Repeated drying–rewetting cycles and their effects on the emission of CO2, N2O,NO, and CH4 in a forest soil

Prolonged summer droughts due to climate change are expected for this century, but little is known about the effects of drying and wetting on biogenic trace‐gas fluxes of forest soils. Here, the response of CO₂, N₂O, NO, and CH₄ fluxes from temperate forest soils towards drying–wetting events has been investigated, using undisturbed soil columns from a Norway spruce forest in the “Fichtelgebirge”, Germany. Two different types of soil columns have been used for this study to quantify the contribution of organic and mineral horizons to the total fluxes: (1) organic horizons (O) and (2) organic and mineral soil horizons (O+M). Three drying–wetting treatments with different rewetting intensities (8, 20, and 50 mm of irrigation d^–1) have been compared to a constantly moist control to estimate the influence of rainfall intensity under identical drying conditions and constant temperature (+15°C). Drought significantly reduced CO₂, N₂O, and NO fluxes in most cycles. Following rewetting, CO₂ fluxes quickly recovered back to control level in the O columns but remained significantly reduced in the O+M columns with total CO₂ fluxes from the drying–wetting treatment ranging approx. 80% of control fluxes. Fluxes of N₂O and NO remained significantly reduced in both O and O+M columns even after rewetting, with cumulative fluxes from drying–wetting treatments ranging between 20% and 90% of the control fluxes, depending on gas and cycle. Fluxes of CH₄ were small in all treatments and seem to play no significant role in this soil. No evidence for the release of additional gas fluxes due to drying–wetting was found. The intensity of rewetting had no significant effect on the CO₂, N₂O, NO, and CH₄ fluxes, suggesting that the length of the drought period is more important for the emission of these gases. We can therefore not confirm earlier findings that fluxes of CO₂, N₂O, and NO during wetting of dry soil exceed the fluxes of constantly moist soil.     

Distribution of microbial biomass and phospholipid fatty acids in Podzol profiles under coniferous forest

Microbial‐derived phospholipid fatty acids (PLFAs) can be used to characterize the microbial communities in soil without the need to isolate individual fungi and bacteria. They have been used to assess microbial communities of humus layers under coniferous forest, but nothing is known of their distribution in the deeper soil. To investigate the vertical distribution we sampled nine Podzol profiles on a 100‐m‐long transect in a coniferous forest and analysed for their microbial biomass and PLFA pattern to a depth of 0.4 m. The transect covered a fertility gradient from Vaccinium vitis‐idaea forest site type to Vaccinium myrtillus forest site type. The cores were divided into humus (O) and eluvial (E) layers and below that into 10‐cm sections and designated as either illuvial (B) or parent material (C), or as a combination (BC). Two measures of microbial biomass analyses were applied: substrate‐induced respiration (SIR) to determine microbial biomass C (C_mic), and the sum of the extracted microbial‐derived phospholipid fatty acids (totPLFA). The soil fertility had no effect on the results. The C_mic correlated well with totPLFA (r= 0.86). The microbial biomass decreased with increasing depth. In addition the PLFA pattern changed with increased depth as assessed with principal component analysis, indicating a change in the microbial community structure. The composition of the PLFAs in the O layer differed from that in the E layer and both differed from the upper part of the B layer and from the rest of the BC layers. The deeper parts of the B layer (BC₁, BC₂ and BC₃) were similar to one other. The O layer had more 18:2ω6, a PLFA indicator of fungi, whereas the E layer contained relatively more of the PLFAs 16:1ω9, 18:1ω7 and cy19:0 common in gram‐negative bacteria. With increased depth the relative amount of 10Me18:0, the PLFA indicator for actinomycetes, increased. We conclude that the PLFA method is a promising discriminator between the microbial community structures of the horizons in Podzols.     

Incorporation of 13C-labelled rice rhizodeposition carbon into soil microbial communities under different water status

The overall processes by which carbon is fixed by plants in photosynthesis then released into the soil by rhizodeposition and subsequently utilized by soil micro-organisms, links the atmospheric and soil carbon pools. The objective of this study was to determine the plant derived ¹³C incorporated into the phospholipid fatty acid (PLFA) pattern in paddy soil, to test whether utilization of rice rhizodeposition carbon by soil micro-organisms is affected by soil water status. This is essential to understand the importance of flooded conditions in regulating soil microbial community structure and activity in wetland rice systems. Rice plants were grown in soil derived from a paddy system under controlled irrigation (CI), or with continuous waterlogging (CW). Most of the ¹³C-labelled rice rhizodeposition carbon was distributed into the PLFAs 16:0, 18:1ω7 and 18:1ω9 in both the CW and CI treatments. The bacterial PLFAs i15:0 and a15:0, both indicative of gram positive bacteria, were relatively more abundant in the treatments without rice plants. When rice plants were present rates of ¹³C-incorporation into i15:0 and a15:0 was slow; the microbes containing these PLFAs may derive most of their carbon from more recalcitrant C (soil organic matter). PLFAs, 18:1ω7 and 16:1ω7c, indicative of gram negative bacteria showed a greater amount incorporation of labelled plant derived carbon in the CW treatment. In contrast, 18:2ω6,9 indicative of fungi and 18:1ω9 indicative of aerobes but also potentially fungi and plant roots had greater incorporation in the CI treatment. The greater root mass concomitant with lower incorporation of ¹³C into the total PLFA pool in the CW treatment suggests that the microbial communities in wetland rice soil are limited by factors other than substrate availability in flooded conditions. In this study differing soil microbial communities were established through manipulating the water status of paddy soils. Steady state ¹³C labelling enabled us to determine that the microbial community utilizing plant derived carbon was also affected by water status.     

Organic matter dynamics in a temperate forest soil following enhanced drying

Climate models predict an increase in global surface temperature and a change in precipitation intensity during this century. For Europe, extended drought periods followed by heavy rainfall are expected. The consequences for soil organic matter (SOM) dynamics are poorly understood. In this study, we investigated the effect of changing soil moisture regime on SOM quality under field conditions. For this purpose, a throughfall exclusion (TE) experiment was conducted in the summers 2006 and 2007 on a Haplic Podzol under a 140 years old Norway spruce stand using a roof installation followed by re-wetting compared to non-manipulated control plots. Total organic carbon, lignin (stable carbon pool), plant and microbial sugars (labile carbon pool) and microbial biomass (phospholipid fatty acids) were determined before, during and after the experiment in the L, O, A and B horizons. No significant treatment effects could be observed for SOM quantity. Amounts of lignin and soil microbial biomass were also not affected by the moisture regime but structure of soil microbial community. In the L and organic layers, gram + bacteria and actinomycetes were reduced during water stress, while gram- bacteria, fungi and protozoa increased during drought. Warmer and drier weather led to a dominance of fungi while a cooler and moister regime favoured bacteria, at least in the L horizon. An increasing PLFA (cy17:0 + cy19:0)/(16:1ω7c + 18:1ω7c) ratio in the O layer and A horizon suggests that the microbes suffered from water stress in these horizons. This agrees with a decreasing contribution of microbial sugars to SOM with decreasing water content in the O and A horizons. Although the original plant material exhibited increasing plant sugar content with increasing dryness, the contribution of the plant sugars to total soil organic carbon (SOC) generally decreased with decreasing water content. Physical-chemical changes of soil structure can theoretically change the sugar extractability from soils and/or chemical changes of sugars structure can probably affect the analysis. Therefore, chemical alteration and stabilization could be responsible for sugar decrease in soil with increasing dryness explaining the contrast compared to the original plant material.     

Organic matter dynamics in a temperate forest as influenced by soil frost

In the future, climate models predict an increase in global surface temperature and during winter a changing of precipitation from less snowfall to more raining. Without protective snow cover, freezing can be more intensive and can enter noticeably deeper into the soil with effects on C cycling and soil organic matter (SOM) dynamics. We removed the natural snow cover in a Norway spruce forest in the Fichtelgebirge Mts. during winter from late December 2005 until middle of February 2006 on three replicate plots. Hence, we induced soil frost to 15 cm depth (at a depth of 5 cm below surface up to –5°C) from January to April 2006, while the snow‐covered control plots never reached temperatures < 0°C. Quantity and quality of SOM was followed by total organic C and biomarker analysis. While soil frost did not influence total organic‐C and lignin concentrations, the decomposition of vanillyl monomers (Ac/Ad)_V and the microbial‐sugar concentrations decreased at the end of the frost period, these results confirm reduced SOM mineralization under frost. Soil microbial biomass was not affected by the frost event or recovered more quickly than the accumulation of microbial residues such as microbial sugars directly after the experiment. However, in the subsequent autumn, soil microbial biomass was significantly higher at the snow‐removal (SR) treatments compared to the control despite lower CO₂ respiration. In addition, the water‐stress indicator (PLFA [cy17:0 + cy19:0] / [16:1ω7c + 18:1ω7c]) increased. These results suggest that soil microbial respiration and therefore the activity was not closely related to soil microbial biomass but more strongly controlled by substrate availability and quality. The PLFA pattern indicates that fungi are more susceptible to soil frost than bacteria.     

Changes in the pore space of soil constructions in physical laboratory models

The dynamics of pore space structure in different filled soil constructions during water infiltration and wetting–drying processes is studied. Model laboratory experiments in columns physically simulate water infiltration after penetration at a rate of 600 mm with free outflow from the lower end of the column followed by multiple drying of soil constructions composed by alternating layers of sand, peat, and A and В horizons of soddy-podzolic soil. In two- and three-dimensional tomographic images, changes in the pore space and the interpenetration of solid phase at the boundaries between individual horizons of soil constructions are analyzed.     

Depth‐related responses of soil microbial communities to experimental warming in an alpine meadow on the Qinghai‐Tibet Plateau

Although the effect of experimental warming on soil microorganisms has been well documented at surface horizons, less is known about its influence in subsurface horizons. An experiment was therefore carried out in an alpine meadow on the Qinghai‐Tibet Plateau to examine the responses of microbial communities to experimental warming at five soil depths (0–10, 10–20, 20–30, 30–40 and 40–50 cm). Plots were passively warmed for 3 years in open‐top chambers and compared with adjacent control plots at ambient temperature. Soil microbial communities were assessed by using phospholipid fatty acid (PLFA) analysis. Our results showed clearly that 3 years of experimental warming increased microbial biomass consistently and significantly throughout the upper 50‐cm soil profiles, as indicated by the changes in both microbial biomass carbon (C) and total PLFA contents. The composition of microbial communities was also affected significantly by warming, but its effect depended on soil depth. While warming induced a community shift towards bacteria at the 0–10‐cm depth, it tended to shift microbial communities towards fungi at the other, deeper, layers. These results indicate that warming had strong effects on soil microbial communities, including even those residing in subsurface horizons, which may help us to understand the microbial mediation of the feedback between terrestrial C cycling and climate warming.     

干湿交替对水稻土碳氮矿化的影响

通过室内培育试验,研究干湿交替条件下长期不同施肥处理水稻土微生物生物量和理化性状变化对土壤C、N矿化的影响机制.结果表明,与连续淹水(Cw)处理相比,干燥处理不仅显著地提高了所有施肥处理土壤有机C的矿化速率,其幅度为78%～204%,而且也提高了各处理土壤微生物生物量C和N,其幅度分别为55%～77%和57%～72%;干燥后淹水处理土壤有机C矿化速率的提高幅度为74%～95%,呈先降低再升高的趋势.土壤N的矿化在干湿交替过程的干燥处理中降低34%～78%:干燥后淹水过程仅使NPK处理的升高21%,而CK和NPKOM处理分别降低5%和13%.在培养过程中土壤Eh值仅在-60～60 mV范围时,与土壤微生物生物量C之间有显著的负相关关系.在干湿交替的干燥过程,随土壤pH值的升高土壤微生物生物量C有增加的趋势,在淹水条件下土壤pH值则仅与NPKOM处理土壤微生物生物量C之间有明显的负相关关系.干湿交替条件下土壤 pH和 Eh 值、微生物群落组成和数量与有机质的矿化之间的相互作用关系复杂,三者间的作用机理需进一步研究.     

不同有机肥料对土壤生物活性有机质组分的动态影响

研究了红砂土中加入稻草秸秆和猪粪后土壤中微生物生物量碳、水溶性有机碳、溶解性酚等活性有机质组分的动态变化。有机肥处理一周后 ,微生物生物量碳、水溶性有机碳、溶解性酚等都达到最高值。随着培养时间的推移 ,不同处理的土壤中微生物生物量碳和水溶性有机碳含量都逐渐下降 ,而溶解性酚含量在整个培养过程中基本保持不变。相关分析表明 ,土壤中微生物生物量碳与水溶性有机碳和溶解性酚的含量都呈极显著正相关 ,而水溶性有机碳和溶解性酚的含量不相关。     

Mineralization of soil organic matter initiated by the application of an available substrate to the profiles of surface and buried podzolic soils

The priming effect (PE) initiated by the application of ¹⁴C-glucose was studied for copiotrophic microbial communities of organic horizons and for oligotrophic microbial communities of mineral soil horizons, as well as for mineral horizons of buried soils depleted in the input of fresh organic matter. The intensity of the PE depended on the reserves of C_org, the initial amount of the microbial biomass, and the enzymatic activity, which decreased from the organic to the mineral soil horizons. The ratio of the PE to the applied carbon was two times higher in the mineral horizons as compared with the organic horizons. This is explained by the predominance of K-strategists capable of decomposing difficultly available organic compounds in the mineral horizons, so that the turnover of the microbial biomass in the mineral horizons was more active than that in the organic horizons. The predominance of K-strategists was confirmed by the close correlation between the PE and the activity of the cellobiohydrolase enzyme decomposing cellulose (R = 0.96). In general, the absolute value of the PE was controlled by the soil organic matter content, whereas the specific PE was controlled by the functional features of the microorganisms. It was shown that the functional features of the soil microorganisms remained unchanged under the conditions of their preservation in the buried soil.     

干湿交替灌溉与施氮耦合对水稻根际环境的影响

为了探讨不同水氮耦合对水稻根际土壤环境及根系分泌有机酸总量的影响,以新稻20号为材料,进行盆栽试验,设置浅水层、轻度(-20 k Pa)和重度干湿交替灌溉(-40 k Pa)3种灌溉方式及不施氮肥,中氮(normal nitrogen,MN,240 kg/hm~2)和高氮(high nitrogen,HN,360 kg/hm~2)3种氮肥水平9个处理。结果表明:轻度干湿交替灌溉及中氮增加了土壤酶活性,提高土壤中微生物数量,根系分泌有机酸总量显著提高(P0.05);重度干湿交替灌溉及重施氮肥则降低土壤酶活性及微生物的数量,显著(P0.05)减少根系分泌有机酸的总量;相关分析表明:根际土壤酶活性及微生物数量与不同生育期根系分泌有机酸总量呈显著(P0.05)或极显著(P0.01)的正相关关系。土壤酶活性、微生物数量及有机酸总量的供氮效应为正效应,轻度干湿交替灌溉供水效应及耦合效应均为正效应,而重度干湿交替灌溉的控水及耦合效应则为负效应。研究可为通过水氮耦合调控水稻良好的根际环境提供依据。     

Microbial biomass dynamics and soil wettability as affected by the intensity and frequency of wetting and drying during straw decomposition

Water repellency is influenced by soil management and biological process. We carried out a 60‐day laboratory incubation experiment to evaluate the effects of straw amendment, together with the intensity and frequency of wetting and drying (W/D), on microbial processes and water repellency. One W/D cycle consisted of 1.5‐day wetting at −0.03 kPa from the soil core bottom and different drying lengths in a temperature‐controlled laboratory, resulting in different drying intensities. At a regular interval, soil respiration rate (SRR) on drying and wetting, soil microbial biomass C and N (SMB‐C and N), and soil water repellency (SWR) after the wetting were measured simultaneously. Rice straw amendment had a greater effect on SRR, but smaller influences on SMB and SMB‐C : N than W/D frequency and drying intensity. The first W/D caused the largest decrease in soil respiration and the soil respiration recovered partly in the subsequent W/D cycles. The increase in SMB and SMB‐C : N as well as metabolic quotient with W/D frequency and intensity suggested a shift of microbial community from bacterial dominance to fungal dominance. SWR was significantly related to SMB‐C (R²= 0.689, P < 0.001). However, this study was limited to these indirect measurements. Direct measurements of fungal biomass and microbial community are needed in the future. The results suggest that rice straw amendment in dry season may increase C sequestration due to reduced decomposition and stabilize soil structure due to the enhancement of microbial induced water repellency.     

Changes in soil microbial community composition in response to fertilization of paddy soils in subtropical China

Repeated fertilizer applications to cultivated soils may alter the composition and activities of microbial communities in terrestrial agro-ecosystems. In this study, we investigated the effects of different long term fertilization practices (control (CK), three levels of mineral fertilizer (N₁P₁K₁, N₂P₂K₂, and N₃P₃K₃), and organic manure (OM)) on soil environmental variables and microbial communities by using phospholipid fatty acid (PLFA) biomarkers analysis in subtropical China. Study showed that OM treatment led to increases in soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) contents, while the mineral fertilizer treatment led to increases in dissolved organic carbon (DOC) content. Changes in soil microbial communities (eg. bacteria, actinomycetes) were more noticeable in soils subjected to organic manure applications than in the control soils or those treated with mineral fertilizer applications. Fungal PLFA biomarkers responded differently from the other PLFA groups, the numerical values of fungal PLFA biomarkers were similar for all the OM and mineral fertilizer treatments. PCA analysis showed that the relative abundance of most PLFA biomarkers increased in response to OM treatment, and that increased application rates of the mineral fertilizer changed the composition of one small fungal PLFA biomarker group (namely 18:3ω6c and 16:1ω5c). Further, from the range of soil environmental factors that we examined, SOC, TN and TP were the key determinants affecting soil microbial community. Our results suggest that organic manure should be recommended to improve soil microbial activity in subtropical agricultural ecosystems, while increasing mineral fertilizer applications alone will not increase microbial growth in paddy soils.     

Fungal and bacterial recolonisation of acid and alkaline forest soils following artificial heat treatments

The direct response and the short-term recolonisation of soil by fungi and bacteria were studied after heat treatments of a humus soil with high carbon content and low pH, and a calcareous soil with lower carbon content and high pH. Heating was administered using a muffle furnace or an autoclave, with different temperatures and times of heat exposure, after which fresh soil (1%) was added as inoculum. Autoclaved soil showed more marked increases in bacterial growth during the recovery phase than oven-heated soil, and the bacterial growth response was more rapid in calcareous than in humus soil. Fungal growth recovered more rapid and reached values higher than the control in humus soil, while it remained low until the end of the study in calcareous soil. Respiration rate showed similar patterns in both soils. Fungal biomass (ergosterol and PLFA 18:2ω6,9) indicated that fungi benefited by autoclaving in humus soil, while they were disfavoured by this treatment in calcareous soil. The sum of bacterial PLFAs did not change due to heating, but some bacterial PLFAs (e.g. cy17:0) increased in both soils. We propose that the community assembly of the microbial communities after heating were mainly driven by pH, in that the high pH soil selected primarily for bacteria and the low pH soil for fungi.     

The structure of microbial communities in redoximorphic microsites of Gleysol

Microbial communities were studied in redoximorphic microsites of highly heterogeneous Gleysol at a mm scale using 16S and 18S amplicon sequencing to demonstrate if the composition of soil microbes reflects the differences in ferric and ferrous micro-sites. In both explored gley horizons with redoximorphic features (Bg2 and Cg), ferric mottles were significantly enriched with total P and Fe and depleted of O, Si, Al, K and Ca compared with the adjacent ferrous groundmass (SEM–EDS). Ferric mottles were determined as Fe oxide coatings and hypocoatings. In Bg2, both prokaryotic and micro-eukaryotic communities differed significantly between mottles and groundmass in composition of operational taxonomic units (OTUs) and in proportions of phyla, reflecting heterogeneities in the soil properties there. Mottles in Bg2 were characterized by increased proportion of Proteobacteria, decreased proportion of Acidobacteriota among prokaryotes and by dominance of a single proteobacterial OTU from Anaplasmataceae compared to all other samples. The composition of micro-eukaryotes showed an opposite trend, as micro-eukaryotes of Bg2 groundmass were unique among the other horizons, while micro-eukaryotes of Bg2 mottles had similar composition to neighbouring horizons. Microbial communities of adjacent samples were not more similar to each other than communities of randomly selected ones in Bg2 horizon. That suggests that at mm scale, the sample distance does not represent the driving factor of microbial community composition and that the adjacent samples differ rather due to physicochemical factors. The spatial organization of microbial communities revealed in Bg2 has not reappeared in similarly organized Cg horizon, probably due to other overriding factors. The differences revealed between Bg2 and Cg horizons, including granulometric composition, content of crystalline Fe, exchangeable Al, and organic carbon, as well as exposition to groundwater, were discussed as possible reasons of the distinct organization in Cg. The similarity of pro−/eukaryotic communities of adjacent and non-adjacent couples suggests no distance decay pattern at a mm scale. The agreement between patchiness in soil properties and microbial communities was revealed for the first time and confirms the importance of microscale patterns in soil.     

不同施肥处理对长期不施肥区稻田土壤微生物生态特性的影响

采用室内恒温培养方法,研究了不同施肥处理对水稻长期肥料试验中不施肥区（CK）和全肥区（NPK）土壤酶活性及微生物群落结构的变化。结果表明,施肥处理（单施化肥、施猪粪和施秸杆）可以显著提高土壤的微生物量碳以及脲酶、酸性磷酸酶的活性,施用有机肥的效果明显大于单施化肥; 有机肥在无肥区（CK）的施用效果与在全肥区（NPK）的效果接近。PLFA分析表明,施肥使无肥区（CK）土壤微生物群落结构发生了显著的变化,施用有机肥显著增加了土壤微生物群落结构的多样性。与不施肥和单施化肥相比,施有机肥主要增加了细菌和真菌的特征脂肪酸如不饱和脂肪酸、环状脂肪酸cy19∶0等的相对含量,而降低了放线菌标记性脂肪酸10Me18∶0的相对含量。     

Composition of the microbial communities in the mineral soil under different types of natural forest

Phospholipid fatty acid (PLFA) patterns were used to describe the composition of the soil microbial communities under 12 natural forest stands including oak and beech, spruce-fir-beech, floodplain and pine forests. In addition to the quantification of total PLFAs, soil microbial biomass was measured by substrate-induced respiration and chloroform fumigation-extraction. The forest stands possess natural vegetation, representing an expression of the natural site factors, and we hypothesised that each forest type would support a specific soil microbial community. Principal component analysis (PCA) of PLFA patterns revealed that the microbial communities were compositionally distinct in the floodplain and pine forests, comprising azonal forest types, and were more similar in the oak, beech and spruce-fir-beech forests, which represent the zonal vegetation types of the region. In the nutrient-rich floodplain forests, the fatty acids 16:1ω5, 17:0cy, a15:0 and a17:0 were the most prevalent and soil pH seemed to be responsible for the discrimination of the soil microbial communities against those of the zonal forest types. The pine forest soils were set apart from the other forest soils by a higher abundance of PLFA 18:2ω6,9, which is typical of fungi and may also indicate ectomycorrhizal fungi associated with pine trees, and high amounts of PLFA 10Me18:0, which is common in actinomycetes. These findings suggest that the occurrence of azonal forest types at sites with specific soil conditions is accompanied by the development of specific soil microbial communities. The study provides information on the microbial communities in undisturbed forest soils which may facilitate interpretation of data derived from managed or even damaged or degraded forests.     

Distribution of Microorganisms,Biomass ATP,and Enzyme Activities in Organic and Mineral Particles of a Long‐Term Wastewater Irrigated Soil

The aim of the study was to elucidate the spatial distribution of soil microorganisms and enyzme activities in a long‐term wastewater treated soil. Soil was sampled from a plough layer of the Ah horizon of a sandy Haplic Luvisol which was either (1) irrigated with municipal wastewater for almost 100 years, or (2) no more irrigated since 20 years, or (3) never received wastewater. The samples were fractionated by wet sieving to obtain seven size fractions of organic and mineral soil particles, and a separate silt+clay fraction. The individual soil samples contained between 1.2% (never irrigated) and 4.1% (long‐term irrigated) organic particles by weight, but these particles harboured up to 47.8% of the total soil carbon and 41.7% of nitrogen, and thus represented an important storage of energy and nutrient for microorganisms. In total, however, the highest C and N amounts were accumulated in the silt+clay fraction, whereas coarser mineral particles which dominanted by weight in the Haplic Luvisol were low in C and N. The highest numbers of bacteria, actinomycetes and fungi per gram of the individual soil fractions were found in organic particles of the long‐term irrigated soil. Less nutrient‐dependent oligotrophic bacteria were for the most part associated with the silt+clay fraction, irrespective of the soil treatment with wastewater. Similar to microbial counts, also the ATP content, as a measure of active microbial biomass, and the activities of β‐glucosidase, β‐acetylglucosaminidase, and proteinase were higher in the long‐term irrigated soil than in that which was never irrigated. In most cases slightly enhanced values of microbiological and biochemical parameters were still detectable 20 years after the wastewater irrigation was terminated. The values of the individual parameters decreased in all soil samples under testing in general gradually with decrease in size of the organic soil particles. In conclusion, the coarse soil organic particles > 5 mm and the silt+clay fraction < 0.05 mm represent the sites with the highest microbial inhabitance, ATP contents and enzyme activities in the Ah horizon of an Haplic Luvisol. Long‐term wastewater irrigation resulted in an increase of microbial counts, total biomass and soil enzyme activities.     

长期绿肥和秸秆还田替代部分化肥提升红壤性水稻土酸解有机氮组分比例及供氮能力

[目的]氮是限制土壤生产力的重要营养元素.研究长期施用绿肥和秸秆下,红壤性稻田土壤氮组分含量的变化及其与氮素供应容量和强度的关系,深化理解有机肥提高土壤肥力的理论.[方法]长期定位试验位于江西农业大学科技园内,始于1981年,供试土壤为第四纪红色粘土发育的潴育性水稻土.设置4个处理:无肥(CK);单施化肥(F);翻压紫...     

长期不同施肥模式对大麦-双季稻田根际土壤有机氮组分的影响

根际土壤有机氮组分在土壤养分和作物氮素营养中具有重要作用。本研究依托长期（37年）定位施肥试验田,设置4个施肥处理：不施肥对照（CK）、单独施用化肥（CF）、秸秆还田+化肥（RF）和30%有机肥+70%化肥（OM）,于晚稻成熟期测定大麦-双季稻田根际土壤基础理化性质、微生物量氮和有机氮组分（氨基酸态氮、氨基糖态氮、酸解氨态氮、酸解未知态氮、非酸解性氮）含量。研究表明：相对CK处理,RF和OM处理显著增加了稻田根际土壤有机碳、全氮、铵态氮和硝态氮的含量。RF和OM处理土壤微生物量氮含量分别比CK处理增加了19.8%和30.7%。酸解性氮作为根际土壤全氮的主体部分,占全氮的59.6%~72.1%;各处理根际土壤酸解性氮含量大小顺序表现为OM>RF>CF>CK。各施肥处理中,酸解有机氮中的氨基糖态氮、氨基酸态氮和酸解未知态氮含量均以OM处理最大,分别比CK处理增加139.3%、47.9%和110.0%;酸解氨态氮以RF处理最大,比CK处理增加69.9%。土壤有机碳、全氮、铵态氮、硝态氮与土壤氨基酸态氮、氨基糖态氮、酸解未知态氮以及微生物量氮均呈极显著（p<0.01）正相关。因此,秸秆、有机肥配施化肥均能有效提高大麦-双季稻田根际土壤的供氮能力,是改善稻田土壤肥力的有效手段。