齐齐哈尔草原生态状况及防治对策的研究

研究了齐齐哈尔市草原生态状况、发展趋势 ,并提出防治对策。     

Response of Organic and Inorganic Carbon and Nitrogen to Long-Term Grazing of the Shortgrass Steppe

We investigated the influence of long-term (56 years) grazing on organic and inorganic carbon (C) and nitrogen (N) contents of the plant–soil system (to 90 cm depth) in shortgrass steppe of northeastern Colorado. Grazing treatments included continuous season-long (May–October) grazing by yearling heifers at heavy (60–75% utilization) and light (20–35% utilization) stocking rates, and nongrazed exclosures. The heavy stocking rate resulted in a plant community that was dominated (75% of biomass production) by the C₄ grass blue grama (Bouteloua gracilis), whereas excluding livestock grazing increased the production of C₃ grasses and prickly pear cactus (Opuntia polycantha). Soil organic C (SOC) and organic N were not significantly different between the light grazing and nongrazed treatments, whereas the heavy grazing treatment was 7.5 Mg ha^–1 higher in SOC than the nongrazed treatment. Lower ratios of net mineralized N to total organic N in both grazed compared to nongrazed treatments suggest that long-term grazing decreased the readily mineralizable fraction of soil organic matter. Heavy grazing affected soil inorganic C (SIC) more than the SOC. The heavy grazing treatment was 23.8 Mg ha^–1 higher in total soil C (0–90 cm) than the nongrazed treatment, with 68% (16.3 Mg ha^–1) attributable to higher SIC, and 32% (7.5 Mg ha^–1) to higher SOC. These results emphasize the importance in semiarid and arid ecosystems of including inorganic C in assessments of the mass and distribution of plant–soil C and in evaluations of the impacts of grazing management on C sequestration.     

Modelling above- and below-ground mass loss and N dynamics in wooden dowels (LIDET) placed across North and Central America biomes at the decadal time scale

This article focuses on modelling above and below-ground mass loss and nitrogen (N) dynamics based on the wooden dowels (Gonystylus bancanus [Miq.] Kurz) of the decadal Long-term Intersite Decomposition Experiment (LIDET) data. These dowels were placed at 27 locations across North and Central America, involving tropical, temperate and boreal forests, grasslands, wetlands and the tundra. The dowel, inserted vertically into the soil with one half remaining exposed to the air, revealed fast mass and N losses under warm to humid conditions, and slow losses under wet as well as cold to dry conditions. The model formulation, referred to as the Wood Decomposition Model, or WDM, related these losses to (i) mean annual precipitation, mean monthly January and July air temperatures, and (ii) mean annual actual evapotranspiration (AET) at each location. The resulting calibrations conformed well to the time-in-field averages for mass remaining by location: R² = 0.83 and 0.90 for the lower and upper parts, respectively. These values dropped, respectively, to 0.41 and 0.55 for the N concentrations, and to 0.28 and 0.43 for N remaining. These reductions likely refer to error propagation and to as yet unresolved variations in N transference into and out of the wood specific to each individual dowel location. Recalibrating the model parameters by ecosystem type reduced the R² values for actual versus best-fitted mass loss by about 0.15. Doing the same without location- or ecosystem-specific adjustments reduced the R² values further, by about 0.3.     

Fear in grasslands: the effect of Eurasian kestrels on skylark abundances

Predation has received considerable theoretical and empirical support in population regulation. The effect of predators, however, could be achieved in direct (killing) or indirect effects (such as displacement). In this paper, we explored the relationship between Eurasian kestrels Falco tinnunculus and skylarks Alauda arvensis in Mediterranean grasslands. First, we analysed the presence of skylarks in the kestrel diet over 9 years. We also compared a grassland area of experimentally increased kestrel density and a second grassland as control area to evaluate the direct or indirect effect on skylark abundance. We also considered two different habitats, grazed and ungrazed plots. If skylark abundance decreased as the kestrel breeding season progressed in high-density kestrel area compared with the control area, it would suggest a direct effect (predator hypothesis). If skylark abundance remains constant in both areas of contrasting kestrel density, it would suggest that skylarks avoid kestrels (avoidance hypothesis). We found that skylark abundance decreased in the kestrel area from the beginning of kestrel nest-box installation to recent years. The rate of skylark consumption decreased in a 9-year period as kestrel abundance increased, although the total amount skylark consumption did not show a decreasing trend. In addition, skylarks were more abundant in the kestrel-free area than in the kestrel area. Finally, we found that skylark abundance did not change through the kestrel breeding period in relation to grazing. We suggest that an increased breeding density of kestrels during their breeding period may force the skylarks to breed in other areas, which may explain the decline of their abundance.     

Soil organic matter dynamics in Portuguese natural and sown rainfed grasslands

Soil organic matter (SOM) is a particularly important parameter in soil management, especially in mineral soils in Mediterranean and semi-arid countries where its concentration is low. In these conditions, increasing SOM concentration has several agronomic and environmental benefits, ranging from increase in water holding capacity to soil protection and carbon sequestration. We develop a model to express the short-term trend of SOM increase in grasslands as the balance between input and mineralization. This model is calibrated using five years of soil analyses from eight locations. In each location there were either two or three plots with the different grassland systems considered: sown biodiverse permanent pastures rich in legumes (SBPPRLs), fertilized natural grasslands (FNGs), and (un-improved) natural grasslands (NGs). SBPPRL are a new system consisting in the use of plant biodiversity to increase pasture productivity and resilience. So far, they exist mostly in Portugal.We use statistical calibration to adjust an asymptotic curve to the data and obtain the model parameters. Under the assumption of equal mineralization rates across grassland systems, we find that the expected steady-state long term SOM concentration in undisturbed SBPPRL is higher than in NG and FNG. Fertilization does not significantly increase SOM input, and so the trend in SOM is equal for NG and FNG. In 10 years, there is an average increase of 0.21 percentage points per year in SBPPRL. In turn, SOM increases in FNG and NG are 0.08 percentage points per year.     

Relationship between plant biodiversity and heavy metal bioavailability in grasslands overlying an abandoned mine

Abandoned metal mines in the Sierra de Guadarrama, Madrid, Spain, are often located in areas of high ecological value. This is true of an abandoned barium mine situated in the heart of a bird sanctuary. Today the area sustains grasslands, interspersed with oakwood formations of Quercus ilex and heywood scrub (Retama sphaerocarpa L.), used by cattle, sheep and wild animals. Our study was designed to establish a relationship between the plant biodiversity of these grasslands and the bioavailability of heavy metals in the topsoil layer of this abandoned mine. We conducted soil chemical analyses and performed a greenhouse evaluation of the effects of different soil heavy metal concentrations on biodiversity. The greenhouse bioassays were run for 6 months using soil samples obtained from the mine polluted with heavy metals (Cu, Zn, Pb and Cd) and from a control pasture. Soil heavy metal and Na concentrations, along with the pH, had intense negative effects on plant biodiversity, as determined through changes in the Shannon index and species richness. Numbers of grasses, legumes, and composites were reduced, whilst other species (including ruderals) were affected to a lesser extent. Zinc had the greatest effect on biodiversity, followed by Cd and Cu. When we compared the sensitivity of the biodiversity indicators to the different metal content variables, pseudototal metal concentrations determined by X-ray fluorescence (XRF) were the most sensitive, followed by available and soluble metal contents. Worse correlations between biodiversity variables and metal variables were shown by pseudototal contents obtained by plasma emission spectroscopy (ICP-OES). Our results highlight the importance of using as many different indicators as possible to reliably assess the response shown by plants to heavy metal soil pollution.     

Initial effects of light armored vehicle use on grassland vegetation at Fort Lewis, Washington

Sustainable use of military training lands requires understanding and prediction of the effects of military vehicles on vegetation. We examined the initial impacts of an 8-wheeled, light armored vehicle (LAV) on grassland vegetation at Fort Lewis, Washington. The LAV drove replicate spiral paths at two starting velocities, 10.3 and 5.1 m s(-1). The disturbed width (width of ground impacted by the tires) increased as turning radius decreased, but was unaffected by vehicle velocity. An inverse-exponential model predicted disturbed width (r(2)=0.68) at all turning radii for both velocities combined. In low-velocity spirals, and for straight tracking (turning radius>40 m) and moderate turns (radius 20-40 m) in high-velocity spirals, all vegetation damage was imprint (plants flattened by wheels). During sharp (radius <20 m), high-velocity turns, most or all of the disturbed width was scraped free of surface vegetation and soil, which was piled to the outside of each tire track. Total plant cover (all species) was not affected by track curvature in low-velocity spirals, but decreased in the order straight tracking>moderate turns>sharp turns in high-velocity spirals. In low-velocity spirals, post-tracking cover of several plant growth forms (non-native species, perennial species, sod-forming grasses) was similar to pre-tracking cover, but in high-velocity spirals, post-tracking cover of these growth forms decreased in the order straight > or =moderate=sharp. Cover of native species and forbs decreased more in high- than in low-velocity spirals, but was unaffected by curvature. Pre- and post-tracking cover of annual species, bunchgrasses, and shrubs was < or =3%. The most severe vegetation damage caused by operation of wheeled LAVs on grasslands is associated with sharp, high-velocity turns.     

Sheepfolds as “hotspots” of nitric oxide (NO) emission in an Inner Mongolian steppe

We investigated nitric oxide (NO) fluxes at a summer and a winter sheepfold in the Baiyinxile livestock farm, near Xilinhot, Inner Mongolia, which are a typical feature of the regional husbandry. Using a manual static opaque chamber/chemiluminescence measuring system, we intermittently observed fluxes in the summer sheepfold between May 28th and September 26th 2005 and in both winter and summer sheepfolds between March 8th and October 18th 2006. During these periods, mean NO emissions (±S.E., in terms of mass of nitrogen) were 124.0 ± 28.7, 134.6 ± 23.3 (summer sheepfold) and 214.4 ± 79.6 μg NO–N m⁻² h⁻¹ (winter sheepfold), respectively, and thus, three magnitudes higher than observed steppe NO emissions in the same region. The NO fluxes were not significantly different between the 2 years, but in summer they were much higher than in spring (p < 0.05). Temperature and moisture of the faeces layer significantly regulated the NO fluxes (p < 0.01). The direct NO emission factor (EF) for faeces and urine excreted in the sheepfolds was 0.7 g NO–N_emitted kg⁻¹ N_excreted, which was almost 37 times lower than a recently reported N₂O EF. We estimated the total NO emission from the sheepfolds of the Baiyinxile livestock farm to be 1.82 ± 0.43 tons NO–N year⁻¹, which accounts to approximately 12.3% of the total NO emission from this steppe region. With the rapid increase of livestock numbers, sheepfold NO emissions may further increase and contribute to high N deposition in confined areas around sheepfolds.     

Causes and consequences of woody plant encroachment into western North American grasslands

As woody plants encroach into grasslands, grass biomass, density and cover decline as wood plant biomass, density and cover increase. There is also a shift in location of the biomass from mostly belowground in the grasslands to aboveground in the woodlands. In addition, species richness and diversity change as herbaceous species are replaced by woody species. This is not a new phenomenon, but has been going on continually as the climate of the Planet has changed. However, in the past 160 years the changes have been unparalleled. The process is encroachment not invasion because woody species that have been increasing in density are native species and have been present in these communities for thousands of years. These indigenous or native woody species have increased in density, cover and biomass because of changes in one or more abiotic or biotic factors or conditions. Woody species that have increased in density and cover are not the cause of the encroachment, but the result of changes of other factors. Globally, the orbit of the Earth is becoming more circular and less elliptical, causing moderation of the climate. Additional global climate changing factors including elevated levels of CO₂ and parallel increases in temperature are background factors and probably not the principal causes directing the current wave of encroachment. There is probably not a single reason for encroachment, but a combination of factors that are difficult to disentangle. The prime cause of the current and recent encroachment appears to be high and constant levels of grass herbivory by domestic animals. This herbivory reduces fine fuel with a concomitant reduction in fire frequency or in some cases a complete elimination of fire from these communities. Conditions would now favor the woody plants over the grasses. Reduced grass competition, woody plant seed dispersal and changes in animal populations seem to modify the rate of encroachment rather than being the cause. High concentrations of atmospheric CO₂ are not required to explain current woody plant encroachment. Changes in these grassland communities will continue into the future but the specifics are difficult to predict. Density, cover and species composition will fluctuate and will probably continue to change. Increased levels of anthropogenic soil nitrogen suggest replacement of many legumes by other woody species. Modification and perhaps reversal of the changes in these former grassland communities will be an arduous, continuing and perhaps impossible management task.     

Base cation depletion, eutrophication and acidification of species-rich grasslands in response to long-term simulated nitrogen deposition

Pollutant nitrogen deposition effects on soil and foliar element concentrations were investigated in acidic and limestone grasslands, located in one of the most nitrogen and acid rain polluted regions of the UK, using plots treated for 8-10years with 35-140kg Nha(-2)y(-1) as NH(4)NO(3). Historic data suggests both grasslands have acidified over the past 50years. Nitrogen deposition treatments caused the grassland soils to lose 23-35% of their total available bases (Ca, Mg, K, and Na) and they became acidified by 0.2-0.4 pH units. Aluminium, iron and manganese were mobilised and taken up by limestone grassland forbs and were translocated down the acid grassland soil. Mineral nitrogen availability increased in both grasslands and many species showed foliar N enrichment. This study provides the first definitive evidence that nitrogen deposition depletes base cations from grassland soils. The resulting acidification, metal mobilisation and eutrophication are implicated in driving floristic changes.