Environmental Engineering Reference
In-Depth Information
3.1 Soil Respiration
In the soil respiration process, CO
2
fixed by terrestrial plants returns to the atmos-
phere.Changes in soil respiration in response to warming may contribute to the
increase of CO
2
atmospheric levels (Bradford et al.
2008
; Bahn et al.
2010
; Feng
et al.
2010
; Raich and Schlesinger
1992
; Oechel et al.
2000
; Schlesinger and
Andrews
2000
; Luo et al.
2001
; Melillo et al.
2002
,
2004
). CO
2
is produced in
soils by roots, soil organisms and by chemical oxidation of carbon-containing
materials (Lundegårdh
1927
). Note that soil respiration through microbial activity
can lead to the degradation to CO
2
of long chain (>C
20
) alkanols, fatty acids (e.g.
n-alkanoic acids), hydroxy fatty acids and di-acids that are major components of
hydrolysable aliphatic lipids in soil organic matter (Feng et al.
2010
; Nierop et al.
2003
; Hajje and Jaffé
2006
; Otto and Simpson
2006
). These studies demonstrate
that the average soil respiration rates are very variable depending on the nature of
vegetation and on ambient temperature. For example, the lowest respiration rate
is detected in tundra (60
±
6 gC m
−
2
yr
−
1
), northern bogs and mires (94
±
16
gC m
−
2
yr
−
1
), desert scrub (224
±
38 gC m
−
2
yr
−
1
), boreal forests (322
±
31 gC
m
−
2
yr
−
1
) and marshes (413
±
76 gC m
−
2
yr
−
1
). In contrast, respiration rates are
highest in tropical moist forests (1260
±
57 gC m
−
2
yr
−
1
), Mediterranean wood-
lands and heath (713
±
88 gC m
−
2
yr
−
1
), temperate coniferous forests (681
±
95
gC m
−
2
yr
−
1
), tropical dry forests (673
±
134 gC m
−
2
yr
−
1
) and temperate decid-
uous forests (647
±
51 gC m
−
2
yr
−
1
) (Raich and Schlesinger
1992
). Temperature
is the single best predictor of the annual respiration rate at a specific location,
because soil respiration rates correlate significantly with average annual air tem-
peratures and precipitation on a global scale (Raich and Schlesinger
1992
).
Microbial decomposition of soil OM constituents such as lignin and hydrolys-
able lipids is promoted under both elevated CO
2
and N fertilization (Feng et al.
2010
). Traditional tillage cultivation and rising temperature increase the flux of
CO
2
from soils without increasing the stock of soil organic matter (Schlesinger
and Andrews
2000
). Soil warming can increase the relative abundance of Gram-
positive bacteria (Frey et al.
2008
; Bardgett et al.
1999
; Biasi et al.
2005
). It has
also been shown that soil respiration is initially enhanced by warming for a few
years, but that this effect is subsequently reduced over time (Frey et al.
2008
;
Oechel et al.
2000
; Luo et al.
2001
; Melillo et al.
2002
,
2004
). The following fac-
tors can be involved: (i) reduced plant production can lead to lower root respira-
tion rates, decrease microbial activity because of soil drying, and to losses of labile
soil organic carbon substrates such as amino acids, carbohydrates, and carboxylic
acids (Frey et al.
2008
; Oechel et al.
2000
; Luo et al.
2001
; Melillo et al.
2002
).
(ii) Increases in temperature can significantly change the microbial community
structure that ultimately affects the soil respiration (Lloyd and Taylor
1994
; Petersen
and Klug
1994
; Arnold et al.
1999
; Feng and Simpson
2008
,
2009
; Frey et al.
2008
).
Causes of diversity in respiration in the soil ecosystems are the variation in
the decomposition factors of particulate detrital pools or vascular plant materi-
als, which are regulated by numerous physical (temperature, moisture), chemi-
cal (redox, nutrient availability) and microbial (microfloral successional
