气象因子和土壤质地影响下刺槐蒸腾对土壤水分有效性的响应

On the Loess Plateau of China, a dry soil layer may form due to excess transpiration, leading to degradation of black locust(Robinia pseudoacacia) stands. In order to better manage projects involving black locust, this study was intended to investigate the response of black locust transpiration rate to soil water availability as affected by meteorological factors using two representative soils(loamy clay and sandy loam) on the Loess Plateau. Four soil water contents were maintained for black locust seedlings grown in pots initially outdoors and then in a climate-controlled chamber, by either drying or irrigating the pots. In both environments, daily transpiration rates were related by a power function to air temperature and by a logistic function to reference evapotranspiration(ET0). Transpiration rates were more susceptible to changes in the meteorological conditions in the sandy loam than in the loamy clay soil. The transpiration rate in the well-watered treatment was greater for black locust grown in the sandy loam than in the loamy clay soil. Normalized transpiration rates were unaffected by ET0 until a critical value of soil water content(θc) was attained; the θc value decreased significantly for the loamy clay soil but increased significantly for the sandy loam soil when ET0 increased. These suggested that the effect of the meteorological condition on the transpiration characteristics of black locust was dependent on soil texture.     

氮肥用量和水分淋溶对土壤和小麦氮素平衡的影响

:利用标记15N尿素研究不同施肥量和淋溶对小麦生长的影响 ,结果表明水分淋溶对小麦生长的影响不明显 ;地上部生物产量与肥料利用率成正相关 .小麦根系越发达 ,收集到的淋溶液越少 ,损失的肥料N越少 .施用相同量的氮肥 ,淋溶处理的氮肥利用率略低于正常浇水的处理     

Hyphal transport by a vesicular-arbuscular mycorrhizal fungus of N applied to the soil as ammonium or nitrate

Summary Transport of N by hyphae of a vesicular-arbuscular mycorrhizal fungus was studied under controlled experimental conditions. The N source was applied to the soil as ¹⁵NH _inf4 ^sup+ or ¹⁵NO _inf3 ^sup- . Cucumis sativus was grown for 25 days, either alone or in symbiosis with Glomus intraradices, in containers with a hyphal compartment separated from the root compartment by a fine nylon mesh. Mineral N was then applied to the hyphal compartment as ¹⁵NH _inf4 ^sup+ or ¹⁵NO _inf3 ^sup- at 5 cm distance from the root compartment. Soil samples were taken from the hyphal compartment at 1, 3 and 5 cm distance from the root compartment at 7 and 12 days after labelling, and the concentration of mineral N in the samples was measured from 2 M KCl extracts. Mycorrhizal colonization did not affect plant dry weight. The recovery of ¹⁵N in mycorrhizal plants was 38 or 40%, respectively, when ¹⁵NH _inf4 ^sup+ or ¹⁵NO _inf3 ^sup- was applied. The corresponding values for non-mycorrhizal plants were 7 and 16%. The higher ¹⁵N recovery observed in mycorrhizal plants than in non-mycorrhizal plants suggests that hyphal transport of N from the applied ¹⁵N sources towards the host plant had occurred. The concentration of mineral N in the soil of hyphal compartments was considerably less in mycorrhizal treatments than in controls, indicating that the hyphae were able to deplete the soil for mineral N.     

Dinitrogen fixation and soil n uptake by soybean as affected by phosphorus availability

The effects of phosphorus supply (0, 30, and 90 mg P kg^‐1) on growth, N₂ fixation, and soil N uptake by soybean (Glycine max (L.) Merr.) were studied in a pot experiment using the ¹⁵N isotope technique. Phosphorus supply increased the top dry matter production at flowering and the dry matter production of seeds, straw, pod shells, and roots at late pod filling of inoculated soybeans. Phosphorus supply reduced the N concentration of plant tops at flowering, but increased the amount of N accumulated at both flowering and late pod filling. In inoculated soybeans total N accumulation paralleled the dry matter production. The P concentration in above‐ground plant parts of nodulated soybeans was not affected by P application. At flowering only 18 to 34% of total N was derived from N₂ fixation, whereas as much as 74% was derived from N₂ fixation at late pod filling. Only the addition of 90 mg P kg^‐1 soil significantly increased the amount of N₂ fixed at the late pod filling stage. Phosphorus supply did not influence the uptake of fertilizer or soil N in soybeans, even if the root mass was increased up to 60% by the P supply.     

Phosphorus uptake and growth of barley as affected by soil temperature and mycorrhizal infection

A glasshouse study was conducted to investigate the effects of soil temperatures of 20, 15 and 10°C on growth and phosphorus (P) uptake of barley (Hordeum vulgare L. cv. Galleon) inoculated with Glomus intraradices Schenck & Smith. Vesicular‐arbuscular (VA) mycorrhiza formation was significantly reduced as the soil temperature decreased. Plant growth depression due to temperature stress was more pronounced in mycorrhizal plants than in non‐mycorrhizal plants. The lower the soil temperature, the higher was the root‐shoot ratio. The ratio was also higher in non‐mycorrhizal plants than in mycorrhizal plants. Concentration of P in roots was influenced by mycorrhiza. Significant interaction between mycorrhiza and soil temperature was observed for root dry matter and specific P uptake (P uptake per unit weight of root). Compared to non‐mycorrhizal plants, specific P uptake in mycorrhizal plants was higher.     

Microbial processes controlling P availability in forest spodosols as affected by soil depth and soil properties

Because carbon dioxide (CO₂) concentration is rising, increases in plant biomass and productivity of terrestrial ecosystems are expected. However, phosphorus (P) unavailability may disable any potential enhanced growth of plants in forest ecosystems. In response to P scarcity under elevated CO₂, trees may mine deeper the soil to take up more nutrients. In this scope, the ability of deep horizons of forest soils to supply available P to the trees has to be evaluated. The main objective of the present study was to quantify the relative contribution of topsoil horizons and deep horizons to P availability through processes governed by the activity of soil micro-organisms. Since soil properties vary with soil depth, one can therefore assume that the role of microbial processes governing P availability differs between soil layers. More specifically, our initial hypothesis was that deeper soil horizons could substantially contribute to total plant available P in forested ecosystems and that such contribution of deep horizons differs among sites (due to contrasting soil properties). To test this hypothesis, we quantified microbial P and mineralization of P in ‘dead’ soil organic matter to a depth of 120 cm in forest soils contrasting in soil organic matter, soil moisture and aluminum (Al) and iron (Fe) oxides. We also quantified microbiological activity and acid phosphomonoesterase activity. Results showed that the role of microbial processes generally decreases with increasing soil depth. However, the relative contribution of surface (litter and 0–30 cm) and deep (30–120 cm) soil layers to the stocks of available P through microbial processes (51–62 kg P ha^?1) are affected by several soil properties, and the contribution of deep soil layers to these stocks vary between sites (from 29 to 59%). This shows that subsoils should be taken into account when studying the microbial processes governing P availability in forest ecosystems. For the studied soils, microbial P and mineralization of P in ‘dead’ soil organic matter particularly depended on soil organic matter content, soil moisture and, to a minor extent, Al oxides. High Al oxide contents in some sites or in deep soil layers probably result in the stabilization of soil organic compounds thus reducing microbiological activity and mineralization rates. The mineralization process in the litter also appeared to be P-limited and depended on the C:P ratio of soil organic matter. Thus, this study highlighted the effects of soil depth and soil properties on the microbial processes governing P availability in the forest spodosols.     

Uptake and distribution of selenium in tomato plants as affected by genotype and sulphate supply

Aim of this work was to investigate if the variation among tomato genotypes in selenium (Se) uptake and accumulation observed in short term experiments are maintained over longer growth periods and if there is a positive correlation in shoot between sulphur (S) accumulation and Se accumulation across different genotypes or if higher tissue S results in greater feedback inhibition of Se uptake. Two experiments were carried out under greenhouse conditions and different genotypes of Lycopersicon lycopersicum (UC82B and LA2711), Lycopersicon pennellii (LA716) and Lycopersicon peruvianum (LA2157) were grown until fruit ripening. The results obtained in the two experiments confirmed that sulphate in the growth solution reduced selenate uptake by plants and increased the S content of the leaves. Under low sulphate treatment there was a clear correlation (R²=0.82) between leaf S content and shoot Se content across genotypes in both experiments, indicating that the overall activity of the S transport systems also determines Se transport. Selenium was translocated from shoot to fruit, but the edible portion of the plant contained much less total Se than the inedible plant parts. The difference in Se content between the low and the high sulphate treatments was significantly higher in shoot than in root, confirming that the Se translocation from root to shoot is probably more affected by high sulphate supply than Se uptake by root. In the first experiment the genotype LA716 showed ah higher Se, accumulation together with higher S content in leaves, indicating a marked ability of this genotype to absorb ions from substrate. In the second experiment UC82B appeared to be more capable to accumulate Se and S rather than LA2711 and LA2157. In both experiments Lycopersicon peruvianum appeared to be less affected by the high concentration of ions in the growth solution and to be able to reduce ion uptake than Lycopersicon lycopersicum and Lycopersicon pennellii.     

丛枝菌根根外菌丝对铵态氮和硝态氮吸收能力的比较

采用空气隔板分室法并结合15N标记技术,以玉米为宿主植物并接种Glomus mosseae和Glomus intraradices,比较了这两种真菌根外菌丝对铵态氮和硝态氮吸收传递能力的差异。结果表明,丛枝菌根根外菌丝吸收传递氮的能力因菌种和氮素形态而异。两种真菌根外菌丝吸收传递NH4+-N能力均高于NO3--N;G. intraradices根外菌丝吸收传递氮的能力高于G. mosseae,这可能与两种真菌根外菌丝生长量有关。     

Significance of temperature and water availability for soil phosphorus transformation and microbial community composition as affected by fertilizer sources

Little is known about the effects of temperature and drying–rewetting on soil phosphorus (P) fractions and microbial community composition in regard to different fertilizer sources. Soil P dynamics and microbial community properties were evaluated in a soil not fertilized or fertilized with KH₂PO₄ or swine manure at two temperatures (10 and 25 °C) and two soil water regimes (continuously moist and drying–rewetting cycles) in laboratory microcosm assays. The P source was the dominant factor determining the sizes of labile P fractions and microbial community properties. Manure fertilization increased the content of labile P, microbial biomass, alkaline phosphomonoesterase activity, and fatty acid contents, whereas KH₂PO₄ fertilization increased the content of labile inorganic P and microbial P. Water regimes, second to fertilization in importance, affected more labile P pools, microbial biomass, alkaline phosphomonoesterase activity, and fatty acid contents than temperature. Drying–rewetting cycles increased labile P pools, decreased microbial biomass and alkaline phosphomonoesterase activity, and shaped the composition of microbial communities towards those with greater percentages of unsaturated fatty acids, particularly at 25 °C in manure-fertilized soils. Microbial C and P dynamics responded differentially to drying–rewetting cycles in manure-fertilized soils but not in KH₂PO₄-fertilized soils, suggesting their decoupling because of P sources and water regimes. Phosphorus sources, temperature, and water regimes interactively affected the labile organic P pool in the middle of incubation. Overall, P sources and water availability had greater effects on P dynamics and microbial community properties than temperature.     

喷灌施肥灌溉均匀性对土壤硝态氮空间分布影响的田间试验研究

在2002～2003年冬小麦生育期内进行了喷灌施肥条件下均匀系数对土壤水氮时空分布及淋失影响的田间试验。试验中,喷灌均匀系数设置低、中、高三个处理,灌溉季节内的平均喷灌均匀系数分别为72%、79%和84%,施肥灌溉均匀系数分别为71%、78%和85%。对70和90 cm深度处的土壤水势进行了监测以评估均匀系数对水氮淋失的影响,结果表明,在所研究的喷灌均匀系数范围内深层渗漏量很小。试验结果还指出,土壤硝态氮随时间和空间表现出很强的变化特征,均匀系数变化范围为23%～97%,变差系数的变化范围为0.04～1.00;灌溉季节内土壤硝态氮分布的均匀性主要取决于初始硝态氮分布的均匀程度,而喷灌均匀系数对土壤氮素的空间分布无明显影响。     

Shear strength of surface soil as affected by soil bulk density and soil water content

This paper proposes a new method to measure the soil strength parameters at soil surface in order to explain the processes of soil erosion and sealing formation. To simulate the interlocks between aggregates or particles within top 2 mm of the soil, a piece of sandpaper (30 particles cm⁻²) was stuck on the bottom face of a plastic box of diameter of 6.8 cm with stiffening glue and used as shear media. The soil strength for the soils from sandy loam to clayey loam was measured with penetrometer and the new shear device at soil surface at different bulk density and soil water content. The normal stresses of 2, 5, 8, 10 and 20 hPa were applied for the new shear device. The results indicated that significant effect of bulk density on soil strength was detected in most cases though the difference in bulk density was small, ranging from 0.01 to 0.09 g cm⁻³. It was also indicated that the measurement with the new shear device at soil surface was reproducible. The changes in soil shear strength parameters due to changes in bulk density and soil moisture were explainable with the Mohr–Coulomb’s failure equation and the principles of the effective stress for the unsaturated soils. The implications of the method were later discussed.     

Uptake and partitioning of 32P and 65Zn by white clover as affected by eleven isolates of mycorrhizal fungi

We compared the effect of eleven mycorrhizal fungi populations (Glomus spp.) from two different climatic regions (Iran vs. Switzerland) on the uptake and partitioning of ³²P and ⁶⁵Zn by white clover (Trifolium repens L. var. Milkanova). Fungi significantly differed in the colonization of roots with hyphae, vesicles or arbuscules and in their effect on the uptake of ³²P or ⁶⁵Zn by white clover. Fungi also differed in their effects on the percentages of ³²P or ⁶⁵Zn transported to the plant tops. There was no relationship between the uptake of ³²P and that of ⁶⁵Zn in plants colonized by different fungi. Isolates Z7 and Q12 (from Iran) were superior to Swiss isolates for their effect on the uptake of zinc (Zn) by white clover. Among the Swiss isolates, that from Langwiese and Hausweid resulted in the highest and lowest partitioning of both ³²P and ⁶⁵Zn to the plant tops, respectively. We conclude that the effectiveness of vesicular arbuscular mycorrhizae in uptake of phosphorus (P) and Zn may be nutrient specific and that some fungal isolates may also affect the relative partitioning of P and Zn between plant roots and tops.     

Yield and N uptake as affected by soil tillage and catch crop

Two field trials with spring barley (Hordeum vulgare L.) were conducted at two locations in Denmark in order to evaluate the effects of tillage and growth of a catch crop on yield parameters under temperate coastal climate conditions. Ploughing in autumn or spring in combination with perennial ryegrass (Lolium perenne L.) as a catch crop was evaluated on a coarse sand (Orthic Haplohumod) from 1987 to 1992 at three rates of N fertiliser application (60, 90 and 120 kg N ha⁻¹ year⁻¹). Rotovating and direct drilling were also included as additional tillage practices. The experiment was conducted on a 19-year-old field trial with continuous production of spring barley. Ploughing in autumn or spring in combination with stubble cultivation and a catch crop, in addition to minimum tillage, was evaluated in a newly established field trial on a sandy loam (Typic Agrudalf) from 1988 to 1992. Yield parameters and N concentrations in grain and straw were determined. On the coarse sand, N uptake in the grain in ploughed plots without a catch crop was significantly greater when spring ploughed as opposed to autumn ploughed, but grain and straw yields did not differ significantly. Grain yield, straw yield and total N uptake did not differ significantly between direct drilled and autumn ploughed plots, but the trend was for grain yield to be lower with direct drilling. After 19 years of catch crop use, yield parameters in ploughed plots were greater than in plots without catch crops. This was most pronounced in the autumn ploughed plots. Rotovating the catch crop in the spring decreased grain yield compared with underploughing the catch crop in autumn or spring. No significant interactions were found between tillage and N rates. On the sandy loam, grain as well as straw yield and total N uptake were not significantly affected by catch crop or time of ploughing. Grain yield was significantly lower with reduced tillage (stubble cultivation in autumn) than in all other treatments.     

Rice yield and water use as affected by soil management practices

A field experiment was conducted at the Shenyang Experimental Station of Ecology, Chinese Academy of Sciences,to study the effects of soil management practices on water use and rice (Oryza sativa L.) yield in an axtuic brown soil during 2001 and 2002. A completely random experimental design with three replications was employed, having four soil management practices as treatments, namely: an undisturbed plow layer (CK), a thin plastic film (TN), a thick plastic film (TI) and subsoil compacting (CP). Results indicated no significant differences among all treatments for rice biomass and grain yields. Also, water consumption was about the same for treatments TN and CK, however the treatments TI and CP were much lower with more than 45% and 40% of the irrigation water in the treatments TI and CP, respectively,saved each year compared to CK. Therefore, water use efficiency was higher in the treatments TI and CP. These results will provide a scientific basis for the water-saving rice cultivation.     

黄土沟壑区小流域不同地形条件下土壤锰的形态分布及其有效性

黄土高原复杂的地形条件因改变了土壤的基本性质而成为影响土壤锰素有效性的主要原因,本文研究了黄土沟壑区不同地形条件对锰的形态分布及其有效性的影响。结果表明,研究区土壤有效锰的含量因地形条件不同差异很大,有效锰在土壤剖面呈下降趋势,在塬面土壤含量最高,沟道土壤含量最低。交换态锰在塬面、梯田土壤含量较低,在坡地和沟道土壤含量较高;塬面、梯田和坡地土壤碳酸盐结合态和有机结合态锰的含量高于沟道土壤,氧化物结合态锰的含量显著低于沟道土壤;矿物态锰以塬面土壤最低,沟道和梯田土壤较高,坡地土壤居中。土壤交换态锰是有效锰的直接来源,但因其含量低而对锰的有效性贡献很小;有机结合态锰是有效锰的潜在来源,对锰的有效性贡献最大。     

Methane concentration and emission as affected by methane transport capacity of plants in freshwater marsh

To elucidate effect of the CH₄ transport capacity of plants on CH₄ production and CH₄ emission, we measured CH₄ emission and the CH₄ transport capacity of plants as well as CH₄ and dissolved organic carbon (DOC) concentrations in porewater and redox potential in the freshwater marsh vegetated with Carex lasiocarpa, Carex meyeriana and Deyeuxia angustifolia. Although only 31% of CH₄ emitted was released via Deyeuxia angustifolia into the atmosphere compared to 72–86% via Carex plants and the CH₄ transport capacity of per stem of Deyeuxia angustifolia was only 8.0 g CH₄ stem^–1 h^–1 being equal to half for Carex plants, the flux of CH₄ emission from the Deyeuxia angustifolia marsh was just lower by 17–28% than those from the Carex marshes as the standing water depth decreased significantly from 15–20 to 5 cm, indicating that despite the poor CH₄ transport capability of Deyeuxia angustifolia partly reduced CH₄ emission via plants, however CH₄ emission was not greatly reduced as expected. This is because although the poor gas transport capability of Deyeuxia angustifolia lowered CH₄ emission to some extent, however it also decreased the input of O₂ into the rhizosphere via plants; the latter not only reduced CH₄ oxidation in the rhizosphere and/or rhizome but also lowered redox potential in the vertical profile resulting in an increase in CH₄ production potential and CH₄ concentration especially at 5 cm depth, which in turn facilitated CH₄ emission through diffusion in the Deyeuxia angustifolia marsh. This study suggests that the sharp decrease in the CH₄ transport capacity of plants did not necessary result in an expected lowering of CH₄ emission in the freshwater marsh.     

肥际氮素浓度下添加不同碳源对水稻土微生物特性的影响

研究肥际氮素浓度下添加不同碳源后微生物的变化特征,对于了解不同活性碳源对肥际养分浓度下氮素转化和调控作用以及提高氮素利用率等具有重要意义。采集我国亚热带地区典型的水稻土,模拟肥际氮素浓度,设置不同硫铵用量和葡萄糖、纤维素或木质素碳源添加处理,进行室内培养试验,研究了各处理土壤微生物生物量碳氮、矿化及微生物群落功能多样性的变化。结果表明,在培养7天和35天,高氮素用量下与不添加碳源处理相比,添加葡萄糖、纤维素和木质素各处理土壤微生物生物量碳分别增加5.0%～126.8%、17.5%～210.9%和14.7%～210.0%,微生物生物量氮分别增加-5.4%～109.3%、32.0%～173.1%和-14.2%～194.8%(负数表示减少)。而中等和常量氮素条件下添加这3种碳源,土壤微生物生物量碳氮也呈增加趋势。肥际氮素各浓度下添加葡萄糖处理CO2释放量最多,其次是添加纤维素,最后是添加木质素。BIOLOG分析显示,高、中氮素用量下,平均吸光值(AWCD)、Shannon、Simpson和McIntosh指数都较低,添加3种碳源处理后均有提高,而单独添加不同碳源及添加常量氮素和碳源处理,AWCD值和微生物功能多样性指数水平较高。较高的肥际氮素浓度下添加葡萄糖、纤维素或木质素可提高土壤微生物活性。在当前大量施无机氮肥的条件下,注重有机物的配合施用,有利于减小氮素损失的风险。     

土壤斥水性影响土壤水分运动研究进展

土壤斥水性广泛存在于各类土壤,是影响植物生长、土壤水分运动以及土壤侵蚀等水土过程的重要因素。该文阐述了土壤斥水性的基本概念,介绍了几种常用的斥水性强度测定方法及适用范围。在此基础上,论文对土壤斥水性如何影响土壤水力性质以及水分运动特征等研究现状作了全面评述,重点讨论了近年来该领域的研究热点,如土壤斥水性影响下的指流观测和理论模拟以及斥水性土壤蒸发过程等。最后,提出了相关研究中亟待解决的若干关键科学问题,主要包括确定土壤斥水性影响指流现象和蒸发过程的物理机制的揭示;考虑土壤斥水性参数的土壤水分运动数学模型的构建;以及对新模型的求解及对数值解的理论分析。由于土壤斥水性对土壤水分运动有重要的关联效应,相关问题的深入研究对进一步认识土壤水分运动的内在物理机制具有重要理论意义,也将为掌握和有效利用土壤斥水性提供实践指导。