Water stress and seedling growth of two eucalypt species from contrasting habitats

Seedlings of Eucalyptus maculata Hook (mesic environment) and E. brockwayi C.A. Gardn. (arid environment) were supplied 100, 70 or 40% of their water requirements estimated from leaf area and the water used by well-watered seedlings. Restricting water supply caused large differences in growth rates, which were related to large differences in total leaf area. There was a fivefold range of variation in number of leaves per plant, and a reduction of up to 20% in average leaf size as a consequence of restricting water supply. Eucalyptus maculata seedlings produced more dry matter than E. brockwayi seedlings, but net assimilation rate was higher in E. brockwayi seedlings. Transpiration rates were also higher in E. brockwayi than in E. maculata. Leaf expansion was analyzed as a function of water stress integral (S(Psi)), which is the cumulative integral over time of predawn water potential below a datum. The leaf area achieved at any stress level was not uniquely dependent on total S(Psi), there was a secondary effect associated with reduced leaf growth caused by previous stress. At any value of S(Psi), reductions in leaf growth of water-stressed seedlings relative to leaf growth of well-watered control seedlings were greater in E. maculata seedlings than in E. brockwayi. Treatment differences in both species showed that, within the levels of stress applied, a moderate water stress over a long period of time was more detrimental to dry matter production than a severe stress for a short time.     

Distinct physiological mechanisms underpin growth and rehydration of Hymenaea courbaril and Hymenaea stigonocarpa upon short-term exposure to drought stress

Plants hold biochemical and physiological mechanisms to withstand drought conditions.Generally,depending on water deficit interval,plant rehydration relies on how it can retain growth or a positive water balance—or rarely both.In this study,two species of Hymenaea,one from the Amazon and the other from the Brazilian Cerrado,were investigated for their physiological mechanism associated with growth rehydration upon short-term exposure to drought stress.Our findings demonstrate that Hymenaea courb...     

Relationship between tree morphology and growth stress in mature European beech stands

Aims

In European Beech (Fagus sylvatica L.) large growth stresses lead to severe log end splitting that devaluate beech timber. Our study aimed at detecting relationships between growth stress and some morphology parameters in trees.

Methods

Growth stress indicators were recorded for 440 mature trees in nine stands from five European countries, together with morphology parameters.

Results

Most trees displayed an uneven distribution of growth stress around the trunk. Moreover, growth stress intensity varied largely between individual trees. Geometry of the trunk was a poor predictor of growth stress intensity. Crown asymmetry resulted in a larger stress dissymmetry within trees. Trunk inclination was not correlated to max tension stress, contrary to what is usually found in younger trees. In the case of small inclination, growth stress was close to expected from biomechanics of restoring verticality. Trees exhibiting a larger inclination probably evolved a different mechanical solution: a rather large crown, lower tree slenderness and a sufficient asymmetry in growth stress as to prevent a higher inclination due to growth.

Conclusion

A large slenderness is the best accurate predictor of a large growth stress, although variations in the ratio height/diameter at breast height explained only 10 % of the variability of growth stress. A large crown surface was the best predictor of a low level of growth stress. A large spacing between trees seems a good solution to lower the risk of growth stress in mature beech.     

Water stress, photosynthesis and early growth patterns of cuttings of three Populus clones

Photosynthetic attributes, leaf area and early root growth patterns were studied in three Populus clones to identify traits associated with superior growth potential on sites where water could be a limiting factor. It was found that early root growth and superior leaf area production were more closely related to growth potential than were photosynthetic capacity or carboxylation efficiency. A hybrid clone of Populus nigra var. charkowiensis (syn. P. nigra var. plantierensis) x P. nigra cv. 'Incrassata' (NE308) had more leaf area production and greater root system development in both wet and dry soil than did a P. trichocarpa clone (T6) and a P. balsamifera clone (B3). Despite greater above- and below-ground productivity, plants of clone NE308 had significantly lower photosynthetic capacity and carboxylation efficiency and a slightly higher CO(2) compensation point than plants of clones T6 and B3. Rapid early leaf and root growth appear to be key attributes associated with productivity in these clones regardless of soil water availability.     

Leaf nitrogen productivity is the major factor behind the growth reduction induced by long-term salt stress

Plant growth response to salinity on a scale of years has not been studied in terms of growth analysis. To gain insights into this topic, 2-year-old Mediterranean Fan Palm (Chamaerops humilis L.) and Mexican Fan Palm (Washingtonia robusta H. Wendl) seedlings, each with its own distinct plant morphology, were grown for 2 years in a peat soil and irrigated with water of 2 dS m(-1) (control) or 8 dS m(-1) (saline). Plants were harvested on seven occasions and the time trends in relative growth rate (RGR, the rate of increase of biomass per unit of biomass already existing) and its components were analysed. In the long term, salinity produced a slight reduction in the mean RGR, values in both species. In the short term, salinity caused a reduction in RGR. However, during the second year, plants irrigated with 8 dS m(-1) grew somewhat more quickly than the control plants, probably as a result of delay in the growth kinetics due to salinity. Regarding RGR components, leaf nitrogen productivity (the rate of biomass gain per unit leaf N and time) was the major factor causing the differences in RGR resulting from salinity. Washingtonia robusta showed a relatively high plasticity in plant morphology by increasing root and decreasing stem biomass allocation in the presence of salinity. However, the long-term response of W. robusta to salinity, based to a great extent, on this morphological plasticity, was less effective than that of C. humilis, which is based mainly on the contribution of leaf N to RGR values.     

Tree growth stress and related problems

Tree growth stress, resulted from the combined effects of dead weight increase and cell wall maturation in the growing trees, fulfills biomechanical functions by enhancing the strength of growing stems and by controlling their growth orientation. Its value after new wood formation, named maturation stress, can be determined by measuring the instantaneously released strain at stem periphery. Exceptional levels of longitudinal stress are reached in reaction wood, in the form of compression in gymnosperms or higher-than-usual tension in angiosperms, inspiring theories to explain the generation process of the maturation stress at the level of wood fiber: the synergistic action of compressive stress generated in the amorphous lignin–hemicellulose matrix and tensile stress due to the shortening of the crystalline cellulosic framework is a possible driving force. Besides the elastic component, growth stress bears viscoelastic components that are locked in the matured cell wall. Delayed recovery of locked-in components is triggered by increasing temperature under high moisture content: the rheological analysis of this hygrothermal recovery offers the possibility to gain information on the mechanical conditions during wood formation. After tree felling, the presence of residual stress often causes processing defects during logging and lumbering, thus reducing the final yield of harvested resources. In the near future, we expect to develop plantation forests and utilize more wood as industrial resources; in that case, we need to respond to their large growth stress. Thermal treatment is one of the possible countermeasures: green wood heating involves the hygrothermal recovery of viscoelastic locked-in growth strains and tends to counteract the effect of subsequent drying. Methods such as smoke drying of logs are proposed to increase the processing yield at a reasonable cost.     

Relation between growth stress and lignin concentration in the cell wall: Ultraviolet microscopic spectral analysis

Lignin content in the cell wall was investigated to examine its relation with growth stress, using an ultraviolet microscopic spectrum analyzer. Although a weak correlation existed between the growth stress and lignin concentration in the compound middle lamella, it was believed that the compound middle lamella did not contribute to compressive growth stress generation as there was no correlation between growth stress and lignin concentration in the cell corner part of the intercellular layer. In the secondary wall, larger compressive growth stress was associated with higher lignin concentration especially in the outer part. This finding confirms that lignin contributes positively to the generation of compressive longitudinal growth stresses in the compression wood and more substantially in the outer part of the secondary wall. This experimental result strongly supports our hypothesis of growth stress generation given by the model.This paper was presented at the International Academy of Wood Science Meeting at Vancouver, Canada, July 1997     

Evaluation of non-destructive methods of measuring growth stress in Eucalyptus globulus: relationships between strain, wood properties and stress

High levels of growth stress are implicated in causing end splitting of logs, deflection during sawing and deformation of boards as stresses are released during sawing operations. Level of stress is a function of strain and the elastic modulus of the wood (MOE). Levels of peripheral strain can be measured on standing trees and, if the MOE is known, stresses can be estimated. The validity of using peripheral strain measurements relies on underlying theoretical models that relate strain to expected patterns of stress distribution and levels of board deflection. This study evaluates these theoretical relationships by determining relationships of stress and strain with board deflection, end splitting and a range of wood properties.

Peripheral strain levels were extremely variable within the bottom log and little evidence was found for consistent patterns of variation, although measurements generally increased with increasing height above ground. Sampling on two sides of the standing tree at breast height appeared to be a suitable strategy, with the mean for these strain readings having a correlation (r) of 0.86 with the average strain in the bottom log.

Growth strain was not a reliable predictor of board deflection and cannot be recommended as a non-destructive sampling method. Overall there was a poor relationship between growth strain and board deflection. No consistent relationships were found between a range of wood properties and growth strain or board deflection across both sites. Stress levels were calculated for each tree as the product of growth strain and modulus of elasticity and the relationship between calculated stress and mean board deflection determined. No relationship was found at either site with correlations being very close to zero.

The underlying theoretical relationships between stress and strain were examined and several questions raised about the validity of such models.     

Water and nutrient dynamics and tree growth

The balance in the investment of assimilate at any time into leaves and roots may depend on whether water, nutrients or radiation are limiting to growth. Also, for the same investment of assimilate into roots, the root configuration may range from intensive to extensive in both space and time, to take best advantage of the distribution and amount of water and nutrients. Intensive root configurations, which include mycorrhizas and proteoid roots, assist in the uptake of nutrients (such as phosphorus) which are rate-limiting in soil. Mycorrhizas may assist in water uptake in dry or coarse textured soils with low unsaturated hydraulic conductivities.

Adaptations which assist trees to survive in dry and nutrient-deficient environments are discussed. These mechanisms may reduce, maintain or increase growth. In production forestry, it is desirable to exploit those mechanisms which increase growth. When soil water and nutrients limit tree growth, productivity may be improved by increasing the amount of uptake of water and nutrients, or by increasing the efficiency by which they are used in growth. Maximizing water-use efficiency when soil water supply is limiting may be dependent on whether the trees are in mixed stands or in monoculture. Selecting trees with relatively less root may improve productivity in monocultures when weeds are controlled and fertilizer is added. It is well known that trees can ‘re-use’ nutrients by retranslocating them within the tree to zones of demand. Relatively little is known, though, about differences in the biochemical involvement of nutrients at the cellular and subcellular level which contribute to differences in nutrient-use efficiency in trees.     

On the prediction bias and variance in long-term growth projections

Forest growth is often projected for several subsequent periods. This being the case, the independent variables of a growth model will contain error due to prediction errors in the preceding periods, which cumulate through the simulation process. Thus, the accuracy of growth predictions depends on the number of growth periods. In this paper, the effect of cumulating errors is considered by conducting a simulation study using models estimated from thinning experiments carried out in Finland. The aim of the study is to estimate the prediction bias and the precision of long-term growth projections due to sequential use of growth models. The study demonstrates that it is important to take the residual variation of the models into account in long-term projections in order to reduce the prediction bias.     

胁迫温度短期冲击对松毛虫赤眼蜂羧酸酯酶活性的影响

以松毛虫赤眼蜂为对象,在不同温度胁迫短期冲击条件下对其羧酸酯酶比活力进行测定,结果表明:在15℃条件下,羧酸酯酶的比活力最高,为270.00±28.50;35℃条件下最低,为101.50±3.60;25℃条件下介于两者之间,为150.00±3.00;3种温度条件下的羧酸酯酶比活力存在显著差异(P0.05),且随着温度的升高羧酸酯酶比活力显著下降。     

Water stress responses of two Mediterranean tree species influenced by native soil microorganisms and inoculation with a plant growth promoting rhizobacterium

Soil microorganisms, such as plant growth-promoting rhizobacteria (PGPR), play crucial roles in plant growth, but their influence on plant water relations remains poorly explored. We studied the effects of native soil microorganisms and inoculation with the PGPR strain Aur6 of Pseudomonas fluorescens on water stress responses of seedlings of the drought-avoiding Pinus halepensis Mill. and the drought-tolerant Quercus coccifera L. Plant growth, nutrient concentrations and physiology (maximum photochemical efficiency of photosystem II (PSII; F(v)/F(m)), electron transport rate (ETR), stomatal conductance (g(s)) and predawn shoot water potential (Psi(PD))) were measured in well-watered plants, and in plants under moderate or severe water stress. Inoculation with PGPR and native soil microorganisms improved tree growth, and their interactions had either additive or synergistic effects. Both F(v)/F(m) and ETR were significantly affected by PGPR and native soil microorganisms. Marked differences in g(s) and Psi(PD) were found between species, confirming that they differ in mechanisms of response to water stress. A complex tree species x treatment interactive response to drought was observed. In P. halepensis, F(v)/F(m) and ETR were enhanced by PGPR and native soil microorganisms under well-watered conditions, but the effects of PGPR on Psi(PD) and g(s) were negative during a period of water stress. In Q. coccifera, F(v)/F(m) and ETR were unaffected or even reduced by inoculation under well-watered conditions, whereas Psi(PD) and g(s) were increased by PGPR during a period of water stress. Our results indicate that microbial associates of roots can significantly influence the response of tree seedlings to drought, but the magnitude and sign of this effect seems to depend on the water-use strategy of the species.     

Post-fire tree stress and growth following smoldering duff fires

Understanding the proximate causes of post-fire conifer mortality due to smoldering duff fires is essential to the restoration and management of coniferous forests throughout North America. To better understand duff fire-caused mortality, we investigated tree stress and radial growth following experimental fires in a long-unburned forest on deep sands in northern Florida, USA. We burned basal fuels surrounding 80 mature Pinus palustris Mill. in a randomized experiment comparing the effects of basal burning treatments on stem vascular meristems; surficial roots; root and stem combinations; and a non-smoldering control. We examined the effects of duration of lethal temperatures (>60 °C) on subsequent pine radial growth and root non-structural carbohydrates (starch and sugar). Duff and mineral soil temperatures in the experimental fires consistently exceeded 60 °C for over an hour following ignition, with lethal temperatures of shorter duration recorded 20 cm below the mineral soil surface. Duff heating was best explained by day-of-burn Oe horizon moisture (P = 0.01), although little variation was explained (R² = 0.24). Post-fire changes in latewood radial increment in the year following fires was related to duration of temperatures >60 °C 10 cm deep in the mineral soil (P = 0.07), but explained little variability in post-fire growth (R² = 0.17). In contrast, changes in non-structural carbohydrate content in coarse roots (2–5 mm diameter) 120 days following burning were more strongly correlated with the duration of lethal heating 5 cm below the mineral soil surface (P = 0.02; R² = 0.53). Results from this study implicate the role of mineral soil heating in the post-fire decline of mature longleaf pine following restoration fires in sandy soils.     

胁迫温度短期冲击对松毛虫赤眼蜂谷胱甘肽硫转移酶活性的影响

以松毛虫赤眼蜂为对象,对其不同温度条件下的谷胱甘肽硫转移酶比活力进行测定,结果表明:在15℃处理条件下,谷胱甘肽硫转移酶的比活力最低,为6.80±4.71;在35℃处理条件下最高,为98.22±1.76;25℃处理介于两者之间,为32.49±2.60;3种温度条件下的谷胱甘肽硫转移酶比活力存在显著差异(P0.05),且随着温度的升高比活力显著上升。     

高温干旱对油茶生长的影响

调查了干旱、高温等自然因素对不同林分、不同栽培模式油茶生长的影响.结果表明,不同油茶物种抗旱性差异显著,在调查的3个物种中,小果油茶的抗旱性最强,普通油茶次之,腾冲油茶的抗旱性最差;不同林龄林分的抗旱性不同,1～2年生新造林分的抗旱能力明显低于3年生或以上林龄的林分,且3～4年生林分抵御夏季高温干旱的能力要强于5～7年生林分;山坡中下部造林、大苗造林、减少新造林套作经营(花生)、科学覆膜管理措施能显著提高新造林的抗旱能力,加强修剪和抚育管理是改善油茶成林和老林抗旱性的重要技术手段.在今后的油茶生产过程中,应从油茶育种、育苗、造林和栽培管理一系列环节出发,研究形成一整套油茶抗旱栽培的技术体系,才能够真正地提高油茶抗旱生产水平.     

Relationships between long-term trends of air temperature,precipitation, nitrogen nutrition and growth of coniferous stands in Central Europe and Finland

Height growth of 19 Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) stands in Germany, Austria and Finland, for which long-term records of foliar nutrient levels were available, was assessed retrospectively by stem analyses and compared with data from regionally applied yield tables as references. Gridded historical time series of monthly temperature and precipitation were used to characterise the meteorologic conditions at the sampling sites. Climate parameters were tested against height growth in period 1950–2000, and needle N content was tested against height growth for the periods where N measurements were available by means of graphical comparison, as well as simple and multiple regression analyses with the aim to get evidence for causes of possible growth acceleration. Trends of referenced height increment of six out of nine Scots pine stands in Germany were positive during the observation period, and improved N nutrition appeared to be the most important driving factor for this growth acceleration. The variation of precipitation—exhibiting no consistent and uniform long-term temporal trend during the observation period—in contrast seems to be mainly responsible for the interannual fluctuation of height growth. We were not able to detect any general statistical influence of temperature parameters on height growth, although they generally increased. The referenced height growth of three Finnish pine stands slightly decreased during the observation period and there was no indication of a significant improvement of their N supply. Among four Norway spruce stands investigated in Germany and Austria, referenced height increment also increased in three cases; there was again some evidence that improved N nutrition was the stimulating factor. At three study sites in Finland, however, referenced height growth of this species decreased at least from 1985 onwards, whereas mostly no significant trends in N nutrition or precipitation were identified. These differences observed between species and regions are discussed in detail.     

干旱胁迫对植物生长及其生理的影响

干旱胁迫严重影响植物的生长、发育和繁殖等生命活动,也是人们研究最多的逆境因子之一。干旱胁迫影响植物的形态结构和生理功能。植物生物量、用水效率、光合系统、渗透调节能力、细胞膜的稳定性、抗氧化系统的防御能力及激素水平等指标的变化,常被用来判断植物抵御干旱胁迫的能力。该文就干旱胁迫下植物上述指标等方面响应变化的研究做了简要综述。     

干旱胁迫与彩色树生长状况关系研究

以金叶榆、金枝梾木和俄罗斯红叶李3种彩色树2a生苗木为试材,测定了不同程度干旱胁迫下净光合速率、蒸腾速率、细胞膜透性、叶片含水量以及高生长等指标,分析了3种彩色树的抗旱性。结果表明:在轻度干旱胁迫条件下,金叶榆和金枝梾木受到的影响小于俄罗斯红叶李;重度干旱条件下,金叶榆表现出较强的抗旱性,而金枝梾木和俄罗斯红叶李受到的影响较大。3种彩色树的抗旱性强弱排序为:金叶榆金枝梾木俄罗斯红叶李。     

Importance of root growth in overcoming planting stress

Root growth is critical to the establishment of planted seedlings. Seedlings can undergo stress just after planting if root growth is not sufficient to couple the seedling to available soil water. Stress occurs when a newly planted seedling’s root system can not supply enough water to transpiring needles to maintain a proper water balance and ensure survival. Thus, a newly planted seedling’s ability to overcome planting stress is affected by its root system size and distribution, root–soil contact, and root hydraulic conductivity. This paper describes how factors of root growth and water status of newly planted seedlings are important in overcoming the phenomenon of planting stress which then allows a newly planted seedling to enter the establishment phase of development.     

Mixed Nothofagus forest management: a crucial link between regeneration,site and microsite conditions

New Forests - Canopy openings due to harvesting practices constitute a disturbance that changes the environmental conditions of microsites. Its impact on the relative performance of the...