Task S7 Characterize soil microbial community composition among successional stages and seasons in floodplain and upland

1. Successional processes Hypothesis: Climate influences the rate and trajectory of succession by altering disturbance regime and the abundance of key species. How do plant, animal and microbial communities change through succession and what are the consequences for ecosystem processes? Task S7 Characterize soil microbial community composition among successional stages and seasons in floodplain and upland ecosystems.

2. Studying plant-microbial interactions in the cycling of soil C and N(The black box approach) Soil C and N levels are determined by the balance between organic matter inputs and losses due to decomposition, erosion and leaching. Plant inputs • Litterfall • Root turnover • Exudation Soil microbial community • Decomposition • Formation of organic matter Schimel et al 2006

3. Microbial contributions to soil C storage What role does microbial community composition play in soil C sequestration? • Microbial growth efficiency • Recalcitrance of microbially- derived organic matter How does community composition change across successional development? • Substrate availability • Substrate quality Six et al 2006

4. Proposed research Assess soil microbial composition and biomass along floodplain and upland chronosequences using PFLA analysis. WHY? In order to develop and test hypotheses about the role of soil microbes in C cycling in forested ecosystems of interior Alaska, we need to have empirical observations of how community structure varies over time and space.

5. PLFA • Unlike CF methods, PLFA is useful as a proxy for living and possibly active biomass • Phosphate group is quickly consumed upon cell death • Not found in storage products • Found in relatively constant proportion of the biomass • Great structural diversity, coupled with high biological specificity

6. Taxonomic groups

7. Experimental design • All major stages of succession in FP (n=5) and UP (n=3) communities • 3-5 replicate stands per stage • 3 sampling periods • May • Mid July • Late September • 2 horizons • O (integrated organic) • A (mineral) • 50 cores composited from each 30m x 30m plot • 2+ years??

8. Predictions Broader patterns • Microbial biomass ↑ along the chronosequence. • FP: Microbial community shifts from bacterial-dominated to fungal-dominated over succession. UP: ↓ B:F. • Potential for vertical stratification in community structure as a function of substrate availability and water-filled pore space. Seasonal patterns • Bacterial:Fungal ↓ seasonally.

9. Successional processes Hypothesis: Climate influences the rate and trajectory of succession by altering disturbance regime and the abundance of key species. How do plant, animal and microbial communities change through succession and what are the consequences for ecosystem processes? Task S8 Determine the direct and interactive effects of soil resources, microclimate, and microbial symbionts on the cumulative nitrogen fixation through succession by alder in floodplain and upland ecosystems.

10. Physiological ecology of the Alnus-Frankia-EMF tripartite A. tenuifolia – a key player in the N economy of floodplain forest ecosystems in interior AK Persists throughout successional development How important are coordinated changes in ectomycorrhizal and Frankia associations of alder in enabling species persistence and N fixation capacity throughout succession?

11. Objectives • Identify EMF composition and functional traits in Alnus tenuifolia across a 200 year floodplain chronosequence • Characterize the ecophysiology of host selection for EMF in response to N and P fertilization in field plots, and in response to controlled partner choice experiments in the greenhouse.

12. Hypothesis Alder shifts associations with ectomycorrhizal species based on variation in plant demand for N and P, combined with the availability and forms of these nutrients in soil.

13. Objective 1: Describe EMF community composition and functional traits across succession • Prediction: Successional nutrient gradients favor selection of different fungal species across successional stages. • Task 1 - Extract DNAs from randomly subsampled EM root tips (control plots) and identify fungal associates through PCR and sequence analysis of the ITS region • Seasonality of mycorrhizal development • Task 2 - Determine whether the activities of key enzymes related to nutrient acquisition vary among fungal associates and successional stages • Acid phosphatase and phytase activity in single root tips using methylumbelliferone (MU)-labelled fluorescent substrate analogues.

14. Objective 2: Characterize host selection of EMF in response to N and P fertilization Prediction: N fertilization will have the greatest effect on N-mobilizing EMF species and enzymes in late succession, while P fertilization will down-regulate acid phosphatase activity primarily in early succession Task 1 - Extract and sequence DNAs from randomly subsampled EM root tips across N and P ammended plots Task 2 – Controlled greenhouse experiment to examine the capacities of the dominant alder EMF species to mobilize different forms of P, organic vs. inorganic.

15. Field study • 3 successional stages • Alder, balsam poplar, white spruce • 3 sampling periods • June, mid-July, early September 3 stand replications • 20m x 20m plot divided into 16 5m x 5m subplots

16. Results (to date) • Overall EMF diversity appears low • Strong core to core as well as site to site variation • Most sites ‘appear’ to be dominated by <6 morphotypes with several ‘rare’ morphotypes mixed within. • Fine root development delayed in alder relative to other taxon