土壤氮水交互对马尾松和杉木COS和CO2通量的影响

羰基硫(COS)和CO_2化学结构相似,且植物对COS和CO_2具有共吸收特性,因此可利用COS作为示踪物来估算生态系统总初级生产力,而不同植物吸收COS和CO_2对环境因子变化的响应差异较大。以南亚热带典型树种马尾松(Pinus massoniana)和杉木(Cunninghamia lanceolata)为研究对象,设置2个氮水平及3个土壤水分梯度处理。采取顶空套袋法采集气体样品,用预浓缩—气质联用仪分析样品COS浓度,同时测量植物光合参数。结果表明:马尾松和杉木吸收COS,吸收速率均值分别为39.58—127.27 pmol m~(-2) s~(-1)和0.81—66.92 pmol m~(-2) s~(-1)。整体而言,施氮可促进植物吸收COS,但除施氮对马尾松COS通量有显著影响外(P0.05),施氮、土壤水分和两者交互作用对马尾松和杉木的COS和CO_2通量及其比值均无显著性影响。施氮情况下,高土壤水分处理促进马尾松COS吸收而低土壤水分处理促进杉木COS吸收。中等土壤水分和高土壤水分条件下马尾松和杉木COS通量与气孔导度呈正相关关系。线性拟合结果表明,植物COS通量(F_(COS))与CO_2通量(F_(CO_2))呈极显著正相关(P0.01),马尾松和杉木F_(COS)/F_(CO_2)值分别为1.48×10~(-6)和1.01×10~(-6)。中等土壤水分条件均可提高马尾松F_(COS)/F_(CO_2)比值,而低土壤水分条件下施氮增加杉木F_(COS)/F_(CO_2)比值,高土壤水分条件下施氮降低杉木F_(COS)/F_(CO_2)比值。低土壤水分和高土壤水分使马尾松蒸汽压亏缺增大,促使气孔导度减小从而降低净光合速率。低土壤水分和高土壤水分下施氮导致杉木气孔导度增加从而增强净光合速率。研究结果不仅对进一步了解区域氮沉降和降水对树木COS通量及F_(COS)/F_(CO_2)的影响有重要意义,而且可为模型估算总初级生产力提供区域性数据支持。

Effects of soil nitrogen and water interaction on COS and CO2 fluxes of Pinus massoniana and Cunninghamia lanceolata

Due to the similar chemical structure of carbonyl sulfide (COS) and carbon dioxide (CO₂) as well as the co-absorption of COS and CO₂ by plants, it is possible to employ COS as a proxy for estimating the gross primary productivity (GPP). However, the response of COS and CO₂ fluxes to environmental factors varies between different plants. Two typical subtropical tree species, namely Pinus massoniana and Cunninghamia lanceolata were selected, two nitrogen levels, and three soil water gradients were set in this study. Gas samples were collected in sample bags with dynamic headspace cuvettes methods, and the COS concentration inside was determined by preconcentrator-GC-MS. The photosynthetic parameters of plants was measured simultaneously. The results showed that P. massoniana and C. lanceolata could assimilate COS, with the rates of 39.58-127.27 pmol m^-2 s^-1 and 0.81-66.92 pmol m^-2 s^-1, respectively. Generally, COS absorption by plants could be promoted by nitrogen application. Except for the significant effect of nitrogen application on the COS flux of P. massoniana (P < 0.05), soil moisture, nitrogen application and their interactions had no significant effect on COS and CO₂ fluxes (F_COS and F_CO2) and their ratios of F_COS and F_CO2 for P. massoniana and C. lanceolata. With nitrogen application, the COS absorption by P. massoniana could be promoted at high soil moisture, while at low soil moisture for C. lanceolata. Under moderate soil water and high soil water conditions, the COS fluxes of P. massoniana and C. lanceolata were positively correlated with stomatal conductance. The linear fitting results showed that the COS fluxes of plants were extremely significantly positively correlated with the CO₂ fluxes (P < 0.01), with the F_COS/F_CO2 value of 1.48×10^-6 and 1.01×10^-6 for P. massoniana and C. lanceolata, respectively. Moderate soil moisture could increase F_COS/F_CO2 value for P. massoniana, while nitrogen application increased F_COS/F_CO2 value under low soil water conditions, and the value decreased under high soil water conditions for C. lanceolata. Low and high soil moisture increased the vapor pressure deficit of P. massoniana, which promoted the reduction of stomatal conductance and reduced the net photosynthetic rate. Nitrogen application increased the stomatal conductance of C. lanceolata under low and high soil moisture conditions and thus enhanced net photosynthetic rate. The results not only have important implications for further understanding of the effects of regional nitrogen deposition and precipitation on tree COS flux and F_COS/F_CO2, but also provide regional data for modelling and estimating gross primary productivity.