Background and aims
In recent decades, an increasing proportion of alpine shrub meadow has become severely degraded owing to the combined effects of global climate warming and rodent infestation, ...with significant impacts on soil water retention. The present paper investigates the patterns and controlling factors of soil water retention of alpine shrub meadow under different degrees of degradation, to help inform decisions on the management of degraded alpine shrub meadow.
Methods
Four degradation stages were defined: non-degradation (ND); light degradation (LD); moderate degradation (MD) and higher degradation (HD). Pearson correlation and redundancy analysis were used to examine the relationships between soil physical properties and soil hydraulic properties.
Results
Sand content increased while clay content decreased with increasing degree of degradation. In HD treatment, the available nitrogen and soil bulk density of surface soil layer was significantly lower than that in the other three stages, whereas the soil organic matter content and soil total porosity of surface soil layer was increased significantly, the soil compaction of 0–10 cm soil depth in HD was reduced significantly. The soil water retention of 0–60 cm soil depth first decreased and then increased with increasing degradation, with the maximum values occurring in HD, and the soil organic matter has an overwhelming effect on soil water retention than soil texture.
Conclusions
As the degree of degradation increased, the surface soil structure deteriorated, and available nitrogen reduced while soil organic matter increased sharply in higher degradation, which leads to the highest soil water retention in higher degradation. Our results suggested that the soil water retention in degraded alpine grassland was largely determined by soil organic matter, and the soil organic matter parameters should be incorporated in hydrological models of degraded alpine ecosystem.
The effects of mineral fertilizer (NPK) and organic manure on phospholipid fatty acid profiles and microbial functional diversity were investigated in a long-term (21-year) fertilizer experiment. The ...experiment included nine treatments: organic manure (OM), organic manure plus fertilizer NPK (OM + NPK), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer N (N), fertilizer P (P), fertilizer K (K), and the control (CK, without fertilization). The original soil was extremely eroded, characterized by low pH and deficiencies of nutrients, particularly N and P. The application of OM and OM + NPK greatly increased crop yields, soil pH, organic C, total N, P and K, available N, P and K content. Crop yields, soil pH, organic C, total N and available N were also clearly increased by the application of mineral NPK fertilizer. The amounts of total PLFAs, bacterial, Gram-negative and actinobacterial PLFAs were highest in the OM + NPK treatment, followed by the OM treatment, whilst least in the N treatment. The amounts of Gram-positive and anaerobic PLFAs were highest in the OM treatment whilst least in the P treatment and the control, respectively. The amounts of aerobic and fungal PLFAs were highest in the NPK treatment whilst least in the N and P treatment, respectively. The average well color development (AWCD) was significantly increased by the application of OM and OM + NPK, and the functional diversity indices including Shannon index (H ′ ), Simpson index (D) and McIntosh index (U) were also significantly increased by the application of OM and OM + NPK. Principal component analysis (PCA) of PLFA profiles and C source utilization patterns were used to describe changes in microbial biomass and metabolic fingerprints from nine fertilizer treatments. The PLFA profiles from OM, OM + NPK, NP and NPK were significantly different from that of CK, N, P, K and NK, and C source utilization patterns from OM and OM + NPK were clearly different from organic manure deficient treatments (CK, N, P, K, NP, NK 6 and NPK). Stepwise multiple regression analysis showed that total N, available P and soil pH significantly affected PLFA profiles and microbial functional diversity. Our results could provide a better understanding of the importance of organic manure plus balanced fertilization with N, P and K in promoting the soil microbial biomass, activity and diversity and thus enhancing crop growth and production.
Aims We assessed the effects of native and exotic tree leaf litter on soil properties in two contrasting scenarios. The native Quercus robur and Pinus pinaster tree species coexist with the aliens ...Eucalyptus globulus and Acacia dealbata in acid soils of NW Spain. The native trees Fraxinus angustifolia and Ulmus minor coexist with the aliens Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila in eutrophic basic riparian soils in Central Spain. Methods Four plastic trays per species were filled with homogenized top-soil of the site and covered with leaf litter. Before and after 9 months of incubation, litter mass, soil pH, organic matter, mineral and total N were measured. Available mineral N (NO3−-N and NH4+-N) was assessed every 2 months. Results Soil biological activity was higher in the basic than in the acid soil. Litter of the exotic trees tended to decompose less than litter of native species, probably due to the presence of secondary metabolites in the former. Soil pH, mineral and total N responded differently to different litter types, irrespective of their exotic or native origin (acid soil), or was similar across litter treatments (basic riparian soil). The similar response of the basic soil to the addition of different litter types may be due to the low contrast of litter quality between the species. E. globulus litter inhibitied soil microbial activity much more than the rest of the studied litter types, leading to a drastic impoverishment of N in soils. Conclusion Litter of exotic N-fixing trees (A. dealbata and R. pseudoacacia) did not increase soil N pools because of the inhibition of microbial activity by secondary compounds. Therefore, secondary metabolites of the litter played a major role explaining exotic litter impact on soil properties.
BACKGROUND AND AIMS: The introduction of Acacia mangium in Eucalyptus urophylla x grandis stands improves wood production on poor sandy soils of coastal plains of the Congo. We assessed the impact of ...A. mangium plantations in pure stands and in mixture with eucalypt trees on the physico-chemical properties of the soil after one rotation. METHODS: Bulk densities, N, C, available P and pH were determined on soil sampled in the pure acacia (100A), pure eucalypt (100E) and mixed-species (50A:50E) stands. N and P were determined in aboveground litters and in leaves, bark and wood of trees. RESULTS: N and C concentrations were higher in 50A:50E than in 100A and 100E in the top soil layer. The pH was lower in 100A and higher in 100E than in 50A:50E. The available P was lower in 50A:50E than in 100A and 100E. Leaf N was lower in 50A:50E than in 100A for acacia, and higher than in 100E for eucalypt. Leaf P was similar for acacia but higher for eucalypt in 50A:50E than in 100E. In contrast to P, the amount of N in aboveground litterfall increased with the proportion of acacia in the stand. CONCLUSIONS: The introduction of acacia trees in eucalypt plantations increased C and N contents of the soil but decreased the available P content in the mixed-species stand. This may be related to a higher uptake of P needed to maintain the N:P stoichiometry in eucalypt leaves.
Overgrazing significantly affects alpine meadows in ways similar to grasslands in other areas. Fencing to exclude grazers is one of the main management practices used to protect alpine meadows. ...However, it is not known if fencing can improve soil properties and soil organic carbon storage by restraining grazing in alpine meadows. We studied the long-term (nine-year) effects of fencing on soil properties, soil organic carbon and nitrogen storage compared with continued grazing in an alpine swamp meadow of the Qinghai-Tibetan Plateau, NW China. Our results showed that fencing significantly improved vegetation cover and aboveground biomass. There were significant effects of fencing on pH value, soil bulk density, and soil moisture. Long-term fencing favored the increase of soil total nitrogen, soil organic matter, soil organic carbon, soil microbial biomass carbon and soil carbon storage compared with grazed meadows. Our study suggests that long-term fencing to prevent disturbance could greatly affect soil organic carbon and nitrogen storage with regard to grazed meadows. Therefore, it is apparent from this study that fencing is an effective restoration approach of with regard to the soil's storage ability for carbon and nitrogen in alpine meadow of the Qinghai-Tibetan Plateau.
Aims Areas affected by wildfire comprise spatially complex mosaics of burned patches in which a wide range of burn severities coexist. Rapid diagnosis of the different levels of soil burn severity ...and their extents is essential for designing emergency post-fire rehabilitation treatments. The main objective of this study was to determine whether visual signs of soil burn severity levels are related to changes in soil chemical and microbial properties immediately after fire. Methods Eight areas affected by wildfires in NW Spain were selected immediately after fire, and soil chemical and biological properties (pH, extractable Ca, K, Mg and P, SOC, total N, δC, basal soil respiration, Cmic, phosphatase activity, extractable NH₄⁺ and NO₃⁻, ammonification and nitrification rates and potential N mineralization) were analysed in relation to five levels of soil burn severity (0: Unburned; 1: Oa layer partially or totally intact; 2: Oa layer totally charred; 3: Bare soil and soil structure unaffected; 4: Bare soil and soil structure affected; 5: Bare soil and surface soil structure and colour altered). Results The five visually assessed levels of soil burn severity adequately reflected changes in SOC, pH, and phosphatase activity, which varied gradually with increasing soil burn severity. However, alterations in certain indicators related to the soil organic quality (C/N, Cmic/SOC, qCO₂, δ¹³C) were only detected in the most severely burned areas. Discriminant analysis revealed that the best combination of variables was acid phosphatase activity, SOC and pH, which correctly classified between 64 and 76 % of samples, depending on the levels of soil burn severity considered. Conclusions The results showed that the proposed soil burn severity categories may be useful for indicating the degree of degradation of important soil chemical and microbiological properties in sites similar to the study area. This, in combination with other factors, will allow prioritization of areas for rehabilitation.
Carbon (C) metabolism is at the core of ecosystem function. Decomposers play a critical role in this metabolism as they drive soil C cycle by mineralizing organic matter to CO2. Their growth depends ...on the carbon-use efficiency (CUE), defined as the ratio of growth over C uptake. By definition, high CUE promotes growth and possibly C stabilization in soils, while low CUE favors respiration. Despite the importance of this variable, flexibility in CUE for terrestrial decomposers is still poorly characterized and is not represented in most biogeochemical models. Here, we synthesize the theoretical and empirical basis of changes in CUE across aquatic and terrestrial ecosystems, highlighting common patterns and hypothesizing changes in CUE under future climates. Both theoretical considerations and empirical evidence from aquatic organisms indicate that CUE decreases as temperature increases and nutrient availability decreases. More limited evidence shows a similar sensitivity of CUE to temperature and nutrient availability in terrestrial decomposers. Increasing CUE with improved nutrient availability might explain observed declines in respiration from fertilized stands, while decreased CUE with increasing temperature and plant C : N ratios might decrease soil C storage. Current biogeochemical models could be improved by accounting for these CUE responses along environmental and stoichiometric gradients.
This is the first part of a study focusing on evaluating the performance of the Noah land surface model (LSM) in simulating surfacewater and energy budgets for the high-elevation source region of the ...Yellow River (SRYR). A comprehensive dataset is utilized that includes in situ micrometeorological and profile soil moisture and temperature measurements as well as laboratory soil property measurements of samples collected across the SRYR. Here, the simulation of soil water flow is investigated, while Part II concentrates on the surface heat flux and soil temperature simulations. Three augmentations are proposed: 1) to include the effect of organic matter on soil hydraulic parameterization via the additivity hypothesis, 2) to implement the saturated hydraulic conductivityK
sas an exponentially decaying function with soil depth, and 3) to modify the vertical root distribution to represent the Tibetan conditions characterized by an abundance of roots in the topsoil. The diffusivity form of Richards’ equation is further revised to allow for the simulation of soil water flow across soil layers with different hydraulic properties. Usage of organic matter for calculating the porosity and soil suction improves the agreement between the estimates and laboratory measurements, and the exponential function together with the Kozeny–Carman equation best describes the in situK
s. Through implementation of the modified hydraulic parameterization alone, the soil moisture underestimation in the upper soil layer under wet conditions is resolved, while the soil moisture profile dynamics are better captured by also including the modified root distribution.
Today, soil metal pollution has become a significant environmental issue of great public concern. This is because soil is both a major sink for heavy metal(loid)s (HMs) released into the environment, ...by both pedogenic and anthropogenic activities; and also a major source of food chain contamination mainly through plant uptake and animal transfer. In addition, HM contamination of soil leads to negative impacts on soil characteristics and function by disturbing both soil biological and physiochemical properties (e.g. extreme soil pH, poor soil structure and soil fertility and lack of soil microbial activity). This eventually leads to decreased crop production. Various soil remediation techniques have been successfully employed to reduce the risks associated with HMs efflux into soil. Among these, the use of low-cost and environmentally safe inorganic and organic amendments for the in-situ immobilization of HMs has become increasingly popular. Immobilization agents have successfully reduced the availability of metal ions through a variety of adsorption, complexation, precipitation, and redox reactions. Soil amendments can also be a source of nutrients and thus can also act as a soil conditioner, improving the soil's physiochemical properties and fertility, resulting in enhanced plant establishment in metal contaminated soils. This article critically reviews the use of immobilizing agents in HM contaminated agricultural and mining soils paying particular attention to metal immobilization chemistry and the effects of soil amendments on common soil quality parameters.
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