Stem Growth Rate Research Articles

Mach Stem Height and Growth Rate Predictions

A new, more accurate prediction of Mach stem height in steady flow is presented. In addition, starting with a regular reflection in the dual-solution domain, the growth rate of the Mach stem from the time it is first formed till it reaches its steady-state height is presented. Comparisons between theory, experiments, and computations are presented for the Mach stem height. The theory for the Mach stem growth rate in both two and three dimensions is compared to computational results. The Mach stem growth theory provides an explanation for why, once formed, a Mach stem is relatively persistent. Nomenclature g = spacing between wedge and axis of symmetry M = Mach number P = pressure s = Mach stem height U = speed w = wedge length � = leading shock angle with respect to the freestream � = ratio of specific heats � = triple-point slip-line angle � = wedge angle with respect to the freestream � = Mach angle � = density � = triple-point reflected shock angle Subscripts

Decelerating growth in tropical forest trees

The impacts of global change on tropical forests remain poorly understood. We examined changes in tree growth rates over the past two decades for all species occurring in large (50-ha) forest dynamics plots in Panama and Malaysia. Stem growth rates declined significantly at both forests regardless of initial size or organizational level (species, community or stand). Decreasing growth rates were widespread, occurring in 24-71% of species at Barro Colorado Island, Panama (BCI) and in 58-95% of species at Pasoh, Malaysia (depending on the sizes of stems included). Changes in growth were not consistently associated with initial growth rate, adult stature, or wood density. Changes in growth were significantly associated with regional climate changes: at both sites growth was negatively correlated with annual mean daily minimum temperatures, and at BCI growth was positively correlated with annual precipitation and number of rainfree days (a measure of relative insolation). While the underlying cause(s) of decelerating growth is still unresolved, these patterns strongly contradict the hypothesized pantropical increase in tree growth rates caused by carbon fertilization. Decelerating tree growth will have important economic and environmental implications.

Growth in stem diameter of Larix principis-rupprechtii and its response to meteorological factors in the south of Liupan Mountain, China

Research related to daily and seasonal pattern of stem growth of Larix principis-rupprechtii was carried out with the help of a dendrometer from June to September in 2005 in the Liupan Mountain, Ningxia, Northwestern China. The results indicated that daily fluctuation of stem diameter was rhythmic and it could be divided into three continuous phases: contraction, expansion and stem diameter growth when daily rainfall < 10 mm during the measurement period. Comparatively, it showed a different pattern compared with the former when daily rainfall ≥10 mm and in the subsequent days. Based on the work done by Deslauriers et al. a modified method was designed to calculate daily and cumulative stem growth, and it showed that seasonal pattern of cumulative stem growth was similar among five sample trees. From June and July, stem growth rate was quick and the values were in the range 27.0–44.2 μm per day. Relatively, they took on a slow growth rate from August to September, and the values were under 10 μm per day. And it also showed that there existed a significant difference in stem growth among sample trees, which could be as a result of the difference in tree domain and their positions in the stand. The relationship between daily stem growth and meteorological factors was studied by principle component analysis and partial correlation analysis, and the result indicated that the daily rainfall, daily minimum temperature, daily average solar radiation and vapor pressure deficit were four significant factors which determined the daily stem growth.

Daytime Depression in Tree Stem CO 2 Efflux Rates: Is it Caused by Low Stem Turgor Pressure?

Daytime CO2 efflux rates (FCO2) from tree stems are often reported to be lower than expected from the exponential relationship between temperature and respiration. Explanations of daytime depression in FCO2 have focused on the possible role of internal CO2 transport in the xylem. However, another possible cause that has been overlooked is the daily dynamics of the water status in the living stem tissues and its influence on stem growth rate and thus respiration. The objective of this study was to assess the daily dynamics of stem water status and growth rate and to determine the extent to which they may be linked to daily variations in stem FCO2. FCO2 of young beech and oak stems were measured under controlled conditions. Relative stem turgor pressure (Psi(p)), obtained from simulations with the 'RCGro' model, was used as an indicator of the water status in the living stem tissues. Daily dynamics of stem growth were derived from Psi(p): growth was assumed to occur when Psi(p) exceeded a relative threshold value. There was a strong correspondence between fluctuations in FCO2 and simulated Psi(p). The non-growth conditions during daytime coincided with depressions in FCO2. Moreover, FCO2 responded to changes in Psi(p) in the absence of growth, indicating also that maintenance processes were influenced by the water status in the living stem tissues. Daytime depressions in stem FCO2 correlate with the daily dynamics of turgor, as a measure of the water status in the living stem tissues: it is suggested that water status of tree stems is a potentially important determinant of stem FCO2, as it influences the rate of growth and maintenance processes in the living tissues of the stem.

Green Light Adjusts the Plastid Transcriptome during Early Photomorphogenic Development

During the transition from darkness to light, a suite of light sensors guides gene expression, biochemistry, and morphology to optimize acclimation to the new environment. Ultraviolet, blue, red, and far-red light all have demonstrated roles in modulating light responses, such as changes in gene expression and suppression of stem growth rate. However, green wavebands induce stem growth elongation, a response not likely mediated by known photosensors. In this study, etiolated Arabidopsis (Arabidopsis thaliana) seedlings were treated with a short, dim, single pulse of green light comparable in fluence and duration to that previously shown to excite robust stem elongation. Genome microarrays were then used to monitor coincident changes in gene expression. As anticipated, phytochrome A-regulated, nuclear-encoded transcripts were induced, confirming proper function of the sensitive phytochrome system. In addition, a suite of plastid-encoded transcripts decreased in abundance, including several typically up-regulated after phytochrome and/or cryptochrome activation. Further analyses using RNA gel-blot experiments demonstrated that the response is specific to green light, fluence dependent, and detectable within 30 min. The response obeys reciprocity and persists in the absence of known photosensors. Plastid transcript down-regulation was also observed in tobacco (Nicotiana tabacum) with similar temporal and fluence-response kinetics. Together, the down-regulation of plastid transcripts and increase in stem growth rate represent a mechanism that tempers progression of early commitment to the light environment, helping tailor seedling development during the critical process of establishment.

Is long primary growth associated with stem sinuosity in Douglas-fir?

Stem sinuosity is a highly visible stem-form trait in the leaders of fast-growing Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) trees, yet its cause is unknown. We tested the hypotheses that sinuous stems have longer expanses of primary growth than nonsinuous stems (putting the leader at higher risk for curvature, induction of compression wood formation, and possibly overcorrection) and higher leader angle using 4- to 5-year-old saplings in raised beds. As hypothesized, sinuous stems had longer expanses of primary growth than did nonsinuous stems (13.5 vs. 12.3 cm, respectively). However, for the dates for which growth (length/day, primary growth, secondary growth, and total growth) differed significantly among sinuosity class, sinuosity class only explained 15%–21% of the variation in growth rate. There were no significant differences in leader angle for saplings of the three sinuosity classes. Contingency tables indicated some consistency in the category of sinuosity to which we assigned the stems in 2001 and 2002 (χ2 = 11.2, p &lt; 0.004). When we used a more quantitative measure, the ratio of stem length/stem distance, there was a tendency toward a significant relationship between the two years (r = 0.272, p = 0.0893). These data suggest that, counter to expectation, the rate of stem growth was not a large factor in determining whether leaders become sinuous for this population of trees.

Effects of canopy cover and seasonal reduction in rainfall on leaf phenology and leaf traits of the fern Oleandra pistillaris in a tropical montane forest, Indonesia

Leaf phenology and leaf traits of the fern Oleandra pistillaris were examined in relation to canopy cover (open and understorey) and seasonal reduction in rainfall in a wet tropical montane forest, Indonesia. Although the annual rainfall is high, rainfall is relatively less in June and July. Stomatal density and diameter were greater in the open than in the understorey (229 versus 167 mm−2 for stomatal density and 33 versus 29 μm for stomatal diameter). The stable carbon isotope ratio (δ13C) of leaves, positively correlated with water use efficiency, was higher in the open than in the understorey (mean δ13C −30 versus −33‰). Therefore, it is considered that leaves have high gas-exchange capacities per leaf area in the open where water availability would be limited, compared with the understorey. In contrast, leaf mass per area (LMA) was lower and leaf life span was longer in the understorey than in the open (25 versus 34 g m−2 for LMA and 2.1 and 1.6 y for leaf life span). These thin leaves with a long life span in the understorey would contribute to efficient light capture and photosynthetic production per leaf mass. The number of leaves per stem decreased during the period with less rainfall in both the open and understorey conditions, which should reduce the water loss from plants, but increased again after the period with less rainfall. Stem growth rate was higher in the open than in the understorey, and the seasonal reduction in rainfall hardly affected stem growth rate in either open or understorey conditions. This study concludes that O. pistillaris responds to canopy cover and seasonal reduction in rainfall by adjusting leaf traits and leaf phenology, respectively.

Use of stem diameter variations to detect plant water stress in tomato

The sensitivity of stem diameter variations (SDV) measured with linear variable transducer (LVDT) sensors as indicators of plant water status in tomato was evaluated. Two tomato crops were grown sequentially in a sandy loam soil in an unheated plastic greenhouse. These were an autumn–winter tomato crop (autumn crop) and a spring–summer tomato crop (spring crop). One drying cycle of 61 days was imposed to the autumn crop in winter at 92 days after transplanting (DAT). Two drying cycles, each of 29 days, were applied to the spring crop, to young (58 DAT) and mature plants (121 DAT). For each drying cycle, four replicate plots did not receive irrigation, and four were well watered. During each drying cycle, LVDT sensors continuously measured SDV, and daily measurements were made of leaf (Ψ leaf) and stem water potential (Ψ stem). SDV data was interpreted using the SDV-derived indices, maximum daily shrinkage (MDS) and stem growth rate (SGR). The response of SDV-derived indices to water deficit differed with (1) climatic conditions during stress imposition and (2) crop age. In the winter drying cycle of the autumn crop, the responses of the SDV-derived indices to soil drying were relatively small and slower than Ψ leaf and Ψ stem. Under warmer conditions, the SDV-derived indices were much more responsive to soil drying. In rapidly growing young plants, where SDV was characterized by high SGR and small MDS, SGR was the most sensitive SDV-derived index. In more mature plants with little stem growth, MDS was the most sensitive SDV-derived index. In mature plants grown in warm to hot conditions, MDS (1) responded at a similar time or earlier than Ψ leaf and Ψ stem and (2) had larger “signal” values (ratio of values from unwatered to control plants) than Ψ leaf and Ψ stem. However, there was appreciably more “noise” (coefficient of variation, CV) associated with the SDV-derived indices, giving lower “sensitivity” values, determined from “signal” to “noise” ratios, than for Ψ leaf and Ψ stem. Regression analysis between MDS of well-watered plants and climatic variables gave best results for a linear relationship between MDS and daily maximum vapor pressure deficit. There were strong linear relationships between MDS and Ψ leaf for each drying cycle. The slopes of these relationships differed with crop age indicating that there was no constant relationship between MDS and Ψ leaf for a whole season. Overall these results demonstrated that MDS and SGR can be sensitive indicators of the water status of tomato crops under conditions of moderate to high evaporative demand. However, the variability associated with the SDV-derived indices and the changing MDS–Ψ leaf relationship with crop age represent major issues regarding the development of irrigation scheduling protocols for tomato.

Diel patterns of leaf C export and of main shoot growth for Flaveria linearis with altered leaf sucrose–starch partitioning

Diel C export from source leaves of two Flaveria linearis lines [85-1: high cytosolic fructose-1,6-bisphosphatase (cytFBPase) and 84-9: low cytFBPase] were estimated using three methods, including leaf steady-state (14)CO(2) labelling, leaf metabolite analysis, and leaf dry mass analysis in conjunction with leaf CO(2) exchange measurements. Synthesis and accumulation of starch during the daytime were much higher in 84-9. Relative (14)C-export (export as a % of photosynthesis) in the light was 36% higher in 85-1. The diel export patterns from (14)C-analyses correlated with those based on metabolite or dry weight/gas exchange analyses during the daytime, but not during the night. Night-time export estimated from (14)C-disappearance was 3.6 times lower than those estimated using the other methods. Even though the starch degradation at night was greater for 84-9, night-time export in 84-9 was similar to 85-1, since 84-9 showed both higher respiration and accumulation of soluble sugars (i.e. glucose) at night. Patterns of (14)C allocation to sink organs were also different in the two lines. Main stem growth was less in 84-9, being reduced most in the light when leaf export was lower relative to 85-1. Supplementation with sucrose for 1 h daily via the roots at a time when leaf export in 84-9 was low relative to 85-1 increased the stem growth rate of 84-9 to a level similar with that of 85-1. This study provides evidence that diel C availability predicted by source strength (e.g. C-export rate) influences main stem extension growth and the pattern of sink development in F. linearis.

Growth and water relations of walnut trees (Juglans regia L.) on a mesic site in central Italy: effects of understorey herbs and polyethylene mulching

The establishment of trees and associated herbaceous understorey vegetation during the afforestation of former arable lands can decrease soil erosion, increase soil fertility and diversify plantation income. This study reports on the five-year results from experimental plots of common walnut (Juglans regia L.) established in association with two different herbaceous understoreys in 1994 in central Italy. Treatments included: (i) walnut established with plastic film mulching in association with subclover (Trifolium subterraneum L.); (ii) walnut with subclover; (iii) walnut with a spontaneous herbaceous cover (grassing treatment); (iv) clean-cultivated walnut (control). Stem growth rates and the periodical changes in predawn and midday leaf water potentials of walnut, as well as the annual sward dry matter production, were measured. Over the five-years, the understorey vegetation was competitive towards trees, negatively affecting their leaf water status relative to the control, especially during mid-summer observations, with the onset of summer drought. Tree growth in the grassing treatment was slightly but significantly (p < 0.05) reduced in height in comparison to unmulched trees with subclover. Subclover competitiveness towards walnut was completely masked by the plastic mulching, so that mulched walnut with subclover had the highest cumulative stem diameter and height (+20% than control treatment). This was associated with water potentials that were never higher than the control. The subclover-mulched treatment, due to its three main advantages (highest cumulative stem growth, an annual dry matter fodder production of 6.3 t/ha, and soil erosion protection), appears to be a promising cultural model for walnut cultivation in areas without marked drought.

Dry matter production and partitioning in rose ( Rosa hybrida) flower shoots

Dry matter production and allocation to the different organs of rose ( Rosa hybrida, cv. Dallas) flower shoots were investigated during three growth cycles (spring, summer and late autumn). The crop was grown under greenhouse conditions in a Mediterranean climate (Valencia, Spain). Fresh and dry matter, leaf area, and thermal time were determined at eight phenological stages of the flower shoot, from cutting to harvest. The increase in the shoot dry matter followed an expolinear function quite closely, suggesting that the shoot growth rate was near its maximum value at the time of harvest. The appearance of the flower bud drastically changed the dry matter distribution between the organs (stem, leaves and flower bud). Leaves were the first organs to be affected by the bud demand, showing a strong decrease in growth rate just after bud appearance. Stem growth rate was also affected, but later, and to a lesser extent. Flower bud growth was exponential until harvest. When expressed as a function of thermal time, dry matter partitioning was rather similar during the three growth cycles. Empirical functions are proposed that quantify dry matter partitioning in the organs of flower shoots as a function of thermal time. The overall results stressed the key role played by the flower bud in determining the dynamics of dry matter allocation in rose flower shoots.

Secondary succession and dipterocarp recruitment in Bornean rain forest after logging

To understand succession in dipterocarp rain forest after logging, the structure, species composition and dynamics of primary (PF) and secondary (SF) forest at Danum were compared. In 10 replicate 0.16-ha plots per forest type trees ≥10 cm gbh (3.2 cm dbh) were measured in 1995 and 2001. The SF had been logged in 1988, which allowed successional change to be recorded at 8 and 13 years. In 2001, saplings (1.0–3.1 cm dbh) were measured in nested quadrats. The forest types were similar in mean radiation at 2 m height, and in density, basal area and species number of all trees. Among small (10 ≤ 31.4) and large (≥31.4 cm gbh) trees, in both 1995 and 2001, there were 10- and 3-fold more dipterocarps in SF than PF respectively; and averaging over the two dates, there were correspondingly ca. 10- and 18-fold more pioneers. Mortality was ca. 60% higher in SF than PF, largely due to a seven-fold difference for pioneers: for dipterocarps there was little difference. Recruitment was similar in PF and SF. Stem growth rates were 37% higher in SF than PF for all trees, although dipterocarps showed the opposite trend. Among saplings, dipterocarps dominated SF with a 10-fold higher density than in PF. For dipterocarps, the light (LH) and medium-heavy (MHH) canopy hardwoods, and the shade-tolerant, smaller-stature other (OTH) species (e.g. Hopea and Vatica) were in the ratios ca. 40:15:45 in SF and 85:<1:15 in PF. LHs had higher mortality than OTHs in SF. In PF ca. 80% of the saplings were LH: in SF ca. 70% were OTH. The predominance of OTHs in SF is explained by the logging of primary rain forest which was in a likely late stage of recovery from natural disturbance, plus the continuing shaded conditions in the understorey promoted by dense pioneer vegetation. At 13 years after logging succession appeared to be inhibited: LHs were being suppressed but MHHs and OTHs persisted. Succession in lowland dipterocarp rain forests may therefore depend on the successional state of the primary forest when it is logged. A review of logged versus unlogged studies in Borneo highlights the need for more detailed ecological comparisons.

Pre-sowing magnetic treatment of tomato seeds: effects on the growth and yield of plants cultivated late in the season

The effects of pre-sowing magnetic treatments on the growth and yield of tomatoes (cv. Vyta), cultivated late in the season, were studied under field conditions. Tomato seeds were exposed either to a 120 mT dynamic magnetic field (induced by an experimental electromagnet) for 10 min or to a 80 mT field for 5 min. Non-treated seeds were used as controls. Plants were grown in experimental plots (20.2 square m) and cultivated according to standard agriculture practices. At physiological maturity, the plants were harvested from each plot and the number of fruits, mean fruit weight, fruit yield per plant and fruit yield per area determined. In the nursery stage, the treatments led to a significant increase in root length, fresh and dry root weight, stem length, fresh and dry stem weight, leaf area and foliole dry weight. During the vegetative stage, the leaf, stem and root relative growth rates of plants derived from magnetically-treated seeds were greater than those shown by control plants. In the generative stage, the relative growth rate of the fruits belonging to the "magnetically treated plants" was greater than that of control plant fruits. At the fruit maturity stage, the magnetically treated seeds produced plants with significantly more fruits (17.9-21.3%), with a significantly greater mean fruit weight (22.3-25.5%), and with a greater fruit yield per plant (47.3-51.7%) and per area (48.6-50.8%) than did the control plants. Pre-sowing magnetic treatments would appear to enhance the growth and yield of tomatoes cultivated late in the season.

Understanding a flammable planet – climate, fire and global vegetation patterns

Understanding a flammable planet – climate, fire and global vegetation patterns

Demographic and life-history correlates for Amazonian trees

Abstract Questions: Which demographic and life-history differences are found among 95 sympatric tree species? Are there correlations among demographic parameters within this assemblage? Location: Central Amazonian rain forest. Methods: Using long-term data from 24 1-ha permanent plots, eight characteristics were estimated for each species: wood density, annual mortality rate, annual recruitment rate, mean stem diameter, maximum stem diameter, mean stem-growth rate, maximum stem-growth rate, population density. Results: An ordination analysis revealed that tree characteristics varied along two major axes of variation, the major gradient expressing light requirements and successional status, and the second gradient related to tree size. Along these gradients, four relatively discrete tree guilds could be distinguished: fast-growing pioneer species, shade-tolerant subcanopy species, canopy trees, and emergent species. Pioneers were uncommon and most trees were canopy or emergent species, which frequently had...

Effects of planting density on canopy dynamics and stem growth for intensively managed loblolly pine stands

Leaf area index (LAI), intercepted photosynthetically active radiation (IPAR), and foliar nitrogen content are related to stand growth. However, they are all a function of canopy size, and their relative importance is hard to determine. We used intensively managed, 4-year-old loblolly pine (Pinus taeda L.) stands planted at densities ranging from 740 to 4440 trees ha −1 that possessed very different canopy structures to separate the relationships between IPAR, LAI, and foliar N content. Our objectives were to determine whether stem growth was best correlated with LAI, IPAR, or foliar N content and to determine how the relationship between LAI and IPAR varied among stands of different planting densities. While stem growth rates increased significantly with planting density, from 12.0 to 35.2 m 3 ha −1 y −1, increases were not proportional, indicating the presence of competition-induced limitations to growth. Annual IPAR (863–2345 MJ m −2 y −1), LAI (2.5–4.9), and foliar N content (67–122 kg ha −1) all increased as stand density increased from 740 to 4440 trees ha −1. Stem growth rates were better correlated with annual IPAR ( r 2 = 0.90), than LAI ( r 2 = 0.67) or foliar N content ( r 2 = 0.55). The efficiency of LAI to capture radiation (IPAR LAI −1) increased with stand density even though the higher density stands possessed greater LAI, which increased the likelihood of within canopy shading. The increase in IPAR LAI −1 corresponded to significantly decreased variation in light interception within plots as planting density increased. These results indicate that stem growth is best correlated with annual IPAR and underscore the importance of stand structure since the more even distribution of foliage within canopies of higher density stands increased the efficiency of light interception.

Co-regulation Of ear growth and internode elongation in corn

Ear is the harvest part of corn (Zea mays L.) and we are interested in studying its growth and development in our effort in corn yield improvement. In our current study, we examined the relationship between ear growth and internode characteristics using different approaches. Correlations between stem growth rate and number of ears per plant (prolificacy) were assessed among several genotypes. Internode elongation of 2 genotypes was modified by plant hormones and by population density manipulations. Among the 7 genotypes examined that have different prolificacy levels, there was a general correlation of slower stem elongation at middle growth stages and larger ear number. When the internode elongation was enhanced by application of gibberellic acid (GA), ear growth was suppressed; and when a GA synthesis inhibitor uniconazole was applied at early stages, internode length was reduced and ear growth was promoted in terms of both ear size and visible ear number at silking stage. Higher population density caused longer internodes and fewer ears per plant and the effect of lower density was the opposite. Our results suggested that internode elongation in the middle section of corn plants was linked to suppression of ear development in corn.

Resistance of a lowland rain forest to increasing drought intensity in Sabah, Borneo

Occasional strong droughts are an important feature of the climatic environment of tropical rain forest in much of Borneo. This paper compares the response of a lowland dipterocarp forest at Danum, Sabah, in a period of low (LDI) and a period of high (HDI) drought intensity (1986–96, 9.98 y; 1996–99, 2.62 y). Mean annual drought intensity was two-fold higher in the HDI than LDI period (1997 v. 976 mm), and each period had one moderately strong main drought (viz. 1992, 1998). Mortality of ‘all’ trees ≥10 cm gbh (girth at breast height) and stem growth rates of ‘small’ trees 10–&lt;50 cm gbh were measured in sixteen 0.16-ha subplots (half on ridge, half on lower slope sites) within two 4-ha plots. These 10–50-cm trees were composed largely of true understorey species. A new procedure was developed to correct for the effect of differences in length of census interval when comparing tree mortality rates. Mortality rates of small trees declined slightly but not significantly between the LDI and HDI periods (1.53 to 1.48% y−1): mortality of all trees showed a similar pattern. Relative growth rates declined significantly by 23% from LDI to HDI periods (11.1 to 8.6 mm m−1 y−1): for absolute growth rates the decrease was 28% (2.45 to 1.77 mm y−1). Neither mortality nor growth rates were significantly influenced by topography. For small trees, across subplots, absolute growth rate was positively correlated in the LDI period, but negatively correlated in the HDI period, with mortality rate. There was no consistent pattern in the responses among the 19 most abundant species (n≥50 trees) which included a proposed drought-tolerant guild. In terms of tree survival, the forest at Danum was resistant to increasing drought intensity, but showed decreased stem growth attributable to increasing water stress.

Effects of elevated CO2 concentration on growth, annual ring structure and photosynthesis in Larix kaempferi seedlings

We evaluated the effects of elevated carbon dioxide concentration ([CO2]) and two nutrient regimes on stem growth rate, annual ring structure and temporal variations in photosynthetic characteristics of seedlings of Japanese larch (Larix kaempferi (Lamb.) Carr.). Seedlings were grown in phytotron chambers in an ambient (360 ppm) or an elevated (720 ppm) [CO2] in two nutrient regimes for one growing season. Elevated [CO2] reduced stem height and increased stem basal diameter compared with ambient [CO2]. The effect of elevated [CO2] on growth tended to be greater at high-nutrient supply than at low-nutrient supply. Elevated [CO2] had no significant effect on ring width or the number of tracheids per radial file. There was no obvious difference in cell wall thickness or the relative area of the cell wall between seedlings grown in ambient or elevated [CO2]. Although growth in elevated [CO2] resulted in a slight increase in cell diameter, the increase had a relatively minor effect on the relative area of the cell wall. Net assimilation rate increased in response to elevated [CO2]; however, the increase in whole-crown photosynthetic rate (Total Agrowth) in seedlings in the elevated [CO2] treatment was minimal because of the smaller specific needle area and acclimation of the photosynthetic characteristics of the needles to the growth [CO2]. In conclusion, we observed no obvious enhancement in the capacity for carbon fixation in Japanese larch seedlings grown in the presence of elevated [CO2] that might be attributable to changes in stem growth. However, elevated [CO2] caused changes in the temporal pattern of stem growth and in some anatomical features of the tracheids.

Leaf area index and net primary productivity along subtropical to alpine gradients in the Tibetan Plateau

ABSTRACTAim Our aims were to quantify climatic and soil controls on net primary productivity (NPP) and leaf area index (LAI) along subtropical to alpine gradients where the vegetation remains relatively undisturbed, and investigate whether NPP and LAI converge towards threshold‐like logistic patterns associated with climatic and soil variables that would help us to verify and parameterize process models for predicting future ecosystem behaviour under global environmental change.Location Field data were collected from 22 sites along the Tibetan Alpine Vegetation Transects (TAVT) during 1999–2000. The TAVT included the altitudinal transect on the eastern slope of the Gongga Mountains in the Eastern Tibetan Plateau, with altitudes from 1900 m to 3700 m, and the longitudinal‐latitudinal transect in the Central Tibetan Plateau, of approximately 1000 km length and 40 km width.Methods LAI was measured as the product of foliage biomass multiplied by the ratio of specific leaf area. NPP in forests and shrub communities was estimated as the sum of increases in standing crops of live vegetation using recent stem growth rate and leaf lifespan. NPP in grasslands was estimated from the above‐ground maximum live biomass. We measured the soil organic carbon (C) and total and available nitrogen (N) contents and their pool sizes by conventional methods. Mean temperatures for the year, January and July and annual precipitation were estimated from available meteorological stations by interpolation or simulation. The threshold‐like logistic function was used to model the relationships of LAI and NPP with climatic and soil variables.Results Geographically, NPP and LAI both significantly decreased with increasing latitude (P &lt; 0.02), but increased with increasing longitude (P &lt; 0.01). Altitudinal trends in NPP and LAI showed different patterns. NPP generally decreased with increasing altitude in a linear relationship (r2 = 0.73, P &lt; 0.001), whereas LAI showed a negative quadratic relationship with altitude (r2 = 0.58, P &lt; 0.001). Temperature and precipitation, singly or in combination, explained 60–68% of the NPP variation with logistic relationships, while the soil organic C and total N variables explained only 21–46% of the variation with simple linear regressions of log‐transformed data. LAI showed significant logistic relationships with both climatic and soil variables, but the data from alpine spruce‐fir sites diverged greatly from the modelled patterns associated with temperature and precipitation. Soil organic C storage had the strongest correlation with LAI (r2 = 0.68, P &lt; 0.001).Main conclusions In response to climatic gradients along the TAVT, LAI and NPP across diverse vegetation types converged towards threshold‐like logistic patterns consistent with the general distribution patterns of live biomass both above‐ground and below‐ground found in our earlier studies. Our analysis further revealed that climatic factors strongly limited the NPP variations along the TAVT because the precipitation gradient characterized not only the vegetation distribution but also the soil N conditions of the natural ecosystems. LAI generally increased with increasing precipitation and was well correlated with soil organic C and total N variables. The interaction between LAI growth and soil N availability would appear to have important implications for ecosystem structure and function of alpine spruce‐fir forests. Convergence towards logistic patterns in dry matter production of plants in the TAVT suggests that alpine plant growth would increase in a nonlinear response to global warming.