Reproductive Allocation of Cotton in Response to Plant and Environmental Factors

Abstract

We measured the responses of cotton reproductive allocation (reproductive dry matter/total shoot dry matter) to environmental and plant factors in five field experiments. A wide range of growing conditions were generated by manipulation of sowing date, nitrogen fertilizer, and plant density. Plant factors that varied included phenological development (short- vs. long-season cultivars), and leaf morphology (normal- vs. okra-leaf types). We quantified the relationships between reproductive dry matter and shoot dry matter using allometric analysis, and calculated the daily rate of increase in reproductive allocation. Shoot dry 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 regression between log e - reproductive dry matter and log e - shoot dry matter had an r2 =0.81 ( P =0.0001). Differences among experiments were significant, but they accounted for only a small proportion of the variance of reproductive dry matter (8%). The dynamics of reproductive allocation followed a logistic pattern. The rate during the linear phase of increase in reproductive allocation was fairly stable across experiments (≈0.006 d −1 ). The effect of experiments was significant, but it accounted for only 7% of the variance in the rate of reproductive allocation increase. Analysis of treatment effects on both allometric coefficients and on the rate of increase in reproductive allocation showed that: ( a ) few of the sources of variation included in these experiments caused significant changes in reproductive allocation; 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 developed on the basis of a fixed rate of increase in reproductive allocation.