title: Spacial distribution of photosynthetic capacity and performance in a mountain spruce forest of Northern Germany : III. The significance of the evergreen habit.
abstract: Growth and CO2uptake in the crown of a spruce tree is described and the production processes of this evergreen conifer are compared with those of a deciduous beech. Spruce had 60% lower rates of net photosynthesis per dry weight than beech. But, beech had a 30% shorter growing season and a 84% smaller biomass than spruce. The annual CO2gain was 40% lower in beech than it was in spruce.An analysis shows the following conclusions for this habitat. (1) The effect of a prolonged growing season is small. The annual CO2gain of spruce would be reduced only by 9% if the growing season was the same length as for beech. (2) The annual CO2gain would increase 14% if all needles in spruce were deciduous, because the current year needles have a higher average rate of CO2uptake than 3-year old and older needles, but a lower average rate than 1- and 2-year old ones. However, the carbon balance of the tree shows that spruce could not afford to produce the existing needle biomass (14 t ha-1) each year. (3) If spruce were to produce the same deciduous foliage biomass during the same growing season as beech then total production by spruce would be reduced 67%. (4) The annual CO2uptake by evergreen spruce was higher than deciduous beech not because of a long growing season, but because of the longevity of its needles, which during their total life time (an average of 5 years) have a two to three times greater CO2uptake than a deciduous leaf in one summer season. The relatively small investment in current year needles produces an annually low, but long lasting assimilation of CO2.
authors.affiliation: Lehrstuhl für Pflanzenökologie der Universität Bayreuth, Am Birkengut, D-8580, Bayreuth, Germany.
authors.forename: E -D
authors.initials: E-
authors.lastname: Schulze
authors.affiliation: Lehrstuhl für Pflanzenökologie der Universität Bayreuth, Am Birkengut, D-8580, Bayreuth, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Fuchs
authors.affiliation: Lehrstuhl für Pflanzenökologie der Universität Bayreuth, Am Birkengut, D-8580, Bayreuth, Germany.
authors.forename: M I
authors.initials: MI
authors.lastname: Fuchs