Needle water potential of selected pine species during the off-season: A case study

In this study we investigated the needle water potential of different pine species using a pressure chamber during winter months. Totally, seven pine species Pinus jeffreyi Greville & Balfour, Pinus ponderosa P. & C. Lawson, Pinus uncinata Ramond ex de Candolle, Pinus nigra Arnold, Pinus sylvestris Linnaeus, Pinus heldreichii Christ, Pinus cembra Linnaeus representing ecological variability of this genus were selected for measurements. Although the water potential is well documented in many tree species during the vegetation season, data from the off-season are scarce. During the investigated seasons (November 2014, January and February 2016), days with air temperature (T) above and below 0°C were selected for the measurement. During the days with air T above 0°C and global radiation reaching 3,000 kJ·m^–2·day^–1, the water potential averaged –0.6 ± 0.4 MPa. On the contrary, under T below 0°C and global radiation above 6,000 kJ·m^–2·day^–1, the needle water potential was close to zero (–0.3 ± 0.2 MPa) regardless of the pine species. The reason why the needle water potential reflects air T and is negatively correlated with the global radiation in winter will be an objective of our future investigations.

Drought and aluminium as stress factors in Norway spruce (Picea abies) seedlings

Effects of drought, Al and their possible interaction on physiological characteristics were studied in four-years-old Norway spruce seedlings in a pot experiment. Drought stress was imposed by withholding irrigation. Al was applied to the soil as an AlCl₃ solution at a concentration of 1,500 μmol·l^–1. Water deficit caused a decrease in needle water potential, net photosynthetic rate (P_n) and an increase in proline accumulation. On the other hand, water potential, P_n and proline concentration in seedlings subjected to Al remained unchanged. During the experiment, no significant variation was registered in the chlorophyll a fluorescence parameters. Chlorophyll content was significantly reduced in the Al presence. Drought led to a lower Al accumulation in needles in comparison with well-watered seedlings. Progressive dehydration influenced the physiological state of spruce seedlings. The presence of Al in soil did not cause any negative changes in the physiological parameters under an optimal water regime. By contrast, the synergic effect of drought and Al induced the most marked changes in measured characteristics, which may indicate a possible enhanced impact of drought and Al interaction in comparison with the single effect of these stress factors.

Effects of drought stress and severe pruning on the reaction zone induced by single inoculations with a bark beetle associated fungus (Ophiostoma ips) in the phloem of young Scots pines

The objective of this study was to test the effect of water stress and pruning on the resistance of young Scots pines (Pinus sylvestris L.) to a bark beetle associated fungus. Six-year-old potted trees were either pruned (70% of needles removed) or subjected to several successive episodes of severe water stress, prior to inoculation of inner bark with the fungus Ophiostoma ips (Rumb.) Nannf., which is usually associated with the bark beetle Ips sexdentatus Boern. Well-watered, nonpruned trees served as controls. Predawn needle water potential reached -2.5 MPa and net CO2 assimilation rates were reduced to almost zero during each water stress episode. The length of the reaction zones around inoculation points reached 3-4 cm after 3 weeks. It was higher during Spring than during Autumn. Impact of water stress on the length of the reaction zone was very limited and independent of the number of drought episodes that had been imposed prior to inoculation. The only visible change was a slight decrease when the inoculation was done during the period of maximum water stress intensity. Growth of the pathogen in the phloem was not affected by water stress. Correspondingly, pruning had no effect on either of these two parameters. Induced reaction zones accumulated monophenolic compounds that were undetectable in unwounded phloem. These included pinocembrin and pinosylvin and its monomethylether known to contribute to the defence against the fungus. Neither drought nor severe pruning induced any change in the nature or concentrations of these compounds in the unwounded phloem or in the reaction zone.

Vapor Pressure Deficit, Temperature, and Light Affect Postharvest Drying of Fraser Fir and Eastern White Pine

Branches of Fraser fir [Abies fraseri (Pursh) Poir.] and eastern white pine (Pinus strobus L.) were subjected to various temperatures, vapor pressure deficits (VPD), and light regimes in controlled-environment chambers. Drying rates, based on measurements of needle water potential (ψ), were accelerated by increasing VPD, high temperature, and light. Fraser fir and white pine dried to – 4.0 MPa and – 3.0 MPa, respectively, in about the same time. The relationship of moisture content (MC) to ψ was linear for Fraser fir, quadratic for white pine. The MC of Fraser fir at – 4.0 MPa was also a linear function of VPD during drying. Water loss was greatest early in the drying cycle, and high temperature (25C) promoted rapid drying, even at low VPD.

Effects of slash and litter management on fluxes of nitrogen and tree growth in a young Pinusradiata plantation

The effects of slash and litter management practices on soil water and temperature, fluxes of mineral N, needle water potential, and tree nutrition and growth were studied in a young Pinusradiata D. Don plantation growing on a sandy Podzol in southeastern Australia. Treatments were slash and litter retained (SL), litter only retained (L), litter ploughed (LP), and slash and litter removed (SLR). Soils without slash or litter cover (LP and SLR) were up to 4 °C warmer on average than soils overlaid by slash or litter and were subjected to greater extremes of temperature. Treatments had relatively little effect on soil water content and needle water potential in trees. Carbon in surface soil increased from 1.14 to 1.83% after incorporation of litter by ploughing, but decreased to 1.37% during the next 40 months. Smaller but significant decreases in C also occurred in other treatments. LP and SLR led to the highest rates of N mineralization in the 1st year. During the first 3 years after clear-felling, rates of N mineralization increased in SL, L, and LP but decreased in SLR. During the 4th year, rates of N mineralization were low (20–30 kg N•ha−1•year−1) in all treatments. Over 4 years, 211, 170, 210, and 147 kg N•ha−1 were mineralized in treatments SL, L, LP, and SLR, respectively. Rates of mineralization and leaching were strongly correlated (R2 = 0.82) and leaching below 30 cm accounted for 75–85% of N mineralized irrespective of treatment. Incorporation of litter by ploughing doubled concentrations of mineral N during the first summer after planting and increased early tree growth. However, rates of N mineralization in the slash and litter treatments, which were high compared with potential rates of uptake, were weakly correlated with tree growth. Factors controlling N supply were of little consequence for tree growth during this early phase of plantation establishment.

Water stress of Pinusponderosa in relation to foliage density of neighboring plants

The relationship of predawn needle water potential of ponderosa pine (Pinusponderosa Dougl. ex Laws.) and the foliage density of neighboring plants was examined after experimental gradients of foliage were established on two sites in northwestern Montana. In late summer, soil water content linearly decreased in relation to the amount of foliage of herbs and shrubs. Predawn needle water potential of pine seedlings planted along the gradient ranged from −0.5 MPa when competitor foliage was near zero to less than −3.0 MPa when such foliage was more extensive. Even when neighboring plants had a small amount of transpiring foliage at this time of year, the pine seedlings had an increased level of water stress.

Promotion of flowering in potted Piceaengelmannii (Perry) grafts: effects of heat, drought, gibberellin A4/7, and their timing

Young, potted grafts ofPiceaengelmannii were moved into a 30:20 °C (day:night) heated polyethylene house at different stages of lateral shoot elongation; and there they were subjected to low, moderate, or severe drought stress with and without branch applications of gibberellin A4/7 (GA4/7). The critical time for promoting flowering by high temperature was the late stage of slow shoot elongation, whereas for drought it was during early and rapid shoot growth. Each treatment inhibited flowering at the time the other was maximally effective and the effective treatment period for GA4/7 appeared to include that both for high temperature and drought. In contrast to drought, optimally timed heat treatment did not retard shoot elongation, nor did it result in a decreased needle water potential relative to well-watered grafts outdoors. It appears that heat and drought promote flowering through different mechanisms, albeit mechanisms which may be mediated, at least in part, through their influence on gibberellin metabolism. Advantages of indoor-potted orchards over conventional soil-based orchards for accelerating the breeding and production of genetically improved P. engelmannii seeds are discussed.

Needle water potential and soil-to-foliage flow resistance during soil drying: a comparison of Douglas-fir, western hemlock, and mountain hemlock

Needle water potential in western and mountain hemlock falls as the soil dries, but under our experimental conditions, it remained stable in Douglas-fir. Resistance to water flow from soil to foliage is higher for the hemlocks and increases more steeply as the soil dries. These findings physically account for the observation that water uptake is reduced relatively more for the hemlocks than for Douglas-fir, as soil water potential declines.

Water relations of Pinusradiata in competition with weeds

Soil water profiles up to 2 m in depth and diurnal patterns of needle water potential and stomatal resistance were measured over a dry summer period in 5-, 16-, and 28-month-old radiata pine (Pinusradiata D. Don) plantations, growing with and without weed competition. Severe water stress with consequent productivity loss occurred in trees with weed competition but the severity of stress decreased progressively with increasing tree age. Transplanted seedlings in their first growing season had shallow root systems which could not efficiently exploit water at depth. By contrast, seedlings in their second and third growing seasons extracted water from at least a depth of 2 m. Trees without weed competition were not water stressed over this period even when planted at three times their normal stocking rate. Thus there is considerable capacity to increase early growth rates of radiata pine without water being the limit to growth if weeds are adequately controlled.