Effects of soil moisture-tension on rubidium uptake by sunflowers Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/mw22v8392

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  • There is considerable evidence that the growth and elongation of plant roots increases linearly or almost linearly with increasing water contents or decreasing moisture-tension of soil. If this is true it is difficult to distinguish the effects of different water contents on absorption phenomena such as water or ion uptake from the effects of the water contents on the root growth itself. Any absorption process which directly correlates with the amount of root growth is subject to misinterpretation as to the ultimate effect of changing water contents on the particular process. One useful alternative is to measure the root growth precisely and account for, through covariance, the differences in root growth as a result of differences in water contents or moisture-tensions in the soil. Samples of soil at various water contents and containing rubidium ions, were placed around the stems of six-week old sunflower plants and adventitious roots allowed to grow into the soil samples. The period of adventitious root growth was six days. Root growth water lost from the soil samples and the rubidium taken up into the above-ground parts of the plants were measured. All experiments were conducted in a controlled-environment growth room. Root growth was found to be closely related to the initial water contents of the soil samples. The relationship was slightly curvilinear. Water taken up by the adventitious roots was found to be dependent upon the amount of root growth and therefore closely related to the initial water contents. In all cases where the adventitious root systems were exposed to soil that was drier than that containing the main root systems of the plants the amounts of water which moved into the plants appeared to be small, much of the water remained in the adventitious roots themselves. When the water content of the soil for the adventitious roots was at a higher water content than that containing the main root systems, considerably more water appeared to move into the plants through the adventitious root systems. Rubidium uptake was not consistently affected by the different water contents, nor was the uptake correlated with the amount of root growth. There was, however, at least as much rubidium accumulated in the plants in 28 hours, when the adventitious roots were wetter than the main root systems, as was accumulated in the plants in six days when the adventitious roots were drier than the main root systems. It appears that the transport of water from the roots to the plants may be an important factor in ion accumulation and it may be that the uptake of ions will not correlate with water conditions at the root surface unless and until rapid transport of water takes place. Since water uptake appears to be closely related to the amount of root growth, the effects of water contents on the absorption process itself must be interpreted with caution or the root growth measured and accounted for. It is not known if the same holds true for ion uptake. In these experiments the rubidium uptake was not closely related to root growth but it is not possible to say if this holds true for ion absorption in general.
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