Extracting water from discrete xylem and soil samples and continuous (long-term) monitoring of water vapor across the soil-plant-atmosphere continuum remains challenging and under a large debate. Here, we present a detailed one-year study in the Fort Worth Botanic Garden (north-central Texas) to evaluate the analytical robustness of the centrifugation extraction method and understand water sourcing from three common urban tree species (Elderberry, Sambucus canadensis; Cherry Laurel, Prunus caroliniana; and Boxelder Maple, Acer negundo). Xylem (N=110) isotope ratios (δ 18O and δ 2H) are compared to local precipitation (N=498), throughfall (N=33), and soil water (N=105) at different depths (0-38 cm). Complementary soil water samples were obtained from cup suction lysimeters (N=42) (0-38 cm). Soil and xylem water extraction volumes ranged from 100 µL to 7.5 mL in plant samples and from 100 µL to 10.5 mL in soil samples. Extraction success rates were 68.8% and 75.2% for xylem and soil samples, respectively. The minimum sample total water content for effective extractions was determined as 10.6% (soil) and 17.8% (xylem). Xylem mean narrowband and broadband (proxy for organic contamination) were 0.23±0.40 (-) and 1.00±0.01 (-), respectively. These values agree with mean narrowband and broadband metrics from throughfall and soils, which highlight the non-invasive nature of centrifugated extractions. Annual mean soil δ 18O compositions (-3.6±1.7‰) corresponded with the throughfall input (-3.6±2.4‰). Xylem δ 18O compositions exhibited a strong temporal enrichment trend at the end of the winter, summer, and fall seasons. Mean spring xylem δ 18O (-2.85‰) was less variable and close to soil mean compositions (-2.82‰). For this season, Bayesian mixing analysis showed source water contributions from distinct soil depths: 0 cm to 12.7 cm for Boxelder Maple, 12.7 cm to 25.4 cm for Cherry Laurel, and 12.7 cm to 38.1 cm for Elderberry. Our results offer a standardized and effective protocol for centrifugation extractions and reveal plant water uptake preferences in a highly altered urban green space during an unprecedented warm year.

Tracer-aided studies to understand source water partitioning in tropical ecosystems are limited. Here we report dry season source water partitioning in five unique ecosystems distributed across Costa Rica in 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 (2021). Plant and soil water extractions (triplicates) were conducted using controlled centrifugation. Stem water extraction efficiency and stem water content were calculated via gravimetric measurements. Water source contributions were estimated using a Bayesian mixing model. Isotope ratios in soil and stems exhibited a strong meteoric origin. Enrichment trends were detected mainly in stems and cactus samples within the dry forest ecosystem. Soil profiles revealed nearly uniform isotopic profiles; however, a depletion trend was observed in the Páramo ecosystem below 25 cm depth. 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 with 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 precipitation (38.6%) and baseflow (33.1%) were the dominant sources. The latter highlights the prevalence of distinct water uptake sources between recent cold front’s rainfall to more well-mixed soil moisture during the dry season.