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121.
Changes in carbon storage in temperate humic loamy soils after forest clearing and continuous corn cropping in France 总被引:3,自引:0,他引:3
Soil samples from forest and agricultural sites in three areas of southwest France were collected to determine the effect
of forest conversion to continuous intensive corn cropping with no organic matter management on soil organic carbon (C) content.
Soils were humic loamy soils and site characteristics that may affect soil C were as uniform as possible (slope, elevation,
texture, soil type, vegetation).
Three areas were selected, with adjacent sites of various ages of cultivation (3 to 35 yr), and paired control forest sites.
The ploughed horizon (0-Dt cm) and the Dt-50 cm layer were collected at each agricultural site. In forest sites, each 10 cm
layer was collected systematically down to 1 meter depth. Carbon concentrations were converted to total content to a given
depth as the product of concentration, depth of sample and bulk density, and expressed in units of kg m-2. For each site and each sampled layer, the mineral mass of soil was calculated, in order to base comparisons on the same
soil mass rather than the same depth.
The pattern of C accumulation in forest soils showed an exponential decrease with depth. Results suggested that soil organic
carbon declined rapidly during the first years of cultivation, and at a slower rate thereafter. This pattern of decrease can
be fitted by a bi-exponential model assuming that initial soil organic carbon can be separated into two parts, a very labile
pool reduced during the first rapid decline and more refractory fractions oxidizing at a slower rate. Sampling to shallow
depths (0-Dt cm) resulted in over-estimation of the rate of carbon release in proportion to the initial amount of C, and in
under-estimation of the total loss of C with age. The results for the 0–50 cm horizon indicated that losses of total carbon
average about 50% in these soils, ranging in initial carbon content from 19 to 32.5 kg m-2. Carbon release to the atmosphere averaged 0.8 kg m-2 yr-1 to 50 cm depth during the first 10 years of cultivation. The results demonstrate that temperate soils may also be an important
source of atmospheric carbon, when they are initially high in carbon content and then cultivated intensively with no organic
matter management. 相似文献
122.
Lolium perenne growing with high root density on a fine nylon mesh (Kuchenbuch and Jungk, 1982) caused the development of element gradients in the rhizosphere below the mesh. Micro-liter soil solutions from 2-mg soil samples were sprayed onto Formvar-coated grids and analyzed by X-ray microanalysis in a transmission electron microscope. The results were comparable to those obtained by flame photometry and atomic absorption spectrometry (AAS) of conventional soil solutions from 1 g soil. X-ray microanalysis of micro-soil solutions allows the application of different extraction procedures to even small amounts of soil usually available from rhizosphere experiments. Information about soil buffering characteristics in the rhizosphere can thus be obtained. Aluminum accumulation in the rhizosphere of small segments of single Picea abies fine roots grown in undisturbed natural forest soil could be detected with this technique. 相似文献
123.
Pruning of hedgerow trees is an important management practice for the successful establishment of an alley cropping system. Although pruning affects biomass production, only meager evidence of this management on distribution of nutrients among the different plant organs after tree regrowth is available. This study examined the effect of pruning on the distribution and use efficiency of N and P in a N2 fixing leguminous tree species, Gliricidia sepium, and two non-N2 fixing leguminous tree species, Senna siamea and S. spectabilis, grown in a field on an Alfisol (low in P) at Fashola (Guinea Savanna Zone), Southwestern Nigeria. Four P rates, 0, 20, 40 and 80 kg P ha–1 as single superphosphate were used and management treatments included pruned versus unpruned plants. The 15N isotope dilution technique was used to measure N2 fixation in G. sepium. Partitioning of total P among different plant organs was influenced by plant species and pruning management, but was not affected by P application rates. The distribution of total P in the various plant organs followed that of dry matter yield while N partitioning had a different pattern. Pruned plants distributed about 118% more total P to branches and had a higher physiological P use efficiency (PPUE) than unpruned plants. Leaves were the biggest sink for total N and N allocation in the other plant organs was influenced by plant species and pruning management, G. sepium had relatively more of its total N and P partitioned into roots (about double that of the non-N2 fixing trees) but had a lower PPUE. Unpruned and pruned G. sepium derived 35 and 54% respectively of their total N from atmospheric N2, with about 54% of the fixed N2 being allocated to leaves and roots. Results showed that N and P pools turned over in the branches during plant regrowth after pruning but the causative factors associated with this phenomenon were not clear. 相似文献
124.
Soil P resources,plant growth and rooting characteristics in nutrient poor upland grasslands 总被引:1,自引:1,他引:0
A. E. S. Macklon L. A. Mackie-Dawson A. Sim C. A. Shand A. Lilly 《Plant and Soil》1994,163(2):257-266
A field study was undertaken to establish the demand for P by mixed herbage, manipulated by cutting regimes, and the extent to which orthophosphate alone in soil solution could meet this demand from three cambisols derived from different parent materials. Differences in soil types were sufficient to produce significantly different rooting patterns at each site. Yields for 7-and 10-cm treatments generally exceeded those for swards cut to 2-and 4-cm. The highest yields were from plots cut once at the end of the season, or when herbage was cut in June and October only. Yields fell in the second season by an average of 30%. Two cuts in the season resulted in almost twice the P uptake compared with other treatments, leading to the view that a silage cut stimulated root growth. Rooting was deepest in Tarves Association soil (Dystric cambisol), densest in Insch Association soil (Eutric cambisol) and intermediate in Foudland Association soil (Dystric cambisol) but herbage yield at each site was similar. Whole season mean P and N content in roots ranged from 1.0 to 3.4 and from 8.1 to 27.9 mg g–1 dry weight, respectively. The lowest values were in once cut herbage and were half those in herbage cut in June and October only. Data for the total P resources of the soils, extractable P, and shoot and root P at each site are presented together with data for P in soil solution (principally organic) from an associated soil solution study. There was a disparity between daily uptake and orthophosphate in soil solution. These findings suggested that it was probable that soluble organic forms of P are important for P nutrition in these nutrient poor soils, and could account for the excess of observed P uptake (from soils low in P) over that predicted by mechanistic mathematical models. 相似文献
125.
The effect of soil phosphorus on the external mycelium growth of arbuscular mycorrhizal fungi during the early stages of mycorrhiza formation 总被引:1,自引:0,他引:1
The effects of soil P amendments and time of application on the formation of external mycelium by different arbuscular mycorrhizal (AM) fungi were studied. In the first experiment the external mycelium produced in the soil by the AM fungus Glomus etunicatum Beck. and Gerd., during the early stages of root colonization (7 and 14 days after inoculation), was quantified by the soil-agar film technique. A Brazilian Oxisol was used with three different phosphate levels, varying from deficient to supra-optimal for the plant. Significant differences were observed in the phosphate and inoculation treatments for plant dry weight, P content in the tissue, root length and root colonization, at fourteen days after planting. At 7 days, mycelium growth, root colonization and their relationship were reduced at supra-optimal P concentrations. Applications of P one week after planting reduced mycelium growth and root colonization more than when applied to the soil before planting. In a second experiment the arbuscular mycorrhizal (AM) fungi, Scutellospora heterogama (Nicol. and Gerd.) Walker and Sanders and E3 were tested and compared with Glomus etunicatum. For the species studied, the length of external hyphae per unit of colonized root length was affected by small P additions but no further significant differences were observed at high P levels. The three AM endophytes showed marked differences in their response to P in the soil: Scutellospora heterogama, although producing external mycelium more profusely than the Glomus spp., showed a higher sensitivity to soil P supply. 相似文献
126.
The duckweed Lemna gibba required light and a suitable energy source such as sucrose, glucose or fructose, for maximum growth in culture. The requirement
for light was relatively unimportant and the plants grew well in a photon flux density of only 52 μmol m-2s-1 PAR. The uptake and incorporation of uniformly labelled 14C-glucose into fronds was related only to the concentration of the sugar.
When incubated with soil, labelled L. gibba behaved in a manner similar to that of labelled ryegrass roots which had been produced by a more elaborate technique using
a 14CO2 labelled atmosphere. During incubation with soil for 224 days the L. gibba material (specific activity 6133 Bq mg-1 d. wt) lost 64% of its radioactivity as 14CO2 and ryegrass (specific activity 6634 Bq mg-1 d. wt) lost 49%. Alkaline extracted humic and fulvic acids from soil had specific activities for the L. gibba incubation of 3409 and 407 Bq mg-1 solid and for ryegrass roots of 4609 and 546 Bq mg-1 solid respectively. The production of 13C or 14C-labelled L. gibba can be undertaken using only simple equipment producing material the specific radioactivity of which can be controlled by
adjusting the activity of the sugar energy source. 相似文献
127.
Nutrient distribution in a Swedish tree species experiment 总被引:2,自引:0,他引:2
The influence of four tree species on the distribution of nutrients between different compartments of the ecosystem was examined.
In a randomized block (n=3) experiment in south-western Sweden, Ca, Mg and K were determined as exchangeable amounts in the
mineral soil and as total amounts in the O+A1 horizons (topsoil) and in the aboveground tree biomass. N contents were determined in all compartments as well as P contents
of the aboveground tree biomass and the topsoil. The four tree species planted were: silver fir [Abies alba Mill.] (AA), grand fir [Abies grandis Lindl.] (AG), Norway spruce [Picea abies L. Karst.] (PA) and Japanese larch [Larix leptolepis (Sieb. och Zucc.) Endl.] (LL). At the age of 35–36 years, the total stemwood production of the most productive species, AG,
was estimated at 471 m3 ha−1. In relation to AG, LL had produced 80%, PA 73% and AA 37%.
The system totals [aboveground tree biomass total + topsoil total + exchangeable (Ca, Mg, K) or total (N) in the mineral soil]
of Ca, K and N did not differ significantly at the 5% level between the investigated species. For Mg, the system total in
LL was significantly higher than for the other species.
There was an indication that LL and AA contained higher amounts of Ca, Mg, K and N in the topsoil but less in the biomass
than did AG and PA (partly significant). In the mineral soil, there were no significant differences in the exchangeable pools
of Ca and K, nor in the total amounts of N.
The biomass nutrient concentrations generally decreased in the order: AA > PA > AG > LL. At stem or whole-tree harvest, the
Ca export per biomass unit would more than double in the case of PA compared to LL. LL also contained less N in the biomass
than the other species. However, the N content in the biomass did not differ between the most (AG) and the least (AA) productive
species, although the production of dry weight biomass (standing + harvested) of AG had been twice that of AA. It is concluded
that the nutrient budget of a managed forest may vary considerably depending on the choice of tree species. 相似文献
128.
Rhizodeposition has been proposed as one mechanism for the accumulation of significant amounts of N in soil during legume growth. The objective of this experiment was to directly quantify losses of symbiotically fixed N from living alfalfa (Medicago sativa L.) roots to the rhizosphere. We used 15N-labeled N2 gas to tag recently fixed N in three alfalfa lines [cv. Saranac, Ineffective Saranac (an ineffectively nodulated line), and an unnamed line in early stages of selection for apparent N excretion] growing in 1-m long polyvinylchloride drainage lysimeters in loamy sand soil in a greenhouse. Plants were in the late vegetative to flowering growth stage during the 2-day labelling period. We determined the fate of this fixed N in various plant organs and soil after a short equilibration period (2 to 4 days) and after one regrowth period (35 to 37 days). Extrapolated N2 fixation rates (46 to 77g plant–1 h–1) were similar to rates others have measured in the field. Although there was significant accretion of total N in rhizosphere compared to bulk soil, less than 1% was derived from newly fixed N and there were no differences between the excreting line and Saranac. Loss of N in percolate water was small. These results provide the first direct evidence that little net loss of symbiotically-fixed N occurs from living alfalfa roots into surrounding soil. In addition, these results confirm our earlier findings, which depended on indirect 15N labelling techniques. Net N accumulation in soil during alfalfa growth is likely due to other processes, such as decomposition of roots, nodules, and above ground litter, rather than to N excretion from living roots and nodules. 相似文献
129.
Iron toxicity and other chemical soil constraints to rice in highland swamps of Burundi 总被引:1,自引:0,他引:1
Iron toxicity is suspected to be a major nutritional disorder in rice cropping systems established on flooded organic soils that contain reductible iron. A pot trial was carried out to assess Fe toxicity to rice in flooded Burundi highland swamp soils with a wide range of organic carbon contents. Soil and leaf analyses were performed and total grain weight was determined. Clear Fe toxicity was diagnosed, based on leaf Fe content at panicle differentiation. Leaf Fe contents higher than 250 g g–1 dry matter induced lower Mg (and probably Mn) uptake, and a 50% total grain weight reduction. These features were associated with exchangeable Fe equivalent fractions higher than 86%. Besides, several non-Fe toxic soils exhibited an Mg-Mn imbalance. 相似文献
130.
Uptake kinetics of arsenate were determined in arsenate tolerant and non-tolerant clones of the grassDeschampsia cespitosa under differing root phosphorus status to investigate the mechanism controlling the suppression of arsenate influx observed in tolerant clones. Influx was always lower in tolerants compared to non-tolerants. Short term influx of arsenate by the high affinity uptake system in both tolerant clones was relatively insensitive to root phosphorus status. This was in contrast to the literature where the regulation of the phosphate (arsenate) uptake system is normally much more responsive to plant phosphorus status. The low affinity uptake system in both tolerant and non-tolerant clones, unlike the high affinity uptake system, was more closely regulated by root phosphate status and was repressed to a much greater degree under increasing root phosphorus levels than the high affinity system. 相似文献