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| Titel |
Effects of heat and drought on carbon and water dynamics in a regenerating semi-arid pine forest: a combined experimental and modeling approach |
| VerfasserIn |
N. K. Ruehr, B. E. Law, D. Quandt, M. Williams |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 15 ; Nr. 11, no. 15 (2014-08-06), S.4139-4156 |
| Datensatznummer |
250117539
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| Publikation (Nr.) |
 copernicus.org/bg-11-4139-2014.pdf |
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| Zusammenfassung |
Predicting the net effects on the carbon and water balance of semi-arid
forests under future conditions depends on ecosystem processes responding to
changes in soil and atmospheric drought. Here we apply a combination of field
observations and soil–plant–atmosphere modeling (SPA) to study carbon and
water dynamics in a regenerating ponderosa pine forest. The effects of soil
and atmospheric drought were quantified based on a field irrigation
experiment combined with model simulations. To assess future effects of
intensifying drought on ecosystem processes, the SPA model was run using
temperature and precipitation scenarios for 2040 and 2080.
Experimentally increased summer water availability clearly affected tree
hydraulics and enhanced C uptake in both the observations and the model.
Simulation results showed that irrigation was sufficient to eliminate soil
water limitation and maintaining transpiration rates, but gross primary
productivity (GPP) continued to decrease. Observations of stomatal
conductance indicated a dominant role of vapor pressure deficit (VPD) in
limiting C uptake. This was confirmed by running the simulation under reduced
atmospheric drought (VPD of 1 kPa), which largely maintained GPP rates at
pre-drought conditions.
The importance of VPD as a dominant driver was underlined by simulations of
extreme summer conditions. We found GPP to be affected more by summer
temperatures and VPD as predicted for 2080 (−17%) than by reductions in
summer precipitation (−9%). Because heterotrophic respiration responded
less to heat (−1%) than to reductions in precipitation (−10%),
net ecosystem C uptake declined strongest under hotter (−38%) compared
to drier summer conditions (−8%).
Considering warming trends across all seasons (September–May: +3 °C
and June–August: +4.5 °C), the negative drought effects were
largely compensated by an earlier initiation of favorable growing conditions
and bud break, enhancing early season GPP and needle biomass. An adverse
effect, triggered by changes in early season allocation patterns, was the
decline of wood and root biomass. This imbalance may increase water stress
over the long term to a threshold at which ponderosa pine may not survive,
and highlights the need for an integrated process understanding of the
combined effects of trends and extremes. |
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