Download Document

1.3.3. Soil biota
There is a positive correlation between soil fertility, on the one side, and diversity and abundance
of the soil biota, on the other side. Thus, the number of soil invertebrates varies between 110-135
ex/m2 in the rich chernozems in the North of Moldova, and 42-64 ex/m2 in the South; where the
soils are, generally, less fertile. The same tendency has been recorded for fungi (53,000-68,000
and 15,000-22,000 per one gram of soil, respectively).
During the last decades, the anthropic activity resulted in a substantial deterioration of the soil
biota. Both diversity and total biomass of the soil organisms decreased. For example, the
Sorenson diversity index for invertebrates diminished to 0.582, and presently only five species
from the Lumbricidae family can be found in Moldovan soils compared to nine species 40 years
ago. This was accompanied by a succession of species that resulted in slowing down the natural
processes of accumulation of organic substances in soils. The activity of microbiological
processes of humus mineralization has increased while the biomass and activity of saprophagous
invertebrates, contributing to humus accumulation, fell sharply. According to last data, the
activity of saprophytes decreased 4-10 times, and the coefficient of humus accumulation, 1.7-3.3
times. Besides, the fixation of atmospheric nitrogen in soils decreased sharply. In the same time,
the number of toxic species (Penicillium purpurogenum, Aspergillus ustus, Penicillium
funiculosum etc.) increased dramatically. All these reduce the biological productivity and
ecological stability of the soils.
Data on several indicators of the anthropic impact on the status of soil organisms are presented in
Table 1.14.
Table 1.14
Dynamics of soil organisms in different types of chernozems subject to agriculture use
Year
Humus
Microorganisms
Invertebrates
content,
Chernozem
%
Ammoni ActinoFungi
Total
Biomass of
Subtype
ficators micetes
number
Lumbricidae
2
million/g soil
thousand/
org/m
g/m2
g soil
Typical
1958
5.18
5.0
3.4
39
227
25.0
1994
4.00
4.3
2.2
31
135
17.1
Levigated
1958
4.24
3.6
1.8
50
88
13.0
1994
3.30
3.1
1.4
25
76
8.3
Common
1958
4.30
5.5
5.6
60
72
10.0
1994
3.30
3.3
2.5
15
62
6.7
Carbonated
1958
3.70
3.2
4.3
14
47
8.0
1994
2.92
2.2
2.0
30
44
5.8
After 1994, there were no systematic investigations on the microbiological diversity of the soil
biota. Under such circumstances, indirect methods of qualitative and quantitative evaluation of
the status of soil organisms like carbon balances can be applied. The emissions of CO2 are an
indirect indicator of the soil biota status. The factors causing carbon losses from the topsoil have
been intensified during the last decades while the inputs of carbon – mainly from vegetal
residues and organic fertilizer - have diminished (Table 1.15). In general, a positive carbon
balance sustains higher biomass and diversity while a negative carbon balance causes the
suppression of soil organisms.
Table 1.15
Emissions of carbon dioxide from arable soils in the Republic of Moldova
Carbon inputs
Anul
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
Vegetal
residues
699
653
497
644
352
478
350
553
397
516
Organic
fertilizers
242
215
132
77
35
37
20
-
Carbon outputs*, thousand tons
Total
941
868
629
721
387
515
370
553
397
516
Inorganic
carbon
40
40
31
10
4
5
6
-
Orga
nic
carbon
6
5
3
2
1
1
0,5
-
Symbiotic
carbon
12
10
11
5
3
3
1
2
2
3
Car- Carbon
bon
from
from humus
vegetal
rezidues
17
18
14
16
11
14
11
15
12
15
77
72
52
104
58
82
62
102
75
98
Carbon balance
CO2 emissions
,000
tons
(Gg)
t/ha
1629
998
1479
1299
2323
1649
2099
1,18
0,81
1,16
1,01
1,77
1,57
1,61
Carbon
export,
total
Carbon
outputs
,000
tons
(Gg)
t/ha
152
145
111
137
77
105
80
119
87
113
862
789
570
1165
659
918
724
1886
845
1129
79
79
59
-444
-272
-403
-354
-633
-448
-613
0,050
0,051
0,043
-0,321
-0,221
-0,316
-0,277
-0,483
-0,348
-0,440
* Calculated according to the C:N ratio and the amount of N released as a result of biochemical degradation of
organic matter from the soil.
Erosion processes have a deleterious effect on the soil organisms. In the low, moderate and
highly eroded soils, their number and biomass may be reduced by 20-30%, 30-60% and over
60%, respectively. In eroded soils the biodiversity suffers a sharp reduction, many species
disappear. Per total, the changes mentioned above lead to more intense dehumification, loss of
soil texture and soil self-purification capacity. Therefore, the recovery of the invertebrates and
microorganisms diversity and functions is a precondition for resolving the problem of soil
conservation and enhancement of soil fertility.
The excessive use of mineral fertilizers herbicides and pesticides is just another important factor
that led to essential changes in the soil biota structure and functions. The herbicides are an
essential source of soil pollution with mutagenic substances. The indicator microorganisms from
the soils processed with herbicides show a mutagenic level increased by 10-20 times compared
to the level of spontaneous mutations. The presence of pesticides with mutagenic potential leads
to changes in the populations of soil microorganisms. The microflora is now less abundant and
diverse, the species communities have been restructured and presently are less stable. The
communities of nitrogen fixing bacteria were particularly affected by the use of herbicides. This
hampered the nitrogen cycle in soils and limited soil productivity. The rehabilitation of the soil
biota is possible through more active introduction of organic agriculture approach and through
reduction of agrochemicals use.