Response of Soil Carbon to Temperature Change

Transcription

1 Response of Soil Carbon to Temperature Change Weixin Cheng Environmental Studies University of California Santa Cruz

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5 610 Land plants GPP R p /Yr Atmosphere Fossil fuels NPP - 60? R s = 2 1,580 39,200 Soils Ocean Based on Schimel et al. 1995

6 IPCC 2007

7 Baseline= ; dots are yearly data, lines are decadal averages; shade=uncertainty

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9 How will soil organic C pool respond to global warming? 1. General temperature sensitivity of SOM decomposition 2. Substrate availability vs. T-sensitivity 3. T-sensitivity of labile vs. recalcitrant SOM decomposition 4. Rhizosphere interactions vs. T-sensitivity

10 How will soil organic C pool respond to global warming? 1. General temperature sensitivity of SOM decomposition 2. Substrate availability vs. T-sensitivity 3. T-sensitivity of labile vs. recalcitrant SOM decomposition 4. Rhizosphere interactions vs. T-sensitivity

11 As commonly recognized, understanding of temperature sensitivity stems from enzyme kinetics. Most enzymatic reaction rates double with a 10 ºC increase in temperature. when substrate concentration is at or near saturation level and the temperature is within the optimal range of the enzyme. This why Q 10 =2 is often assumed. Q 10 = R (t+10) / R t 2

12 Kirschbaum SBB

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14 NATURE 2000

15 Kirschbaum 2000 BioGeoChem

16 Giardina & Ryan, Luo et al. Miko Kirschbaum 2004 GCB 10:

17 NATURE 2005

18 Knorr et al NATURE

19 Based on theoretical analysis, Bosatta & Agren 1999 (SBB) concluded that the decomposition of lower quality SOM should have higher temperature sensitivity than higher quality SOM. This conclusion is consistent with Arrhenius (1889) equation----lower quality substrates require higher activation energy.

20 Davidson & Janssens 2006 Nature G=glucose T=Tannin Red=increasing Blue=decreasing

21 How will soil organic C pool respond to global warming? 1. General temperature sensitivity of SOM decomposition 2. Substrate availability vs. T-sensitivity 3. T-sensitivity of labile vs. recalcitrant SOM decomposition 4. Rhizosphere interactions vs. T-sensitivity

22 Why does Q 10 value decreases as incubation temperature increases? Kirschbaum SBB

23 Theoretically, both V max and K m are temperature-dependent, but can cancel each other out. K m is only effective when C is low. We tested this using glucose saturation.

24 Hypothesis: As incubation temperature increases, substrate availability decreases, the canceling effect of K m increases, and the apparent Q 10 value decreases. Decreasing [C a ] Increasing K m effect

25 Cheng & Virginia 1993, SBB

26 Gershenson et al GCB

27 Gershenson et al GCB

28 How will soil organic C pool respond to global warming? 1. General temperature sensitivity of SOM decomposition 2. Substrate availability vs. T-sensitivity 3. T-sensitivity of labile vs. recalcitrant SOM decomposition 4. Rhizosphere interactions vs. T-sensitivity

29 Fierer et al Ecology

30 Reichstein et al BioGeoSci

31 NATURE 2005

32 Vanhala et al SBB

33 Conant et al GCB

34 Conant et al GCB

35 Conant et al GCB

36 How will soil organic C pool respond to global warming? 1. General temperature sensitivity of SOM decomposition 2. Substrate availability vs. T-sensitivity 3. T-sensitivity of labile vs. recalcitrant SOM decomposition 4. Rhizosphere interactions vs. T-sensitivity

37 Which component of the total soil respiration is more sensitive to warming? Soil Basal Respiration Root Respiration SOM-derived Plant-derived Rhizosphere Priming Rhizo-Microbial Respiration

38 From: Kuzyakov, Y J. Plant Nutr. Soil Sci.

39 SCIENCE 2002

40 Boone et al NATURE

41 WHERE DO YOU ALL COME FROM? C O I am from roots C O C O C O C O C O I am from soil organic matter C O I am from the rhizosphere C O C O C O C O C O

42 C3 plants δ 13 C: - 27 C4 plants δ 13 C: - 12 Naturally Occurring C3 soil δ 13 C: - 25 C4 soil δ 13 C: - 14 C4 plants δ 13 C: - 12 C3 plants δ 13 C: - 27 Switched in Experiments C3 soil δ 13 C: - 25 C4 soil δ 13 C: - 14

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44 Continuous 13 C-labeling Greenhouse at UCSC [CO 2 ] = 400 ppm δ 13 C = -17

45 Magnitude of the rhizosphere effect on SOM decomposition measured by isotope methods (Based on Cheng and Kuzyakov 2005). Plant Type Treatment Soil Type 1 PGC 2 %Priming 3 Time 4 (d) Reference Wheat CLO GC Cheng 96 Wheat Ambient CO 2 CLK GC Cheng & Johnson 98 Wheat Elevated CO 2 CLK GC Cheng & Johnson 98 Wheat Ambient CO 2, +N CLK GC Cheng & Johnson 98 Wheat Elevated CO 2, +N CLK GC Cheng & Johnson 98 Sunflower Ambient CO 2 CLK GH Cheng et al. 00 Sunflower Elevated CO 2 CLK GH Cheng et al. 00 Wheat 12/12 hrs light/dark CLK GC Kuzyakov & Cheng 01 Wheat 12/60 hrs light/dark CLK GC Kuzyakov & Cheng 01 Soybean Growing season mean CLK GH Fu & Cheng 02 Sunflower Growing season mean CLK GH Fu & Cheng 02 Sorghum Growing season mean SLC GH Fu & Cheng 02 Amaranthus Growing season mean SLC GH Fu & Cheng 02 Soybean CLK GH 3 35 Cheng et al. 03 Wheat CLK GH 7 35 Cheng et al. 03 Soybean CLK GH Cheng et al. 03 Wheat CLK GH Cheng et al. 03 Soybean CLK GH Cheng et al. 03 Wheat CLK GH Cheng et al. 03 Soybean CLK GH Cheng et al. 03 Wheat CLK GH Cheng et al. 03 Soybean Growing season mean CLK GH Cheng et al. 03 Wheat Growing season mean CLK GH Cheng et al. 03 %priming is calculated as: (planted - unplanted)/unplanted X 100.

46 A summary: Based on results from 16 papers over 20 years of research, both positive and negative rhizosphere effects on SOM decomposition have been found in numerous experiments. The magnitude of the effects varies widely, from -50% to as high as +380% above the unplanted control.

47 Which component of the total soil respiration is more sensitive to warming? Soil Basal Respiration Root Respiration SOM-derived Plant-derived Rhizosphere Priming Rhizo-Microbial Respiration

48 Bader & Cheng, 2007 SBB

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50 Measuring total soil CO 2 efflux Sealant Mylar balloon NaOH trap Pump Water trap

51 From the GROWTH CHAMBER experiment, all components of the total soil respiration is sensitive to warming! Plant-derived > SOM-Derived >Basal Soil Basal Respiration Root Respiration SOM-derived Plant-derived Rhizosphere Priming Rhizo-Microbial Respiration

52 In summary, rhizosphere priming may increase the temperature sensitivity of SOM decomposition.

53 RPE? RPE? Source: M U F Kirschbaum, Soil Biology & Biochemistry 38 (2006)

54 How will soil organic C pool respond to global warming? 1. General temperature sensitivity of SOM decomposition Conclusion-I: it is still controversial. 2. Substrate availability vs. T-sensitivity Conclusion-II: substrate availability is an important factor. 3. T-sensitivity of labile vs. recalcitrant SOM decomposition Conclusion-III: it is inconclusive. 4. Rhizosphere interactions vs. T-sensitivity Conclusion-IV: rhizosphere processes modulate T-sensitivity. 5. What s next? More research is needed.

55 Acknowledgements Thanks to Feike Dijkstra, Nick Bader, Daniel Keck, and Biao Zhu for doing the work. Dyke Andreasen & David Harris analyzed all samples for isotopes. Many undergraduate students provided assistance. USDA NRI program (Grant # ) and Kearney Foundation of Soil Science provided the funding.