Abstract:
Tracer-aided studies to understand plant water uptake sources and dynamics in tropi-
cal ecosystems are limited. Here, we report the analysis of dry season source water
uptake patterns of five unique ecosystems of Costa Rica across altitudinal (<150–
3,400 m asl) and latitudinal (Caribbean and Pacific slopes) gradients: evergreen and
seasonal rainforests, cloud forest, Páramo and dry forest. Soil and plant samples were
collected during the dry season in 2021. Plant and soil water extractions were con-
ducted using centrifugation. Stem water extracted volume and stem total water con-
tent were calculated via gravimetric analysis. Water source contributions were
estimated using a Bayesian mixing model. Isotope ratios in soil and stems exhibited a
strong meteoric origin. Enrichment trends were only detected in stems and cactus
samples within the dry forest ecosystem. Soil profiles revealed nearly uniform isoto-
pic profiles; however, a depletion trend was observed in the Páramo ecosystem
below 25 cm. More enriched compositions were reported in cactus samples for
extracted water volumes above 20% (adj. r2
= 0.34, p < 0.01). The most prominent
dry season water source in the evergreen rainforest (74.0%), seasonal rainforest
(86.4%) and cloud forest (66.0%) corresponded to well-mixed soil water. In the
Páramo ecosystem, recent rainfall produced by trade wind incursions resulted in the
most significant water source (61.9%), whereas in the dry forest, mean annual precip-
itation (38.6%) and baseflow (33.1%) were the dominant sources. The latter highlights
the prevalence of distinct water uptake sources between recent cold front rainfall
(near-surface soil storage) to more well-mixed soil moisture during the dry season,
revealing ecohydrological processing previously unknown in this tropical region.
