Introduction
Soil stores twice carbon (C) more than the atmosphere (Jobbágy and
Jackson, 2000; Lal, 2004; Scharlemann et al. , 2014), and the
decomposition of soil C (also called as soil microbial respiration, MR)
releases 6-10 times more CO2 into atmosphere than the
current levels of fossil fuel consumption every year (Boden et
al. , 2009; Friedlingstein et al. , 2021). Thus, soil C cycling
plays critical role in regulating global C budget and atmosphere
CO2 concentration (Bond-Lamberty et al. , 2018;
Friedlingstein et al. , 2021). Moreover, large amount of studies
has confirmed that MR is critically sensitive to current climate change,
especial rising temperature (Davidson and Janssens, 2006; Bond-Lamberty
and Thomson, 2010; Bradford et al. , 2021). The ongoing global
warming may potentially accelerate soil C loss (Friedlingstein et
al. , 2021) and thus makes soil a large C source to atmosphere in the
future (Davidson and Janssens, 2006; Bond-Lamberty and Thomson, 2010;
Bond-Lamberty et al. , 2018). Quantifying the variations and
drivers of MR and its response to rising temperature (also called
temperature sensitivity, Q 10) is a high priority
in order to better model and predict terrestrial C cycle under global
warming (Zhou et al. , 2009).
Elevational gradients are ideal platform to study the response of soil C
cycling under climate warming (Kong et al. , 2022). Different
elevational gradients cause various climate levels, such as temperature
and precipitation (He et al. , 2021; Kong et al. , 2022),
but with similar soil parent material and plant species pool. Therefore,
elevational gradients could provide more realistic insight in the
underlying mechanism driving MR and Q 10 (Conantet al. , 2011; Longbottom et al. , 2014). Various studies
found that MR declined along the elevational gradients (Garten and
Hanson, 2006; Gutiérrez-Girón et al. , 2015), since warmer soils
in low elevation contribute to more active soil microorganisms and high
decomposition rates (Gutiérrez-Girón et al. , 2015). In contrast,
there is also study suggesting that elevation positively affects MR
(Kong et al. , 2022), due to high soil C concentration at high
elevation that offset the negative effect of low temperature. Therefore,
the net elevational effect on MR depends on the tradeoff between climate
and respirated substrate along the elevation. More studies are still
needed to figure out this question and its regional characteristic.
Lab incubation is a commonly used method to determine the microbial
respiration, which usually incubates multiple soil samples at the same
time under the same temperature or temperature range (Ding et
al. , 2016; Liu et al. , 2017; Li et al. , 2020; Zhanget al. , 2022). The unified incubation temperature might be too
high to samples from cold sites, while too low to samples from warm
sites (Li et al. , 2020). However, it’s critical difficulty to set
a specific incubation temperature for each soil samples in the lab
incubation. Instead, recent studies used an adjusted MR by the field
temperature of each site based on the unify incubation temperature,
which easily solve the difference between field temperature and
incubated temperature (Li et al. , 2020).
Temperature sensitivity (Q 10) of MR also serve as
a reference for how regional C pools may respond to future warming
(Davidson and Janssens, 2006). To date, there is still no consistent
elevational trend of temperature sensitivity along the elevational
gradients. Several studies suggest that high elevation increasesQ 10 (Gutiérrez-Girón et al. , 2015; Konget al. , 2022; Okello et al. , 2022; Zeng et al. ,
2022), while others reported higher Q 10 at lower
elevations (Lipson, 2007), or no significantly elevational trend
(Schindlbacher et al. , 2010; Xu et al. , 2014; Wanget al. , 2016; Zuo et al. , 2021). This indicates that the
current understanding of the elevational effect onQ 10 is not comprehensive enough.
To further quantify the underlying mechanism in driving MR andQ 10, we applied a standardized sampling along 9
elevational gradients from 400 m to 1100 m in a subtropical forest in
South China. These soil samples were incubated in the lab to determine
MR and Q 10. Our objectives were to examine the
response of MR and Q 10 to the environmental
change induced by elevational gradients in the subtropical forest, and
then quantify their main drivers. We hypothesized that: 1) high
elevation reduces MR but increase Q 10, and 2) the
varied MR and Q 10 along elevation would be
largely explained by the soil and plant community structure and
environmental change induced by the elevational difference.