Search

Microbial activity of top soils is directly linked with carbon (C) and nitrogen (N) turnover in terrestrial ecosystems, and thus is an indicator to identify hot spot areas of C and N cycling in forest habitats. The Hyrcanian forests are one of the last remnants of natural deciduous forests in the world and Oriental Beech (Fagus orientalis Lipsky) is one of the most abundant tree species of these forests. It has not been resolved which forest properties of Hyrcanian forests facilitate hotspots with high microbial process rates. We studied those primary causes (i.e. forest properties) of changes on soil characters and processes within old-growth Vaz forests, Northern Iran, and separately sampled different landform positions (i.e. catena, pit-mound and gilgai), single-trees, deadwoods and canopy gaps. Principal component analysis (PCA) of the 31 soil parameters resulted in two principal components that explained more than 60% of the total variance. The first component (PC1) explained the highest variance (48.13%) in the results; while second component (PC2) accounted for 13.68% of the variance. The obtained PCA results indicate a clear differentiation in selected soil properties among forest properties and thus, three groups of drivers for microbial activities were identified. Group 1 (foot and toe slope of V-shape catena, toe slope ofΛ-shape catena, pit structure of hornbeam, decay class 4 of beech deadwoods, small and medium canopy gaps) enhanced soil microbial process and enzyme activities. Group 2 (pit structure of beech, control or non-gilgai position, beech and hornbeam single-trees, decay class 3 and 4 of hornbeam deadwoods and large canopy gap) enhanced soil microbial biomass and greenhouse gas fluxes. Group 1 and 2 drivers were associated with high values of soil water content, organic C, total N, available nutrients, organic matter fractions, earthworm and nematode activities. Group 3 drivers (summit and shoulder slope of V- and Λ-shape catena, back slope of V-and Λ-shape catena, foot slope ofΛ -shape catena, mound of beech and hornbeam, position in a gilgai, decay class 2 and 3 of beech deadwoods, decay class 1 and 2 of hornbeam deadwoods and very large canopy gap) correlated with lowest microbial activities and was associated with high values of soil bulk density, pH, electrical conductivity and C/N ratio. Thus, distribution of microbial hotspot areas in the Hyrcanian forests can be considered as mosaic of pedons characterized by specific sets of key parameters, which depend on landform, especially the toe slope of V-shape catena, and stand characteristics (e.g. tree species or canopy gap).

Soil plays an essential role in providing ecosystem services, especially in mountain ecosystems which are often considered as fragile and sensitive systems and commonly consist of a mosaic of forest and rangeland plant communities. The relationship between above-ground plant cover and the properties of soil organic and mineral layers in mountain areas are rarely studied. This research aimed to assess the effect of different land covers (i.e. forest, forest-rangeland ecotone, and rangeland) on soil functional indicators, i.e. fertility and biological activities, in the Hyrcanian region of northern Iran. We hypothesized that (i) the presence of tree cover enhances soil fertility and biological activities and creates hot spots (islands) of soil functional indicators especially in the topsoil, (ii) litter quality and organic matter fractions are the drivers for activities of soil organisms, nutrient cycles and transformation processes in mountain ecosystems. Litter (O-horizon including L, F and H layers) and mineral soil samples (in two separate depths of 0–10 cm and 10–20 cm) were taken using iron frames (30 × 30 cm). In total, 45 litter and 90 soil samples were transferred to the laboratory. Soil characteristic especially in the 0–10 cm depth, litter carbon (C), nitrogen (N) and C/N ratio were significantly affected by different land covers showing the maximum of soil organic C and microbial activity under forest. Our findings showed that the studied land covers, as well as litter and soil properties can be separated by PCA output. The first and second axes, accounted more than 50% of the explained variance in each of the studied soil depths. Soils with a better quality of litter (i.e. lower C/N ratio), higher values for organic matter fractions, soil fertility indicators and soil biological activities can be attributed to the forest. In contrast, positions of low soil fertility indicator values and biota abundance were imposed by forest-rangeland ecotone and rangeland. Although each land cover plays a prominent ecological role and takes its place in the evolutionary process, forests are essential because of their capacity to store and transform carbon and nutrients and to create hotspots identified by functional soil indicators. Based on our findings, soil functions decreased ranked in the order forest > forest-rangeland ecotone > rangeland, which can be assigned to the lower density of trees, and the amount of litter mass and litter quality. It can be concluded that tree covers have a prominent role in increasing soil functions, which should be given special consideration in the restoration of degraded mountain ecosystems.

International audience; The relationships between woody species, soil biota activity and soil quality were largely ignored in semi-arid areas. This study evaluated the influence of life form and seasonal variation on the mesofauna activity and soil chemical and microbial properties under three tree species (Quercus brantii (QU), Acer monspessulanum (AC) and Pistacia atlantica (PI), and three shrub species (Crataegus puntica (CR), Amygdalus scoparia (AM) and Lonicera nummularifolia (LO)) in a semiarid oak forest in western Iran. Soils were sampled beneath each individual woody species in spring and winter. Soil chemical and biological properties and soil mesofauna diversity were measured and soil quality index (SQI) was produced. The comparison of soil chemical properties under tree and shrub species showed that only soil total nitrogen (Ntot), available potassium (Kava) and soil organic carbon (SOC) were significantly higher under trees than shrubs (respective mean values for spring: 0.31 vs 0.19%; 1304 vs 1103 mg/kg, 3.94 vs 3.16%). In contrast, all of the studied soil biological characteristics including microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), basal respiration (BR), and substrate induced respiration (SIR) were significantly higher under trees than under shrubs (respective mean values for spring in mg/kg soil/day: 603.5 vs 431.2, 49.6 vs 35, 46 vs 35 and 57.6 vs 36.5). Besides, we found clear seasonal and species effects for most soil properties. Values were higher in spring than in winter and were the most similar for QU and AC for tree species (especially due to the higher content of SOC and MBN under these species in spring) and for AM and LO for shrub species. The Shannon-Wiener diversity index and richness of the soil mesofauna were significantly higher under trees than under shrubs (respective mean values for spring: 1.59 vs 1.09 and 6.5 vs 3.8). The Shannon-Wiener diversity and richness indices for soil mesofauna were positively linearly related to the soil quality index (SQI) in spring and winter. These relationships were weaker in winter than in spring and showed an increase of both indices from shrubs (LO, AM and CR) with low SQI values to trees (QU and AC) with higher SQI values. Based on these results, we conclude that these indices can be used as efficient soil bioindicators which can be helpful in restoration or conservation projects in semi-arid areas.

Temperate forest productivity and functioning may be explained by complex interactions among tree canopy composition, topographic conditions, climate, morphogenetic identification and classification of humus forms. In this study, we report the main morphological feature of humus profiles classified according to both American (AHCM) and European (EHCM) classifications under the six most common forest stands in northern Iran, i.e., Alnus subcordata (AS), Acer velutinum (AV), Fagus orientalis-Carpinus betulus (FO-CB), Carpinus betulus (CB), Fagus orientalis (FO), and Fagus orientalis-Carpinus betulus-Parrotia persica (FO-CB-PP). Organic and organic-mineral layers samples were collected in 61 permanent plots (20 × 20 m) within a 30 × 30 cm metal frame, for identification. Our result showed that Mull was the dominant humus system according to both classifications, whereas Mor (AHCM) and Amphi (EHCM) were the less frequent humus systems in the study area. Mull and Amphi (EHCM) were dominant at the lowest slope and altitude under AS canopy cover; Moder was usually present at intermediate slope and altitude under FO-CB and FO-CB-PP; while Mor was the dominant form at intermediate slopes and highest altitudes under FO and FO-CB. Due to the temperature changes and litter decomposition, altitude seems to be the best predictor of humus type and litter thickness. Our findings also indicate that EHCM could be preferred in the identification and classification of humus forms in temperate deciduous forests in Iran.

Our findings show the differential impacts of tree types (hornbeam–ironwood natural forest and plantations of ash, maple, cypress and pine) on soil physical–chemical characteristics and how dominant tree species regulate the size and activity of soil microbial and enzymes. Soil microbial and enzyme activities have an important influence on nutrient cycling. The variation in soil carbon (C) and nitrogen (N) microbial indices as well as enzyme activities were determined under hornbeam–ironwood natural forest and 25-years old plantations of ash, maple, cypress and pine in northern Iran. Four soil profiles were dug along the four parallel transects in the central part of each forest stand, resulting in 16 soil samples for each stand at a depth of 0–15 cm. The results showed significant differences in most of studied soil physico-chemical properties among different land covers. Soil microbial basal respiration (MR) and substrate induced respiration (SIR) were found to be significantly higher under natural forest than in the plantation stands. Microbial biomass C (MBC) did not differ for the forest stands, whereas natural forest had significantly higher qCO2 (MR: MBC), microbial entropy (MBC: Corg) and C availability index (MR: SIR) values. The establishment of plantations reduced the values of soil microbial biomass N, mineral nitrogen (NH4–N and NO3–N) and N mineralization with the least under coniferous stands of cypress and pine, while greater amounts were observed under natural forest. With replacement in the type of tree species from natural forest to plantations, acid phosphatase, arylsulphatase and invertase enzyme activities decreased significantly in the topsoil, whereas like natural forest, ash plantation improved urease enzyme. This research recommends conservation of natural forests for increase of soil quality and plantation of suitable native broad-leaved species for rehabilitation of degraded natural forests.

Mountainous sites can only grow a limited variety of vegetation types due to their fragile soil conditions. In the north of Iran, mountainous sites are commonly occupied by Crataegus and Berberis shrubs, which are natively distributed in Asia, Europe, North America and Africa. Despite the widespread distribution of these two species, the effect of pure and mixed canopy composition of these species on soil fertility and microbial activities (as soil function indicators) has not been considered. In this paper, five types of canopy composition have been studied for their effect on soil function; including pure Crataegus (PC), and pure Berberis (PB), as well as mixed Crataegus and Berberis with almost equal canopy cover (50C:50B), Crataegus-dominated stand (70C:30B), and Berberis-dominated stand (30C:70B). A total of 225 soil samples (5 plant types × 15 samples × 3 soil depths including 0–10 cm, 10–20 cm and 20–30 cm belowground) were taken from the field, transferred to the laboratory and analyzed. PCA results showed a difference in the soil characteristics between the canopy composition types, with the first and second axes justifying 46.67% and 14.12% of the total variance, respectively. The 50C:50B mixed canopy composition resulted in soils with higher values of soil organic matter fractions (i.e. particulate and dissolved C and N), C and nutrient (N, P, K, Ca and Mg) pools, and soil microbial (i.e. respiration and biomass) and enzyme (urease, acid phosphatase, arylsulfatase and invertase) activities, especially in the topsoil (0–10 cm). Soil function indicators decreased in ranked order of 70C:30B > 30C:70B > PC > PB plant types. As a conclusion, it can be stated that the equal ratio of Crataegus and Berberis can enhance soil function and create fertile islands in the high altitudes of natural ecosystems.

Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, and biomass. We found that local species richness and abundance typically peaked at higher latitudes, displaying patterns opposite to those observed in aboveground organisms. However, high species dissimilarity across tropical locations may cause diversity across the entirety of the tropics to be higher than elsewhere. Climate variables were found to be more important in shaping earthworm communities than soil properties or habitat cover. These findings suggest that climate change may have serious implications for earthworm communities and for the functions they provide., 677232 to N.E.). K.S.R. and W.H.v.d.P. were supported by ERC-ADV grant 323020 to W.H.v.d.P. Also supported by iDiv (DFG FZT118) Flexpool proposal 34600850 (C.A.G. and N.E.); the Academy of Finland (285882) and the Natural Sciences and Engineering Research Council of Canada (postdoctoral fellowship and RGPIN-2019-05758) (E.K.C.); DOB Ecology (T.W.C., J.v.d.H., and D.R.); ERC-AdG 694368 (M.R.); and the TULIP Laboratory of Excellence (ANR-10-LABX-41) (M.L.). In addition, data collection was funded by the Russian Foundation for Basic Research (12-04-01538-a, 12-04-01734-a, 14-44-03666-r_center_a, 15-29-02724-ofi_m, 16-04-01878-a 19-05-00245); Tarbiat Modares University; Aurora Organic Dairy; UGC(NERO) (F. 1-6/Acctt./NERO/2007-08/1485); Natural Sciences and Engineering Research Council (RGPIN-2017-05391); Slovak Research and Development Agency (APVV-0098-12); Science for Global Development through Wageningen University; Norman Borlaug LEAP Programme and International Atomic Energy Agency (IAEA); São Paulo Research Foundation - FAPESP (12/22510-8); Oklahoma Agricultural Experiment Station; INIA - Spanish Agency (SUM 2006-00012-00-0); Royal Canadian Geographical Society; Environmental Protection Agency (Ireland) (2005-S-LS-8); University of Hawai‘i at Mānoa (HAW01127H; HAW01123M); European Union FP7 (FunDivEurope, 265171); U.S. Department of the Navy, Commander Pacific Fleet (W9126G-13-2-0047); Science and Engineering Research Board (SB/SO/AS-030/2013) Department of Science and Technology, New Delhi, India; Strategic Environmental Research and Development Program (SERDP) of the U.S. Department of Defense (RC-1542); Maranhão State Research Foundation (FAPEMA); Coordination for the Improvement of Higher Education Personnel (CAPES); Ministry of Education, Youth and Sports of the Czech Republic (LTT17033); Colorado Wheat Research Foundation; Zone Atelier Alpes, French National Research Agency (ANR-11-BSV7-020-01, ANR-09-STRA-02-01, ANR 06 BIODIV 009-01); Austrian Science Fund (P16027, T441); Landwirtschaftliche Rentenbank Frankfurt am Main; Welsh Government and the European Agricultural Fund for Rural Development (Project Ref. A AAB 62 03 qA731606); SÉPAQ; Ministry of Agriculture and Forestry of Finland; Science Foundation Ireland (EEB0061); University of Toronto (Faculty of Forestry); National Science and Engineering Research Council of Canada; Haliburton Forest and Wildlife Reserve; NKU College of Arts and Sciences Grant; Österreichische Forschungsförderungsgesellschaft (837393 and 837426); Mountain Agriculture Research Unit of the University of Innsbruck; Higher Education Commission of Pakistan; Kerala Forest Research Institute, Peechi, Kerala; UNEP/GEF/TSBF-CIAT Project on Conservation and Sustainable Management of Belowground Biodiversity; Ministry of Agriculture and Forestry of Finland; Complutense University of Madrid/European Union FP7 project BioBio (FPU UCM 613520); GRDC; AWI; LWRRDC; DRDC; CONICET (National Scientific and Technical Research Council) and FONCyT (National Agency of Scientific and Technological Promotion) (PICT, PAE, PIP), Universidad Nacional de Luján y FONCyT [PICT 2293 (2006)], Fonds de recherche sur la nature et les technologies du Québec (131894), Deutsche Forschungsgemeinschaft [SCHR1000/3-1, SCHR1000/6-1, 6-2 (FOR 1598), WO 670/7-1, WO 670/7-2, and SCHA 1719/1-2], CONACYT (FONDOS MIXTOS TABASCO/PROYECTO11316); NSF (DGE-0549245, DGE-0549245, DEB-BE-0909452, NSF1241932); Institute for Environmental Science and Policy at the University of Illinois at Chicago; Dean’s Scholar Program at UIC; Garden Club of America Zone VI Fellowship in Urban Forestry from the Casey Tree Endowment Fund; J. E. Weaver Competitive Grant from the Nebraska Chapter of The Nature Conservancy; the College of Liberal Arts and Sciences at DePaul University; Elmore Hadley Award for Research in Ecology and Evolution from the UIC Dept. of Biological Sciences; Spanish CICYT (AMB96-1161; REN2000-0783/GLO; REN2003-05553/GLO; REN2003-03989/GLO; CGL2007-60661/BOS); Yokohama National University; MEXT KAKENHI (25220104); Japan Society for the Promotion of Science KAKENHI (25281053, 17KT0074, 25252026); ADEME (0775C0035); Ministry of Science, Innovation and Universities of Spain (CGL2017-86926-P); Syngenta Philippines; UPSTREAM; LTSER (Val Mazia/Matschertal); Marie Sklodowska Curie Postdoctoral Fellowship (747607); National Science and Technology Base Resource Survey Project of China (2018FY100306); McKnight Foundation (14-168); Program of Fundamental Researches of Presidium of Russian Academy of Sciences (AAAA-A18-118021490070-5); Brazilian National Council of Research CNPq; and French Ministry of Foreign and European Affairs. Author contributions: H.R.P.P. led the analysis, data curation, and writing of the original manuscript draft. C.A.G. assisted in analyses and writing of the original manuscript draft. E.K.C. and N.E. revised subsequent manuscript drafts. J.v.d.H., D.R., and T.W.C. provided additional analyses. E.K.C., N.E., and M.P.T. acquired funding for the project. J.K., K.B.G., B.S., M.L.C.B., M.J.I.B., and G.B. contributed to data curation. H.R.P.P., C.A.G., M.L.C.B., M.J.I.B., G.B., O.F., A.O., E.M.B., J.B., U.B., T.D., F.T.d.V., B.K.-R., M.L., J.M., C.M., W.H.v.d.P., K.S.R., M.C.R., D.R., M.R., M.P.T., D.H.W., D.A.W., E.K.C., and N.E. contributed to the project conceptualization. All authors reviewed and edited the final draft manuscript. The majority of the authors provided data for the analyses. Competing interests: The authors declare no competing interests. Data and materials availability: Data and analysis code are available on the iDiv Data repository (DOI: 10.25829/idiv.1804-5-2593) and GitHub (https://github.com/helenphillips/GlobalEWDiversity; DOI: 10.5281/zenodo.3386456).

Native to Eurasia, Eastern Europe, and Western Asia, Oriental beech (Fagus orientalis Lipsky) stands extend from the north-western part of Turkey, the eastern part of the Caucasus Mountains in Georgia and Russia to the Alborz Mountains in Iran. The effect of different development stages of beech stands on the forest floor and soil characteristics are so far almost unknown. For this purpose, the Langa forest that is located in northern Iran was investigated to detect the effect of forest development on major traits of soil biology and related soil characteristics. For this aim, 45 forest floors and soil samples (15 samples per each development stage i.e. initial, optimal, and decay stage) were analysed. In addition, the water content, temperature, and biological dynamics were monitored over the different development stages in summer and fall. Among the considered independent factors, the development stage of beech had the largest explanatory power for the variations of the soil water content (34.7%), total earthworm density and biomass (29.6% and 32.3%, respectively), Acarina (30.3%), nematode (64.3%), protozoa (57.7%), bacteria, (62.8%), fungi (59.5%), basal respiration (53.0%), substrate-induced respiration (53.8%), microbial biomass carbon (30.4%), microbial biomass nitrogen (36.0%), microbial biomass phosphorous (59.1%) and net nitrification rate (19.1%). Soil temperature (42.5%), collembola density (18.2%), net ammonification rate (29.9%), and net N mineralization rate (2.1%) were predominantly determined by the seasons. With the ageing of the forest stands, soil fertility, biota abundance, and soil function were enhanced. To figure out the most vital soil features affecting C and N sequestrations, a stepwise regression model was applied. Carbon sequestration correlated positively to N, the C/N ratio, and negatively to porosity, and the nematode abundance. In addition, nitrogen sequestration correlated positively to C, the sand content, and fine root biomass and negatively to the C/N ratio, soil porosity, and aggregate stability. Although all forest stages of the Oriental beech have an important ecological role and their place in the evolutionary process, the old-growth (i.e. decay) stage is especially important for the soil functions exhibiting the highest fertility and biological relevance. The understanding of ecological changes within different development stages can be helpful in forest management and the evaluation of silvicultural methods.

We examined the variation in woody plant species composition, regeneration and biodiversity in relation to topographic heterogeneity, specifically catena shape (V and Λ) and slope position (summit, shoulder, back slope, foot slope and toe slope). All research took place at the TMU Experimental Forest Station, located in northern Iran. Two sets of replicated quadrats were established along transects that encompassed the different catena shapes and positions. We recorded the density, height, and canopy cover of all trees ≥12 cm diameter at breast height within 30 quadrats (400m2), as well as the density of all tree regenerations within 120 quadrats (4m2). In addition, three measurements of biodiversity were calculated for both mature trees and regenerations. Mature tree species composition varied greatly with catena shape and slope position, as did that of regenerating trees. Despite differences in species composition, the various measurements of biodiversity were consistent across the landscape for...

The degradation of forest ecosystems has an important role in global warming through the carbon (C) and nitrogen (N) cycles. The response of soil organic matter fractions and microbial activities to forest degradation has been poorly studied. The purpose of the current research was to evaluate the effect of different intensities (i.e. low, moderate, and high) of forest degradation in northern Iran on the fractions of particulate and dissolved organic matter, microbial and enzyme activities as indicators of soil function. In this research, a total of 15 soil samples (30 × 30 × 10 cm) from each studied forest sites were transferred to the laboratory. Fifty-two soil characteristics of those forest ecosystems were studied by principal component analysis (PCA), with an explanation of more than 55% of the variance by axes 1 and 2. The fractions of soil organic matter (particulate and dissolved organic matter), fertility, microbial activities (microbial respiration and microbial biomass of carbon, nitrogen, and phosphorous), enzyme indices (urease, acid phosphatase, arylsulfatase, invertase, geometric mean of enzyme activities, and Shannon’s diversity index), and stoichiometry of enzyme activity/organic C were enhanced at sites with low degradation intensity. Instead, all studied soil characteristics were suppressed at sites showing high forest degradation. The stoichiometry of enzyme activity/microbial biomass of C were not significantly different among the studied stands. It was concluded that the degradation intensity of natural forests can play a very important role in the soil function of temperate ecosystems.

Human activities, such as tree cutting and land-use change, have significantly altered the forests of Iran's Zagros Mountains. In plantation projects within these forests, maintaining soil structure and fertility is necessary for sustainable forest management. Ideally, the soil quality of tree plantations should be as good as that of natural forests. In this study, we investigated the long-term impact of land-use change, i.e. conversion of natural oak forest to tree plantations or cultivated fields, on soil quality (i.e., physicochemical, biological and biochemical soil properties) in the forests of the Zagros Mountains. We found that the conversion of natural oak forest to tree plantations (in this case Cupressus arizonica, Cedrus libani, Elaeagnus angustifolia, Quercus brantii (persica), Robinia pseudoacacia and Fraxinus rotundifolia) and agriculture caused declines in soil organic carbon content, especially in the cultivated fields where it fell by around 60%. Overall, the lowest contents of soil nutrients, except Cu, were measured in agricultural soils. Interestingly, the plantation of a non-native tree (Cedrus libani) sequestrated more atmospheric carbon and nitrogen than native Persian oak forests. The impact on soil biological activity remains unclear: the conversion of natural forests into cultivated fields reduced soil biological activity, while conversion from forest to tree plantations had little influence. Finally, the conversion of natural forest to tree plantations had less impact on soil properties than conversion to cultivated fields. In conclusion, to maintain soil fertility, forest managers should avoid forest conversion to agriculture. Moreover, we do not recommend plantation of Cupressus arizonica in the Zagros region for the purpose of carbon and nitrogen sequestration and the increase of soil productivity.

Foresters always emphasize the understanding of soil properties in evaluating site capacity to support productive forests. In order to conserve and improve soil quality and functions, sophisticated forest management systems are of particular importance. Hyrcanian forests of Iran have been harvested under different silvicultural operations such as shelterwood and selective cutting systems. So far, no studies have been conducted to explore the effects of forest management systems on soil properties in this ecosystem. Consequently, the present study aimed to investigate the impact of shelterwood and single-tree cutting systems on soil quality and functions (i.e. organic matter fractions, biota and microbial/enzyme activities), 10 and 20 years after employing these systems in Hyrcanian beech stands, compared to intact forests (control areas). A total of 60 soil samples (30 × 30 × 10 cm) including 30 samples in August 2008 and 30 samples in August 2018 from each site (i.e. control areas, shelterwood and single-tree systems) were transferred to the laboratory. In addition, topsoil water content, temperature and biological dynamics (August 2008, November 2008, August 2013, November 2013, August 2018 and November 2018) were monitored across the different forest management systems. Based on our data, the studied forest sites and soil properties could be separated by PCA output. The first and second axes, respectively, accounted for 38.59 and 10.95% of the explained variance. The control areas enhanced soil organic matter fractions, biota and microbial/enzyme activities. Between different silvicultural operations, the single-tree system, which is considered as a close-to-nature system, has provided better conditions for soil quality and functions as compared to the shelterwood management system. The understanding of ecological changes within widespread forest management systems can be helpful in forest management and plays a significant role in evaluating silvicultural systems.

Forest degradation causes soil carbon losses and affects soil C and N cycling. However, it is not clear how reforestation of degraded areas with different species affects soil and ecosystem restoration, particularly in northern Iran. The aim of this study was to evaluate the effect of forest degradation and reforestation with two contrasting species: Alnus and Quercus as N2-fixing and non N2-fixing tree species, respectively, on soil quality and function after 30 years in the northern Iran region. We selected four forest stands: Carpinus betulus-Parrotia persica natural forest (NF), Alnus subcordata (AP) and Quercus castaneifolia (QP) plantations as rehabilitated areas, and a degraded natural forest (DNF). We examined the main litter and soil chemical properties and soil C and N microbial fractions. Litter and soil physico-chemical properties and microbial activity differed among land covers. As expected, deforestation caused a decrease in most soil C and N fractions as well as in soil microbial activity with an increase in metabolic quotient-qCO2. The plantation with Quercus spp. improved substrate induced respiration, as well as microbial biomass carbon and dissolved organic carbon compared to the Alnus plantation, whereas mineral N was similar in the natural site and the Alnus plantation. Although forest plantations had not reached the same values of microbial activity as the natural forest soils, soil C and N fractions were similar to the natural site after 30 years. The findings of this study support the importance of preserving natural forests for soil conservation. In addition, employing of N2 fixing trees such as Alnus spp. or, Quercus spp., suitable native broadleaved species, is proposed for the rehabilitation of degraded natural forests. Although both forest plantations led to soil recovery after 30 years, Quercus plantations were more efficient in restoring microbial communities than Alnus plantations indicating that litter quantity is more important than litter quality for soil recovery.

Water stress is one of the most important environmental stresses which can adversely affect soil fertility and plant growth in arid and semiarid regions. In this study, biochar was used as a type of soil amendment to improve the physiology of Chestnut-leaved oak (Quercus castaneifolia C.A.M.) seedlings and soil quality in water-deficit conditions. A randomized complete block design was conducted using three water regime treatments [100, 70 and 40% field capacity (FC)] and four application rates of produced biochar from hornbeam wood chips (control without biochar, B1, B2 and B3 with 10, 20 and 30 g kg−1 soil, respectively) in potted seedlings. The soil water-holding capacity in the 30 g kg−1 biochar was found to be higher than that in the non-biochar treatment under 100 and 40% FC. Water supply reduction to 40% FC decreased the soil total N, the available P and K, CEC, SOC and microbial respiration, as compared to the non-biochar soil used as the control; however, an increase in the B3 treatment was detected in the soil P and K at 100% FC. Severe water deficit (40% FC) induced a significant decrease in photosynthesis, transpiration, stomatal conductance and xylem water potential seedlings; even, in this case, the addition of the highest dose of biochar under the lowest water supply increased photosynthesis and stomatal conductance by 38% and 39%, respectively. Leaf nutrient concentration was also influenced by the treatment. The highest diameter and height growth and dry weight of the seedlings were observed in 100 and 40% FC under the B3 treatment. Plant biomass of the seedlings treated by B3 was increased by 55, 70 and 73%, in comparison with those attained by the control under 100, 70 and 40% FC irrigation, respectively. Generally, the use of the 30 g kg−1 biochar in the soil could alleviate the negative effects of water deficit and improve the growth of Q. castaneifolia seedling and soil quality with increasing the soil water-holding capacity, organic carbon and nutrient.

This study investigated the interactions between tree-herb layer diversity and some physico-chemical and eco-physiological characteristics of soil in natural oriental beech stand in western Guilan, Iran. The data were collected from nine research sites (50 m × 50 m) which were described as a gradient from pure oriental beech (Fagus orientalis Lipsky) stands to mixed stands with up to nine deciduous tree species (n = 27) in Hyrcanian forest. Herbaceous plants were sampled within ten 1 m × 1 m sub-plots in two plots of 400 m2 which were installed randomly in each research site. Composite soil samples were taken at five positions in each research site. We found that the increase in tree diversity in mature oriental beech stands brought about an increase in microbial biomass carbon, soil carbon content, and the ratio of microbial biomass carbon to the organic carbon (Cmic/Corg). Increased soil organic carbon raised microbial biomass carbon through creating suitable environment for microorganisms. The findings also indicated that the ratio of microbial biomass carbon to the organic carbon (Cmic/Corg) increased as a quantitative indicator of soil carbon dynamics that finally benefits soil fertility of mixed oriental beech stands compared to pure oriental beech stands. The results showed that humus layer and litter thickness were negatively correlated with tree layer richness. Generally, it can be stated that maintaining a mixture of tree layer species in natural oriental beech stands results in an increase in richness and diversity values of herb plants as well as carbon content and microbial biomass carbon of soil.

Labile soil organic matter, which is an important supply of energy for soil micro-organisms, has been suggested as a sensitive indicator of soil organic matter (SOM). In this study, the effects of forest vegetation on forest floor thickness and quality, labile SOM fractions and soil properties were examined in five different forest ecosystems, such as beech-hornbeam-alder, beech-hornbeam, beech-alder, beech-oak, and pure beech in the Hyrcanian region, northern Iran. Each forest type was replicated three times. In each plot, six forest floors and soil samples were taken in a 30 × 30 cm area. Pure beech had always a higher forest floor thickness than the other studied forest types. Increase in tree diversity in beech forest type reduced forest floor C:N ratio, more than three-fold, compared to pure beech. Based on our data, the influence of forest type on labile SOM was generally higher in the 0–10 cm soil layer than in the 10–20 cm layer. Beech-hornbeam-alder and beech-alder forest types, with high quality of forest floor and more values of N fractions in labile SOM, increased soil biological activities and fertility whereas pure beech and beech-oak forest types, with lower quality of forest floor and more values of C fractions in labile SOM reduced soil biological activities and fertility. Based on the result, the abundance of beech influenced nutrient cycling via forest floor quality. This led to an increase in labile SOM and subsequent soil fertility through the admixture of broadleaf species into beech forests.