Wayne, I think you are right: phytolith C may number in the giga-tons globally, but it is most likely very small compared to other C pools.
After reading through Parr's phytolith C paper (Parr & Sullivan 2005, Soil Biology & Biochemistry), I noticed a few problems. First, the authors state that C in phytoliths "account[s] for up to 82% of the total carbon in well-drained soils after 1000 years of organic matter decomposition." True enough, which is why phytoliths are a great tool for paleoecological studies. But it should be recognized that the amount of phytoliths (and therefore occluded C) remaining after 1000 years will be just a tiny fraction of the modern soil phytolith pool. Second, the planting of phytolith-rich species such as sugarcane or bamboo may increase the soil phytolith pool slightly, but they most likely will not result in huge gains of C sequestration. Only in very special circumstances will you find enormous gains of soil phytoliths (Meunier et al 1999, Geology; Henriet et al 2008, Biogeochemistry), and these examples are due to local soil properties, not the species growing on them. Third, the authors imply that phytolith C sequestration is essentially a never ending process, and that huge sequestration numbers can be expected indefinitely. If that were the case, common sense tells us that we would be swimming in a sea of phytoliths. The authors then go on to state that a forest can sequester large amounts of C only while it is growing. That may be the case, but I think most of us would agree that a forest is preferable to a sugarcane field in so many other ways: biodiversity, ecosystem services, etc. After thinking the issue over, I don't see how phytolith C sequestration can eliminate our CO2 woes, let alone even put a dent in it. Since these phytoliths are in the soil, perhaps we should focus on increasing organic matter (humus) as well. I consider soil organic matter (SOM) and soil phytoliths to be linked in this regard. Both are part of the C and Si cycles, respectively, and are thus subject to inputs (through litterfall) and outputs (through decay). Therefore, SOM and phytolith pools are dynamic: they are always undergoing turnover. If we really want to increase phytolith C sequestration, then we need to increase the input into soils, while reducing the output. Sure, phytolith-rich species may help in this regard, but I'd be willing to bet that a simple policy of minimizing soil disturbance (tilling, erosion, compaction, etc.) would result in the retention of more phytoliths. However, these practices would also result in the retention of SOM, which is always going to be a much larger pool. Paul Reyerson PhD candidate University of Wisconsin-Madison -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[email protected]] On Behalf Of Wayne Tyson Sent: Friday, February 12, 2010 11:30 PM To: [email protected] Subject: Re: [ECOLOG-L] CLIMATE Change Warming CO2 reduction phytoliths? Re: [ECOLOG-L] Plantstones - a solution for increaseing CO2 in atmosphere? Paul and Ecolog: Paul, would you also say that "phytolith sequestration" might not be a cheap way to sequester C? With respect to the "whole pie," I would like to understand what the net effects would be of the program suggested and how such a conclusion is reached. Especially with regard to policy and the allocation of scarce (grant, etc.) resources, it would seem prudent to both demonstrate and test the theoretical foundations before doing anything else, and I don't know just how, beyond blind faith, just how this would be done. I would also like to gain a greater understanding of the predictive ability of the models, particularly with regard to the null hypothesis. Right now, my gut tells me (it has been wrong many times) that the fraction of the pie attributable to phytoliths would be, while perhaps impressive in pure quantitative terms, insignificant in terms of the actual percentage slice of the whole pie. I would be interested in Ryerson's gut feeling on this, and those of similarly-qualified researchers. WT ----- Original Message ----- From: "Paul E. Reyerson" <[email protected]> To: <[email protected]> Sent: Friday, February 12, 2010 5:44 AM Subject: Re: [ECOLOG-L] CLIMATE Change Warming CO2 reduction phytoliths? Re: [ECOLOG-L] Plantstones - a solution for increaseing CO2 in atmosphere? Perhaps I should rephrase my original statement regarding phytolith C sequestration: This MAY be a cheap way to sequester C, but it should be considered as just one piece, not the whole pie. It is true that a small amount of organic C is occluded in phytoliths, and this can be sequestered for long periods of time. (As an aside, the occluded C can be used for radiocarbon dating and stable isotope research.). Many plants produce phytoliths, but grasses tend to produce more than trees. Crops such as maize, wheat, sorghum, sugarcane, etc. all produce sizeable amounts of phytoliths, so it seems to me that modern agriculture is already practicing the phytolith sequestration technique. The fundamental issue here centers on the biogeochemical cycle of silica, of which phytoliths are largely composed. Plants remove dissolved silica through their roots, make phytoliths, and release them back into the soil upon death or litterfall. If a soil is in stasis, then one would expect to see annual phytolith inputs offset by outputs (dissolution). From this one can determine the average residence time of phytoliths in the soil. As stated above, forests produce less phytoliths. Coupled with a more humid climate, phytolith residence times in forest soils is quite short. On the other hand, phytoliths can persist much longer in grassland ecosystems due to large production and drier climate. Long story short, one would expect to find much larger soil phytolith pools (and hence more occluded C) in grassland ecosystams than forests. With that said, I find it difficult to imagine that the conversion of native grassland to crop monoculture (maize, say) would ultimately sequester more C. To my knowledge, no one has studied this. Conversely, conversion of forests to crops may indeed increase phytolith C sequestration by increasing the soil phytolith pool. But does anyone really expect this to replace the C lost from the forest biomass? No. In my opinion, phytolith C sequestration in agriculture must be considered with all other forms of C sequestration/release. Responsible farming practices will reduce soil erosion and increase soil organic matter and phytolith content. On the other hand, application of petrochemical fertilizers, burning of fossil fuels, and removal of native vegetation can all release large amounts of C into the atmosphere. Besides climate and vegetation I (and other researchers) have found that localized soil properties may influence soil phytolith concentrations. A recent paper demonstrated that a direct relation exists between soil phytolith concentration and volcanic glass content (Henriet et al 2008, Biogeochemistry). Both are forms of highly soluble, amorphous silica. Thus it appears that volcanic glass can act as a buffer for soil phytoliths, independent of climate. I have found similar results when working with North American Mollisols which contain a sizeable amount of glass. Paul Reyerson PhD candidate University of Wisconsin-Madison -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[email protected]] On Behalf Of Wayne Tyson Sent: Thursday, February 11, 2010 4:33 PM To: [email protected] Subject: [ECOLOG-L] CLIMATE Change Warming CO2 reduction phytoliths? Re: [ECOLOG-L] Plantstones - a solution for increaseing CO2 in atmosphere? The article at the link apparently has zero references and zero theoretical or evidentiary foundation that can be independently verified (unless one counts the following: "We have developed and hold IP on proceedures [sic] for quantification and for the practical application of this process as well as both a granted and pending international patent applications on the use of these proceedures [sic] for the purpose of carbon sequestration (Parr and Sullivan, 2004"). This seems more in the nature of promotion than science, not to say that science is not involved, only that it is apparently secret and proprietary. If that is correct (and I am eager to have my misapprehensions corrected), it would seem questionable whether this particular item belongs on an avowedly science-based listserv. (I am not suggesting that the communication or any others in this vein be removed; only that subscribers be vigilant and challenge such posts, for the benefit of subscribers who might become converts to such a pitch--if "pitch" is the right word. The site does seem to be "encouraging" that grants be directed to "research," but that makes me wonder how the customary aspects of science such as peer review and replication of research figure into this issue, and when. Reyerson's agreement "that phytoliths (plantstones) offer a cheap way to sequester carbon" doesn't seem to square with his doubts, which seem reasonable to me. It would be nice for Reyerson to supply links or copies of his references and/or to expand on/link/reference "his own research." At the moment, I don't share Reyerson's optimism, but am subject to being converted. I haven't looked into phytoliths in years, but if I recall correctly, they are silicaceous remains, primarily of grasses and cactus (calcium oxalate) . It would seem that a fundamental bit of arithmetic based on some fairly simple-to-acquire data (content in standing vegetation, content in soils, rate of sequestration, term of sequestration compared to other forms, etc.) might bring the facts into focus. References to sources of such data and discussion of the plus-or-minus fudge factor involved in the estimates might be useful in understanding the true impact of any proposed "program" for said sequestration. For example, what percent of the sequestered carbon in present-day standing vegetation is represented by phytolith-sequestered carbon, and how much longer, considering the net effects of their rate and volume of re-absorption of carbon by non-phytolith-bearing plants, represents an actual net increase over present-day conditions? Also, what will be the effects of displacing functioning ecosystems with anthropogenic applications ("As an indication of the importance of this research, the Australian Research Council Discovery Grant Program has funded further development during 2007-2009. We firmly expect that as a result of this work, plantstone carbon research will reach industries such as forestry, horticulture, mining and the rehabilitation of salt affected land, as well as crops such as wheat, barley, sugarcane and maize, as well as pastures."). Until there is something the authors or promoters care to share with the scientific community, endorsement of their conclusions would seem a bit premature. I hope that they will clarify such issues soon. I likewise hope that other Ecolog subscribers will add clarity and any necessary corrections. I sincerely hope that I am wrong in my impressions, and stand ready to be corrected by specific evidence and logic. WT ----- Original Message ----- From: "Paul E. Reyerson" <[email protected]> To: <[email protected]> Sent: Thursday, February 11, 2010 11:17 AM Subject: Re: [ECOLOG-L] Plantstones - a solution for increaseing CO2 in atmosphere? I agree that phytoliths (plantstones) offer a cheap way to sequester carbon. However it is not at all clear that phytoliths are retained in soils for millenia on a large scale. Recent studies (I'm thinking of Alexandre et al 1997) showed that, in humid tropical regions at least, that soil phytoliths undergo an annual turnover rate of 92%. Turnover rates in drier regions will undoubtedly be lower, but there is very little research out there which documents this. For example, Blecker et al (2006) documented higher concentrations of soil phytoliths in shortgrass and mixed grass steppes when compared to tall grass, which they attributed to drier climate. My own research has suggested that higher retention rates in these regions may not be as simple as climate. Localized soil properties may also have an impact. Paul Reyerson PhD candidate University of Wisconsin-Madison -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[email protected]] On Behalf Of Matheus Carvalho Sent: Thursday, February 11, 2010 12:41 PM To: [email protected] Subject: [ECOLOG-L] Plantstones - a solution for increaseing CO2 in atmosphere? Dear list: I watched a very interesting talk yesterday about this. They are the "plantstones": http://www.plantstone.com.au/ Matheus C. Carvalho Senior Research Associate Centre for Coastal Biogeochemistry Southern Cross University Lismore - Australia ____________________________________________________________________________ ________ Veja quais são os assuntos do momento no Yahoo! +Buscados http://br.maisbuscados.yahoo.com ---------------------------------------------------------------------------- ---- No virus found in this incoming message. 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