Competition between Chara aspera and P. pectinatus as a function of temperature and light BY HASt0203 Critical Review 1 Competition between Chara aspera and Potamogeton pectinatus as a function of temperature and light Introduction In the article “Competition between Chara aspera and Potamogeton pectinatus as a function of temperature and light” by authors Marcel S. Van den Berg, Hugo Coop, Jan Simons and Annemarie de Keizer, it was theorized that one type of aquatic plant may be a better competitor for sunlight than another plant that is more of a bottom dweller. They argue that “P. ectinatus and C. spera have different growth forms and the canopy forming P. pectinatus may be a better competitor for light than the bottom-covering C. aspera. ” to support this first argument. In addition they also put forth a second argument in that the bottom dwelling aquatic plant may, in the long run, be a better competitor in clear water as it may be better able to use sunlight in a more efficient manner and also due to its faster emergence in the annual life cycle of both plants, “The latter however, might be able to survive in clear water due to a more efficient use of light.
Because both species have an annual life cycle, P. ectinatus might be outcompeted for light or space in Lake Veluwemeer due to the emergence of C. aspera earlier in the year. ” The scientific team certainly does make a valiant effort to prove that this hypothesis is true and it can be deduced that the authors took great time in conceptualizing, realizing and working through the experiment and prove this for the most part but it does fall short in some areas. Summary The authors include a brief history of Lake Veluwemeer and give a concise overview of how eutrophication led to the survival of the P. ectinatus species within the lake and later C. aspera. They then go into the specifics of how the emergence experiment was set up and carried out. This is the first of two experiments conducted and revolves around the effects of temperature and length of day on the emergence of the two specified species of plants. The article then goes on to reveal how the second experiment was set up and conducted and revolved around light source competition between the two plant species.
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It was then explained how the data collected was processed and analyzed using a “statistical treatment” involving various logarithmic functions. The results were then presented for the two experiments with the mergence experiment first and then the competition experiment lastly. In general, plants emerged more rapidly at a higher temperature than they did at a lower temperature. It was also revealed that different planting techniques emerged faster than others and which type of technique ended up being more dominant to the conclusion of the experiment.
The results of the second experiment were presented and confirmed that P. pectinatus was the larger plant species and, for the most part, thrived better in a more generous light area of the water (near the surface) due to its shape and size. Although it was noted that both plants had diminished growth and biomass in the lower light areas of the lake (near the sediment). Not surprisingly it was also determined that due to the canopy shape of C. aspera, the irradiance levels were drastically lower underneath the plant leaves.
In the discussion section of the article, the data and results were reiterated and the authors then compared the results to their hypothesis. It was then stated that although the results should have shown that P. pectinatus outcompeted the plant species C. aspera, this was not the case. The results showed that C. spera outcompeted the plant species P. pectinatus and there was no reason or theory given as to why this was the result of the experiment. It was noted that neither light nor early emergence explained this twist. Possible errors in the study were then given by the authors.
Critique To start, the experiment and the execution were both a great design. There was very little to disagree with on both of these points as the authors were very thorough and completed the experiment with accuracy and knowledge of the subject. The use of different planting techniques (the use of tubers, bulbils and oospores) and their ollection was also very detailed and methodic. The only issue that can be pointed out with this step was that the tubers were not collected from Lake Veluwemeer but from Lake Eemmeer although the two locations are in close proximity to each other.
To account for the diminishment of the water due to evaporation, water from Lake Veluwemeer was used to replenish the tanks but this perhaps contributed to the experiment going awry in the end and also to the pH issues that were later addressed in the Discussion section of the article. The fact that artificial light was also used in replacement of natural sunlight was another point that was roublesome. This may or may not have affected the speed of the plants natural growth patterns or cycle and even their ability to carry out the process of photosynthesis but that can only be speculated by the reader.
There is no indication that this was the case but there is also no indication that it was not. Another factor was somewhat perplexing, in that plants were being removed from the experimental environment when they broke through the surface of the sediment. It is unclear whether this may have been a factor in emergence of plants that occurred after these plants removed. Could these plants have played a factor in the way later emergent plants grew or sprouted? Would these plants have been a hindrance or in completion for nutrients and resources to those plants that had not yet broke through.
The answer to these questions is unclear, as in a real lake environment, the plants would have remained in the sediment. On the flip side of that argument, it is also possible that aquatic organisms could have fed off of these newly sprouted plants and essentially mimicked the removal by the scientists. The same issues were apparent in the second experiment as were in the first. In addition, the scientists worked off of an assumption that “irradiance used probably would not limit growth” which throws a whole gamete of problems into the experiment.
This was also based on unpublished results, so they were not totally reliable. The use of tweezers in the control experiment was also something that raised an eyebrow. Although these were used as more of a place setting between the C. aspera plants, they do not have roots and compete for nutrients as will a P. pectinatus plant, but in either case this did not have any effect on the C. aspera plants so it may be a nonissue. It was also stated that were also “No corrections were made for multiple reflection between light sensor and water surface occurring in the surface layer”.
Could this oversight or omission have affected the efficiency of both plant species in comparison to a more direct and natural light source, or was it purely another nonissue within the confines of the experiment? This was not addressed in the article. The use of visual data in the article was used wisely and helped to better explain the experiment and the data that was collected throughout. The two visuals that I ound to be most helpful was Fig. 2 on page 246 showing the Time of Emergence (in days) vs. the Temperature and Table 2 on page 247.
Fig. 2 on page 246 was a good visualization of the data, in which, it was clear that the higher the temperature was, the faster the plants emerged. In Table 2 on page 247, it stated and gave evidence of confidence levels as to the data; simply stating that C. aspera density was rejected and why. Fig. 3 on the same page (247) was a nice graphic of how P. pectinatus cover effected the irradiance to the plants beneath it; the more coverage the plant had the ess light was available to the plants below said cover.
Table 1 was not that helpful as it was previously stated above that there was an issue with pH levels and this was, in the end, not accounted for. This, ultimately, lowered the value of this graph in the whole scheme of the article. The Discussion section on the article was altogether precise and accurate save for the lines, “The fact that C. aspera became dominant over P. pectinatus cannot be explained by competition for light nor by the early emergence of C. aspera. Another factor must be involved in this shift, which unfortunately we were not able to emonstrate this factor in the laboratory. I found this to be quite odd as this was a major part of the experiment and article subject matter and was almost a throwaway of the entire experiment. Basically, I read this as “Oh well, it didn’t work out and we don’t know why’, but the saving grace is that they did present a possible theory that HC03- levels may be a part of the reason the experiment did not work. Conclusion The article was very informative and resulted in an interesting take on competing plant species and the effects of light on these same plant species.
Although there ere a few places that I thought needed to be addressed further such as the pH levels and the source lake of P. pectinatus tubers, I found the overall experiment and follow through to be executed well and worthy of appreciation. The inclusion of visual graphics also was a great source within the article to help understand and process the data, as well as, break up the wall of print and give the eyes some “candy’ whilst reading. References Van den Berg, M. S. , H. Coops, J. Simons & A. De Keizer, 1998. Competition between Chara aspera and Potamogeton pectinatus as a function of temperature and light. Aquatic Botany 60: 241-250.