Impact of deforestation on soil physicochemical characteristics,microbial biomass and microbial activity of tropical soil

The study dealt with the assessment of the impact of deforestation on tropical soil through a comparative analysis of physicochemical and microbiological parameters of natural forest and a deforested barren site. With significant decline in clay, texturally the soil of the deforested barren site was observed to be different from that of natural forest. Bulk density and porosity data revealed structural deterioration of deforested barren soil. The soil hydrological regime was also adversely affected by the deforestation. Levels of soil organic carbon, total nitrogen, microbial biomass C, N and microfungal biomass also exhibited significant decline in deforested site. Analysis of microbial respiratory quotient (q CO₂) was also observed to be impaired in the deforested site. Copyright © 2001 John Wiley & Sons, Ltd.     

Interactions between microclimatic variables and the soil microbial biomass

Summary Soil moisture, temperature, microbial substrate-induced respiration and basal respiration were monitored in two plots in an agricultural field from April 30 to September 25, 1987, and in a further two plots from May 26 to August 27, 1988. An attempt to relate biological variables to microclimatic variables was made through the use of correlation analysis. The microbial substrate-induced and basal respiration were both strongly positively correlated with the soil moisture content, and to a lesser extent positively related to soil temperature, especially when partial correlation was used to control for variation in soil moisture. Short-term changes in substrate-induced and basal respiration were correlated with changes in soil moisture but were largely independent of soil temperature. The ratio of basal to substrate-induced respiration (indicating the respiration: biomass ratio and therefore ecosystem stability or persistence) was negatively associated with the soil moisture content and in some instances with soil temperature when partial correlation analysis (correcting for soil moisture variation) was used. This suggests that the climatic conditions which contributed to the lowest ecosystem stability were low temperature, low moisture conditions.     

Dynamics of soil microbial biomass C, N and P in disturbed and undisturbed stands of a tropical wet-evergreen forest

To understand the spatial and temporal dynamics of soil microbial biomass and its role in soil organic matter and nutrient flux in disturbed tropical wet-evergreen forests, we determined soil microbial biomass C, N and P at two soil depths (0–15 and 15–30 cm), along a disturbance gradient in Arunachal Pradesh, northeastern India. Disturbance resulted in considerable increase in air temperature and light intensity in the forest and decline in the soil nutrients concentration, which affected the growth of microbial populations and soil microbial biomass. There were significant correlations between bacterial and fungal populations and microbial biomass C, N and P. Soil microbial population was higher in the undisturbed (UD) forest stand than the disturbed forest stands during post-monsoon and less during rainy season due to heavy rainfall. Greater demand for nutrients by plants during rainy season limited the availability of nutrients to soil microbes and therefore, low microbial biomass C, N and P. Microbial biomass was negatively correlated with soil temperature and pH in all the forest stands. However, there were significant positive relationships among microbial biomass C, N and P. Percentage contribution of microbial C to soil organic C was higher in UD forest, whereas percentage contribution of microbial biomass N and P to total N and total P was higher in the moderately disturbed site than in the highly disturbed (HD) site. These results reveal that the nutrient retention by soil microbial biomass was greater in the selective logged stand and would help in the regeneration of the forest upon protection. On the other hand, the cultivated site (HD) that had the lowest labile fractions of soil organic matter may recover at a slower phase. Further, minimum and maximum microbial biomass C, N and P during rainy and winter seasons suggest the synchronization between nutrient demand for plant growth and nutrient retention in microbial biomass that would help in ecosystem recovery following disturbance.     

Microbial biomass and activity at various soil depths in a Brazilian oxisol after two decades of no-tillage and conventional tillage

The advantages of no-tillage (NT) over conventional tillage (CT) systems in improving soil quality are generally accepted, resulting from benefits in soil physical, chemical and biological properties. However, most evaluations have only considered surface soil layers (maximum 0-30 cm depth), and values have not been corrected to account for changes in soil bulk density. The objective of this study was to estimate a more realistic contribution of the NT to soil fertility, by evaluating C- and N-related soil parameters at the 0-60 cm depth in a 20-year experiment established on an oxisol in southern Brazil, with a soybean (summer)/wheat (winter) crop succession under NT and CT. At full flowering of the soybean crop, soil samples were collected at depths of 0-5, 5-10, 10-20, 20-30, 30-40, 40-50 and 50-60 cm. For the overall 0-60 cm layer, correcting the values for soil bulk density, NT significantly increased the stocks of C (18%) and N (16%) and microbial biomass C (35%) and N (23%) (MB-C and -N) in comparison to CT. Microbial basal respiration and microbial quotient (qMic) were also significantly increased under NT. When compared with CT, NT resulted in gains of 0.8 Mg C ha⁻¹ yr⁻¹ (67% of which was in the 0-30 cm layer) and 70 kg N ha⁻¹ yr⁻¹ (73% in the 0-30 cm layer). In the 0-5-cm layer, MB-C was 82% higher with NT than with CT; in addition, the 0-30 cm layer accumulated 70% of the MB-C with NT, and 58% with CT. In comparison to CT, the NT system resulted in total inputs of microbial C and N estimated at 38 kg C ha⁻¹ yr⁻¹ and 1.5 kg N ha⁻¹ yr⁻¹, respectively. Apparently, N was the key nutrient limiting C and N stocks, and since adoption of NT resulted in a significant increase of N in soils which were deficient in N, efforts should be focused on increasing N inputs on NT systems.     

The spatial distribution of soil microbial biomass in a permanent row crop

The effects of soil texture (silt loam or sandy loam) and cultivation practice (green manure) on the size and spatial distribution of the microbial biomass and its metabolic quotient were investigated in soils planted with a permanent row crop of hops (Humulus lupulus). The soil both between and in the plant rows was sampled at three different depths (0–10, 10–20, and 20–30 cm). The silt loam had a higher overall microbial biomass C concentration (260 g g^-1) than the sandy loam (185 g g^-1), whereas the sandy loam had a higher (3.1 g CO₂-C mg^-1 microbial Ch^-1) metabolic quotient than the silt loam (2.6 g CO₂-C mg^-1 microbial C h^-1), on average over depth (0–30 cm) and over all treatments. There was a sharp decrease in the microbial biomass with increasing depth for all plots. However, this was more pronounced in the silt loam than in the sandy loam. There was no distinct influence of sampling depth on the metabolic quotient. The microbial biomass was considerably higher in the rows than between the rows, especially in the silt loam plots. There was no significant difference between plots without green manure and plots with green manure for either the microbial biomass or the metabolic quotient.     

Influence of vegetation types and soil properties on microbial biomass carbon and metabolic quotients in temperate volcanic and tropical forest soils

Abstract

There is limited knowledge about the differences in carbon availability and metabolic quotients in temperate volcanic and tropical forest soils, and associated key influencing factors. Forest soils at various depths were sampled under a tropical rainforest and adjacent tea garden after clear-cutting, and under three temperate forests developed on a volcanic soil (e.g. Betula ermanii and Picea jezoensis, and Pinus koraiensis mainly mixed with Tilia amurensis, Fraxinus mandshurica and Quercus mongolica), to study soil microbial biomass carbon (MBC) concentration and metabolic quotients (qCO₂, CO₂-C/biomass-C). Soil MBC concentration and CO₂ evolution were measured over 7-day and 21-day incubation periods, respectively, along with the main properties of the soils. On the basis of soil total C, both CO₂ evolution and MBC concentrations appeared to decrease with increasing soil depth. There was a maximal qCO₂ in the 0–2.5 cm soil under each forest stand. Neither incubation period affected the CO₂ evolution rates, but incubation period did induce a significant difference in MBC concentration and qCO₂ in tea soil and Picea jezoensis forest soil. The conversion of a tropical rainforest to a tea garden reduced the CO₂ evolution and increased the qCO₂ in soil. Comparing temperate and tropical forests, the results show that both Pinus koraiensis mixed with hardwoods and rainforest soil at less than 20 cm depth had a larger MBC concentration relative to soil total C and a lower qCO₂ during both incubation periods, suggesting that microbial communities in both soils were more efficient in carbon use than communities in the other soils. Factor and regression analysis indicated that the 85% variation of the qCO₂ in forest soils could be explained by soil properties such as the C:N ratio and the concentration of water soluble organic C and exchangeable Al (P < 0.001). The qCO₂ values in forest soils, particularly in temperate volcanic forest soils, decreased with an increasing Al/C ratio in water-soluble organic matter. Soil properties, such as exchangeable Ca, Mg and Al and water-soluble organic C:N ratio, were associated with the variation of MBC. Thus, MBC concentrations and qCO₂ of the soils are useful soil parameters for studying soil C availability and microbial utilization efficiency under temperate and tropical forests.     

Consequences of forest conversion to pasture and fallow on soil microbial biomass and activity in the eastern Amazon

The main change in soil use in Amazonia is, after slash and burn deforestation followed by annual crops, the establishment of pastures. This conversion of forest to pasture induces changes in the carbon cycle, modifies soil organic matter content and quality and affects biological activity responsible for numerous biochemical and biological processes essential to ecosystem functioning. The aim of this study was to assess changes in microbial biomass and activity in fallow and pasture soils after forest clearing. The study was performed in smallholder settlements of eastern Brazilian Amazonia. Soil samples from depths of 0–2, 2–5 and 5–10 cm were gathered in native forest, fallow land 8–10 yr old and pastures with ages of 1–2, 5–7 and 10–12 yr. Once fallow began, soil microbial biomass and its activity showed little change. In contrast, conversion to pasture modified soil microbial functioning significantly. Microbial biomass and its basal respiration decreased markedly after pasture establishment and continued to decrease with pasture age. The increase in metabolic quotient in the first years of pasture indicated a disturbance in soil functioning. Our study confirms that microbial biomass is a sensitive indicator of soil disturbance caused by land‐use change.     

Effect of temperature on soil microbial biomass and its metabolic quotient in situ under different tillage systems

Variations in the microbial biomass and the in situ metabolic quotient (qCO₂) due to climatic conditions were determined in a typical soil from the Argentine Rolling Pampa. Microbial C was evaluated by fumigation-incubation and qCO₂ was calculated using soil respiration in the field. An inverse relationship between microbial C and soil temperature was fitted to a model (r ²=0.90, P=0.01). No significant association with the soil water content was detected because the soil was generally near field capacity and thus water availability did not limited microbial growth and activity. Values of qCO₂ increased (r ²=0.89, P=0.01) as the result of metabolic activatìon, likely induced by a higher maintenance energy requirement at high temperatures. The highest values of qCO₂ were obtained when microbial C was the lowest, which was attributed to self consumption of microbial C in the presence of high temperatures. Consequently, microbial C was generally higher (P=0.05) in winter than in summer. Therefore, when microbial C is used as an index of soil biological activity, the influence of temperature should be taken into account.     

Size and activity of the soil microbial biomass under grass and arable management

 The effects of 5 years of continuous grass/clover (Cont grass/clover) or grass (Cont grass) pasture or 5 years of annual grass under conventional (Ann grass CT) or zero tillage (Ann grass ZT) were compared with that of 5 years of continuous barley (LT arable) on a site which had previously been under arable crops for 11 years. For added comparison, a long-term grass/clover pasture site (LT past) nearby was also sampled. Soil organic C (C_org) content followed the order LT arable=Ann grass CT<Ann grass ZT<Cont grass=Cont grass/clover<LTpast. Trends with treatment for microbial biomass C (C_mic), basal respiration, flourescein diacetate (FDA) hydrolytic activity, arginine ammonification rate and the activities of dehydrogenase, protease, histidase, acid phosphatase and arylsulphatase enzymes were broadly similar to those for C_org. For C_mic, FDA hydrolysis, arginine ammonification and the activities of histidase, acid phosphatase and arylsulphatase, the percentage increase caused by 5 years of continuous pasture (in comparison with LT arable) was 100–180%, which was considerably greater than that for organic C (i.e. 60%). The microbial metabolic quotient (qCO₂) was higher for the two treatments which were mouldboard ploughed annually (LT arable and Ann grass CT) than for the undisturbed sites. At the undisturbed sites, C_org declined markedly with depth (0–15 cm) and there was a similar stratification in the size and activity of C_mic and enzyme activity. The microbial quotient (C_mic/C_org) declined with depth whilst qCO₂ tended to increase, reflecting a decrease in the proportion of readily available substrate with depth. Received: 7 July 1998     

The effect of converting tropical native savanna to Eucalyptus grandis forest on soil microbial biomass

The aim of this work was to investigate the effect of converting native savanna to Eucalyptus grandis forest on soil microbial biomass in tropics. Soil samples were collected from three sites: undisturbed native savanna (savanna), the site of a 1‐year‐old E. grandis forest (1 y), and the site of a 2‐year‐old E. grandis forest (2 y). Soil microbial biomass C (MBC), basal respiration, substrate induced respiration (SIR), soil organic carbon (SOC), microbial, and respiratory quotients were evaluated in soil samples collected from 0–20 cm depth. One year converted forest caused a significant reduction in MBC, SIR, and microbial quotient (about 70, 65 and 75 per cent, respectively). However, after 2 years of E. grandis forest growth, there was recovery of these variables. Soil basal respiration and respiratory quotient were significantly higher in 1 y forest (about 4 and 14 times, respectively) than in savanna. The results showed a significant decrease, after 2 years, in soil respiration and respiratory quotient, suggesting a recovery of soil microorganisms as time passes. In the short term, our results showed negative changes in soil microbial biomass following the conversion of native savanna to E. grandis. Copyright © 2010 John Wiley & Sons, Ltd.     

Near-infrared characteristics of forest humus are correlated with soil respiration and microbial biomass in burnt soil

Near-infrared spectroscopy and soil physicochemical determinations (pH_H2O, organic matter content, total C content, NH _inf4 ^sup+ , total N content, cation-exchange capacity, and base saturation) were used to characterize fire-or wood ash-treated humus samples. The spectroscopic and the soil physicochemical analysis data from the humus samples were used separately to explain observed variations in soil respiration and microbial biomass C by partial least-square regression. The first regression component obtained from the physicochemical and spectroscopic characterization explained 10–12% and 60–80% of the biological variation, respectively. This suggests that information on organic material collected from near-infrared spectra is very useful for explaining biological variations in forest humus.     

Examination of microbial biomass in beech forest moder profiles

Microbial biomass C, ATP, and substrate-induced respiration were measured in the organic layers and the mineral A horizon of three beech forest soils with moder humus differing in Ca and Mg supply. Analyses of variance showed that horizon-specific differences explained most of the variance in the three microbial parameters. All three were significantly interrelated, with Spearman rank correlation coefficients of between 0.86 and 0.93. However, differences in the decline of these parameters with depth led to horizon-specific differences in their ratios. Thus, the ratios were not markedly interrelated. The mean ATP: microbial C ratio was 5.2 mol ATP g^-1 C in the L 2 layer, 19.5 in the F layers, and 9.6 in the H and A horizons. The ratio of substrate-induced respiration to microbial C varied between 39.3 and 82.2 O₂h^-1 g^-1 C in the F1 layers and between 5.3 and 32.1 l in the other layers. It is concluded that the use of different parameters can help to analyze both horizonand site-specific differences in microbial performance.     

Long-term tillage effects on the distribution patterns of microbial biomass and activities within soil aggregates

The effects of tillage on the interaction between soil structure and microbial biomass vary spatially and temporally for different soil types and cropping systems. We assessed the relationship between soil structure induced by tillage and soil microbial activity at the level of soil aggregates. To this aim, organic C (OC), microbial biomass C (MBC) and soil respiration were measured in water-stable aggregates (WSA) of different sizes from a subtropical rice soil under two tillage systems: conventional tillage (CT) and a combination of ridge with no-tillage (RNT). Soil (0–20 cm) was fractionated into six different aggregate sizes (> 4.76, 4.76–2.0, 2.0–1.0, 1.0–0.25, 0.25–0.053, and < 0.053 mm in diameter). Soil OC, MBC, respiration rate, and metabolic quotient were heterogeneously distributed among soil aggregates while the patterns of aggregate-size distribution were similar among properties, regardless of tillage system. The content of OC within WSA followed the sequence: medium-aggregates (1.0–0.25 mm and 1.0–2.0 mm) > macro-aggregates (4.76–2.0 mm) > micro-aggregates (0.25–0.053 mm) > large aggregates (> 4.76 mm) > silt + clay fractions (< 0.053 mm). The highest levels of MBC were associated with the 1.0–2.0 mm aggregate size class. Significant differences in respiration rates were also observed among different sizes of WSA, and the highest respiration rate was associated with 1.0–2.0 mm aggregates. The C_mic/C_org was greatest for the large-macroaggregates regardless of tillage regimes. This ratio decreased with aggregate size to 1.0–0.25 mm. Soil metabolic quotient (qCO₂) ranged from 3.6 to 17.7 mg CO₂ g^− 1 MBC h^− 1. The distribution pattern of soil microbial biomass and activity was governed by aggregate size, whereas the tillage effect was not significant at the aggregate scale. Tillage regimes that contribute to greater aggregation, such as RNT, also improved soil microbial activity. Soil OC, MBC and respiration rate were at their highest levels for 1.0–2.0 mm aggregates, suggesting a higher biological activity at this aggregate size for the present ecosystem.     

Influence of leaf litter types on microbial functions and nutrient status of soil: Ecological suitability of forest trees for afforestation in tropical laterite wastelands

The impact of forest tree leaf litters on microbial activity and nutrient status of red laterite soil was tested for the ecological suitability of Cassia siamea, Shorea robusta, Acacia auriculiformes and Dalbergia sissoo, which are typically used for afforestation of wastelands in eastern India. The objectives were to compare seasonal variation in soil enzyme activity in 30-years old afforested sites, and to study nutrient status and microbial biomass and function during short-term in-situ incubation of litter in decomposition pits. In afforested soils, enzyme activities significantly varied between litters and seasons. All enzyme activity except invertase dominated in the soils containing Dalbergia and Cassia litters compared to the others. The seasonal effect was enzyme-dependent, with amylase and cellulase reaching peaks during the rainy season but invertase activity showed a reverse trend with lowest values in rainy season, except in Acacia soil, and protease activity was lowest in the soil containing Cassia and Dalbergia during the rainy season. Dehydrogenase activity was negligible in the soils containing Shorea and Acacia, but remained high with respect to Dalbergia and Cassia during all seasons. The decomposition pit study showed significant increase of soil nutrients with respect to litter types and intervals, except with respect to electrical conductivity. Cassia and Dalbergia litters enabled notable increase of soil nutrients than Shorea and Acacia. The soil enzyme activity, in general, increased with duration of litter decay, but microbial biomass C (MBC) decreased over time except in Shorea. Therefore, the enzyme rates normalized to the MBC indicated inverse relations for all enzymes, except in the soil containing Shorea. A positive relationship existed between MBC and soil respiration in Cassia, Acacia and Dalbergia. Analysis of variance revealed main effects of litter types for increasing protease, MBC and CO₂ output, and a main effect of intervals for enhancing enzymes other than cellulase. Rates of soil respiration were greater in soils contain Cassia and Dalbergia, and showed significant differences between litters and between intervals. All enzymes were significantly correlated with electrical conductivity, organic carbon and available phosphorus contents, and all enzymes except invertase were correlated with nitrate concentrations. The acidic soil pH did not affect enzyme activities, and soil nutrients exerted only weak effect on MBC and respiration. Our study showed that leaf litters of Cassia and Dalbergia trees improved the nutrient status and microbial activity in soil more so than Shorea and Acacia litters, and therefore, afforestation using Cassia and Dalbergia trees may be particularly suitable for soil restoration in tropical laterite wastelands.     

Salinity and sodicity effects on respiration and microbial biomass of soil

An understanding of the effects of salinity and sodicity on soil carbon (C) stocks and fluxes is critical in environmental management, as the areal extents of salinity and sodicity are predicted to increase. The effects of salinity and sodicity on the soil microbial biomass (SMB) and soil respiration were assessed over 12weeks under controlled conditions by subjecting disturbed soil samples from a vegetated soil profile to leaching with one of six salt solutions; a combination of low-salinity (0.5dSm⁻¹), mid-salinity (10dSm⁻¹), or high-salinity (30dSm⁻¹), with either low-sodicity (sodium adsorption ratio, SAR, 1), or high-sodicity (SAR 30) to give six treatments: control (low-salinity low-sodicity); low-salinity high-sodicity; mid-salinity low-sodicity; mid-salinity high-sodicity; high-salinity low-sodicity; and high-salinity high-sodicity. Soil respiration rate was highest (56–80mg CO₂-C kg⁻¹ soil) in the low-salinity treatments and lowest (1–5mg CO₂-C kg⁻¹ soil) in the mid-salinity treatments, while the SMB was highest in the high-salinity treatments (459–565mg kg⁻¹ soil) and lowest in the low-salinity treatments (158–172mg kg⁻¹ soil). This was attributed to increased substrate availability with high salt concentrations through either increased dispersion of soil aggregates or dissolution or hydrolysis of soil organic matter, which may offset some of the stresses placed on the microbial population from high salt concentrations. The apparent disparity in trends in respiration and the SMB may be due to an induced shift in the microbial population, from one dominated by more active microorganisms to one dominated by less active microorganisms.     

镁碱化盐土微生物生物量和土壤基础呼吸

通过测定甘肃河西走廊疏勒河中游昌马冲积扇缘不同镁碱度条件下10个采样点30个土样的化学性质和生物化学性质指标,研究了电导率和镁碱度对土壤微生物生物量及其基础呼吸的影响。结果表明:微生物生物量碳(氮)和土壤基础呼吸与电导率、镁碱度和Mg2+/Ca2+之间显著负相关,表明盐度和镁碱度对土壤微生物群落有显著的抑制作用,而且盐度的抑制作用比镁碱度更大;微生物代谢熵(qCO2)和电导率、镁碱度、Mg2+/Ca2+之间为正相关关系,也说明镁碱化盐土对土壤微生物而言是一种严重的胁迫环境。     

红壤丘陵区人工林恢复措施对土壤酶活性和微生物学性质的影响

我国红壤丘陵区水土流失较严重。本文研究人工林对土壤(0～20和20～40 cm)酶活性和微生物学性质的短期(13～14年)影响。土壤转化酶、脲酶、多酚氧化酶活性在次生天然林和湿地松樟树混交林中高于其他林分。次生天然林和湿地松樟树混交林土壤微生物生物量和土壤呼吸值较大、有机碳活性较强、土壤微生物基质利用效率较高。因此,短期影响下,湿地松樟树混交林较之针叶纯林和针叶混交林可改善土壤生化强度和微生物活性。     

不同农田生态系统土壤微生物生物量碳的变化研究

试验研究不同农田生态系统土壤微生物生物量碳的变化结果表明,长期单施N、P肥处理对土壤有机碳和微生物生物量碳的影响不明显,施有机肥处理土壤微生物生物量碳及微生物生物量碳/有机碳值均高于其他施肥处理,轮作中引入豆科作物或豆科连作均对土壤微生物生物量碳的积累有显著作用。     

Remnant tree effects on soil microbial carbon and nitrogen in tropical seasonal pasture in western Mexico

Selection of plant species for agro-silvo-pastoral or ecological reclamation programs must be based on a deeper knowledge of the existing relationships between plant species and soil nutrient dynamics in each ecosystem. We evaluated the seasonal pattern of soil microbial carbon (C) and nitrogen (N) under two remnant tree species (Caesalpinia eriostachys and Cordia elaeagnoides) in a tropical seasonal pasture dominated by Panicum maximum in western Mexico. Soil samples were taken from under two arboreal species and P. maximum in rainy and dry seasons. The soil C:N ratio was higher under P. maximum [17] than under both tree species [15]. The soil microbial C (Cm) was higher under C. elaeagnoides than under C. eriostachys and P. maximum. Magnitude and direction of effect of the two remnant tree species on soil biogeochemistry changed with seasonal rainfall. The interaction of plant species and seasonal rainfall did have an effect on soil microbial N (Nm). Soil samples from April and July had the lowest microbial N concentrations under the three plant species, increasing four fold in September under C. elaeagnoides and P. maximum. At the end of the wet season, C. elaeagnoides clearly had the highest Nm values (130 μg N g⁻¹), suggesting that this tree species has a higher capacity to protect soil N within microbial biomass than C. eriostachys, because under C. elaeagnoides the soil had more organic matter due a higher input of litter and root chemical quality. Therefore, C. elaeagnoides would be the best plant species to implement in agro-silvo-pastoral programs or ecological reclamation of TDF pastures.