Some results of monitoring (for the period from 1992 to 2005) related to transformations of carbon in agroecosystems of Baikal Siberia (Russia) characterized by unpolluted grey forest soils as well as the soils technogenically polluted with heavy metals are discussed with use the unique approach to integrated assessment of the agroecosystem’s functioning regime. The peculiarities of accumulation of carbon in soil microbial biomass and CO 2 emission during the years differing in climate conditions are demonstrated. Analysis of formation of net-mineralized and (re)immobilized carbon is conducted, their ratio being used for the purpose of assessment of the level of influence upon the agroecosystem. The agroecosystems having technogenically polluted soils are characterized by processes of the soil microbial biomass reduction and by an obvious increase of CO 2 emission into the atmosphere. Negative changes, which are bound up with carbon transformation, are intensified under unfavorable climate conditions. Intensification of processes of carbon net mineralization and, vice versa, lowering the intensity of processes related to carbon (re)immobilization (especially under the effect of soil pollution and climate changes) provoke instability of the agroecosystem and cause formation of a new regime of its functioning.
The negative anthropogenic impact on land ecosystems is known to be bound up not only with technogenic pollution of the environment but also with variations of climate conditions. Dynamic variations of greenhouse gas concentration in the atmosphere are considered to be the main factor, which influence the climate [
Presently, the international scientific community relates the problem to not only technogenic CO2 emission but also to the growth of carbon flow from the anthropogenic transformed ecosystems [
The importance of investigations related to carbon transformation in agroecosystems, which has become especially obvious in recent decades [
The objectives of the present investigation include: 1) revealing the specific properties bound up with carbon transformations and with carbon balance parameters characteristic of the agroecosystems with grey forest soils depending on technogenic pollution and hydrothermal conditions; 2) assessment of the influence of the environmental factors on the formation of the operating regime of agroecosystems and on the possible levels of their loading.
The object of our investigation is represented by the agroecosystems with grey forest soils of Baikal Siberia. According to the norms of geographic zoning, the Irkutsk-Cheremkhovo site (52˚S-55˚S and 100˚E-108˚E) belongs to the East-Sayan Province of the forest-steppe zone, which represents its eastern border of Eurasia, which contacts with the zone East-Siberian permafrost-taiga soils. The geological structure of the territory is repre- sented by Cambrian deposits covered with Jurassic ones. The soils are affected by aero-technogenic pollution from industrial enterprises located along the Trans-Siberian railroad and from the corresponding motorway. The largest contribution is made by power plants (66%) and fuel producing enterprises (12%). The fact that the arable lands are traditionally close to industrially developed districts of Siberia is one of the causes of soil pollution (mainly with heavy metals (HMs)).
The Irkutsk-Cheremkovo forest-steppe is characterized by sharply continental character of the climate. The mean annual air temperature varies from −1˚C to −3˚C. The temperate-severe and snow-deficient winter lasts for over 5 months. The soils get frozen down to the depth of 2 to 2.5 m and thaw out very slowly. The frostless period lasts for 75 to 100 days. The spring is short. It is characterized by unstable weather and recurrence of frosts. The moisture content of the soils depends on the autumn reserves of moisture. The summer is short. The mean July temperature is 17.2˚C to 18.2˚C. The total of the temperatures over 10˚C is small (1595˚). Furthermore, autumn and summer frosts are possible. The annual precipitation varies from 270 to 386 mm, the maximum being characteristic of the warm period (80 to 90 percent of the annual total). The spring and early summer are often arid. The autumn period is short and characterized by unstable weather with the precipitation in the form of rain or sometimes snow. By mid October, the temperature abruptly goes down. The restricted agro-climate resources allow us to consider the scrutinized territory as a zone of risk agriculture.
The results of generalized analysis of 1) the agro-climate conditions during the recent decades and 2) the expected climate changes in some parts of Russia have been described in the materials prepared by the Russian Federal Department of Hydrometeorology and Environmental Monitoring [
The cogency of the arguments in favor of the anthropogenic nature of warming may be confirmed by the fact of indirect (mediated) negative influence of technogenic soil pollution. The role of soils in stabilizing the atmosphere gas content is well known [
The Methodology of our investigations is represented by systems analysis and comparative analysis. The scrutinized agroecosystem is considered as an experimental model of interacting components (soil-microorgan- isms-plants-atmosphere), which form a system integrated by flows of carbon. As a complete and open system, which is considered as having both spatial-temporal and functional structures, it exists at the expense of coordinated interaction of its components, owing to processes of metabolism and energy exchange inside the system and with the environment.
The regime of functioning and the level of influence upon the agroecosystem were assessed integrally, on the basis of an elaborated and probated approach [
The state of the scrutinized agroecosystem was also assessed in terms of the load exerted upon it. For example, in case of some increase in the external effect (load), the regime of functioning was changing, while being graded from stress to resistance or adaptation exhaustion or else repression. The ecological load upon the agroe- cosystem for each of the regimes was assessed, respectively, as “admissible”, “maximum admissible”, “critical”, “inadmissible”.
The regularities related to formation of carbon flows (the ratio NM:RI), which are dependent on variations of the external conditions, have been used for the purpose of a) integrated assessment of the functioning regime (the state) of the agroecosystem and b) normalization of the load. A scale of estimating criteria has been developed [
The field experiments have been conducted on grey forest soils either unpolluted or polluted, the sources of pollutants being atmospheric discharges of Sayanskchemplast, Ltd., i.e. mainly heavy metals (HMs). The unpolluted soil of the stationary field, which belongs to Siberian Institute of Plant Physiology and Biochemistry, Siberian Branch, Russian Academy of Sciences, was the check soil sample in the experiments. The influence of hydrothermal conditions upon transformation of carbon during the vegetation period was analyzed in 1994, 2001, 2004, which differed from the average norm for the region during the period 1961-1990. The results were compared also to the average data for 14 years of monitoring. The integrated assessment of the state of the agroecosystem was conducted during all the years of the monitoring.
These field experiments were conducted in accordance with the technique elaborated earlier [
The properties of the soils and the content of HMs in them were determined before the beginning of the field experiments. The experiments on the fallow and on the wheat crops (after the fallow) presumed the conjugated monitoring of 1) the content carbon in the soil microbial biomass (Cmicr), 2) CO2 emission from the soils (the step being 7 to 14 days from April to October). The values of Cmicr and C-CO2 (g/m2) averaged for the vegetation period were computed on account of the density of the plough layer structure. The content of HMs in the soil was measured by the method of atomic absorption [Perkin-Elmer 503]. Cmicr was determined by the rehydration method [
Some of the agrochemical characteristics of the scrutinized gray forest soils are presented in
Variations of the hydrothermal conditions during the vegetation period (May to August) and in different years of the monitoring were considered with respect to the “climatic norm” (for the basic period from 1961 to 1990 [
Soil | Humus, % | Ntot, % | рНKCl | S, mg-equiv/100g of soil |
---|---|---|---|---|
Grey forest (В) clay loam, unpolluted | 4.8 | 0.29 | 5.8 | 27.2 |
Grey forest (В/HMs) clay loam, polluted with heavy metals | 2.9 | 0.16 | 5.8 | 22.8 |
Soil | Cd | Cr | Cu | Hg | Pb | Zh | Mn |
---|---|---|---|---|---|---|---|
В | 0.2 | 40 | 25 | 0.04 | 22 | 51 | 870 |
В/HMs | 0.4 | 51 | 22 | 0.2 | 20 | 85 | 1000 |
Year | Precipitation totals, mm (May-August) | Total daily average temperature per May-August, ˚С | Precipitation totals per July, mm | Average air temperature per July, ˚С | HTC (June-August) |
---|---|---|---|---|---|
“Climatic norm”* | 220 | 1300 | 83 | 18 | 1.5 |
1994 | 273 | 1290 | 90 | 19 | 1.5 |
2001 | 367 | 1945 | 221 | 18 | 1.9 |
2004 | 297 | 1469 | 34 | 18 | 2.0 |
*“Climatic norm” represents average data for 1961-1990 years [
close to the “climatic norm”. The highest amount of precipitation was registered in July, 2001. In 1994, the hydrothermal coefficient (HTC) characterizing the degree of humidification in summer period was closer to the “norm”. The values of HTC during 2001 and 2004 years were above the “norm”.
The dependence of carbon transformation in land ecosystems on climate conditions is known. There exists also a feedback, i.e. the intensity of transformation processes favors the growth in the concentration of greenhouse gases in the atmosphere, what influences the climate changes. In this connection, both the emission of CO2 from soils and its dependence on technogenic pollution and hydrothermal factors are of substantial scientific interest. The correlation analysis of the monitoring data has shown that the dependence of the CO2 emission rate on the air temperature was positive (r = 0.37 - 0.46), while the dependence on the humidity of the soils was negative (r = −0.41 - −0.47), furthermore, it was independently of the pollution.
As obvious from
According to the data for many years, the total C-CO2 (g/m2) emission during the vegetation period (110 days) reached the level of 70% to 75% of the total annual emission. This may be due to peculiar properties of the local climate: late thawing the soil out in spring; sharp lowering the soil temperature and its fast freezing in autumn. The computations have shown that during the frostless period the loss of carbon owing to CO2 emission on the unpolluted soil in the fallow was 2.8%, and for the wheat crops it was 2.5%, while for the polluted soil the values were larger (respectively, 4.4% and 3.5% of the total carbon content in the soil).
The content of Cmicr in the soil was also dependent on the hydrothermal factors (see
It is known, under extreme conditions, the strategy of microorganisms is oriented sooner adaptation rather than intensification of growth [
Soil | Treatment | Cmicr. | С-СО2 | С-СО2/Cmicr. (NM:RI) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1994 | 2001 | 2004 | Average long-term data | 1994 | 2001 | 2004 | Average long-term data | 1994 | 2001 | 2004 | Average long-term data | ||
В | Follow | 103 | 99 | 77 | 93 ± 6 | 168 | 162 | 143 | 141 ± 7 | 1.6 | 1.6 | 1.9 | 1.5 |
Wheat | 91 | 106 | 80 | 94 ± 7 | 214 (143) | 192 (128) | 173 (116) | 172 ± 7 (115) | 1.6 | 1.2 | 1.5 | 1.5 | |
В/HMs | Follow | 66 | 61 | 48 | 57 ± 2 | 153 | 132 | 128 | 125 ± 6 | 2.3 | 2.2 | 2.6 | 2.2 |
Wheat | 60 | 55 | 47 | 63 ± 4 | 209 (139) | 196 (130) | 185 (123) | 172 ± 6 (115) | 2.3 | 2.4 | 2.7 | 1.8 |
Note: In brackets the data excluding the root respiration.
of our monitoring, which was approximately the same for both the fallow and the crops, but was higher for the polluted soil than for the unpolluted one (respectively, 0.81 and 0.55 mg/g·h), what confirmed the same fact. We revealed that the content of Cmicr was lower for the soil polluted with HMs, while the expenses of carbon needed for respiration (C-CO2) grew. Respectively, the flow of net mineralized carbon (N-M) was larger than the flow of (re)immobilized (RI) carbon, especially in 2001 and 2004 unfavorable with respect to hydrothermal conditions (see
Therefore, both of the factors—pollution of the soil with HMs and hydrothermal conditions—negatively influence the soil properties (while including the dynamics of organic matter) and its fertility, what is the cause of direct and mediated impacts the process of carbon transformation in the agroecosystem. Although, in connection with existence of multifactor interrelations in such a complex open dynamic system, it is hardly ever possible to unequivocally define the roles of each of these factors. So, the estimate of behavior and the forecast of the agroecosystem’s state under variations of internal and external factors represents a complex problem, whose solution necessitates nonstandard analytical approaches. One of such approaches at the ecosystem level may be approach presuming integrated assessment of the ecological load upon the agroecosystem.
In order to assess the level of influences upon the agroecosystem we employed such an ratio as NM:RI (see
Dynamic variations of the ratio NM:RI obvious from
Functioning regime | Level of load | Criteria | |
---|---|---|---|
RI:М, %* | N-M:RI* | ||
Homeostasis | Norm | 50 ± 5 | 0.8 - 1.2 |
Stress | Admissible | 45 - 35 | 1.2 - 2.0 |
Resistance | Maximum admissible | 35 - 25 | 2.0 - 3.0 |
Adaptation exhaustion | Critical | 25 - 15 | 3.0 - 5.0 |
Repression | Inadmissible | <10 - 15 | >5.0 |
Note: *Legends in the text.
abrupt change of the regime in 2001, 2003 and 2004 gives evidence of instability of agroecosystems with polluted soils. So, the load corresponds to the “maximum admissible load”, and the regime is closer to the adaptation exhaustion (i.e. the “critical” load).
Instability of agroecosystems located upon polluted soils leads to the unpredictable character of their behavior, in particular, under simultaneous effect of the technogenic pollution and the climate factors. The integrated effect of the latter influences the process of formation of carbon flows. These flows may (from our viewpoint) be the direct and reverse feedbacks, which determine the functioning regime of the agroecosystem as an open and dynamically non-equilibrium system. The flow of (re)immobilized carbon (“return from the output”, or the feedback) involves newly formed substances, which are formed mainly in the processes of microbiological transformations. According to the theoretical provisions, these newly formed substances may be considered as “dissipative structures”, which favor the maintenance of metabolic carbon reserves in the soil, this carbon participating in metabolic processes in the agroecosystem. We assume, the process of formation of the (re)immobi- lized carbon flow performs the role of the auto-regulation mechanism, which is needed for maintaining the dynamic equilibrium in the agroecosystem [
It is known that any ecological investigation necessitates substantial time. The problem of behavior of the agroecosystem in response to climate variations and/or to the increase of the level of technigenic pollution cannot be considered as solved even under definite environmental conditions. Practical solution of ecological problems necessitates an optimal strategy. Our experimental material is good enough for conducting systems analysis and may be the basis for mathematical modeling.
The present paper discussed the results of authors’ investigations of carbon transformations in agroecosystems on account of natural-climate factors. These investigations were bound up with the conjugate assessment of the microbial biomass in soils and CO2 emission into the atmosphere. These were conducted on the agroecosystems having grey forest soils (both unpolluted and polluted with heavy metals), which belonged to the territory of Baikal Siberia. A unique technique of integrated assessment of both the agroecosystem’s functioning regime and the level of loads upon the agroecosystem was applied. In the process of long-term field experiments the authors discovered the following. The agroecosystems having technogenically polluted soils are characterized by pro- cesses of the soil microbial biomass reduction and by an obvious increase of CO2 emission into the atmosphere. Negative changes, which are bound up with carbon transformation, are intensified under unfavorable climate conditions. Intensification of processes of carbon net mineralization and, vice versa, lowering the intensity of processes related to carbon (re)immobilization (especially under the effect of soil pollution and climate changes) provoke instability of the agroecosystem and cause formation of a new regime of its functioning. The integrated assessment gives evidence of some increase of the ecological load upon the agroecosystem (which ranges from a “maximum admissible” level load to a “critical” one) under the simultaneous effect of unfavorable climate factors and technogenic pollution of the soil.
The investigations related to the project have been conducted with the support of grants of Russian Foundation for Basic Research (03-04-49450-а, 05-04-97206 r_Baikal_a, 14-45-04040r_Siberia_a).