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To eliminate the negative effect of soil contamination with heavy metals on plant growth and crop yield, different methods and techniques are the subject of discussion and study. In this study, we aimed to evaluate the effect of secondary pulp and paper-mill sludge application to soil on the response of the main physiological processes such as the growth, photosynthesis, and respiration of lettuce (Lactuca sativa L.) plants to soil contamination with Pb. For the pot experiment, Pb was added to sandy loam soil at concentrations of 0, 50, and 250 mg Pb(NO3)2 per kg of the soil, and secondary sludge was added to a 0, 20, or 40% sludge solution during each plant watering. The Pb-mediated change in plant biomass allocation, decrease in the photosynthetic rate, increase in leaf respiration rate, and the degree of light inhibition of respiration were closely associated with increases in both root and shoot Pb content. For the Pb-free soil condition, secondary sludge application contributed to the allocation of plant biomass towards a greater accumulation in the shoots than in the roots. Although stomatal opening was not affected by either Pb or sludge, sludge application increased photosynthetic CO2 assimilation regardless of soil Pb content, which was associated with an increase in the electron-transport rate and carboxylase activity of Rubisco. Soil contamination with Pb significantly increased the ratio of respiration to photosynthesis, reflecting a shift in the carbon balance toward carbon losses in the leaves, but sludge application modified the coupling between the processes with a decrease in the proportion of respiratory carbon losses. The sludge-mediated recovery of the physiological processes of L. sativa reflected an increase in plant tolerance to soil contamination with heavy metals, the formation of which is associated with plant and soil adjustments initiated by secondary sludge application.

The absence of an externally-imposed 24 h light/dark cycle in closed plant production systems allows setting the light environmental parameters in unconventional ways. Innovative lighting modes for energy-saving, high-quality, and yield production are widely discussed. This study aimed to evaluate the effects of the light/dark cycles of 16/8 h (control) and 24/12 h, 48/24 h, 96/48 h, 120/60 h (unconventional cycles) based on the same total light amount, and continuous lighting (360/0 h) on plant performance of some Solanaceae species. Responses of eggplant (Solanum melongena L.), sweet pepper (Capsicum annuum L.), tobacco (Nicotiana tabacum L.), and tomato (Solanum lycopersicum L.) plants to extended light/dark cycles and continuous lighting were studied under controlled climate conditions. Plants with two true leaves were exposed to different light/dark cycles for 15 days. Light intensity was 250 µmol m−2 s−1 PPFD, provided by light-emitting diodes (LEDs). After the experiment, tomato, sweet pepper, and eggplant transplants were planted in a greenhouse and grown under identical conditions of natural photoperiod for the estimation of the after-effect of light treatments on fruit yield. Extended light/dark cycles of 24/12 h, 48/24 h, 96/48 h, 120/60 h, and 360/0 h affected growth, development, photosynthetic pigment content, anthocyanin and flavonoid content, and redox state of plants. Effects varied with plant species and length of light/dark cycles. In some cases, measured parameters improved with increasing light/dark periods despite the same total sum of illumination received by plants. Treatments of tomato and pepper transplants with 48/24 h, 96/48 h, and 120/60 h resulted in higher fruit yield compared to conventional 16/8 h photoperiod. The conclusion was made that extended light/dark cycles can result in increased light use efficiency compared to conventional photoperiod and, therefore, reduced product cost, but for practical application, the effects need to be further explored for individual plant species or even cultivars.

A positive effect of pulp and paper mill sludges as a rich source of organic substrates on soil properties was previously found for some types of sludge and soil. In this study, the effect of secondary pulp and paper sludge on water characteristics and thermal properties of Retisol, as well as the growth parameters of lettuce (Lactuca sativa L.), was tested on the basis of a pot experiment when watering plants with a 20 or 40% sludge solution. The sludge application enhanced plant growth with an increase in biomass accumulation of 21 and 53%, respectively, for 20 and 40% sludge treatments. When the sludge dose was increased from 0 to 40%, the number of leaves increased by 25%, and the leaf mass per area value increased by 42%. Due to the accumulation of more biomass in the shoots than in the roots, sludge causes a change in the allocation of plant biomass. A significant effect of the sludge application on soil particle and microaggregate sized compositions, as well as on the saturated soil hydraulic conductivity, was not found in this study. However, fitted soil water retention curves showed an increased soil water content in sludge-treated soil at all water content values exceeding field capacity. Secondary sludge application led to an increase in the saturated water content from 0.50 to 0.56 cm3 cm−3. The 40% sludge solution increased soil thermal conductivity from 0.92 to 0.98 W m−1 K−1 under saturated water content and from 0.83 to 0.92 W m−1 K−1 under field capacity. The thermal conductivity was higher in the sludge-treated than untreated soil due to a more pronounced positive effect of increased saturated water content than the negative effect of the increased organic matter content on heat transfer. The positive impact of secondary sludge application on both plant growth parameters and physical properties of Retisol, such as increased soil water-holding capacity and thermal conductivity coefficient confirms the possibility of using it to improve soil characteristics and plant productivity.

The application of pulp and paper mill sludge to agricultural soils is commonly considered as a strategy to improve soil properties, promote plant growth, and reduce the demand for costly chemical fertilization. The aim of this study was to evaluate if sodium lignosulfonate (sLS), one of the sludges of pulp production, may affect the biomass production, the respiration (R) and net CO2 assimilation rate (An) at the leaf level, and the content and accumulation of trace elements in the leaves of cucumbers grown under a sufficient nutrient supply or soil nutrient deficit. A pot culture experiment was conducted using sLS application rates of 0, 1.0, 2.5, 5.0, and 10 vol% to sandy loam soil. The decline in nutrient availability caused an increase in the R/An ratio and dramatically depressed biomass accumulation. The leaf Fe, Ni, Cr, Co, Al, and Pb contents were lower under low nutrient availability than under sufficient nutrient supply. Although sLS was not very effective in lessening the negative effect of nutrient deficiency on biomass accumulation, it reduced respiratory carbon losses and cell membrane permeability in the leaves of cucumbers grown under nutrient deficit. The reduction in the toxic level of leaf Mn in seedlings grown under sufficient nutrient availability and the toxic level of leaf Fe under a nutrient deficit might also be considered as a positive effect of the sLS application to sandy soil.

Contamination of agricultural soils with heavy metal leads to a decrease in the crop quality and yield, as well as increases in public health risks. In this study, we aimed to evaluate the impact of soil contamination with lead (Pb) on the growth, photosynthesis, respiration, and coupling between these physiological processes, as well as temporal dynamics of Pb uptake and accumulation by lettuce (Lactuca sativa L.) plants. For this 46-day pot experiment, Pb(NO3)2 was mixed with loamy Retisol soil with the rate of 0, 50, and 250 mg kg−1. No significant differences in plant biomass accumulation were found between plants grown on Pb-free and Pb-rich soil, but root-weight ratio, root-to-shoot weight ratio, and leaf area were lower, and the number of leaves and leaf weight per unit area were significantly higher in plants grown on soil contaminated with Pb than in their counterparts grown on Pb-free soil. The concentration of Pb in plant root and shoot followed the increase in soil Pb, with Pb content in the roots being higher than in the shoots. Soil Pb decreased chlorophyll content, net CO2 assimilation rate and photosynthetic light use efficiency, but caused an increase in the leaf respiration rate regardless of whether respiration was performed in the light or in darkness. Increased ratio of respiration to photosynthesis reflects the shift in the carbon balance of lettuce plants toward carbon losses under stress conditions of soil contamination with Pb.

The possibility of using brown algae in agriculture as an alternative source of nutrients is currentlyunder study and discussion. Our study aimed to evaluate the effect of F. vesiculosus on the agrochemical properties of four soil types: Retisol loamy sand soil, Retisolloam, Retisol clay, and Histosol. The F. vesiculosus waste was added to soil samples at a rate of 0, 0.5, 1.0, 2.0, 5.0, and 10 wt%. The brown algaewaste application significantly decreased soil acidity in the substrates of all soil types, with the larger increasesfor Retisol loamy sand and Retisol clay than for Retisol loam and Histosol. The application of F. vesiculosus waste products increased the C content in all soil types except Histosol. The N and P content in soil substrates were not significantly affected by algaewaste application regardless of soil type. This study showed that the effect of F. vesiculosus waste application varies depending on the soil type, with the strongest impact on Retisol clay and the lowest on Histosol.

For agricultural soils with low natural fertility, the possibility of using rock powders as an alternative source of nutrients and/or improver of soil physical parameters is under discussion and study. Shungite rocks, carbon-bearing volcanic sedimentary rock, are characterized by a high content of carbon and nutrients. This study aimed to evaluate whether shungite application to Umbric Podzols may affect leaf and root mitochondrial respiratory pathways, and the leaf response to temperature change. A pot culture experiment was conducted with Allium cepa L. seedlings, using soil shungite concentrations of 0, 5, 10, and 20 g kg−1 and two soil water regimes: well-watered (WW) and drying-wetting (DW) cycles. Soil water deficit increased total respiration (Vt) of onion leaves, but not roots, under low (13 °C) and high (33 °C) measurement temperature. Shungite application affected leaf Vt only at 13 °C: it increased the Vt rate under WW and decreased one under DW. An increase in the measurement temperature to 33 °C enhanced the sensitivity of leaf respiration to the inhibitor of the alternative respiratory pathway (salicylhydroxamic acid, SHAM). Shungite application increased the contribution of SHAM-sensitive pathway to the leaf Vt rate under WW, but not under the DW regime, regardless of the leaf temperature. In contrast to the SHAM-resistant pathway, the temperature sensitivity of the SHAM-sensitive rate decreased following the decrease in soil water availability. Shungite application increased the temperature sensitivity of both SHAM-sensitive and SHAM-resistant pathways under DW, and significantly decreased these parameters under WW. In summary, the decrease in temperature sensitivity of alternative SHAM-sensitive respiratory pathway with a decrease of soil water availability or shungite-related decrease of both SHAM-sensitive and SHAM-resistant leaf respiration may play an important role in enhancing the resistance of plant respiration to stress temperature.

We studied the response of light-loving (Quadrille, Courage, Hasbulat) and shade-tolerant (Berendey, Girlyanda, Rafael) hybrids of cucumber (Cucumis sativus L.) to a daily 2 h temperature drop (DROP) to 9°C at the end of the night or at the beginning of the light period. All DROP-treated plants irrespective of their demand for light had a slower growth rate and were more compact than control plants. Light had a significant modifying effect on the plant response to DROP, and although similarity was observed among the hybrids’ responses to this type of low temperature treatment, there was also a certain varietal (ecotypic) specificity. The most pronounced differences between light-loving and shade-tolerant hybrids were related to their ability to adapt to low temperatures. In particular, light-loving hybrids treated by DROP in the light had higher ability to increase chilling tolerance. Besides, in shade-tolerant hybrids, in contrast to the light-loving ones, DROP given in the end of the night did not lead to a decrease in chlorophyll content, while DROP given at the beginning of the light period reduced chlorophyll content in all hybrids. Long-term effect of DROP was manifested in shade-tolerant hybrids only as lower yields(especially in terms of early yields, which were decreased by 50–65 %) in plants treated by DROP at the beginning of the light period.

We studied the apparent quantum yield of photosynthesis in the leaves of cucumber (Cucumis sativus L.) plants exposed to daily short-term (2 h) temperature drops to 12°C in the darkness (in the end of the night) or light (at the beginning of the day). In order to assess the effect of leaf age on their response to DROP, plants were exposed to DROP treatments when the first leaf was non-mature (in the exponential growth phase) or mature, or during the entire period of leaf expansion. It was shown that DROP causes a decrease in the efficiency with which light energy is utilized in photosynthesis regardless of leaf age. It is suggested that changes in the apparent quantum yield under the influence of DROP treatments are associated with changes in the pigment composition. Unlike leaf age, the presence of light during DROP treatments significantly affected the degree of changes in apparent quantum yield of photosynthesis. In particular, DROP in the light caused significantly greater reduction in the apparent quantum yield than DROP in the darkness. Moreover, DROP in the light reduced not only the apparent quantum yield, but also the rate of photosynthesis. DROP in the darkness did not affect the rate of photosynthesis. It is assumed that the decrease in the light use efficiency in DROPtreated plants results from the initiation of plant defense response to low temperatures that allow avoiding photosynthetic apparatus damage.

To reduce the use of commercial conventional inorganic fertilizers, the possibility of using pulp and paper industry wastes in agriculture as an alternative source of nutrients is recently under study and discussion. This work aimed to evaluate the effect of sodium lignosulfonate application to soil on photosynthetic leaf nutrient (N, P, K, Ca, Mg, Fe, Mn, and Na) and water use efficiency. A pot culture experiment was conducted with cucumber seedlings, using five lignosulfonate concentrations (0, 1, 2.5, 5, and 10 vol. %) in sandy soil under sufficient or low nutrient availability for plants. The impact of nutrient availability on the plants’ physiological traits was stronger than the lignosulfonate impact. Under sufficient nutrient availability, the lignosulfonate application resulted in decreased photosynthetic N, P, K, Ca, Mg, Fe, and Na use efficiency. Cucumber growth and development, and photosynthetic nutrient, water, and light use efficiency were significantly reduced with a nutrient deficiency. The sodium lignosulfonate application was not successful in eliminating the negative effects of nutrient deficit on cucumber seedlings.

The review presents own and published data on the effects of a daily temperature drop (DROP) of different intensity and duration on plants. It is concluded that the effect of a temperature drop on morphological, physiological and biochemical characteristics of chilling-sensitive and chilling-tolerant plants depends to a large extent on the absolute value of the lower temperature used for DROP treatments. The morphogenetic effect of DROP treatments, measured by changes in linear growth parameters, increases with the lowering of the temperature used for DROP treatments, while the plant response, estimated by other physiological and biochemical parameters (biomass accumulation, chlorophyll content, photosynthetic activity, water relations indices, chilling tolerance) depends more on whether the temperature falls below the critical level, resulting in a plant stress response. The response of plants to DROP treatments depends more on the absolute value to which the temperature is dropped and on the duration of the chill (since in this case the stress response is triggered in the plant) than on the temperature gradient. The duration of the temperature drop becomes more important when the temperature is lowered to values beyond the optimum range. The optimum temperature ranges for different processes (characteristics) (for example, plant height or time until flowering) can vary significantly, determining the nature and effectiveness of DROP treatments with certain parameters in relation to various processes (characteristics). In most cases, the differences in plant response to DROP treatments of different duration are not determined by the usual dose-effect relationship, since beside the duration, the mode of temperature exposure (single long-term or daily short-term) plays a significant role. In addition, the effectiveness of the DROP treatments of a given intensity and duration for practical purposes in horticulture and floriculture is largely species- (variety-) specific.

We studied the effect of short-term (2 hours at the end of the night) daily temperature reductions to 12 °C (DROP treatment) on the activity of antioxidant (AO) enzymes in cucumber (Cucumis sativus L.) leaves of various ages. Plants were DROP-treated for 6 days during the exponential growth of the second true leaf (DROP 1) or when the second leaf was mature (DROP 2). DROP 3 plants were DROP-treated for 12 days during the DROP 1+DROP 2 period. In mature leaves (DROP 2) DROP treatment did not cause any changes in the activity of AO enzymes or lipid peroxidation rates, as estimated by the content of malondialdehyde (MDA). In young leaves (DROP 1 and DROP 3) DROP treatment reduced the activity of superoxide dismutase and ascorbate peroxidase and induced a short-term increase followed by a decrease in the activity of catalase and guaiacol-dependent peroxidase. Chilling tolerance was higher in all DROP-treated plants compared to untreated plants. Thus, we found that a daily short-term temperature drop (DROP) modified the activity of AO enzymes in young leaves, but did not affect the activity of the studied enzymes in mature leaves. Changes in the activity of AO enzymes did not correlate with changes in chilling tolerance. Apparently, the increased antioxidant activity in low temperature-treated plants described in the literature for chilling-sensitive species is not involved in cucumber response to temperature DROP, and some other mechanism is responsible for the higher chilling tolerance in DROP-treated plants. The differential response of young and mature leaves points to some developmental controls in the induction of plant adaptations to short-term chilling.

En México, en particular en el estado de Michoacán, el estudio sobre la génesis, morfología y función de los suelos hidromórficos no ha sido explorado de forma suficiente, pese a contar con grandes extensiones de humedales continentales, como la zona vadosa del lago de Pátzcuaro. Se estudiaron dos humedales representativos de la costa del lago de Pátzcuaro, Michoacán: uno de ellos saturado permanentemente, con desarrollo de gleysoles, y un humedal con inundación periódica, fluvisoles, desarrollados en una gran planicie aluvial. Los resultados indican la presencia de un gleysol háplico (colúvico, éutrico) (WRB, 2006), de coloración pardo oscuro, con cantidades moderadas de carbono orgánico (0.87% promedio), arcilloso > 30%, de estructura predominante de poliedros subangulares y prismas con segregación de sesquióxidos ferromanganosos, sobresaliendo los hiporrevestimientos de óxidos de fierro, y presencia de restos de ostrácodos en la mayor parte del perfil. Destaca una discontinuidad litológica. Por su parte, en el humedal aluvial se presenta un fluvisol háplico (hiperhúmico, éutrico) (WRB, 2006), un suelo con matriz de color pardo grisáceo, con altos contenidos de materia orgánica en todo el perfil (> 7 %) y restos de ostrácodos. Son suelos con alta saturación de bases (> 50 %). Tres zonas de humedad son bien definidas al interior de los suelos: una zona baja de endosaturación permanente, una zona intermedia producto de la capilaridad, y una zona de secado-humedecimiento alternado en los epipedones

In this laboratory experiment we measured soil gas diffusion coefficients (D) on undisturbed cores of anthropogenic chinampas soils and tested the validity of some classical gas diffusivity models for predicting the ratio of D to the gas diffusion coefficient in free air (D0) as a function of the soil air-filled porosity (?). The A1 horizon (0-7 cm) of chinampas soils had the highest gas diffusivity and a linear relationship between D/D0 and ?, and thus, the Penman model gave an adequate prediction for this sub-horizon. The Millington-Quirk model was similar to the D/D0 at all values of ? for the A2 sub-horizon (7-18 cm) and at ? < 0.5 cm3 cm-3 for the A3 (18-30 cm) and A4 (30-50 cm) sub-horizons. Gas diffusivities in chinampas soils were lower than in mineral soils, as predicted by D/D0(?) models, likely due to the high content of soil organic carbon. The predictive models could be used for the evaluation of greenhouse gases emission from chinampas soil.En este experimento de laboratorio medimos los coeficientes de difusión de gas (D) en núcleos inalterados de suelos antropogénicos de chinampas y probamos la validez de algunos modelos clásicos de difusión de gases para predecir la relación de D al coeficiente de difusión de gas en aire libre (Do) como una función de la porosidad del suelo llena de aire (?). El horizonte A1 (0-7cm) de los suelos de chinampas alcanzó la difusividad de gas más alta y una relación lineal entre D/Do y ?, y así, el modelo de Penman mostró una predicción adecuada para este subhorizonte. El modelo de Millington-Quick tuvo un D/Do similar en todo el rango de ? para el subhorizonte A2 (7-18 cm) y a la ? < 0,5 cm3 cm-3 para los subhorizontes A3 (18-30 cm) y A4 (30-50 cm). La difusividad de gas en suelos de chinampas fue menor que en suelos minerales, como predijeron los modelos D/Do(?), debido probablemente al contenido elevado de carbono orgánico del suelo. Los modelos predictivos podrían ser utilizados para la valoración de la emisión de gases de efecto de invernadero de los suelos de chinampas.Neste ensaio laboratorial, mediram-se os coeficientes de difusão de gás do solo (D) em "cores" não perturbados de solos antropogénicos de chinampas e testou-se a validade de alguns modelos clássicos de difusividade de gás para prever a relação de D com o coeficiente de difusão do gás ao ar livre (D0) como função da porosidade de arejamento do solo (?). O horizonte A1 (0-7 cm) dos solos chinampas apresentaram a difusão de gás mais elevada e uma relação linear entre D/D0 e ? e como tal, o modelo de Penman forneceu uma previsão adequada para este sub-horizonte. O modelo de Millington-Quirk foi semelhante ao de D/D0 para todos os valores de ? para o sub-horizonte A2 (7-18 cm) e para ? < 0.5 cm3 cm-3 para os sub-horizontes A3 (18-30 cm) e A4 (30-50 cm). As difusividades de gás em solos chinampas foram inferiores em solos minerais, como previsto pelos modelos D/D0(?) provavelmente devido ao alto teor de carbono orgânico do solo. Os modelos preditivos poderão vir a ser usados para a avaliação da emissão de gases de efeito estufa do solo chinampas.

We studied microbial-associated C?2 production in anthropogenic chinampas soils. The soils were constructed by the accumulation of materials such as organic matter and loamy lacustrine sediments in Pre-Hispanic cultures in Mexico. To study the temperature sensitivity of C?2 production related to soil depth, moisture and oxygen availability, soil samples were collected at depths of 0-7, 7-18, 18-30, 30-40 and 40-50 cm. The soil samples were incubated under aerobic and anaerobic conditions at controlled temperatures (-5, 0, 5, 10, 20, 30 °C) and soil moistures of 10, 30, 60 and 90% water-filled pore space. For all the soil depths, incubation temperatures and soil moistures, the mean rate of aerobic CO2 production was 58.0 mg CO2 kg-1 d-1 and that of anaerobic CO2 production 31.2 mg CO2 kg-1 d-1, with the highest rate found in the soil samples collected at a depth of 0-7 cm. A decrease in soil organic carbon content inhibited CO2 production more under anaerobic than aerobic conditions. The dependence of aerobic ??2 production on soil moisture increased at what constituted both unusually high and low temperatures for the study area. Since the response of ??2 production to temperature was lower under anaerobic than aerobic conditions, the increase in soil moisture content led to a decrease in the temperature sensitivity of ??2 production. The response of microbial activity to other factors may be modified under what constitutes the limiting conditions for any of the factors considered, as follows: (i) when anaerobiosis increases in the soil, the limiting effect of substrate availability on microbial activity increases; (ii) the CO2 production rate becomes more dependent on soil moisture under temperature stress; (iii) the sensitivity of CO2 production to temperature is highest under drought stress.En este trabajo estudiamos la producción de CO2 asociada a la actividad de los microorganismos en suelos antropogénicos de chinampa, construidos por las culturas Pre-Hispánicas en México mediante la acumulación de materia orgánica, sedimentos lacustres limosos o por diferentes materiales utilizados para consolidarlos en islotes separados por un sistema de canales. Se tomaron muestras de suelo a las profundidades de 0-7, 7-18, 18-30, 30-40 y 40-50 cm para evaluar la sensibilidad a la temperatura de la producción de CO2 y su variación en relación con la profundidad del suelo, la humedad y la disponibilidad de oxígeno. Se incubaron en condiciones aerobias y anaerobias a temperatura controlada (-5, 0, 5, 10, 20 y 30 °C) y a humedad controlada de 10, 30, 60 y 90% de las condiciones de saturación en agua del espacio poroso del suelo. Para todas las profundidades del suelo, temperaturas de incubación y humedad del suelo, la velocidad promedio de producción de CO2 fue de 58,0 mg CO2 kg-1 d-1 en condiciones aerobias y de 31,2 mg CO2 kg-1 d-1en condiciones anaerobias, obteniéndose la mayor producción de CO2 en las muestras de suelo de la capa de 0-7 cm de profundidad. La disminución en el contenido de carbono orgánico del suelo inhibió la producción de CO2 asociada a la actividad de los microorganismos del suelo con mayor intensidad bajo condiciones anaerobias que aerobias. A temperaturas inusualmente bajas o altas para el área de estudio, la dependencia de la producción aerobia de CO2 con respecto a la humedad del suelo aumentó. Puesto que la respuesta de la producción de CO2 a la temperatura fue menor bajo condiciones anaerobias que aerobias, el aumento en el contenido de humedad del suelo condujo a la disminución de la sensibilidad a la temperatura de la producción del CO2. En condiciones limitantes de cualquier factor, la respuesta de la actividad microbiana a otros factores puede modificarse como se muestra a continuación: (i) el aumento de la anaerobiosis en el suelo aumenta el efecto limitante de la disponibilidad de sustrato sobre la actividad microbiana; (ii) bajo estrés de temperatura, la velocidad de producción de CO2 se hace mas dependiente de la humedad del suelo; (iii) bajo el estrés de sequía, la sensibilidad de la producción de CO2 a la temperatura es máxima.Este trabalho estuda a produção de CO2 associada à actividade de microrganismos em solos de Chinampa antropogénica, construídos por culturas Pre-Hispânicas do México através da acumulação de matéria orgânica, sedimentos lacustres limosos ou diferentes materiais usados para a sua consolidação, em ilhotas separadas por um sistema de canais. Colheram-se amostras de terra às profundidades de 0-7, 7-18, 18-30, 30-40 y 40-50 cm para avaliar a sensibilidade da produção de CO2 à temperatura e a sua variação em função da profundidade do solo, da humidade e disponibilidade de oxigénio. As amostras de terra foram incubadas em condições aeróbias e anaeróbias a temperatura controlada (- 5, 0, 5, 10, 20 e 30 °C) e humidade controlada a 10, 30, 60 e 90% das condições de saturação de água no solo. Para todas as profundidades do solo, temperaturas de incubação e teores de humidade, a velocidade média da produção de CO2 foi de 58,0 mg CO2 kg-1 d-1 em condições aeróbias e 31,2 mg CO2 kg-1 d-1, em condições anaeróbias, tendo-se obtido a maior produção de CO2 nas amostras de solo colhidas na camada de 0-7 cm de profundidade. A diminuição do teor de carbono orgânico do solo inibiu a produção de CO2 associada à actividade dos microrganismos no solo com maior intensidade em condições anaeróbias do que em condições aeróbias. Para a área de estudo, e para valores de temperatura anormalmente altos ou baixos aumentou a dependência da produção aeróbia de CO2 com a humidade do solo. Uma vez que a resposta da produção de CO2 à temperatura foi menor em condições anaeróbias do que aeróbias, o aumento do teor de humidade do solo conduziu a uma diminuição da sensibilidade à temperatura da produção de CO2. Sob condições limite de qualquer um dos factores, a resposta da actividade microbiana aos outros factores pode ser modificada conforme se refere a seguir: (i) o aumento de anaerobiose no solo aumenta o efeito limitante da disponibilidade do substrato sobre a actividade microbiana; (ii) em condições stress de temperatura, a velocidade da produção de CO2 torna-se mais dependente da humidade do solo; (iii) em condições stress de seca, é máxima a sensibilidade à temperatura da produção de CO2.