Root cold tolerance of black spruce seedlings: viability tests in relation to survival and regrowth

Root systems of 6-month-old, cold-hardened, container-grown black spruce seedlings (Picea mariana (Mill.) B.S.P.) were exposed to 0, -5, -10, -15, -20, or -22.5 degrees C. Freezing-induced damage to fine roots, coarse roots and the whole root system was assessed by various viability tests including leakage of electrolytes, leakage of phenolic compounds, water loss, root and shoot water potentials, and live root dry mass. To assess the long-term effects of freezing-induced root damage, seedling survival and regrowth were measured. Leakage of both electrolytes and phenolic compounds differed among fine roots, coarse roots, and whole root systems. In coarse roots and the whole root system, but not in fine roots, leakage of electrolytes, leakage of phenolic compounds, water loss, and root and shoot water potentials were correlated with percentage of live root dry mass which, in turn, was highly correlated with seedling survival and regrowth. Compared with live root dry mass, electrolyte and phenolic leakage, water loss, and root and shoot water potentials were less well correlated with seedling survival and regrowth. Among the viability tests, electrolyte leakage of the whole root system correlated most closely with seedling survival and regrowth. Under freezing conditions that destroyed less than 50% of each seedling's root system, about 70% of the seedlings survived and subsequent growth was little affected, whereas under freezing conditions that destroyed 70% of each seedling's root system, only about 30% of the seedlings survived and subsequent growth was reduced compared with that of undamaged plants.     

Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species

Variability of soil CO₂ efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO₂ efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO₂ flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO₂ efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO₂ efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration.     

Early root development of poplars (Populus spp.) in relation to moist and saturated soil conditions

Poplars (Populus spp.) are among the fastest growing trees raised in temperate regions of the world. Testing of newly developed cultivars informs assessment of potential planting stock for local environments. Initial rooting by nine poplar clones was tested in moist and saturated soil conditions during an 18-day greenhouse experiment. Clones responded differently to soil moisture, particularly in number of roots, root distribution, and root dry mass accumulation. About 73% of cuttings planted in moist soil produced roots from callus tissue, whereas only 1% of cuttings planted in saturated soil developed such roots. This drove root distribution towards the basal section of cuttings in moist soil, while in saturated soil roots were more evenly distributed among all three below-ground sections of cuttings. Roots originating from the basal section of cuttings planted in moist soil were longer than roots originating from apical and middle sections. Conversely, roots from the apical and middle sections of cuttings planted in saturated soil were longer than those originating from the basal section. Initial rooting among poplar clones established under two soil moisture regimes has implications for genotype deployment in the field, but long-term effects in the field are still unknown.     

Responses of citrus fine roots to localized soil drying: a comparison of seedlings with adult fruiting trees

We studied the responses of citrus (Citrus volkameriana Tan. & Pasq.) roots to 15 weeks of soil drying. A comparison was made between the fine roots of 1-year-old seedling root systems (seedling) and the fine roots of woody laterals of 6-year-old grafted trees (adult). Each seedling and woody lateral root system was established in a pair of vertically separated and independently irrigated soil compartments located in field root chambers excavated adjacent to the trees to which the woody laterals were attached. Root + soil respiration and fine root survival of seedlings and adults were similar for the first 5 weeks. However, eight weeks after termination of irrigation to the upper soil compartments, mortality of fine roots was high in adults but not seedlings. Fine roots of adults exposed to dry soil for 5, 8 and 15 weeks exhibited 2, 26 and 33% mortality, respectively, whereas the corresponding values for fine roots of seedlings were 2, 6 and 8%. Although root + soil respiration rates of adults and seedlings were similar before the soil drying treatment, rates for adults were only 25% of those for seedlings after 15 weeks of soil drying. We conclude that, although fine roots of adults and seedlings are similar in form, they respond differently to soil drying.     

Hydraulic redistribution of soil water by neotropical savanna trees

The magnitude and direction of water transport by the roots of eight dominant Brazilian savanna (Cerrado) woody species were determined with a heat pulse system that allowed bidirectional measurements of sap flow. The patterns of sap flow observed during the dry season in species with dimorphic root systems were consistent with the occurrence of hydraulic redistribution of soil water, the movement of water from moist to drier regions of the soil profile via plant roots. In these species, shallow roots exhibited positive sap flow (from the soil into the plant) during the day and negative sap flow (from the plant into the soil) during the night. Sap flow in the taproots was positive throughout the 24-h period. Diel fluctuations in soil water potential, with maximum values occurring at night, provided evidence for partial rewetting of upper soil layers by water released from shallow roots. In other species, shallow roots exhibited negative sap flow during both the day and night, indicating that hydraulic redistribution was occurring continuously. A third sap flow pattern was observed at the end of the dry season after a heavy rainfall event when sap flow became negative in the taproot, and positive in the small roots, indicating movement of water from upper soil layers into shallow roots, and then into taproots and deeper soil layers. Experimental manipulations employed to evaluate the response of hydraulic redistribution to changes in plant and environmental conditions included watering the soil surface above shallow roots, decreasing transpiration by covering the plant and cutting roots where probes were inserted. Natural and manipulated patterns of sap flow in roots and stems were consistent with passive movement of water toward competing sinks in the soil and plant. Because dry shallow soil layers were often a stronger sink than the shoot, we suggest that the presence of a dimorphic root system in deciduous species may play a role in facilitating leaf expansion near the end of the dry season when the soil surrounding shallow lateral roots is still dry.     

Carbon and phosphorus partitioning in Pinus serotina seedlings growing under hypoxic and low-phosphorus conditions

Ten-week-old pond pine (Pinus serotina Michx.) seedlings were grown in solution culture at 5 or 100 microM P and under aerobic or hypoxic solution conditions. After 6 and 10 weeks in the treatments, changes in relative growth rate (RGR), P acquisition and allocation, and carbohydrate partitioning were determined by analyzing tissue for total P, soluble sugars and starch. Six weeks of low-P growth conditions decreased seedling dry weight and the ratio of shoot dry weight to root dry weight (S/R) by 39 and 51%, respectively, in comparison to seedlings from the aerobic, high-P (control) treatment. Mean RGRs of shoots in the low-P treatment were reduced by 33%, whereas root growth was unaffected. After 10 weeks of low-P growth conditions, however, both shoot and root RGRs were significantly reduced, and plants had lower S/R ratios than in any other treatment. Slowed shoot growth was accompanied by starch and nonstructural carbohydrate accumulation in needles, indicating that needle growth was not limited by carbohydrate supply. Six weeks of low-P growth conditions decreased total seedling P by 75%, reflecting a 97% reduction in the net uptake rate (NUR). Shoot NUR as a fraction of seedling NUR was also greatly reduced in the low-P treatment, indicating that low-P growth conditions affected P translocation to the shoot more than P accumulation by roots. In contrast, 6 weeks of hypoxic growth conditions decreased total dry weight of seedlings in the high-P treatment by 41% relative to their aerobic counterparts. Root growth was affected more than shoot growth, however, and S/R ratios increased. After 10 weeks, S/R ratios doubled, primarily because of the reduction in root RGR. Nevertheless, roots of hypoxic seedlings contained a higher percentage of total seedling P than their aerobic counterparts. Net P acquisition per seedling decreased by more than 50% under hypoxic growth conditions, as a result of reductions in both root RGR and seedling NUR. Starch accumulation in shoots of hypoxic seedlings reflected reductions both in root growth and in transport of carbohydrates to nonwoody roots. Carbohydrate availability did not appear to be limiting growth of hypoxic woody roots, which are well-aerated internally, but it may have limited metabolic processes in nonwoody roots of seedlings from the high-P treatment.     

Manual recording of minirhizotron data and its application to study the effect of herbicide and nitrogen fertiliser on tree and pasture root growth in a silvopastoral system

The use of a simple counting method using a borescope and minirhizotron system to study the interaction of roots of wild cherry trees (Prunus avium L) and pasture in an upland silvopastoral system is described. Operator variation was greatest when distinguishing different tree root categories (e.g. white, brown, woody) but was not significant in relation to total tree or grass root counts or species differences. Analysis of covariance was used to take these differences into account in a field trial using several operators. The seasonal patterns of tree and pasture root growth were different. Tree roots peaked in May before maximal shoot growth. The peak in pasture roots occurred two weeks earlier. Tree height growth was increased by the use of herbicides to control grass growth but this effect was only apparent during August when the soil was dry and when pasture root counts were reduced.     

Hydraulic responses of whole vines and individual roots of kiwifruit (Actinidia chinensis) following root severance

Whole vine (K(plant)) and individual root (K(root)) hydraulic conductances were measured in kiwifruit (Actinidia chinensis Planch. var. chinensis 'Hort16A') vines to observe hydraulic responses following partial root system excision. Heat dissipation and compensation heat pulse techniques were used to measure sap flow in trunks and individual roots, respectively. Sap flux and measurements of xylem pressure potential (Ψ) were used to calculate K(plant) and K(root) in vines with zero and ～80% of roots severed. Whole vine transpiration (E), Ψ and K(plant) were significantly reduced within 24 h of root pruning, and did not recover within 6 weeks. Sap flux in intact roots increased within 24 h of root pruning, driven by an increase in the pressure gradient between the soil and canopy and without any change in root hydraulic conductance. Photosynthesis (A) and stomatal conductance (g(s)) were reduced, without significant effects on leaf internal CO(2) concentration (c(i)). Shoot growth rates were maintained; fruit growth and dry matter content were increased following pruning. The woody roots of kiwifruit did not demonstrate a rapid dynamic response to root system damage as has been observed previously in monocot seedlings. Increased sap flux in intact roots with no change in K(root) and only a moderate decline in shoot A suggests that under normal growing conditions root hydraulic conductance greatly exceeds requirements for adequate shoot hydration.     

Growth and nutrition of containerized Pinus Resinosa seedlings at varying moisture regimes

Containerized red pine (Pinus resinosa Ait.) seedlings were grown over a 16-week rotation at different irrigation treatments to assess moisture stress on plant growth and nutrition, and to evaluate container capacity as a guide for irrigation. Wet, moist and dry moisture regimes were induced by watering trees to the container capacity weight of the growing medium after declining to respective 92, 73 and 57% of this reference weight. The seedlings received the same amount of fertilizer over the growth period. Maximum shoot and root growth was attained under the wet moisture regime, but biomass was reduced 21 and 43% for the moist and dry regimes. Plant nutrient concentrations were not significantly affected by watering treatment, and vector diagnosis of dry matter production and element composition indicated that macronutrients were non-limiting. Seedling nutrient uptake however, was significantly diminished by moisture stress which was attributed to decreased root growth and lower mass flow and diffusion of nutrients when moisture availability was reduced in the peat rooting media. Container capacity was found to be a sensitive reference for judging the watering requirements of greenhouse-grown containerized seedlings. The method can be relatively easily applied on an operational basis.     

Influences of canopy photosynthesis and summer rain pulses on root dynamics and soil respiration in a young ponderosa pine forest

Our first objective was to link the seasonality of fine root dynamics with soil respiration in a ponderosa pine (Pinus ponderosa P. & C. Lawson) plantation located in the Sierra Nevada of California. The second objective was to examine how canopy photosynthesis influences fine root initiation, growth and mortality in this ecosystem. We compared CO2 flux measurements with aboveground and belowground root dynamics. Initiation of fine root growth coincided with tree stem thickening and shoot elongation, preceding new needle growth. In the spring, root, shoot and stem growth occurred simultaneously with the increase in canopy photosynthesis. Compared with the other tree components, initial growth rate of fine roots was the highest and their growing period was the shortest. Both above and belowground components completed 90% of their growth by the end of July and the growing season lasted approximately 80 days. The period for optimal growth is short at the study site because of low soil temperatures during winter and low soil water content during summer. High photosynthetic rates were observed following unusual late-summer rains, but tree growth did not resume. The autotrophic contribution to soil respiration was 49% over the whole season, with daily contributions ranging between 18 and 87%. Increases in soil and ecosystem respiration were observed during spring growth; however, the largest variation in soil respiration occurred during summer rain events when no growth was observed. Both the magnitude and persistence of the soil respiration pulses were positively correlated with the amount of rain. These pulses accounted for 16.5% of soil respiration between Days 130 and 329.     

Preplanting indicators of survival and growth of desiccated Abies procera bareroot planting stock

Plant moisture loss during preplanting handling is considered one of the major elements in transplanting shock. The aim of the present study was to evaluate test parameters that may be suitable for assessment of the physiological condition of noble fir (Abies procera Rehd.) planting stock that has been subjected to desiccation stress. The transplanting-sensitive species was subjected to full exposure (roots and shoots) for 0, 0.5, 1.5, 3.0 and 6?h, or partial exposure (shoots) for 0, 3, 10, and 24?h before planting. The effects of desiccation on moisture content (MC), shoot water potential (ψ), root growth potential (RGP), root electrolyte leakage (REL), survival and height growth were evaluated. Desiccation effects on plant parameters and performance were generally significant after 1.5?h of full or 10?h of partial exposure to treatment. REL explained the largest percentage of performance variation in fully exposed plants, followed by MC and ψ. RGP tended to underestimate performance potential. Factors affecting the reliability of the test parameters, e.g. moisture loss rate, root rewetting and site conditions, are discussed.     

Physiological and field growth responses of oak seedlings to warm storage

The effect of warm storage (15°C) for 0, 15 or 31 days, applied after cold storage until April, and date of lifting to cold storage on the physiological condition and field performance of two-year-old oak seedlings (Quercus robur L.) was investigated. Assessments before planting included plant moisture status, root and shoot dry weight, root growth potential (RGP), while after planting root growth, shoot growth phenology, shoot and root dry matter accumulation and stem quality were assessed. Warm storage effects were large, but lift date effects were small. Warm storage for 31 days reduced height and diameter growth, stem quality, total biomass, root growth, and reduced stem quality in the field, but 15 days storage had a smaller effect. Warm storage delayed bud break and shoot growth cessation but survival was unaffected. The depletion of food reserves during storage and low moisture availability might have caused shoot dieback leading to the development of poor quality stems. There was evidence that dry weight fraction of both the shoot tip and the taproot provided good information on the quality of the stock before planting. RGP was also a good indicator of quality. Electrolyte leakage readings from fine and taproots were not reliable indicators of plant quality.     

Coarse root–shoot allometry of Pinus radiata modified by site conditions in the Western Cape province of South Africa

The relationship between root and shoot growth and how it is modified by chronic or episodic drought stress is so far not well understood. Allometric partitioning theory (APT) supposes a constant root–shoot allometry. Optimal partitioning theory (OPT) assumes that plants’ root growth is enhanced under water limitation. However, recent studies show that fine and coarse roots react differently. This paper draws attention to the root–shoot allometry of adult Monterey pines (Pinus radiata D.Don) and its dependency on site conditions in South Africa. For assessment of the root–shoot-diameter relationship as an allometric relationship in general and for comparison with APT we used a sample of nine radiata pines from Jonkershoek and three maritime pines (Pinus pinaster Aiton) from Napier. In order to test for a site-dependency of the root–shoot allometry we sampled increment cores from stem and coarse roots of 48 radiata pines along a gradient from moist to dry sites in the Western Cape province. Tree ring analysis revealed an allometric relationship between root diameter (dr) and shoot diameter (ds) (ln(dr) = a + α _dr,ds × ln(ds)). Despite strong variation of the allometric exponent α _dr,ds we found a systematic deviation from 1.0 as would be predicted by APT. We also found α _dr,ds to decrease with drought stress, which is contradictory to both APT and OPT. However, on sites with more pronounced drought stress we detected greater allometric factors a. We hypothesise that fine root growth, and also fine root mortality, is higher on dry sites. On these sites coarse roots seem to be less necessary for matter transport compared with moist and fertile sites. On the latter, fine roots are less ephemeral and require larger coarse roots for transport. We conclude that combined root shoot tree ring analyses have the potential for improving understanding and modelling ecosystems and better assessment of forest functions such as resource use efficiency, stand stability and belowground carbon storage.     

Morphological and physiological differences in Scots pine seedlings of six seed origins

One-year-old seedlings of Scots pine (Pinus sylvestris L.) offour native seed origins (Loch Maree Islands, Glengarry/GlenMorriston, Glen Affric and Abernethy), a commercial Britishseedlot, and a seedlot from Hedesunda, in middle Sweden, werecompared at monthly intervals from October 1993 to April 1994.Seedling morphology, root condition, root frost hardiness andbud dry matter were determined at each date. There were clear morphological differences among seed origins.Seedlings raised from the commercial seedlot (A70) were largerbut had a poorer root:shoot ratio than the other seed origins.Of the native pines tested, the Loch Maree Islands origin allocateda larger proportion of its photosynthate to fine roots and needlesand smaller proportion to woody structures. Seedlings raised from the commercial British seedlot tendedto have poorer bud lignification than the other origins andalso, in autumn, higher electrolyte leakage rates from its fineroots. During winter, the Swedish origin had the lowest fineroot electrolyte leakage. Seedlings of all origins showed aprogressive increase in fine root hardiness towards mid-winterwith maximum hardiness (–7°C) in January. Dehardeningoccurred over subsequent months reaching –3°C in April.Differences among origins were evident. The Swedish seedlotdeveloped greater frost resistance than the other origins, hardeningbegan earlier in autumn and dehardening began later in spring.The commercial seedlot hardened later than the other originsbut reached a similar level of frost hardiness by January. Ofthe native pines, seedlings of the Loch Maree Islands originwere slowest to develop root hardiness.     

Effects of contrasting fertilization and moisture regimes on biomass,nutrients, and water relations of container grown red pine seedlings

Red pine seedlings were grown for 16 weeks under contrasting fertilizat (conventional, exponential) and moisture (wet, moist, dry) regimes to assess preconditioning effects of treatments on biomass production, nutrient uptake and allocation, and water relations. Growth, nutrient status, and water relations were affected more by moisture availability than by fertilization regime. Exponential fertilization under limited irrigation lowered shoot/root mass ratio, increased root nutrient reserves, and enhanced drought avoidance compared to conventional fertilization regimes. Drought treatments decreased nutrient uptake in the shoots of both fertilization regimes by 24%, but increased nutrient accumulation in the roots by 39% in the exponential regime compared to 17% in the conventional. These results may explain improved outplanting performance noted for exponentially fertilized container stock.     

New insights into the survival strategy of the invasive soilborne pathogen Phytophthora cinnamomi in different natural ecosystems in Western Australia

Despite its importance as one of the most notorious, globally distributed, multihost plant pathogens, knowledge on the survival strategy of Phytophthora cinnamomi in seasonally dry climates is limited. Soil and fine roots were collected from the rhizosphere of severely declining or recently dead specimens of 13 woody species at 11 dieback sites and two dieback spots and from healthy specimens of five woody species at four dieback‐free sites in native forests, woodlands and heathlands of the south‐west of Western Australia (WA). Phytophthora cinnamomi was recovered from 80.4, 78.1 and 100% of tested soil, fine root and soil–debris slurry samples at the 11 dieback sites, in some cases even after 18‐month storage under air‐dry conditions, but not from the small dieback spots and the healthy sites. Direct isolations from soil–debris slurry showed that P. cinnamomi colonies exclusively originated from fine roots and root fragments not from free propagules in the soil. Microscopic investigation of P. cinnamomi‐infected fine and small woody roots and root fragments demonstrated in 68.8, 81.3 and 93.8% of samples from nine woody species the presence of thick‐walled oospores, stromata‐like hyphal aggregations and intracellular hyphae encased by lignitubers, respectively, while thin‐walled putative chlamydospores were found in only 21.2% of samples from five woody species. These findings were confirmed by microscopic examination of fine roots from artificially inoculated young trees of 10 woody species. It is suggested that (i) the main function of chlamydospores is the survival in moderately dry conditions between consecutive rain events and (ii) selfed oospores, hyphal aggregations, and encased hyphae and vesicles in infected root tissue of both host and non‐host species are the major long‐term survival propagules of P. cinnamomi during the extremely dry summer conditions in WA.     

Coarse and fine root respiration in aspen (Populus tremuloides)

Coarse and fine root respiration rates of aspen (Populus tremuloides Michx.) were measured at 5, 15 and 25 degrees C. Coarse roots ranged from 0.65 to 4.45 cm in diameter, whereas fine roots were less than 5 mm in diameter. To discriminate between maintenance and growth respiration, root respiration rates were measured during aboveground growing periods and dormant periods. An additional measurement of coarse root respiration was made during spring leaf flush, to evaluate the effect of mobilization of resources for leaf expansion on root respiration. Fine roots respired at much higher rates than coarse roots, with a mean rate at 15 degrees C of 1290 micromol CO2 m-3 s-1 during the growing period, and 660 micromol CO2 m-3 s-1 during the dormant period. The temperature response of fine root respiration rate was nonlinear: mean Q10 was 3.90 for measurements made at 5-15 degrees C and 2.19 for measurements made at 15-25 degrees C. Coarse root respiration rates measured at 15 degrees C in late fall (dormant season) were higher (370 micromol CO2 m-3 s-1) than rates from roots collected at leaf flush and early summer (200 micromol CO2 m-3 s-1). The higher respiration rates in late fall, which were accompanied by decreased total nonstructural carbohydrate (TNC) concentrations, suggest that respiration rates in late fall included growth expenditures, reflecting recent radial growth. Neither bud flush nor shoot growth of the trees caused an increase in coarse root respiration or a decrease in TNC concentrations, suggesting a limited role of coarse roots as reserve storage organs for spring shoot growth, and a lack of synchronization between above- and belowground growth. Pooling the data from the coarse and fine roots showed a positive correlation between nitrogen concentration and respiration rate.     

Assessment of Root Freezing Damage of Two-year-old White Spruce,Black Spruce and Jack Pine Seedlings

Whole root systems of 2-yr-old containerized white spruce [Picea glauca (Moench) Voss], black spruce [Picea mariana (Mill.) B.S.P.] and jack pine (Pinus banksiana Lamb.) seedlings, with intact root plugs, were exposed to various frost temperatures, which a preliminary test indicated would induce approximately 0 (control), 20, 40, 60, 80 and nearly 100% frost damage. Damage to root systems was evaluated using: (1) two measures of electrolyte leakage (relative conductivity and total tissue leakage after autoclaving); (2) water loss after pressurization; (3) chlorophyll fluorescence (Fv/Fm, maximal PSII photochemical efficiency) measured 4, 21 and 30 days after the beginning of seedling regrowth and (4) live root dry mass measured 21 days after the artificial frost and 60 days after the beginning of regrowth. Seedling survival and growth after the artificial frost were evaluated using live root dry mass measured after 60 days of regrowth and new shoot length, stem diameter, and root and shoot dry mass. Live root dry mass, dead tissue leakage, jack pine root water loss and fluorescence measurements were all significantly correlated with one or more of the growth variables and the number of significant correlations varied with species. Dead tissue leakage measurements appear to be the most promising method for evaluating root damage to 2-yr-old well-developed root systems of these species.     

Change of allometry between coarse root and shoot of Lodgepole pine (Pinus contorta DOUGL. ex. LOUD) along a stress gradient in the sub-boreal forest zone of British Columbia

Abstract

This transect study in 41–178 year-old stands of Lodgepole pine (Pinus contorta DOUGL. ex. LOUD.) in the southern boreal forest of British Columbia, Canada, analyses how site conditions modify the coarse root–shoot dynamics of trees. The allometric relationship between diameter growth of coarse roots and trunk is scrutinised for long-term site dependence, and short-term reactions to periodic climate conditions. Along a gradient from poor to rich sites, we analysed 54 trees. The sampling scheme provided two increment cores each from the three main roots and the shoot at breast height per tree. From the year-ring series, we calculated diameter time series for each shoot and each root. With these data, we show (1) that the trees’ coarse root diameter and shoot diameter are linearly related in a double-logarithmic coordinate system, thus representing constant allometry on the long run. Statistical analysis of these long-term trajectories reveals that (2) the relative allocation to coarse roots versus shoot is much higher on poor sites compared to rich sites. A closer look at the short-term reaction to stress events in the period from 1995 to 2000, where several dry years occurred, underpins that (3) a lack of water supply triggers biomass allocation in favour of coarse roots at the expense of shoot growth most pronouncedly on poor sites. Implications of this morphological plasticity for allometric theory, method development, tree and stand dynamics and carbon storage assessment are discussed.     

Growth of Eucalyptus marginata (Jarrah) seedlings in a greenhouse in response to shade and soil temperature

The effects of shade and soil temperature on growth of Eucalyptus marginata Donn ex Sm (jarrah) seedlings were studied in greenhouse experiments. Plant dry weight and that of all plant parts declined in response to shade, as did root/shoot ratio. Plant leaf area was less in unshaded plants than in plants grown in shade, and specific leaf area increased with shade. Unshaded seedlings had a higher light-saturated rate of photosynthesis, a higher light compensation point and a higher light saturation point than seedlings grown in 70% shade. The relationship between plant dry weight and leaf dry weight was independent of shading, whereas the relationship between plant dry weight and plant leaf area was dependent on shading. Therefore, leaf dry weight may be a better predictor of biomass production than leaf area in forest stands where shade is likely to affect growth significantly. Soil temperature had a significant effect on the growth of all plant parts except cotyledons. Total plant growth and shoot growth were maximal at a soil temperature of 30 degrees C, but root growth had a slightly lower temperature optimum such that the root/shoot ratio was highest at 20 degrees C. Roots grown at 15 degrees C were about 30% shorter per unit of dry weight than roots grown at 20 to 35 degrees C. We conclude that increases in irradiance and soil temperature as a result of overstory removal in the forest will cause significant increases in growth of E. marginata seedlings, but these increases represent a relatively small component of the growth response to overstory removal.