新型根系分泌物采样装置的介绍与应用

根系分泌物在土壤-植物养分循环和缓解植物环境胁迫方面具有重要作用。根系分泌物的收集是研究植物根系过程和相应机制的基础。通常所用的溶液收集法简单易操作,但由于人为扰动大,不能反应根系分泌物的真实情况。介绍了一种新型根系分泌物原位连续采样装置,该装置由根系生长箱和根系分泌物收集装置二部分组成。根系生长箱中土壤和根系之间由滤膜隔开,土壤中的营养元素可以透过滤膜供应植物生长,带有真空抽气泵的根系分泌物收集装置可以实现用去离子水原位淋洗根系、收集根系分泌物的目的。该收集装置外源葡萄糖加标回收率为89%±2%。小麦种植在根系生长箱中,在小麦生长42 d期间,用新型采样装置和溶液收集法分别收集了根系分泌物,研究了小麦根系分泌DOC能力随生长时间的变化。结果表明,收集方法不同,小麦根系分泌DOC能力随生长时间变化不同。在新型收集装置法中,小麦根系分泌DOC能力随着生长时间呈现降低的态势,而溶液收集法则呈现出上升的态势。新型采样装置能实现植物土壤生长条件下原位收集根系分泌物,采样中扰动小,为根系分泌物研究提供了较好的收集方法。但也存在设备复杂、采样流量不易控制等缺点,是今后需要改进的方向。     

植物生长环境与根系分泌物的关系

植物所处环境条件会影响植物根系分泌物的数量和组成,同时,植物根系分泌物也会影响根际环境条件。本文综述了植物种类(品种、生长发育阶段)和光温水、养分胁迫、重金属胁迫、微生物活动等环境条件对植物根系分泌物的影响;植物根系分泌物对根际微区土壤结构性、pH、CEC、养分活化和微生物区系等方面的影响,并提出了今后植物根系分泌物与环境条件研究中在研究方法、不同环境条件等方面值得关注的问题。     

根系分泌物

概述了根系分泌物的产生,收集与分析及其影响因素和根系分泌物组分。阐明了根系分泌物与根际土壤微生物相互关系。     

一种新型根系分泌物收集装置与收集方法的介绍

根系分泌物在养分活化、改善环境胁迫方面具有重要作用,很多科技工作者对根系分泌物的研究表现出极大兴趣,取得了一系列进展。但土壤栽培条件下,根系分泌物收集是一个难点。本文介绍了一种新型根系分泌物的收集装置与收集方法。该装置由根系生长箱和分泌物收集箱组成,植物在生长箱土壤中生长,通过定向引导作用,根系从生长箱穿过琼脂层进入收集箱中生长,待收集箱内积累一定根系后,通过淋洗收集箱内的介质,实现根系分泌物收集。研究发现,利用该装置收集分泌物,植物总根尖数的90%分布在收集箱。外源有机酸加样回收率可达70%以上。土壤栽培条件下,随生长时期延长,大豆有机酸分泌量逐渐增加,苹果酸分泌量高于柠檬酸。而且土壤栽培条件下大豆柠檬酸和苹果酸分泌量是溶液栽培时的11.4倍和6.7倍。上述研究表明,该装置可以用于土壤栽培条件下根系有机酸的分泌研究。     

根系分泌物主要作用及解析技术进展

根系分泌物是植物保持根际微生态系统活力的关键因素，也是根际物质循环的重要组成部分，对根际土壤生态环境中的物质循环具有重要的驱动作用。根系分泌物可以刺激微生物生长，增强其活性，加速根际养分循环，增加土壤养分利用率，并在小规模空间引起温室气体通量的变化。此外，它也是植物参与竞争的重要策略，植物通过根分泌物以获取种间长期生存的养分，甚至分泌对自身有害的化感物质来排挤其他植物，实现自我生存，即使存在自毒作用或引起连作障碍等。植物的健康生长依赖于自身与土壤微生物复杂动态群落的相互作用，但是根际微生物群落结构和组成却又受植物物种、植物生长期、土壤性质、功能基因等因素影响，这些因素的动态变化可能导致根系分泌物的多样化，从而形成复杂多变的根系分泌物与植物的关系，进而影响植物的健康生长。目前，对植物根系分泌物的研究是土壤生态学、植物营养与代谢等领域的研究热点，且随着分析技术手段的快速发展，根系分泌物相关研究也逐渐深入，进一步揭示植物与微生物间的协同作用机理对农、林等行业生产具有重要的指导意义。     

根系分泌物及其在修复多环芳烃污染土壤中的应用

修复被多环芳烃污染的土壤是目前环境和生态领域的一个前沿课题,植物修复是一种经济廉价、可操作性强、美化景观的绿色技术,而根系分泌物在植物修复污染土壤过程中有着重要的意义。总结了近年来国内外植物根系分泌物研究的主要成果,系统介绍了根系分泌物的定义、组成、影响因素及其收集和分离纯化方法,综述了近年来根系分泌物在植物修复技术中的应用情况,以期为进一步开展多环芳烃污染土壤植物修复研究提供实践参考和理论依据。     

植物对不同形态磷响应特征研究进展

磷是植物生长发育所必需的大量营养元素之一,参与植物体内许多重要化合物的合成与代谢。土壤中磷素具有多种形态,且不同形态磷的植物有效性差异较大;植物在不同形态磷环境下,体内会形成相应的适应性机制。植物吸收积累磷通常与根形态、根系分泌物、体内磷转运等因素有关,受到特异基因表达的调控。了解植物对磷的吸收积累特性是筛选磷高效植物或磷富集植物的前提,也是充分利用土壤磷素资源、修复磷过剩环境的关键。根据国内外研究现状,本文从磷素吸收积累、根系形态特征、磷酸酶与植酸酶的变化以及磷营养高效的分子机制,综述了植物对不同形态磷的响应特征,并对未来该领域的研究进行了展望。     

土壤—植物根际磷的生物有效性研究进展

探讨土壤－植物根际磷素养分状况及利用机理，提高土壤磷的生物有效性，使土壤中潜在的难溶性磷库活化，提高磷肥利用率，对促进农业生产的持续发展和陆地生态系统的良性循环具有重大的现实意义。文章从这一角度出发，论述了根际土壤中根际微生物，根际pH值，根系分泌物，菌根，根际土壤磷酸酶等各种因素对提高土壤磷素利用率的机理。     

根系分泌物

概述了根系分泌物的产生、收集与分析方法及其影响因素和根系分泌物组分。闸明了根系分泌物与根际土壤微生物的相互关系。     

间套作体系土壤磷素吸收优势和机理研究进展

利用间套作农业生态工程种植技术可以充分挖掘土壤累积态磷素,减少农田磷肥投入,对于维持磷素资源和土壤肥力的可持续性,防控农田面源污染,具有重要的现实意义。系统总结了间套作体系对土壤磷素的挖掘利用优势,从间套作体系的根系形态、分布特征、根系分泌物、根系活性和根间菌丝桥角度并结合生态位互补和种间促进作用的原理分析了磷素吸收优势的机理。指出了此项研究存在的问题,对今后的研究方向和发展趋势进行了展望。     

Kinetics of phosphorus release from calcareous soils under different land use in Iran

The rate of phosporus (P) release from soils can significantly influence P fertility of soils. The objectives of this study were to investigate the effects of land‐use types on the kinetics of P release under different management practices and the relationship between kinetic parameters and soil physical and chemical properties from calcareous soils. The kinetics of P release in 0.01 M CaCl₂ was studied in surface samples of 30 calcareous soils planted to garlic, garden, pasture, potato, vegetables, and wheat. Trend in P‐release kinetics was similar between land‐use types. Significantly different quantities of P were released under different land use. The maximum amount (average of five soils) (46.4 mg kg^–1) of P was released in soil under potato and the minimum amount (10.4 mg kg^–1) under pasture. The kinetics of P release from soils can be described as an initial rapid rate followed by a slower rate. Different models were used to describe P release. In general, parabolic diffusion and power equation were found to be appropriate for modeling P release. The P‐release rate for the soils was estimated by parabolic equation for the studied land‐use types. The constant b was lower for pasture and wheat than for garlic and potato. The relationship between the rate of P release with Olsen‐P was linear, while it was curved with respect to the CaCl₂‐P, indicating that release of P was diffusion‐controlled. When the kinetic parameters of models were regressed on soil properties, CaCl₂‐P and CaCO₃ appeared to be the most important soil properties influencing P‐release rates in these soils.     

Effects of the Incorporation of Phosphorus and Iron into Arsenic-Spiked Artificial Soils on Root Growth of Lettuce using Response Surface Methodology

We investigated effects of phosphorus (P) and iron (Fe) on root elongation (RE) of lettuce in arsenic (As)–spiked soils using response surface methodology (RSM). To stabilize interactions between As and Fe in a soil preparation, the sequential incorporation method using Fe and P (SIM_Fe-P) was applied. From a phytotoxicity assay, As in roots (As_root) was negatively associated with RE, Fe in soils, and P in roots and soils. The P in roots was also positively related to RE. In a model study, As and interaction factor between P and Fe showed negative coefficients but others showed positive ones. From a confirmation study, RE on exposure to As was verified to be much greater in soils treated by SIM_Fe-P than in soils separately treated with both elements. These results indicated that application of SIM_Fe-P to As-contaminated soils might be expected to have an advantage during the early stage of plant root growth.     

Soil and Compost Type Affect Phosphorus Leaching from Inceptisol,Ultisol, and Andisol in a Column Experiment

A column leaching experiment using three soils (Inceptisol, Ultisol, and Andisol) and seven livestock manure composts that had different characteristics was conducted for 19 weeks to investigate the interactive effects of composts and soils on the phosphorus (P) leaching potential of compost-amended soils and to identify the principal variables that affect P leaching. Cumulative total P leaching (TP_cum) tended to increase with increasing total and available P concentration in the soils. Among various compost properties, total P concentration was positively correlated with TP_cum from the compost-amended soils, except for the Andisol, which has a high P-sorption capacity. There was no significant relationship between TP_cum and water-extractable P concentration of the composts, suggesting that total P rather than inorganic P concentration of composts may be successfully used in predicting P leaching potential from compost-amended soils except for soils that have a high P-sorption capacity, as in Andisol.     

Can P NMR spectroscopy be used to indicate the origins of soil organic phosphates?

The relationship between organic P status of 4 soils, 20 microorganisms isolated from these soils (2 bacteria and 3 fungi for each soil) and 13 dominant plant species of typical natural ecosystems of these soils was evaluated. The soils used were represented by two pairs with different ratios of monoester and diester P, and of DNA and other diester P. A Dystric Podzoluvisol and an alpine Umbric Leptosol were characterized by a relatively high proportion of diester P including much DNA P, while a Calcic Chernozem and subalpine Umbric Leptosol had lower proportion of diesters containing relatively less DNA P. The proportions of P compounds in bacteria and plants were very similar on average, based on the monoester to diester P ratio and on the proportions of different diesters in alkaline extract, whereas fungi contained considerably higher proportions of monoesters and polyphosphates, and a higher proportion of phospholipids in the diester fraction. The results showed that the P_org composition of NaOH extracts from different soils was more similar to the composition of extracts from different groups of microorganisms. There was no clear correspondence between soil and microbial diester P proportion and composition. A high proportion of polyphosphate P including pyrophosphate P in soil extracts indicates a significant contribution of fungal P compounds in the soil while the monoester to diester P ratio, and DNA to non-DNA P ratio should be used with caution to interpret the origins of soil P_org. The relative contributions of microorganisms and plants to monoester and diester P in soils is only partially understood.     

Adsorption and bonding energy indexes for phosphorus in four soils of northeast thailand

Abstract

Four important soils of Thailand were studied in the laboratory and greenhouse to determine the relationship between the relative uptake of P by tomato plants, the P in the presence of added P absorption maximum, and the bonding energy. The relative uptake of P was higher in soils which had low initial available soil P and was lower in soils that had an initially high P status. The sorption of P was less in those soils which had the higher initial water‐soluble P. Generally, as the absorption maximum and bonding energy of the soils decreased, the relative yield response to added P increased.     

Microbial biomass phosphorus and its significance in predicting phosphorus availability in red soils

Abstract

Red soils are widespread in Southern China and other subtropical regions in the world. An improved management of phosphorus (P) is crucial for sustainable agriculture and environmental quality in red soil regions. Plant‐availability of P in red soils mainly depends on fertilization and biological cycling. Both laboratory analyses and greenhouse experiments were conducted to examine the relationships between plant P uptake, chemical index of P, and microbial biomass P in red soils with different fertility levels. Microbial biomass P ranged from 2.1 to 43 mg kg^‐1 in the red soils and was significantly correlated with total P (r=0.84*), organic P (r=0.87*), or Bray I extractable P (r=0.94**). Extractable P plus organic carbon accounted for >85% of the variation in microbial biomass P in the red soils. The significant relationship between microbial biomass P and extractable P suggests that microbial biomass P has a great potential in predicting P‐supply ability in soil. Greenhouse experiments showed that there were close relationships between ryegrass dry matter yield, plant P uptake or tissue P concentration and microbial biomass P in the red soils. The corresponding correlation coefficients were 0.79*, 0.90*, and 0.91*, respectively. These results imply that microbial biomass P plays an important role in the availability of P to plants, and is a potential biological index of P availability in the red soils.     

Organic phosphorus species in humic acids of mountain soils along a toposequence in the Northern Caucasus

Organic P was investigated in humic acids extracted from mountain soils developed in the subalpine, upper subalpine and alpine zones of the Northern Caucasus. P contents of humic acids varied between 3.4 and 14.2 g P kg^?1, depending on P contents of the parent vegetation and on site conditions. Organic P was accumulated at sites where microbial activity is restrained due to soil acidity, low soil temperature and hydromorphy.³¹ P NMR spectroscopy revealed that orthophosphate monoesters were the dominent P species (72–85% of extract- able P), orthophosphate diesters amounted to 12–21%, and phospho- nates ranged between 0 and 9%. Humic acids of soils under cold and wet climatic conditions showed highest concentrations in phospho- nates and orthophosphate diesters. Hence, the accumulation of organo-P in the Caucasian mountain soils was partly due to increasing proportions of potentially available organic P species.     

Phosphorus balances for arable soils in Southern England 1986–1999

The behaviour of P in a range of English arable soils was examined by plotting the change in resin P in the topsoil (ΔPres) at the end of a 3‐ to 5‐year period, against the P balance over the same period (fertilizer P applied minus offtake in crops, estimated from farmers’ reported yields and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops are valid averages, 20–60% of ΔPres was explained by the balance. Applying excess P fertilizer increased Pres, and reducing P fertilizer use decreased it; typically 3–4 kg P ha^?1 was required for each mg L^?1ΔPres (6–8 kg ha^?1 for each mg L^?1 of Olsen P). About half the P balance seems to be resin extractable and this differed little between soil groups, except in cases of very low P (index 0) in which the P buffering was stronger, and on very high P soils (index 4/5) when buffering was less. However, on calcareous soils and red soils, when fertilizer was applied in accord with offtake, Pres fell by up to 4 mg L^?1 year^?1 (2 mg L^?1 yr^?1 olsen P) and to prevent this an extra 3–10 kg P ha^?1 year^?1 fertilizer was required. But on most non‐calcareous soils, replacing offtake maintained Pres, with perhaps slight rises on soils of low clay content or greater organic matter content. In soils under arable rotations, the apparent recovery of P from fertilizer was often around 100%, falling to 85% on Chalk soils and 75% on medium–heavy soils on limestone or Lower Chalk. The fate of the ‘missing’ P needs clarification. The case for corrections to current P fertilizer recommendations in the UK on certain soil types is discussed.     

Phosphorus speciation in temperate basaltic grassland soils by solution 31P NMR spectroscopy

Phosphorus (P) speciation in 21 basaltic and four non-basaltic Irish grassland soils was determined by NaOH–EDTA extraction and ³¹P NMR spectroscopy. Organic P in basaltic soils ranged between 30 and 697 mg P kg⁻¹ and consisted of phosphate monoesters (84–100%), DNA (0–16%) and phosphonates (0–5%). Inorganic P was mainly phosphate (83–100%) with small concentrations of pyrophosphate (0–17%). Phosphate monoesters were more important as a proportion of extracted P in basaltic soils, probably because of their greater oxalate-extractable Fe and Al contents. Phosphate monoesters appeared to be strongly associated with non-crystalline Al and increased with total soil P concentration, indicating that they do accumulate in grassland soils. In non-basaltic soils myo -inositol hexakisphosphate constituted between 20 and 52% of organic P, while scyllo -inositol hexakisphosphate constituted between 12 and 17%. These compounds were not quantified separately in basaltic soils because of poor NMR resolution in the phosphate monoester region, but appeared to represent a considerable proportion of the organic P in most samples. DNA concentrations were greater in basaltic soils compared with non-basaltic soils and were associated with acidic pH and large total C contents. The inability of the Olsen P test to assess effectively the P status of basaltic soils may result from strong phosphate sorption to Fe and Al oxides, inducing plant utilization of soil organic P. Phosphorus nutrient management should account for this to avoid over-application of P and associated financial and environmental costs.     

The use of biological methods to determine the microbiological activity of soils under cultivation

Summary In Ap horizons of typical arable soils under cereals in Northwest Germany, biological activity was estimated by measuring microbial activity. Twelve soils on local farms and six soils on a research farm were analysed. Microbial biomass, dehydrogenase activity, and alkaline phosphatase activity were compared with the biological availability of P, an index describing the relationship among several P fractions that has been used in ecological agriculture. The correlation between the microbial biomass and dehydrogenase and alkaline phosphatase activity was strong but the correlation between the biological availability of P and the enzyme activities was weak. In contrast, in the farm fields, there was a significant correlation between the microbial biomass and the biological availability of P. The correlation between the biological availability of P and pH was highly significant (r=0.65–0.93^***). Explanations for these correlations are discussed and proposals for further investigations are made. (1) Is the pH effect a direct chemical one or an indirect biological one? (2) Which soil organisms affect the biological availability of P in contrast to the microbial biomass, dehydrogenase activity, and alkaline phosphatase activity? (3) Is the method suitable for the investigation of all arable soils?