LBA-ECO CD-08 COARSE WOOD LITTER RESPIRATION AND DECOMPOSITION, MANAUS, BRAZIL

Respiration from coarse litter (trunks and large branches > 10 cm diameter) was studied in central Amazon forests. Respiration rates varied over almost two orders of magnitude (1.003-0.014 mug C g(-1) C min(-1), n = 61), and were significantly correlated with wood density (r(adj)(2) = 0.42), and moisture content (r(adj)(2) = 0.39). Additional samples taken from a nearby pasture indicated that wood moisture content was the most important factor controlling respiration rates across sites (r(adj)(2) = 0.65). Based on average coarse litter wood density and moisture content, the mean long-term carbon loss rate due to respiration was estimated to be 0.13 yr(-1) (range of 95% prediction interval (PI) = 0.11-0.15 yr(-1)). Comparing mean respiration rate with mean mass loss (decomposition) rate from a previous study, respiratory emissions to the atmosphere from coarse litter were predicted to be 76% (95% PI = 65-88%) of total carbon loss, or about 1.9 (95% PI = 1.6-2.2) Mg C ha(- 1) yr(-) (1). Optimum respiration activity corresponded to about 2.5 g H2O g(-1) dry wood, and severely restricted respiration to < 0.5 g H2O g(-1) dry wood. Respiration from coarse litter in central Amazon forests is comparable in magnitude to decomposing fine surface litter (e.g. leaves, twigs) and is an important carbon cycling component when characterizing heterotrophic respiration budgets and net ecosystem exchange (NEE).

本研究针对亚马逊中部森林内直径大于10 cm的树干与大枝条构成的粗枯落物的呼吸作用展开系统探究。研究结果显示，粗枯落物的呼吸速率变化跨度近两个数量级，范围为1.003~0.014 μg C·g⁻¹(C)·min⁻¹，有效样本量n=61；且呼吸速率与木材密度（调整决定系数r_adj²=0.42）、木材含水率（调整决定系数r_adj²=0.39）均呈显著相关关系。从附近牧场采集的额外样本结果表明，在不同样地中，木材含水率是调控呼吸速率的最核心影响因子，调整决定系数r_adj²=0.65。基于粗枯落物的平均木材密度与含水率，本研究估算得到由呼吸作用驱动的长期平均碳损失速率为0.13 yr⁻¹，其95%预测区间（Prediction Interval, PI）为0.11~0.15 yr⁻¹。结合此前研究中的平均呼吸速率与平均质量损失（分解）速率，可预测粗枯落物向大气排放的呼吸碳通量占总碳损失的76%，95%预测区间（PI）为65%~88%，约合1.9（95% PI=1.6~2.2）Mg C·ha⁻¹·yr⁻¹（1）。呼吸作用的最适活性对应约2.5 g H₂O·g⁻¹干木材，当木材含水率低于0.5 g H₂O·g⁻¹干木材时，呼吸作用会受到严重抑制。亚马逊中部森林的粗枯落物呼吸作用规模与分解精细地表枯落物（如叶片、细枝）的呼吸规模相当，在表征异养呼吸收支（heterotrophic respiration budgets）与生态系统净交换（Net Ecosystem Exchange, NEE）时，粗枯落物呼吸是重要的碳循环组成部分。