Biology

Summary of the article
The research article entitled, Effects of soil salt levels on the growth and water use efficiency of Atriplex canescens (Chenopodiaceae) varieties in drying soil, authored by Glenn and Brown (1998) described the performance of three plant varieties to varying degrees of salt and water concentrations.  It has long been established that maximal growth and development of any plant species are mainly dependent on optimal environmental conditions.  These include an ample supply of water, as well as nutrients from the soil, sun and sunlight.  Any significant decrease or absence of any of these factors may induce stress to a plant species.  Moreover, the combinatorial effect of at least two external factors may pose more harmful effects on a plant.

The quality of soil that is used for planting may also affect the growth and development of plants It should be understood that the soil serves as a water reservoir to the growing plant.  Water also serves as a matrix for transporting organic, as well as inorganic solutes to the plant.  The main region of entry for these solutes is the root of the plant, which is strategically located adjacent to the soil.  It has been suggested that the any perturbation of two external factors may impose an additive effect on the performance of a plant.  However, there are certain research reports that describe a more complicated mechanism, wherein the soil would mitigate conditions of water stress.  For example, soil that contains some amount of salt may assist in a plants survival when there is not enough water on the ground.  It is possible that plants may have adapted a response to water insufficiency by imbibing salts into its system, as this condition would retain moisture within the plant.

A number of water retention mechanisms have been earlier described, including the inherent increase in the number of salt ions within the leaves of the plant.  Another mechanism associated with water retention is the reduction in the frequency of opening the stomata of the leaf, thus reducing the transpiration of water to the environment.  It has also been suggested that plants may have learned to survive through scarce water conditions, by adjusting their osmotic potential to only require a minute amount of hydration each day.

The study of Glenn and Brown (1998) thus investigated the response of the C4 xerohalophytic shrub Atriplex canescens on salt stress.  This shrub is generally found in saltbushes in regions of North America, where the soil is often saline and dry.  Currently, there are six varieties of Atriplex and each could be differentiated through its degree of salt tolerance and water efficiency.  Despite the established features of this plant species, the investigators wanted to determine whether there was any interrelationship between the capacity of this species to adapt to salt and water stress.  The employment of three varieties of Atriplex would also allow the investigators to probe the actual association of salt tolerance to water stress.

Briefly, seedlings of Atriplex were transplanted to three different salinity conditions, namely 0, 85 and 520 molm3, representing suboptimal, optimal and supraoptimal conditions for plant growth.  The soil used in the study consisted of a mixture of river sand and peat-based potting soil, of which the mean initial water content was estimated to be 0.899 Lpot.  The seedlings were maintained in a greenhouse that had day temperatures ranging from 25oC to 35oC and light transmission of 65.  The seedlings were allowed to grow until 80 of the plant was wilted.  The plants were also measured for growth, as well as cation content and efficiency of use of water.  The results of the study showed that combinatorial effect of salt and water stress was not additive or increased, but instead, facilitated in the growth and survival of the plant.  The researchers found that seedlings that were subjected to higher salt conditions performed better under insufficient water conditions, as compared to seedlings that were subjected to optimal and suboptimal salt conditions.

Critique of the article
The research article of Glenn and Brown (1998) is a very informative report on the response of three varieties of Atriplex to varying external conditions.  The results of their study were novel because contrary to what has been upheld for decades, the plants they studied did not experience an additive impact when two external factors were introduced.  It has long been thought that the occurrence of two stressful factors to a plant would result in a double burden on the plant and that its capacity for growth and development would be significantly retarded.  However, this research report changes the belief that the effect of two stress factors would add up and impose developmental problems to plants.

The presentation of the rationale of the study was very clear.  The investigators explained the current concepts that have been established with regards to optimal growth and development of plants.  The citations of prior research reports are also comprehensive, as the investigators attempted to fully explain the basis and objectives of their study.  The methodology of the study was also good, wherein they attempted to keep the conditions of the experiment constant, except for the variable factors.  For example, the amount and components of the soil mixture was precisely determined based on weight.  In addition, the growth stage of the seedlings at the start of the study was also determined to be almost within the same range.

The data collected from the study was clearly presented, as seen in the graphs and tables.  The graphs for each plant variety clearly showed that there was indeed a difference in the growth and development of the seedlings based on the amount of salt in the soil.  The tables also showed that the investigators were cautious in the analysis of their data, as shown in their employment of the statistical test of analysis of variance (ANOVA).  This statistical test has the capability of identifying any significance differences between experimental conditions.  The investigators also employed the calculation of standard errors, which could also determine the robustness of the values of their measurements.  The data presented in the articles strongly support the conclusions of the investigation, wherein seedlings subjected to higher salt concentrations performed better than those subjected to normal or optimal external conditions.  The paper clearly presented their bottom line that salt and water stress did not impose an additive effect on the growth and development of the Atriplex varieties.

One weakness of the study was that the investigators did not attempt to determine any genetic factors that may have influenced such performance in salt conditions.  It is possible that there are certain genes that have been activated in the seedlings when a change in its external environment is detected.  For example, there are heat shock genes that are activated when an organism is exposed to extreme temperatures.  It is thus likely that the plants in this study were capable of activating salt and water shock genes that allowed them to adapt and ultimately survive such specific conditions.  The genetics aspect of this study may be performed through the rapid amplification of polymorphic DNA (RAPD) analysis, which can generate a DNA profile of each seedling.  It would also have been more informative if the investigators presented any tissues sections that would show how water and salt stress have affected the internal structure of the growing plants.
 
The tables and figures of the research article are clearly presented and easily understood.  The labels of each axis and column are properly labeled and thus as a reader, there is no difficulty in finding any information of interest from the report.  However, it would have been more interesting if the investigators provided images of the plant itself, possibly comparing a normal, affected and wilted plant.