Polyploidy in Dalea formosa (Fabaceae) on the Chihuahuan Desert

Dalea formosa consists of diploids (n = 7), tetraploids (n = 14), and hexaploids (n = 21), the polyploids restricted to the Chihuahuan Desert region or its immediate borders. There is very little morphological differentiation between the three chromosome races and, therefore, the polyploids are assumed to be primarily autoploid. Tetraploids discovered were few and were very similar to hexaploids; the two ploidy levels were combined as “polyploids” for analyses of geographically and cytologically correlated morphological variation. Pollen length generally was found to be greater in known polyploids than in known diploids. Through the use of pollen length and geographic origin, chromosomally unknown specimens were estimated as to ploidy level. This produced four groups, known diploids and polyploids, and putative diploids and polyploids, which were then subjected to stepwise discriminant analysis (SDA) to search for other morphological characters that might indicate ploidy level, to evaluate the assignments to putative ploidy level in unknown plants, and to assess correlation of these plants of putative ploidy level to geographic regions. SDA also indicated that pollen length, among ten morphological features, is the primary discriminator between ploidy levels, and that putative polyploids are confined primarily to the Chihuahuan Desert. Chromosomally unknown specimens that were originally assigned to one ploidy level, but were classified by SDA as another, are viewed as indicative of areas where further cytological sampling is particularly needed. These areas are southeastern Arizona, where pollen among known diploids is comparatively large, northeastern New Mexico, where polyploids might occur off the Chihuahuan Desert, east edge of the Chihuahuan Desert in Texas, a cytologically poorly sampled contact zone between diploids and polyploids, and central Coahuila, where no cytological sampling has been done. Canonical variate analysis is used to aid in the visualization of the general morphological relationship between diploids and polyploids.     

Late Quaternary biomes of Canada and the eastern United States

Pollen data have been used to construct biome maps for today, 6000 ¹⁴C yr bp and 18,000 ¹⁴C yr bp for Canada and the eastern United States. The inferred modern biome distributions agree well with independent reconstructions of North American vegetation prior to European settlement. Some discrepancies between the pollen data and the modern potential vegetation are caused by post‐settlement clearing of the landscape and the consequent increase of herbaceous types in the recent pollen record. Biome distributions at 6000 ¹⁴C yr bp reflected the warmer and drier conditions then prevalent in the continental interior, but the overall position of biomes was similar to that of today. The boreal treeline in North America was not significantly north of its present position, in contrast to the 100–200 km shift reported for Siberia. At the last glacial maximum (18,000 ¹⁴C yr bp ), steppe and tundra were prevalent in the Midwest and north‐western Canada, and coniferous forests and woodlands grew in eastern North America. The open vegetation at 18,000 ¹⁴C yr bp was probably due to drier conditions and/or lower concentrations of atmospheric CO₂. The composition and physical structure of biomes is not constant over time. Mid‐Holocene biomes were similar in structure to those of today, but shifts in the relative importance of individual plant functional types are large enough that the physical properties of biomes, such as albedo, canopy conductance and surface roughness, are likely to have varied even during the Holocene. Last glacial maximum biomes were structurally different from their modern counterparts. The biome maps therefore may obscure significant vegetational changes in space and time during the late Quaternary. The difference between the highest and next highest affinity scores for each sample measures how strongly affinity scores discriminate among biomes. For many biomes, the difference is not large, and affinity score ties are not uncommon, highlighting the importance of tie‐break procedures when using the biomization method.     

Pollen-based reconstructions of Japanese biomes at 0, 6000 and 18,000 14C yr bp

A biomization method, which objectively assigns individual pollen assemblages to biomes ( Prentice et al., 1996 ), was tested using modern pollen data from Japan and applied to fossil pollen data to reconstruct palaeovegetation patterns 6000 and 18,000 ¹⁴C yr bp Biomization started with the assignment of 135 pollen taxa to plant functional types (PFTs), and nine possible biomes were defined by specific combinations of PFTs. Biomes were correctly assigned to 54% of the 94 modern sites. Incorrect assignments occur near the altitudinal limits of individual biomes, where pollen transport from lower altitudes blurs the local pollen signals or continuous changes in species composition characterizes the range limits of biomes. As a result, the reconstructed changes in the altitudinal limits of biomes at 6000 and 18,000 ¹⁴C yr bp are likely to be conservative estimates of the actual changes. The biome distribution at 6000 ¹⁴C yr bp was rather similar to today, suggesting that changes in the bioclimate of Japan have been small since the mid‐Holocene. At 18,000 ¹⁴C yr bp the Japanese lowlands were covered by taiga and cool mixed forests. The southward expansion of these forests and the absence of broadleaved evergreen/warm mixed forests reflect a pronounced year‐round cooling.     

Biomes of western North America at 18,000, 6000 and 0 14C yr bp reconstructed from pollen and packrat midden data

A new compilation of pollen and packrat midden data from western North America provides a refined reconstruction of the composition and distribution of biomes in western North America for today and for 6000 and 18,000 radiocarbon years before present (¹⁴C yr bp ). Modern biomes in western North America are adequately portrayed by pollen assemblages from lakes and bogs. Forest biomes in western North America share many taxa in their pollen spectra and it can be difficult to discriminate among these biomes. Plant macrofossils from packrat middens provide reliable identification of modern biomes from arid and semiarid regions, and this may also be true in similar environments in other parts of the world. However, a weighting factor for trees and shrubs must be used to reliably reconstruct modern biomes from plant macrofossils. A new biome, open conifer woodland, which includes eurythermic conifers and steppe plants, was defined to categorize much of the current and past vegetation of the semiarid interior of western North America. At 6000 ¹⁴C yr bp , the forest biomes of the coastal Pacific North‐west and the desert biomes of the South‐west were in near‐modern positions. Biomes in the interior Pacific North‐west differed from those of today in that taiga prevailed in modern cool/cold mixed forests. Steppe was present in areas occupied today by open conifer woodland in the northern Great Basin, while in the central and southern Rocky Mountains forests grew where steppe grows today. During the mid‐Holocene, cool conifer forests were expanded in the Rocky Mountains (relative to today) but contracted in the Sierra Nevada. These differences from the forests of today imply different climatic histories in these two regions between 6000 ¹⁴C yr bp and today. At 18,000 ¹⁴C yr bp , deserts were absent from the South‐west and the coverage of open conifer woodland was greatly expanded relative to today. Steppe and tundra were present in much of the region now covered by forests in the Pacific North‐west.     

Palaeovegetation of China: a pollen data-based synthesis for the mid-Holocene and last glacial maximum

Pollen data from China for 6000 and 18,000 ¹⁴C yr bp were compiled and used to reconstruct palaeovegetation patterns, using complete taxon lists where possible and a biomization procedure that entailed the assignment of 645 pollen taxa to plant functional types. A set of 658 modern pollen samples spanning all biomes and regions provided a comprehensive test for this procedure and showed convincing agreement between reconstructed biomes and present natural vegetation types, both geographically and in terms of the elevation gradients in mountain regions of north‐eastern and south‐western China. The 6000 ¹⁴C yr bp map confirms earlier studies in showing that the forest biomes in eastern China were systematically shifted northwards and extended westwards during the mid‐Holocene. Tropical rain forest occurred on mainland China at sites characterized today by either tropical seasonal or broadleaved evergreen/warm mixed forest. Broadleaved evergreen/warm mixed forest occurred further north than today, and at higher elevation sites within the modern latitudinal range of this biome. The northern limit of temperate deciduous forest was shifted c. 800 km north relative to today. The 18,000 ¹⁴C yr bp map shows that steppe and even desert vegetation extended to the modern coast of eastern China at the last glacial maximum, replacing today’s temperate deciduous forest. Tropical forests were excluded from China and broadleaved evergreen/warm mixed forest had retreated to tropical latitudes, while taiga extended southwards to c. 43°N.     

GEOGRAPHIC DIFFERENTIATION IN ATRIPLEX CONFERTIFOLIA

Atriplexconfertifolia (Chenopodiaceae) consists of ploidy races extending from diploid through decaploid and is dissected into many racial groups by cytological and flavonoid relationships. On the basis of morphology, the species can be divided into two major subdivisions, one centered in western Nevada and inhabiting chiefly the Great Basin, and one centered in the Colorado Plateau. Western Nevada plants are distinguished by smaller and narrower leaves, as well as by darker spines and other charactristics. Because western Nevada is situated in the lee of the Sierra Nevada Range, it received reduced amounts of rainfall during Pleistocene and Holocene times. These reduced leaf dimensions of A. confertifolia of the rain shadow zone may thus reflect an evolutionary response to aridity.     

Phytoplankton dynamics in the Congo River

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A new species of <Emphasis Type="Italic">Mentzelia</Emphasis> section <Emphasis Type="Italic">Bartonia</Emphasis> (Loasaceae) from the Grand Canyon,Arizona

Mentzelia hualapaiensis, a new species of Mentzelia sect. Bartonia, is described from the Grand Canyon region of Arizona. The new species is closely related to M. puberula, which is found west of M. hualapaiensis along the Colorado River, and to M. oreophila, M. polita, and M. tiehmii. It shares with these species a suffrutescent shoot system characterized by a subterranean, branching caudex, multiple annual branches, and similar leaves that have shallowly lobed or toothed to entire laminas. The flowers of M. hualapaiensis differ from those of its closest relatives in having cream-white, linear to narrowly spatulate petals and staminodes, characteristics that are convergent with those of the flowers of the Chihuahuan Desert species M. humilis.     

Flavonoid chemistry of Chenopodium fremontii. Infraspecific variation and systematic implications at the interspecific level

Four flavonoid geographical races based on twenty flavonol 3-O-glycosides were found to exist in Chenopodium fremontii with those populations from the northern part of the range (northern Colorado, Wyoming. and western Nebraska) producing 7-methyl ethers and 3-O-galactosides and glucosides. Plants from Arizona. southern Colorado and New Mexico lack 7-methyl ethers and contain 3-O-rhamnogalactosides and rhamnoglucosides (rutinosides). California populations are chemically similar to those from Arizona, southern Colorado and New Mexico but contain arabinosides while lacking rutinosides. No morphological features could be correlated with the chemical races. Chenopodium fremontii can be distinguished chemically from other closely related diploid species of the western U.S., all of which exhibit simpler flavonoid patterns. It is suggested that the simpler chemical patterns for the latter species (which include C. atrovirens, C. desiccatum, C. hians. C. incanum, C. leptophyllum, and C. pratericola) are a derived condition relative to C. fremontii.     

Mid-Holocene and glacial-maximum vegetation geography of the northern continents and Africa

BIOME 6000 is an international project to map vegetation globally at mid‐Holocene (6000 ¹⁴C yr bp ) and last glacial maximum (LGM, 18,000 ¹⁴C yr bp ), with a view to evaluating coupled climate‐biosphere model results. Primary palaeoecological data are assigned to biomes using an explicit algorithm based on plant functional types. This paper introduces the second Special Feature on BIOME 6000. Site‐based global biome maps are shown with data from North America, Eurasia (except South and Southeast Asia) and Africa at both time periods. A map based on surface samples shows the method’s skill in reconstructing present‐day biomes. Cold and dry conditions at LGM favoured extensive tundra and steppe. These biomes intergraded in northern Eurasia. Northern hemisphere forest biomes were displaced southward. Boreal evergreen forests (taiga) and temperate deciduous forests were fragmented, while European and East Asian steppes were greatly extended. Tropical moist forests (i.e. tropical rain forest and tropical seasonal forest) in Africa were reduced. In south‐western North America, desert and steppe were replaced by open conifer woodland, opposite to the general arid trend but consistent with modelled southward displacement of the jet stream. The Arctic forest limit was shifted slighly north at 6000 ¹⁴C yr bp in some sectors, but not in all. Northern temperate forest zones were generally shifted greater distances north. Warmer winters as well as summers in several regions are required to explain these shifts. Temperate deciduous forests in Europe were greatly extended, into the Mediterranean region as well as to the north. Steppe encroached on forest biomes in interior North America, but not in central Asia. Enhanced monsoons extended forest biomes in China inland and Sahelian vegetation into the Sahara while the African tropical rain forest was also reduced, consistent with a modelled northward shift of the ITCZ and a more seasonal climate in the equatorial zone. Palaeobiome maps show the outcome of separate, independent migrations of plant taxa in response to climate change. The average composition of biomes at LGM was often markedly different from today. Refugia for the temperate deciduous and tropical rain forest biomes may have existed offshore at LGM, but their characteristic taxa also persisted as components of other biomes. Examples include temperate deciduous trees that survived in cool mixed forest in eastern Europe, and tropical evergreen trees that survived in tropical seasonal forest in Africa. The sequence of biome shifts during a glacial‐interglacial cycle may help account for some disjunct distributions of plant taxa. For example, the now‐arid Saharan mountains may have linked Mediterranean and African tropical montane floras during enhanced monsoon regimes. Major changes in physical land‐surface conditions, shown by the palaeobiome data, have implications for the global climate. The data can be used directly to evaluate the output of coupled atmosphere‐biosphere models. The data could also be objectively generalized to yield realistic gridded land‐surface maps, for use in sensitivity experiments with atmospheric models. Recent analyses of vegetation‐climate feedbacks have focused on the hypothesized positive feedback effects of climate‐induced vegetation changes in the Sahara/Sahel region and the Arctic during the mid‐Holocene. However, a far wider spectrum of interactions potentially exists and could be investigated, using these data, both for 6000 ¹⁴C yr bp and for the LGM.     

A study of morphological variability in chenopodium incanum (Chenopodiaceae) and the recognition of two new varieties

Study ofChenopodium incanum has revealed considerable variability in what has been viewed previously as a uniform species. Variation is correlated with geographic distribution, and thus two new varieties are described. Varietyeatum Crawford occurs in western Texas, southern New Mexico and southern Arizona, whereas var.occidentale Crawford is restricted to the Great Basin and Mohave Desert. The var.incanum grows primarily on the western Great Plains and eastern slopes of the Rocky Mountains. Morphological features serving to distinguish the varieties are presented and discussed. Also considered are the characters that allow the separation ofC. incanum andC. fremontii.     

Comparative ecophysiology of the chromosome races in Viola adunca J.E. Smith

Summary Comparisons of net CO₂ assimilation, dark respiration, leaf resistance, and leaf water potential were made between diploid and polyploid races of Viola adunca from the Cypress Hills, Alberta, Canada. The mean maximum net CO₂ assimilation rate, at 20 C and 500 E m^-2 s^-1 (phAR) was 26 mg CO₂ g^-1 h^-1 (12 mg CO₂ dm^-2 h^-1) for polyploids, and 23 mg CO₂ g^-1 h^-1 (11 mg dm^-2 h^-1) for diploids. The difference is not statistically significant. Net CO₂ assimilation rates at low (0° C) and high (40° C) temperatures were virtually the same for diploids and polyploids. There were no statistically significant differences between the chromosome races in light compensation or light saturation over the 0° to 40° C temperature range studied. Average dark respiration of the polyploid race at 20 C was 2.2 mg CO₂ g^-1 h^-1 (1.0 mg CO₂ dm^-2 h^-1) compared with 2.0 mg CO₂ g^-1 h^-1 (0.95 mg CO₂ dm^-2 h^-1) for the diploid race. The mean maximum leaf water potential of well watered plants was-7.9 bars for both ploidy levels. Minimum leaf resistance was ca. 3.6 s cm^-1 for both ploidy levels. Maximum net CO₂ assimilation rates in both ploidy levels occurred at-9 bars leaf water potential. Based upon the plant responses studied, there are no differences between chromosome races collected from the same general area, and the polyploids do not respond more favorably to extremes of temperature and water potential. Ploidy per se does not affect the response of Viola adunca to its environment in this particular case.     

The social and ecological consequences of early cattle ranching in the Little Colorado River Basin

Commercial cattle ranching began in east central Arizona during the late 1880s when thousands of head of cattle were introduced onto the previously unexploited grasslands of the Little Colorado River Basin. Most of these animals were imported from western Texas where serious overgrazing had resulted in both catastrophic cattle losses and widespread range deterioration. By the turn of the century, the Texas experience had been repeated in Arizona, because Texas cattlemen continued to follow the same destructive stocking practices in this new region. This paper examines: (1) the early development of cattle ranching in the Little Colorado River Basin; (2) the various factors which contributed to overgrazing in the region; and (3) the consequences that commercial cattle ranching had on the local environment and on the pre-existing farming communities of the region.     

Fungal contributions to carbon flow and nutrient cycling during decomposition of standing Typha domingensis leaves in a subtropical freshwater marsh

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Predicting long‐term carbon mineralization and trace gas production from thawing permafrost of Northeast Siberia

The currently observed Arctic warming will increase permafrost degradation followed by mineralization of formerly frozen organic matter to carbon dioxide (CO₂) and methane (CH₄). Despite increasing awareness of permafrost carbon vulnerability, the potential long‐term formation of trace gases from thawing permafrost remains unclear. The objective of the current study is to quantify the potential long‐term release of trace gases from permafrost organic matter. Therefore, Holocene and Pleistocene permafrost deposits were sampled in the Lena River Delta, Northeast Siberia. The sampled permafrost contained between 0.6% and 12.4% organic carbon. CO₂ and CH₄ production was measured for 1200 days in aerobic and anaerobic incubations at 4 °C. The derived fluxes were used to estimate parameters of a two pool carbon degradation model. Total CO₂ production was similar in Holocene permafrost (1.3 ± 0.8 mg CO₂‐C gdw^?1 aerobically, 0.25 ± 0.13 mg CO₂‐C gdw^?1 anaerobically) as in 34 000–42 000‐year‐old Pleistocene permafrost (1.6 ± 1.2 mg CO₂‐C gdw^?1 aerobically, 0.26 ± 0.10 mg CO₂‐C gdw^?1 anaerobically). The main predictor for carbon mineralization was the content of organic matter. Anaerobic conditions strongly reduced carbon mineralization since only 25% of aerobically mineralized carbon was released as CO₂ and CH₄ in the absence of oxygen. CH₄ production was low or absent in most of the Pleistocene permafrost and always started after a significant delay. After 1200 days on average 3.1% of initial carbon was mineralized to CO₂ under aerobic conditions while without oxygen 0.55% were released as CO₂ and 0.28% as CH₄. The calibrated carbon degradation model predicted cumulative CO₂ production over a period of 100 years accounting for 15.1% (aerobic) and 1.8% (anaerobic) of initial organic carbon, which is significantly less than recent estimates. The multiyear time series from the incubation experiments helps to more reliably constrain projections of future trace gas fluxes from thawing permafrost landscapes.     

Holocene vegetation and climate change on the Colorado Great Plains,USA, and the invasion of Colorado piñon (Pinus edulis)

Aim To reconstruct the last c. 7000 years of vegetation and climate change in an unusual region of modern Great Plains grassland and scarp woodland in south‐east Colorado (USA), and to determine the late Holocene biogeography of Colorado piñon (Pinus edulis) at its easternmost extent, using a series of radiocarbon‐dated packrat (Neotoma sp.) middens. Location The West Carrizo Canyon drains the Chaquaqua Plateau, a plateau that projects into the western extent of the southern Great Plains grasslands in south‐eastern Colorado, USA. Elevations of the study sites are 1448 to 1525 m a.s.l. Today the plateau is mostly Juniperus scopulorum–P. edulis woodland. Methods Plant macrofossils and pollen assemblages were analysed from 11 ¹⁴C‐dated packrat middens. Ages ranged from 5990 yr bp (6839 cal. yr bp ) to 280 yr bp (485 cal. yr bp ). Results The results presented here provide information on the establishment and expansion of Juniperus–P. edulis woodland at its eastern limits. The analysis of both plant macrofossils and pollen from the 11 middens documents changes in plant communities over the last 7000 years, and the establishment of P. edulis at its easternmost limit. Though very minor amounts of P. edulis pollen occur as early as the middle Holocene, plant macrofossils were only recovered in middens dating after c. 480 cal. yr bp . Main conclusions Originally, midden research suggested a late glacial refuge to the north‐east of the Carrizo Canyon site, and a middle Holocene expansion of P. edulis. Results reported here are consistent with a late Holocene expansion, here at its eastern limits, but noted elsewhere at its northern and north‐eastern limits. In general, this late Holocene expansion is consistent with pollen data from sediments in Colorado and New Mexico, and suggests that P. edulis is still expanding its range at its present extremes. This has implications for further extension of its range due to changing climatic conditions in the future.     

Plant community structure determines primary productivity in shallow,eutrophic lakes

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Colony ergonomics for a desert-dwelling bumblebee species (Hymenoptera: Apidae)

Abstract.

• 1 Data on worker traffic, size and concentration of nectar loads, and size and composition of pollen loads were collected for a colony of Bombus pennsylvanicus sonorus Say in the Chihuahuan Desert in Arizona, U.S.A.
• 2 Foraging activity increased through the morning to a peak level in early afternoon and then declined steadily thereafter. Pollen collection occurred primarily in the morning, whereas nectar was harvested throughout the day. Nectar loads decreased in size but increased in sugar concentration during the day.
• 3 Following field observations, we excavated the nest and counted the numbers of immatures and adults present and measured the honey and pollen reserves. A total of 150 workers were present, and we estimate that the colony would have produced 174 queens and 192 males. Food reserves appeared small: pollen and honey stored in the nest represented only 18% and 35%, respectively, of the daily input.
• 4 These results are compared to ergonomic data collected for B.vosnesenskii in the only other similar study.

     

ADAPTATION OF DIPLOID AND TETRAPLOID CHAMERION ANGUSTIFOLIUM TO ELEVATION BUT NOT LOCAL ENVIRONMENT

Polyploid organisms often have different geographic ranges than their diploid relatives. However, it is unclear whether this divergence is maintained by adaptation or results from historical differences in colonization. Here, we conducted a reciprocal transplant experiment with diploid and autotetraploid Chamerion angustifolium to test for adaptation at the ploidy and population level. In the Rocky Mountains, pure diploid populations occur at high elevations and pure autotetraploid populations occur at low elevations with mixed ploidy populations between. We planted 3134 seedlings in 2004 and 3890 juveniles (bolting) in 2005 among nine plots, three in each of the diploid, mixed ploidy, and tetraploid zones, and monitored survival until 2008. For both seedlings and juvenile plants, elevation significantly influenced survival. The juvenile plants also showed a significant ploidy by elevation interaction, indicating that diploids and tetraploids survived best at their native elevations. In contrast, we found no evidence of local adaptation to plot within elevation. This suggests that the current distribution of diploids and tetraploids across elevations is the result of adaptation and that genome duplication may have facilitated the invasion of lower elevation habitats by limiting the movement of maladapted alleles from diploid populations at higher elevations.     

Improved experimental protocols to evaluate cold tolerance thresholds in Miscanthus and switchgrass rhizomes

This study investigates protocols to evaluate cold tolerance thresholds for overwintering rhizomes of perennial bioenergy grasses. Protocols examined include the temperature at which ice formation occurs, cooling rate, incubation time at the treatment temperature, and the electrolyte leakage (EL) method to assess mortality thresholds. Using these protocols, we assessed low temperature injury in two genotypes of Miscanthus and two genotypes of lowland switchgrass (Panicum virgatum). Ice formed near ?1 C in the rhizomes cooled at 1 C h^?1, but at variable temperatures at cooling rates of 3  and 5 C h^?1. Rhizome temperature followed chamber temperature at a cooling rate of 1 C h^?1, whereas at faster cooling rates, there was a lag in rhizome temperature that affected treatment exposure time. A 1 C h^?1 cooling rate is thus suitable. In rhizomes incubated for <4 h at the treatment temperature, EL values were variable, while there was no change in EL when samples were incubated 4–20 h. A continuous, steady rate of cooling at 1 C h^?1 demonstrated the Miscanthus and lowland switchgrass varieties exhibited lethal levels of electrolyte leakage below ?6 C. Continuous cooling does not allow for subzero acclimation and reflects thermal tolerances of sampled tissue in situ. To allow for maximum acclimation at subzero temperatures, a prolonged, staged‐cooling procedure was adopted. This procedure showed diploid Miscanthus rhizomes could acclimate and adjust their tolerance limit to ?12 C, while a triploid Illinois line showed little acclimation and was still killed below ?6 C.