Stand dynamics during a 12-year period in a second-growth stand in a cool temperature forest in northern Japan

In 1981 and 1993, trees over 2 m high were measured and mapped to clarify stand dynamics in two permanent plots of 0.1 ha in a secondary, cool temperate, mixed broadleaf/conifer forest after logging in the Tomakomai Experiment Forest, central Hokkaido, northern Japan. The species could be placed in two groups according to the change in basal area and density, and annual height growth:Quercus mongolica var.grosseserrata, Phellodendron amurense, Prunus sargentii andTilia japonica (Group I: GI) showed episodic regeneration and/or fast height growth;Acer mono, Acer palmatum var.matsumuae andSorbus alnifolia (Group II: GII) showed continuous regeneration and/or slow height growth. The age distribution of stems over 10 cm in d.b.h. suggests synchronous regeneration of GI and GII species. Vertical stratification was promoted during the 12-year period by the difference in annual height growth between the two species groups. Additional tree censuses in both remnant old-growth stands and second-growth stands after large scale blowdowns demonstrated thatQ. mongolica var.grosseserrata is most dominant in stands varying in the stages of development. Disturbance history and successional trends in dominant species implied that stand-devastating disturbances were responsible for the regeneration ofQ. mongolica var.grosseserrata in the study forest.     

Quantitative analysis of a stand of Pinus densiflora undergoing succession to Quercus mongolica ssp. crispula : II. Growth and population dynamics of Q. mongolica ssp. crispula under the P. densiflora canopy

We report here the results of an 8-year study of the growth and population dynamics of Quercus mongolica ssp. crispula in a Pinus densiflora stand in a state of succession. In 1998, there were 169 Q. mongolica ssp. crispula individuals in a 400-m² plot under the P. densiflora canopy. This number remained nearly constant between 1998 and 2005. Mean recruitment of new individuals was 11 year⁻¹, while mean mortality was 12 year⁻¹. Of the 35 individuals ≥60 cm in height existing in 1998, 30 were still surviving in 2005. We were able to represent the height growth of Q. mongolica ssp. crispula individuals as H=30 [1+21.96 exp(−0.0839t)]⁻¹, with t = years since 1998 and H = height in meters. Using this equation we predict that by 2015 the mean height of Q. mongolica ssp. crispula trees in the stand will exceed those of understory trees, such as Rhus trichocarpa and Prunus maximowiczii. Once above the understory stratum, the Q. mongolica ssp. crispula trees can be expected to grow more rapidly due to the better light conditions, thereby rapidly reaching the canopy stratum of the P. densiflora stand.     

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.     

大青沟自然保护区主要森林群落优势种的叶性状

植物功能性状是近年来生态学研究的热点。其中叶功能性状与植株生物量和植物对资源的获得、利用及利用效率的关系最为密切。大青沟森林植物群落分布于科尔沁沙地,生境条件非常特殊,在沙沟里存在着一片茂密的森林,与周围浩瀚无垠的沙坨景观形成极为鲜明的对照。从沟底到沟顶,虽然海拔高度仅相差六、七十米,但由于距离沟底水源不同,土壤条件差异大,形成了不同的森林植物群落类型。大果榆群落、蒙古栎群落和水曲柳群落分别分布在大青沟自然保护区的沟顶、沟中和沟底。为了对大青沟自然保护区,不同环境梯度下的森林植物群落叶片功能性状进行研究,以大青沟自然保护区大果榆、蒙古栎、水曲柳3种主要森林群落为研究对象,分别测定不同群落优势种的叶厚度、比叶面积、叶干物质含量、叶大小和叶干重等5项叶功能性状,研究叶功能性状之间的关系,并对不同生长型、不同群落叶功能性状进行比较。相关分析结果表明,叶厚度与比叶面积呈极显著负相关,与叶大小和叶干重呈极显著正相关;比叶面积与叶干物质含量、叶干重呈极显著负相关,与叶大小呈显著正相关;叶干物质含量与叶大小呈极显著负相关,与叶干重呈极显著正相关;叶大小与叶干重呈极显著正相关。不同生长型植物叶片性状的分析表明,草本植物的叶干物质含量比乔木和灌木低,而其比叶面积高于乔木和灌木;对不同群落叶功能性状进行比较发现,大果榆群落和蒙古栎群落乔木、灌木叶厚度与干物质含量显著高于水曲柳群落的叶厚度与干物质含量,二者比叶面积显著低于水曲柳群落。大果榆群落和蒙古栎群落从叶功能性状的角度,它们具有较高的叶干物质含量和较低的比叶面积,体现出适应干旱生境叶片的特征。水曲柳群落呈现出低叶干物质含量、高比叶面积的特征,体现出适应湿润、土壤水分较好生境的特征。不同群落通过调节自身的物种组成,形成不同的功能性状组合来适应环境。     

Inequality of size and size increment in Pinus banksiana in relation to stand dynamics and annual growth rate

BACKGROUND AND AIMS: Changes in size inequality in tree populations are often attributed to changes in the mode of competition over time. The mode of competition may also fluctuate annually in response to variation in growing conditions. Factors causing growth rate to vary can also influence competition processes, and thus influence how size hierarchies develop. METHODS: Detailed data obtained by tree-ring reconstruction were used to study annual changes in size and size increment inequality in several even-aged, fire-origin jack pine (Pinus banksiana) stands in the boreal shield and boreal plains ecozones in Saskatchewan and Manitoba, Canada, by using the Gini and Lorenz asymmetry coefficients. KEY RESULTS: The inequality of size was related to variables reflecting long-term stand dynamics (e.g. stand density, mean tree size and average competition, as quantified using a distance-weighted absolute size index). The inequality of size increment was greater and more variable than the inequality of size. Inequality of size increment was significantly related to annual growth rate at the stand level, and was higher when growth rate was low. Inequality of size increment was usually due primarily to large numbers of trees with low growth rates, except during years with low growth rate when it was often due to small numbers of trees with high growth rates. The amount of competition to which individual trees were subject was not strongly related to the inequality of size increment. CONCLUSIONS: Differences in growth rate among trees during years of poor growth may form the basis for development of size hierarchies on which asymmetric competition can act. A complete understanding of the dynamics of these forests requires further evaluation of the way in which factors that influence variation in annual growth rate also affect the mode of competition and the development of size hierarchies.     

Effects of individual size,local competition and canopy closure on the stem volume growth in a monoclonal Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) plantation

We studied how the dominant factor affecting stem volume growth changes during stand development in a monoclonal stand of Cryptomeria japonica D. Don. Stem analysis was used to compare growth history of trees in an unthinned plot (closed canopy) and a thinned plot (open canopy). In the unthinned plot, the dominant factor affecting stem volume growth was basal area (BA) before canopy closure, whereas neighborhood competition index (CI) was the dominant factor after canopy closure. In contrast, the dominant factor affecting stem volume in the thinned plot was BA throughout stand development. Spearman’s rank correlation coefficient between BA and CI continued to increase after canopy closure and size rank among individuals became increasingly fixed. Our results indicated that stem volume growth shifts from size-dependent to competition-dependent growth at canopy closure. The apparent correlation between tree size and growth rate observed in many previous studies may be the result of competition-mediated positive feedback between size and growth.     

Response of Japanese beech (Fagus japonica Maxim.) sprouts to canopy gaps

The response of Japanese beech (Fagus japonica Maxim.) sprouts to canopy gaps in natural beech forest in central Japan was studied using two contrasted gaps in which tree-ring chronologies of regenerating stems were analyzed. The gaps were created by uprooting of a single Quercus mongolica var. grosseserrata stem (diameter: 50 cm; gap size: 40 m²; 23 years old) and by concurrent uprootings of four F. japonica stools (gap size: 180 m²; 30 years old). Japanese beech sprouts emerged before and after the gap formation and dominated stem populations in both gaps. In gaps, growth of F. japonica sprouts was equal or lower than growth of stems of seed origin, but most sprouts (F. japonica, Acer mono var. marmoratum) appeared a few years before emergence of seedlings. The small gap created by single stem fall was dominated by some beech sprouts from stools adjacent to the gap. The multiple gap was not closed by beech sprouts from stools surrounding the gap, but some dominant beech stems were resprouts from the uprooted beech stools. The existence of a sprout bank under the canopy may play an important role in the closing process of gaps in natural Japanese beech forest.     

Characteristics of gas exchange and morphology of a spring ephemeral, Erythronium japonicum, in comparison with a sun plant, Glycine max

Morphological characteristics and responses of gas exchanges to light intensity were examined in a typical vernal species, Erythronium japonicum Decne (E. japonicum), grown (i) on the floor of a deciduous broad-leaved Quercus mongolica forest (one of its native habitats, the Q. mongolica stand); (ii) bare land left undisturbed for 9 years after forest clearing (the bare stand); and (iii) in a sun crop, soybean, grown for 110 days in an experimental field and for 17 days in pots, in order to evaluate the adaptability of the photosynthetic process of this vernal species to its shady native habitats. The daytime solar radiation, ai and leaf temperatures and leaf–air vapor pressure difference (VPD) were significantly higher at the bare stand than at the Q. mongolica stand. When environmental factors observed at the Q. mongolica and bare stands were reproduced in an assimilation chamber, leaf temperatures of E. japonicum plants increased markedly with increased radiation, whereas those of soybean plants differed little from the respective air temperatures. The photosynthetic and transpiration rates and stomatal conductance in the former plants placed under conditions at the Q. mongolica stand increased with radiation and reached respective steady state values at maximum radiation at the site; whereas, under the conditions at the bare stand, they also increased and reached respective steady state values, but then continuously decreased to be lower than the respective value at the Q. mongolica stand. However, both rates and the conductance in the soybean plants under both conditions increased significantly with radiation and reached much higher respective values at the respective maximum radiations. Water use efficiency for E. japonicum plants was much higher under conditions at the Q. mongolica stand than at the bare stand and was practically equal to those for soybean plants under both conditions. Water potential in the leaves of E. japonicum at maximum radiation at the bare stand was one-third that of those at the Q. mongolica stand. The potential in soybean leaves differed little between both conditions and was roughly equal to the low value in E. japonicum leaves at the bare stand conditions. The stomatal densities on upper and lower leaf surfaces and the ratio of root weight to leaf area (R : L) differed little between E. japonicum plants grown at both stands as well as between young and adult soybean plants. However, the densities on the upper and lower surfaces of E. japonicum were 25% and 60% of the respective values of both soybean plants. The ratios of R : L of the E. japonicum plants were only one-quarter that of the young and adult soybean plants. The cooperation between these morphological and gas exchange characteristics in E. japonicum plants is discussed in relation to adaptation to the environment in native habitats.     

Dry matter production, population structure and environmental conditions of the spring ephemeralErythronium japonicum growing in various habitats differing in sunlight exposure in cool temperate Japan

Phenology, dry matter production, population structure and environmental conditions were examined inErythronium japonicum Decne plants growing on the floor of a deciduous broad-leavedQuercus mongolica forest (Q.m. stand), an evergreen coniferousCryptomeria japonica plantation (C. j. stand) and bare ground left for 3 years after the clearing of a forest composed of youngQ. mongolica andPinus densiflora trees (bare stand) in the cool temperate zone of Japan. The average population density of the plants growing at theQ.m. stand was much higher than that observed at the bare stand, whereas the average number of flowering plants at the former stand was less than half of that at the latter. The population density and number of flowering plants growing at theC. j. stand were both less than 30% of those at theQ. m. stand. The number of seedlings at theQ. m. stand was much more than that at the bare andC. j. stands. Their survivorship rate over 1 year at the former stand also seems to be significantly higher than those at the other stands. Their aboveground and belowground parts at the bare stand were exposed to more severe heat and water stress than those at the other two stands. The net production per leaf area of the plants growing at theQ. m. stand was two and six times larger than those at the bare andC. j. stands, respectively. The plants at the bare stand did not use the available solar radiation as efficiently for dry matter production through photosynthesis as those growing at theQ. m. stand, whereas those at theC. j. stand are strongly restricted in their photosynthetic process by the significantly limited light condition on the floor of the evergreen coniferous plantation. The differences in the number of plants reaching sexual maturity, the density and structure of the population and the net production between their three habitats are discussed here from the standpoint of differences in environmental conditions.     

Dwarf bamboos affect the regeneration of zoochorous trees by providing habitats to acorn-feeding rodents

The effects of dwarf bamboos (Sasa spp.) on the regeneration of trees in a natural hardwood forest were studied by analysing the spatial dispersion of seedlings and saplings of anemochores (Acer palmatum var. matsumurae, Fraxinus lanuginosa, and Carpinus laxiflora) and zoochores (Quercus mongolica var. grosseserrata and Q. serrata). Relative photosynthetic photon flux density at 10 cm above ground was significantly correlated with the coverage of dwarf bamboos (r=0.661, P<0.001). Seedlings were abundant and were randomly distributed in the anemochores, other than the shade-intolerant species C. laxiflora which was significantly more sparse in sites with dense Sasa than in sites where Sasa was rare. Distribution of saplings was also random in the shadetolerant anemochores A. palmatum var. matsumurae and F. lanuginosa but aggregated in sites with sparse Sasa in the shade-intolerant anemochore C. laxiflora. In contrast to the anemochores, seedlings of zoochores were very few and were distributed in sites with sparse Sasa. Saplings were also aggregated and negatively correlated with Sasa cover in the shade-intolerant species Q. serrata and the tolerant species Q. mongolica var. grosseserrata. The acorns put on the forest floor in a site with dense Sasa were quickly removed by small rodents such as Apodemus speciosus and A. argenteus. Trap census of rodents revealed that those mammals prefer the dense Sasa habitat to the sparse Sasa habitat. This suggests that the dwarf bamboos strongly affect the regeneration of zoochorous trees not only by shading the seedlings but also by providing habitats to acorn-feeding small mammals.     

Tree dispersion in oak-dominated forests along an environmental gradient

Summary Spatial pattern was analyzed in seventeen stands of oak-dominated forest to address the hypothesis that species tended to be aggregated under favorable conditions and widely spaced in xeric, nutrient poor conditions. Trees were sampled at 80–100 points in each stand with the distance-to-nearest neighbor method. Soil samples were collected in each stand for analysis of total nitrogen, total phosphorus, total potassium, soil pH, soil texture, and soil organic matter. Growing season precipitation was also recorded from climate stations near each stand. Quercus stellata (Wang.) dominated 10 stands, Q. marilandica (Muenchh.) dominated three stands and these species were codominant in four stands. Principal components analysis identified a soil texture/fertility gradient across the study area. Quercus stellata and all species combined were aggregated in most stands, whereas Q. marilandica was mostly randomly distributed within a stand. Small trees of all species combined tended to be aggregated and large trees were randomly dispersed in all but two stands, suggesting competition. Mean distance between large-large pairs was always greater than mean distance between small-small pairs in all stands, but this difference was only significant in one stand. Correlations between nearest neighbor distance and combined size of nearest neighbors were significant and positive in 12 of 17 stands. In all cases, however, slopes were shallow suggesting that competition is weak in these communities and has a limited effect on spacing of neighboring trees. Contrary to our hypothesis, trees were more aggregated on coarse-textured soils with low organic matter content. For all species combined, degree of aggregation was unrelated to growing season precipitation. Aggregation appears to be common in these forests because environmental stress in many stands reduces growth rates. Trees have not yet reached a size at which competition or other interactions can greatly increase interplant distances and reduce the degree of aggregation. A simple graphical model is developed to describe the relationship between patterns, stress and competition in plant communities.     

Development of ten microsatellite markers for <Emphasis Type="Italic">Quercus mongolica</Emphasis> var. <Emphasis Type="Italic">crispula</Emphasis> by database mining

Simple sequence repeats (SSRs) in the NCBI dbEST database were surveyed to identify potential SSR markers for Quercus mongolica. In total, 2,691 gene sequences, mainly from expressed sequence tags (ESTs) for Q. robur and Q. petraea had been registered. Twenty-two PCR primers were designed for SSRs in these sequences and screened for polymorphisms in 16 Q. mongolica trees. Ten loci were easily genotyped and showed polymorphism, with numbers of alleles and expected heterozygosity ranging from 3 to 15 and 0.28 to 0.94, respectively. These EST-SSR markers should be useful for studying the genetic diversity of Quercus species.     

Density effects and self-thinning in even-aged pure stands ofEucalyptus camaldulensis Dehn

The competition density effect and changes of mean total tree weight (w) and stand density (ρ) during course of self-thinning were examined in even-aged pure stands ofEucalyptus camaldulensis Dehn. which were planted in the tropical monsoon region. The level of competition was controlled by changing the initial stand density from 625 trees ha⁻¹ to 40,000 trees ha⁻¹. Hozumi's model was used to describe thew-ρ trajectory with aging of each stand and thew-ρ relation between stands of different densities at each time. The higher density produced trees of smaller mean tree sizes. The higher the density, the sooner self-thinning began. The growth curve ofE. camaldulensis followed the logistic growth curve where both maximum size and intrinsic growth rate change with time. Mean intrinsic growth rate was maximized at initiation of growth after lag time and then gradually decreased as time progressed. Hozumi's model was considered to be the best model with wide applicability for describing and comparing the growth characteristics during the course of self-thinning among different species, especially in tropical forest plantations, in which many diverse species were used for reforestation.     

Photosynthetic, hydraulic and biomechanical responses of Juglans californica shoots to wildfire

Leaf gas exchange and stem xylem hydraulic and mechanical properties were studied for unburned adults and resprouting burned Juglans californica (southern California black walnut) trees 1 year after a fire to explore possible trade-offs between mechanical and hydraulic properties of plants. The CO₂ uptake rates and stomatal conductance were 2–3 times greater for resprouting trees than for unburned adults. Both predawn and midday water potentials were more negative for unburned adult trees, indicating that the stems were experiencing greater water stress than the stems of resprouting trees. In addition, the xylem specific conductivity was similar in the two growth forms, even though the stems of resprouting trees were less vulnerable to water-stress-induced embolism than similar diameter, but older, stems of adult trees. The reduced vulnerability may have been due to less cavitation fatigue in stems of resprouts. The modulus of elasticity, modulus of rupture and xylem density were all greater for resprouts, indicating that resprouts have greater mechanical strength than do adult trees. The data suggest that there is no trade-off between stem mechanical strength and shoot hydraulic and photosynthetic efficiency in resprouts, which may have implications for the success of this species in the fire-prone plant communities of southern California.     

林龄和竞争对日本落叶松各组分生物量异速关系的影响

基于7-、17-、30-和40年生日本落叶松生物量测定数据,应用方差分析和多重比较分析了林龄和林分内树木竞争类型(优势木、平均木和被压木)对各组分生物量分配比例和异速关系的影响,构建了含林龄和树木竞争类型作为哑变量的生物量异速方程,为准确估算日本落叶松人工林生物量和碳储量提供依据。结果表明:(1)林龄显著影响生物量分配比例的异速关系。随林龄增加干生物量比例增大,枝叶生物量比例减小,根生物量逐渐稳定。加入林龄的干、枝和叶生物量方程显著改善。年龄效应在幼龄林阶段作用最显著,需单独构建生物量模型。(2)树木竞争类型对生物量分配的影响小于林龄。立地条件一致下,虽然相同胸径的优势木比劣势木积累更多的枝叶生物量和少的干生物量,但它们分配生物量到不同器官的比例和方式是基本相同的,林内竞争不会导致生物量分配规律由"异速关系理论"向"环境优先理论"转化。因此,常规采用平均木法估算各组分生物量是可行的。(3)在近成熟林分中不同竞争类型树木的根生物量分配比例均较为稳定,采用根茎比比值来估算根生物量是可行的。     

Relationship between size hierarchy and density of trees in a tropical dry deciduous forest of western India

Questions: Density dependence is thought to restrict exponential growth as well as give rise to size structure in populations. Size hierarchy in trees from tropical dry deciduous forests is studied to ask (1) whether nature of competition is symmetric or asymmetric and (2) what is the self thinning trajectory under a natural gradient of tree density. Location: Western India. Methods: Density was measured as the number of trees in 10‐m radius circular plots (n= 96) and size was measured at DBH. Size variation was evaluated by the Gini coefficient (n= 1239 trees). Results: Size inequality between neighbours decreased with density but in a non‐linear manner. In the backdrop of existing theory this indirectly suggests that competitive interactions may be symmetric over a ‘depletive’ resource such as below‐ground water (rather than a ‘pre‐emptive’ resource such as light), which is very plausible in a semi‐arid environment. The self thinning coefficient derived from the relationship between stem diameter and density (γ～?1/4), is higher than expected from existing models of allometric plant growth (γ=?1/3) which are based on above‐ground interactions alone. Seen in conjunction, these results suggest that above‐ground structures, such as stem size, do not adequately represent the outcome of competitive interactions when below‐ground resources, such as water, may be more important under semi‐arid conditions. Conclusions: The non‐linear relationship between size inequality and density indicates that there exists a density threshold beyond which investment in above‐ground biomass becomes sluggish in semi‐arid, deciduous forests. Since current allometric models do not incorporate below‐ground biomass for trees, these data suggest that a more comprehensive allometric growth model may have higher predictive power and wider applicability.     

Modelling the distribution of diameter growth along the stem in Scots pine

This paper presents an empirical model for the distribution of diameter growth along the stem in Scots pine (Pinus sylvestris L.) and for the consequent stem form over time. First, the distribution of annual mass growth in the stem is determined as a function of the total annual growth in stem mass, current stem mass and the distribution of the latter along the stem. Second, the distribution of diameter growth is obtained by converting the fraction of annual growth in the stem mass at a given height in the stem into the thickness of the annual ring at the same height. Application of the model to Scots pine data sets including both young and mature trees not used in parameter estimation showed that the model was capable of reconstructing the distribution of diameter growth from the stem butt to the apex and from the pith to the stem surface at any height in the stem in both young and mature trees. The resulting empirical model was also linked to a physiological, process-based model in order to study its performance in a simulated stand. Simulations representing trees grown in unthinned and thinned Scots pine stands with trees of different status (from dominant to suppressed) showed that the response in tree growth to thinning in terms of the distribution of diameter growth along the stem was quite realistic relative to measured data.     

竞争强度变化对针阔混交林红松和水曲柳径向生长的影响

以3种间伐强度处理下(15%,30%和50%)针阔混交林内优势树种红松(Pinus koraiensis)和水曲柳(Fraxinus mandshurica)为研究对象,基于3次复测数据和树轮宽度数据分析不同间伐强度处理下红松和水曲柳的竞争变化特征,探讨竞争环境变化对保留木径向生长的影响。结果表明,1)红松保留木竞争环境发生变化的单木比例随着间伐强度增加而有所下降,但竞争减弱的保留木所占比例与间伐强度正相关,重度间伐样地内竞争减弱的红松保留木所占比例最大达到63%。不同间伐强度下水曲柳保留木竞争环境发生变化的单木比例一致,竞争减弱的单木比例占50%。2)不同竞争环境的水曲柳保留木径向生长趋势基本一致,而红松保留木径向生长变化趋势有所不同。轻度和重度间伐样地内竞争减弱的红松保留木径向生长在间伐后均呈上升趋势,而中度间伐样地内竞争减弱的红松保留木和各样地竞争不变的红松保留木以及不同竞争强度下水曲柳保留木均在2013年和2014年(间伐后2年内)出现生长抑制,而在2015年(伐后第3年)得到促进。3)随着间伐强度上升,自2015年(伐后第3年)竞争减弱的红松保留木径向生长年增量明显增加,显著高于竞争不变的红松(P0.05),而竞争减弱的水曲柳保留木径向生长年增量自2014年(伐后第2年)在重度间伐样地内增加幅度最大,其次为轻度间伐样地,而在中度间伐样地内增加幅度最低。     

Comparative study of leaf carbon gain in saplings ofThujopsis dolabrata var.hondai andQuercus mongolica var.grosseserrata in a cool-temperate deciduous forest

Seasonal courses of leaf CO₂ gas exchange in a growing season were examined in saplings ofThujopsis dolabrata var.hondai andQuercus mongolica var.grosseserrata in a cool temperate deciduous forest. Between the two tree species there were no large differences in the light compensation point of leaf photosynthesis, except for the season of new leaf expansion. However, light-saturated rates of net photosynthesis were obviously high inT. dolabrata var.hondai. EvergreenT. dolabrata var.hondai saplings had large photosynthetic production in two seasons, before the emergence of new foliage and after foliage fall of the overstory deciduous trees, because of the significantly high solar radiant energy penetrating under the forest canopy during the seasons. Saplings of deciduousQ. mongolica var.grosseserrata were heavily shaded throughout the growing season by foliage of the overstory trees, which resulted in a low daily surplus production. The annual surplus production of leaves in the growing season was estimated to be 2300 mmol CO₂ m⁻² inT. dolabrata var.hondai and −100 mmol CO₂ m⁻², slightly negative, inQ. mongolica var.grosseserrata. These results supported the high survivability ofT. dolabrata var.hondai saplings and the high mortality ofQ. mongolica var.grosseserrata in the deciduous forest.     

Effects of micro-environmental factors on photosynthetic CO2 uptake and carbon fixation metabolism in a spring ephemeral, Erythronium japonicum, growing in native and open habitats

Microenvironmental factors and physiological parameters (such as water potential, activity of ribulose 1,5-bisphosphate carboxylase (RuBPcase), levels of ribulose 1,5-bisphosphate (RuBP), 3-phosphoglyceric acid (PGA) and sucrose in leaves) affecting photosynthetic processes of the typical vernal species Erythronium japonicum Decne. were examined on the floor of a deciduous broad-leaved Quercus mongolica forest (Q.m. stand) and on bare land left undisturbed for 7 years after forest clearing (bare stand). Daytime solar radiation and the air and leaf temperatures at the bare stand were significantly higher than those at the Q.m. stand. The relative air humidity was very low and did not differ much between the stands, whereas the leaf–air vapor pressure difference (VPD) at the bare stand was twice as high as that at the Q.m. stand. The water potential in leaves at the bare stand was lower than two times that at the Q.m. stand. Therefore, the aboveground parts of the plants at the bare stand were subjected to much more severe heat stress than those at the Q.m. stand. When these environmental factors observed at the bare stand were reproduced in an assimilation chamber, the rate of photosynthetic CO₂ uptake, stomatal conductance and water potential in leaves were significantly low in comparison with those when the factors at the Q.m. stand were simulated. The internal CO₂ partial pressure in leaves at the bare stand was considerably lower than that at the Q.m. stand. Consequently, the decrease in the photosynthetic rate of the plants at the bare stand was caused mainly by a decrease in stomatal conductance through a lowering of water potential due to subjection of the aboveground parts to much more severe heat stress than that at the Q.m. stand. The possibility that an inhibition of the photosynthetic carbon fixation metabolism induced by the decrease in water potential contributes to the reduction in photosynthetic CO₂ uptake in the plants at the bare stand is also discussed in light of physiological characteristics such as the activity of RuBPcase and levels of PGA, RuBP and sucrose in the leaves.