Story. Copied from Gary Larson, who likes to know where his kids are when it gets dark. Soil CO 2

Transcription

1 A SOIL BIOTA Story Copied from Gary Larson, who likes to know where his kids are when it gets dark.

2 Federal Department of Economic Affairs DEA Agroscope Reckenholz-Tänikon Research Station ART Swiss Federal Research Station for Agroecology and Agriculture Air Pollution/Climate Group δ C of a subalpine pasture under increased N- and O 3-deposition Matthias Volk and Moritz Lehmann* *Institute for Environmental Geoscience, University of Basel, Switzerland

3 12 C/ C isotope discrimination Photosynthetic fractionation + post-carboxylation fractionation (e.g. starch synthesis) adapted from

4 Assumptions Young organic C, fresh from the leaf, is light ( C depleted) Older soil C is heavier ( C enriched) as it becomes increasingly more metabolised over time: root C < litter C < SOM (eg. Ehleringer et al. 2000). Microbial respiration CO 2 δ C reflects ± substrate C δ C (e.g. Santruckova et al. 2000). δ C reflects the age (quality) of the substrate predominantly metabolized. Change in CO 2 δ Ci implies: Change in relative abundance of soil C pools (substrates).

5 Earlier findings Effects of O 3 and N deposition treatment suggest a climate dependent change of the CO 2 exchange-balance of the grassland system: C-pool reduced by > 70 g C season -1 m -2 likely under high N.

6 Earlier findings Effects of O 3 and N deposition treatment suggest a climate dependent change of the CO 2 exchange-balance of the grassland system: C-pool reduced by > 70 g C season -1 m -2 likely under high N. Hypotheses 1. Seasonal development of vegetation is reflected in soil CO 2 δ C, because it alters the supply of light (more negative) young C compounds. 2. Mitigation of N limitation of soil microbial growth accelerates the consumption of labile C substrates. This leads to a depletion of labile (more negative) C pools and soil CO 2 δ C heavier (less negative) under high N.

7 Gaswell (courtesy Chris Andersen, EPA)

8 Summer sampling environment May June August September

9 Seasonal changes of δ C C Date dc mean Apr Mai Jun Jul Aug Sep Okt Nov

10 Seasonal changes of δ C C dc mean Apr Mai Jun Jul Aug Sep Okt Nov Date

11 Seasonal changes of δ C C Date Soil temperature Soil water content 0 dc mean Apr Mai Jun Jul Aug Sep Okt Nov depth) Soil temp perature ( C at 5cm Soil water con tent (vol. %)

12 Seasonal changes of δ C C GPP mean dc ) GP PP ( mol CO 2 m -2 s Apr Mai Jun Jul Aug Sep Okt Nov Date

13 Leaves δ C of Carex sempervirens -24 C ( ) N4 N14 N54 Seraina Bassin data (unpublished) Increased 2005 productivity 2006 increased A/g s = N4 N14 N54 increased WaterUseEfficiencyU E N load [kg N ha -1 y -1 ] less discrimination - Enriched δ C

14 Ozone induced changes of δ C ** * C O3 control O3+ O3++ *P<0.05; **P<0.01; ***P< Apr Mai Jun Jul Aug Sep Okt Nov Date

15 Nitrogen induced changes of δ C * C *** ** N 4 N 14 N54 *P<0.05; **P<0.01; ***P< Apr Mai Jun Jul Aug Sep Okt Nov Date

16 Summary δ C of soil air CO 2 revealed a strong seasonality of respiration substrate t quality. N effects also support the hypothesis, that reduced N limitation of microbial growth accelerates the consumption of labile C substrates. Consequently, increased N supply may have led to a depletion of labile SOM pools.