Stream diatom assemblages as predictors of climate

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宝天曼自然保护区不同针叶树径向生长对气候的响应

树木年轮资料能够提供区域内过去长时间的环境和气候信息,成为获取过去气候变化信息的重要手段之一。利用采自宝天曼自然保护区的两种针叶树种油松和华山松树木年轮样本分别建立了油松和华山松树轮宽度标准年表PT和PA,并将油松和华山松样本合并建立了联合树种的区域年表(RC)。3种年表分别与不同气候要素(月平均气温、月平均最高气温、月平均最低气温、月降水量)及其不同月份组合进行相关分析,结果表明,油松年表PT和华山松年表PA都包含较高的气候信息,且都和生长季不同月份温度显著负相关和降水显著正相关。其中,油松和华山松都与当年4月和5月降水显著正相关,油松还与当年5月的平均最高温度和上年11月最低温显著负相关,与当年3月平均最低气温显著正相关;华山松与上年10月和当年4月的平均最高温度显著负相关,与上年12月和当年7月平均最低温度显著正相关;联合年表RC包含了单个年表PT和PA共同的气候信息,与当年4—5月降水和3月最低温显著正相关,与当年7月最低温和4、5月最高温显著负相关。不同年表与生长季(3—8月)内气候要素月份组合的相关分析也表明联合年表RC包含和单物种年表PT、PA相似的气候信息并加强了PT、PA受当年生长季气候变化影响的公共信号。可见,同一地区的多树种联合年表一定程度上能体现出区域性树木生长对气候变化响应的生态生理特征,为同地区建成多树种联合年表来探讨当地区域性气候变化提供了可行性的理论基础和一定的参考作用.     

A global meta‐analysis of forest bioenergy greenhouse gas emission accounting studies

The potential greenhouse gas benefits of displacing fossil energy with biofuels are driving policy development in the absence of complete information. The potential carbon neutrality of forest biomass is a source of considerable scientific debate because of the complexity of dynamic forest ecosystems, varied feedstock types, and multiple energy production pathways. The lack of scientific consensus leaves decision makers struggling with contradicting technical advice. Analyzing previously published studies, our goal was to identify and prioritize those attributes of bioenergy greenhouse gas (GHG) emissions analysis that are most influential on length of carbon payback period. We investigated outcomes of 59 previously published forest biomass greenhouse gas emissions research studies published between 1991 and 2014. We identified attributes for each study and classified study cases by attributes. Using classification and regression tree analysis, we identified those attributes that are strong predictors of carbon payback period (e.g. the time required by the forest to recover through sequestration the carbon dioxide from biomass combusted for energy). The inclusion of wildfire dynamics proved to be the most influential in determining carbon payback period length compared to other factors such as feedstock type, baseline choice, and the incorporation of leakage calculations. Additionally, we demonstrate that evaluation criteria consistency is required to facilitate equitable comparison between projects. For carbon payback period calculations to provide operational insights to decision makers, future research should focus on creating common accounting principles for the most influential factors including temporal scale, natural disturbances, system boundaries, GHG emission metrics, and baselines.     

Differential physiological and antioxidative responses to drought stress and recovery among four contrasting Argania spinosa ecotypes

Our study was undertaken to ascertain whether the change of the water status and the activation of superoxide dismutase and their isoenzymes in Argan tree can support edaphic drought tolerance and its recovery under rehydration. An experiment was conducted on four contrasting ecotypes of Argania spinosa plants: two contrasting coastal ecotypes (Admine (Adm) and Rabia (Rab)) and two contrasting inland ecotypes (Aoulouz (Alz) and Lakhssas (Lks)). Drought stress significantly decreased the leaf water potential and stomatal conductance in the four contrasted ecotypes. In terms of biochemical responses, significant accumulation of carbonyl groups, hydrogen peroxide and superoxide radical has been recorded in the leaves of stressed plants reflecting oxidative stress. In parallel, the activities of total superoxide dismutase (SOD) and their isoenzymes Cu/Zn-SOD, Cu/Zn-SOD and Fe-SOD were also found to have increased to scavenging ROS and protecting the cell against induced oxidative stress. The recovery kinetics of A. spinosa, as a response to rehydration, were significant and rapid. According to the traits having the most discriminating power, both inland ecotypes (Lks and Alz) showed a better upregulation of its protective mechanisms compared to coastal ecotypes (Rab and Adm). All these adaptive traits make the inland ecotypes as an elite resource of drought tolerance and might become the new focus of domestication research of argan tree in arid and semi-arid environments.     

Diversification in wild populations of the model organism Anolis carolinensis: A genome‐wide phylogeographic investigation

The green anole (Anolis carolinensis) is a lizard widespread throughout the southeastern United States and is a model organism for the study of reproductive behavior, physiology, neural biology, and genomics. Previous phylogeographic studies of A. carolinensis using mitochondrial DNA and small numbers of nuclear loci identified conflicting and poorly supported relationships among geographically structured clades; these inconsistencies preclude confident use of A. carolinensis evolutionary history in association with morphological, physiological, or reproductive biology studies among sampling localities and necessitate increased effort to resolve evolutionary relationships among natural populations. Here, we used anchored hybrid enrichment of hundreds of genetic markers across the genome of A. carolinensis and identified five strongly supported phylogeographic groups. Using multiple analyses, we produced a fully resolved species tree, investigated relative support for each lineage across all gene trees, and identified mito‐nuclear discordance when comparing our results to previous studies. We found fixed differences in only one clade—southern Florida restricted to the Everglades region—while most polymorphisms were shared between lineages. The southern Florida group likely diverged from other populations during the Pliocene, with all other diversification during the Pleistocene. Multiple lines of support, including phylogenetic relationships, a latitudinal gradient in genetic diversity, and relatively more stable long‐term population sizes in southern phylogeographic groups, indicate that diversification in A. carolinensis occurred northward from southern Florida.     

The tortoise and the hare: ecology of angiosperm dominance and gymnosperm persistence

Gymnosperms, and conifers in particular, are sometimes very productive trees yet angiosperms dominate most temperate and tropical vegetation. Current explanations for angiosperm success emphasize the advantages of insect pollination and seed dispersal by animals for the colonization of isolated habitats. Differences between gymnosperm and angiosperm reproductive and vegetative growth rates have been largely ignored. Gymnosperms are all woody, perennial and usually have long reproductive cycles. Their leaves are not as fully vascularized as those of angiosperms and are more stereotyped in shape and size. Gymnosperm tracheids are generally more resistant to solute flow than angiosperm vessels. A consequence of the less efficient transport system is that maximum growth rates of gymnosperms are lower than maximum growth rates of angiosperms in well lit, well watered habitats. Gymnosperm seedlings may be particularly uncompetitive since their growth depends on a single cohort of relatively inefficient leaves. Later, some gymnosperms attain a higher productivity than co-occurring angiosperm trees by accumulating several cohorts of leaves with a higher total leaf area. These functional constraints on gymnosperm growth rates suggest that gymnosperms will be restricted to areas where growth of angiosperm competitors is reduced, for example, by cold or nutrient shortages. Biogeographic evidence supports this prediction since conifers are largely confined to high latitudes and elevations or nutrient-poor soils. Experimental studies show that competition in the regeneration niche (between conifer seedlings and angiosperm herbs and shrubs) is common and significantly affects conifer growth and survival, Fast-growing angiosperms, especially herbs and shrubs, may also change the frequency of disturbance regimes thereby excluding slower-growing gymnosperms. Shade-tolerant and early successional conifers share similar characteristics of slow initial growth and low plasticity to a change in resources. Shade-tolerant gymnosperms would be expected to occur only where forest openings are small or otherwise unsuitable for rapid filling by fast-growing angiosperm trees, lianas or shrubs. The limited evidence available suggests that shade-tolerant conifers are confined to forests with small gap sizes where large disturbances are very rare. The regeneration hypothesis for gymnosperm exclusion by angiosperms is consistent with several aspects of the fossil record such as the early disappearance of gymnosperms from early successional environments where competition with angiosperms would have been most severe. However there are unresolved difficulties in interpreting process from paleoecological pattern which prevent the testing of alternative hypotheses.     

Utilization of nitrogen from storage and current-year uptake in walnut spurs during the spring flush of growth

[¹⁵N]-depleted (NH₄)₂SO₄ applied to the soil in 1985 resulted in residual labeling of about 16% of the storage nitrogen (N) pool of mature walnut ( Juglans regia L. cv. Serr) trees in 1987. Application of [¹⁵N]-depleted (NH₄)₂SO₄ fertilizer to a different set of mature walnut trees in 1987 allowed monitoring of the kinetics and utilization of N from current year uptake in 1987 and resulted in >20% labeling of fruit N following completion of leaf expansion. Redistribution of storage N to the new growth predominated during the spring flush of growth although N derived from the soil during current-year uptake contributed increasingly during leaf expansion. Labeled N from current year uptake accumulated preferentially in the leaves as compared with reproductive organs during leaf expansion but subsequent to leaf expansion, fruit were more highly labeled with N derived from current-year uptake than leaves. Pistillate flower abortion was coincident with an apparent competition for N among developing vegetative and reproductive organs and preceded the period of significant N contribution from current-year uptake.     

三种正常与矮化植物的木材比较观察

本文比较观察了三种不同木材类型的正常与矮化树木的木材结构:针叶材的太白红杉(Larix chinensis Beissn.)、散孔材的辽东桤木(Alnus sibirica Fisch.)和环孔材的蒙古栎(Quercus mongolica Fisch.)。这些植物在个体发育过程中,各年的年轮宽度及管状分子长度、宽度等变化,存在各自的规律性。这些规律并不因生长环境的差异而变更。不过,逆境下生长的矮化植株的年轮宽度和管状分子的大小明显地比正常的要窄小,同时在木材结构的其它数量性状上,也有较大变化;然而,其各自的种属定性特征仍保持稳定。这些似乎可说明:生态环境的变化对木材结构的数量性状有较大影响,但是对木材种属的定性特征则无明显作用。