Growth and biomass turnover ofHydrocharis dubia L. cultured under different nutrient conditions

Growth of a floating-leaved plant,Hydrocharis dubia L., was examined under varying nutrient conditions between 0.3 and 30 mgN l⁻¹ total inorganic nitrogen.H. dubia plants cultured under the most nutrient-rich condition showed the highest maximum ramet density (736 m⁻²), the highest maximum biomass (80.4 g dry weight m⁻²), and the highest total net production (185 g dry weight m⁻² in 82 days). Plants under nutrient-poor conditions had a relatively large proportion of root biomass and a small proportion of leaves with a long life span. Compared with other floating-leaved and terrestrial plants, the maximum biomass ofH. dubia was relatively small. This, and the rapid biomass turnover, was related to the short life span of leaves (13.2–18.7 days) and large biomass distribution to leaves.     

ANATOMICAL AND PHYSIOLOGICAL ACCLIMATION OF FATSIA JAPONICA LEAVES TO IRRADIANCE

Anatomical and physiological leaf characteristics and biomass production of Fatsia japonica plants were studied. Plants were grown in a growth chamber at 300 μmol m^-2 s^-1 (high light) and 50 μmol m^-2 s^-1 (low light) photosynthetic photon flux density. Plants grown under high light showed a net maximum photosynthetic rate 44% higher than plants grown under low light; the light compensation point and the light saturation point were also higher in high-light plants. Photosynthetic oxygen evolution in isolated chloroplasts was about 40% higher in high-light plants. However, chlorophyll content on a dry weight basis, on a leaf area basis, and per chloroplast was greater in plants grown under low light. Leaf thickness in high-light plants was 13% higher than in low-light plants. The number of chloroplasts was 30% higher in high-light leaves, while chloroplast size was only slightly higher. Chloroplast ultrastructure was also affected by light. Leaf dry weight, leaf area, and biomass production per plant were drastically reduced under low light. Thus, F. japonica is a plant that is able to acclimate to different photosynthetic photon flux density by altering its anatomical and physiological characteristics. However, low-light acclimation of this plant has a considerable limiting effect on biomass production.     

Salinity effect on plant growth and leaf demography of the mangrove, Avicennia germinans L.

We assessed the effect of salinity on plant growth and leaf expansion rates, as well as the leaf life span and the dynamics of leaf production and mortality in seedlings of Avicennia germinans L. grown at 0, 170, 430, 680, and 940 mol m⁻³ NaCl. The relative growth rates (RGR) after 27 weeks reached a maximum (10.4 mg g⁻¹ d⁻¹) in 170 mol m⁻³ NaCl and decreased by 47 and 44% in plants grown at 680 and 940 mol m⁻³ NaCl. The relative leaf expansion rate (RLER) was maximal at 170 mol m⁻³ NaCl (120 cm m⁻² d⁻¹) and decreased by 57 and 52% in plants grown at 680 and 940 mol m⁻³ NaCl, respectively. In the same manner as RGR and RLER, the leaf production (P) and leaf death (D) decreased in 81 and 67% when salinity increased from 170 to 940 mol m⁻³ NaCl, respectively. Since the decrease in P with salinity was more pronounced than the decrease in D, the net accumulation of leaves per plant decreased with salinity. Additionally, an evident increase in annual mortality rates (λ) and death probability was observed with salinity. Leaf half-life (t _0.5) was 425 days in plants grown at 0 mol m⁻³ NaCl, and decreased to 75 days at 940 mol m⁻³ NaCl. Thus, increasing salinity caused an increase in mortality rate whereas production of new leaves and leaf longevity decreased and, finally, the leaf area was reduced.     

Matter-economical roles of the evergreen foliage ofAucuba japonica,an understory shrub in the warm-temperate region of Japan

Leaf demography and productivity ofAucuba japonica, an understory shrub in the warm-temperate region, were examined and dry matter economy was analyzed to evaluate the roles of the evergreen foliage. Turnover of leaves occurred during a short period in spring. The mean leaf life span was about 2.6 years. Annual NAR (net assimilation rate) of each sample shoot was calculated from the biomass and the total dead mass estimated from scars of leaves and floral parts. The average NAR was 1.34±0.22 g·g⁻¹·yr⁻¹. The ratio of dry matter produced by leaves during their whole life span to the initial investment was 3.45±0.37. The annual NAR calculated for individual plants was negatively related to the life span of their leaves. The seasonal change in SLW (specific leaf weight) showed that the reserve material in leaves was accumulated from autumn to early spring and was consumed for the growth of new organs in the following season. The dry matter withdrawn in spring from the overwintering foliage amounted to 40% of dry mass of the new organs developed.     

Above-ground biomass structure of a Chusquea tessellata bamboo páramo,Chingaza National Park,Cordillera Oriental,Colombia

The present study was carried out in the bamboo (Chusquea tessellata) páramo of Parque Natural Nacional de Chingaza, Eastern Cordillera, Colombia from December 1987 to April 1988. Above-ground biomass structure of bamboo páramo was quantified in 16 plots. These data are compared with previous results on above-ground biomass structure of bunch-grass (Calamagrostis spp.) páramos.The total (non-living and living) above-ground biomass of a Chusquea tessellata bamboo páramo was low (2,625 g DW · m^–2) compared to bunch-grass páramo. Nevertheless, higher values of standing living biomass and litter are found in the bamboo páramo due to the leaf shed of the bamboo. The thick litter layer may inhibit germination and growth of nearby plants.Maximum biomass is found near the ground surface. Cumulative LAI (In transformed) and height in the bamboo vegetation are related parabolically for Chusquea tessellata and linearly for bunch-grass due to differences in leaf distribution. The mean bifacial LAI of living Chusquea tessellata leaves is 2.2 m² · m^–2, whereas it is 2.5 m² · m^-2 for all Poaceae.     

Interspecific difference in the photosynthesis–nitrogen relationship: patterns,physiological causes,and ecological importance

The photosynthesis–nitrogen relationship is significantly different among species. Photosynthetic capacity per unit leaf nitrogen, termed as photosynthetic nitrogen-use efficiency (PNUE), has been considered an important leaf trait to characterise species in relation to their leaf economics, physiology, and strategy. In this review, I discuss (1) relations between PNUE and species ecology, (2) physiological causes and (3) ecological implications of the interspecific difference in PNUE. Species with a high PNUE tend to have high growth rates and occur in disturbed or high productivity habitats, while those with a low PNUE occur in stressful or low productivity habitats. PNUE is an important leaf trait that correlates with other leaf traits, such as leaf mass per area (LMA) and leaf life span, irrespective of life form, phylogeny, and biomes. Various factors are involved in the interspecific difference. In particular, nitrogen allocation within leaves and the mesophyll conductance for CO₂ diffusion are important. To produce tough leaves, plants need to allocate more biomass and nitrogen to make thick cell walls, leading to a reduction in the mesophyll conductance and in nitrogen allocation to the photosynthetic apparatus. Allocation of biomass and nitrogen to cell walls may cause the negative relationship between PNUE and LMA. Since plants cannot maximise both PNUE and leaf toughness, there is a trade-off between photosynthesis and persistence, which enables the existence of species with various leaf characteristics on the earth.     

Carbon assimilation in contrasting streamside and inland Spartina alterniflora salt marsh

Carbon assimilation and standing crop biomass of Spartina alterniflora were studied in a contrasting streamside and inland salt marsh in Louisiana Gulf coast, USA. A substantially lower leaf dry weight, leaf area index, and standing crop biomass were recorded for inland plants as compared to streamside plants. Net assimilation rates ranged between 8 to 25 mol m^–2 s^–1 for streamside and between 4 to 19 mol m^–2 s^–1 for inland plants. The average photosynthetic rates were significantly lower for inland plants which were growing in an apparently more stressed environment. In addition, the differences were more profound with progression of the growing season. The reduced photosynthetic activity in the inland marsh was attributed to greater soil waterlogging, increased anaerobic root respiration, plant toxins (sulfide), restricted nutrient uptake or a combination of these factors.Abbreviations E_h = redox potential - g_w = stomatal conductance - LAI = leaf area index - P_n = net photosynthesis - PPFD = photosynthetic photon flux density - T₁ = leaf temperature     

Light acclimation in leaves of the juvenile and adult life phases of ivy (Hedera helix)

Hoflacher, H. and Bauer, H. 1982. Light acclimation in leaves of the juvenile and adult life phases of ivy (Hedera helix). – Physiol. Plant. 56: 177–182. Light acclimation was investigated during the juvenile and adult life phases of the whole-plant-development in Hedera helix L. For this purpose, cuttings of the juvenile and adult parts of one single parent plant were grown under low-light (PAR 30–50 μmol photons m^?2 s^?1) and high-light (PAR 300–500 μmol m^?2 s^?1) conditions: CO₂ exchange, chloroplast functions, and specific anatomy of fully developed leaves differentiated under these conditions were determined. In juvenile plants the leaves formed under low and high light had light-saturated rates of net photosynthesis of 6.5 and 11.1 mg CO₂ (dm leaf area)^?2 h^?1, respectively. In adult plants the rates were 9.4 and 22.2 mg dm^?2 h^?1, indicating a more pronounced capacity for acclimation to strong light in the adult life phase. Higher photosynthetic capacities were accompanied by higher conductances for the CO₂ transfer through the stomata, leading to almost the same CO₂ concentration in the intercellular spaces. Thus, stomatal conductances were not primarily responsible for the different photo-synthetic capacities. The higher rates in adult and high-light grown leaves were mainly the result of formation of thicker leaves with more chloroplasts per unit leaf area. Expressed per chloroplast, the photosynthetic capacity, the Hill reaction, and the activity of ribulose bisphosphate carboxylase were almost identical in plants grown in low-light and high-light. Measurements of photosynthetic capacity and thickness of leaves of Hedera sampled from field habitats with contrasting light regimes confirm the results of growth chamber studies. It is, therefore, concluded that both life phases of Hedera are capable of acclimating to strong light, but that during the juvenile phase this capacity is not fully developed.     

Morphological and anatomical determinants of mesophyll conductance in wild relatives of tomato (Solanum sect. Lycopersicon,sect. Lycopersicoides; Solanaceae)

Natural selection on photosynthetic performance is a primary factor determining leaf phenotypes. The complex CO₂ diffusion path from substomatal cavities to the chloroplasts – the mesophyll conductance (g_m) – limits photosynthetic rate in many species and hence shapes variation in leaf morphology and anatomy. Among sclerophyllous and succulent taxa, structural investment in leaves, measured as the leaf dry mass per area (LMA), has been implicated in decreased g_m. However, in herbaceous taxa with high g_m, it is less certain how LMA impacts CO₂ diffusion and whether it significantly affects photosynthetic performance. We addressed these questions in the context of understanding the ecophysiological significance of leaf trait variation in wild tomatoes, a closely related group of herbaceous perennials. Although g_m was high in wild tomatoes, variation in g_m significantly affected photosynthesis. Even in these tender‐leaved herbaceous species, greater LMA led to reduced g_m. This relationship between g_m and LMA is partially mediated by cell packing and leaf thickness, although amphistomy (equal distribution of stomata on both sides of the leaf) mitigates the effect of leaf thickness. Understanding the costs of increased LMA will inform future work on the adaptive significance of leaf trait variation across ecological gradients in wild tomatoes and other systems.     

A new life table of leaves ofPhaseolus vulgris L. in relation to their position within the canopy and plant density

In order to demonstrate in detail the relationship between the longevity and productivity of leaves within a canopy, a new life table approach, the ‘bioeconomic life table’, was applied to the leaves of kidney bean plants (Phaseolus vulgaris L.) in relation to planting density and their position within the canopy. The net photosynthetic rate for upper leaves under full daylight tended to decline gradually due to leaf senescence from about 20 days after leaf emergence, and for the lower leaves the decrease was very rapid due to both shading and senescence about 10 days after emergence. Analysis of the survivorship curves and daily surplus production of leaves suggested that the lower and middle leaves, especially the latter, survived without surplus production of dry matter after they had reached mean longevity, and while the upper leaves at high density had a much shorter mean longevity, they had very large values of daily surplus production throughout the survival period. For the total foliage, the summed value of accumulated surplus production during the survival period was about five times as large as the summed value of the dry weight of the dead leaves, regardless of planting density. The daily rate of canopy leaf respiration was almost proportional to that of canopy gross photosynthesis for the various leaf area indices of the canopy, so that there was no optimum leaf area index that maximized canopy daily surplus production.     

Elevated [CO2] and increased N supply reduce leaf disease and related photosynthetic impacts on Solidago rigida

To evaluate whether leaf spot disease and related effects on photosynthesis are influenced by increased nitrogen (N) input and elevated atmospheric CO₂ concentration ([CO₂]), we examined disease incidence and photosynthetic rate of Solidago rigida grown in monoculture under ambient or elevated (560 μmol mol⁻¹) [CO₂] and ambient or elevated (+4 g N m⁻² year⁻¹) N conditions in a field experiment in Minnesota, USA. Disease incidence was lower in plots with either elevated [CO₂] or enriched N (−57 and −37%, respectively) than in plots with ambient conditions. Elevated [CO₂] had no significant effect on total plant biomass, or on photosynthetic rate, but reduced tissue%N by 13%. In contrast, N fertilization increased both biomass and total plant N by 70%, and as a consequence tissue%N was unaffected and photosynthetic rate was lower on N fertilized plants than on unfertilized plants. Regardless of treatment, photosynthetic rate was reduced on leaves with disease symptoms. On average across all treatments, asymptomatic leaf tissue on diseased leaves had 53% lower photosynthetic rate than non-diseased leaves, indicating that the negative effect from the disease extended beyond the visual lesion area. Our results show that, in this instance, indirect effects from elevated [CO₂], i.e., lower disease incidence, had a stronger effect on realized photosynthetic rate than the direct effect of higher [CO₂].     

Effect of soil moisture on leaf ecophysiology of <Emphasis Type="Italic">Parasenecio yatabei</Emphasis>, a summer-green herb in a cool–temperate forest understory in Japan

Leaf physiological and gas-exchange traits of a summer-green herbaceous perennial, Parasenecio yatabei, growing along a stream were examined in relation to leaf age. In its vegetative phase, the aerial part of this plant consists of only one leaf and provides an ideal system for the study of leaf longevity. Volumetric soil water content (SWC) decreased with increasing distance from the stream, whereas relative light intensity was nearly constant. The light-saturated net CO₂ assimilation rate (A _sat) and leaf stomatal conductance (gs) were approximately 1.5-fold and 1.4-fold higher, respectively, in the lower slope near the mountain stream than in the upper slope far from the mountain stream. The lifespan of aerial parts of vegetative plants significantly increased with decreasing SWC. The leaf mass-based nitrogen content of the leaves (N _mass) was almost constant (ca. 2.2%); however, the maximum carboxylation rate by ribulose-1,5-biphosphate carboxylase/oxygenase (rubisco) (V _cmax) and photosynthetic nitrogen use efficiency (PNUE, A _sat/N _area) decreased more slowly in the upper slope than in the lower slope. The higher leaf photosynthetic activity of P. yatabei plants growing lower on the slope leads to a decrease in V _cmax and PNUE in the early growing season, and to a shorter leaf lifespan.     

Contrasting patterns of photosynthetic acclimation and photoinhibition in two evergreen herbs from a winter deciduous forest

The relationship between the microclimate within an Oak-Hickory forest and photosynthetic characters of two resident evergreen herbs with contrasting leaf phenologies was investigated on a monthly basis for 1 full year. Heuchera americana has leaf flushes in the spring and fall, with average leaf life spans of 6–7 months. Hexastylis arifolia produces a single cohort of leaves each spring with a leaf life span of 12–13 months. We predicted that among evergreen plants inhabiting a seasonal habitat, a species for which the frequency of leaf turnover is greater than the frequency of seasonal extremes would have a greater annual range in photosynthetic capacity than a species that only produced a single flush of leaves during the year. Photosynthetic parameters, including apparent quantum yield, maximum photosynthetic capacity (P_max), temperature of maximum photosynthesis, photochemical efficiency of PSII and leaf nitrogen (N) and chlorophyll concentrations, were periodically measured under laboratory conditions in leaves sampled from natural populations of both species. Mature leaves of both species acclimated to changing understory conditions with the mean seasonal differences being significantly greater for Heuchera than for Hexastylis. Area based maximum photosynthetic rates at 25°C were approximately 250% and 100% greater in winter leaves than summer leaves for Heuchera and Hexastylis respectively. Nitrogen concentrations were highest in winter leaves. Chlorophyll concentrations were highest in summer leaves. Low P_max/N values for these species suggest preferential allocation of leaf nitrogen into non-photosynthetic pools and/or light-harvesting function at the expense of photosynthetic enzymes and electron transport components. Despite the increase in photosynthetic capacity, there was evidence of chronic winter photoinhibition in Hexastylis, but not in Heuchera. Among these ecologically similar species, there appears to be a trade-off between the frequency of leaf production and the balance of photosynthetic acclimation and photoinhibition.     

Structure and annual biomass production of Nymphoides peltata (Gmel.) O. Kuntze (Menyanthaceae)

In 1980, the monthly changes in biomass and plant surface area, together with aspects of production of Nymphoides peltata (Gmel.) O. Kuntze were studied in a backwater of the river Waal (The Netherlands). Furthermore, the seasonal changes in the vertical stratification of the biomass were studied in concrete tanks. These seasonal changes were studied with the harvest method, while the estimation of the net primary production was based upon biomass data and turnover rates of various plant parts. The data thus obtained are compared with those of other water plants, especially other floating-leaved macrophytes. In 1980, N. peltata reached its peak biomass in August being 372 g AFDW m⁻² (ash-free dry weight). The annual net productivity of Nymphoides was estimated to be 1036 g AFDW m⁻². The leaf blades and their petioles contributed most to the production.     

Seasonal patterns in water use and leaf turnover of different plant functional types in a species-rich woodland,south-western Australia

Woodlands in south-western Australia are evergreen and transpire throughout the year despite the long, hot and dry summers of the Mediterranean climate. Results from a case study in a species-rich Banksia woodland are used to discuss the ecological and physiological properties that appear to be essential features of this and similar communities. Tree, shrub and perennial herbaceous species with long-lived leaves dominate the community, whereas winter-green herbaceous species with short-lived leaves constitute a minor group. The total leaf area index is therefore reasonably constant in all seasons. Leaf area index is low and canopies are open, causing good coupling between the vegetation and the atmosphere, and making stomatal control an effective regulator of transpiration. Mean maximum (winter) stomatal conductances were high at approximately 300 mmol m^–2 s^–1. Deep-rootedness allows the dominant species to access soil moisture throughout the unsaturated zone, and down to the capillary fringe of the saturated zone. Shrubs and herbs with shallow roots experience greater drought stress during summer. Rates of community evapotranspiration are limited by leaf area index in the wet season, and further reduced by stomatal closure in the dry season. Deep-rooted plants appear to decrease their stomatal conductance before the development of severe drought stress. Such conservative behaviour, possibly related to plant hydraulic constraints, is a contributing factor to the limited seasonality in community water use.     

Contrasting modes of light acclimation in two species of the rainforest understory

In tropical rainforests, the increased light associated with the formation of treefall gaps can have a critical impact on the growth and survivorship of understory plants. Here we examine both leaf-level and whole-plant responses to simulated light gap formation by two common shade-tolerant shrubs, Hybanthus prunifolius and Ouratea lucens. The species were chosen because they differed in leaf lifespans, a trait that has been correlated with a number of leaf- and plant-level processes. Ouratea leaves typically live about 5 years, while Hybanthus leaves live less than 1 year. Potted plants were placed in the understory shade for 2 years before transfer to a light gap. After 2 days in high light, leaves of both species showed substantial photoinhibition, including reduced CO₂ fixation, F _v/F _m and light use efficiency, although photoinhibition was most severe in Hybanthus. After 17 days in high light, leaves of both species were no longer photoinhibited. In response to increased light, Ouratea made very few new leaves, but retained most of its old leaves which increased photosynthetic capacity by 50%. Within a few weeks of transfer to high light, Hybanthus had dropped nearly all of its shade leaves and made new leaves that had a 2.5-fold greater light-saturated photosynthetic rate. At 80 days after transfer, the number of new leaves was 4.9-fold the initial leaf number. After 80 days in high light, Hybanthus had approximately tenfold greater productivity than Ouratea when leaf area, photosynthetic capacity, and leaf dark respiration rate were all taken into account. Although both species are considered shade tolerant, we found that their growth responses were quite different following transfer from low to high light. The short-lived Hybanthus leaves were quickly dropped, and a new canopy of sun leaves was produced. In contrast, Ouratea showed little growth response at the whole-plant level, but a greater ability to tolerate light stress and acclimate at the leaf level. These differences are consistent with predictions based on leaf lifespan and are discussed within the context of other traits associated with shade-tolerant syndromes. Received: 25 March 1999 / Accepted: 16 August 1999     

The influence of leaf area on the rooting physiology of leafy stem cuttings of Terminalia spinosa Engl.

Summary The effect of different leaf areas on the rooting of Terminalia spinosa Engl. cuttings in an non-mist propagation system in glasshouses at Edinburgh was investigated by trimming the leaves to 0, 7.5, 15 and 30 cm² before cuttings were severed from stockplants. Cuttings were taken to a standard length of 5 cm from the lateral shoots of previously pruned stockplants grown in a tropicalised glasshouse. During the rooting period, photosynthetic rate, stomatal conductance, water potential and relative water content of the cuttings were assessed at regular intervals. It was found that (i) removal of the entire leaf area prevented rooting; (ii) cuttings with a 7.5 cm², 15 cm² and 30 cm² leaf all achieved 80% rooting after 3 weeks; (iii) an increase in leaf area from 7.5 cm² to 30 cm² increased the rate of rooting and the length of the longest root after 2 weeks, but also increased the number of original leaves abscised after 6 weeks; and (iv) the greatest number of new leaves were produced by cuttings with 7.5 cm² and 15 cm² leaf area per cutting. All leafy cuttings actively photosynthesized during the propagation period, with a mean rate of 2 mol CO₂ m^-2 s^-1 with an irradiance of 100 mol m^-2 s^-1. Cuttings with 30 cm² leaf area had lower relative water contents, lower stomatal conductances and lower photosynthetic rates per unit leaf area than those with a 7.5 cm² and 15 cm² leaf. It was concluded that T. spinosa cuttings are easy to root, provided the cuttings have leaves to produce current assimilates.A member of the Edinburgh Centre for Tropical Forests     

Structure of the Photosynthetic Apparatus in Leaves of Freshwater Hydrophytes: 1. General Characteristics of the Leaf Mesophyll and a Comparison with Terrestrial Plants

The structure of photosynthetic elements was investigated in leaves of 42 boreal plant species featuring different degrees of submergence (helophytes, neustophytes, and hydatophytes). The mesophyll structure types were identified for all these species. Chlorenchyma tissues and phototrophic cells were quantitatively described by such characteristics as the sizes of cells and chloroplasts in the mesophyll and epidermis, the abundance of cells and chloroplasts in these tissues, the total surface area of cells and chloroplasts per unit leaf area, the number of plastids per cell, etc. The hydrophytes typically had thick leaves (200–350 m) with a well-developed aerenchyma; their specific density per unit area (100–200 mg/dm²) was lower than in terrestrial plants. Mesophyll cells in aquatic plants occupied a larger volume (5–20 × 10³m³) than epidermal cells (1–15 × 10³m³). The number of mesophyll cells per unit leaf area was nearly 1.5 times higher than that of epidermal cells. Chloroplasts were present in the epidermis of almost all species, including emergent leaves, but the ratio of the chloroplast total number to the number of all plastids varied depending on the degree of leaf submergence. The total number of plastids per unit leaf area (2–6 × 10⁶/cm²) and the surface of chloroplasts per unit leaf area (2–6 cm²/cm²) were lower in hydrophytes than in terrestrial plants from climatically similar habitats. The functional relations between mesophyll parameters were similar for hydrophytes and terrestrial plants (a positive correlation between the leaf weight per unit area, leaf thickness, and the number of mesophyll cells per unit leaf area), although no correlation was found in hydrophytes between the volume of mesophyll cells and the leaf thickness. Phototrophic tissues in aquatic plants contributed a larger fraction to the leaf weight than in terrestrial plants, because the mechanical tissues were less developed in hydrophytes. The CO₂assimilation rates by leaves were lower in hydrophytes than in terrestrial plants, because the total surface area of chloroplasts per unit leaf area is comparatively small in hydrophytes, which reduces the conductivity for carbon dioxide diffusion towards the carboxylation sites.     

Leaf dynamics of seedlings of rain forest species in relation to canopy gaps

Summary Leaf dynamics of eight tropical rain forest species seedlings was studied in three environments: the shaded forest understorey, a small gap of ±50 m², and a large gap of ±500 m². Leaf production rate and leaf loss rate were enhanced in gaps, and a large gap resulted in larger increases than a small gap. For most species net leaf gain rate was larger in gaps, although this rate was not always largest in the large gap. Leaf loss decreased, and leaf survival percentages increased with increasing shade tolerance of species, indicating a slower leaf turnover for more shade tolerant species. Leaf area growth rate was only partly determined by net leaf gain rate. Ontogenetic effects on leaf size were also important, especially in the large gap. Species which possessed leaves with high specific leaf weight (SLW) showed lower leaf loss rates and higher leaf survival percentages than species with low SLW leaves. Leaf life span seemed to be related to leafcost per unit area. The relation of specific patterns in leaf production and leaf loss to the regeneration mode of the species is briefly discussed.     

Trade-offs between the persistence of foliage and productivity in two<Emphasis Type="Italic"> Pinus</Emphasis> species

We investigated interspecific variation in leaf lifespan (persistence) and consequent differences in leaf biochemistry, anatomy, morphology, patterns of whole-tree carbon allocation and stand productivity. We tested the hypothesis that a species with short-lived foliage, Pinus radiata D. Don (mean leaf lifespan 2.5 years), grows faster than P. pinaster Ait., a species with more persistent foliage (leaf lifespan 5.6 years), and that the faster growth rate of P. radiata is associated with a greater allocation of nitrogen and carbon to photosynthetic tissues across a range of scales. In fully sunlit foliage, the proportion of leaf N in the major photosynthetic enzyme Rubisco (ribulose-1, 5-bisphosphate carboxylase) was greater in P. radiata than in P. pinaster, and, in mid-canopy foliage, the proportion of leaf N in thylakoid proteins was greater in P. radiata. A lesser proportion of needle cross-sectional area was occupied by structural tissue in P. radiata compared to P. pinaster. Foliage mass in stands of P. radiata was 9.7 t ha^–1 compared with 18.2 t ha^–1 in P. pinaster while leaf area index of both species was similar at 4.6 m² m^–2, owing to the compensating effect of differences in specific leaf area. Hence trade-offs between persistence and productivity were apparent as interspecific differences in patterns of whole-tree carbon allocation, needle morphology, anatomy and biochemistry. However, these interspecific differences did not translate into differences at the stand scale since rates of biomass accumulation were similar in both species (P. radiata 6.9±0.9 kg year^–1 tree^–1; P. pinaster 7.4±0.9 kg year^–1 tree^–1). The similarities in performance at larger scales suggest that leaf area index (and radiation interception) determines growth and productivity. Received: 13 July 1999 / Accepted: 31 January 2000