Relative Rate Of Increase Research Articles

Systolic blood pressure relates to the rate of progression of albuminuria in NIDDM

We prospectively followed a cohort of 278 non-insulin-dependent (NIDDM) patients for a 6-year period, intending to estimate the rate of increase of albuminuria and to identify clinical variables that influence this increase. At baseline, normo-albuminuria (N) was seen in 74%, microalbuminuria (M) in 19% and 7% presented with proteinuria (P). A total of 80 patients died; they were older (p < 0.001) and had higher albumin excretion both at baseline and as an average during follow-up (p < 0.01). At baseline, patients with proteinuria had higher blood pressures (systolic and diastolic), whereas there was no difference between patients with normo-and microalbuminuria. Glycaemic control was increasingly poor throughout the three groups. At follow-up, an average relative rate of increase of albuminuria (slope) of 17% per year was seen both for patients with complete 6 years, follow-up (n - 135) and patients with at least 4 years follow-up (n = 178). Slope correlated significantly with systolic blood pressure (r = 0.26 and 0.29) in both groups, diastolic blood pressure only in the 4-year group (r = 0.22) and average albuminuria in both (r = 0.31 and 0.24). By multiple regression analyses systolic blood pressure and average albuminuria remained with significant influence on slope. Progression was defined as an increase in the category (e.g. normo- to microalbuminuria) as well as an increase of more than 20% in albumin excretion, and was seen in 46 patients with at least 4 years' follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)

Some studies on low-frequency signal in relation to X-ray flares and climatic conditions

Abstract. The statistical behaviour of the sudden enhancement in signal strength (SES) in relation to solar X-ray flares has been studied for the near east-west propagation of 40 kHz radio waves from Sanwa (36°11'N; 139°51'E) in Japan to Calcutta (22°34'N; 88°24'E) over a long distance path of 5100 km for a period of two years. The period has been divided into four phases - P1, P2, P3 and P4, according to the position of the overhead sun. The change in signal strength during X-ray flares is dependent on the solar zenith angle and climatic conditions. The statistical modal values of the time lag of the SES peak with respect to that solar X-ray flare is found to increase as solar zenith angle increases. The relative rates of increase and decrease of the signal strength (RRISS and RRDSS respectively) have been evaluated for a number of SES which are related to large X-ray flares. Their characteristics have also been investigated. The modal values of the relaxation time have been found to be highly correlated with climatic conditions like temperature and humidity of the propagation path.

Growth and nutrition of small Betula pendula plants at different relative addition rates of iron

Small birch plants (Betula pendula Roth.) were cultivated in a hydroponic spray solution where the relative addition rate of iron (RFe; g g−1 day−1), was the growth-controlling variable. All other elements were added in free access. An additional treatment was performed where all nutrients, including iron, were in free access (FA). The plants showed deficiency symptoms at steady-state growth and severe limitation of iron, RFe 0.05 and 0.10 day−1. There were few symptoms at RFe of 0.15 or above. Plant relative growth rate (RG; g g−1 day−1), equalled the relative rate of increase in iron supply, RFe. Internal iron concentration of the plants ranged from 40 to 70 μg g−1 dry weight (DW) over the range for which iron supply was limiting growth. At FA, the internal concentration was approximately 200 μg g−1 DW without further increase in RG, demonstrating that iron may be taken up in excess without affecting growth. Internal concentrations of macronutrients were stable at the different RFe, except for Ca and Mg in shoots which were higher at low iron supply. Uptake rates of iron, calculated per root growth rate (μmol g−1 root DW), were approximately twice as high at RFe 0.20 as at 0.05 day−1. The effect of iron limitation on dry matter allocation to leaves was small, with increases in the root fraction being largely at the expense of the stem. Leaf area ratio was constant regardless of RFe and the specific leaf area tended to increase with increasing iron limitation. Net assimilation rate decreased by a factor of 6 from free access to severe iron limitation, largely accounting for the differences in plant RG.

Potential Measures for Use in Developing Selection Procedures for High Timber Density in Juvenile Wood of Picea sitchensis

Four clones of Picea sitchensis, each growing on two sites with contrasting growth rates, were examined for the rate at which wood density decreased as growth rate increased during successive years of juvenile wood formation. The clones with the greatest and least rates of change were consistent between contrasting sites. It was determined that the most effective measure of change in wood density was the relative rates of increase in wood volume and wood weight increment in successive annual increments. Wood volume increased more rapidly than wood weight for all clones but there were differences between them. The rankings for these relative rates of change were not (he same as those for mean density nor density of the last annual wood increment. Within a single annually produced sheath of wood, wood density was found to decrease with increasing distance down the main stem. In the outermost sheath, volume increment was at a maximum at least two and more usually three interwhorl positions. Dierences between...

External morphology of Dall's porpoise (Phocoenoides dalli): growth and sexual dimorphism

We studied development and sexual dimorphism in external measurements of Dall's porpoises (Phocoenoides dalli) from the northwestern North Pacific. Relative rates of increase in the measurements of the head and flipper decrease postnatally, while those of the flukes, dorsal fin, and girths in the posterior part of the body do not. Growth patterns of the flukes and increase in girth at the anus are different from those in other small odontocetes. This is considered to be related to the fast swimming and presumed deep diving behavior of Dall's porpoise. Growth rates of appendages decrease with time after birth, as in other cetaceans. Secondary sexual features of males appear in the dorsal fin, flukes, and girth at the anus; the flukes show more distinct sexual dimorphism than the dorsal fin.

Reproductive Effort and Maternal Age in Iteroparous Insects Using Aphids as a Model Group

Life-history theory predicts that as the residual reproductive value of an organism declines its current investment in reproduction should increase. This hypothesis has not been previously tested for insects. The results of a laboratory study on the reproductive investment of the willow-carrot aphid, Cavariella aegopodii and the vetch aphid, Megoura viciae were compared with the predictions of the aphid optimal energy partitioning model. The model's assumption that the fecundity function in aphids is triangular was supported. As predicted by the model, the sizes of gonads decrease and those of the offspring increase with the age of the mother. The large offspring born towards the end of a mother's life achieve a greater adult weight, mean relative growth rate and potential intrinsic rate of increase than the small offspring born early in a mother's life. The better performance of the last born is a consequence of their large birth size

Apex size, flowering and grain yield of wheat as affected by sowing date

Abstract Wheat ( Triticum aestivum L.) cultivars Hartog (a spring type) and Rosella (winter type) were sown at seven dates in 1987–1988 using conventional and minimum tillage in the central-west of N.S.W. Apex or spike sizes were measured on six to eight occasions until terminal-spikelet formation. Some plants at the boot stage were transferred from the field to a glasshouse so that their grain matured in a common thermal environment, to allow estimation of the effect of time of sowing and environment prior to anthesis on yield and yield components. Double-ridge formation occurred when apices reached certain sizes, irrespective of sowing dates and tillage practices. The results support the hypothesis that apex development depends on the shoot apex reaching a certain size irrespective of environment. Apex volume increased exponentially with thermal time (°Cd) and the relative rate of increase in apex size appeared to be less before double-ridge formation than between double-ridge and terminal-spikelet formation. The thermal time required for apex development was reduced in later sowings, presumably because of the influences of photoperiod and vernalization in addition to that of day degrees on speed of development. The timing of developmental events could be predicted for the spring cultivar but not the winter cultivar from simple Australian models using thermal time and photoperiod and for both cultivars using the CERES Wheat model which incorporated a vernalization function in addition to thermal time and photoperiod. The importance of environment prior to anthesis was indicated by grain yield and its components generally decreasing with lateness of sowing, even in plants which were transferred at the boot stage from the field to a glasshouse so that grain grew in a common thermal environment. Moreover, the relationships among yield components (paths to yield, ascertained by path coefficient analysis) varied among sowings and cultivars in plants in which grain growth occurred in a glasshouse. The importance of environment after anthesis was indicated by a single, general relationship (correlation) between grain yield in the field and grain yield from plants which matured in the glasshouse, in which field yield was 0.76 of glasshouse yield irrespective of sowing date.

The development of fruit shape in kiwifruit: Growth characteristics and positional differences

The distribution of normal and aberrant shaped flower buds and floral clusters was examined for a sample of kiwifruit vines. Normal, flat and fan shaped flowers, and floral clusters were described relative to their position along a lateral shoot and to the position of the shoot along a cane. The total number of flowers was greater on lateral shoots at more distal regions of the cane than on proximal shoots. The proportionate number of flat and fan shaped buds was similar among all but the most proximal lateral shoots on the cane. No flower was found distal to the nine proximal nodes of a lateral shoot. Flat and fan shaped flower buds were maximal at nodes 3 and 1 of the lateral shoot respectively. Possible pathways by which fans and floral clusters may arise are discussed. Growth of normal and flat fruit was compared from anthesis to maturation. There was no significant difference in relative rates of increase in length or in maximum and minimum diameters between the two fruit types. The evolving shape of...

Net assimilation rate and shoot area development in birch (Betula pendula Roth.) at different steady-state values of nutrition and photon flux density

Small birch plants (Betula pendula Roth.) were grown in a climate chamber at different, exponentially increasing rates of nitrogen supply and at different photon flux densities. This resulted in treatments with relative growth rate equal to the relative rate of increase in nitrogen supply and with different equilibrium values of plant nitrogen concentration. Nitrogen productivity (rate of dry matter increase per plant nitrogen) was largely independent of nitrogen supply and was greater at higher photon flux density. Leaf weight ratio, average specific leaf area (and thus leaf area ratio) were all greater at better nitrogen supply and at lower values of photon flux density. The dependencies were such that the ratio of total projected leaf area to plant nitrogen at a given photon flux density was similar at all rates of nitrogen supply. The ratio was greater at lower values of photon flux density. At a given value of photon flux density, net assimilation rate and net photosynthetic rate per shoot area (measured at the growth climate) were only slightly greater at better rates of nitrogen supply. Values were greater at higher photon flux densities. Acclimation of the total leaf area to plant nitrogen ratio and of net assimilation rate was such that nitrogen productivity was largely saturated with respect to photon flux density at values greater than 230 μmol m-2 s-1. At higher photon flux densities, any potential gain in nitrogen productivity associated with higher net assimilation rates was apparently offset by lower ratios of total leaf area to plant nitrogen.

Observations on the crack-enhanced creep-fracture of a polycrystalline alumina with a glassy grain-boundary phase

An experimental study was conducted of the role of cracks in the creep-rupture behaviour of a polycrystalline alumina with glassy grain-boundary phase at stress regimes and temperatures at which failure is anticipated to occur from pre-existing flaws. Samples were tested without and with artificial flaws in the form of slots or indentation cracks. All three sample types exhibited non-linear creep. The relative rate of increase in creep rate with increasing dimension of slot-depth greatly exceeded the corresponding increase in specimen compliance, as expected for non-linear creep. An analysis of the data indicated that the observed creep behaviour was primarily controlled by crack-enhanced creep with a minor contribution from elastic creep by crack growth. Very poor correlations were found for the stress dependence of the creep rate and time-to-failure. In terms of Monkman-Grant behaviour, good correlations existed between creep rate and time-to-failure, independent of stress and size of the slots or indentation cracks. Because failure originated from pre-existing flaws, the experimental findings of this study suggest the existence of a failure mechanism referred to by the present authors as “crack-enhanced creep fracture”.

RELATIVE GROWTH RATES OF VINES AND SHRUBS OF WESTERN POISON OAK, TOXICODENDRON DIVERSILOBUM (ANACARDIACEAE)

Because of the different mechanical constraints on vines and self‐supporting plants, vines are thought to differ from trees and shrubs in a variety of their growth characteristics. I tested the hypotheses that vines grow faster than shrubs and that supported shoots have delayed leaf expansion relative to stem elongation, using western poison oak, Toxicodendron diversilobum (T. &amp; G.) Greene, a plant that grows as a vine when externally supported but otherwise as a shrub. In the field, supported shoots (vines) had significantly higher aboveground biomass and relative growth rates than did their paired unsupported shoots (shrubs) growing nearby. This was not due to differences in leaf phenology, but may have resulted from vines growing into more favorable habitats for growth. In contrast, whereas 2‐yr‐old cloned plants in a common garden differed in their stem and internode lengths, they had the same aboveground dry weight, proportion of dry weight that was leaf, and relative rate of increase in primary stem length whether grown with stakes (vines) or without stakes (shrubs). These results suggest that there is no inherent requirement of vines to grow faster than shrubs. As hypothesized, leaf elongation was more delayed relative to stem elongation in staked than unstaked individuals in 19 paired plants (each pair cloned from a different source plant). Thus, physical cues resulting from the presence of support can alter the plant's spatial and temporal patterns of development, but do not necessarily dictate the quantity of biomass that will be produced.

Growth and nitrate uptake properties of plants grown at different relative rates of nitrogen supply. II. Activity and affinity of the nitrate uptake system inPisumandLemnain relation to nitrogen availability and nitrogen demand

AbstractNet nitrate uptake rates were measured and the kinetics calculated in non‐nodulatedPisum sativumL. cv. Marma andLemna gibbaL. adapted to constant relative rates of nitrate‐N additions (RA), ranging from 0.03 to 0.27 d−1forPisumand from 0.05 to 0.40 d−1forLemna, Vmaxof net nitrate uptake (measured in the range 10 to 100 mmol m−3nitrate, i.e. ‘system I’) increased with RAin the growth limiting range but decreased when RAexceeded the relative growth rate (RGR), Kmwas not significantly related to changes in RA. On the basis of previous13N‐flux experiments, it is concluded that the differences in Vmaxat growth limiting RAare attributable to differences in influx rates. Linear relationships between Vmaxand tissue nitrogen concentrations were obtained in the growth limiting range for both species, and extrapolated intercepts relate well with the previously defined minimal nitrogen concentrations for plant growth (Oscarson, Ingemarsson &amp; Larsson, 1989). Analysis of Vmaxfor net nitrate uptake on intact plant basis in relation to nitrogen demand during stable, nitrogen limited, growth shows an increased overcapacity at lower RAvalues in both species, which is largely explained by the increased relative root size at low RA. A balancing nitrate concentration, defined as the steady state concentration needed to sustain the relative rate of increase in plant nitrogen (RN), predicted by RA, was calculated for both species. In the growth limiting range, this value ranges from 3.5 mmol m−3(RA0.03 d−1) to 44 mmol m−3(RA0.21 d−1) forPisumand from 0.2 mmol m−3(RA0.05 d−1) to 5.4 mmol m−3(RA0.03 d−1) forLemna.It is suggested that this value can be used as a unifying measure of the affinity for nitrate, integrating the performance of the nitrate uptake system with nitrate flux and long term growth and demand for nitrogen.

Effects of hypoxia and metabolic inhibition on the intracellular sodium activity of mammalian ventricular muscle.

1. Intracellular Na+ activity (aiNa) has been measured in Purkinje fibres from sheep heart and in ventricular muscle from rabbit heart during hypoxia and metabolic inhibition. The aiNa was measured using liquid sensor ion-sensitive microelectrodes. 2. Hypoxia, produced by replacement of O2 with N2 in the superfusate, produced an increase in aiNa. This increase was larger if sucrose replaced glucose in the superfusing Tyrode solution. The increase in aiNa was accompanied by a small depolarization. Upon reoxygenation aiNa decreased and cells rapidly repolarized. 3. When oxidative phosphorylation was inhibited by application of 2 mM-cyanide, aiNa increased. This increase was also accompanied by a small depolarization. Upon removal of cyanide, aiNa and membrane potential recovered to control levels. 4. After inhibiting glycolysis, by replacing glucose with 2-deoxy-D-glucose, inhibition of oxidative phosphorylation (by addition of cyanide or exposure to hypoxia) produced a much more rapid increase in aiNa and a large contracture. The rise in aiNa and the occurrence of a contracture could not be inhibited by application of amiloride (1 mM) or tetrodotoxin (1 microgram ml-1). Removal of cyanide or reoxygenation and replacement of glucose resulted in a rapid relaxation of the contracture and a slower decrease in aiNa. 5. The relative rates of increase in aiNa during metabolic inhibition were compared with the rate observed when Na+-K+-ATPase was inhibited by application of 10 mumols l-1 of the cardio-active steroid strophanthidin. The rate of increase of aiNa when both oxidative phosphorylation and glycolysis were inhibited was approximately twice that observed with only oxidative phosphorylation inhibited and approximately half that observed in the presence of 10 microM-strophanthidin. 6. Cyanide, applied when aiNa had been elevated (i.e. during exposure to 10 microM-strophanthidin to inhibit Na+-K+-ATPase), did not produce a contracture. The contracture observed in the presence of cyanide and 2-deoxy-D-glucose still occurred when Ca2+ was removed from the superfusate.

Unifying Nutrient–Chlorophyll Relationships in Lakes

We used data drawn from the literature to test some basic predictions derived from nutrient limitation theory. Contrary to expectation, nitrogen was not better correlated to chlorophyll in nitrogen limited lakes (as measured by the total nitrogen:total phosphorus (TN:TP) ratio). We also examined whether the variability in published relationships between chlorophyll a (Chla) and nutrient levels in lakes can be explained by differences in the relative concentrations of nitrogen and phosphorus (TN:TP ratio). Our results show that the coefficients and precision of the Chla = f(TP) and Chla = f(TN) regression equations vary systematically and concomitantly with TN:TP ratios, and are highest for lakes with TN:TP ratios of 23–28 (by weight). These findings were confirmed with independent data and explain the variability of published Chla = f(TP) relationships. We propose a model that predicts the coefficients of Chla = f(TP) and Chla = f(TN) equations for lakes with different TN:TP ratios. This model proved useful in predicting the chlorophyll trajectories of lakes over time. The results imply an "optimal" TN:TP ratio beyond which the relative rates of increase in chlorophyll with increasing nutrient concentrations are reduced.

Nitrate availability and shoot area development in small willow (Salix viminalis)

Abstract. The effect of nitrate supply upon leaf area development in willow (Salix viminalis) was investigated. Rooted cuttings were grown in culture solution at two different rates of exponentially‐increasing nitrate supply and with free access to other nutrients. During the lag‐phase in attaining stable nutrition, the rate of production of unfolded leaves, in the treatment with poorer N‐supply, decreased. After acclimation to the different N‐availabilities, the rate of dry matter increase per plant nitrogen was constant and the same in both treatments. The ratio of total leaf area to total amount of nitrogen in the plant was slightly higher in the treatment with poorer nitrogen supply. During the exponential (stable) phases of growth, nearly all the increase in total leaf area was attributable to main‐stem leaves; large numbers of leaves on axillary shoots in the treatment with better N‐supply contributed little to the total area. During the stable growth phase, the rate of production of unfolded leaves was the same in both treatments. Higher maximum values of relative rate of increase in area of single leaves were found with a better N‐supply and at higher leaf positions on the main stem. The duration of leaf expansion was not much affected by N‐supply. Final leaf size was greater at higher positions on the main‐stem. Within a treatment (investigated for poorer N‐supply), differences in final leaf size were proportional to differences in numbers of epidermal cells. Final leaf size was greater, at the same node, in the treatment with better N‐supply. Better N‐availability had increased the final size but not the number of epidermal cells. It was concluded that the higher exponential rate of total area increase with a better N‐supply was largely associated with higher rates of expansion in epidermal cells.

Tillering behavior in Oryza sativa I. III. The pattern and the relative rate of increase in tiller number.

孤立状態で育てた水稲の茎数増加について検討した. 茎数増加曲線は, 止葉より2葉下位の葉が抽出する頃までは, ロジスチック曲線で近似できた. 一方, タイムスケールを主茎葉齢でとると指数曲線で近似できた. このことから, 主茎葉齢を基準とした相対分げつ増加率(Rt)を求めた. まず, 茎数増加曲線を指数曲線で近似し, その係数から「平均的Rt」を求め, さらに, 具体的に一定期間ごとのRtを算出して検討した. その結果, 同周期生長を仮定した場合, 葉齢1ごとに計算したRtは変動が少なく, 平均的Rtとよく一致した. しかし, 約1葉齢間隔での実測値から直接算出したRtは, 葉齢10前後にピークを持っていた. ピークのできることは相対葉齢差の影響と考えられ, ピークのパターンには品種による差が認められた. さらに, 全ての分げつが出現すると仮定した場合の茎数増加曲線について, 同周期生長でのRtと, 相対葉齢差を加味した場合のRtとを求め検討した. そこから, 同周期生長でのRtの理論的最大値を出した. 同周期生長を仮定した場合のRtは, 比較的安定し, その値の大きさには品種間差が認められた. 従って, 分げつ性に対して好環境で育てた場合の, 同周期生長での平均的Rtを用いて, それぞれの品種の分げつ生産能力を表す指標をつくれる可能性があると考えた. さらにこの指標を用いれば, 品種を多げつ型と少げつ型に, あるいはさらにいくつかの分げつ型に分けることができると推察した.

Rheological studies of aqueous amylose gels: the effect of chain length and concentration on gel modulus

Aqueous amylose gels have been studied kinetically and at pseudoequilibrium as a function of polymer concentration and chain length. Pseudoequilibrium gel moduli (G′) for a range of amylose chain lengths (produced by enzymatic synthesis) show the same concentration dependences as other gelling biopolymers and have been analyzed by the method of Clark and Ross-Murphy (Br. Polym. J. 1985, 17, 164-168). This treatment is shown to lead to the accurate prediction of critical gelling concentrations and suggests that the cross-linking functionality of individual amylose chains is ∼DP/100 (DP = degree of polymerization). For a fixed concentration, shorter chain amylose systems are found to develop turbidity more rapidly and to attain higher final values, suggesting that decreasing amylose chain length results in more heterogeneous gel structures. The relative rates of turbidity and modulus increase for amylose gels are found to be dependent on chain length: for short chains (DP < 300) turbidity precedes gelation, whereas for longer chains (DP < 1100) gelation occurs before significant increase in turbidity.

A Correction for the Effect of Comminution on the Cation Exchange Capacity of Clay-Poor Sandstones

Summary It is well known that comminution (decrease of particle size by grinding) can increase the cation exchange capacity (CEC) of geologic materials. Because comminution is often a "first step" in sample preparation, it is desirable to be able to correct for comminution-induced effects. The relative increase in CEC of poorly lithified clay-poor sandstones and better-lithified shaly sandstones from Caño Limon Well 3 and La Yuca Well 6, Llanos basin, Colombia, correlated well (r≥0.97) with the square root of the duration of sample comminution. A method based on this correlation has been developed to correct for comminution-induced increases in the CEC of poorly lithified clay-poor sandstones. The method was also applied to the better-lithified shaly sandstones with good results. The rate of relative increase of the CEC with comminution showed an inverse correlation with the total weight percent clay in a specimen. This suggested that much of the increase of the CEC of the specimen was caused by an increase in the CEC of quartz, which was the dominant mineral in these rocks.

Band broadening of CH2 vibrations in the Raman spectra of polymethylene chains

The isotropic and anisotropic linewidths of methylene vibrations in a homologous series of alkanes of increasing chain length have been measured in the liquid state as a function of temperature. The bandwidths of the CH2 symmetric stretching modes, which are in Fermi resonance with overtones of the CH2 bending vibrations, are temperature insensitive over a 200 K interval; this is best explained in terms of a vibrational dephasing mechanism (inhomogeneous broadening) for these modes. In contrast, for the bending and antisymmetric stretching vibrations, significant band broadening occurs over this same temperature interval. In addition, for these modes, both the absolute value of the bandwidth and the relative rate of increase of the bandwidth with increasing temperature, decrease with increasing chain length. These observations are consistent with a reorientational broadening mechanism as the principal bandwidth contribution for these vibrations. Hindered end-over-end rotation of the molecules, which contributes to the band broadening for very low molecular weight alkanes, rapidly becomes too slow to be observable on the time scale of the Raman experiment for the higher molecular weight alkanes and polyethylene. For longer chain lengths, torsional backbone motions coupled to the high frequency antisymmetric stretching modes can account for the breadth of the bands.

Growth response to step‐decrease in nutrient availability in small birch (Betula pendula Roth)

Abstract Changes in the uptake and allocation of carbon and nitrogen, after a step‐decrease in nutrient availability, were investigated in small birch (Betula pendula Roth). By demonstrating stable nutrition, before and after the decrease in nutrient supply, it was possible to eliminate the effects of plant size and age. Immediately following the step‐decrease in nutrient availability, net nitrogen uptake to leaves and the relative rate of increase in shoot area tended to zero. Although photosynthetic rate per shoot area decreased, carbon uptake remained in excess of that used in structural growth and respiration. More of the excess carbon was accumulated as starch in leaves than in roots. After a lag phase, the relative rates of increase in plant dry matter, starch amount, net nitrogen uptake to leaves and shoot area development equalled that of the reduced rate of nutrient supply. It is concluded that the reduction in plant relative growth rate was much more attributable to the reduced allocation of photosynthate to leaf area growth than to the reduction in photosynthesis per shoot area.