Plant carbon allocation drives turnover of old soil organic matter in permafrost tundra soils
Plant carbon allocation drives turnover of old soil organic matter in permafrost tundra soils
复制标题
DOI：
10.1111/gcb.15134
复制
发表时间：
2020-06
影响因子：
11.6
通讯作者：
L. Street;M. Garnett;J. Subke;R. Baxter;J. Dean;P. Wookey
中科院分区：
文献类型：
--
作者：
L. Street;M. Garnett;J. Subke;R. Baxter;J. Dean;P. Wookey
冻土生态系统的碳循环反馈预计将加速全球气候变化。多年冻土区植被生产力和组成的变化可能通过根际（根区）启动效应（RPEs）影响土壤有机碳（SOC）周转率，但这些过程目前尚未在模型预测中得到考虑。我们使用放射性碳（bomb - 14C）方法测试了两种北极高灌木，桤木（Alnus viridis (Chaix) DC.）和桦木（Betula glandulosa Michx.）以及白垩系苔原植被的rpe。我们比较了完整植被和由于挖沟和去除地上生物量而阻止了近期光合作用在地下分配的样地之间的地表CO2外排率和14C含量。我们首次表明，在桦树灌木和白垩系苔原下，最近的光合作用驱动了较老（大约50年）的有机碳矿化。相比之下，我们没有发现桤木土壤中存在rpe的证据。这是来自永久冻土系统的第一个直接证据，表明植被通过地下碳分配影响有机碳周转。因此，永久冻土系统中有机碳对分解的脆弱性可能与植被变化直接相关，例如，桦树灌木在北极地区的扩张可能会增加旧有机碳的分解。我们的研究结果表明，不包括rpe的碳循环模型有低估与冻土带地区变化条件相关的碳循环反馈的风险。
Carbon cycle feedbacks from permafrost ecosystems are expected to accelerate global climate change. Shifts in vegetation productivity and composition in permafrost regions could influence soil organic carbon (SOC) turnover rates via rhizosphere (root zone) priming effects (RPEs), but these processes are not currently accounted for in model predictions. We use a radiocarbon (bomb‐14C) approach to test for RPEs in two Arctic tall shrubs, alder (Alnus viridis (Chaix) DC.) and birch (Betula glandulosa Michx.), and in ericaceous heath tundra vegetation. We compare surface CO2 efflux rates and 14C content between intact vegetation and plots in which below‐ground allocation of recent photosynthate was prevented by trenching and removal of above‐ground biomass. We show, for the first time, that recent photosynthate drives mineralization of older (>50 years old) SOC under birch shrubs and ericaceous heath tundra. By contrast, we find no evidence of RPEs in soils under alder. This is the first direct evidence from permafrost systems that vegetation influences SOC turnover through below‐ground C allocation. The vulnerability of SOC to decomposition in permafrost systems may therefore be directly linked to vegetation change, such that expansion of birch shrubs across the Arctic could increase decomposition of older SOC. Our results suggest that carbon cycle models that do not include RPEs risk underestimating the carbon cycle feedbacks associated with changing conditions in tundra regions.