Stand Water Use Research Articles

Sap flow in Bornean heath and dipterocarp forest trees during wet and dry periods.

Daytime xylem sap flow was measured by the compensation heat pulse velocity technique in dipterocarp forest trees growing on sandy loam (haplic acrisol) and in heath forest trees growing on bleached sand (albic arenosol) in Brunei during wet and dry periods. In dipterocarp forest trees, daily sap flow was stable during the dry period but declined on rainy days presumably as a result of reduced transpiration. At the heath site, daily sap flow of the small trees was stable during the dry period, whereas it declined in the large trees as the dry season progressed. In some trees at both sites, the hydroactive area of xylem was less during the dry period than during the wet period. Daily sap flow was linearly related to projected crown area, and a common regression fitted trees of different species from both forest types. The dry/wet period ratio of sap flow (about 0.7) was statistically equivalent for heath and dipterocarp forest trees, whereas it had been expected that trees on the freely draining arenosol would suffer greater water stress during drought. For well-watered trees >/= 0.2 m dbh (diameter at 1.3 m above ground) in both the dipterocarp and heath forests, stand water use was estimated to be 40 mm month(-1).

Scaling theory to extrapolate individual tree water use to stand water use

AbstractExtrapolation of measurements of water use by individual trees to that for a stand of trees is a critical step in linking plant physiology and hydrology. Limitations in sampling resources and variation in tree sizes within a stand necessitate the use of some scaling relationship. Further, to scale tree water use in space as well as time, the relationship must reflect the changing availabilities of energy and water supply. It is argued here that tree leaf area is the most appropriate covariate of water use to achieve this aim. However, empirical results show that the relationship is not always linear. A theory is developed, based on the concepts of hydrological equilibrium (sensu Nemani and Running, 1989) and ecological field theory (Walker et al., 1989) which accounts for (occasional) non‐linear behaviour of the flux/ leaf area relationship in evergreen trees. A key feature of this theory is the notion of a non‐linear, quasi‐equilibrium reflecting plant water stress. An equation is derived from these concepts and a standard, explicit treatment of tree water use (Landsberg and McMurtrie, 1984), which is used to characterise this relationship. This equation has the form Q = aIA + bΨsAf. The theory is tested against field data and published reports on Eucalyptus tree water use.

The effects of elevated carbon dioxide, temperature and soil moisture on the water use of stands of groundnut (Arachis hypogaeaL.)

Stands of groundnut (Arachis hypogaea L. cv. Kadiri 3) were grown in controlled environment glasshouses at two mean air temperatures (28° C and 32° C), two atmospheric CO 2 concentrations (371 ppmv and 700 ppmv) and two soil moisture treatments (irrigated weekly to field capacity or allowed to dry from 22 d after sowing). The transpiration equivalent, Ω w (g kPa kg −1 ) - the product of the accumulated biomass/transpired water ratio and the saturation deficit - was calculated for all the treatments using above-ground harvest, root core and neutron probe measurements. Neither temperature nor soil moisture treatment was found to have an effect on Ω w

An analysis of sap flow in mountain ash (Eucalyptus regnans) forests of different age.

Diurnal measurements of sap velocity were made in 50-, 90-, 150- and 230-year-old mountain ash (Eucalyptus regnans F. Muell.) forests in the North Maroondah catchment (southeast Australia) over the periods January 8, 1990 to April 4, 1990 and October 29, 1990 to April 16, 1991. Over the two periods, daily mean sap velocities for the four forests, in order of increasing age, were 11.5, 11.4, 9.9 and 11.8 cm h(-1) respectively. Daily mean sap velocity did not differ significantly among the 50-, 90- and 230-year-old plots. However, in the 150-year-old trees it was significantly smaller by an average of 14%. Sap velocity varied diurnally and also between positions within individual trees and among trees both within and between stands. Despite this variability, the sampling intensity and duration were sufficient to establish that behavior was highly correlated among individuals within plots. There was a significant decline with age in the overstory sapwood conducting area of these forests. In order of increasing age, the values were 6.7, 6.1, 4.2 and 4.0 m(-2) ha(-1), respectively. When combined with daily mean sap velocity, these data allowed the calculation of overstory water use. Over the experimental period, water use of the overstory decreased with age ranging, on average, from 1.86 mm day(-1) for the 50-year-old plot to 0.81 mm day(-1) for the 230-year-old plot. Mean daily water use for the two intermediate-aged forests was 1.67 and 1.00 mm day(-1), respectively. Annual water use decreased with forest age from 679 mm for the 50-year-old stand to 296 mm for the 230-year-old stand. This difference corresponds to 3.8 x 10(3) m(3) ha(-1). The annual water use of the intermediate-aged stands was 610 and 365 mm for the 90- and 150-year-old stands, respectively.

Supraoptimal Carbon Dioxide Effects on Growth of Soybean [ Glycine max (L.) Merr.

In tightly closed environments used for human life support in space, carbon dioxide (CO2) partial pressures can reach 500 to 1000 Pa, which may be supraoptimal or toxic to plants used for life support. To study this, soybeans [Glycine max (L.) Merr. cvs. McCall and Pixie] were grown for 90 days at 50, 100, 200, and 500 Pa partial pressure CO2 (500, 1000, 2000, and 5000 ppm). Plants were grown using recirculating nutrient film technique with a 12-h photoperiod, a 26 degrees C/20 degrees C thermoperiod, and approximately 300 micromoles m-2 s-1 photosynthetic photon flux (PPF). Seed yield and total biomass were greatest at 100 Pa for cv. McCall, suggesting that higher CO2 levels were supraoptimal. Seed yield and total biomass for cv. Pixie showed little difference between CO2 treatments. Average stomatal conductance of upper canopy leaves at 50 Pa CO2 approximately 500 Pa > 200 Pa > 100 Pa. Total water use over 90 d for both cultivars (combined on one recirculating system) equalled 822 kg water for 100 Pa CO2, 845 kg for 50 Pa, 879 kg for 200 Pa, and 1194 kg for 500 Pa. Water use efficiences for both cultivars combined equalled 3.03 (g biomass kg-1 water) for 100 Pa CO2, 2.54 g kg-1 for 200 Pa, 2.42 g kg-1 for 50 Pa, and 1.91 g kg-1 for 500 Pa. The increased stomatal conductance and stand water use at the highest CO2 level (500 Pa) were unexpected and pose interesting considerations for managing plants in a tightly closed system where CO2 concentrations may reach high levels.

Soil cation accumulation in a mesquite woodland: sustained production and long-term estimates of water use and nitrogen fixation

Historical records indicate sustained production in a stand of phreatophytic mesquite (Prosopis glandulosa var. Torreyana) in the Sonoran Desert of California for 200 to 500 years. The plants are primarily utilizing moderately saline groundwater (electrical conductivity c. 30 dS/m) at 5 m depth. Most of the major cations entering the ecosystem in the groundwater remain in the deep root zone, since root uptake of cations removes only a small proportion of the total input. Under these conditions prolonged root activity could result in excessive salt (cation) accumulation which could limit growth and potentially kill the plant. We measured total Ca, Na, Mg, and K accumulations in the capillary fringe above the water table to determine the pattern and degree of salt accumulation in the active root zone. Possible mechanisms for sustained production by this system include (1) a fluctuating water table which regularly flushes salts out of the root zone; (2) high salt tolerance of the mesquite which prolongs production, but not indefinitely; (3) seasonal fluctuation in water use which allows inverse leaching, capillary rise carrying salts above the most active portion of the root zone during the dormant season. In addition, estimates of total stand water use and symbiotic N-fixation over the total life of the stand may be derived from measurements of total cation accumulation in the plant root zone.