Fungi associated with roots of continuously cropped upland rice

Fungi on and in roots of continuously cropped upland rice were examined. Dominant fungi on the root surfaces were found to be composed of limited genera: Fusarium, Penicillium, and Pyrenochaeta. Among them, only Pyrenochaeta sp. was remarkable in regard to continuous cropping of upland rice. The results showed that Pyrenochaeta sp. penetrated into and multiplied in root tissues of aged plants and could survive during the winter on infected root residues left in the field, and in the next spring colonized the root surfaces of new seedlings, and then penetrate into root tissues and thus be accumulated on and in roots by the continuous cropping of upland rice. Pyrenochaeta sp. was also found to have a considerable specific affinity for roots of upland rice, compared with the roots of several other plants.     

A growth inhibitor specific to upland rice produced by Pyrenochaeta SP.

An attempt was made to isolate a growth inhibitor of upland rice produced by Pyrenochaeta sp. Partially purified pink substance having absorption maxima at 481, 502, 512,537 and 548 nm was obtained from mycelia of Pyrenochaeta sp. This substance inhibited the growth of upland rice at a lower concentration than p-coumaric acid. It inhibited the growth of upland rice and sorghum, but stimulated the growth of Chinese cabbage and cucumber.     

Interaction among free-living N-fixing bacteria isolated from Drosera villosa var. villosa and AM fungi (Glomus clarum) in rice (Oryza sativa)

Rice is usually grown in N-deficient soils, demanding that the element be supplied to the field by commercially available N fertilizers. Unfortunately, a substantial amount of the urea-N or NO₃-N applied as fertilizers is lost through different mechanisms, causing environmental pollution problems. Utilization of biological N₂ fixation (BNF) technology can decrease the application of N fertilizers, reducing environmental risks. This study evaluated the effects of four free-living N-fixing bacterial species, isolated from oligotrophic soil conditions, as single inoculants or combined with arbuscular mycorrhizal fungi (Glomus clarum), on the development of rice plants grown as flooded or upland rice, in the greenhouse. Upland rice roots were inoculated with Methylobacterium sp., Burkholderia sp. and Sphingomonas sp., whereas the species Burkholderia sp., Pseudomonas sp. and Sphingomonas sp., were inoculated on flooded rice. Inoculants consisted of individual bacterial species or their mixtures, with or without G. clarum. Controls included non-bacteria/non-AM fungi, and AM fungi alone. Experiments were carried out in five replicates. The presence of G. clarum decreased or did not significantly affect plant growth under the different culture conditions. The presence of AM fungi stimulated the N-fixing bacterial population of upland rice. Bacterial species had different effects, under both culture conditions, and some genera of N-fixing bacteria increased root and shoot growth at different plant growth stages. The level of mycorrhiza colonization had no influence on plant growth     

Nutrient distribution around roots of Brachiaria,maize, sorghum,and upland rice in an Andisol

Plants grown on Andisols often have an insufficient phosphorus (P) supply, since active aluminium (AI) and iron bind P in low available forms to the plants. The objectives of the present studies were to examine the differences in growth associated with the P-uptake ability among four Gramineae, to determine which P-forms are utilised, and to relate plant growth to the distribution of nutrients in soil close to the roots. Rhizosphere soil was separated from bulk soil by using a rhizobox system. Shoot and root yields and nutrient contents of maize (Zea mays L.), Sorghum bicolor (L.), Brachiaria dictyoneura (Stapf), and upland rice (Oryza sativa L.) were determined after cultivation in rhizoboxes for 105 d. Soil was sampled at increasing distances from the roots and analysed for P compounds, other nutrients, and pH. Maize gave the highest yield by using P reserves in its large seeds, resulting in the greatest depletion of K in the root soil of maize. Brachiaria showed the highest efficiency while upland rice the lowest in using soil P, respectively. The amounts of Bray-2 P and acetic acid-extractable P were significantly lower in root soil compared to bulk soil. Soil pH increased in the root soil of all crops, mainly around the Brachiaria roots.     

Upland rice,common bean,and cowpea response to magnesium application on an oxisol

Abstract

Even though Mg is an essential nutrient. the response of upland rice, common bean, and cowpea to Mg application has not been adequately documented in Brazilian oxisols. This study was conducted to examine the influence of Mg application on growth and nutrient uptake by upland rice (Oryza sativa L.), common bean (Phaseolus vulgaris L.), and cowpea (Vigna unguiculata L. Walp.) on an oxisol. Magnesium levels in the soil were created at sowing by application of MgO at rates of 0.30, 1.05, 1.15, 1.33, 3.52, and 6.22 cmol Mg/kg of soil. Application of Mg did not have a significant beneficial effect on dry weight of roots and tops of rice and cowpea. Common bean root and top dry weights were increased with Mg applications up to 1 cmol Mg/kg of soil. Uptake of N, P, K, Ca, Cu, Zn, Fe, and Mn by the three crops was significantly (P < 0.01) decreased by increasing Mg levels in the soil. Results related to changes in chemical properties of soil with the application of Mg are also presented.     

ROOT GROWTH OF UPLAND RICE GENOTYPES AS INFLUENCED BY NITROGEN FERTILIZATION

The plant root system is an important organ which supplies water and nutrients to growing plants. Information is limited on influence of nitrogen fertilization on upland rice root growth. A greenhouse experiment was conducted to evaluate influence of nitrogen (N) fertilization on growth of root system of 20 upland rice genotypes. The N rate used was 0 mg kg^?1(low) and 300 mg kg^?1(high) of soil. Nitrogen X genotype interactions for root length and root dry weight were highly significant (P < 0.01), indicating that differences among genotypes were not consistent at two N rates. Overall, greater root length, root dry weight and tops-roots ration were obtained at an N fertilization rate of 300 mg kg^?1compared with the 0 mg N kg^?1soil. However, genotypes differ significantly in root length, root dry weight and top-root ratio. Nitrogen fertilization produced fine roots and more root hairs compared with absence of N fertilizer treatment. Based on root dry weight efficiency index (RDWEI) for N use efficiency, 70% genotypes were classified as efficient, 15% were classified as moderately efficient and 15% were classified as inefficient. Root dry weight efficiency index trait can be incorporated in upland rice for improving water and nutrient efficiency in favor of higher yields.     

The relationship of soil and leaf nutrients to rice leaf oranging

A symptom called leaf‐oranging, indicating a deficiency of many nutrients, occurs in paddy rice (Oryzasativa L.) when production expands into some upland soils. Rice (Gui Chou cv.) was grown in culture pots in a flooded, weathered, upland soil (Nacogdoches) and compared to rice growth in a flooded soil currently used for paddy rice production (Dacosta) in Texas to understand the soil and plant factors involved in leaf‐oranging. Fertilizer rates of 0, 10, and 100 mg N/kg as (NH₄)₂SO₄ were applied to each soil along with phosphorus (P) and potassium (K) fertilizer. The orange Leaf Index (OLI), a measure of leaf‐oranging, was determined weekly and increased to 60–70% for plants grown in the upland soil but its progression was delayed by higher N treatments. No leaf‐oranging was observed in the paddy soil. The soil evoking leaf‐oranging was low in silicon (Si) and high in iron (Fe). In addition, analysis of leaves from these plants showed 19–25% higher leaf ammonium‐nitrogen (NH₄‐N), 9–137% higher manganese (Mn) levels and lower total N:NH₄ concentration compared to normal rice leaves four weeks after transplanting. This inferred that leaf‐oranging probably was associated with some degree of NH₄‐N toxicity and antagonism with K. Leaf‐oranging was also associated with low calcium (Ca) assimilation or Ca uptake inhibition because of the heavy Fe‐oxide coating of the roots of the affected rice plants. In this experiment, leaf‐oranging was not associated with toxic levels of Fe or Mn.     

Uptake of carbon and nitrogen through roots of rice and corn plants,grown in soils treated with 13C and 15N dual-labeled cattle manure compost

Nitrogen and carbon dynamics in paddy and upland soils for rice cultivation and in upland soil for corn cultivation was investigated by using ¹³C and ¹⁵N dual-labeled cattle manure compost (CMC). In a soil with low fertility, paddy and upland rice took up carbon and nitrogen from the CMC at rates ranging from 0.685 to 1.051% of C and 17.6–34.6% of N applied. The ¹³C concentration was much higher in the roots than in the plant top, whereas the ¹⁵N concentration differed slightly between them, indicating that organic carbon taken up preferentially accumulated in roots. The ¹³C recovery in the plant top tended to be higher in upland soil than in paddy soil, whereas ¹⁵N applied was recovered at the same level in both paddy and upland soils. In the experiment with organic farming soil, paddy rice took up C and N from the CMC along with plant growth and the final recovery rates of ¹³C and ¹⁵N were 2.16 and 17.2% of C and N applied. In the corn experiment, a very large amount of carbon from the CMC was absorbed, accounting for at least 7 times value for rice. The final uptake rates of ¹³C and ¹⁵N reached about 13 and 10% of C and N applied, respectively. Carbon emission from the CMC sharply increased by 2 weeks after transplanting and the nitrogen emission was very low. It is concluded that rice and corn can take up an appreciable level of carbon and nitrogen from the CMC through roots.     

Bacterial communities associated with nodal roots of rice plants along with the growth stages: Estimation by PCR-DGGE and sequence analyses

Bacterial communities in rice roots that developed from different nodes and at different growth stages were compared by using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA. Rice root samples were collected at three stages, namely tillering (July 2), maximum tillering (July 21), and ripening (September 12). The bacterial diversity in rice roots was found to increase along with the growth stages of the rice plants as well as the root age from the numbers of DGGE bands. The community structure of the bacteria was also found to change with the growth stages and root age from cluster analysis. Sequence analysis of the DGGE bands indicated that the dominant bacteria associated with rice roots were Gram-negative bacteria, especially β-Proteobacteria irrespective of the growth stages and root age. DGGE bands related to Janthinobacterium agaricidamnosum W1r3T and Clostridium sp. FCB90-3 were ubiquitous in many roots irrespective to the sampling date. Principal component analysis enabled to characterize the DGGE bands related to nitrogen-fixing Azoarcus spp., and Azovibrio sp. BS20-3 in the samples collected on July 2 and on July 21, and the myxobacteria collected on September 12, respectively, as representative bacteria in the bacterial communities. The habitat around older rice roots at every sampling date was more reductive than that around younger rice roots, and the DGGE bands related to Spirochaeta spp. were specific in older roots at every sampling date. Some specific bacteria that were most closely related to the DGGE bands were found from principal component analysis to characterize young and old. roots at each growth stage as follows: aerobes Flavobacterium sp. 90 clone 2 and Janthinobacterium agaricidamnosus W1r3T in young roots and facultative anaerobes Dechloromonas sp. MissR and Anaeromyxobacter dehalogenans 2CP-3 in old nodal roots on July 2, strict anaerobe Geobacter pelophilus Dfr2 and aerobes Nitrosospira sp. Nsp17 and uncultured Nitrospira sp. clone 4-1 in old roots on July 21, and different Clostridium spp. in both young and old roots and Desulfovibrio magneticus RS-1 in old roots on September 12, respectively. A larger number of the closest relatives of anaerobic bacteria grew at the late stage than at the early stages, and in old roots than in younger roots. Thus, the environment of paddy roots was remarkably heterogeneous as a bacterial habitat, where not only the whole root system but also a root may create oxic and anoxic environments.     

Effect of root residues on the growth of upland rice

The effect of root residues of upland rice, which had been left in a field for ca. 7 months from autumn to the next spring, on the growth of succeeding upland rice was examined. The root residues incorporated into field soil inhibited the upland rice growth. This effect was considered to be caused not by toxic substances accumulating in root residues, but by aerobic detrimental organisms inhabiting root residues.     

Arbuscular Mycorrhizal Fungi Contribute to Resistance of Upland Rice to Combined Metal Contamination of Soil

A greenhouse pot experiment was conducted to investigate heavy metal [copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd)] uptake by two upland rice cultivars, ‘91B3’ and ‘277’, grown in a sterilized field soil contaminated by a mixture of Cu, Zn, Pb, and Cd. Rice plants were inoculated with each of three arbuscular mycorrhizal fungi (AMF), Glomus versiforme (GV), Glomus mosseae (GM), and Glomus diaphanum (GD), or remained noninoculated (NM). Both rice cultivars could be colonized by the three AMF used in this experiment. The percentage of mycorrhizal colonization by the three AMFs on the two rice cultivars ranged from 30% to 70%. Mycorrhizal colonization of both upland rice cultivars had a large influence on plant growth by increasing the shoot and root biomass compared with non-inoculated (NM) plants. The results indicate that mycorrhiza exert some protective effects against the combined toxicity of Cu, Zn, Pb, and Cd in the contaminated soil. This conclusion is supported by the partitioning of heavy metals (HMs) in the two cultivars. In the two cultivars, colonization by AMF reduced the translocation of HMs from root to shoot (except that the colonization of AMF increased the Cu translocation of HMs in cultivar ‘277’). Immobilization of the HMs in roots can alleviate the potential toxicity to shoots induced by the mixture of Cu, Zn, Pb, and Cd. The two rice cultivars showed significant differences in uptake of Cu, Zn, Pb, and Cd when uninoculated. GM inoculation gave the most protective effects on the two cultivars under the combined soil contamination.     

Green manure production of Azolla microphylla and Sesbania rostrata and their long-term effects on rice yields and soil fertility

Summary Azolla spp. and Sesbania spp. can be used as green manure crops for wetland rice. A long-term experiment was started in 1985 to determine the effects of organic and urea fertilizers on wetland rice yields and soil fertility. Results of 10 rice croppings are reported. Azolla sp. was grown for 1 month and then incorporated before transplanting the rice and 3–4 weeks after transplanting the rice. Sesbania rostrata was grown for 7–9 weeks and incorporated only before transplanting the rice. Sesbania sp. grew more poorly before dry season rice than before wet season rice. Aeschynomene afraspera, which was used in one dry season rice trial, produced a larger biomass than the Sesbania sp. The quantity of N produced by the Azolla sp. ranged from 70 to 110 kg N ha^-1. The Sesbania sp. produced 55–90 kg N ha^-1 in 46–62 days. Rice grain yield increases in response to the green manure were 1.8–3.9 t ha^-1, similar to or higher than that obtained in response to the application of 60 kg N ha^-1 as urea. Grain production per unit weight of absorbed N was lower in the green manure treatments than in the urea treatment. Without N fertilizer, N uptake by rice decreased as the number of rice crops increased. For similar N recoveries, Sesbania sp. required a lower N concentration than the Azolla sp. did. Continuous application of the green manure increased the organic N content in soil on a dry weight basis, but not on a area basis, because the application of green manure decreased soil bulk density. Residual effects in the grain yield and N uptake of rice after nine rice crops were found with a continuous application of green manure but not urea.     

Effects of mycorrhizal inoculation of upland rice on uptake kinetics of arsenate and arsenite

We assessed the effect of mycorrhizal inoculation on short‐term uptake kinetics of arsenate and arsenite by excised roots of upland rice (Oryza sativa L. cv. Zhonghan 221). A concentration of 0.01–0.05 mM arsenic (As) differentially affected the influx rates of both arsenate and arsenite into rice roots non‐inoculated or inoculated with Glomus mosseae and G. versiforme. While V_max for arsenate uptake by non‐mycorrhizal roots was 1.02 µmol g^?1 fresh weight h^?1, it was reduced by a factor of 2.4 for mycorrhizal roots (about 0.42 µmol g^?1 fresh weight h^?1) in the high‐affinity uptake system. However, at high concentrations of 0.5–2.5 mM As only G. versiforme was able to reduce As influx. The results show that mycorrhizal effects on As uptake of upland rice are both concentration and species‐specific.     

Influence of pH on growth and nutrient uptake by crop species in an Oxisol

Abstract

Crop growth in Oxisols is known to be limited by high soil acidity and low levels of basic cations. Five greenhouse experiments were conducted to evaluate the effects of soil pH on the growth and nutrient uptake of upland rice (Oryza sativa L.), wheat (Triticum aestivum L.), corn (Zea mays L.), common bean (Phaseolus vulgaris L.), and cowpea (Vigna unguiculata L. Walp.). Six levels of soil pH (4.1, 4.7, 5.3, 5.9, 6.6, and 7.0) were achieved by addition of various levels of CaCO₃. Crop species responded differently to pH, reflecting the genetic diversity among species. Higher dry matter accumulation in roots and tops of rice, corn, and cowpea was observed at acidic pH ranges indicating that these species are tolerant to soil acidity. However, increasing soil pH enhanced dry matter accumulation in roots and tops of wheat and common bean, reflecting their intolerance to soil acidity. In all of the crop species, uptake of calcium (Ca) and magnesium (Mg) decreased with a decrease in soil pH. Overall uptake of zinc (Zn), manganese (Mn), and iron (Fe) in all species increase with a decrease in soil pH. Higher pH in an Oxisol might induce micronutrient deficiencies; therefore, one has to avoid overliming. In general, increasing soil pH decreased the uptake of nitrogen (N), phosphorus (P), and potassium (K) in rice, but uptake of these elements increased in wheat, corn, and common bean. In order to achieve the full genetic potential of any given species on an Oxisol, one needs to consider the species tolerance to soil acidity and its nutrient demand.     

A fungal substance of selective action on plant growth produced by Pyrenochaeta sp.

The effect of the pink substance extracted from mycelia of Pyrenochaela sp. on growth of 10 kinds of plants was examined by germination test in the light. The substance inhibited the growth of germinating seedlings of 5 monocotyledonous plants (upland rice, sorghum, wheat, barley, and oat) at a concentration higher than 10 ppm of the partially purified pink substance, while it rather stimulated that of 5 dicotyledonous plants (chinese cabbage, cucumber, radish, turnip, and burdock) at 10-100 ppm. When the substance was sprayed on shoots of upland rice and Chinese cabbage germinated in pot, it inhibited the growth of seedlings of the former and stimulated that of the latter.     

A simple method to study the oxidizing power of rice roots under submerged soil conditions

A method was developed to visualize and to study the oxidizing power of rice roots growing under submerged soil conditions. The experimental set up consisted of a transparent jar with an inner core containing the submerged soil surrounded by a coarse (500 μm) and a fine (30 μm) meshed nylon net and a plastic folio. The space of about 1 cm between the jar wall and the soil column was either filled with water (before removing the plastic folio) or with agar containing the redox indicator. Three-week-old rice (Oryza saliva L.) seedlings grown in a sandy soil under controlled growth chamber conditions were transplanted into the jars between the plastic folio and the fine-meshed (30 μm) nylon net. The agar medium (0.5% agar) containing 10 ppm leuco melhylene blue redox indicator or 5 mM ferrous sulphate or precipitated ferrous sulfide (10 m M ferrous sulphate + 4 m M Na₂S) was filled in the transparent jars immediately after sucking out water. Within 4 h the oxidizing power of rice roots became visible by bluish coloration all along of roots and the agar medium around roots due to oxidation of leuco methylene blue. In case of ferrous sulphate reddish brown coloration was observed after one day around the roots and on the surface of roots because of ferrous iron oxidation. When agar medium blackened by precipitated FeS was used the root zone first became transparent because of oxidation of FeS and after few days the roots became reddish brown indicating iron oxyhydroxide deposition. The use of ferrous sulphate and ferrous sulfide enables to study the oxidizing power of rice roots for extended periods, whereas it is not possible to grow rice plants in leuco methylene blue for more than a few hours. However (results not shown), rice cultivars showed differences in oxidizing power of the roots.     

Community structure of bacteria and fungi responsible for rice straw decomposition in a paddy field estimated by PCR-RFLP analysis

Rice straw including leaf sheaths and blades put in nylon mesh bags was placed in the plow layer of a Japanese paddy field after harvest under upland conditions and after transplanting of rice seedlings under flooded conditions. In addition, rice straw that was decomposed under the upland conditions during the off-crop season in winter was placed again in soil at the time of transplanting. The materials were collected periodically to analyze the community structure of the bacteria and fungi responsible for rice straw decomposition by PCR-RFLP analysis. The PCR products with 27f and 1492r primers designed for bacterial 16S rDNA and with EF3 and EF4 primers designed for fungal 18S rDNA were digested with four restriction endonucleases (Hinf I, Sau3A I, Hae III, EeoR I). Bacterial communities in the decomposing rice straw were different from each other between upland and flooded conditions, between leaf sheaths and blades, and between straw samples with and without decomposition under upland conditions during the off-crop season. Fungal communities in the decomposing rice straw were also different between the leaf sheaths and blades under upland soil conditions. Score plots of bacterial and fungal communities in the principal component analysis were separated from the plot of the straw materials along with the duration of the placement, indicating the succession of bacterial and fungal communities in decomposing rice straw with time.     

Organic matter production in rice field flood water

To assess the contribution of organic matter produced in the flood water to the fertility of a rice soil, the primary productivity and the algal biomass therein were examined throughout one crop. Primary productivity was estimated from the diurnal curve of dissolved oxygen.

Just after transplanting, an algal bloom developed due to fert,ilizer or ploughing or both. After submerged weeds occupied the whole paddy no distinct algal growth was found. At the ripening stage, the rice plant canopy suppressed the growth of aquatic plants. Benthic algal biomass did not change much throughout the crop period. The standing crop of algae ranged from 2 to 114 kg/ha by fresh weight, while the maximum standing crop of submerged weeds (Najas sp., Chara sp.) was 400 kg/ha by dry weight.

The primary productivity of the flood water community was high (0.6-3.3 g 0 1 m^-2day^-l) and equivalent to productivity values in eutrophic lakes. The total gross primary production of the flood water community during the cropping period corresponded to 10% and 15% of that of rice plant in the fertilized plot and non-fertilized plot, respectively.

Considering the movement of CO₂ in the flood water, it is suggested that the photosynthesis activity in the flood water prevents surplus CO₂ from being lost.     

Lime and phosphorus interactions on growth and nutrient uptake by upland rice,wheat, common bean,and corn in an Oxisol

Liming and phosphorus (P) applications are common practices for improving crop production in acid soils of the tropical as well as temperate regions. Four greenhouse experiments were conducted on an Oxisol (clayey, kaolinitic, isothermic, Typic Haplustox) to evaluate response of liming (0,2, and 4 g/kg) and P application (0, 50, and 175 mg P/kg) in a factorial combination on growth and nutrient uptake by upland rice (Oryza sativa L.), wheat (Triticum aestivum L.), common bean (Phaseolus vulgaris L.), and corn (Zea mays L.). Phosphorus application significantly (P<0.01) increased dry weight of tops of all the four crop species as well as dry weight of roots of wheat and corn. Liming significantly (P<0.01) improved growth of common bean and corn but had significant negative effects on rice growth. Maximum dry weight of tops of rice and wheat was obtained at 175 mg P/kg without lime. Maximum dry weight of tops in common bean was obtained at 4 g lime/kg with 175 mg P/kg of soil. In all the crops, increasing levels of applied P significantly increased nutrient uptake. With some exceptions, increasing levels of lime tend to reduce uptake of P, zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) and increase the uptake of calcium (Ca) and magnesium (Mg) in all the crop species. Decrease in potassium (K) uptake, due to high lime, is probably due to antagonistic effects of Ca and Mg and reduced micronutrients uptake is probably due to increased soil pH resulting in decreased availability of these elements to plants. Therefore, in these types of acid soils, one should avoid over liming.     

Combined effects of soil waterlogging and compaction on rice (Oryza sativa L.) growth, soil aeration, soil N transformations and 15N discrimination

 The combined effects of soil compaction and soil waterlogging on the growth of two rice cultivars (Oryza sativa L., cultivars Kanto 168 and Koshihikari) and soil N transformations were studied in pots. Although waterlogging eliminated initial differences in mechanical resistance between compacted and loose soils, Kanto 168 and Koshihikari roots had, respectively, less biomass and a lower porosity if soil was compacted prior to waterlogging. The cause for this was probably established before waterlogging. Redox values showed that upland soils were well aerated. Loose waterlogged soils contained oxic sites, but compacted waterlogged soils did not. Potential denitrification was stimulated by waterlogging and, to a larger extent, by plant presence. Waterlogging lowered potential nitrifying capacities, by competition between plants and micro-organisms for NH₄ ⁺ rather than by oxygen shortage. Compaction prior to waterlogging benefited the potential nitrifying capacity of soils with either cultivar and the potential denitrifying capacity for soils with Koshihikari. Compaction had no effect on nitrification or denitrification in upland soils. N recoveries were low, especially in pots without plants, as a result from sampling strategy and N loss. On day 42/43 after potting, total δ¹⁵N values of waterlogged pots were positive, whereas after 22 days all pots had negative total δ¹⁵N values. Final δ¹⁵N values of plant parts from waterlogged and upland soils were positive and negative, respectively. Although the δ¹⁵N values generally accorded well with the other results, they did not support higher N losses from compacted waterlogged soils than from loose waterlogged soils with plants, as suggested by potential denitrifying activities. Received: 4 February 2000