Mercury in forest canopy throughfall water and its relation to atmospheric deposition

A seasonal variation of both particle and gaseous Hg concentrations in the atmosphere is present in south-western Sweden. An average gaseous Hg level of 3.7 ng m⁻³ is found in winter, compared to 2.8 ng m⁻³ in summer. A weak decreasing south-north gradient for gaseous Hg in air over the Nordic countries is also present, with yearly average values from 3.2 to 2.8 ng m⁻³. A gradient for particulate Hg is less clear. An air parcel trajectory sector classification of gaseous Hg levels in air, and to some extent the particulate associated Hg, clearly demonstrates the increased concentrations in the southern sectors, especially in south-western Sweden where the gaseous Hg increase is about I ng m⁻³. These observations are consistent with an influence from the European continent. The average concentrations of Hg in precipitation at the various stations show a pronounced decreasing south-north gradient. A major portion of the total Hg present in precipitation is associated with particles. For the southern stations, a strong correlation between Hg and sulfate, or pH, is present suggesting a connection between Hg in precipitation and anthropogenic activities.     

Chemistry of bulk precipitation throughfall,soil water and stream water in a small catchment in Devon,England

Monthly mean concentrations of potassium, calcium, sodium, magnesium chloride and nitrate-nitrogen were determined from samples of bulk precipitation, throughfall, soil water and streamflow collected weekly between April 1975 and September 1977 in a small catchment in Devon, England. Soil water concentrations are compared with the analysis of exchange capacity in composite soil samples. Rain contributed much sodium and chloride to total catchment output, and potassium was selectively enriched in throughfall. Calcium and magnesium concentrations were high in soil water samples and on the soil exchange complex.     

Dissolved organic carbon and nitrogen in precipitation,throughfall, soil solution,and stream water of the tropical highlands in northern Thailand

Dissolved organic matter (DOM) is important for the cycling and transport of carbon (C) and nitrogen (N) in soil. In temperate forest soils, dissolved organic N (DON) partly escapes mineralization and is mobile, promoting loss of N via leaching. Little information is available comparing DOC and DON dynamics under tropical conditions. Here, mineralization is more rapid, and the demand of the vegetation for nutrients is larger, thus, leaching of DON could be small. We studied concentrations of DOC and DON during the rainy seasons 1998–2001 in precipitation, canopy throughfall, pore water in the mineral soil at 5, 15, 30, and 80 cm depth, and stream water under different land‐use systems representative of the highlands of northern Thailand. In addition, we determined the distribution of organic C (OC) and N (ON) between two operationally defined fractions of DOM. Samples were collected in small water catchments including a cultivated cabbage field, a pine plantation, a secondary forest, and a primary forest. The mean concentrations of DOC and DON in bulk precipitation were 1.7 ± 0.2 and 0.2 ± 0.1 mg L^–1, respectively, dominated by the hydrophilic fraction. The throughfall of the three forest sites became enriched up to three times in DOC in the hydrophobic fraction, but not in DON. Maximum concentrations of DOC and DON (7.9–13.9 mg C L^–1 and 0.9–1.2 mg N L^–1, respectively) were found in samples from lysimeters at 5 cm soil depth. Hydrophobic OC and hydrophilic ON compounds were released from the O layer and the upper mineral soil. Concentrations of OC and ON in mineral‐soil solutions under the cabbage cultivation were elevated when compared with those under the forests. Similar to most temperate soils, the concentrations in the soil solution decreased with soil depth. The reduction of OC with depth was mainly due to the decrease of hydrophobic compounds. The changes in OC indicated the release of hydrophobic compounds poor in N in the forest canopy and the organic layers. These substances were removed from solution during passage through the mineral soil. In contrast, organic N related more to labile microbial‐derived hydrophilic compounds. At least at the cabbage‐cultivation site, mineralization seemed to contribute largely to the decrease of DOC and DON with depth, possibly because of increased microbial activity stimulated by the inorganic‐N fertilization. Similar concentrations and compositions of OC and ON in subsoils and streams draining the forested catchments suggest soil control on stream DOM. The contribution of DON to total dissolved N in those streams ranged between 50% and 73%, underscoring the importance of DOM for the leaching of nutrients from forested areas. In summary, OC and ON showed differences in their dynamics in forest as well as in agricultural ecosystems. This was mainly due to the differing distribution of OC and ON between the more immobile hydrophobic and the more easily degradable hydrophilic fraction.     

Neutralization of atmospheric acid inputs in small spring catchments in the Frankenwald mountains,Germany

Investigations on soil and freshwater acidification are usually focused on well-aerated systems. This study deals with the role of reductive processes for the neutralization of acid soil solution within helocrene springs. Two toposequences consisting each of three profiles (forest soil, margin of fen, fen) were established to study the chemistry of the solid phase (soil pH, CEC, pedogenic Fe- and Al-oxides) and the soil solution in two small spring catchments on three dates during 1991 and 1992. Despite high acid inputs and acidified forest soils the pH of the spring outflow is near neutral, and the soil solid phases of the spring fens are not acidified. The results support the following hypothesis: Aluminum with its corresponding anion sulfate is leached with the soil solution into the water-saturated fens. Dissimilatory iron and sulfate reduction take place within the fen and generate alkalinity. Reduced iron either reacts with sulfide to form pyrite or migrates within the fen profile and precipitates in the uppermost, oxic horizons, consuming part of the generated alkalinity. Due to the higher pH values in the fens the incoming aluminum precipitates releasing acidity. The alkalinity generated exceeds the amount of acidity released by oxidation and precipitation of iron and the precipitation of aluminum. A balance of alkalinity consuming and alkalinity generating processes based on solid phases showed that iron and sulfate reduction can account for at least 67% of the neutralization of acidity entering the fen of one of the catchments. Due to shorter water retention times and higher discharge these processes are of minor importance in the other catchment.     

Effects of simulated throughfall pH and sulfate concentration on a deciduous forest soil

A model deciduous forest soil (Schaffenaker loamy sand) was treated for 8 mo in the greenhouse in 25 cm reconstructed columns with simulated throughfall at pH 6.0 or 4.0, and SO₄ ^2? levels of 12.8 or 24.8 mg L^?1. Red oak seedlings grown in the microcosms showed no growth or foliar element response to the treatments. Sulfate loading had a greater impact on soil and leachate chemistry than pH. Higher available soil P in the A, horizon was associated with the pH 6.0 and high SO₄ ^2?2 treatment combination. High SO₄ ^2? loading also reduced exchangeable K⁺ in the A_1?. Other soil horizons were unaffected by either treatment. Leachate chemistry was not significantly altered by througfall pH, but significantly greater export of Na⁺, Ca²⁺, Mg²⁺, Al³⁺, and NO₃ ^?, and lower SO₄ ^2? loss, occurred with low SO₄ ^? input. Comparatively half as much NO₃ ^? loss was associated with high SO₄ ^2? deposition. The high rate of NO₃ ^? leaching appeared responsible for greater equivalent mass loss of cations from the low SO₄ ^2? treatment. Leachate removal of SO₄ ^2? approximated input after 8 mo. The capacity of this soil to adsorb SO₄ ^2? appeared relatively limited in the absence of normal element cycling. The sulfate component of simulated deciduous forest throughfall was shown to have a potentially greater impact than pH on ion leaching from forest soil. Additional consideration of the role of SO^2? ₄ deposition, in the context of throughfall rather than incident precipitation, is warranted in studies of acidic deposition effects on internal forest soil processes.     

Effects of forest age on surface drainage water and soil solution aluminium chemistry in stagnopodzols in Wales

The influence of forest development on soil solution and surface drainage water aluminium chemistry was investigated in Sitka spruce (Picea sitchensis) plantations in Wales. Comparisons with semi-natural grassland and moorland sites are described. A highly significant positive relationship was shown between increasing forest age and soilwater aluminium concentrations in the B horizons. Shortterm/episodic peaks in Al concentrations were strongly related to incidences of high concentrations of neutral, marine-derived, salts in the soilwater. Nitrification may be an important factor in soil acidification and the mobilization of Al in soilwaters beneath the older mature-forest plantations in Wales. Labile monomeric Al concentrations were largest in surface waters draining the oldest forestry plantations compared with younger forest catchments and moorland, although response to discharge of soilwater acidity to the surface waters at individual sites was dependent on the acid neutralizing capacity of the groundwater component of the surface waters.     

Effect of summer throughfall exclusion, summer drought, and winter snow cover on methane fluxes in a temperate forest soil

Soil moisture strongly controls the uptake of atmospheric methane by limiting the diffusion of methane into the soil, resulting in a negative correlation between soil moisture and methane uptake rates under most non-drought conditions. However, little is known about the effect of water stress on methane uptake in temperate forests during severe droughts. We simulated extreme summer droughts by exclusion of 168 mm (2001) and 344 mm (2002) throughfall using three translucent roofs in a mixed deciduous forest at the Harvard Forest, Massachusetts, USA. The treatment significantly increased CH₄ uptake during the first weeks of throughfall exclusion in 2001 and during most of the 2002 treatment period. Low summertime CH₄ uptake rates were found only briefly in both control and exclusion plots during a natural late summer drought, when water contents below 0.15 g cm⁻³ may have caused water stress of methanotrophs in the A horizon. Because these soils are well drained, the exclusion treatment had little effect on A horizon water content between wetting events, and the effect of water stress was smaller and more brief than was the overall treatment effect on methane diffusion. Methane consumption rates were highest in the A horizon and showed a parabolic relationship between gravimetric water content and CH₄ consumption, with maximum rate at 0.23 g H₂O g⁻¹ soil. On average, about 74% of atmospheric CH₄ was consumed in the top 4-5 cm of the mineral soil. By contrast, little or no CH₄ consumption occurred in the O horizon. Snow cover significantly reduced the uptake rate from December to March. Removal of snow enhanced CH₄ uptake by about 700-1000%, resulting in uptake rates similar to those measured during the growing season. Soil temperatures had little effect on CH₄ uptake as long as the mineral soil was not frozen, indicating strong substrate limitation of methanotrophs throughout the year. Our results suggest that the extension of snow periods may affect the annual rate of CH₄ oxidation and that summer droughts may increase the soil CH₄ sink of temperate forest soils.     

沂蒙山林区不同森林群落土壤水分贮存与入渗特征

为给沂蒙山区森林植被建设中合理群落类型的选择与配置提供参考,采用森林水文学方法,对淮河流域沂蒙山林区典型森林群落的土壤水分贮存与人渗特征进行研究。结果表明：1）森林群落具有显著提高林地土壤孔隙度、土壤贮水量和土壤入渗速率的作用,其作用程度混交林大于纯林,阔叶林大于针叶林;2）森林群落对土壤（非毛管）滞留贮水量的提高程度明显大于土壤毛管吸持贮水量,因而具有明显的涵养水源作用;3）Horton模型和Kostiakov模型能较好模拟研究区森林群落的土壤人渗过程,但通用经验模型和Philip模型的适用性较差;土壤入渗速率与孔隙度之间具有明显的线性正相关关系。     

Counteractions Against Acidification in Forests Ecosystems. Effects on stream water quality after dolomite application to forest soil in Gjerstad,Norway

The deposition of strong acids is one of many threats to forest ecosystems and viable forestry. Several counteractions against acidification have been launched, e.g. changes in forestry management and the introduction of chemicals. The inter-institutional programme “Counteractions Against Acidification in Forest Ecosystems” was established in 1993 to evaluate existing knowledge and run experimental and fullscale field experiments. A total of 240 metric tons of coarse dolomite powder was spread by helicopter in September 1994 on 84 ha forest catchment dominated by pine (Pinus sylvestris) and Norway spruce (Picea abies). Potential desirable and undesirable effects after this carbonate application may be less pronounced than recorded at other sites due to the relatively moderate dose (3 tons ha^?1). Pre-liming stream water quality (mean values for May 1993-September 1994) was as follows: pH 4.8; Ca 1.13 mg L^?1; reactive Al (RAl) 248 μg L^?1; inorganic monomeric Al (Al) 72 μg L^?1. The reference station was slightly higher in Ca and slightly lower in both RAl and Al. Dolomite application resulted in a significant increase in pH to 5.7 as mean value for the post-liming period (September 1994-April 1995). Both Ca and Mg increased significantly after liming, and both RAl and Al, declined significantly. The rapid detoxification of stream-water may be explained by dissolution of dolomite particles in both streams and catchment, a resulting pH increase and change in Al species composition. Retention of Al in the catchment probably explains the reduction in RAl. No increase in NO₃, total N, total P or TOC was recorded the first seven months.     

模拟自然条件下黄土区坡地的大气、土表及土壤水交互作用的动力学模型及其应用

The mechanism of atmospheric,surface and soil water interactions( water transformation) in hillslope under natural conditions was analyzed,and a dynamic model was developed to simulate infiltration,overland flow and soil water movement during natural rainfall in hillslope,by bringing froward concepts such as rainfall intensity on slope and a correction coefficient of saturated soil water content for soil surface seal.Some factors,including slope angle,slope orientation and raindrop inclination,which affect the rainfall amount on slope, were taken into account while developing the dynamic model.The effect of surface seal on infiltration and water balance under a boundary condition of the second kind was aslo considered. Application of the model in a field experiment showed that the model simulated precisely the infiltration,overland flow and sol water monvement in hillsope under natural rainfall conditions.     

Liming and fertilization of acid forest soil: Short-term effects on runoff from small catchments

Increased atmospheric deposition of strong acids and deposition of potentially acidifying compounds (e.g. ammonium) has caused a decline in pH and exchangeable base cations in forest soils in Sweden. In recent years, attention has been paid to liming of forest soil as a method to counteract the effects of acid deposition. Experiments with liming, fertilization and woodash treatment of acid forest soils started in 1984. The aim of this study was to determine the effects of low doses of lime (500 to 1500 kg ha^?1) in combination with N fertilizers on tree growth, nutritional status of trees as well as soil, and runoff chemistry. This paper describes the short term effects of liming and fertilization on runoff from ten small catchments in two regions in south Sweden. The effects of liming were small in both areas. In the catchments fertilized with N (NH₄NO₃), a substantial leakage of various N species appeared in runoff after treatment. The increased N output was dominated by nitrate. The excess leakage of N during 2 yr after fertilization was 25 and 13% as an average of the applied N in the two study areas. The mobile nitrate increased the base cations output via runoff with 10 to 100% during 1 yr after N treatment. The runoff of Al increased with 60 to 100% the first year in the fertilized catchments. Mobilization of cations was also influenced by ammonium, especially K that was exchanged by ammonium on the surface of the soil particles. The effects of woodash-treatment were small, however, sulfate in the ash leaked out following application and about 100% of the added sulfate was found in runoff during the first year.     

Liming and fertilization of acid forest soil: Short-term effects on runoff from small catchments

Increased atmospheric deposition of strong acids and deposition of potentially acidifying compounds (e.g. ammonium) has caused a decline in pH and exchangeable base cations in forest soils in Sweden. In recent years, attention has been paid to liming of forest soil as a method to counteract the effects of acid deposition. Experiments with liming, fertilization and woodash treatment of acid forest soils started in 1984. The aim of this study was to determine the effects of low doses of lime (500 to 1500 kg ha^–1) in combination with N fertilizers on tree growth, nutritional status of trees as well as soil, and runoff chemistry. This paper describes the short term effects of liming and fertilization on runoff from ten small catchments in two regions in south Sweden. The effects of liming were small in both areas. In the catchments fertilized with N (NH₄NO₃), a substantial leakage of various N species appeared in runoff after treatment. The increased N output was dominated by nitrate. The excess leakage of N during 2 yr after fertilization was 25 and 13% as an average of the applied N in the two study areas. The mobile nitrate increased the base cations output via runoff with 10 to 100% during 1 yr after N treatment. The runoff of Al increased with 60 to 1009, the first year in the fertilized catchments. Mobilization of cations was also influenced by ammonium, especially K that was exchanged by ammonium on the surface of the soil particles. The effects of woodash-treatment were small, however, sulfate in the ash leaked out following application and about 100% of the added sulfate was found in runoff during the first year.     

Residue impacts on runoff and soil erosion for different corn plant populations

The year to year carry-over effects of biomass additions under different plant populations on runoff and erosion are unclear. The objective of this study was to quantify the impact of different plant populations on residue cover to elucidate the effects of residue cover on runoff and erosion. The residue management system involved shredding of corn (maize) biomass after harvest, incorporating the residue in the spring, and leaving the land fallow until it was no-till planted the following spring. Runoff and soil losses were measured on 18 runoff plots with plots arranged in two areas with each having three randomized treatments (0%, 50%, and 100% plant population) with three replications. The two areas were managed as a fallow/no-till corn rotation in two cycles of alternating years. Surface residue cover was highly dynamic with significant changes between cycles and seasons in response to the management practices. The annual soil losses were reduced by 47% and 54% for the 50% and 100% plant populations, respectively compared to the control. However, the annual soil loss even for the 100% plant population was still nearly seven times the tolerable soil loss limit of 7 ton ha⁻¹. The normal erosion protection afforded by no-till practices was lost by the incorporation of residue the previous year.     

Temporal variability and time compression of sediment yield in small Mediterranean catchments: impacts for land and water management

Increased soil erosion, pressure on agricultural land, and climate change highlight the need for new management methods to mitigate soil loss. Management strategies should utilize comparable data sets of long‐term soil erosion monitoring across multiple environments. Adaptive soil erosion management in regions with intense precipitation requires an understanding of inter‐annual variability in sediment yield (SY ) at regional scales. Here, a novel approach is proposed for analysing regional SY . We aimed to (i) investigate factors controlling inter‐ and intra‐annual SY , (ii) combine seasonality and time compression analyses to explore SY variability and (iii) discuss management implications for different Mediterranean environments. Continuous SY measurements totalling 104 years for eight small catchments were used to describe SY variability, which ranged from 0 to 271 t/ha/year and 0 to 116 t/ha/month. Maximum SY occurs in spring to summer for catchments with oceanic climates, while semi‐arid or dry summer climates experience SY minimums. We identified three time compression patterns at each time scale. Time compression was most intense for catchments with minimum SY in spring to summer. Low time compression was linked to very high soil loss, low run‐off and sediment production thresholds, and high connectivity. Reforestation, grassland and terracing changed SY magnitudes and time compression, but failed to reduce SY for large storm events. Periods with a high probability of high SY were identified using a combination of intra‐annual SY variability, seasonality analysis, and time compression analysis. Focusing management practices on monthly flow events, which account for the majority of SY , will optimise returns in Mediterranean catchments.     

不同微咸水组合灌溉对土壤水盐分布和冬小麦产量影响的田间试验研究

为了研究不同组合灌溉顺序对土壤水盐分布状况和冬小麦产量的影响,2003年-2005年在河北省中科院南皮生态试验站进行了冬小麦田间微咸水灌溉试验。通过对冬小麦主根区和100 cm深度土壤的水、盐分布状况和冬小麦产量进行分析,结果表明3 g/L的微咸水可以作为冬小麦的灌溉用水,但连续使用会导致土壤发生积盐;拔节期应尽量避免使用微咸水,且不宜连续使用微咸水进行灌溉,组合灌溉最好采用咸淡交替的方式;综合土壤的积盐状况和冬小麦产量分析,淡（拔节水）淡（抽穗水）咸（灌浆水）的组合灌溉顺序为最优方案,该研究为合理开发利用灌区地下微咸水提供了依据。     

Effects of changed litter inputs on soil labile carbon and nitrogen pools in a eucalyptus-dominated forest of southeast Queensland,Australia

Purpose

The quantity and quality of litter inputs to forest soils are likely to be changed as a result of the climate change and human disturbances. However, the effects of changed litter inputs on soil labile carbon (C) and nitrogen (N) pools still remain unclear.

Materials and methods

A 15-month in situ field experiment was conducted within both high and low litter quality site in a eucalyptus-dominated native forest of Queensland, Australia. Three rates of litter inputs were applied, including (i) no litter (NL); (ii) single litter (SL), representing the average condition of the surrounding forest floor; and (iii) double litter (DL). Water-extractable organic C (WEOC) and total N (WETN), hot water-extractable organic C (HWEOC) and total N (HWETN), microbial biomass C (MBC), and N (MBN) were analyzed in the 0–5-cm soil layer seasonally.

Results and discussion

Litter input rates had no significant effects on litter decomposition at both sites (P?>?0.05). After 15-month of decomposition, mean litter mass loss was 46.3% and 31.2% at the HQ and LQ sites, respectively. Changed litter quantity had no significant effects on any of the soil labile C and N pools, regardless of litter quality. However, soil labile C and N pools significantly varied with sampling times, and the samples of different sampling times were clearly separated at both sites according to the redundancy analysis (RDA). WEOC peaked in summer, declined in autumn and winter, and increased again in spring, while the concentrations of HWEOC and MBC peaked in the winter period. The seasonal trends of MBN were opposite to the trends of WETN, which might be due to the temporal partitioning of N between plants and microbes.

Conclusions

The findings indicated that soil labile C and N pools in the eucalyptus-dominated forest of subtropical Australia were resistant to a short-term change in aboveground litter inputs. Future research should expand on these findings by keeping observing over a longer time period and considering the influence of changed belowground litter inputs.

     

The impact of reduced atmospheric depositions on soil microbial parameters in a strongly acidified Norway spruce forest at Solling,Germany

To simulate a future ion input reduction scenario in forests, a large scale field experiment was set up in a (1999) 66‒year‒old Norway spruce plantation at Solling, central Germany. Throughfall input of H⁺, SO₄^2—, and N‒compounds is artificially reduced by means of a permanent roof construction below the canopy and a de‒ionizing equipment since 1991. Here we present long term soil solution records for SO₄^2—, NO₃^—, Al³⁺ and the pH of the 10 cm mineral soil sampling depth. A significant decrease in ion concentrations since the start of the treatment is observed, but no change of the soil solution pH. Even in the fourth year pH values remained well within the aluminium buffer range (pH < 4.2). Three years after the start of the experiment (July 1994) it was examined whether microbial biomass (C_mic), specific activity (heat production per unit biomass), and the percentage of C_mic in organic C material indicated any changes. Furthermore chemical standard parameters (CEC, base saturation, pH) were analyzed for all soil samples. Results indicate that despite of drastic decreases of soil solution ion concentrations in the upper soil horizons microbial parameters were not affected and that the soil solid phase is not deacidified by the treatment until now.     

The impacts of forest clearance on lizard, small mammal and bird communities in the arid spiny forest, southern Madagascar

Madagascar is a global biodiversity hotspot threatened by forest loss, degradation and fragmentation, all of which are detrimental to the future survival of forest-dwelling organisms. For conservation purposes it is essential to determine how species respond to habitat disturbance, specifically deforestation. In this study we investigated the impacts of deforestation on three vertebrate communities, lizards, small mammals and birds, in an area of spiny forest subjected to anthropogenic forest clearance. Spiny forest has high levels of endemism, but conservation in this unique ecosystem is hindered by the lack of research. We undertook standardised trapping, time-constrained and timed species searches to assess species richness, species abundance and community composition of lizards, small mammals and birds in six areas of ‘forest’ and six ‘cleared’ areas. From surveys and opportunistic sightings we recorded a total of 70 species of birds, 14 species of mammals and 38 species of reptiles and amphibians. We found forest clearing to have a negative effect on species richness and community structure of all groups and identified loss of canopy cover as a driving factor behind this. However, the response and sensitivity to clearing varied between groups and species. Lizards (50%) and small mammals (40%) had the greatest decline in species richness in response to clearing as compared to birds (26%), although birds showed the greatest shift in community structure. The community in cleared areas contained more generalist and introduced species that have wider geographic ranges and habitat preferences, than those unique to the spiny forest. We found the first suite of species to suffer from forest clearance were those of high conservation priority due to their restricted geographic range. Our findings are discussed in relation to future spiny forest conservation and management.     

Enzymatic activity and stabilization of organic matter in soil with different detritus inputs

ABSTRACT

The aim of the study was to assess the effects of different forest stands (Silver fir (Abies alba) and sycamore maple (Acer pseudoplatanus) with common hornbeam (Carpinus betulus)) on the enzymes activities and microbial biomass. The objective was to explore how changes in the detritus inputs affect soil organic matter (SOM) composition. The content of SOM fraction has been compared with soil enzyme activities. The investigation was carried out in the ?wi?tokrzyskie Mountains of central Poland. Twenty investigation plots were selected, including fir stands (10 plots) and maple with hornbeam stands (10 plots). Contents of organic C, N and base cations, pH, hydrolytic acidity, and soil texture were investigated. The content of C and N in the physically separated SOM fractions was distinguished. The study indicated only small changes in soil properties and stabilization of organic matter as a result of different detritus inputs. The maple-hornbeam and fir stands have a similar influence on microbiological processes and the SOM. Acidity of soil is a major factor affecting microbial activity and therefore pH affects enzyme dynamics. Differences in soil pH confirmed the stronger acidifying effects of fir stands compared to maple-hornbeam stands. Additionally, fir stands stimulate β-glucosidase activity, probably through a simultaneous interaction of mycorrhizal fungi in the roots of fir stands.     

Bioavailability of DOC in leachates, soil matrix solutions and soil water extracts from beech forest floors

The biodegradability of dissolved organic carbon (DOC) in different fractions from the forest floor was studied. Soil leachate (SL, the soil solution in macropores which is freely drained from forest floor after rainfall), the soil matrix solution (SMS, the soil solution in meso-/micropores of the soil matrix), and soil water extracts (SWE) from two different beech forest floors were compared. Zero-tension and tension lysimeters were used to collect SL and SMS, respectively. Loss of DOC (during 21 days) and respiration of CO₂-C (during 7 days) were used as conventional measures of the availability of DOC. Bacterial production, measured using the leucine incorporation technique, and bacterial growth efficiency were also estimated. All methods were used to study differences in biodegradability between plots with and without ground flora (Deschampsia flexuosa or Anemone nemorosa) and different type of forest floor (with an organic (O) horizon or a mull (A) horizon). There were no differences in bioavailability of DOC from soil solutions extracted from plots with and without ground flora. The bioavailability of DOC in the different collected soil solutions varied, however. DOC in SWE was the most available, with a mean of 39% of DOC-loss in 21 days, and 18% of DOC being respired in 7 days. DOC in soil matrix solution was the least available of the soil solutions (7% respired), significantly less than DOC in soil leachate (11% respired). The methods measuring biodegradation of DOC, DOC-loss and CO₂-C respiration gave similar results and were comparable to bacterial production and bacterial growth efficiency, with the exception of SWE from the O-horizon at the D. flexuosa site, which had low bacterial production and bacterial growth efficiency, indicating a limitation of the bacterial growth. This study is one of the first to use bacterial production and bacterial growth efficiency for measuring bioavailability in terrestrial environments, giving an extra dimension for the process of biodegradation of DOC.