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1.
We measured the growth, nutrition, and N assimilation of arbuscular-mycorrhizal and non-mycorrhizal lettuce (Lactuca sativa L.) as affected by forms of N and drought. Moisture was maintained at 80% water-holding capacity, and N was applied as NO inf3 sup- , NH inf4 sup+ , or NO inf3 sup- /NH inf4 sup+ (3:1, 1:1, or 1:3). The growth of Glomus fasciculatum-colonized plants was comparable to that of uncolonized P-supplemented plants when N was provided as NH inf4 sup+ or combined NO inf3 sup- /NH inf4 sup+ . When N was supplied solely as NO inf3 sup- , G. fasciculatum-colonized plants produced a higher yield than P-fertilized plants, suggesting that the uptake and/or assimilation of NO inf3 sup- was particularly affected by mycorrhizal status in this water-limited situation. Nutrient availability, except Ca, was less limited for mycorrhizal plants than for P-fertilized plants. P fertilization increased the growth, glutamine synthetase activity, and protein content of lettuce to the same extent that G. fasciculatum colonization did when N was applied as NH inf4 sup+ . With NO inf3 sup- -fertilization, G. fasciculatum-colonized plants showed increased growth, nitrate reductase activity, and protein content compared to P-fertilizer treatment. Plants colonized by G. mosseae showed increased photosynthetic activity and proline acumulation, and these mechanisms may be important in adaptation by the plant to drought conditions. The present results confirmed that under drought conditions, the uptake or metabolism of N forms is particularly affected in mycorrhizal fungi-colonized plants, depending on the mycorrhizal endophyte and the N source added. Thus the significance of arbuscular-mycorrhizal fungus selection for plant growth in drought conditions is a consideration for management strategy.  相似文献   

2.
Summary Transport of N by hyphae of a vesicular-arbuscular mycorrhizal fungus was studied under controlled experimental conditions. The N source was applied to the soil as 15NH inf4 sup+ or 15NO inf3 sup- . Cucumis sativus was grown for 25 days, either alone or in symbiosis with Glomus intraradices, in containers with a hyphal compartment separated from the root compartment by a fine nylon mesh. Mineral N was then applied to the hyphal compartment as 15NH inf4 sup+ or 15NO inf3 sup- at 5 cm distance from the root compartment. Soil samples were taken from the hyphal compartment at 1, 3 and 5 cm distance from the root compartment at 7 and 12 days after labelling, and the concentration of mineral N in the samples was measured from 2 M KCl extracts. Mycorrhizal colonization did not affect plant dry weight. The recovery of 15N in mycorrhizal plants was 38 or 40%, respectively, when 15NH inf4 sup+ or 15NO inf3 sup- was applied. The corresponding values for non-mycorrhizal plants were 7 and 16%. The higher 15N recovery observed in mycorrhizal plants than in non-mycorrhizal plants suggests that hyphal transport of N from the applied 15N sources towards the host plant had occurred. The concentration of mineral N in the soil of hyphal compartments was considerably less in mycorrhizal treatments than in controls, indicating that the hyphae were able to deplete the soil for mineral N.  相似文献   

3.
A laboratory incubation experiment was conducted to compare the effects of NH inf4 sup+ and NO inf3 sup- on mineralization of N from 15N-labelled vetch (Vicia villosa Rotn) in an Illinois Mollisol, and to determine the effect of a nitrification inhibitor (nitrapyrin) on mineralization of vetch N when used with NH inf4 sup+ . The addition of either NH inf4 sup+ or NO inf3 sup- (100 and 200 mg N kg-1 soil) significantly increased mineralization of vetch N during incubation for 40 days. The effect was greater with NH inf4 sup+ than with NO inf3 sup- , and a further increase occurred in the presence of nitrapyrin (10 mg kg-1 soil). The addition of NO inf3 sup- retarded the nitrification of NH inf4 sup+ -N derived from vetch.  相似文献   

4.
The effects of radial O2 loss from roots on nitrification and NO inf3 sup- availability were studied. Plants of the flooding-resistant species Rumex palustris and the flooding-sensitive species Rumex thyrsiflorus were grown on drained and waterlogged soils with an initially high nitrifying capacity. Nitrate reductase activity in the plant leaves was used as an indicator of NO inf3 sup- availability to the plants. In a separate experiment these species were shown to have higher levels of nitrate reductase activity when NO inf3 sup- was added to the soils compared to when only NH inf4 sup+ was provided. In drained soils nitrification was maintained and both plant species showed relatively high nitrate reductase activities in their leaves. In the water-logged series planted with R. thyrsiflorus, nitrification was inhibited, NH inf4 sup+ accumulated, and the plants grew less well compared to those on drained soils. In contrast, waterlogged soils planted with R. palustris had a redox potential high enough for O2 to be continuously replenished. Furthermore, the nitrifying capacity of these latter soils was maintained at a high level. R. palustris grew well and NO inf3 sup- must have been available to the plant, since a high level of nitrate reductase activity was observed in the leaves.  相似文献   

5.
Summary Three Illinois Mollisols were incubated for 2 weeks at 25°C after treatment with different amounts of glucose and/or 15N-labelled (NH4)2SO4 or 15N-labelled KNO3. The objectives were: (1) to compare the immobilization and interaction of NH inf4 sup+ –N and NO inf3 sup- –N with the native soil N, and (2) to study the relationship between immobilization of applied N and the added N interaction. As determined, immobilized N refers to forms not extractable with 2 MKCl (immobilized 15N+clay-fixed 15NH inf4 sup+ ). In all cases, both NH inf4 sup+ –N and NO inf3 sup- –N were actively immobilized and transformed into organic forms in the presence of glucose. In the absence of glucose, a higher proportion of NH inf4 sup+ than NO inf3 sup- was recovered in organic forms. Although the three soils differed considerably in the amounts of applied N immobilized, similar trends in N immobilization were observed. A positive added N interaction occurred with all soils, the magnitude increasing with the rate of N addition. In the absence of glucose, higher added N interactions were obtained for NH inf4 sup+ than NO inf3 sup- , whereas there was very little difference between NH inf4 sup+ and NO inf3 sup- in the presence of glucose. The results indicate that under conditions of rapid immobilization (e.g., in the presence of glucose), NH inf4 sup+ and NO inf3 sup- will show comparable interaction with the native soil N, whereas in unamended soil, the extent of this interaction will be greater with NH inf4 sup+ than with NO inf3 sup- . Significant correlations were observed between applied N immobilized and the added N interaction only in one soil having a high initial mineral N content.  相似文献   

6.
A pot experiment was conducted to compare the uptake and dry matter production potential of NH inf4 sup+ and NO inf3 sup- and to study the effect of Baythroid, a contact poison for several insect pests of agricultural crops, on growth and N uptake of maize (Zea mays L.). Nitrogen was applied as (15NH4)2SO4, K15NO3, or 15NH4NO3 and in one treatment Baythroid was combined with 15NH4NO3. Source of N had, in general, a nonsignificant effect on dry matter and N yield, but uptake of NO inf3 sup- was significantly higher than that of NH inf4 sup+ when both N sources were applied together. Substantial loss of N occurred from both the sources, with NH inf4 sup+ showing greater losses. Baythroid was found to have a significant positive effect on dry matter yield of both root and shoot; N yield also increased significantly. Uptake of N from both the applied and native sources increased significantly in the presence of Baythroid and a substantial added nitrogen interaction (ANI) was determined. The positive effect of Baythroid was attributed to: (1) a prolonged availability of NH inf4 sup+ due to inhibition of nitrification, (2) an increased availability of native soil N through enhanced mineralization, and (3) an enhanced root proliferation.  相似文献   

7.
Summary A pot experiment in the greenhouse was conducted to compare the contribution of N derived from the atmosphere or from biological N2 fixation by Sesbania rostrata inoculated with Azorhizobium caulinodans, applied either to roots or to roots and stems (single or multiple stem inoculation). Two subsequent crops were grown for 50 days under flooded conditions. N derived from air was estimated by 15N dilution using 15N enrichment of soil NH inf4 sup+ -N and of Echinochloa crusgalli as the non-N2-fixing reference datum and compared with estimates obtained by the N-difference method. The first crop was grown to stabilize the 15N into the soil organic N fraction. The 15N enrichment of soil NH inf4 sup+ -N in the second crop declined slowly. The extractability ratio (15N enrichment of extractable soil N to 15N enrichment of total soil N) decreased from 4.8 to 4.1 50 days after planting. The enrichment of soil NH inf4 sup+ -N was comparable to that of E. crus-galli, resulting in similar estimates of N derived from air when either soil NH inf4 sup+ -N or enrichment of E. crus-galli was used as a non-fixing reference. The N-difference method did not always provide reliable estimates of N derived from air; percentages ranged from 75 to more than 80 by 50 days after planting in both crops and did not differ among treatments. The study demonstrates the potential of using 15N enrichment of soil NH inf4 sup+ -N as a non-N2-fixing reference for reliable BNF estimates of crops in lowland puddled soil.  相似文献   

8.
A rhizosphere application of NO inf3 sup- and/or naringenin affected the Pisum sativum — Rhizobium leguminosarum biovar viciae symbiosis. NO inf3 sup- (5 mM) lowered while naringenin raised the nodulation status (nodule numbers and weight) and nodule efficiency (C2H2 reduction activity). However, the inhibitory effect of NO inf3 sup- was to some extent alleviated when applied in combination with naringenin. The plant biomass was increased by the application of NO inf3 sup- and naringenin, either alone or in combination, while a higher root: shoot ratio was observed only in the naringenin-treated plants. Root flavonoids are known to regulate the expression of nod genes; their high-performance liquid chromatography profile was influenced in different ways by NO inf3 sup- and naringenin.  相似文献   

9.
Seventeen strains of Rhizobium leguminosarum biovar viceae specific to the lentil (Lens culinaris L.) were screened, using the high-yielding lentil cultivar L 4076, for their tolerance to three levels of NO inf3 sup- : 0, 4, and 8 mM NO inf3 sup- . Preliminary screening of this symbiosis for nodulation and N fixation in the presence of NO inf3 sup- showed significant variations among the strains. The number of nodules decreased and nitrogenase activity was depressed in all strains in the presence of NO inf3 sup- . Strains L-1-87, L-27-89, L-33-89, and L-40-89 tolerated 8 mM NO inf3 sup- . Four strains, three tolerant of NO inf3 sup- (L-1-87, L-27-89, and L-33-89), and one sensitive (L-11-89) to NO inf3 sup- , were selected from preliminary screening and used in a pot experiment to assess the symbiosis in the presence of 6 mM NO inf3 sup- at three stages of plant growth, viz., 40 days, 60 days, and at the final harvest. In general, the weight of nodules and C2H2 reduction activity was significantly higher after 60 days than after 40 days. Inoculation with strain L-1-87 produced the maximum number of nodules, and root and shoot biomass both in the presence and the absence of NO inf3 sup- . Nitrate reductase activity in the tops and nodules was assayed only after 60 days and did not show significant variations among strains and NO inf3 sup- treatments. The grain yields for all strains except L-11-89 were significantly higher in the presence of NO inf3 sup- than in the absence of NO inf3 sup- , indicating that tolerant strains contributed symbiotically fixed N to the plant's N pool, resulting in an additive effect on yield. Inoculation with strain L-1-87 produced the maximum grain yield and this strain appears to have potential use as an inoculant in the presence of high levels of soil N.  相似文献   

10.
Summary In model experiments with a silty loam soil the effect of different C : NO inf3 sup- -N ratios on the reliability of C2H2 (1% v/v) in blocking N2O-reductase activity was examined. The soil was carefully mixed with different amounts of powdered lime leaves (Tilia vulgaris) to obtain organic C contents of about 1.8, 2.3, and 2.8%, and of NO inf3 sup- solution to give C : NO inf3 sup- -N ratios of 84, 107, 130, 156, 200, and 243. The soil samples were incubated in specially modified anaerobic jars (22 days, 25°C, 80% water-holding capacity, He atmosphere) and the atmosphere was analysed for N2, N2O, CO2, and C2H2 by gas chromatography at regular intervals. Destruction jars were used to analyse soil NO inf3 sup- , NH 4 + and C. The results clearly showed that N2O-reductase activity was completely blocked by 1% (v/v) C2H2 only as long as NO inf3 sup- was present. In the presence of C2H2, NO inf3 sup- was apparently entirely converted into N2O. The C2H2 blockage of N2O-reductase activity ceased earlier in soils with a wide C : NO inf3 sup- -N ratio (156, 200, and 243) than in those with closer C : NO inf3 sup- -N ratios (84, 107, and 130). As soon as NO inf3 sup- was exhausted, N2O was reduced to N2 in spite of C2H2. The wider the C : NO inf3 sup- -N ratio, the earlier the production of N2 and the less the reliability of the C2H2 blockage. In the untreated control complete inhibition of N2O-reductase activity by C2H2 lasted for 7–12 days. In the field, estimates of total denitrification losses by the C2H2 inhibition technique should be considered reliable only as long as NO inf3 sup- is present. Consequently, NO inf3 sup- monitoring in the field is essential, particularly in soils supplied with easily decomposable organic matter.  相似文献   

11.
The effects of wheat straw and different forms of N on denitrification and N immobilization were studied in an anaerobic water-sediment system. The water-sediment system was supplemented with various combinations of wheat straw and 15N-labelled and unlabelled (NH4)2SO4 or KNO3, and incubated anaerobically at 30°C for 10 days. 15N-labelled and unlabelled NO inf3 sup- , NO inf2 sup- , NH inf4 sup+ , and organic N were determined in the water-sediment system. The gases evolved (N2, CO2, N2O, and CH4) were analyzed by gas chromatography at regular intervals. Larger quantities of 15N2–N and organic 15N were formed in wheat straw-amended systems than in non-amended systems. Trends in CO2 production were similar to those of N2–N evolution. The evolution of N2O and CH4 was negligible. Denitrification processes accounted for about 22 and 71% of the added 15NO inf3 sup- –N in the absence and presence of wheat straw, respectively. The corresponding denitrification rates were 3.4 and 12.4 g 15Ng-1 dry sediment day-1. In systems amended with 15NO inf3 sup- –N and 15NO inf3 sup- +NH inf4 sup+ –N without wheat straw, 1.82 and 1.58%, respectively, of the added 15NH inf3 sup- –N was immobilized. The corresponding figures for the same systems supplemented with wheat straw were 5.08 and 4.10%, respectively. Immobilization of 15NO inf4 sup+ –N was higher than that of 15NO inf3 sup- –N. The presence of NO inf3 sup- –N did not stimulate NH inf4 sup+ –N immobilization.  相似文献   

12.
Summary Recent developments in biotechnology industries produce increasing amounts of byproducts with potential uses in agriculture. The present research focused on the nitrification of NH inf4 sup+ -N in biotechnology byproducts added to soils, and on the effects of 29 naturally occurring organic acids (19 aliphatic and 10 aromatic) on nitrification in soils. A 10-g soil sample was incubated for 10 days at 30°C with 2.0 mg NH inf4 sup+ -N in a byproduct or with 10 or 50 mol organic acid and 2.0 mg reagent-grade NH inf4 sup+ -N. In condensed molasses-fermentation solubles, produced during the microbial fermentation of sugar derived from corn (Zea mays L.) and molasses derived from beets (Beta sp.), in the production of lysine as a supplement in animal food, the nitrification of NH inf4 sup+ -N was similar to that of byproduct or reagent-grade (NH4)2SO4. Nitrite accumulated when either of these materials was added to a calcareous Canisteo soil. The NH inf4 sup+ -N in slops (produced during microbial fermentation processes occurring in the production of citric acid) was not nitrified in soils. Some organic acids inhibited, whereas others activated, nitrification in soils. Formic, acetic, and fumaric acids enhanced the production of NO inf2 sup- -N in a calcareous Canisteo soil, whereas all other aliphatic and aromatic acids studied decreased the accumulation of NO inf2 sup- -N. It is concluded that the addition or production of organic acids in soils affects the microbial dynamics, leading to significant changes in rates of nitrification and possibly in other N-transformation processes in soils.  相似文献   

13.
Summary The temperature dependence of the NO production rate and the NO consumption rate constant was measured in an Egyptian soil, a soil from the Bavarian Forest, and a soil from the Donau valley, together with the temperature dependence of the potential rates of ammonium oxidation, nitrite oxidation, and denitrification, and the temperature dependence of the growth of NH inf4 sup+ -oxidizing, NO inf2 sup- -oxidizing, and NO inf3 sup- -reducing bacteria in most probable number assays. In the acidic Bavarian Forest soil, NO production was only stimulated by the addition of NO inf3 sup- but not NH inf4 sup+ . However, NO production showed no temperature optimum, indicating that it was due to chemical processes. Most probable numbers and potential activities of nitrifiers were very low. NO consumption, in contrast, showed a temperature optimum at 25°C, demonstrating that consumption and production of NO were regulated individually by the soil temperature. In the neutral, subtropical Egyptian soil, NO production was stimulated only by the addition of NH inf4 sup+ but not NO inf3 sup- . All activities and most probable numbers showed a temperature optimum at 25° or 30°C and exhibited apparent activation energies between 61 and 202 kJ mol-1. However, a few nitrifiers and denitrifiers were also able to grow at 8° or 50°C. Similar temperature characteristics were observed in the Donau valley soil, although it originated from a temperate region. In this soil NO production was stimulated by the addition of NH inf4 sup+ or of NO inf3 sup- . Both NO production and consumption were stimulated by drying and rewetting.  相似文献   

14.
Summary Gross rates of N mineralization, assimilation, nitrification, and NO in3 sup- reduction were determined in soil from a wet riparian fen by 1-day incubations of soil cores and slurries with 15N-labelled substrates. N mineralization transformed 0.1% of the total organic N pool daily in the soil cores, of which 25% was oxidized through autotrophic nitrification and 53%–70% was incorporated into microorganisms. N mineralization and nitrification were markedly inhibited below 5 cm in soil depth. At least 80% of the NO in3 sup- reduction in aerated cores occurred through dissimilatory processes. Dissimilatory reduction to NH in4 sup+ (DNRA) occurred only below 5 cm in depth. The results show that NH in4 sup+ oxidation was limited by available substrate and was itself a strong regulator of NO in3 sup- -reducing activity. NO in3 sup- reduction was significantly increased when the soil was suspended under anaerobiosis; adding glucose to the soil slurries increased NO in3 sup- reduction by 2.4–3.7 times. Between 3% and 9% (net) of the added NO in3 sup- was reduced through DNRA in the soil slurries. The highest percentage was observed in soil samples from deeper layers that were pre-incubated anaerobically.  相似文献   

15.
Summary The functional roles of the fungivorous collembolan Tomocerus minor and the detritivorous isopod Philoscia muscorum during the decomposition of Pinus nigra needles were studied in mesocosms filled with two different types of F1 litter, obtained from two different forest soils. The effects of the animals on the availability of K+, Ca2+, NO inf3 sup- , NH inf4 sup+ , and PO inf4 sup3- and on the respiration, dehydrogenase, and cellulase activity of microorganisms were measured over one growing season. The animals were introduced into the F1 litter in three densities. The most important animal effect was a buffering effect, in that addition of the animals increased nutrient availability and microbial activity where the corresponding values in control mesocosms without animals were low, and decreased the nutrient availability and microbial activity where control values were high. This effect occurred for both species and was most evident in the substrate with the highest temporal fluctuations. The effects on nutrient availability are attributed to an animal effect on the activity of and successional stage reached the microbial community, with NH inf4 sup+ availability seen as the most important factor. The concept of functional groups in relation to these animal effects is discussed.  相似文献   

16.
Summary The effect of inoculation with a selected isolate of Glomus etunicatum Becker and Gerdemann and one of G. intraradices Schenck and Smith on the growth and nutrient content of Macroptilium atropurpureum Urb. cv. Siratro and Aeschynomene americana L., at applied P levels of 10, 30, 60, and 120 kg ha-1, was studied under field conditions. At all P levels and for all harvests, the shoot dry mass of Siratro and A. americana were greater for the plants inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungi than the control plants. Differences between the VAM fungus-inoculated and the control plants were most marked between 30 and 90 kg ha-1 of applied P and diminished at 120 kg ha-1. At the first harvest of Siratro, the plants inoculated with G. etunicatum had a greater shoot dry mass than those inoculated with G. intraradices, for all levels of applied P. However, for subsequent harvest of Siratro and for the one harvest of A. americana the response of shoot dry mass to the two VAM fungi was equivocal. Fungal inoculation gave at least a 30% saving in the amount of P fertilizer required (40 kg ha-1) for the maximum yield. The plants inoculated with VAM fungi had a greater tissue concentration and total content of P and N than the control plants at low and intermediate levels of applied P. The percentage of root colonized by VAM fungi for the inoculated plants of the two legumes increased linearly with P additions up to 60 kg ha-1. The conclusion is that under amended (limed and fertilized) soil conditions, inoculation with selected VAM fungi can improve the establishement and growth of forage legumes in fields that contain ineffective populations of native VAM fungi.  相似文献   

17.
We studied the effects of fast- and slow-release organic N fertilizers (urea and urea-formaldehyde, Nitroform) on mineralization, nitrification, and N leaching in an acid, poor forest soil. We also studied the effects of a nitrification inhibitor (dicyandiamide) applied together with urea. Net nitrification, mineralization of N and C were determined by aerobic laboratory incubation of soil samples taken one and three growing seasons after N application. Numbers of autotrophic nitrifiers were estimated by a most probable number method three growing seasons after the treatment. Urea increased the CO2 production immediately after application, but after three growing seasons, CO2 production was the lowest in the urea-treated soils. In the nitroform-treated soils, the concentration of exchangeable NH inf4 sup+ after the first and third growing seasons was of the same magnitude, in contrast to the urea-treated soils, where hydrolysis took place immediately. Three growing seasons after application, the highest amount of NH inf4 sup+ accumulated during the laboratory incubation was in the nitro-form-treated soils. Unlike urea, nitroform did not increase the production of NO inf3 sup- or the number of NH inf4 sup+ oxidizers. In the urea+dicyandiamide-treated soils there was less NO inf3 sup- and a lower number of nitrifiers than in the urea-treated soils. The results showed that a slow-release N fertilizer, such as nitroform, increases the availability of mineral N in acid forest soils without increasing nitrification and hence the risk of NO inf3 sup- leaching.  相似文献   

18.
Thiosulfate and CS2 inhibit nitrification. The effect of the addition of thiosulfate on the turnover of inorganic N compounds was tested in an Egyptian and a German arable soil under nitrifying and denitrifying conditions. For nitrification, the soils were amended with NH inf4 sup+ and incubated under aerobic conditions. For denitrification, the soils were amended with NO inf3 sup- and incubated under anaerobic conditions. In both cases, the thiosulfate decreased with time while tetrathionate accumulated to an intermediate extent. Both compounds disappeared completely after <25 days. Production of CS2 was not observed. Carbonyl sulfide was produced only in the Egyptian soil, but production decreased with increasing amounts of added thiosulfate. Under nitrifying conditions, the addition of increasing amounts of thiosulfate (25, 50, and 100 g S g-1 dry weight) resulted in decreasing rates of NH inf4 sup+ oxidation to NO inf3 sup- ; it also resulted in an increasing intermediate accumulation of NO inf2 sup- and NO, and in an increasing production of N2O. Under denitrifying conditions, the addition of increasing amounts of thiosulfate did not significantly affect the rate of NO inf3 sup- reduction, and resulted in an increasing intermediate accumulation of NO inf2 sup- and of NO only in the German soil in which the production of N2O was slightly inhibited by thiosulfate. These results demonstrate that the nitrification of NH inf4 sup+ and NO inf2 sup- was inhibited by increasing concentrations of thiosulfate and/or tetrathionate without involving the formation of volatile S compounds as potential nitrification inhibitors. Denitrification was not affected by the addition of thiosulfate.  相似文献   

19.
Summary Using microcosms containing decomposing Pinus nigra litter, the effects of introducing two species of soil arthropods, the fungivorous collembolan Tomocerus minor and the detritivorous isopod Philoscia muscorum, have been studied. The effects of these animals on microbial respiration, on dehydrogenase and cellulase activity, and on the concentration of exchangeable macronutrients (Ca2+, Mg2+, K+, NO inf3 sup- , NH inf4 sup+ , PO inf4 sup3- ) were measured. Both species enhanced microbial activity and the concentration of exchangeable nitrate, ammonium, and phosphate. Ca2+ and Mg2+ concentrations were lowered in the microcosms with animals. The differences between the two species were mainly quantitative, and it appears that the effect of isopods is direct, whereas the collembolans show direct and indirect effects. Positive effects of the presence of animals were found when microbial activities or concentrations of exchangeable nutrients in microcosms without animals were low; negative effects were found when they were relatively high. Thus, soil arthropods have a buffering role in soil processes. These results ae discussed against a background of a supposed succession of sugar fungi/bacteria to more slowly growing decomposing fungi.Dedicated to the late Prof. Dr. W. Kühnelt  相似文献   

20.
Summary Forest floor litter, duff, and underlying soils were assembled in laboratory microcosms representing pinyon, juniper, and interspace field conditions. Burning removed more than 95% of both N and C from the litter, with losses from the duff dependent on soil moisture conditions. No significant changes in total N or C were noted in the soil. Immediate increases were observed in soil NH inf4 sup+ , decreasing with depth and related to soil heating. The greatest increases were noted in both the pinyon and juniper soils that were dry at the time of the burn, with interspace soils exhibiting the least changes. Soil NH inf4 sup+ closely approximated the controls on day 90 after the burns in all treatments. Ninety days after the burn microbial biomass N was highest in the controls, followed by the wet and then the dry-burned soils, in both the pinyon and juniper microcosms. This was inversely related to the levels of accumulated NO inf3 sup- . Nitrifying bacteria populations were indirectly correlated to soil temperatures during the burn. Population levels 90 days after the burn showed increases in both the wet- and the dry-burn treatments, with those in the pinyon treatments exceeding those found in the nitial controls of pinyon soils.The use of trade and company names in this paper is for the benefit of the reader; such use does not constitute an official endorsement or approval of any service or product by the U.S. Department of Agriculture to the exclusion of others that may be suitable  相似文献   

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