On the Reason for the Different Photosynthetic Rates of Seedlings of Pinus silvestris and Betula verrucosa

The growth and net photosynthetic properties of seedlings of Pinus silvestris L. and Betula verrucosa Ehrh., grown under identical conditions in a controlled environment chamber, were compared. The relative growth rate of birch was about twice that of pine. The rates of in situ net photosynthesis were 1.50 and 2.30 micromoles CO₂ meter⁻² second⁻¹ and the photosynthetic quantum yields under light-limiting conditions were 0.022 and 0.032 for pine and birch, respectively. The total leaf surface areas were used for calculating the CO₂ flux densities. The difference in the rates of in situ net photosynthesis depended equally on morphological and metabolic factors. It was assumed that a pronounced mutual shading and an unfavorable leaf inclination made the pine seedlings less efficient in absorbing the unidirectional light of the climate chamber than the broadleaved seedlings of birch. Both pine and birch were adapted to the growth conditions so the flux densities of absorbed quanta were rate-limiting for in situ net photosynthesis. It was concluded that the difference in the photosynthetic quantum yields (i.e. the linear slope of the photosynthetic light curve) of the two species defined the metabolically controlled part of the difference in the rate of in situ net photosynthesis. The quantum yield of pine was lower than that of birch and was partly explained by pine having a higher rate of photorespiration than birch. The remaining difference was most likely controlled by the properties of the chloroplast thylakoids, e.g. energy transfer efficiency between pigments, photosynthetic electron transport, or coupling between electron transport and photophosphorylation.     

Relationships of microclimatic variables to colonization of rose debris by Botrytis cinerea and the biocontrol agent Clonostachys rosea

Biological control of Botrytis cinerea by Clonostachys rosea is an alternative to chemical control of rose Botrytis blight in greenhouses. Environmental conditions affect the colonization of senescing and dead tissues by both fungi. The contribution of microclimatic variables to debris colonization/sporulation by both fungi was estimated by path coefficient analysis. We monitored daily values of: maximum, average, and minimum temperatures (T _max, T _ave, and T _min), and relative humidity (RH_max, RH_ave, and RH_min); accumulated rainfall; vapour pressure deficit average; hours with RH?>?90% (RH₉₀); and average temperature during RH₉₀ (T _ave90). Association of variables accumulated between the first and seventh day before sampling explained colonization/sporulation variation: R ²=0.81–0.86 for B. cinerea and 0.91–0.96 for C. rosea. RH_max and RH₉₀ were the main factors that directly favoured colonization/sporulation of both fungi. Colonization/sporulation negatively correlated with RH_min, T _min, and T _ave for B. cinerea and T _min, T _ave, and T _ave90 for C. rosea. The antagonist can suppress B. cinerea colonization/sporulation on rose debris under a wide range of environmental conditions.     

南方红壤典型水土流失区马尾松林地上林木碳储量的遥感监测——以长汀县河田镇为例

森林碳储量动态变化对揭示区域水土流失治理成效具有重要指示意义。以长汀县河田镇为例,2017年随机设置34个马尾松林样本作为建模集,分别与同期Landsat影像的原始波段、植被指数及主成分因子进行回归分析,构建马尾松（（Pinus massoniana））林地上林木碳储量的最佳反演模型,基于伪不变特征原理的线性归一化法实现该模型在2003、2010年影像上的适用性校正转换,实现研究区2003、2010、2017年马尾松林地上林木碳储量的反演及时空分异特征的研究。结果表明：研究区2017年马尾松林地上林木碳储量最佳遥感反演模型是以绿色植被指数（GNDVI）为自变量构建的指数模型：C₂₀₁₇=0.006e^{14.357GNDVI₂₀₁₇},该模型拟合的决定系数为0.57,平均相对精度为82.19%;2003年、2010年马尾松林地上林木碳储量遥感估测模型为：C₂₀₀₃=0.006e^{（16.4086GNDVI₂₀₀₃+1.1428）}、C₂₀₁₀=0.006e^{（15.1677GNDVI₂₀₁₀+1.5821）},两期校正模型的决定系数均在0.85以上;2003、2010及2017年碳储量分别为8.24 t/hm²、11.34t/hm²、16.14 t/hm²,整体呈上升趋势;地上林木碳储量随海拔、坡度的升高而增加,向阳坡地上林木碳储量高于背阴坡;碳储量增长率随海拔、坡度的升高而降低,背阴坡碳储量增长率高于向阳坡。     

Quantification of Trends in Wood Production Within Trees of Silver Birch (Betula pendula Roth.)

Trends in rate and duration of wood production are analysedalong and between branches, and along main stems of silver birch(Betula pendula Roth.) trees (at early canopy closure and closedcanopy stages of growth). These data are discussed in relationto the control of knot size, log diameter and taper. To providea field guide to cambial reactivation, progress of vessel productionhas been related to stages of leaf expansion.Copyright 1994,1999 Academic Press Betula pendula (Roth.), silver birch, cambial activity, wood production, wood quality, vessel production     

7. The role of plant growth regulators in forest tree cambial growth

The regulation of cell-division activity in the vascular cambium and of secondary xylem and phloem development is reviewed for temperate-zone tree species in relation to auxins, gibberellins, abscisic acid, cytokinins, and ethylene. Representatives of the first four of these PGR classes (IAA, GA₁, GA₄, GA₇, GA₉, GA₂₀, ABA, Z, ZR, DCA) have been identified conclusively by mass spectrometry in the cambial region in some Pinaceae, but not in any hardwood species. Endogenous ethylene has yet to be definitively characterized in this region in any species. Evidence concerning the source and metabolism of cambial PGRs is scanty and inconclusive for both conifers and hardwoods.Most cambial PGR research has focused on IAA. Much evidence indicates that this PGR is transported primarily in the cambial region at a rate of about 1 cm h^–1, and that the transport is basipetally polar. GC-MS measurements have established that endogenous IAA levels in the cambial region of Pinaceae are highest during earlywood development, and that cambial IAA levels may be considerably lower in hardwoods than in conifers. IAA appears to be involved in the control of cambial growth in conifers and hardwoods in at least three specific ways, viz. maintenance of the elongated form of fusiform cambial cells, promotion of radial expansion in primary walls of cambial derivatives, and regulation of reaction wood formation. In addition, it is well established that exogenous IAA promotes vessel development in hardwoods. In both conifers and hardwoods, exogenous IAA stimulates cambial growth in 1-year-old shoots treated late in the dormant period or after the start of the cambial growing period. However, exogenous IAA has little effect on cambia that are older or are in what is hypothesized to be the resting stage of dormancy. Thus it is uncertain whether IAA is directly involved in the control of cambial growth, or acts indirectly through a process such as hormone-directed transport.It is not yet clear if gibberellins play a role in the control of cambial growth in conifers. However, in hardwoods, there is evidence that they inhibit vessel development and act synergistically with IAA in promoting cambial activity and fiber elongation. In both conifers and hardwoods, foliar sprays of gibberellins increase the accumulation of biomass above-ground, particularly in the main axis, while decreasing it in the roots.There are as yet no definite conclusions to be drawn concerning the involvement of ABA, cytokinins, and ethylene in the regulation of cambial growth in conifers or hardwoods. In conifers, ABA may antagonize the promotory effect of IAA on cambial cell division and tracheid radial expansion under conditions of water stress, but high endogenous ABA levels do not appear to be associated with the formation of latewood or the onset of cambial dormancy. Some evidence suggests that exogenous cytokinins enhance the promotory effect of IAA on cambial growth, particularly ray formation, in both hardwoods and conifers. However, exogenous cytokinins, by themselves, appear to be ineffective. In hardwoods, ethylene-generating compounds satisfy the chilling requirement of the dormant cambium and promote the formation of wood having an apparently greater content of lignin and extractives. Ethylene-generators also affect wood development in conifers and accelerate cambial growth at the application site in both hardwoods and conifers.     

三种温带树种叶片呼吸的时间动态及其影响因子

为认知叶片呼吸(RL)的季节变化格局及其影响因子,以东北东部山区3个主要树种(红松Pinus koraiensis、樟子松P.sylvestris var.mongolica和白桦Betula platyphylla)为对象,采用红外气体分析法在2011年生长季(常绿树4月至10月;落叶树6月至9月)测定了自然条件下叶片气体交换及其相关生理特征的季节变化,探索了RL与空气温度(Tair)和相关叶片特征之间的关系.结果表明:红松和樟子松基于叶面积的RL(RL-area)表现为生长季初期和末期较大,而白桦RL-area则随生长季进程而逐渐减小.在生长季中,RL-area与叶片总光合之比的时间动态明显.红松、樟子松RL-area与Tair关系显著,而白桦RL-area与Tair关系不显著;但3种树种基于叶质量的RL(RL-mass)与Tair均呈显著的指数函数关系.叶片特征(包括可溶性糖、淀粉、氮、比叶面积等参数)也有明显的季节变化.影响RL的叶片特征参数因树种而异,其中可溶性糖浓度对3种树种的RL均有显著影响.可见,RL的季节变化格局受树木的生长节律、温度和叶片特征的联合控制.     

Dimensionless analysis of the microbial growth rate dependence on sub-optimal temperatures

The influence of sub-optimal temperatures (T) on the microbial growth rate (μ) has been assessed by means of dimensionless variables: T_dim = [T−T_min]/[T_opt−T_min] and μ_dim = μ/μ_opt. T_min represents the temperature at which there is no growth, T_opt the optimum temperature at which the growth rate, μ_opt, is maximum. Data sets, growth rate vs temperature, have been taken from the literature for 12 organisms (psychrotrophs, mesophiles and thermophiles). In order to compare these organisms, the power law function has been used: [μ_dim] = [T_dim]^α. The parameters μ_opt and T_opt are determined from direct readings whereas T_min and αare estimated by means of a non-linear regression. An accurate estimation of T_min is obtained providing low growth rate data are available. A wide range of optimal temperatures where the growth rate almost equals μ_opt prevents one from obtaining a narrow confidence interval forα. On the basis of the analysis hereafter developed, thermophiles are characterized by values of the power α less than mesophiles and psychrotrophs. Almost all of these values are significantly different from two, previously determined for Staphylococcus xylosus and widely used for predicting the microbial growth in foods. Received 15 May 1998/ Accepted in revised form 25 September 1998     

Hormonal Responses to Water Deficit in Cambial Tissues of Populus alba L.

Changes in the concentrations of bioactive gibberellins and abscisic acid in the cambial region of white poplar (Populus alba L.) were investigated in 1-year-old plants, to highlight how these phytohormone signals are modulated in response to water deficit. Plants were cultivated in pots outdoor and, at the time of maximum cambial growth (T ₀), irrigation was withdrawn for 8 days, inducing a mild water deficit, thus mimicking a condition that is recurrent in Mediterranean climates when white poplar attains its maximum growth rate. The water deficit was suspended by resuming irrigation (T _max) throughout a recovery period of 2 weeks (T _rec). Cambial tissues were sampled at T ₀, T _max, and T _rec. Significant changes of leaf and stem relative water content, leaf water potential, stomatal conductance, transpiration, carbon assimilation, stem shrinkage, and leaf number were induced by soil water shortage, which also negatively affected cambium development. Nevertheless, these responses were almost fully reversed following the resumption of irrigation. Water deficit induced the accumulation of large amounts of abscisic acid in cambial tissues, but the hormone was brought back to pre-stress levels after the recovery period. With regard to bioactive gibberellins, GA₁ was several folds more abundant than GA₄ and reached the greatest level in the plants recovering from the water status imbalance. The possible functions of gibberellins and abscisic acid in the response of cambial tissues to water deficit are discussed in view of the known physiological roles and molecular mechanisms of action of these hormonal signals.     

Longevity and temperature response of pollen as affected by elevated growth temperature and carbon dioxide in peanut and grain sorghum

It is important to understand the effects of environmental conditions during plant growth on longevity and temperature response of pollen. Objectives of this study were to determine the influence of growth temperature and/or carbon dioxide (CO₂) concentration on pollen longevity and temperature response of peanut and grain sorghum pollen. Plants were grown at daytime maximum/nighttime minimum temperatures of 32/22, 36/26, 40/30 and 44/34 °C at ambient (350 μmol mol⁻¹) and at elevated (700 μmol mol⁻¹) CO₂ from emergence to maturity. At flowering, pollen longevity was estimated by measuring in vitro pollen germination at different time intervals after anther dehiscence. Temperature response of pollen was measured by germinating pollen on artificial growth medium at temperatures ranging from 12 to 48 °C in incubators at 4 °C intervals. Elevated growth temperature decreased pollen germination percentage in both crop species. Sorghum pollen had shorter longevity than peanut pollen. There was no influence of CO₂ on pollen longevity. Pollen longevity of sorghum at 36/26 °C was about 2 h shorter than at 32/22 °C. There was no effect of growth temperature or CO₂ on cardinal temperatures (T_min, T_opt, and T_max) of pollen in both crop species. The T_min, T_opt, and T_max identified at different growth temperatures and CO₂ levels were similar at 14.9, 30.1, and 45.6 °C, respectively for peanut pollen. The corresponding values for sorghum pollen were 17.2, 29.4, and 41.7 °C. In conclusion, pollen longevity and pollen germination percentage was decreased by growth at elevated temperature, and pollen developed at elevated temperature and/or elevated CO₂ did not have greater temperature tolerance.     

Effect of laterally applied gibberellin A4/7 on cambial growth and the level of indole-3-acetic acid in Pinus sylvestris shoots

Gibberellin A_4/7 (GA_4/7) was applied in lanolin or ethanol around the circumference at the midpoint of the previous-year terminal of dormant Pinus sylvestris seedlings. After cultivating the seedlings under environmental conditions favorable for growth for up to 10 weeks, cambial growth was measured as the radial widths of xylem and phloem, and the level of indole-3-acetic acid (IAA) was determined by combined gas chromatography-mass spectrometry using [¹³₆](IAA) as the internal standard. In intact seedlings, both 1 mg GA_4/7 g^?1 lanolin and 50 mg GA_4/7 I^?1 ethanol increased phloem production and the cambial region IAA level in the current-year terminal, without significantly altering its longitudinal growth. In the previous-year terminal, 1 mg GA_4/7 g^?1 lanolin promoted phloem production at the application point and increased the cambial region IAA level above this point, whereas 50 mg GA_4/7 I^?1 ethanol stimulated the production of both xylem and phloem at the treatment site and elevated the cambial region IAA level beneath it. Laterally applied GA_4/7 at 50 mg I^?1 ethanol stimulated xylem and phloem production in debudded previous-year terminals treated at the apical cut surface with 1 mg IAA g^?1 lanolin, but not in those treated with plain lanolin. However, the promotion of cambial growth in debudded terminals treated apically with 1 mg IAA g^?1 lanolin and laterally with 50 mg GA_4/7 I^?1 ethanol was not associated with an elevated IAA content in the cambial region. The results indicate that exogenous GA_4/7 can promote xylem and phloem production provided an IAA source is present, and that it or a metabolic product acts directly, rather than indirectly by stimulating longitudinal growth and/or raising the cambial region IAA level.     

Pisolithus arhizus ectomycorrhiza affects plant competition for phosphorus between Pinus elliottii and Panicum chamaelonche

 Our objective was to evaluate the ability of an ectomycorrhizal fungus to alter the competitive interaction of pine seedlings growing with grass, and to determine whether the interaction was modified by soil-phosphorus (P) concentration. Slash pine (Pinus elliottii), inoculated with the ectomycorrhizal fungus Pisolithus arhizus or fortuitously colonized by Thelephora terrestris, and a native grass (Panicum chamaelonche) were grown in a greenhouse at three P levels (0.32, 3.22, 32.26 μM H₃PO₄). Pine inoculated with P. arhizus took up more P when competing with the nonmycorrhizal grass than when competing with another pine (irrespective of pine mycorrhizal status). Phosphorus uptake kinetics (C_min, the minimum concentration at which P can be absorbed from a solution; I_max, the maximum uptake rate) for pine and grass were also determined under hydroponic conditions. Pine had a higher I_max than grass but grass had a lower C_min, suggesting that pine is more competitive at higher nutrient concentrations while grass is more competitive at lower nutrient concentrations. The controlled conditions used in these experiments allowed us to evaluate specific parameters (P uptake and absorbing surface area) affecting plant competition. Accepted: 7 August 1999     

六种温带森林类型凋落物量长期动态及其环境驱动

阐明凋落物动态及其环境控制机制,可以为森林生态系统生产力及碳汇功能的维持提供重要的数据支持和理论依据。以长白山系余脉张广才岭西坡林龄相近但立地条件不同的4种天然次生林（即硬阔叶林、杨桦林、杂木林和蒙古栎林）和2种人工林（落叶松人工林和红松人工林）为研究对象,对其地上凋落物产量及其组分以及相关环境因子进行了14年（2008-2021年）的连续测定,旨在揭示森林凋落物量及其组分的时空变化（林型间和年际变异）及其环境驱动机制。结果表明：6种森林类型的凋落总量（TL）无显著差异,波动范围为500.5-556.1 g m^-2 a^-1;但其叶凋落量（LL）、繁殖组织凋落量（RT）和其他组织凋落量（OT）均存在显著差异,波动范围依次分别为333.9-391.8 g m^-2 a^-1、8.43-69.93 g m^-2 a^-1和93.4-185.9 g m^-2 a^-1。6种森林类型的TL均存在显著的年际变化;其中LL和OT年际变化的显著性因森林类型而不同,而RT的年际变化不显著。除落叶松人工林外,其余5种森林类型的LL与生长季平均气温、日最低气温均值、土壤10 cm深度处的平均温度、最低温度（Ts_min）和土壤5 cm含水量（Ms）均呈显著正相关。杂木林、硬阔叶林和红松人工林的RT与Ms呈显著负相关;杂木林、杨桦林和硬阔叶林的OT与Ts_min呈显著负相关。样地水平的LL与土壤10 cm处含水量存在显著的正相关关系,而RT和OT则与其呈现显著负相关关系。这些结果表明林龄相似的温带森林地上凋落物总量有趋同趋势,但其通过改变组分分配格局来适应立地条件的变化;土壤湿度和温度变化会引起凋落物量的年际变化,但不同森林类型的凋落物量对环境波动的敏感性不同。     

Differential anatomical responses to elevated CO2 in saplings of four hardwood species

To determine whether an elevated carbon dioxide concentration ([CO₂]) can induce changes in the wood structure and stem radial growth in forest trees, we investigated the anatomical features of conduit cells and cambial activity in 4‐year‐old saplings of four deciduous broadleaved tree species – two ring‐porous (Quercus mongolica and Kalopanax septemlobus) and two diffuse‐porous species (Betula maximowicziana and Acer mono) – grown for three growing seasons in a free‐air CO₂ enrichment system. Elevated [CO₂] had no effects on vessels, growth and physiological traits of Q. mongolica, whereas tree height, photosynthesis and vessel area tended to increase in K. septemlobus. No effects of [CO₂] on growth, physiological traits and vessels were seen in the two diffuse‐porous woods. Elevated [CO₂] increased larger vessels in all species, except B. maximowicziana and number of cambial cells in two ring‐porous species. Our results showed that the vessel anatomy and radial stem growth of Q. mongolica, B. maximowicziana and A. mono were not affected by elevated [CO₂], although vessel size frequency and cambial activity in Q. mongolica were altered. In contrast, changes in vessel anatomy and cambial activity were induced by elevated [CO₂] in K. septemlobus. The different responses to elevated [CO₂] suggest that the sensitivity of forest trees to CO₂ is species dependent.     

Strong impacts of daily minimum temperature on the green‐up date and summer greenness of the Tibetan Plateau

Understanding vegetation responses to climate change on the Tibetan Plateau (TP) helps in elucidating the land–atmosphere energy exchange, which affects air mass movement over and around the TP. Although the TP is one of the world's most sensitive regions in terms of climatic warming, little is known about how the vegetation responds. Here, we focus on how spring phenology and summertime greenness respond to the asymmetric warming, that is, stronger warming during nighttime than during daytime. Using both in situ and satellite observations, we found that vegetation green‐up date showed a stronger negative partial correlation with daily minimum temperature (T_min) than with maximum temperature (T_max) before the growing season (‘preseason’ henceforth). Summer vegetation greenness was strongly positively correlated with summer T_min, but negatively with T_max. A 1‐K increase in preseason T_min advanced green‐up date by 4 days (P < 0.05) and in summer enhanced greenness by 3.6% relative to the mean greenness during 2000–2004 (P < 0.01). In contrast, increases in preseason T_max did not advance green‐up date (P > 0.10) and higher summer T_max even reduced greenness by 2.6% K^?1 (P < 0.05). The stimulating effects of increasing T_min were likely caused by reduced low temperature constraints, and the apparent negative effects of higher T_max on greenness were probably due to the accompanying decline in water availability. The dominant enhancing effect of nighttime warming indicates that climatic warming will probably have stronger impact on TP ecosystems than on apparently similar Arctic ecosystems where vegetation is controlled mainly by T_max. Our results are crucial for future improvements of dynamic vegetation models embedded in the Earth System Models which are being used to describe the behavior of the Asian monsoon. The results are significant because the state of the vegetation on the TP plays an important role in steering the monsoon.     

Patterns of daily stem growth in different tree species in a warm-temperate forest in northern China

Radial growth in trees responds to environmental changes in various ways ranging from immediate to hysteretic responses. However, species-specific tree radial growth patterns and their responses to short-term weather changes are not fully understood. Here, the daily stem radial changes (SRCs) in four common tree species, linden (Tilia mongolica), birch (Betula dahurica), oak (Quercus wutaishanica) and larch (Larix principis-rupprechtii), were monitored with high-resolution point dendrometers during the main growing seasons in 2017–2019 on Dongling Mountain, northern China. The SRC was differentiated into tree water deficit-induced stem shrinkage (TWD) and growth-induced irreversible stem expansion (GRO) to evaluate species-specific responses to weather variables and short-term drought events. We found that the TWD and GRO of the four species were significantly different. The TWD was influenced primarily by the vapor pressure deficit (VPD), whereas the GRO was influenced primarily by precipitation (P). In linden and birch, a larger proportion of the GRO occurred at higher air temperature (T_mean) and VPD values; in contrast, the range of these changes was lower in oak and larch. With the increased durations of drought periods, oak and larch experienced large and rapid increases in TWD, whereas birch and linden showed small and slow increases. These results indicate that oak and larch would be sensitive to warmer and drier weather conditions predicted for the future, while linden and birch would have a conservative growth strategy. Our results provide further insights into the physiology of these four tree species and allow us to better predict the growth response of forest dynamics under climate change.     

基于日均温度的华山松径向生长敏感温度研究

树干木质部形成周期与温度密切相关,存在影响形成层活动的敏感温度,但是尚未研究尝试从树木年轮中探索影响径向生长的敏感温度。华山主峰的华山松径向生长对气候变化较敏感,且华山西峰的气象站记录了1953年以来气象资料,这为探索树木径向生长与温度的关系提供了宝贵的材料。以华山主峰的华山松年轮资料和日值温度资料为基础,通过分析历年日平均温度的变化过程和年轮宽度、早材宽度、晚材宽度、最小密度以及最大密度的相关性,尝试探索华山松径向生长与日均温度变化的关系。结果表明春季一定温度的初日时间对华山松径向生长有较大的影响,其中3 ℃和8 ℃初日时间和持续时间对年轮宽度的促进作用最明显,而3 ℃对早材宽度影响较大,8℃初日时间对晚材的影响较大;高于11 ℃的温度会对华山松的径向生长造成限制,其中以11 ℃的作用最明显;而温度的终日时间对年轮特征影响较小。说明3 ℃是早材形成的敏感温度,8 ℃是晚材形成的敏感温度,温度高于11 ℃会对华山松的径向生长构成胁迫。这证明华山松年轮特征中包含了较多的气候信息,形成层活动和木质部的生长存在阈值温度,通过分析不同温度的生长期与年轮特征的关系可以找到影响华山松径向生长的敏感温度。这些敏感的温度是通过什么生理过程影响木质部的形成尚无法得知,但是这为解释树木生长对全球温度升高的响应以及利用华山松年轮重建历史气候提供了重要依据。     

Indole-3-Acetic Acid Controls Cambial Growth in Scots Pine by Positional Signaling

The vascular cambium produces secondary xylem and phloem in plants and is responsible for wood formation in forest trees. In this study we used a microscale mass-spectrometry technique coupled with cryosectioning to visualize the radial concentration gradient of endogenous indole-3-acetic acid (IAA) across the cambial meristem and the differentiating derivatives in Scots pine (Pinus sylvestris L.) trees that had different rates of cambial growth. This approach allowed us to investigate the relationship between growth rate and the concentration of endogenous IAA in the dividing cells. We also tested the hypothesis that IAA is a positional signal in xylem development (C. Uggla, T. Moritz, G. Sandberg, B. Sundberg [1996] Proc Natl Acad Sci USA 93: 9282–9286). This idea postulates that the width of the radial concentration gradient of IAA regulates the radial number of dividing cells in the cambial meristem, which is an important component for determining cambial growth rate. The relationship between IAA concentration in the dividing cells and growth rate was poor, although the highest IAA concentration was observed in the fastest-growing cambia. The radial width of the IAA concentration gradient showed a strong correlation with cambial growth rate. The results indicate that IAA gives positional information in plants.     

Effects of CO2-mediated changes in paper birch and white pine chemistry on gypsy moth performance

We examined the effects of CO₂-mediated changes in the foliar chemistry of paper birch (Betula papyrifera) and white pine (Pinus strobus) on performance of the gypsy moth (Lymantria dispar). Trees were grown under ambient or enriched CO₂ conditions, and foliage was subjected to plant chemical assays and insect bioassays. Enriched CO₂ atmospheres reduced foliar nitrogen levels and increased condensed tannin levels in birch but not in pine. Foliar carbohydrate concentrations were not markedly altered by CO₂ environment. Gypsy moth performance was significantly affected by CO₂ level, species, and the CO₂ x species interaction. Under elevated CO₂ conditions, growth was reduced for larvae fed birch, while development was prolonged for larvae fed pine. Although gypsy moths performed better overall on birch than pine, birch-fed larvae were influenced more by CO₂-mediated changes in host quality.