2.3 Sample analysis
The phytoliths within plant parts were extracted using a microwave
digestion process (Parr et al., 2001) followed by a Walk-Black type
digestion to ensure the purity of the phytoliths (Parr & Sullivan,
2014; Walkley & Black, 1934). Two duplicates were analyzed for each
plant sample. The exacted phytoliths were dried at 65℃ to a constant
weight. The PhytOC was determined using the PhytOC alkalidis solution
spectrophotometer method (Yang et al., 2014). In this method, sodium
hydroxide solution was used to dissolve the Si compound in order to
release the occluded organic carbon from the phytoliths, then potassium
dichromate
(K2Cr2O7)-sulfuric acid
(H2SO4) solution was used to oxidize the
released organic carbon, and the concentration of Gr3+produced in this oxidation was determined by spectrophotometer with its
absorbance at 590 mm wavelength. The organic carbon concentration was
calculated based on the amounts of potassium dichromate consumed, and
the accuracy and repeatability of the method was well verified against
the results obtained with acid dissolution-Elementar Vario MAX CN method
(Germany) (Yang et al., 2014). The phytoliths and PhytOC contents of the
two parts of each plant species were calculated as the average of the
three replicate plots. For each species, the ratio of aboveground to
belowground biomass (shoots/roots) was calculated based on the sampled
plant individuals. The ratio was used to calculate the belowground
biomass of the species in 1 m2 based on the measured
aboveground biomass of the species. The estimation of plant root biomass
in the soil profile and the turn-over rate of the belowground biomass
were quoted from previous studies (Chai et al., 2014; Hou et al., 2014).
The air dried soil samples were separated into the 100 mesh soil samples
and the 10 mesh soil samples. The soil organic carbon (SOC) was
determined with the 100 mesh soil samples using the method of classical
potassium dichromate (Walkley & Black, 1934), and the soil pH and
bioavailable Si content were analyzed with 10 mesh soil samples using a
pH meter (Yang et al., 2018) and silicomolybdic acid method (Yang et
al., 2018), respectively.