Estimating heat tolerance among plant species by two chlorophyll fluorescence parameters

The heat tolerance of 8 temperate- and 1 subtropical-origin C₃ species as well as 17 tropical-origin ones, including C₃, C₄, and CAM species, was estimated using both F₀-T curve and the ratio of chlorophyll fluorescence parameters, prior to and after high temperature treatment. When leaves were heated at the rate of ca. 1 °C min⁻¹ in darkness, the critical temperature (T_c) varied extensively among species. The T_c's of all 8 temperate-origin species ranged between 40–46 °C in winter (mean temperature 16–19 °C), and between 32–48 °C in summer (mean temperature ca. 30 °C). Those for 1 subtropical- and 12 tropical-origin C₃ species ranged between 25–44 °C and 35–48 °C, and for 1 CAM and 4 C₄ species were 41–47 and 45–46 °C, respectively. Acclimating three C₃ herbaceous plants at high temperature (33/28 °C, day/night) for 10 d in winter caused their T_c's rising to nearly the values measured in summer. When leaves were exposed to 45 °C for 20 min and then kept at room temperature in darkness for 1 h, a significant correlation between RF_v/m (the ratio of F_v/F_m before and after 45 °C treatment) and T_c was observed for all tested temperate-origin C₃ species as well as tropical-origin CAM and C₄ species. However, F₀ and F_v/F_m of the tropical-origin C₃ species were less sensitive to 45 °C treatment, regardless of a large variation of T_c; thus no significant correlation was found between their RF_v/m and T_c. Thus T_c might not be a suitable index of heat tolerance for plants with wide range of environmental adaptation. Nevertheless, T_c's of tropical origin C₃ species, varying and showing high plasticity to seasonal changes and temperature treatment, appeared suitable for the estimation of the degree of temperature acclimation in the same species.     

Seed Menus: An integrated decision‐support framework for native plant restoration in the Mojave Desert

The combination of ecosystem stressors, rapid climate change, and increasing landscape‐scale development has necessitated active restoration across large tracts of disturbed habitats in the arid southwestern United States. In this context, programmatic directives such as the National Seed Strategy for Rehabilitation and Restoration have increasingly emphasized improved restoration practices that promote resilient, diverse plant communities, and enhance native seed reserves. While decision‐support tools have been implemented to support genetic diversity by guiding seed transfer decisions based on patterns in local adaptation, less emphasis has been placed on identifying priority seed mixes composed of native species assemblages. Well‐designed seed mixes can provide foundational ecosystem services including resilience to disturbance, resistance to invasive species, plant canopy structure to facilitate natural seedling recruitment, and habitat to support wildlife and pollinator communities. Drawing from a newly developed dataset of species distribution models for priority native plant taxa in the Mojave Desert, we created a novel decision support tool by pairing spatial predictions of species habitat with a database of key species traits including life history, flowering characteristics, pollinator relationships, and propagation methods. This publicly available web application, Mojave Seed Menus, helps restoration practitioners generate customized seed mixes for native plant restoration in the Mojave Desert based on project locations. Our application forms part of an integrated Mojave Desert restoration program designed to help practitioners identify species to include in local seed mixes and nursery stock development while accounting for local adaptation by identifying appropriate seed source locations from key restoration species.     

Habitat Invasibility and Dominance by Alien Annual Plants in the Western Mojave Desert

Patterns of habitat invasibility and alien dominance, respectively measured as species richness and biomass of alien annual plants, were evaluated in association with four habitat factors at the Desert Tortoise Research Natural Area (DTNA) in the western Mojave Desert, USA. Habitat factors varied in levels of disturbance outside (high) and inside (low) the DTNA, and in levels of soil nutrients in washlet (high) and hummock (low) topographic positions, in Larrea-north (high), Larrea-south (medium), and interspace (low) microhabitats near creosote bushes (Larrea tridentata), and during 1995 when rainfall was 207% (high) and 1994 when rainfall was 52% (low) of the long-term average. Dominant alien plants included the annual grasses Bromus rubens, Bromus trinii, and Schismus spp., and the forb Erodium cicutarium. Species richness and dominance of alien annual plants were slightly higher where disturbance was high, and much higher where soil nutrients were high. B. rubens and B. trinii were most dominant in washlets and in the Larrea-north microhabitats during both years. These two species evolved in mesic ecosystems, and appeared to be particularly limited by soil nutrients at this site. Schismus spp. and E. cicutarium were also most dominant in washlets, but their dominance varied between interspaces in 1994 and the Larrea-south microhabitat in 1995. Monitoring to detect the invasion of new annual plants should focus on regions of high rainfall and nitrogen deposition and on washes and beneath-canopy microhabitats. The ecological range of each alien species should be evaluated separately, because their evolutionary origins may greatly affect their patterns of invasion and dominance in the Mojave Desert. This revised version was published online in July 2006 with corrections to the Cover Date.     

C<Subscript>3</Subscript> and C<Subscript>4</Subscript> photosynthetic pathways and life form types for native species from agro-forestry region,Northeastern China

Of the total 570 species, 194 species in 116 genera and 52 families were found with C₃ photosynthesis, 24 species in 17 genera and 6 families with C₄ photosynthesis, and 2 species in 1 genera and 1 family with CAM photosynthesis. 90 % of the total species can be found in Changbai Mountain flora, more a half (69 %) in North China flora, and about 1/3 in Mongolian flora and Xinan flora, respectively. The occurrence of C₄ species was not as common as that in adjacent grasslands and deserts, but relatively more than in the adjacent forests. Of the total 24 C₄ species, 63 % C₄ species (15 of 24) was found in Gramineae. Nine life form types can be found, reflecting the moist climate in the region, especially the occurrence of epiphyte and liana forms. Relatively more geophyte life form plants suggested the winter in the region was much colder than in grasslands. These indicated that both ecological studies and land management decisions must take into account plant photosynthetic pathway and life form patterns, for both of them are closely related to climatic changes and land use.     

Soil Water Retention on Gold Mine Surfaces in the Mojave Desert

An experimental analysis of soil water retention was conducted on three substrates (an abandoned road, an overburden pile, and a heap leach) created by gold mining activities in the Mojave Desert in southeastern California. We mixed each substrate with straw, and the overburden pile and heap leach with growth medium, then applied surface rock mulch to half the plots in an attempt to increase soil water‐holding capacity for revegetation efforts. For each of the six treatments (controls included) we monitored soil water with time domain reflectometry following both a simulation of a rainfall event and a natural rainfall that occurred immediately following the simulation. Both the simulation and the rainfall increased soil water between 3 and 8%, depending on the substrate. Water retention patterns in the two‐week periods following each water addition were similar between the simulation and rainfall, and among all substrate types as values returned to background (pre‐water) conditions. The abandoned road substrate had higher background water content (16.5%) than the overburden pile (6%) and heap leach (5%). The road also had three times higher organic matter and five times higher soil nitrogen than the other two sites. Soil water retention was improved on the overburden pile by the addition of just surface rock mulch or of straw‐plus‐rock mulch. On the heap leach, increases were found with rock mulch only or with growth medium‐plus‐rock mulch. Rock mulches did not improve soil water retention and straw additions decreased soil water on the abandoned road. Judicious use of soil amendments can improve soil water conditions and improve revegetation efforts on disturbed lands in desert environments.     

Photosynthetic and morphological functional types for native species from mixed prairie in Southern Saskatchewan, Canada

Photosynthetic pathways (e.g. C₃, C₄) and morphological functional types (e.g. trees, shrubs, high perennial grasses, perennial forbs) were identified for the native species from the Saskatchewan mixed prairie, using the data from references published between 1950 and 2003. Of the total 219 identified species in 145 genera and 45 families, 208 species in 137 genera and 44 families were found with C₃ photosynthesis, and most of these species are dominants (e.g. Agropyron dasystachyum Hook. and Stipa spartea var. curtiseta Hitchc.). 11 species in 10 genera and 3 families were identified with C₄ photosynthesis (e.g. Atriplex argentea Nutt., Andropogon scoparius Michx., Boutelou gracilis Lag., Calamovilfa longifolia Hook.). The amount of total identified C₄ species in the region is much less than that from the South Dakota mixed prairie (27 species). Gramineae is the leading family with C₄ photosynthesis (8 species), Chenopodiaceae ranks the second (2 species). Relatively less forb types [50 % perennial forbs (PEF) and 12 % annual forbs (ANF)] and more graminoid types (25 %) composition suggested that the rangelands in the region are relatively stable. Lacking of the knowledge on the optimal traits for PFTs classification in the region, further studies (e.g. C₃ and C₄ plant identification and optimal trait selection) are needed to explore the relationships between PFTs and vegetation variations, as well as land-use and climate changes.     

Photosynthetic Pathways,Life Forms,and Reproductive Types for Forage Species Along the Desertification Gradient on Hunshandake Desert,North China

Floristic compositions, life forms, reproductive types for forage species, and their responses to desertification in Hunshandake desert were studied. 164 species, in 30 families and 94 genera, were identified with C₃ (137 species), C₄ (25 species), and CAM (2 species) photosynthesis. Of the 25 C₄ species, 76 % were grasses and Chenopodiaceae species (hereafter chenopods). This suggests that the C₄ species mainly occurred in a few families in the desert region. The reduction of C₃ species and the increase of C₄ species with desertification indicated that C₄ species might have higher tolerance to environmental stresses (e.g. dry and poor soil). Relatively more hemicrytophyte and therophyte forms in the desert are related to the local temperate climate and vegetation dynamics. Relatively greater proportions of C₄/C₃ and clonal species/sexual species at mobile dune showed that the C₄ species and clonal species could make greater contribution to sand land restoration in the Hunshandake desert.     

Carbon isotope composition as a tool to control the quality of herbs and medicinal plants

Isotope screening is a simple test for determining the photosynthetic pathway used by plants. The scope of this work was to classify the photosynthetic type of some herbs and medicinal plants through studies of the carbon isotope composition (δ¹³C). Also, we propose the use of carbon isotope composition as a tool to control the quality of herbs and medicinal plants. For studies of δ¹³C, δ¹³C‰ = [R (sample)/R (standard) − 1] × 10⁻³, dry leaves powdered in cryogenic mill were analyzed in a mass spectrometer coupled with an elemental analyzer for determining the ratio R = ¹³CO₂/¹²CO₂. In investigation of δ¹³C of 55 species, 23 botanical families, and 44 species possessed a C₃ photosynthetic type. Six species found among the botanical families Euphorbiaceae and Poaceae were C₄ plants, and 5 species found among the botanical families Agavaceae, Euphorbiaceae, and Liliaceae possessed CAM-type photosynthesis. Carbon isotope composition of plants can be used as quality control of herbs and medicinal plants, allowing the identification of frauds or contaminations. Also, the information about the photosynthetic type found for these plants can help in introducing and cultivating exotic and wild herbs and medicinal plants.     

Photosynthetic pathway of dominant plant species in the Qaidam Basin: evidence from foliar stable carbon isotope measurement

Foliar δ¹³C values of Calligogum kozlovi and Haloxylon ammodendron ranged from −13.13 to −15.11 ‰, while those of the rest 11 species were in the range of −22.22 to −27.73 ‰. This indicates that two of 13 dominant plant species in the Qaidam Basin possess a C₄ photosynthetic pathway. Significant differences were observed for the average foliar δ¹³C values between C₃ or C₄ plant communities, between grass and shrub communities, even between the same species derived from different sites. Precipitation accounted for the major part of the differences.     

Photosynthetic Pathways and Life Form Types for Native Plant Species from Hulunbeier Rangelands,Inner Mongolia,North China

Photosynthetic pathway Types (C₃, C₄, and CAM) and life forms of native species from Hulunbeier rangelands, north China were studied. Of the total 258 species, 216 species in 132 genera and 42 families had C₃ photosynthetic pathway, including dominant herbs, e.g. Stipa baicalensis Roshev. and Leymus chinensis (Trin.) Tzvel., Filifolium sibiricum Kitam. and Arudinella hirta (Thunb.) Koidz. 38 species in 28 genera and 10 families were found with C₄ photosynthesis, and 4 species in 2 genera and 1 family had CAM photosynthetic pathway. The occurrence of C₄ species was common in Gramineae and Chenopodiaceae, and the two families were leading ones within C₄ plants. More than 52 % of the total 258 species were in H form, 21 % in Th form, 19 % in G form; the other life form Types, e.g. Ch, M, N, and HH, formed less than 3 %. 68 % of C₄ species were in Th form and 24 % in H form, indicating that these Types were the dominant life forms for C₄ species in the rangeland region. The occurrence of C₄ species was closely related with plant habitats, disturbed lands had the highest C₄ abundance (55 % of the total C₄ species), followed by grasslands and sandy soil, and forests had the lowest C₄ abundance (8 %). Hence the occurrence of C₄ species could be efficient indicator for rangeland dynamics in Hulunbeier rangelands.     

Africa's wild C4 plant foods and possible early hominid diets

A small minority of Africa's wild plant foods are C4. These are primarily the seeds of some of the C4 grasses, the rootstocks and stem/leaf bases of some of the C4 sedges (especially papyrus), and the leaves of some of the C4 herbaceous dicots (forbs). These wild food plants are commonly found in disturbed ground and wetlands (particularly the grasses and sedges). Multiple lines of evidence indicate that C4 grasses were present in Africa by at least the late Miocene. It is a reasonable hypothesis that the prehistory of the C4 sedges parallels that of the C4 grasses, but the C4 forbs may not have become common until the late Pleistocene. CAM plants may have a more ancient history, but offer few opportunities for an additional C4-like dietary signal. The environmental reconstructions available for the early South African hominid sites do not indicate the presence of large wetlands, and therefore probably the absence of a strong potential for a C4 plant food diet. However, carbon isotope analyses of tooth enamel from three species of early South African hominids have shown that there was a significant but not dominant contribution of C4 biomass in their diets. Since it appears unlikely that this C4 component could have come predominantly from C4 plant foods, a broad range of potential animal contributors is briefly considered, namely invertebrates, reptiles, birds, and small mammals. It is concluded that the similar average C4 dietary intake seen in the three South African hominid species could have been acquired by differing contributions from the various sources, without the need to assume scavenging or hunting of medium to large grazing ungulates. Effectively similar dominantly dryland paleo-environments may also be part of the explanation. Theoretically, elsewhere in southern and eastern Africa, large wetlands would have offered early hominids greater opportunities for a C4 plant diet.     

Linking water uptake with rooting patterns in grassland species

Water availability strongly governs grassland primary productivity, yet this resource varies dramatically in time (seasonally) and space (with soil depth and topography). It has long been assumed that co-occurring species differ in their partitioning of water use by depth, but direct evidence is lacking. We report data from two growing seasons (2004–2005) in which we measured the isotopic signature of plant xylem water from seven species (including C₃ forbs and shrubs and C₄ grasses) growing along a topographic gradient at the Konza Prairie Biological Station. Plant xylem stable oxygen isotope ratio (δ¹⁸O) values were compared to soil water δ¹⁸O profiles, recent rainfall events, and groundwater. Species varied in both their temporal patterns of water use and their responses to seasonal droughts in both years. During wet periods, species differences in water use were minimal, with common dependency on recent rainfall events stored in the upper soil layers. However, during dry periods, most C₃ species used proportionally more water from deeper portions of the soil profile relative to the C₄ grasses. Plants in uplands used more shallow soil water compared to those in lowlands, with the greatest differences across the topographic gradient occurring during dry periods. While the documented vertical root distribution varies by species and growth form in this grassland, each of the species we measured appeared to compete for the same surface layer soil moisture when water was not limiting. Thus, our results suggest that variation in precipitation history and landscape positions are greater determinants of water-use patterns than would be expected based on absolute rooting depth.     

Diurnal changes in chlorophylla fluorescence and carotenoid composition inOpuntia ficus-indica,a CAM plant,and in three C3 species in Portugal during summer

Summary Diurnal changes in chlorophylla fluorescence were determined in four species, differing in life form, in Portugal during the summer of 1989. These includedOpuntia ficus-indica, a CAM plant, andHelianthus annuus, Ficus carica andArbutus unedo, three C₃ species. Steady state fluorescence yield,F _S, and maximum fluorescence yield,F _M′, were determined at different times of the day. Using the model of Genty et al. (1989), the photon use efficiency of photosystem II electron transport,φ _e, was calculated from (F _M′−F _S)/F _M′. Diurnal changes in relative rate of non-cyclic electron transport through photosystem II,J _e, were derived by multiplyingφ _e by the incident photon flux density (PFD). WhenJ _e, determined for each species for various points in time throughout the day, was plotted against corresponding values of PFD, the light response curves obtained showed thatJ _e was linearly dependent on PFD in low light and approached saturation in high light. The highest values ofJ _e were observed inHelianthus annuus, followed byOpuntia ficus-indica, Ficus carica andArbutus unedo. The proportion of the xanthophyll zeaxanthin to total carotenoids, determined around noon, was inversely related to maximum rates ofJ _e.     

Long-term effects of elevated atmospheric CO<Subscript>2</Subscript> on species composition and productivity of a southern African C<Subscript>4</Subscript> dominated grassland in the vicinity of a CO<Subscript>2</Subscript> exhalation

We describe the long-term effects of a CO₂ exhalation, created more than 70 years ago, on a natural C₄ dominated sub-tropical grassland in terms of ecosystem structure and functioning. We tested whether long-term CO₂ enrichment changes the competitive balance between plants with C₃ and C₄ photosynthetic pathways and how CO₂ enrichment has affected species composition, plant growth responses, leaf properties and soil nutrient, carbon and water dynamics. Long-term effects of elevated CO₂ on plant community composition and system processes in this sub-tropical grassland indicate very subtle changes in ecosystem functioning and no changes in species composition and dominance which could be ascribed to elevated CO₂ alone. Species compositional data and soil δ¹³C isotopic evidence suggest no detectable effect of CO₂ enrichment on C₃:C₄ plant mixtures and individual species dominance. Contrary to many general predictions C₃ grasses did not become more abundant and C₃ shrubs and trees did not invade the site. No season length stimulation of plant growth was found even after 5 years of exposure to CO₂ concentrations averaging 610 μmol mol⁻¹. Leaf properties such as total N decreased in the C₃ but not C₄ grass under elevated CO₂ while total non-structural carbohydrate accumulation was not affected. Elevated CO₂ possibly lead to increased end-of-season soil water contents and this result agrees with earlier studies despite the topographic water gradient being a confounding problem at our research site. Long-term CO₂ enrichment also had little effect on soil carbon storage with no detectable changes in soil organic matter found. There were indications that potential soil respiration and N mineralization rates could be higher in soils close to the CO₂ source. The conservative response of this grassland suggests that many of the reported effects of elevated CO₂ on similar ecosystems could be short duration experimental artefacts that disappear under long-term elevated CO₂ conditions.     

Physiological variation among native and exotic winter annual plants associated with microbiotic crusts in the Mojave Desert

An experiment was established in 1992 in eastern Ontario, Canada to determine the effects of crop rotation (continuous maize, soybean-maize and alfalfa-maize) and nitrogen (N) amendment [0, 100 and 200 kg N ha^–1 of fertilizer (NH₄NO₃), and 50 and 100 Mg ha^–1 (wet wt.) each of stockpiled and rotted dairy manure] on maize production and soil properties. From 1997 to 1999, an additional study was added to the experiment to investigate treatment effects on the susceptibility of maize hybrids to gibberella ear rot. A moderately resistant and a susceptible hybrid were planted in each plot and inoculated with a macroconidial suspension of Fusarium graminearum by both the silk channel injection and the kernel-wound techniques. At harvest, ears were rated for the severity of disease symptoms and harvested kernels were analyzed for the mycotoxin deoxynivalenol (DON). The greatest number of significant N effects were found in the continuous maize treatments and with the susceptible hybrid. Most N amendments decreased both disease severity and DON accumulation in the susceptible hybrid. The most consistent effect was a decrease in disease severity with 100 kg N ha^–1 fertilizer and an increase in disease severity with the higher rate of 200 kg N ha^–1. This study is the first to report on the effects of soil N amendments on gibberella ear rot susceptibility.     

Le vie fotosintetiche C3, C4 e CAM nel contesto ecologico

Abstract

Ecological aspects of C₃, C₄ and CAM photosynthetic pathways. - Three different photosynthetic CO₂ fixation pathways are known to occur in higher plants. However all three pathways ultimately depend on the Calvin-Benson cycle for carbon reduction. The oxygenase activity of RuBP carboxilase is responsible for photorespiratory CO₂ release. Both C₄ and CAM pathways behave as a CO₂ concentrating mechanism which prevent photorespiration. The CO₂-concentrating mechanism in C₄ plants is based on intracellular symplastic transport of C₄ dicarboxylic acids from mesophyll-cells to the adjacent bundle-sheath cells. On the contrary in CAM plants the CO₂-concentrating mechanism is based on the intracellular transport of malic acid into and out of the vacuole.

The C₄ photosynthetic pathway as compared to the C₃ pathway permits higher rates of CO₂ fixation in high light and high temperature environments at low costs in terms of water loss, given the stability of the photosynthetic apparatus under such conditions.

CAM is interpreted as an adaptation to arid environments because it enables carbon assimilation to take place at very low water costs during the night when the evaporative demand is low. Nevertheless many aquatic species of Isoetes and some relatives are CAM, suggesting the adaptive role of CAM to environments which become depleted in CO₂.

The photosynthetic carbon fixation pathway certainly contributes to the ecological success of plants in different environments. However the distribution of plants may also reflect their biological history. On the other hand plants with different photosynthetic pathways coexist in many communities and tend to share resources in time. In any case some generalizations are possible: C₄ plants enjoy an ecological advantage in hot, moist, high light regions while the majority of species in desert environments are C₃; CAM plants are more frequent in semiarid regions with seasonal rainfall, coastal fog deserts, and in epiphytic habitats in tropical rain forests.     

Photosynthetic and morphological functional types from different steppe communities in Inner Mongolia, North China

Morphological functional types and photosynthetic pathway types were identified for the forage species from steppe communities in Inner Mongolia, China, using the data of both field survey and published papers. Seven typical steppe communities were selected to investigate the morphological functional type and photosynthetic pathway type compositions and plant functional type (PFT) diversity in steppe communities at regional scale. Morphological functional types, based on plant height and leaf type combined with life span, were optimal for comparing the community differences in the region, while photosynthetic pathway types were fairly coarse for such studies. Of the seven morphological functional types in the steppe communities, perennial forbs (PEF) were the dominant type, and 60 % of species belonged to this type. Each of the high perennial grass (HPG), short perennial grass (SPG), and annual grass (ANG) types represented less than 10 % of the total, even though the grass species were dominant in the seven steppe communities. The differences of PFTs between the steppe communities were remarkable, and the PFT richness and diversity increased from the communities with moist conditions to the ones with dry environments.This revised version was published online in March 2005 with corrections to the page numbers.     

Biomass production and nitrogen content of C3- and C4- grasses in pure and mixed culture with different nitrogen supply

Summary Two C₃ grasses (Hordeum vulgare L., Avena sativa L.) and two C₄ grasses (Panicum miliaceum L., Panicum crus-galli L.) were cultivated in standard soil in the open air in pure cultures and in various mixed cultures at low and high nitrogen fertilization levels. After three months the dry weight, length and nitrogen content of the aboveground and below-ground parts of the plants and the shoot/root ratios were determined. Hordeum vulgare was the most successful species irrespective of the nitrogen fertilization level, and also exhibited in most cases the highest nitrogen concentrations. Panicum miliaceum, on the other hand, was the species least able to compete. The production of biomass was reduced in cultures growing under nitrogen starvation conditions, this phenomenon being more pronounced with respect to the C₄ than to the C₃ species. The decrease in the production of biomass at low N conditions was most drastic with Panicum crus-galli, the species with the lowest nitrogen content and thus assumed to be best adapted to nitrogen starvation conditions. In cultures growing at low nitrogen fertilization levels the shoot/root ratios of all species.shifted in favour of an increasing root proportion. The extent of this shift, however, differed from species to species.