小麦和玉米生长对土壤碳输入和输出的贡献

在农业生态系统中,区分土壤外源碳输入和内源碳输出是量化土壤碳平衡的前提。借助碳同位素方法,可以精确区分不同碳源对土壤有机碳(SOC)和二氧化碳(CO_2)的贡献,一方面定量根际沉积碳对土壤碳的输入,另一方面还可以量化根系生长对SOC分解的根际激发效应,进而提高土壤碳平衡评估的精确度。本文整合了关于小麦和玉米~(13)C/~(14)C示踪实验的文献,对作物-土壤系统光合碳分配、向地下部碳输入量、根际土壤CO_2区分以及根际激发效应进行分析,最终明确了小麦和玉米生长对土壤碳输入和输出的贡献。在作物-土壤系统中,小麦光合碳分配到地上部、根系、土壤和土壤释放CO_2的平均比例分别为73.1%、12.5%、4.6%、9.8%,玉米分别为68.4%、16.0%、4.6%和11.1%。小麦和玉米通过根系和根际沉积碳对土壤碳输入量均值分别为1 058 kg·hm~(-2)和1 025 kg·hm~(-2),其中根际沉积碳占地下输入的贡献均值分别为0.45和0.38。小麦和玉米根源呼吸占根际土壤CO_2释放的贡献值均达到50%以上,分别为51.3%和56.7%。小麦和玉米生长促进SOC的分解,根际激发效应平均值分别为172%和15%,若采用传统根去除法来区分土壤呼吸,根际激发效应则会被忽略,这可能导致根源呼吸的高估。小麦和玉米生长过程中释放的净根际沉积碳占地下部净碳输入(根系+根际沉积物)比例分别为27%和22%,如果利用传统洗根法,这部分光合碳量就无法量化,导致输入到地下部的光合碳量被低估。

Contributions of wheat and maize growth to soil carbon input and output

In agroecosystem, partitioning exogenous C input and endogenous C release is a prerequisite for quantifying soil C balance. The contribution of different C sources to soil organic C(SOC) and soil CO₂ can be accurately distinguished using the C isotope method. This method can not only quantify soil C input in the form of rhizodeposition but can also estimate the rhizosphere priming effects on SOC decomposition, which increases the accuracy of soil C balance assessments. Through a survey of the literature on ¹³C/¹⁴C tracer experiments, the study analyzed photosynthetic C allocation, belowground C input, different contributions of soil CO₂ emission, and rhizosphere priming effects. The results showed that the photosynthesized C of wheat allocated to aboveground, roots, SOC, and soil CO 2 emissions were 73.1%, 12.5%, 4.6%, 9.8% of the net assimilated C, respectively, and those of maize were 68.4%, 16.0%, 4.6%, and 11.1%, respectivedly. The amounts of the photosynthetic C transferred into soil were 1 058 kg·hm^-2 and 1 025 kg·hm^-2 by wheat and maize, among which the contribution of rhizodeposition was 0.45 and 0.38, respectively. The contribution of root-derived respiration to total soil CO₂ emissions in wheat- and maize-planted soils accounted for 51.3% and 56.7%, respectively. The growth of wheat and maize showed positive rhizosphere priming effects on SOC decomposition, with average magnitudes of 172% and 15%, respectively. If the traditional root exclusion method was used to distinguish soil respiration, the positive rhizosphere priming effects would be ignored, which might lead to the overestimation of root-derived respiration. The net rhizodeposition during the growth of wheat and maize accounted for 27% and 22% of the net belowground C input(root + rhizodeposition), respectively. If the traditional root washing method was used, rhizodeposition could not be quantified, resulting in an underestimation of the net belowground C input.