Stem CO₂ efflux of a Populus nigra stand: effects of elevated CO₂, fertilization, and shoot size

Abstract

To determine whether long-term growth in elevated atmospheric CO 2 concentration [CO 2 ] and nitrogen fertilization affects woody tissue CO 2 efflux, we measured stem CO 2 efflux as a function of temperature in three different size classes of shoots of Populus nigra L. (clone Jean Pourtet) on two occasions in 2004. Trees were growing in a short rotation coppice in ambient (370 µmol mol -1 ) and elevated (550 µmol mol -1 , realised by a Free Air Carbon dioxide Enrichment system) [CO 2 ], and measurements were performed during the third growing season of the second rotation. Elevated CO 2 did not affect Q 10 or specific stem CO 2 efflux (E 10 ) of overall poplar shoots. The lack of any effect of N on stem CO 2 efflux indicated that nutrients were sufficient. Specific stem CO 2 efflux differed significantly between shoot sizes, emphasizing the importance of tree size when scaling-up respiration measurements to the stand level. Variation in stem CO 2 efflux could not be satisfactorily explained by temperature as the only driving variable. We hypothesize that transport of CO 2 with the sapflow might have confounded our results and could explain the high Q 10 values reported here. Predicting the respiratory carbon loss in a future elevated [CO 2 ] world must therefore move beyond the single-factor temperature dependent respiration model and involve multiple factors affecting stem CO 2 efflux rate.

Elevated CO2 does not affect stem CO2 efflux nor stem respiration in a dry Eucalyptus woodland, but it shifts the vertical gradient in xylem [CO2]

“…Contribution of each of these components to R S during each measurement campaign is shown in Table 3 balance approach. Elevated CO 2 did not affect E A nor R S in mature Eucalyptus trees, as similarly observed in poplar and spruce trees when stem growth did not respond to eCO 2 (Gielen et al, 2003;Liberloo et al, 2008;Mildner et al, 2015). At EucFACE, stem growth is nutrient-limited and phosphorous (P) fertilization stimulated stem growth by 54% (Crous et al, 2015).…”

“…In the case of pine trees, higher maintenance respiratory costs were ascribed to greater nitrogen (N) content in stem living cells (Carey et al, ), whereas in spruce trees, eCO 2 did not result in differential N content (Ceschia et al, ). No effect of eCO 2 on E A was also observed in several Populus species (Gielen, Scarascia‐Mugnozza, & Ceulemans, ; Liberloo, De Angelis, & Ceulemans, ) and mature Picea abies trees (Mildner, Bader, Baumann, & Körner, ) due to the neutral response of stem growth to eCO 2 , whereas eCO 2 did not affect E A in pine trees despite stimulated stem growth (Hamilton et al, ). Contrarily, eCO 2 inhibited E A in spruce (Dvorak, Oplustilova, Mohren, Kramer, & Sabate, ; Janous, Pokorny, Brossaud, & Marek, ) and beech (Ceschia et al, ) trees.…”

“…Because a portion of locally respired CO 2 dissolves in the sap solution and is transported upward with the transpiration stream, E A can deviate from R S , thus confounding comparisons between trees grown under ambient and eCO 2 . For instance, the effect of root water uptake under high atmospheric [CO 2 ] in experimentally enriched plots could enhance E A due to a greater amount of exogenous CO 2 in the xylem leading to equivocal conclusions about the response of R S to eCO 2 (Liberloo et al, ; Moore et al, ). Evidence of the uncertain origin of CO 2 in E A was observed in Pinus taeda in a FACE experiment wherein the isotopic composition of E A was partially explained by that of soil CO 2 (Moore et al, ).…”

Effects of sap velocity on the daytime increase of stem CO2 efflux from stems of Schima superba trees

“…Many studies have reported the daytime depression in stem CO 2 efflux compared to the predicated based on temperature-dependent model (Negisi 1979;Gansert and Burgdorf 2005). Although an important explanation found in literature on inconsistency between stem CO 2 efflux and stem temperature was due to the influence of sap flux, namely, a large amount of CO 2 produced by stem live tissues remained within stems and was moved upward in the transpiration stream (Teskey and McGuire 2002;McGuire 2005, 2007;Liberloo et al 2008;Gansert and Burgdorf 2005), the relationship between stem CO 2 efflux and sap flux was still uncertain. Most studies found that stem CO 2 efflux decreased with the increase of sap velocity ; Gansert and Burgdorf 2005;McGuire and Teskey 2004;Bowman et al 2005), while some other studies indicated that CO 2 transported by transpiration stream from the soil or lower location of the stem contributed to stem CO 2 efflux and stem CO 2 efflux increased with the rise of sap velocity (Levy et al 1999;Moore et al 2008;Teskey and McGuire 2007).…”

Diurnal and Seasonal Change in Stem Respiration of Larix principis-rupprechtii Trees, Northern China

“…Numerous studies on temperature sensitivity of stem respiration have been conducted across different forest types of the world and reported different Q 10 values of stem respiration for different forests, varying from 1.00 to 6.40 [26] , [29] – [32] . It should be noted, however, that most of these previous studies estimated Q 10 values based on the measurement of daytime stem respiration [33] , and few studies measured diurnal change in stem respiration as well as its linkage with climate [34] . Since stem respiration is also influenced by other environmental and physiological processes [16] , [23] , [35] – [39] , such as photosynthesis that occurs only during the daytime, it is possible that stem respiration responds to temperature changes in daytime and nighttime differently.…”