Temperature sensitivity (Q₁₀) of ecosystem respiration (ER) is a crucial parameter for predicting the fate of CO₂ in terrestrial e cosystems under global warming. Most studies focus their attention in the variation of Q₁₀ in one or two components of ER, but not in the integration or comparison among Q₁₀ in major components of ER. Vertical and seasonal variations in individual components, including leaf respiration, stem respiration and soil respiration, of ER were observed synchronously along the gradient of leaf–stem–soil over a 2 year period in three forest stands dominated by masson pine, loblolly pine and oak, respectively, in a subtropical forest ecosystem of central China. We found that Q₁₀ in individual components of ER increased along the vertical gradient of leaf–stem–soil. The vertical pattern of Q₁₀ in individual components of ER was ascribed to variations of diurnal temperature range (DTR) and activation energy (ΔH_a). These results suggest that a vertical pattern of Q₁₀ in individual components of ER along the gradient of leaf–stem–soil should be taken into consideration in process-based models that simulate respiratory carbon flux in terrestrial ecosystems.

Rhizodeposition-derived carbon plays an important role in plant nutrient acquisition and soil carbon sequestration. However, how nitrogen deposition affects the distribution of rhizodeposition-derived carbon into aggregate classes (macrogagregates, microaggregates, and silt and clay) is unclear. We conducted a nitrogen addition experiment on Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) seedlings with continuously labeled ¹³CO₂ for 120 days. Plant growth and the distribution of rhizodeposition-derived carbon into aggregate classes were assessed. Results showed that nitrogen additionconsiderably increased the ratio of aboveground to belowground biomass, but not aboveground and belowground biomass. Compared with the control, nitrogen addition resulted in a significantdecreaseby 52% inrhizodeposition-derived carbon in bulk soil.We found that more rhizodeposition-derived carbon was incorporated into macroaggregate, followed by microaggregate, and silt and clay regardless of nitrogen addition. The rhizodeposition-derived carbon was significantly decreased by 40% in macroaggregate, 60% in microaggregate, and 61% in silt and clay after nitrogen addition. Nitrogen addition and aggregate classes had no interactive effect on the rhizodeposition-derived carbon. Our results suggest that nitrogen deposition decreases the rhizodeposition of Chinese fir and its distributionin aggregate classes.

Acid rain is one of the most serious environmental issues in Southern China. The composition of acid rain has gradually changed from sulfuric acid rain (SAR) to nitric acid rain (NAR) due to the rapid development of industry, and controls on SO₂ emissions. However, a comprehensive understanding of how changes in the type of acid rain affect soil respiration (Rs) in forest ecosystems is still lacking. In this study, we investigated the influence of simulated acid rain with different ${\mathrm{SO}}_4^{2-}$/${\mathrm{NO}}_3^{-}$ ratios, namely, SAR (4:1), MAR (mixed acid rain, 1:1), and NAR (1:4), on Rs in Cunninghamia lanceolata (Lamb.) Hook. (CL) and Michelia macclurei Dandy (MM) plantations from 2019 to 2020. A trenching method was used to partition Rs into heterotrophic respiration (Rh) and autotrophic respiration (Ra). The results showed that acid rain did not significantly influence Rs in the two plantations, which could be mainly attributed to the unchanged soil pH. Neither SAR, MAR, nor NAR affected Ra in the two plantations, possibly due to the unchanged root biomass. The SAR treatment only significantly increased Rh in the MM plantation, not in the CL plantation. The temperature sensitivity (Q₁₀) of Rs and its components was not significantly different among different acid rain types in either of the plantations. Our results suggest that the impact of acid rain on Rs and its components depends on the forest ecosystem and the type of acid rain. Different biological processes complicate the response of soil CO₂ emissions to acid rain pollution.