| Popis: |
In order to examine the below ground response of a mature upland hardwood forest in the southeastern U.S., to increases and decreases in water inputs, the gross production, mortality, and net production of fine roots were examined over the first and third years of a long-term water manipulation experiment (Throughfall Displacement Experiment). Treatments involved a 33% decrease (DRY), 33% increase (WET), and ambient (AMB) levels of throughfall to the forest floor, begun in July, 1993. Video images of roots appearing on minirhizotron faces installed on both upper and lower slopes were recorded biweekly to a depth of 90 cm from April through October of 1994 and of 1996. Comparisons were made between treatments in amounts of new root elongation, root mortality, and calculated net root production. Minirhizotron observations during 1994 growing season, immediately following winter 1994 installation, revealed a strong effect of installation disturbance and were therefore not considered valid reflections of the response of the stand to the treatments. The 1996 data, on the other hand, exhibited absence of installation biases inherent in 1994 data because of a longer period since treatment initiation (2 2/3 yr vs. 8 mths), and favorable root growth conditions in all treatments during a greater portion of the year. The 1996 data were, therefore, considered realistic measures of below ground treatment responses. During 1996, net root production at 0-30 cm depth, at the upper slope positions, was significantly greater in DRY than in WET and AMB. Net root production was also greater at the lower slope position, but not significantly so. Treatment differences were the result of gross root production, as patterns of mortality did not differ across treatments. Nor were there significant treatment differences at depths below 30 cm. Whether trees in DRY produced more roots to replace root biomass lost during a previous drought year, or whether a new root:shoot ratio was beginning to develop in response to treatments, will require observations from the response of the stand in future years to be determined. |
Full text from SpringerLink