Carbon cycling in temperate grassland under elevated temperature

Abstract

An increase in mean soil surface temperature has been observed over the last century, and it is predicted to further increase in the future. The effect of increased temperature on ecosystem carbon fluxes in a permanent temperate grassland was studied in a long‐term (6 years) field experiment, using multiple temperature increments induced by IR lamps. Ecosystem respiration (R‐eco) and net ecosystem exchange (NEE) were measured and modeled by a modified Lloyd and Taylor model including a soil moisture component for R‐eco (average R 2 of 0.78) and inclusion of a photosynthetic component based on temperature and radiation for NEE (R 2 = 0.65). Modeled NEE values ranged between 2.3 and 5.3 kg CO 2 m−2 year−1, depending on treatment. An increase of 2 or 3°C led to increased carbon losses, lowering the carbon storage potential by around 4 tonnes of C ha−1 year−1. The majority of significant NEE differences were found during night‐time compared to daytime. This suggests that during daytime the increased respiration could be offset by an increase in photosynthetic uptake. This was also supported by differences in δ 13C and δ 18O, indicating prolonged increased photosynthetic activity associated with the higher temperature treatments. However, this increase in photosynthesis was insufficient to counteract the 24 h increase in respiration, explaining the higher CO 2 emissions due to elevated temperature.

Long-Term Warming Shifts the Composition of Bacterial Communities in the Phyllosphere of Galium album in a Permanent Grassland Field-Experiment

“…( Delmotte et al, 2009 ). Jansen-Willems et al (2016) showed, that the plant biomass increased in T plots, which indicated changes of the plant physiology and morphology. A first insight into metabolome profiles of G. album leaves of C and T plots indicated significant differences among leave metabolomes (unpublished data).…”

“…Global warming is an ongoing climate change effect and will lead to an increase of the mean global air temperature by 2–3°C until 2050 as predicted by the Intergovernmental Panel on Climate Change ( IPCC, 2013 ). Elevated surface temperature can affect plants and their symbiotic microbiota (the plant holobiont; Margulis, 1993 ; Vandenkoornhuyse et al, 2015 ) by influencing plant growth, health, and yield ( Wu et al, 2011 ; Jansen-Willems et al, 2016 ). An important plant-associated habitat colonized by specific bacterial communities is the phyllosphere, the aerial part of plants dominated by leaves ( Vorholt, 2012 ; Bringel and Couée, 2015 ).…”

“…In a 6.5-year experiment examining the effects of increasing the leaf surface temperature (by +2°C), an increase in the aboveground biomass was observed ( Jansen-Willems et al, 2016 ). This experiment was used to get a first insight on the effect of a moderate, (+2°C) long-term warming on the composition of the phyllosphere inhabiting microbial community of the most abundant forb, Galium album Mill., within the permanent grassland.…”

Long-term elevation of temperature affects organic N turnover and associated N<sub>2</sub>O emissions in a permanent grassland soil

“…A possible explanation for the in situ reduction of denitrification could be the altered field soil moisture content. While during the incubation, soil moisture was purposely kept constant (WFPS of 64 %); in the field, however, moisture conditions were affected by the heating treatment, leading to generally drier, and thus more aerated, conditions in the heated plots (Jansen-Willems et al, 2016). Under low WFPS, nitrification is predominantly responsible for N 2 O efflux (Bollmann and Conrad, 1998;Bateman and Baggs, 2005).…”

“…The temperature treatments (including any moisture effect) are referred to as T control , T 1 , T 2 and T 3 , respectively. The infrared heaters were installed at different heights to create the different temperature elevations (Jansen-Willems et al, 2016).…”