Effects of soil type and light on height growth, biomass partitioning, and nitrogen dynamics on 22 species of tropical dry forest tree seedlings: Comparisons between legumes and nonlegumes.
OBJECTIVE
The seedling stage is particularly vulnerable to resource limitation, with potential consequences for community composition. We investigated how light and soil variation affected early growth, biomass partitioning, morphology, and physiology of 22 tree species common in tropical dry forest, including eight legumes. Our hypothesis was that legume seedlings are better at taking advantage of increased resource availability, which contributes to their successful regeneration in tropical dry forests.


METHODS
We grew seedlings in a full-factorial design under two light levels in two soil types that differed in nutrient concentrations and soil moisture. We measured height biweekly and, at final harvest, biomass partitioning, internode segments, leaf carbon, nitrogen, δ13C, and δ15N.


RESULTS
Legumes initially grew taller and maintained that height advantage over time under all experimental conditions. Legumes also had the highest final total biomass and water-use efficiency in the high-light and high-resource soil. For nitrogen-fixing legumes, the amount of nitrogen derived from fixation was highest in the richer soil. Although seed mass tended to be larger in legumes, seed size alone did not account for all the differences between legumes and nonlegumes. Both belowground and aboveground resources were limiting to early seedling growth and function.


CONCLUSIONS
Legumes may have a different regeneration niche, in that they germinate rapidly and grow taller than other species immediately after germination, maximizing their performance when light and belowground resources are readily available, and potentially permitting them to take advantage of high light, nutrient, and water availability at the beginning of the wet season.
Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108, USA smit7586@umn.edu.
Christina M
CM
Smith-Martin
Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota 55108, USA.
Maria G
MG
Gei
College of Biological Sciences, University of Minnesota, St. Paul, Minnesota 55108, USA.
Ellie
E
Bergstrom
Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota 55108, USA.
Kristen K
KK
Becklund
Institute at Brown for Environment and Society, Brown University, Providence, Rhode Island 02912, USA.
Justin M
JM
Becknell
Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota 55108, USA.
Bonnie G
BG
Waring
Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108, USA.
Leland K
LK
Werden
Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota 55108, USA.|Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota 55108, USA.|Smithsonian Tropical Research Institute, Balboa, Republic of Panama.
Jennifer S
JS
Powers
D018533:Biomass; D007887:Fabaceae / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D065928:Forests; D018525:Germination; D008027:Light; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D012621:Seasons; D036226:Seedlings / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D012987:Soil / Q000737:chemistry; D014197:Trees / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D014329:Tropical Climate; D014867:Water / Q000378:metabolism
D012987:Soil; D014867:Water; D009584:Nitrogen
legumes; light availability; nitrogen fixation; soil resources; tree seedlings