganic layer in the middle stages of succession. The observed effects of N deposition were (1) decrease of microbial biomass, (2) higher net N mineralization per m², (3) higher levels of free nitrogen in the soil, and (4) a higher microbial N:P ratio.

Conclusions

Elevated N deposition leads to higher N availability which may cause accelerated succession.     

Plant species influence on soil microbial short-term response after fire simulation

Aims

Plant species can influence fire intensity and severity causing different immediate and long-term responses on the soil microbial community. The main objective of this work was to determine the role of two representative Mediterranean plant species as soil organic matter sources, and to identify their influence on microbial response before and after heat exposure.

Methods

A laboratory heating experiment (300 °C for 20 min) was performed using soil collected under Pinus hallepensis (PIN) and Quercus coccifera (KER). Dried plant material was added before heating for a total of six different treatments: non-heated control samples amended with the original plant material (PIN₀ and KER₀); PIN samples heated with pine (PIN_p) or kermes oak litter (PIN_k); KER samples heated with kermes oak (KER_k) or pine litter (KER_p). Heated soils were inoculated with the original fresh soil and different microbial parameters related to abundance, activity and possible changes in microbial community composition and chemical soil parameters that could be conditioning microbial response were measured for 28 days after inoculation.

Results

The effect of heating on the soil microbial parameters studied was influenced to a small extent by the plant species providing fuel, being evident in soil samples taken under pine influence. Nevertheless heating effect showed marked differences when plant species influence on soil origin was analyzed.

Conclusions

In general, samples taken under pine appear to be more negatively affected by heating treatment than samples collected under kermes oak, highlighting the importance of vegetation as a fresh organic matter source in soil ecosystems before and after fire.     

Forest soil organic carbon dynamics as affected by plant species and their corresponding litters: a fluorescence spectroscopy approach

Background and aims

The effect of forest cover distribution and plant litter input on soil organic carbon were analyzed to better understand the dynamics of carbon cycling across ecosystems on the “Natural Oriented Reserve Bosco delle Pianelle”. Fluorescence spectroscopy represents a very useful tool to characterize soil organic matter properties, since it allows to directly monitor the molecular status of a fluorophore depending on its chemical environment, as well as on its structure, substituents of the aromatic moieties, and molecular weight. Here, fluorescence analysis was performed on humic acids isolated from four litters (HALs) and their underlying soils (HAs) at three depths.

Methods

All samples were collected from a protected forest area, Southern Italy, under different plant covering: Quercus ilex L. (Q), mixed Carpinus betulus L. and Carpinus orientalis Mill. (CC), Pinus halepensis L. (P), and mixed Quercus trojana Webb. and Quercus ilex L. (QQ).

Results

Data obtained showed a fast decomposition process for P and QQ litters, with HAs in the underlying soils characterized by the presence of simple, highly fluorescent structural components also in the deepest layers. On the contrary, a slow decomposition process was observed for Q and CC litters, whose underlying soil HAs were characterized by an increasing aromatic polycondensation and humification degree from the surface to the deepest layers, as supported by low values of fluorescence intensity and high wavelength maxima.

Conclusions

Results obtained indicate that P and QQ species promote C accumulation and stock in the underlying soils, thanks to a greater decomposition of their litter, and fluorescence spectroscopy is a very simple and suitable method to evaluate the influence of three species distribution on soil organic carbon pools.     

The impact of land degradation on the C pools in alpine grasslands of the Qinghai-Tibet Plateau

Aims

To determine the effect of grassland degradation on the soil carbon pool in alpine grassland.

Methods

In this study, we calculated the carbon pool in the above-and below-ground biomass, the soil microbial biomass carbon pool, the total organic carbon pool and the soil total carbon.

Results

Grassland degradation has resulted in decreases in biomass and carbon content and has changed the ratio of roots to shoots. However, there was less influence of degradation on dead root biomass. There was most likely a lag effect of changes in dead root biomass following grassland degradation. In the alpine grassland ecosystem, the carbon pool in soil accounts for more than 92 % of the total carbon both in vegetation and soil. The carbon in alpine grassland is stored primarily in the form of total organic carbon below-ground. As organic carbon decreases, the ratio of the microbial biomass carbon pool to the total organic carbon pool increases and then declines with increasing degradation level. Along the grassland degradation gradient, the total vegetation biomass (above-and below-ground) and the soil carbon pool (microbial biomass C, total organic C and total C) all decreased.     

Effect of organic amendment on soil fertility and plant nutrients in a post-fire Mediterranean ecosystem

Backgrounds and aims

In Mediterranean frequently burnt areas, the decrease of soil fertility leads to regressive vegetation dynamics. Organic amendments could help to accelerate post-fire ecosystem resilience, by improving soil properties and plant nutrition. This study was conducted to assess the potential of a composted biosolid to restore an early post-fire shrubland.

Methods

About 50 Mg.ha^?1 of fresh co-composted sewage sludge and green wastes were surface applied 7 months after fire on a silty-clayey soil. We monitored over a 2-year period organic matter and nutrient transfers to soil, nutrient responses of dominant plant species, and ecosystem contamination by potentially toxic trace elements.

Results

Over the experimental survey, compost rapidly and durably improved soil P₂O₅, MgO and K₂O content, and temporarily increased N-(NO₃ ^? + NO₂ ^?) content. Plant nutrition was improved more or less durably depending species. The most positive compost effect was on plant and soil phosphorus content. Plant nutrient storage was not improved 2 years after amendment, suggesting luxury consumption. No contamination by trace elements was detected in soil and plant.

Conclusions

The use of compost after fire could help for rapidly restoring soil fertility and improving plant nutrition. The increase of soil nutrient pools after amendment emphazised the diversity of plant nutritional traits. Eutrophication risk could occur from high compost and soil P₂O₅ content.     

Stable isotope ratios of soil carbonate and soil organic matter as indicators of forest invasion of prairie near Ames,Iowa

Stable isotope ratios of pedogenic carbonate and organic matter were measured in a prairie-transition-forest soil biosequence near Ames, Iowa to determine the vegetation succession. The modern vegetation is dominated by non-native C₃ plants which have been introduced by agricultural practices. The ¹³C values of soil organic matter from the prairie and forest endmembers indicate C₄ and C₃ dominated ecosystems, respectively, during the accumulation of soil organic matter. Pedogenic carbonate from all soils, including rare pedogenic carbonate from the forested soil, has an average ¹³C of-2.0, indicating that the carbonate formed under a C₄ vegetation. These results indicate that the ecosystem was a C₄-dominated prairie and therefore suggest a recent arrival of forests and other C₃ plants in the area. This study also implies that the primary features of the transitional Lester soil series, which has soil properties intermediate between Alfisols and Molisolls, formed under prairie conditions and were overprinted by an invading forest.     

Aspect-vegetation complex effects on biochemical characteristics and decomposability of soil organic carbon on the eastern Qinghai-Tibetan Plateau

Background

Meadows and shrublands are two major vegetation types on the Qinghai-Tibetan Plateau, but little is known about biochemical characteristics and its relation to decomposability of soil organic carbon (OC) under these two vegetation types. The present study was designed to evaluate effects of aspect-vegetation complex on biochemical characteristics and decomposability of soil OC.

Methods

Two hills were randomly selected; both with vegetation being naturally divided into southward meadows and northward shrublands by a ridge, and soils were sampled at depths of 0–15 and 15–30 cm, along contours traversing the meadow and shrubland sites. Particulate (particle size 2–0.05 mm) OC and nitrogen (N), microbial biomass C and N, non-cellulosic sugars, and CuO lignin were analyzed, and OC mineralization was measured for 49 days at 18 and 25 °C under laboratory incubation, respectively.

Results

More than half of soil OC was present as particulate fraction across all samples, indicating the coarse nature of soil organic matter in the region. Averaging over depths, shrublands contained 87.7???114.1 g OC and 7.7???9.3 g N per kg soil, which were 63???78 and 26???31 % higher than those in meadows, respectively. Meanwhile the C/N ratio of soil organic matter was 11.4???12.3 under shrublands, being 29???40 % higher than that under meadows. Soil OC under meadows was richer in noncellulosic carbohydrates and microbial biomass in the 0–15 and 15–30 cm depths but contained less lignin in the 15–30 cm depth. Ratios of microbially- to plant-derived monosaccharides and between acid and aldehyde of the vanillyl units were greater in soils under shrublands, showing more abundant microbially-derived sugars and microbially-transformed ligneous substances in OC as compared to meadow soils. By the end of 49 days’ incubation, total CO₂–C evolution from soils under meadows was 15.0–16.2 mg g^?1 OC averaging over incubation temperatures and soil depths, being 27–55 % greater than that under shrublands. Across all soil samples over two sites, total CO₂ ? C evolved per g OC at either 18 or 25 °C was closely correlated to enrichments of noncellulosic carbohydrates and microbial biomass. This indicates that the greater soil OC decomposability under meadows was associated with its larger abundances of readily mineralizable fractions compared with shrublands. However, temperature increase effect on soil OC decomposability did not differ between the two types of vegetation.

Conclusions

Our findings suggest that the aspect-vegetation complex significantly affected pool size, biochemical characteristics, and decomposability of soil OC on the northeastern edge of Qinghai-Tibetan Plateau. However, the response of soil OC decomposability to temperature was similar between southward meadows and northward shrublands.