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1.
This study addresses the issue of carbon (C) fluxes through below ground pools within the rhizosphere of Lolium perenne using the 14C pulse labeling. Lolium perenne was grown in plexiglas chambers on topsoil of a Haplic Luvisol under controled laboratory conditions. 14C‐CO2 efflux from soil, as well as 14C content in shoots, roots, soil, dissolved organic C (DOC), and microbial biomass were monitored for 11 days after the pulsing. Lolium allocates about 48 % of the total assimilated 14C below the soil surface, and roots were the primary sink for this C. Maximum 14C content in the roots was observed 12 hours after the labeling and it amounts to 42 % of the assimilated C. Only half of the 14C amount was found in the roots at the end of the monitoring period. The remainder was lost through root respiration, root decomposition, and rhizodeposition. Six hours after the 14C pulse labeling soil accounted for 11 %, DOC for 1.1 %, and microbial biomass for 4.9 % of assimilated C. 14C in CO2 efflux from soil was detected as early as 30 minutes after labeling. The maximum 14C‐CO2 emission rate (0.34 % of assimilated 14C h—1) from the soil occurred between four and twelve hours after labeling. From the 5th day onwards, only insignificant changes in carbon partitioning occurred. The partitioning of assimilated C was completed after 5 days after assimilation. Based on the 14C partitioning pattern, we calculated the amount of assimilated C during 47 days of growth at 256 g C m—2. Of this amount 122 g C m—2 were allocated to below ground, shoots retained 64 g C m—2, and 70 g C m—2 were lost from the shoots due to respiration. Roots were the main sink for below ground C and they accounted for 74 g C m—2, while 28 g C m—2 were respired and 19 g C m—2 were found as residual 14C in soil and microorganisms.  相似文献   

2.
The minor isotopes of carbon (13C and 14C) are widely used as tracers in studies of the global carbon cycle. We present carbon‐isotope data for the 0–5 cm layer of soil on a transect from 49.6°N to 68°N, from mature forest and tundra ecosystems in the boreal‐arctic zone of interior western Canada. Soil organic carbon in the < 2000 μm fraction of the soil decreases from 3.14 kg m?2 in the south to 1.31 kg m?2 in the north. The 14C activity of the organic carbon decreases as latitude increases from 118.9 to 100.7 per cent modern carbon (pMC). In addition, the 14C activities of organic carbon in the particle‐size fractions of each sample decrease as particle size decreases. These results suggest that organic carbon in the 0–5 cm layer of these soils transfers from standing biomass into the coarsest size fractions of the soil and is then degraded over time, with the residue progressively transferred into the more resistant finer particle sizes. We calculate residence times for the coarsest size fractions of 21 years in the south to 71 years in the north. Residence times for the fine size fractions (< 63 μm) are considerably longer, ranging from 90 years in the south to 960 years in the north. The δ13C of the organic carbon decreases from ?26.8 ± 0.3‰ in soil under forest in the south to ?26.2 ± 0.1‰ for tundra sites in the north. At all sites there is an increase in δ13C with decreasing particle size of 0.7–1.6‰. These changes in δ13C are due to the presence of ‘old’ carbon in equilibrium with an atmosphere richer in 13C, and to the effects of microbial degradation.  相似文献   

3.
The methods used for estimating below‐ground carbon (C) translocation by plants, and the results obtained for different plant species are reviewed. Three tracer techniques using C isotopes to quantify root‐derived C are discussed: pulse labeling, continuous labeling, and a method based on the difference in 13C natural abundance in C3 and C4 plants. It is shown, that only the tracer methods provided adequate results for the whole below‐ground C translocation. This included roots, exudates and other organic substances, quickly decomposable by soil microorganisms, and CO2 produced by root respiration. Advantages due to coupling of two different tracer techniques are shown. The differences in the below‐ground C translocation pattern between plant species (cereals, grasses, and trees) are discussed. Cereals (wheat and barley) transfer 20%—30% of total assimilated C into the soil. Half of this amount is subsequently found in the roots and about one‐third in CO2 evolved from the soil by root respiration and microbial utilization of rootborne organic substances. The remaining part of below‐ground translocated C is incorporated into the soil microorganisms and soil organic matter. The portion of assimilated C allocated below the ground by cereals decreases during growth and by increasing N fertilization. Pasture plants translocated about 30%—50% of assimilates below‐ground, and their translocation patterns were similar to those of crop plants. On average, the total C amounts translocated into the soil by cereals and pasture plants are approximately the same (1500 kg C ha—1), when the same growth period is considered. However, during one vegetation period the cereals and grasses allocated beneath the ground about 1500 and 2200 kg C ha—1, respectively. Finally, a simple approach is suggested for a rough calculation of C input into the soil and for root‐derived CO2 efflux from the soil.  相似文献   

4.
The soil organic matter plays a key role in ecological soil functions, and has to be considered as an important CO2 sink on a global scale. Apart from crop residues (shoots and roots), left over on the field after harvest, carbon and nitrogen compounds are also released by plant roots into the soil during vegetation, and undergo several transformation processes. Up to now the knowledge about amount, composition, and turnover of these root‐borne compounds is still very limited. So far it could be demonstrated with different plant species, that up to 20 % of photosynthetically fixed C are released into the soil during vegetation period. These C amounts are ecological relevant. Depending on assimilate sink strength during ontogenesis, the C release varies with plant age. A large percentage of these root‐borne substances were rapidly respired by microorganisms (64—86 %). About 2—5 % of net C assimilation was kept in soil. The root exudates of maize were mainly water‐soluble (79 %), and in this fraction about 64 % carbohydrates, 22 % amino acids/amides and 14 % organic acids could be identified. Plant species and in some cases also plant cultivars varied strongly in their root exudation pattern. Under non‐sterile conditions the exuded compounds were rapidly stabilized in water‐insoluble forms and bound preferably to the soil clay fraction. The binding of root exudates to soil particles also improved soil structure by increasing aggregate stability. Future research should focus on quantification and characterization of root‐borne C compounds during the whole plant ontogenesis. Apart from pot experiments with 14CO2 labeling, it is necessary to conduct model field experiments with 13CO2 labeling in order to be able to distinguish between CO2 originating from the soil C pool and rhizosphere respiration, originating from plant assimilates. Such a separation is necessary to assess if soils are sources or sinks of CO2. The incorporation of root‐borne C (14C, 13C) into soil organic matter of different stability is also of particular interest.  相似文献   

5.
Abstract

Soluble salts found in wastewater can be toxic when used for irrigation of forages. Thus, two greenhouse experiments were conducted to investigate effects of saline [CaCl2NaCl (3:1, w:w)] treatments on soil chemical properties and ‘Dekalb FS‐5’ forage sorghum [Sorghum bicolor(L.) Moench]. Treatments for the first experiment consisted of a nonsaline control or 500 mL of a solution with an electrical conductivity (EC) of 10 dS m?1 applied once. In the second experiment, treatments were salinity levels of 1.7,3.5,5.2,8.5, and 12.2 dS m?1, applied in non‐nitrogenous Hoagland's solution as the sole source of irrigation. Both experiments were replicated four times. For both experiments forage sorghum was seeded in pots containing 7 kg of air‐dried Amarillo fine sandy loam soil. Sorghum survivability and plant height were measured. In the second experiment, water use by sorghum was also measured. Plants were harvested 7 wk after seeding, weighed, dried at 55°C, weighed, and ground for subsequent mineral analysis. After harvest, soil salinity, pH, and in the second experiment, extractable soil elements were determined. Soil salinity increased, while soil pH decreased, with the salinity treatments. Extracted soil calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), manganese (Mn), and cadmium (Cd) increased while sulfur (S), iron (Fe), and copper (Cu) decreased, and aluminum (Al) and zinc (Zn) exhibited no change with increasing salinity. Sorghum aerial plant and root production decreased with increasing salinity. Plant Ca, strontium (Sr), Mn, and Cd levels increased with increasing salinity. In contrast, sorghum K, P, and S levels declined with increasing salinity.  相似文献   

6.
The distribution of vegetational organic matter above‐ and below‐ground and its productivity was analyzed in an alpine area along a climosequence ranging from subalpine to alpine climates. Emphasis is placed on the quantification of carbon (C) and nitrogen (N) fixed in the above‐ground and below‐ground vegetation and its annual input. Annual C‐input ranged from 17.9 to 60.2 g m—2 year—1 and the N‐input from 0.74 to 2.48 g m—2 year—1. Above‐ground phytomass and the annual production rate of organic matter showed a distinct correlation with the altitude and, thus, the climate. However, the measurement of the above‐ground phytomass is bound to methodological problems: the commonly used harvesting method seems to underestimate the real situation. The harvesting method yielded in its average 100 to 300 g m—2 phytomass which was 35—83% of the values obtained by the soil core method. Thus, the calculation of turnover times of above‐ground vegetation greatly depends on the method used. Calculated turnover times based on the harvesting method did not correlate with the climate while a clear tendency of lower turnover times with increasing altitude could be observed using the soil core method. The amount of below‐ground phytomass was in the range of 1880 to 2469 g m—2 and the corresponding annual C‐input (fixation in the roots) between 91.1 and 162 g m—2 year—1 and the N‐input between 2.68 and 4.99 g m—2 year—1. The below‐ground phytomass and its production rate in high alpine zones are of greater importance and exceed the above‐ground ones. With increasing altitude, furthermore, the importance of the below‐ground phytomass increases with respect to the biomass and to the C‐ and N‐input. For high alpine areas, the phytomass is concentrated in the uppermost soil horizons. About 88.7 to 94.5% of the below‐ground phytomass was found in the soil compartment 0‐20 cm. The below‐ground production rate of phytomass in alpine grassland is fundamental in order to calculate any C or N budgets and potential inputs to SOM: its neglection would introduce most significant errors in modeling any C or N cycles.  相似文献   

7.
Current interest in soil‐conserving tillage in China has developed from the concern that Chinese agricultural land loses 73·8 Mg C annually. Previous research has shown that changing from conventional tillage to conservation tillage field management increases soil C sequestration. The aim of this study is to determine if no tillage with stubble retention can reduce soil carbon loss and erosion compared with conventional tillage for a cornfield in northern China. We found that soil organic C storage (kg m−2) under conservation tillage in the form of no post‐harvest tillage with stubble retention increased from 28% to 62% in the soil depths of 0–30 cm (p < 0·01) compared with the conventional tillage. Retaining post‐harvest stubble with a height of 30 cm and incorporating the stubble into the soil before seeding the next spring increased soil organic carbon the most. Carbon storage (kg ha−1) in aboveground and belowground biomass of the corn plants in seedling and harvest stages was significantly greater (p < 0·01) with stubble retention treatments than with conventional tillage. Carbon content in root biomass in all treatments with stubble retention was significantly greater than that with conventional tillage. Soil erosion estimates in the study area under conservation tillage with stubble retention was significantly lower than that under conventional tillage during the monitoring period. Given the complexities of agricultural systems, it is unlikely that one ideal farming practice is suitable to all soils or different climate conditions, but stubble retention during harvesting and incorporation of the stubble into soil in the next spring appears to be the best choice in the dry northern China where farmlands suffer serious wind erosion. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

8.
Knowledge about carbon allocation below ground is necessary to understand soil ecosystem functioning and the global C cycle. It is common knowledge that different plant species coexist in natural and agricultural systems. By using a modified 13C pulse-chase approach, which enabled us to label individual plants in either mono- or mixed cultures, we investigated the effect of coexistence of different neighboring species on plant carbon partitioning. Maize and faba bean were used as our test plants and isotope pulse labeling was performed twice at 26 and 54 d after emergence. The results showed that a higher proportion of photoassimilates was distributed below ground in maize than in faba bean, resulting in a greater ratio of root to shoot biomass for maize plants during the experiment. The carbon distribution to roots was slightly higher in mixed cultures at 26 d than the counterpart monocultures. The distribution of the plant-assimilated 13C to soil dissolved organic carbon was also greater in mixed cultures at 26 d relative to the monocultures. The most significant effect of the mixed culturing was a dramatic increase of 13C incorporation into the soil microbial biomass. These results indicated that the plant carbon allocation below ground was altered in the presence of a different neighboring species. The increase of plant diversity probably enhances the soil microbial activity and hence the turnover of the plant-derived carbon in soil.  相似文献   

9.
Active fractions of soil carbon (C) and nitrogen (N) can undergo seasonal changes due to environmental and cultural factors, thereby influencing plant N availability and soil organic matter (SOM) conservation. Our objective was to determine the effect of tillage (conventional and none) on the seasonal dynamics of potential C and N mineralization, soil microbial biomass C (SMBC), specific respiratory activity of SMBC(SRAC), and inorganic soil N in a sorghum [Sorghum bicolor (L.) Moench]-wheat (Triticum aestivum L.)/soybean [Glycine max (L.) Merr.] rotation and in a wheat/soybean double crop. A Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas was sampled to 200 mm depth 57 times during a 2-yr period. Potential C mineralization was lowest (≈?2 to 3 g · m?2 · d?1) midway during the sorghum and soybean growing seasons and highest (≈?3 to 4 g · m?2 · d?1) at the end of the wheat growing season and following harvest of all crops. Addition of crop residues increased SMBC for one to three months. Potential N mineralization was coupled with potential C mineralization, SRAC, and changes in SMBC at most times, except during the wheat growing season and shortly after sorghum and soybean residue addition when increased N immobilization was probably caused by rhizodeposition and residues with low N concentration. Seasonal variation of inorganic soil N was 19 to 27%, of potential C and N mineralization and SRAC was 8 to 23%, and of SMBC was 7 to 10%. Soil under conventional tillage experienced greater seasonal variation in potential C and N mineralization, SRAC, bulk density, and water-filled pore space than under no tillage. High residue input with intensive cropping and surface placement of residues were necessary to increase the long-term level of active C and N properties of this thermic-region soil due to rapid turnover of C input.  相似文献   

10.
Abstract

Zinc (Zn) deficiency in crops is a major micronutrient disorder particularly in alkaline‐calcareous soils like those of the rainfed Potohar plateau in Pakistan. A nutrient indexing of sorghum (cv. Potohar 4–8) by sampling <30 cm tall whole shoots and associated soils from 255 random field locations revealed that the crop was deficient in Zn in 54% fields in Jehlum district and 64% in Chakwal. In a greenhouse experiment using a Zn‐deficient calcareous Typic Ustorthents, maximum increase in grain yield with Zn fertilizer was 177% over control in improved sorghum variety (cv. PARC‐SS‐1) and only 10% in local sorghum (cv. Potohar 4–8). Although biomass production of cv. PARC‐SS‐1 was much greater compared with cv. Potohar 4–8, fertilizer Zn requirement for the two cultivars was not much different, 8.3 mg Zn/kg soil for improved sorghum variety and 7.3 mg Zn/kg for local sorghum variety. Contrary to its higher sensitivity to Zn deficiency, the improved sorghum variety was more efficient in utilizing fertilizer Zn. Despite low Zn availability in the Potohar fields, local sorghum is not expected to respond to fertilizer Zn. However, adequate Zn fertility must be assured for cultivating improved sorghum in these soils. Zinc content in mature grains of sorghum proved a good index of soil Zn fertility status. Internal Zn requirement in foliar plant parts of cv. PARC‐SS‐1 (whole shoots, 33 mg/kg; leaves, 22 mg/kg) was greater than in cv. Potohar 4–8 (whole shoots, 27 mg/kg; leaves, 20 mg/kg). In contrast, critical Zn content in grains of the improved sorghum variety (10 mg/kg) was lower than of local variety (14 mg/kg). Three soil tests were equally effective in determining soil Zn fertility. Critical soil Zn levels for cv. PARC‐SS‐1 were: DTPA, 3.4 mg/kg; AB‐DTPA, 3.7 mg/kg; and Mehlich 3, 8.0 mg/dm3. Similar to internal Zn requirement in foliar plant parts, soil test critical Zn levels were lower for cv. Potohar 4–8, i.e., DTPA, 3.1 mg/kg; AB‐DTPA, 3.5 mg/kg; and Mehlich 3, 7.2 mg/dm3. Because of their better efficiency, ‘universal’ soil tests appear superior to the DTPA test for routine Zn analysis.  相似文献   

11.
Abstract

The present study was carried out at ICAR-IIHR, Bengaluru to assess biomass accumulation, nutrient distribution, nutrient/water/energy use, plant available soil nutrients and carbon storage in different categories of roses in open-grown and protected systems. In open-grown roses, biomass of leaves, stalk and flowers represented 31.9%, 41.1% and 26.95%, respectively. In protected condition, flower biomass accounted for 17.62% of the total compared to leaf (51.0%), and stalk biomass (31.4%). The carbon stocks in plant biomass and soil accounted for 22% and 78% of total in open-grown rose system. In protected condition, plant and soil carbon stocks accounted for 11% and 89% of the total carbon stocks. Soil carbon stocks increased from 2.214 to 3.958?kg m?2 during 4-year period in open field. In protected condition, soil carbon stock was increased from 3.315 to 5.104?kg m?2 registering an increase of 1.789?kg m?2. In rose production system, leaves registered highest levels of macronutrients while flowers acquired more micronutrients. The water use was 45% higher in protected cultivation (344?L yr?1 m?2) than in open condition (232?L yr?1 m?2). Based on nutrient use indicators and energy use of nutrient inputs, Arka Savi and Arka Swadesh were identified as efficient nutrient use and energy use (74.6% and 37.3%) genotypes in open and protected conditions, respectively. Plant available nutrient stocks in soil were optimum to above optimum in rose system. The results imply that precision nutrient application is most important to save inputs/energy, avoid environmental pollution and to develop sustainable land use system.  相似文献   

12.
Understanding rhizodeposited carbon (C) dynamics of winter wheat (Triticum aestivum L.) is important for improving soil fertility and increasing soil C stocks. However, the effects of nitrogen (N) fertilization on photosynthate C allocation to rhizodeposition of wheat grown in an intensively farmed alkaline soil remain elusive. In this study, pot‐grown winter wheat under N fertilization of 250 kg N ha?1 was pulse‐labeled with 13CO2 at tillering, elongation, anthesis, and grain‐filling stages. The 13C in shoots, roots, soil organic carbon (SOC), and rhizosphere‐respired CO2 was measured 28 d after each 13C labeling. The proportion of net‐photosynthesized 13C recovered (shoots + roots + soil + soil respired CO2) in the shoots increased from 58–64% at the tillering to 86–91% at the grain‐filling stage. Likewise, the proportion in the roots decreased from 21–28% to 2–3%, and that in the SOC pool increased from 1–2% to 6–7%. However, the 13C respired CO2 allocated to soil peaked (17–18%) at the elongation stage and decreased to 6–8% at the grain‐filling stage. Over the entire growth season of wheat, N fertilization decreased the proportion of net photosynthate C translocated to the below‐ground pool by about 20%, but increased the total amount of fixed photosynthate C, and therefore increased the below‐ground photosynthate C input. We found that the chase period of about 4 weeks is sufficient to accurately monitor the recovery of 13C after pulse labeling in a wheat–soil system. We conclude that N fertilization increased the deposition of photoassimilate C into SOC pools over the entire growth season of wheat compared to the control treatment.  相似文献   

13.
The cycling of root-deposited photosynthate (rhizodeposition) through the soil microbial biomass can have profound influences on plant nutrient availability. Currently, our understanding of microbial dynamics associated with rhizosphere carbon (C) flow is limited. We used a 13C pulse-chase labeling procedure to examine the flow of photosynthetically fixed 13C into the microbial biomass of the bulk and rhizosphere soils of greenhouse-grown annual ryegrass (Lolium multiflorum Lam.). To assess the temporal dynamics of rhizosphere C flow through the microbial biomass, plants were labeled either during the transition between active root growth and rapid shoot growth (Labeling Period 1), or nine days later during the rapid shoot growth stage (Labeling Period 2). Although the distribution of 13C in the plant/soil system was similar between the two labeling periods, microbial cycling of rhizodeposition differed between labeling periods. Within 24 h of labeling, more than 10% of the 13C retained in the plant/soil system resided in the soil, most of which had already been incorporated into the microbial biomass. From day 1 to day 8, the proportion of 13C in soil as microbial biomass declined from about 90 to 35% in rhizosphere soil and from about 80 to 30% in bulk soil. Turnover of 13C through the microbial biomass was faster in rhizosphere soil than in bulk soil, and faster in Labeling Period 1 than Labeling Period 2. Our results demonstrate the effectiveness of using 13C labeling to examine microbial dynamics and fate of C associated with cycling of rhizodeposition from plants at different phenological stages of growth.  相似文献   

14.
The Grain to Green Program in China which began in 1999 led to the conversion of 0.64 million ha of cropland to grassland on steep sloping landscapes. However, the pattern of natural vegetation succession following cropland has not been well represented in previous regional syntheses of land use change effects on soil organic carbon (SOC). A chronosequence study focusing on the vegetation succession and soil carbon stocks was conducted in the center of the Loess Plateau. The chronosequence included fields of 0, 2, 5, 8, 9, 10, 12, 15 and 25 years of self‐restoration after cropland abandonment, as well as a natural grassland reference. Plant coverage, species richness and plant biomass increased significantly with time of cropland abandonment. Over time, the species composition more nearly resembled a natural grasslands community. Cropland abandonment replenished SOC stocks by 3.6 kg C m−2 during the 25‐year self‐restoration, but the SOC accumulation was restricted to the upper soil profiles (0–60 cm). SOC accumulation rate was 88 g C m−2 y−1 in 0–30 cm and 55 g C m−2 y−1 in 30–60 cm soil depth, respectively. These carbon stocks were still significantly lower than those found in the natural grassland soil. Our results suggest that the recovery of plant communities and SOC stocks appears to be slow in this semiarid environment without revegetation effort along with appropriate field management, although the post‐agricultural soils have a high potential for carbon sequestration. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

15.
不同种植方式及肥密因素下饲用甜高粱的产量表现   总被引：1，自引：0，他引：1  
探讨了不同肥密因素下分期青刈、麦茬复种与常规种植饲用杂交甜高梁的产量变化.结果表明,常规种植饲用杂交甜高粱,在25种肥密组合中4个组合效果较好者,产量可达59.6 t/hm2以上;相同肥密条件下分期青刈效果优于常规一次性收获,表现产量高,植株鲜嫩.麦茬复种饲用杂交甜高粱在地处寒地的黑龙江是可行的,其最佳肥密组合产量可以达到31.3样t/hm2,日产鲜草量高于常规种植及分期青刈的最高产量组合,达9.3%和8.3%.黑龙江省小麦种植面积近2.00×105hm2,若进行麦茬复种每年可生产优质鲜饲料达6.00×105t,这即能充分利用寒地有限的光温资源,又可减少水土流失,更利于促进畜牧业的发展.  相似文献   

16.
To investigate C and N rhizodeposition, plants can be 13C‐15N double‐labeled with glucose and urea using a stem‐feeding method (wick method). However, it is unclear how the 13C applied as glucose is released into the soil as rhizorespiration in comparison with the 13C applied as CO2 using a natural uptake pathway. In the present study, we therefore compared the short‐term fate of 14C and 15N in white lupine and pea plants applied either by the wick method or the natural pathways of C and N assimilation. Plants were pulse‐labeled in 14CO2‐enriched atmosphere and 15N urea was applied to the roots (atmosphere–soil) following the natural assimilation pathways, or plants were simultaneously labeled with 14C and 15N by applying a 14C glucose–15N urea solution into the stem using the wick method. Plant development, soil microbial biomass, total rhizorespiration, and distribution of N in plants were not affected by the labeling method used but by plant species. However, the 15N : N ratio in plant parts was significantly (p < 0.05) affected by the labeling method, indicating more homogeneous 15N enrichment of plants labeled via root uptake. After 14CO2 atmosphere labeling of plants, the cumulated 14CO2 release from roots and soil showed the common saturation dynamics. In contrast, after 14C‐glucose labeling by the wick method, the cumulated 14CO2 release increased linearly. These results show that 14C applied as glucose using the wick method is not rapidly transferred to the roots as compared to a short‐term 14CO2 pulse. This is partly due to a slower 14C uptake and partly due to slow distribution within the plant. Consequently, 14C‐glucose application by the wick method is no pulse‐labeling approach. However, the advantages of the wick method for 13C‐15N double labeling for estimating rhizodeposition especially under field conditions requires further methodological research.  相似文献   

17.
To obtain information on regional soil carbon (C) stocks, we prepared a soil C inventory for the central German State Saxony‐Anhalt. We used the State Soil Database SABO_P ( S achsen‐ A nhalt Bo den_ P rofildatenbank), which contains data from 3,600 soil profiles with 16,300 individual soil horizons and combined it with a geographic information system (GIS ArcView). Soil C stocks down to a depth of 100 cm were compiled for the three major soil regions of Saxony‐Anhalt (soil region 2: river valleys and floodplains; soil region 4: pre‐Weichselian moraines, and soil region 6: loess‐covered areas), which represent 83 % of the total state territory. The three major soil regions in Saxony‐Anhalt comprise on average 12.7 (soil region 2), 8.9 (soil region 4), and 12.8 kg C m–2 (soil region 6). Total C content of the area investigated was 191 tg. The typical soils of the region, Haplic Chernozems, contain on average 13.9 kg C m–2. With few exceptions, soil C did not vary significantly within identical taxonomic groups among different soil subregions. However, Chernozems of soil subregion 3 (Wanzlebener Löß‐Plateau; 19.8 kg C m–2) contain significantly more C than the Chernozems of soil subregions 9 (Pollebener, Gerbstedter and Lettewitzer Löß‐Plateau; 12.1 kg C m–2) and 15 (Barnstädter Löß‐Plateau 12.2 kg C m–2). The spatial distribution of C stocks in Saxony‐Anhalt was represented in a map which suggests the existence of a strong link between the geomorphologic position of a given soil and its capacity to store organic C. Within the same taxonomic unit, finer textured soils stored more carbon than coarse‐textured ones.  相似文献   

18.
The Kyoto Protocol explicitly allows the storage of carbon (C) in ecosystems resulting from afforestation to be offset against a nation's carbon emissions and paves the way for carbon storage in soils to be eligible as carbon offsets in the future. More information is required about how afforestation affects carbon storage, especially in the soil. We report a study in which soil carbon storage in first‐rotation Mediterranean Pinus radiata plantations, established on former cereal fields and vineyards, was measured and modelled. Measurements were made on plantations of several ages, as well as repeat measurements at the same site after 5 years. We tested the ability of two widely used soil organic matter models (RothC and Century) to predict carbon sequestration in Mediterranean forest soils. Increases in the top 5 cm of soil of about 10 g C m?2 year?1 were observed after afforestation of former vineyards, but nitrogen (N) either remained the same or decreased slightly. During afforestation, most organic matter accumulated in the ectorganic layers at a rate of 19 g C m?2 year?1 in former vineyards and 41 g C m?2 year?1 in former cereal fields. The RothC and Century models were sensitive to previous land use and estimated a carbon sequestration potential over 20 years of 950 and 700 g C m?2, respectively. The accurate simulation of the dynamics of soil organic matter by RothC, together with measured above‐ground inputs, allowed us to calculate below‐ground inputs during afforestation. The Century model simulated total C and N, including the ectorganic horizons, well. Simulations showed a depletion of N in the below‐ground fractions during afforestation, with N limitation in the former vineyard but not on former cereal land. The approach demonstrates the potential of models to enhance our understanding of the processes leading to carbon sequestration in soils.  相似文献   

19.
Soil respiration is an important process for carbon geochemical cycling. Based on our five long‐term fertilizer experiments, soil respiration was measured using pot experiments with or without planting soybean. Soil respiration rates and soybean root biomass were determined at different observation times. Soil respiration rates due to soil microbial activity could be estimated by extrapolating a newly derived regressive equation at zero root biomass. Soil microbial respiration rates in the control were also observed directly, ranging from 16.0 to 42.7 mg carbon (C) m?2 h?1. Average soil microbial respiration rates from the regression analyses and direct observations were 32.9 and 27.8 mg C m?2 h?1, respectively. The average proportions of soil respiration rates due to the soybean growth were 63.0% using the regressive equation and 69.8% from direct observation. Therefore, the application of these two methods could provide new insight for separating plant root respiration from soil microbial respiration, which is important for estimating their individual contributions to atmospheric carbon dioxide.  相似文献   

20.
青冈栎混交林生物量及碳储量分布特征   总被引：1，自引：1，他引：0  
以湖南永顺43年生青冈栎混交林为研究对象,采用平均木法和样方收获法测定乔木层生物量和林下植被层生物量,采用重铬酸钾—水合加热法测定样品碳素含量,对林分各组分的生物量和碳储量分布特征进行研究。结果表明:青冈栎混交林单位面积生物量为320.03t/hm~2,各组分单位面积生物量由大到小的排列顺序为乔木层、枯落物层、灌木层和草本层。林分单位面积碳储量高达389.43t/hm~2,其中植被层和土壤层分别为249.02,140.41t/hm~2。林分内青冈栎、栲树和杉木单株平均蓄积分别为0.156 1,0.2912,0.296 0m~3,单株平均碳储量分别为103.85,99.15,97.90kg。青冈栎属于生长速度较慢但木材密度大的树种,单株平均蓄积仅有栲树和杉木的单株平均蓄积的1/2左右,但其单株平均生物量和碳储量却比栲树和杉木的单株平均生物量和碳储量要高,表明树种碳汇能力的高低并不完全取决于树种生长速度的快慢,这对今后生态公益林树种的选择提供了一个新的方向。  相似文献   

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