Microbial responses to changes in land use

Background/Question/Methods
Land use change is one of the greatest threats to biodiversity worldwide. This is especially true for land use change that results in the destruction of intact forest, or "deforestation”. Deforestation is causing a loss of biological diversity on an unprecedented scale, especially in the Tropics. It is unclear how the majority of the biodiversity on Earth – microbial biodiversity – is responding to these extraordinary rates of deforestation. I will provide an overview of our current understanding of microbial responses to deforestation. I will focus, as an example, on our current research regarding the effects of deforestation on the diversity of arbuscular mycorrhizal fungi (AMF), bacteria and archaea within Amazon Rainforest soils. This study takes advantage of an established chronosequence of primary rainforest, pastures of various ages, and secondary rainforest to determine the effect of deforestation on the taxonomic, phylogenetic and functional diversity of soil microorganisms, assayed using culture-independent methods.

Results/Conclusions
There is increasing evidence that deforestation significantly affects microbial diversity, and that “recovery” of microbial diversity in secondary forest soils is incomplete. For example, rarefaction curves suggest that the accumulation of AMF taxa is higher for Amazon primary forest soil relative to secondary forest soil. In addition, the community composition varies with land use; three AMF taxa were shared between primary and secondary forests, seven were found only in primary forest, and three were found exclusively in secondary forest soil. We also observed that the phylogenetic diversity of AMF is more reduced in secondary forest soils than expected given the regional pool of AMF taxa.

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The importance of tree allometry for local-scale variation in aboveground biomass

Aboveground biomass (AGB) plays a critical role in determining the long-term dynamics of carbon in tropical forests. Consequently, understanding what factors are important in controlling AGB in tropical forests has major implications for projecting the terrestrial carbon stocks, in the context of an increasingly uncertain future. In this study, we aimed to explore the local-scale AGB variation in two forest sites in northern Congo, representative of contrasted forest types under the same climate but growing on vastly different soils and parent material (quartzite substrate for CIB and sandstone substrate for Mokabi). Tree diameter was measured in 36 permanent forest plots of 1-ha in each site, and tree allometry (total tree height, height of the first branch and crown dimensions) was measured on a subsample of 18 plots of 1-ha in each site. Allometric data were available for a total of 2202 trees (1040 for CIB and 1162 for Mokabi) covering a large range of diameters (10-200 cm). We first developed site-specific allometric models that were used to estimate AGB at plot level. We then explore the determinants of AGB variation at plot level using multiple regressions and mixed linear models. For a given diameter, trees tended to be taller and to have deeper crown in the Celtis forest of the CIB (rich soils), while they tended to have larger crown in the Manilkara forest of the Mokabi (sandy soils). Similar trends were reported within species for the sixteen species shared by both sites, suggesting an environmental control of tree allometry. We found that AGB strongly varied between the two forest sites, with greater AGB per hectare in the Celtis forest of the CIB site. Within-site AGB variation was positively related to basal area, though between-site AGB variation was determined by tree allometry (height-diameter and crown allometries). These results have strong implications for forest biomass and carbon monitoring

Nitrous oxide consumption potentials of well-drained forest soils in Southern Québec, Canada.

To establish the major controls on N2O consumption by forest soils, we conducted laboratory incubations of 16 samples from four soil types, two organic and two mineral, varying in overlying forest vegetation (sugar maple, American beech and eastern hemlock). The fastest potential consumption of N2O occurred under anoxic conditionswith little soil nitrate and under elevated headspaceN2O concentration. Potential N2O consumption rates were fastest in organic soils under hemlock and beech trees (111 and 75 ng N2O-Ng−1 d−1, respectively) compared to mineral soils under beech and maple trees (45 and 41 ng N2O-N g−1 d−1). Organic soils showed faster N2O consumption rates than mineral soils, possibly due to larger organic C levels and higher C:N ratios. Acetylene treatment confirmed that denitrification was the process underlyingN2Oconsumption. These results suggest that soils regularly consume N2O with varying magnitude, most likely in anoxic microsites throughout the soil profile and that the potential for N2O consumption is larger in organic than in mineral forest soils

Soil bacterial communities of a calcium-supplemented and a reference watershed at the Hubbard Brook Experimental Forest (HBEF), New Hampshire, USA

Soil Ca depletion because of acidic deposition-related soil chemistry changes has led to the decline of forest productivity and carbon sequestration in the northeastern USA. In 1999, acidic watershed (WS) 1 at the Hubbard Brook Experimental Forest (HBEF), NH, USA was amended with Ca silicate to restore soil Ca pools. In 2006, soil samples were collected from the Ca-amended (WS1) and reference watershed (WS3) for comparison of bacterial community composition between the two watersheds. The sites were about 125 m apart and were known to have similar stream chemistry and tree populations before Ca amendment. Ca-amended soil had higher Ca and P, and lower Al and acidity as compared with the reference soils. Analysis of bacterial populations by PhyloChip revealed that the bacterial community structure in the Ca-amended and the reference soils was significantly different and that the differences were more pronounced in the mineral soils. Overall, the relative abundance of 300 taxa was significantly affected. Numbers of detectable taxa in families such as Acidobacteriaceae, Comamonadaceae, and Pseudomonadaceae were lower in the Ca-amended soils, while Flavobacteriaceae and Geobacteraceae were higher. The other functionally important groups, e.g. ammonia-oxidizing Nitrosomonadaceae, had lower numbers of taxa in the Ca-amended organic soil but higher in the mineral soil

Impact of mechanized harvesting on compaction of sandy and clayey forest soils : results of a meta-analysis

Nowadays, harvest operations are predominantly performed fully mechanized using heavy tractors or forestry machines. The resulting soil compaction may negatively affect the soil ecosystem. We wanted to draw general conclusions concerning the impact of mechanized harvesting on forest soil bulk density and the influencing factors. Therefore, we combined the data of several studies using a meta-analysis approach. The impact decreased from the surface towards deeper soil layers. At 0-10 cm depth, the impact on clayey soils was highest although not significantly different from the impact on sandy soils. Higher initial bulk densities, i.e., on already compacted forest soils, generally led to smaller extra increases of bulk density after machine traffic. For sandy soils, the impact was also significantly smaller when machines were lighter. No significant relationship was observed between the compaction degree and traffic intensity. We observed clear compaction on both clayey and sandy soils, especially in case of low initial soil compaction degrees and heavy machines. The compacted initial state of many forest soils, the long recovery period, and the generally high impact of the first passes that is frequently mentioned in literature all count in favour of designated skid trails and an adjustment of the machine type to the job

Abiotic retention of nitrogen and dissolved organic matter by forest mineral soils

The effect of NO3- deposition on NH4 +, DON, and DOC retention as well as abiotic NO3 - retention via the hypothesized ferrous wheel mechanism was examined in oxic and anoxic tropical and oxic temperate soils using sorption isotherm experiments. Adsorption of NH4+, DON, and DOC by mineral soils was examined in forest floor extracts with DOC levels of 0-50 mg/L. Experimental treatments included no added NO3-, 4mg/L of added NO3-, or 4 mg/L of NO3 - and 2 mg/L of Fe3+. Ferric iron was added since it would likely increase DOC retention in the context of podzolization, and it might also influence N retention. Retention of NH4 + and DOC did not change upon NO3- addition in any of the soils. Although there are some experimental conditions that could be changed, the results indicate that the ferrous wheel hypothesis does not explain the NO3- retention by mineral soils that has been observed in the field. (Abstract shortened by UMI.)

Forestry in Poland with special attention to the region of the Pomeranian Young Moraine

In the year 2004 the ASFV celebrated its 50th anniversary holding a conference in Sulczyno, Kartuzy. This event offered the possibility to give an actual overview of forest resources and forest functions in Poland. The excursions of the meeting focused on the fascinating, diversified forest landscape formed by the Pomeranian phase of the Baltic glaciation. The Kartuzy Forest District is situated in the heart of the Kashubian Lakeland and the moraine hills. The landscape is not only characterized by the natural occurrence of Baltic beech forests but also by high diversity of soils and meso- and microclimatic de-viations providing habitats for rare plant species, including some plants typical of mountain regions. The tree species combination of the District is formed by pine, spruce, and beech. The oldest parts of the forests are legally protected as nature reserves

Detailed regional predictions of N2O and NO emissions from a tropical highland rainforest [Discussion paper]

Tropical forest soils are a significant source for the greenhouse gas N2O as well as for NO, a precursor of tropospheric ozone. However, current estimates are uncertain due to the limited number of field measurements. Furthermore, there is considerable spatial and temporal variability of N2O and NO emissions due to the variation of environmental conditions such as soil properties, vegetation characteristics and meteorology. In this study we used a process-based model (ForestDNDC-tropica) to estimate N2O and NO emissions from tropical highland forest (Nyungwe) soils in southwestern Rwanda. To extend the model inputs to regional scale, ForestDNDC-tropica was linked to an exceptionally large legacy soil dataset. There was agreement between N2O and NO measurements and the model predictions though the ForestDNDC-tropica resulted in considerable lower emissions for few sites. Low similarity was specifically found for acidic soil with high clay content and reduced metals, indicating that chemo-denitrification processes on acidic soils might be under-represented in the current ForestDNDC-tropica model. The results showed that soil bulk density and pH are the most influential factors driving spatial variations in soil N2O and NO emissions for tropical forest soils. The area investigated (1113 km2) was estimated to emit ca. 439 ± 50 t N2O-N yr−1 (2.8–5.5 kg N2O-N ha−1 yr−1) and 244 ± 16 t NO-N yr−1 (0.8–5.1 kg N ha−1 yr−1). Consistent with less detailed studies, we confirm that tropical highland rainforest soils are a major source of atmospheric N2O and NO

Characterization of Acid Deposition at Pasoh Forest Reserve and Sepang Fire-Peat Swamp

Pasoh Forest Reserve is located away from industrialized or urbanized areas. As a remote area, therefore Pasoh Forest Reserve is important to provide baseline information on the level of soil acidification in Malaysia. Furthermore, studies on the natural fires soil such as Sepang fire-peat are rare in Malaysia. The investigation of natural fires soil is essential for comparison purposes to Pasoh Forest Reserve. Hence, the objective of the study was to determine the physico-chemical properties of soils at Pasoh Forest Reserve and Sepang fire-peat swamp for evaluating the extent of acid deposition. Six subplots with dimension of 1 m x 1 m x 1 m were selected at the Pasoh Forest Reserve, while, only one plot with dimension of 1 m x 1 m x 1m was dug at the Sepang fire-peat swamp. Soil samples were taken from every 10 cm layer until 1 m depth. For each soil sample, acidity (PH), moisture content, bulk density, electrical conductivity, available phosphate (P042), available sulphate (sol"), exchangeable acidity, exchangeable A1 and H, exchangeable base cations, effective cation exchangeable capacity (BeEC) and base saturation were determined. At top part of soil profile at Pasoh Forest Reserve, there was an A horizon, characterized by dark brown colour as a result of an accumulation of humified organic matter intimately mixed with mineral matter. Below the A horizon, there was an E horizon, which was lighter in colour and texture. Below the E horizon, there was an EB horizon, which was dominated by the properties of E master horizon but with some properties of B master horizon. The B horizon was granular, blocky, or prismatic structure. The Pasoh Forest Reserve soils are clayey and acidic. The natural soil fires at Sepang caused destruction of soil structure as well as its texture, thus no clear horizon could be observed and the soil was sandy. Throughout 1 m soil depth, Pasoh Forest Reserve and Sepang fire-peat soils showed variation of soil properties. The results indicated that Pasoh Forest Reserve soils were more acidic than Sepang fire-peat soils. By comparing to the Pasoh Forest Reserve soils, the Sepang fire-peat soils showed lower mean values in bulk density and exchangeable acidity, but higher mean values in electrical conductivity, pH, base saturation, available sulphate and available phosphate. Sepang fire-peat soils were also showed relatively high values in exchangeable Mg and Ca, but low values in exchangeable K and Na. Furthermore, mean base saturation values of Sepang fire-peat soils and Pasoh Forest Reserve soils were 97.87 ± 2.42% and 78.77 ± 3.78%, respectively. The base saturation ofPasoh Forest Reserve soil was strongly correlated with the exchangeable Ca, whereas the base saturation of Sepang fire-peat soil was strongly correlated with exchangeable acidity. The significant differences between Pasoh Forest Reserve and Sepang firepeat soils were attributable to changes of soil composition after soil fires in Sepang causing mineral transformation. However, the physico-chemical properties of Pasoh Forest Reserve soils were similar to the previous findings by the Allbrook (1973) and Yoda (1978). Thus, the Pasoh Forest Reserve soils were presumably not unaffected by acid deposition. Additionally, there was no appreciable soil acidification occurred in the Pasoh Forest Reserve since 1973 (29 years)

Effect of Coriaria arborea on seed banks during primary succession on Mt Tarawera, New Zealand

An experiment was conducted over two years to investigate the effect of Coriaria arborea, a native nitrogen-fixing shrub, on soil seed banks at sites representing a post-volcanic successional sequence on Mt Tarawera, New Zealand. The sites ranged from bare volcanic ash and lapilli substrate, through low-growing pre-Coriaria vegetation, to dense stands of Coriaria scrub. Soils (to a depth of 50 mm) under recently established Coriaria and older stands had more seedlings (1096 and 1585 seedlings 0.4 m-2, respectively) and species (37 and 45 species 0.4 m-2, respectively) emerge than where there was no Coriaria (243-320 seedlings 0.4 m-2, 14-25 species 0.4 m-2) and were the only soils with Coriaria seedlings. In total, 3488 seedlings representing 63 taxa were recorded. Seeds were still germinating after 24 months but rates declined markedly in the second year. For example, Coriaria reached a germination peak at 8 weeks but continued to germinate sporadically over the 2-year period. Tree species present in young forest within 0.5 km of the sites were absent. Establishment of Coriaria greatly accelerated an underlying trend of gradually increasing abundance and diversity of seeds in the soil with vegetation age. Adventive, wind-dispersed, and annual species were over-represented in the seed banks compared with the regional evergreen forest-dominated flora. These proportions are expected to decline as succession to forest gradually occurs