Plant functional group controls litter decomposition rate and its temperature sensitivity: An incubation experiment on litters from a boreal peatland in northeast China
Graphical abstract
Introduction
In many terrestrial ecosystems, the majority of plant productivity enters the detritus food web through plant litters. Thus, litter decomposition plays an essential role in regulating soil carbon (C) sequestration and nutrient availability (Mann, 1988; Mcnaughton et al., 1989; Menéndez et al., 2003). Litter decomposition rates are influenced by both abiotic and biotic factors, including climate and litter identity (Aerts, 2006). In general, traits of the litter species are intrinsic determinants controlling litter decomposition rates (Aerts and Chapin, 1999; Cornwell et al., 2008), while climate is regarded as a primary abiotic factor (Hobbie, 1996; Fierer et al., 2005). Therefore, climate change and altered litter quality could cause substantial changes in litter decomposition rates, exerting crucial influences on C budget and nutrient turnover in terrestrial ecosystems.
Boreal peatlands, despite the low plant productivity, have accumulated a large amount of organic matter in soils since the Holocene mainly because of the extremely slow rates of decomposition, and now contain approximately one-third of the world soil C pool (Gorham, 1991; Yu et al., 2011). In these ecosystems, litter decomposition is strongly constrained by low temperature and recalcitrant substrate quality (Aerts, 2006; Moore et al., 2007). In recent decades, both observational and modeling studies have found that boreal peatlands are subject to severe climate warming (Aerts, 2006). This warming may enhance soil microbial activity and accelerate the decomposition of plant litters in these ecosystems (Cornelissen et al., 2007). Meanwhile, climate warming generally leads to changes in vegetation composition and structure (Dieleman et al., 2015; Robroek et al., 2017), which can indirectly influence litter decomposition rates by altering the quality of litter inputs into soils. In these peatlands, litter quality differs markedly among plant functional groups (Hobbie and Gough, 2004; Dorrepaal et al., 2005). For example, Sphagnum mosses generally produce a higher proportion of recalcitrant plant litter than vascular plants (Lang et al., 2009). Moreover, previous studies have found that the responses of litter decomposition to warming are modulated by the initial substrate quality (Fierer et al., 2005; Kim et al., 2015; Zhang et al., 2017). However, empirical studies that determine the interactive effect between elevated temperature and litter quality on litter decomposition are still limited for boreal peatlands. Given the critical role of litter decomposition in regulating C accumulation and nutrient availability, it is essential to understand the influences of elevated temperature on decomposition of plant litters with contrasting substrate quality in these C-rich ecosystems.
Here, the interactive effects of temperature and litter quality on decomposition rates were assessed in fresh litters from 16 species belonging to six plant functional groups (Sphagnum moss, graminoid, deciduous shrub, evergreen shrub, deciduous tree, and nitrogen (N)-fixing species) that are most commonly distributed in boreal peatlands in northeast China. The decomposition rates of these plant litters were measured under different temperature conditions using a laboratory incubation method. We assessed litter decomposition rates by measuring CO2 production and mass loss, which have been widely used to characterize litter decomposability (Hobbie, 1996; Güsewell and Verhoeven, 2006). The aims of this study were to (1) determine the differences in litter decomposition rates among plant functional groups at different incubation temperatures, and (2) reveal how plant functional group affects the temperature sensitivity of litter decomposition in boreal peatlands.
Section snippets
Study site
The study was conducted in a boreal peatland (52°56′N, 122°51′E, 467 m a.s.l.) north of Great Hing'an Mountain, Heilongjiang Province, Northeast China. The Great Hing'an Mountain is located at the southern boundary of the Eurasian continuous permafrost and boreal peatlands, where the mean air temperature has increased by >1.5 °C since the 1960s (Jin et al., 2006). Mean annual temperature (1980–2010) is −3.9 °C, and mean annual precipitation is about 450 mm. In this peatland, the thickness of
Results
In litters collected from a boreal peatland, organic C, N, and P concentrations, and C:N and C:P ratios varied significantly with plant functional group (Table 1). Organic C concentration was highest in evergreen shrub litters and lowest in graminoid litters. Litter N concentration was 14.90 mg g−1 in N-fixing species, but was only from 2.73 mg g−1 (graminoid) to 4.49 mg g−1 (deciduous tree) in other plant functional groups. In addition, litter P concentration was highest in deciduous shrub
Discussion
In this study, we used a standard laboratory incubation method to determine litter decomposability and its temperature sensitivity in 16 common species belonging to six plant functional groups in a boreal peatland located in northeast China. Our results show that incubation temperature and plant functional group significantly interact to affect litter decomposition rates. Moreover, temperature sensitivity of litter decomposition varied substantially with plant functional group. Our results
Conclusions
We determined the decomposition dynamics at 10 °C and 20 °C of plant litters from 16 species belonging to six plant functional groups in a boreal peatland located in northeast China, and assessed the temperature sensitivity of litter decomposition among the six plant functional groups. We found that litter decomposition rate and its temperature sensitivity varied remarkably among plant functional groups. Specifically, vascular plant litters, especially N-fixing species, deciduous tree, and
Acknowledgements
This study was financed by the National Natural Science Foundation of China (Nos. 31570479, 41671091, and 41103037) and the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (QYZDJ-SSW-DQC013). We thank the editor (Dr. Elena Paoletti) and two anonymous reviewers for their constructive comments on the manuscript.
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