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PubMed2006

Suillus variegatus causes significant changes in the content of individual polyamines and flavonoids in Scots pine seedlings during mycorrhiza formation in vitro.

Changes in the concentrations of individual flavonoids and polyamines (PAs) in Scots pine (Pinus sylvestris L.) cotyledonary seedlings were studied during the establishment of an ectomycorrhizal (ECM) symbiosis with two Suillus variegatus strains in vitro. Both flavonoids and PAs were analysed after 3, 7, and 14 d in dual culture, and changes in concentrations were compared with growth of the seedlings. Both S. variegatus strains caused similar responses in Scots pine seedlings. Free putrescine accumulated immediately but only transiently after inoculation. This was followed by continuous accumulation of PA conjugates in needles and stems, and free spermidine and spermine in roots, which was accompanied by mycorrhiza formation and improved growth. The fungi induced lateral root formation and main root and primary needle elongation. Inoculation caused no qualitative changes in flavonoid composition, while quantitative changes in flavonols, catechins, and condensed tannins were observed in shoots during mycorrhiza formation. These results indicate that in this in vitro system conjugated PAs and specific flavonoids, generally related to the plant's defence reactions, did not play a major role in the regulation of the establishment of the ectomycorrhizal (ECM) symbiosis in Scots pine roots. The results also clearly show that positive growth responses in shoots and roots due to S. variegatus were supported by different and highly specific changes in the synthesis of both primary and secondary metabolites in these parts of the seedling.

Basidiomycota↗

PubMed2006

Genetic transformation and gene silencing mediated by multiple copies of a transgene in eastern white pine.

An efficient transgenic eastern white pine (Pinus strobus L.) plant regeneration system has been established using Agrobacterium tumefaciens strain GV3850-mediated transformation and the green fluorescent protein (gfp) gene as a reporter in this investigation. Stable integration of transgenes in the plant genome of pine was confirmed by polymerase chain reaction (PCR), Southern blot, and northern blot analyses. Transgene expression was analysed in pine T-DNA transformants carrying different numbers of copies of T-DNA insertions. Post-transcriptional gene silencing (PTGS) was mostly obtained in transgenic lines with more than three copies of T-DNA, but not in transgenic lines with one copy of T-DNA. In situ hybridization chromosome analysis of transgenic lines demonstrated that silenced transgenic lines had two or more T-DNA insertions in the same chromosome. These results suggest that two or more T-DNA insertions in the same chromosome facilitate efficient gene silencing in transgenic pine cells expressing green fluorescent protein. There were no differences in shoot differentiation and development between transgenic lines with multiple T-DNA copies and transgenic lines with one or two T-DNA copies.

Agrobacterium tumefaciens↗

PubMed2003

Changes in alpha-xylosidase during intact and auxin-induced growth of pine hypocotyls.

A complete cDNA from Pinus pinaster Aiton, potentially coding for an alpha-xylosidase able to remove the xylose residue from xyloglucan oligosaccharides, has been cloned. Its sequence was homologous to previously published alpha-xylosidase genes from Arabidopsis and nasturtium. The protein also showed the two signature regions of family 31 of glycosyl hydrolases. The gene expression level was quantified by competitive RT-PCR, under different growth conditions, throughout seedling development, in different regions along the hypocotyls and in auxin-treated hypocotyl segments, and related with growth capacity and alpha-xylosidase activity. A role of alpha-xylosidase in regulating the level of xyloglucan oligosaccharides within the apoplast is proposed. The action of an alpha-xylosidase removing the xylose residue, would make possible the action of a beta-glucosidase deblocking the xyloglucan oligosaccharide degradation and it could serve as a control point for the regulation of the apoplastic levels of xyloglucan oligosaccharides.

Amino Acid Sequence↗

PubMed2005

Inducible antisense-mediated post-transcriptional gene silencing in transgenic pine cells using green fluorescent protein as a visual marker.

An inducible post-transcriptional gene silencing (PTGS) system was established in Virginia pine (Pinus virginiana Mill.) cells. This system is based on the activation of an antisense gfp gene construct by a chimeric transcriptional activator GVG (Gal4-binding domain-VP16 activation domain-glucocorticoid receptor fusion) upon application of the inducer to gfp transgenic cell lines. A detailed characterization of the inducible PTGS system in transgenic cell lines demonstrated that this system is stringently controlled. The degree of silencing with this construct could be regulated by the concentration of inducer and the time of treatment. Such transgenic cell lines may provide a useful system to study signaling mechanisms of gene silencing in transgenic pine cells. The inducible system could be a useful tool for functional discovery of novel plant genes.

Cell Line↗

PubMed2000

Xylem conductivity and vulnerability to cavitation of ponderosa pine growing in contrasting climates.

We examined the effects of increased transpiration demand on xylem hydraulic conductivity and vulnerability to cavitation of mature ponderosa pine (Pinus ponderosa Laws.) by comparing trees growing in contrasting climates. Previous studies determined that trees growing in warm and dry sites (desert) had half the leaf/sapwood area ratio (A(L)/A(S)) and more than twice the transpiration rate of trees growing in cool and moist sites (montane). We predicted that high transpiration rates would be associated with increased specific hydraulic conductivity (K(S)) and increased resistance to xylem cavitation. Desert trees had 19% higher K(S) than montane trees, primarily because of larger tracheid lumen diameters. Predawn water potential and water potential differences between the soil and the shoot were similar for desert and montane trees, suggesting that differences in tracheid anatomy, and therefore K(S), were caused primarily by temperature and evaporative demand, rather than soil drought. Vulnerability to xylem cavitation did not differ between desert and montane populations. A 50% loss in hydraulic conductivity occurred at water potentials between -2.61 and -2.65 MPa, and vulnerability to xylem cavitation did not vary with stem size. Minimum xylem tensions of desert and montane trees did not drop below -2.05 MPa. Foliage turgor loss point did not differ between climate groups and corresponded to mean minimum xylem tensions in the field. In addition to low A(L)/A(S), high K(S) in desert trees may provide a way to increase tree hydraulic conductivity in response to high evaporative demand and prevent xylem tensions from reaching values that cause catastrophic cavitation. In ponderosa pine, the flexible responses of A(L)/A(S) and K(S) to climate may preclude the existence of significant intraspecific variation in the vulnerability of xylem to cavitation.

Climate↗

PubMed2001

Water use by whitebark pine and subalpine fir: potential consequences of fire exclusion in the northern Rocky Mountains.

In subalpine forests of the northern Rocky Mountains, fire exclusion has contributed to large-scale shifts from early-successional whitebark pine (Pinus albicaulis Engelm.) to late-successional subalpine fir (Abies lasiocarpa (Hook.) Nutt.), a species assumed to be more shade tolerant than whitebark pine and with leaf to sapwood area ratios (A(L):A(S)) over twice as high. Potential consequences of high A(L):A(S) for subalpine fir include reduced light availability and, if hydraulic sufficiency is maintained, increased whole-tree water use. We measured instantaneous gas exchange, carbon isotope ratios and sap flow of whitebark pine and subalpine fir trees of different sizes in the Sapphire Mountains of western Montana to determine: (1) whether species-specific differences in gas exchange are related to their assumed relative shade tolerance and (2) how differences in A(L):A(S) affect leaf- and whole-tree water use. Whitebark pine exhibited higher photosynthetic rates (A = 10.9 micromol x m(-2) x s(-1) +/- 1.1 SE), transpiration rates (E = 3.8 mmol x m(-2) x s(-1) +/- 0.7 SE), stomatal conductance (g(s) = 166.4 mmol x m(-2) x s(-1) +/- 5.3 SE) and carbon isotope ratios (delta13C = -25.5 per thousand +/- 0.2 SE) than subalpine fir (A = 5.7 micromol x m(-2) x s(-1) +/- 0.9 SE; E = 1.4 mmol x m(-2) x s(-1) +/- 0.3 SE; g(s) = 63.4 mmol x m(-2) x s(-1) +/- 1.2 SE, delta13C = -26.2 per thousand +/- 0.2 SE; P < 0.01 in all cases). Because subalpine fir had lower leaf-area-based sap flow than whitebark pine (QL = 0.33 kgx m(-2) x day(-1) +/- 0.03 SE and 0.76 kg x m(-2) x day(-1) +/- 0.06 SE, respectively; P < 0.001), the higher A(L):A(S) in subalpine fir did not result in direct proportional increases in whole-tree water use, although large subalpine firs used more water than large whitebark pines. The linear relationships between tree size and daily water use (r2 = 0.94 and 0.97 for whitebark pine and subalpine fir, respectively) developed at the Sapphire Mountains site were applied to trees of known size classes measured in 12 natural subalpine stands in the Bob Marshall Wilderness Complex (western Montana) ranging from 67 to 458 years old. Results indicated that the potential for subalpine forests to lose water by transpiration increases as succession proceeds and subalpine fir recruits into whitebark pine stands.

Abies↗

PubMed2001

Fast, nondestructive measurement of frost hardiness in conifer seedlings by VIS+NIR spectroscopy.

Frost hardiness development from mid-August to mid-November was evaluated in seedlings of three provenances of Norway spruce (Picea abies (L.) Karst.) and three provenances of Scots pine (Pinus sylvestris L.) raised at nurseries in north, central and south Sweden. Measurements of the visible + near infrared (VIS+NIR) spectra of shoots were made simultaneously with estimates of frost hardiness based on electrolyte leakage following artificial freezing. Nine physiological variables known to influence frost hardiness were measured throughout the experiment. Multivariate analysis showed that VIS+NIR spectra explained 69% and 72% of the variation in frost hardiness in Scots pine and Norway spruce, respectively. Stem lignification, dry weight fraction, and starch, glucose, fructose, galactose, sucrose, raffinose and stachyose concentrations together explained 80% and 85% of the variation in frost hardiness in Scots pine and Norway spruce, respectively when used as independent X variables in a partial least squares model. These physiological variables could be related to varying degrees with variation in the VIS+NIR spectra. We conclude that VIS+NIR spectroscopy provides a rapid nondestructive technique for measuring frost hardiness in conifer seedlings based on causal relationships between the spectra and the physiology of seedling frost hardiness.

Freezing↗

PubMed2001

Interception loss, throughfall and stemflow chemistry in pine and oak forests in northeastern Mexico.

Interception loss, gross precipitation, throughfall and stemflow solution chemistry beneath pine (Pinus pseudostrobus Lindl.), oak (Quercus sp.) and pine-oak natural forest canopies in northeastern Mexico were measured. Coefficients of variation for throughfall were 12% in pine and oak canopies and 17% in the mixed pine-oak canopy. The variability of stemflow averaged 66, 126 and 73% for pine, oak and the mixed pine-oak canopies, respectively. Linear regression analysis of net versus gross precipitation for the three canopies showed highly significant correlations (r = 0.974-0.984). Total precipitation during the experimental period was 974 mm and estimated interception loss was 19.2, 13.6 and 23% for the pine, oak and pine-oak canopies, respectively. Stemflow did not occur following rainfall events of less than 4 mm and, in all canopies, stemflow represented a minimal proportion of gross precipitation (0.60, 0.50 and 0.03% for pine, oak and pine-oak, respectively). Throughfall pH in pine (6.2), oak (6.3) and pine-oak (6.3) canopies was significantly more acidic than gross precipitation (6.6). Stemflow pH ranged from 3.7 (pine) to 6.0 (oak). The pine-oak canopy registered the highest throughfall and stemflow electrical conductivities, 104 and 188 microS cm(-1), respectively. Net nutrient leaching of K, Mg, Na, Fe, Mn and Zn was significantly higher from the pine-oak canopy than from the pure pine and oak canopies. Mean depositions of Ca and Cu in throughfall behaved similarly among the three types of canopies. A greater proportion of Zn in gross precipitation was absorbed by the oak canopy than by the pine and pine-oak canopies. Enrichment factors beneath the pine-oak canopy relative to gross precipitation varied from 1.2 to 3.2 for macro-nutrients (Ca, K, Mg and Na) and from 1.4 to 3.1 for micro-nutrients (Cu, Fe, Mn and Zn). Stemflow depositions of Ca, K, Mg and Cu were higher in the pine-oak canopy, whereas stemflow depositions of Na, Fe, Mn and Zn were higher in the pine canopy.

Mexico↗

PubMed2001

Leaf area distribution and radiative transfer in open-canopy forests: implications for mass and energy exchange.

Leaf area and its spatial distribution are key canopy parameters needed to model the radiation regime within a forest and to compute the mass and energy exchange between a forest and the atmosphere. A much larger proportion of available net radiation is received at the forest floor in open-canopy forests than in closed-canopy forests. The proportion of ecosystem water vapor exchange (lambda E) and sensible heat exchange from the forest floor is therefore expected to be larger in open-canopy forests than in closed-canopy forests. We used a combination of optical and canopy geometry measurements, and robust one- and three-dimensional models to evaluate the influence of canopy architecture and radiative transfer on estimates of carbon, water and energy exchange of a ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forest. Three-dimensional model simulations showed that the average probability of diffuse and direct radiation transmittance to the forest floor was greater than if a random distribution of foliage had been assumed. Direct and diffuse radiation transmittance to the forest floor was 28 and 39%, respectively, in the three-dimensional model simulations versus 23 and 31%, respectively, in the one-dimensional model simulations. The assumption of randomly distributed foliage versus inclusion of clumping factors in a one-dimensional, multi-layer biosphere-atmosphere gas exchange model (CANVEG) had the greatest effect on simulated annual net ecosystem exchange (NEE) and soil evaporation. Assuming random distribution, NEE was 41% lower, net photosynthesis 3% lower, total lambda E 10% lower, and soil evaporation 40% lower. The same comparisons at LAI 5 showed a similar effect on annual NEE estimates (37%) and lambda E (12%), but a much larger effect on net photosynthesis (20%), suggesting that, at low LAI, canopies are mostly sunlit, so that redistribution of light has little effect on net photosynthesis, whereas the effect on net photosynthesis is much greater at high LAIs.

Biomass↗

PubMed2001

Shoot structure and photosynthetic efficiency along the light gradient in a Scots pine canopy.

We examined the effects of structural and physiological acclimation on the photosynthetic efficiency of Scots pine (Pinus sylvestris L.) shoots. We estimated daily light interception (DLI) and photosynthesis (DPHOT) of a number of sample shoots situated at different positions in the canopy. Photosynthetic efficiency (epsilon) was defined as the ratio of DPHOT to the potential daily light interception (DLI(ref)) defined as the photosynthetically active radiation (PAR) intercepted per unit area of a sphere at the shoot location. To calculate DLI(ref), DLI and DPHOT, the radiation field surrounding a shoot in the canopy was first modeled using simulated directional distributions of incoming PAR on a clear and an overcast day, and estimates of canopy gap fraction in different directions provided by hemispherical photographs. A model of shoot geometry and measured data on shoot structure and photosynthetic parameters were used to simulate the distribution of PAR irradiance on the needle surface area of the shoot. Photosynthetic efficiency (epsilon) was separated into light-interception efficiency (epsilon(I) = DLI/DLI(ref)) and conversion efficiency (epsilon(PHOT) = DPHOT/DLI). This allowed us to quantify separately the effect of structural acclimation on the efficiency of photosynthetic light capture (epsilon(l)), and the effect of physiological acclimation on conversion efficiency (epsilon(PHOT)). The value of epsilon increased from the top to the bottom of the canopy. The increase was largely explained by structural acclimation (higher epsilon(I)) of the shade shoots. The value of epsilon(PHOT) of shade foliage was similar to that of sun foliage. Given these efficiencies, the clear-day value of DPHOT for a sun shoot transferred to shade was only half that of a shade shoot at its original position. The method presented here provides a tool for quantitatively estimating the role of acclimation in total canopy photosynthesis.

Light↗

PubMed2001

Tree stem diameter variations and transpiration in Scots pine: an analysis using a dynamic sap flow model.

A dynamic model for simulating water flow in a Scots pine (Pinus sylvestris L.) tree was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration, together with the elasticity of wood tissue, causes variations in the diameter of a tree stem and branches. The change in xylem diameter can be linked to water tension in accordance with Hookeâ s law. The model was tested against field measurements of the diurnal xylem diameter change at different heights in a 37-year-old Scots pine at Hyytiälä, southern Finland (61 degrees 51' N, 24 degrees 17' E, 181 m a.s.l.). Shoot transpiration and soil water potential were input data for the model. The biomechanical and hydraulic properties of wood and fine root hydraulic conductance were estimated from simulated and measured stem diameter changes during the course of 1 day. The estimated parameters attained values similar to literature values. The ratios of estimated parameters to literature values ranged from 0.5 to 0.9. The model predictions (stem diameters at several heights) were in close agreement with the measurements for a period of 6 days. The time lag between changes in transpiration rate and in sap flow rate at the base of the tree was about half an hour. The analysis showed that 40% of the resistance between the soil and the top of the tree was located in the rhizosphere. Modeling the water tension gradient and consequent woody diameter changes offer a convenient means of studying the link between wood hydraulic conductivity and control of transpiration.

Models, Biological↗

PubMed2001

The ratio of NPP to GPP: evidence of change over the course of stand development.

Using Scots pine (Pinus sylvestris L.) in Fenno-Scandia as a case study, we investigate whether net primary production (NPP) and maintenance respiration are constant fractions of gross primary production (GPP) as even-aged mono-specific stands progress from initiation to old age. A model of the ratio of NPP to GPP is developed based on (1) the classical model of respiration, which divides total respiration into construction and maintenance components, and (2) a process-based model, which derives respiration from processes including construction, nitrate uptake and reduction, ion uptake, phloem loading and maintenance. Published estimates of specific respiration and production rates, and some recent measurements of components of dry matter in stands of different ages, are used to quantify the two approaches over the course of stand development in an average environment. Both approaches give similar results, showing a decrease in the NPP/GPP ratio with increasing tree height. In addition, we show that stand-growth models fitted under three different sets of assumptions-(i) annual specific rates of maintenance respiration of sapwood (mW) and photosynthesis (sC) are constant; (ii) m(W) is constant, but sC decreases with increasing tree height; and (iii) total maintenance respiration is a constant fraction of GPP and s(C) decreases with increasing tree height-can lead to nearly identical model projections that agree with empirical observations of NPP and stand-growth variables. Remeasurements of GPP and respiration over time in chronosequences of stands may be needed to discern which set of assumptions is correct. Total (construction + maintenance) sapwood respiration per unit mass of sapwood (kg C (kg C year)-1) decreased with increasing stand age, sapwood stock, and average tree height under all three assumptions. However, total sapwood respiration (kg C (ha year)-1) increased over the course of stand development under (i) and (ii), contributing to a downward trend in the time course of the NPP/GPP ratio after closure. A moderate decrease in mW with increasing tree height or sapwood cross-sectional area had little effect on the downward trend. On the basis of this evidence, we argue that a significant decline in the NPP/GPP ratio with tree size or age seems highly probable, although the decline may appear insignificant over some segments of stand development. We also argue that, because stand-growth models can give correct answers for the wrong reasons, statistical calibration of such models should be avoided whenever possible; instead, values of physiological parameters should come from measurements of the physiological processes themselves.

Mathematics↗

PubMed2001

Nitrogen availability modifies the ozone responses of Scots pine seedlings exposed in an open-field system.

Three-year-old Scots pine (Pinus sylvestris L.) seedlings were exposed to either ambient or elevated (1.5-1.6 x ambient) ozone concentration ([O3]) for three growing seasons in an open-field fumigation facility where they were irrigated during the growing season with a nutrient solution providing nitrogen (N) at 70 (LN treatment), 100 (control) or 150% (HN treatment) of the optimum supply rate. Treatment effects were most evident during the third year of exposure, when the ambient [O3] + HN treatment enhanced whole-plant biomass, root/shoot dry weight ratio, needle pigment concentrations and the number of chloroplast plastoglobuli in the mesophyll cells in current-year (C) needles, whereas it reduced starch accumulation in C needles and abscission of 2-year-old (C+2) needles. In the control fertilization, 3 years of exposure to elevated [O3] decreased stem-base diameter and increased K concentration and electron density of chloroplast stroma in C needles. Plants in the HN treatment exposed for 3 years to elevated [O3] had significantly lower heights, current-year main shoot length and root/shoot dry mass ratio than control plants, and increased abscission of C+2 needles. In contrast, O3-induced changes in the ultrastructure of mesophyll cells were most evident in seedlings grown for 3 years in the LN treatment. We conclude that, in Scots pine, a relatively O3-tolerant species, chronic O3 exposure leads to cumulative growth reduction, increased needle abscission and changes in carbon allocation that are strongly influenced by plant N availability.

Chloroplasts↗

PubMed2001

Effects of elevated carbon dioxide concentration and temperature on needle growth, respiration and carbohydrate status in field-grown Scots pines during the needle expansion period.

We determined effects of long-term elevation of carbon dioxide concentration ([CO2]) and temperature on growth, respiration and carbohydrate concentration in needles of field-grown Scots pine (Pinus sylvestris L.) trees during the needle expansion period. Sixteen 20-year-old Scots pine trees were individually enclosed in closed-top, environmentally controlled chambers for 4 years in one of four environments: ambient conditions (CON); elevated [CO2] (EC); elevated temperature (ET); and a combination of both (EC + ET). Needle growth, carbohydrate concentration and dark respiration were measured at 3-day intervals throughout the needle expansion period. Dark respiration was partitioned into growth and maintenance components by regressing specific respiration rate against specific growth rate. In all treatments, growth, carbohydrate concentration and daily dark respiration rates of needles followed a similar seasonal pattern throughout the needle expansion period. Treatments EC, ET and EC + ET increased individual needle area and dry weight compared with the CON treatment. Carbohydrate concentrations in needles were increased by EC, but reduced by ET and EC + ET. Daily respiration rates increased slightly in the early stage of needle expansion and decreased gradually in the late stage when needles were exposed to EC, but increased consistently throughout the growing period when needles were exposed to ET or EC + ET. Partitioning of respiration into its two functional components showed that the growth respiration coefficient was unaffected by the treatments, whereas maintenance respiration was reduced by EC but increased by ET and EC + ET. Maintenance respiration was more sensitive to elevated temperature than growth respiration. We conclude that the difference in respiration rates between expanding and expanded needles should be taken into account when estimating the respiratory responses of needles to elevated [CO2] and temperature.

Carbohydrates↗

PubMed2001

Growth of conifer seedlings on organic and inorganic nitrogen sources.

Effects of organic and inorganic nitrogen sources on growth and mineral nutrient concentrations of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings were compared in a 100-day experiment in a greenhouse. Seedlings were grown in pots containing peat. Nutrient solutions differing in ammonium, nitrate, arginine and glycine composition were supplied to the seedlings at three nitrogen (N) concentrations: 1, 3 and 10 mM. We used dual (13C, 15N) and single (15N) isotopic labeling to determine the uptake of organic and inorganic N at the end of the experiment. Seedling dry weights and mineral nutrient concentrations of the needles showed that both conifer species were able to grow well and maintain nutrient balance on all investigated N forms except for the ammonium-dominated nutrient mixtures at the 10 mM N concentration. In Scots pine, no significant differences in dry weights were found between seedlings grown on the amino acids and seedlings grown on a commercial fertilizer containing 61.5% NO(3-)-N and 38.5% NH(4+)-N. Isotopic labeling of seedlings indicated that uptake rates of arginine-N, glycine-N and NH(4+)-N were similar, and 7-8 times greater than uptake rates for NO(3-)-N in both species. In Scots pine seedlings, 100% of arginine-N, and at least 67% of glycine-N was derived from the uptake of intact amino acids through seedling roots or mycorrhizae. Corresponding figures for Norway spruce were 83% for arginine and 96% for glycine. The gas chromatography-mass spectrometry analyses confirmed the presence of intact labeled molecules of both arginine and glycine in seedlings. We conclude that arginine and glycine are comparable to inorganic N as N sources for growth of conifer seedlings.

Amino Acids↗

PubMed2001

Fine root biomass and production in Scots pine stands in relation to stand age.

We determined fine root biomass and production of 15-, 35- and 100-year-old Scots pine (Pinus sylvestris L.) stands during three growing seasons. Fine roots were sampled by the soil core method. Mean (+/- SE) annual fine root biomass of Scots pine in the 15-, 35- and 100-year-old stands was 220 +/- 25, 357 +/- 21 and 259 +/- 26 g m(-2), respectively. Fine root biomass of the understory vegetation was 159 +/- 54 g m(-2), 244 +/- 30 and 408 +/- 81 g m(-2), and fine root necromass was 500 +/- 112, 1,047 +/- 452 and 1,895 +/- 607 g m(-2) in the sapling, pole stage and mature stands, respectively. Both understory and Scots pine fine root production increased with stand age. Mean annual Scots pine fine root production was 165 +/- 131, 775 +/- 339 and 860 +/- 348 g m(-2) year(-1) in the sapling, pole stage and mature stand, respectively. The respective mean annual production of all fine roots (Scots pine and understory) was 181 +/- 129, 1,039 +/- 497 and 1,360 +/- 869 g m(-2) year(-1). The Scots pine and understory fine root biomass, necromass and production varied in relation to stand age, although the variation was not statistically significant.

Biomass↗

PubMed2001

Changes in physiological attributes of ponderosa pine from seedling to mature tree.

Plant physiological models are generally parameterized from many different sources of data, including chamber experiments and plantations, from seedlings to mature trees. We obtained a comprehensive data set for a natural stand of ponderosa pine (Pinus ponderosa Laws.) and used these data to parameterize the physiologically based model, TREGRO. Representative trees of each of five tree age classes were selected based on population means of morphological, physiological, and nearest neighbor attributes. Differences in key physiological attributes (gas exchange, needle chemistry, elongation growth, needle retention) among the tree age classes were tested. Whole-tree biomass and allocation were determined for seedlings, saplings, and pole-sized trees. Seasonal maxima and minima of gas exchange were similar across all tree age classes. Seasonal minima and a shift to more efficient water use were reached one month earlier in seedlings than in older trees because of decreased soil water availability in the rooting zone of the seedlings. However, carbon isotopic discrimination of needle cellulose indicated increased water-use efficiency with increasing tree age. Seedlings had the lowest needle and branch elongation biomass growth. The amount of needle elongation growth was highest for mature trees and amount of branch elongation growth was highest for saplings. Seedlings had the highest biomass allocation to roots, saplings had the highest allocation to foliage, and pole-sized trees had the highest allocation to woody tissues. Seedlings differed significantly from pole-sized and older trees in most of the physiological traits tested. Predicted changes in biomass with tree age, simulated with the model TREGRO, closely matched those of trees in a natural stand to 30 years of age.

Biomass↗

PubMed2001

Use of a simulation model and ecosystem flux data to examine carbon-water interactions in ponderosa pine.

Drought stress plays an important role in determining both the structure and function of forest ecosystems, because of the close association between the carbon (C) and hydrological cycles. We used a detailed model of the soil-plant-atmosphere continuum to investigate the links between carbon uptake and the hydrological cycle in a mature, open stand of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) at the Metolius river in eastern Oregon over a 2-year period (1996-1997). The model was parameterized from local measurements of vegetation structure, soil properties and meteorology, and tested against independent measurements of ecosystem latent energy (LE) and carbon fluxes and soil water content. Although the 2 years had very different precipitation regimes, annual uptake of C and total transpiration were similar in both years, according to both direct observation and simulations. There were important differences in ratios of evaporation to transpiration, and in the patterns of water abstraction from the soil profile, depending on the frequency of summer storms. Simulations showed that, during periods of maximum water limitation in late summer, plants maintained a remarkably constant evapotranspirative flux because of deep rooting, whereas changes in rates of C accumulation were determined by interactions between atmospheric vapor pressure deficit and stomatal conductance. Sensitivity analyses with the model suggest a highly conservative allocation strategy in the vegetation, focused belowground on accessing a soil volume large enough to buffer summer droughts, and optimized to account for interannual variability in precipitation. The model suggests that increased allocation to leaf area would greatly increase productivity, but with the associated risk of greater soil water depletion and drought stress in some years. By constructing sparse canopies and deep rooting systems, these stands balance reduced productivity in the short term with risk avoidance over the long term.

Carbon↗