Publication Date:
2011-04-29
Description:
The terrestrial carbon cycle is influenced by environmental variability at scales ranging from diurnal to inter-annual. Here we present five-years of growing season (day 131-275) observations of the carbon isotope ratio of ecosystem respiration (δ 13 C R ) from a semi-arid woodland. This ecosystem has a large necromass component resulting from 97% Pinus edulis mortality in 2002, is dominated by drought-tolerant Juniperus monosperma trees, and experiences large variability in the timing and intensity of seasonal and synoptic water availability. Mean growing season δ 13 C R was remarkably invariant (-23.57±0.4‰), with the exception of particularly enriched δ 13 C R in 2006 following a winter with anomalously low snowfall. δ 13 C R was strongly coupled to climate during pre-monsoon periods (∼May-June), including fast (≤two days) responses to changes in crown-level stomatal conductance ( G c ) and vapor pressure deficit ( vpd ) following rain pulses. In contrast, δ 13 C R was relatively de-coupled from G c and environmental drivers during monsoon and post-monsoon periods (July-August and September, respectively), exhibiting only infrequent couplings of δ 13 C R to vpd and soil water content ( SWC ) with longer lags (∼eight days) and variable response slopes (both positive and negative). Notably, δ 13 C R exhibited consistent dynamics after rainfall events, with depleted δ 13 C R occurring within one hour, progressive hourly δ 13 C R enrichment over the remainder of the night, and net δ 13 C R depletions over the multiple nights post-event in monsoon and post-monsoon periods. Overall this ecosystem demonstrated strong dependence of δ 13 C R on precipitation, with an apparent dominance by the autotrophic δ 13 C signal in pre-monsoon periods when deep soil moisture is abundant and surface soil moisture is low, and weaker coupling during monsoonal periods consistent with increasing heterotrophic dominance when deep soil moisture has declined and surface moisture is variable.
Print ISSN:
1354-1013
Electronic ISSN:
1365-2486
Topics:
Biology
,
Energy, Environment Protection, Nuclear Power Engineering
,
Geography
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