Main points:

Moisture and temperature controls over the season- three regimes Nov-March cold and wet April October warm and very dry September rain warm and wetAnnual respiration balance may depend on the occurrence of warm rains

During the April-October period (summer), roots in the top ~40 cm do not contribute significantly to soil respiration - very little difference between trenched versus untrenched plots - no isotopic differences between trenched and untrenched plots

3. Isotopes show shifts in the importance of different respiration sources Wetup of litter layer only (experiment) did not show the same response as wetup of plants + litter implies that

4. Diel controls also show shifts with season; when it is wet, temperature is the main control; when it is dry, relative humidity? Is the main control or there is no diel variability (also little surface autotrophic respiration source to drive respiration).

Nov 06Jan 07March 07May 07TrenchingJuly 07Sept 07Flux mgC m-2 hr-1Brown = trenchedGreen = untrenched

Litter Relative HumidityTemperature at 2 cm depth (C)Three regimes of temperature, moisture. Nov-March is cold and humidApril- october is dry but warm; one rain event in september stands out as a time when it is wet and warm. Next slide shows fuel rod moisture Data showns are daily averages.

Fuel Rod (water content)Temperature at 2 cm depth (C)

Temperature (2 cm)Litter relative HumidityFlux mgC m-2 hr-1Flux mgC m-2 hr-1Chamber 8 (untrenched)Chamber 5 (trenched)Temperature (2 cm)Litter relative Humidity

Temperature (2 cm)Litter relative HumidityFlux mgC m-2 hr-1Flux mgC m-2 hr-1Chamber 7 (untrenched)Chamber 6 (trenched)Temperature (2 cm)Litter relative Humidity

Flux mgC m-2 hr-1Chamber 2 (untrenched)Chamber 1 (trenched)Temperature (2 cm)Litter relative HumidityFlux mgC m-2 hr-1Temperature (2 cm)Litter relative Humidity

Flux mgC m-2 hr-1Chamber 3 (untrenched)Chamber 4 (trenched)Temperature (2 cm)Litter relative HumidityFlux mgC m-2 hr-1Temperature (2 cm)Litter relative Humidity

Days 335 to 340 Days 407 to 412 Days 468 to 473

Day 500-505Day 468 -473Day 531 - 538

Day 603-607Day 615-617Day 640-643

D14C of respired CO2

T,DT,DT,WT,WU,WU,WU,DU,DD14CNo difference between trenched/untrenchedFor 7 of 8 chambers, 14C during the day after wetting was higher than the previous nightFor chambers 1-4, wetted chambers (2,4) had higher 14C than controls (1,3) regardless of trenching treatmentThis trend is less obvious for chambers 5,7 (dry) versus 6,8 (wet).T = trenched U = untrenchedD = dry W = wetted

****These slides show fluxes plotted for the three moisture temperature regimes In dry season fluxes do not correlate (or are anticorrelated with) temperature; in wet seasons there is a linear relation with temperature; sept rain stands out as a time when temperature control comes into play. ****First rain event (blue line). Day 609 marks the increase in the fuel rod water content, but the increase in soil respiration lags behind. The red line marks a litter wet-up experiment. If anything more water was added than fell in the blue event, so the difference in response is either (1) the prior buildup of decomposable material or (2) the addition of autrotrophic respiration in the first event. Note that the green (untrenched plots) increase more than the brown (trenched plots), though only temporarily.*****Isotope data . 1) No difference between trenched and untrenched plots shows small contribution from autotrophic respiration.2) Root respiration isotope signature drops from spring to summer (NB there are more root respiration data collected). Lower 14C in July likely linked to increased importance of sources deeper than 40 cm (the trenching depth). *********