Search

Ecological stoichiometry reflects the element content and energy flow, which are important for biogeochemical cycling in ecosystems. However, the ecological stoichiometry in leaves, roots, litter and soil is largely unknown, especially in the desertified region of Northern China. Here, six dominant plant communities (Stipa bungeana, Agropyron mongolicum, Glycyrrhiza uralensis, Cynanchum komarovii, Artemisia ordosica, and Sophora alopecuroides) were collected, and the carbon (C), nitrogen (N) and phosphorus (P) contents of leaves, roots, litters and soil were measured to explore the C:N:P stoichiometry and its driving factors. The C:N:P stoichiometry in leaves, roots, litters, and soil varied widely, and the plant community had a significant effect on the C:N:P stoichiometry in this region. There were high soil C:N, C:P and N:P ratios in non-leguminous plant communities and a high leaf N:P ratio in leguminous plant communities, and the C:N and C:P ratios in leaves were higher than in those in roots in all plant communities (p

Black locust (Robinia pseudoacacia, RP) has been widely grown for soil and water conservation in erosion regions. However, the effect on soil microbial profiles after long-term implementation of vegetation plantation was still unclear. In this study, soil samples from RP plantations of 10-, 15-, 30- and 38-year-old in a typical vegetation-recovering region on the Chinese Loess Plateau were investigated for microbial biomass carbon (MBC), nitrogen (MBN), phosphorous (MBP) and microbial community-profiles (revealed by phospholipid fatty acids, PLFAs). The results showed SOC, total N, MBC and MBP were significant (P These findings indicate that RP plantation has the potential to transform soil microbial biomass and microbial communities in the direction of improving soil P content in loess soil.

Soil stability is a characteristic property and is frequently used as an indicator of soil quality. Considering the large variation among stability tests, existing studies usually employ more than one stability test in order to better understand soil behavior against various disruptive forces. The main purposes of this study were to evaluate the impact of aggregate disruptive mechanisms (slaking, clay swelling, mechanical breakdown, and cavitation) on soils developed under different plant species. We aimed as well to compare the results of three renowned soil stability methods: modified Yoder (Yod), Le Bissonnais (LB) and Ultrasonic agitation (UA) on surface (0–20 cm) and subsurface (20–40 cm) soils. Overall, soils of three plant communities developed under eight plant species were investigated. These include forestland (Quercus wutaishansea, Pinus tubulaeformis, Platycladus orientalis, and Robinia pseudoacacia), shrubland (Sophora viccifolia, Hippophae rhamnoides, and Rosa xanthina) and grassland (Stipa bungeana). The mean weight diameter (MWD) was used as a stability parameter for modified Yoder’s and Le Bissonnais’ methods. In contrast, specific dispersion energies (SE) at the initial (10%, w/w), middle (50%, w/w) and final (90%, w/w) stages of aggregate disruption were used as stability parameters by the UA method. The results of MWD (Yod) indicated that surface and subsurface soils were in the range of 1.23–2.86 mm, which accounted for medium (0.8–1.3 mm) to very stable (>2 mm) soils. Among the three LB tests (fast wetting (FW), slow wetting (SW), and wet stirring (WS)), the order of aggregate disruption was FW > WS > SW, suggesting that FW was the most destructive among the three tests with the lowest MWD value (0.45 mm, unstable soil). SW showed the highest MWD values (0.82–2.82 mm), and most of the soils were ranked in the stable (1.3–2 mm) to very stable (>2 mm) range. The MWD trend of WS was similar to FW test. Although the range of SE at three levels was different: SE10 (8.1–29.4 J g−1), SE50 (53.0–193.4 J g−1), and SE90 (176–642 J g−1), they all showed a similar association with soil characteristics and stability parameters of other tests. The strong positive correlation of soil organic carbon (SOC), total nitrogen (TN), fine root biomass (FRB), and clay contents, and the negative correlation of soil water content (SWC) with the five tests, indicated that these five factors were the major characteristics responsible for the resistance of the studied soils against different destructive mechanisms (p

Microbial necromass plays an essential role in soil organic carbon (SOC) accumulation. Nevertheless, how microbial necromass carbon (C) concentrations and their contributions to SOC sequestration change from litter to mineral soil and what factors influence its accumulation remain poorly understood. To address this knowledge gap, we performed a field experiment to investigate the compositional distribution characteristics of microbial necromass C and its contributions to SOC sequestration in an oak forest (Quercus wutaishanica) litter-mineral soil profile of the Chinese Loess Plateau. The present study estimated the microbial necromass C concentrations based on the microbial cell wall's biomarker amino sugars. Our results demonstrated that microbial necromass C increased from the Oi1 to Oa layers but decreased from the Ah1 to AB horizons. The highest accumulation of microbial necromass C was found at the litter-mineral soil interface (i.e., total microbial necromass in the Oa layer was 39.5 Mg ha−1, and Ah1 was 22.8 Mg ha−1). The contribution of total microbial necromass C to SOC increased from Oi1 to Ah2. Specifically, the total microbial necromass C accounted for 40.7%, 47.7%, and 37.0% of the average bulk SOC in the Ah1, Ah2, and AB horizons of the oak forest mineral soil, respectively. The ratio of fungal to bacterial necromass C decreased from litter to mineral soil, indicating that the relatively higher bacterial necromass C increasingly accumulated in the deeper litter layers and upper mineral soil horizons. Fungal and bacterial necromass C increased with increasing labile organic C, nitrogen (N), and labile inorganic phosphorus (P), suggesting that higher easily accessible soluble nutrients lead to higher microbial biomass levels, which in turn lead to higher microbial necromass accumulation. Overall, our findings suggested that microbial demand for C or N influences the quantity of soluble nutrients and further lead to changes in microbial necromass C decomposition/accumulation.

Vegetation type and topographic characteristics are important factors that affect the amount and spatial distribution of the forest floor and the soil carbon cycling. However, the relationships among vegetation type, topographic characteristics, forest floor properties, soil properties and soil labile organic carbon (LOC) fractions remain to be elucidated. Here, we conducted a field observational study to explore the relationships between the soil LOC fractions (microbial biomass carbon (MBC), extractable organic carbon (EOC) and permanganate oxidizable carbon (Pox-C)) and forest floor characteristics under various vegetation types (forest, forest-steppe and steppe) and topographic features (slope position and aspect). Our results showed that the vegetation type and topography are both important factors that significantly influence the forest floor properties (i.e., stock, thickness and coverage). The soil total nitrogen and phosphorus were significantly increased, and the soil pH and bulk density were decreased, with an increase in litter stock, coverage and thickness. Simultaneously, the SOC and soil LOC fractions were increased significantly with the increase in litter stock, coverage and thickness. Over 50% of the variation in the SOC and soil LOC fractions was jointly explained by environmental factors, litter properties and soil properties. Our results demonstrated that the SOC and soil LOC fractions are directly influenced by soil physical and chemical properties (e.g., pH, bulk density and soil total nitrogen) and indirectly affected by external environmental factors. Changes in vegetation and topography lead to increases in the litter stock, coverage, thickness and water content in the backslope position and northern slope, which could create favorable soil nutrient and environmental conditions (e.g., higher soil moisture and lower bulk density) to further enhance SOC and soil LOC fraction sequestration. The forest floor potentially links environmental factors and soil properties and serves as an important factor for soil C cycling.

Soil microbes are essential to biogeochemical cycling, soil organic matter decomposition and climate regulation in terrestrial ecosystems. The biogeography of soil bacteria and fungi lags behind in animals and plants, especially in arid areas with alkaline conditions. Understanding the biogeographic of soil microbes and the interactions with environmental factors will provide new insights into the ecosystem functions and services droved by soil bacteria and fungi. Therefore, we chose 48 dryland sites from two transects (north-south and east-west transects) on the Loess Plateau (an arid area) to determine soil bacterial and fungal diversity and community compositions in response to environmental factors and geographic distance. The results showed that soil organic carbon enhanced soil fungal diversity rather than soil bacterial diversity, while soil bacterial diversity was not affected by the environmental factors on the Loess Plateau. The significant associations between the abundance of main bacteria and fungi and soil pH, suggesting that soil pH was the predominant factor affecting soil microbial community structure. In the alkaline soils (pH = 7.4–9.1), soil bacterial community compositions were limited by soil pH, while soil fungal community composition was less sensitive in response to the alterations in soil pH, revealing soil fungi has a wider optimal pH range than bacteria. Compered to historical contingencies, local environment mainly controlled the geography of bacteria and fungi in soils. On the Loess Plateau, soil microbial communities diverge most by soil pH, especially for soil bacteria. These results provide a well understanding of soil microbial geography and associated biogeochemical cycling in arid areas with higher soil pH.

Vegetation restoration may affect soil aggregate stability and the ability of soil to resist erosion. To evaluate the influence of vegetation restoration measures on the stability of soil aggregate and soil erodibility, we chose 7 types of vegetation restoration measures, which included artificial forest (AF), artificial mixed forest (AMF), economic forest (EF), artificial shrub (AS), natural shrub (NS), artificial grass (AG) and natural grass (NG). Then, we analyzed the distribution of water-stable aggregate fractions, mean weight diameter (MWD), geometric mean diameter (GMD), soil erodibility (K value) and other soil properties in the 0–20 cm and 20–40 cm soil layers, as well as aboveground and underground biomass (AGB and UGB). The results showed that under 7 kinds of vegetation restoration measures, the aggregate fraction 5 mm aggregates fluctuated greatly and ranged from 1.87% to 32.50%. And for 7 different vegetation restoration measures, the percentage of aggregate 5 mm was higher than the CK. Overall, compared with CK, the MWD (2.22 and 1.93 mm) and GMD (2.86 and 2.66 mm) were both highest in two soil layers under the NS but lowest under the EF (MWD 0.68 and 0.49 mm, GMD 1.08 and 0.93 mm). The trend of the K value was opposite to these values. These results indicated that the stability of soil aggregate and the ability of soil to resist erosion under NS were strongest. The soil organic carbon (SOC), total nitrogen (TN) and UGB had significantly positive correlations with the proportion of >1 mm aggregates and MWD but had negative correlations with the percentage of

Soil fungi play critical ecological roles in terrestrial ecosystem function, soil formation and element cycles. However, the biogeography of soil fungi in the forest ecosystem is poorly understand, especially in arid or semiarid areas. Here, a regional scale study in an arid area was conducted on the Loess Plateau to illustrate the geographic distributions of soil fungi and their driving forces. The results showed that Ascomycota, Basidiomycota and Zygomycota were the most dominant phyla in 24 sample sites. Fungal Shannon diversity and OTUs richness were significantly correlated with mean annual precipitation (MAP), total soil nitrogen (TN), ammonium nitrogen (NH4N) and soil organic carbon (SOC) levels. The decay-curve analysis demonstrated that soil fungal Bray-Cutis dissimilarities were significantly regressed with geographic distance, revealing that the soil fungal community structure was affected by historical factors. Variation partitioning analysis revealed that the soil properties (15%) contributed more to the fungal community variations than geographic distance (9%). Additionally, there were many predictors of soil fungi geography that were not detected. These results suggest that the fungal geography on the Loess Plateau is mainly regulated by soil properties or other unmeasured variables. Such findings advance our understanding of fungal diversity patterns on the Loess Plateau, which will help us better understand the functions and services in underground ecosystems in arid areas.

As the “Grain for Green” project goes on in the Loess Plateau, some drawbacks, such as the low survival rate, the appearances of dry soil layers and little old trees are appearing, especially for introduced tree species. Ecological stoichiometry, which indicates the balance of elements and the flow of energy, plays a vital role in exploring biogeochemical cycling in ecosystems. To investigate the carbon (C), nitrogen (N) and phosphorus (P) balance and flow of energy, the stoichiometry characteristics and stoichiometry homeostasis for introduced and natural forests on the Loess Plateau, four typical forests were selected, including three introduced forests composed of Robinia pseudoacacia (R. pseudoacacia), Pinus tabuliformis (P. tabuliformis) and Platycladus orientalis (P. orientalis) and a natural forest composed of Quercus wutaishansea (Q. wutaishansea) and the C, N and P in the plant-litter-soil system were measured. The results showed that the C, N and P contents and C:N:P in leaves, branches, fruits, litters and soils varied widely and were influenced strongly by forest species. The N content in R. pseudoacacia leaves, branches, fruits and litters and the soil C, N and P contents in Quercus wutaishansea were higher than those in other forest species. The soil C:N:P stoichiometry in Quercus wutaishansea was higher than that in introduced forest species, while the reverse was found for plant tissues and litter C:N:P. According to the leaf N:P, with the exception of R. pseudoacacia, growth of the other three forest species was limited by N. The N, P and N:P homeostasis exist in trees, especially in Quercus wutaishansea, forest species and plant tissues had significant effects on the strength of homeostasis. Overall, the results of C, N and P content and stoichiometric homeostasis revealed that the natural forest was more adaptable to the arid environment in the Loess Plateau compared to the introduced forests.

Revegetation is a very important way to improve soil quality and fertility in the hilly–gully region of the Loess Plateau, where serious soil nutrient loss and degradation due to water loss and soil erosion were experienced. The creation of an artificial forest is an important measure to restore the local vegetation. Caragana korshinskii (CK) is an ideal tree species in the recovery of vegetation in the Loess hilly regions because it has a strong compatibility and reproduction ability and the ability to artificially regenerate vegetatively. The slope aspects of the Loess Plateau influenced its community and asexual reproduction characteristics. Determining the relationship between the soil physicochemical properties and the soil microbial characteristics under different slope aspects can provide useful information for vegetation restoration in the Loess Plateau. This study aimed to investigate the effects of different slope aspects on soil nitrogen, soil microbial activity and community structures in a Loess hilly–gully region. According to the levels of sun exposure, four sample sites (about 35-year-old CK plantation) were selected from four different slope aspects, including sunny, shady, half-shady and hilltop slopes in the Zhifanggou watershed of Ansai (Shaanxi Province). The soil samples were collected at three different depths (0–10 cm, 10–30 cm and 30–60 cm) at each site and analyzed to determine the nitrogen (N) content, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), basal respiration (BR) and level of microbial phospholipid fatty acids (PLFAs). The slope aspect affected (p

Revegetation has been reported to be one of the most effective measures for reducing soil erosion on the Loess Plateau in China. The Yunwu observatory, located in the northwestern Loess Plateau of China, was selected to study the effect of vegetation succession on total carbon (C), aggregate C, and intra-aggregate particulate organic matter-carbon (iPOM-C) concentrations. The vegetation types studied, listed from the shortest to the longest enclosure duration order, were abandoned grazed grassland (Ab.G3), Hierochloe odorata Beauv. (Hi.07), Thymus mongolicus Ronnm (Th.M15), Artemisia sacrorum Ledeb (At.S25), Stipa bungeana Trin Ledeb (St.B36), and Stipa grandis P. Smim (St.G56) communities. Five sizes of aggregates were separated using the modified Yoder method (

Soil organic carbon (SOC) is an important component in agricultural soil, and its stock is a major part of global carbon stocks. Estimating the SOC distribution and storage is important for improving soil quality and SOC sequestration. This study evaluated the SOC distribution different land uses and estimated the SOC storage by classifying the study area by land use in a small watershed on the Loess Plateau. The results showed that the SOC content and density were affected by land use. The SOC content for shrubland and natural grassland was significantly higher than for other land uses, and cropland had the lowest SOC content. The effect of land use on the SOC content was more significant in the 0–10 cm soil layer than in other soil layers. For every type of land use, the SOC content decreased with soil depth. The highest SOC density (0–60 cm) in the study area was found in shrublandII (Hippophae rhamnoides), and the other land uses decreased in the SOC density as follows: natural grassland > shrublandI (Caragana korshinskii) > abandoned cropland > orchard > level ground cropland > terrace cropland > artificial grassland. Shrubland and natural grassland were the most efficient types for SOC sequestration, followed by abandoned cropland. The SOC stock (0–60 cm) in this study was 23,584.77 t with a mean SOC density of 4.64 (0–60 cm).

Soil fertility is important for vegetation growth and productivity. The relationship between vegetation and soil fertility is important for both scientific and practical reasons. However, the effects of soil fertility on vegetation development and succession are poorly documented on the Loess Plateau. In this study, we compared soil properties of the Yanhe Watershed in northern Shaanxi across five different land uses (shrubland, farmland, natural grassland, woodland and artificial grassland) and a chronosequence of soils undergoing restoration for 5, 10, 15, 20, 25, 30, 35, 40 and 45 years. We found that revegetation had a positive effect on soil bulk density decrease, total porosity and capillary porosity increase in the surface soil layers but not in the subsurface layer. Additionally, soil organic matter, total nitrogen, available nitrogen and available potassium were greater at shrubland and woodland sites compared with other land uses. Total phosphorus and available phosphorus were greater at farmland sites. Results of the study indicate that revegetation on eroded soil can produce important increases in soil fertility on older plantations and in areas with natural succession. (C) 2011 Elsevier B.V. All rights reserved.

Revegetation has been reported as one of the most effective counter measures to reduce soil and water erosion on the Loess plateau in China. Soil aggregate stability and the distribution of organic carbon and nitrogen in different aggregate fractions would be affected by different plant communities. The objectives of this study were to elucidate the effects of different plant communities on soil aggregate stability and the distribution of organic carbon and nitrogen in different aggregate fractions in order to prove that the different plant covers enhance soil aggregate stability. Six kinds of soil samples under forest (Quercus liaotungensis, Populus davidiana, Pinus tabulaeformis, Bothriochloa, a 14 year abandoned land, and a 19 year bare fallow soil. Four kinds of soil samples under shrub land (the 24 year old Caragana Korshinskii Kom.; the 14 year old C Korshinskii Kom., 3 year old abandoned grazing land and traditional slope cropland which is claimed by the farmers for production with very low fertilizers) were collected from the hilly-gully area on the Loess Plateau, which was divided into 0-10 cm and 10-20 cm. We investigated soil aggregate stability and soil aggregate fractions by ultrasonic fractionation (USAS), and the distribution of organic carbon and nitrogen in different fractions under forest and afforested land, as key indicators for soil remediation through revegetation. The results showed that soil organic carbon (Corg) and total nitrogen (Nt) were strongly increased under forest and artificial shrub land compared to cropland and bare fallow land and were higher in the surface layers (0-10 cm) than in the subsurface (10-20 cm). Soil aggregate stability (SAS) was quite low under bare fallow land and cropping land soils, in comparison with the 4 forest communities. The three main fractions of soil aggregates, obtained by ultrasonic fractionation, were 630-250 mu m had a higher Corg content than micro-aggregates, 250-100 mu m > 100-63 mu m >> 63 mu m. In comparison to cropland and bare fallow land, forest and artificial shrub can protect and enhance the Corg, Nt and soil aggregate stability. The higher C:N ratio of macro-aggregate fractions indicates a rapid turnover of soil organic carbon in the top soil of forest sites and even on bare fallow and crop land. The narrow range of C:N ratio in micro-aggregates indicates that soil organic carbon in micro-aggregates is more stable than that in the macro-aggregates. We concluded that revegetation of eroded soils accelerates soil remediation and rehabilitation. (C) 2010 Elsevier B.V. All rights reserved.

Accelerated erosion caused by deforestation and soil degradation has become the primary factor limiting sustainable utilization of soil resources on the Loess Plateau of Northwestern China. We studied the physical, chemical, and microbiological processes of soil degradation along a chronosequence of deforestation in the Ziwuling area of northwestern Shaanxi province. The results indicated that soil wet aggregate stability, mean aggregate diameter decreased with years following deforestation. Accelerated erosion resulted in soil nutrient loss, and a decrease in soil enzyme activities including notable losses of total soil N, organic C, alkaline phosphatase activity, and invertase activity. During the early time period, the rates of total soil N, organic C, alkaline phosphatase activity, and invertase activity decreasing were rapid and gradually decreased with deforestation years. Increased use of nitrogen fertilizers made determination of soil quality based on measured NO(3)-N and NH(4)-N inconclusive. The differences in measured parameters between the topsoil and subsoil horizons decreased with time since deforestation, and we concluded that soil erosion was the primary process responsible for the degradation of measured soil physical, chemical, and microbiological properties. (C) 2008 Elsevier B.V. All rights reserved.