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CHANGES OF PROTOZOA POPULATIONS IN AN ARID
SOIL TRANSITING FROM WET TO DRY SEASON
Salvador Rodríguez ZaragozaMicrobiology Lab. UBIPRO,
FES Iztacala, UNAM
Global Warming Effects• The concentration of
greenhouse gases in the Atmosphere have been stabilized in 2000, however, thermal expansion will continue by the end of the 21st
century (Meehl et al, 2005)
• Due to Oceanic Thermal Inertia, the global temperature would increase more than 1°C in the following years (Wigley 2005)
• Increment of soil’s evapotranspiration
• Reduction of water income to soils
• Reduction of quantity and quality of plant exudatesdue to excessive stress
What’s the importance of soil protozoa?
• Temperature affects evapotranspiration, which affects soil water content and this affects soil’s organic matter decomposition.
• However this is just part of the story, because SOM decomposition is also affected by mineralogy, porosity, chemical composition of roots and litter, and macro and microfaunal activity
Plant productivity
Light, Water, CO2 and Temperature
Aboveground
Below ground
Soil NutrientsRoot exudes
Mycorrhiza and Bacteria
Microbial Predators
As predator’s wastes
Consumers
SugarsAmino Acids
Mites, nematodes,earthworms, AND Protozoa
Species Diversity of Soil Protozoa
Ciliates 400 species (Couteux y Darbyshire, 1997)! 35 to 200 microns
Flagellates 260 species (Foisner, 1991)! <5 (nanoflagelados) to 50 microns
Naked Amoebae 60 species (Couteux y Darbyshire, 1997) 140 at Villa del Carbón, Mex. (Rodríguez-Zaragoza 2000) 90 in the Negev Desert (Rodríguez-Zaragoza et al., 2005) and 59 in Tehuacan, Mex. (Rodríguez-Zaragoza et al., 2005) 2 microns (nanoamoebae?) to 2 mm
Species Identification of all of these groups is very difficult
Flagellates and Amoebae are scarcely studied (there are many species to describe)
Alternative: Morphological groups of soil protozoa are easier to study than species
Ciliates Flagelates
Amoebae
1
2
3
4
41
It is easier to follow up the population changes of the protozoan groups than trying to trace population changes of all the species at once
Question: Does the population of all the soil protozoan groups follow the same tendency during the shift from wet to dry season?
Hypothesis: Amoebae populations will remain high longer (as long as food lasts) since they need no water film for swimming
Porosity
0 20 40 60 80
1
2
3
4
5
6
Sam
plin
g Si
tes
%
Water Holding Capacity, Real and Apparent density
0 2 4 6 8
1
2
3
4
5
6
Ssam
plin
g Si
tes
g/cm3
DRDACC
pH
6 7 8 9
123
456
Sam
plin
g S
ites
values
Conductivity
0 50 100 150 200 250
1
2
3
4
5
6
Sam
plin
g Si
tes
moh
Microbial Nitrogen
0 0.2 0.4 0.6
123456
Sam
plin
g Si
tes
g/kg
Microbial Carbon
0 5 10 15
123456
Sam
plin
g Si
tes
g/kg
Organic Matter
0 2 4 6 8
1
2
3
4
5
6
Sam
plin
g Si
tes
%
Ciliates
0
1
2
3
4
A-00 M-00 J-00 A-00 N-00 J-01 F-01 M-01 A-01 M-01 J-01 j-01 jb-01 A-01 S-01
Month
Log
A B C D E
Nanoflagellates
0
1
2
3
4
5
A-00 M-00 J-00 A-00 N-00 J-01 F-01 M-01 A-01 M-01 J-01 j-01 jb-01 A-01 S-01
Month
Log
A B C D E
Flagellates
0
1
2
3
4
A-00 M-00 J-00 A-00 N-00 J-01 F-01 M-01 A-01 M-01 J-01 j-01 jb-01 A-01 S-01
Month
Log
A B C D E
Amoebae Type 3
0
1
2
3
4
M1 M2 M3 M4 M7 M9 M10 M11 M12 M13 M14 M15 M16 M17 Mx
Month
Log
A B C D E
Amoebae Type 1
0
1
2
3
4
5
A-00 M-00 J-00 A-00 N-00 J-01 F-01 M-01 A-01 M-01 J-01 j-01 jb-01 A-01 S-01
Month
Log
A B C D E
Amoebae Type 4
01234
A-00 M-00 J-00 A-00 N-00 J-01 F-01 M-01 A-01 M-01 J-01 j-01 jb-01 A-01 S-01
Month
Log
A B C D E
Amoebae Type 2
0
1
2
3
4
A-00 M-00 J-00 A-00 N-00 J-01 F-01 M-01 A-01 M-01 J-01 j-01 jb-01 A-01 S-01
Month
Log
A B C D E
The morphological groups of Protozoa had the same population dynamic across the different “environmental layers” of temperature-precipitation, which means the system is stabilized for such conditions along the gradient
However, stabilized doesn’t mean stress-free and the temporal environmental variation may have the effect of diminishing trophicdiversity, represented here by the reduction of type 3 amoebae (that feed mostly on bacteria) and the barely existence of type 4 amoebae (which feed on algae as well)
Amoebae types 1 and 3 follow the same dynamic than the other groups of protozoa. However, the variation observed in amoebae types 2 and 4 would have been masked if counting amoebae as one single group
There is an increased concern about conservation programs for several species of plants, especially cacti, for which many studies are under way taking in account only temperature and precipitation as the main factors for planning and designing areas for conservation
Should Microorganisms be also taken in consideration for planning?
Distribution of Echinocactus platyacanthus f. Grandis in 100 years (scenario +2° C, -10% mm) (Davila et al 2004)
Potential distribution of Cephalocereus columna-trajaniin 100 years (scenario +2° C, -10% mm) (Davila et al
2004)
After all, Microorganisms are also part of the plants’ “environment”
© American Society for Microiology 1995
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