Pe. Levy et Pg. Jarvis, STEM CO2 FLUXES IN 2 SAHELIAN SHRUB SPECIES (GUIERA-SENEGALENSIS AND COMBRETUM-MICRANTHUM), Functional ecology, 12(1), 1998, pp. 107-116
1. Measurements are presented of CO2 flux from woody stems of two shru
b species in the Sahelian zone of West Africa (Guiera senegalensis and
Combretum micranthum). Measurements were made on excised stems and in
situ. 2. An experiment suggested. that the respiration rate was close
ly related to the stem surface area but showed little relationship wit
h stem volume, and was therefore associated with the cambium and phloe
m rather than the sapwood. This contrasts with several studies in whic
h sapwood volume appeared to be the dominant component and the differe
nce is attributed to the comparatively small diameter of stems in the
shrubs studied here. 3. Measurements were made of the response of stem
CO2 flux to photosynthetic photon flux density (Q) and gave evidence
of corticular photosynthesis in the stems. 4. The response of stem res
piration to temperature was determined in situ. The data were analysed
using a variant on the standard exponential relationship with tempera
ture, R = (R-om + R-og) exp(k T), where R is respiration rate, R-om is
maintenance respiration rate at 0 degrees C, R-og is growth respirati
on rate at 0 degrees C, k is a temperature coefficient and Tis tempera
ture. Data from the dry season were assumed to represent maintenance r
espiration and used to define R-om and k. The R-og term thus quantifie
s the increase in respiration during the wet season beyond this baseli
ne level, presumably attributable to growth. Values of R were 0.054 an
d 0.074 mu mol m(-2) s(-1) in G. senegalensis and C. micranthum, respe
ctively, whilst R-og ranged between 0.061 and 0.96 mu mol m(-2) s(-1)
during the wet season. 5. At ecosystem scale On an annual basis, stem
respiration represented 17% of leaf photosynthesis, whilst corticular
photosynthesis was at most 11.1% of stem respiration.