Downed logs improve soil properties in old-growth temperate forests of northern Iran

Dead trees, particularly downed logs, play an important role in the dynamics of forest ecosystem. Contribution of decaying wood to C and nutrient pools of forest soils depends on the tree species and degree of wood decay. However, the extent to which the downed logs affect the soil properties of temperate forests has rarely been evaluated. In this study, a mixed beech forest was selected in Liresar region of Mazandaran Province, northern Iran, to investigate if and how the presence of downed logs affected soil quality and function by comparing soils underneath degraded logs and nearby soils of the two dominant tree species(beech and hornbeam). We then explored how these effects occurred as downed logs decomposed by comparing the woods of both tree species at four degrees of decomposition. Degree of decay of downed logs was classified into four classes(DC1–DC4). Eight dead trees of each tree species were selected at the center of each sample plot. Three composite soil samples underneath each decaying log and 100 cm away from a decaying log were collected at two soil depths(0–15 and 15–30 cm) to analyze soil main physicochemical properties and microbial activity. The results revealed that downed logs affected soil physical(5% wetter than control soils), chemical(2% lower pH, 100% increase in organic C and total N in the case of hornbeam, and 2% increase in P), and biological characteristics(soil microbial respiration enhanced by 10%, and microbial biomass C 620 and 351.5 mg kg~(-1) and microbial biomass N 66.47 and 32.18 mg kg~(-1), respectively, in the cases of beech and hornbeam), thus resulting in significantly different soil microsites from those without downed logs. Presence of downed logs increased soil microbial activity and soil fertility as wood decayed. Thus, the presence of downed logs is an important factor influencing forest soils and should be taken into consideration in forest management practices.     

Multiple effects of reindeer grazing on the soil processes in nutrient-poor northern boreal forests

Reindeer grazing has a great influence on the ground vegetation of nutrient-poor northern boreal forests dominated by Cladonia lichens in Fennoscandia. Grazing may influence the soil processes in these systems either by influencing the quality of plant litter, or by indirect effects through the soil microclimate. In order to investigate the mechanisms underlying the effects of reindeer on boreal forest soils, we analyzed litter decomposition, soil and microbial C and N, microbial community composition, and soil organic matter quality in three forest sites with old reindeer exclosures adjacent to grazed areas. There was no effect of grazing on soil C/N ratio, inorganic N concentrations, microbial biomass C, microbial community structure analyzed by phospholipid fatty acid (PLFA) analysis, and organic matter quality analyzed by sequential fractionation, in the soil organic layer. However, microbial N was enhanced by grazing at some of the sampling dates and was negatively correlated with soil moisture, which indicates that increased microbial N could be a stress response to drought. The effect of grazing on litter decomposition varied among the decomposition stages: during the first 1.5 months, the litter C loss was significantly higher in the grazed than the ungrazed areas, but the difference rapidly levelled out and, after one year, the accumulated litter C loss was higher in the ungrazed than the grazed areas. Litter N loss was, however, higher in the grazed areas. Our study demonstrates that herbivores may influence soil processes through several mechanisms at the same time, and to a varying extent in the different stages of decomposition.     

Land-use/cover change effects and carbon controls on volcanic soil profiles in highland temperate forests

The stabilization of SOM by Al–humus complexes and non-crystalline minerals is a key issue to explain the soil-C variability and the biogeochemical processes that determine the fate of soil C following land-use/cover change (LUCC) in volcanic landscapes. In an altitudinal gradient of volcanic soils (2550–3500 masl), we quantified the total soil C (C_T) concentrations and stocks in soil pits sampled by genetic horizons. We performed analyses at landscape and local scales in order to identify and integrate the underlying environmental controls on C_T and the effects of LUCC. We selected four sites, two on the upper piedmont, one on the lower mountain slope and one on the middle mountain slope at Cofre de Perote volcano (eastern central Mexico) where temperate forests are the natural vegetation. At each site we selected three to five units of use/cover as a chronosequence of the LUCC pathways. In each soil horizon chemical characteristics (i.e. N, C/N ratio, pH, exchangeable bases) were determined and mineralogical properties were estimated from selective Al, Fe and Si oxalate and pyrophosphate extractions (i.e. the Alp/Alo ratio, the active Al related to non-crystalline minerals as Al_o ? Al_p, the allophane concentration, and the non-crystalline Al and Fe minerals as Al_o + 1/2Fe_o). At landscape scale, the Al–humus complexes were strongly related to the C_T concentration in topsoil (A horizons) but this relationship decreased with depth. In turn, the non-crystalline minerals and the C/N ratio explained the variability of the C_T concentrations in C horizons. At local scale, C_T concentrations and stocks were depleted after conversion of forest to agriculture in Vitric Andosols at the upper piedmont but this was not observed in Silandic Andosols. However, in Vitric Andosols the reduction of the C_T stocks is partially recovered throughout the regeneration/reforestation processes. The results suggest that the lower vulnerability of Silandic Andosols than Vitric Andosols to changes in the C_T after LUCC is due to the higher levels of SOM stabilized by Al–humus complexes and non-crystalline minerals in the Silandic soils. Furthermore, the importance of the allophane to explain the C_T stocks in the Silandic Andosols of the middle slopes suggests that the C_T stabilized by this mineral fraction in the subsoil adds an important fraction of the C_T to the estimates of the stocks.     

北京山区主要人工林枯落物水文效应

为探究北京山区主要人工林枯落物水文效应,以北京市怀柔区汤河口镇庄户沟小流域油松、刺槐、侧柏3种林分为研究对象,利用枯落物现存量样地调查、浸泡实验和抗冲槽法,建立枯落物持水量、吸水速率和浸水时间相关关系,定量研究枯落物层水文效应,结果表明:1)3种林分枯落物现存量和总厚度表现为油松最大,分别为6.37t/hm2和4.0c...     

华北山地6种天然次生林土壤氮素的空间异质性特征

 利用地统计学理论和方法研究华北山地次生林区6种天然次生林土壤氮素的空间异质性特征。结果表明:1)次生阔叶林土壤总氮质量分数相对较高（3 1004 500 mg/kg）,而针叶林相对较低（9001 300 mg/kg）,各森林类型土壤中有效NH4+-N质量分数均高于有效NO3--N,形成以NH4+-N占优势的氮营养生境;2)针阔混交林中,土壤全氮的变异强度最大,变异的空间相关性较差（随机性变异占总变异的42.7%）,针叶林中,全氮空间变异强度相对较弱,但以自相关变异为主（结构方差比为72.2%81.0%）,呈现弱的斑块分布特征;3)阔叶林中,NH4+-N具有很强的空间自相关变异,NO3--N异质性程度相对较弱,针叶林中,NH4+-N变异强度较小,而NO3--N空间变异却相对明显;4)不同森林类型对土壤全氮及各有效氮形态的空间异质性特征有影响;5)植被种类、植被组成、植被多样性等因素的差异及由此导致的树种空间分布格局是影响总氮量及氮矿化,进而导致氮素不同形态在林分间甚至林分内不同空间样点间异质性形成的重要原因。     

Predicting soil organic carbon density using auxiliary environmental variables in northern Iran

In the present study, artificial neural networks (ANNs) were employed to develop models to predict soil organic carbon density (SOCD) at different depths of soil layers. Selected environmental variables such as vegetation indices, soil particle size distribution, land use type, besides primary and secondary terrain attributes were considered as the input variables. According to the results, the ANN models explained 77% and 72% of the variability in SOCD at soil layer depths of 0–20 cm and 20–40 cm, respectively, at the site studied. Sensitivity analyses showed that the most considerable positive contribution of variables for predicting SOCD included the land use type, normalized difference vegetation index (NDVI) > normalized difference water index (NDWI) > silt > clay > elevation in the 0–20 cm soil layer. On the other hand, for the 20–40 cm soil layer, the land use type following NDVI > NDWI > clay > silt were identified as the most powerful predictive factors. In the Deylaman region, in both soil layers, sand had a considerable negative effect on SOCD and most of the terrain attributes had no significant impact on the SOCD prediction. Therefore, these results provide valuable information for sustainable management and decision-making on a landscape scale for governors and other users.     

The effects of irrigation and cultivation on the quality of desert soil in central Iran

Cultivation of irrigated desert soils in Central Iran is one way of utilizing under‐exploited land to produce more food. This study explores the value of soil quality indicators as measures when converting desert to croplands. Soil samples from unfarmed desert, wheat and alfalfa sites in the Abarkooh Plain (Central Iran) were taken from 0–10, 10–20 and 20–30 cm depths. Soil quality indicators including organic carbon, total nitrogen, carbohydrate, particulate organic carbon (POC) in aggregate fractions, and aggregate water‐stability were determined. The desert soils contained organic carbon of 0·26–0·56 g kg⁻¹, total nitrogen of 0·05–0·08 g kg⁻¹ and carbohydrate of 0·03–0·11 g kg⁻¹ at 0–30 cm depth. Across this depth, the contents of organic carbon, total nitrogen and carbohydrate in wheat were about 3–7, 2–3 and 6–26‐times higher than those of desert soils, respectively. These values for alfalfa were 5–12, 3–4 and 7–35 times, respectively. The POC (near zero in desert soils) and generally other soil quality indicators showed greater improvement in alfalfa than in wheat fields. The results indicated a significant decrease in proportion of the fraction <0·05 mm in cultivated soils, whereas the proportion of the large aggregate size classes (2–4 and 1–2 mm) was increased by irrigation and cultivation. A significant improvement in aggregate water‐stability was observed in cultivated soils. At all depths, a large portion of the total soil organic carbon was stored in the fractions <0·05 mm for desert and macroaggregates (0·25–2 mm) for cultivated soils. Copyright © 2010 John Wiley & Sons, Ltd.     

Tillage and cropping effects on soil quality indicators in the northern Great Plains

The extreme climate of the northern Great Plains of North America requires cropping systems to possess a resilient soil resource in order to be sustainable. This paper summarizes the interactive effects of tillage, crop sequence, and cropping intensity on soil quality indicators for two long-term cropping system experiments in the northern Great Plains. The experiments, located in central North Dakota, were established in 1984 and 1993 on a Wilton silt loam (FAO: Calcic Siltic Chernozem; USDA¹: fine-silty, mixed, superactive frigid Pachic Haplustoll). Soil physical, chemical, and biological properties considered as indicators of soil quality were evaluated in spring 2001 in both experiments at depths of 0–7.5, 7.5–15, and 15–30 cm. Management effects on soil properties were largely limited to the surface 7.5 cm in both experiments. For the experiment established in 1984, differences in soil condition between a continuous crop, no-till system and a crop–fallow, conventional tillage system were substantial. Within the surface 7.5 cm, the continuous crop, no-till system possessed significantly more soil organic C (by 7.28 Mg ha⁻¹), particulate organic matter C (POM-C) (by 4.98 Mg ha⁻¹), potentially mineralizable N (PMN) (by 32.4 kg ha⁻¹), and microbial biomass C (by 586 kg ha⁻¹), as well as greater aggregate stability (by 33.4%) and faster infiltration rates (by 55.6 cm h⁻¹) relative to the crop–fallow, conventional tillage system. Thus, soil from the continuous crop, no-till system was improved with respect to its ability to provide a source for plant nutrients, withstand erosion, and facilitate water transfer. Soil properties were affected less by management practices in the experiment established in 1993, although organic matter related properties tended to be greater under continuous cropping or minimum tillage than crop sequences with fallow or no-till. In particular, PMN and microbial biomass C were greatest in continuous spring wheat (with residue removed) (22.5 kg ha⁻¹ for PMN; 792 kg ha⁻¹ for microbial biomass C) as compared with sequences with fallow (SW–S–F and SW–F) (Average=15.9 kg ha⁻¹ for PMN; 577 kg ha⁻¹ for microbial biomass C). Results from both experiments confirm that farmers in the northern Great Plains of North America can improve soil quality and agricultural sustainability by adopting production systems that employ intensive cropping practices with reduced tillage management.     

Distribution of inorganic phosphorus fractions in some soil profiles of Zagros forest of Iran

The aim of the present study was to evaluate the status of inorganic phosphorus (P) fractions in ten virgin soil profiles, and to study the relationships between P fractions and soil properties from Kohgyloyeh and Boir Ahmad province, Iran. The soils belonged to Alfisols, Entisols, Mollisols, and Inceptisols. Mean annual precipitation and temperature ranges were 450–850 mm and 12.2–22.4°C, respectively. Inorganic P was fractionated by sequential extraction with NaHCO₃, NH₄OAc, MgCl₂, NH₄F, NaOH, citrate-dithionite-bicarbonate (CBD), and H₂SO₄, which are referred to as NaHCO₃–P, NH₄OAc–P, MgCl₂–P, NH₄F–P, NaOH–P, CBD–P, and H₂SO₄–P, respectively. Generally, the NaHCO₃–P, NH₄OAc–P, MgCl₂–P, and NH₄F–P were higher in surface horizons, especially wherever there was higher annual precipitation. Results showed that H₂SO₄–P constituted the largest inorganic P fractions in all profiles. For all the soils studied the distribution of P fractions was similar to that of weakly weathered soils under arid and semi-arid regions which represent an early stage of development. Pedogenic P compounds were higher where weathering was higher, i.e., in surface horizons and at higher annual precipitation.     

Earthworms increase soil microbial biomass carrying capacity and nitrogen retention in northern hardwood forests

Earthworms have been shown to produce contrasting effects on soil carbon (C) and nitrogen (N) pools and dynamics. We measured soil C and N pools and processes and traced the flow of ¹³C and ¹⁵N from sugar maple (Acer saccharum Marsh.) litter into soil microbial biomass and respirable C and mineralizable and inorganic N pools in mature northern hardwood forest plots with variable earthworm communities. Previous studies have shown that plots dominated by either Lumbricus rubellus or Lumbricus terrestris have markedly lower total soil C than uncolonized plots. Here we show that total soil N pools in earthworm colonized plots were reduced much less than C, but significantly so in plots dominated by contain L. rubellus. Pools of microbial biomass C and N were higher in earthworm-colonized (especially those dominated by L. rubellus) plots and more ¹³C and ¹⁵N were recovered in microbial biomass and less was recovered in mineralizable and inorganic N pools in these plots. These plots also had lower rates of potential net N mineralization and nitrification than uncolonized reference plots. These results suggest that earthworm stimulation of microbial biomass and activity underlie depletion of soil C and retention and maintenance of soil N pools, at least in northern hardwood forests. Earthworms increase the carrying capacity of soil for microbial biomass and facilitate the flow of N from litter into stable soil organic matter. However, declines in soil C and C:N ratio may increase the potential for hydrologic and gaseous losses in earthworm-colonized sites under changing environmental conditions.     

Catabolic profiles of soil fungal communities along a geographic climatic gradient in Israel

The great distances that typically separate different climatic zones have previously restricted the investigation of climatic controls over soil microbial function to only short-scale gradients, or alternatively, to the investigation of extreme instead of real gradients. In this study, we comparatively assessed sole carbon source utilization profiles and resultant catabolic diversity levels of soil fungal communities along a geographically continuous steep climatic gradient, stretching from the Upper Galilee in the north of Israel to the Negev Desert in the south. Four sites along the gradient were studied, representing humid-Mediterranean, Mediterranean, semi-arid and arid climate types, and they were characterized by a mean annual rainfall of 780, 537, 300, and 90 mm, respectively.The relationships between abiotic soil characteristics and fungal activity parameters (basal respiration, biomass, and the metabolic quotient qCO₂) as well as fungal substrate utilization profiles and functional diversity were explored in the context of climate and seasonality (rainy versus dry seasons).To make an ecologically relevant assessment of fungal activity in soil, a MicroResp? microrespiratory system capable of analyzing whole-soil samples was modified to allow, for the first time, the testing of fungal utilization of low-solubility carbon substrates, alongside other major plant-derived substrates, reflective of the soil environment.The accurate profiling of substrate utilization in the calcareous soils comprising this Mediterranean gradient could not have been accomplished without the correction of measured CO₂ evolution data, which were biased due to CaCO₃–CO₂–H₂O equilibria reactions. The correction of the data was conducted according to a protocol presented in the preceding article of this series.The utilization potential of all 14 substrates tested was higher during the dry than during the rainy season, particularly in the Mediterranean sites, with polymeric substrates being utilized preferentially in the arid sites in comparison with the Mediterranean sites.The distinctive approach exercised in this study enabled us to make a relevant ecological interpretation, particularly in face of the prospect of fungi being responsible for the bulk of recalcitrant organic matter decomposition in soil.     

Measurement and modelling of the effects of initial soil conditions and slope gradient on soil translocation by tillage

Tillage erosion studies have mainly focused on the effect of topography and cultivation practices on soil translocation during tillage. However, the possible effect of initial soil conditions on soil displacement and soil erosion during tillage have not been considered. This study aims at investigating the effect of the initial soil conditions on net soil displacement and the associated erosion rates by a given tillage operation of a stony loam soil. Tillage erosion experiments were carried out with a mouldboard plough on a freshly ploughed (pre-tilled) soil and a soil under grass fallow in the Alentejo region (Southern Portugal).

The experimental results show that both the downslope displacement of soil material and the rate of increase of the downslope displacement with slope gradient are greater when the soil is initially in a loose condition. This was attributed to: (i) a greater tillage depth on the pre-tilled soil and (ii) a reduced internal cohesion of the pre-tilled soil, allowing clods to roll and/or slide down the plough furrow after being overturned by the mouldboard plough.

An analysis of additional available data on soil translocation by mouldboard tillage showed that downslope displacement distances were only significantly related to the slope gradient when tillage is carried out in the downslope direction. When tillage is carried out in the upslope direction, the effect of slope gradient on upslope displacement distances was not significant. This has important implications for the estimation of the tillage transport coefficient, which is a measure for the intensity of tillage erosion, from experimental data. For our experiments, estimated values of the tillage transport coefficient were 70 and 254 kg m⁻¹ per tillage operation for grass fallow and pre-tilled conditions, respectively, corresponding to local maximum erosion rates of ca. 8 and 35 Mg ha⁻¹ per tillage operation and local maximum deposition rates of ca. 33 and 109 Mg ha⁻¹ per tillage operation.     

北方土石山区横坡垄作坡面土壤氮的空间分布特征

横坡垄作是坡耕地广泛采用的水土保持措施,垄沟内雨水的汇聚和泥沙沉积,使得土壤氮的空间分布特征明显有别于传统耕作坡面。以北方土石山区横坡垄作坡面为研究对象,样带法采集土壤样品,基于经典统计、地统计学、Kriging插值等方法,分析垄面、垄沟等特征点位全氮(TN)、硝态氮(NO^3--N)、铵态氮(NH4+-N)含量沿坡位变化及其剖面分布,明晰横坡垄作坡面土壤氮的空间分布特征。结果表明:北方土石山区土壤氮含量属于中低水平,变异系数介于17.64%～33.60%,但垄面土壤氮的变异水平高于垄沟。TN含量沿坡位的变异最为显著,表现为坡下>坡脚>坡中>坡上;仅垄沟NO^3--N、NH4+-N含量沿坡位存在显著变化,坡脚NO^3--N、NH4+-N含量较其他坡位显著增加66.30%～83.85%。垄面与垄沟间氮含量的差异在坡上、坡下和坡脚体现的较为明显;与垄沟相比,垄面坡上TN含量减少21.34%,坡脚NO^3--N和NH4+-N含量减少17.42%～37.47%,坡下土壤氮含量增加21.56%～38.16%。TN剖面分布与坡位和特征点位有关,NO^3--N、NH4+-N的剖面分布主要受控于特征点位,但氮含量剖面分布符合指数函数关系。综上,横坡垄作坡面土壤氮空间异质性明显,且主要受控于特征点位和坡位。研究结果可为提高横坡垄作措施下氮肥利用效率、精准农业的顺利推广提供技术支撑。     

Plant canopy effects on litter accumulation and soil microbial biomass in two temperate forests

The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha⁻¹) compared to oak stands (15.7t ha⁻¹). Canopy leaf area was also significantly larger in mixed stands (1.96m² m⁻²) than in oak stands (1.73m² m⁻²). Soil organic carbon (C _org) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (C _mic), nitrogen (N _mic), and total soil nitrogen (N _tot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean C _org/N _tot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as C _mic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.     

Geostatistics-based spatial distribution of soil moisture and temperature regime classes in Mazandaran province,northern Iran

Soil moisture regime (SMR) and soil temperature regime (STR) classes as soil classification criterions are required by US Soil Taxonomy because they affect genesis, use, and management of soils. The lack of sufficient soil moisture and temperature data requires the characterization of the pedoclimate on the basis of climatic data processed by simulation models. This research was conducted to consider the new approach for SMR and STR mapping. The objectives of this study were to compare the four interpolation schemes including ordinary kriging (OK), cokriging (Co-K), inverse distance weighting, and conditional simulation for interpolating the monthly mean total precipitation (MMTP) and monthly mean air temperature (MMAT) and to apply the Java Newhall simulation model for the MMTP and MMAT predictive values at each node of 1 km² grids across the Mazandaran province, northern Iran, for delineating the SMR and STR classes. The semivariogram analyses showed moderate to strong spatial dependence of data sets. The accuracy of interpolators varied within months for both MMTP and MMAT data sets. In most cases, OK and Co-K methods had the highest accuracy with lower mean error, root mean square error, and higher concordance correlation coefficient. The predictive maps show high diversity of SMR classes including Aridic, Ustic, Udic, and Xeric. The STR classes comprise Mesic, Thermic, and Cryic regimes. Results herein indicated that geostatistical approaches can potentially provide the opportunity for mapping of SMR and STR classes in data scarce regions.     

Environmental effects on soil NO concentrations and root N uptake in beech and spruce forests

This study aimed to investigate the shifts in net nitrogen (N) uptake and N compounds of fine roots over the vegetation period (i.e., spring, summer, autumn) and correlate this with NO concentration in the soil. Soil NO concentration was measured using gas lysimeters for collection and a chemiluminescence analyzer for quantification. Net N uptake by the roots was determined using the ¹⁵N enrichment technique. N pools were quantified using spectrophotometric techniques. Soil NO concentrations at beech and spruce forest sites were highest in spring (June), and lowest in winter (December). Total N of the roots was similar during the seasons and between the two years under study despite considerable variation of different N compounds. Net N uptake generally increased with higher N supply. Correlation analysis revealed a positive relationship between soil NO concentration and net N uptake only for spruce trees. This relationship seemed to be modulated by environmental factors and tree species.     

Climatic effects on soil trophic networks and the resulting humus profiles in holm oak (Quercus rotundifolia) forests in the High Atlas of Morocco as revealed by correspondence analysis

Multivariate methods have been widely used for revealing the structures of communities, and in this paper we explore one particular method, namely correspondence analysis (also called reciprocal averaging), for studying humus profiles by the ‘method of small volumes’. The present study was done on humus profiles under holm oak (Quercus rotundifolia), an evergreen Mediterranean species, in the High Atlas of Morocco. Three sites (1500 m, 1700 m, 1900 m altitude) and 2 years (1999 and 2002) were compared. The humus form is Dysmull (mull with thick litter horizons), with variations in the thickness of the OL (entire leaves), OF (fragmented leaves with faecal pellets) and A (hemorganic) horizons according to altitude and year. The dead leaves are rapidly incorporated into holorganic (earthworm, insect) and hemorganic (enchytraeid) animal faeces, which form the bulk of the OF and A horizons. The S horizon (weathering parent rock) shows the greatest development of the root system. As altitude increases more fresh litter (OL) or more humified organic matter (OF, A) is accumulated. Variation from year to year is depicted by opposite differences in the amount of entire oak leaves and of dead roots. Humus components (classes) are used as active (main) variables, after standardization of their means and variances. The addition of numerous passive (additional) variables, standardized in the same way as active variables, enabled us to understand the influence of biological and climatic effects on the composition of humus profiles and soil trophic networks.     

北京山区典型人工林的耗水规律

在我国的北方地区植被与水资源之间的关系是森林植被构建的关键性问题.如何依据水分条件的承载力,构建水分稳定的森林植被是一项重要研究.以北京妙峰山侧柏、油松为研究对象,应用大型可称量式蒸渗仪测定林木个体耗水规律,并在此基础上进行尺度扩展,分析2种林分群体耗水特征.研究发现：在晴天条件下,侧柏和油松蒸腾强度的日变化趋势均为单峰曲线;在典型阴天和雨天条件下,2树种间蒸腾速率差异明显,受云量动态变化影响,蒸腾强度的日变化趋势为多峰曲线.通过相关分析发现,在选定的环境因子中太阳辐射通量、大气水汽压饱和差、空气温度、土壤含水率和土壤水势均与林木蒸腾速率呈正相关,而空气相对湿度与林木蒸腾速率呈负相关.另外,利用边材面积作为尺度转换因子实现由单木到林分的尺度扩展,根据测定的样木蒸腾量,推算得出侧柏林6-9月总蒸腾量为321.43 mm,油松林的总蒸腾量为192.83 mm.     

Stand-scale spatial patterns of soil microbial biomass in natural cold-temperate beech forests along an elevation gradient

This study focuses on spatial heterogeneity in the soil microbial biomass (SMB) of typical climax beech (Fagus crenata) at the stand scale in forest ecosystems of the cold-temperate mountain zones of Japan. Three beech-dominated sites were selected along an altitudinal gradient and grid sampling was used to collect soil samples at each site. The highest average SMB density was observed at the site 1500 m a.s.l. (44.9 gC m⁻²), the lowest was recorded at the site 700 m a.s.l. (18.9 gC m⁻²); the average SMB density at the 550 m site (36.5 gC m⁻²) was close to the overall median of all three sites. Geostatistics, which is specifically designed to take spatial autocorrelation into account, was then used to analyze the data collected. All sites generally exhibited stand-scale spatial autocorrelation at a lag distance of 10-18 m in addition to the small-scale spatial dependence noted at <3.5 m at the 550 m site. Correlation analysis with an emphasis on spatial dependency showed SMB to be significantly correlated with bulk density at the 550 and 1500 m sites, dissolved organic carbon (DOC) at the 700 and 1500 m sites, and nitrogen (N) at the 550 and 700 m sites. However, no soil parameter showed a significant correlation with SMB at every site, and some variables were also differently correlated (negative or positive) with SMB at different sites. This suggests that the factors controlling the spatial distribution of SMB are very complex and responsive to local in situ conditions. SMB regression models were generated from both the ordinary least-squares (OLS) and generalized least-squares (GLS) models. GLS performance was only superior to OLS when cross-variograms were accurately fitted. Geostatistics is preferable, however, since these techniques take the spatial non-stationarity of samples into account. In addition, the sampling numbers for given minimum detectable differences (MDD_s) are provided for each site for future SMB monitoring.