Aims

该研究采用红外气体分析法(IRGA)于2013年3–12月原位测定了北京市东升八家郊野公园中2个主要阔叶树种(槐(Sophora japonica)、旱柳(Salix matsudana))3个高度上的枝干呼吸(Rw)日进程,旨在量化Rw的种间差异,探索种内Rw及其温度敏感系数(Q10)的时间动态和垂直分布格局。研究结果显示:(1)Rw在不同树种之间差异明显,相同月份(4月份除外)槐Rw是旱柳的1.12(7月)–1.79倍(5月)。两树种枝干表面CO2通量速率均表现出明显的单峰型季节变化,峰值分别出现在7月((5.13±0.24)μmol·m–2·s–1)和8月((3.85±0.17)μmol·m–2·s–1)。同一树种在生长月份内的平均呼吸水平显著高于非生长季,但其Q10值季节变化趋势与之相反。(2)RW随测量高度的增加而升高,并在3个高度上表现出不同的日变化规律:其中,树干基部及胸高位置为单峰格局,而一级分枝处的呼吸速率在一天内存在两个峰值,中间出现短暂的"午休"现象。温度是造成一天内呼吸变化的主要原因。此外,顶部Rw及其对温度的敏感程度明显高于基部。温度本身和Q10值差异可在一定程度上解释RW的垂直梯度变化。(3)在生长月份,单位体积木质组织的日累积呼吸速率(mmol·m–3·d–1)与受测部位直径倒数(D–1)呈极显著正相关关系。单位面积(μmol·m–2·s–1)可准确表达两树种在生长期间的RW水平,能合理有效地比较不同个体的呼吸差异及同一个体的时空变异。这些结果表明,采用局部通量法上推至树木整体呼吸时,应全面考虑Rw的时、空变异规律,并选择恰当的表达单位,以减小估测误差。

Respiration rates of stems at different heights and their sensitivity to temperature in two broad-leaved trees in Beijing

Aims Woody-tissue respiration (R_w) is well known to be a large component of the terrestrial ecosystem carbon balance. In order to quantify the intra- and inter-specific variations in stem respiration, investigations were made on the temporal and vertical variations in R_w in order to reveal the vertical pattern and the regulatory mechanisms of the temperature-sensitivity coefficient (Q₁₀). Methods CO₂ release rates and stem temperature were measured in two typical deciduous species (Sophora japonica and Salix matsudana) from March through December 2013 in a suburban park in Beijing. All measurements were carried out at three heights (10 cm, 140 cm and 270 cm) corresponding to the base, breast height and first branch of the trees. Important findings It was found that the stem respiration differed significantly between the two tree species. The R_w in Sophora japonica was 1.12 (July) to 1.79 (May) times of that in Salix matsudana for the same months except in April. Clear diurnal cycles and strong seasonal variations were found in the stem respiration per unit surface area (R_S). The seasonal variation patterns of R_w were unimodal for both species; however, the peak month differed between the two species, i.e. July ((5.13 ± 0.24) μmol·m^–2·s^–1) for Sophora japonica and August ((3.85 ± 0.17) μmol·m^–2·s^–1) for Salix matsudana. Stem respiration during the growing season (July and August) was higher than in the dormant season (November and December); whereas the seasonal variations of Q₁₀ showed opposite trend, i.e. higher in the dormant season than during the growing season. R_w increased and the diel patterns of R_w varied with height; the pattern of stem respiration was unimodal for trunk and diauxie for branches, respectively. Stem temperature was found to be the dominant factor regulating the diurnal dynamics of stem respiration at a daily scale. In addition, Q₁₀ higher at the top than at the base. Stem temperature and Q₁₀ collectively determined the temporal and vertical patters of stem respiration. During the growing months, daily accumulated respiration per volume of woody tissue (mmol·m^–3·d^–1) was linearly related to the inverse of stem diameter measured at breast height. The level of respiration was better expressed on area base (μmol·m^–2·s^–1) for comparisons among individuals and examination of temporal and spatial variations of the same individual. Therefore, the spatial and temporal variability of R_w should be considered in the construction of city forest carbon budget model so as to reduce the estimation error.