Carbon and Mineral Element Accumulation and Allocation in Two Annual Plant Species in Response to Timing of Nutrient Addition

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Abstract
(1) The effects of the timing of a large ''pulse'' addition of mineral nutrients on accumulation and allocation of C, N, P, K and Ca, and on seed production and element status, were examined in the annual plants Abutilon theophrasti and Datura stramonium. (2) Nutrient addition increased total plant weight and element content, but the increase occurred over a period of several weeks rather than within the week after the addition. (3) The various mineral elements were allocated independently of carbon and of each other in both species. A. theophrasti started reproduction later than did D. stramonium and had lower proportional allocations of weight, N and P to reproduction at the final harvest. (4) Although nutrient pulse addition produced a temporary increase in proportional allocation of weight, N and P to leaves shortly after the addition, pulse timing had little effect on final proportional allocations. Plant age had a greater effect on allocation patterns than did the nutrient treatments. (5) Differences in seed production observed among nutrient treatments appeared to result primarily from differences in total accumulation of carbon and other elements and hence total plant growth, rather than from differences in proportional allocations. (6) Element concentrations of seeds and capsules, and mineral element contents per seed, did not differ among the treatments, and variation in mean seed weight among treatments was relatively small.