Prediction Of PhytOC Storage And Spatial Distribution In Rice Ecosystem Based On BP Neural Network

Phytolith-occluded carbon（PhytOC）is an important mechanism for long-term organic carbon storage in terrestrial ecosystems.Phytoliths are returned to soil with plants,and the organic carbon contained within phytoliths can be preserved in soil for a long time under the protection of phytoliths,which plays a vital role in achieving carbon neutrality and alleviating global warming.Rice ecosystem has the highest PhytOC production rate in the farmland ecosystem.However,the current PhytOC storage studies in the rice ecosystem focus on aboveground plant parts,but research on soil PhytOC storage and spatial distribution is scant.Therefore,it is of great significance to explore PhytOC storage and its spatial distribution in the whole rice ecosystem.This study used the 71 rice varieties of rice straw and the surface soil（0～20 cm）from nine provinces to analyze soil physicochemical properties,phytolith and PhytOC contents,then using BP（Back propagation）neural network to predict the rice ecosystem PhytOC storage.I aimed to provide data support for PhytOC sequestration mechanism in rice ecosystem.The main results of the study are presented as follows:（1）The phytolith contents of straw were significantly positively correlated with available silicon,available phosphorus and p H value,and negatively correlated with organic matter,total nitrogen and total carbon of alkali-hydrolyzable nitrogen.The PhytOC contents were only positively correlated with phytolith,alkali-hydrolyzed nitrogen content,soil p H value and total nitrogen.The variation coefficient of PhytOC contents was 1.9～2.4 times that of straw phytolith contents,the PhytOC sequestration potential in japonica rice was higher than that in indica rice,indicating that the PhytOC contents of straw were more affected by rice varieties.Soil physicochemical properties affect the spatial distribution of phytoliths.North China（such as the Hebei and Tianjin provinces）had the highest phytolith contents,while the phytolith contents were higher in Jiangxi,Hunan and Guizhou provinces.In contrast,the phytolith contents were relatively low in southwestern,central and eastern China.（2）Phytolith contents in rice soil were positively correlated with available silicon content and p H value,but negatively correlated with total nitrogen.Soil PhytOC contents were significantly positively correlated with soil organic matter,total nitrogen and alkali-hydrolyzable nitrogen,and negatively correlated with available silicon,soil phytolith content and p H.The influence of soil physicochemical properties on soil PhytOC contents was greater than that on soil phytolith contents.The phytolith contents of soil in North China and Southwest China were higher than that in East China,Central China and South China,while that in North China,Northwest China and Hainan Province were lower.The spatial distribution of soil PhytOC contents was more fragmented,and the spatial distribution heterogeneity was more intense.The higher value of soil PhytOC contents appeared in Shaanxi,Jilin and Fujian provinces.The contents of PhytOC in East and Central China were medium,and there were large areas with low PhytOC contents in Guangxi and Guizhou provinces.（3）The PhytOC storage of rice straw in China is 0.26 Tg CO₂ yr^-1(9.6 kg CO₂ ha^-1 yr^-1),soil PhytOC storage in 0～20 cm soil layer of rice in China is 7.16×10⁶ t,and the average value of soil PhytOC storage is 0.24 t ha^-1.The rice ecosystem’s total carbon storage is 7.24×10⁶ t,equivalent to the occlusion of 26.5 Tg CO₂ in China’s rice ecosystem.In the Middle-Lower Yangtze Plain,South China and the eastern coastal areas,the PhytOC storage of rice ecosystems is high.There are scattered patches of high-value areas in the northeastern provinces,but most of them are patches of low-value areas.The PhytOC storage in North China was low.The five provinces with the highest PhytOC storage were Hunan（1.1×10⁶ t）、Jiangxi（8.3×10⁵ t）、Heilongjiang（5.9×10⁵ t）、Anhui（5.6×10⁵ t）and Guangdong（5.2×10⁵ t）.（4）Straw phytolith and PhytOC contents are highly correlated with soil phytolith and PhytOC contents.The result indicates that the ability of phytoliths to store organic carbon during plant growth may be an important factor determining the PhytOC storage in a system.Therefore,selection of rice varieties with high PhytOC sequestration potential is effective way to increase the long-term carbon sequestration and contribute to the mitigation of global warming.