Differences in transpiration rates between tropical and temperate grasses under controlled conditions

Summary Two experiments were conducted to determine the transpiration rates of tropical and temperate grasses under a range of environmental conditions. In dense populations, three temperate grasses lost considerably more water per unit leaf area than did four tropical grasses, though tropical grasses tended to produce more dry matter per unit leaf area. The efficiency of production in relation to water use was thus greater in tropical than in temperate grasses. Wheat, a temperate grass, lost water at an average rate 2.25 times that of sorghum, a tropical grass, on a unit leaf area basis when single leaves were exposed to temperatures from 17 to 32° and light intensities from 1.7 to 4.4×10⁴ ergs cm^-2 sec^-1 at 0.55 (1,100 to 2,800 ft.-c.). The measurement of transpiration and leaf temperature indicated that latent heat loss was much more important in wheat, and sensible heat loss was more important in sorghum as means of dissipating excess energy absorbed. These findings were attributed to the greater resistance to gas diffusion offered by sorghum than by wheat stomata in each environment.     

The isolation of factor V from bovine plasma

1. The activity per unit of chlorophyll of certain carboxylases, and of other enzymes involved in photosynthesis, was determined in leaf extracts of the tropical grasses, sugar-cane, maize and sorghum, and compared with the activities for wheat, oat and silver-beet. Maximum rates of photosynthetic carbon dioxide uptake were also measured for comparison with enzyme activities. 2. Phosphopyruvate carboxylase activity was about 60 times greater in the tropical grasses than in wheat, oat and silver-beet and was severalfold higher than the rates of photosynthetic carbon dioxide uptake. Most of the enzyme was located in the chloroplast fraction of cell extracts. 3. Phosphopyruvate carboxylase was apparently the major photosynthetic carbon dioxide-fixing enzyme in the tropical grasses, although malic enzyme may contribute to a lesser extent. 4. Tropical grasses contained less than one-tenth of the ribulose diphosphate carboxylase activity present in wheat, oat and silver-beet. For the tropical grasses this activity, determined with a saturating concentration of bicarbonate, was approx. 10% of the rate of photosynthesis. 5. The fraction-1 protein content of leaf extracts paralleled the ribulose diphosphate carboxylase activity. 6. In contrast, the activity of several other enzymes of the Calvin cycle was similar in the different species examined.     

Climate, phylogeny and the ecological distribution of C4 grasses

'C4 photosynthesis' refers to a suite of traits that increase photosynthesis in high light and high temperature environments. Most C4 plants are grasses, which dominate tropical and subtropical grasslands and savannas but are conspicuously absent from cold growing season climates. Physiological attributes of C4 photosynthesis have been invoked to explain C4 grass biogeography; however, the pathway evolved exclusively in grass lineages of tropical origin, suggesting that the prevalence of C4 grasses in warm climates could be due to other traits inherited from their non-C4 ancestors. Here we investigate the relative influences of phylogeny and photosynthetic pathway in determining the ecological distributions of C4 grasses in Hawaii. We find that the restriction of C4 grasses to warmer areas is due largely to their evolutionary history as members of a warm-climate grass clade, but that the pathway does appear to confer a competitive advantage to grasses in more arid environments.     

Growth responses of tropical forage plant species to vesicular-arbuscular mycorrhizae

Summary Growth and mineral uptake of twenty-four tropical forage legumes and grasses were compared under glasshouse conditions in a sterile low P oxisol, one part inoculated and the other not inoculated with mycorrhizal fungi. Shoot and root dry weights and total uptake of P, N, K, Ca, and Mg of all the test plants were significantly increased by mycorrhizal inoculation. Mycorrhizal inoculation, with few exceptions, decreased the root/shoot ratio. Non-mycorrhizal plants contained always lower quantities of mineral elements than mycorrhizal plants. Plant species showed differences in percentage mycorrhizal root length and there was no correlation between percentage mycorrhizal infection and plant growth parameters. A great variation in dependence on mycorrhiza was observed among forage species. Total uptake of all elements by non-mycorrhizal legumes and uptake of P, N and K by non-mycorrhizal grasses correlated inversely with mycorrhizal dependency. Mycorrhizal plants of all species used significantly greater quantities of soil P than the nonmycorrhizal plants. Utilization of soil P by non-mycorrhizal plants was correlated inversely with mycorrhizal dependency.     

A numerical taxonomic study of lactic acid bacteria from tropical silages

Lactic acid bacteria were isolated from various tropical silages made from either forage sorghum ( Sorghum bicolor cv. Sugardrip): three tropical grasses: hamil grass ( Panicum maximum cv. Hamil), pangola grass ( Digitaria decumbens ) and setaria ( Setaria anceps cv. Kazungula) either with or without addition of molasses and from mixtures of pangola or setaria grasses with leucaena ( Leucaena leucocephala ) or gliricidia ( Gliricidia sepium ). The 311 wild strains isolated and 13 reference strains were examined by 80 biochemical, physiological and morphological tests. A computer-assisted complete linkage analysis produced 16 clusters and five unclustered strains at 82% S. The largest cluster included 134 wild strains and the reference strain Lactobacillus plantarum . The results showed that Lactobacillus plantarum was the predominant lactic acid bacterium in all of the tropical silages.     

Flowering phenology of some native perennial tropical grasses from north-eastern Australia

The division of north-eastern Australia into tropical and sub-tropical zones at approximately the latitude of 20° S, as suggested by the flowering phenology of Heteropogon contortus, is supported by studies on other perennial grasses of the native pastures. A progressive evolution away from an obligate short-day flowering response which characterizes the tropical forms of Bothriochloa bladhii, perhaps Themeda australis, and the exclusive tropical species Dicanthium tenuiculum, through a quantitative short-day response, as in the more widely distributed B. decipiens var. cloncurrensis, to the day-neutral or opportunistic and largely subtropical species of B. decipiens and D. sericeum, is suggested as a sequence of flowering strategies leading to wider adaptation into the sub-tropics. There is evidence from here and elsewhere that tropical forms or species of perennial grasses are grosser than their subtropical counterparts and this is coupled with their short-day flowering behaviour. The evidence suggests that B. decipiens and D. sericeum are the evolutionary products of taxa nearer to B. decipiens var. cloncurrensis and D. tenuiculum which exhibit day-length control of flowering.     

Morphological variations of lobate phytoliths from grasses in China and the south-eastern United States

Abstract. Phytolith analysis of grasses is a useful tool in palaeoenvironmental and archaeobotanical research. Lobate phytolith is one of the most important morphotypes of grass phytoliths. This study describes morphological variations of diagnostic lobate phytoliths and produces a tentative classification scheme based on 250 modern grass species from China and the south‐eastern U.S.A. Eighty‐five grass species were found to contain lobate phytoliths. They are derived mainly from Panicoideae, but also include the Chloridoideae, Oryzoideae and Arundinoideae subfamilies. Twenty‐five lobate morphological types were observed from different subfamilies, genera or tribes of grasses, based on two important parameters: (1) the length of the lobate shank and (2) the shape of the outer margin of the two lobes. The identification of grass tribe or even genus is possible based on the differences in lobate shape parameters or the composition of assemblages. However, not all of the lobate assemblages have a definite relationship with the genera that produce them, because grasses can only produce a limited range of lobate shapes that often overlap from one genus to another. Several C₃ grasses and Chloridoideae subfamily grasses also produce characteristic lobate phytoliths. The variations of lobate morphologies can be related to environmental factors, especially moisture. Typical hygrophytic grasses tend to yield lobate phytoliths with very short shank, whereas typical xerophytic grasses tend to produce lobate phytoliths with a very long shank. The potential link between phytolith morphology, grass taxonomy and environmental conditions opens the possibility that phytolith morphology may be used as a proxy in palaeoclimatic reconstruction.     

A new Chorizococcus species (Coccoidea, Pseudococcidae) from Taiwan with transferring of Chorizococcus mirzayansi Moghaddam to genus Spilococcus Ferris

A new mealybug species, Chorizococcus zoysiaesp. n., feeding on Zoysia tenuifolia (Poaceae), is described from Taiwan. Adult female, third-instar female, second-instar female and first-instar nymph were described and illustrated in this article. Keys are provides to (a) separate this new species from similar species of Chorizococcus and those of same genus on zoysia grasses and (b) to identify instars of the new species. In addition, Chorizococcus mirzayansi Moghaddam is transferred to the genus Spilococcus as Spilococcus mirzayansi (Moghaddam), comb. n.     

CHLOROPLAST SPECIALIZATION IN DICOTYLEDONS POSSESSING THE C4-DICARBOXYLIC ACID PATHWAY OF PHOTOSYNTHETIC CO2 FIXATION

The C₄-dicarboxylic-acid pathway of photosynthetic CO₂ fixation found in tropical grasses has recently been demonstrated in members of the Amaranthaceae and Chenopodiaceae. In the tropical grasses this CO₂-fixation pathway is correlated with specialized leaf anatomy and chloroplast structure. This investigation was undertaken to determine if leaf cells of some representatives of these other families had structural features similar to those of tropical grasses. The leaf anatomy of Amaranthus edulis and a variety of Atriplex species is very similar and it resembles that of grasses such as sugar cane. Prominent bundle sheaths are surrounded by a layer of palisade cells. Bundle-sheath cells of Am. edulis have large chloroplasts containing much starch, but the chloroplasts have grana. The palisade cells have much smaller chloroplasts containing very little starch. The bundle-sheath cell chloroplasts of At. lentiformis have grana, their profiles tend to be ovoid, and they contain abundant starch grains. The palisade cell chloroplasts contain little starch and their profiles are discoid. The bundle-sheath cells of both species contain mitochondria which are much larger than those in the palisade cells. The chloroplasts in both types of cells in both species have a highly developed peripheral reticulum. This reticulum is composed of anastomosing tubules which are contiguous with the inner plastid membrane. The leaf anatomy and cell ultrastructure of these dicots are similar to those of the tropical grasses possessing this new photosynthetic carbon-fixation pathway. These morphological features are interpreted as adaptations for the rapid transport of precursors and end products of photosynthesis. A hypothesis is presented stating that the unique morphological and biochemical characters of these plants represent adaptations for efficient and rapid carbon fixation in environments where water stress frequently limits photosynthesis.     

An illustrated guide to the identification of the known species of Diatraea Guilding (Lepidoptera,Crambidae, Crambinae) based on genitalia

The genus Diatraea Guilding is one of the most economically important groups of moths in the Western Hemisphere. The larvae are stem borers that feed on species of Poaceae, or grasses, such as sugarcane, corn, rice, and sorghum, as well as many other native grasses. Interest in this group has risen considerably since sugarcane and other grasses have been utilized and/or investigated as biofuels. This is the first modern study to treat all 41 valid described species. Most type specimens were examined and we provide a checklist with 19 new synonyms. We provide keys for the identification of most species in this genus based on morphology of the male and female genitalia and modern illustrations of male and female genitalia. We also provide an updated table of species distribution by country.     

An endophyte of the tropical forage grass Brachiaria brizantha: isolating, identifying, and characterizing the fungus, and determining its antimycotic properties

Brachiaria, predominantly an African genus, contains species, such as B. brizantha, an apomictic C4 grass, that are commercially important forage grasses in tropical America, where they now cover about 55 million hectares. From B. brizantha accession CIAT 6780, we isolated an endophytic fungus that may be economically significant. The fungus was identified as Acremonium implicatum (J. Gilman & E.V. Abott). 18S rDNA and ITS rDNA sequences were used to characterize isolates of the endophyte, and showed that they belonged to the Acremonium genus, being close to A. strictum and A. kiliense. Using the random amplified polymorphic DNA (RAPD) technique, involving arbitrary primers of 10 bases, we showed that the isolates were highly similar to each other. Antiserum produced from a monoconidial culture of A. implicatum isolated from B. brizantha 6780, differentiated the isolates consistently in line with the DNA data. When we compared endophyte-free with endophyte-infected B. brizantha CIAT 6780 plants, both artificially inoculated with the pathogenic Drechslera fungus, we found that the endophyte-infected plants had fewer and smaller lesions than did the endophyte-free plants. Sporulation of Drechslera sp. on artificially inoculated leaf sheath tissues was also much less on tissue infected with the endophyte.     

Bud banks of perennial savanna grasses in Botswana

Three semi‐arid savanna grasses in Botswana (Stipagrostis uniplumis, Eragrostis lehmanniana, and Aristida stipitata) were sampled to quantify their belowground bud banks during the dormant season and to estimate their relative allocation to vegetative and sexual reproduction. Bud banks of these African perennial caespitose grasses were also compared with four perennial caespitose grasses of semi‐arid North American grasslands. The three African grasses each maintained approximately two buds per tiller and showed a high percentage (88–99%) of tillers producing seed. Only E. lehmanniana produced new aerial tillers from axillary buds at elevated nodes on the stem as well as from the belowground bud bank. Compared with species of North American grasslands, these African grasses produced fewer belowground buds but showed a much higher percentage of tillers producing seed. These patterns indicate relatively greater belowground meristem limitation, lower allocation to vegetative reproduction (tillering) and higher allocation to seed reproduction in these African grasses, although studies of more species are needed to assess the generality of this pattern. The management of savannas in ways that favour the maintenance of a reserve population of belowground buds may increase the ability of grasses to respond to pulses of resource availability, increase their compensatory growth capacity following grazing or drought, and decrease the invasibility of these plant communities by exotic species, whereas maintaining allocation to sexual reproduction may be important for conserving genetic variation and enhancing their capacity to adapt to environmental change.     

Variation in potential for isoprene emissions among Neotropical forest sites

As part of the Large Scale Biosphere–Atmosphere Experiment in Amazônia (LBA), we have developed a bottom‐up approach for estimating canopy‐scale fluxes of isoprene. Estimating isoprene fluxes for a given forest ecosystem requires knowledge of foliar biomass, segregated by species, and the isoprene emission characteristics of the individual tree species comprising the forest. In this study, approximately 38% of 125 tree species examined at six sites in the Brazilian Amazon emitted isoprene. Given logistical difficulties and extremely high species diversity, it was possible to screen only a small percentage of tree species, and we propose a protocol for estimating the emission capacity of unmeasured taxa using a taxonomic approach, in which we assign to an unmeasured genus a value based on the percentage of genera within its plant family which have been shown to emit isoprene. Combining this information with data obtained from 14 tree censuses at four Neotropical forest sites, we have estimated the percentage of isoprene‐emitting biomass at each site. The relative contribution of each genus of tree is estimated as the basal area of all trees of that genus divided by the total basal area of the plot. Using this technique, the percentage of isoprene‐emitting biomass varied from 20% to 42% (mean=31%; SD=8%). Responses of isoprene emission to varying light and temperature, measured on a sun‐adapted leaf of mango (Mangifera indica L.), suggest that existing algorithms developed for temperate species are adequate for tropical species as well. Incorporating these algorithms, estimates of isoprene‐emitting biomass, isoprene emission capacity, and site foliar biomass into a canopy flux model, canopy‐scale fluxes of isoprene were predicted and compared with the above‐canopy fluxes measured at two sites. Our bottom‐up approach overestimates fluxes by about 50%, but variations in measured fluxes between the two sites are largely explained by observed variation in the amount of isoprene‐emitting biomass.     

Is there a temporal niche separation in the leaf phenology of savanna trees and grasses?

Aim It has been proposed that, in tropical savannas, trees deploy their leaves earlier in the growing season and grasses deploy their leaves later. This hypothesis implies a mechanism that facilitates the coexistence of trees and grasses in savannas. If true, this hypothesis would also allow algorithms to use differences in the phenological timing of grass and tree leaves to partition the relative contribution of grasses and trees to net primary production. In this study we examine whether a temporal niche separation between grasses and trees exists in savanna. Location A semi‐arid, subtropical savanna, Kruger National Park, South Africa. Methods We use a multi‐spectral camera to track through an entire growing season the normalized difference vegetation index (NDVI) of individual canopies of grasses and trees at eight sites arranged along a precipitation and temperature gradient. Results Among trees, we identified two distinct phenological syndromes: an early flushing syndrome and a late‐flushing syndrome. Leaf flush in the tree strategies appears to pre‐empt rainfall, whereas grass leaf flush follows the rain. The growing season of trees is 20 (late‐flushing trees) to 27 (early flushing trees) days longer than that of the grasses. Main conclusions We show that grasses and trees have different leaf deployment strategies. Trees deployed leaves at lower temperatures than grasses and retained them for longer at the end of the growing season. The timing of the increase in NDVI is, however, similar between grasses and late‐flushing trees and this complicates the separation of grass and tree signals from multi‐spectral satellite imagery.     

Arberella (Poaceae: Bambusoideae): A new genus from tropical America

Arberella, a new genus of bambusoid grasses, is established, based on the newly described species,A. dressiert. Also belonging to this new genus are the taxa originally namedOlyra flaccida andRaddia costa-ricensis and several new species from Panama and Brazil which will be described later. The new genus is presented in a key to the genera of the tribe Olyreae, of which it is a member, and a key is given to the three species treated in this paper.     

Interspecific variation in plant responses to mycorrhizal colonization in tallgrass prairie

Symbiotic associations between plants and arbuscular mycorrhizal fungi are ubiquitous and ecologically important in many grasslands. Differences in species responses to mycorrhizal colonization can have a significant influence on plant community structure. The growth responses of 36 species of warm- and cool-season tallgrass prairie grasses and 59 tallgrass prairie forbs to arbuscular mycorrhizal (AM) fungal colonization were assessed in greenhouse studies to examine the extent of interspecific variation in host-plant benefit from the symbiosis and patterns of mycorrhizal dependence among host plant life history (e.g., annual, perennial) and taxonomic (e.g., grass, forb, legume, nonlegume) groups and phenological guilds. There was a strong and significant relationship between phenology of prairie grasses and mycorrhizal responsiveness, however this relationship was less apparent in forbs. Perennial warm-season C(4) grasses and forbs generally benefited significantly from the mycorrhizal symbiosis, whereas biomass production of the cool-season C(3) grasses was not affected. The root systems of the cool-season grasses were also less highly colonized by the AM fungi, as compared to the warm-season grasses or forbs. Unlike the native perennials, annuals were generally not responsive to mycorrhizal colonization and were lower in percentage root colonization than the perennial species. Plant growth responsiveness and AM root colonization were positively correlated for the nonleguminous species, with this relationship being strongest for the cool-season grasses. In contrast, root colonization of prairie legumes showed a significant, but negative, relationship to mycorrhizal growth responsiveness.     

C4 photosynthesis evolved in warm climates but promoted migration to cooler ones

C₄ photosynthesis is considered an adaptation to warm climates, where its functional benefits are greatest and C₄ plants achieve their highest diversity and dominance. However, whether inherent physiological barriers impede the persistence of C₄ species in cool environments remains debated. Here, we use large grass phylogenetic and geographical distribution data sets to test whether (1) temperature influences the rate of C₄ origins, (2) photosynthetic types affect the rate of migration among climatic zones, and (3) C₄ evolution changes the breadth of the temperature niche. Our analyses show that C₄ photosynthesis in grasses originated in tropical climates, and that C₃ grasses were more likely to colonise cold climates. However, migration rates among tropical and temperate climates were higher in C₄ grasses. Therefore, while the origins of C₄ photosynthesis were concentrated in tropical climates, its physiological benefits across a broad temperature range expanded the niche into warmer climates and enabled diversification into cooler environments.     

Germinable soil seed banks in a tropical savanna: seasonal dynamics and effects of fire.

Abstract The germinable soil seed bank of a tropical eucalypt savanna of north‐eastern Australia was found to be dominated by grasses and forbs, with seed bank density ranging from 58 to 792 seeds per square metre, from a total of 53 species. Late dry season fires and the fire‐related cues, heat shock and smoke, broke the seed dormancy of a range of tropical savanna species. Heat shock promoted the germination of the species groups natives, exotics, subshrubs, ephemeral and twining perennial forbs, and the common species Indigofera hirsuta, Pycnospora lutescens and Triumfetta rhomboidea. Exposure to smoke at ambient temperature promoted germination from the soil seed bank of the species groups combined natives, upright perennial forbs and grasses, as well as the common grasses Digitaria breviglumis and Heteropogon triticeus. The germinable soil seed bank varied seasonally, increasing from the mid wet season (February) and early dry season (May) to a maximum in the late dry season (October). The effect of recent fire history on soil seed bank dynamics was limited to the immediate release of some seed from dormancy; a reduction in seed densities of subshrubs and monocots, other than grasses, in recently burnt savanna; and enhanced seed density of the ephemeral I. hirsuta in the year following fire. The seed banks of most savanna species were replenished in the year following burning.     

The contribution of epiphyton to the primary production of tropical floodplain wetlands

Tropical floodplains are one of the most productive ecosystems on earth. Studies on floodplain productivity have primarily focused on trees and macrophytes, rather than algae, due to their greater biomass. However, epiphyton—algae and bacteria attached to the submerged portion of aquatic macrophytes—is a major source of energy in many tropical floodplains. Epiphyton productivity rates are unknown for most tropical floodplain wetlands, and spatial variability is not well understood. In this study, we measured primary productivity of epiphyton in Kakadu National Park in northern Australia. We estimated the relative contribution of epiphyton to aquatic production (epiphyton, + phytoplankton + macrophytes). We sampled sites dominated by different macrophyte structural types: vertical emerging grasses, horizontal emerging grasses, submerged macrophytes, and macrophytes with floating leaves. Epiphyton productivity was highly influenced by the structural type of the macrophyte. Highest potential productivity per weight was measured from epiphyton growing on macrophytes with floating leaves and horizontal grasses (1.52 ± 0.53 and 1.82 ± 0.61 mgC/dw g epiphyton/h, respectively) and lowest in submerged macrophytes and vertical grasses (0.57 ± 0.26 and 0.66 ± 0.47 mgC/dw g epiphyton/h, respectively). When considering the areal biomass of the macrophyte and the amount of epiphyton attached, epiphyton on horizontal grasses and submerged macrophytes had productivity values approximately ten times higher (45–219 mgC/m²/d) compared to those on vertical grasses and macrophytes with floating leaves (2–18 mgC/m²/d). Epiphyton contributed between 2 to 13 percent to the aquatic production of these tropical floodplain wetlands.