Shade Species Research Articles

Shade effect on coffee production at the northern Tzeltal zone of the state of Chiapas, Mexico

The necessity of on-farm research to assess the relationship between shade ecological features and yields has been broadly recognised. On this basis, a more sustainable coffee system could be developed, with better conservation of natural resources. An on-farm research project was conducted in the municipality of Chilón, Chiapas, Mexico, with the objectives of investigating the effect of shade structure on coffee grain yield and assessing the potential uses of associated plant species. Results showed that shade cover percentage and coffee shrub density had significant effects on yields. Maintaining coffee shrub density as a constant, a regression equation related yield to percentage shade by a quadratic polynomial. Coffee density had a significant effect on yields but shade tree density had no effect. Coffee cultivar, age of coffee stand, species richness, shade tree density, basal area, slope and aspect did not have significant effects on coffee yields. Shade tree cover had a positive effect between 23 and 38% shade cover and yield was then maintained up to 48%. Production may decrease under shade cover >50%. A total of 61 shade species were found, with an average density of 260 trees per hectare, the majority of them being indigenous species, used as food, construction materials and as firewood. The role of ecological features associated with shade on yields and availability of natural resources obtained from coffee systems are discussed.

The relevance of morphological plasticity in the simulation of competition between maize and Datura stramonium

The INTERCOM model was calibrated for Datura stramonium and maize with data from monoculture plots, and used to simulate the competition between the weed and the crop. The model adequately simulated the growth (leaf area index, above‐ground biomass, plant height, yield) of both species in monoculture. In competition, the growth of D. stramonium and the competitive effect of D. stramonium on the growth of maize were clearly underestimated. Simulation of competition was improved when the observed morphological adaptations of D. stramonium under competitive light stress, as reflected in dry‐matter partitioning, height growth and specific leaf area (SLA) were considered. Model analysis demonstrated that the observed changes in SLA and height growth were more relevant for the increased competitive ability of D. stramonium. The modification of the model in order to simulate the effect of shading by an overtopping species in the SLA of the shaded species improved model simulation of competition.

Open spaces as habitats for vascular ground flora species in the woods of central Lincolnshire, UK

The vascular flora of open space habitats was examined in 89 ancient woods and 273 recent secondary woods in Central Lincolnshire by means of whole-site species lists. 467 species were found in the ground vegetation of all 362 woods combined, of which the majority (60%) were strongly associated with open space habitats. Within individual woods, however, shade species generally constituted a majority of the total flora, and in several very small woods open space species were completely absent, but in large woods (>40 ha) open space species often outnumbered the shade species. Open space habitats within woods were not adequate substitutes for semi-natural grassland, heath and mire, for most of the rare and specialised species of these habitats were rarely or never found in woods. Nevertheless, woodland rides supported rich mixtures of grassland and edge species, many of which have been largely eliminated from the intensively farmed land around the woods. If new woods on farmland (i) are located close to existing woods and non-woodland semi-natural habitats, (ii) extend to at least 3ha and (iii) include some permanent open spaces, the individual woods may become diverse habitats, and they will make a significant contribution to regional biodiversity.

309 Fertilizer Applications on the Growth of Three Groundcover Species in Sun and Shade

Use of groundcovers in the landscape is often limited due to their slow establishment rate compared to that of turf. Hedera helix L., (English ivy), Euonymus fortunei `Coloratus' (Turcz.) Hand.-Mazz. (purpleleaf wintercreeper euonymus), and Liriope spicata Lour. (creeping lily-turf) were evaluated in a full sun and 50% shade environment to determine the effects of fertilizer applications on their establishment and growth. Fertilizer treatments, of 13N-13P-13K at a rate of.45 kg/93 m2, used were: 1) at planting only; 2) at planting and once during the summer; 3) at planting, in summer, and once in the fall; or 4) at planting, in summer, in fall, and once the following spring. Data collected included fresh and dry weight comparisons of pruned material, percentage canopy cover, plant quality and vigor by visual assessment and photographs, and time required for maintenance of each plot. Results show limited fertilizer effects and interaction according to species during the first several months of growth. Establishment and survivability of Hedera was influenced mainly by light exposure rather than fertilizer applications. There was no difference in establishment rates between Liriope and Euonymus, however, under shade, Euonymus did not develop its characteristic fall color. Hedera was established in one season under 50% shade and can be considered very competitive with turf under the same conditions.

Photosynthetic responses to CO2 concentration and photon fluence rates in the CAM‐cycling plant Delosperma tradescantioides (Mesembryanthemaceae)

Responses of gas exchange and photosynthesis to changes in CO2 concentration and PPFD were examined in well watered plants of Delosperma tradescantioides Bgr. to establish the relative importance of these environmental changes on the photosynthetic machinery in this CAM‐cycling species which grows naturally in both exposed and partly shaded environments. Plants were grown at two PPFDs (220 [LL] and 550 [HL]μmol m−2 s−1). HL plants had larger leaves with higher specific weight, water content and diurnal malic acid fluctuation. Photosynthetic PPFD responses were typically those of sun and shade species for HL and LL plants, both under 21% O2 and non‐photorespiratory (2% O2) conditions. The CO2 compensation point in the absence of non‐photorespirational CO2 evolution in the light (Γ∗) was c. 30 μmol mol−1. Irradiation reduced mitochondrial respiration by >50%. Comparison of the PPFD responses of linear electron flow rates derived from gas exchange measurements and from fluorescence analysis (𝒥F) indicated effective photosynthetic control. 𝒥F was always larger than electron flow rates calculated from gas exchange, indicating that processes other than carboxylation and oxygenation were consistently important in energy consumption under all sampled environmental conditions. Regardless of PPFD during growth, electron flow to carboxylation and 𝒥F were linearly correlated, demonstrating that the photosynthetic apparatus was well adapted to PPFD during growth. In HL plants, non‐photochemical quenching increased, and photochemical quenching and the quantum yield of linear electron transport through PS II decreased more slowly with increasing PPFD than in LL plants. In plants of both treatments non‐photochemical energy dissipation seemed to be exhausted when the proportion of photons not utilizable by photochemistry exceeded 0·7. Results illustrate a pronounced ability of D. tradescantioides to acclimate to a 100% change in the prevailing PPFD and lend support to the hypothesis that CAM cycling might act as a photoprotective process.

Relationships between pupil working range and habitat luminance in flies and butterflies

The luminance range over which the pupil mechanism operates was measured with pupil reflectometry in 11 species of butterflies and 13 species of dipteran flies. The different species were selected to be as different as possible regarding the range of ambient luminances in which they are active. Habitat luminance ranges were also measured and correlated to luminances in the experimental situation. The pupil mechanism in butterflies operates in the centre of the luminance range in which the different species are active. Three distinct groups of butterflies with pupil sensitivities matched to their specific types of activity pattern were identified: species active only in direct sunlight, species active also in shaded places and species extending their activity into dawn and dusk. Quite differently, the pupil mechanisms of dipteran flies operate in the upper end of the ambient luminances, and in some species well above the luminances normally encountered by the animal. All fly pupils start to close roughly at the same luminance, irrespective of the luminances in which the species are active. The results suggest that the most important role for the pupil mechanism in many of the butterfly species is to maximize acuity over a wide range of luminances, whereas in flies it is to avoid saturation of transduction units and thereby maximize the photoreceptor's signal-to-noise ratio at high light intensities.

Different regulation of leaf respiration between Spinacia oleracea, a sun species, and Alocasia odora, a shade species

Mature leaves of shade species exhibit lower respiratory rates than those of sun species. To elucidate the mechanism underlying different respiratory rates between sun and shade species, we examined respiratory properties of leaves in Spinacia oleracea L., a sun species, and Alocasia odora (Lodd.) Spach, a shade species, with special reference to changes in the respiratory rate throughout the night. In S. oleracea, rates of both CO2 efflux and O2 uptake decreased with time during the night, whereas in A. odora both rates were virtually constant at lower levels. The rates of O2 uptake in S. oleracea increased upon addition of sucrose, and the rates attained were virtually identical throughout the night. However, the addition of an uncoupler [carbonyl cyanide p‐(trifluoromethoxy)‐phenylhydrazone; FCCP] did not alter the rates. In contrast, the rates of O2 uptake in A. odora were enhanced by the addition of FCCP, but not by sucrose. The concentrations of carbohydrates in the tissue decreased throughout the night in both species and the ATP/ADP ratio was always greater in A. odora. These results indicate that, in S. oleracea, the availability of respiratory substrate determines the respiratory rate, while the low respiratory rate in A. odora is ascribed to its low demand for ATP.

Different regulation of leaf respiration between Spinacia oleracea, a sun species, and Alocasia odora, a shade species

Different regulation of leaf respiration between Spinacia oleracea, a sun species, and Alocasia odora, a shade species

Acclimation of photosynthesis to irradiance and spectral quality in British plant species: chlorophyll content, photosynthetic capacity and habitat preference

ABSTRACTTwenty‐two common British angiosperms were examined for their ability to acclimate photosynthetically to sun and shade conditions. Plants were grown under low irradiance, far‐red enriched light (50 μmol m−2 s−1), selected to mimic as closely as possible natural canopy shade, and moderately high light of insufficient irradiance to induce photoinhibitory or photoprotective responses (300 μmol m−2 s−1). Light‐and CO2‐saturated photosynthetic rates of oxygen evolution (Pmax) and chlorophyll content were measured. Large variation was found in both parameters, and two ‘strategies’ for long‐term acclimation were identified: firstly a change in chlorophyll per unit leaf area which was found to correlate positively with photosynthetic capacity, and secondly changes in chlorophyll alb ratio and Pmax, indicative of alterations at the chloroplast level, which were not associated with a change in chlorophyll content per unit leaf area. Combinations of these two strategies may occur, giving rise to the observed diversity in photosynthetic acclimation. The extent and nature of photosynthetic acclimation were compared with an index of shade association, calculated from the association each species has with woodland. It was found that the greatest flexibility for change at the chloroplast level was found in those species possessing an intermediate shade association, whilst acclimation in ‘sun’ species proceeded by a change in chlorophyll content; obligate shade species showed little capacity for acclimation at either the chloroplast or leaf level. A framework for explaining the variation between plant species in leaf‐level photosynthetic capacity, in relation to the natural light environment, is presented. This is the first time the potential for light acclimation of photosynthesis in different plant species has been satisfactorily linked to habitat distribution.

Irradiance and nitrate‐dependent variation in growth and biomass allocation of Mycelis muralis. An analysis of its significance for a functional categorization of ‘sun’ and ‘shade’ plants

summaryThe biomass of Mycelis muralis (L.) Dumort plants increased with increases in growth irradiance and nitrate supply. Comparisons of the data from this study with published information indicate that biomass production and growth rate of M. muralis are comparable to that of a number of slow‐growing species from resource‐poor environments. Biomass allocation varied with growth irradiance and nitrate supply. At high irradiances and low nitrate supplies there was a significantly greater allocation of plant mass to roots, resulting in a lower leaf area ratio (LAR) and leaf mass ratio (LMR). In contrast to the findings of a number of other studies, light level and nitrate supply had interactive effects on leaf mass per unit area (LMA). Changes in LAR due to variations in irradiance were mainly a consequence of changes in LMR. Given the ability of M. muralis to grow in deep shade, this suggests that large changes to within‐leaf allocation (LMA) are not an essential requirement for growth at low irradiances. Conversely, because M. muralis can also grow in fully exposed situations, these traits might not exclude some shade species from high irradiance habitats. However, a low growth rate, or traits which result in a low growth rate, might be advantageous in a number of resource‐poor environments.

Establishment of Fagus sylvatica and Fraxinus excelsior in an old‐growth beech forest

Abstract. Distribution of tree seedlings, forest architecture, light conditions, ground vegetation and humus conditions were studied in a 45 m × 100 m area including multiple gaps in an old‐growth beech forest. Gaps were created after some beech trees had been felled in severe storms in February 1990. A group of adult ash trees is found near the study site. The data were analyzed by Correspondence Analysis. Young seedlings (< 4 yr), of both Fraxinus (a sun species) and Fagus (a shade species), were most abundant under the crown of beech trees in semi‐shade conditions, and where beech litter did not accumulate.Differences in the dissemination of Fraxinus and Fagus explained differences in the establishment of the two species. In contrast, older seedlings of beech established before the storms were more numerous in the gaps, suggesting a change in the ecological requirements of beech seedlings in the course of time.

Nitrogen Partitioning among Photosynthetic Components and its Consequence in Sun and Shade Plants

1. Chenopodium album (a sun species) and Alocasia macrorrhiza (a shade species) plants were grown under various photon flux densities (PFDs) to investigate whether nitrogen partitioning among photosynthetic components was optimized under any light conditions. The amounts of several photosynthetic components of the leaves were determined to examine nitrogen partitioning. 2. For the same PFD, nitrogen partitioning among photosynthetic components was similar in both species, except for leaves of C. album grown at 5% PFD, which showed a markedly smaller fraction of nitrogen in photosystem I. 3. Optimal nitrogen partitioning among photosynthetic components was estimated for various PFDs using a simulation model of leaf photosynthesis. At any PFD, the actual nitrogen partitioning was very similar to the estimated optimal partitioning. However, partitioning in C. album grown at 5% PFD deviated from the optimum. 4. For both species grown under any light conditions, estimated daily photosynthesis of actual leaves was very close to that of leaves with optimal partitioning. It is concluded that both species achieve nitrogen partitioning leading to nearly maximum carbon gain under any light condition.

Acclimation of Respiratory Properties of Leaves of Spinacia oleracea L., a Sun Species, and of Alocasia macrorrhiza (L.) G. Don., a Shade Species, to Changes in Growth Irradiance

To clarify the way in which the light available for growth affects respiration in leaves of sun and shade plants, we examined the respiratory properties of mature leaves of Spinacia oleracea L., a sun species, and of Alocasia macrorrhiza (L.) G. Don., a shade species, that had been grown at various irradiances. In leaves of S. oleracea, the respiratory rates, on a dry mass basis, decreased with time during the night, and the higher was the growth irradiance during the day, the higher was the respiratory rate. The marked decreases in the respiratory rate during the night were accompanied by decreases in the concentration of carbohydrates in the leaves. By contrast, the respiratory rates of leaves of A. macrorrhiza were virtually constant throughout the night and the absolute rates were lower than those of S. oleracea even though the absolute value of the concentration of carbohydrates and its decrease at night resembled to those in S. oleracea. The maximum activities of respiratory enzymes were also similar to those in S. oleracea. However, the leaves of A. macrorrhiza contained less soluble protein than those of S. oleracea. These results suggest that, in S. oleracea, the concentration of carbohydrates might determine the respiratory rate while such is not the case in A. macrorrhiza. The lower respiratory rates in A. macrorrhiza might be due to a lower demand for ATP.

Contribution of intercellular reflectance to photosynthesis in shade leaves

ABSTRACTThe potential contribution of intercellular light reflectance to photosynthesis was investigated by infiltrating shade leaves with mineral oil. Infiltration of leaves of Hydrophyllum canadense and Asarum canadense with mineral oil decreased adaxial leaf reflectance but increased transmittance. As a result of the large increase in transmittance, infiltration caused a decrease in absorptance of 25% and 30% at 550 and 750 nm, respectively. Thus, intercellular reflectance increased absorptance in these species by this amount. In a comparison of sun and shade leaves of Acer saccharum and Parthenocissus quinquefolia, oil infiltration decreased absorptance more in shade than in sun leaves. This difference suggests that the higher proportion of spongy mesophyll in shade leaves may increase internal light scattering and thus absorptance. The importance of the spongy mesophyll in increasing internal reflectance was also evident in comparisons of the optics of Populus leaves and in the fluorescence yield of oil‐infiltrated leaves of several sun and shade species. Oil infiltration decreased the quantum yield of fluorescence (Fo) by 39–52% for shade leaves but only 21–25% for sun leaves. We conclude that the greater proportion of spongy parenchyma in shade leaves increased intercellular light scattering and thus absorptance. Direct measurements with fibre‐optic light probes of the distribution of light inside leaves of Hydrophyllum canadense confirmed that oil infiltration decreased the amount of back‐scattered light and that most of the light scattering for this species occurred from the middle of the palisade layer to the middle of the spongy mesophyll. We were not, however, able to assess the potential contribution of reflectance from the internal abaxial epidermis to total internal light scattering in these experiments. Using a mathematical model to compare the response of net photosynthesis (O2, flux) to incident irradiance for control leaves of H. canadense and theoretical leaves with no intercellular reflectance, we calculated that intercellular reflectance caused a 1.97‐fold increase in photosynthesis at 20 μmol m−2s−1 (incident photon flux density). This enhancement of absorption and photosynthesis by inter‐cellular reflectance, without additional production and maintenance of photosynthetic pigments, may maintain shade leaves above the photosynthetic light compensation point between sunflecks and maintain the light induction state during protracted periods of low diffuse light.

Conservation of mammalian biodiversity in coffee plantations of Central Veracruz, Mexico

The diversity and organization of the mammalian community is related to the vegetation structure of the coffee plantations in the area of Barranca Grande, in the State of Veracruz, Mexico. Four transects (each 200 m in length) were used to study the vegetation structure within the coffee plantation, and 178 night/traps, tracks registration and information from local people, were used in order to become familiar with the mammaliancommunity. The sample period was from October 1989 to February 1991. The 24 mammals of medium-size species present in the area were classified using two measures of ecological diversity, locomotion and foraging in order to understand the guild organization. If the complexity of the plantation is reduced, the number of guilds occupied could suffer a loss of 45% and 43% in ecological richness and diversity, respectively, and 24% in the equitability of the mammalian fauna. We recommend the maintenance of a high diversity in the tree stratum (shade species), in this case, species such as Inga jinicuil, banana (Musa sapientum), Citrus spp., coyo avocado (Persea schiedeana), mango (Mangifera indica); species which could provide food resources and protection for the mammals.

Patterns of Attack by Insect Herbivores and a Fungus on Saplings in a Tropical Tree Plantation

We investigated the effects of plant density, plant diversity, and light availability on susceptibility of saplings of Stryphnodendron microstachyum Poeppig & Endlicher to attack by herbivores and pathogens in the lowlands of northeastern Costa Rica. Seedlings of S. microstachyum were planted at either low or high density. High density stands were planted in 2 environments with 2 plant diversities within each environment : monocultures in abandoned pastures (=sun) and in 5-yr-old secondary forest (=shade), or polycultures in which S. microstachyum was planted with 4 other species also in sun and shade. Low density stands consisted of isolated individuals in 4 types of sites (abandoned pasture, secondary forest understory, primary forest understory, and primary forest light gap). Numbers of galls (Diptera : Cecidomyiidae), larvae (Lepidoptera : Noctuidae : Euclystis), and fungal spots (Melanconiales : Pestalotia) were greater in the high density stand than in low density stands, and greater in the shade than in sun. We found no differences in infection between monocultures and polycultures at high density, nor did we find Euclystis larvae or Cecidomyiidae galls in low density stands. Numbers of fungal spots per leaf and density of galls were greater on larger plants. These data suggest that higher plant densities increase the probability of attack by herbivorous insects and leaf pathogens, and that plantations of tropical native tree species in partial shade, as a means of reforestation, run the risk of outbreaks of normally rare plant enemies. Furthermore, the observed positive relation between plant size and attack suggests that plantations of this tree species will become more susceptible to pest outbreaks as the trees mature.

LEAF OPTICAL PROPERTIES ALONG A VERTICAL GRADIENT IN A TROPICAL RAIN FOREST CANOPY IN COSTA RICA

Leaf optical properties (400–1,100 nm) were compared for four species of rain forest trees with crowns in understory, mid‐canopy, and canopy positions to test whether optical properties change with light environment. The species tested represent a spectrum of regeneration patterns ranging from shade tolerant to light demanding. Overall, leaf optical properties of the four species were similar. Differences in absorptance were small, but statistically significant among the species and positions along the canopy gradient. Species absorptance differences corresponded somewhat to shade tolerance; two of the shade species showed higher absorptance in lower light environments, while the sun species showed the reverse pattern. Specific leaf mass (leaf weight per unit area) and chlorophyll content per unit leaf weight also changed along the canopy gradient. Specific leaf mass was positively correlated and chlorophyll per unit leaf weight was negatively correlated with increasing light environment. Consequently, the efficiency of absorption, as represented by the absorptance per unit leaf weight, increased as light level decreased, largely due to changes in specific leaf mass. In contrast, efficiency of absorption per unit leaf chlorophyll was relatively constant with light environment for the two species measured for chlorophyll.

A Comparison of Light Quality and Quantity Effects on the Growth and Steady-State and Dynamic Photosynthetic Characteristics of Three Tropical Tree Species

1. The role of light quality and quantity on steady-state photosynthetic characteristics, efficiency of lightfleck utilization (LFUE) and growth was evaluated in seedlings of tropical rain-forest trees. 2. The pioneer species, Cecropia obtusifolia and Heliocarpus appendiculatus, and the shade tolerant species, Rheedia edulis, were grown in a greenhouse under contrasting red/far-red (R/FR) ratios characteristic of the open and the shaded forest understorey but with the same low photosynthetically active radiation (PAR). Additionally plants were grown in a high PAR environment with a R/FR characteristic of the open. 3. The pioneer species responded strongly to R/FR in terms of greater height growth and a shift in allocation to stem growth over leaf growth in low R/FR (simulated shade) as compared to high R/FR (open). Light quality, however, had no significant effect on steady-state photosynthetic characteristics or LFUE for any species. 4. Increased light quantity, by contrast, caused photosynthetic acclimation leading to higher photosynthetic capacities. The pioneer species showed a larger capacity for photosynthetic acclimation to light environment than the shade species. LFUE was also affected by light quantity, with the low-light grown plants showing higher LFUE than the high-light grown plants. 5. Results provide evidence that light quality does not play an important role in modulating steady-state and dynamic photosynthetic characteristics during acclimation to shade, even in species that exhibit morphogenetic responses to light quality

Relative importance of photosynthetic traits and allocation patterns as correlates of seedling shade tolerance of 13 tropical trees.

Among 13 tropical tree species on Barro Colorado Island, species with high seedling mortality rates during the first year in shade had higher reltive growth rates (RGR) from germination to 2 months in both sun (23% full sun) and shade [2%, with and without lowered red: far red (R:FR) ratio] than shade tolerant species. Species with higher RGR in sun also had higher RGR in shade. These interspecific trends could be explained by differences in morphological traits and allocation paterns among species. Within each light regime, seedlings of shade-intolerant species had lower root: shoot ratios, higher leaf mass per unit area, and higher leaf area ratios (LAR) than shade tolerant species. In contrast, leaf gas exchange characteristics, or acclimation potential in these traits, had no relationship with seedling mortality rates in shade. In both shade tolerant and intolerant species, light saturated photosynthesis rates, dark respiration, and light compensation points were higher for sungrown seedlings than for shade-grown seedlings. Differences in R:FR ratio in shade did not affect gas exchange, allocation patterns, or growth rates of any species. Survival of young tree seedlings in shade did not depend on higher net photosynthesis or biomass accumulation rates in shade. Rather, species with higher RGR died faster in shade than species with lower RGR. This trend could be explained if survival depends on morphological characteristics likely to enhance defense against herbivores and pathogens, such as dense and tough leaves, a well-established root system, and high wood density. High construction costs for these traits, and low LAR as a consequence of these traits, should result in lower rates of whole-plant carbon gain and RGR for shade tolerant species than shade-intolerant species in shade as well as in sun.

Photosynthesis and photorespiration in the genus Oryza

Photosynthetic gas exchange has been surveyed in 22 of the 23 species currently placed in the genus Oryza and constituting the wild relatives of cultivated rice. Unimproved, wild germplasm of a number of species showed light-saturated assimilation rates in atmospheric air at least as great as cultivars and elite breeding material of the cultigen O. sativa. One of these species was O. australiensis, different accessions of which were significantly (P = 0.001) superior in assimilation rate to the O. sativa genotypes tested, including representatives of the Indica, Japonica and Javanica subgroups. Amongst species, assimilation rate was correlated positively with light saturation and with carboxylation efficiency. The wild species fell into two distinct groupings according to whether they originated from sun or shade habitats, with the higher assimilation rates being associated with the sun species. Assimilation rates were also higher in diploids than in tetraploids and this was associated with the fact that all sun species are diploids and all tetraploids are shade species. The carbon dioxide compensation concentrations ranged from 28 to 43 mu mol mol(-1) with the two lowest values (28 and 32 mu mol mol(-1)) coming from accessions of O. rufipogon. The mean value for the absolute quantum yield of photosynthesis measured on attached leaves was 0.060. There was a large range in the activity of phosphoenolpyruvate (PEP) carboxylase with a number of species having rates several times those of C-3 species. Some species with the highest assimilation rates were assessed for photorespiratory losses and these were generally around 30% and similar to O. sativa cultivars. However, a range of O. rufipogon accessions had photorespiration rates significantly (P = 0.01) lower than the O. sativa genotypes tested. No species in the genus possessed C-4 photosynthetic metabolism though some did overlap with compensation concentrations and phosphoenolpyruvate carboxylase activities reported for C-3-C-4 intermediate species. The potential value of wild relatives to the improvement of cultivated rice is discussed.