School of Soil and Water Conservation, Beijing Forestry University, Beijing, China.
Beijing Engineering Research Center of Soil and Water Conservation, Beijing Forestry University, Beijing, China.
Glob Chang Biol. 2022 Aug;28(15):4605-4619. doi: 10.1111/gcb.16218. Epub 2022 May 14.
Recent evidence suggests that the relationships between climate and boreal tree growth are generally non-stationary; however, it remains uncertain whether the relationships between climate and carbon (C) fluxes of boreal forests are stationary or have changed over recent decades. In this study, we used continuous eddy-covariance and microclimate data over 21 years (1996-2016) from a 100-year-old trembling aspen stand in central Saskatchewan, Canada to assess the relationships between climate and ecosystem C and water fluxes. Over the study period, the most striking climatic event was a severe, 3-year drought (2001-2003). Gross ecosystem production (GEP) showed larger interannual variability than ecosystem respiration (R ) over 1996-2016, but R was the dominant component contributing to the interannual variation in net ecosystem production (NEP) during post-drought years. The interannual variations in evapotranspiration (ET) and C fluxes were primarily driven by temperature and secondarily by water availability. Two-factor linear models combining precipitation and temperature performed well in explaining the interannual variation in C and water fluxes (R > .5). The temperature sensitivities of all three C fluxes (NEP, GEP and R ) declined over the study period (p < .05), and, as a result, the phenological controls on annual NEP weakened. The decreasing temperature sensitivity of the C fluxes may reflect changes in forest structure, related to the over-maturity of the aspen stand at 100 years of age, and exacerbated by high tree mortality following the severe 2001-2003 drought. These results may provide an early warning signal of driver shift or even an abrupt status shift of aspen forest dynamics. They may also imply a universal weakening in the relationship between temperature and GEP as forests become over-mature, associated with the structural and compositional changes that accompany forest ageing.
最近的证据表明，气候和北方树木生长之间的关系通常是非稳定的；然而，目前尚不确定气候与北方森林碳（C）通量之间的关系是否稳定，或者在最近几十年是否发生了变化。在这项研究中，我们使用了加拿大萨斯喀彻温省中部一个拥有 100 年历史的颤杨林中 21 年（1996-2016 年）的连续涡度协方差和小气候数据，来评估气候与生态系统 C 和水通量之间的关系。在研究期间，最引人注目的气候事件是一场严重的三年干旱（2001-2003 年）。在 1996-2016 年期间，总生态系统生产力（GEP）的年际变化比生态系统呼吸（R）更大，但在干旱后年份，R 是导致净生态系统生产力（NEP）年际变化的主要因素。蒸散（ET）和 C 通量的年际变化主要由温度驱动，其次是水分供应。结合降水和温度的两因素线性模型在解释 C 和水通量的年际变化方面表现良好（R>0.5）。在研究期间，所有三种 C 通量（NEP、GEP 和 R）的温度敏感性都有所下降（p<0.05），因此，对年度 NEP 的物候控制作用减弱。C 通量的温度敏感性下降可能反映了森林结构的变化，这与 100 年生颤杨林的过度成熟有关，并因 2001-2003 年严重干旱后树木大量死亡而加剧。这些结果可能为驱动因素变化甚至白杨林动态的突然状态变化提供早期预警信号。它们还可能意味着随着森林变得过度成熟，与森林老化相关的结构和组成变化，温度与 GEP 之间的关系普遍减弱。
