| The objective of this study was to define the relationships among genome size, cell dimensions, tissue water relations, whole plant hydraulic dynamics, environmental factors, and natural distribution in the genus Pinus. Genome size of 19 Pinus species, which was determined using megagametophyte tissues with three plant species as standards by scanning Feulgen microspectrophotometry and laser flow cytometry, ranged from 21 pg to 31 pg with small variances. The ratio of DNA content in embryo tissues to that in megagametophyte tissues was 1.7 in Pinus eldarica. Genome size was significantly correlated with seed dimensions, seed-bearing age, lowest mean precipitation, and highest mean spring air temperature. There is an apparent relationship between genome size and tracheid cell dimensions in mature trees through the precipitation effects. There was no observed specific trend in the relationships among genome size, conductive cell radii, and xylem hydraulic conductivity. The species with a larger genome size had thicker conductive cell walls and smaller ratios of lumen radii to tracheid cell walls, and lost their turgor at a lower water potential. Characteristics of tolerance to tissue dehydration seemed to partially explain pine genome size diversity and the natural habitats. Water conduction characteristics relative to soil dehydration were examined using two Pinus taeda and one Pinus virginiana sources in an environmentally-controlled growth chamber. A Texas P. taeda and a P. virginiana sources had higher transpiration rates, higher needle conductance, and higher plant hydraulic conductivity under moist soil conditions than did a North Carolina P. taeda source. The former two sources reduced day-time fascicle (needle) water potential under moderate soil water stress conditions more than did the North Carolina P. taeda source, with no disruption of recovery at predawn. This characteristic is considered to be effective and important for pine survival in drought-prone environment. |
