Does photosynthesis affect grassland soil‐respired CO₂ and its carbon isotope composition on a diurnal timescale?

Abstract

Summary• Soil respiration is the largest flux of carbon (C) from terrestrial ecosystems to the atmosphere. Here, we tested the hypothesis that photosynthesis affects the diurnal pattern of grassland soil-respired CO 2 and its C isotope composition (δ 13 C SR ).• A combined shading and pulse-labelling experiment was carried out in a mountain grassland. δ 13 C SR was monitored at a high time resolution with a tunable diode laser absorption spectrometer.• In unlabelled plots a diurnal pattern of δ 13 C SR was observed, which was not explained by soil temperature, moisture or flux rates and contained a component that was also independent of assimilate supply. In labelled plots δ 13 C SR reflected a rapid transfer and respiratory use of freshly plant-assimilated C and a diurnal shift in the predominant respiratory C source from recent (i.e. at least 1 d old) to fresh (i.e. photoassimilates produced on the same day).• We conclude that in grasslands the plant-derived substrates used for soil respiratory processes vary during the day, and that photosynthesis provides an important and immediate C source. These findings indicate a tight coupling in the plant-soil system and the importance of plant metabolism for soil CO 2 fluxes.

Ecosystem photosynthesis regulates soil respiration on a diurnal scale with a short-term time lag in a coastal wetland

“…Firstly, there might be a fast transport of recent photosynthesis and substrate supply from the canopy to the soil (Högberg et al, 2008;Bahn et al, 2009;Vargas et al, 2011a). High transport rates of assimilates from leaves into roots and their subsequent loss in the processes of root respiration have been demonstrated by previous laboratory experiments (e.g.…”

“…The time lags of 0e4 h in our results are consistent with previous findings. For example, a free air CO 2 enrichment experiment (FACE) in a mixed deciduous forest showed that the diurnal cycle of soil respiration was correlated with PAR with a 1 h lag (Liu et al, 2006), and a pulselabelling experiment also showed that under sunny conditions photoassimilates in a mountain grassland were transported and respired belowground within less than 2 h (Bahn et al, 2009). More recently, soil respiration showed significant responses to plant photosynthetic activity with a time lag of about 0e3 h in a steppe ecosystem (Yan et al, 2011).…”

“…It is well documented that soil respiration may lag canopy photosynthesis by times that vary from hours to weeks in different ecosystems including forests Tang et al, 2005;Baldocchi et al, 2006;Moyano et al, 2008;Wingate et al, 2010), grasslands (Bahn et al, 2008(Bahn et al, , 2009Yan et al, 2011;Vargas et al, 2011a) and croplands Cheng, 2001, 2004;Han et al, 2007). The highly variable time lags between photosynthesis and soil respiration might be controlled by the species, transport distance (plant height and phloem path-length), root depth, plant physiology and growth stage, and environmental conditions (Davidson and Holbrook, 2009;Kuzyakov and Gavrichkova, 2010;Mencuccini and Hölttä, 2010;Wingate et al, 2010).…”

“…However, doubts remain as to the extent to which primary productivity controls soil respiratory and the speed of the link between soil respiration and photosynthesis (Gaumont-Guay et al, 2008;Kayler et al, 2010). For instance, the immediate link of soil respiration to photosynthesis is still uncertain on the diurnal scale (Bahn et al, 2009). Therefore, current major challenges remain ahead of us for developing process-based models of soil respiration at short and medium temporal scales, including the lags and transport of carbon from photosynthesis to soil respiration (Vargas et al, 2011b).…”

Frontiers and challenges in soil respiration research: from measurements to model-data integration

“…Högberg et al (2008) traced the fate of new C through various tree components, and into microbial pools. Most recently, Bahn et al (2009) reported an innovative study in which 13 C of soil respiration was measured by tunable diode laser absorption spectrometry (TDLAS). This combination of high-temporal resolution 13 C measurements of soil respiration (i.e.…”