Patterns of wood carbon dioxide efflux across a 2,000-m elevation transect in an Andean moist forest

During a 1-year measurement period, we recorded the CO2 efflux from stems (RS) and coarse woody roots (RR) of 13–20 common tree species at three study sites at 1,050, 1,890 and 3,050 m a.s.l. in an Andean moist forest. The objective of this work was to study elevation changes of woody tissue CO2 efflux and the relationship to climate variation, site characteristics and growth. Furthermore, we aim to provide insights into important respiration–productivity relationships of a little studied tropical vegetation type. We expected RS and RR to vary with dry and humid season conditions. We further expected RS to vary more than RR due to a more stable soil than air temperature regime. Seasonal variation in woody tissue CO2 efflux was indeed mainly attributable to stems. At the same time, temperature played only a small role in triggering variations in RS. At stand level, the ratio of C release (g C m−2 ground area year−1) between stems and roots varied from 4:1 at 1,050 m to 1:1 at 3,050 m, indicating the increasing prevalence of root activity at high elevations. The fraction of growth respiration from total respiration varied between 10 (3,050 m) and 14% (1,050 m) for stems and between 5 (1,050 m) and 30% (3,050 m) for roots. Our results show that respiratory activity and hence productivity is not driven by low temperatures towards higher elevations in this tropical montane forest. We suggest that future studies should examine the limitation of carbohydrate supply from leaves as a driver for the changes in respiratory activity with elevation

Furin-dependent Intracellular Activation Of The Human Stromelysin-3 Zymogen

HUMAN stromelysin-3, a new member of the matrix metalloproteinase family, is expressed in tissues undergoing the active remodelling associated with embryonic development, wound healing and tumour invasion(1-3). But like all other members of the matrix metalloproteinase gene family, stromelysin3 is synthesized as an inactive precursor that must be processed to its mature form in order to express enzymic activity(4,5). Here we identify stromelysin-3 as the first matrix metalloproteinase to be discovered that can be processed directly to its enzymically active form by an obligate intracellular proteolytic event that occurs within the constitutive secretory pathway. Intracellular activation is regulated by an unusual 10-amino-acid insert sandwiched between the pro- and catalytic-domains of stromelysin-3, which is encrypted with an Arg-X-Arg-X-Lys-Arg recognition motif for the Golgi-associated proteinase, furin, a mammalian homologue of the yeast Kex2 pheromone convertase(6,7). A furin-stromelysin-3 processing axis not only differentiates the regulation of this enzyme from all previously characterized matrix metalloproteinases, but also identifies pro-protein convertases as potential targets for therapeutic intervention in matrix-destructive disease states.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62522/1/375244a0.pd