青冈栎次生林土壤活性有机碳对间伐强度的响应

目的 探索不同间伐强度对青冈栎次生林土壤活性有机碳的响应。 方法 以湖南省天心阁林场青冈栎次生林为研究对象,于2018年设置4种间伐强度（对照：0%;弱度间伐：15%;中度间伐：30%;强度间伐：50%）,探讨不同间伐强度下4种土壤活性有机碳（土壤微生物量碳、可溶性有机碳、颗粒有机碳和易氧化有机碳）含量变化及其在总有机碳中的分配比例。 结果 （1）与对照样地相比,中度间伐和强度间伐显著提高了土壤总有机碳含量,弱度间伐降低了土壤总有机碳含量;（2）间伐提高了土壤微生物量碳的含量,降低了可溶性有机碳的含量,土壤颗粒有机碳和易氧化有机碳含量在不同间伐处理下的变化趋势与总有机碳一致;（3）不同间伐强度下土壤微生物量碳、可溶性有机碳、颗粒有机碳和易氧化有机碳的分配比例分别为：0.23%～0.54%、0.40%～0.78%、16.54%～47.30%和6.46%～14.29%,强度间伐显著提高了微生物量碳、颗粒有机碳和易氧化有机碳分配比例,降低了可溶性有机碳的分配比例,表明间伐提高了不稳定碳的比例,且颗粒有机碳对间伐处理更敏感;（4）相关性分析表明,土壤总有机碳与各活性有机碳组分间呈极显著正相关,且活性有机碳与土壤含水量和总氮含量呈正相关;土壤活性组分碳间转化依赖于总有机碳量的变化,且在一定的水分和氮素条件下易发生分解转变。 结论 不同间伐处理对土壤有机碳及其活性组分的含量有显著影响,强度间伐显著提高土壤有机碳及其活性组分的含量,加快土壤中的碳素循环。     

Relation between soil P test values and mobilization of dissolved and particulate P from the plough layer of typical Danish soils from a long‐term field experiment with applied P fertilizers

Accumulation of phosphorus (P) in agricultural topsoils can contribute to leaching of P which may cause eutrophication of surface waters. An understanding of P mobilization processes in the plough layer is needed to improve agricultural management strategies. We compare leaching of total dissolved and particulate P through the plough layer of a typical Danish sandy loam soil subjected to three different P fertilizer regimes in a long‐term field experiment established in 1975. The leaching experiment used intact soil columns (20 cm diameter, 20 cm high) during unsaturated conditions. The three soils had small to moderate labile P contents, expressed by water‐extractable P (3.6–10.7 mg/kg), Olsen P (11–28 mg/kg) and degree of P saturation (DPS) (25–34%). Mobilization of total dissolved P (TDP) increased significantly (P < 0.05) from the intact soil columns with increasing labile P, whereas the increase in particulate P (PP) with increasing labile P content was modest and statistically insignificant. We found concentrations up to 1.5 mg TP/L for the plough layer of this typical Danish sandy loam soil. This highlights that even a moderate labile P content can be a potential source of TDP from the plough layer, and that a lower concentration margin of optimum agronomic P levels should be considered.     

Tillage and residue management effects on temporal changes in soil organic carbon and fractions of a silty loam soil in the North China Plain

Soil degradation and associated depletion of soil organic carbon (SOC) have been major concerns in intensive farming systems because of the subsequent decline in crop yields. We assessed temporal changes in SOC and its fractions under different tillage systems for wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping in the North China Plain. Four tillage systems were established in 2001: plow tillage (PT), rotary tillage (RT), no‐till (NT), and plow tillage with residues removed (PT0). Concentrations of SOC, particulate organic carbon (POC), non‐POC (NPOC), labile organic carbon (LOC), non‐LOC (NLOC), heavy fraction carbon (HFC) and light fraction carbon (LFC) were determined to assess tillage‐induced changes in the top 50 cm. Concentrations of SOC and C fractions declined with soil depth and were significantly affected by tillage over time. The results showed that SOC and its fractions were enhanced under NT and RT from 0 to 10 cm depth compared with values for PT and PT0. Significant decreases were observed below 10 cm depths (P < 0.05) regardless of the tillage system. The SOC concentration under NT for 0–5 cm depth was 18%, 8%, and 10% higher than that under PT0 after 7, 9, and 12 yr of NT adoption, respectively. Apparent stratification of SOC occurred under NT compared with PT and PT0 for depths >10 cm. All parameters were positively correlated (P < 0.01); linear regressions exhibited similar patterns (P < 0.01). Therefore, to maintain and improve SOC levels, residue inputs should be complemented by the adoption of suitable tillage systems.     

Comparison of Organic and Inorganic Phosphorus Fractions in an Established Buffer and Adjacent Production Field

Abstract

Since the U.S. Department of Agriculture's Conservation Reserve Program was established in 1985, thousands of acres of cropland have been converted to conservation buffers. The distributions of soil phosphorus (P) in various organic and inorganic fractions in a buffer and an adjacent crop production field were compared. Most of the extractable inorganic P (32 to 39%) in both the crop field and the buffer was present in the calcium (Ca)‐P fraction. Levels of the most labile P fractions were higher in the cropped area; however, more P was in the iron (Fe)‐P fraction in the buffer (23 vs. 18%). There were few differences among organic P fractions between the buffer and crop field. Soil sampling depth had a significant effect on the distribution of P. Differences between the cropped area and the buffer were less significant as depth increased. These results suggest that care should be taken in choosing sampling depths when relating P fraction distribution to potential P loss.     

Modified Labile Phosphorus Estimation Method for Arid Ecosystem

A new method for estimation of resin phosphorus (P) in arid soils was developed. Four extractants [hydrochloric acid (HCl), sulfuric acid, nitric acid, and sodium bicarbonate] at various concentrations were used by different ion exchange resins. The results clearly showed HCl was the best extractant at 1.0 N concentration and that 6 h was the optimum time for more adsorption. The optimum adsorption and extraction occurred at 200 rpm and 75 rpm, respectively. Basic anion exchange resin in chloride form was the best resin for P mobilization. A strong correlation (P < 0.001) with the P uptake by different arid crops (pearl millet, clusterbean) was observed. Resin P showed correlation with soil total P (P < 0.001), available and mineral P (P < 0.01), and soil organic P (P < 0.05). The present method for resin-P estimation is found to be an important tool to determine plant P availability and available soil P status under arid environments.     

施用液态家畜废物的水稻田土壤中硝酸盐异化还原成铵过程的研究

Most studies on dissimilatory nitrate reduction to ammonium (DNRA) in paddy soils were conducted in the laboratory and in situ studies are in need for better understanding of the DNRA process.In this study,in situ incubations of soil DNRA using 15 N tracer were carried out in paddy fields under conventional water (CW) and low water (LW) managements to explore the potential of soil DNRA after liquid cattle waste (LCW) application and to investigate the impacts of soil redox potential (Eh) and labile carbon on DNRA.DNRA rates ranged from 3.06 to 10.40 mg N kg 1 dry soil d 1,which accounted for 8.55%-12.36% and 3.88%-25.44% of consumption of added NO 3-15 N when Eh at 5 cm soil depth ranged from 230 to 414 mV and 225 to 65 mV,respectively.DNRA rates showed no significant difference in paddy soils under two water managements although soil Eh and/or dissolved organic carbon (DOC) were more favorable for DNRA in the paddy soil under CW management 1 d before,or 5 and 7 d after LCW application.Soil DNRA rates were negatively correlated with soil Eh (P < 0.05,n=5) but positively correlated with soil DOC (P < 0.05,n=5) in the paddy soil under LW management,while no significant correlations were shown in the paddy soil under CW management.The potential of DNRA measured in situ was consistent with previous laboratory studies;and the controlling factors of DNRA in paddy soils might be different under different water managements,probably due to the presence of different microfloras of DNRA.     

产肠毒素性大肠杆菌肠毒素的研究概况

本文分析了大肠杆菌耐热肠毒素 (heat-stable,ST)和不耐热肠毒素 (heat- labile,LT)生物学特性、分子水平机制及其应用价值。一方面着重讲述 LT作为粘膜免疫佐剂的研究前景 ,利用体外定点突变方法构建不同的突变株并且均具有不同程度的佐剂活性 ,是霍乱毒素 (Choleratoxin,CT)很有希望的替代品。另一方面讲述ETEC基因工程亚单位疫苗的研究概况。ETEC只有 LT、ST两类肠毒素 ,通过不同方式构建融合基因探讨对 ETEC性腹泻防治效果。目前 ,这两方面均卓有成效 ,但还有许多的难点需进一步的研究     

Bioavailability of Reversibly Sorbed and Desorption-Resistant 1,3-Dichlorobenzene from a Louisiana Superfund Site Soil

Microcosm batch studies were conducted to study the biodegradation of 1,3-dichlorobenzene (1,3-DCB) from the aqueous (soil free) and soil phases. For soil phase experiments, a freshly contaminated soil and a soil containing only the desorption-resistant or irreversibly bound or non-labile fraction of the contaminant were used. These experiments were designed to simulate biodegradation at Superfund site assuming sorption/desorption equilibrium was reached. The presence of the soil reduced the rates of biodegradation significantly. Nearly 100% of the total 1,3-DCB in the aqueous phase was biodegraded by enriched bacterial cultures within 7 days compared to about 55% over a 6-week incubation period from the freshly contaminated soil. The biodegradation in the soils containing only the desorption-resistant fraction of the contaminant was considerably lower (about 30%). It is believed that for freshly contaminated soil, 1,3-DCB readily desorbed into the aqueous phase and was available for microbial consumption whereas for soils containing mostly the desorption-resistant fraction of 1,3-DCB, the contaminant availability was limited by the mass transfer into the aqueous phase. Our earlier studies concluded that about 20–30% of the sorbed contaminant is tightly bound (even larger for weathered or aged soils) and is not easily extractable. This fraction is typically present in micropores or chemically bound to soil humic matter and thus is not readily accessible for microbial utilization. The findings presented here for 1,3-DCB are in agreement with those reported for other chemicals in the literature and could have implications to the current remedy, the monitored natural attenuation at the Petro Processors Inc. Superfund site in Louisiana.     

Nitrogen addition change soil N pools with litter removal or not in subtropical forest

ABSTRACT

There are many nitrogen (N) pools in soil, so their availability and different status can give information about bulk soil response to N deposition. However, the different size of N pools in forest soils and the relationship between them have not been well studied under N deposition when considering the role of litter. Here soil in an N-deposition experiment carried out for 5 years in a broad-leaved forest was used as an object to study the response of N pools to N deposition by stepwise extraction using water or solutions containing 0.5 M K₂SO₄, 2.5 M H₂SO₄ (LPI), or 13 M H₂SO₄ (LPII), and calculation of recalcitrant (RC) N pool. Under N control (CT), soil with the presence of litter had a higher N of 23.8–106.8% in the first four pools, but lower of 80.6% in recalcitrant N pool compared with soil with the absence of litter. In the absence of litter, N addition increased soil N in labile pool but decreased N in the RC pool compared to CT and these impacts were greater at high added N (HN) than low-added N (LN) rates. However, in the presence of litter, LN increased the amount of N in the K₂SO₄- extracted pool and HN reduced that in the water extracted pool. Additionally, LN and HN increased TN in the RC pool and HN increased the total soluble N (TSN) in the LPI and LPII pool. N changes in the water extraction pool were attributed to inorganic N, whereas they were NH₄ ⁺ and soluble organic N (SON) in the K₂SO₄-extracted, LPI, and LPII pools. In the presence of litter, HN increased the SON concentration in the K₂SO₄, LPI, and LPII extractions; thus, SON may be a potentially important N form for N availability. These results suggested that N additions improve the accumulation of N in RC pool with the presence of litter. The different effects of N additions on soil N pool or N form in each pool depend on litter present or not.