Regulation Of Silicon Nutrition On Silicon Accumulation And Phytolith Carbon Sequestration In Rice

PhytOC(phytolith-occluded-carbon) is some organic carbon occluded within phytolith. After dead plant materials decompose, PhytOC is released into the soil with phytolith, and may be preserved in soils for several thousand years. It also is one of the most important component of the soil carbon pool. Phytolith maybe a long-time biogeochemical carbon sequestration mechanism in terrestrial ecosystems. Phytolith carbon sequestration may contribute 15%~37% of the soil carbon sink quantity. Rice(Oryza sativa) is a significant cereals crop, a typical Si-accumulator, has a tremendous phytolith carbon sink potential. It is of great significance to explore the regulating mechanisms of cropland ecosystems phytolith C sink.This study selected the rice samples with different silicon fertilization(basalt powder and Si-P fertilization). Rice samples were fused with Li-metaborate at 950°C in order to determine the silica content. Microwave digestion in combination with Walkley-Black digestion were used to extract phytoliths from all rice samples. Understanding the variation of SiO2 content, phytolith content and Phyt OC content in rice samples with different silicon fertilization. Investigating the response of silicon accumulation and phytolith carbon sink potential of rice ecosystem to Si nutrient regulation. The objective of this study is to provide scientific references for the Si cycle and regulation mechanisms of agricultural ecosystems(1) Silica content of all rice organs significantly ranged from 6.97 to 47.28 mg g-1 through the amendment with the rock powder fertilization. Generally, the silica content in leaf(33.48~47.28 mg g-1) was much higher than other organs with the following trend: leaf > flag leaf > sheath > stem. Rock powder amendment significantly increased the fluxes of silica production in all rice organs(P<0.05), showing the following trend: sheath(313.99~557.32 kg ha-1 a-1) > leaf(197.99~405.89 kg ha-1 a-1) > flag leaf(136.21~302.73 kg ha-1 a-1) > stem(105.09~320.45 kg ha-1 a-1). The treatment of CK-4(60 g kg-1) had the biggest contribution to improve the flux of Si production among all treatments. Although the results are only based on a pot experiment, this study suggests that optimization of silica amendment(e.g., rock powder) can be used as a potential measure for promoting both cropland phytolith C sink and soil fertility, a win-win situation, cultivated with high Si-accumulator crops.(2) The contents of phytolith and PhytOC in rice increased with BP amendment. The PhytOC production flux in different rice plant parts varied considerably(0.005~0.041 t CO2 ha-1 a-1), with the highest flux in the sheath. BP amendment can significantly enhance flux of phytolith carbon sequestration in croplands by 150%. If the global rice cultivation of 1.55 × 108 ha had a similar flux of PhytOC production to this study, 0.61 × 107 to 1.54 × 107 t CO2 would be occluded annually within global rice phytoliths. These findings highlight that external silicon amendment such as BP amendment represents an effective potential management tool to increase long-term biogeochemical carbon sequestration in crops such as rice and may also an efficient way to mitigate the global warming indirectly.(3) Si-P fertilizer application significantly increased phytolith content and Phyt OC production fluxes in rice organs,but PhytOC content. The fluxes of PhytOC production in different rice organs varied significantly from 0.004 to 0.021 t CO2 ha-1 a-1. Si-P application significantly increased the PhytOC production flux by 150%(0.004 t CO2 ha-1 a-1 to 0.01 t CO2 ha-1 a-1) in the rice stems, compared to other organs at the SihPm level(Si= 0.52 g kg-1; P= 0.2 g kg-1). There was also a 100% increase(0.03 t CO2 ha-1 a-1 to 0.06 t CO2 ha-1 a-1) in the PhytOC production rate in the above-ground rice parts at the SihPm level relative to the treatment without Si-P fertilization(Si0P0). These results are the powerful support to verify a theoretical hypothesis that for cropland, regulating Si-nutrient supply can be a potentially significant regulation mechanism that will further enhance phytolith C sequestration in croplands.