Group selection tree harvest has been proposed as an ecologically sustainable silvicultural technique in mixed conifer forests of the western Bhutan Himalayas. To evaluate this silvicultural technique, we studied the ecological consequences of a group selection tree harvest in mixed conifer forests by assessing 127 circular plots (71 in logged and 56 in unlogged stands) in two forest management units (FMUs). Tree species composition and diversity were similar between logged and unlogged stands. Seedling density and height growth vary by species and were influenced by logging and microsites, with generally taller seedlings found in the logged versus unlogged stands. Early successional shade-intolerant species colonized logged stands. Seedlings growing on bare soil scarified by harvesting had medium vigour while seedlings growing on bryophyte mats showed good vigour in both logged and unlogged stands. Moist sites with a northerly aspect supported profuse conifer seedling regeneration, compared to sites with a dry southerly aspect. Damage to conifer seedlings from herbivore browsing was minimal. Conifer seedling density and height growth was negatively affected by competition from herbaceous vegetation, most notably Salvia officinalis. Group selection tree harvest in southern dry exposures in spruce-dominated stands is silviculturally unsuitable because it alters tree succession. 相似文献
This study investigates the dimensional stability and mechanical properties of plywood boards made of thermally modified and unmodified beech veneers that have undergone plasma pre-treatment before melamine resin impregnation. The water and melamine resin uptake and resulting weight percent gain of the veneers were investigated, whereby the air plasma pre-treated veneers showed improved liquid uptake. Five-layer plywood boards were then manufactured and tested for their dimensional stability, compressive strength, bending strength, and tensile strength. Plywood boards made of thermally modified and plasma pre-treated veneers showed a significantly improved dimensional stability, along with small influences on their mechanical properties. 相似文献
This study aimed to better understand the stabilisation of rice rhizodeposition in paddy soil under the interactive effects of different N fertilisation and water regimes. We continuously labelled rice (‘Zhongzao 39’) with 13CO2 under a combination of different water regimes (alternating flooding-drying vs. continuous flooding) and N addition (250 mg N kg?1 urea vs. no addition) and then followed 13C incorporation into plant parts as well as soil fractions. N addition increased rice shoot biomass, rhizodeposition, and formation of 13C (new plant-derived C) in the rhizosphere soils under both water regimes. By day 22, the interaction of alternating flooding-drying and N fertilisation significantly increased shoot and root 13C allocations by 17 and 22%, respectively, over the continuous flooding condition. The interaction effect also led to a 46% higher 13C allocation to the rhizosphere soil. Alone, alternating water management increased 13C deposition by 43%. In contrast, N addition increased 13C deposition in rhizosphere soil macroaggregates under both water regimes, but did not foster macroaggregation itself. N treatment also increased 13C deposition and percentage in microaggregates and in the silt and clay-size fractions of the rhizosphere soil, a pattern that was higher under the alternating condition. Overall, our data indicated that combined N application and a flooding-drying treatment stabilised rhizodeposited C in soil more effectively than other tested conditions. Thus, they are desirable practices for improving rice cropping, capable of reducing cost, increasing water use efficiency, and raising C sequestration. 相似文献
Seasonal changes of the mineral components Na, K, Mg, Ca, Mn, Fe, Al, Si and ash were investigated in the L1 horizon of an acidic beech (Fagus sylvatica L.) forest using litterbags (1 mm and 45 μm mesh-size) buried for up to 467 days in the forest floor. The element dynamics in this surface horizon were compared with the concentration and the total amount stored in a complete sequence of horizons (L1, L2, F1, F2 and H) taken from a moder profile in the Solling area. In the 1 mm litterbags with free access of the mesofauna, the concentrations of all cations were increased in comparison to the 45 μm treatment. This increase was highly significant, especially with regard to Fe and Al. The concentrations of these two cations were closely related to Si during the decomposition of fresh leaf litter in the L1 horizon. Si is the dominant element of ash in the litterbags and down the profile. The total amounts stored in the forest floor revealed that the Fe and Al input considerably exceeded the input by litter fall, and dry and wet deposition due to incorporation of mineral soil material. The input of soil material was also indicated by a decrease in the molar Si/Al ratio from 17 to 6 and in the relation of nutrient cations to ash from 30% to 2.5%. 相似文献
The fungi-to-bacteria ratio in soil ecological concepts and its application to explain the effects of land use changes have gained increasing attention over the past decade. Four different main approaches for quantifying the fungal and bacterial contribution to microbial tissue can be distinguished: (1) microscopic methods, (2) selective inhibition, (3) specific cell membrane components and (4) specific cell wall components. In this review, the different methods were compared and we hypothesized that all these approaches result in similar values for the fungal and bacterial contribution to total microbial biomass, activity, and residues (dead microbial tissue) if these methods are evenly reliable for the estimation of fungal biomass. The fungal contribution to the microbial biomass or respiration varied widely between 2 and 95% in different data sets published over the past three decades. However, the majority of the literature data indicated that fungi dominated microbial biomass, respiration or non-biomass microbial residues, with mean percentages obtained by the different methodological approaches varying between 35 and 76% in different soil groups, i.e. arable, grassland, and forest soils and litter layers. Microscopic methods generally gave the lowest average values, especially in arable and grasslands soils. Very low ratios in fungal biomass C-to-ergosterol obtained by microscopic methods suggest a severe underestimation of fungal biomass by certain stains. Relatively consistent ratios of ergosterol to linoleic acid (18:2ω6,9) indicate that both cell membrane components are useful indicators for saprotrophic and ectomycorrhizal fungi. More quantitative information on the PLFA content of soil bacteria and the 16:1ω5 content of arbuscular mycorrhizal fungi is urgently required to fully exploit the great potential of PLFA measurements. The most consistent results have been obtained from the analysis of fungal glucosamine and bacterial muramic acid in microbial residues. Component-specific δ13C analyses of PLFA and amino sugars are a promising prospect for the near future. 相似文献
Burning of sugarcane residues contributes to air pollution and sugarcane producers have been forced to abandon it. The change from burning to residue retention is likely to alter the cycling of nutrients. Additionally, there is often a time gap of 6–8 months between two different sugarcane cycles during which legumes could be planted. Thus, the objective of this study was to assess the effects of burning, mulching or incorporation of sugarcane residues on residue decomposition and N mineralization (sugarcane residue management period) and subsequently upon ploughing (legume period) on N dynamics, N2 fixation, development and nutrient yields of groundnut and soybean grown between two sugarcane cycles on a sandy soil in Northeast Thailand.
Soil microbial biomass N increased when sugarcane residues were incorporated instead of burned or surface applied at 14 days after initiation of cane residue management. Thereafter, high net N mineralization was accompanied by a reduction in microbial biomass N, indicating that mineralized N was derived from microbial N turnover. However, upon ploughing after 96 days the different previous sugarcane residue management strategies had no significant (P > 0.05) effect on net mineral N and microbial biomass N during the subsequent legume period. Although, 15N enrichment in control reference plants and plant N uptake indicated significant N immobilization effects persisting into the legume crop phase, the proportion of N derived from N2 fixation (%Ndfa) or amount of N2 fixed were not significantly different between sugarcane residue management treatments. Soybean fixed more N2 (78%Ndfa, 234 kg N fixed ha−1) than groundnut (67%Ndfa, 170 kg N fixed ha−1) due to its larger N demand and a poorer utilization of soil N (64 kg N ha−1 vs. 85 kg N ha−1). Groundnut led to a positive soil N balance while that of soybean was negative due to its high nitrogen harvest index. Legume residues returned 61 and 146 kg N ha−1 to the soil for soybean and groundnut, respectively, compared to only 34–39 kg N ha−1 by fallow weeds. Sugarcane residue retention improved soil organic carbon and N content. The results suggested that although a change from burning to sugarcane residues retention led to alterations in N cycling and improved soil organic matter it did not significantly affect N2 fixation due to the uniforming action of ploughing and the extended time gap between sugarcane residue incorporation and legume planting. 相似文献
Eight vineyards in Pfaffenheim (P) and Turckheim (T) close to Colmar, France, forming four pairs of organic and conventional
vineyards, were analyzed for microbial biomass and activity indices in relation to important soil chemical properties (carbon,
nutrient elements, heavy metals) and also to differences between the bottom and top positions on the vineyard slope. The question
was whether the vineyard management affects especially the soil microbiological indices. Three locations were on limestone
(P-I, P-II, T-II), one on granite (T-I). The gravel content (>2 mm) ranged from 9 to 47%. The management systems had no significant
main effect on the contents of organic C, total N, P, and S. The mean total contents of man-derived heavy metals decreased
in the order Cu (164 μg g−1 soil) > Zn (100 μg g−1 soil) > Pb (32 μg g−1 soil). The contents of microbial biomass C varied between 320 and 1,000 μg g−1 soil. The significantly highest content was found at location P-II, the significantly lowest at the moderately acidic location
T-I. The contents of microbial biomass N and adenosine triphosphate showed a similar trend. At location T-I, the fungal ergosterol-to-microbial
biomass C ratio and the metabolic quotient qCO2 were significantly highest, whereas the percentage of soil organic C present as microbial biomass C was lowest. Highest percentages
of soil organic C present as microbial biomass C and lowest qCO2 values were found in the organic in comparison with the conventional vineyards. None of the soil microbiological indices
was significantly affected by the position on the slope, but all were significantly affected by the management system. This
was mainly due to the highest index levels in the organic vineyard location P-II with the longest history in organic management. 相似文献
An incubation experiment was carried out to investigate the interactions of two straw qualities differing in N content and two soils differently accustomed to straw additions. One soil under conventional farming management (CFM) regularly received straw, the other soil under organic farming management (OFM) only farmyard manure. The soils of the two sites were similar in texture, pH, cation‐exchange capacity, and glucosamine content. The soil from the OFM site had higher contents of organic C, total N, muramic acid, microbial biomass C and N (Cmic and Nmic), but a lower ergosterol content and lower ratios ergosterol to Cmic and fungal C to bacterial C. The straw from the CFM had threefold higher contents of total N, twofold higher contents of ergosterol and glucosamine, a 50% higher content of muramic acid, and a 30% higher fungal C–to–bacterial C ratio. The straw amendments led to significant net increases in Cmic, Nmic, and ergosterol. Microbial biomass C showed on average a 50% higher net increase in the organic than in the CFM soil. In contrast, the net increases in Nmic and ergosterol differed only slightly between the two soils after straw amendment. The CO2 evolution from the CFM soil always exceeded that from the OFM, by 50% or 200 µg (g soil)–1 in the nonamended control soil and by 55% or additional 600 µg (g soil)–1 in the two straw treatments. In both soils, 180 µg g–1 less was evolved as CO2‐C from the OFM straw. The metabolic quotient qCO2 was nearly twice as high in the control and in the straw treatments of the CFM soil compared with that of the OFM. In contrast, the difference in qCO2 was insignificant between the two straw qualities. Differences in the fungal‐community structure may explain to a large extent the difference in the microbial use of straw in the two soils under different managements. 相似文献