REPRODUCTIVE ALLOCATION OF COTTON IN RESPONSE TO PLANT AND ENVIRONMENTAL-FACTORS

We measured the responses of cotton reproductive allocation (reproduct ive dry matter/total shoot dry matter) to environmental and plant fact ors in five field experiments. A wide range of growing conditions were generated by manipulation of sowing date, nitrogen fertilizer, and pl ant density. Plant factors that varied included phenological developme nt (short- vs. long-season cultivars), and leaf morphology (normal- os . okra-leaf types). We quantified the relationships between reproducti ve dry matter and shoot dry matter using allometric analysis, and calc ulated the daily rate of increase in reproductive allocation. Shoot dr y matter ranged from 4 to 235 g per plant, and reproductive dry matter from negligible to 138 g per plant. Within these ranges, the linear r egression between log(e)- reproductive dry matter and log(e)-shoot dry matter had an r(2) = 0.81 (P = 0.0001). Differences among experiments were significant, but they accounted for only a small proportion of t he variance of reproductive dry matter (8%). The dynamics of reproduct ive allocation followed a logistic pattern. The rate during the linear phase of increase in reproductive allocation was fairly stable across experiments (approximate to 0.006 d(-1)). The effect of experiments w as significant, but it accounted for only 7% of the variance in the ra te of reproductive allocation increase. Analysis of treatment effects on both allometric coefficients and on the rate of increase in reprodu ctive allocation showed that: (a) few of the sources of variation incl uded in these experiments caused significant changes in reproductive a llocation; and (b) when significant changes occurred, their magnitude was comparatively small. The relative stability of cotton reproductive allocation suggests that for some applications simple models can be d eveloped on the basis of a fixed rate of increase in reproductive allo cation. (C) 1997 Annals of Botany Company.