The spatial distribution of phytoliths and phytolith-occluded carbon in wheat (Triticum aestivum L.) ecosystem in China

Phytolith is a form of SiO₂ in plants. Carbon can be sequestrated as phytolith-occluded carbon (PhytOC) during the formation of phytoliths. PhytOC is characterized by its high resistance to temperature, oxidation and decomposition under protection of phytoliths and can be stored in the soil for thousands of years. Soil also is a huge PhytOC sink; however, most studies focus on PhytOC storage in straw and other residues. Wheat is a major staple food crop accumulating high content of Si and distributed widely, while its potential for PhytOC is not clear. At present, PhytOC storage only considers on the average value, but not on the relationship between ecological factors and the spatial distribution of PhytOC sequestration. Climatic factors and soil physiochemical properties together affect the formation process and stability of phytoliths. In our study, we collected wheat straw and soil samples from 95 sites among five provinces to extract phytolith and PhytOC. We constructed XGBoost model to predict the spatial distribution of phytolith and PhytOC across the country using the national soil testing and formula fertilization nutrient dataset and climate data. As a result, soil physiochemical factors such as available silicon (Siₐᵥₐᵢₗ), total carbon (Cₜₒₜ) and total nitrogen (Nₜₒₜ) and climate factors related to temperature and precipitation have a great positive impact on the production of phytoliths and PhytOC. Meanwhile, PhytOC storage in wheat ecosystems was estimated to be 7.59 × 10⁶ t, which is equivalent to 27.83 Tg of CO₂. In China, the distribution characteristics of phytoliths and PhytOC in wheat straw and soil display a trend of decrease from south to north. He’nan Province is the largest wheat production area, producing approximately 1.59 × 10⁶ t PhytOC per year. Therefore, PhytOC is a stable CO₂ sink pathway in the agricultural ecosystems, which is of great importance for mitigating climate warming.