Root biomass distribution and soil properties of an open woodland on a duplex soil

Data on the distribution of root biomass are critical to understanding the ecophysiology of vegetation communities. This is particularly true when models are applied to describe ecohydrology and vegetation function. However, there is a paucity of such information across continental Australia. We quantified vertical and horizontal root biomass distribution in a woodland dominated by Angophora bakeri and Eucalyptus sclerophylla on the Cumberland Plains near Richmond, New South Wales. The site was characterised by a duplex (texture contrast) soil with the A horizon (to 70 cm) consisting of loamy sand and the B horizon (to < 10 m) consisting of sandy clay. The topsoil had a smaller bulk density, a smaller water holding capacity but a larger organic component and a larger hydraulic conductivity in comparison to the subsoil. Root biomass was sampled to 1.5 m depth and declined through the soil profile. Whilst total biomass in the B horizon was relatively small, its contribution to the function of the trees was highly significant. Coarse roots accounted for approximately 82% of the root mass recovered. Lateral distribution of fine roots was generally even but coarse roots were more likely to occur closer to tree stems. Variation in tree diameter explained 75% of the variation in total below-ground biomass. The trench method suggested the belowground biomass was 6.03 ± 1.21 kg m-2 but this method created bias towards sampling close to tree stems. We found that approximately 68% of root material was within a 2 m radius of tree stems and this made up 54% of the total number of samples but in reality, only approximately 5 to 10% of the site is within a 2 m radius of tree stems. Based on these proportions, our recalculated belowground biomass was 2.93 ± 0.59 kg m-2. These measurements provide valuable data for modeling of ecosystem water use and productivity. © Springer Science + Business Media B.V. 2009.C. M. O. Macinnis-Ng, S. Fuentes, A. P. O’Grady, A. R. Palmer, D. Taylor, R. J. Whitley, I. Yunusa, M. J. B. Zeppel and D. Eamu

Precipitation partitioning - Hydrologic highways between microbial communities of the plant microbiome?

International audienceThere are multiple distinct habitats for microbiota inhabiting the plant microbiome (phyllosphere, endosphere, litter, rhizosphere) and habitats that act as additional sources (and sinks) of microbes and nutrients for the plant microbiome (atmosphere, pedosphere, bedrock, and fauna). These habitats harbor distinctive microbial communities that differ in structure, composition, function, and spatiotemporal dynamics. Each habitat also differs in the mechanisms that provide “gateways” of exchange of microbes (and microbial products) between two communities, or in their access to “highways” that connect multiple communities. Of the environmental processes driving microbial community exchanges, precipitation events seem to represent the only one highway that can connect all the abovementioned habitats—the “hydrologic highway”. When precipitation contacts plants, it is partitioned into interception (water stored on, and evaporated from, plant surfaces), throughfall (water that drips from canopy surfaces and through gaps), and stemflow (water that is drained down the stem). This chapter describes the ways that precipitation partitioning in vegetated ecosystems (into interception, throughfall, and stemflow) may connect microbial communities from the top (atmospheric boundary layer) to the bottom (bedrock face) of the critical zone via these hydrologic highways