Summary The 13C isotopic signature (δ13C) of CO2 respired from plants is widely used to assess carbon fluxes and ecosystem functioning. There is, however, a lack of knowledge of the metabolic basis of the δ13C value of respired CO2. To elucidate the physiological mechanisms driving 12C/13C fractionation during respiration, the δ13C of respired CO2 from dark‐acclimated leaves during the night, from darkened leaves during the light period, and from stems and roots of Ricinus communis was analysed. The δ13C of potential respiratory substrates, the respiratory quotient and the activities of phosphoenolpyruvatecarboxylase (PEPc) and key respiratory enzymes were also measured. It is shown here that the CO2 evolved from darkened light‐acclimated leaves during the light period is 13C‐enriched, and that this correlates with malate accumulation in the light and rapid malate decarboxylation just after the onset of darkness. Whilst CO2 evolved from leaves was generally 13C‐enriched (but to a lesser extent during the night), CO2 evolved from stems and roots was depleted compared with the putative respiratory substrates; the difference was mainly caused by intensive PEPc‐catalysed CO2 refixation in stems and roots. These results provide a physiological explanation for short‐term variations of δ13C in CO2, illustrating the effects of variations of metabolic fluxes through different biochemical pathways.

Climatic hazards, such as severe droughts and floods, affect extensive areas across monsoon Asia and can have profound impacts on the populations of that region. The area surrounding Indonesia, including large portions of the eastern Indian Ocean and Java Sea, plays a key role in the global climate system because of the enormous heat and moisture exchange that occurs between the ocean and atmosphere there. Here, we evaluate the influence of rainfall variability on multiple treering parameters of teak (Tectona grandis) trees growing in a lowland rain forest in Central Java (Indonesia). We assess the potential of, annually resolved, tree-ring width, stable carbon ( 13 C) and oxygen ( 18 O) isotope records to improve our understanding of the Asian monsoon variability.Climate response analysis with regional, monthly rainfall data reveals that all three tree-ring parameters are significantly correlated to rainfall, albeit during different monsoon seasons. Precipitation in the beginning of the rainy season (Sep-Nov) is important for tree-ring width, confirming previous studies. Compared to ring width, the stable isotope records possess a higher degree of common signal, especially during portions of the peak rainy season (

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Measuring canopy height using satellite-based X-band interferometric SAR (InSAR) is promising for accurate monitoring of forest biomass. A prerequisite for applying this at large scale is that the penetration of the radar microwaves into the forest canopy is stable over time, i.e. not influenced by weather conditions. We investigated this in a tropical rainforest in Indonesia using 10 TanDEM-X InSAR data sets acquired during a 2-year period. We found that mean InSAR-derived canopy height varied with a standard deviation of about 0.5 m between acquisitions. The standard variation was 0.8 m; however, about 0.3 m could be attributed to errors stemming from technical properties of the acquisitions. In conclusion, this further supports the use of X-band InSAR from satellite missions for forest monitoring.