PARENT SESSION
Oral Session #63: Plant Ecology: Water Relations. Presiding: J. Cleverly.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.
Contrasting seasonal patterns of root and stem sap flow in three tree species in a desert arroyo.
Hultine, Kevin 1, Williams, David1, Burgess, Steve2, 1 2
ABSTRACT- Temporal and spatial patterns of plant available water are highly variable in desert arroyos (ephemeral drainages) of desert environments. Uptake and redistribution of water by phreatophytic trees in these environments has important consequences for ecosystem productivity, nutrient cycling, and landscape water balance. In this study, we used the "heat ratio" method to assess sap flow in taproots, lateral roots, and stems of three co-occurring riparian tree species in a Chihuahuan Desert arroyo. Nocturnal reverse flow (hydraulic redistribution) was detected in surface lateral roots of Juglans major and Fraxinus velutina before the monsoon season when surface soil was dry. Reverse flow ceased when soils were wetted by monsoon rains. We found no reverse flow or seasonal variation in root sap flow in Celtis reticulata. Excavation of root systems revealed that J. major, and F. velutina deployed a network of lateral roots and a discernable taproot. C. reticulata, however, was unique in that it had no discernable taproot, and all lateral roots ultimately extended into the shallow groundwater table (approximately 2m). Further, root sap flow in C. reticulata lagged approximately one hour behind sap flow in the main stem, suggesting that it has a large diurnal storage capacitance relative to the other two species. These data suggest that hydraulic redistribution measured in lateral roots of J. major and F. velutina may enhance daily transpiration and nutrient uptake during the dry season, while diurnal storage capacitance likely contributes to daily transpiration in C. reticulata.
KEY WORDS: sap flow, hydraulic redistribution, diurnal storage capacitance, Chihuahuan Desert