Soil-litter System Research Articles

Habitat structure and prey aggregation determine the functional response in a soil predator–prey interaction

Functional responses describe the per capita consumption rates of predators depending on prey density, which quantifies the energy transfer between trophic levels. We studied a typical interaction of the litter–soil systems between hunting spiders ( Pardosa lugubris ; Araneae: Lycosidae) and springtails ( Heteromurus nitidus ; Collembola: Entomobryidae) at varying habitat structure, i.e. with moss vs. without moss. We found a hyperbolic increase in consumption (functional response type II) in the treatment without habitat structure that was converted into a roller-coaster (or dome-shaped in a broad sense) functional response in treatments with habitat structure. Additional experiments suggest that the reduced per capita consumption rates at high prey densities may be explained by aggregative defence behaviour of the springtails. Experimentally, this behaviour was induced by the presence of habitat structure. We analyzed the net-energy gain of this predator–prey interaction by comparing the predator’s metabolic energy loss to its energy gain by consumption. In treatments with habitat structure, the net-energy gain of the predator was limited at intermediate prey densities where prey aggregation reduced the consumption rates. Our results stress the importance of habitat structure and prey behaviour in shaping the functional response in a typical soil–litter predator–prey interaction.

Simulating dynamics of managed monsoon evergreen broad-leaved forest in south China

The forest succession model FORDYN is developed based on TREEDEV model. TREEDEV is a process-based tree growth model, that calculates tree growth based on carbon and nitrogen balance, and is calculated using on the photo-production of leaves, respiration, nitrogen content of all organisms and that in soil, and other losses due to respiration, litter and renewal of stems, branches, leaves and roots. In the FORDYN model succession is divided into three phases called early, middle and late succession, and the transition between these three succession phases is distinguished by a difference in leaf area index. As a verification of the model we used the characteristics and available data of a monsoon evergreen broad-leaved forest in Dinghushan Biosphere Reserve (DHS-BR). The model was validated with natural forest data. In addition, a sensitivity analysis was performed in which 30 independent variables were varied and analyzed in connection with their influence on 16 dependent variables describing forest conditions. The simulation results describe the changes in total biomass, carbon and nitrogen change in plant–litter–soil system of an undisturbed monsoon evergreen broad-leaved forest during succession. We compared these findings with simulation in which different logging management strategies were used. The results show that having a longer logging cycle, delaying the first logging time and a smaller logging fraction the scenario can contribute to a sustainable forest development, while still having a positive economic yield.

Testing a New Model for the L-Band Radiation of Moist Leaf Litter

The crown vegetation of a deciduous forest is known to be semitransparent at low microwave frequencies, and leaf litter covering the forest soil has been recognized to have a significant impact on ground emission. The proposed approach for modeling the L-band radiative transfer through leaf litter consists of an isotropic effective medium approach for the litter permittivities, a coherent radiative transfer model for computing the coherent reflectivities from dielectric depth profiles, and an averaging procedure for computing the reflectivities determining the field-scale brightness temperatures. Evaluations were performed for the case of leaf litter on top of a conducting wire grid (litter-grid formation) and for litter on underlying soil (litter-soil formation). A model sensitivity analysis was performed with respect to parameters characterizing litter thickness variations and boundary roughness. For the litter-soil formation, the model was rather sensitive to local irregularities at the air-to-litter boundary. Modeled microwave signatures reproduced the major features of the measurements performed on a site comprising a litter-grid formation. Under dry conditions, the investigated litter layer was nearly ldquoinvisible.rdquo When the same litter layer was wetted, it acted as an important radiation source to be taken into account for the quantitative remote soil moisture detection of forested areas. Under certain conditions, the simulations revealed an increasing brightness when the litter is wetted prior to the underlying soil. Further wetting of the litter-soil system then resulted in a decreasing brightness as expected for increased moisture. Such effects are important to know to avoid misleading interpretations of L-band signatures.

Application of mathematical modelling techniques for evaluation of radionucleide accumulation levels in biota

In the majority of the cases associated with radioactive contamination of the environment, forest and lake ecosystems as natural filters and radionuclide storages relate to critical ecosystems. These two types of natural ecosystems as well as meadow prevail in the areas where NPP are located. To solve the entire complex of radioecological problems, the authors have developed the models for 137Cs and 90Sr migration in forest ecosystems that take into account the transformation processes of 137Cs and 90Sr in a soil-litter system, age- and season-specific dynamics for the tree layer and seasonal biomass changes in the understory, as well as radionuclide entering into food chains. A mathematical model for the migration of varied kinds of admixtures is developed and enhanced on the pattern of the 90Sr, 106Ru, 125Sb, 137Cs, 144Ce radioactive micro-admixture in lake ecosystems. The model takes into account the fact that micro-admixture withdraws out of the water both as a result of molecular/ ion-exchanging sorption on the boundary of the bottom sediments/ water layer and as a result of the detritus-forming process. When describing a vertical radionuclide migration in bottom sediments through a diffusion equation, the increase in the bottom sediment layer is considered. The authors have developed the mathematical models describing a long-term behavior of 90Sr and 137Cs in meadow ecosystems and taking into account basic processes that define the 90Sr and 137Cs biological accessibility for root absorption as well as the transformation processes in soil. For the assessment of biological effects of a radiation factor on the biota, a complex of dosimeter models is developed to evaluate the internal/ external doses to biota taking into account different geometry of the exposure source of ionizing radiation. The represented mathematical models were successfully used during an environmental expertise performed for a number of Russian NPP and also when assessing environmental effects from the implementation of countermeasures in the Mayak facility region, as well as the effects of radioactive contamination in the Bryansk Region resulted from the Chernobyl accident. The complex of mathematical migration and dosimeter models developed by the authors may be used to solve theoretical or applied radioecological issues with regard to the investigation of radionuclide behavior peculiarities in different ecosystems, as well as the evaluation of radiation impacts on organisms, populations or entire ecosystems. Besides, the models can be parameterized for specific forest/ water/ meadow ecosystems in varied situations associated with nuclear pollution of environment.

Enriquecimento do sistema solo-serapilheira com espécies arbóreas aptas para recuperação de áreas degradadas

Este estudo teve como objetivo avaliar o comportamento do enriquecimento no sistema solo orgânico-serapilheira, com sementes de espécies arbóreas nativas, para revegetação de áreas degradadas. O trabalho foi conduzido em casa de sombra e em bancadas a pleno sol, no Viveiro de Pesquisas do Departamento de Engenharia Florestal, situado no Campus da Universidade Federal de Viçosa (UFV). No levantamento do banco de sementes, foram encontrados 508 indivíduos, dos quais foram identificadas 38 espécies, pertencentes a 34 gêneros e distribuídas em 22 famílias. As avaliações da germinação das sementes introduzidas e do banco de sementes indicaram não haver diferença entre os ambientes testados (sombreado e a pleno sol). O crescimento das mudas, tanto das espécies provenientes dos propágulos contidos na serapilheira e no solo orgânico quanto das espécies utilizadas no enriquecimento, foi maior no ambiente sombreado. Os solos não adubados tiveram maior porcentual de sementes germinadas em relação aos solos adubados. A adubação dos substratos foi fundamental para o crescimento das mudas. Os resultados, portanto, demonstraram a eficiência do enriquecimento do banco de sementes e confirmaram o potencial dessa técnica para revegetação de áreas degradadas.

Occupation of artificial microhabitats by soil invertebrates in a forest fragment in Southern Brazil

portuguesA degradacao do sistema edafico e a perda de seus horizontes orgânicos podem ocasionar um decrescimo da biodiversidade da fauna do solo, afetando diretamente suas caracteristicas funcionais. Estrategias que visem a restauracao ecologica de areas degradadas devem levar em conta a heterogeneidade dos sistemas originais, em especial da superficie do solo. Este estudo teve como objetivo geral investigar a importância da presenca de microhabitats cripticos para as comunidades de invertebrados do solo a partir da introducao de estruturas artificiais (telhas de barro) sobre a serapilheira. A area de estudo consistiu em um fragmento de mata nativa no municipio de Triunfo, RS, Brasil, no qual foram distribuidas 40 telhas em cima da serapilheira. Trimestralmente, ate o termino de um ano, foram amostradas 10 telhas e retiradas 10 amostras de serapilheira (controle) do local. Foram coletados 1.025 individuos, distribuidos em 17 grupos taxonomicos de invertebrados sob as telhas e 935 individuos e 13 grupos na serapilheira. Foram verificadas maior abundância de formigas e opilioes nas amostragens de telhas e maior abundância de coleopteros, isopodes e insetos imaturos nas amostragens controle de serapilheira. Aranhas e moluscos nao apresentaram abundâncias diferentes entre os tratamentos. A riqueza media de taxons foi considerada maior abaixo da telha e foram observados mais herbivoros e onivoros abaixo destas estruturas. As telhas de barro, neste experimento, cumpriram a tarefa de fornecer informacoes basicas sobre a importância de microhabitats cripticos a fauna de invertebrados. Mais pesquisas deveriam ser realizadas, esclarecendo e ressaltando a importância da heterogeneidade espacial na dinâmica do sistema solo-serapilheira e nas estrategias de restauracao de areas degradadas. EnglishThe degradation of the soil system and loss of organic layer can cause a decrease in the biodiversity of soil fauna, directly affecting its functional characteristics. Strategies that aim at ecological restoration of degraded areas, must take into account the heterogeneous nature of original systems, especially in the soil surface. The general objective of this study was to investigate the importance of cryptic microhabitats for soil invertebrate communities, through the introduction of artificial structures (mud tiles) on the litter fall. The study area consisted of native forest fragment in Triunfo, RS, Brazil, in which 40 mud tiles were distributed. Every quarter, for a year, 10 tiles were surveyed and 10 litter samples (control group) were collect. A total of 1025 individuals were found distributed in 17 taxonomic groups of invertebrates under the tiles and 935 individuals in 13 groups in the litter fall (control). It was verified that ants and harvestman had been more abundant under tiles than in the control. The abundance of spiders and molluscs was not significantly different between treatments. There were larger amounts of beetle, woodlice and immature insects in the litter fall samples. The mean richness of taxa was larger below the tile and a trend of finding more herbivores and omnivores below these structures was observed. The mud tiles, in this experiment, had fulfilled its task to supply basic information on the importance of cryptic microhabitats for the invertebrate fauna. More research needs to be conducted to clarify and establish the influence of spatial heterogeneity on the dynamics on the soil-litter system for restoring degraded areas.

Elevated temperature, soil moisture and seasonality but not CO 2 affect canopy assimilation and system respiration in seedling Douglas-fir ecosystems

We investigated the effects of elevated atmospheric CO 2 and air temperature on C cycling in trees and associated soil system, focusing on canopy CO 2 assimilation ( A sys) and system CO 2 loss through respiration ( R sys). We hypothesized that both elevated CO 2 and elevated temperature would stimulate A sys and R sys. The study was conducted in sun-lit controlled-environment mesocosms using Douglas-fir ( Pseudotsuga menziesii Mirb. Franco) seedlings grown in reconstructed plant–litter–soil systems. A completely randomized design with two atmospheric CO 2 and two air temperature levels was used. A mass-balance approach was used to calculate daily mean A sys and R sys rates for 19 months. A mixed model analysis was used to test the effects of CO 2 and air temperature on daily A sys and R sys adjusted for covariates of time, light, soil moisture and seasonality. Elevated temperature stimulated A sys and R sys but elevated CO 2 did not. Elevated CO 2 and temperature both increased light sensitivity and the light saturation level of photosynthesis. Both A sys and R sys were controlled by temperature, soil moisture and endogenous seasonal processes. Temperature sensitivity of R sys varied seasonally but there was no acclimatization. Because of the close linkage between assimilation and respiration, elevated CO 2 failed to stimulate A sys and R sys. Although CO 2 is a substrate, assimilate is also controlled by its concentration. Needle-level studies established that increasing CO 2 down regulates assimilation through changes in Rubisco, especially if resources are limited. This study shows that increasing CO 2 also regulates assimilation allometrically through changes in needle area. Stimulation of assimilation is offset by a reduction in needle area such that the A sys and R sys are similar in ambient and elevated treatments.

Does soil CO2 efflux acclimatize to elevated temperature and CO2 during long‐term treatment of Douglas‐fir seedlings?

We investigated the effects of elevated soil temperature and atmospheric CO2 on soil CO2 efflux (SCE) during the third and fourth years of study. We hypothesized that elevated temperature would stimulate SCE, and elevated CO2 would also stimulate SCE with the stimulation being greater at higher temperatures. The study was conducted in sun-lit controlled-environment chambers using Douglas-fir (Pseudotsuga menziesii) seedlings grown in reconstructed litter-soil systems. We used a randomized design with two soil temperature and two atmospheric CO2 treatments. The SCE was measured every 4 wk for 18 months. Neither elevated temperature nor CO2 stimulated SCE. Elevated CO2 increased the temperature sensitivity of SCE. During the winter, the relationship between SCE and soil moisture was negative but it was positive during the summer. The seasonal patterns in SCE were associated with seasonal changes in photosynthesis and above-ground plant growth. SCE acclimatized in the high-temperature treatment, probably because of a loss of labile soil carbon. Elevated CO2 treatment increased the temperature sensitivity of SCE, probably through an increase in substrate availability.

Caracterização da fauna edáfica em diferentes coberturas vegetais na região norte Fluminense

O sistema solo-serapilheira é o habitat natural para grande variedade de organismos, que diferem em tamanho e metabolismo, responsáveis por inúmeras funções. O monitoramento dos grupos de fauna no sistema solo-serapilheira permite não só uma inferência sobre a funcionalidade destes organismos, mas também uma indicação simples da complexidade ecológica dessas comunidades. O presente trabalho teve como objetivo caracterizar a distribuição da fauna edáfica nos compartimentos solo e serapilheira em duas épocas do ano e em cinco diferentes coberturas vegetais (eucalipto, floresta não preservada, floresta preservada, capoeira, pasto) no Norte Fluminense. As coberturas de floresta natural, especialmente das florestas preservadas e não preservadas, mostraram, de maneira geral, valores de densidade e riqueza de fauna superiores aos de eucalipto e pasto, tanto no solo quanto na serapilheira, nas duas épocas de coleta. Em geral, não houve preferência dos grupos de fauna pelos compartimentos solo e serapilheira. A densidade de fauna, riqueza de espécies, índice de Shannon e índice de Pielou também variaram conforme a época de coleta, sendo, no verão, estabelecidas maiores diferenças entre as diferentes coberturas vegetais estudadas do que no inverno. O índice de Pielou foi a variável mais estável e, portanto, mais apropriada para o estudo da dissimilaridade entre as coberturas vegetais em termos de distribuição dos grupos de fauna.

Contrasting responses to drought of forest floor CO2 efflux in a Loblolly pine plantation and a nearby Oak‐Hickory forest

AbstractForest floor CO2 efflux (Fff) depends on vegetation type, climate, and soil physical properties. We assessed the effects of biological factors on Fff by comparing a maturing pine plantation (PP) and a nearby mature Oak‐Hickory‐type hardwood forest (HW). Fff was measured continuously with soil chambers connected to an IRGA during 2001–2002. At both sites, Fff depended on soil temperature at 5 cm (T5) when soil was moist (soil moisture, θ>0.20 m3 m−3), and on both T5 and θ when soil was drier. A model (Fff (T5, θ)) explained 92% of the variation in the daily mean Fff at both sites. Higher radiation reaching the ground during the leafless period, and a thinner litter layer because of faster decomposition, probably caused higher soil temperature at HW compared with PP. The annual Fff was estimated at 1330 and 1464 g C m−2 yr−1 for a year with mild drought (2001) at PP and HW, respectively, and 1231 and 1557 g C m−2 yr−1 for a year with severe drought (2002). In the wetter year, higher soil temperature and moisture at HW compared with PP compensated for the negative effect on Fff of the response to these variables resulting in similar annual Fff at both stands. In the drier year, however, the response to soil temperature and moisture was more similar at the two stands causing the difference in the state variables to impel a higher Fff at HW. A simple mass balance indicated that in the wetter year, C in the litter–soil system was at steady state at HW, and was accruing at PP. However, HW was probably losing C from the mineral soil during the severe drought year of 2002, while PP was accumulating C at a lower rate because of a loss of C from the litter layer. Such contrasting behavior of two forest types in close proximity might frustrate attempts to estimate regional carbon (C) fluxes and net C exchange.

Litter Placement Effects on Microbial and Organic Matter Dynamics in an Agroecosystem

Two different agricultural tillage practices were used to study how changes in the structure of the soil—litter system affected litter decomposition rates, microbial community composition, and soil organic matter dynamics. Surface straw placement results in spatial separation of carbon—rich litter (C:N ratio 80:1) and mineralized soil nitrogen. In contrast, when the litter is plowed into the soil, straw carbon and soil nitrogen are in intimate contact. Our field studies in Colorado showed that fungal biomass in surface—straw treatments was 144% of that in the incorporated—straw treatments, probably because fungi, with their extensive hyphal networks, are able to utilize both the surface straw carbon and the available soil nitrogen. Field studies using 14C—labeled wheat straw showed that a greater proportion of added 14C was retained in the surface—straw treatment than in the incorporated—straw treatment. Maximum net N immobilization was higher and litter decomposition was slower in the surface straw than in the incorporated straw placements both with and without experimental nitrogen addition. Slower litter decomposition of the surface litter may contribute to reduced soil organic matter losses. Soil organic matter losses may also be reduced in no—till systems as a result of the increase in the ratio of fungal to bacterial activity because of the greater growth efficiency of fungi and the accumulation of carbon in the less decomposable fungal biomass. The surface placement of straw in no—till agriculture allowed management of microclimate and microbial populations so that losses of soil organic matter and nutrients were minimized.

The behaviour of hexachlorobenzene in pine forest microcosms: Transport and effects on soil processes

Hexachlorobenzene (HCB) is an organic contaminant with a potential of ecosystem level impacts. Using pine forest microcosms, the transport and effects of HCB on soil processes were studied. HCB-contaminated litter (0, 0·085, 0·730, 7·42 mg/cm 3) was applied to replicate soils in filtered, flow-through microcosm systems. Transport of HCB as H 14CB and two soil process parameters—CO 2 efflux and Ca loss—were monitored. HCB was mobilised from litter-soil systems by both volatisation and leaching. Both process parameters were altered by HCB: CO 2 efflux decreased and Ca loss increased in the HCB-treated microcosms.

Response of soil Testacea to soil moisture fluctuations

Experiments illustrated that, as soil moisture increased in a Rocky Mountain aspen woodland soil-litter system, all species of Testacea recorded showed a significant increase in number of active individuals and a proportionate significant decrease in the number of cysts. The trends were less evident in the A 0L layer because of low variation in moisture content compared to the A 0F and A 0H layers. At higher soil moisture the larger species present (> 60μm) tended to retain a larger proportion of living individuals as cysts than did the smaller forms (⩽ 60μm) which numerically dominated the population.