title: Water relations of evergreen and drought-deciduous trees along a seasonally dry tropical forest chronosequence.
abstract: Seasonally dry tropical forests (SDTF) are characterized by pronounced seasonality in rainfall, and as a result trees in these forests must endure seasonal variation in soil water availability. Furthermore, SDTF on the northern Yucatan Peninsula, Mexico, have a legacy of disturbances, thereby creating a patchy mosaic of different seral stages undergoing secondary succession. We examined the water status of six canopy tree species, representing contrasting leaf phenology (evergreen vs. drought-deciduous) at three seral stages along a fire chronosequence in order to better understand strategies that trees use to overcome seasonal water limitations. The early-seral forest was characterized by high soil water evaporation and low soil moisture, and consequently early-seral trees exhibited lower midday bulk leaf water potentials (Ψ(L)) relative to late-seral trees (-1.01 ± 0.14 and -0.54 ± 0.07 MPa, respectively). Although Ψ(L) did not differ between evergreen and drought-deciduous trees, results from stable isotope analyses indicated different strategies to overcome seasonal water limitations. Differences were especially pronounced in the early-seral stage where evergreen trees had significantly lower xylem water δ(18)O values relative to drought-deciduous trees (-2.6 ± 0.5 and 0.3 ± 0.6‰, respectively), indicating evergreen species used deeper sources of water. In contrast, drought-deciduous trees showed greater enrichment of foliar (18)O (∆(18)O(l)) and (13)C, suggesting lower stomatal conductance and greater water-use efficiency. Thus, the rapid development of deep roots appears to be an important strategy enabling evergreen species to overcome seasonal water limitation, whereas, in addition to losing a portion of their leaves, drought-deciduous trees minimize water loss from remaining leaves during the dry season.
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agriculture Sciences (SLU), Umea, Sweden. Niles.Hasselquist@seksko.slu.se
authors.forename: Niles J
authors.initials: NJ
authors.lastname: Hasselquist
authors.forename: Michael F
authors.initials: MF
authors.lastname: Allen
authors.forename: Louis S
authors.initials: LS
authors.lastname: Santiago
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis / Q000378:metabolism; D055864:Droughts; D017753:Ecosystem; D008800:Mexico; D010103:Oxygen Isotopes / Q000032:analysis / Q000378:metabolism; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D012621:Seasons; D013997:Time Factors; D014197:Trees / Q000145:classification / Q000254:growth & development* / Q000378:metabolism; D014329:Tropical Climate; D014867:Water / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D014867:Water