Tracing recent carbon from photosynthesis to stem and soil respiration in an experimental tropical rainforest in response to drought
Abstract
Tropical rainforests play a major role for the terrestrial carbon (C) cycle. However, to date little is known about the mechanisms and processes controlling carbon fluxes in tropical forests. Within the carbon cycle of a forest carbon, trees allocate a substantial amount of assimilated C belowground, where it is respired by stems, roots and microorganisms. This link of assimilation and respiration represents a significant pathway by which assimilated C is quickly returned to the atmosphere. However, the nature of this coupling, including the speed of above- to below-ground C allocation and the proportion of rapidly metabolized assimilates is yet unknown for mature tropical rainforest systems. Furthermore, the role of different tree species and the relative roles of tall trees versus understory plants are still unresolved. Drought spells can exert a major control on the C balance of such ecosystems by altering the partitioning of C and the dynamics of C allocation and belowground utilization. As such responses are difficult to measure in large-stature forest systems, the consequences of drought for the dynamics of stem and soil respiration and the role of recent C in such ecosystems remain unclear.
To address these questions, we make use of the tropical rainforest at the Biosphere-2 research complex in Arizona, US. This infrastructure provides unique opportunities to study drought effects on the C dynamics in a well-known experimental rainforest ecosystem with a completely controlled environment. We simulate a drought spell for several weeks and continuously measure stem and soil CO2 fluxes using isotope laser spectroscopy. We perform two ecosystem-scale 13CO2 pulse labeling campaigns, in which we label the canopy of the whole forest greenhouse, first under ambient environmental conditions and a second time during the experimental drought. This allows us to improve our understanding of the allocation dynamics of recently assimilated C to stem and soil respiration under moist conditions and under severe drought. Our study is part of a large-scale experiment that aims to disentangle C- and water-cycle processes underpinning ecosystem responses to drought from a molecular to an ecosystem-scale level, with particular focus on plant-soil and plant-atmosphere interfaces.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B11O2182L
- Keywords:
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- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0452 Instruments and techniques;
- BIOGEOSCIENCES;
- 0454 Isotopic composition and chemistry;
- BIOGEOSCIENCES;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE