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| Titel |
Vegetation-induced soil water repellency as a strategy in arid ecosystems. A geochemical approach in Banksia woodlands (SW Australia) |
| VerfasserIn |
Miriam Muñoz-Rojas, Nicasio T. Jiménez-Morillo, José Antonio González-Pérez, Lorena M. Zavala, Jason Stevens, Antonio Jordán |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122715
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| Publikation (Nr.) |
 EGU/EGU2016-1820.pdf |
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| Zusammenfassung |
| Introduction
Banksia woodlands (BW) are iconic ecosystems of Western Australia (WA) composed by an overstorey dominated by Proteaceae, e.g. Banksia menziesii and Banksia attenuata, in combination with other species, such as Eucalyptus spp., Verticordia spp. or Melaleuca spp. Although located in very poor dune soils, BW provide numerous ecosystem services and sustain a high biodiversity. In this area, annual rainfall is relatively high (about 800 mm) but permeability of the sandy substrate leads to a functionally arid ecosystem. Currently, BW are threatened by sand mining activities and urban expansion; therefore conservation and restoration of these woodlands are critical. Despite numerous efforts, the success of restoration plans is usually poor mostly due to the high sensitivity to drought stress and poor seedling survival rates (5-30%) (Benigno et al., 2014). A characteristic feature of BW is their root architecture, formed by a proteoid (cluster) system that spreads to form thick mats below the soil surface, favouring the uptake of nutrients (especially, P), and preventing soil erosion. Root exudates are related to numerous plant functions, as they facilitate penetration of roots in soil and enhance the extraction of scarce mineral nutrients and its further assimilation. Exudates may also interact directly with soil or indirectly through microbial mediated events being also related to soil water repellency (SWR; Lozano et al, 2014). Knowledge about the specific compounds able to induce SWR is limited (Doerr et al., 2000), but it is generally accepted that is caused by organic molecules coating the surface of soil mineral particles and aggregates (Jordán et al., 2013). Proteaceae release short-chained organic acids to enhance phosphate acquisition, which have been also reported to be related with SWR (Jiménez-Morillo et al., 2014).
It is hypothesized that disruption of water dynamics in mature BW soils is underlying the failure of restoration plans. This research aims to study SWR and its impact on water economy in relation with soil functioning and plant strategies for water uptake in pristine BW. Results are expected to shed light on the origin and implications of SWR in the area and provide useful information for improving ongoing restoration plans.
Materials and methods
The study was conducted in natural BW of WA. Soil samples were collected at different soil depths (0-1, 1-10, 20-30 and 40-50 cm). Rationale for sampling depths was based on the different severities of SWR at each layer under field conditions. Soil water repellency was assessed under laboratory conditions in oven-dry samples (48 h, 105 ºC) and the chemical organic assemblage of bulked soil subsamples from each layer was analysed by direct analytical pyrolysis (Py-GC/MS).
Results and discussion
Soil water repellency distributed discontinuously through the soil profile. The first thin layer (0-1 cm) composed of coarse sand and litter, located immediately above Banksia root clusters, showed wettable conditions. In contrast, the relatively well aggregated soil layer where the Banksia cluster root system is located (1-10 cm) was severely water-repellent. The 20-30 and 40-50 cm deep layers rendered wettable or subcritically water-repellent. After Py-GC/MS analysis, major compounds were identified and grouped according to their probable biogenic origin (lignin, polysaccharides, peptides, etc.). Among other soil organic compounds, well resolved bimodal alkane/akene (C8-C31, maxima at C13 and C26) and fatty acids series (short-chained, C5-C9, and long-chained even-numbered C12-C18) were associated to the root cluster soil layer (1-10 cm). Also, a relatively high contribution of fire-derived polycyclic aromatic hydrocarbons (PAHs) was observed (7%), which is consistent with frequent fires occurring in BW.
These results point to possible indirect links between organic substances released by roots and soil wettability involving soil microorganisms. Further discussion should shed light on possible ecological plant strategies and specific adaptations for water uptake in such arid ecosystems of WA.
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
Benigno SM, Dixon KW, Stevens JC. 2014. Seedling mortality during biphasic drought in sandy Mediterranean soils. Funct Plant Biol 41: 1239-1248 DOI: 10.1071/FP13366
Doerr SH, Shakesby RA, Walsh RPD. 2000. Soil water repellency: its causes, characteristics and hydro-geomorphological significance. Earth-Sci Rev 51: 33–65. DOI: 10.1016/S0012-8252(00)00011-8.
Jordán A, Zavala LM, Mataix-Solera J, Doerr SH. 2013. Soil water repellency: origin, assessment and geomorphological consequences. Catena 108: 1–8. DOI: 10.1016/j.catena.2013.05.005.
Jiménez-Morillo NT, González-Pérez JA, Jordán A, Zavala LM, de la Rosa JM, Jiménez-González MA, González-Vila FJ. 2014 Organic matter fractions controlling soil water repellency in sandy soils from the Doñana National Park (Southwestern Spain). Land Degrad. Develop. published online. DOI: 10.1002/ldr.2314
Lozano E, Garcia-Orenes F, Barcenas-Moreno G, Jimenez-Pinilla P, Mataix-Solera J, Arcenegui V, Morugan-Coronado A, Mataix-Beneyto J. 2014. Relationships between soil water repellency and microbial community composition under different plant species in a Mediterranean semiarid forest. J Hydrol Hydromech 62: 101-107. DOI: 10.2478/johh-2014-0017 |
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