Abstract
Litter decomposition is a key process for carbon and nutrient cycling in terrestrial ecosystems and is mainly controlled by environmental conditions, substrate quantity and quality as well as microbial community abundance and composition. In particular, the effects of climate and atmospheric nitrogen (N) deposition on litter decomposition and its temporal dynamics are of significant importance, since their effects might change over the course of the decomposition process. Within the TeaComposition initiative, we incubated Green and Rooibos teas at 524 sites across nine biomes. We assessed how macroclimate and atmospheric inorganic N deposition under current and predicted scenarios (RCP 2.6, RCP 8.5) might affect litter mass loss measured after 3 and 12 months. Our study shows that the early to mid-term mass loss at the global scale was affected predominantly by litter quality (explaining 73% and 62% of the total variance after 3 and 12 months, respectively) followed by climate and N deposition. The effects of climate were not litter-specific and became increasingly significant as decomposition progressed, with MAP explaining 2% and MAT 4% of the variation after 12 months of incubation. The effect of N deposition was litter-specific, and significant only for 12-month decomposition of Rooibos tea at the global scale. However, in the temperate biome where atmospheric N deposition rates are relatively high, the 12-month mass loss of Green and Rooibos teas decreased significantly with increasing N deposition, explaining 9.5% and 1.1% of the variance, respectively. The expected changes in macroclimate and N deposition at the global scale by the end of this century are estimated to increase the 12-month mass loss of easily decomposable litter by 1.1–3.5% and of the more stable substrates by 3.8–10.6%, relative to current mass loss. In contrast, expected changes in atmospheric N deposition will decrease the mid-term mass loss of high-quality litter by 1.4–2.2% and that of low-quality litter by 0.9–1.5% in the temperate biome. Our results suggest that projected increases in N deposition may have the capacity to dampen the climate-driven increases in litter decomposition depending on the biome and decomposition stage of substrate.
Highlights
Litter decomposition is a fundamental process in the carbon and nutrient cycling across all ecosystems (Chapin et al, 2011; Berg and McClaugherty, 2020)
When the analysis was run for each tea type separately, precipitation was positively correlated with mass loss for both Green tea (4.2% of variance) and Rooibos tea (9.2% of variance)
Temperature was positively correlated with mass loss of Green tea (0.9% of variance) and Rooibos tea (0.6% of variance; Table 3 and Figure 3)
Summary
Litter decomposition is a fundamental process in the carbon and nutrient cycling across all ecosystems (Chapin et al, 2011; Berg and McClaugherty, 2020). Climate variables can explain up to 68% of the variability in litter decomposition rates on a global scale (Parton et al, 2007); changes in environmental conditions may have a significant impact on litter decomposition processes via both direct and indirect pathways. Carbon to nitrogen ratio and lignin content of the initial litter are considered to be good indicators of litter quality as they are related to nutrient availability and chemical properties of the studied substrate. The early stage of litter decomposition (i.e., 0–30% mass loss) where most of the watersoluble compounds are released is especially sensitive to the environmental changes and the decomposition of holocellulose is promoted by higher nitrogen (N) contents in initial litter and soil. The central role of climate and litter quality in controlling litter decomposition rates is widely recognized, results on the effects of increased N input and climate on the decomposition in the field are inconsistent
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