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Acknowledgments

Acknowledgments University of Toledo, Maumee Valley Audubon Society, Daryl Moorhead, Tom Weicht, Alison Spongberg, Li Fafeng, Brian Marlow, Jayne Belnap. MICROBIOTIC CRUST COMMUNITIES: NITROGEN FIXATION AND LEACHING WITHIN A MESIC TEMPERATE OAK SAVANNA. by Roberta Veluci & Deborah A. Neher.

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Acknowledgments

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  1. Acknowledgments University of Toledo, Maumee Valley Audubon Society, Daryl Moorhead, Tom Weicht, Alison Spongberg, Li Fafeng, Brian Marlow, Jayne Belnap. MICROBIOTIC CRUST COMMUNITIES: NITROGEN FIXATION AND LEACHING WITHIN A MESIC TEMPERATE OAK SAVANNA by Roberta Veluci & Deborah A. Neher Cladina cristatella Tuck.

  2. ABSTRACT Microbiotic crust is a biological soil crust composed of lichens, cyanobacteria, green algae, mosses, and fungi. Although crusts are a dominant source of nitrogen in arid ecosystems, this study is the first to examine their contribution to nitrogen (N) availability in xeric temperate habitats in Northwest Ohio. N fixation occurs in these crusts covering sandy, low N soil. Moss-crust surfaces are covered with cyanobacteria responsible for N fixation and cyanobacterial abundance was independent from days since last rainfall. Moreover, increases in temperature correspond with amount of N fixed. N leaching from the crust layer was quantified using ion exchange resin bags inserted at 2.5-cm depth from surface of intact cores. Leaching of NO3- and NH4 +were reduced in forest edge relative to shrub or grass vegetations, and did not vary significantly among months. Leaching of NO3- is retarded with temperature rise and, thus, a function of temperature. Conversely, precipitation increased N leaching, and is expected to maximize during rain fall events. Furthermore, environmental parameters such as moisture and temperature fluctuations in soil are moderated under crust compared to bare soil without crust. We conclude that biological crusts in northwestern Ohio enhance N fixation, moderate soil microclimate and, impact N leaching.

  3. STUDY SITE • Oak Openings Metropark • 4.0 to 5.4 pH • 91-94% sand • Low N soil

  4. NITROGEN FIXATION Algae Bare A B C Lichen Moss Video Imaging Analysis: estimate crust type and extent Acetylene Reduction Assay: confirmed N fixation in 50% of samples. A) Well established crust, B) Intermediate crust and C) Bare Soil.

  5. 0.20 Moss y = 0.006 + 0.0043x R2 = 0.09 & p < 0.003 0.15 0.10 0.05 0.00 0.20 0.40 0.60 0.80 1.00 0.00 Ethylene proportion (10-4) 0.40 Lichen 0.30 0.20 0.10 y = 0.021 + 0.044x R2 = 0.03 & p < 0.003 0.00 0.20 0.40 0.60 0.80 1.00 0.00 Extent Cover (proportion) Fig. 6 Moss cover and lichen explained more N fixation than did cyanobacteria or bare soil

  6. 8 a Contrasting letters (p= 0.0002) 7 6 5 Cyanobacteria (105 cells/g of dry soil) 4 ab 3 2 b 1 0 3 6 9 Crust depth (mm) Fig. 8 Method: Fluorescent microscopy to quantify cyanobacterial populations Result: Abundance of cyanobacteria decreased with crust depth

  7. Moss surfaces are covered with cyanobacteria and its abundance was independent from days since last rainfall 3 p = 0.70 2 Cyanobacteria (106, total cells/g of dry soil) 1 0 0 7 14 Days since rainfall Fig. 7

  8. 1.0 0.8 0.6 0.4 NO3- = 1N KHSO4- 0.2 NH4+ = 1N K2SO4 Proportion of ion recovery (µg/g) 0.0 1.0 NH4+ = 0.5 N K2SO4+ B 0.8 0.6 0.4 0.2 0.0 150 300 600 900 1500 NITROGEN LEACHING Method Development Recovery efficiency of NO3- and NH4+ from resins were 33 and 70%, respectively. Volume (ml) Fig. 2 Recovery efficiency of resin bags

  9. 10 70 NO3- 60 8 50 6 40 30 4 20 2 10 % Total Recovery 0 0 30 70 Mean recovery (µg/g) NH4+ 60 25 50 20 40 15 30 10 20 5 10 0 0 inside core around core below core Nitrogen source NITROGEN LEACHING 2) Method Development Ion exchange resin bags placed flush with the bottom surface of an intact core collected most NO3- or NH4+ from outside the core than from directly above or underneath the resin bag inside the core (p < 0.0067). Therefore, resin bags were inserted at 2.5-cm depth from surface of intact cores in field experiments. Fig. 3 Relatively flow of N to resin bags flush with bottom of core

  10. 2) Field Measurements Concentrations of NO3-(r2 = 0.33) and NH4+(r2 = 0.21) on resins were associated linearly with soil concentrations. Concentrations of N on resins were typically greater than in soil (p = 0.0001), although they were in equilibrium through time (p = 0.18). 0.5 = resins O = soil NO3- 0.4 0.3 0.2 0.1 Resin and soil nitrogen (µg/g) 0.0 0.5 NH4+ 0.4 0.3 0.2 0.1 0.0 3 5 7 10 18 22 1 Time (weeks) Fig. 4 Dynamic equilibrium of N on resins and in soil

  11. 10 NO3- p = 0.009 8 6 4 2 0 49 80 98 127 10 NH4+ p = 0.03 Nitrogen leaching (µg/g) 8 6 4 2 0 40 80 98 127 Aug Sept Nov Dec Oct Time (days) Concentration of NO3- (A, p = 0.0089) and NH4+(B, p = 0.0314) leaching were less at forest edge than shrub or grass, and did not vary significantly among months. A ■= SHRUB ●= GRASS ▲= FOREST B Fig. 5 N leaching among vegetation types

  12. Soil crusts moderate soil climate 0 A -1 -2 -3 Moisture (MPa) -4 -5 -6 -7 0 5 10 15 20 25 40 B 30 20 Temperature (°C) 10 0 MAY SEPT 0 5 10 15 20 25 Time since deployment (weeks) Fig 1.Soil A) water potential & B) temperature for bare ( ) or crust soils ( ) through time.

  13. CONCLUSIONS • This is the first study to: • Confirm N fixation of microbiotic crusts in mesic temperate biome • Employ IRN-77/78 resins in sandy soil, low in both N & organic matter

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