It is commonly assumed that the nitrogen to phosphorus (N:P) ratio of a terrestrial plant reflects the relative availability of N and P in the soil in which the plant grows. Here, this was assessed for a tropical pioneer tree, Ficus insipida. Seedlings were grown in sand and irrigated with nutrient solutions containing N:P ratios ranging from <1 to >100. The experimental design further allowed ...

Increasing the nitrate (N) concentration in the rooting substrate above deficiency decreased stomatal conductance and leaf growth rate compared with sufficient N in maize seedlings (Zea mays L.) growing in drying substrate. Novel effects were detected when N in the non-deficient range was supplied directly to the xylem of detached shoots: concentrations above 2.0 mol m-3 KNO3 reduced transpirat...

An apparatus was designed that permitted acetylene reduction (N(2) fixation) by root nodules to be measured in situ simultaneously with net photosynthesis, dark respiration, and transpiration of the shoot in soybean plants (Glycine max [L.] Merr. var. Beeson). Tests showed that acetylene reduction was linear with time for at least 5 hours, except for the first 30 to 60 minutes. Endogenous ethyl...

Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water transport and hence carbon uptake by leaves. While more negative xylem water potentials provide a larger driving force for water transport, they also cause cavitation that limits hydraulic conductivity. An optimum balance between driving force and cavitation occurs at intermediate water potentials, th...

Acer rubrum L., A. saccharum Marsh., Quercus alba L. and Q. rubra L. seedlings subjected to soil and stem base heat treatments showed rapid declines in rates of transpiration and photosynthesis. Reductions in photosynthetic rate were partly attributable to mesophyll inhibition. Quercus seedlings were less able to maintain transpiration and photosynthesis after heat treatment than Acer seedlings...

During daylight hours, the isotope composition of leaf water generally approximates steady-state leaf water isotope enrichment model predictions. However, until very recently there was little direct confirmation that isotopic steady-state (ISS) transpiration in fact exists. Using isotope ratio infrared spectroscopy (IRIS) and leaf gas exchange systems we evaluated the isotope composition of tra...

Water-limited ecosystems are characterized by precipitation with low annual totals and significant temporal variability, transpiration that is limited by soil-moisture availability, and infiltration events that may only partially rewet the vegetation root zone. Average transpiration in such environments is controlled by precipitation, and accurate predictions of vegetation health require adequa...

At the onset of ripening, some fleshy fruits shift the dominant water import pathway from the xylem to the phloem, but the cause for the decline in xylem inflow remains obscure. This study found that xylem-mobile dye movement into grape berries decreased despite transient increases in berry growth and transpiration during early ripening, whereas outward dye movement continued unless the roots w...

A new and simple greenhouse crop transpiration model enabling predictions from outdoor conditions is presented and the parameters involved are discussed with respect to different types of greenhouse-crop systems. This transpiration model was validated against experimental data measured in a soil-less tomato crop cultivation in Avignon in summer conditions, when the greenhouse is open, and early...

This study determined whether the field level concentration of root zone CO2 affects transpiration rate and root water transport in soybean (Glycine max L. Merr.). In an upland field converted from a paddy field, topsoil CO2 during the cropping season rose to 8 kPa of partial pressure after rainfall, whereas O2 dropped only to a minimum of 7 kPa. An elevated root zone CO2 pressure of 6 kPa sign...