A model of the effect of temperature and moisture on pollen longevity in air-dry storage environments

Data on the survival of pollen of Typha latifolia L. stored for up to 261 d over seven different saturated salt solutions (providing 0.5 to 66 % relat ive humidity) and six different constant temperatures (from -5 to +45 degre es C) were analysed to quantify the effect of air-dry storage environment o n pollen longevity. Pollen survival curves conformed much more closely to n egative cumulative normal distributions than to negative exponential relati ons. Estimates of p(50) (storage period required to reduce pollen viability to 50 %), provided by negative cumulative normal distributions, were avail able from 37 different storage environments in which pollen viability was r educed below 50%. Once observations at 0.5% and 5.5% relative humidity were excluded from analysis, there was a negative logarithmic relation between these estimates of longevity and pollen moisture content (%, wet basis) and a curvilinear semilogarithmic relation between longevity and temperature. When the negative logarithmic relation between longevity and moisture conte nt was replaced by a negative semi-logarithmic relation between longevity a nd the relative humidity of the storage environment the resultant model was less satisfactory, principally because pollen longevity over saturated sol utions of calcium nitrate (43-62 % relative humidity) and sodium nitrite (6 0-66 % relative humidity) were consistently greater and smaller, respective ly, than fitted values. Notwithstanding these errors, comparison between th e fitted relations and observations at the two lowest relative humidities p rovided estimates of the lower-relative-humidity limits to these relations. These provisional estimates varied with storage temperature being lowest a t 25 degrees C (< 5.5% relative humidity). However, there was no linear tre nd to that variation (P > 0.25): the mean estimate was 11.9 (s.e. = 1.4)%. The considerable similarities among models of pollen longevity in air-dry s torage, and their estimated lower limits, and those developed previously fo r orthodox seeds and spores are discussed. (C) 1999 Annals of Botany Compan y.