Temporal annotation of high-resolution intra-annual wood density information of Eucalyptus urophylla and its correlation with hydroclimatic conditions

Three different Eucalyptus urophylla clones grown under two different spacing regimes in an experimental site in the state of São Paulo, Brazil, were analyzed to test effects of clone identity, spacing, cambial age and hydroclimatic conditions on high-resolution intra-annual wood density profiles. Since distinct periodic tree-ring boundaries were not visible on the stem cross-sectional surfaces, finding an alternative method for synchronization of density profiles was crucial for the analysis. The challenge was to generate intra- and inter-tree synchronized density profiles that possess high amplitude variation and low phase variation. Thus, we developed a protocol and workflow of how such high-resolution density profiles can be spatially aligned and temporally annotated to enable correlation analyses between trees and with time series of environmental stimuli. Mean wood density was significantly different between clones, but not between the spacings. Wood density increased significantly with increasing cambial age and decreasing growth rate. Principal component analysis showed that the overall variability in the temporally annotated density profiles is dominated by a highly significant common signal. We found significant negative correlation values for precipitation, indicating that water supply is the main driver of stem growth at the site, and providing evidence for the correctness of the method. The developed workflow can easily be adjusted to the analysis of other intra-annual tree-ring features like anatomical xylem cell traits or isotopic signals in the wood. It has a large potential to be used as a general guideline for the synchronization of intra-annual tree-ring traits, especially when distinct tree-ring boundaries are missing, as it is often the case under tropical climatic conditions. The workflow supports the development of spatially aligned and temporally annotated chronologies under non-annual growth rhythms.     

Highly heterogeneous residual malaria risk in western Thailand

Over the past decades, the malaria burden in Thailand has substantially declined. Most infections now originate from the national border regions. In these areas, the prevalence of asymptomatic infections is still substantial and poses a challenge for the national malaria elimination program. To determine epidemiological parameters as well as risk factors for malaria infection in western Thailand, we carried out a cohort study in Kanchanaburi and Ratchaburi provinces on the Thailand-Myanmar border. Blood samples from 999 local participants were examined for malaria infection every 4 weeks between May 2013 and Jun 2014. Prevalence of Plasmodium falciparum and Plasmodium vivax was determined by quantitative PCR (qPCR) and showed a seasonal variation with values fluctuating from 1.7% to 4.2% for P. vivax and 0% to 1.3% for P. falciparum. Ninety percent of infections were asymptomatic. The annual molecular force of blood-stage infection (_molFOB) was estimated by microsatellite genotyping to be 0.24 new infections per person-year for P. vivax and 0.02 new infections per person-year for P. falciparum. The distribution of infections was heterogenous, that is, the vast majority of infections (>80%) were found in a small number of individuals (<8% of the study population) who tested positive at multiple timepoints. Significant risk factors were detected for P. vivax infections, including previous clinical malaria, occupation in agriculture and travel to Myanmar. In contrast, indoor residual spraying was associated with a protection from infection. These findings provide a recent landscape of malaria epidemiology and emphasize the importance of novel strategies to target asymptomatic and imported infections.     

Cryopreservation of shoot tips of recalcitrant and tropical species: Advances and strategies

There is a pressing need for practical and successful conservation efforts to establish long-term germplasm collections of recalcitrant and tropical species, given the challenge and threat that these plants are facing. Cryopreservation is the only way of conserving some of these species, especially those with temperature or desiccation sensitive (recalcitrant) seeds. This review covers reports on cryopreservation studies of shoot tips (apical and axillary) of tropical and subtropical plants. Since many of these species have recalcitrant seeds, the cryopreservation successes, failures and problems involved with these seeds are also discussed. The methodologies, important factors and steps involved in successful cryopreservation protocols are analyzed. Finally strategies are suggested to develop a successful cryopreservation protocol for new plant species, in particular those with tropical recalcitrant seeds.     

Glomalean mycorrhizal fungi from tropical Australia

 A comparison of different methods for isolation of vesicular-arbuscular mycorrhizal (VAM) fungi into open-pot cultures was undertaken as part of a study of the diversity of these fungi. Four different isolation techniques using spores separated from soil, soil trap cultures, root samples, or transplanted seedlings grown in intact soil cores were used to obtain as many fungi as possible from each site. Isolation methods were compared using paired samples from the same locations within natural (savanna, rocky hill, wetland, rainforest) and disturbed (minesite) habitats in a seasonally dry tropical region in the Northern Territory of Australia. There were large differences in (i) the efficiency (rate of increase in mycorrhizal colonisation), (ii) the proportion of successful cultures, (iii) fungal diversity (number of fungal species in each culture) and (iv) specificity (identity of species isolated) between these four procedures. However, the less-efficient procedures generally resulted in a higher proportion of cultures of one fungus, which could be used without further isolation steps. Most species of Scutellospora, Acaulospora and Gigaspora were obtained primarily from field-collected spores, but only 50% of these culture attempts were successful. Spores from these initial cultures produced mycorrhizas much more rapidly and successfully when used to start second-generation cultures. Several species of fungi, rarely recovered as living spores from field soils, were dominant in many trap cultures started from soil or roots. Most of these fungi were Glomus species, that were first distinguished by colonisation patterns in roots and eventually identified after sporulation in second- or third-generation trap cultures. These experiments demonstrated that glomalean fungi in the habitats sampled belonged to two functional categories, based on whether or not spores were important propagules. The "non-sporulating" fungi were dominant in many trap cultures, which suggests that these fungi had higher total inoculum levels in soils than other fungi. Pot-culturing methods provided additional information on fungal diversity which complemented spore occurrence data obtained using the same soil samples and provided valuable new information about the biology of these fungi. Accepted: 26 December 1998     

Structure,composition and species diversity in an altitude-substrate matrix of rain forest tree communities on Mount Kinabalu,Borneo

We studied forest structure, composition and tree species diversity of eight plots in an environmental matrix of four altitudes (700, 1700, 2700 and 3100 m) and two types of geological substrates (ultrabasic and non-ultrabasic rocks) on Mount Kinabalu, Borneo. On both substrate series, forest stature, mean leaf area and tree species diversity (both 4.8 cm and 10 cm diameter at breast height [dbh]) decreased with altitude. The two forests on the different substrate series were similar at 700 m in structure, generic and familial composition and tree species diversity, but became dissimilar with increasing altitude. The decline in stature with altitude was steeper on the ultrabasic substrates than on the non-ultrabasic substrates, and tree species diversity was generally lower on ultrabasic substrates than on non-ultrabasic substrates at 1700 m. The forests on non-ultrabasic substrates at higher altitudes and those on ultrabasic substrates at the lower altitudes were similar in dbh versus tree height allometry, mean leaf area, and generic and familial composition at 1700 m. These contrasting patterns in forest structure and composition between the two substrate series suggested that altitudinal change was compressed on the ultrabasic substrates compared to the non-ultrabasic substrates. Tree species diversity was correlated with maximum tree height and estimated aboveground biomass, but was not with basal area, among the eight study sites. We suggest that forests with higher tree species diversity are characterized by greater biomass allocation to height growth relative to trunk diameter growth under more productive environment than forests with lower tree species diversity.     

西双版纳热带雨林蚁科昆虫区系分析

在西双版纳热带雨林已鉴定蚊科昆虫９亚科７６属２６７种。西双版纳地区的蚂蚁区系以热带至亚热带分布的东洋界成分最为丰富。在属级水平上,与马来西亚界关系最为密切。与澳洲界关系较密切;与非洲界和马拉加西界的关系知中。与新北界,新热带界和古北界的关系最为疏远。可见西双版纳的蚂蚁区系具有典型的热带亚洲起源特征,同时与澳洲和非洲的热带区系有一定的渊源关系。     

Arbuscular mycorrhizal fungi colonize decomposing leaves of<Emphasis Type="Italic"> Myrica parvifolia</Emphasis>,<Emphasis Type="Italic"> M. pubescens</Emphasis> and<Emphasis Type="Italic"> Paepalanthus</Emphasis> sp.

Hyphae and vesicles of arbuscular mycorrhizal fungi (AMF) were found within the decomposing leaves of Myrica parvifolia, M. pubescens and Paepalanthus sp. at three montane sites in Colombia. Hyphae, vesicles, and arbuscule-like structures were also found within scale-like leaves of the rhizomes of Paepalanthus sp. The litter found in the vicinity of the roots was divided into three decomposition layers. The highest AMF colonization occurred in the most decomposed leaves, which were in close association with roots. In contrast, there were no differences in AMF colonization of roots present in the different decomposition layers. Colonization of decomposing leaves by AMF did not differ between the two closely related species M. parvifolia and M. pubescens, nor between two sites (Guatavita and Zipacón, Colombia) differing in soil fertility. Occurrence of vesicles in decomposing leaves was correlated with abundant AMF extraradical hyphae among the leaves. We propose that AMF enter decomposing leaves mechanically through vascular tissue. As a consequence, AMF are well positioned to obtain and efficiently recycle mineral nutrients released by decomposer microorganisms before their loss by leaching or immobilization in soil.     

Mapping the spatial distribution of plant diversity indices in a tropical forest using multi-spectral satellite image classification and field measurements

The relationships among alpha and beta diversity indices, computed from 141 randomly sampled quadrats, and the vegetation classes obtained by multi-spectral satellite image classification, were used as a strategy for mapping plant diversity in a tropical landscape mosaic. A relatively high accuracy of the land cover map was revealed by the overall accuracy assessment and the Cohen's Kappa statistic. Species accumulation models were used to evaluate how representative the sample size was the different vegetation types. A standard one-way, between-subjects ANOVA confirmed a significant reduction of the within-class variance of plant diversity with respect to their total variance across the landscape. Computed uniformity indices, to assess the internal uniformity of vegetation classes on the diversity indices, confirmed the goodness of the mapped classes in stratifying variability of plant diversity. This allowed for the use of the mapped classes as spatial interpolators of plant diversity values for estimation and up-scaling purposes. Finally, it was revealed that the plant diversity of the landscape depends, to a large extent, on the diversity contained in the most mature forest class, which is also the most diverse community in the studied area. High and moderate beta diversity values between mature forests and both the secondary associations and the first stages of succession, respectively, indicated that there is a significant contribution to the diversity of the landscape by those vegetation classes.     

Leaf photosynthetic traits scale with hydraulic conductivity and wood density in Panamanian forest canopy trees

We investigated how water transport capacity, wood density and wood anatomy were related to leaf photosynthetic traits in two lowland forests in Panama. Leaf-specific hydraulic conductivity (k_L) of upper branches was positively correlated with maximum rates of net CO₂ assimilation per unit leaf area (A_area) and stomatal conductance (g_s) across 20 species of canopy trees. Maximum k_L showed stronger correlation with A_area than initial k_L suggesting that allocation to photosynthetic potential is proportional to maximum water transport capacity. Terminal branch k_L was negatively correlated with A_area/g_s and positively correlated with photosynthesis per unit N, indicating a trade-off of efficient use of water against efficient use of N in photosynthesis as water transport efficiency varied. Specific hydraulic conductivity calculated from xylem anatomical characteristics (k_theoretical) was positively related to A_area and k_L, consistent with relationships among physiological measurements. Branch wood density was negatively correlated with wood water storage at saturation, k_L, A_area, net CO₂ assimilation per unit leaf mass (A_mass), and minimum leaf water potential measured on covered leaves, suggesting that wood density constrains physiological function to specific operating ranges. Kinetic and static indices of branch water transport capacity thus exhibit considerable co-ordination with allocation to potential carbon gain. Our results indicate that understanding tree hydraulic architecture provides added insights to comparisons of leaf level measurements among species, and links photosynthetic allocation patterns with branch hydraulic processes.     

Colony structure in a plant-ant: behavioural,chemical and genetic study of polydomy in<Emphasis Type="Italic"> Cataulacus mckeyi</Emphasis> (Myrmicinae)

Social organisation of colonies of obligate plant-ants can affect their interaction with myrmecophyte hosts and with other ants competing for the resources they offer. An important parameter of social organisation is whether nest sites of a colony include one or several host individuals. We determined colony boundaries in a plant-ant associated with the rainforest understorey tree Leonardoxa africana subsp. africana, found in coastal forests of Cameroon (Central Africa). This myrmecophyte is strictly associated with two ants, Petalomyrmex phylax and Cataulacus mckeyi. Plants provide food and nesting sites for P. phylax, which protects young leaves against insect herbivores. This mutualism is often parasitised by C. mckeyi, which uses but does not protect the host. The presence of C. mckeyi on a tree excludes the mutualistic ant. Because Petalomyrmex -occupied trees are better protected, their growth and survival are superior to those of Cataulacus -occupied trees, giving P. phylax an advantage in occupation of nest sites. C. mckeyi often colonises trees that have lost their initial associate P. phylax, as a result of injury to the tree caused by disturbance. Polydomy may allow C. mckeyi to occupy small clumps of trees, without the necessity of claustral colony foundation in each tree. Investigating both the proximate (behavioural repertoire, colony odour) and the ultimate factors (genetic structure) that may influence colony closure, we precisely defined colony boundaries. We show that colonies of C. mckeyi are monogynous and facultatively polydomous, i.e. a colony occupies one to several Leonardoxa trees. Workers do not produce males. Thus, the hypothesis that polydomy allows workers in queenless nests to evade queen control for their reproduction is not supported in this instance. This particular colony structure may confer on C. mckeyi an advantage in short-distance dispersal, and this could help explain its persistence within the dynamic Leonardoxa system.