Needle Dry Mass Research Articles

Двухротационное выращивание контейнерных сеянцев Pinus sylvestris L. в условиях короткого вегетационного периода в высоких широтах

The quality of forest crops significantly depends on the characteristics of the planting stock. To obtain high-quality conifer seedlings, the process of container cultivation is used and optimized and a double-cropping mode is introduced. The aim of this study has been to conduct a comparative analysis of one-year-old containerized seedlings of Pinus sylvestris L. according to morphometric parameters under a double-cropping regime under short growing season conditions at high latitudes. The experiment has been carried out in a forest nursery in southern Karelia, Russia. The duration of the first rotation (1rot) has been 146 days, the second one (2rot) – 91 days, the control one (0rot) – 132 days. The following parameters of seedlings have been determined: seedling height (SH, cm), root length (cm), bud length (mm), root collar diameter (RCD, mm), tree dry mass (TDM, g), shoot dry mass (SDM, g), root dry mass (RDM, g) and needle dry mass. The integral quality indices have been assessed, such as: shoot : root dry mass ratio (SRR) = SDM/RDM, sturdiness quotient (SQ) = SH(cm)/RCD(mm) and Dickson Quality Index (DQI) = TDM/(SH + SRR). The lowest values of seedling dry mass have been revealed in the 2rot variant. For all variants, the difference between the mean SQ and DQI values has been statistically significant at the p < 0.05 level. SRR was the lowest in the 1rot seedlings. The high correlation coefficients between the TDM and RCD for all variants confirm the high significance of the latter index. The results indicate the need to adjust the time regime and use additional agricultural practices to obtain high-quality planting stock.

Does leaf mass per area (LMA) discriminate natural pine populations of different origins?

Tree provenance trials are believed to be a valuable tool for assessing the adaptive potential of a population to a changing environment and ultimately for predicting the populations that are best adapted to global warming. Here, the phenotypic plasticity of morphometric traits of needles and lateral shoots of pines growing in a provenance plot in central Poland was examined to assess the inter- and intra-population variability. No significant differences were found in the measured and counted morphometric features, i.e., needle length (NL), cumulative needles length (CNL), thickness (ST), volume (SV) and shoot density (SD), number of needles per 5 cm fragment of shoot (NN), dry weight of needles (NDW) and shoot (SDW), thickness of bark (BT) and wood (WT), pith diameter (PD), and needle dry mass per area (LMA) among three pine populations while accounting for their region of origin (inter-population variability). In terms of the above-mentioned features, individual populations differed significantly from each other, except for NN and ST. We also noticed a positive, significant relationship between LMA and ST in all studied populations and based on Euclidean distances of measurable or counted traits, three population groups were identified. We concluded that LMA, which is commonly used to quantify leaf structure, is helpful in differentiating intra-population variability.

Effects of mild drought on the morphology of sun and shade needles in 20-year-old Norway spruce trees

Several studies have looked at how individual environmental factors influence needle morphology in conifer trees, but interacting effects between drought and canopy position have received little attention. In this study, we characterized morphological responses to experimentally induced drought stress in sun exposed and shaded current-year Norway spruce needles. In the drought plot trees were suffering mild drought stress, with an average soil water potential at 50 cm depth of -0.4 MPa. In general, morphological needle traits had greater values in sun needles in the upper canopy than in shaded needles in the lower canopy. Needle morphology 15 months after the onset of drought was determined by canopy position, as only sun needle morphology was affected by drought. Thus, canopy position was a stronger morphogenic factor determining needle structure than was water availability. The largest influence of mild drought was observed for needle length, projected needle area and total needle area, which all were reduced by ~27% relative to control trees. Needle thickness and needle width showed contrasting sensitivity to drought, as drought only affected needle thickness (10% reduction). Needle dry mass, leaf mass per area and needle density were not affected 15 months after the onset of mild drought. Our results highlight the importance of considering canopy position as well as water availability when comparing needle structure or function between conifer species. More knowledge about how different canopy parts of Norway spruce adapt to drought is important to understand forest productivity under changing environmental conditions.

Sustained growth suppression in forest-floor seedlings of Sakhalin fir associated with previous-year springtime photoinhibition after a winter cutting of canopy trees

Springtime photoinhibition in 1-year-old shoots, exacerbated by a clear-cutting during winter, was recently found to reduce the current-year shoot growth of forest-floor seedlings of Sakhalin fir (Abies sachalinensis). In the present study, we conducted a follow-up survey in the following year in these seedlings, which were subjected to different cutting rates of canopy trees (100: clear-cutting, 66, 50, 30, and 0%: control) in the previous spring. No photoinhibition (Fv/Fm ≈ 0.8) was observed in the 1-year-old needles, developed after the cuttings in spring and summer, across the sites with different cutting rates. The ratio of current-shoot dry mass to 1-year-old needle dry mass (Shootcurrent/Needle1-year) measured in early summer, as a measure of photosynthetic carbon gain in the 1-year-old needles, showed an increasing trend with increasing growth irradiance when excluding the data of clear-cutting sites, which had a large variation. The variation in Shootcurrent/Needle1-year within the clear-cutting sites can be explained by the remaining amount of 2-year-old needles, which suggests that defoliation of 2-year-old needles damaged by photoinhibition in the previous spring may associate with a sustained suppression in the growth of current shoot even in the second year.

Long-term effects of stem girdling on needle structure in Scots pine

Abstract: Stem girdling is the process of completely removing a strip of cork and phloem tissue. Phloem is the living tissue which serves as the main long-distance pathway for transporting carbohydrates produced during photosynthesis to all parts of the plant where needed, from source leaves to sinks. Stem girdling has been used to study several functional aspects of phloem and their direct impacts on tree growth. Although both photosynthesis and transpiration processes take place in needles, no studies exist which investigate the effect of source-sink disturbance on needle structure. In this study, we evaluated changes in needle morphology and anatomy in current-year Scots pine needles 227 and 411 days after girdling (DAG). Although the studied needle parameters recorded 227 DAG were from 2 to 20% higher than the same parameters in control needles, the differences were not significant. On the other hand, needles 411 DAG were thinner, with decreased cross-sectional areas, phloem areas, vascular cylinder areas, needle dry mass, needle density, and needle flatness when compared to control needles. Marked variations in needle growth were observed 411 DAG, with a smaller number of correlations among almost all studied needle parameters in needles 411 DAG when compared to control needles or needles 227 DAG. Structural development determining needle flatness, needle density, and leaf mass per area (LMA) appeared to have driving factors that were independent of the other studied needle parameters, as correlations with other parameters were not significant in any treatment. The changes in overall needle structure observed after long-term stem girdling provide new insights into the processes that occur as a result of source-sink disturbances. This type of data could be helpful, for example, in studies specifically focused on phloem transport, tree carbon relationships, or investigations modeling gas exchange. Our study might also support gene expression studies, which could provide further knowledge about the regulatory mechanisms that determine needle size and structural form.

Combined effects of irrigation amount and nitrogen load on growth and needle biochemical traits of Cryptomeria japonica seedlings

Growth of C. japonica under highly irrigated and N-loaded soil is noticeable because of N-induced increase of needle mass and alleviation of high irrigation-induced reduction in photosynthesis. To clarify the combined effects of change in precipitation amount and increasing nitrogen load on Japanese forest trees, 2-year-old seedlings of Cryptomeria japonica were treated with combinations of four irrigation levels (80, 100, 120, or 140% of annual precipitation) and three nitrogen loads (15, 50, or 100 kg ha−1 year−1). The 100% of annual precipitation corresponded to 1520 mm year−1 which was the average annual precipitation in the habitats of C. japonica in Japan. High irrigation amount significantly enhanced the whole-plant dry mass of the seedlings. The N load significantly enhanced the extent of high irrigation-induced increase in needle dry mass. As a result, the irrigation-induced increase in the whole-plant dry mass was greater in the treatment with the highest N. However, increase in needle dry mass induced by high irrigation enhanced plant water consumption and caused dehydration and oxidative damage in needles, thus resulting in reduced net photosynthetic rate. The high irrigation-induced reduction in net photosynthetic rate was alleviated by N load. This alleviation was not caused by N load-induced changes in antioxidative capacity but by a N load-induced increase in ribulose 1,5-bisphosphate carboxylase/oxygenase activity. These results indicate that an increase in the whole-plant dry mass of C. japonica seedlings grown in highly irrigated and N-loaded soil was attributed to N load-induced enhancement of high irrigation-induced increase in needle dry mass and alleviation of high irrigation-induced reduction in net photosynthetic rate.

Seasonal variations in red pine (Pinus resinosa) and jack pine (Pinus banksiana) foliar physio-chemistry and their potential influence on stand-scale wildland fire behavior

The ‘Spring Dip’ in conifer live foliar moisture content (LFMC) has been well documented but the actual drivers of these variations have not been fully investigated. Here we span this knowledge gap by measuring LFMC, foliar chemistry, foliar density and foliar flammability on new and old foliage for an entire year from both Pinus resinosa (red pine) and Pinus banksiana (jack pine) at a site in Central Wisconsin. We found that needle dry mass increased by up to 70% in just three weeks and these increases were manifested as strong seasonal variations in foliar moisture content and foliar density. These needle dry mass changes were driven by an accumulation of starch in old foliage, likely resulting from springtime photosynthesis onset, and also by accumulations of sugar and crude fat in new needles as they fully matured. Foliar starch, sugar and crude fat content accounted for 84% of the variation in foliar density across both species. Flammability differences were also strongly related to changes in foliar density, where density accounted for 39% and 25% of the variations in foliar time-to-ignition of jack pine and red pine respectively. Finally, we use the computational fluid dynamics-based wildland fire model FIRETEC to examine how these foliar physio-chemical changes may influence wildland fire behavior. Under the lowest canopy density and windspeed, simulated fires in dormant condition stands did not propagate as crown fires while spring dip stands successfully spread as crown fires as a result of the higher potential energy content of the canopy. Simulated wildland fire spread rates increased by as much as 63%, nominal fireline width increased by as much as 89% and active fire area more than doubled relative to dormant season fuel conditions and the most significant changes occurred in areas with low canopy cover and low within-tree bulk density. Our results challenge the assumption that live conifer foliage flammability is limited only by its water content; this study suggests a new theory and an expanded view of the factors that dominate live fuel flammability and that subsequently influence larger scale wildland fire behavior.

Growth and development of Norway spruce and Scots pine seedlings under different light spectra

The goal of this study was to examine how different light spectra affect growth and development of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) seedlings. The seedlings were grown in a darkened greenhouse under four light spectra consisting of different proportions of blue (B, 400–500nm), red (R, 600–700nm), and far-red (FR, 700–800nm) light, with high-pressure sodium lamps (HPS) serving as controls. The light treatments (250μmolm−2s−1 photosynthetically active radiation) were provided using light-emitting diodes (LEDs), and the treatments included the following: (1) 25% B+70% R+5% FR; (2) 25% B+75% R; (3) 55% B+45% R; and (4) HPS: 6% B+44% green (500–600nm)+41% R+9% FR. We measured germination, growth, morphology, gas exchange, N concentration in needles and stem, and terminal bud set of the seedlings after a 4-month growth period. Our results showed that the physiological and morphological responses of shade-intolerant Scots pine seedlings to light quality were more pronounced than those of the shade-tolerant Norway spruce seedlings. Growth under the FR-containing light treatments produced tall seedlings with larger needle dry mass. Removal of FR and addition of B in the growth light reduced the height growth, and it increased the sturdiness and altered the branching patterns in the seedlings. Growth under the treatment containing about 25% B and 75% R resulted in the highest root-to-shoot ratios in both species and highest root growth capacity and water-use efficiency in Scots pine. Timing of bud set was independent of growth light spectra. Our results show that it is possible to improve the seedling attributes that are contributing to good performance potential by using different wavelength combinations in growth light, particularly in Scots pine. However, the potential after-effects of growth under an incomplete light spectrum on seedling performance after planting to forest regeneration site are still unknown.

Spectroscopic analysis of seasonal changes in live fuel moisture content and leaf dry mass

Live fuel moisture content (LFMC), the ratio of water mass to dry mass contained in live plant material, is an important fuel property for determining fire danger and for modeling fire behavior. Remote sensing estimation of LFMC often relies on an assumption of changing water and stable dry mass over time. Fundamental understanding of seasonal variation in plant water and dry mass is needed to explain the spectral expression of LFMC changes over time. We conducted a five-month experiment to continuously measure field LFMC samples, biochemical components of dry matter, and leaf spectroscopic data for two species common in the western U.S., lodgepole pine (Pinus contorta Douglas ex Loudon) and big sagebrush (Artemisia tridentata Nutt). Our results showed that new lodgepole pine needles initially had higher LFMC and a smaller proportion of dry mass, but differences between new and old needles converged as the new needles matured. New needle dry mass had strong temporal trends, and dry mass explained more variation in LFMC than water in both new and old needles. Sagebrush leaves exhibited decreasing trends in LFMC, but water and dry mass comparably contributed to LFMC seasonal variation. Spectroscopic analysis using partial least squares regression (PLSR) showed good modeling accuracy for LFMC temporal variation in new needles (R2=0.94, RMSE=5.84%), old needles (R2=0.72, RMSE=3.51%), and sagebrush (R2=0.91, RMSE=21.03%). Spectral variation in response to changing LFMC and dry mass was difficult to isolate from broader spectral trends due to chlorophyll absorption, leaf structure, water absorption, and co-varied biochemical components. Our results stress cautious spectral interpretation and wavelength selection for LFMC estimation in some species (e.g. lodgepole pine), since temporal changes in spectra may dominantly reflect temporal variation in dry mass, pigments, and/or structure rather than water content. Since new needles should have stronger spectral expression at the canopy scale, differing temporal trends in new and old lodgepole pine needles provides an additional complicating factor for remote monitoring of LFMC.

Stem biomass, C and N partitioning and growth efficiency of mature pedigreed black spruce on both a wet and a dry site

Worldwide, efforts to manage atmospheric CO2 are being explored both by reducing emissions and by sequestering more carbon (C). Stem biomass, C, and nitrogen (N) parameters were measured in plots of first-generation (F1), 32-year-old black spruce (Picea mariana (Mill.) B.S.P.) from four full-sib families studied previously for drought tolerance and differential productivity on both a dry and a wet site in central Ontario, Canada. The wet site had greater stem wood N and bark N concentrations than the dry site. Site differences in N were most likely driven by soil moisture stress impairing N uptake, as soil N was equal at both sites. Drought-tolerant (faster growing) families had lower wood density than drought-intolerant families on the wet site but there were no wood density differences between families on the dry site. Allometric analysis showed greater total stem dry mass per unit total belowground dry mass for drought-tolerant than intolerant families and for wet than dry sites, indicating a differential allocation of photosynthate dependent on both genotype and environment. Allometric analysis also showed greater total stem dry mass per unit total needle dry mass (growth efficiency) for drought-tolerant than intolerant families and for the wet than the dry site. This indicates greater productivity is a result of greater growth efficiency caused by greater net photosynthesis (shown previously) and greater partitioning of biomass to stem relative to total roots. The variation in physiological processes documented in our previous investigations and the biomass allocation variation shown here most probably underlie the increase in stem productivity from both black spruce tree improvement programs and increased water availability.

Needle parameter variation of mature black spruce displaying genetic × soil moisture interaction in growth

To examine soil moisture stress, light, and genetic effects on individual needle parameters and investigate total needle contribution to productivity, indi- vidual and total needle parameter variation were quantified in 32-year-old black spruce from five crown positions from four full-sib families studied previously for drought toler- ance and differential productivity on a dry and a wet site. The wet site had greater average needle length (NL), spe- cific needle area (SNA), and needle N concentration (NN) than the dry site. Site differences in NN were most likely driven by soil moisture stress impairing N uptake as soil N was equal at both sites. Drought-tolerant families had greater average needle area (NA), but also greater needle dry mass (NDM), than drought-intolerant families. From the top to bottom crown position, needle parameters showing a linear or near linear increase were NL, SNA, and NN; needle parameters showing a linear decrease were NW, NA, NDM and C:N ratio. For total tree needle area, the wet and dry sites had 18.7 and 16.0 m 2 tree -1 (leaf area index (LAI) 5.6 and 4.8), respectively, whereas total needle C mass was not significantly different between sites. Drought-tolerant and intolerant families had a total NA of 18.8 and16.0 m 2 tree -1 , respectively. However, the greater total NA of drought-tolerant families was driven by one family. Thus, the role of total foliage area at these high LAI values in genetic differences in productivity is inconsistent and most likely low. Therefore, based on a previous 3-year campaign of gas exchange measurements and confirmed independently with carbon isotope analyses, the rate of net photosynthesis is a more important component of site and genetic growth differential in mature black spruce than total needle area.

Effects of Fertilizer on Growth, Carbon and Nitrogen Responses of Foliage in a Red Pine Stand

This study was to examine growth, carbon and nitrogen responses in foliage following forest fertilization in a red pine stand. Two types of fertilizer (N:P:K=113:150:37 kg <TEX>$ha^{-1}$</TEX>; P:K=150:37 kg <TEX>$ha^{-1}$</TEX>) were applied on late April 2011. Growth, carbon and nitrogen responses of foliage were monitored 3 times (July, September, November) after fertilization. Morphological growth responses (dry mass, leaf area, specific leaf area) with foliage age were not significantly (P > 0.05) affected by fertilizer application, while needle dry mass and leaf area of July were significantly lower in current-year-old than in one-year-old or two-year-old needles of September or November. Carbon concentration and content in foliage was little affected by fertilizer application compared with sampling month or needle age, while the NPK fertilizer produced high nitrogen concentration and content of foliage. The results indicate that nitrogen concentration and content in foliage may serve as an indicator of the nitrogen status by fertilization in a red pine stand.

Growth and Photosynthetic Responses of Cuttings of a Hybrid Larch (Larix gmelinii var. japonica x L. kaempferi) to Elevated Ozone and/or Carbon Dioxide

We studied the effects of elevated ozone ([<TEX>$O_3$</TEX>]) and <TEX>$CO_2$</TEX> concentrations ([<TEX>$CO_2$</TEX>]) on the growth and photosynthesis of the hybrid larch <TEX>$F_1(F_1)$</TEX> and on its parents (the Dahurian larch and Japanese larch). <TEX>$F_1$</TEX> is a promising species for timber production in northeast Asia. Seedlings of the three species were grown in 16 open top chambers and were exposed to two levels of <TEX>$O_3$</TEX> (<10 ppb and 60 ppb for 7 h per day) in combination with two levels of <TEX>$CO_2$</TEX> (ambient and 600 ppm for daytime) over an entire growing season. Ozone reduced the growth as measured by height and diameter, and reduced the needle dry mass and net photosynthetic rate of <TEX>$F_1$</TEX>, but had almost no effect on the Dahurian larch or Japanese larch. There was a significant increase in whole-plant dry mass induced by elevated [<TEX>$CO_2$</TEX>] in <TEX>$F_1$</TEX> but not in the other two species. Photosynthetic acclimation to elevated [<TEX>$CO_2$</TEX>] was observed in all species. The net photosynthetic rate measured at the growing [<TEX>$CO_2$</TEX>] (i.e. 380 ppm for ambient treatment and 600 ppm for elevated <TEX>$CO_2$</TEX> treatment) was nevertheless greater in the seedlings of all species grown at elevated [<TEX>$CO_2$</TEX>]. The high [<TEX>$CO_2$</TEX>] partly compensated for the reduction of stem diameter growth of <TEX>$F_1$</TEX> at high [<TEX>$O_3$</TEX>]; no similar trend was found in the other growth and photosynthetic parameters, or in the other species.

Effects of ozone and/or nitrogen load on the growth of Larix kaempferi, Pinus densiflora and Cryptomeria japonica seedlings

To obtain basic information on the critical levels of O3, for the protection of Japanese coniferous forests, the growth responses of Larix kaempferi, Pinus densiflora and Cryptomeria japonica seedlings to 03 under different nitrogen (N) loads were investigated. The seedlings were grown in 12 experimental treatments, which were comprised of four gas treatments (charcoal-filtered air and three levels of 03 at 1.0, 1.5 and 2.0 times ambient concentration) in combination with three N treatments (0, 20 and 50 kg ha-1 year 1), during the two growing seasons. Although no significant interaction between O3 and N load was detected for the growth of P. densiflora and C. japonica seedlings, significant interaction between O3 and N load for the growth of L. kaempferi seedlings was found at the end of the second growing season. The N load reduced the sensitivity of growth of L. kaempferi seedlings to O3. Critical levels of O3 expressed as AOT40 for one growing season from April to September, corresponding to a 10% reduction in the whole-plant dry mass increment, were evaluated to be 28 (NO), 29 (N 20) and 53 (N 50) iimol mol 1 h in L. kaempferi, 38 ƒEmol mol- 1 h in P. densiflora and 111 umol mot- 1 h in C. japonica. In the three tree species, a high correlation was found between the sensitivity to O3 of the whole- plant dry mass increment and that of the total net photosynthetic rate (Atotal), expressed as the product of needle dry mass and net photosynthetic rate in the summer of the second growing season. It was concluded that N deposition must be taken into account in the evaluation of the critical level of O3 for the protection of L. kaempferi forests. The Aotal can be used as an indexical plant factor for estimating the sensitivity to O3 of Japanese coniferous forest tree species under different N loads.

Short-term responses of soil chemistry, needle macronutrients and tree growth to clinker dust and fertiliser in a stand of Scots pine

Waste management of clinker dust by spreading it on forest soil was studied in a 25-year-old Scots pine stand on acidic sandy soil. Clinker dust (0.5 kg m⁻²), fertiliser (N, P, K, Mg, 0.05 kg m⁻²; N 190 kg ha⁻¹) and untreated soil were applied on 120-m² plots in four replicates. The fertiliser was included to confirm the nutrient limitation in the stand. Clinker dust increased the soil pH by 1.2 units relative to the pH of 4.6 in the untreated soil by the second year. Soil K and Mg concentrations were larger in the dust and fertiliser treatments. Nutrient diagnostics indicated that needles of untreated trees were deficient in N and K. Fertiliser treatment indicated that the growth of trees was limited by N, since the fertiliser tended to increase needle K, N, N/P, needle dry mass and diameters of stem and shoots. By an auxiliary dataset, no effects of the dust and fertiliser on possible excess of the micronutrient Mn were observed. Clinker dust increased needle K concentration, but due to the N limitation, there was no increase in the growth of stems, branches, shoots and needles. It was concluded that in plots of 120 m² application of clinker dust at a rate of 0.5 kg m⁻² was safe for the 21-year-old Scots pine stand in this trial on an acid nutrient-poor sandy soil during 4 years after the treatment.

Fluoranthene fumigation and exogenous scavenging of reactive oxygen intermediates (ROI) in evergreen Japanese red pine seedlings ( Pinus densiflora Sieb. et. Zucc.)

Generation of reactive oxygen intermediates (ROI) such as O 2 - , H 2O 2, and OH is known to be a major mechanism of damage in biological systems. This study investigated and compared effectiveness of scavenging ROI generated in fluoranthene (FLU) pre-fumigated Japanese red pine seedlings. Three kinds of eco-physiological assessments were used to express the impact of the different fumigants used inside the green house. Gas exchange measurements showed negative changes induced by 10 μM FLU on Japanese pine seedlings during a 10 d exposure period whilst no negative change was found during a 5 d exposure period. Moreover, during a 14 d FLU exposure incorporating ROI scavengers, results revealed that chlorophyll fluorescence, needle chemical contents and needle dry mass per unit area of the seedlings were affected. The negative effects of FLU on the conifer were dependent on both the dose and period of FLU fumigation. Peroxidase (PERO), superoxide dismutase (SOD) and mannitol (MANN) were all effective scavengers of ROI. MANN scavenged OH, the most lethal of the ROI. For practicable use, MANN is more economical, and may be the best ROI scavenger among the three considered. It can be concluded that efficient scavenging of ROI in biological systems is important to mitigate the negative effects of FLU on Japanese red pine trees.

Plasticity in mesophyll volume fraction modulates light-acclimation in needle photosynthesis in two pines

Acclimation potential of needle photosynthetic capacity varies greatly among pine species, but the underlying chemical, anatomical and morphological controls are not entirely understood. We investigated the light-dependent variation in needle characteristics in individuals of Pinus patula Schlect. & Cham., which has 19-31-cm long pendulous needles, and individuals of P. radiata D. Don., which has shorter (8-17-cm-long) stiffer needles. Needle nitrogen and carbon contents, mesophyll and structural tissue volume fractions, needle dry mass per unit total area (M(A)) and its components, volume to total area ratio (V/A(T)) and needle density (D = M(A)/(V/A(T))), and maximum carboxylase activity of Rubisco (V(cmax)) and capacity of photosynthetic electron transport (J(max)) were investigated in relation to seasonal mean integrated irradiance (Q(int)). Increases in Q(int) from canopy bottom to top resulted in proportional increases in both needle thickness and width such that needle total to projected surface area ratio, characterizing the efficiency of light interception, was independent of Q(int). Increased light availability also led to larger M(A) and nitrogen content per unit area (N(A)). Light-dependent modifications in M(A) resulted from increases in both V/A(T) and D, whereas N(A) changed because of increases in both M(A) and mass-based nitrogen content (N(M)) (N(A) = N(M)M(A)). Overall, the volume fraction of mesophyll cells increased with increasing irradiance and V/A(T) as the fraction of hypodermis and epidermis decreased with increasing needle thickness. Increases in M(A) and N(A) resulted in enhanced J(max) and V(cmax) per unit area in both species, but mass-based photosynthetic capacity increased only in P. patula. In addition, J(max) and V(cmax) showed greater plasticity in response to light in P. patula. Species differences in mesophyll volume fraction explained most of the variation in mass-based needle photosynthetic capacity between species, demonstrating that differences in plastic adjustments in mass-based photosynthetic activities among these representative individuals were mainly associated with contrasting investments in mesophyll cells. Greater area-based photosynthetic plasticity in P. patula relative to P. radiata was associated with larger increases in M(A) and mesophyll volume fraction with increasing irradiance. These data collectively demonstrate that light-dependent increases in mass-based nitrogen contents and photosynthetic activities were associated with an increased mesophyll volume fraction in needles at higher irradiances. They also emphasize the importance of light-dependent anatomical modifications in determining needle photosynthetic capacity.

One-hundred-year foliage comparison of Pinus ponderosa and Pinus sylvestris under dry growing conditions in Brandenburg, Germany

The dynamics of six different needle parameters of Pinus sylvestris L. and Pinus ponderosa Dougl. ex P. & C. Laws. were examined retrospectively for a 112-year-old mixed stand in Brandenburg, Germany, using the needle trace method. Similarities were found in needle production, needle loss and needle density. However, needle age, needle retention and total number of needles revealed significant differences between the tree species, with higher values for P. ponderosa. Pinus ponderosa yielded approximately twice as much mean whole-crown needle dry mass as P. sylvestris. Furthermore, different branching systems could be detected between the species, with both pines following “Corner's rule”. The results suggest that under identical growing conditions, P. ponderosa exhibits more efficient water use and can therefore maintain a bigger crown (as the basis for increased growth) than P. sylvestris.

Radiative transfer, interception and scattering in coniferous forests: models and applications for production ecology and remote sensing

This work develops methods to account for shoot structure in models of coniferous canopy radiative transfer. Shoot structure, as it varies along the light gradient inside canopy, affects the efficiency of light interception per unit needle area, foliage biomass, or foliage nitrogen. The clumping of needles in the shoot volume also causes a notable amount of multiple scattering of light within coniferous shoots. The effect of shoot structure on light interception is treated in the context of canopy level photosynthesis and resource use models, and the phenomenon of within-shoot multiple scattering in the context of physical canopy reflectance models for remote sensing purposes. Light interception. A method for estimating the amount of PAR (Photosynthetically Active Radiation) intercepted by a conifer shoot is presented. The method combines modelling of the directional distribution of radiation above canopy, fish-eye photographs taken at shoot locations to measure canopy gap fraction, and geometrical measurements of shoot orientation and structure. Data on light availability, shoot and needle structure and nitrogen content has been collected from canopies of Pacific silver fir (Abies amabilis (Dougl.) Forbes) and Norway spruce (Picea abies (L.) Karst.). Shoot structure acclimated to light gradient inside canopy so that more shaded shoots have better light interception efficiency. Light interception efficiency of shoots varied about two-fold per needle area, about four-fold per needle dry mass, and about five-fold per nitrogen content. Comparison of fertilized and control stands of Norway spruce indicated that light interception efficiency is not greatly affected by fertilization. Light scattering. Structure of coniferous shoots gives rise to multiple scattering of light between the needles of the shoot. Using geometric models of shoots, multiple scattering was studied by photon tracing simulations. Based on simulation results, the dependence of the scattering coefficient of shoot from the scattering coefficient of needles is shown to follow a simple one-parameter model. The single parameter, termed the recollision probability, describes the level of clumping of the needles in the shoot, is wavelength independent, and can be connected to previously used clumping indices. By using the recollision probability to correct for the within-shoot multiple scattering, canopy radiative transfer models which have used leaves as basic elements can use shoots as basic elements, and thus be applied for coniferous forests. Preliminary testing of this approach seems to explain, at least partially, why coniferous forests appear darker than broadleaved forests in satellite data.

Variation in needle longevity is related to needle-fascicle production rate in Pinus sylvestris

Latitudinal variation in needle longevity of conifers in response to climatic variability is a well-known phenomenon, but its significance has only rarely been studied. Scots pine (Pinus sylvestris L.) stands were investigated in four locations in Lapland (northern Finland and northern Sweden, 67-68 degrees N) and in four locations in Estonia (59 degrees N) to test the hypothesis that plasticity in needle longevity results in similar needle biomass per foliated shoot length across latitudes. The needle-trace method (NTM) revealed the dynamics of needle fascicles attached to stem shoots. Long-term mean needle age was 2 years greater in Lapland than in Estonia. In both regions, mean needle age was strongly and negatively related to yearly needle-fascicle production rate relative to the number of needles on the same shoot axis. Although significantly fewer needle-fascicles were produced annually in trees in Lapland than in Estonia, the overall number of fascicles attached to the stem shoots, needle-fascicle density and individual needle dry mass did not differ between regions. Consequently, needle biomass per foliated shoot length was similar in trees in both regions. Thus, our results support the theory that plasticity in needle longevity helps Scots pine to compensate for reduced needle production so that the same foliar biomass per shoot is retained under a wide range of growth conditions.