Bowman William P, Turnbull Matthew H, Tissue David T, Whitehead David, Griffin Kevin L
Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA.
Tree Physiol. 2008 Oct;28(10):1553-9. doi: 10.1093/treephys/28.10.1553.
Temperature plays a critical role in the regulation of respiration rates and is often used to scale measurements of respiration to the stand-level and calculate annual respiratory fluxes. Previous studies have indicated that failure to consider temperature gradients between sun-exposed stems and branches in the crown and shaded lower stems may result in errors when deriving stand-level estimates of stem CO(2) efflux. We measured vertical gradients in sapwood temperature in a mature lowland podocarp rain forest in New Zealand to: (1) estimate the effects of within-stem temperature variation on the vertical distribution of stem CO(2) efflux; and (2) use these findings to estimate stand-level stem CO(2) efflux for this forest. Large within-stem gradients in sapwood temperature (1.6 +/- 0.1 to 6.0 +/- 0.5 degrees C) were observed. However, these gradients did not significantly influence the stand-level estimate of stem CO(2) efflux in this forest (536 +/- 42 mol CO(2) ha(-1) day(-1)) or the vertical distribution of stem CO(2) efflux, because of the opposing effects of daytime warming and nighttime cooling on CO(2) efflux in the canopy, and the small fraction of the woody biomass in the crowns of forest trees. Our findings suggest that detailed measurements of within-stand temperature gradients are unlikely to greatly improve the accuracy of tree- or stand-level estimates of stem CO(2) efflux.
温度在呼吸速率调节中起着关键作用，并且常被用于将呼吸测量值按林分水平进行缩放，并计算年度呼吸通量。先前的研究表明，在推导林分水平的树干二氧化碳排放估计值时，如果未考虑树冠中暴露于阳光下的树干和树枝与被遮蔽的下部树干之间的温度梯度，可能会导致误差。我们在新西兰一片成熟的低地罗汉松雨林中测量了边材温度的垂直梯度，目的是：（1）估计树干内温度变化对树干二氧化碳排放垂直分布的影响；（2）利用这些发现来估计这片森林林分水平的树干二氧化碳排放量。观测到边材温度存在较大的树干内梯度（1.6±0.1至6.0±0.5摄氏度）。然而，由于白天升温与夜间降温对树冠中二氧化碳排放的相反作用，以及林木树冠中木质生物量所占比例较小，这些梯度并未显著影响这片森林林分水平的树干二氧化碳排放估计值（536±42摩尔二氧化碳·公顷⁻¹·天⁻¹）或树干二氧化碳排放的垂直分布。我们的研究结果表明，对林分内温度梯度进行详细测量不太可能大幅提高树木或林分水平的树干二氧化碳排放估计值的准确性。
