Root traits of perennial C4 grasses contribute to cultivar variations in soil chemistry and species patterns in particulate and mineral-associated carbon pool formation

<strong>Abstract:</strong> Recent studies have indicated that the C4 perennial bioenergy crops switchgrass (<em>Panicum virgatum</em>) and big bluestem <em>(Andropogon gerardii</em>) accumulate significant amounts of soil carbon (C) owing to their extensive root systems. Soil C accumulation rates under these grasses are likely driven by inter- and intra-specific variability in plant traits. However, the mechanisms that underpin this variability in soil C storage remain unresolved. In this study we evaluated how inter- and intra-specific variation in root traits of cultivars from switchgrass (Cave-in-Rock, Kanlow, Southlow) and big bluestem (Bonanza, Southlow, Suther) affected the associations of soil C accumulation across soil fractions using stable isotope techniques. Our experimental field site was established in June 2008 at Fermilab in Batavia, IL. In 2018, soil cores were collected (30 cm depth; 4.8 cm diameter) from the root zone of all cultivars. We measured root biomass, root diameter, specific root length, bulk soil C and C associated with coarse and fine particulate organic matter (CPOM, FPOM) plus silt- and clay-sized fractions. Cultivar monocultures of both C4 species were established on soils that supported C3 grassland for 36 years before planting, which allowed us to use differences in the natural abundance of stable C isotopes to quantify C4 plant-derived C. We also characterized organic matter chemical class composition in root-zone soil using high resolution FTICR mass spectrometry. We found that species accumulated C through different mechanisms. Big bluestem cultivars had larger root systems that increased C4 plant-derived C in the POM-C pool, while switchgrass cultivars increased the C4 plant-derived C in the clay fraction via differences in root morphology and soil chemistry. This highlights the importance of both POM-C and mineral associated C in building soil carbon pools. <br> <br> <strong>Abbreviations:</strong> <strong>Species:</strong> BB = Big Bluestem SG = Switchgrass <strong>Cultivars:</strong> BO = Bonanza BSL = BB Southlow ST = Suther CR = Cave-in-Rock KA = Kanlow SSL = SG Southlow <strong>Depth:</strong> A = 0-10 cm B = 10-20 cm C = 20-30 cm

**摘要：** 近期研究表明，C4多年生能源作物柳枝稷（switchgrass，*Panicum virgatum*）与大须芒草（big bluestem，*Andropogon gerardii*）凭借其发达的根系，可积累大量土壤碳（C）。此类禾本科植物的土壤碳积累速率，大概率受种间与种内植物性状变异的调控。然而，支撑土壤碳储量这种变异的核心机制仍未阐明。

本研究借助稳定同位素技术，探究了柳枝稷（Cave-in-Rock、Kanlow、Southlow）与大须芒草（Bonanza、Southlow、Suther）各品种的根性状种间及种内变异，如何影响不同土壤组分中的土壤碳积累关联模式。本实验于2008年6月在伊利诺伊州巴达维亚市费米实验室（Fermilab）正式搭建。2018年，我们从所有供试品种的根际区域采集了土壤岩心（采样深度30 cm，直径4.8 cm）。我们测定了根生物量、根直径、比根长、全土碳，以及与粗颗粒有机质（coarse particulate organic matter, CPOM）、细颗粒有机质（fine particulate organic matter, FPOM）相关联的碳，同时测定了粉粒与黏粒组分中的碳含量。

两个C4物种的品种单作种植区，均设置在曾种植C3禾本科草原达36年的土壤上，这使得我们可借助稳定碳同位素的自然丰度差异，定量区分C4植物来源的碳。我们还借助高分辨率傅里叶变换离子回旋共振质谱（FTICR mass spectrometry），对根际土壤的有机质化学类别组成进行了表征。

研究发现，两个物种通过不同机制积累碳：大须芒草品种拥有更发达的根系，可提升颗粒态碳（POM-C）库中C4植物来源碳的占比；而柳枝稷品种则通过根形态与土壤化学性质的差异，提升了黏粒组分中C4植物来源碳的占比。这凸显了颗粒态碳与矿质结合态碳在构建土壤碳库过程中的双重重要性。

<br><br>**缩写说明：**
**物种代号：** BB = 大须芒草（Big Bluestem），SG = 柳枝稷（Switchgrass）
**品种代号：** BO = Bonanza，BSL = 大须芒草Southlow，ST = Suther，CR = Cave-in-Rock，KA = Kanlow，SSL = 柳枝稷Southlow
**土层深度代号：** A = 0~10 cm，B = 10~20 cm，C = 20~30 cm