The contents and distributions of phytolith and phytolith-occluded carbon in different rice genotypes

Objectives Rice is a well-known silicon (Si) accumulator. The phytolith enriched with Si in rice plant is able to occlude organic carbon. In order to explore the effect of Si-uptake ability on the content, distribution and carbon sequestration characteristic of phytoliths in rice, we selected four rice genotypes for investigation, different for illuminating the mechanism of phytolith carbon sequestration in rice.

Methods A pot experiment was conducted in the glass room of Zhejiang University using two rice mutants and their wild types, i.e. Lsi1, a mutant defective in Si-uptake (low silicon rice 1) and Lsi2, a mutant defective in Si-uptake (low silicon rice 2). Si-uptake ability on the contents of SiO₂, phytolith and phytolith-occluded carbon (PhytOC) were measured in different aboveground organs (stem, leaf and sheath). All treatments were under the same fertilization and management conditions.

Results 1) Different rice genotypes had significant differences in contents of SiO₂, phytolith and PhytOC per gram of dry biomass with the following decreased order: Lsi1 wild type > Lsi2 wild type > Lsi2 mutant > Lsi1 mutant. The PhytOC contents were in the order of Lsi1 mutant > Lsi2 mutant > Lsi2 wild type > Lsi1 wild type. The contents of SiO₂, phytolith and PhytOC in Lsi1 and Lsi2 wild type were significantly higher than in its corresponding mutant, while the PhytOC contents showed an opposite trend. 2) The contents of SiO₂ and phytolith in the rice mutants were the highest in leaf, followed by sheath and stem, while in the rice wide types, their contents were the highest in sheath, followed by leaf and stem. The PhytOC contents and PhytOC per gram of dry biomass of rice were the highest in leaf of the four rice genotypes. The distribution trend of PhytOC content was in the order of leaf > stem > sheath, while that of PhytOC per gram of dry biomass of rice was in the order of leaf > sheath > stem. 3) There existed a positive correlation between phytolith contents and SiO₂ contents (P<0.01). Higher contents and smaller specific surface area of phytolith were observed in the rice genotypes with higher Si-uptake ability, indicating that both of the content and form of phytolith were affected by the genetic characteristics. A positive correlation was also found between phytolith contents and PhytOC (P<0.01), while negative correlation was observed between PhytOC contents and PhytOC (P<0.01), suggesting that the PhytOC per gram of dry biomass of rice was closely related to not only the phytolith content but the content of PhytOC. 4) The storages of phytolith and PhytOC, dry biomasses of the wild types of rice were significantly higher compared with their mutants.

Conclusions Compared with the mutants, the wild types of rice has the higher contents of SiO₂ and phytolith, dry biomasses and PhytOC per gram of dry biomass of rice, although the distributions are different. The wild types has lower PhytOC contents, but higher PhytOC storages than the mutants. Therefore, Lsi1 and Lsi2 wild type rice with higher Si-uptake ability have higher carbon sequestration potential than their corresponding mutants.