溶液pH值及模拟酸雨对两种磺酰脲类除草剂在土壤中行为的影响

采用平衡振荡法和土柱淋洗法,研究了溶液pH及模拟酸雨对土壤中苄嘧磺隆和甲磺隆行为的影响.结果表明,Freundlich方程能较好地描述苄嘧磺隆和甲磺隆的吸附等温线,水-土壤系统pH升高能明显地降低这两种除草剂在土壤中的吸附,促进其在土壤中的迁移,且吸附常数(K_f)与土壤有机质含量、粘土含量呈正相关,而与土壤pH呈负相关.pH值高的模拟酸雨对除草剂在土壤中淋溶贡献较大,且淋溶量随雨量的增大而增大.除草剂在土壤中的淋溶与土壤性质密切相关,有机质含量和粘粒含量较高的土壤对除草剂的持留能力较强.     

Adsorption of linuron and metamitron on soil and peats at two different decomposition stages

We studied the adsorption of two herbicides of different polarity, linuron and metamitron, by a mineral soil and two peats at different decomposition stages and determined Freundlich and distribution coefficients per unit of organic matter. The Freundlich adsorption constant (K₁) was 20‐to 30‐fold higher in the case of linuron and 40‐to 90‐fold higher for metamitron for the organic materials (peats) than for the mineral soil, reflecting adsorption dependence on both organic matter content and type. The well‐decomposed peat showed the highest affinity for both herbicides. Hydro‐phobic bonding is suggested as a possible explanation. For linuron, the variation in K, was reduced to less than a twofold variation in K_oc by normalizing adsorption to organic carbon, whereas for metamitron, K_oc values were not constant, confirming that this parameter may be of little meaning for polar compounds.     

Some continuing uncertainties in knowledge of herbicide behaviour in the soil

Recent developments concerned with the variability in the performance of soil- applied herbicides are reviewed with particular reference to phytotoxicity and to factors controlling persistence. It remains questionable that measurements of adsorption and herbicide concentration in the soil solution can adequately predict the phytoxicity of a herbicide in the soil. This is because such an approach ignores the spatial distribution of the herbicide and the parts of the plant through which a herbicide can be taken up. It also ignores the influence of climatic factors on persistence, uptake and plant response. In a general way persistence and the factors which control it are understood but detailed, reliable, quantitative analyses of the phenomena are not yet available. Much remains to be done before the interactions of the soil microflora with its environment and consequent effects on herbicides can be defined. There are still opportunities to improve the precision of use of soil-applied herbicides based on better comprehension of the processes involved in the expression and duration of phytotoxicity.     

有机物质对土壤镉有效性的影响研究综述

土壤中的低分子有机酸和腐殖酸对镉的有效性有重要作用。根系分泌的低分子量有机酸能提高土壤镉的可提取率、移动性和生物有效性,但是更大分子量的有机酸EDTA却抑制植物对镉的吸收,腐殖酸促进土壤镉的溶解性;因腐殖酸组分和环境条件,腐殖酸能够促进也能抑制土壤镉活性,因此有必要深入研究影响腐殖酸固定镉的因素,以达到利用有机质抑制土壤镉活性的目的。     

Transfer of water from roots into dry soil and the effect on wheat water relations and growth

This investigation was performed to study the effect on plant water relations and growth when some of roots grow into dry soil. Common spring water (Triticum aestivum) plants were grown from seed in soil in 1.2 m long PVC (polyvinyl chloride) tubes. Some of the tubes had a PVC partition along their center so that plants developed a split root system (SPR). Part of the roots grew in fully irrigated soil on one side of the partition while the rest of the roots grew into a very dry (-4.1 MPa) soil on the other side of the partition. Split root plants were compared with plants grown from emergence on stored soil moisture (STOR) and with plants that were fully irrigated as needed (IRR). The experiment was duplicated over two temperature regimes (10°/20°C and 15°/25°C, night/day temperatures) in growth chambers. Data were collected on root dry matter distribution, soil moisture status, midday leaf water potential (LWP), leaf relative water content (RWC) and parameters of plant growth and yield.Some roots were found in the dry side of SPR already at 21 DAE (days after emergence) at a soil depth of 15 to 25 cm. Soil water potential around these roots was -0.7 to -1.0 MPa at midday, as compared with the initial value of -4.1 MPa. Therefore, water apparently flowed from the plant into the dry soil, probably during the night. Despite having most of their roots (around 2/3 of the total) in wet soil, SPR plants developed severe plant water stress, even in comparison with STOR plants. Already at 21 DAE, SPR plants had a LWP of -1.5 to -2.0 MPa, while IRR and STOR had a LWP of -0.5 MPa or higher. As a consequence of their greater plant water stress, SPR as compared with IRR plants were lower in tiller number, ear number, shoot dry matter, root dry matter, total biomass, plant height and grain yield and had more epicuticular wax on their leaves.It was concluded that the exposure of a relatively small part of a plant root system to a dry soil may result in a plant-to-soil water potential gradient which may cause severe plant water stress, leading to reduced plant growth and yield.     

Incorporation of shoot versus root-derived <Superscript>13</Superscript>C and <Superscript>15</Superscript>N into mineral-associated organic matter fractions: results of a soil slurry incubation with dual-labelled plant material

Mineral-associated organic matter (MAOM) is a key component of the global carbon (C) and nitrogen (N) cycles, but the processes controlling its formation from plant litter are not well understood. Recent evidence suggests that more MAOM will form from higher quality litters (e.g., those with lower C/N ratios and lower lignocellulose indices), than lower quality litters. Shoots and roots of the same non-woody plant can provide good examples of high and low quality litters, respectively, yet previous work tends to show a majority of soil organic matter is root-derived. We investigated the effect of litter quality on MAOM formation from shoots versus roots using a litter-soil slurry incubation of isotopically labeled (¹³C and ¹⁵N) shoots or roots of Big Bluestem (Andropogon gerardii) with isolated silt or clay soil fractions. The slurry method minimized the influence of soil structure and maximized contact between plant material and soil. We tracked the contribution of shoot- and root-derived C and N to newly formed MAOM over 60 days. We found that shoots contributed more C and N to MAOM than roots. The formation of shoot-derived MAOM was also more efficient, meaning that less CO₂ was respired per unit MAOM formed. We suggest that these results are driven by initial differences in litter chemistry between the shoot and root material, while results of studies showing a majority of soil organic matter is root-derived may be driven by alternate mechanisms, such as proximity of roots to mineral surfaces, greater contribution of roots to aggregate formation, and root exudation. Across all treatments, newly formed MAOM had a low C/N ratio compared to the parent plant material, which supports the idea that microbial processing of litter is a key pathway of MAOM formation.     

植物根系固坡抗蚀的效应与机理研究进展

植物根系对抵抗坡体浅层滑坡和表土侵蚀起着巨大的作用.植物根系通过增强土体的抗剪强度发挥固坡效应.目前有关植物根系固坡机理的模型较多,普遍接受的是Wu-Waldron模型.该模型表明,植物根系产生的土体抗剪强度的增量与根系的平均抗拉强度和根面积比成正比,应用该模型评价根系固坡效应的2个最重要因素是根系的平均抗拉强度和根面积比.研究发现,土壤抗侵蚀性随着植物根系数量的增加而提高,但未有一致的定量函数关系.植物根系提高土壤抗侵蚀性主要通过直径小于1mm的须根起作用.须根通过增加土壤水稳性团聚体的数量与粒径等作用来提高土壤的稳定性,以抵抗水流分散;须根还能有效地增强土壤渗透性,减少径流,从而达到减少土壤冲刷的目的.     

The effect of grass maturing and root decay on N2O production in soil

The N₂O flux from the surface of grass-covered pots was only significant following grass maturing. Removal of the above-ground plant material resulted in an immediate and long-lasting increase in N₂O production in the soil. The results suggest that easily available organic matter from the roots stimulates the denitrification when the plants are damaged. Grass cutting might therefore result in a marked nitrogen loss through denitrification. The quantitative effect was equal in soil with and without succinate added. The size of the anaerobic zone around the roots is therefore sufficient to allow for denitrification activity mediated by increased organic matter availability because of plant cutting.     

Modelling crop growth and biomass partitioning to shoots and roots in relation to nitrogen and water availability,using a maximization principle

Many crop models relate the allocation of dry matter between shoots and roots exclusively to the crop development stage. Such models may not take into account the effects of changes in environment on allocation, unless the allocation parameters are altered. In this paper a crop model with a dynamic allocation parameter for dry matter between shoots and roots is described. The basis of the model is that a plant allocates dry matter such that its growth is maximized. Consequently, the demand and supply of carbon, nitrogen, and water is maintained in balance. This model supports the hypothesis that a functional equilibrium exists between shoots and roots.This paper explains the mathematical computation procedure of the crop model. Moreover, an analysis was made of the ability of a crop model to simulate plant dry matter production and allocation of dry matter between plant organs. The model was tested using data from a greenhouse experiment in which spring wheat (Triticum aestivum L.) was grown under different soil moisture and nitrogen (N) levels.Generally, the model simulations agreed well with data recorded for total plant dry matter. For validation data the coefficient of determination (r²) between simulated and measured shoot dry weight was 0.96. For the validation treatments r² was slightly lower, 0.94. In addition to dry matter production the model succeeded satisfactorily in simulating the dry weight of different plant organs. The response of simulated root to shoot ratio to the level of soil moisture was mainly in accordance with the measured data. In contrast, the simulated ratio seemed to be insensitive to the changes in the levels soil N concentration used in the experiment.The data used in the present study were not extensive, and more data are needed to validate the model. However, the results showed that the model responses to the changes in soil N and water level were realistic and mostly agreed with the data. Thus, we suggest that the model and the method employed to allocate dry matter between roots and shoots are useful when modelling the growth of crops under N and water limited conditions.     

Vegetative reproduction and chemical control with post-emergent herbicides of field bindweed (Convolvulus arvensis L.)

It is clearly seen from data that roots of Convolvulus arvensis L. have more and less intensive regenerative period during growing season. The more intensive period is in autumn, because in that time roots culminate nutrients, carbohydrate as starch and sugar. The less intensive regenerative or shoot-growing period is in spring, called "late spring bud dormancy". Experiments were conducted to get more information and further details about the regenerative capacity of roots close to and far from the collar of Convolvulus arvensis L. Root segments closer to collar have an intensive regenerative capacity than those ones further to collar. By data of Bakke et al. (1939) is well known, roots exhumed from deep soil layers are able to create shoots with low intensity. So finally we can exclaim that regenerative capacity is decreasing further to collar. Using mechanical weed control it is sufficient to till the upper layer of soil, but many times. Chemical treatments are most effective in the integrated weed control. It is clearly seen that auxin-type herbicide such as 2,4-D, fluroxipir, MCPA. dicamba give the best result. They gave 95% weed control effect used them separately or in combination with other herbicides. Combination of Banvel 480 S (dicamba) and Logran 75 WG (triasulfuron) introduced 95% weed control effect. Only one time got absolutely 100% weed control effect, in the case of Glyphosate active substance. Caused total plant destruction. Excellent result was given with the application of Pledge 50WP (flumioxazin). Herbicides mentioned above are absolutely allowed to take an important and significant part in chemical plant protection against Convolvulus arvensis L. Other herbicides like Granstar 75DF (tribenuron-methyl), Basis 75DF (rimsulfuron + tifensulfuron-methyl) and Huszár (jodosulfuron-methyl-sodium + mefenpir-diethyl) are not so effective against Convolvulus arvensis L., as compared to the previous ones.     

土壤深层供水对冬小麦干物质生产的影响

采用根系研究装置研究了土壤深层供水对冬小麦干物质生产的影响 .结果表明 ,上层低湿度下层高湿度的处理在小麦灌浆期仍然保持了较高的土壤和叶片含水量 ,具有发达的根系 ,特别是 1m以下的根量在 4个处理中为最高 ,旗叶和穗的干重也最大 ,具有最大的产量潜力 .本研究表明 ,上层土壤较干下层土壤湿润有利于发挥小麦根信号的积极作用 ,平衡水分利用 ,同时通过对土壤水分的合理调节可以促进深层根的发育 ,有利于提高产量和水分利用效率 .     

Modelling the effect of varying soil water on root growth dynamics of annual crops

We present a simple framework for modelling root growth and distribution with depth under varying soil water conditions. The framework considers the lateral growth of roots (proliferation) and the vertical extension of roots (root front velocity). The root front velocity is assumed to be constant when the roots descend into an initially wet soil profile. The lateral growth of roots is governed by two factors: (1) the current root mass or root length density at a given depth, and (2) soil water availability at that depth.Under non-limiting soil water conditions, the increase in root mass at any depth is governed by a logistic equation so that the root length density (R _v) cannot exceed the maximum value. The maximumR _v, is assumed to be the same for all depths. Additional dry matter partitioned to roots is initially distributed according to the current root mass at each depth. As the root mass approaches the maximum value, less dry matter is partitioned to that depth.When soil water is limiting, a water deficit factor is introduced to further modify the distribution of root dry matter. It is assumed that the plant is an energy minimiser so that more root mass is partitioned to the wetter regions of the soil where least energy will be expended for root growth. Hence, the model allows for enhanced root growth in areas where soil water is more easily available.Simulation results show that a variety of root distribution patterns can be reproduced due to varying soil water conditions. It has been demonstrated that broad patterns of root distribution reported in the literature can also be simulated by the model.     

Temporal and spatial profiling of root growth revealed novel response of maize roots under various nitrogen supplies in the field

A challenge for Chinese agriculture is to limit the overapplication of nitrogen (N) without reducing grain yield. Roots take up N and participate in N assimilation, facilitating dry matter accumulation in grains. However, little is known about how the root system in soil profile responds to various N supplies. In the present study, N uptake, temporal and spatial distributions of maize roots, and soil mineral N (N(min)) were thoroughly studied under field conditions in three consecutive years. The results showed that in spite of transient stimulation of growth of early initiated nodal roots, N deficiency completely suppressed growth of the later-initiated nodal roots and accelerated root death, causing an early decrease in the total root length at the rapid vegetative growth stage of maize plants. Early N excess, deficiency, or delayed N topdressing reduced plant N content, resulting in a significant decrease in dry matter accumulation and grain yield. Notably, N overapplication led to N leaching that stimulated root growth in the 40-50 cm soil layer. It was concluded that the temporal and spatial growth patterns of maize roots were controlled by shoot growth and local soil N(min), respectively. Improving N management involves not only controlling the total amount of chemical N fertilizer applied, but also synchronizing crop N demand and soil N supply by split N applications.     

除草剂对桉树人工林下植物及土壤微生物群落的影响

除草剂在桉树人工林中的应用越来越普遍,但关于除草剂对桉树人工林林下植物和土壤微生物群落的影响知之甚少。通过桉树人工林低剂量高频率(LHF)、中剂量中频率(MMF)、高剂量低频率(HLF)除草剂喷施试验,并与人工除草(MT)为对照,比较分析不同剂量、不同频率除草剂施用对林下植物和土壤微生物群落的影响。结果表明,施用除草剂导致桉树人工林林下植物种类和功能群组成发生显著变化,但并未显著降低林下植物群落物种丰富度和多样性,随除草剂施用频率的降低及恢复时间的增加,物种丰富度及多样性指数呈恢复趋势。除草剂施用也导致土壤养分含量降低。除草剂通过对林下植物群落和土壤养分的负面影响间接影响土壤微生物群落。LHF显著降低藤本植物而显著提高蕨类植物功能群的重要值,从而显著降低了微生物群落、真菌和放线菌的磷脂脂肪酸(PLFA)含量。MMF显著降低木本和藤本植物而显著提高禾草植物功能群的重要值,导致土壤微生物群落和放线菌的PLFA含量显著降低。HLF未显著影响林下植物及土壤微生物群落,但土壤全磷含量显著降低,速效磷含量也大幅下降。施用除草剂显著降低了土壤微生物生物量碳、氮的含量。因此,生产上应减少除草剂的施用,...     

磺酰脲除草剂在土壤中的环境行为研究进展

概述了磺酰脲除草剂在土壤中的吸附与解吸附,降解与残留、迁移以及抑制土壤酶活性等环境行为,探讨了土壤pH值、不同土壤类型、土壤水分含量及有机质等环境行为过程的影响,引用分布活性模型来解释除草剂的解吸滞后现象,并对磺酰脲除草剂在土壤中的生物降解和非生物降解机理进行了探讨,并从生态毒性,吸附作用力以及降解模型方面对今后的研究进行了展望。     

Soil acidification and adaptations of plants and microorganisms in Bornean tropical forests

In tropical forest ecosystems, a paradoxical relationship is commonly observed between massive biomass production and low soil fertility (low pH). The loss and deficiency of soil phosphorus (P) and bases generally constrain biomass production; however, high productivity on nutrient-deficient soils of Bornean tropical forests is hypothesized to be maintained by plant and microorganism adaptation to an acidic soil environment. Proton budgets in the plant–soil system indicated that plants and microorganisms promote acidification to acquire bases, even in highly acidic tropical soils. The nitric and organic acids they produce contribute to the mobilization of basic cations and their uptake by plants. In response to soil P deficiency and the recalcitrance of lignin-rich organic matter, specific trees and fungi can release organic acids and enzymes for nutrient acquisition. Organic acids exuded by roots and rhizosphere microorganisms can promote the solubilization of P bonded to aluminum and iron oxides and its uptake by plants from P-poor soils. Lignin degradation, a rate-limiting step in organic matter decomposition, is specifically enhanced in acidic organic layers by lignin peroxidase, produced by white-rot fungi, which may solubilize recalcitrant lignin and release soluble aromatic substances into the soil solution. This dissolved organic matter functions in the transport of nitrogen, P, and basic cations in acidic soils without increasing leaching loss. In Bornean tropical forests, soil acidification is promoted by plants and microorganisms as a nutrient acquisition strategy, while plant roots and fungi can develop rhizosphere and enzymatic processes that promote tolerance of low pH.     

A Soil-free Plant Growth System to Facilitate Analysis of Plant Pathogen Interactions in Roots

Analysis of the interaction of pathogens with plant roots is often complicated by the growth of plants in a soil substrate. A soil-free plant growth system (SPS) was developed that removes the need for a substrate while supporting the growth of seedlings in a nutrient rich, oxygenated environment. The model legume Lupinus angustifolius was used to compare the growth of seedlings within soil and the SPS. Seedlings grown under both conditions were similar in morphology, anatomy and health (measured by leaf chlorophyll abundance) and importantly there was little difference in root growth and development although straighter and fuller root systems were achieved in the SPS. The ease of access to the root system proved efficient for the analysis of root and pathogen interactions with no interference from soil or adhering particulate matter. Following inoculation of L. angustifolius roots with Phytophthora cinnamomi the host/pathogen interaction was easily observed and tissues sampled undamaged.     

Effects of humic acid-herbicide interactions on the growth of Pisum sativum in nutrient solution

Slight increases in root length and dry matter production were measured in roots and shoots of Pisum sativum seedlings, when germinated seeds were grown for eight days in a controlled environment chamber, on Nitch nutrient solution to which 10 mg L^-1 soil humic acid (HA) had been added. A concentration of 100 mg L^-1 of HA produced a small reduction in dry matter production of shoots. In the presence of herbicides, 10 mg L^-1 cycluron or 100 mg L^-1 prometone, root elongation and shoot growth was reduced by varying degrees with respect to the control. Nutrient solutions containing 100 mg L^-1 cycluron, 10 or 100 mg L^-1 alachlor, or as little as 0.1 mg L^-1 of 2,4-D resulted in an almost complete suppression of the growth of pea seedlings. The addition of 10 or 100 mg L^-1 of HA to nutrient solution containing the herbicide was found to be either ineffective in enhancing growth, or even further reduced growth, compared to samples grown in the presence of the herbicide alone. The results of this preliminary study suggest that the generally accepted view that humic substances exert a positive effect on plant growth may not occur when humic substances interact with herbicides.     

Elemental sulfur improves growth and phytoremediative ability of wheat grown in lead-contaminated calcareous soil

Little is known about the effect of elemental sulfur on lead uptake and its toxicity in wheat. A pot experiment was conducted with the purpose to examine the impact of sulfur on improving Pb solubility in soil, and uptake and accumulation in wheat plants. The effect of three levels of lead (0, 50, and 100 mg/kg soil) and sulfur (0, 150, and 300 mmol/kg soil) was tested in all possible combinations. Root dry matter, straw, and grain yields, and the photosynthetic and transpiration rates decreased significantly with increase in the concentration of Pb in the soil. However, sulfur fertilization in the presence of Pb improved the photosynthetic and transpiration rates and consequently increased the straw and grain yields of wheat. It also enhanced Pb accumulation in roots, its translocation from roots to shoot, and accumulation in grain. S and Zn contents of different plant parts were also enhanced. Thus, by mitigating the toxic effect of Pb and improving wheat growth, sulfur enhances Pb accumulation by the aboveground plant parts and hence the phytoextraction capacity of wheat. However, total accumulation of Pb shows that wheat plant cannot be considered as a suitable candidate for phytoremediation.     

Earthworms,Collembola and residue management change wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>) and herbivore pest performance (Aphidina: <Emphasis Type="Italic">Rhophalosiphum padi</Emphasis>)

Management practices of arable systems determine the distribution of soil organic matter thereby changing decomposer animal activity and their impact on nutrient mineralization, plant growth and plant-herbivore interactions. Decomposer-mediated changes in plant growth and insect pest performance were investigated in wheat-aphid model systems in the greenhouse. Three types of litter distribution were established: litter patch at the soil surface (simulating mulching), litter patch deeper in soil (simulating ploughing) and litter homogeneously mixed into soil (simulating disk cultivation). The litter was labelled with (15)N to follow the mineralization and uptake of nutrients by the plants. Earthworms (Aporrectodea caliginosa) and Collembola (Protaphorura armata) were included as representatives of major functional groups of decomposers. Wheat (Triticum aestivum) was planted and aphids (Rhophalosiphum padi) were introduced to leaves as one of the most important pests. Earthworms, Collembola and litter distribution affected plant growth, N acquisition and aphid development in an interactive way. Earthworms and Collembola increased biomass of seeds, shoots and roots of wheat. Increased plant growth by earthworms and Collembola was mainly due to increased transfer of N from soil (rather than litter) into plants. Despite increasing plant growth, earthworms reduced aphid reproduction. Aphid reproduction was not correlated closely with plant N concentrations, but rather with the concentration of litter N in wheat. Unexpectedly, both Collembola and earthworms predominantly affected the mobilization of N from soil organic matter, and by altering the distribution of litter earthworms reduced infestation of crops by aphids via reducing plant capture of litter N, in particular if the litter was concentrated deeper in soil. The results suggest that management practices stimulating a continuous moderate increase in nutrient mobilization from soil organic matter rather than nutrient flushes from decomposing fresh organic matter result in maximum plant growth with minimum plant pest infestation.