Climate,landscape and microenvironment interact to determine plant composition in naturally discrete gravel beach communities

Question: What is the relative importance of national‐, regional‐ and within‐beach‐scale influences on vegetation composition and floristic affinities of New Zealand gravel beaches? Location: Coastal New Zealand. Methods: We sampled vegetation composition at 61 gravel beaches, quantifying site factors and adjacent landscape characteristics. Site, climate and geographic relationships between gravel beaches and related ecosystems were inferred using GIS data layers. To simultaneously investigate influences at different spatial scales, we used ordination and variation partitioning to examine relationships between composition and environment, and hierarchical models to understand floristic affinities with related ecosystems. Results: At a national scale, compositional variation among beaches reflects mean annual temperature and spring vapour pressure deficit; within regions, proximity of native woody vegetation and coastal turfs are important; within‐beach variation is related to substrate stability and particle size distribution. The gravel beach flora is 50% exotic, reflecting the highly modified nearby landscapes; 30% of species are characteristic of coastal sands, 20% of braided riverbeds and 8% of coastal turfs. Affinities with coastal sand communities are unrelated to microsite sandiness or area of sand dunes within 50 km. Affinities with braided riverbeds are related to the bed area of those rivers draining within 200 km and proportion of gravel in the substrate. Affinities with coastal turfs are related to proximity to the nearest turf and the proportion of humus in the substrate. Conclusions: Examining multiple scales of influence in a landscape context is essential to understand composition of naturally discrete ecosystems that span wide geographic ranges and to underpin their conservation management.     

Disentangling the relative effects of environmental versus human factors on the abundance of native and alien plant species in Mediterranean sandy shores

Aim Mediterranean coastal sand dunes are characterized by both very stressful environmental conditions and intense human pressure. This work aims to separate the relative contributions of environmental and human factors in determining the presence/abundance of native and alien plant species in such an extreme environment at a regional scale. Location 250 km of the Italian Tyrrhenian coast (Region Lazio). Methods We analysed alien and native plant richness and fitted generalized additive models in a multimodel‐inference framework with comprehensive randomizations to evaluate the relative contribution of environmental and human correlates in explaining the observed patterns. Results Native and alien richness are positively correlated, but different variables influence their spatial patterns. For natives, human population density is the most important factor and is negatively related to richness. Numbers of natives are unexpectedly lower in areas with a high proportion of natural land cover (probably attributable to local farming practices) and, to a lesser degree, affected by the movement of the coastline. On the other hand, alien species richness is strongly related to climatic factors, and more aliens are found in sectors with high rainfall. Secondarily, alien introductions appear to be related to recent urban sprawl and associated gardening. Main conclusions Well‐adapted native species in a fragile equilibrium with their natural environment are extremely sensitive to human‐driven modifications. On the contrary, for more generalist alien species, the availability of limited resources plays a predominant role.     

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.     

Interaction between a fungal endophyte and root herbivores of Ammophila arenaria

The effect of an endophytic fungus (Acremonium strictum) on plant-growth related parameters of marram grass (Ammophila arenaria), and its potential as a protective agent against root herbivores (Pratylenchus dunensis and Pratylenchus penetrans, root-lesion nematodes) was investigated in two inoculation experiments under different conditions. Acremonium strictum-inoculated plants showed increased plant development in terms of root biomass in the first experiment and increased number of tillers in the second experiment and biomass was less suppressed by nematodes than the Acremonium strictum-free plants. In neither experiment did Acremonium strictum reduce multiplication of root herbivores. On the contrary, Acremonium strictum-inoculated plants seemed to increase herbivore multiplication. Plants infected with P. penetrans benefitted more from the endophytic fungus than those with P. dunensis in terms of total biomass. The effect of Acremonium strictum on interspecific competition was also analyzed by plant inoculation with both nematode species. In Acremonium strictum-free plants with mixed nematode inoculum, the total number of nematodes, compared to numbers observed in one-species inoculation, was less than expected, suggesting that interspecific competition took place. In Acremonium strictum-inoculated plants no interspecific competition was observed. Plants inoculated with P. dunensis, P. penetrans and Acremonium strictum showed decreased total biomass compared to Acremonium strictum-free plants inoculated with the same nematodes. The implications of increased tillering and root growth of plants with Acremonium endophytes are discussed in relation to the sand stabilizing role of Ammophila arenaria in coastal dunes.     

Seed germination and seedling establishment of an invasive tropical tree species under different climate change scenarios

Increasing air temperature and atmospheric CO₂ levels may affect the distribution of invasive species. Whereas there is wide knowledge on the effect of global change on temperate species, responses of tropical invasive species to these two global change drivers are largely unknown. We conducted a greenhouse experiment on Terminalia catappa L. (Combretaceae), an invasive tree species on Brazilian coastal areas, to evaluate the effects of increased air temperature and CO₂ concentration on seed germination and seedling growth on the island of Santa Catarina (Florianópolis, Brazil). Seeds of the invasive tree were subjected to two temperature levels (ambient and +1.6 °C) and two CO₂ levels (ambient and ~650 ppmv) with a factorial design. Increased temperature enhanced germination rate and shortened germination time of T. catappa seeds. It also increased plant height, number of leaves and above‐ground biomass. By contrast, increased atmospheric CO₂ concentration had no significant effects, and the interaction between temperature and CO₂ concentration did not affect any of the measured traits. Terminalia catappa adapts to a relatively broad range of environmental conditions, being able to tolerate cooler temperatures in its invasive range. As T. catappa is native to tropical areas, global warming might favour its establishment along the coast of subtropical South America, while increased CO₂ levels seem not to have significant effects on seed germination or seedling growth.     

Mycorrhizal features and leaf traits covary at the community level during primary succession

The mycorrhizal association between fungi and plants is thought to be an important component of the functional diversity of plant communities, although evidence is weak. We explored community-level changes to mycorrhizal features and leaf traits along a primary successional gradient on a sedimentation coast. We found that community weighted mean values of mycorrhizal features and leaf traits varied systematically along the successional series, representing a transition from communities dominated by more stress-tolerant plant species (less mycorrhizal colonization and lower specific leaf area) to less stress-tolerant plant species (higher mycorrhizal colonization and specific leaf area). Despite the co-variation in leaf traits and mycorrhizal features at the community level, only mycorrhizal features showed an increasing functional diversity with successional age. These results suggest that mycorrhizal fungi should not be forgotten in trait-based plant community ecology.     

Photosynthetic responses of plant communities to sand burial on the machair dune systems of the outer hebrides, Scotland

BACKGROUND AND AIMS: The effects of both short-term (2 weeks) and long-term (6 weeks) burial on the photosynthetic efficiency of four typical plant sub-communities of the machair sand dunes of the Outer Hebrides are described. Previous studies have examined the photosynthetic responses on individual species rather than the response at the community level. METHODS: Three replicate turves from four different sub-community types (foredune grassland, dune slack, three-year fallow and unploughed grassland) were subjected to short- and long-term burial treatments after acclimatisation in an unheated greenhouse for approximately 10 weeks. Three replicate control turves from each sub-community were left unburied. After treatment, photosynthetic rate was measured at 16-20 h and 40-44 h after re-exposure, using an infra-red gas analyser, with standardization by total leaf area for each turf. Effects of sub-community type, burial duration and time since re-exposure were analysed by 3-factor split-plot analysis of variance (ANOVA) with repeated measures for time since re-exposure in the subplots. KEY RESULTS: Buried turves were characterized by a low dark respiration rate, which may represent a maintenance response to burial. After removal of sand, each machair sub-community showed some capacity for an elastic photosynthetic response. There were no differences between the effects of short- and long-term burial on the photosynthetic efficiency of machair vegetation, although turves buried for 6 weeks generally attained photosynthetic rates approaching those of control rates sooner than turves buried for 2 weeks. Photosynthetic responses to burial varied between sub-communities, with the slack turves exhibiting the poorest capacity for recovery within the investigated 44-h period. CONCLUSIONS: In the machair environment, the ability to maintain photosynthetic equipment whilst buried, and the ability to bring about a relatively rapid reinstatement of photosynthetic mechanisms on emergence or exposure, is an important adaptation for survival. Survival is closely related to the ability of a plant to replenish carbohydrate reserves before the next burial event.     

新月形沙丘稳定性机理——以甘肃河西沙区为例

新月形沙丘是一种重要的沙丘类型,一般存在于绿洲边缘。研究新月形沙丘的稳定性,对于揭示绿洲缘的风沙运动规律有重要学术价值,而到目前新月形沙丘的稳定性还是沙漠生态学领域中一个的尚未解决的科学问题。以河西沙区新月形沙丘为例,通过调查其分布环境、测定沙丘各部位风速和风蚀积沙等,分析了新月形沙丘顶部稳定机理。结果表明:1)甘肃河西沙区的新月形沙丘分布在沙漠边缘的下风向,一般为斑块状分布。分布区域为平坦的沙粘质或沙砾质滩地,丘间地较为开阔且具有明显的主风向。2)主风向(NW)过程是新月形沙丘顶点与沙脊线重合的过程,也是新月形沙丘前移和高度降低的过程;反主风向(SE)过程是新月形沙丘顶点与沙脊线分离的过程,也是新月形沙丘背风坡上部风蚀与沙丘增高的过程。3)新月形沙丘越高大,两翼越长、夹角越小。4)较为开阔的前后滩地是新月形沙丘及新月形沙丘链存在所必须的环境条件,相对单一的主风向是新月形沙丘及新月形沙丘链维持其稳定性的关键因子,反向风及两翼的廊道效应是新月形沙丘增高增大的关键因子,主、反两个方向的风速及其分布频率是控制该区域新月形沙丘及新月形沙丘链高度的限制因子。     

Collembola as bioindicators of restoration in mined sand dunes of Northeastern Brazil

Opencast mining causes severe environmental impacts by removing the vegetation cover and depleting the fauna. Reforestation methods using native species and diverse pre- and post-disturbance approaches aim to recover the original richness and diversity of species found before the impact. Bioindicators are powerful tools to evaluate the restoration of the original environmental conditions in disturbed areas. We used species richness, endemism and diversity measurements of Collembola to compare successional stages in reforested sites of different ages compared with a control undisturbed area. Richness and abundance of Collembola were subjected to correlation analysis with age of plots and vegetational variables. Areas that were reforested for up to 16 years supported a much lower Collembola species richness than undisturbed areas. Both the age of reforestation plots and vegetation variables (number of trees, diameter of crowns, depth of leaf litter and tree species richness) were positively and significantly correlated to collembolan abundance and richness. The results showed that the diversity of the 16-year-old plot was significantly higher than that of younger areas, but significantly less diverse than that of the control area. Endemic species were more sensitive to disturbance than non-endemics. Thus, species richness and diversity of soil Collembola can be only partially restored with appropriate reforestation methods, and although it takes many years, to some extent even endemic species can be gradually restored. Nevertheless, the maintenance of undisturbed diversity reservoirs linked by ecological corridors to reforested plots is imperative, as only undisturbed areas can support most of the endemic species able to re-colonize reforested sites.