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Article Critique

Gordon, Helen, Haygarth Philip and Bardgett Richard. “Drying and Rewetting effects on Soil Microbial Community Composition and Nutrient Leaching.” Soil Biology & Biochemistry, vol. 40, 2008, pp. 302-311.

Background and Purpose

The article finds that there is an escalating recognition that the environmental perturbations and stressors have significant effects on community composition and microbial physiology, with effects for nutrient flows and energy in terrestrial ecosystems. A good example of an effect of such change is soil drying and rewetting (D/RW), which according to Gordon, Haygarth and Bardgett (302) exposes soil microbes to physiological pressure by lowering substrate diffusion resulting in alterations in metabolism. The investigators feel that it is critical to acquire more information on the topic because D/RW affects a soil’s potential to withhold water thereby building osmotic stress. The emerging issues in this area prompt the researchers conduct a trial to confirm whether D/RW stress contributes to more nutrient leaching from developed that from undeveloped grassland soils that have different features.

Summary of Findings

The scholars find from the study that soils from the poorly maintained grassland (no history of fertilizer application) had relatively higher levels of fungi relative to bacteria and microbial biomass compared to the soil from areas where people continuously utilize fertilizers. The finer details of the study revealed that the D/RW stress lowered fungal phospholipid fatty acid analysis, the ratio of fungal to bacterial and microbial biomass carbon in soils from both grasslands (Gordon, Haygarth and Bardgett 305). The D/RW reduced the levels of microbial biomass nitrogen in both settings, but more so in the developed areas.

Description of Study

The experimenters apply the phospholipid fatty acid analysis (PLFA) to tests soils from different grasslands. Gordon, Haygarth and Bardgett (304) started with maintaining soils from both settings at fifty five percent at WHC (water holding capacity) or dried to ten percent WHC and then rewetted to fifty five percent WHC. The researchers then sampled the specimen on the first, third, ninth, sixteenth, thirtieth, and fiftieth days after rewetting.

Assessment of the Results

The experimenters bring out the findings in a convincing manner by offering in-depth information about what they study. The three use tables and figures to summarize their performance and this make it easier for readers to acquire the major arguments in the article. The graphs on page 306, for example, provide users with a quick preview of some of the concepts that could take much longer to understand. A reader can easily understand the implications of D/RW on microbial biomass compared to the period of study by simplify studying the pictorial presentation on page 306. Otherwise, failure to use graphical features and figures to summarize the content could expose the article users to so much content to read.

Discussion

The argument that it is important to identify the effects of environmental alterations on soils is convincing to readers. Even though the scholars do not provide any guidelines for future study, they article would be of value to future learners, tutors, and investigators. The study by Gordon, Haygarth and Bardgett can become better by testing samples of soils from more settings than grasslands to identify the effects of D/RW on other areas. The similar feature in this article and others is that the authors concur that the ability of soils to retain water and nutrients vary depending on the conditions.

Questions to ask Mentor

  • What could other alternative study methodology lead to the same or almost similar findings?
  • Are there any limitations with the statistics presented in the paper?
  • Provide any future suggestions concerning studies in this field.

Harrison, Kathryn and Bardgett Richard. “Influence of Plant Species and Soil Conditions on Plant-Soil Feedback in Mixed Grassland Communities.” Journal of Ecology, vol. 98, 2010, pp. 384-395.

Background and Purpose

The study by Harrison and Bardgett, who both serve at the Soil and Ecosystem Ecology Laboratory at the Lancaster University, seeks to find more information on the plant-soil feedback in communities with mixed grassland and its importance to plant output and community ingredient relative to abiotic elements of soil fertility and type. The escalating awareness among environmentalists and ecologists concerning the advantages of plant-soil interconnection as a driver of the dynamics of plants in a community, particularly in the field of plant invasion and succession drive the investigators to experiment.

Summary of Findings

The results show that during the conditioning stage of the trial, that variations that existed among individual plants affected soil nutrient availability and microbial communities. The biotic effects in this phase, however, had little influence as drivers of the presence of nutrients and soil microbial elements that were the abiotic features of fertility and soil type. The second stage of the study shows substantial coordination effects of conditioning in the growth rate of individual plants in mixed settings. The investigators noted that the feedback harmonization in the second phase was independent of soil fertility or type and mostly had adverse effects. The study showed that in many individual plants, the species performed relatively poorer in mixed environments placed in soil that had initially supported their species.

Description of Study

Harrison and Bardgett complete a four-year mesocosm study to find out the effects of the type of soil, soil conditioning, and important management using several plant species from the mesotrophic grassland region. The researchers conditioned soils from two settings using the monocultures of nine unique grassland species during the first phase (Harrison and Bardgett 386). The investigators in the subsequent section (the feedback phase) mixed nine species grown in developed (conditioned) soils to investigate the effects of experimental elements on the productivity and distribution of individual and mixed communities plant species.

Assessment of the Results

The scholars present their findings in a way that makes it easy for readers to grasp the content of the study, and apply methodologies that make the presentation much easier to follow. The results summarize the findings in phase one (soil conditioning) then proceeds to summarize the results in phase two (feedback face). The researchers use figures and graphs to present a comprehensive summary of their conclusion, and this makes it easy to retrieve data from the document. Even though some of the numbers and scientific presentations may be difficult for learners at lower levels to understand, they contain vital information that through guidance can be of help to students. The figures, nevertheless, may be of great importance to investigators in this field who rely on such data to complete their studies.

Discussion

The information in the article is convincing despite the fact that the scholars do not provide any suggestions for future investigations. The separation of the explanations into diverse areas makes it easy for users to understand the analysis of the different sections and this makes the discussion part more convincing. Additionally, the researchers utilize the writings of other scholars to support their argument, and this makes the paper more convincing. The executors of the study can make it better by coming up with further studies to support the idea that the plant-soil feedback determines the performance of a broad category of individual plant species in mixed grassland environments over a longer period. The development of follow-up exercises will offer firm confidence to the audience that the entire message is credible and reliable.

Questions to ask Mentor

  • What are the significant environmental effects on how plant-soil feedback regulates the performance of individual plant species in mixed grassland communities?
  • Are there any weaknesses with the findings?
  • What contrary opinions exist concerning the results of this experiment?

Hoogmoed, Michael et al. “N-Fixing Trees in Restoration Plantings: Effects on Nitrogen Supply and Soil Microbial Communities.” Soil Biology & Biochemistry, vol. 77, 2014, pp. 203-212.

Background and Purpose

The investigators seek to expound how afforestation of agricultural land contributes to carbon sequestration which has the capability to address climate change and to restore native ecosystems. The researchers state that even though single-species tree plantations serve as the prevalent forms of afforestation systems, restoration plantings which include a combination of native tree species that are not for harvest are becoming popular. The background information pushes the team to perform a study which finds out whether nitrogen-fixing trees can reach the nitrogen derived from the fixation of atmospheric nitrogen by neighboring nitrogen-fixing trees (Hoogmoed 204). The study further seeks to find out whether soil microbial communities vary under nitrogen-fixing trees and non-nitrogen-fixing trees in a mixed-species planting.

Summary of Findings

The study found that fixed atmospheric nitrogen was used by the nitrogen-fixing trees through root connections or organic matters of nitrogen from the litter cover, rather than through the putrefaction of nitrogen-fixers litter. The research finds that even though the two nitrogen-fixing trees under study appeared to fix atmospheric nitrogen, they varied regarding nitrogen and carbon contribution to the soil, and also differ in their microbial community ingredient beneath them. The team concludes that the implications of nitrogen-fixing trees types on soil carbon sequestration depends on a particular species and cannot be argued on a general basis.

Description of Study

Hoogmoed and his team use the N natural abundance methodology to sample leaves from the crowns as well as soil and little under the crowns of two nitrogen-fixing tree species that prevailed the planting. The field study that takes place in northern Victoria, south-eastern Australia collected standing litter from a designated quadrant (20cmX20cm) to assess the availability of the amount of fixed atmospheric nitrogen in fresh leaves and litter (Hoogmoed 204). The researchers further apply the phospholipid fatty acid (PLFA) analysis to analyze soil microbial environments among tree species to come up with findings that would suit the research questions.

Assessment of the Results

The panel of researchers present the results in a transparent manner which minimizes the stress readers would undergo to acquire the original message. The article, similar to the prior ones, makes use of graphical presentations to summarize concepts that may need more time to understand if the reader opts to go through the document bit by bit. The panel tries to achieve accuracy in the way they present figures in many tables that spread across the paper, and this eradicates doubts that could harm credibility.

Discussion

The message by the authors is convincing and of value to present and future investigators who may acquire valuable insight from the document. Apart from using the works of other researchers to back up their points, the discussion section is convincing because this area also makes use of graphical presentation to provide a more comprehensive description. The team suggests that future investigators should identify whether there would be consistency between the current and the future findings arguing that a connection would prove beyond doubt that even in young planting where the environment is dry and where the rate of litter decomposition is slow, nitrogen fixers may serve a critical purpose in facilitating the growth of non-nitrogen fixing trees. The chief connection between this article and the others that shed light on this subject is that it agrees with the idea that nitrogen-fixing is a fundamental purpose that boosts the growth of plants in grassland settings.

 

 

Questions to ask Mentor

  • Are the nitrogen-fixing trees that fix atmospheric nitrogen substantially the same regarding nitrogen and carbon content?
  • What other factors affect nitrogen-fixing tree species on carbon sequestration on soil?
  • What are the possible positive and adverse effects of the findings in the trial?

Perkins, Lora and Nowak Robert. “Native and Non-Native Grasses Generate Common Types of Plant-Soil Feedbacks by Altering Soil Nutrients and Microbial Communities.” Oikos, vol. 122, 2013, pp. 199-208.

Background and Purpose

Perkins (Department of Natural Resource Management, South Dakota State University) and Howak (Department of Natural Resources and Environment Science, University of Nevada) understand the value of the connection between soil and plants. The authors begin by describing soil conditioning as the effect that occurs when the vegetation switch the features of the soil environment (Perkins and Nowak 199). The background information motivates the researchers to conduct a study that identifies the plant-soil feedback connection of seven co-existing indigenous and non-indigenous grass species to highlight on how plants alter their soil environment.

Summary of Findings

The experiment reveals species-specific soil conditioning effects on soil microbial and soil nutrients by plants. Also, the study showed how indigenous specifies produced types of plant-soil feedback that is beneficial to other plant species.

Description of Study

The experimenters utilize a two-phased framework where they breed first generation vegetation to stimulate alterations in specific plant species in the soil, and vegetation of the second generation that served as a bioassay to ascertain the effects of any contradictions. The data collectors also employed the path-analysis method to recognize the possible series of variations in the vegetative cover (first generation) on the microbial and nutrients ingredients in the soil, and development in plants.

Assessment of Results

The use of figures and graphical presentation make the results more clear and easy to understand. The statistics are appropriate because it relates to the topic under study, and because they emerge from the confirmations of other scholars. Even though some of the scientific presentation may appear difficult to understand for early learners, one gets to understand the concept after several readings and proper guidance.

Discussion

The analysis part and the entire article provide a convincing message that is reliable and which may be of value to parties that have an interest in this area. The investigators do not guide future studies, but when comparing the article with others that highlight on the same topic, it emerges that this one is equally important. The best way to make the study better is to include the findings of many recent documents because some elements might have changed over the four years since the production of this paper.

Questions to ask Mentor

  • What teachings do future researchers gain from the study?
  • What significant differences exist in this finding compared to others?

Spedding, Tim et al. “Soil Microbial Dynamics in Maize-Growing Soil under Different Tillage and Residue Management Systems.” Soil Biology & Biochemistry, 36, 2004, pp. 499-512.

 

Background and Purpose

The study by Spedding, Hamel, and Mehuys who serve at the Department of Natural Resource Sciences at the McGill University, and Madramootoo of the Department of Agricultural and Biosystems Engineering at the McGill University seeks to explore the long-term effects of residue management and tillage on soil microorganism. The team of investigators has the desire to expound on the idea that soil microorganism and all the activities that they control are significant for the sustainability of systems in the agricultural system.

Summary of Findings

The soil microbial biomass carbon exemplified little change soil microbial biomass nitrogen responded to post-emergence nitrogen fertilization, the experiment using the PLFA exhibited an escalation in the total amount of PLFA all through the season as well as an increase in the number of fungi. The profiles using PLFA indicated better variation between the sampling depth and time. The study reiterates that measuring the quality of soil based on its microbial content must consider seasonal alterations in soil chemical and physical conditions.

Description of Study

The investigators began by imposing residue and tillage treatments on plots in 1991. The treatment consisted of conventional tillage, reduced tillage, and no till with crop residue either eliminated or maintained in the experimental fields, arranged in a random absolute complete block plan. The researchers test contents of the phospholipid fatty acid, SMB-C (soil microbial biomass carbon), and SMB-N (soil microbial biomass nitrogen) four times at two different depths (0 to 10cm and 10 to 20cm), over the growing season in 2001. The researchers placed the sample times as follows; May 7 (pre-planting), June 25th, July 16th, and September 29th. The data collectors noted that the impact of time was of greater value than the ones attributed to residue or tillage treatment.

Assessment of Results

The results in the article by Spedding and his affiliates are clear, and the figures provide confidence to the readers that the information is credible and sound. The authors use tables to present their findings, and this makes the results more visible. The table on page 503, for example, gives a summary of the significance of tillage, the date of moister or water content (WC), and residue which saves readers the process of going through all the information. The other factor that makes the results clear is that the authors provide an extensive explanation of their findings thus satisfying the readers’ desire.

Discussion

The discussion part and the entire article provide a convincing argument which would cast any doubts the readers might have. The scholars do not offer any suggestions for future study, but it is evident that the writing will be beneficial for many years to come. The researchers can improve the nature of the study by joining hands with other specialists in this field to come up with advanced findings in this area.

Questions to ask Mentor

  • What the robust and weak features of the study?
  • Would the hypothesis still hold a decade or two from now?

 

 

 

 

Works Cited

Gordon, Helen, Haygarth Philip and Bardgett Richard. Drying and Rewetting effects on Soil Microbial Community Composition and Nutrient Leaching. Soil Biology & Biochemistry, vol. 40, 2008, 302-311.

Harrison, Kathryn and Bardgett Richard. “Influence of Plant Species and Soil Conditions on Plant-Soil Feedback in Mixed Grassland Communities.” Journal of Ecology, vol. 98,

2010, pp. 384-395.

Hoogmoed, Michael et al. “N-Fixing Trees in Restoration Plantings: Effects on Nitrogen Supply and Soil Microbial Communities.” Soil Biology & Biochemistry, vol. 77, 2014, pp. 203-212.

Perkins, Lora and Nowak Robert. “Native and Non-Native Grasses Generate Common Types of Plant-Soil Feedbacks by Altering Soil Nutrients and Microbial Communities.” Oikos, vol. 122, 2013, pp. 199-208.

Spedding, Tim et al. “Soil Microbial Dynamics in Maize-Growing Soil under Different Tillage and Residue Management Systems.” Soil Biology & Biochemistry, 36, 2004, pp. 499-512.

 

 

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