Photosynthesis and water-relation traits of the summer annual C4 grasses, Eleusine indica and Digitaria adscendens, with contrasting trampling tolerance

Two summer annual C₄ grasses with different trampling susceptibilities were grown as potted plants, and diurnal leaf gas exchange and leaf water potential in each grass were compared. The maximum net photosynthetic rate, leaf conductance and transpiration rate were higher in the trampling-tolerant Eleusine indica (L.) Gaertn. than in trampling sensitive Digitaria adscendens (H. B. K.) Henr. Leaf water potential was much lower in E. indica than in D. adscendens. There were no differences in soil-to-leaf hydraulic conductance and leaf osmotic potential at full turgor as obtained by pressure–volume analysis. However, the bulk modulus of elasticity in cell walls was higher in E. indica leaves than in D. adscendens leaves. This shows that the leaves of E. indica are less elastic. Therefore, the rigid cell walls of E. indica leaves reduced leaf water potential rapidly by decreasing the leaf water content, supporting a high transpiration rate with high leaf conductance. In trampled habitats, such lowering of leaf water potential in E. indica might play a role in water absorption from the compacted soil. In contrast, the ability of D. adscendens to colonize dry habitats such as coastal sand dunes appears to be due to its lower transpiration rate and its higher leaf water potential which is not strongly affected by decreasing leaf water content.     

Aechmea itapoana,a new species from Bahia (Brazil): Taxonomy and ecology

Aechmea itapoana is a new, conspicuous and distinct species from the coastal sand dune scrub of N.E. Brazil. Its possible relationships within subgenusChevaliera, toA. multiflora andA. rodriguesia are discussed.     

Seedling growth variation in response to sand burial in four <Emphasis Type="Italic">Artemisia</Emphasis> species from different habitats in the semi-arid dune field

We compared seedling growth of four Artemisia species dominated at different habitats to determine whether interspecific seedling growth variation of a same genus in tolerance to burial can be used to explain plant distribution in the sand dune field. Interdune lowland species, Artemisia gmelinii, stabilized dune species, A. frigida, semi-stabilized dune species, A. halodendron, and active dune species, A. wudanica were selected. Seedlings grown for 3 weeks were treated at five burial depths for three burial times in pot experiments. Species from the habitats with little burial had smaller survival rate, dry weight and stem elongation speed than those from the habitats with intensive burial when buried. Furthermore, when buried, the former tended to adjust biomass allocation between shoot and root and produce adventitious buds, while the latter tended to maintain a constant root:shoot ratio and produce adventitious roots. We conclude that (1) seedlings of species with a long evolutionary history of exposure to sand burial (from the active sand dune), show quicker stem growth when buried than do seedlings of species from the habitats with little or no sand burial; (2) seedlings of species which do not change root:shoot ratio might be more tolerant of sand burial than those do; (3) seedlings of species from the habitats with intensive sand burial is prone to produce adventitious roots and seedlings of species from the habitats with little or no sand burial tend to produce adventitious buds when buried.     

Cytotaxonomic study on two putative hybrids in the genusDuchesnea (Rosaceae)

The karyotypes and chromosome associations at meiosis in two types of natural hybrids, 7x and 8x, betweenDuchesnea chrysantha (2x) andD. indica (12x) were investigated. The 7x hybrid had a haploid chromosome set from each parent plant, whereas the 8x hybrid was considered to have a full set ofD. chrysantha and half a set ofD. indica. In the two hybrids, the chromosomes ofD. chrysantha andD. indica conjugated only slightly at meiosis. It is probable that no common genome set between the diploidD. chrysantha and the dodecaploidD. indica exists. The present evidence indicates thatD. chrysantha andD. indica should be considered to be distinct species, although they have sometimes been treated as a single species.     

Ecophysiological behavior ofArtemisia ordosica on the process of sand dune fixation

The population structure and water relations ofArtemisia ordosica were studied at different stages of the sand dune fixation process. Vegetation coverage and biomass increased as the sand dune fixation process progressed. In contrast, individual growth rate decreased in the late fixation stage. On fixed sand dunes the modal age ofA. ordosica plants was higher and seedlings or saplings were rearely observed. On active sand dunes, settlement of seedlings was regulated by sand mobility; that is, seedlings were observed only when sand mobility was below 10 cm per year. Leaf transpiration was highest in active sand dunes. Stand transpiration in fixed sand dunes was lower than in semi-fixed sand dunes. These differences in transpiration were related to a decrease in soil water availability, which was affected by the increase in the aeolian fine soil component during the course of sand dune fixation. The reduction in soil water status and the cessation of sand movement were considered to be important factors in the decline of theArtemisia ordosica community.     

Accumulation of nutrients by eucalyptus seedlings from acidic and calcareous soils of the cerrado region of Central Brazil

Summary The accumulation of nutrients by seedlings ofEucalyptus grandis andE. saligna from a latosol and two other fertile soils was compared. Both species performed well in a calcareous soil and an acidic but fertile gallery forest soil but not in the dystrophic latosol.E. grandis accumulated more nutrients from the calcareous soil thanE. saligna. In the other two soils these two species showed similar growth and nutrient accumulation. In spite of the high acidity, manganese toxicity did not seem to be a limiting factor in the latosol or the gallerty forest soil. Correlations among the shoot concentrations were not always the same as those among the total contents of the nutrients in the aerial biomass.     

Colonization of the root zone ofAmmophila arenaria by harmful soil organisms

The role of harmful soil organisms in the degeneration ofAmmophila arenaria at coastal foredunes was examined by the growing of seedlings ofA. arenaria in soil samples collected from its root zone. Three sites, each representing a successive stage in foredune succession were examined: (1) a highly mobile dune (sand accretion of 80 cm year⁻¹) with vigorousA. arenaria, colonizing only the upper 30-cm of the annually deposited layer of sand, (2) a mobile dune with vigorousA. arenaria (sand accretion of 22 cm year⁻¹) and a 1-metre soil profile completely colonized by roots and (3) a stable dune (no sand accretion) with degeneratedA. arenaria and young roots mainly present in the upper 0–10 cm. In the upper part of the highly mobile site, the presence of harmful soil organisms was confined to the root layers and at the mobile site for all depth layers a significant growth reduction ofA. arenaria was observed due to the activity of harmful soil organisms. At the stable site, however, growth had only been reduced in some of the depth layers. At all sites newly formed roots ofA. arenaria had been colonized by harmful soil organisms within one year. If present in sand prior to root growth harmful soil organisms reduced root length and root hair formation severely and they enhanced branching of the roots. It is concluded that harmful soil organisms initiate degeneration ofA. arenaria in stable dunes by attack of the root system, which makes the plants suffer from abiotic stress.     

Adaptations enhancing survival and establishment of seedlings on coastal dune systems

Studies on the survival and establishment of seedlings in coastal and lacustrine sand dune systems suggest that nutrient deficiency, lack of moisture, sand accretion, salt spray and predation are probably the most important limiting factors. Seedlings employ both avoidance and tolerance strategies to with-stand the different stresses. For example, seedling recruitment of dune species coincided with periods of high moisture availability and occurred in years with high well distributed rainfall. The seedlings exhibited rapid vertical elongation of roots, avoided moisture stress by leaf rolling, dense hair on leaves, fleshy cotyledonary leaves, and by growing in the shade of nurse plants. A certain proportion of seedlings of all species survived partial burial and showed stimulation of leaf growth, total leaf area, number of tillers and total dry matter. Seedlings of most species could not survive complete burial, however, some species did grow through the sand deposit by an increase in the number of nodes and length of internodes. Plants responded to salt spray by inhibition of seed germination, developing resistance, increase in leaf thickness and reduced uptake of Na and Cl ions. Several characters such as higher vigour of seedlings, larger seed size and seed polymorphism were also of adaptive significance to the species.     

Soil particle sizes and plant communities on coastal dunes

To identify and assess the distribution patterns of coastal dune vegetation along the eastern, southern, and western coasts of South Korea, we investigated the plant communities and soil factors at 30 sites. In all, 12 communities on CCA (canonical correspondence analysis) Axis 1 and 2 could be arranged into 3 groups: 1 ) 2 communities ofElymus mollis andIschaemum anthephoroides, with medium sand contents; 2) 6 communities ofCarex pumila, Carex kobomugi, Ixeris repens, Zoysia mac-rostachya, Calystegia soldanella, andVitex rotundifolia, with coarse sand contents; and 3) 4 communities ofLathyrus japonicus,Glehnia littoralis, Messerschmidia sibirica, andRosa rugosa, with very coarse sand contents. As identified via CCA ordination, the distribution of these groups was positively correlated with soil particle sizes.     

Ontogenetic shifts in interactions of two dominant shrub species in a semi‐arid coastal sand dune system

Question: How does the interaction between two dominant shrub species in a coastal sand dune community change during their life history? Does this interaction influence their population dynamics? Location: A semiarid coastal sand dune system in southeast Spain. Methods: For 3 years we monitored physiological status, growth and reproductive effort of Juniperus phoenicea and Pistacia lentiscus, the dominant shrub species, growing either alone or in close spatial association. We also recorded adult mortality patterns and characterized seedling survival, soil properties and microclimate conditions beneath canopies and in bare ground. Results and conclusions: There was a strong bi‐directional interaction between the two studied species, with a net balance that changed in sign with increasing plant development. While mature individuals facilitated the establishment of seedlings of both species, adult mortality patterns suggested asymmetric competition at later life stages. The interaction with Pistacia negatively affected growth of juniper and contributed to its high mortality rates, while juniper had almost no effect on mature Pistacia individuals. Physiological data suggested that Pistacia had a competitive advantage over juniper, most likely because of differences in rooting patterns and tolerance to salinity, which may determine the source of water available for each species. Community dynamics are governed by facilitation at the seedling stage and shaped by differences in physiological traits in adult plants. Plant‐plant interactions, which are strongly affected by environmental gradients, are important drivers of community dynamics in this system.     

Influence of water availability on competitive interactions between plant species on sandy soils

The gravimetric soil water content of four different successional stages of inland dune vegetation revealed pronounced seasonal changes and particularly a major drought period in the late summer. In order to analyze the effect of these seasonal water changes on the competitive interactions of two dominant species (Carex arenaria andDeschampsia flexuosa) in one of these stages root development was compared under experimentally manipulated water conditions in a minirhizotron experiment. Under well-watered conditions, the root growth ofC. arenaria andD. flexuosa was not influenced by competition, but was significantly reduced forC. arenaria at low water availability. Accordingly, the relative yield based on total biomass was significantly lower under water shortage than under well-watered conditions forC. arenaria, indicating higher interspecific competition compared to intraspecific competitive interactions. These results indicate (i) that soil water status is an important factor for belowground competitive interactions and (ii) that seasonal changes in soil water content may have a pronounced effect on the outcome of competition and, in consequence, on the structure of the respective plant communities.     

种子萌发和幼苗生长对沙丘环境的适应机制

综述了植物沙生适应机制的研究及其进展.一些植物的种子在刚成熟时具有休眠特性.种子需要适度沙埋促进萌发并实现幼苗定居,但过度沙埋则会抑制种子萌发和出苗.在沙层深处,没有萌发的种子会进入休眠状态,形成土壤种子库.幼苗通过增加节数和延长节间来适应沙埋.沙埋深度超过植物的忍耐限度会抑制幼苗生长,甚至导致幼苗死亡.沙生植物必须适应其他环境因子,如盐风与土壤盐分、昆虫采食、土壤养分亏缺等,才能在沙丘上成功生长.沙蚀可导致幼苗根系暴露并干燥脱水.一些沙漠植物的幼苗在萌发后可忍耐一段时期的干燥,水分条件得到满足之后,幼苗能够恢复生长.     

Effects of salt spray and sand burial on Spinifex sericeus R. Br.

Abstract Spinifex sericeus, a common coastal sand dune grass, typically exhibits decreased vigour in the more stabilized section of the dunes when compared with the active foredune. These differences in vigour appear to be related to different environmental conditions across the dunes such as sand burial and salt spray deposition, both generally decreasing with distance inland. An experiment following the fate of foliar and root applications of ²²Na indicated that it may be taken up by the roots or the foliage and then translocated throughout the whole plant, and perhaps even extruded by the roots. Salt spray appeared to have a positive effect on the growth of S. sericeus when applied in conjunction with N and P but had no effect when N and P were not added. Adding acid-washed or non acid-washed foredune sand also resulted in a positive growth response. The results of these experiments indicate that the vigorous growth of S. sericeus on the dynamic sections of the foredunes is due to a stimulation of growth caused by sand deposition.     

Competition between Bufo larvae in a eutrophic pond

Competition between larvae of two anuran species (Bufo bufo and B. calamita) was investigated under field conditions likely to disfavour cell-mediated interference mechanisms. The experiment used triplicated cage treatments in an unshaded farm pond, a poor habitat for the unicellular pathogen Anurofeca richardsi implicated in interference competition between these anurans in sand dune ponds. The farm pond experienced lower maximum temperatures than a nearby dune pond but sustained larger numbers of eukaryotic algae and therefore had higher primary productivity. Survival and growth of B. calamita larvae were inversely related to density in all treatments but interspecific effects were much more severe than intraspecific ones. There was no evidence of A. richardsi in any treatment and competition between the Bufo larvae was therefore intense in the absence of Anurofeca-mediated interference effects. Anuran larvae reduced the standing crop and altered the community composition of algae in the treatment cages but larval growth rates were not simply related to food availability. Algal cell numbers in larval guts, a measure of food acquisition, were however inversely related to tadpole density in both species. Feeding niche overlap was high but decreased as larval density increased. Resource competition was implicated as the most probable major mechanism. Received: 1 September 1999 / Accepted: 20 January 2000     

Positive responses of coastal dune plants to soil conditioning by the invasive Lupinus nootkatensis

Invasive nitrogen-fixing plants drive vegetation dynamics and may cause irreversible changes in nutrient-limited ecosystems through increased soil resources. We studied how soil conditioning by the invasive alien Lupinus nootkatensis affected the seedling growth of co-occurring native plant species in coastal dunes, and whether responses to lupin-conditioned soil could be explained by fertilisation effects interacting with specific ecological strategies of the native dune species. Seedling performance of dune species was compared in a greenhouse experiment using field-collected soil from within or outside coastal lupin stands. In associated experiments, we quantified the response to nutrient supply of each species and tested how addition of specific nutrients affected growth of the native grass Festuca arundinacea in control and lupin-conditioned soil. We found that lupin-conditioned soil increased seedling biomass in 30 out of 32 native species; the conditioned soil also had a positive effect on seedling biomass of the invasive lupin itself. Increased phosphorus mobilisation by lupins was the major factor driving these positive seedling responses, based both on growth responses to addition of specific elements and analyses of plant available soil nutrients. There were large differences in growth responses to lupin-conditioned soil among species, but they were unrelated to selected autecological indicators or plant strategies. We conclude that Lupinus nootkatensis removes the phosphorus limitation for growth of native plants in coastal dunes, and that it increases cycling of other nutrients, promoting the growth of its own seedlings and a wide range of dune species. Finally, our study indicates that there are no negative soil legacies that prevent re-establishment of native plant species after removal of lupins.     

Vesicular-arbuscular mycorrhizal fungi in coastal dune plant communities I. Spore formation ofGlomus spp. predominates under a patch ofElymus mollis

Vesicular-arbuscular (VA) mycorrhizal fungi in pure patches of coastal dune plantsElymus mollis, Wedelia prostrata andZoysia macrostachya were examined for frequency of occurrence and number of spores of VA mycorrhizal fungi over one year. Six species in three genera of VA mycorrhizal fungi were recovered. Under a patch ofE. mollis, spores ofAcaulospora sp. 1,Glomus tortuosum, Glomus sp. 1,Glomus sp. 2 andScutellospora gregaria were recovered. Spores ofGlomus spp. were most common. In patches ofW. prostrata andZ. macrostachya spores ofAcaulospora sp. 1,G. tortuosum, Glomus sp. 1,Glomus sp. 2,S. gregaria andScutellospora sp. 1 were found.Contribution No. 112, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Initial regenerative processes ofDistylium racemosum andPersea thunbergii in an evergreen broad-leaved forest

We studied the initial regenerative processes ofDistylium racemosum andPersea thunbergii, major canopy species, in an old-growth evergreen broad-leaved forest, Kagoshima, southwestern Japan. Although the two species coexisted, the patterns of seed production, seedling emergence, and sapling survival were different between them. During the observation (1989–1991),P. thunbergii produced large numbers of seeds in alternate years, whileD. racemosum had no mast year. The density of established seedlings was high and increased with mass seed production forP. thunbergii, but was fairly low forD. racemosum. The mortality of seedlings and saplings ofP. thunbergii was higher than that ofD. racemosum. In a closed stand, the sapling bank was maintained by dense seedling supply forP. thunbergii, and by extremely low mortality of individuals germinated before the beginning of observation forD. racemosum. Since saplings ofD. racemosum showed continuous height growth beneath the closed canopy, the possibility of recruitment into the upper layer seems to be high. The strategy ofP. thunbergii might be to wait for suitable conditions favoring sapling growth on various site by means of frequent and large seed productivity and wide dispersal of seeds. Thus both species might be able to coexist through environmental heterogeneity.     

State of Scots pine (Pinus sylvestris L.) under nutrient and water deficit on coastal dunes of the Baltic Sea

The aim of the present study was to assess the ecophysiological state of Scots pine (Pinus sylvestris L.) growing at different heights on one of the typical coastal sand dunes in the dune field situated in southwestern Estonia. Dependence of the anatomical structure, morphological parameters, nutrients accumulation and biochemical characteristics of needles on the location of the site on the dune and on the concentration of nutrients in soil and in needle tissues was established. Correlation analysis revealed the dependence of chlorophyll a on the concentration of N and Mg in soil as well as in needles. The mesophyll area and chlorophyll concentration in needles were smallest on the top of the dune. The proportion of epidermis in the total needle cross-section area from the top was a little larger than in the needles from the bottom; the epicuticular wax layer on needles decreased towards the top. The length of needles and shoots was the lowest on the top of the dune, where the growth substrate contains notably less nutrients and water than needed for optimum growth of trees. The t test showed statistically significant larger average tree-ring width of the pines growing at the bottom. The pines on the top and at the bottom of the dune were not sensitive to temperature conditions. The radial growth of pines on the top of the dune was positively correlated with the total precipitation of the previous year.     

Carbon input from plant to soil through root exudation inDigitaria adscendens andAmbrosia artemisiifolia

The amount of carbon released into soil through root exudation byDigitaria adscendens Herrm. andAmbrosia artemisiifolia L. var.elatior Desc., which often predominate at the early stages of secondary succession, was evaluated in a laboratory experiment conducted over a 60-day period. Differences in the amount of exuded carbon between these species and between the developmental stages were examined. The amount of carbon exuded increased with growth in both species. The percentage of exuded carbon to photosynthetically net fixed carbon, which was higher at younger stages (13%) inD. adscendens, decreased to 3.1% with time. On the other hand, no reduction in the amount of carbon exuded was observed inA. artemisiifolia (4.7–8.1% range). The total amount of carbon released through root exudation inD. adscendens andA. artemisiifolia was estimated at 3.1% and 6.9% of photosynthetically net fixed carbon, respectively. These results suggest the possibility that wild plants exude a considerable amount of carbon from their roots to the soil, and emphasizes the necessity for considering root exudation in the carbon cycle.     

Is zonation on coastal sand dunes determined primarily by sand burial or by salt spray? A test in New Zealand dunes

There has long been controversy on which environmental factor is the predominant determinant of community zonation on sand dunes. It is demonstrated here that, on a dune system in southern New Zealand, several environmental factors that could limit growth all vary along the sea-to-inland sand dune zonation: soil moisture, soil nutrients, wind exposure, sand burial, salt spray and soil salinity. Correlation of the responses of 30 species to experimental stress (burial, darkness, rooting-medium salinity and salt spray) with the zonation of the species in the field indicates that, in the four dune systems studied, sand burial and salt are both important, with salt generally being the more important. However, the relative importance of the factors differs between sites.