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BIOLOGICAL SOIL CRUSTS CONTROL N DYNAMICS AND MICROBIAL FUNCTIONAL DIVERSITY IN RESPONSE TO NUTRIENT ADDITIONS Manuel Delgado-Baquerizo ([email protected]) 1 , Lourdes Morillas ([email protected] ) 1 , Fernando T. Maestre ([email protected]) 2 & Antonio Gallardo ([email protected]) 1 . 1 Área de ecología, Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Carretera de Utrera km. 1, 41013 Sevilla, Spain. 2 Área de Biodiversidad y Conservación, Departamento de Biología y Geología, Escuela Superior de Ciencias Experimentales y Tecnología, Universidad Rey Juan Carlos, 28933 Móstoles, Spain STUDY SITE AND SAMPLING DESIGN NUMERICAL AND STATISTICAL ANALYSES DISCUSSION The Shannon-Weaver (S-W) Diversity Index (H') was calculated by using the CO2 responses to the different C sources. Pi is the % of response of a each C substrate in regard to the total 6 . We calculated the increment in the relative dominance of N-forms (NH4+, N03- and DON), total available N, potential net N transformation rates and SW-diversity index in regard to control. The effects of incubation period, microsite and nutrient treatments on the increment of all these variables in regard to control were tested by using PERMANOVAs 7 . This study was conducted in a semi-arid grassland at the Aranjuez experimental station (Fig 1). Soil sampling was carried at Spring (2010). Five soil samples (top 4 cm) were taken under two microsites: bare soil (BS) and BSC (Fig 1). Soil were incubated using different N (100 mg N kg-1), C (2.323 mg C kg-1) and P (20 mg P kg-1) treatments (Control, N, C, P, C+N, N+P, C+P, and C+N+P) 4 at 20ºC during 2 different incubation periods (1-week and 3-week) in a factorial design. The functional diversity of soil heterotrophic microbial communities was analyzed with the MicroResp technique 5 NH4+, N03- and dissolved organic nitrogen (DON) were estimated by colorimetry from K2SO4 0.5 M extracts in the incubated and initial (air-dried) soil samples 2 . The potential net N trasnformation rates (depolymerization, ammonification and nitrification; [NTRs]) were calculated for each nutrient treatment 3 . REFERENCES: 1. Finzi, A.C., Austin, A.T., Cleland, E.E., Serita D Frey, S.D., Houlton, B.Z. & Wallenstein, M.D. 2011. Coupled Biochemical Cycles: Responses and feedbacks of coupled biogeochemical cycles to climate change: examples from terrestrial ecosystems. Frontiers in Ecology and the Environment, 9, 61–67. 2. Delgado-Baquerizo, M., Castillo-Monroy, A.P., Maestre, F.T., Gallardo. A., 2010. Change in the dominance of N forms within a semi-arid ecosystem. Soil Biology and Biochemistry 42: 376–378 3. Castillo-Monroy, A.P., Delgado-Baquerizo, M., Maestre, F.T., Gallardo, A., 2010. Biological soil crusts modulate nitrogen availability in semi-arid ecosystems: Insights from a Mediterranean grassland. Plant and Soil 333: 21-34. 4. Qiu, S., McComb, A.J. & Bell, R.W. 2008 Ratios of C, N and P in soil water direct microbial immobilisation–mineralisation and N availability in nutrient amended sandy soils in southwestern Australia. Agriculture, Ecosystems & Environment, 127, 93-99. 5. Garcia-Palacios, P.; Bowker, M.A.; Chapman, S.J.; Maestre, F.T.; Soliveres, S.; Gallardo, A.; Valladares, F.; Guerrero, C. & Escudero, A. (2011). Early-successional vegetation changes after roadside prairie restoration modify processes related with soil functioning by changing microbial functional diversity. Soil Biology & Biochemistry, 43, 1245-1253. 6. Shannon, C.E. & Weaver, W. 1963. The mathematical theory of Comunication. Univ. of Illinois Press. 117 pp. 7. Anderson, M.J., 2001. A new method for non-parametric multivariate analysis of variance. Austral Ecology 26: 32-46. 8. Belnap, J. & Lange, O.L. 2003. Biological Soil Crusts: Structure, Function, and Management. Berlin: Springer-Verlag. New York. Pp 3-30. 9. Cookson, W. R., Müller, C., O'Brien, P. A., Murphy D. V. & Grierson. P. F. 2006. Nitrogen dynamics in an australian semiarid grassland soil. Ecology, 87, 2047–2057 10. Schimel, J.P., Bennett, J., 2004. Nitrogen mineralization: challenges of a changing paradigm. Ecology 85, 591-602. Human activities are changing carbon (C), nitrogen (N), and phosphorus (P) ratios in soil ecosystems 1 . In drylands, biological soil crusts (BSCs) play a prevalent role in the Nitrogen (N) cycle 2-3 , however its influence on the phosphorus (P) cycle is poorly known. We evaluated how BSCs and different N, C and P ratios affect to the N dynamics and microbial functional diversity In general, when C and P was added, BSC showed a higher increase in DON, depolymerization and the S-W diversity index than bare soil microsite (Fig 1-3). N treatment decrease the microbial functional diversity in both microsites (p<0.01). Complex processes as depolymerization may require a larger and diverse group of heterotrophic microorganisms. Besides, P may be an essential nutrient in BSC communities where N fixation. N addition derived from human activities may have an important impact on the N dynamics and microbial functional diversity 8 . Changes in the labile C:N ratio more than N availability modulate the N-forms and NTRs in both microsites (Fig 1 and 3). Thus, in the 3-week period of incubation, NO3- and nitrification dominate when N treatments (N and N+P), NH4+ and amonification in the C+N+P treatments and DON and depolymerization when C treatments (C and C+P; p<0.01) 9-10 . INTRODUCTION LAB ANALISYS Figure 1. Study site. A: Localization of our study site at the Iberian peninsula map; B: semi-arid grassland (Stipa tenacissima L); C: BS microsite (Dominate by Diploschistes diacapsis; ratio C:N: 11.24; pH: 7.2); D: BSC microsite (Ratio C:N: 10.11; pH: 7.4). C D B A The increase in depolymerization, DON and microbial functional diversity in the BSC microsite with regard to bare soil, when C or P were added, suggest that BSC may confer resistance to this variables to changes in nutrient ratios derived from human activities. Changes in the ratios of labile C:N more than N availability seems to modulate the N dominance form and N transformation processes. CONCLUDING REMARKS Figure 1. Increment in the relative dominance of N-forms (NH4+, NO3- and DON) under the different nutrient treatments along the periods of incubation, in the BSC and BS microsites. Means ± SE (n = 5). Figure 2. Increment in the S-W diversity index for the different nutrient treatments along the periods of incubation, in the BSC and BS microsites Means ± SE (n = 5). Figure 3. Increment in the NTRs for the different nutrient treatments, in the BSC and BS microsites. Means ± SE (n = 5).
