Physics of Root Growth

THE elongation of a plant cell involves the yielding of the cell wall under the action of tensile stresses in the wall¹. The rate of elongation, R, can be expressed simply as R=mW, where m is the extensibility of thé cell wall material and W is the wall pressure. Changes in either m or W have been used to explain the effect of biochemical factors on the growth rate of plant cells^2,3. Cell growth is also affected by the physical environment and this becomes particularly important in the case of plant roots where soil water potential and the mechanical resistance of the soil to deformation can become rate controlling. Working with 3-5 day old radicles of Pisum sativum, growing in soil cores, we have obtained values of wall pressure in terms of these two properties and we find that the rate of root elongation can be described by a simple extensibility equation.     

Risk reduction strategies in <Emphasis Type="Italic">Branchipus schaefferi</Emphasis> (Crustacea: Anostraca: Branchiopoda) as adaptation to a variable environment

The effect of long-term changes in total precipitation on physical and chemical parameters of the water and the structure of phytoplankton community during a year were studied in a deep hard water lake. With respect to total precipitation, two different periods were distinguished: dry and wet. In the wet period, the water level rose and caused an increase in the water colour and a decrease in the electrolytic conductivity and concentration of nutrients. These changes were reflected in the composition and amount of phytoplankton. Certain phytoplankton groups, e.g. Cryptophyceae, Dinophyceae, Chrysophyceae, Bacillariophyceae and Chlorophyta/Charophyta, were positively affected by the environmental changes; instead, these effects were not observed in Cyanobacteria and Euglenophyta. The development of flagellates, such as Cryptomonas curvata, Plagioselmis nannoplanctica and Ceratium hirundinella, was enhanced during the wet period, whereas the dry period favoured non-flagellates, such as Planktothrix agardhii, Planktothrix rubescens and Limnothrix planctonica. Hence, the long-term variability in total precipitation can be a switch from non-flagellate- to flagellate-dominated phytoplankton in lakes. Moreover, a short time of ice cover duration in winter linked with the wet period promoted phytoplankton groups typical for spring and autumn, e.g. Cryptophyceae and Bacillariophyceae.     

Seasonal variation of food and feeding in burrowing goby <Emphasis Type="Italic">Parapocryptes serperaster</Emphasis> (Gobiidae) at different body sizes

Diet composition and feeding habits of the burrowing fish Parapocryptes serperaster were investigated on different fish sizes across dry and wet seasons in the Mekong Delta, Vietnam. The gut length was positively related to fish length; the gut length was 1.57 ± 0.30 times the total length, which is in the range for omnivore (1–3). Detritus, algae and copepods were the main food items in the foregut. The diet composition showed seasonal and intraspecific variations in all fish sizes. The diet diversity varied with fish size and the dry-wet season pattern, and small fish had a higher diet diversity than large fish. The diet evenness index and Costello graphic analysis indicate that this goby is a generalist feeder and feeds mainly on detritus, followed by diatoms, and could obtain food from the bottom and the water column. The feeding intensity of P. serperaster was higher in the wet season than in the dry season, but was not significantly affected by fish size. The P. serperaster fed on Navicula spp. in the wet season, but on Nitzschia spp. in the dry season. The understanding of food and feeding habits of P. serperaster contributes to our knowledge on feeding adaptation of small-bodied bottom-dwelling gobies to the mud flat habitats in tropical monsoonal regions.     

Reduced Winter Snowpack and Greater Soil Frost Reduce Live Root Biomass and Stimulate Radial Growth and Stem Respiration of Red Maple (<Emphasis Type="Italic">Acer rubrum</Emphasis>) Trees in a Mixed-Hardwood Forest

Northeastern U.S. forests are currently net carbon (C) sinks, but rates of C loss from these ecosystems may be altered by the projected reduction in snowpack and increased soil freezing over the next century. Soil freezing damages fine roots, which may reduce radial tree growth and stem respiration. We conducted a snow removal experiment at Harvard Forest, MA to quantify effects of a reduced winter snowpack and increased soil freezing on root biomass, stem radial growth and respiration in a mixed-hardwood forest. The proportion of live fine root biomass during spring (late-April) declined with increasing soil frost severity (P = 0.05). Basal area increment index was positively correlated with soil frost severity for Acer rubrum, but not Quercus rubra. Rates of stem respiration in the growing season correlated positively with soil frost duration in the previous winter, (\( R^{2}_{{{\text{LMM}}({\text{m}})}} \) = 0.15 and 0.24 for Q. rubra and A. rubrum, respectively). Losses of C from stem respiration were comparable to or greater than C storage from radial growth of Q. rubra and A. rubrum, respectively. Overall, our findings suggest that in mixed-hardwood forests (1) soil freezing has adverse effects on spring live root biomass, but at least in the short-term could stimulate aboveground processes such as stem respiration and radial growth for A. rubrum more than Q. rubra, (2) stem respiration is an important ecosystem C flux and (3) the increasing abundance of A. rubrum relative to Q. rubra may have important implications for C storage in tree stem biomass.     

Comparative analysis of diploid species of <Emphasis Type="Italic">Avena</Emphasis> L. using cytogenetic and biochemical markers: <Emphasis Type="Italic">Avena canariensis</Emphasis> Baum et Fedak and <Emphasis Type="Italic">A. longiglumis</Emphasis> Dur.

The diploid oat species containing the A genome of two types (Al and Ac) were studied by electrophoresis of grain storage proteins (avenins), chromosome C-banding, and in situ hybridization with probes pTa71 and pTa794. The karyotypes of the studied species displayed similar C-banding patterns but differed in size and morphology of several chromosomes, presumably, resulting from structural rearrangements that took place during the divergence of A genomes from a common ancestor. In situ hybridization demonstrated an identical location of the 45S and 5S rRNA gene loci in Avena canariensis and A. longiglumis similar to that in the A. strigosa genome. However, the 5S rDNA locus in A. longiglumis (5S rDNA1) was considerably decreased in the chromosome 3Al long arm. The analysis demonstrated that these oat species were similar in the avenin component composition, although individual accessions differed in the electrophoretic mobilities of certain components. A considerable similarity of A. canariensis and A. longiglumis to the Avena diploid species carrying the As genome variant was demonstrated.     

Responses of Tree Transpiration and Growth to Seasonal Rainfall Redistribution in a Subtropical Evergreen Broad-Leaved Forest

Precipitation changes such as more frequent drought and altered precipitation seasonality may impose substantial impacts on the structure and functioning of forest ecosystems. A better understanding of tree responses to precipitation changes can provide fundamental information for the conservation and management of forests under future climate regimes. We conducted a 2-year seasonal rainfall redistribution experiment to assess the responses of tree transpiration and growth to manipulated precipitation changes in a subtropical evergreen broad-leaved forest. Three precipitation treatments were administered including a drier dry season and wetter wet season treatment (DD), an extended dry season and wetter wet season treatment (ED), and an ambient control treatment, with the total amount of annual rainfall being kept the same among the three treatments. Our results showed that the DD and ED treatments reduced daily transpiration of Schima superba by 8–16 and 13–25%, respectively. The ED treatment also reduced the DBH increment of larger S. superba individuals. In contrast, neither treatment showed obvious effects on the transpiration and DBH increment of another dominant species Michelia macclurei. However, the transpiration of both species showed clear inter-annual differences between the 2 years with contrasting annual rainfall (2094 vs 1582 mm). S. superba had a lower transpiration-to-precipitation ratio (T/P) compared to M. macclurei and showed decreased sensitivities to total solar radiation and vapor pressure deficit under the DD and ED treatments. These results indicate the deep-rooted S. superba may be suppressed with a lower ability to obtain water and assimilate carbon compared to the shallow-rooted M. macclurei under the precipitation seasonality changes, which could potentially cause shifts in species dominance within the forest community.     

Detection and Quantification of <Emphasis Type="Italic">Vibrio cholerae,Vibrio parahaemolyticus</Emphasis>, <Emphasis Type="Italic">and Vibrio vulnificus</Emphasis> in Coastal Waters of Guinea-Bissau (West Africa)

V. cholerae, V. parahaemolyticus, and V. vulnificus are recognized human pathogens. Although several studies are available worldwide, both on environmental and clinical contexts, little is known about the ecology of these vibrios in African coastal waters. In this study, their co-occurrence and relationships to key environmental constraints in the coastal waters of Guinea-Bissau were examined using the most probable number-polymerase chain reaction (MPN-PCR) approach. All Vibrio species were universally detected showing higher concentrations by the end of the wet season. The abundance of V. cholerae (ISR 16S-23S rRNA) ranged 0–1.2 × 10⁴ MPN/L, whereas V. parahaemolyticus (toxR) varied from 47.9 to 1.2 × 10⁵ MPN/L. Although the presence of genotypes associated with virulence was found in environmental V. cholerae isolates, ctxA+ V. cholerae was detected, by MPN-PCR, only on two occasions. Enteropathogenic (tdh+ and trh+) V. parahaemolyticus were detected at concentrations up to 1.2 × 10³ MPN/L. V. vulnificus (vvhA) was detected simultaneously in all surveyed sites only at the end of the wet season, with maximum concentrations of 1.2 × 10⁵ MPN/L. Our results suggest that sea surface water temperature and salinity were the major environmental controls to all Vibrio species. This study represents the first detection and quantification of co-occurring Vibrio species in West African coastal waters, highlighting the potential health risk associated with the persistence of human pathogenic Vibrio species.     

Laboratory tests of oviposition by the African malaria mosquito, <Emphasis Type="Italic">Anopheles gambiae</Emphasis>, on dark soil as influenced by presence or absence of vegetation

Background

Physical objects like vegetation can influence oviposition by mosquitoes on soil or water substrates. Anopheles gambiae s. l. is generally thought to utilize puddles over bare soil as its prime larval habitat and to avoid standing water populated with vegetation. In Kisian, Kenya near Kisumu, water often pools in grassy drainage areas both during and after periods of infrequent rains, when typical puddle habitats become scarce because of drying. This raised the question of whether An. gambiae has the behavioural flexibility to switch ovipositional sites when puddles over bare soil are unavailable.

Methods

To test whether presence and height of grasses influenced oviposition, wild-caught gravid An. gambiae s. l. were offered paired choices between wet, bare soil and wet soil populated with mixed grasses or grasses of differing height. No-choice tests were also conducted by giving females either grassy soil or bare soil.

Results

In choice tests, females laid four times more eggs on bare, wet soil than soil populated with grasses. However in no-choice tests, egg output was not significantly different whether grasses were present or not. Females laid significantly more eggs on soil populated with short grass than with medium, or tall grass.

Conclusion

This work shows An. gambiae s. l. has the capacity to oviposit into grassy aquatic habitats when typical puddles over bare soil are unavailable. This knowledge will need to be considered in the design and implementation of programmes aimed at reducing malaria transmission by suppression of An. gambiae s. l. immatures.

     

What are palm groves of <Emphasis Type="Italic">Phoenix</Emphasis>? Conservation of <Emphasis Type="Italic">Phoenix</Emphasis> palm groves in the European Union

There are three species of Phoenix (Arecaceae) in the territory of the European Union, P. canariensis, P. dactylifera and P. theophrasti, found in wild-native populations, feral, planted and intermediate states, accounting each for thousands of individuals. The EU Habitats Directive has addressed the conservation of P. theophrasti and P. canariensis under the habitat type 9370, ‘Palm groves of Phoenix,’ but neglected to include the wild-growing populations of P. dactylifera palms in southern Spain. In this paper, we survey the habitats and status of both representative native and naturalized populations of Phoenix, in total 103, through fieldwork, image analysis and review of literature. We underline the significance of feral populations and palms originating from ancient abandoned plantations, existing in protected areas as a reservoir of genetic variation. We conclude that, in order to improve their conservation status by adequate protection and conservation management, the concept of Phoenix palm groves in the Habitats Directive should be redefined to include the western group of P. dactylifera and the various habitats of P. canariensis and P. theophrasti that do not appear in the current definition.     

Fine root production in three zones of secondary mangrove forest in eastern Thailand

Key message

High root productions, especially in the fine roots, estimated by ingrowth cores were confirmed in mangrove forests. The zonal variation in root production was caused by inundation regime and soil temperature.

Abstract

Mangrove forests have high net primary productivity (NPP), and it is well known that these trees allocate high amounts of biomass to their root systems. In particular, fine root production (FRP) comprises a large component of the NPP. However, information on root production remains scarce. We studied FRP in three zones (Avicennia, Rhizophora, and Xylocarpus) of a mangrove forest in eastern Thailand using ingrowth cores (0–30 cm of soil depth). The root biomass and necromass were periodically harvested from the cores and weighed during the one-year study. The FRP was determined by summation of the fine root biomass (FRB) and root necromass. The results showed that the FRB clearly increased in the wet and cool dry seasons. Magnitude of FRB in the Rhizophora and Xylocarpus zones was 1171.07 and 764.23 g/m²/30 cm, respectively. The lowest FRB (292.74 g/m²/30 cm) was recorded in the Avicennia zone locating on the river edge where there is a greater frequency of inundation than the other zones. Root necromass was high in the Rhizophora and Xylocarpus zones, and accumulated noticeably when soil temperatures rapidly declined during the middle of the wet season to cool dry season. However, root necromass in the Avicennia zone varied within a small range. We attributed the small accumulation of root necromass in the Avicennia zone to the relative high soil temperature that likely caused a high root decomposition rate. The average FRP (3.403–4.079 ton/ha/year) accounted for 74.4, 81.5, and 92.4 % of the total root production in the Avicennia, Rhizophora, and Xylocarpus zone, respectively. The root production and causative factors (i.e., soil temperature and inundation regime) are discussed in relation to the carbon cycle of a mangrove forest.

     

Seasonal differences in arbuscular mycorrhizal fungal communities in two woody species dominating semiarid caatinga forests

Tropical dry forests are strongly affected by seasonality, but its effects on belowground communities are poorly studied. Thus, the objective of this study was to reveal the effect of the season (dry versus wet) on the mycorrhizal status of roots and their potential colonization, and to determine the composition and abundance of spore-based communities of arbuscular mycorrhizal fungi (AMF) in rhizospheric soil of two dominant woody species in caatinga communities (tropical dry forest of the Brazilian Northeast). Soil and root samples were taken four times in each season (dry and wet). In the cases of the number of glomerospores and the number of infective propagules of AMF, there were significant differences between the hosts, with greater values observed in the rhizosphere of Commiphora leptophloeos than Mimosa tenuiflora. Mycorrhizal colonization and the number of infective propagules of AMF differed also between the seasons, being higher in the dry than the wet season. In total, fourteen AMF species were found in the rhizosphere of C. leptophloeos and twelve species were associated with M. tenuiflora. There was a predominance of the fungal genus Acaulospora, with seven species, followed by Gigaspora and Glomus. The species studied and the seasons differ in the composition and structure of the AMF community in the rhizosphere of the plants. The ecological significance of those differences needs to be examined further.     

Development and relations of <Emphasis Type="Italic">Fusarium culmorum</Emphasis> and <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> in soil

The development of Fusarium culmorum and Pseudomonas fluorescens in soil, and the relations between them, were studied using membrane filters containing the fungus, the bacterium, or both microorganisms; the filters were incubated in soil. F. culmorum was identified by indirect immunofluorescence; the GUS-labeled strain was used to visualize P. fluorescens. It was found that F. culmorum introduced in soil can develop as a saprotroph, with the formation of mycelium, macroconidia, and a small amount of chlamydospores. Introduction of glucose and cellulose resulted in increased density of the F. culmorum mycelium and macroconidia. P. fluorescens suppressed the development of the F. culmorum mycelium in soil, but stimulated chlamydospore formation. Decreased mycelial density in the presence of P. fluorescens was more pronounced in soil without additions and less pronounced in the case of introduction of glucose or cellulose. F. culmorum had no effect on P. fluorescens growth in soil.     

Life history differences and latitudinal variation in recruitment in two species of arctic-boreal perciform fishes,the fish doctor <Emphasis Type="Italic">Gymnelus viridis</Emphasis> and the Arctic shanny <Emphasis Type="Italic">Stichaeus punctatus</Emphasis>

Growth and recruitment were examined in two arctic-boreal, shallow water marine perciform species: the fish doctor Gymnelus viridis (Zoarcidae) and the Arctic shanny Stichaeus punctatus (Stichaeidae). G. viridis ranges in the Canadian Arctic from northern Hudson Bay to northern Ellesmere Island, whereas S. punctatus has a more southerly range from Nova Scotia coastal waters to northern Hudson Bay. At Nuvuk Islands in northeastern Hudson Bay, where the two species are sympatric in shallow water, they had comparable juvenile growth rates but temporal variation in 0+ recruitment was substantially greater in S. punctatus. This difference may stem from their contrasting early life histories. S. punctatus spawns large numbers of small demersal eggs that hatch into pelagic larvae, whereas G. viridis spawns small numbers of large demersal eggs that hatch directly into demersal juveniles with no pelagic stage, suggesting that recruitment in G. viridis should be less sensitive to yearly variation in the onset of the ice-free period in Hudson Bay and the subsequent pulse of pelagic invertebrate production. Relative to Nuvuk, recruitment variation in G. viridis was found to be greater at Resolute, Cornwallis Island, close to its northern range limit, whereas recruitment variation in S. punctatus was not evident in Newfoundland, closer to its southern range limit.     

Photosynthetic responses to soil water stress in summer in two Japanese urban landscape tree species (<Emphasis Type="Italic">Ginkgo biloba</Emphasis> and <Emphasis Type="Italic">Prunus yedoensis</Emphasis>): effects of pruning mulch and irrigation management

Key message

Stomatal regulation involves beneficial effects of pruning mulch and irrigation on leaf photosynthesis in Prunus yedoensis and Ginkgo biloba under moderate drought. G. biloba showed conservative water use under drought.

Abstract

Leaf photosynthesis is highly sensitive to soil water stress via stomatal and/or biochemical responses, which markedly suppress the growth of landscape trees. Effective irrigation management to maintain leaf photosynthesis and information on species-specific photosynthetic responses to soil water stress are essential for the sustainable management of landscape trees in Japan, in which summer drought often occurs. In order to investigate effective irrigation management, we used plants with moderate soil water stress as controls, and examined the effects of daily irrigation and pruning mulch on leaf photosynthesis in container-grown Ginkgo biloba and Prunus yedoensis, which are the first and second main tall roadside trees in Japan. Stomatal conductance was significantly increased by pruning mulch and daily irrigation, with similar increases in leaf photosynthesis being observed in P. yedoensis and G. biloba. In order to obtain information on species-specific photosynthetic responses to soil water stress, we compared the responses of leaf photosynthesis and leaf water status to reductions in soil water content (SWC) between the two species. G. biloba maintained a constant leaf water potential, leaf water content, maximum carboxylation rate, and electron transport rate with reductions in SWC, whereas reductions were observed in P. yedoensis. We concluded that pruning mulch and irrigation effectively offset the negative impact of moderate water stress on leaf photosynthesis in summer in P. yedoensis and G. biloba via stomatal regulation, and also that G. biloba maintained its photosynthetic biochemistry and leaf water status better than P. yedoensis under severe water stress.

     

<Emphasis Type="Italic">Antrodia multiformis</Emphasis> and <Emphasis Type="Italic">A. tenerifensis</Emphasis> spp. nov. (Fomitopsidaceae,Basidiomycota): new brown rot polypores

Based on molecular evidence and morphological studies, the new polypores Antrodia multiformis and A. tenerifensis are described. Both species were discovered in arid biotope, A. multiformis in southwestern USA and A. tenerifensis in Tenerife (Canary Islands). Both of the new species show unique morphological and cultural features and are different in phylogeny. The structure of the Antrodia core clade of brown rot polypores is discussed.     

Climate/growth relations and teleconnections for a <Emphasis Type="Italic">Hymenaea courbaril</Emphasis> (Leguminosae) population inhabiting the dry forest on karst

Key message

Both water availability and temperature modulate the growth of Hymenaea courbaril on karst in Central Brazil. There is evidence of teleconnections between South Atlantic SST and tree growth.

Abstract

Tropical dry forests have low annual precipitation and long dry seasons. Water availability, the main restrictive growth factor, becomes more pronounced in the shallow and highly porous soil of karst regions. Understanding how climate regulates tree growth in stressful environments is essential for predicting climate change impacts on trees. The aim of this study was to build a tree-ring chronology of Hymenaea courbaril growing in a karst dry forest and evaluate how local climate and teleconnections modulate its growth. To accomplish this, increment cores of 19 individuals were sampled in Terra Ronca State Park located in Goiás State, Central Brazil. After surface polishing, tree rings were identified, measured, dated, and a tree-ring chronology was built with 17 individuals. The chronology was correlated with local and regional climate data (temperature, precipitation, air humidity). We also tested teleconnections with sea surface temperature (SST) of the Equatorial Pacific and South Atlantic. Results show that air humidity, precipitation amount, and its distribution during the transition period between dry and wet seasons positively regulate this species growth. On the other hand, growth is negatively correlated with temperature during the middle of the previous year’s dry season. Additionally, growth is negatively correlated with SST of the Southern Atlantic, but not with Equatorial Pacific. These relationships between climate and growth indicate that predicted increases in regional temperature and decreases in water availability may limit the growth of H. courbaril in karst dry forests.

     

Ectomycorrhizal pre-inoculation of <Emphasis Type="Italic">Pinus hartwegii</Emphasis> and <Emphasis Type="Italic">Abies religiosa</Emphasis> is replaced by native fungi in a temperate forest of central Mexico

Few studies have focused on analyzing the effect of native inoculated ectomycorrhizal (ECM) fungal strains on seedlings under field conditions in temperate forests. However, it is crucial to verify that the positive effects of ECM under nursery conditions also occur in the field, favoring their performance. We evaluated the short-term effect of ECM on three-year-old seedlings of Pinus hartwegii and Abies religiosa in central Mexico by subjecting them to four treatments: inoculation with Inocybe splendens, inoculation with Suillus brevipes (both native strains), inoculation with forest soil, and non-inoculated plants. Percentage of ECM colonization, plant growth (shoot height and stem diameter), and physiological (osmotic potential, stomatal conductance, CO₂ assimilation and water use efficiency) responses were evaluated. We found that these two ECM species were partial (P. hartwegii) or totally (A. religiosa) replaced after one and a half years in the field. P. hartwegii seedlings increased their water use efficiency during the dry season, but in A. religiosa seedlings, a clear strategy for avoiding water stress was not detected. This ECM replacement had a negative effect on the physiological performance Of A. religiosa. Our results emphasize the importance of selecting compatible fungal-host species combinations for nursery inoculation and of using sources of inoculum adapted to the environmental conditions of the transplant site, ensuring root colonization prior to field transplanting to minimize seedling mortality due to water stress.     

A morphophysiological analysis of the effects of drought and shade on <Emphasis Type="Italic">Catalpa bungei</Emphasis> plantlets

The interactive effects of shade and drought on the morphological and physiological traits of Catalpa bungei plantlets were assessed. Seedling growth, biomass, biomass allocation, leaf morphology, chlorophyll (Chl) content and gas-exchange parameters were measured in plants raised for 3 months under three light levels [80% (HI), 50% (MI), 30% (LI)] and two water levels [moisture (M) and drought (D)]. The results showed that shade greatly decreased growth, biomass, leaf area (LA) and Chl a/b; increased specific leaf area (SLA) and Chl content; and reduced photosynthetic rate (P _n). Drought reduced the growth, biomass, LA, SLA, Chl a/b, P _n, stomatal conductance (G _s), transpiration rate (T _r) and intercellular carbon dioxide concentration (C _i) and increased the Chl content. Stomatal closure was an early physiological response to water stress. Light, water and their interaction significantly affected plant traits and their bivariate relationships. The phenotypic plasticity index of light (0.47) was much higher than that of water (0.21), indicating that light was the main driver of the variations observed. Under drought stress, growth, biomass, leaf and stem biomass allocation significantly decreased in the HI and MI environments, whereas no significant difference was observed in growth or biomass parameters under the LI condition. Furthermore, no significant difference was observed in P _n, G _s, or T _r under the LI condition under water stress. Our results showed that shade did not alter the negative effects caused by drought stress in MI but did alleviate the negative effects of the LI condition. In summary, the effect of drought on C. bungei plantlets depends on the irradiance conditions.