Tropical Ecology53(2): 235-240, 2012
International Society for Tropical Ecology www.tropecol.com
Differences in soil moisture, nutrients and the microbial community between forests on the upper Pacific and Caribbean slopes at Monteverde, Cordillera de Tilaran: implications for responses to climate change
WILLIAM D. EATON1*, MELANIE ROED2,3, OLIVIER CHASSOT4 & DWIGHT BARRY2.3
1School of Environmental and Life Sciences, Kean University, 1000 Morris Ave., 2Peninsula College, Center of Excellence in Environmental Science and Natural Resources, 1502, E. Lauridsen Blvd. Port Angeles, WA 98362 USA 3Huxley College of the Environment at Peninsula College, Western Washington University, 1502 E. Lauridsen Blvd. Port Angeles, WA 98362 USA 4Centro Científico Tropical (CCT), Apdo 8-3870-1000 San José, Costa RicaAbstract: A study was conducted to identify soil ecosystem metrics for use in monitoring
soil ecosystem health in tropical montane cloud forest habitats, and to establish a baseline of soil community characteristics. This work was performed in six unique forested habitats on the Caribbean and Pacific slopes of the Monteverde Reserve in Costa Rica. Comparisons were made of the soil moisture, nitrogen fixation activity, microbial biomass, fungal and bacterial abundance and diversity, and the abundance of key functional genes laccase (for lignin degradation by basidiomycete fungi) and nifH (for bacterial N- fixation). Differences were found in these metrics between habitats, which were correlated with soil moisture. The results of this work show that these metrics can be used as part of a program to monitor the soil ecosystems for early indicators of shifts in conditions in response to environmental change within this part of a fragile ecosystem.
Resumen: Se realizó un estudio para identificar las métricas del ecosistema edáfico que
pueden usarse en el monitoreo de la salud de este ecosistema en hábitats de bosque nublado montano y para establecer información de línea base de las características de la comunidad del suelo. Este trabajo se llevó a cabo en hábitats forestales únicos en las laderas del Caribe y del Pacífico de la Reserva Monteverde, Costa Rica. Se hicieron comparaciones de la humedad del suelo, la actividad de fijación de nitrógeno, la biomasa microbiana, la abundancia y la diversidad de hongos y bacterias, y la abundancia de los genes funcionales clave de la lacasa (para la degradación de la lignina por hongos basidiomicetos) y nifH (para la fijación bacteriana de N). Se encontraron diferencias para estas métricas entre hábitats, las cuales estuvieron correlacionadas con la humedad del suelo. Los resultados de este trabajo muestran que estas métricas pueden usarse en programas de monitoreo de ecosistemas edáficos como indicadores tempranos de modificaciones en las condiciones como respuesta al cambio ambiental en este componente de un ecosistema frágil.
Resumo:Este estudo foi conduzido para identificar as métricas do ecossistema do solo para
uso na monitorização da saúde do ecossistema em habitats florestais tropicais montanos de nevoeiros, e estabelecer uma linha básica quanto às características da comunidade do solo. Este trabalho foi efectuado em seis habitats florestados únicos nas vertentes das Caraíbas e do
* Corresponding Author;e-mail:[email protected]
Pacífico na Reserva Monteverde na Costa Rica. Foram efetuadas comparações na humidade do solo, abundância fúngica e bacteriana e diversidade, bem como a abundância de genes funcionais chave de lacase (para a degradação da lenhina pelo basidiomicetas) e nifH (para as bactérias de fixação de N). Encontraram-se diferenças nestas métricas entre habitats, os quais estavam correlacionadas com a humidade do solo. Os resultados deste trabalho mostraram que estas métricas podem ser utilizadas como parte de um programa para monitorizar os ecossistemas do solo como indicadores precoces de mudanças nas suas condições em resposta à mudança climática no seio desta parte de um ecossistema frágil.
Key words:Climate change, microbial biomass, microbial community structure,
monteverde, montane forest, soil moisture.
Tropical montane cloud forests require both diameter soil cores were collected, pooled by
rain and frequent immersion in clouds for their
subplot, and the soil sieved while field moist. The
maintenance. However, the cloud forests of Monte-
soil was composed of highly decomposed materials,
verde, Costa Rica, are currently threatened by and all soil cores contained only organic layer
documented increases in mist-free periods (Lawton
material. All data were adjusted per dry weight of
et al. 2001; Pounds & Puschendorf 2004; Ray et al.
the soil and bulk density, and results are presen-
2006). Modeling studies there also have provided
ted per volume of soil. Each of the four subplot soil
significant reason to believe that orographic cloud
samples per forest type were analyzed for levels of
base height is increasing, that frequency of forest
microbial biomass C (Cmic), total mineral nitrogen
immersion in cloud is decreasing, and that the (TMN), the PCR-based relative percent contri-
area immersed in clouds for significant times is
bution (RPC) of bacterial rRNA (primers 27f/
decreasing (Lawton et al. 2001; Ray et al. 2006). In
1492r), fungal rRNA (primers EF4/Fung5), nitrogen
response to this concern, the first study was fixation gene (primers nifHf/nifHr), and laccase
conducted in these forests to compare soil mois-
gene (primers lacIf/lacII), and the restriction frag-
ture, nitrogen (N) fixation activity, microbial bio-
ment length polymorphism (RFLP)-based relative
mass, fungal and bacterial abundance and diver-
diversity and abundance of the bacterial and fungal
sity, and the abundance of key functional genes
community as described by Eaton et al. (2011).
laccase (for lignin degradation by basidiomycete
fungi) and nifH (for bacterial N- fixation). This
differences by 2-tailed t-test and mean effect size
study is part of a larger project to monitor these
(d) analysis. To account for the small sample sizes,
forests for impacts of decreasing precipitation a weight-of-evidence approach was used in which
(Salazar et al. 2009). As such, the goals were to
mean differences with P values < 0.15, or 0.15 to
identify metrics for use in monitoring soil ecosys-
< 0.25 and d values > 0.9 were considered to repre-
tem health in these habitats over time, and to
sent meaningful differences between two mean
begin establishing a baseline of soil community
values. The RFLP data were used to determine the
Shannon-Weiner diversity index (H′ by habitat
Six naturally occurring and undisturbed mon-
type), and for cluster analysis using a similarity
tane cloud forest habitats, representing various matrix and Ward’s minimum variance method of
Hartshorn (1983) life zones, were identified in the
measuring Euclidean distances in NCSS software.
Monteverde Reserve, from various life zones, three
Metrics most influenced or influenced by Cmic and
on the Caribbean slope (El Valle, Aleman, Eladios)
soil moisture were identified as critical corre-
and three on the Pacific (Brillantes, Pantanoso,
lations for application in future monitoring and
Alondra sites) slope. The georeferences, altitude
model development if correlation coefficient r values
and Hartshorn (1983) life zones are provided in
(at P = 0.1) were > 0.2 or < -0.2, considered medium
Table 1. In each habitat, a single 50 x 50 m plot
was established, divided into four equal subplots,
The habitats with the greatest soil moisture on
and, following removal of the upper layer of soil
both the Pacific and Caribbean slopes (Brillantes
debris, 16 randomly located 10 cm deep and 2 cm
and El Valle, respectively) had the most fungal-
Table 1. Summary of the sample sites, georeferences, altitude, and Hartshorn (1983) life zones. Fig. 1. Dendrograms comparing the relatedness of the RFLP-based diversity of bacterial and fungal commu- nity rRNA in soil collected from Pacific slope (ALO, BRI, PAN) and Caribbean slope forests (ALE, ELA, VAL). (A) Bacterial rRNA diversity, (B) Fungal rRNA diversity. dominated soils, with greater fungal to bacterial
closely related to those from the Caribbean slope
rRNA ratios, greater amount of laccase and (gene-
soils (Fig. 1A & 1B). Interestingly, the Brillantes
rally) fungal rRNA genes, the lowest amount of
and Alondra soils also had significantly greater
bacterial rRNA gene, with less bacterial and greater
Cmic values than the other four soils, suggesting
fungal rRNA diversity. These habitats also had the
that the diversity and structure of the microbial
lowest levels of total mineral N and greatest amount
populations might differ in correlation with C cycle
of nifH gene, which, along with the generally dynamics. As well, the RFLP data showed that
greater biomass, suggests that more active nitrogen
there were clearly unique fungal and bacterial
fixation and incorporation of mineral N into the
population components in the more moist soils
biomass is occurring in these forests (Tables 2 &
(Fig. 1A & 1B). When examined along with the
3). The diversity of both the bacterial and fungal
RPC, N and biomass data, this suggests the possi-
rRNA of the Brillantes and Alondra soils from the
bility that selection is occurring for N-fixing bacteria
Pacific slope were closely related, as were the and basidiomycete fungi (and lignin degradation)
Eladios and Aleman soils of the Caribbean slope.
in the more moist soils of forests from both slopes.
Both types of rRNA from the Pantanoso (Pacific
Soil moisture influences microbial biomass
slope) and El Valle (Caribbean) soils were more
(Arunachalam et al. 1997; Eaton 2001; Eaton et al.Table 2. The mean value, standard deviation (SD), P-value from t-test, and mean effect size (d) are presented for soil moisture (as % moisture), total mineral nitrogen (TMN as µg g-1), microbial biomass carbon (Cmic as mg C g-1), and the PCR-based relative percent contribution (RPC) of bacterial rRNA (RPC bact), fungal rRNA (RPC fung), ratio of fungal to bacterial rRNA (Fung:bact), N- fixation gene (RPC nifH), and laccase gene (RPC lac) from Monteverde soil samples collected from different forests on the from Pacific slope (Brillantes, Alondra, Pantanoso) and Caribbean slope forests (Valle, Eladios, Aleman). Table 3. The mass and diversity index (H′) of the
vated soil moisture levels increase the release of
bacterial rDNA and fungal rDNA bands following
organic matter from woody debris, stimulating an
RFLP analysis of DNA products from PCR increase in microbial activity, nutrient utilization, amplification of soil DNA collected from Pacific slope
and microbial biomass development, thus lowering
(ALO, BRI, PAN) and Caribbean slope forests (ALE,
the pools of inorganic N (Arunachalam et al. 1997;
ELA, VAL) in the Monteverde cloud forest reserve.
Eaton 2001; Eaton et al. 2011; Schulze 2004;
The soil DNA was amplified by PCR methods using
Schwendenmann & Veldkamp 2006). These factors
the universal bacterial and fungal rRNA primers
along with lower soil oxygen levels that occur with
increased soil moisture positively regulate the nifH
gene activity, which is also associated with
biomass development (White et al. 2007). Conver-
sely, lower levels of soil moisture decrease N cycle
activities and microbial biomass, and result in
increased concentrations of pools of inorganic N
(Eaton 2001; Eaton et al. 2011; Ewing et al. 2007),
which can inhibit both bacterial N-fixation and
1.47 90 1.38 lignin degradation by basidiomycetes, thus decrea-
1.62 92 1.25 sing the microbial biomass and sequestration of
1.54 90 1.31 organic C into the soil biota (Ewing et al. 2007; De
Boer et al. 2005). The data from the current study
suggest that these relationships have important
1.35 implications for soil ecosystem quality should
1.46 61 1.18 moisture levels decrease in the Monteverde forests.
This was the first study to demonstrate that
measurable differences existed in the soil nutrients,
2011; Schwendenmann & Veldkamp 2006), which
microbial community, and microbial biomass in
is also influenced by a wide variety of nutrient and
the different habitats, that were correlated with
microbial community components (Anderson 2003;
soil moisture. Due to the concern of the observed
Schulze 2004) in establishing healthy-functioning
decreasing amounts of precipitation in the Mont-
soils (Doran 2002). Thus, the metrics that most
verde cloud forest region (Pounds et al. 1999), the
influence or are influenced by soil moisture and
metrics suggested by this work should be used as
Cmic were considered as target indicators of “soil
part of a program to monitor the soil ecosystems
quality” in this study. The soil moisture was posi-
early indicators of shifts in conditions in response
tively correlated (at P = 0.1) with Cmic (r = 0.52),
to environmental change within this part of a
RPC of fugal rRNA (r = 0.21), fungal to bacterial
rRNA ratio (0.22), laccase (0.27) and nifH genes (r
= 0.26), and negatively correlated with the TMN
levels (r = - 0.20) and RPC of bacterial rRNA (r =
-0.24). The Cmic was positively correlated with soil
This project was supported by the National
moisture (r = 0.52), RPC of fungal rRNA (r = 0.21),
Science Foundation grants DBI-0452328 and was
fungal to bacterial rRNA ratio (0.22), laccase (0.27)
conducted under the Costa Rican Government
and nifH genes (r = 0.26), and negatively corre-
Permit #063-2008-SINAC. The authors especially
lated with the TMN levels (r = - 0.20) and RPC of
wish to acknowledge and thank all the Tropical
bacterial rRNA (r = - 0.24). Thus, it appears that Science Center staff, Brenda Campbell, Emily Giles,
these metrics are good indicators of differences in
and Robert S. J. Eaton for their incredible effort
made in collecting soils samples in the field under
Lower concentrations of mineralized N are the most difficult of circumstances.
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2004), microbial biomass development (Eaton 2001;
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