Using 139 flux studies, we addressed the variability of net ecosystem surfa
ce assimilation (A(smax)), net ecosystem surface respiration (R-smax), as w
ell as net surface evapotranspiration (E-smax) among and within vegetation
types. While forests and C-3 crops, particularly in the northern hemisphere
, have been preferentially investigated, information on tropical forests, C
-4 grasslands or wetlands is rather limited. Almost no data are available f
or disturbed sites. Despite large variations within a vegetation type, encl
osure studies tended to give highest A(smax) rates compared to micrometeoro
logical techniques. Excluding enclosure studies, we tested the effect of st
and age and leaf area index (LAI) on net ecosystem gas exchange. For grassl
ands, A(smax) increased by 7 mu mol m(-2) s(-1) per unit LAI, for C-4 crops
by 11 mu mol m(-2) s(-1) and for coniferous forests by 0.9 mu mol m(-2) s(
-1) per unit LAI. In contrast, A(smax) of broad-leaved forests and C-3 crop
s as well as R-smax stayed m(-2) s(-1) constant over a wide range of LAI. A
(smax) and R-smax of forests were lowest in young stands (< 20 years old) a
nd highest in stands of age 38-80 years. A(smax) of old forests (> 160 year
s) was within the same range as those of 30- to 80-year-old forests, and al
ways higher than those of regenerating stands. R-smax seemed to decrease wi
th age. A(smax) increased linearly with ecosystem surface conductance for a
ll vegetation types (r(2) = 0.65). A(smax) of forests and grasslands was cl
osely related to E-smax (r(2) = 0.87), with a slope of 0.082 mu mol CO2 m(-
2) s(-1)/mmol H2O m(-2) s(-1). The results clearly illustrated where gaps i
n our knowledge exist and how ecosystem properties affect the capacity of n
et ecosystem gas exchange.