Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
Department of Plant Ecology, Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan.
Tree Physiol. 2017 Oct 1;37(10):1269-1284. doi: 10.1093/treephys/tpx012.
Leaf respiration (R) is a major component of carbon balance in forest ecosystems. Clarifying the variability of leaf R within a canopy is essential for predicting the impact of global warming on forest productivity and the potential future function of the forest ecosystem as a carbon sink. We examined vertical and seasonal variations in short-term temperature responses of leaf R as well as environmental factors (light and mean air temperature) and physiological factors [leaf nitrogen (N), leaf mass per area (LMA), and shoot growth] in the canopy of a 10-year-old stand of hinoki cypress [Chamaecyparis obtusa (Sieb. et Zucc.) Endl.] in Kyushu, Japan. Leaf respiration rate adjusted to 20 °C (R20) exhibited evident vertical gradients in each season and was correlated with light, LMA and leaf N. In contrast, the temperature sensitivity of leaf R (Q10) did not vary vertically throughout the seasons. Seasonally, Q10 was higher in winter than in summer and was strongly negatively correlated to mean air temperature. A negative correlation of R20 with mean air temperature was also observed for each of the three canopy layers. These results clearly indicate that leaf R was able to adjust to seasonal changes in ambient temperature under field conditions and down-regulate during warmer periods. We also found that the degree of thermal acclimation did not vary with canopy position. Overall, our results suggest that vertical and seasonal variations in temperature responses of leaf R within a hinoki cypress canopy could be predicted by relatively simple parameters (light and temperature). There was an exception of extremely high R20 values in April that may have been due to the onset of shoot growth in spring. Understanding thermal acclimation and variations in leaf R within forest canopies will improve global terrestrial carbon cycle models.
叶片呼吸（R）是森林生态系统碳平衡的主要组成部分。阐明冠层内叶片 R 的可变性对于预测全球变暖对森林生产力的影响以及森林生态系统作为碳汇的未来潜在功能至关重要。我们研究了日本九州地区 10 年生扁柏（Chamaecyparis obtusa（Sieb. et Zucc.）Endl.）林冠中叶片 R 的短期温度响应的垂直和季节性变化以及环境因素（光照和平均空气温度）和生理因素[叶片氮（N）、比叶面积（LMA）和新梢生长]。在每个季节，调整到 20°C 的叶片呼吸速率（R20）都表现出明显的垂直梯度，并与光照、LMA 和叶片 N 相关。相比之下，叶片 R 的温度敏感性（Q10）在整个季节都没有垂直变化。季节性地，冬季的 Q10 高于夏季，并且与平均空气温度呈强烈负相关。在三个冠层中，R20 与平均空气温度也呈负相关。这些结果清楚地表明，叶片 R 能够在田间条件下适应环境温度的季节性变化，并在温暖时期下调。我们还发现，R20 值与平均空气温度之间的相关性在树冠位置上没有差异。总的来说，我们的结果表明，扁柏林冠内叶片 R 的温度响应的垂直和季节性变化可以通过相对简单的参数（光照和温度）来预测。四月份出现的极高 R20 值可能是由于春季新梢生长的开始。了解森林冠层内的热驯化和叶片 R 的变化将提高全球陆地碳循环模型的准确性。
