Effects of Pressure Increase and Release on Temperature within a Pressure Chamber Used to Estimate Plant Water Potential

During a water-potential measurement sequence, temperature changewithin the pressure chamber exhibits certain distinct phases.At the introduction of gas into the chamber there is a rapidincrease in temperature, normally in excess of 8 ?C above ambient,which is directly related to the rate of pressure increase.After reaching a maximum, temperature begins to decline graduallyduring continued pressure increase, and subsequently falls toambient after gas entry coases. When pressure is rapidly releasedfrom the chamber at the end of a measurement, temperature instantlyfalls to subzero values. The causes of these temperature changes are explained in termsof simple thermodynamics, and ways of reducing them are described.     

Water Permeability of the Wood of Grand Fir (Abies grandis (Doug.) Lindl.) in Relation to Infestation by the Balsam Woolly Aphid, Adelges piceae (Ratz.)

The water permeability of sapwood and heartwood of Abies grandis(Doug.) Lindl. was found for normal trees and those infestedby balsam woolly aphid Adelges Piceae (Ratz.). It was determinedas the rate of flow of water through plugs of the wood of standarddimensions and under constant suction. The permeability of normaltrees was less in the inner than the outer sapwood and thisdifference was correlated with a greater void space (gas-filledtracheids) in the inner sapwood. The permeability of the heartwoodwas less than 5 per cent that of the sapwood. Aphid infestationreduced the permeability of the outer sapwood to about the samelevel as normal heartwood. The infested wood had a high percentageof void space and again permeability was negatively correlatedwith void space. But for a given level of void space the infestedwood had a much lower permeability than normal wood. This suggeststhat there was factor additional to the air in the tracheids,which contributed to the low permeability of infested wood.The possible nature of this factor is briefly discussed.     

Effect of Water Stress on the Rate of Non-suberized Impervious Tissue Formation Following Wounding in Abies grandis

The formation of non-suberized impervious tissue (NIT) at injuries,regardless of the cause, is an integral part of the processof periderm formation. Interference with this process is associatedwith susceptibility to insect and fungal pathogens. To understandhow disease agents interfere with the process, it is necessaryto know how the process is affected by environmental factors.This paper shows that water stress greatly retards the rateof NIT formation after mschanical wounding. Different levels of water stress were obtained by watering Abies,seedlings after the required stress had been reached, accordingto the amount of water lost by transpiration and by monitoringwater potential with a pressure chamber. Rates of NIT formationin well watered plants, at about 0.5 MPa stress, were similarto those subjected to 1.5 MPa³ of stress. At water stressesgreater than l.5 MPa, NIT formation was delayed; for example,in one experiment it formed at 17 d in 1.5 MPa-stressed seedlings,29 d in 2.0 MPa seedlings and 49 d in 3.0 MPa seedlings. Thestress symptoms were alleviated on rewatering with the resumptionof the normal rate of NIT development. The significance of thefindings in susceptible responses to insects and fungi is discussed.     

Effect of Balsam Woolly Aphid, Adelges piceae (Ratz.), Infestation on the Xylem of Abies grandis (Doug.) Lindl.

Studies of the sapwood of aphid-attacked Abies grandis (Doug.)Lindl. showed that the infestation by Adelges piceae (Ratz.)did not cause ‘rotholz’, the abnormal xylem usuallyproduced in response to aphid attack. The tracheid length, annualring width, and per cent latewood per annual ring were not significantlydifferent between the wood of infested and non-infested trees. Gas permeability, in combination with a modified Adzumi equation,was used to determine the total number and size of the conductingpit-membrane pores and tracheid lumina. In infested and non-infestedsapwood dried by solvent exchange, the average pore radius ofthe pit membrane was calculated to be about 0.l µm. Theradius of the pit pore, and the tracheid lumina and the numberof conducting tracheid lumina were not significantly differentin the infested and non-infested wood. Infestation reduced thenumber of pit pores per conducting tracheid in the wood by afactor of about three. The reduced number of conducting pitpores may have lowered the permeability of the infested woodby directly reducing the number of available flow channels.     

Effects of Infestation by the Balsam Woolly Aphid, Adelges Piceae (Ratz.) on the Ultrastructure of Bodered-Pit Membranes of Grand Fir, Abies grandis (Doug.) Lindl.

The ultrastructure of bordered-pit membranes in normal grandfir trees, Abies grandis (Doug.) Lindl., was compared with thatin trees infested with the blasam woolly aphid, Adelges piceae(Ratz). In sapwood of non-infested trees the membranes of earlywoodpits were well perforated, whereas those of latewood pits wereeither heavily incrusted or incompletely developed and showedfew perforations. In the heartwood pit membranes from both earlywoodand latewood were heavily incrusted. In aphid-infested trees all the pit membranes from the sapwoodwere incrusted and resembled those from heartwood of non-infestedtrees. These incurstations reduced the number of pores in themargo of pit membranes, and could account for the reduced permeabilityto water reported for sapwood trees attacked by the aphid. Wesuggest that the incrustation of pit membranes in sapwood inAbies grandis infested with Adelges piceae occurs because theseaphids cause heartwood to form prematurely.