Soil drainage facilitates earthworm invasion and subsequent carbon loss from peatland soil

Abstract

Summary 1. Human activities have been a significant driver of environmental changes with tremendous consequences for carbon dynamics. Peatlands are critical ecosystems because they store ~30% of the global soil organic carbon pool and are particularly vulnerable to anthropogenic changes. The Zoige peatland on the eastern Tibet Plateau, as the largest alpine peatland in the world, accounts for 1‰ of global peat soil organic carbon storage. However, this peatland has experienced dramatic climate change including increased temperature and reduced precipitation in the past decades, which likely is responsible for a decline of the water table and facilitated earthworm invasion, two major factors reducing soil organic carbon (SOC) storage of peatlands. 2. Because earthworms are often more active in low- than in high- moisture peatlands, we hypothesized that the simultaneous occurrence of water table decline and earthworm invasion would synergistically accelerate the release of SOC from peatland soil. We conducted a field experiment with a paired split-plot design, i.e. presence vs. absence of the invasive earthworms (Pheretima aspergillum) nested in drained vs. undrained plots, respectively, for three years within the homogenous Zoige peatland. 3. Water table decline significantly decreased soil water content and bulk density, resulting in a marked reduction of SOC storage. Moreover, consistent with our hypothesis, earthworm presence dramatically reduced SOC in the drained but not in the undrained peatland through the formation of deep burrows and decreasing bulk density of the lower soil layer over three years. The variation in SOC likely was due to changes in aboveground plant biomass, root growth, and earthworm behavior induced by the experimental treatments. 4. Synthesis and applications. We suggest that incentive measures should be taken to prevent further water table decline and earthworm invasion for maintaining the soil C pool in Zoige peatland. Artificial filling of drainage canals should be implemented to increase the water table level, facilitating the recovery of drained peatlands. Moreover, the dispersal of earthworms and their cocoons attached to the roots of crop plants and tree saplings from low-lying areas to the Zoige region should be controlled and restricted.

Effects of water level alteration on carbon cycling in peatlands

“…See aerobic and anaerobic decomposition in Figure 1. Drawdown alleviates oxygen limitation and increases soil aeration, which promotes the activities of soil organisms and microbial mineralization of organic substrates in peatlands (Moore and Dalva 1997;Laiho et al 2001;Makiranta et al 2009;Hribljan et al 2014;Bragazza et al 2016;Schmidt et al 2016), as well as the activities of phenoloxidase and peroxidase (Fenner and Freeman 2011;Peacock et al 2015;Dieleman et al 2016a), hence leading to an increase in hydrolase activity and decomposition rate (Moore and Knowles 1989;Silvola et al 1996;Nykanen et al 1998;Minkkinen et al 1999;Freeman, Ostle, and Kang 2001;Jaatinen et al 2008;Peacock et al 2015;Wu et al 2017). For example, phenolic-degrading bacteria are more diverse and have higher phenoloxidase activity under short-term drought, which further increases CO 2 flux (Fenner, Freeman, and Reynolds 2005).…”

Carbon emission flux and storage in the degraded peatlands of the Zoige alpine area in the Qinghai–Tibetan Plateau

“…The decline in water table through processes, such as drainage, could increase the CO 2 emission fluxes and reduce the CH 4 emission fluxes (Gorham, 1991; Moore & Knowles, 1989; Roulet, 2000; Urbanová et al., 2013), resulting in a net loss of C storage from soil (Heinemeyer & Swindles, 2018; Wu et al., 2017). In this study, the C emission fluxes associated with the wet and dry meadows were 2.51 and 4.94 times more than that in the peatland, respectively (Figure 3c).…”

Controls on variation of soil organic carbon concentration in the shrublands of the north‐eastern Tibetan Plateau

“…Secondly, increasing soil pH can also have significant effects on relative abundance of arbuscular mycorrhizal fungi (i.e., Glomus and Acaulospora), which can result in considerable SOC decomposition under elevated CO 2 (Cheng et al, 2012). Additionally, soil pH can also have significant effects on soil fauna (Liu et al, 2007), which can stimulate soil microorganisms and, further, speed up SOC losses (Wu et al, 2017;Zhou et al, 2014).…”

“…Regarding the Tibetan Plateau, SOC levels were reported in grasslands (Yang et al, 2009;Wu, Wang, & Sun, 2019), wetlands (Ma, Zhang, Tang, & Liu, 2016;Wang, Qian, Cheng, & Lai, 2002) and permafrost regions (Mu et al, 2015), including alpine swamp meadow, meadow, steppe and desert vegetation (Shang et al, 2016), and SOC was significantly different in various ecosystems (Shang et al, 2016). The SOC variation is likely to be shaped by the following factors: aboveground plant biomass, root biomass, soil texture and mineralogy (Doetterl et al, 2015(Doetterl et al, , 2018Feng, Plante, & Six, 2013;Rasmussen et al, 2018;Wu et al, 2017). Piao et al (2009) have indicated that shrublands were identified as being the most uncertain factor that was contributing to China's C stock due to their less extensive investigation.…”