Variation of water relations parameters with extended rehydration time, leaf form, season, and proportion of leaf

Abstract

Pressure–volume curves were measured in October, February, and July for twigs of three deciduous, three evergreen broadleaf, four pine, and two other conifer species in the southern Appalachian Mountains, U.S.A. Data were analyzed to determine the influence on water relations parameters of rehydration time, sample leafiness, leaf form, season, and species within leaf form. Results of samples rehydrated overnight did not differ significantly from results of samples rehydrated overnight plus 24 h. Leafiness (leaf dry mass/sample dry mass) was occasionally related to water relations parameters. Water relations parameters usually varied with leaf form, and occasionally with sampling location. Patterns of variation among leaf forms differed for each combination of parameter and season: the strongest generality was that leafy deciduous twigs and pines had high tissue elasticity, whereas evergreen broadleaf species had low elasticity. Evergreen broadleaf species had a consistently high relative water content at zero turgor. Compared with literature values, these species had average to very high osmotic potentials. There was little consistency of water relations parameters among leaf forms and seasons in the overall (literature and current) data, although osmotic potential of all evergreen leaf forms rose from winter to summer.