 |
| Titel |
Geochemical indicators and characterization of soil water repellence in three dominant ecosystems of Western Australia |
| VerfasserIn |
Miriam Muñoz-Rojas, Nicasio T. Jiménez-Morillo, Antonio Jordán, Lorena M. Zavala, Jason Stevens, José Antonio González-Pérez |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131019
|
| Publikation (Nr.) |
 EGU/EGU2016-11368.pdf |
|
|
|
|
|
| Zusammenfassung |
| Introduction
Soil water repellency (SWR) has critical implications for restoration of vegetation in degraded areas as it is responsible of poor plant establishment and a high incidence of erosion processes. Different organic substances are capable of inducing SWR but polar molecules such as certain fatty acids, and waxes i.e. esters and salts of fatty acids, appear to be the main constituents of hydrophobic coatings on soil mineral particles (Doerr et al., 2005). Plant species most commonly associated with SWR are evergreen trees with a considerable amount of resins, waxes or aromatic oils such as eucalypts and pines. Most of these substances are abundant in ecosystems and are released to soil by plants as root exudates or decaying organic debris, and by soil fauna, fungi and other microorganisms, but a thorough knowledge of substances capable of inducing hydrophobicity in soils is still not complete (Jordan et al., 2013). Although SWR has been reported in most continents of the world for different soil types, climate conditions and land uses, there are still many research gaps in this area, particularly in semi-arid areas largely affected by this phenomenon.
Materials and methods
This research was conducted in three dominant ecosystems of Western Australia (WA), e.g. semi-arid grassland in the Pilbara region (North WA), Banksia woodland, and a coastal dune (both located in South WA). These environments have different climate characteristics and soil types but similar vegetation communities. Soil samples were collected under the canopy of a broad range of plant species that compose the dominant vegetation communities of these ecosystems, and SWR was measured under lab conditions in oven-dry samples (48 h, 105 ºC). Soil microbial activity was measured with the 1-day CO2 test, a cost-effective and rapid method to determine soil microbial respiration rate based on the measurement of the CO2 burst produced after moistening dry soil (Muñoz-Rojas et al., 2016). Soil pH and electrical conductivity (EC) were determined in deionised water (1:2.5 and 1:5 w/v, respectively). The structural characterization of soil organic matter (SOM) was analysed by direct analytical pyrolysis (Py-GC/MS) performed at 500 °C (González-Vila et al., 2009). Only chromatogram peaks with an area higher than 0.2 % were identified and used to obtain the relative abundance of main chemical families in each vegetation cover.
Results
Our results show that soil water repellence is strongly correlated to microbial activity, pH and electrical conductivity. After Py-GC/MS analysis, soil organic matter in the Banksia woodland and the coastal dune showed a high heterogeneity. In the Banksia woodland two different patterns were observed. Samples under Banksia spp. showed a SOM with clear signs of altereation (humified) that included a high contribution of stable families like unspecific aromatic compounds and alkane/alkene pairs whereas under Eucalyptus spp. showed a less altered SOM with a high relative contribution from lignocellulose (lignin and carbohydrates), together with a low relative content of recalcitrant families. However in the soil samples from coastal dunes a very similar SOM chemical composition was found in all cases. The dominant family was unspecific aromatic compounds (>30%), followed by alkane/alkene pairs and a high relative contribution from N bearing peptide compounds. This, together with a low relative amount of carbohydrate and lignin derived (methoxyphenols) compounds points to a SOM that undergoes great alteration processes, possible because of high turn-over rates. Very low contents of SOM were found in the Pilbara system, under Py-GC/MS detection levels, and therefore it was not possible to establish its chemical composition.
A principal components analysis (PCA) axes based on the relative abundances of chemical families of compounds released after SOM pyrolysis (70.9 % of total variation explained in the two first axes) indicate that water repellence is closely related with fatty acids and the presence of short chain hydrocarbons.
Acknowledgements
This research has been funded by the University of Western Australia (Research Collaboration Award 2015: ‘Soil water repellence in biodiverse semi arid environments: new insights and implications for ecological restoration’) and the Spanish Ministry of Economy and Competitiveness (research projects GEOFIRE, CGL2012-38655-C04-01, and POSTFIRE, CGL 2013-47862-C2-1-R.
References
Doerr, S.H., Llewellyn, C.T., Douglas, P., Morley, C.P., Mainwaring, K.A., Haskins, C., Johnsey, L., Ritsema, C.J., Stagnitti, F., Allison, G., Ferreira, A.J.D., Keizer, J.J., Ziogas, A.K., Diamantis, J. 2005. Extraction of compounds associated with water repellency in sandy soils of different origin. Australian Journal of Soil Research 43, 225-237.
Gonzalez-Vila, F.J., Gonzalez-Perez, J.A., Akdi, K. Gomis, M.D. Perez-Barrera, F., Verdejo, T. 2009. Assessing the efficiency of urban waste biocomposting by analytical pyrolysis (Py-GC/MS). Bioresource Technology 100, 1304-1309.
Jordán, A., Zavala, L.M., Mataix-Solera, J., Doerr, S.H. 2013. Soil water repellency: origin, assessment and geomorphological consequences. Catena 108, 1-8.
Muñoz-Rojas, M., Erickson, T,E., Martini, D., Dixon, K.W., Merritt, D.J. 2016. Soil physicochemical and microbiological indicators of short, medium and long term post-fire recovery in semi-arid ecosystems. Ecological indicators 63, 14-22. |
|
|
|
|
|
|