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排序方式: 共有189条查询结果,搜索用时 15 毫秒
181.
182.
内蒙古乌拉特前旗属干旱、半干旱地区,地形、地貌复杂,土壤类型多样,造林立地条件较差。恶劣的自然条件,严重制约着造林成活率和保存率的提高。文章对当前制约该区造林成活率、保存率的因素进行调查分析,提出提高"两率"的具体措施,可为同类地区提供造林技术参考。 相似文献
183.
Seasonal and annual N2O fluxes from urine-affected pasture were approximated with a mechanistic model based on Michaelis-Menten kinetics. The model
combined the effects of soil nitrate-N, soil ammonium-N, soil temperature and soil moisture (all from the top 5cm) to calculate
N2O emissions from nitrification (F
nit
) and denitrification (F
den
), with total N2O emission being the sum of the two (F
tot
=F
nit
+F
den
). Best results were obtained when different kinetic parameters were used for periods of constant soil moisture conditions
and after heavy rainfalls when a rapid change of the soil moisture status occurred. Modelled N2O emissions over a year were within the range of uncertainties of measured N2O emissions. Results indicate that the spatial variability of N2O emissions at times when all the model inupt variables were constant may be related to microorganism growth dynamics or enzyme
production rates.
Received: 2 October 1995 相似文献
184.
Hong J. Di Keith C. Cameron Rob R. Sherlock Ju-Pei Shen Ji-Zheng He Chis S. Winefield 《Journal of Soils and Sediments》2010,10(5):943-954
Purpose
Nitrous oxide (N2O) is a potent greenhouse gas and, in grazed grassland systems where animals graze outdoor pastures, most of the N2O is emitted from animal urine nitrogen (N) deposited during grazing. Recently, ammonia-oxidizing archaea (AOA) were found to be present in large numbers in soils as well in the ocean, suggesting a potentially important role for AOA, in addition to ammonia-oxidizing bacteria (AOB), in the nitrogen cycle. The relationship between N2O emissions and AOB and AOA populations is unknown. The objective of this study was to determine the quantitative relationship between N2O emissions and AOB and AOA populations in nitrogen-rich grassland soils. 相似文献185.
C. R. Chen L. M. Condron Z. H. Xu M. R. Davis & R. R Sherlock 《European Journal of Soil Science》2006,57(1):58-66
Plants significantly affect rates of carbon (C) turnover in soils, both because they are sources of carbon through exudation in the rhizosphere and litter‐fall, and because rhizosphere microbes stimulated by roots also metabolize native soil carbon. Different plant species affect these components of soil carbon turnover in different ways, but the quantitative information on this is lacking for different ecosystems and soil‐plant combinations. To compare the effects of grassland and forest plant species on the components of rhizosphere respiration in different soils, we grew ryegrass (Lolium perenne) and radiata pine (Pinus radiata D. Don) in two silt loam soils in pots in a glasshouse, and in seven samplings over 45 weeks measured total (Rtotal), root (Rroot) and root‐free soil respiration (Rrfs), the latter from respiration in unplanted controls. We calculated rhizosphere respiration (Rrhizo), defined here as the net of that fuelled by native soil C and root‐derived C, from Rtotal less Rroot+Rrfs. We also measured plant growth and total, water‐soluble and microbial biomass C in the soils at each sampling. Results showed that Rrfs decreased over the experimental period in both soils. Under ryegrass, Rroot, Rrhizo and Rtotal increased up to 14 weeks after planting and then stabilized, whereas under radiata pine, they continued to increase throughout the experiment. By the end of the experiment, the Rroot, Rrhizo and Rrfs components accounted for 49–58, 31–50 and 1–11% of soil total respiration under ryegrass, respectively, and 43–66, 29–53 and 1–5% under radiata pine. The greater Rroot, Rrhizo and Rtotal values under radiata pine were related to greater root biomass and root‐derived organic C, and enhanced microbial mineralization of native soil organic C. 相似文献
186.
K.H. Orwin J.E. Bertram T.J. Clough L.M. Condron R.R. Sherlock M. O’Callaghan J. Ray D.B. Baird 《Applied soil ecology》2010,44(1):89-100
Nitrogen (N) from urine excreted by grazing animals can be transformed into N compounds that have detrimental effects on the environment. These include nitrate, which can cause eutrophication of waterways, and nitrous oxide, which is a greenhouse gas. Soil microbes mediate all of these N transformations, but the impact of urine on microbes and how initial soil conditions and urine chemical composition alter their responses to urine are not well understood. This study aimed to determine how soil inorganic N pools, nitrous oxide fluxes, soil microbial activity, biomass, and the community structure of bacteria containing amoA (nitrifiers), nirK, and nirS (denitrifiers) genes responded to the addition of urine over time. Bovine urine containing either a high (15.0 g K+ l?1) or low salt content (10.4 g K+ l?1) was added to soil cores at either low or high moisture content (hereafter termed dry and wet soil respectively; 35% or 70% water-filled pore space after the addition of urine). Changes in soil conditions, inorganic N pools, nitrous oxide fluxes, and the soil microbial community were then measured 1, 3, 8, 15, 29 and 44 days after urine addition. Urine addition increased soil ammonium concentrations by up to 2 mg g d.w.?1, soil pH by up to 2.7 units, and electrical conductivity (EC) by 1.0 and 1.6 dS m?1 in the low and high salt urine treatments respectively. In response, nitrate accumulation and nitrous oxide fluxes were lower in dry compared to wet urine-amended soils and slightly lower in high compared to low salt urine-amended soils. Nitrite concentrations were elevated (>3 μg g d.w.?1) for at least 15 days after urine addition in wet urine-amended soils, but were only this high in the dry urine-amended soils for 1 day after the addition of urine. Microbial biomass was reduced by up to half in the wet urine-amended soils, but was largely unaffected in the dry urine-amended soils. Urine addition affected the community structure of ammonia-oxidising and nitrite-reducing bacteria; this response was also stronger and more persistent in wet than in dry urine-amended soils. Overall, the changes in soil conditions caused by the addition of urine interacted to influence microbial responses, indicating that the effect of urine on soil microbes is likely to be context-dependent. 相似文献
187.
Nitrous oxide (N2O) emissions via the nitrification (I
nit) and denitrification (I
den) pathways were successfully measured with in-field incubation of soil cores in preserving jars at 0 Pa and 5–10 Pa acetylene.
From the incubations, fractions of nitrification – N2O over total N2O (I
nit / I
tot) – and denitrification – N2O over total N2O (I
den / I
tot) – were obtained. Actual field emissions of N2O via nitrification (F
nit) and denitrification (F
den) were calculated by multiplying the fractions from the incubation technique with the daily N2O emission (F
day) determined with a direct soil cover method. The approach presented here was successful for a whole range of soil moisture
conditions in intensive grassland. F
nit and F
den followed the trends of soil ammonium and soil nitrate.
Received: 31 October 1997 相似文献
188.
Effects of plant species on microbial biomass phosphorus and phosphatase activity in a range of grassland soils 总被引:1,自引:0,他引:1
C.?R.?ChenEmail author L.?M.?Condron M.?R.?Davis R.?R.?Sherlock 《Biology and Fertility of Soils》2004,40(5):313-322
Soil P transformations are primarily mediated by plant root and soil microbial activity. A short-term (40 weeks) glasshouse experiment with 15 grassland soils collected from around New Zealand was conducted to examine the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil microbial properties and microbiological processes involved in P dynamics. Results showed that the effect of plant species on soil microbial parameters varied greatly with soil type. Concentrations of microbial biomass C and soil respiration were significantly greater in six out of 15 soils under radiata pine compared with ryegrass, while there were no significant effects of plant species on these parameters in the remaining soils. However, microbial biomass P (MBP) was significantly lower in six soils under radiata pine, while there were no significant effects of plant species on MBP in the remaining soils. The latter indicated that P was released from the microbial biomass in response to greater P demand by radiata pine. Levels of water soluble organic C were significantly greater in most soils under radiata pine, compared with ryegrass, which suggested that greater root exudation might have occurred under radiata pine. Activities of acid and alkaline phosphatase and phosphodiesterase were generally lower in most soils under radiata pine, compared with ryegrass. The findings of this study indicate that root exudation plays an important role in increased soil microbial activities, solubility of organic P and mineralization of organic P in soils under radiata pine. 相似文献
189.
TAKASHI KITAGAWA RE M. BOUSTANY CHARLES J. FARWELL THOMAS D. WILLIAMS MICHAEL R. CASTLETON BARBARA A. BLOCK 《Fisheries Oceanography》2007,16(5):409-421
Electronically tagged juvenile Pacific bluefin, Thunnus orientalis, were released off Baja California in the summer of 2002. Time‐series data were analyzed for 18 fish that provided a record of 380 ± 120 days (mean ± SD) of ambient water and peritoneal cavity temperatures at 120 s intervals. Geolocations of tagged fish were estimated based on light‐based longitude and sea surface temperature‐based latitude algorithms. The horizontal and vertical movement patterns of Pacific bluefin were examined in relation to oceanographic conditions and the occurrence of feeding events inferred from thermal fluctuations in the peritoneal cavity. In summer, fish were located primarily in the Southern California Bight and over the continental shelf of Baja California, where juvenile Pacific bluefin use the top of the water column, undertaking occasional, brief forays to depths below the thermocline. In autumn, bluefin migrated north to the waters off the Central California coast when thermal fronts form as the result of weakened equatorward wind stress. An examination of ambient and peritoneal temperatures revealed that bluefin tuna fed during this period along the frontal boundaries. In mid‐winter, the bluefin returned to the Southern California Bight possibly because of strong downwelling and depletion of prey species off the Central California waters. The elevation of the mean peritoneal cavity temperature above the mean ambient water temperature increased as ambient water temperature decreased. The ability of juvenile bluefin tuna to maintain a thermal excess of 10°C occurred at ambient temperatures of 11–14°C when the fish were off the Central California coast. This suggests that the bluefin maintain peritoneal temperature by increasing heat conservation and possibly by increasing internal heat production when in cooler waters. For all of the Pacific bluefin tuna, there was a significant correlation between their mean nighttime depth and the visible disk area of the moon. 相似文献