Potential effects of management practices on nitrogen nutrition and long-term productivity of western hemlock stands

The FORCYTE-10 computer model, developed by J.P. Kimmins and K. Scoullar for Douglas-fir forests in British Columbia, was modified to simulate growth and nutrient cycling of coastal western hemlock stands. Initial calibration indicated that predicted yield was extremely sensitive to the rate of mineralization of soil organic matter (SOM), variation in SOM C:N ratio with site quality, the soil extractable NO₃⁻:NH₄⁺ ratio, and the decomposition rate and N mineralization pattern of large and medium-size roots and woody debris. The predictions suggested that yield and SOM remain stable under a management system consisting of six successive 90-year rotations. More intensive utilization (e.g., shorter rotations, whole-tree harvesting and commercial thinning) causes depletion of soil and forest floor nitrogen and a small decline in site productivity in later rotations.     

Effects of elevated nitrogen deposition on soil microbial biomass carbon in major subtropical forests of southern China

2003

Wallenstein M D.McNulty S.Fernandez I J.Boggs J Schlesinger W H Nitrogen fertilization decreases forest soil fungal and bacterial biomass in three long-term experiments [其它论文] 2006

Wang X F.Li S Y.Bai K J.Kuang T Y Influence of doubled CO2 on plant growth and soil microbial biomass C and N 1998(12)

Xue J H.Mo J M.Li J.Li D J The short-term response of soil microorganism number to simulated nitrogen deposition 2007(02)

Yao W H.Yu Z Y The nutrient content of throughfall inside the artificial forests on downland 1995

Yi Z G.Yi W M.Zhou L X.Wang X M Soil microbial biomass of the main forests in Dinghushan Biosphere Reserve 2005(05)

Zhou G Y.Yan J H The influence of region atmospheric precipitation characteristics and its element inputs on the existence and development of Dinghushan forest ecosystems [其它论文] -Acta Ecologica Sinica2001

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Carbon, nitrogen, organic phosphorus, microbial biomass and N mineralization in soils under cacao agroforestry systems in Bahia, Brazil

Large amounts of plant litter deposited in cacao agroforestry systems play a key role in nutrient cycling. Organic matter, nitrogen and phosphorus cycling and microbial biomass were investigated in cacao agroforestry systems on Latosols and Cambisols in Bahia, Brazil. The objective of this study was to characterize the microbial C and N, mineralizable N and organic P in two soil orders under three types of cacao agroforestry systems and an adjacent natural forest in Bahia, Brazil and also to evaluate the relationship between P fractions, microbial biomass and mineralized N with other soil attributes. Overall, the average stocks of organic C, total N and total organic P across all systems for 0?C50?cm soil depth were 89,072, 8,838 and 790?kg?ha^?1, respectively. At this soil depth the average stock of labile organic P was 55.5?kg?ha^?1. For 0?C10?cm soil depth, there were large amounts of microbial biomass C (mean of 286?kg?ha^?1), microbial biomass N (mean of 168?kg?ha^?1) and mineralizable N (mean of 79?kg?ha^?1). Organic P (total and labile) was negatively related to organic C, reflecting that the dynamics of organic P in these cacao agroforestry systems are not directly associated with organic C dynamics in soils, in contrast to the dynamics of N. Furthermore, the amounts of soil microbial biomass, mineralizable N, and organic P could be relevant for cacao nutrition, considering the low amount of N and P exported in cacao seeds.     

Comparison of two coniferous plantations in central Japan with respect to forest productivity, growth phenology and soil nitrogen dynamics

Japanese cypress (Chamaecyparis obtusa Endl.) and Japanese cedar (Cryptomeria japonica D. Don) are common species for plantation forestry in Japan. Cypress is conventionally planted on sites of low fertility whereas for cedar high fertility sites are used. Objectives of this study were to compare the productivities of cypress and cedar plantations grown on adjacent sites where common properties of soils, such as pH values and C and N contents, were similar, and to relate the N cycling at their site with productivities. The stem diameter of trees, aboveground litter production and fine root biomass were measured as indices of forest productivity. Parameters of N cycling included pools of total N and mineral N (ammonium + nitrate), annual N leaching, and potentially mineralizable N. The radial stem increment of the two tree species was similar. However, cedar site had higher total basal area and annual basal increment than cypress site reflecting higher tree density on the cedar site. Aboveground litter, fine root biomass, soil organic matter, and N turnover were higher on the cedar site than on the cypress site. However, litter production and fine root biomass per unit basal area was greater at the cypress site. Phenological pattern of stem growth and periodical litter production were similar for both species during the study period (1992–2000), but showed distinct annual variations caused by the fluctuation in the ambient temperature and precipitation. Mineral N content and the N mineralization potential were greater on the cedar site, indicating greater N availability and higher total tree productivity at the cedar site than those at the cypress site. When provided with more space in the canopy to expand more needles and in the soil to develop more fine roots to exploit sufficient resources, the individual cypress trees have the potential to grow faster. On fertile site and at lower tree density, thicker logs of cypress might be yielded.     

Carbon fractions as indicators of organic matter dynamics in chestnut orchards under different soil management practices

Several studies have emphasized the negative impact of the conventional soil management (CT) system on productivity and sustainability of chestnut orchards (Castanea sativa Mill.) when compared to no-tillage with grass cover (NT). However, scarce information is available regarding the effects of these soil management systems on soil organic matter (SOM) dynamics and soil quality. SOM or soil organic carbon is a key component of soil quality and has different fractions with different lability, namely, organic C (POC), active C (AC) and hot-water extractable carbon (HWC). These are considered as indicators of changes in management-induced soil quality. Thus, a study was carried out to evaluate the effects of NT and CT systems applied in the chestnut orchards on: (i) total amount of soil organic C (TOC), including C from both organic and mineral layers; (ii) soil organic C concentration of mineral horizons (OC); (iii) labile soil organic fractions (POC, AC, HWC); (iv) and soil mineral-associated C. The study was developed in two 30-year old chestnut orchards located in Northeast Portugal, that were kept under different soil management systems (NT or CT) during the preceding 17 years. Soil samples were taken at 0–10 and 10–20 cm soil depth. No significant differences in OC concentration were observed between NT and CT, while TOC was significantly higher in NT than in CT (22.54 and 12.17 Mg/ha or 34.16 and 22.90 Mg/ha, considering the organic layer plus mineral layers at 0–10 and 0–20 cm depth (set of two depths). The NT practice led to significantly higher concentration of labile C fractions (POC, AC and HWC) than CT at 0–10 cm soil depth. These results indicate that measurement of labile soil organic C fractions, such as POC, AC and HWC, may provide a sensitive and consistent indication of changes in soil C and SOM dynamics in response to soil management practices. Overall, NT seems to ensure better soil quality than CT in chestnut orchards under Mediterranean climate conditions.     

Changes in soil physicochemical and microbial properties along elevation gradients in two forest soils

The effects of the interaction between tree species composition and altitude on soil microbial properties are poorly understood. In this study, soil samples (0–20?cm) were collected in August 2011 from Betula platyphylla and Picea crassifolia forests along two different altitudinal gradients. Soil microbial activity and biomass were measured using Biolog-ECO plates and phospholipid fatty acid analysis. Both of the forest soils were characterized by a significantly lower soil pH (p?p?相似文献   

Characteristics of soil microbial biomass and community composition in Pinus yunnanensis var. Tenuifolia secondary forests

Pinus yunnanensis var. Tenuifolia is an important species of timber and grease in southern China, but the characteristics of the soil microbial community in P. yunnanensis var. natural secondary forests are still poorly understood. Using a fumigation-extraction method and phospholipid fatty acid (PLFA) analysis, we study microbial biomass and community composition in the topsoil (0–10 cm) of three types of secondary forests (PYI, PYII, PYIII) dominated by P. yunnanensis var. to varing degrees. Microbial biomass carbon and nitrogen, total PLFA, and PLFA contents of bacterial, fungal, and arbuscular mycorrhizal fungi were significantly lower in PYI than PYII or PYIII, and there were significant differences in the monounsaturated/saturated fatty acid ratio among the tested forests. Principal component analysis indicated that the soil microbial community structure of the tested forests differed significantly. The changes in soil microbial biomass and community composition were positively correlated with soil water content, pH, organic matter (SOM), total nitrogen (TN), and total phosphorus. Season did not significantly affect the soil microbial community structure, but significantly affected soil microbial biomass, SOM, and TN, which were higher in the dry season than in the wet season.     

The effect of understory removal on microclimate and soil properties in two subtropical lumber plantations

Understory vegetation is an important component in forest ecosystems. However, the effects of understory on soil properties in subtropical forests are not fully understood. We thus conducted an experimental manipulative study in two young fast-growing plantations—Eucalyptus urophylla and Acacia crassicarpa—in southern China, by removing understory vegetation in both plantations, to estimate the effects of understory vegetation on microclimate, soil properties and N mineralization. Our data showed that, after 6 months, understory removal (UR) in both plantations had greatly increased soil surface luminous intensity (90–500 cd) and temperature (0.5–0.8 °C); soil moisture was reduced in the Eucalyptus plantation but not in the Acacia plantation. Understory removal also reduced soil organic matter (SOM), but had little impact on other soil chemical properties, including total phosphorus, C/N, pH, exchangeable cations (K, Ca, Mg), available P, ande extractable NH₄–N and NO₃–N. We found a significant decline of soil N mineralization and nitrification rates in the 0–5 cm soils of UR in both plantations. The decline of SOM in UR may contribute to the lower N transformations rates. This study indicates that a better understanding of understory vegetation effects on soil N cycling would be beneficial to forest management decisions and could provide a critical foundation for advancing management practices.     

Climate and forest management influence nitrogen balance of European beech forests: microbial N transformations and inorganic N net uptake capacity of mycorrhizal roots

The effects of local climate and silvicultural treatment on the inorganic N availability, net N uptake capacity of mycorrhizal beech roots and microbial N conversion were assessed in order to characterise changes in the partitioning of inorganic N between adult beech and soil microorganisms. Fine root dynamics, inorganic N in the soil solution and in soil extracts, nitrate and ammonium uptake kinetics of beech as well as gross ammonification, nitrification and denitrification rates were determined in a beech stand consisting of paired sites that mainly differed in aspect (SW vs. NE) and stand density (controls and thinning treatments). Nitrate was the only inorganic N form detectable in the soil water. Its concentration was high in control plots of the NE aspect, but only in canopy gaps and not influenced by thinning. Neither thinning nor aspect affected the abundance of root tips in the soil. Maximum nitrate net uptake by mycorrhizal fine roots of beech, however, differed with aspect, showing significantly lower values at the SW aspect with warm–dry local climate. There were no clear-cut significant effects of local climate or thinning on microbial N conversion, but a tendency towards higher ammonification and nitrification and lower denitrification rates on the untreated controls of the SW as compared to the NE aspect. Apparently, the observed sensitivity of beech towards reduced soil water availability is at least partially due to impaired N acquisition. This seems to be mainly a consequence of reduced N uptake capacity rather than of limited microbial re-supply of inorganic N or of changed patterns of inorganic N partitioning between soil bacteria and roots.     

Short-term effects of forest restoration management on non-symbiotic nitrogen-fixation in western Montana

Forest restoration treatments involving selection harvest and prescribed fire have been applied throughout the Rocky Mountain West with only a limited understanding of how these treatments influence plant community composition and soil processes. Forest restoration treatments, especially those involving fire, have the potential to reduce N capital on site. Unfortunately there has been only limited effort to investigate the effects of forest restoration treatments on forest ecosystem N inputs, especially free living N-fixation in soil and woody residues. Recent studies have highlighted the potential for decaying woody roots to serve as hot spots for N-fixation. The fire and fire surrogates (FFS) study site at Lubrecht Experimental Forest in Western Montana provided a unique opportunity to investigate the effect of restoration treatments on N-fixation. We set out to examine how prescribed fire, selection harvest, and a combination of both influence free living N-fixing bacteria that colonize decomposing woody roots, mineral soil, and soil crusts. Soil, root, and soil crust samples were collected from replicated treatment plots in August 2005 and soil samples were recollected in May 2006 just following snowmelt. Acetylene reduction assays were run on all samples, and extractable inorganic N and potentially mineralizable N (PMN) were measured in mineral soil. While restoration treatments caused an increase in dead roots associated with stumps and fire killed trees, N-fixation rates were nearly non-existent in these root systems. Nitrogen-fixation rates were not significantly influenced by treatments in decomposing woody roots or in mineral soil, but were slightly greater (P < 0.10) in soil crusts when the control stand was compared to treated plots. Nitrogen-fixation rates were also greater in mineral soil than in roots. Soil collected in August exhibited greater rates of N-fixation than soil collected in May which we attributed to higher moisture and an increase in available N following spring thaw. Average rates of free living N-fixation across the treatment plots at Lubrecht were low (0.26 kg N ha⁻¹ year⁻¹), but over time we estimate that these sources, along with the sparse population of symbiotic N-fixing plants and wet N deposition, would replenish soil N lost through fire or harvesting in approximately 40–100 years.     

Influence of climate change,fire and harvest on the carbon dynamics of black spruce in Central Canada

The results of EFIMOD simulations for black spruce (Picea mariana [Miller]) forests in Central Canada show that climate warming, fire, harvesting and insects significantly influence net primary productivity (NPP), soil respiration (Rs), net ecosystem production (NEP) and pools of tree biomass and soil organic matter (SOM). The effects of six climate change scenarios demonstrated similar increasing trends of NPP and stand productivity. The disturbances led to a strong decrease in NPP, stand productivity, soil organic matter (SOM) and nitrogen (N) pools with an increase in CO₂ emission to the atmosphere. However the accumulated NEP for 150 years under harvest and fire fluctuated around zero. It becames negative only at a more frequent disturbance regime with four forest fires during the period of simulation. The results from this study show that changes in climate and disturbance regimes might substantially change the NPP as well as the C and N balance, resulting in major changes in the C pools of the vegetation and soil under black spruce forests.     

岷江上游干旱河谷区植被多样性与环境因子的相关性研究

对岷江上游干旱河谷区植被多样性与环境因子相关研究表明：1）阴、阳坡灌、草丛植物群落物种α多样性指标均随海拔升高表现出明显的增加趋势,阳坡呈现出中间低两头高的海拔梯度格局;阴坡总体呈现直线上升的趋势。2）该区土壤肥力总体水平高低表现为：中上部〉中部〉下部〉中下部、阴坡〉阳坡。低海拔地区土壤破碎,土壤含水量和土壤肥力极低,高海拔地区的土壤水分含量和土壤肥力都相对较高,立地条件也较适宜植物的生长。3）植被多样性与环境因子的相关分析表明,海拔、坡向、坡度、土壤含水量、速效N、速效K、有机质、全N、全K与灌丛群落多样性和生物量均呈正相关关系,而pH值、速效P、全P、全Ca与多样性和生物量呈负相关关系。通过逐步回归分析和主成分分析筛选出环境主导因子为全N、速效P、土壤含水量和速效N。     

林火干扰对森林土壤活性有机碳影响的研究

土壤活性有机碳作为森林土壤有机碳的活跃成分,在凋落物分解和土壤碳循环中发挥着重要作用。林火干扰通过改变土壤底物的数量和理化性质进而影响土壤活性有机碳,因而阐明林火干扰对土壤活性有机碳的影响是开展森林碳循环研究的基础。文中以6种土壤活性有机碳为研究对象,分别阐述林火干扰对土壤活性有机碳影响的研究进展。针对目前研究现状及存在问题,认为应进一步深化探究林火干扰后土壤微生物活性变化机制对土壤活性有机碳的影响,揭示土壤碳库平衡的影响机理;加强林火干扰后C-N耦合循环特征的研究;深入研究林火干扰后影响土壤活性有机碳的内在因素和外在因素的相互作用,综合评价林火干扰对土壤活性有机碳的短期与长期影响;加强林火干扰—土壤碳库—全球气候变化的交互关系研究,深入探讨林火干扰与土壤活性有机碳的相互作用关系及影响机理。     

Decomposing stumps influence carbon and nitrogen pools and fine-root distribution in soils

Decomposing stumps could significantly increase soil resource heterogeneity in forest ecosystems. However, the impact of these microsites on nutrient retention and cycling is relatively unknown. Stump soil was defined as the soil fraction directly altered by the decomposition of the primary rooting system (e.g. taproots) and aboveground stumps. Study sites were located in mature hardwood stands within the Jefferson National Forest in the Ridge and Valley Physiographic region of southwest Virginia. The objectives of this study were to: (i) determine the total soil volume altered by the decomposition of stumps and underlying root system, (ii) compare and contrast total C and N, extractable ammonium (NH₄⁺) and nitrate (NO₃⁻), potentially mineralizable N, microbial biomass C (MBC), root length and root surface area between the bulk soil (i.e. O, A, B and C horizons) and stump soil and (iii) evaluate how nutrient concentrations and fine-root dynamics change as stumps decompose over time using a categorical decay class system for stumps. Potentially mineralizable N was 2.5 times greater in stump soil than the A horizon (103 mg kg⁻¹ vs. 39 mg kg⁻¹), 2.7 times greater for extractable NH₄⁺ (16 mg kg⁻¹ vs. 6 mg kg⁻¹) and almost 4 times greater for MBC (1528 mg kg⁻¹ vs. 397 mg kg⁻¹). Approximately 19% of the total fine-root length and 14% of fine-root surface area occurred in the stump soil. Significant differences occurred in C and N concentrations between all four decay classes and the mineral soil. This validated the use of this system and the need to calculate weighted averages based on the frequency and soil volume influenced by each decay class. In this forest ecosystem, approximately 1.2% of the total soil volume was classified as stump soil and contained 10% and 4% of soil C and N. This study illustrates that including stump soil in soil nutrient budgets by decay class will increase the accuracy of ecosystem nutrient budgets.     

Alley cropping in the moist savanna of West-Africa: III. Soil organic matter fractionation and soil productivity

In cropping systems with limited amounts of external inputs, the soil organic matter pool (SOM) may contribute significantly to plant nutrition. The impact of organic inputs on total SOM and particulate organic matter (POM) N contents as affected by soil type and the relationships between sources of N and maize N uptake were assessed for a set of alley cropping trials in the West- African moist savanna. The trials were established in Niaouli (Bénin Republic), in Glidji, Amoutchou, and Sarakawa (Togo), and in Bouaké and Ferkessédougou (Côte d‘ Ivoire). The total soil N content, averaged over all treatments and years, varied between 324 and 1140 mg N kg?1 soil. The POM-N content varied between 50 and 160 mg N kg?1 soil. The average proportion of soil N belonging to the POM pool ranged between 9% and 29%. This was significantly related to the annual N inputs from maize stover and prunings, when averaged over the different alley cropping treatments. The trial ‘age‘ also appeared to be related to the impact of the different treatments on the POM-N content. The Ferkessédougou soil contained a relatively higher proportion of total soil N in the POM pool because of its relatively high silt and clay content, compared to the other sites. The relative change in POM-N content between 1996 and the initial sampling was about twice the relative change in total soil N content. This suggests that N incorporated in the POM is relatively labile, compared to N incorporated in the other SOM fractions. Maize N uptake was related to the amount of add pruning-N (partial r2 of 27%), the rainfall during the growing season (partial r2 of 17%), the POM-N content (partial r2 of 14%), and to a lesser degree to the POM N concentration (partial r2 of 5%), the fertilizer N addition rate (partial r2 of 3%), and the silt and clay content of the soil (partial r2 of 3%). The POM-N content was shown to be influenced by organic matter additions and soil characteristics and to contribute significantly to maize N supply. This pool may be an important indicator for the soil fertility status of savanna soils.     

The North American long-term soil productivity experiment: Findings from the first decade of research

First decade findings on the impacts of organic matter removal and soil compaction are reported for the 26 oldest installations in the nation-wide network of long-term soil productivity sites. Complete removal of surface organic matter led to declines in soil C concentration to 20 cm depth and to reduced nutrient availability. The effect is attributed mainly to the loss of the forest floor. Soil C storage seemed undiminished, but could be explained by bulk density changes following disturbance and to decomposition inputs of organic C from roots remaining from the harvested forest. Biomass removal during harvesting had no influence on forest growth through 10 years. Soil compaction effects depended upon initial bulk density. Soils with densities greater than 1.4 Mg m⁻³ resisted compaction. Density recovery was slow, particularly on soils with frigid temperature regimes. Forest productivity response to soil compaction depended both on soil texture and the degree of understory competition. Production declined on compacted clay soils, increased on sands, and generally was unaffected if an understory was absent.     

Soil denitrification rates in a subalpine watershed of the eastern Sierra Nevada

Denitrification rates in soils of six subalpine plant communities in an eastern Sierra Nevada watershed were determined by the acetylene inhibition method. Soil atmosphere samples were collected monthly from June 1986 through May 1987 in a riparian, wet meadow, dry meadow, north-facing forest, south-facing forest and barren site and analyzed for N₂O content using gas chromatography. Soil temperature, moisture, organic matter, C,N,C:N ratio, NO₃N and pH were examined to assess their effects on denitrification rates. Mean denitrification rates for the year varied from 103.3 μg m⁻²h⁻¹ in the north-facing forest to 120.2 μg m⁻²h⁻¹ at the barren site, but did not differ significantly among any of the six plant communities. However, comparisons among months within individual communities revealed that the denitrification rates in each community varied significantly over the year, and in three of the six sites significant correlations between denitrification rates and other soil parameters were detected. Soil acidity was positively correlated with denitrification rate in the riparian and wet meadow communities, and in the dry meadow, soil moisture was positively correlated while soil temperature and organic matter were negatively correlated with denitrification rate. Comparisons among sites within individual months revealed significant differences in denitrification rates in June, September, October and January, but no single site consistently exhibited the highest or lowest rate in all 4 months, and only in October, when denitrification rates were positively correlated with soil temperature and moisture, was variation in denitrification rates among sites explained by other soil parameters. For the six plant communities overall, soil denitrification rates were highly variable from June to October, increased sharply from October to December, and then declined from December to May.     

地震滑坡区覆盖生态毯对土壤湿度和养分的影响

为了研究生态毯覆盖对土壤湿度和养分的影响,首次将生态毯应用于地震滑坡区砾石泥沙堆积区和泥沙堆积区。结果表明:铺设生态毯的土壤含水量均高于裸地的;各层的土壤水分含量随干旱日数的增加呈下降的趋势,生态毯的下降趋势较为平稳;保水效果为椰纤维生态毯秸秆+椰纤维生态毯秸秆生态毯裸地。覆盖生态毯可以提高土壤有机质含量和p H值;土壤速效N、P、K和全N、全P、全K的含量也有一定程度的提高。铺设生态毯能有效固定地震滑坡区的砾石泥沙,改善土壤的水热条件,进而增加根系、微生物的活动和植被有机体的积累,促进枯落物的分解,逐步提高土壤中的养分含量。     

Bioamelioration of a sodic soil by silvopastoral systems in northwestern India

In sodic soils, excessive amounts of salts have an adverse effect on soil biological activity and stability of soil organic matter. The study analyzes the role of silvopastoral systems to improve soil organic matter and microbial activity with a view for effective management of soil fertility. The silvopastoral systems for the present study (located at Saraswati Reserved Forest, Kurukshetra; 29°4′ to 30°15′ N and 75°15′ to 77°16prime; E) are characterized by tree species of Acacia nilotica, Dalbergia sissoo and Prosopis juliflora along with grass species of Desmostachya bipinnata and Sporobolus marginatus. Soil microbial biomass carbon was measured using the fumigation extraction technique and nitrogen mineralization rates using aerobic incubation method. The microbial biomass carbon in the soils of D. bipinnata and S. marginatus treatments were low. In silvopastoral systems, microbial biomass carbon increased due to increase in the carbon content in the soil – plant system. A significant relationship was found between microbial biomass carbon and plant biomass carbon (r = 0.83) as well as the flux of carbon in net primary productivity (r = 0.92). Nitrogen mineralization rates were found greater in silvopastoral systems compared to 'grass-only' system. Soil organic matter was linearly related to microbial biomass carbon, soil N and nitrogen mineralization rates (r = 0.95 to 0.98, p < 0.01). On the basis of improvement in soil organic matter, enlarged soil microbial biomass pool and greater soil N availability in the tree + grass systems, agroforestry could be adopted for improving the fertility of highly sodic soil. This revised version was published online in June 2006 with corrections to the Cover Date.     

The influence of land-use change on the organic carbon distribution and microbial respiration in a volcanic soil of the Chilean Patagonia

Land-use changes can modify soil carbon contents. Depending on the rate of soil organic matter (SOM) formation and decomposition, soil-vegetation systems can be a source or sink of CO₂. The objective of this study was to determine the influence of land-use change on SOM distribution, and microbial biomass and respiration in an Andisol of the Chilean Patagonia. Treatments consisted of degraded natural prairie (DNP), thinned and pruned Pinus ponderosa plantations (PPP), and unmanaged second-growth Nothofagus pumilio forest (NPF). The soil was classified as medial, amorphic, mesic Typic Hapludands. Soil microbial respiration and microbial biomass were determined in the laboratory from soil samples taken at 0–5, 5–10, 10–20 and 20–40 cm depths obtained from three pits excavated in each treatment. Physical fractionation of SOM was performed in soil of the upper 40 cm of each treatment to obtain the three following aggregate-size classes: macroaggregates (>212 μm), mesoaggregates (212–53 μm) and microaggregates (<53 μm). Plant C content was 68% higher in PPP than in DNP and 635% higher in NPF than in PPP. Total soil and vegetation C content in both DNP and PPP were less than half of that in NPF. Total SOC at 0–10 cm depth decreased in the order DNP (7.82%) > NPF (6.16%) > PPP (4.41%), showing that land-use practices affected significantly (P < 0.01) SOC stocks. In all treatments, microbial biomass C and respiration were significantly higher (P < 0.05) in the upper 5 cm. Soil microbial respiration was also correlated positively with microbial biomass C and SOC. The different land uses affect the formation of organic matter, SOC and microbial biomass C, which in turn will affect soil microbial respiration. Conversion of DNP to PPP resulted in a 44% decrease of SOC stocks in 0–10 cm mineral soil. The largest amount of SOC was stabilized within the mesoaggregate fraction of the less disturbed system, NPF, followed by PPP. In the long term, formation of stable mesoaggregates in soils protected from erosion can behave as C sinks.