长江中游水稻土潜育作用的特点

The gleyization of representative paddy soils in the middle reaches of the Yangtze River was characterized, taking oxidation-reduction potential(Eh), the amount of active reducing substances and the forms of iron and manganese as the parameters. The Eh value was linearly related with the logarithm of the amount of active reducing substances, which was contributed by ferrous iron by 83% on an average. The degree of gleyization of different horizons was graded as ungleyed, slightly gleyed, mildly gleyed and gleyed. The Eh of the four grades was > 500, 300-500, 100-300 and < 100 mV, respectively, and the corresponding amount of active reducing substances was < 1, 1-7, 7-30 and > 30 mmol_c kg^-1, respectively. The amount of ferrous iron of the four grades was < 0.5, 0.5-5, 5-25 and > 25 mmol kg^-1, respectively. The extent of gleyization of a soil was classified as upper-gleyed, middle-gleyed and lower-gleyed, depending on whether the depth of the gley horizon was less than 30 cm, 30-60 cm or more than 60 cm.     

Oxidation-reduction regimes in some Oxisols of tropical China

The oxidation-reduction regimes of some Oxisols of tropical China were investigated on the basis of the Eh values and the amounts of reducing substances, both measured by newly devised methods. The Eh values in the surface layers of soil profiles under natural forest and commercial forest were 400–550 mV, lower by 100–200 mV than the deeper horizons. The concentrations of reducing substances in the surface layers corresponded to 0.5–5.0 · 10^?5M of Mn²⁺. In the cultivated layer of a submerged paddy soil the concentration of reducing substances was as high as 13·10^?5M, with an Eh value of less than 100 mV. There was a negative correlation between the Eh value and the logarithm of the concentration of reducing substances, showing that the intensity aspect and the capacity aspect of the oxidation-reduction status of a soil are closely interrelated.     

土壤对磷的吸持特性及其与土壤供磷指标之间的关系

本试验测定了浙江省几种代表性土壤对磷的等温吸持特性。实测值与Frundlich、Langmuir、两项式Langmuir和Temkin方程都很符合,相关系数变化范围在0.919-0.999之间,都达到极显著水平。其中以简单Langmuir等温式与本实验资料最为吻合。从Langmuir方程得到的土壤吸持特性值(k×q_m)被认为与土壤供磷特性有关。几种供试样品的(k×q_m)值是:针铁矿21100>黄筋泥4218>黄筋泥田991>青紫泥798>粉泥田660>高岭石485>老黄筋泥田423>泥质田298。根据土壤吸持特性值以田菁进行盆栽试验来估算作物磷肥需要量,结果表明,供磷强度0.3ppm P基本能满足田菁早期生长的需要。为使不同土壤达到相同的供磷强度,(k×q_m)值大的土壤要求更高的有效磷值。供试土壤的几种磷素指标:E值、Bray1-P值和(NaOH-Na₂C₂O₄)法值对(k×q_m)值的变化比较敏感,而EDTA-P和Olsen-P指标对(k×q_m)值的变化较为迟钝。     

石灰性紫色土渍水氧化还原状况的研究

本文通过模拟培育试验，研究了石灰性紫色土渍水状态下氧化还特征。结果表明，石灰性紫色土与普通紫色土，不饱和紫色土相比，不易向强还原状况发育，这些其富含碳酸钙和低量的活性铁有关；不同种类有机物料对其还原程度的影响是不同的；表征土壤氧化还原过程的强度因素Ｅｈ和数量因素还原性物质含理有很好的相关性，并与水稻的生长状况相一致，当土壤Ｅｈ小于－１００ｍＶ，还原物总量大于３．６３ｃｍｏｌ＾（＋）／ｋｇ时，土壤极     

围海造田长期耕种稻田和旱地土壤氮矿化速率及供氮潜力比较

围海造田是沿海地区拓展土地面积的主要途径。土壤氮矿化参数是揭示围海造田土壤肥力演变和土壤氮供应的重要指标,但是我国沿海造田土壤的相关研究少有报道。本研究以杭州湾南岸海积平原上慈溪市1000年和520年筑塘造田区为对象,选择4个代表性采样点,每个点从低洼稻田采集1个表层混合水稻土,在其相邻高地采集1个表层混合旱地土壤,共8个样品。采用间隙淋洗法研究了土壤样品氮矿化动力学特征。结果如下: 119 d培养试验证实水稻土和旱地土壤有机氮矿化动力学符合一级反应动力学方程Nt=N0(1-e-kt); 水稻土有机氮矿化势（N0）为82.7～161.9 mg/kg（平均114 mg/kg）,占有机氮的7.3%,旱地土壤N0为63.9～104.4 mg/kg（平均83.4 mg/kg）,占有机氮的7.3%; 水稻土有机氮矿化速率（k）为0.033～0.114/d（平均0.064/d）,旱地土壤k为0.007～0.023/d（平均0.020/d）。土壤综合供氮指标（N0k）,水稻土为3.8418.46 mg/(kgd)［平均8.0 mg/(kgd)］,旱地土壤为0.54～2.66 mg/(kgd)［平均1.6 mg/(kgd)］。水稻土总氮含量为1.4～2.0 g/kg （平均1.6 g/kg）,旱地为0.87～2.0 g/kg（平均1.3 g/kg）。可见,水稻土氮库、供氮潜力和速率均大于相邻旱地土壤。因此,从土壤氮肥力来讲,相对于旱地,围海形成的水稻田更具有可持续利用性。     

农药污染对水稻田土壤硫酸盐还原菌种群数量及其活性影响的研究

在实验室条件下 ,施用杀虫剂 (呋喃丹 )、杀菌剂 (多菌灵 )和除草剂 (丁草胺 )后 ,对黄松稻田土壤、紫色稻田土壤和红壤稻田土的硫酸盐还原细菌 (Sulfate reducingbacteria ,SRB)种群数量和硫酸盐还原活性的影响。结果表明 ,紫色稻田土壤、黄松稻田土壤和红壤稻田土的SRB种群数量和硫酸盐还原活性的范围分别为 (66 83～ 12 7 81)× 10 4 cfug- 1干土、(45 87～ 10 5 0 7)× 10 4 cfug- 1干土和 (3 81～ 61 62 )× 10 4 cfug- 1干土和S- 2 (7 14～ 11 57) μgg- 1d- 1干土、S- 2 (6 84～ 9 0 7) μgg- 1d- 1干土、S- 2 (1 91～ 6 67) μgg- 1d- 1干土 ,且稻田土SRB种群数量和土壤硫酸盐还原活性之间具有正相关性。每kg干土中加入 1mg的丁草胺或呋喃丹 ,能促进SRB的生长及其硫酸盐还原活性。 1kg干土中加入 5mg的多菌灵、50mg的丁草胺或呋喃丹 ,对SRB的生长和硫酸盐还原活性有明显的抑制作用。施用丁草胺和呋喃丹 7d时 ,多菌灵 14d时 ,对水稻田土壤的SRB种群数量和硫酸盐还原活性的抑制影响最大 ,然后逐渐减轻 ,最后显示出某种程度的促进作用     

Effects of biochar addition on N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions from two paddy soils

Impacts of biochar addition on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from paddy soils are not well documented. Here, we have hypothesized that N₂O emissions from paddy soils could be depressed by biochar incorporation during the upland crop season without any effect on CO₂ emissions. Therefore, we have carried out the 60-day aerobic incubation experiment to investigate the influences of rice husk biochar incorporation (50 t ha⁻¹) into two typical paddy soils with or without nitrogen (N) fertilizer on N₂O and CO₂ evolution from soil. Biochar addition significantly decreased N₂O emissions during the 60-day period by 73.1% as an average value while the inhibition ranged from 51.4% to 93.5% (P < 0.05–0.01) in terms of cumulative emissions. Significant interactions were observed between biochar, N fertilizer, and soil type indicating that the effect of biochar addition on N₂O emissions was influenced by soil type. Moreover, biochar addition did not increase CO₂ emissions from both paddy soils (P > 0.05) in terms of cumulative emissions. Therefore, biochar can be added to paddy fields during the upland crop growing season to mitigate N₂O evolution and thus global warming.     

不同类型水稻土微生物群落结构特征及其影响因素

选取基于我国土壤地理发生分类的不同类型土壤发育的四种水稻土,利用¹⁵N₂气体示踪法测定生物固氮速率,采用实时荧光定量PCR（Real-time PCR）技术测定细菌丰度,通过16S rRNA基因高通量测序分析微生物群落组成和多样性。结果表明：变形菌门（Proteobacteria）、酸杆菌门（Acidobacteria）、绿弯菌门（Chloroflexi）和蓝藻门（Cyanobacteria）是水稻土中优势微生物类群。四种类型土壤发育的水稻土细菌群落结构差异显著（Stress<0.001）,群落结构分异（NMDS1）与土壤pH存在极显著正相关关系（P<0.01）。土壤有机碳和碱解氮含量显著影响水稻土中细菌丰度和群落多样性（P<0.01）。红壤发育的水稻土细菌16S rRNA基因拷贝数显著高于其他三种类型水稻土,但OTU数量、Chao1指数和PD指数均低于其他三种类型水稻土。土壤pH对水稻土生物固氮速率有显著影响（P<0.01）,紫色土发育的水稻土具有最高的生物固氮速率（3.2±0.7 mg×kg^-1×d^-1）,其中优势类群细鞘丝藻属（Leptolyngbya）可能是生物固氮的主要贡献者。研究结果丰富了对水稻土微生物多样性的认识,为通过调控土壤pH和微生物群落组成来提高稻田生物固氮潜力提供了理论依据。     

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.     

Effect of land use on the abundance and diversity of autotrophic bacteria as measured by ribulose-1,5-biphosphate carboxylase/oxygenase (RubisCO) large subunit gene abundance in soils

Elucidating the biodiversity of CO₂-assimilating bacterial communities under different land uses is critical for establishing an integrated view of the carbon sequestration in agricultural systems. We therefore determined the abundance and diversity of CO₂ assimilating bacteria using terminal restriction fragment length polymorphism and quantitative PCR of the cbbL gene (which encodes ribulose-1,5-biphosphate carboxylase/oxygenase). These analyses used agricultural soils collected from a long-term experiment (Pantang Agroecosystem) in subtropical China. Soils under three typical land uses, i.e., rice–rice (RR), upland crop (UC), and paddy rice–upland crop rotation (PU), were selected. The abundance of bacterial cbbL (0.04 to 1.25?×?10⁸ copies g^?1 soil) and 16S rDNA genes (0.05–3.00?×?10¹⁰ copies g^?1 soil) were determined in these soils. They generally followed the trend RR?>?PU?>?UC. The cbbL-containing bacterial communities were dominated by facultative autotrophic bacteria such as Mycobacterium sp., Rhodopseudomonas palustris, Bradyrhizobium japonicum, Ralstonia eutropha, and Alcaligenes eutrophus. Additionally, the cbbL-containing bacterial community composition in RR soil differed from that in upland crop and paddy rice–upland crop rotations soils. Soil organic matter was the most highly statistically significant factor which positively influenced the size of the cbbL-containing population. The RR management produced the greatest abundance and diversity of cbbL-containing bacteria. These results offer new insights into the importance of microbial autotrophic CO₂ fixation in soil C cycling.