Biological soil crusts promote N accumulation in response to dew events in dryland soils

1. Biological soil crusts promote N accumulation in response to dew events in dryland soils Manuel Delgado-Baquerizo; Fernando T. Maestre; Jesús G.P. Rodríguez & Antonio Gallardo. Soil Biology and Biochemistry (2013).

2. Introducction In drylands, water is the most important factor limiting plant growth, net primary production and microbial decomposition (Austin et al. 2004; Schwinning and Sala2004; Robertson and Groffman 2007) In theseecosystemsdeweventsmay provide up to 40% of the water inputs received every year (from ~0.15 mm to ~ 0.30 mm per day; Kidron2000; Jacobs et al., 2000; Moro et al., 2007; Lekouch et al., 2011) However, not much is known about the influence that very small water pulses, such as those from dew events, have on biogeochemical cycles in drylands.

3. Introducction Aranjuez experimental station (central Spain)

4. Introducction N cycle in drylands After water, nitrogen (N) is the main factor limiting plant growth and decomposition in drylands (Schlesinger 1996) Biocrusts, usually located in the open areas between plant canopies, largely modulate the N cycle in these ecosystems.

5. Introducction Ex: 1 Increasetotal N and % of dissolvedorganic N regardingBS Delgado-Baquerizo et al. 2010; SoilBiology and Biochemistry Other examples in: Belnap (2002), Zaady (2005) Su et al. (2011)

6. Introducction Ex: 2 increaseDON production in response to C, N and P additionregardingBS Delgado-Baquerizo et al. (2013); Plant and Soil

7. Introducction Ex: 3 more homogeneous soilconditionsthanplantcanopiesforInorganic N Delgado-Baquerizo et al. 2013; Journal of aridenvironments

8. G: ¿Howbiocrustsmodulatethe response of N availabilitytodewevents in semiariddrylands? H: Biocrustswillincrease N availability in response todewevents

9. Methods Aranjuez experimental station (349 mm; 14.5 ºC). Spring of 2010. Twelve intact soil cores (5 cm depth, 7.5 cm diameter) were collected under each of two microsites: well-developed biocrusts and bare ground areas (BG) Crust dominated by Diploschistesdiacapsis

10. Methods Air-dried soil cores with and without biocrusts (six replicates each) were incubated in a plant growth chamber for 14 days under two treatments: with and without (control) dew Soil cores were incubated for 9 hours of light (20% RH, 20ºC) and 15 hours darkness (80% RH, 10ºC) simulating spring conditions in Aranjuez In the dew treatment, soils were watered automatically three times during the darkness period to keep soil humidity constant at a 1% of SWC. Before and after the experiment, we collected 2.5 g of soil (0-2 cm depth) from each replicated core.

11. Material y Métodos Ammonium Nitrate Dissolvedorganic N (DON) Available N = Ammonium + Nitrate + DON Amino acids Carbohydrates= hexoses + pentoses Phenols Pentoses: hexoses -> proxy of originfromorganicmatterlichen vs. microorganisms Carbohydrates: available N -> proxy of organicmatterquality We calculated the absolute increment in the values of each variable after 14 days of incubation (regarding initial concentrations). Differences in the increment of these variables were evaluated using two-way ANOVAs: microsite & treatment

12. Results Differencesbetweentreatments and micrositeswerenotobservedforeither amino acidsornitrate (P > 0.05)

13. Results

14. Discusion Functionaldiversity and Fungal:bacterial ratio (Delgado-Baquerizo et al. 2013; Plant and soil) DON & available N Dew pulses available N forplant in theirperiods of activity available N Organic matter quality (lower labile C:N ratio)

15. Discusión Phenols production under biocrusts Allelopathic effect on other groups of microorganisms from occupying a relative “N-rich” microsite OM decomposition in response to a small water pulses (Austin et al. 2004). Pentose: hexose ratio Carbohydrates and N inmobilizationunderbiocrust and BG forthe control treatments 80% of RHmay active the N and C cycles in drylands

16. Conclusions We found that dew-like water inputs can promote the activation of microorganisms involved in the C and N cycles in dryland soils, and that this response is modulated by well developed biocrusts communities. Biocrustincreasedthe N availability in response tosmall pulses of water similar todewevents in semiaridecosystems. Given the degree of development of BSCs in drylandsworldwide, the high homogeneity of N cycle under biocrusts and the importance of water inputs from dew, the production of N under dew conditions can make an important contribution to the total N available for plants and microorganisms in these regions. Biocrustincrease the amount of soil phenols which may have a Allelopathic effect on other groups of microorganisms