Biological soil crusts promote N accumulation in
response to dew events in dryland soils
Manuel Delgado-Baquerizo; Fernando T. Maestre; Jesús G.P. Rodríguez &
Antonio Gallardo. Soil Biology and Biochemistry (2013).
Introducction
In drylands, water is the most important factor limiting plant growth, net
primary production and microbial decomposition (Austin et al. 2004; Schwinning
and Sala 2004; Robertson and Groffman 2007)
In these ecosystems dew events may provide up to 40% of the water inputs
received every year (from ~0.15 mm to ~ 0.30 mm per day; Kidron 2000; Jacobs
et al., 2000; Moro et al., 2007; Lekouch et al., 2011)
However, not much is known
about the influence that very
small water pulses, such as those
from dew events, have on
biogeochemical cycles in
drylands.
Introducction
Aranjuez experimental station (central Spain)
Introducction
N cycle in drylands
After water, nitrogen (N) is the main factor limiting
plant growth and decomposition in drylands (Schlesinger 1996)
Biocrusts, usually located
in the open areas
between plant canopies,
largely modulate the N
cycle in these ecosystems.
Introducction
Ex: 1 Increase total N and % of dissolved organic N regarding BS
Delgado-Baquerizo et al. 2010; Soil Biology and Biochemistry
Other examples in: Belnap (2002), Zaady (2005) Su et al. (2011)
Introducction
Ex: 2 increase DON production in response to C, N and P addition regarding BS
Delgado-Baquerizo et al. (2013); Plant and Soil
Introducction
Ex: 3 more homogeneous soil conditions than plant canopies for Inorganic N
Delgado-Baquerizo et al. 2013; Journal of arid environments
G: ¿How biocrusts modulate the response of N availability to dew
events in semiarid drylands?
H: Biocrusts will increase N availability in response to dew events
Methods
Aranjuez experimental station (349 mm; 14.5 ºC).
Spring of 2010.
Twelve intact soil cores (5
cm depth, 7.5 cm
diameter) were collected
under each of two
microsites: well-developed
biocrusts and bare ground
areas (BG)
Crust dominated by
Diploschistes diacapsis
Methods
Air-dried soil cores with and without biocrusts (six
replicates each) were incubated in a plant growth
chamber for 14 days under two treatments: with
and without (control) dew
Soil cores were incubated for 9 hours of light (20%
RH, 20ºC) and 15 hours darkness (80% RH, 10ºC)
simulating spring conditions in Aranjuez
In the dew treatment, soils were watered
automatically three times during the darkness
period to keep soil humidity constant at a 1%
of SWC.
Before and after the experiment, we collected
2.5 g of soil (0-2 cm depth) from each
replicated core.
Material y Métodos
Ammonium
Nitrate
Dissolved organic N (DON)
Available N = Ammonium + Nitrate + DON
Amino acids
Carbohydrates= hexoses + pentoses
Phenols
Pentoses: hexoses -> proxy of origin from organic matter
lichen vs. microorganisms
Carbohydrates: available N -> proxy of organic matter
quality
We calculated the absolute increment in the values of each variable after 14 days of
incubation (regarding initial concentrations).
Differences in the increment of these variables were evaluated using two-way ANOVAs:
microsite & treatment
Results
Differences between
treatments and microsites
were not observed for
either amino acids or
nitrate (P > 0.05)
Results
Discusion
DON & available N
Dew pulses
available N
Functional diversity and
Fungal:bacterial ratio (DelgadoBaquerizo et al. 2013; Plant and soil)
available N for plant in their periods of activity
Organic matter quality (lower labile C:N ratio)
Discusión
Phenols
production
under biocrusts
Allelopathic effect on other groups of
microorganisms from occupying a
relative “N-rich” microsite
Pentose: hexose ratio
OM decomposition in response to a
small water pulses (Austin et al. 2004).
80% of RH may active the
N and C cycles in drylands
Carbohydrates and N
inmobilization under
biocrust and BG for the
control treatments
Conclusions
We found that dew-like water inputs can promote the activation of
microorganisms involved in the C and N cycles in dryland soils, and that this
response is modulated by well developed biocrusts communities.
Biocrust increased the N availability in response to small pulses of water similar
to dew events in semiarid ecosystems. Given the degree of development of BSCs
in drylands worldwide, the high homogeneity of N cycle under biocrusts and the
importance of water inputs from dew, the production of N under dew conditions
can make an important contribution to the total N available for plants and
microorganisms in these regions.
Biocrust increase the amount of soil phenols which may have a Allelopathic
effect on other groups of microorganisms