[{"id":141,"title":"How Significant are Conifers for the Silicon Biogeochemical Cycle?","sha":"61b79e3f1978c1dd240411779488a985","user_id":504,"state":"published","body":"The conifers were generally shown by [Hodson et al. (2005)](http://aob.oxfordjournals.org/content/96/6/1027.short) to be low silicon accumulators. The apparent reason is that conifers (and many gymnosperms) largely lack NIPIIs, aquaporins that are involved in silicon transport in plants ([Trembath-Reichert et al. 2015](http://www.pnas.org/content/early/2015/03/24/1500289112.abstract)). This led Trembath-Reichert et al. to propose that the terrestrial silicon biogeochemical cycle would be decreased in the Mesozoic Era because of the dominance of conifers.\r\nHowever, scrutiny of the supplementary data from Hodson et al. suggests that there are some conifer species (e.g. *Abies alba*, *Larix decidua*, *Picea abies*) where silica is over 2% dry weight in the needles, well within the range for the silicon-accumulating Poales (which include the grasses). Moreover, in species that retain their needles longer than one year, silicon accumulates steadily over several seasons ([Hodson and Sangster, 1998](http://aob.oxfordjournals.org/content/82/3/375); [Wyttenbach et al. 1991](http://onlinelibrary.wiley.com/doi/10.1002/jpln.19911540403/abstract)).\r\n[Gerard et al. (2008)](http://www.sciencedirect.com/science/article/pii/S0016703707006679) modeled the silicon biogeochemical cycle in a Douglas fir (*Pseudotsuga menziesii*) forest. They found that the needles contained up to 2.7% silica, that 60% of the biogeochemical cycle was controlled by biological processes, and it was calculated that 37% of silicon was taken up actively by the trees. The available data suggest that some important conifer species, including fir, larch, spruce and Douglas fir, can accumulate significant amounts of silica in their needles, and that silicon cycling in conifer-dominated systems will not necessarily be lower.\r\n","created_at":"2015-04-07T09:10:43.480Z","updated_at":"2015-08-06T21:44:37.890Z","zenodo_id":26526,"doi":"http://dx.doi.org/10.5281/zenodo.16669","subject":null,"tags":["biogeochemical cycling","conifer","plant","silicon"],"vote_count":5,"view_count":1,"score":5.1,"deleted":false,"muted":false,"tweeted":true,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null},{"id":336,"title":"Carbon concentrations in phytoliths and carbon sequestration in soil","sha":"c2ee0d247f8fc516a87f2b0f385c6031","user_id":null,"state":"published","body":"In recent years there has been much work on the possibility that carbon could be sequestered in phytoliths and contribute to solving global warming.\u003csup\u003e[1](http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2009.02118.x/full), [2](http://link.springer.com/article/10.1007/s11368-016-1527-x)\u003c/sup\u003e There have been a number of calculations of how much is sequestered globally. The crucial figure in these calculations is the concentration of carbon in the phytoliths that is used, so-called phytolith occluded carbon. These figures are derived from phytoliths that have been acid digested or dry ashed at 450-500\u003csup\u003eo\u003c/sup\u003eC. Values vary from less than 0.1% to 6% depending on the technique used. But are any of these measurements realistic? In native unprocessed material the lemma macrohair from *Phalaris canariensis* contained 40% silica, 55%, polysaccharides and 5% proteins.\u003csup\u003e[3](http://www.sciencedirect.com/science/article/pii/S0176161787800287)\u003c/sup\u003e At maturity these hairs consist entirely of wall material. I know of no data for lumen deposits, which undoubtedly have a higher percentage silica in the native state. Some of the carbon in both cell wall and lumen phytoliths cannot be accessed by hot acid or dry ashing. I suspect that more carbon is inaccessible to breakdown processes in soil than is estimated by our “occluded carbon” determinations. My question is whether these measurements are a good estimate of what is present in soil phytoliths?","created_at":"2016-09-18T13:47:38.507Z","updated_at":"2016-09-19T06:00:20.925Z","zenodo_id":154351,"doi":"https://doi.org/10.5281/zenodo.154351","subject":null,"tags":["carbon","silicon","phytolith","plant","soil"],"vote_count":0,"view_count":1,"score":0.1,"deleted":false,"muted":false,"tweeted":true,"attachment_file_name":null,"attachment_content_type":null,"attachment_file_size":null,"attachment_updated_at":null}]