Tree-rings,a key ecological indicator of environment and climate change

Due to wide spatial distribution, high annual resolution, calendar-exact dating, and high climate sensitivity, tree-rings play an important role in reconstructing past environment and climate change over the past millennium at regional, hemispheric or even global scales, so tree-rings can help us to better understand climate behaviour and its mechanisms in the past and then predict variation trends for the future. In this paper, we will review latest advances in tree-ring-based climate reconstructions in China and their applications in modelling past local/regional climate change, capturing historical climatic extreme events, as well as analyzing their link to large-scale climate patterns.     

Light response in seedlings of a temperate (<Emphasis Type="Italic">Quercus petraea</Emphasis>) and a sub-Mediterranean species (<Emphasis Type="Italic">Quercus pyrenaica</Emphasis>): contrasting ecological strategies as potential keys to regeneration performance in mixed marginal populations

In order to understand better the ecology of the temperate species Quercus petraea and the sub-Mediterranean species Quercus pyrenaica, two deciduous oaks, seedlings were raised in two contrasting light environments (SH, 5.3% full sunlight vs. HL, 70% full sunlight) for 2 years, and a subset of the SH seedlings were transferred to HL (SH–HL) in the summer of the second year. We predicted that Q. pyrenaica would behave more as a stress-tolerant species, with lower specific leaf area (SLA), allocation to leaf mass, and growth rate and less responsiveness to light in these metrics, than Q. petraea, presumed to be more competitive when resources, especially light and water, are abundant. Seedlings of Q. petraea had larger leaves with higher SLA, and exhibited a greater relative growth rate (RGR) in both SH and HL. They also displayed a higher proportion of biomass in stems (SMF), and a lower root to shoot ratio (R/S) in HL than those of Q. pyrenaica, which sprouted profusely, and had higher rates of photosynthesis (A_n) and stomatal conductance (g_wv), but lower whole-plant net assimilation rate (NAR). On exposure to a sudden increase in light, SH–HL seedlings of both species showed a short period of photoinhibition, but fully acclimated photosynthetic features within 46 days after transference; height, main stem diameter, RGR and NAR all increased at the end of the experiment compared to SH seedlings, with these increases more pronounced in Q. petraea. Observed differences in traits and responses to light confirmed a contrasting ecology at the seedling stage in Q. petraea and Q. pyrenaica in consonance with differences in their overall distribution. We discuss how the characteristics of Q. petraea may limit the availability of suitable regeneration niches to microsites of high-resource availability in marginal populations of Mediterranean climate, with potential negative consequences for its recruitment under predicted climatic changes.     

Exome resequencing reveals signatures of demographic and adaptive processes across the genome and range of black cottonwood (Populus trichocarpa)

Extant variation in temperate and boreal plant species has been influenced by both demographic histories associated with Pleistocene glacial cycles and adaptation to local climate. We used sequence capture to investigate the role of these neutral and adaptive processes in shaping diversity in black cottonwood (Populus trichocarpa). Nucleotide diversity and Tajima's D were lowest at replacement sites and highest at intergenic sites, while LD showed the opposite pattern. With samples grouped into three populations arrayed latitudinally, effective population size was highest in the north, followed by south and centre, and LD was highest in the south followed by the north and centre, suggesting a possible northern glacial refuge. F_ST outlier analysis revealed that promoter, 5′‐UTR and intronic sites were enriched for outliers compared with coding regions, while no outliers were found among intergenic sites. Codon usage bias was evident, and genes with synonymous outliers had 30% higher average expression compared with genes containing replacement outliers. These results suggest divergent selection related to regulation of gene expression is important to local adaptation in P. trichocarpa. Finally, within‐population selective sweeps were much more pronounced in the central population than in putative northern and southern refugia, which may reflect the different demographic histories of the populations and concomitant effects on signatures of genetic hitchhiking from standing variation.     

Improving efficiency of breeding for higher crop yield

Summary Exclusive selection for yield raises, the harvest index of self-pollinated crops with little or no gain in total bipmass. In addition to selection for yield, it is suggested that efficient breeding for higher yield requires simultaneous selection for yield's three major, genetically controlled physiological components. The following are needed: (1) a superior rate of biomass accumulation. (2) a superior rate of actual yield accumulation in order to acquire a high harvest index, and (3) a time to harvest maturity that is neither shorter nor longer than the duration of the growing season. That duration is provided by the environment, which is the fourth major determinant of yield. Simultaneous selection is required because genetically established interconnections among the three major physiological components cause: (a) a correlation between the harvest index and days to maturity that is usually negative; (b) a correlation between the harvest index and total biomass that is often negative, and (c) a correlation between biomass and days to maturity that is usually positive. All three physiological components and the correlations among them can be quantified by yield system analysis (YSA) of yield trials. An additive main effects and multiplicative interaction (AMMI) statistical analysis can separate and quantify the genotype × environment interaction (G × E) effect on yield and on each physiological component that is caused by each genotype and by the different environment of each yield trial. The use of yield trials to select parents which have the highest rates of accumulation of both biomass and yield, in addition to selecting for the G × E that is specifically adapted to the site can accelerate advance toward the highest potential yield at each geographical site. Higher yield for many sites will raise average regional yield. Higher yield for multiple regions and continents will raise average yield on a world-wide basis. Genetic and physiological bases for lack of indirect selection for biomass from exclusive selection for yield are explained.     

An ecological network analysis of the structure,development and sustainability of China’s natural gas supply system security

Mitigating the impacts of climate change and ensuring energy supply security has compelled China’s policy makers to maximise the use of alternative and low carbon fuels. Use and production of natural gas (an energy source with low carbon emissions) has experienced remarkable growth in China during the last decade, making China the third largest consumer and importer in the world. This study applied a powerful system-oriented ecological network analysis (ENA) technique to study China’s natural gas policies as they pertain to guarantee supply security. Several indicators based on the ENA were measured to analyse the degree of connectivity, the contributions of different compartments, resource utilisation (aggradation), development (ascendancy) and sustainability of China’s natural gas supply system. It was found that China’s source and route diversification policy have caused the natural gas supply system to exhibit considerable network complexity, demonstrating the high level of development, flexibility and diversity of China’s natural gas supply system. However, the policy also has caused a decrease in the aggradation and sustainability from the perspective of an ecological system network. The most important compartments in terms of their contribution to China’s natural gas supply system were found to be domestic natural gas production and transit compartments.     

Assessment of quality of three marine benthic habitat types in northern Baltic Sea

The European Union Habitats Directive (HD) obliges member states to assess the conservation status of marine habitat types but no explicit methodologies for assessing the quality of habitats have been stated in the directive or accompanying documents. In this study, a system was developed to assess the structure and functioning of three important marine habitat types in the Estonian sea area: sandbanks (HD code 1110), mudflats (1140), and reefs (1170). The assessment system includes a list of ecological criteria and favourable reference values together with procedural rules and field sampling locations. The habitat types listed in the HD are broadly defined and may encompass different communities depending upon distinct environmental gradients. By considering these environmental gradients the habitat types reefs and sandbanks were zoned and the assessment criteria and corresponding favourable reference values were defined separately for each zone. A set of several metrics like benthos indices, community variables, presence of sensitive or typical species, proportions of functional or taxonomic groups were tested as potential criteria for determining habitat quality. The most appropriate criteria were selected for incorporation into the assessment system based on ecological eligibility, suitability to local conditions, occurrence rates of benthic species, responses to disturbances, statistical properties of distribution of measured values, and practical considerations. Extensive benthos database (records from the whole Estonian sea area, 1995–2014) was used to calculate values of criteria to support the selection of criteria and to derive reference values. In order to fully take into account their crucial role in maintaining the structure and functioning of habitats, the criteria on habitat-forming species were assigned higher hierarchical order in the assessment scheme compared to other criteria. Special field works were carried out to assess the status of the three habitat types in 2015. The quality of all three monitored habitats was assessed to be in a favourable status. Additionally, the distributions of the three habitat types were mapped. To date, this is the first study in the Baltic Sea region that formulates HD compliant explicit criteria, reference values, and assessment procedures for several marine habitat types. The main challenges of the study were to derive assessment criteria and favourable reference values that are ecologically relevant and practically feasible.     

Optimal gillnet sampling design for the estimation of fish community indicators in heterogeneous freshwater ecosystems

Monitoring of biota in heterogeneous ecosystems requires sampling in different habitats and across environmental gradients. The resulting multivariate community data are typically aggregated into one or several indicator values for the entire ecosystem, but the relationship between the robustness of such indicators and sampling effort, including the identification of minimum acceptable sampling designs, is not fully understood.We address this issue for multi-mesh gillnet sampling of freshwater fish communities in deep-valley reservoirs, using data from 29 detailed annual surveys in eight reservoirs in the Czech Republic that account for the inherent longitudinal and depth gradients and the qualitatively different benthic and pelagic habitats. We evaluate the performance of eight sampling scenarios, created by variously reducing the full dataset. To this end, we use 31 fish-based, community-, size- and species-level indicators calculated separately for benthic and pelagic habitats, and fit the relationships between the indicator values based on the reduced and full sampling design using Bayesian generalized linear models.The ability of reduced data to estimate the “true” indicator value across the entire dataset, expressed as the adjusted R² value of the best model for the given indicator, increased with sampling effort. However, the relationships differed between indicators: R² values were higher for abundance-based than for biomass-based indicators. We identified three suitable reduced sampling designs: (1) sampling the entire longitudinal profile in the epilimnion, yielding on average the highest R² values (0.97), (2) same as before but limited to one sampling layer closest to the surface (R² = 0.91), and (3) sampling all depth strata at the farthest points of the longitudinal gradient (i.e., dam and tributary, R² = 0.83). These results demonstrate that, in order to obtain robust estimates of fish community indicators, current gillnet sampling protocols can be optimized to reduce effort and minimize unwanted fish mortality.     

Identifying ecologically valuable and sensitive areas: a case study analysis from China

The expansion of artificial constructs with the rapid economic development in China has led to ecological and environmental emergencies. The extent of the decline in natural resources and environmental conditions has recently been recognized. Identifying “ecological protection redlines”, i.e. ecological limits, to guarantee ecological baselines for natural resources and ecosystem service functions would therefore help to coordinate economic development and to protect ecological resources in the coming years. We used remotely sensed and climatic data to delimit the ecological protection redlines for Zibo, a typical and important city in Shandong province, as an example to illustrate the principles and methodology of ecological protection redlines. The area of the ecological protection redlines for Zibo encompassed 1132.26 km², accounting for 18.98% of the total area of Zibo, were mainly distributed in the southern regions of the municipality, and consisted of extremely important areas of ecosystem service functions, including water conservation, both soil and water conservation, windbreaks and sand fixation, and the conservation of biodiversity. This area is extremely sensitive, and development is forbidden. Strict measures of management and control should be implemented to protect the long-term effectiveness of ecological protection redlines.