Incorporation of heavy metals by the mud snail,Cipangopaludina chinensis malleata Reeve,in submerged paddy soil treated with composted sewage sludge

Summary The biomass of newborn snails was higher in paddy soil without rice plants than in the soil with rice plants. There was an inverse correlation between shell width and concentratins of Zn and Cu in snail flesh. The Zn and Cu concentrations in snail flesh were extremely high compared with those in the paddy soil surrounding the snails, possibly because snails ingest sludge, one of the main components of the composts. These results suggest that this type of snail may be used to eliminate Zn and Cu from paddy soil when composted sewage sludge has been applied.     

Rice yield nutrient uptake as affected by cyanobacteria soil amendments—a pot experiment

Rice production and cyanobacterial N in acid soil can be improved by liming. There is evidence that the organic amendments can increase the soil pH. The aim of this study was to find appropriate combination of soil amendments and cyanobacteria capable for enhancing nutrient uptake and improving rice yield in acidic paddy soil. Three soil amendments (rice straw, sewage‐sludge composts, NPK) with and without inoculation of cyanobacteria were studied for rice plants (Oryza sativa L.) in a pot experiment. The sludge compost had significantly reduced soil acidity from 5.44 to 6.67. The plant N and K uptake increased significantly with sludge and cyanobacteria application. The yield components increased significantly with sludge, but decreased thereafter, an exception was the number of panicles, with straw compost. These characters were also significantly affected by inoculation with cyanobacteria except 100‐grain weight, filled‐grain percentage, and harvest index. The combination of sludge compost and cyanobacteria improved the yield components and consequently grain yield (138 g pot^–1) compared with sludge treatment only (132 g pot^–1). The amount of cyanobacterial N absorbed (N‐difference method) by rice plant under sludge compost was higher than that of soils amended with either rice straw or NPK treatments. Therefore, the addition of sewage sludge to acid paddy soil not only amended the soil properties but also activated the cyanobacteria and consequently improved rice plant nutrition and grain yield.     

Changes in natural 15N abundance in paddy soils under different,long-term soil management regimes in the Tohoku region of Japan

Abstract

Long-term temporal changes in natural ¹⁵N abundance (δ¹⁵N value) in paddy soils from long-term field experiments with livestock manure and rice straw composts, and in the composts used for the experiments, were investigated. These field experiments using livestock manure and rice straw composts had been conducted since 1973 and 1968, respectively. In both experiments, control plots to which no compost had been applied were also maintained. The δ¹⁵N values of livestock manure compost reflected the composting method. Composting period had no significant effect on the δ¹⁵N value of rice straw compost. The δ¹⁵N values increased in soils to which livestock manure compost was successively applied, and tended to decrease in soils without compost. In soils to which rice straw compost was successively applied, the δ¹⁵N values of the soils remained constant. Conversely, δ¹⁵N values in soils without rice straw compost decreased. The downward trend in δ¹⁵N values observed in soils to which compost and chemical N fertilizer were not applied could be attributed to the natural input of N, which had a lower δ¹⁵N value than the soils. Thus, the transition of the δ¹⁵N values in soils observed in long-term paddy field experiments indicated that the δ¹⁵N values of paddy soils could be affected by natural N input in addition to extraneous N that was applied in the form of chemical N fertilizers and organic materials.     

氮肥对稻田土壤反硝化细菌群落结构和丰度的影响

以氮肥田间定位试验为研究对象,利用PCR-DGGE(聚合酶链反应变性梯度凝胶电泳)和荧光定量PCR(real-time PCR)技术,通过对反硝化细菌nirS基因的检测,分析了定位试验第2年稻田反硝化细菌群落结构和丰度的变化。DGGE图谱及依据其条带位置和亮度数字化数值进行的主成分分析(PCA)结果均显示:在氮肥定位试验第2年,与不施肥对照(CK)比较,在水稻各个生育期(分蘖期、齐穗期和成熟期)内,施用氮肥[150kg(N)·hm-2]的稻田根层土或表土中的反硝化细菌群落结构均无明显变化;且稻田根层土或表土中的反硝化细菌群落结构在水稻各个生育期间也均无明显差异。荧光定量PCR结果显示,在水稻生长发育过程中,施用氮肥的稻田根层土或表土中的反硝化细菌nirS基因拷贝数始终显著(P<0.05)高于其对应的不施肥对照。此外,无论施用氮肥与否,根层土中的反硝化细菌nirS基因拷贝数在水稻成熟期时都会显著(P<0.05)降低;但表土中的nirS基因拷贝数在水稻各生育期间无明显变化;且水稻成熟期时施用氮肥和不施肥的稻田表土中nirS基因拷贝数都显著(P<0.05)高于根层土。同时,与对照比较施用氮肥可促进水稻增产44%。研究表明,短期定位试验中施用氮肥能够显著提高稻田土壤反硝化细菌的丰度,但对其群落结构没有明显影响。     

Stable carbon isotope ratios of water-extractable organic carbon affected by application of rice straw and rice straw compost during a long-term rice experiment in Yamagata,Japan

ABSTRACT

Hot-water- and water-extractable organic matter were obtained from soil samples collected from a rice paddy 31 years after the start of a long-term rice experiment in Yamagata, Japan. Specifically, hot-water-extractable organic carbon and nitrogen (HWEOC and HWEON) were obtained by extraction at 80°C for 16 h, and water-extractable organic carbon and nitrogen (WEOC and WEON) were obtained by extraction at room temperature. The soil samples were collected from surface (0–15 cm) and subsurface (15–25 cm) layers of five plots that had been treated with inorganic fertilizers alone or with inorganic fertilizers plus organic matter, as follows: PK, NPK, NPK plus rice straw (RS), NPK plus rice straw compost (CM1), and NPK plus a high dose of rice straw compost (CM3). The soil/water ratio was 1:10 for both extraction temperatures. We found that the organic carbon and total nitrogen contents of the bulk soils were highly correlated with the extractable organic carbon and nitrogen contents regardless of extraction temperature, and the extractable organic carbon and nitrogen contents were higher in the plots that were treated with inorganic fertilizers plus organic matter than in the PK and NPK plots. The HWEOC and WEOC δ¹³C values ranged from ?28.2% to ?26.4% and were similar to the values for the applied rice straw and rice straw compost. There were no correlations between the HWEOC or WEOC δ¹³C values and the amounts of HWEOC or WEOC. The δ¹³C values of the bulk soils ranged from ?25.7% to ?23.2% and were lower for the RS and CM plots than for the PK and NPK plots. These results indicate that HWEOC and WEOC originated mainly from rice plants and the applied organic matter rather than from the indigenous soil organic matter. The significant positive correlations between the amounts of HWEOC and HWEON and the amount of available nitrogen (P < 0.001) imply that extractable organic matter can be used as an index for soil fertility in this long-term experiment. We concluded that the applied organic matter decomposed more rapidly than the indigenous soil organic matter and affected WEOC δ¹³C values and amounts.     

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.     

紫茎泽兰和黄顶菊入侵对土壤微生物群落结构和旱稻生长的影响

为比较入侵植物与本地植物对土壤微生态影响的差异, 探索外来植物入侵的土壤微生物学机制, 本研究通过同质园试验, 比较分析了2种入侵菊科植物(紫茎泽兰、黄顶菊)和2种本地植物(马唐、猪毛菜)对土壤肥力和微生物群落的影响, 并通过盆栽反馈试验验证入侵植物改变后的土壤微生物对本地植物旱稻生长的反馈作用。同质园试验结果表明: 2种入侵植物和2种本地植物分别对土壤微生态产生了不同的影响, 尤其是紫茎泽兰显著提高了土壤有效氮、有效磷和有效钾含量,紫茎泽兰根际土壤中有效氮含量为39.80 mg·kg^-1,有效磷含量为48.52 mg·kg^-1。磷脂脂肪酸指纹图谱结果表明, 2种入侵植物与2种本地植物相比, 较显著增加了土壤中放线菌数量, 而紫茎泽兰比其他3种植物显著增加了细菌和真菌数量。盆栽结果表明: 黄顶菊生长过的土壤灭菌后比灭菌前旱稻株高增加113%, 紫茎泽兰也使旱稻的株高增加17%。由以上结果可知, 紫茎泽兰和黄顶菊可能通过改变入侵地土壤的微环境, 形成利于其自身生长扩散的微生态环境从而实现其成功入侵。     

千金子与异型莎草对直播水稻产量的影响及其生态经济阈值研究

千金子和异型莎草均是直播稻田的恶性杂草,危害水稻的生长发育,对水稻生产造成严重威胁。为明确千金子和异型莎草对直播稻产量的影响及其生态经济阈值,采用添加系列试验法和模型拟合法研究不同密度千金子和异型莎草组合和与水稻不同共生时间下水稻产量性状的变化规律。结果表明,随着千金子和异型莎草组合密度增加以及与水稻共生时间延长,水稻的有效穗数、每穗实粒数、千粒重和产量均逐渐下降。当千金子+异型莎草密度增加至8株·m~(-2)+8株·m~(-2),水稻产量仅2 236.37kg·hm~(-2),与空白对照相比产量损失率为71.14%;在千金子4.67株·m~(-2)+异型莎草3.50株·m~(-2)的平均密度下,二者与水稻在整个生育期共生时,水稻产量为5 138.33 kg·hm~(-2),与空白对照相比产量损失率为33.37%。低密度、短时间共生的两杂草组合对水稻产量无显著影响。但从密度梯度看,在两种杂草与水稻整个生育期共生条件下,杂草复合密度达到4.14株·m~(-2)时,则必须对其进行防除;从共生时间的尺度看,在试验设置密度条件下,必须在水稻种植后的16.7 d进行杂草防除,否则将对水稻产量和经济效益造成显著影响。在对复合杂草生态经济阈值分析的基础上进行杂草防除,可避免除草剂盲目使用,对减少除草剂使用次数,降低除草剂用量、节约除草成本和保护农田生态环境具有指导作用。     

不同母质土壤-水稻系统Cd吸收累积特征及差异

通过选取土壤有效态镉(Cd)含量相近、母质不同的水稻土河沙泥(河流冲积物发育)和紫泥田(紫色砂页岩母质发育),添加不同浓度的外源Cd(0,0.5,1,2,5mg/kg)模拟Cd污染稻田土壤进行盆栽试验,研究不同母质稻田土壤Cd胁迫条件下水稻不同生育期对Cd吸收累积的差异,并推算出土壤Cd环境安全临界值。结果表明,水稻生育期2种土壤有效态Cd含量均在分蘖期最高,河沙泥有效态Cd含量平均为0.47mg/kg,紫泥田平均为0.36mg/kg,同一外源Cd水平下,河沙泥土壤有效态Cd含量高于紫泥田。对河沙泥而言,随着外源Cd浓度的增加,水稻总生物量呈现先增加后下降的趋势,当外源Cd浓度为1mg/kg时达到最大生物量,为47.11g/pot;而紫泥田水稻生物量呈现逐渐增加的趋势,但各处理间差异不显著(P0.05)。2种土壤中水稻糙米、谷壳、茎叶、根Cd含量均随外源Cd浓度的增加而增加,整体分布特征为根茎叶谷壳糙米,且河沙泥高于紫泥田;河沙泥水稻平均Cd累积量为51.71μg/pot,紫泥田平均Cd累积量为42.56μg/pot,2种土壤成熟期水稻Cd累积量对比分蘖期分别增加1.45,1.07倍。回归分析表明,河沙泥和紫泥田稻米Cd超标的土壤Cd安全临界值分别为2.03,3.14mg/kg。水稻对Cd的吸收累积特征及土壤Cd安全临界值因土壤母质不同而存在显著差异。     

Paddy System with a Hybrid Rice Enhances Cyanobacteria Nostoc and Increases N2 Fixation

Biological nitrogen(N) fixation(BNF) plays a significant role in maintaining soil fertility in paddy field ecosystems. Rice variety influences BNF, but how different rice varieties regulate BNF and associated diazotroph communities has not been quantified. Airtight,field-based ~(15)N_2-labelling growth chamber experiments were used to assess the BNF capacity of different rice varieties. In addition,both the 16 S rRNA and nifH genes were sequenced to assess the influence of different rice varieties on bacterial and diazotrophic communities in paddy soils. After subjecting a rice-soil system to 74 d of continuous airtight, field-based ~(15)N_2 labelling in pots in a growth chamber, the amounts of fixed N were 22.3 and 38.9 kg ha~(-1) in inbred japonica(W23) and hybrid indica(IIY) rice cultivars planted in the rice-soil systems, respectively, and only 1%–2.5% of the fixed N was allocated to the rice plants and weeds. A greater abundance of diazotrophs was found in the surface soil(0–1 cm) under IIY than under W23. Sequencing of the 16 S rRNA gene showed significantly greater abundances of the cyanobacterial genera Nostoc, Anabaena, and Cylindrospermum under IIY than under W23.Sequencing of the nifH gene also showed a significantly greater abundance of Nostoc under IIY than under W23. These results indicate that the hybrid rice cultivar(IIY) promoted BNF to a greater extent than the inbred rice cultivar(W23) and that the increase in BNF might have been due to the enhanced heterocystous cyanobacteria Nostoc.     

Adsorption and Desorption of Cry1Ab Proteins on Differently Textured Paddy Soils

In recent years, selected cry genes from Bacillus thuringiensis (Bt) encoding the production of Cry proteins (Bt toxins) have been engineered into crop plants (Bt-crops). Through the cultivation of Bt crops and the application of Bt pesticides, Cry proteins could be introduced into arable soils. The interaction between the proteins and soils was analyzed in this study to investigate the affinity of Cry proteins in paddy soil ecosystems. Four Paddy soils were selected to represent different soil textures. Cry proteins were spiked in soils, and the amount of protein adsorbed was measured over 24 h. Desorption of Cry1Ab proteins from paddy soils was performed by washing with sterile Milli-Q water (H₂O_MQ), and subsequently extracted with an extraction buffer. The paddy soils had a strong affinity for Cry1Ab proteins. Most of the Cry1Ab proteins added (> 98%) were rapidly adsorbed on the paddy soils tested. More Cry1Ab proteins were adsorbed on non-sterile soils than on sterile soils. Less than 2% of the adsorbed Cry1Ab proteins were desorbed using H₂O_MQ, while a considerable proportion of the adsorbed proteins could be desorbed with the buffer, ranging from 20% to 40%. The amount of proteins desorbed increased with the increases in the initial amount of Cry1Ab proteins added to the paddy soils. The concentration of Cry1Ab proteins desorbed from the paddy soils was higher for sterile soils than non-sterile ones. Our results indicate that Bt toxins released via the cultivation of Bt crops, the application of Bt pesticides can be adsorbed on paddy soils, and soil texture could impose an impact on the adsorption capability.     

Diversity of methanogenic archaeal communities in Japanese paddy field ecosystem, estimated by denaturing gradient gel electrophoresis

Diversity of methanogenic archaeal communities in Japanese paddy field ecosystem was evaluated by the denaturing gradient gel electrophoresis (DGGE) after PCR amplification of the 16S rRNA genes (16S rDNAs), sequencing analysis and data evaluation by principal component analysis. Data were obtained from samples collected from the plowed soil layer, rice roots, rice straws incorporated in soil, plant residues (mixture of weeds, rice litters, rice roots, and rice stubbles) in soil, and composing rice straw. The number of bands of DGGE profiles ranged from 12 to 26 with the highest numbers in rice roots and rice straws incorporated in soil. However, the diversity indices based on both the numbers and intensity of bands indicated that the community of the plowed soil layer was the most diverse, even, and stable. Sequencing of the main DGGE bands showed the presence of Methanomicrobiales, Methanosarcinales, Methanobacteriaceae, and Methanocellales. The plowed soil layer included all phylogenetic groups of the methanogenic archaea of the other studied habitats, with prevalence of the members of Methanomicrobiales and Methanocellales. The phylogenetic diversity was compared with that of paddy soils collected in Italy, China, and the Philippines and that of 12 anaerobic environments (fen, waste, coast, permafrost, natural gas field, bovine rumen, riparian soil, termite, ciliate endosymboints, lake sediment, landfill, and seep rumen). The phylogenetic diversity was more similar among paddy soils than with the other anaerobic environments. Probably, the methanogenic archaeal communities of the paddy field soils were characterized by indigenous members and some of the members of the community of the plowed soil layer colonized rice roots, rice straws, and plant residues.     

旱改水对水稻幼苗生长的影响及秸秆的改良作用

本研究以江汉平原旱改水为研究背景,采用土壤盆栽试验和室内淹水培养相结合的方法,以多年水稻土为对照,研究了多年棉田土旱改水及添加秸秆(9 g·kg-1)对水稻幼苗生长和矿质元素吸收的影响以及土壤氧化还原电位和有效态铁、锰、铜、锌含量变化,为旱改水水稻的种植提供参考。结果表明,棉田土旱改水后,水稻幼苗生长缓慢并出现失绿黄化症状,其地上部干重和叶绿素含量仅分别约为水稻土处理的30%和20%。旱改水处理水稻植株Fe含量显著低于、而Cu和Zn含量则显著高于水稻土处理。棉田土旱改水土壤氧化还原电位(Eh)显著高于水稻土;淹水处理10 d,土壤DTPA-Fe含量仅为水稻土的7%左右,而DTPA-Cu和DTPA-Zn含量则分别是水稻土的1.4~2.5倍和1.6~1.8倍。随着淹水时间的延长,棉田土旱改水土壤有效态铁含量逐渐增加,有效态锰、铜和锌含量呈先升高后降低趋势;到淹水处理的第28 d,棉田土旱改水土壤有效态铁、锰、铜和锌含量与水稻土之间的差异逐渐缩小。Fe不足及Cu过量可能是导致旱改水水稻幼苗生长缓慢、失绿黄化的主要原因。旱改水条件下添加秸秆可以降低土壤的Eh值,提高土壤DTPA-Fe含量及降低土壤DTPA-Cu和DTPA-Zn含量,显著提高旱改水初期水稻幼苗叶绿素含量,但对水稻生物量无显著影响。添加秸秆并不能完全消除旱改水对水稻幼苗生长的抑制作用。     

Dynamics of microbial biomass nitrogen as influenced by organic matter application in paddy fields

The effects of annual application of rice straw or cow manure compost for 17–20 y on the dynamics of fertilizer N and soil organic N in Gley paddy fields were investigated by using the ¹⁵N tracer technique during the rice cropping season. The chloroform fumigation-extraction method was evaluated to determine the properties of soil microbial biomass under submerged field conditions at the tillering stage before mid-summer drainage, with special reference to the fate of applied NH₄ ⁺-¹⁵N.

The transfer ratios from applied NH₄ ⁺-¹⁵N to immobilized N in soil and to uptake N by rice during given periods varied with the rice growth stages and were affected by organic matter application. The accumulated amounts of netmineralized soil organic N (net-M_j ), immobilized N (I_j ), and denitrified N (D_j ) during the cropping season were estimated to be 14.0–22.5, 6.3–11.2, and 3.4–5.3 g N m^-2, respectively. Values of net-M_j and I_j were larger in the following order: cow manure compost plot > rice straw plot > plot without organic matter application, and their larger increase by the application of cow manure compost contributed to a decrease of the D_j values, as compared with rice straw application.

Values of E _N extra extractable soil total N after fumigation, increased following organic matter application, ranging from 2.1 to 5.4 g N m^-2. Small residual ratios of applied ¹⁵N in the fraction E _N at the end of the given period indicated that re-mineralization of newly-assimilated ¹⁵N through the easily decomposable fraction of microbial biomass had almost ended. Thus, the applicability to paddy field soils of the chloroform fumigation-extraction method was confirmed.     

Arsenic phytotoxicity and accumulation in rice seedlings grown in arsenic‐contaminated soils as influenced by the characteristics of organic matter amendments and soils

Organic matter (OM) application into soils is a common agricultural practice. Previous studies have shown that in arsenic (As)‐contaminated paddy soils, OM has the potential to alter the behavior of As and affects the growth and As accumulation of rice plants. In this study, pot experiments were conducted to investigate the differences in the amounts of As released into soil solutions, its toxicity, and accumulation in rice seedlings caused by application of three different OM amendments [soybean meal (SB), sugarcane dreg compost (SC), and cattle‐dung compost (CD)]. These OM amendments were each applied to three As‐contaminated soils, Guandu (Gd), Pinchen (Pc), and Chengchung (Cf), which have different characteristics. The results indicate that after addition of two easily decomposable OMs (SB and SC), the As toxicity and concentrations increased in rice plants, especially in As‐spiked Cf soils which had low As retention capacity. This was the result of elevated As concentration in soil solutions due to a decrease in soil redox potential and competition between dissolved organic carbon (DOC) and As for sorption sites, as well as the formation of As–DOC complexes. However, there were no significant effects on plant growth and As accumulation in rice seedlings after treatments with CD (not easily decomposable OM). Another important finding was that the amount of iron plaque on the surface of rice roots increased with OM amendments in the Gd soils rich in iron oxides and hydroxides, thus reducing the As uptake by rice plants. These results suggest that the characteristics of OM and soils should be considered when OM amendments are applied to As‐contaminated soils.     

Evolution of dinitrogen and nitrous oxide from the soil to the atmosphere through rice plants

Summary It is commonly assumed that a large fraction of fertilizer N applied to a rice (Oryza sativa L.) field is lost from the soil-water-plant system as a result of denitrification. Direct evidence to support this view, however, is limited. The few direct field, denitrification gas measurements that have been made indicate less N loss than that determined by ¹⁵N balance after the growing season. One explanation for this discrepancy is that the N₂ produced during denitrification in a flooded soil remains trapped in the soil system and does not evolve to the atmosphere until the soil dries or is otherwise disturbed. It seems likely, however, that N₂ produced in the soil uses the rice plants as a conduit to the atmosphere, as does methane. Methane evolution from a rice field has been demonstrated to occur almost exclusively through the rice plants themselves. A field study in Cuttack, India, and a greenhouse study in Fort Collins, Colorado, were conducted to determine the influence of rice plants on the transport of N₂ and N₂O from the soil to the atmosphere. In these studies, plots were fertilized with 75 or 99 atom % ¹⁵N-urea and ¹⁵N techniques were used to monitor the daily evolution of N₂ and N₂O. At weekly intervals the amount of N₂+N₂O trapped in the flooded soil and the total-N and fertilized-N content of the soil and plants were measured in the greenhouse plots. Direct measurement of N₂+N₂O emission from field and greenhouse plots indicated that the young rice plant facilitates the efflux of N₂ and N₂O from the soil to the atmosphere. Little N gas was trapped in the rice-planted soils while large quantities were trapped in the unplanted soils. N losses due to denitrification accounted for only up to 10% of the loss of added N in planted soils in the field or greenhouse. The major losses of fertilizer N from both the field and greenhouse soils appear to have been the result of NH₃ volatilization.     

Long-term submergence of non-methanogenic oxic upland field soils helps to develop the methanogenic archaeal community as revealed by pot and field experiments

The community structure of methanogenic archaea is relatively stable,i.e.,it is sustained at a high abundance with minimal changes in composition,in paddy field soils irrespective of submergence and drainage.In contrast,the abundance in non-methanogenic oxic soils is much lower than that in paddy field soils.This study aimed to describe methanogenic archaeal community development following the long-term submergence of non-methanogenic oxic upland field soils in pot and field experiments.In the pot experiment,a soil sample obtained from an upland field was incubated under submerged conditions for 275 d.Soil samples periodically collected were subjected to culture-dependent most probable number(MPN)enumeration,polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE)analysis of archaeal 16 S r RNA gene,and quantitative PCR analysis of the methyl-coenzyme M reductase alpha subunit gene(mcr A)of methanogenic archaea.The abundance of methanogenic archaea increased from 102 to 103 cells g-1 dry soil and 104 to 107 copies of mcr A gene g-1 dry soil after submergence.Although no methanogenic archaeon was detected prior to incubation by the DGGE analysis,members from Methanocellales,Methanosarcinaceae,and Methanosaetaceae proliferated in the soils,and the community structure was relatively stable once established.In the field experiment,the number of viable methanogenic archaea in a rice paddy field converted from meadow(reclaimed paddy field)was monitored by MPN enumeration over five annual cycles of field operations.Viability was also determined simultaneously in a paddy field where the plow layer soil from a farmer’s paddy field was dressed onto the meadow(dressed paddy field)and an upland crop field converted from the meadow(reclaimed upland field).The number of viable methanogenic archaea in the reclaimed paddy field was below the detection limit before the first cultivation of rice and in the reclaimed upland field.Then,the number gradually increased over five years and finally reached 103–104 cells g-1 dry soil,which was comparable to that in the dressed paddy field.These findings showed that the low abundance of autochthonous methanogenic archaea in the non-methanogenic oxic upland field soils steadily proliferated,and the community structure was developed following repeated and long-term submergence.These results suggest that habitats suitable for methanogenic archaea were established in soil following repeated and long-term submergence.     

关于集约农作制下的土壤结构问题——Ⅰ.有机物料及其利用方式对土壤结构的影响

对稻草、紫云英有机物料不同用量和混施、单施或沤制后施用等不同施用方式对土壤结构的影响进行了四年模拟试验。四年培育期中的水分条件和其他物理条件均控制一致。测定表明,有机物料能明显改善土壤的结构性和孔隙性,降低原状土核的破裂系数。有机质、重组有机质、无定形氧化铁、氧化铁的活度与团聚体的稳定性呈正相关;而与原状土的破裂系数呈负相关。看来,无定形氧化铁的含量可以作为高产水稻土具有良好结构性的一个间接指标。施加有机物料的土壤,当脱水时其中大孔隙显著增多,这对粘质水稻土回旱种旱作十分有利。稻草直接施入土中的改土效果优于沤制后施入土中,且不亚于高用量稻草和紫云英混施的效果。可见,如绿肥施用量减少时,只要保持一定量的稻草回田,亦能改善土壤的结构。     

Alleviation of noxious effects of cattle ranch composts on wheat seed germination by inoculation with Azospirillum spp.

Two commonly-used composts from dairy cow manure that are used to improve poor structure and fertility of desert soils have inhibitory effects on wheat seed germination, probably as a result of their high levels of humic acids. Inoculation of wheat seeds with two species of the plant growth-promoting bacteria Azospirillum brasilense Cd and A. lipoferum JA4 (separately) prior to sowing in these amended soils improved germination, similar to the natural level of germination of seeds in desert soil without compost amendment. Both compost amendments increased height of wheat seedlings in the range of 20–25%, increased shoot dry weight by 15–19%, but severely decreased (51–54% less) root dry weight. Inoculation of wheat seeds with A. brasilense Cd, but not with A. lipoferum JA4, significantly increased plant growth parameters (height, shoot and root dry weight) over control plants grown in soil-compost mixtures. This bacterial species could survive for a period of 20 days in compost humic acid solution, could increase its population when the humic acids served as the sole carbon source, and may change the composition of humic acids in which it grows. We suggest that inoculation with A. brasilense may alleviate noxious effects on germinating seeds caused by compost application by possibly transforming the composition of humic acids in the compost.     

苏南典型区农田土壤硒-镉拮抗作用研究

以苏南典型区2027套稻米-土壤样品的Se、Cd含量及其相关的元素地球化学调查数据为基础,通过元素相关性统计分析及生物富集系数(BCF)等分布特征研究,本文探讨了农田土壤中Se与Cd的拮抗作用及其控制因素。结果表明：1)土壤中Se和Cd分布共消长特征明显,两者之间具有显著正相关性、相关系数R最高可达0.87；2)有关岩石、陶瓷原料、河泥等均可成为农田富集Se、Cd的物质来源,且多为富Cd强于富Se,只有源于富硒岩石的富硒土壤可排除Cd污染干扰、其开发利用价值最高；3)稻米Se与Cd的生物富集系数多介于0.1～0.8之间,土壤偏碱性有利于稻籽吸收Se、偏酸性则有助于稻籽吸收Cd,受土壤Se、Cd同富集之影响,富硒米与镉超标大米可能同时出现；4)土壤富Se抑制稻米Cd吸收是有条件的,当土壤Se大于0.4mg/kg、总有机碳大于1.5%时,稻米Cd与土壤Se、Cd生物富集系数与土壤Se之间均存在显著负相关性,相关系数R分别为-0.74、-0.56；5)pH与Cd生物富集系数、TOC与Se生物富集系数之间也有显著负相关性,其相关系数R分别为-0.79、-0.65。