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1.
Eva Kroener 《植物养料与土壤学杂志》2021,184(1):20-24
Mucilage is a hydrogel exuded at root tips, which can hold large amounts of water but turns hydrophobic once dried. It is very challenging to understand the interplay of these opposite mechanisms and to incorporated them into hydraulic soil models. My summary of experimental and modelling approaches and observations at various scales is meant to help improving soil–plant water dynamic models and may also be helpful when water dynamics need to be considered in biogeochemical rhizosphere models. 相似文献
2.
Take home message Mucilage secreted by roots and EPS produced by microorganisms alter the physical properties of the soil solution and impact the water dynamics in the rhizosphere. The high viscosity of mucilage and EPS is responsible for the formation of thin filaments and interconnected thin lamellae that span throughout the soil matrix maintaining the continuity of the liquid phase across the pore space even during severe drying. The impact of these mechanisms on plant and microorganisms needs to be explored. 相似文献
3.
A greenhouse pot experiment was carried out to assess the effects of fermented coffee mucilage applied as mulch together with maize leaves on the growth of young coffee plants of two different varieties and on soil microbial biomass indices. The coffee variety Catuai required 32% more water per g plant biomass than the variety Yellow Caturra, but had a 49% lower leaf area, 34% less shoot and 46% less root biomass. Maize and mucilage amendments did not affect leaf area, shoot and root yield, or the N concentration in shoot and root dry matter. The amendments always reduced the water use efficiency values, but this reduction was only significant in the maize+mucilage‐14 (= 14 g mucilage pot?1) treatment. Soil pH significantly increased from 4.30 in the control to 4.63 in the maize+mucilage‐14 treatment. Microbial biomass C increased by 18.5 µg g?1 soil, microbial biomass N by 3.1 µg g?1 soil, and ergosterol by 0.21 µg g?1 soil per g mucilage added pot?1. The presence of mucilage significantly reduced the microbial biomass‐C/N ratio from a mean of 13.4 in the control and maize treatments to 9.3, without addition rate and coffee variety effects. The application of non‐composted mucilage is recommended in areas where drought leads to economic losses and in coffee plantations on low fertility soils like Oxisols, where Al toxicity is a major constraint. 相似文献
4.
Emile Benizri Christophe Nguyen Sophie Slezack-Deschaumes 《Soil biology & biochemistry》2007,39(5):1230-1233
The organic compounds released from roots (rhizodeposits) stimulate the growth of the rhizosphere microbial community. They may be responsible for the differences in the structure of the microbial communities commonly observed between the rhizosphere and the bulk soil. Rhizodeposits consists of a broad range of compounds including root mucilage. The aim of this study was to investigate if additions of maize root mucilage, at a rate of 70 μg C g−1 day−1 for 15 days, to an agricultural soil could affect the structure of the bacterial community. Mucilage additions moderately increased microbial C (+23% increase relative to control), which suggests that the turnover rate of microorganisms consuming this substrate was high. Consistent with this, the number of cultivable bacteria was enhanced by +450%. Catabolic (Biolog® GN2) and 16S-23S intergenic spacer fingerprints exhibited significant differences between control and mucilage treatments. These data indicate that mucilage can affect both the metabolic and genetic structure of the bacterial community as shown by a greater catabolic potential for carbohydrates. We concluded that mucilage is likely to significantly contribute to differences in the structure of the bacterial communities present in the rhizosphere compared to the bulk soil. 相似文献
5.
An efficient method for the collection of root mucilage from different plant species—A case study on the effect of mucilage on soil water repellency 
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下载免费PDF全文 Ina‐Maria Zickenrott Susanne K. Woche Jörg Bachmann Mutez A. Ahmed Doris Vetterlein 《植物养料与土壤学杂志》2016,179(2):294-302
Root mucilage may play a prominent role in understanding root water uptake and, thus, there is revived interest in studying the function of root mucilage. However, mucilage research is hampered by the tedious procedures of mucilage collection. We developed a mucilage separator which utilizes low centrifugal forces (570 rpm) to separate the mucilage from seminal roots without the need of handling individual seeds or removing the germinated seeds from the tray/mesh to a centrifuge tube. For the different plant species, between 1 and 3.7 mL tray?1 of hydrated mucilage could be produced, with 6 trays being handled successively within 45 min. For Triticum aestivum, which showed a dry matter content of 0.5%, this was equivalent to 98.6 mg mucilage dry matter. The lowest total production was found for Zea mays with just 34 mg dry matter. The amounts of mucilage produced normalized to root tip agree well with literature data. The mucilage obtained by the new method was used to measure its effect on repellency of soil as this property directly relates to the phenomenon of lower rhizosphere soil water content during rewetting. It could be shown that repellency of the rhizosphere is affected by the quantity as well as by species‐dependent quality of mucilage in the rhizosphere. Among the species tested (Lupinus albus, Vicia faba, Zea mays, Triticum aestivum), the largest differences were observed between the two legumes. For Zea mays seminal root mucilage obtained with the new system was compared to mucilage of air born brace roots. The differences between these two mucilages, representing different root orders, indicate clearly that there is still a need for methods which enable the investigation of roots from older plants. 相似文献
6.
Root mucilage modulates soil-plant-water dynamics, but its interactions with microbial community functioning remain poorly understood. The aims of this study were to estimate (I) the impacts of mucilage and soil water content on the microbial community composition and (II) the mucilage consumption by individual microbial groups. C4 root mucilage from maize (at 40 and 200 μg C per gram dry soil, corresponding to 10 and 50% of soil microbial biomass, respectively) was added in single pulses to a C3 soil at two moisture levels: optimum (80% of water-holding capacity (WHC)) and drought (30% of WHC). After 15 days of incubation, the microbial community composition was studied by phospholipid fatty acids (PLFA) analysis and incorporation of mucilage-derived 13C into individual microbial groups was determined by compound-specific isotope analysis. Microbial community composition remained largely unaffected by mucilage addition but was affected by moisture. Whereas an increase in water content reduced mucilage 13C recovery in PLFA for the low-dose mucilage amendment from 19 to 9%, it had no effect under the high-dose amendment (11–12%). This suggests that the role of mucilage for microbial functioning is especially pronounced under drought conditions. The fungal PLFA 18:2ω6,9 was present only under drought conditions, and fungi profited in their mucilage C utilisation from the lower competitiveness of many bacterial groups under drought. In this study, Gram-negatives (G?, characterised by PLFA 18:1ω9c, 18:1ω7c, 16:1ω7c and cy17:0) showed the highest mucilage-derived 13C in PLFA, especially at the high-dose amendment, suggesting them to be the major decomposers of mucilage, especially when the availability of this C source is high. Gram-positives (G+) included different sub-groups with distinct responses to moisture: G+ 1 (a15:0) were only competitive for mucilage C under drought, whereas G+ 3 (i17:0) were only able to utilise mucilage-derived C under optimal moisture conditions. During the 15-day incubation, they built up more than 40% of their membranes from mucilage-derived C, suggesting that in the case of high availability, mucilage can act as an important C source for this microbial group. However, under drought, G? 1 and fungi were incorporating the most mucilage C into their membranes (approx. 20% of PLFA-C). The observation that, for some groups, the high-dose mucilage amendments under drought led to higher 13C incorporation into PLFA than under optimum moisture suggests that mucilage can compensate drought effects for particular microbial groups. Thus, mucilage may not only act as a C source for microorganisms but may also mitigate drought effects for specific rhizosphere microbial groups. 相似文献
7.
8.
Polygalacturonic acid (PGA) has frequently been suggested and used as a model substance for studying mucilage properties and effects in soil. While PGA has a defined chemical structure, the composition of mucilage as natural product can vary in space and time depending on the plant and soil conditions. However, it is still unclear if PGA can be used as surrogate for original mucilage when considering soil–mucilage interactions in the rhizosphere. Here the organic matter (OM) composition of PGA was compared with that of Chia seed mucilage and small‐scale spatial distribution of OM composition in mucilage droplets was analysed using Fourier transform mid infrared spectroscopy in KBr‐transmission technique (FTIR). Selected regions of dried Chia seed mucilage droplets were analysed using micro‐ Fourier transform mid infrared spectroscopy in transflection technique (micro‐FTIR). For PGA, the FTIR spectra revealed lower C–H/C=O and higher C=O/C–O–C ratios as compared to Chia seed mucilage, indicating a relatively lower potential hydrophobicity and higher sorption capacity of the OM in PGA than OM in mucilage. The micro‐FTIR spectra revealed that the potential hydrophobicity of a single freeze‐dried mucilage droplet was higher at the tip as compared to regions located above the tip. The results suggest that the use of PGA as model substance for mucilage is limited especially when trying to imitate the sorption and wettability properties of the Chia seed mucilage OM. The spatial heterogeneity in OM composition as well as shifts in maxima of C=O and O–H bands in micro FTIR spectra of the cross sectioned mucilage droplet suggest that the composition of mucilage is changing with time. These findings may help initiating future studies on the dynamics and variability of OM composition of mucilage. 相似文献
9.
O. Traoré V. Groleau-Renaud S. Plantureux A. Tubeileh & V. Boeuf-Tremblay 《European Journal of Soil Science》2000,51(4):575-581
Plant roots release in the rhizosphere diverse organic materials which may have different effects on soil structure. We have evaluated the effect of natural and modelled root‐released materials on soil aggregates and the biodegradation of carbon from roots in the soil. The effects of root mucilage from maize and of a modelled soluble exudate were compared with those of simple compounds (glucose, polygalacturonic acid). For all treatments, soil was amended with 2 g C kg?1 soil and incubated for 30 days at 25°C. The biodegradation of mucilage was similar to that of polygalacturonic acid, and slower than the decomposition of modelled exudates and glucose. Addition of all substrates increased the stability of aggregates, but the duration of this effect depended on the chemical nature of the material. Compared with the control, the proportion of stable aggregates after 30 days of incubation was multiplied by 3.8 for root mucilage, by 4.2 for modelled soluble exudates, by 2.5 for polygalacturonic acid and by 2.0 for glucose. The different fractions of root exudates in the rhizosphere evidently affected the aggregate stability. 相似文献
10.
Polygalacturonic acid (PGA) is considered as a model substance for mucilage to study mucilage–soil interactions, assuming that the gel formation mechanism of mucilage is comparable to the one of PGA. However, some studies question the accepted hypothesis, which states that, like for PGA, this mechanism relies on cross‐links between uronic acid and calcium for mucilage. The aim of this study was therefore to understand the influence of the abundance and degree of esterification of uronic acids and the influence of calcium on the gel formation mechanism in mucilage as compared to model substances. The mucilage used was from chia seeds, as it is easily available in great quantity and has gel properties shared by root mucilage. Results reported here demonstrate that, while the gel formation mechanism of PGA relied on specific cross‐links with calcium and led to heterogeneous gels, low‐methoxy pectin (LMP) formed homogeneous calcium gels also characterized by nonspecific ionic interactions with calcium. On the contrary, despite similar uronic acid content to LMP, chia seed mucilage was mostly governed by weak electrostatic interactions between entangled polymer chains, which conferred the gel poor water retention. Addition of calcium reduced repulsion and molecular expansion, resulting in a reduction of the water content in chia seed mucilage. Finally, the discrepancies between PGA, LMP and chia seed mucilage discredit the use of PGA as model for chia seed mucilage. Comparison with root mucilage is still needed. This study offers the keys for further mechanistic understanding on the influence of mucilage on soil properties. 相似文献
11.
Nasrin Chowdhury 《Soil biology & biochemistry》2011,43(11):2265-2272
Drying and rewetting are common events in soils during summer, particularly in Mediterranean climate where soil microbes may be further challenged by salinity. Previous studies in non-saline soils have shown that rewetting induces a flush of soil respiration, but little is known about how the extent of drying affects the size of the respiration flush or how drying and rewetting affects soil respiration in saline soils. Five sandy loam soils, ranging in electrical conductivity of the saturated soil extract (ECe) from 2 to 48 dS m−1 (EC2, EC9, EC19, EC33 and EC48), were kept at soil water content optimal for respiration or dried for 1, 2, 3, 4 or 5 days (referred to 1D, 2D, 3D, 4D and 5D) and maintained at the achieved water content for 4 days. Then the soils were rewet to optimal water content and incubated moist for 5 days. Water potential decreased with increasing drying time; in the 5D treatment, the water potential ranged between −15 and −30 MPa, with the lowest potentials in soil EC33. In moist and dry conditions, respiration rates per unit soil organic C (SOC) were highest in soil EC19. Respiration rates decreased with increasing time of drying; when expressed relative to constantly moist soil, the decline was similar in all soils. Rewetting of soils only induced a flush of respiration compared to constantly moist soil when the soils were dried for 3 or more days. The flush in respiration was greatest in 5D and smallest in 3D, and greater in EC2 than in the saline soils. Cumulative respiration per unit SOC was highest in soil EC19 and lowest in soil EC2 Cumulative respiration decreased with increasing time of drying, but in a given soil, the relationship between water potential during the dry phase and cumulative respiration at the end of the experiment was weaker than that between respiration rate during drying and water potential. In conclusion, rewetting induced a flush in respiration only if the water potential of the soils was previously decreased at least 3-fold compared to the constantly moist soil. Hence, only marked increases in water potential induce a flush in respiration upon rewetting. The smaller flush in respiration upon rewetting of saline soils suggests that these soils may be less prone to lose C when exposed to drying and rewetting compared to non-saline soils. 相似文献
12.
A pot experiment with Maahas clay soil covered three consecutive crops. After uniform growth of the first crop, the soils were subjected to different moisture conditions during the dry season. Prolonged drying before wet season flooded rice stimulated increased release of mineral nitrogen but moistening of the dry soil for a dryland crop or by occasional rain during the dry season reduced nitrogen use from the soil in the next wet season. One cycle of alternate wet and dry soil preparation for 20 days before transplanting rice improved soil nitrogen availability and plant uptake of fertilizer nitrogen. The initial growth of rice was retarded after flooding the previously moist dryland or dried soil, but not in the continuously flooded soils. Losses of applied nitrogen were small in continuously flooded soils and were greater in the previously moist dryland and dry treatments. Uptake of soil nitrogen, however, was much higher in the air-dried soil treatment and in the dry with alternate wet and dry preparation treatments. Total nitrogen uptake (soil+fertilizer) was also greater in those dry treatments. Uptake of soil nitrogen in the wet-season crop was roughly proportional to the amounts of ammonia measured just before transplanting. The proportion of the uptake of immobilized fertilizer nitrogen to available soil nitrogen was constant among treatments. Release of immobilized fertilizer nitrogen was also greatly enhanced by soil drying. For 1976 wet-season crop, the availability of fertilizer nitrogen immobilized in the 1975 wet season was three times higher than that of native soil nitrogen. 相似文献
13.
This work was carried out to determine the influence of root exudates on phosphorus solubility in the presence of a strong
phosphate sorbant. Root mucilage was collected from maize grown under field conditions. Polygalacturonic acid (PGA) was also
used as a model of exudates. Adsorption of phosphate by synthetic goethite was measured in the absence of either (1) root
mucilage collected from maize in the field, or (2) PGA. The ranking order of the adsorption on goethite was phosphate at low
concentration >PGA >mucilage >phosphate at high concentration. Then, competitive adsorption between phosphate ions and PGA
or mucilage was studied. Increasing the concentration of PGA or mucilage added to the goethite suspension decreased the amount
of phosphate adsorbed on goethite. It is likely that PGA, mucilage and phosphate compete for the same adsorption sites on
goethite: the effect of the coating of the mineral by the mucilage is another possible explanation.
Received: 18 April 2000 相似文献
14.
Pore size distributions in the 10/104 nm e.c.d. range in aggregates from three New Zealand soils with largely monomineralic clay fractions, were determined by mercury porosimetry after oven drying and also after critical point drying following methanol and then CO2 exchange from a range of water contents. A soil containing halloysite showed considerable porosity in the fine pores (10–30 nm) regardless of the method of drying. A smectitic soil showed virtually no porosity in the 102–104 nm range when oven dry. A soil containing allophane was dominated by large pores (> 103 nm). The change from a fine (clayey) to a coarser (clay loam) texture within the profile of one soil was reflected in an increase in large pores. 相似文献
15.
Benjamin L Turner Jennifer P DriessenPhilip M Haygarth Ian D Mckelvie 《Soil biology & biochemistry》2003,35(1):187-189
Soil drying renders considerable amounts of phosphorus soluble upon rewetting, which may be partly derived from lysed microbial cells. Using direct bacterial cell counting in water and tetra-sodium pyrophosphate extracts of two Australian pasture soils, we found that almost all extractable cells were lysed following the rewetting of dry soils. The amounts of phosphorus in the lysed cells corresponded closely to the increases in water-extractable phosphorus following soil drying, suggesting that bacterial cell lysis is a major source of the released phosphorus. 相似文献
16.
A number of field-moist strongly acid soils, NaObr-treated soils, and Al-saturated clays were subjected to drying and wetting treatments in the laboratory. Oven drying of samples resulted in decreases in extractable Al and increases in extractable H from field-moist soils containing more than 12 mequiv./100 g exchange acidity and from Al-saturated clays, and wetting the samples resulted in the reverse. However, when field-moist soil samples containing less than 7 mequiv./100 g exchange acidity were oven dried, both the extractable Al and extractable H tended to increase. Removing organic matter with NaOBr from a soil sample low in exchange acidity resulted in a change from an increase to a decrease in extractable Al upon oven drying. In all cases, the extractable Al and extractable H contents fluctuated cyclically with repeated drying and wetting. The cause for the observed changes was attributed to Al hydrolysis, with additional influence from soil acidity buffering, Al interlayer formation, and inorganic and organic matter dissolution. 相似文献
17.
Naturally occurring wetting‐and‐drying cycles often enhance aggregation and give rise to a stable soil structure. In comparatively dry regions, such as large areas of Australia, organic‐matter (OM) contents in topsoils of arable land are usually small. Therefore, the effects of wetting and drying are almost solely reliant on the clay content. To investigate the relations between wetting‐and‐drying cycles, aggregation, clay content, and OM in the Australian environment, an experiment was set up to determine the relative influence of both clay content (23%, 31%, 34%, and 38%) and OM amendments of barley straw (equivalent to 3.1 t ha–1, 6.2 t ha–1, and 12.4 t ha–1) on the development of water‐stable aggregates in agricultural soil. The aggregate stability of each of the sixteen composite soils was determined after one, three, and six wet/dry cycles and subsequent fast and slow prewetting and was then compared to the aggregate stabilities of all other composite soils. While a single wet/dry cycle initiated soil structural evolution in all composite soils, enhancing macroaggregation, the incorporation of barley straw was most effective for the development of water‐stable aggregates in those soils with 34% and 38% clay. Repeated wetting‐and‐drying events revealed that soil aggregation is primarily based on the clay content of the soil, but that large straw additions also tend to enhance soil aggregation. Relative to untreated soil, straw additions equivalent to 3.1 t ha–1 and 12.4 t ha–1 increased soil aggregation by about 100% and 250%, respectively, after three wet/dry cycles and fast prewetting, but were of less influence with subsequent wet/dry cycles. Straw additions were even more effective in aggregating soil when combined with slow prewetting; after three wet/dry cycles, the mean weight diameters of aggregates were increased by 70% and 140% with the same OM additions and by 160% and 290% after six wet/dry cycles, compared to samples without organic amendments. We suggest that in arable soils poor in OM and with a field texture grade of clay loam or finer, the addition of straw, which is often available from preceding crops, may be useful for improving aggregation. For a satisfactory degree of aggregate stability and an improved soil structural form, we found that straw additions of at least 6.2 t ha–1 were required. However, rapid wetting of straw‐amended soil will disrupt newly formed aggregates, and straw has only a limited ability to sustain structural improvement. 相似文献
18.
干湿循环条件下重庆地区三种土壤抗剪强度的动态变化 总被引：7，自引：1，他引：6
选择广泛分布于重庆丘陵山区的黄壤、钙质紫色土和中性紫色土3种土壤,通过对室内三轴剪切试验,测定含水率和干密度交互作用对土壤抗剪强度指标的影响,在含水率和干密度对土壤抗剪强度影响分析的基础上,3土壤按各自最优含水率和干密度制作干湿循环试验土样,进行干湿循环条件下土壤抗剪强度的动态变化分析。试验结果显示：(1)在相同干密度情况下,3种土壤粘聚力c值随着含水率的增加呈现出先增加后减小的趋势,在相同土壤含水率水平下,土壤粘聚力c值随干密度增大而增大,3种土壤内摩擦角φ值在各干密度条件下均随着含水率增加呈明显减小的趋势。(2)含水率和干密度的交互作用对土壤粘聚力c值有显著影响,粘聚力c值在1.3-1.7g/cm3干密度范围内随着干密度的增大而增大,且每一个干密度都有一个含水率与之对应,在这样一个交互作用下粘聚力c值达到最大,含水率和干密度的交互作用对内摩擦角φ值影响相对较小,同一干密度下,其φ值差异不大,随干密度的增大缓慢增大。(3)3种土壤的粘聚力c值均随干湿循环次数的增加均呈减小趋势,且前两次循环c值衰减幅度都很大,从第三次干湿循环到第五次干湿循环粘聚力c值衰减幅度很小,趋于稳定。(4)3种土壤在干湿循环后内摩擦角φ值总体呈减小趋势,但不同土壤类型间存在差异,第五次循环结束后,黄壤为24.6?,中性紫色土为22.6?,钙质紫色土为19.3?。 相似文献
19.
《Communications in Soil Science and Plant Analysis》2012,43(4):277-286
Abstract Few references explain the effects of dry‐heat sterilization on soil chemical properties. Yet dry heating at 121°C for 2 hours is the prescribed USDA Animal, Plant, and Health Inspection Service basic treatment for soils entering United States ports of entry. This study concerns the effects of air drying and dryheat sterilization on chemical properties of Puerto Rican soils, chiefly macronutrients and micronutrients, found after extracting with Mehlich‐1 and Olsen solutions. Results for dry heating are compared with reported results for other sterilization procedures. Dry heating did not significantly alter soil N, organic matter content, or soil bases. Depending on the extractant used, changes in P concentrations were significant. Results for micronutrient determinations were more variable and also depended on the extractant used after sterilization. Concentrations of Mn and Fe extracted from dry‐heated soils were significantly greater than concentrations extracted from air‐dried soils. Effects of dry‐heat sterilization on soil chemical properties generally followed results published elsewhere for steaming, exceptions depending on the extractant used. Published results from chemical sterilization established methylbromide as being closest to dry heat results. 相似文献
20.
Addition of a clay subsoil to a sandy topsoil changes the response of microbial activity to drying and rewetting after residue addition – a model experiment 下载免费PDF全文
下载免费PDF全文 The effect of drying and rewetting (DRW) on C mineralization has been studied extensively but mostly in absence of freshly added residues. But in agricultural soils large amounts of residues can be present after harvest; therefore, the impact of DRW in soil after residue addition is of interest. Further, sandy soils may be ameliorated by adding clay‐rich subsoil which could change the response of microbes to DRW. The aim of this study was to investigate the effect of DRW on microbial activity and growth in soils that were modified by mixing clay subsoil into sandy top soil and wheat residues were added. We conducted an incubation experiment by mixing finely ground wheat residue (20 g kg–1) into top loamy sand soil with clay‐rich subsoil at 0, 5, 10, 20, 30, and 40% (w/w). At each clay addition rate, two moisture treatments were imposed: constantly moist control (CM) at 75% WHC or dry and rewet. Soil respiration was measured continuously, and microbial biomass C (MBC) was determined on day 5 (before drying), when the soil was dried, after 5 d dry, and 5 d after rewetting. In the constantly moist treatment, increasing addition rate of clay subsoil decreased cumulative respiration per g soil, but had no effect on cumulative respiration per g total organic C (TOC), indicating that the lower respiration with clay subsoil was due to the low TOC content of the sand‐clay mixes. Clay subsoil addition did not affect the MBC concentration per g TOC but reduced the concentration of K2SO4 extractable C per g TOC. In the DRW treatment, cumulative respiration per g TOC during the dry phase increased with increasing clay subsoil addition rate. Rewetting of dry soil caused a flush of respiration in all soils but cumulative respiration at the end of the experiment remained lower than in the constantly moist soils. Respiration rates after rewetting were higher than at the corresponding days in constantly moist soils only at clay subsoil addition rates of 20 to 40%. We conclude that in presence of residues, addition of clay subsoil to a sandy top soil improves microbial activity during the dry phase and upon rewetting but has little effect on microbial biomass. 相似文献