The influence of soil structure on heterotrophic respiration response to soil water content

<p>Soil respiration causes one of the largest terrestrial carbon fluxes and its accurate prediction is still a matter of on-going research. Understanding the functional link between soil heterotrophic respiration and soil water content is relevant for the estimation of climate change impacts on soil CO<sub>2</sub> emissions. <br>In order to quantify the effect of air-drying and sieving with 2 mm meshes on the soil heterotrophic respiration response to water content we incubated intact cores and sieved samples of two loamy and two sandy agricultural topsoils for six levels of effective soil water saturation. We further measured soil textural properties and the soil water retention characteristics of the soils with the aim to identify potential correlations between soil physical parameters and moisture sensitivity functions of heterotrophic respiration. <br>The incubation of sieved and intact soils showed distinct differences in the response of soil heterotrophic respiration to soil water saturation. The sieved soils exposed threshold-type behaviour, whereas the undisturbed soils exposed a quadratic increase of heterotrophic respiration with increasing effective soil water content. Additionally, we found significant correlations between the moisture response functions of the undisturbed soils and soil textural properties.<br>From the comparison of intact and sieved soil incubations we conclude that the destruction of soil structure by sieving hampers the transferability of measured soil moisture response of heterotrophic respiration to real-world conditions. For modelling purposes we suggest the use of a quadratic function between relative respiration and effective saturation for soils with a clay fraction < 20 %.</p>

Effect of soil water saturation on slope stability: Tomsk case study

We investigate in this article the impact of soil water saturation on the slope stability, using a site in Tomsk city as a case study. The dependency of the shear strength parameters of soil on the degree of soil water saturation has been demonstrated. The paper also provides equations for the calculation of slope stability coefficient under different values of soil water saturation.

Soil physical restrictions and hydrology regulate stand age and wood biomass turnover rates of Purus–Madeira interfluvial wetlands in Amazonia

In Amazonia, wetlands constitute about 30% of its entire basin, of which ancient fluvial terraces located in vast interfluvial regions cover a large portion. Although the increased number of permanent plots in the recent years has contributed to improved understanding of regional variation in forest dynamics across the Amazon Basin, the functioning of large lowland interfluvial wetlands remain poorly understood. Here we present the first field-based estimate for tree ages, wood biomass productivity and biomass turnover rates for eight 1 ha plots in wetland and non-flooded forests distributed along the BR-319 Highway along a distance of about 600 km crossing the Purus–Madeira rivers interfluvial region in central-southwestern Amazon Basin. We estimate stand age, wood biomass productivity and biomass turnover rates combining tree-ring data and an allometric equation based on diameter, tree height and wood density and relate these structural parameters to physical soil and hydrological restrictions. Wood biomass and productivity varied twofold among the plots, with wood biomass stocks ranging between 138–294 Mg ha−1 and productivity varying between 3.4–6.6 Mg ha−1 yr−1. Soil effective depth, topography, structure and mainly soil water saturation significantly affected stand age (64–103 yr) and forest dynamics in terms of annual biomass turnover rates (2.0–3.2%). On harsher soils characterized by a poor structure, low effective depth and high water saturation, biomass turnover rates were increased and forests stands were younger compared to well-drained sites. We suggest that soil constraints, especially soil water saturation, limit the development of the stand structure, resulting in forests with younger stand ages and higher biomass turnover rates compared to forests growing on well-drained soils. We do not find, however, any relation between physical soil restrictions or hydrology and wood biomass productivity, but there is a trend of increasing wood biomass productivity and phosphorus concentrations at the soil surface. Based on our results we establish hypotheses for different dynamical processes between forests growing on waterlogged and well-drained soils and discuss how these results can be applied in the background of conservation as well as the potential development of forest management plans in this region, which will experience increased deforestation due to the construction of the BR-319 Highway crossing the interfluvial region of the Purus–Madeira rivers.

Early post-fire changes in Pinus brutia forests (Amanos Mountains, Turkey)

Early post-fire changes inPinus brutiaforests (Amanos Mountains, Turkey)We studied the species composition and soil nutrients in aPinus brutiaforest after a fire that occurred in 1989. Four permanent plots were created in the burnt and not burnt areas in the Amanos Mountains of Turkey. The floristic richness, biological spectra, above ground phytomass and soil features in the study areas were assessed during the first three years after the fire. After the fire, we found a reduced amount of organic matter (14.3%), total nitrogen (22%) and soil water saturation (13.1%), but an increased amount of available phosphorus (71%), acidity (3.6%), cation exchange capacity (9.9%), exchangeable sodium (20.8%) and exchangeable potassium (37.1%). The aboveground phytomass in the burned area reached 5284 kg ha-1, the third year after the fire. Forty-six pre-fire species were renewed in the first three years after the fire.Juniperus oxycedruscould not renew within three years after the fire. Pine phytomass has increased five times within three years after the fire.