Effect of benzonitrile ester herbicides on the growth of some soil bacteria

T. CSERHÁTI, Z. ILLÉS AND S. NEMES-KÓSA. 1992. The effect of some benzonitrile ester herbicides on the growth of Bacillus megaterium, B. cereus var. mycoides, B. polymyxa, B. subtilis, Pseudomonas fluorescens and Azotobacter chrooccum was investigated in the concentration range 20–640 ppm by the agar diffusion method. The zones of inhibition, restricted growth and eventual stimulation were determined. The data matrix was evaluated by principal component analysis. Azotobacter chroococcum was the most resistant to the benzonitrile esters. The influence of benzonitrile esters on the growth of micro-organisms depended equally on the species and on the chemical structure of the herbicides. Chloro substitution considerably modified the effect whereas bromo and iodo substitution resulted in similar biological activity.     

Impact of an Herbicide Combination of Bromoxynil and Prosulfuron on Soil Microorganisms

Soil microcosm experiments were used to investigate the effects on growth and activity of soil microorganisms of an herbicide combination (60% bromoxynil + 3% prosulfuron) frequently used to provide a broad spectrum control of weed species. Culturable aerobic bacteria, fungi, and actinomycetes, the fundamental groups of heterotrophic microorganisms, and nitrifiers, considered a very sensitive group to these compounds, were evaluated. Since herbicides have been found to inhibit decomposition of cellulose in soil, the effects on cellulolytic bacteria and fungi were determined. Dehydrogenase activity as a measure of microbial activity was another parameter considered. The results emphasized a tendency of reversible stimulatory/inhibitory effects of the tested compounds on soil microorganisms, with fungi as an exception. A long-lasting negative action on the activity of the dehydrogenase (DHA), commonly used as an index of the overall microbial activity in soil, was found. The magnitude of these effects were dependent on the assayed concentrations of the herbicides mixture. We concluded that the presence of bromoxynil + prosulfuron could induce significant changes in the microbial populations of the soil, concerning the activity and balance of microbial community. Possible environmental risks must be considered. Dehydrogenase activity was shown to be an important indicator of side-effects attributed to these herbicides.     

Simulation and experimental analysis of the influence of herbicides on soil nitrification

The effect of 35 herbicides on the nitrification process was tested both by experiment, and by simulation of possible mechanisms of inhibition in a mathematical model. The model consists of nine equations with six coordinated constant and seven measurable parameters (or initial values), depending on the specific soil. The only free parameters are the initial values of the oxidative enzyme systems, and the parameters which determine the course of possible inhibition effects. For the majority of the herbicides, the inhibitory effects on the NH₄ ⁺ or NO₂ ^- oxidation were found negligible in the range of practical application. Hypotheses of a completely reversible or partially reversible inhibition of the oxidase systems gave the best correspondence between the model and reality, while an alteration of the growth parameters of the nitrifying populations in the model (death rate, proliferation rate, initial kill) due to the application of herbicides led to strong contrasts between simulated and experimental curves. Significant inhibitory effects became evident only when the hydrogen ion concentration in the soil fell below pH 7. Results with several herbicides indicated that the process of NO₂ ^- oxidation was more sensitive than that of NH₄ ⁺ oxidation. With a number of herbicides, an accumulation of NO₂ ^- ions was noticed during the course of soil percolation. In consideration of the buffering capacity, the model is applicable to other soils.     

Differential effects of the sulfonylurea herbicides chlorsulfuron and sulfometuron methyl on microorganisms

The sulfonylurea herbicides exert their effects on cells via their inhibition of the acetohydroxy acid synthase (AHS) enzymes. Although chlorsulfuron and sulfometuron methyl often affected microbial growth differently their effects on the AHS activities of toluenised cells were similar. Sulfometuron methyl was always a more potent inhibitor than chlorsulfuron. We have postulated that sulfometuron methyl penetrated into microbial cells more readily then did chlorsulfuron. The effect of the herbicides on microbial growth was altered by the composition of the medium and in particular by valine or valine plus isoleucine. Different microorganisms had different complements of AHS isoenzymes which together with differences in permeability were the most likely explanations for the different responses observed. It was pointed out that application of these sulfonylurea herbicides would have significant effects on the microbial ecological balance of soil, and particularly so in alkaline soils. The consequences would be most evident in agricultural situations where the microbial population played an important role in maximising the productivity of crops.     

The effect of herbicides,plant growth regulators and other compounds on phenylalanine ammonia-lyase activity

The in vitro and in vivo effects of a number of herbicides and plant growth regulators on phenylalanine ammonia-lyase (PAL) activity were investigated. The most elective in vitro inhibitors were product analogs, t-cinnamic and p-coumaric acids, and carbonyl reagents, hydroxylamine and nitromethane. Application of the herbicides diuron, dalapon, amiben, and chloropropham, to plants resulted in a decrease in the intracellular concn of PAL. The inhibitory effect of alachlor was found to be dose-responsive and somewhat specific. A correlation between PAL inhibition and herbicidal activity was observed for hydroxylamine. The cytokinin, pyranyl benzyladenine, (PBA) increased PAL activity in pigweed. The possibility of developing herbicides acting through PAL inhibition is discussed.     

Effect of Herbicides on the Toxicity of Fungicides Against Rhizoctonia solani Causing Damping-off of Cotton

The effect of two herbicides (paraquat and simazine on the antifungal activity of two fungicides (captan and mounsrin) against Rhizoctonia solani was studied. when the herbicides paraquat and simazine were applied to soil they altered the effectiveness of both fungicides in controlling R. solani , thus causing damping-off of cotton. Both herbicides increased the toxicity of both fungicides against mycelial growth of the fungus. In pot tests, seeds or soil treated with captan or mounsrin, gave better control of R. solani damping-off disease when the soil was treated with paraquat or simazine compared to untreated soil. Captan was, however, found to be more effective in controlling the disease than mounsrin.     

Impact of rhizobial inoculation on Acacia senegal (L.) Willd. growth in greenhouse and soil functioning in relation to seed provenance and soil origin

Rhizobial inoculation has a positive impact on plants growth; however, there is little information about its effect on soil microbial communities and their activity in the rhizosphere. It was therefore necessary to test the effect of inoculation of Acacia senegal (L.) Willd. seedlings with selected rhizobia on plant growth, structure and diversity of soil bacterial communities and soil functioning in relation to plant provenance and soil origin. In order to carry out this experiment, three A. senegal seeds provenance from Kenya, Niger, and Senegal were inoculated with selected rhizobial strains. They have been further grown during 4 months in greenhouse conditions in two non-disinfected soils, Dahra and Goudiry coming respectively from arid and semi-arid areas. The principal component analysis (ACP) showed an inoculation effect on plant growth, rhizospheric bacterial diversity and soil functioning. However, the performances of the rhizobial strains varied in relation to the seed provenance and the soil origin. The selected rhizobial strains, the A. senegal provenance and the soil origin have modified the structure and the diversity of soil bacterial communities as measured by principal component analysis/denaturing gradient gel electrophoresis analyses. It is interesting to note that bacterial communities of Dahra soil were highly structured according to A. senegal provenance, whereas they were structured in relation to rhizobial inoculation in Goudiry soil. Besides, the impact of inoculation on soil microbial activities measured by fluorescein diacetate analyses varied in relation to plant provenance and soil origin. Nevertheless, total microbial activity was about two times higher in Goudiry, arid soil than in Dahra, semi-arid soil. Our results suggest that the rhizobial inoculation is a suitable tool for improving plants growth and soil fertility. Yet, the impact is dependent on inoculants, plant provenance and soil origin. It will, therefore, be crucial to identify the appropriate rhizobial strains and plant provenance or species in relation to the soil type.     

黄土高原小叶杨与其他树种枯落叶混合分解对土壤性质的影响

将小叶杨分别与其他11个树种枯落叶粉碎混合后进行室内分解培养,分析不同树种枯落叶混合分解对土壤性质的影响及其相互作用.结果表明:12个树种枯落叶单独混土分解均明显提高了土壤脲酶、脱氢酶、磷酸酶活性和有机质、碱解N含量,但对土壤速效P含量和土壤阳离子交换量(CEC)的影响差异较大,其中柠条和紫穗槐枯落叶改善土壤性质的效果明显.小叶杨分别与油松、侧柏、刺槐、白榆枯落叶混合分解,对土壤微生物数量的影响存在相互促进作用;小叶杨分别与侧柏、柠条枯落叶混合分解对土壤有机质、速效P、速效K含量和CEC的影响存在相互促进作用,但对土壤大部分酶活性的影响却存在相互抑制作用;小叶杨与落叶松枯落叶混合分解对土壤多数酶活性和养分含量的影响存在相互促进作用,而与樟子松枯落叶混合分解时则有抑制作用.总体上,小叶杨分别与白榆、油松、落叶松和刺槐枯落叶混合分解可促进土壤性质的改善,而与侧柏、柠条、樟子松、沙棘和紫穗槐枯落叶混合分解时则相互抑制.     

Effect of litter substrate quality and soil nutrients on forest litter decomposition: A review

Forest litter plays an important role in determining nutrient cycling, balance and maintaining ecosystem function of forest ecosystems. Studies have shown that litter substrate quality is one of the most important factors affecting litter decomposition in a given area. It is, hence, important to understand the factors controlling litter decomposition in the late decomposition stage and determining organic matter changes over the duration of litter decomposition. Decomposition rate of mixed litter may differ with that of a single specie litter. Supply of soil nutrients is an important factor controlling litter decomposition rate, because the essential nutrients in soil or litter material influence community and activity of decomposers (soil organisms). There were clear relationships among soil nutrient, litter substrate quality, and decomposition. Soil nutrient contents were positively correlated with litter substrate quality, showing that higher contents of soil nutrient were accompanied with good quality of litter substrate, and lower soil nutrients with poor litter quality. The effects of soil fertility on litter decomposition rate varied with environmental conditions. It was reported that litter quality regulates the early stage of carbon decomposition and its accumulation in soil, however, it could not predict the long-term dynamics of soil organic carbon. Hence, the formation and stabilization of soil organic carbon are controlled by the quantity of litter input and its interaction with the soil circumstances rather than by the litter quality. The present paper reviewed the research findings about litter decomposition related to litter substrate quality and soil nutrients, including short-term and long-term litter decomposition, decomposition of single-species vs. mixed-litter decomposition and litter nutrients release. The present paper aimed to clarify the relationship between soil nutrients and litter decomposition, which will help to understand forest succession, forest water conservation and soil re-production capacity.     

Estimation of the interplay between groups of fast and slow muscle fibers of the tibialis anterior and gastrocnemius muscle while running.

Electromyograms recorded from the lower limbs of humans while running were submitted to a time/frequency analysis using wavelets. The results of the wavelet analysis yielded intensity spectra at every time point during the swing and the stance phase. It was previously shown that more or less high frequency components get activated during different periods of the movement. The purpose of this study was to test to what extent the spectra can be reconstructed by a linear superposition of two generating spectra that were associated to groups of fast and slow muscle fibers. The terms fast and slow do not only refer to the conduction velocity but also to the shape of the motor unit action potential and are used to characterize the groups in a broader sense. The principal component analysis of the spectra confirmed that a two dimensional spectral space was appropriate. A parametric spectral decomposition was used to extract the generating spectra within the two dimensional spectral space. The generating spectra were in turn used to compute the power with which the groups of muscle fibers contribute to the measured spectra and thus to the overall muscular activity. The power that was obtained for the different time points during the movement reflects the biomechanically important interplay between the groups of muscle fibers while running.     

Effect of several herbicides on bacterial populations and activity and the persistence of these herbicides in soil

Summary Samples of a sandy loam soil were supplied with normal, 10-fold and 100-fold rates of ioxynil, dalapon, mecoprop, dichlorprop, MCPA + dichlorprop, picloram, and amitrole-T and incubated at 29°C at 65 per cent of the waterholding capacity. Treated soil samples were compared with untreated samples. Samples supplied with (NH₄)₂SO₄ and herbicides were used to investigate the effect of the herbicides on the rate of nitrification and the production of nitrite. In several cases higher numbers of bacteria were found for a longer or shorter period in soil treated with herbicides. There was some evidence that certain groups of bacteria had adapted to ioxynil in a soil sample supplied with the 100-fold rate of this chemical. After 2 or 4 weeks lower numbers ofAzotobacter chroococcum were found at the normal rate of ioxynil, dalapon, mecoprop, and dichlorprop. At the 100-fold rate of application the numbers of Azotobacter were unfavourably affected by all herbicides. The production of mineral nitrogen was hardly affected by the normal and 10-fold rates of application. In the first week the rate of nitrification was slightly depressed in soil samples treated with the normal rates of dichlorprop and amitrole-T and with the 10-fold rates of dalapon, mecoprop, and MCPA + dichlorprop. Strong inhibition of the nitrification for at least 7 weeks was shown by the 10-fold rate of amitrole-T. At the 100-fold rate all herbicides, with the exception of picloram, depressed the rate of nitrification for a longer or shorter period. During the second week a very small increase of nitrite was found in the samples treated with the normal and 10-fold rates of dalapon, mecoprop, dichlorprop, and amitrole-T. A small increase of nitrite was noted for 26 weeks in samples treated with the 100-fold rates of amitrole-T. A highly significant depression of CO₂ evolution was found in the first week in samples treated with the normal rates of ioxynil, dalapon, mecroprop, dichlorprop, and amitrole-T, also in samples treated with the 10-fold rates of dalapon, mecoprop, dichlorprop, MCPA + dichlorprop, picloram, and amitrole-T. A highly significant depression of CO₂ production was found after 8 weeks in all the samples treated with herbicides at the 100-fold rate with the exception of the sample treated with picloram. The decomposition of the herbicides was studied in soil samples treated with the 100-fold rates of herbicides. Only traces of dalapon and mecoprop were found after 9 months, but 7.2% ioxynil, 29.8% dichlorprop, 39% (MCPA + dichlorprop), 52.1% picloram and 52.2% amitrole-T were still present in active form.     

Impact of allelopathic rice seedlings on rhizospheric microbial populations and their functional diversity

Field performance of rice allelopathic potential is indirectly regulated by the microflora in the rhizosphere. The present study aimed to investigate the dynamics of microbial populations and their functional diversities in the seedling rhizospheres of rice cultivars with varied allelopathic activities by employing agar plate bioassay, fumigation and BIOLOG analysis. Rice cultivars significantly affected the microbial carbon content in their associated rhizospheric soil. The microbial carbon contents were ranked in a decreasing order as Iguape Cateto (441.0 mg·kg^–1) > IAC47 (389.7 mg·kg^–1) > PI312777 (333.2 mg·kg^–1) > Lemont (283.8 mg·kg^–1) with the nil-rice control soil of 129.3 mg·kg^–1. Similarly, the respiration rate of the soils was 1.404, 1.019, 0.671 and 0.488 μgC·g^–1· h^–1 for PI312777, Iguape Cateto, IAC47 and Lemont, respectively. The respiration rate was only 0.304 μ gC·g^–1·h^–1 for the control soil. The microbial flora in the rhizospheric soil of different rice cultivars was dominated by bacteria (58.4%–65.6%), followed by actinomycete (32.2%–39.4%) and fungi (2.2%–2.8%). BIOLOG analysis showed that the value of Average Well Color Development (AWCD) differed significantly among rice cultivars. It was always the highest in the rhizospheric soil of the strongly allelopathic rice cv. PI312777, and the lowest in the rhizospheric soil of the poorly allelopathic rice cv. Lemont. The AWCD value reached the maximum in all the sampled soils after 144 hours of incubation. The AWCD values from the rhizospheric soils of PI312777, IAC47, Iguape Cateto and Lemont were 1.89, 1.79, 1.60 and 1.43 times higher than that of the control soil. Principal Component Analysis (PCA) identified 3 principal component factors (PCF) in relation to carbon sources, accounting for 70.1%, 11.3% and 7.0% of the variation, respectively. 19 categories of carbon sources were significantly positively correlated to the 3 principal components. Phenolic acids, carbohydrates, amino acids and amides were significantly correlated to the principal component 1, phenolic acids, carbohydrates and fatty acids to the principal component 2, and carbohydrates and hydroxylic acids to the principal component 3. Amino acids and amides were the two main carbon sources separating the 3 principal component factors. In addition, the total microbial population in the rhizospheric soil was significantly positively correlated with AWCD, microbial biomass carbon, microbial respiration and Shannon index. There was a significantly positive correlation between the total microbial population and the inhibition rate (IR) on the root length of lettuce owing to the different allelopathic activities of the rice cultivars. These results suggest that changes in microbial population, activity and functional diversity in the rhizospheres are highly cultivar-dependent. These changes might play an important role in governing the rice allelopathic activity in the field.     

Climate,soil resources and microbial activity shape the distributions of mountain plants based on their functional traits

While soil ecosystems undergo important modifications due to global change, the effect of soil properties on plant distributions is still poorly understood. Plant growth is not only controlled by soil physico-chemistry but also by microbial activities through the decomposition of organic matter and the recycling of nutrients essential for plants. A growing body of evidence also suggests that plant functional traits modulate species’ response to environmental gradients. However, no study has yet contrasted the importance of soil physico-chemistry, microbial activities and climate on plant species distributions, while accounting for how plant functional traits can influence species-specific responses. Using hierarchical effects in a multi-species distribution model, we investigate how four functional traits related to resource acquisition (plant height, leaf carbon to nitrogen ratio, leaf dry matter content and specific leaf area) modulate the response of 44 plant species to climatic variables, soil physico-chemical properties and microbial decomposition activity (i.e. exoenzymatic activities) in the French Alps. Our hierarchical trait-based model allowed to predict well 41 species according to the TSS statistic. In addition to climate, the combination of soil C/N, as a measure of organic matter quality, and exoenzymatic activity, as a measure of microbial decomposition activity, strongly improved predictions of plant distributions. Plant traits played an important role. In particular, species with conservative traits performed better under limiting nutrient conditions but were outcompeted by exploitative plants in more favorable environments. We demonstrate tight associations between microbial decomposition activity, plant functional traits associated to different resource acquisition strategies and plant distributions. This highlights the importance of plant–soil linkages for mountain plant distributions. These results are crucial for biodiversity modelling in a world where both climatic and soil systems are undergoing profound and rapid transformations.     

Geographical and climatic differences in long-term effect of organic and inorganic amendments on soil enzymatic activities and respiration in field experimental stations of China

Soil enzymatic activities and basal respiration are two important bio-indicators of soil quality and are closely related to soil fertility and sustainable crop growth. We collected soil samples from four long-term experimental stations of China differing both geographically and climatically – Shenyang Agro-Ecological Experimental Station (brown soil), Fengqiu State Key Agro-Ecological Experimental Station (fluvo-aquic soil), Taoyuan Agro-Ecological Experimental Station (paddy soil) and Qiyang Red Soil Experimental Station (red soil) – to investigate the effect of long-term application of chemical fertilizer and/or organic manure on soil enzymatic activities and basal respiration. In general, soil enzymatic activities and basal respiration increased in soils with long-term application of chemical fertilizers and manures, especially organic manure. Among stations, soil enzymatic activities were not consistently increased with organic manure alone (e.g. the sucrase and phosphatase activities in the paddy soil from Taoyuan and red soil from Qiyang). As well, soil enzymatic activities were characterized by distinct zonality. Soil cellulase and urease activity were the two main indicators of soil fertility as evaluated by principal component analysis. Regression analysis of the major abiotic factor(s) influencing enzyme activity revealed a dependence on the specific enzyme tested and the activity of specific soil enzymes depended on the location of the experimental station. Environmental factors, mainly soil temperature, moisture and pH, as well as soil texture, should be taken into account in evaluating the effects of long-term fertilization on soil biological activity and soil fertility in field experimental stations differing geographically and climatically.     

湿地枯落物分解及其对全球变化的响应

综述了当前湿地枯落物分解及其对全球变化响应的研究动态。湿地枯落物分解研究已随研究方法的改进而不断深化;当前湿地枯落物分解过程研究主要集中在有机质组分和元素含量变化特征的探讨上;湿地枯落物分解同时受生物因素（即枯落物性质以及参与分解的异养微生物和土壤动物的种类、数量和活性等）和非生物因素（即枯落物分解过程的外部环境条件,包括气候条件、水分条件、酸碱度与盐分条件以及湿地沉积的行为与特征等）的制约;模型已成为湿地枯落物分解研究的重要手段,对其研究也在不断深化。还讨论了湿地枯落物分解对于全球变化的响应,指出全球变暖、大气CO2浓度上升、干湿沉降及其化学组成改变可能对枯落物分解产生的直接、间接和综合影响。最后,指出了当前该领域研究尚存在的问题以及今后亟需加强的几个研究方面。     

五大连池新期火山熔岩台地不同植被类型土壤微生物群落的功能多样性

土壤微生物群落是陆地生态系统的重要生物活性成分,其结构和功能多样性直接影响到系统的碳、氮等生态过程,微生物群落功能多样性与地上植被类型变化密切相关,开展植被类型对土壤微生物群落功能多样性的影响研究具有重要意义。以五大连池新期火山熔岩台地苔藓、草本、灌丛、矮曲林、针阔混交林5种典型植被类型为对象,利用BIOLOG微孔板法研究不同演替阶段植被类型土壤微生物群落功能多样性特征。结果表明：不同植被类型土壤微生物群落功能多样性存在显著差异。平均颜色变化率（AWCD）随培养时间延长而逐渐增加,大小顺序为：苔藓 > 针阔混交林 > 矮曲林 > 草本 > 灌丛。灌丛土壤微生物多样性指数与其他植被类型间差异显著。主成分分析结果表明,主成分1和主成分2分别能解释变量方差的56.24%和29.59%,不同植被类型下土壤微生物的碳源利用格局差异主要是由氨基酸类和带磷基糖类引起,二者合计解释总变异量的47.51%。冗余分析表明,速效磷、铵态氮、C：N和pH对微生物功能多样性具有显著的影响,羧酸类、氨基酸类、酯类和胺类的降解更易受到环境因素的影响。研究结果为进一步探讨植被类型与土壤微生物之间在植被演替过程中的关系提供参考。     

生草栽培对山核桃林地土壤养分及微生物多样性的影响

高强度经营导致山核桃林地土壤性质改变,设置了白三叶、黑麦草、油菜、紫云英、自然杂草和清耕(对照)6个处理,以3次重复,随机排列的2年田间试验,研究了不同生草栽培对山核桃林地土壤养分和微生物多样性的影响。结果表明:与清耕相比,生草栽培均能改善土壤养分状况,除全钾外,白三叶和紫云英处理较其他处理能显著提高土壤养分含量,其余几个处理间差异不明显;生草栽培显著提高了土壤微生物生物量碳(MBC)含量,白三叶、黑麦草、紫云英、油菜和自然杂草处理分别较清耕提高了169.6%、159.7%、144.1%、138.6%和58.6%,差异达显著水平(P0.05)。6种不同处理的土壤微生物活性(AWCD)、微生物Shannon指数和均匀度指数均存在明显差异。不同处理的土壤AWCD为白三叶紫云英油菜自然杂草黑麦草清耕;白三叶处理的土壤微生物Shannon指数高于其他处理;白三叶、紫云英和油菜处理的土壤微生物均匀度指数显著高于其他处理。相关性分析表明,土壤微生物活性、微生物Shannon指数和均匀度指数两两之间均达到极显著差异(P0.01),三者与土壤各养分指标之间未达显著差异,但表现为正相关关系。白三叶、紫云英和油菜对改善土壤微生物特性效果较好。     

Positive and negative impacts of insect frass quality on soil nitrogen availability and plant growth

Frass deposition to soil is an important pathway by which herbivorous insects impact decomposition and soil nutrient availability. However, little is known about how frass quality influences ecosystem properties. Here, we examined the effects of frass quality on the decomposition process, soil nitrogen (N) availability, and plant growth, using frass of Mamestra brassicae (L.) that fed on fertilized or unfertilized Brassica rapa L. var. perviridis Bailey. The frass quality was largely dependent on the host plant quality. Frass excreted by larvae that fed on the fertilized plants had higher N than that of larvae that fed on the unfertilized plants. The decomposition rate of the frass did not differ between N-rich and N-poor frass, except during the early decomposition period. The inorganic N concentration decreased during decomposition in both frass types. However, difference in the initial inorganic N concentration led to different consequences regarding soil N availability. Furthermore, addition of frass to the soil differently influenced the growth of B. rapa plants depending on the frass quality: plant biomass was increased by N-rich frass addition but decreased by N-poor frass addition, compared to the biomass without frass addition. These results indicate that frass quality is an important factor in determining the impact of herbivorous insects on nutrient dynamics, and that frass positively or negatively influences soil N availability and plant growth, depending on its quality.     

Influence of the soil conditioner cellulose xanthate on the activity and persistence of nine acetanilide herbicides

Applications of cellulose xanthate equivalent to 25 kg cellulose/ha increased the numbers of weed seedlings by up to 23% compared with untreated controls. With propachlor and prynachlor, weed control was poorer in the presence of cellulose xanthate and analyses of soil samples demonstrated that the rate of herbicide loss from the soil was enhanced. Although the soil conditioner increased the rate of loss of some other acetanilide herbicides, weed control was not greatly affected. The results suggest that interactions between cellulose xanthate and acetanilide herbicides are only important with those compounds which are normally of very short persistence.     

Effects of homosynaptic depression on spectral properties of H-reflex recordings

The purpose of this study was to determine the effects of homosynaptic depression (HD) on spectral properties of the soleus (SOL) H-reflex. Paired stimulations, separated by 100?ms, were used to elicit an unconditioned and conditioned H-reflex in the SOL muscle of 20 participants during quiet standing. Wavelet and principal component analyses were used to analyze features of the time-varying spectral properties of the unconditioned and conditioned H-reflex. The effects of HD on spectral properties of the H-reflex signal were quantified by comparing extracted principal component scores. The analysis extracted two principal components: one associated with the intensity of the spectra and one associated with its frequency. The scores for both principal components were smaller for the conditioned H-reflex. HD decreases the spectral intensity and changes the spectral frequency of H-reflexes. These results suggest that HD changes the recruitment pattern of the motor units evoked during H-reflex stimulations, in that it not only decreases the intensity, but also changes the types of motor units that contribute to the H-reflex signal.