Data from: Early accumulation of active fraction soil carbon in newly established cellulosic biofuel systems

We examined relative changes in soil C pools shortly after the
establishment of six perennial and two annual bioenergy cropping systems
that differed in diversity (monoculture vs. polyculture). Perennial
systems included two monocultures (switchgrass, Panicum virgatum; and
miscanthus, Miscanthus × giganteus) and four polycultures including hybrid
poplar (Populus sp.) + herbaceous understory; mixed native grasses,
successional vegetation, and restored prairie. Two annual systems included
no-till continuous corn (Zea mays) and rotational corn (corn-soybean
(Glycine max)-canola (Brassica napus)). Each crop was planted in a full
factorial design at both a moderate fertility Alfisol and a high fertility
Mollisol site. Relative differences in active, slow, and passive C pools
in surface soils, where C changes are most likely to be detected early,
were evaluated with 322-day laboratory incubations followed by acid
hydrolysis to infer different pools from exponential decay curves. Five
years post-establishment, active C pools under perennial polycultures at
the Alfisol site were up to twice those under annual and perennial
monocultures, and followed the order hybrid poplars (696 ± 216 μg C g− 1
soil, n = 5 replicate blocks) ≈ native grasses (656 ± 155) ≈ restored
prairie (638 ± 44) > early successional (500 ± 54) ≫ continuous
corn (237 ± 68) ≈ rotational corn (180 ± n.a.). Active C pools in
perennial monocultures were similar to those in continuous corn:
switchgrass (274 ± 29) ≈ miscanthus (299 ± 9). In contrast, differences in
active C pools among crops at the more fertile Mollisol site were not
detectable except for greater pools in the restored prairie and rotational
corn systems. At both sites, slow and passive C pools differed little
among systems except that slow pools were greater in the poplar system.
That diversity rather than perenniality itself led to greater active C
pools suggests that polycultures might be used to accelerate soil C
accumulation in bioenergy and other perennial cropping systems.

本研究针对6个多年生、2个一年生生物能源种植系统（bioenergy cropping systems）建立初期的土壤碳库（soil C pools）相对变化展开探究，这些系统的种植多样性存在差异，分为单作（monoculture）与混作（polyculture）两类。其中多年生系统包含2个单作体系：柳枝稷（*Panicum virgatum*）与巨芒草（*Miscanthus × giganteus*）；以及4个混作体系：杂交杨（*Populus* sp.）+ 草本下层植被、本土混合草本群落、演替植被群落以及恢复草原。2个一年生系统分别为免耕连作玉米（*Zea mays*）以及轮作玉米体系（玉米-大豆（*Glycine max*）-油菜（*Brassica napus*））。
所有试验体系均采用完全因子设计，在中等肥力淋溶土（Alfisol）与高肥力软土（Mollisol）两个试验点同步开展种植。针对表层土壤的活性碳库（active C pools）、缓效碳库（slow C pools）与惰性碳库（passive C pools）的相对差异——该土层土壤碳变化最易被早期检测到——本研究通过322天实验室培养（laboratory incubations）结合酸水解（acid hydrolysis）实验，基于指数衰减曲线（exponential decay curves）推算不同碳库组分。
种植建立5年后，淋溶土（Alfisol）试验点的多年生混作体系下的活性碳库最高可达一年生与多年生单作体系的2倍，其活性碳库大小排序为：杂交杨（696 ± 216 μg C g⁻¹ 土壤，n=5个重复区块）≈ 本土混合草本群落（656 ± 155）≈ 恢复草原（638 ± 44）＞早期演替植被群落（500 ± 54）≫ 连作玉米（237 ± 68）≈ 轮作玉米（180 ± n.a.）。多年生单作体系的活性碳库与连作玉米体系相近：柳枝稷（274 ± 29）≈ 巨芒草（299 ± 9）。
与之相对，肥力更高的软土（Mollisol）试验点中，各作物体系间的活性碳库差异并不显著，仅恢复草原与轮作玉米体系的活性碳库略高。在两个试验点中，除杂交杨体系的缓效碳库显著更高外，各体系间缓效碳库与惰性碳库的差异均较小。
研究表明，驱动活性碳库提升的核心因素为种植多样性而非多年生属性本身，这提示混作体系可用于加速生物能源及其他多年生种植系统的土壤碳累积。