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Contrasting diel hysteresis between soil autotrophic and heterotrophic respiration in a desert ecosystem under different rainfall scenarios.

Song W, Chen S, Zhou Y, Wu B, Zhu Y, Lu Q, Lin G - Sci Rep (2015)

Bottom Line: Diel variations of soil CO2 efflux and soil temperature were measured on Day 6 and Day 16 following the rain addition treatments each month during the growing season.We found contrasting responses in the diel hysteresis of R(A) and R(H) to soil temperature, with a clockwise hysteresis loop for R(H) but a counter-clockwise hysteresis loop for R(A).Rain addition significantly increased the magnitude of diel hysteresis for both R(H) and R(A) on Day 6, but had no influence on either on Day 16 when soil moisture was much lower.

View Article: PubMed Central - PubMed

Affiliation: Ministry of Education Key Laboratory for Earth System Modeling, Center for Earth System Science, Tsinghua University, Beijing 100084, China.

ABSTRACT
Diel hysteresis occurs often between soil CO2 efflux (R(S)) and temperature, yet, little is known if diel hysteresis occurs in the two components of R(S), i.e., autotrophic respiration (R(A)) and heterotrophic respiration (R(H)), and how diel hysteresis will respond to future rainfall change. We conducted a field experiment in a desert ecosystem in northern China simulating five different scenarios of future rain regimes. Diel variations of soil CO2 efflux and soil temperature were measured on Day 6 and Day 16 following the rain addition treatments each month during the growing season. We found contrasting responses in the diel hysteresis of R(A) and R(H) to soil temperature, with a clockwise hysteresis loop for R(H) but a counter-clockwise hysteresis loop for R(A). Rain addition significantly increased the magnitude of diel hysteresis for both R(H) and R(A) on Day 6, but had no influence on either on Day 16 when soil moisture was much lower. These findings underline the different roles of biological (i.e. plant and microbial activities) and physical-chemical (e.g. heat transport and inorganic CO2 exchange) processes in regulating the diel hysteresis of R(A) and R(H), which should be considered when estimating soil CO2 efflux in desert regions under future rainfall regime.

No MeSH data available.


Related in: MedlinePlus

Conceptual illustration of factors controlling diel hysteresis patterns of soil CO2 efflux (RS) and its components (RA and RH) in responding to soil temperature in dry (a) and wet (b) soils.The effect of physical (mainly heat) transport processes on the diel hysteresis of RA and RH is same. Besides physical process, the diel hysteresis of RH is also modified by chemical (inorganic CO2 efflux, RINO) process. In dry soil condition (a), the effects of physical and chemical processes to the diel relationship between soil CO2 efflux and soil temperature are pronounced, while the effects are limited under wet soil condition (b). See the text in the Discussion for more details.
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f6: Conceptual illustration of factors controlling diel hysteresis patterns of soil CO2 efflux (RS) and its components (RA and RH) in responding to soil temperature in dry (a) and wet (b) soils.The effect of physical (mainly heat) transport processes on the diel hysteresis of RA and RH is same. Besides physical process, the diel hysteresis of RH is also modified by chemical (inorganic CO2 efflux, RINO) process. In dry soil condition (a), the effects of physical and chemical processes to the diel relationship between soil CO2 efflux and soil temperature are pronounced, while the effects are limited under wet soil condition (b). See the text in the Discussion for more details.

Mentions: Several field studies have found a strong connection between plant photosynthesis and RA at diel and seasonal scales162137. The time required to transport photosynthetic C to roots was found on the order of many hours to a few day10131538. For instance, Tang et al.16 reported that the time for photosynthetic products to be transported to the roots and be respired is less than 1 day. Similarly, by in situ13CO2 pulse labelling of shrubs, Carbone and Trunbore39 demonstrated that a part of photosynthetic C can be rapidly transported to belowground and be quickly metabolized by roots within a few hours. In this study, peak RA occurred at between 18:00–21:00, which was about 3 h after peak 10 cm soil temperature, 6 h after peak PAR. The high correlation between daily mean PAR and daily mean RA (Fig. S1) suggested that the C respired by roots may be related to the same day’s photosynthesis. We speculate that accumulated photosynthetic C during daytime was periodically transported to the roots and metabolized at night, which could have contributed to the counter-clockwise diel hysteresis of RA (Fig. 6a). However, in this study site, most roots biomass was concentrated in the 10–30 cm soil layers, which suggested that the diel hysteresis of RA could have also been modified by physical processes. According to model analysis, Phillips et al.10 demonstrated that the effect of CO2 diffusivity on diel hysteresis can be bypassed because it does little to shift diel oscillation of RA considering the high porosity of sandy soil, which is similar to the soil type in this study. In contrast to CO2 diffusivity, model based on physical first principles (Table 1 and Fig. 3 in Phillips et al.10) proved that thermal transport plays an important role in controlling the diel hysteresis of soil CO2 efflux by controlling the speed of air temperature propagated through soil and by changing the synchronicity of diel variations of soil temperature and efflux10. The asynchronous diel patterns between soil temperature and efflux could result in a clockwise hysteresis loop within an approximate rate (e.g. 1 × 10−7 m2 s−1 based on measurements of a sandy loam soil) of thermal diffusivity for sandy soils experiencing normal field moisture level10 (Fig. 6a). Thus, although the clockwise effect of physical processes had no influence on the rate of RA and the rotational direction of hysteresis loop, it could have modified the orientation of the principal axes of the hysteresis loop of RA (Fig. 6a). Consequently, the co-occurrence of biological mechanism (diel photosynthetic carbon supply) and physical processes, particularly thermal transport, could have contributed to the counter-clockwise diel hysteresis of RA in this desert ecosystem.


Contrasting diel hysteresis between soil autotrophic and heterotrophic respiration in a desert ecosystem under different rainfall scenarios.

Song W, Chen S, Zhou Y, Wu B, Zhu Y, Lu Q, Lin G - Sci Rep (2015)

Conceptual illustration of factors controlling diel hysteresis patterns of soil CO2 efflux (RS) and its components (RA and RH) in responding to soil temperature in dry (a) and wet (b) soils.The effect of physical (mainly heat) transport processes on the diel hysteresis of RA and RH is same. Besides physical process, the diel hysteresis of RH is also modified by chemical (inorganic CO2 efflux, RINO) process. In dry soil condition (a), the effects of physical and chemical processes to the diel relationship between soil CO2 efflux and soil temperature are pronounced, while the effects are limited under wet soil condition (b). See the text in the Discussion for more details.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663751&req=5

f6: Conceptual illustration of factors controlling diel hysteresis patterns of soil CO2 efflux (RS) and its components (RA and RH) in responding to soil temperature in dry (a) and wet (b) soils.The effect of physical (mainly heat) transport processes on the diel hysteresis of RA and RH is same. Besides physical process, the diel hysteresis of RH is also modified by chemical (inorganic CO2 efflux, RINO) process. In dry soil condition (a), the effects of physical and chemical processes to the diel relationship between soil CO2 efflux and soil temperature are pronounced, while the effects are limited under wet soil condition (b). See the text in the Discussion for more details.
Mentions: Several field studies have found a strong connection between plant photosynthesis and RA at diel and seasonal scales162137. The time required to transport photosynthetic C to roots was found on the order of many hours to a few day10131538. For instance, Tang et al.16 reported that the time for photosynthetic products to be transported to the roots and be respired is less than 1 day. Similarly, by in situ13CO2 pulse labelling of shrubs, Carbone and Trunbore39 demonstrated that a part of photosynthetic C can be rapidly transported to belowground and be quickly metabolized by roots within a few hours. In this study, peak RA occurred at between 18:00–21:00, which was about 3 h after peak 10 cm soil temperature, 6 h after peak PAR. The high correlation between daily mean PAR and daily mean RA (Fig. S1) suggested that the C respired by roots may be related to the same day’s photosynthesis. We speculate that accumulated photosynthetic C during daytime was periodically transported to the roots and metabolized at night, which could have contributed to the counter-clockwise diel hysteresis of RA (Fig. 6a). However, in this study site, most roots biomass was concentrated in the 10–30 cm soil layers, which suggested that the diel hysteresis of RA could have also been modified by physical processes. According to model analysis, Phillips et al.10 demonstrated that the effect of CO2 diffusivity on diel hysteresis can be bypassed because it does little to shift diel oscillation of RA considering the high porosity of sandy soil, which is similar to the soil type in this study. In contrast to CO2 diffusivity, model based on physical first principles (Table 1 and Fig. 3 in Phillips et al.10) proved that thermal transport plays an important role in controlling the diel hysteresis of soil CO2 efflux by controlling the speed of air temperature propagated through soil and by changing the synchronicity of diel variations of soil temperature and efflux10. The asynchronous diel patterns between soil temperature and efflux could result in a clockwise hysteresis loop within an approximate rate (e.g. 1 × 10−7 m2 s−1 based on measurements of a sandy loam soil) of thermal diffusivity for sandy soils experiencing normal field moisture level10 (Fig. 6a). Thus, although the clockwise effect of physical processes had no influence on the rate of RA and the rotational direction of hysteresis loop, it could have modified the orientation of the principal axes of the hysteresis loop of RA (Fig. 6a). Consequently, the co-occurrence of biological mechanism (diel photosynthetic carbon supply) and physical processes, particularly thermal transport, could have contributed to the counter-clockwise diel hysteresis of RA in this desert ecosystem.

Bottom Line: Diel variations of soil CO2 efflux and soil temperature were measured on Day 6 and Day 16 following the rain addition treatments each month during the growing season.We found contrasting responses in the diel hysteresis of R(A) and R(H) to soil temperature, with a clockwise hysteresis loop for R(H) but a counter-clockwise hysteresis loop for R(A).Rain addition significantly increased the magnitude of diel hysteresis for both R(H) and R(A) on Day 6, but had no influence on either on Day 16 when soil moisture was much lower.

View Article: PubMed Central - PubMed

Affiliation: Ministry of Education Key Laboratory for Earth System Modeling, Center for Earth System Science, Tsinghua University, Beijing 100084, China.

ABSTRACT
Diel hysteresis occurs often between soil CO2 efflux (R(S)) and temperature, yet, little is known if diel hysteresis occurs in the two components of R(S), i.e., autotrophic respiration (R(A)) and heterotrophic respiration (R(H)), and how diel hysteresis will respond to future rainfall change. We conducted a field experiment in a desert ecosystem in northern China simulating five different scenarios of future rain regimes. Diel variations of soil CO2 efflux and soil temperature were measured on Day 6 and Day 16 following the rain addition treatments each month during the growing season. We found contrasting responses in the diel hysteresis of R(A) and R(H) to soil temperature, with a clockwise hysteresis loop for R(H) but a counter-clockwise hysteresis loop for R(A). Rain addition significantly increased the magnitude of diel hysteresis for both R(H) and R(A) on Day 6, but had no influence on either on Day 16 when soil moisture was much lower. These findings underline the different roles of biological (i.e. plant and microbial activities) and physical-chemical (e.g. heat transport and inorganic CO2 exchange) processes in regulating the diel hysteresis of R(A) and R(H), which should be considered when estimating soil CO2 efflux in desert regions under future rainfall regime.

No MeSH data available.


Related in: MedlinePlus