Search

The article presents the response of the researchers on the comments of Brian J. Enquist concerning their report on global scale variation across the different gradients including biomass, temperature, and successionary age. They argued that variation exists in forest annual autotrophic respiration over the global scale. They assumed that Enquist did not take into account some complexity in forest ecosystems' autotrophic respiration processes.

Forest autotrophic respiration (Ra) plays an important role in the carbon balance of forest ecosystems. However, its drivers at the global scale are not well known. Based on a global forest database, we explore the relationships of annual Ra with mean annual temperature (MAT) and biotic factors including net primary productivity (NPP), total biomass, stand age, mean tree height, and maximum leaf area index (LAI). The results show that the spatial patterns of forest annual Ra at the global scale are largely controlled by temperature. Ra is composed of growth (Rg) and maintenance respiration (Rm). We used a modified Arrhenius equation to express the relationship between Ra and MAT. This relationship was calibrated with our data and shows that a 10°C increase in MAT will result in an increase of annual Rm by a factor of 1.9-2.5 (Q10). We also found that the fraction of total assimilation (gross primary production, GPP) used in Ra is lowest in the. temperate regions characterized by a MAT of ∼11°C. Although we could not confirm a relationship between the ratio of Ra to GPP and age across all forest sites, the Ra to GPP ratio tends to significantly increase in response to increasing age for sites with MAT between 8° and 12°C. At the plant scale, direct up-scaled Ra estimates were found to increase as a power function with forest total biomass; however, the coefficient of the power function (0.2) was much smaller than that expected from previous studies (0.75 or 1). At the ecosystem scale, Ra estimates based on both GPP - NPP and TER - Rh (total ecosystem respiration - heterotrophic respiration) were not significantly correlated with forest total biomass (P > 0.05) with either a linear or a power function, implying that the previous individual-based metabolic theory may be not suitable for the application at ecosystem scale. [ABSTRACT FROM AUTHOR]