The temperature sensitivity of soil organic carbon decomposition is greater in subsoil than in topsoil during laboratory incubation

Abstract

The turnover of soil organic carbon (SOC) in cropland plays an important role in terrestrial carbon cycling, but little is known about the temperature sensitivity (Q 10 ) of SOC decomposition below the topsoil layer of arable soil. Here, samples of topsoil (0-20 cm) and subsoil (20-40 cm) layers were obtained from paddy fields and upland croplands in two regions of China. Using a sequential temperature changing method, soil respiration rates were calculated at different temperatures (8 °C to 28 °C) and fitted to an exponential equation to estimate Q 10 values. The average SOC decomposition rate was 59% to 282% higher in the topsoil than in the subsoil layer because of higher labile carbon levels in the topsoil. However, Q 10 values in the topsoil layer (5.29 ± 1.47) were significantly lower than those in the subsoil layer (7.52 ± 1.84). The pattern of Q 10 values between the topsoil and subsoil was significantly negative to labile carbon content, which is consistent with the carbon quality-temperature hypothesis. These results suggest that the high temperature sensitivity of SOC decomposition in the subsoil layer needs to be considered in soil C models to better predict the responses of agricultural SOC pools to global warming.Soils contain approximately 1,500 Pg organic carbon (C) in the global upper 100 cm, which is about three times the amount stored in terrestrial vegetation (550 Pg) and twice that stored in the atmosphere (750 Pg) 1, 2 . The soil organic carbon (SOC) pool plays important roles in the cycling and balance of global C 3 . The global storage of SOC in cropland is about 128-165 Pg C 4 , which is approximately 8% to 10% of the terrestrial SOC pool 5,6 . In addition to being an important part of global SOC storage, SOC in cropland is the most active SOC pool among terrestrial ecosystems 7 .Global warming has already had observable effects on the environment 8 . Although warming is expected to accelerate SOC decomposition, the responses of SOC to warming still exhibit many uncertainties 3 . One of the key factors leading to these uncertainties is the temperature sensitivity (Q 10 ) of SOC decomposition 3 . SOC storage in cropland is not only influenced by climate change, but is also regulated by human activities over a short period of time. Therefore, understanding the Q 10 of SOC decomposition in cropland is important for understanding global C cycling. Unlike natural soils, cropland soils have relatively low organic C concentrations, and thus a higher C sequestration potential 4 . Sustainable land use and management practices in agroecosystems could have the potential to sequester approximately 55-78 Pg SOC 9 .Many studies have focused on soil respiration in croplands (e.g. Lohila et al. 10 , Fiener et al. 11 , and Campos 12 ). Field-measured soil respiration is the CO 2 flux emitted from the soil surface, which commonly includes both autotrophic and heterotrophic respiration 13 , with autotrophic respiration occupying 30% to 70% of the total 14, 15 . Therefore, field measurements can not clearl...

Increasing temperature can modify the effect of straw mulching on soil C fractions, soil respiration, and microbial community composition

“…respiration increased rapidly at the early stage of incubation (0-15 DAI), decreased rapidly during mid incubation (16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and then decreased relatively slightly during the later stage of incubation (31)(32)(33)(34)(35)(36)(37)(38)(39)(40). These changes in SR suggested that labile organic matter may have depleted quickly along with incubation time as observed in previous studies [6].…”

“…Increasing temperature would stimulate soil microbial metabolisms [15], accelerate SOC decomposition [16] and increase C efflux through SR [17]. Since the temperature sensitivity of SR (Q 10 ) varied with the substrate availability [18], how the comprehensive responses of C soil fractions, SR and microbial communities to straw mulching would vary with different temperature change is now well reported. Here, we carried out an incubation study, aimed to (1) determine changes in carbon fractions and SR rates to different temperatures in soils with and without 9-yr straw mulching, (2) quantify the effect of straw mulching on soil temperature sensitivity; and (3) explore the relationships among soil C fractions, SR rates and the soil microbial community.…”

Different microbial responses in top‐ and sub‐soils to elevated temperature and substrate addition in a semiarid grassland on the Loess Plateau

“…Our results showed that soil microbial respiration in the deep soil had significantly greater temperature sensitivity (1.91–2.11) than in the topsoil (Figure ). These results support the “C quality‐dependent hypothesis” that recalcitrant compounds with more activation energy have larger Q 10 (Bosatta & Agren, ), and they are also consistent with other observations from several long‐term laboratory incubation studies (Xu, Li, Jiang, Wang, & Bai, ; Yan et al, ). Soil microbial communities are generally C‐limited, suggesting that substrate availability can be important in mediating warming effects on microbial respiration (Gershenson, Bader, & Cheng, ).…”

“…However, experimental results are variable. Some studies showed that C mineralization was more sensitive to temperature increases in deep soil rather than topsoils (Yan et al, ), whereas others reported either a similar response (Pries et al, ) or even slower responses (Pang, Zhu, Lu, & Cheng, ). Similarly, the response of recalcitrant soil C decomposition to newly added C substrates (i.e., the priming effect) in deep soils has been shown to be either larger (Fontaine et al, ; Tian et al, ) or smaller than in topsoils (Kuzyakov, ).…”

Effect of Sieving on Ex Situ Soil Respiration of Soils from Three Land Use Types

“…CO 2 flux measured at a single location in situ may not be representative due to soil heterogeneity at the field scale. Excavation of soil, followed by ex situ measurement of soil respiration under controlled conditions, is often performed to compare soils or test specific hypotheses (Gutinas et al 2013;Zhou et al 2014;Bao et al 2016;Yan et al 2017), while minimizing confounding factors. Whereas in situ measurements are more representative of the actual field conditions (Gabriel and Kellman 2011), ex situ measurements can be used to apply treatments in a systematic manner and are thus very useful.…”