ArticlePDF Available

Soil microbial C and N turnover under Cupressus lusitanica and natural forests in southern Ethiopia assessed by decomposition of 13C- and 15 N-labelled litter under field conditions

Authors:

Abstract and Figures

Aims Natural forests in Ethiopia are frequently replaced by Cupressus lusitanica plantations, but little is known about consequences of this land use change for soil C and N dynamics. The objectives of the study were: (i) quantification of microbial incorporation of litter-derived C and N under field conditions, (ii) identification of forest management effects on microbial incorporation of litter-derived C and N and (iii) elucidation of soil moisture effects on microbial utilization of litter-derived C and N. Methods Natural litter in the Munessa forest was replaced by 13C and 15 N labelled litter and its degradation was studied over 2 years. Microbial incorporation of litter-derived C and N was measured by chloroform fumigation extraction and stable isotope analysis. Results Most of the 13C and 15 N tracer remained in the litter or was incorporated into bulk soil, whereas soil microbial biomass showed minor incorporation. Silvicultural management practices influenced microbial litter-derived C utilization with increased microbial incorporation under wet soil conditions under plantations. Thinning of Cupressus trees led to increased litter decomposition during dry soil conditions. Conclusion Soil humidity is the main influencing factor for microbial turnover of litter-derived C in this ecosystem. Fast-growing tree plantations had no negative effects on microbial C and N turnover when compared to natural forests.
Content may be subject to copyright.
REGULAR ARTICLE
Soil microbial C and N turnover under Cupressus lusitanica
and natural forests in southern Ethiopia assessed
by decomposition of
13
C- and
15
N-labelled litter under field
conditions
Marianne Benesch &Bruno Glaser &
Michaela Dippold &Wolfgang Ze ch
Received: 28 February 2014 /Accepted: 23 October 2014 / Published online: 31 October 2014
#Springer International Publishing Switzerland 2014
Abstract
Aims Natural forests in Ethiopia are frequently replaced
by Cupressus lusitanica plantations, but little is known
about consequences of this land use change for soil C
and N dynamics. The objectives of the study were: (i)
quantification of microbial incorporation of litter-
derived C and N under field conditions, (ii) identifica-
tion of forest management effects on microbial incorpo-
ration of litter-derived C and N and (iii) elucidation of
soil moisture effects on microbial utilization of litter-
derived C and N.
Methods Natural litter in the Munessa forest was re-
placed by
13
Cand
15
N labelled litter and its degradation
was studied over 2 years. Microbial incorporation of
litter-derived C and N was measured by chloroform
fumigation extraction and stable isotope analysis.
Results Most of the
13
Cand
15
N tracer remained in the
litter or was incorporated into bulk soil, whereas soil
microbial biomass showed minor incorporation. Silvi-
cultural management practices influenced microbial
litter-derived C utilization with increased microbial in-
corporation under wet soil conditions under plantations.
Thinning of Cupressus trees led to increased litter de-
composition during dry soil conditions.
Conclusion Soil humidity is the main influencing factor
for microbial turnover of litter-derived C in this ecosys-
tem. Fast-growing tree plantations had no negative ef-
fects on microbial C and N turnover when compared to
natural forests.
Keywords Forest management .Soil microbial
biomass .Stable isotope labelling .Tropical forestry.
C and N cycling .Soil organic matter .Silvicultural
management practices
Introduction
In the Munessa forest south of Addis Ababa (Ethiopia),
increased demand of wood leads to a wide-spread de-
forestation strongly reducing species-rich natural forests
Plant Soil (2015) 388:133146
DOI 10.1007/s11104-014-2317-0
Responsible Editor: Alfonso Escudero .
M. Benesch
Soil Physics Department, University of Bayreuth,
Universitätsstraße 30, D- 95440 Bayreuth, Germany
M. Benesch (*):B. Glaser
Institute of Agronomy and Nutritional Sciences,
Soil Biogeochemistry, Martin-Luther-University
Halle-Wittenberg,
Von-Seckendorff-Platz 3, D- 06120 Halle, Germany
e-mail: marianne.benesch@landw.uni-halle.de
M. Dippold
Department of Agroecosystem Research, BAYCEER,
University of Bayreuth,
Universitätsstraße 30, D- 95440 Bayreuth, Germany
M. Dippold
Department of Agricultural Soil Science,
Georg-August-University of Göttingen,
Büsgenweg 2, D- 37077 Göttingen, Germany
W. Ze c h
Soil Science and Soil Geography, University of Bayreuth,
Universitätsstraße 30, D- 95440 Bayreuth, Germany
dominated by Croton macrostachys,Podocarpus
falcatus and Prunus africana. Parts of the deforested
land have been re-forested with exotic tree species such
as Cupressus lusitanica,Eucalyptus saligna and Pinus
radiata. Up to now, these fast-growing plantations were
harvested by clear cutting and forest thinning practices
which are common management strategies in temperate
forests (Dannenmann et al. 2006). It is not known, how
such silvicultural practices and the accompanied trans-
formation of vegetation affect sustainability and espe-
cially C and N turnover under the sub-humid conditions
of the Munessa forest as rotation is much faster com-
pared to temperate regions.
Since soil organic matter (SOM) and its microbial
turnover strongly influence soil fertility (Smith et al.
1993), studying SOM is of crucial interest with respect
to ecosystem resilience and yields. Carbon and nitrogen
turnover in soils are substantially influenced by litter
quantity and quality (Wardle and Nicholson 1996),
chemical and physical soil properties (Insam and
Parkinson 1989) and soil microbial community (Paul
2007). Soil microbial biomass (SMB) provides plant-
available nutrients by decomposing and transforming
organic matter (Smith and Paul 1990), mainly deriving
from above-and belowground plant residues (Ananyeva
et al. 1999). Therefore, SMB is the driving force behind
SOMtransformationactingassourceorsinkfornutri-
ents (Smith and Paul 1990) and functions as a small,
labile nutrient reservoir, which is essential to maintain
long-term soil sustainability (Ananyeva et al. 1999).
Furthermore, SMB and its activity are important biolog-
ical indicators for soil quality reflecting rapid changes in
soil properties caused by disturbance of natural condi-
tions e.g. by human activities (Lopes et al. 2010)in
connection with land use changes like deforestation
and silvicultural management (Mendham et al. 2002).
Stands with high plant diversity such as natural for-
ests show an increased SMB content (Hackl et al. 2004)
compared to monoculture plantations, resulting in faster
SOM turnover (Leon et al. 2011). However, it is widely
known that silvicultural management practices like thin-
ning of plantation stands can improve litter decomposi-
tion compared to non-thinned ones. After canopy open-
ing an increase in soil temperature and substantial input
of decomposable organic matter occurs e.g. as plant
residues (which are left on the sites) or roots of harvest-
ed trees (Thibodeau et al. 2000). Changing microclimat-
ic conditions, due to varying rainfall interception and
shading effects (Hall and Marchand 2010), are
influencing soil moisture which is known to be one of
the controlling factors for SMB (Diaz-Raviña et al.
1995). Therefore, the question arises whether silvicul-
tural management practices of differently aged
Cupressus plantations influence soil microbial C and
N turnover under the sub-humid site conditions of the
Munessa forest.
The objectives of the current study were: (i) the
quantification of microbial incorporation of litter-
derived C and N under field conditions, (ii) the identifi-
cation of forest management effects (tree species, thin-
ning, age classes) on microbial incorporation of litter-
derived C and N and (iii) the elucidation of soil moisture
effects on microbial utilization of litter-derived C and N
under the site conditions of Munessa forest. To address
these objectives, a labelling experiment with
13
C- and
15
N-enriched litter was installed (Glaser et al. 2012).
Chloroform fumigation extraction allowed the quantifi-
cation of microbial C and N storage (C
SMB
and N
SMB
)
and the analysis of litter-derived tracer
13
C and
15
N
incorporation into SMB. By applying these proxies we
aim to answer the question whether Cupressus planta-
tions in the Munessa forest can be considered as sus-
tainable with respect to short-term (microbial) C and N
turnover.
Material and methods
Study site
The study site is located in the Munessa forest (7° 26N
and 38° 52E), 240 km south of Addis Ababa on the
eastern escarpment of the main Ethiopian rift valley with
soils classified as Mollic Nitisols (Fritzsche et al. 2007).
Mean annual temperature during the field experiment
was about 17 °C with a mean annual rainfall of 890 mm
(2009) and 1,633 mm (2010), falling during a long
(JulyNovember) and short (MarchMay) rainy season
(Yohannes et al. 2013). Within the last decade, the
climatic conditions in the Munessa forest have become
more humid, leading to an absence of the small dry
season (May 2010July 2010) (Fig. 1; Strobl et al.
2011). In this paper, the term dry soil conditionis
used for March 2009 and December 2010 with low
precipitation, resulting in decreased gravimetric soil
water contents (SWC), whereas wet soil condition
means increased precipitation accompanied with high
134 Plant Soil (2015) 388:133146
gravimetric SWC in November 2009 and March 2010
(Fig. 1).
Labelling experiment
In the current study the term labelled litterrefers to
13
C- and
15
N-enriched leaf litter excluding twigs and
barks. To produce a sufficient amount of
13
C- and
15
N-
enriched leaf litter, 5 Cupressus lusitanica trees (for
plantation plots) and 1 Podocarpus falcatus,Prunus
africana and Croton macrostachys tree (for natural for-
est plots) were labelled in December 2008. The selection
criterion for trees was the estimated weight of leaf litter
which was supposed to be adequate to produce labelled
litter for all experimental plots (3 kg for individual
Cupressus trees and 1 kg for 1 Podocarpus falcatus,
Prunus africana and Croton macrostachys tree, respec-
tively). Using the in situ tree gassing and stem injection
method described by Glaser et al. (2012)wewereable
to achieve a
13
C- and
15
N- enrichment of 260and
1,609in the homogenized Cupressus litter. The even-
ly mixed natural forest litter showed a
13
C- and
15
N-
enrichment of 188and 301,respectively.
After labelling, four independent sampling plots of
1m
2
were established in each treatment under compa-
rable site conditions between 2,098 m and 2,319 m a.s.l.
below natural forest and Cupressus plantations (Table 1).
Within the plantation stands, two age classes were cho-
sen including young(= age class I, established in
2001) and mature(= age class III, established in
1987) Cupressus trees. Thinning intensity (= forest
management) differed between Conversion (Con),
where 75 % of the trees were harvested and only poten-
tial crop trees were preserved and Intense Promotion
(IP), where 35 % of the trees (direct competitors of
potential crop trees) were harvested. Forest management
took place in January 2008. No management means that
no thinning took place. Cupressus age class I comprised
two treatments (no management and IP), whereas
Cupressus age class III included three treatments (no
management, IP and Con).
Total annual litterfall in the experimental area was
estimated to be about 500 g m
2
year
1
, which is con-
sistent with data from Lisanework and Michelsen
(1994). Therefore, 500 g of labelled litter were applied
on each experimental plot and 500 g of non-labelled
litter on the reference plots. To prevent a dilution by
Fig. 1 Sampling scheme informing about the mean monthly
precipitation, soil temperature (Seyoum et al. 2012), gravimetric
soil water content (SWC), labelled litter application (January and
November 2009) and soil sampling events (March 2009, Novem-
ber 2009, March 2010, December 2010)
Plant Soil (2015) 388:133146 135
non-labelled understory, non-labelled litter on the
ground and non-labelled natural litter fall, plots were
harvested (understory and original litter) before litter
replacement and nets were installed above each 1 m
2
plot. First labelled litter addition took place in January
2009, 2 months before the beginning of the sampling
(Fig. 1). To ensure continuous label incorporation into
SMB, it was necessary to repeat the application in
November 2009 due to fast decomposition of labelled
litter during the first year of the experiment.
Soil sampling and soil microbial biomass analyses
Soil and litter samples were taken 2 and 10 months after
the first labelling event and 4 and 13 months after the
second one (Fig. 1)in02cm,25cmand510 cm
depths using a random grid sampling scheme by divid-
ingthe1m
2
plot into hundred 100 cm
2
subplots
(BGZufGen program) as outlined in Mehring et al.
(2011). At each sampling date, three subplots within
the 1 m
2
plot were sampled randomly, neglecting the
outer grids to prevent border effects.
After drying at 60 °C and grinding, bulk
13
Cand
15
N
enrichment were determined using an elemental analyz-
er (EA) isotope ratio mass spectrometer (IRMS) system
consisting of a Hekatech elemental analyzer coupled via
a Conflo III Interface to a Delta V Advantage IRMS
(Thermo Finnigan, Bremen, Germany). Field-moist in-
tact (non-sieved) soil samples for chloroform fumiga-
tion extraction (Vance et al. 1987)werestoredat5°C
and preparedwithin 2 weeks after sampling. Fumigation
(48 h) with chloroform under vacuum conditions using a
desiccator caused a release of extractable microbial
components (Witt et al. 2000). To analyze C
SMB
and
N
SMB
, 10 g of field-moist soil (without roots) were
extracted with 50 ml 0.5 M K
2
SO
4
solution (extraction
took place twice; 1:3 and 1:2 w/v, after shaking for
20 min and centrifuging for 5 min at 4,000 rmp). The
extract was stored at 20 °C and analyzed using a TC/
TN analyzer (Analytik Jena, multi N/C 2100).
For
13
C
SMB
and
15
N
SMB
analyses, 14 g (fumigated
samples) and 16 g (non-fumigated samples) of field-
moist soil were used. The samples were treated with
70 ml (fumigated) and 80 ml (non-fumigated) 0.03 M
K
2
SO
4
solution (extracted twice 1:3 and 1:2 w/v). Ex-
tracts were freeze-dried and measured using EA-IRMS
as outlined above.
Climatic data such as precipitation and soil tempera-
ture were documented every 10 min by two μMetos
automatic meteorological stations (Pessl Instruments,
Weiz, Austria). The sensors of the climate stations were
installed in the natural forest and on a cleared area 2 m
above the ground (rain collector 1 m above the ground)
and in 20 cm depth (soil temperature). Hourly averages
were reported by a DL 15-data logger (Thies, Göttingen,
Germany) (Strobl et al. 2011). Gravimetric soil water
contents were determined for every soil sampling under
every experimental plot.
Data and statistical analyses
C
SMB
and N
SMB
storage are expressed in mol/m
2
soil in
010 cm depth and were calculated according to the
following Eq. (1):
CSMB¼Ec=kEc ð1Þ
, where Ec is the amount of organic C extracted from
fumigated soil samples minus organic C extracted from
Tabl e 1 Experimental design: Numbers 1, 2 and 3 represent independent 1 m
2
plots treated with labelled litter in threefold field replication
and Rmeans reference plots treated with un-labelled litter. -indicates missing treatment
136 Plant Soil (2015) 388:133146
non-fumigated soil samples. A constant factor (kEc) of
0.45 (Jenkinson and Ladd 1981), taking into account
that only a portion of SMB is extractable with the
applied method, was used for C
SMB
storage. Calculation
of N
SMB
storage was done accordingly with a kEn of
0.54 (Brookes et al. 1985).
Litter-derived
13
Cand
15
N incorporation into SMB,
bulk soil and litter was calculated according to Eq. 2,
Tracer Cpool
applied Tracer C ¼δpool δRe f pool
δTracerδRe f pool

Cpool
applied Tracer C ð2Þ
with δ
pool
being the measured δ
13
CvaluesofSMB,bulk
soil and litter, respectively, from plots treated with la-
belled litter. δ
Ref-pool
is measured δ
13
C values of corre-
sponding control plots with non-labelled litter. δ
Trace r
is
measured δ
13
C value of the labelled litter applied to the
plots and C
pool
is the C content of SMB, bulk soil and
litter, respectively. Applied Tracer C is the
13
Ccontent
of labelled litter applied to the plots. Litter-derived
15
N
incorporation into pools was calculated in the same way
(according to Eq. 2). To calculate the mass balance after
the second labelling event, soil and litter samples were
taken directly before labelled litter addition in Novem-
ber 2009. These data were used as initial values for the
calculation of mass balances in March 2010 and De-
cember 2010.
All statistical tests were conducted using Statistica
6.0. As the data set was not normally distributed and
transformation of data did not lead to normal distribu-
tion, Kruskal-Wallis analysis of variance (ANOVA) was
applied as non-parametric statistical test. Litter-derived
tracer incorporation into SMB (Tracer C
pool
/applied
Tracer C, Tracer N
pool
/applied Tracer N), C/N
SMB
and
C
SMB
and N
SMB
storage were used as dependent vari-
ables, whereas soil water contents (dry soil conditions
vs. wet soil conditions), tree species (natural forest vs.
Cupressus plantation with no management), thinning
(Cupressus plantation with no management vs. IP vs.
Con) and age classes (Cupressus age class I vs. age class
III) represented independent variables used in separate
Kruskal-Wallis one-way analysis of variances. Signifi-
cance intervals were tested at p<0.05 (*), p<0.01 (**)
and p<0.001 (***).
Results
13
Cand
15
N isotope mass balance
During dry soil conditions in March 2009 (Fig. 1), 53 %
of the applied
13
C tracer and 74 % of the applied
15
N
tracer remained in labelled litter, whereas 8 % litter-
derived
13
C and 25 % litter-derived
15
Nwereincorpo-
rated into bulk soil (Fig. 2). However, only 1 % litter-
derived
13
C and 3 % litter-derived
15
Nwereincorporat-
ed into SMB. During wet conditions in November 2009,
only 7 % of the
13
Ctracerand24%ofthe
15
Ntracer
were left in the labelled litter. Bulk soil incorporation of
litter-derived
13
C was still 8 % and litter-derived
15
N
incorporation decreased to 18 %. Incorporation of litter-
derived
13
Cand
15
NinSMBwasmoreorlessconstant
at 1 and 4 %, respectively. In March 2010, 4 months
after the second labelling (Fig. 1), 14 % of
13
Ctracerand
20 % of
15
Ntracerwereleftoverinlitter,whereas8%
of litter-derived
13
C and 21 % of litter-derived
15
Nwere
incorporated into bulk soil. Microbial biomass utilized
3 % of litter-derived
13
Cand
15
N, respectively. Dry soil
conditions in December 2010 showed 10 %
13
Ctracer
and 14 %
15
N tracer remaining in labelled litter and 8 %
litter-derived
13
C and 14 % litter-derived
15
Nincorpo-
rated into bulk soil, whereas SMB utilized 2 % of litter-
derived
13
C and 4 % of litter-derived
15
N.
However, no significant differences between the in-
vestigated management strategies and soil moisture con-
ditions (p>0.05, Table 2) in microbial litter-derived
15
N
utilization could be shown, whereas litter-derived
13
C
incorporation in SMB was significantly affected by tree
species (p<0.001), thinning (p<0.01) and soil moisture
(p<0.001).
Tree species effect on microbial biomass C and N
and on litter
13
Cturnover
Under dry soil conditions (March 2009 and December
2010, Fig. 1)C
SMB
storage was 1214 mol/m
2
under
Cupressus plantation and 1115 mol/m
2
under natural
forest stands. Wet soil conditions (November 2009 and
March 2010) led to C
SMB
storage of 710 mol/m
2
under
plantation stands and natural forest, respectively. Nitro-
gen storage in SMB under Cupressus plantation and
natural forest was 11.4 mol/m
2
, respectively. Microbial
C/N varied from 7 to 11 under dry and from 4 to 7 under
wet soil conditions below natural forest and plantation
stands. However, no significant effect (p>0.05, Table2)
Plant Soil (2015) 388:133146 137
of tree species on these microbial proxies could be
shown.
On contrary, microbial incorporation of litter-derived
13
C showed significant differences (p<0.001; Table 2)
betweentreespecies,with0.52 % under Cupressus
plots (non-thinned) and 24 % under natural forest
stands during dry soil conditions (Fig. 3). Wet soil
conditions led to 23 % of litter-derived
13
Cincorporat-
ed into SMB under Cupressus stands (non-thinned) and
01 % under natural forest stands.
Thinning effect on microbial biomass C and N
and on litter
13
Cturnover
In the Munessa forest, thinning practices led to C
SMB
storage of 814 mol/m
2
and no management resulted in
C
SMB
storage of 714 mol/m
2
. Microbial C/N was about
69 for both thinned and non-thinned stands. Variations
of these microbial proxies showed no significant differ-
ences over the experimental period (p>0.05; Table 2).
On contrary, N
SMB
stocks were significantly lower
Tabl e 2 P values of Kruskal-Wallis ANOVA of microbial proxies
and tracer incorporation. C
SMB
/N
SMB
is the C/N ratio of SMB and
C
SMB
storage and N
SMB
storage are the total amounts of microbial
C and N, respectively, in 010 cm soil depth per m
2
.TracerC
pool
/
applied Tracer C and Tracer N
pool
/applied Tracer N are the
percentage of recovered Tracer C and N in SMB from total applied
13
Cand
15
N, respectively. Tested variables are soil water content,
tree species, thinning and tree ageclass. Significant differences are
expressed as p< 0.05 (*), p<0.01 (**) and p<0.001 (***)
Soil water content Tree species Thinning Age class
C
SMB
/N
SMB
0.0000*** 0.4998 0.0878 0.0132*
C
SMB
storage [mol/m
2
] 0.0364* 0.3080 0.1840 0.0758
N
SMB
storage [mol/m
2
] 0.0729 0.7020 0.0394* 0.0022**
Tracer C
pool
/applied Tracer C [%] 0.0002*** 0.0001*** 0.0034** 0.1372
Tracer N
pool
/applied Tracer N [%] 0.4291 0.0541 0.0596 0.9814
Fig. 2
13
Cand
15
N isotope mass balance (averaged for all forest
types) between applied litter and soil (010 cm depth). Please note
that SMB is part of bulk soil and that a second application of
labelled litter took place in November 2009. Error bars indicate
standard error (N=18)
138 Plant Soil (2015) 388:133146
under non-thinned plots (1.4 mol/m
2
)comparedto
thinned ones (2.1 mol/m
2
under IP) in young Cupressus
stands (Fig. 4). Soil microbial biomass under mature
Cupressus plots showed significantly different
(p<0.05; Table 2) N stocks ranging from 1.0 mol/m
2
under non-thinned plots up to 1.5 mol/m
2
under thinned
plots. Thinning intensity (IP compared to Con under age
class III) did not influence N
SMB
stocks (p>0.05, Ta-
ble 2) during the experiment.
Under thinned Cupressus stands, dry soil conditions
led to a microbial incorporation of litter-derived
13
Cof
35 %, whereas non-thinned stands showed significant-
ly (p<0.01, Table 2) lower values of 0.52 % (Fig. 3).
Wet soil conditions led to 00.5 % of litter-derived
13
C
tracer being incorporated into SMB under thinned
stands and 23 % under non-thinned stands. Intensity
of thinning (IP compared to Con) did not show any
significant effect on litter turnover (p>0.05).
Rotation age effect on microbial biomass C and N
Rotation age within the monoculture plantation had no
significant effect on C
SMB
storage (p>0.05; Table 2).
However, N
SMB
storage (Fig. 4) and C/N
SMB
ratios
(Fig. 5) differed significantly with rotation age
(p<0.05, Table 2) with increased N
SMB
stocks of 1.4
2.1 mol/m
2
under young Cupressus trees and N
SMB
stocks of 1.01.5 mol/m
2
under mature stands. Further-
more, mature Cupressus plots showed significantly in-
creased C/N
SMB
ratios ranging from 6 under wet up to
10 under dry soil conditions compared to young
Cupressus stands with significantly lower C/N
SMB
ra-
tios of 4 during wet and 7 during dry phases.
Soil moisture effect on microbial biomass C and N
Plantation and natural forest samples had significantly
increased (p<0.05, Table 2)C
SMB
stock of about 12
14 mol/m
2
and 1115 mol/m
2
under dry soil conditions,
whereas wet phases led to decreased C
SMB
storage of
about 710 mol/m
2
under both tree species (Fig. 6).
Microbial C/N ratios showed the same trend with sig-
nificantly higher values (p<0.001, Table 2) in dry soil
(711) and lower in wet soil (47) under Cupressus
stands and natural forest, respectively (Fig. 5). In com-
parison to these microbial proxies, N
SMB
storage
showed no significant differences (p>0.05, Table 2)
with varying soil moisture.
As it was stated before, microbial incorporation of
litter-derived
13
C(Fig.3) follows the same trend like
Fig. 3 Litter-derived
13
C incorporation into bulk soil (bulk) and
soil microbial biomass (SMB), summarized for all soil depths (0-
10 cm) under natural forest (nf), Cupressus non-thinned plots (n-
th) and Cupressus thinned plots (th) during the field experiment
from January 2009 until December 2010. Error bars indicate
standard error (N=3)
Plant Soil (2015) 388:133146 139
Fig. 5 Temporal changes of microbial C/N ratio under different age classes of Cupressus plantations and natural forest during the field
experiment from January 2009 until December 2010. Error bars indicate standard error (N=3)
Fig. 4 Soil microbial N storage under different age classes in Cupressus plantations and under natural forest. Data were averaged among all
sampling dates as sampling time represented by SWC in Table 2did not reveal significant differences. Error bars indicate standard error (N=3)
140 Plant Soil (2015) 388:133146
other microbial parameters in this study, with significant
variations between different soil moisture statuses.
Discussion
13
Cand
15
N isotope mass balance
Two months after labelling and under dry soil condi-
tions, most of the
13
C could still be found in the labelled
litter. However, 39 % of litter-derived
13
C was not
incorporated in the soil and presumably lost via miner-
alization, respiration and leaching. Our findings are in
line with results of Hopkins et al. (1997), who studied
the decomposition of
13
Cand
15
N labelled Lolium
perenne leaves under laboratory conditions and found
a loss of 48 % of labelled
13
CasCO
2
within 56 days.
In our experiment, nearly 100 % of litter-derived
15
N
could be found within the SMB, bulk soil and litter
pools, with highest tracer amounts left in the litter
2 months after the labelling. Only 1 % of the
15
Ntracer
was lost probably due to plant uptake, leaching or emis-
sion from the soil. Relatively small losses of
15
Ncanbe
explained by low soil water contents, inhibiting nutrient
leaching from the labelled litter and growth of vegeta-
tion during dry soil conditions.
Increased precipitation and soil water contents
10 months after the first labelling in November 2009
led to enhanced losses of 85 %
13
C and 58 %
15
Nfrom
the system due to increased nutrient leaching and plant
uptake. Our findings are in agreement with results from
Hopkins et al. (1997) who showed a loss of litter-
derived
15
N of 40 % within 224 days under laboratory
conditions. Values of litter-derived
13
Cand
15
Nincor-
poration into bulk soil from the current study are in
agreement with a study conducted in a beech stand in
Germany, where 10 months after
13
Cand
15
N labelling,
15%
13
Cand38%
15
N were found in mineral soil
and <1 %
13
Cand23%
15
N in SMB (Langenbruch
et al. 2014). However, C loss was 2030 % after 5 and
10 months under the beech forest, whereas our results
showed increased C loss already 2 months after label-
ling (39 % C loss 2 months and 85 % 10 months after the
labelling). This can be explained by different climatic
conditions of the experimental areas. Heavy rains ac-
companied with high soil water contents support nutri-
ent leaching and thus a loss of labelled litter C in the
Munessa forest, which may also be the reason why we
could not achieve a high labelling of SMB and bulk soil
Fig. 6 Temporal changes of microbial C (C
SMB
) storage in 1 m
2
(010 cm) under Cupressus plantation and natural forest during the field
experiment from January 2009 to December 2010. Error bars indicate standard error (N=3)
Plant Soil (2015) 388:133146 141
in March 2010. Four and 13 months after the second
labelling, increased system losses between 79 and 82 %
of
13
C and between 59 and 72 % of
15
Noccurredin
March 2010 and December 2010.
However, small microbial litter-derived
13
Cincorpo-
ration during the experimental period leads to the as-
sumption that most of the litter-derived C might just
passed through SMB pool to drive metabolism and got
lost as CO
2
and only a small fraction was incorporated
into SMB to build up biomass.
Tree species effect on microbial biomass C and N
and on litter
13
Cturnover
The absence of any tree species effect on microbial
variables such as C stocks, N stocks and C/N
SMB
in
our study is surprising as far as litter quality is varying
between indigenous and exotic tree species which
should alter SMB dynamics (Sistla and Schimel 2012;
Huang et al. 2013).
However, a significant tree species effect on litter-
derived C utilization by SMB with increased litter-
derived
13
C incorporation under natural forest during
dry soil conditions was documented. These results are in
agreement with a study of da Silva et al. (2012)who
found higher microbial activity under natural forest
during dry phases in the Mata Atlantica of Brazil. Find-
ings from Mamilov and Dilly (2002)verifythatsub-
strate quality including leaf C/N ratio, lignin content and
soluble compounds are important factors regulating lit-
ter turnover by SMB. In addition, SOM with a C/N ratio
lower than 32 supports litter nutrient utilization by SMB
(Troeh and Thompson 2005). In the Munessa forest,
indigenous tree litter showed lower C/N ratios of about
18± 5, whereas Cupressus litter had C/N ratios of 33± 5.
Our litter C/N ratios are in agreement with values from
Lisanework and Michelsen (1994) who found leaf C/N
of 25 for indigenous tree species in the Munessa forest
and explained these results by low leaf lignin and high
leaf N contents. Increased C/N and lower leaf N levels in
Cupressus litter in the current study can presumably be
attributed to higher leaf lignin contents of Cupressus
needles.
However, good quality substrate in the natural forest
allows microbial C incorporation from easily available
litter-derived
13
C even during dry conditions (Schimel
et al. 2007; Tiemann and Billings 2012). We thus con-
firm the results of several other authors, showing an
increased and faster litter nutrient utilization by SMB
under deciduous tree species with better litter quality
compared to conifer tree species (Priha and Smolander
1999;Zelleretal.1999).
Less microbial litter-derived C utilization by SMB
under Cupressus plots might be explained by hardly
decomposable litter (Lemenih et al. 2004) with high
lignin, tannin and low N contents (Lemma et al. 2007)
which inhibits microbial activity in general and espe-
cially under dry conditions where tannins are not
leached from the litter. Therefore, low quality substrates
need a lot of catabolic reworking resulting in decreased
microbial utilization of nutrients (Sugai and Schimel
1993). Furthermore, lignin and other N-poor polymers
are only available for microorganism by exoenzymatic
degradation, which depends on favorable soil moisture
conditions (Coûteaux et al. 1995).
During wet conditions, the soil under natural forest
showed higher soil water contents than under Cupressus
plots resulting in nutrient leaching and anoxic
conditions for SMB, inhibiting litter decomposition.
Yohannes et al. (2013) determined a threshold of 31 %
gravimetric soil water content in the Munessa forest
ecosystem for the switch between oxic and anoxic soil
conditions. Exceeding this value (in November 2009,
March 2010) soil CO
2
efflux declined due to oxygen
deficiency resulting in decreased SOM decomposition
because heterotrophic organism undergo physiological
stress. Shading effects of the dense canopy under
Cupressus plantation with less rainfall interception cre-
ates a more favorable environment for SMB resulting in
higher litter-derived C incorporation in microbial bio-
mass, especially during March 2010 with lower soil
water content.
Thinning effect on microbial biomass C and N
and on litter
13
Cturnover
In the Munessa forest, thinning led to significant in-
creased microbial N stocks. Several studies described
increased N
SMB
contents in forest soils after thinning
events (Kaye and Hart 1998;Hartetal.2005;
Dannenmann et al. 2006), due to variations in microbial
turnover (Cheng et al. 1998). An explanation for this
might be that harvesting of trees results in less compe-
tition for N, thus giving SMB an advantage in nutrient
competition under thinned stands. Furthermore, canopy
opening creates more favorable microclimatic condi-
tions compared to non-thinned plots with less rainfall
interception and shading effects, which may stimulate
142 Plant Soil (2015) 388:133146
microbial biomass growth and activity (Hall and
Marchand 2010). It can be assumed, that the combina-
tion of enhanced soil moisture (Fig. 1) and increased soil
temperature (as reported by Yohannes et al. 2013 for
thinned plots in the Munessa forest) after thinning led to
a stimulation of soil microbial growth and activity,
resulting in higher microbial N stocks compared to
non-thinned stands in the Munessa forest.
Furthermore, our experiment indicates that thinned
plantations led to an increased litter-derived C incorpo-
ration into SMB during dry conditions, whereas wet
conditions support microbial C incorporation from litter
under non-thinned plots. Higher insulation under
thinned stands during dry conditions may increase
SMB activity and growth. Under wet conditions, non-
thinned plots provide a more favourable habitat for total
microbial biomass growth accompanied with increased
litter-derived C incorporation. Due to the dense canopy,
SMB under non-thinned stands are protected against
heavy rains combined with nutrient leaching and lack-
ing oxygen, which inhibits microbial processes under
thinned plots (SWC >31 %).
In the current study, thinning intensity did not influ-
ence microbial N stocks or microbial incorporation of
litter-derived C, although intensity of thinning events
(IP compared to Con) influences various factors like soil
moisture or tree root biomass (Nilsen and Strand 2008)
which alters microbial composition and processes (Peng
and Thomas 2006).
Rotation age effect on microbial biomass C and N
Our study revealed a decline in microbial N stocks with
stand age. Snowson et al. (2000) showed that root
biomass increases with stand age accompanied with
higher fungal abundance due to mycorrhiza. This leads
to enhanced competition for N by trees and a decline in
microbial N accumulation. Furthermore, a higher abun-
dance of fungi under mature stands might possibly be an
explanation for lower microbial N stocks as far as fungi
contain more C and less N in their biomass compared to
bacteria (Jenkinson 1976;Campbelletal.1991). The
shift in microbial community composition towards
higher fungi abundance under mature stands is support-
ed by significantly increased microbial C/N ratios with
stand age, especially under dry conditions in March
2009. It is known, that changes in SMB composition
lead to variations in microbial C/N ratio (Dannenmann
et al. 2006) and fungi show increased C/N values
ranging from 10 to 15 compared to bacteria with C/N
ratios between 3.5 and 7 (Paul 2007;Campbelletal.
1991). However, no significant differences between
stand age classes in litter-derived
13
C utilization by
SMB could be shown.
Soil moisture effect on microbial biomass C and N
and on litter
13
Cturnover
The decline in microbial C storage during wet phases in
November 2009 and March 2010 in the present study
could be caused by increased soil moisture (SWC
>31 %) resulting in nutrient leaching and anoxic condi-
tions, inhibiting microbial activity (Yohannes et al.
2013). The diversity, abundance and activity of micro-
organisms are strongly related to changes in soil tem-
perature and soil humidity (Magurran and May 1999;
Gaston and Blackburn 2000) which is supported by
several studies showing an increasing (Ross 1989;
Yohannes et al. 2013), decreasing (Karlen et al. 1987)
or no response (van Gestel et al. 1992) of SMB with
increasing soil moisture.
Furthermore, high microbial C storage during dry
soil conditions in the Munessa forest may point towards
a higher abundance of fungi. The shift in microbial
community composition towards fungi dominance is
corroborated by the missing significant effect of differ-
ent soil moisture statuses on soil microbial N storage.
Microbial C/N results indicate that soil microbial com-
munity in the Munessa forest is dominated by fungi
during dry soil conditions with a shift to bacteria dom-
inance during wet phases, thus supporting our microbial
C storage findings. Fungi are able to translocate nutri-
ents between surface and soil more effectively due to
their filamentous structure (Holland and Coleman 1987)
and are known to be more resistant to drought stress than
bacteria (Cornejo et al. 1994; Schimel et al. 2007). In
contrast, bacteria are more efficient in utilizing the de-
livered C and N after a re-wetting event which could
lead to the decrease of C/N ratio during humid phases in
the sub-humid Munessa forest ecosystem due to bacte-
rial growth. This assumption is corroborated by a study
of Iovieno and Bååth (2008) showing that after a re-
wetting event on dry soil under laboratory conditions
bacterial growth recovered within 10 h to the same level
like in non-dried control soil.
In the current study, different soil moisture led to
significantly different litter-derived C incorporation into
SMB. Silvicultural management effects were strongly
Plant Soil (2015) 388:133146 143
influenced by varying moisture regimes, resulting in an
opposite pattern of C incorporation into SMB under
natural forests and Cupressus plantations and under
thinned and non-thinned plots. This leads to the assump-
tion that soil moisture is the driving force for microbial
community composition and microbial processes in the
Munessa forest ecosystem which is consistent with
findings from Wagener and Schimel (1998) for other
ecosystems. Findings from our study agree with results
of Yohannes et al. (2013), who identified soil moisture
as key abiotic factor on soil respiration in the Munessa
forest.
Conclusions
Using an in situ labelling approach, we were able to
achieve a sufficient labelling of SMB to study effects
of silvicultural management strategies on microbial
parameters in the Munessa forest ecosystem (objec-
tive i). Microbial incorporation of litter-derived
15
N
was not significantly affected by the investigated
variables over the whole experimental period. How-
ever, litter-derived
13
C analysis showed that C utili-
zation by SMB was higher under natural forest during
dry soil conditions, whereas Cupressus litter was less
utilized by SMB (objective ii). Wet soil conditions
improved microbial litter-derived C utilization under
Cupressus stands due to protecting canopy effects
(objective ii). Within the plantation plots, thinning
led to increased C incorporation during dry soil con-
ditions (objective ii). Heavy rains during wet phases
resulted in anoxic conditions under thinned plots,
inhibiting SMB (objective ii). The intensity of thin-
ning did not show any significant effect on microbial
litter-derived C incorporation. Furthermore, our exper-
iment confirmed that in the Munessa ecosystem, soil
humidity is the main influencing factor, resulting in
significantly different nutrient turnover during dry and
wet soil conditions (objective iii).
Our findings suggest that fast growing tree planta-
tions established on Mollic Nitisols in the Munessa
forest not necessarily contribute to a decline of soil
sustainability with respect to short-term (microbial) C
and N turnover. Furthermore, our results indicate that
shifts in SMB community towards fungal dominance
might occur. Further investigations regarding microbial
community composition are needed to address the sig-
nificance of this aspect.
Acknowledgments This study was financially supported by the
German Research Foundation (DFG GL 327/10-1), the University
of Bayreuth and the Martin-Luther-University Halle-Wittenberg.
We thank Prof. Dr. M. Fetene (Vice President of Addis Ababa
University) and Dr. A. Abate for logistic support during field work.
We are also grateful to Prof. G. Gebauer and his team (University of
Bayreuth) and to Stefanie Bösel (Martin-Luther-University Halle-
Wittenberg) for conducting the EA-IRMS measurements. We ac-
knowledge Prof. B. Huwe for the use of the Soils Physics Labora-
tory at the University of Bayreuth. Our work also greatly profited
from very constructive discussions with Dr. Mario Tuthorn (Uni-
versity of Bayreuth) and PD Dr. Michael Zech (University of
Bayreuth, University of Halle-Wittenberg) and the very
helpful pre-review of Dr. Stephan Unger (University of Bielefeld).
We furthermore thank the two anonymous reviewers for very
constructive comments and suggestions on the manuscript.
References
Ananyeva ND, Demkina TS, Jones WJ, Cabrera ML, Steen WC
(1999) Microbial biomass in soils of Russia under long-term
management practices. Biol Fertil Soils 29:291299
Brookes PC, Landman A, Pruden G, Jenkinson DS (1985)
Chloroform Fumigation and the release of soil nitrogen: a
rapid direct extraction method to measure microbial biomass
nitrogen in soil. Soil Biol Biochem 17(6):837842
Campbell CA, Biederbeck VO, Zentner RP, Lafond GP (1991)
Effect of crop rotations and cultural practices on soil organic
matter, microbial biomass and respiration in a thin black
chernozem. Can J Soil Sci 71:363376
Cheng WX, Virginia RA, Oberbauer SF, Gillespie CT, Reynolds
JF, Tenhunen JD (1998) Soil nitrogen, microbial biomass,
and respiration along an arctic toposequence. Soil Sci Soc
Am J 62:654662
Cornejo FH, Varela A, Wright SJ (1994) Tropical forest litter
decomposition under seasonal drought: nutrient release, fun-
gi and bacteria. Oikos 70:183190
Coûteaux MM, Bottner P, Berg B (1995) Litter decomposition,
climate and litter quality. Trends Ecol Evol 10(2):6366
da Silva DKA, de Oliveir FN, de Souza RG, da Silva FSB, de
Araujo ASF, Maia LC (2012) Soil microbial biomass and
activity under natural and regenerated forests and conventional
sugarcane plantations in Brazil. Geoderma 189190:257261
Dannenmann M, Gasche R, Ledebuhr A, Papen H (2006) Effects
of forest management on soil N cycling in beech forests
stocking on calcareous soils. Plant Soil 287:279300
Diaz-Raviña M, Acea MJ, Carballas T (1995) Seasonal changes in
microbial biomass and nutrient flush in forest soils. Biol
Fertil Soils 19:220226
Fritzsche F, Zech W, Guggenberger G (2007) Soils of the main
Ethiopian Rift Valley escarpment: a transect study. Catena
70:209219
Gaston KJ, Blackburn T (2000) Patterns and process in
macroecology. Blackwell, Oxford
Glaser B, Benesch M, Dippold M, Zech W (2012) In situ
15
Nand
13
C labelling of indigenous and plantation tree species in a
tropical mountain forest (Munessa, Ethiopia) for subsequent
litter and soil organic matter turnover studies. Org Geochem
42:14611469
144 Plant Soil (2015) 388:133146
Hackl E, Bachmann G, Zechmeister-Boltenstern S (2004)
Microbial nitrogen turnover in soils under different types of
natural forest. For Ecol Manag 188(13):101112
Hall SJ, Marchand PJ (2010) Effects of stand density on ecosystem
properties of subalpine forests in the southern Rocky
Mountains, USA Annals of Forest Science. 67:102p1-102p11.
Hart SC, DeLuca TH, Newmana GS, MacKenzie MD, Boyle SI
(2005) Post-fire vegetative dynamics as drivers of microbial
community structure and function in forest soils. For Ecol
Manag 220:166184
Holland EA, Coleman DC (1987) Litter placement effects on
microbial and organic matter dynamics in an agroecosystem.
Ecology 68:425433
Hopkins DW, Chudek JA, Webster EA, Barraclough D (1997)
Following the decomposition of ryegrass labelled with
13
C
and
15
N in soil by solid-state nuclear magnetic resonance
spectroscopy. Eur J Soil Sci 48:623631
Huang Z, Wan X, He Z, Yu Z, Wang M, Hua Z, Yang Y (2013)
Soil microbial biomass, community composition and soil
nitrogen cycling in relation to tree species in subtropical
China. Soil Biol Biochem 62:6875
Insam H, Parkinson D (1989) Influence of macroclimate on soil
microbial biomass. Soil Biol Biochem 21(2):211221
Iovieno P, Bååth E (2008) Effect of drying and rewetting on bacterial
growth rates in soil. FEMS Microbiol Ecol 65:400407
Jenkinson DS (1976) The effects of biocidal treatments on metab-
olism in soil. IV. The decomposition of fumigated organisms
in soil. Soil Biol Biochem 8:203208
Jenkinson DS, Ladd JN (1981) Microbial biomass in soil: mea-
surement and turnover. In: Paul EA, Ladd JN (eds) Soil
Biochemistry, 5th edn. Dekker, New York, pp 415471
Karlen DL, Mausbach MJ, Doran JW, Cline RG, Harris RF,
Schumann GE (1987) Soil quality: a concept, definition,
and framework for evaluation. Soil Sci Soc Am J 61:410
Kaye JP, Hart SC (1998) Ecological restoration alters nitrogen
transformations in a ponderosa pine-bunchgrass ecosystem.
Ecol Appl 8(4):10521060
Langenbruch C, Helfrich M, Joergensen RG, Gordon J, Flessa H
(2014) Partitioning of carbon and nitrogen during decompo-
sition of
13
C
15
N-labeled beech and ash leaf litter. J Plant Nutr
Soil Sci 177:178188
Lemenih M, Gidyelew T, Teketay D (2004) Effects of canopy
cover and understory environment of tree plantations on
richness, density and size of colonizing woody species in
southern Ethiopia. For Ecol Manag 194:110
Lemma B, Nilsson I, Kleja DB, Olsson M, Knicker H (2007)
Decomposition and substrate quality of leaf litters and fine
roots from three exotic plantations and a native forest in the
southwestern highlands of Ethiopia. Soil Biol Biochem
39(9):23172328
Leon JD, Gonzalez MI, GallardoJF (2011) Biogeochemical cycles
in natural forest and conifer plantations in the high mountains
of Colombia. REVISTA DE BIOLOGIA TROPICAL 59(4):
18831894
Lisanework N, Michelsen A (1994) Litterfall and nutrient release
by decomposition in three plantations compared with a nat-
ural forest in the Ethiopian highland. For Ecol Manag 65:
149164
Lopes MM, Salviano AAC, Araujo ASF, Nunes LAPL, Oliveira
ME (2010) Changes in soil microbial biomass and activity in
different Brazilian pastures. Span J Agric Res 8(4):12531259
Magurran AE, May RM (1999) Evolution of biological diversity.
Oxford University Press, Oxford
Mamilov AS, Dilly OM (2002) Soil microbial eco-physiology as
affected by short-term variations in environmental condi-
tions. Soil Biol Biochem 34:12831290
Mehring M, Glaser B, de Camargo PB, Zech W (2011) Impact of
forest organic farming change on soil microbial C turnover
using 13 C of phospholipid fatty acids. Agron Sustain Dev
31:719731
Mendham DS, Sankaran KV, OConnell AM, Grove TS (2002)
Eucalyptus globulus harvest residue management effects on
soil carbon and microbial biomass at 1 and 5 years after
plantation establishment. Soil Biol Biochem 34:19031912
Nilsen P, Strand LT (2008) Thinning intensity effects on carbon and
nitrogen stores and fluxes in a Norway spruce (Picea abies (L.)
Karst.) stand after 33 years. For Ecol Manag 256(3):201208
Paul EA (ed) (2007) Soil Microbiology, Ecology, and
Biochemistry. Academic, Burlington
Peng YY, Thomas SC (2006) Soil CO
2
efflux in uneven-aged
managed forests: temporal patterns following harvest and
effects of edaphic heterogeneity. Plant Soil 289:253264
Priha O, Smolander A (1999) Nitrogen transformations in soil
under Pinus sylvestris, Picea abies and Betula pendula at
two forest sites. Soil Biol Biochem 31:965977
Ross DJ (1989) Estimation of soil microbial C by a fumigation-
extraction procedure: influence of soil moisture content. Soil
Biol Biochem 19:397404
Schimel J, Balser TC, Wallenstein M (2007) Microbial stress-
response physiology and its implications for ecosystem func-
tion. Ecology 88:13861394
Seyoum Y, Fetene M, Strobl S, Beck E (2012) Foliage dynamics,
leaf traits, and growth of co-existing evergreen and deciduous
trees in a tropical montane forest in Ethiopia. Trees 26:1495
1512
Sistla SA, Schimel JP (2012) Stoichiometric flexibility as a regu-
lator of carbon and nutrient cycling in terrestrial ecosystems
under change. New Phytol 196:6878
Smith JL, Paul EA (1990) The significance of soil microbial
biomass estimations. In: Bollag JM, Stotzky G (eds) Soil
Biochemistry. Dekker, New York, pp 357396
Smith JL, Papendick RI, Bezdicek DF, Lynch JM (1993) Soil
organic matter dynamics and crop residue management. In:
Metting FB Jr (ed) Soil Microbial Ecology. Dekker, New
York, pp 6 594
Snowson P, Eamus D, Gibbons P, Khanna P, Keith H, Raison J,
Kirschbaum M (2000) Synthesis of Allometrics, Review of
Root Biomass and Design of Future Woody Biomass
Sampling Strategies. The Australian Greenhouse Office
Technical Report no. 17
Strobl S, Fetene M, Beck EH (2011) Analysis of the shelter tree-
effectof natural and exotic forest canopies on the growth of
young Podocarpus falcatus trees in southern Ethiopia. Trees
25:769783
Sugai SF, Schimel JP (1993) Decomposition and biomass incor-
poration of
14
C-labeled glucose and phenolics in taiga forest
floor: effect of substrate quality, successional state, and sea-
son. Soil Biol Biochem 25:13791389
Thibodeau L, Raymond P, Camiré C, Munson AD (2000) Impact
of precommercial thinning in balsam fir stands on soil nitro-
gen dynamics, microbial biomass, decomposition, and foliar
nutrition. Can J For Res 30(2):229238
Plant Soil (2015) 388:133146 145
Tiemann LK, Billings SA (2012) Tracking C and N flows through
microbial biomass with increased soil moisture variability.
Soil Biol Biochem 49:1122
Troeh FR, Thompson LM (2005) Soils and Soil Fertility.
Blackwell Publishing Professional, USA
van Gestel M, Ladd JN, Amato M (1992) Microbial biomass
responses to seasonal change and imposed drying regimes
at increasing depths of undisturbed top soil profiles. Soil Biol
Biochem 24:103111
Vance ED, Brookes PC, Jenkinson DS (1987) An extraction
method for measuring soil microbial biomass C. Soil Biol
Biochem 19(6):703707
Wagener SM, Schimel JP (1998) Stratification of ecological pro-
cesses: a study of the birch forest floor in the Alaskan taiga.
Oikos 81:6374
Wardle DA, Nicholson KS (1996) Synergistic effects of grassland
plant species on soil microbial biomass and activity: impli-
cations for ecosystem-level effects of enriched plant diversity.
Funct Ecol 10:410416
Witt C, Gaunt JL, Galicia CC, Ottow JCG, Neue H-U (2000) A
rapid chloroform-fumigation extraction method for measur-
ing soil microbial biomass carbon and nitrogen in flooded
rice soils. Biol Fertil Soils 30:510519
Yohannes Y, Shibistova O, Asaye Z, Guggenberger G (2013)
Forest management influence on the carbon flux of cupressus
lusitanica plantation in the munessa forest, Ethiopia. For Res
2(1):110
Zeller B, Colin-Belgrand M, Dambrine E, Martin F (1999) Fate of
nitrogen released from 15 N-labelled litter in European beech
forests. Tree Physiol 21:153162
146 Plant Soil (2015) 388:133146
... Input of litter into the soil can affect soil moisture, alter soil microorganism activities and promote soil C and N mineralization (Hall et al., 2020). A rewetting following drought can increase litter-derived C and CO 2 emission and positively affect microbial biomass (Benesch et al., 2015). Litter-derived CO 2 is significantly higher during the wet than during the dry period in drying-rewetting cycles (Mioko et al., 2014). ...
... The result was consistent with a previous study showing that litter addition enhanced soil respiration in the Zoigê alpine wetland (Zhang et al., 2017). Litter often served as easily degradable labile C pool, and litter decomposition enhanced the concentration of available labile C for soil respiration (Benesch et al., 2015). Additionally, litter mitigated the impact of drying-rewetting cycles on the soil environment and stabilized community structure of microorganisms, and then improved activities of microorganisms that favored CO 2 emission (He et al., 2014). ...
Article
The frequency and intensity of drying-rewetting cycles can influence soil CO2 emission from the soil and carbon (C) and nitrogen (N) in the soil, but little is known about whether such effects can be altered by litter input into the soil, especially for alpine wetland ecosystems. We conducted a 144-day incubation experiment at 15 °C using the soil and litter collected from an alpine wetland on the Qinghai-Tibetan Plateau, China. The soil added with 1 g litter or not was subjected to two frequencies (high vs. low, i.e. 18 vs. 9 cycles with 8 vs. 16 days per cycle, corresponding to 100% vs. 50% of the precipitation frequency in that wetland) and two intensities (high vs. low, i.e. 360 mm vs. 252 mm, corresponding to 100% vs. 70% of precipitation in that wetland) of drying-rewetting cycles. Soil moisture was higher in the high than in the low intensity treatment; litter addition affected soil moisture, but such an effect depended on the time of incubation. Low frequency and high intensity of drying-rewetting cycles significantly enhanced CO2 emission due to increases in available substrate, e.g., soil dissolved organic C, which might result in increased activity of soil microbes such as Acidobacteria, Proteobacteria, Actinobacteria, Basidiomycota and Ascomycota. Adding litter to the soil increased CO2 emission from the soil likely due to increased water holding capability and labile C availability. In the low intensity and high frequency treatment concentrations of inorganic N, ammonium N and nitrate N were higher in the soil with than without litter addition, but in the high intensity treatment of both low and high frequency concentrations of inorganic N and nitrate N were lower. CO2 emission was positively correlated with the concentration of dissolved organic C and soil moisture, but negatively correlated with the concentration of ammonium N. Our results suggest that low frequency of drying-rewetting cycles combined with litter addition can enhance soil CO2 emission, and that effects of drying-rewetting cycles should be taken into account when we consider greenhouse gas emission from alpine wetland soils.
... e phenol oxidase activity (POX). f peroxidase activity (PER) GWC, soil gravimetric water content; WS, soil water saturation; MBC, microbial biomass C concentration; MBN, microbial biomass N concentration; NAG, N-acetyl-glucosaminidase activity; BG, β-glucosidase activity; CBH, cellobiohydrolase activity; BX, β-xylosidase activity; POX, phenol oxidase activity; PER, peroxidase activity *Significant at P < 0.05 pattern might result from the fact that added soil organic C and N could increase microbial biomass by being provided as additional C and N substrates (Benesch et al. 2015) and delaying turnover time of microbial biomass (Wardle 1998). All thinning intensities had no effect on enzyme activities. ...
... At site 2, MBN under the heavy thinning treatment was higher than the control only after the precipitation period. This might result from the fact that seasonally concentrated precipitation could accelerate the water extraction of biologically available C and N into the soil and reduce hydric stress of soil microbes at site 2 (Benesch et al. 2015;Boyle et al. 2005;Park and Matzner 2003). Inversely, the effect of thinning on MBN was consistently significant in both sampling periods at site 1. ...
Article
• Key message Thinning increased microbial biomass but did not alter enzyme activities in the soil of Pinus densiflora Sieb. et Zucc. forests in South Korea. This effect of thinning was larger under a relatively heavy thinning intensity, but there was divergence in the magnitude between sites. • Context The balance between microbial biomass accumulation and enzymatic C and N assimilation determines the level of bioavailable C and N. However, the effects of thinning on these parameters remain contradictory and unconfirmed. - Aims The effects of thinning intensity on microbial biomass and enzyme activity were assessed in the soil of Pinus densiflora Sieb. et Zucc. forests in South Korea. • Methods Un-thinned control and 15 and 30% basal area thinning treatments were applied to two 51- to 60-year-old P. densiflora forests with different management histories, topographies, rainfall amounts, and soils. Seven years after thinning, microbial biomass and activities of N-acetyl-glucosaminidase, β-glucosidase, cellobiohydrolase, β-xylosidase, phenol oxidase, and peroxidase were measured before and after seasonally concentrated rains and at 0–10 cm depth. • Results Microbial biomass was generally highest under the 30% basal area thinning and lowest under the control, and was positively correlated to total soil C and N. The increase in microbial biomass was lower at the site displaying sandier, drier, and more acidic soils and retaining smaller amounts of thinning residue. Conversely, thinning had no significant effect on activities of all enzymes at both sites in both periods. • Conclusion Thinning can promote accumulation of microbial biomass without significant change in enzyme activities participating in the assimilation of C and N. This effect of thinning tended to increase with thinning intensity but differed in magnitude between sites.
... This agrees with Wu and Xiao (2004) who reported soil texture and temperature as the main influencing factors for soil microbial turnover rate, while land-use patterns had only a minor effect. Benesch et al. (2015) considered soil humidity to be the main influencing factor for microbial turnover of litter-derived C in forest ecosystem. Our three adjacent sites had the same soil texture and climatic conditions, which might result in similar microbial turnover. ...
... carried out in equine nutrition studies; hitherto, they have a high potential for future studies. In fact, they are currently almost routinely used in both natural abundance and isotope labelling/tracer studies for a wide range of different applications (Glaser, 2005;Amelung et al., 2008;Zech and Glaser, 2008;Benesch et al., 2015;Zech et al., 2015). From an analytical point of view, this is mostly accomplished by the coupling of a gas chromatograph to an isotope ratio mass spectrometer via an 'online' combustion or pyrolysis/thermo conversion unit (Burgoyne and Hayes, 1998;Hilkert et al., 1999;Meier-Augenstein, 1999). ...
Article
The basis of a successful assessment of the nutritive value of feeds and an animal's supply with dietary energy and nutrients is having sufficient knowledge on key indicators such as feed intake, diet composition, digestibility and the kinetics of gut passage. In horses and other equids, the determination of such indicators is impractical outside controlled conditions, particularly in pasture-based husbandry. Natural wax components such as n-alkanes, alkenes, primary alcohols and fatty acids might be beneficial estimators, but their application is limited in practice. This review provides a concise view into the application of plant wax components, especially alkanes and their external counterparts, in equine nutrition studies. Recent methodological developments and the current state of knowledge are summarized as an interim conclusion. Methodological limitations still hamper an easy application of the method, and some perspectives for future methodological research are discussed. Conclusively, little information is available on feed plant concentrations and variations of primary alcohols, fatty acids and alkenes, and their natural carbon isotope (¹³C/¹²C) ratios. Moreover, the magnitude and the (in)consistency of faecal recovery of these markers is barely described. Methodological research should continue focusing on an effective application of plant markers. In horses, especially plant marker-based methods for the estimation of diet composition and passage kinetics will require much more consideration.
... The cut surface between hole and wick was sealed with PVC glue and the glass fiber wicks were saturated with sterile water and connected with a reservoir containing the 15 NH 4 15 NO 3 tracer solution. The produced labeled plant material was then used to trace and quantify N from litter decomposition, such as in other studies (Schmidt and Scrimgeour, 2001;Bimü ller et al., 2013;Benesch et al., 2015). Leguminous trees stem-labeled with K 15 NO 3 solution showed limited 15 N transfer to associated grass in an agroforestry system and indicated that transfer of the added 15 N was limited in space (i.e., up to 1m from the trees) and delayed in time (i.e., 15 N reached the tree roots more than 3 months after labeling), which prevented estimation based on the stem-15 N labeling method (Sierra and Daudin, 2010). ...
Article
Root-derived resources are receiving increased attention as basal resources for soil animal food webs. They predominantly function as carbon and energy resources for microbial metabolism in the rhizosphere, however, root-derived nitrogen may also be important. We explored both the role of root-derived carbon (C) and nitrogen (N) for the nutrition of soil animal species. Using ¹³C and ¹⁵N pulse labeling we followed in situ the flux of shoot-derived C and N into the soil animal food web of young beech (Fagus sylvatica) and ash (Fraxinus excelsior) trees. For labeling with ¹³C, trees were exposed to increased atmospheric concentrations of ¹³CO2 and for labeling with ¹⁵N leaves were immersed in a solution of Ca¹⁵NO3. Twenty days after labeling root-derived N was detected in each of the studied soil animal species whereas incorporation of root-derived C was only detected in the ash rhizosphere. More root-derived N was incorporated into soil animals from the beech as compared to the ash rhizosphere, in spite of the higher ¹⁵N signatures in fine roots of ash as compared to beech. The results suggest that soil animal food webs not only rely on root C but also on root N with the contribution of root N to soil animal nutrition varying with tree species. This novel pathway of plant N highlights the importance of root-derived resources for soil animal food webs.
... The cut surface between hole and wick was sealed with PVC glue and the glass fiber wicks were saturated with sterile water and connected with a reservoir containing the 15 NH 4 15 NO 3 tracer solution. The produced labeled plant material was then used to trace and quantify N from litter decomposition, such as in other studies (Schmidt and Scrimgeour, 2001;Bimü ller et al., 2013;Benesch et al., 2015). Leguminous trees stem-labeled with K 15 NO 3 solution showed limited 15 N transfer to associated grass in an agroforestry system and indicated that transfer of the added 15 N was limited in space (i.e., up to 1m from the trees) and delayed in time (i.e., 15 N reached the tree roots more than 3 months after labeling), which prevented estimation based on the stem-15 N labeling method (Sierra and Daudin, 2010). ...
Article
The effects of tree species on the N cycle in forest systems are still under debate. However, contradicting results of different 15N labeling techniques of trees and N tracers in the individual studies hamper a generalized mechanistic view. Therefore, we compared Ca(15NO3)2 and 15NH4Cl leaf-labeling method to investigate: (1) N allocation patterns from aboveground to belowground, (2) the cycles of N in soil-plant systems, and (3) to allow the production of highly 15N enriched litter for subsequent decomposition studies. 20 beeches (Fagus sylvatica) and 20 ashes (Fraxinus excelsior) were 15N pulse labeled from aboveground with Ca(15NO3)2 and 40 beeches and 40 ashes were 15N pulse labeled from aboveground with 15NH4Cl. 15N was quantified in tree compartments (leaves, stem, roots) and in soil after 8 d. Beech and ash incorporated generally more 15N from the applied 15NH4Cl compared to Ca(15NO3)2 in all measured compartments, except for ash leaves. Ash had highest 15N incorporation [45% of the applied with Ca(15NO3)2] in its leaves. Both tree species kept over 90% of all fixed 15N from Ca(15NO3) in their leaves, whereas only 50% of the 15N from the 15NH4Cl tracer remained in the leaves and 50% were allocated to stem, roots, and soil. There was no damage of the leaves by both salts, and thus both 15N tracers enable long-term labeling in situ field studies on N rhizodeposition and allocation in soils. Nonetheless, the 15N incorporation by both salts was species specific: the leaf labeling with 15NH4Cl results in a more homogenous distribution between the tree compartments in both tree species and, therefore, 15NH4Cl is more appropriate for allocation studies. The leaf labeling with Ca(15NO3)2 is a suitable tool to produce highly enriched 15N leaf litter for further long term in situ decomposition and turnover studies.
... Neither studies from forest nor from agroecosystems can be transferred to SRC as the tree e soil system is quite complex due to the differences to forests in leaf area index, transpiration rate, root distribution, root depth and effects on microclimate in the soil. Furthermore, especially for trees extreme species specific N and C allocation pattern have been identified [17,18], suggesting that investigations of N uptake as well as allocation has to be performed species specific or even for each of the relevant clones used widely in SRCs. Consequently, the N dynamics during the initial growth period of two SRC genera e poplar and willow -have been investigated in this study. ...
Article
The present study examined microbial substrate utilization by community level physiological profiling and carbon-cycling enzyme assays (cellobiohydrolase, β-xylosidase, and oxidases) in three Japanese larch forests. The forests differed in their locations, topographies, and soil microclimates, and each covered three treatments, namely 20 (IT) and 35% basal area thinning (HT) without intensive residue harvests and an un-thinned control (UTC). Microbial substrate utilization and soil properties (temperature, moisture, total carbon and nitrogen, inorganic nitrogen, and pH) were analyzed at 0–10 cm depth, six years after thinning. Microbial utilization of carbohydrate group under IT was 27 and 62% higher than that under UTC and HT, respectively, in only one of the forests. This might occur because this forest featured a steeper slope, rockier soil texture, and cooler and drier soil surface than the other two forests, where no thinning effect was observed. However, neither microbial utilization of any other substrate groups nor enzyme activity changed by thinning across all forests. It could result from the exclusion of intensive residue harvests or the lack of changes in soil inorganic nitrogen and pH. These results indicate that the thinning effects on microbial substrate utilization might be inconsistent across multiple sites, and at least, not decline the associated forest ecosystem functions and sustainability.
Article
Full-text available
Purpose The quantity and quality of litter inputs to forest soils are likely to be changed as a result of the climate change and human disturbances. However, the effects of changed litter inputs on soil labile carbon (C) and nitrogen (N) pools still remain unclear. Materials and methods A 15-month in situ field experiment was conducted within both high and low litter quality site in a eucalyptus-dominated native forest of Queensland, Australia. Three rates of litter inputs were applied, including (i) no litter (NL); (ii) single litter (SL), representing the average condition of the surrounding forest floor; and (iii) double litter (DL). Water-extractable organic C (WEOC) and total N (WETN), hot water-extractable organic C (HWEOC) and total N (HWETN), microbial biomass C (MBC), and N (MBN) were analyzed in the 0–5-cm soil layer seasonally. Results and discussion Litter input rates had no significant effects on litter decomposition at both sites (P > 0.05). After 15-month of decomposition, mean litter mass loss was 46.3% and 31.2% at the HQ and LQ sites, respectively. Changed litter quantity had no significant effects on any of the soil labile C and N pools, regardless of litter quality. However, soil labile C and N pools significantly varied with sampling times, and the samples of different sampling times were clearly separated at both sites according to the redundancy analysis (RDA). WEOC peaked in summer, declined in autumn and winter, and increased again in spring, while the concentrations of HWEOC and MBC peaked in the winter period. The seasonal trends of MBN were opposite to the trends of WETN, which might be due to the temporal partitioning of N between plants and microbes. Conclusions The findings indicated that soil labile C and N pools in the eucalyptus-dominated forest of subtropical Australia were resistant to a short-term change in aboveground litter inputs. Future research should expand on these findings by keeping observing over a longer time period and considering the influence of changed belowground litter inputs.
Chapter
The subject geology and soils is fundamental for tropical forest management. This chapter is divided into three logical parts: The first describes soil-forming factors and processes. The second provides the exhaustive description of definition, properties of different soil types, and their use for forest purposes. The following soil groups are dealt with: Mature Soils of the Humid and Subhumid Tropics, Representative Soils of the Semiarid and Arid Tropics, Soils Mainly Conditioned by Parent Material and Topography, Temporarily or Permanently Hydromorphic Soils, Soils of the Steppes, and finally Tropical Soils Conditioned by Human Influence. The third part deals with the organization and management of soil surveys; this allows the forest manager to project necessary soil surveys.
Article
Full-text available
Microbial biomass and activity are useful indices for assessing changes in soil ecosystems. The impact of different pastures on microbial biomass and activity was studied in a long-term experiment in Northeast Brazil. For our study the pastures were divided into plots: a) Brachiaria brizantha; b) Leucaena leucocephala; c) Cynodon dactilon; d) Panicum maximum. An adjacent area with native vegetation was used as reference. Soil samples were collected in 0-10 and 10-20 cm depths. No significant differences in soil organic C (C org) was found among all plots at 0-10 and 10-20 cm depth. Soil microbial C (C mic) values were higher in native forest and P. maximum when compared to the other plots. The soil basal respiration (CO 2) values were similar among all plots evaluated. However, respiratory quotients (qCO 2) were significantly lower in native forest and P. maximum when compared to other plots, at 0-10 cm depth. Values of fluorescein diacetate (FDA) hydrolysis were significantly higher in native forest and P. maximum, while values of dehydrogenase activity were found to be signif icantly higher in native forest, C. dactilon and P. maximum. Soil microbial biomass and activity changed when a native forest was converted to pastures. These changes were positive with the inclusion of P. maximum by the high input of C sources.
Article
Full-text available
The effect of plantation forests on the global carbon balance is controversially discussed in recent times. As soil respiration is a decisive component in the carbon exchange between terrestrial ecosystems and atmosphere, effects of forest management measures (e.g. thinning) in the context of driving parameters of soil CO2 efflux is a key issue in optimizing carbon friendly land management. In the present study, we report the effects of thinning, soil temperature and soil moisture, and biotic parameters on soil CO2 efflux rate. Soil CO2 efflux was measured by using an Infrared Gas Analyzer. We selected thinned and un-thinned stands within six years old Cupressus lusitanica plantation forest. Soil respiration rate ranged from 1.47 to 6.92 µmol m-2s-1 (thinned) and 1.31 to 5.20 µmol m-2s-1 (control stand). Generally higher soil respiration rates were measured during wet than in dry season. Seasonal variability of soil CO2 efflux was significantly (p < 0.05) correlated with soil moisture, but poorly correlated with soil temperature. Soil respiration increased with increasing soil moisture and reached maximum at 31% but after this threshold it start to declined. In general, soil CO2 efflux rate in the first and second year after thinning was 24% and 14% higher in the thinned stand. Increased soil temperature at the thinned stand contributed minor to the larger soil CO2 efflux, the more important reason appeared to be the trees' direct response. Higher fine root production together with larger microbial concentrations representing different groups infers a higher autotrophic respiration by roots and associated mycorrhizal fungi as well as by heterotrophic respiration. Despite the higher CO2 losses with soil respiration, the organic C and total N concentrations in soil rather tended to increase, indicating higher organic matter input to soil at the thinned stand.
Article
Firstly, the basic properties and functions of soil organic matter and its decomposition are introduced. The remainder of the chapter is then divided into: detailed breakdowns and modelling of soil organic matter dynamics, including microbial biomass composition, organic matter transformations, turnover and nutrient cycling; the influence of crop residues on soil organic matter dynamics, with data on nutrient content, residue utilization, and the effects on organic matter dynamics and microbial activity. -J.W.Cooper
Article
The effects of crop rotations and various cultural practices in a Rego, Black Chernozem with a thin A horizon were determined in a long-term study at Indian Head, Saskatchewan. Generally, fertilizer increased soil organic C and microbial biomass in continuous wheat cropping. Soil organic C, C mineralization (respiration) and microbial biomass C and N increased with increasing frequency of cropping and with the inclusion of green manure or hay crop in the rotation. The influence of treatments on soil microbial biomass C was less pronounced than on microbial biomass N. The treatments had no effect on specific respiratory activity; however, it appeared that the microbial activity, in terms of respiration, was greater for systems with smaller microbial biomass. Changes in amount and quality of the soil organic matter were associated with estimated amount and C and N content of plant residues returned to the soil. -from Authors
Article
1. The effects of the grass species Lolium perenne L. and nine dicotyledonous grass-land species, grown in monocultures and two-species mixtures, on (i) the soil microbial biomass, (ii) the respiration: biomass ratio and (iii) plant litter decomposition was investigated in a glasshouse experiment. 2. Microbial biomass was sometimes greater and sometimes less in the two-species mixtures than could be explained in terms of the additive effects of the two component species grown singly; this variation was independent of differences in below-ground plant productivity between monoculture and mixture treatments. 3. The microbial respiration: biomass ratios and plant litter decomposition rates in the two-species mixture treatments were either greater or less than expected based on the monoculture treatments; these differences were dependent on the combinations of species present. Because the respiration: biomass ratio is a measure of ecosystem stability, it is here proposed that stability does not respond predictably to shifts in species diversity. 4. These results provide evidence that increasing plant species richness (from one to two species) has the potential to influence soil processes positively or negatively in a non-additive way. The possible ecological implications of this are discussed.
Article
In the forest floor of Alaskan taiga, annual layers of Equisetum (horsetail) litter demarcate cohorts of birch litter. We collected samples of the forest floor monthly during June-September 1993. Forest floor material was separated into each of the three most recent litter cohorts, plus the Oe layer, and the Oa layer. Overall, respiration potential decreased with depth of litter (litter age) and over the growing season. Nitrogen mineralization potential increased with depth, and fluctuated over time. Microbial biomass did not vary with depth, but did increase greatly in September in conjunction with increased litter moisture. Litter C:N ratio decreased with time and varied with depth according to the year-to-year variation in litter chemistry. We present a conceptual model of the forest floor describing microbial activity on a litter cohort as controlled primarily by litter chemistry, but modified by the vertical position in the forest floor and seasonal climatic variation. Litter quality was the main factor associated with changes in microbial activity with season and down the soil profile. Microbial activities occurred within an environment controlled by the climatic buffering of the decomposing leaves themselves. As the quality of litter as a substrate decreased with depth, the quality of the environment for microbial activity increased. Yearly precipitation cycles also played a role in controlling soil biomass and activity.
Article
Irrigation was used to study the consequences of seasonal drought for nutrient release and bacterial and fungal numbers during dry season litter decomposition in tropical forest on Barro Colorado Island, Panama. Litter bags containing a single species of leaves were placed beneath conspecific trees at the onset of the dry season in December 1987 and collected at one-month intervals until the onset of the wet season in May 1988. Serial dilutions were used to quantify densities of fungi and bacteria. Nutrient concentrations in recalcitrant litter fractions showed rapid declines in the first month of exposure (K, P) followed by bioaccumulation (N) or no significant changes over the next four months (P, K, Mg and most Ca). Irrigation depressed K concentrations and enhanced N and Mg concentrations possibly as a consequence of leaching and bioaccumulation, respectively. Irrigation also depressed fungal densities at the community level and for three of eight species that were analysed separately. Densities of three of the remaining species of fungi varied significantly among litter substrate species. Bacterial densities were enhanced by irrigation after one month of exposure but were depressed after five months which may reflect reduced litter substrate quality.
Article
The aim of this study was to determine the influence of leaf-litter type (i.e., European beech—Fagus sylvatica L. and European ash—Fraxinus excelsior L.) and leaf-litter mixture on the partitioning of leaf-litter C and N between the O horizon, the topsoil, the soil microbial biomass, and the CO2 emission during decomposition. In a mature beech stand of Hainich National Park, Thuringia, Germany, undisturbed soil cores (∅ 24 cm) were transferred to plastic cylinders and the original leaf litter was either replaced by 13C15N-labeled beech or ash leaf litter, or leaf-litter-mixture treatments in which only one of the two leaf-litter types was labeled. Leaf-litter-derived CO2-C flux was measured every second week over a period of one year. Partitioning of leaf-litter C and N to the soil and microbial biomass was measured 5 and 10 months after the start of the experiment. Ash leaf litter decomposed faster than beech leaf litter. The decomposition rate was negatively related to initial leaf-litter lignin and positively to initial Ca concentrations. The mixture of both leaf-litter types led to enhanced decomposition of ash leaf litter. However, it did not affect beech leaf-litter decomposition. After 5 and 10 months of in situ incubation, recoveries of leaf-litter-derived C and N in the O horizon (7%–20% and 9%–35%, respectively) were higher than in the mineral soil (1%–5% and 3%–8%, respectively) showing no leaf-litter-type or leaf-litter-mixture effect. Partitioning of leaf-litter-derived C and N to microbial biomass in the upper mineral soil (< 1% of total leaf-litter C and 2%–3% of total leaf-litter N) did not differ between beech and ash. The results show that short-term partitioning of leaf-litter C and N to the soil after 10 months was similar for ash and beech leaf litter under standardized field conditions, even though mineralization was faster for ash leaf litter than for beech leaf litter.