黄河源区建植19年人工草地生物结皮CO2通量与叶绿素荧光参数的变化

为了解黄河源人工草地不同类型生物结皮和植被群落CO₂释放和固定的变化特征，并探讨二者的影响因子，本文通过调查黄河源建植19年人工草地不同类型生物结皮CO₂通量和植被土壤特征变化发现：藻和地衣结皮CO₂通量均显著小于苔藓结皮（10.58 μmol·m^-2·s^-1）（P<0.05）；苔藓结皮对应的植被群落CO₂通量（11.55 μmol·m^-2·s^-1）显著低于藻和地衣结皮（P<0.05）；藻和地衣结皮下的土壤CO₂通量显著大于苔藓结皮（约2倍，P<0.05）。苔藓结皮叶绿素初始荧光参数F₀（Minimal Fluorescence）和最大荧光参数F_m（Maximal Fluorescence）均最大；藻和苔藓结皮的PS Ⅱ最大光化学量子产量F_v/F_m（Optimal/Maximal Quantum Yield of PS Ⅱ）均高于地衣结皮。CO₂通量和叶绿素荧光参数的主要影响因子相似，均与禾本科高度、土壤铵态氮含量正相关，与pH负相关。因此，在研究草地碳平衡过程中应充分考虑生物结皮的贡献，同时需注意不同类型的生物结皮的CO₂通量和叶绿素荧光参数的差异变化。

Changes of CO2 Fluxes and Chlorophyll Fluorescence Parameters of Biological Soil Crusts in a 19-year Artificial Grassland in the Source Zone of the Yellow River

To understand the variation of CO₂ release and carbon fixation in different BSCs and vegetation communities in artificial grassland,and to explore the factors influencing CO₂ release and photosynthesis of BSCs,we measured CO₂ fluxes and chlorophyll fluorescence parameters of different BSCs in a 19-year-old artificial grassland,vegetation and soil characteristics were also investigated at the same time. The results showed that CO₂ flux of algal and lichen crusts was significantly lower than that of moss (10.58 μmol·m^-2·s^-1)(P<0.05). The CO₂ flux of the vegetation community was 11.55 μmol·m^-2·s^-1 in moss crust stage,which was significantly lower than that in algal and lichen crusts (P<0.05). The CO₂ flux of the soil covered by algae and lichen crusts was significantly higher than that of moss crusts in soil CO₂ fluxes test (about 2 times,P<0.05). For chlorophyll fluorescence,the parameters F₀ and F_m of moss were the highest. Algal and moss had a higher F_v/F_m than lichen. Redundancy Analysis (RDA) showed that the CO₂ fluxes and chlorophyll fluorescence were positively correlated with the height of grass and NH⁺₄-N content,but negatively correlated with pH. Thus,it is important to consider the contribution of BSCs to the variability of CO₂ fluxes and chlorophyll fluorescence in different successional stages.