More is not always better: Peat moss mixtures slightly enhance peatland stability

Species-poor peatlands challenge biodiversity–ecosystem function theory,
which generally links high species diversity to stable ecosystem
functions. An open question in ecosystem ecology is whether assemblages of
naturally co-occurring peat mosses contribute to the stability of peatland
ecosystem processes. We used a replacement series mesocosm experiment with
mixtures of Sphagnum cuspidatum and S. medium to assess resistance,
resilience, and recovery rates of net ecosystem CO2 exchange (NEE) under a
mild and a deep water table drawdown event. Our results show a positive
effect of mild water table drawdown on NEE with no apparent role for the
composition of the peat moss assemblage. Our study indicates that the
carbon uptake capacity by peat moss assemblages is rather resilient to
mild water table drawdown, but seriously affected by deeper drought
conditions. Co-occurring peat moss species seem to enhance the resilience
of the carbon uptake function – i.e. ability of NEE to return to
pre-perturbation levels – of peat moss mixtures only slightly. These
findings suggest that assemblages of co-occurring Sphagnum moss species do
only marginally contribute to the stability of ecosystem functions in
peatlands under drought conditions. We did find increased recovery with a
larger share of S. cuspidatum in the mixtures, aiding in the ecosystem’s
role as carbon sink. Above all, our results highlight that predicted
severe droughts can gravely affect the sink capacity of peatlands, with
only a small extenuating role for peat moss mixtures.

物种贫乏的泥炭地对生物多样性-生态系统功能理论构成挑战——该理论通常将高物种多样性与稳定的生态系统功能相挂钩。生态系统生态学领域尚存一则开放性问题：自然共存的泥炭藓组合是否有助于维持泥炭地生态系统过程的稳定性。我们采用尖叶泥炭藓（Sphagnum cuspidatum）与中位泥炭藓（Sphagnum medium）的混播替换系列中型生态箱实验，评估了轻度与重度地下水位下降事件下，净生态系统CO2交换量（net ecosystem CO2 exchange, NEE）的抗性、恢复力及恢复速率。研究结果显示，轻度地下水位下降对NEE存在正向影响，但泥炭藓组合的组成并未发挥显著作用。本研究表明，泥炭藓组合的碳吸收能力对轻度地下水位下降具有较强的恢复力，但会受到重度干旱条件的严重抑制。共存的泥炭藓物种似乎仅能小幅提升泥炭藓混播群落的碳吸收功能恢复力——即NEE恢复至扰动前水平的能力。上述发现表明，在干旱条件下，共存泥炭藓物种的组合仅能小幅提升泥炭地生态系统功能的稳定性。我们确实发现，混播群落中尖叶泥炭藓占比越高，其恢复速率越快，有助于强化生态系统的碳汇功能。总而言之，我们的研究结果凸显：预测中的极端干旱事件将严重削弱泥炭地的碳汇能力，而泥炭藓物种组合仅能发挥有限的缓冲作用。