Methods for measuring nutrient uptake rates of intact roots of seedlings and mature trees

Most studies measuring uptake rates of trees use excised roots, even though excision may lower uptake. In my research I used intact roots to improve estimates of specific uptake rates by seedlings and mature trees.; To determine how uptake varies throughout the year, I measured the temporal variation of nutrient uptake capacity of K+, NH4 +, NO3-, Mg2+ and Ca +2 in mature loblolly pine trees. I expected net uptake to be positive throughout the year but I observed net efflux of K+, NH 4+ and NO3- in July. I also measured uptake at several solution concentrations, expecting uptake to increase with concentration. I observed this pattern in April but not July or October. In October, uptake was constant across concentration; antecedent nutrient concentrations affected the temporal patterns of uptake in July. As expected, I found greater uptake of NH4+ than NO3 -. Temporal patterns of uptake capacity are difficult to predict, since experiment duration, antecedent conditions and nutrient solution concentration, affect measured rates of uptake.; I used a sequence of treatments to measure the effect of disturbance during measurements of NO3- uptake. First, I measured uptake by loblolly pine seedlings in intact columns of sand using the SUM (soil uptake monitoring) method. Second, I removed the seedlings from the columns and measured their uptake using the hydroponic method. Third, I transferred the plants back into the SUM columns. As predicted, uptake by undisturbed SUM plants was higher than plants which had been excavated and repotted back into SUM columns. In addition, transferring plants from the SUM columns to hydroponics caused a delay in uptake. The SUM column technique holds promise for conducting nutrient uptake studies with minimal disturbance to the root.; I reviewed current techniques suitable for measuring uptake by roots of mature trees. Estimates of uptake obtained using these methods are affected by the sampling scheme, experimental conditions, excision, ion concentrations and the rate of ion efflux. I also discussed two new techniques, the SUM column technique described above, and digital autoradiography. A greater focus on methods development is critical to more accurately measuring uptake of mature tree roots under field conditions.