Evaluation of selected provenances of taxodium distichum for drought, alkalinity and salinity tolerance.

摘要

Taxodium distichum (L.) Rich. is a widely adaptable, long-lived tree species forlandscape use. It is tolerant of substantial soil salt levels, but tends to defoliate inperiods of extended or severe drought, when leaves come into contact with saltyirrigation water, and tends to develop chlorosis on high pH soils. The purpose of thisresearch was to identify provenances which may yield genotypes tolerant of thesestresses. The appropriate name for baldcypress is Taxodium distichum (L.) Rich. var.distichum, for pondcypress is T. distichum var. imbricarium (Nutt.) Croom, and forMontezuma cypress is T. distichum var. mexicanum Gordon.A germination study of T. distichum var. mexicanum revealed that if immediategermination of ripe seed is desired, then the best treatments are a citric acid soak and hotwater baths, however, if seeds can be stratified, then no pre-germination seed treatmentis needed. Citric acid scarification and hot water baths produced the best germination.Stratification hastened germination rates and cumulative mean germination percentages.Stratification for 45 d appears to be sufficient, although for the best pre-germinationtreatments stratification requirements were less pronounced. Greenhouse screeningstudies of open-pollinated families for drought tolerance show genotypes from eastern localities were less tolerant than western genotypes. Taxodium distichum likely relies onboth drought avoidance and drought tolerance strategies to deal with drought stress. Afield screening for alkalinity tolerance showed a strong geographic component to thevariation in tolerance of alkaline soils. When selecting plant material for an alkalinesite, genotypes from Mexico and south Texas should be preferred, followed by centralTexas genotypes. Greenhouse salinity screening showed that most genotypes toleratemoderate levels of soil salts, but at high soil salinities the tolerance appears to be highlygenotype-dependent, rather than having a strong geographic pattern. Field evaluationsdemonstrated that T. distichum var. mexicana grew more rapidly on three Texas sitesthan the other varieties. These evaluations also suggest that when selecting plantmaterial for an alkaline or xeric site, Mexican and south Texas genotypes should bepreferred, followed by central Texas genotypes. Cold tolerance was not determinednorth of USDA hardiness zone 8.