The fate of photosynthetically‐fixed carbon in Lolium perenne grassland as modified by elevated CO₂ and sward management

Abstract

Summary Prediction of the impact of climate change requires the response of carbon (C) flow in plant–soil systems to increased CO2 to be understood. A mechanism by which grassland C sequestration might be altered was investigated by pulse‐labelling Lolium perenne swards, which had been subject to CO2 enrichment and two levels of nitrogen (N) fertilization for 10 yr, with 14CO2. Over a 6‐d period 40–80% of the 14C pulse was exported from mature leaves, 1–2% remained in roots, 2–7% was lost as below‐ground respiration, 0.1% was recovered in soil solution, and 0.2–1.5% in soil. Swards under elevated CO2 with the lower N supply fixed more 14C than swards grown in ambient CO2, exported more fixed 14C below ground and respired less than their high‐N counterparts. Sward cutting reduced root 14C, but plants in elevated CO2 still retained 80% more 14C below ground than those in ambient CO2. The potential for below‐ground C sequestration in grasslands is enhanced under elevated CO2, but any increase is likely to be small and dependent upon grassland management.

Fate and dynamics of recently fixed C in pasture plant–soil system under field conditions

“…Similar results were found by Domanski et al (2001), Johnson et al (2002) and Rangel-Castro et al (2004), who found that the maximum incorporation of the assimilated C to roots occurred between 24-48 h. According to Leake et al (2006), the allocation of the fixed carbon from shoots to roots continues for about one week, which indicates that exudation of the "new C" can occur during this time. At the end of the experiment, 1.3% of the fixed C still remained in the roots, which is in accordance with results of Hill et al (2007) from a similar 6-day experiment. This indicates that roots provided a rapid transport of new assimilates to soil and only slowly but gradually incorporated a proportion of them to the root biomass.…”

“…C MIC was the pool with the highest 13 C enrichment during the whole experiment, as also found by Pelz et al (2005), Yevdokimov et al (2006, and Leake et al (2006). It contained almost 4% of the fixed C at the beginning of the experiment and 0.6% of the fixed C at the end (comparable to Rattray et al 1995;Domanski et al 2001;Kuzyakov et al 1999Kuzyakov et al , 2001Lu et al 2004;Hill et al 2007), which represented 40-70% of soil 13 C (Butler et al 2004). The highest enrichment of C MIC within soil C pools and the slower loss of 13 C from C MIC than from other labile C pools (see Fig.…”

“…1a). A total of 67% of the fixed 13 C was exported from the shoots during the 6 days of the experiment, which is close to the 76% found by Hill et al (2007) and within the wide range ca 30-90% of total fixation estimated for grasses (Baxter and Farrar 1999;Dilkes et al 2004). The main proportion of assimilate transport from shoots (>50% of fixation) occurred during the first day, which is in accordance with Butler et al (2004) and Leake et al (2006), who found losses of 31-70% of fixation from shoots within 24 h. It is known that the newly fixed C is preferentially respired by plants, as CO 2 evolved is much more enriched in 13 C in comparison to plant tissue (Staddon et al 2003), but we had no possibility to measure shoot respiration and its δ 13 C signature.…”

Photoassimilate allocation and dynamics of hotspots in roots visualized by 14C phosphor imaging

“…Surprisingly, this ratio did not strongly decrease within 2 or 11 d after labeling. Other authors have also reported this interesting phenomenon (Hill et al, 2007). Similar results were frequently obtained for 13 Cpulse-labeling experiments based on higher 13 C enrichment in shoots versus roots (Kastovska and Santruckova, 2007).…”

Transformations in DOC along a source to sea continuum; impacts of photo-degradation, biological processes and mixing

“…To provide more detailed information on the breakdown and conversion of DOC into other forms of C, such as mineralisation to CO2 and uptake by the biofilm, we added C tracer became incorporated into the plant biomass during photosynthesis, as described by Hill et al (2007). The plant was then ground to a fine powder, incorporated into a sample of peat soil, and left to decompose for 6 months.…”