Showing papers in "Photosynthetica in 1982"

Autumnal photosynthesis in short-rotation intensively cultured Populus clones

Abstract: Many ex otic hybrid Populus clones grown under short-rotation intensive culture (SRIC) in the Lake States region of the U.S.A. retain green leaves in the autumn for 2-6 weeks after native aspen (P. tremuloides and P. grandidentata) have lost their leaves. Leaves on the terminal shoots of five such clones tested in southern Michigan and northern Wisconsin had substantial leaf conductances to C02 and photosynthetic rates (P G) during this late-season period of leaf reten­ tion. PG was high enough to suggest that autumn retention of green leaves may be an important factor contributirg to the rapid growth of poplars under SRIC in this cold northern temperate area. Leaf conductances and P G declined gradually before the first hard frosts of the autumn in the northern Wisconsin experiment, indicating normal autumn leaf aging and senescence, but did not change appreciably in the southern Michigan experiment until the first hard frosts. The first hard frosts reduced P G and leaf conductance in most of the clones, dramatically in the northern Wisconsin experiment. Leaf conductances and P G in two of the clones in the southern Michigan experiment were reduced only moderately by the first hard frosts. Leaf conductance and PG exhibited generally parallel seasonal trends in both experiments. When exotic Populus hybrids are grown under short-rotation intensive culture (SRIC) in the Lake States region of the U.S.A., many clones retain green leaves in the autumn for 2-6 weeks after native aspen (P. tremuloides and P. grandidentata) have lost their leaves. We have suspected that this late season leaf retention may be one factor contributing to the rapid growth of exotic poplars under SRIC. A central question is whether the leaves retained during the autumn period exhibit significant photosynthesis. This study is an investigation of photosynthetic rates in the autumn in several poplar clones grown under SRIC in southern Michigan and northern Wiscon­ sin, U.S.A. In addition to quantifyir:g photosynthetic rates, we also report information on internal a nd environmental control of photosynthesis during the late-season period.