Table_3_Root Functional Trait and Soil Microbial Coordination: Implications for Soil Respiration in Riparian Agroecosystems.DOCX

Predicting respiration from roots and soil microbes is important in agricultural landscapes where net flux of carbon from the soil to the atmosphere is of large concern. Yet, in riparian agroecosystems that buffer aquatic environments from agricultural fields, little is known on the differential contribution of CO2 sources nor the systematic patterns in root and microbial communities that relate to these emissions. We deployed a field-based root exclusion experiment to measure heterotrophic and autotrophic-rhizospheric respiration across riparian buffer types in an agricultural landscape in southern Ontario, Canada. We paired bi-weekly measurements of in-field CO2 flux with analysis of soil properties and fine root functional traits. We quantified soil microbial community structure using qPCR to estimate bacterial and fungal abundance and characterized microbial diversity using high-throughput sequencing. Mean daytime total soil respiration rates in the growing season were 186.1 ± 26.7, 188.7 ± 23.0, 278.6 ± 30.0, and 503.4 ± 31.3 mg CO2-C m–2 h–1 in remnant coniferous and mixed forest, and rehabilitated forest and grass buffers, respectively. Contributions of autotrophic-rhizospheric respiration to total soil CO2 fluxes ranged widely between 14 and 63% across the buffers. Covariation in root traits aligned roots of higher specific root length and nitrogen content with higher specific root respiration rates, while microbial abundance in rhizosphere soil coorindated with roots that were thicker in diameter and higher in carbon to nitrogen ratio. Variation in autotrophic-rhizospheric respiration on a soil area basis was explained by soil temperature, fine root length density, and covariation in root traits. Heterotrophic respiration was strongly explained by soil moisture, temperature, and soil carbon, while multiple factor analysis revealed a positive correlation with soil microbial diversity. This is a first in-field study to quantify root and soil respiration in relation to trade-offs in root trait expression and to determine interactions between root traits and soil microbial community structure to predict soil respiration.

在土壤向大气的碳净通量广受关注的农业景观中，基于根系与土壤微生物预测呼吸作用具有重要研究价值。然而，在为农田缓冲水生环境的河岸农业生态系统中，学界对二氧化碳（CO₂）来源的差异化贡献，以及与这些碳排放相关的根系和微生物群落系统模式仍知之甚少。我们在加拿大安大略省南部的一处农业景观中开展了根排除实验（root exclusion experiment），以测定不同河岸缓冲带类型下的异养呼吸与根际自养呼吸。我们将每两周一次的田间CO₂通量原位测定数据，与土壤性质、细根功能性状的分析结果进行配对整合。我们通过实时荧光定量PCR（qPCR）量化土壤微生物群落结构，以估算细菌与真菌的丰度，并借助高通量测序（high-throughput sequencing）表征微生物多样性。在残留针叶林、混交林、恢复林与草本缓冲带中，生长季日间平均总土壤呼吸速率分别为186.1±26.7、188.7±23.0、278.6±30.0及503.4±31.3 mg CO₂-C m⁻² h⁻¹。各缓冲带的根际自养呼吸对土壤总CO₂通量的贡献占比跨度较大，介于14%至63%之间。根系性状的协同变化规律显示，比根长与氮含量更高的根系，其比根呼吸速率也更高；而根际土壤的微生物丰度，则与直径更粗、碳氮比更高的根系呈现显著相关。以单位土壤面积计，根际自养呼吸的变异可通过土壤温度、细根长密度以及根系性状的协同变化得到有效解释。异养呼吸则主要受土壤湿度、温度与土壤有机碳的调控，多因素分析还揭示其与土壤微生物多样性呈正相关关系。本研究为首次在原位条件下，量化根系性状表达权衡与土壤呼吸的关联，并阐明根系性状与土壤微生物群落结构间的相互作用，从而实现土壤呼吸的预测。