Exploring the functional significance of forest diversity: A new long-term experiment with temperate tree species (BIOTREE)

Effects of biodiversity on ecosystem functioning have been mainly studied in experiments that artificially create gradients in grassland plant diversity. Woody species were largely excluded from these early experiments, despite the ecological and socioeconomic importance of forest ecosystems. We discuss conceptual aspects of mechanistically driven research on the biodiversity–ecosystem functioning relationship in forests, including the comparison of scientific approaches like ‘observational studies’, ‘removal experiments’, and ‘synthetic-assemblage experiments’. We give a short overview on the differences between herbaceous and forest ecosystems, focusing on canopy characteristics, and the possibilities for individual versus population-based investigations.We present detailed information about the first large-scale, multisite and long-term biodiversity–ecosystem functioning experiment with tree species of temperate forests (BIOTREE – BIOdiversity and ecosystem processes in experimental TREE stands). At three sites of differing geology and local climate, we planted 200,000 saplings on a total area of 70 ha. At two sites, diversity gradients were established by varying the number of tree species (BIOTREE-SPECIES). At a third site, only functional diversity at a constant level of tree species richness was manipulated by selecting mixtures that differ in the functional trait values of the corresponding species (BIOTREE-FD). Additional experimental treatments at the subplot level include silvicultural management options, the addition of subdominant species, and the reduction of genetic diversity. Response variables focus on productivity, biogeochemical cycles and carbon sequestration, and resource use complementarity.We explore the use of different measures of functional diversity for a posteriori classifications of functional richness and their use in the analysis of our tree diversity experiment. The experiment is thought to provide a long-term research platform for a variety of scientific questions related to forest biodiversity and ecosystem processes.     

Increasing extent of periods of no flow in intermittent waterways promotes heterotrophy

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The cell biology of lignification in higher plants

Background Lignin is a polyphenolic polymer that strengthens and waterproofs the cell wall of specialized plant cell types. Lignification is part of the normal differentiation programme and functioning of specific cell types, but can also be triggered as a response to various biotic and abiotic stresses in cells that would not otherwise be lignifying.Scope Cell wall lignification exhibits specific characteristics depending on the cell type being considered. These characteristics include the timing of lignification during cell differentiation, the palette of associated enzymes and substrates, the sub-cellular deposition sites, the monomeric composition and the cellular autonomy for lignin monomer production. This review provides an overview of the current understanding of lignin biosynthesis and polymerization at the cell biology level.Conclusions The lignification process ranges from full autonomy to complete co-operation depending on the cell type. The different roles of lignin for the function of each specific plant cell type are clearly illustrated by the multiple phenotypic defects exhibited by knock-out mutants in lignin synthesis, which may explain why no general mechanism for lignification has yet been defined. The range of phenotypic effects observed include altered xylem sap transport, loss of mechanical support, reduced seed protection and dispersion, and/or increased pest and disease susceptibility.     

冻融作用对陆地生态系统氮循环关键过程的影响效应及其机制

冻融作用是中、高纬度及高海拔地区土壤普遍存在的一种自然现象,是非生长季陆地生态系统氮循环的重要影响因素.冻融作用主要通过改变土壤的理化性质及生物学性状来影响氮素在土壤中的迁移与转化.目前,冻融作用对陆地生态系统氮循环各个过程影响的研究结果不尽一致,理论机制尚不明晰,研究方法也需进一步地探索与创新,因此有必要对现有成果进行梳理和分析,以更好地把握冻融作用下的氮循环过程.本文结合国内外已有研究成果,论述了冻融作用对陆地生态系统氮循环关键过程（氮矿化、固持、硝化与反硝化过程、氮淋溶及气态损失）的影响效应及其主要机制,对目前研究中存在的不足进行了剖析,并对未来研究中迫切需要关注的重点研究方向进行了探讨与展望.     

Parallel declines in survival of adult Northern Fulmars Fulmarus glacialis at colonies in Scotland and Ireland

Assessing broad‐scale changes in seabird populations across the North Atlantic requires an integration of available datasets to understand the spatial extent of potential drivers and demographic change. Here, we compared survival of Northern Fulmars Fulmarus glacialis from a Scottish and an Irish colony from 1974 to 2009. Despite lower recapture probabilities of monel‐ringed Irish birds compared with colour‐ringed Scottish birds, survival probability decreased at both colonies. The extent to which the decline in survival is related to density‐dependent processes or other external drivers remains uncertain, but our results suggest that these changes in survival are possibly indicative of larger‐scale processes and are not confined to local colony dynamics.     

Commentary: When does understanding phenotypic evolution require identification of the underlying genes?

Adaptive evolution is fundamentally a genetic process. Over the past three decades, characterizing the genes underlying adaptive phenotypic change has revealed many important aspects of evolutionary change. At the same time, natural selection is often fundamentally an ecological process that can often be studied without identifying the genes underlying the variation on which it acts. This duality has given rise to disagreement about whether, and under what circumstances, it is necessary to identify specific genes associated with phenotypic change. This issue is of practical concern, especially for researchers who study nonmodel organisms, because of the often enormous cost and labor required to “go for the genes.” We here consider a number of situations and questions commonly addressed by researchers. Our conclusion is that although gene identification can be crucial for answering some questions, there are others for which definitive answers can be obtained without finding underlying genes. It should thus not be assumed that considerations of “empirical completeness” dictate that gene identification is always desirable.     

Variability in nitrogen stable isotope ratios of macroalgae: consequences for the identification of nitrogen sources

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Design and performance of combined infrared canopy and belowground warming in the B4WarmED (Boreal Forest Warming at an Ecotone in Danger) experiment

Conducting manipulative climate change experiments in complex vegetation is challenging, given considerable temporal and spatial heterogeneity. One specific challenge involves warming of both plants and soils to depth. We describe the design and performance of an open‐air warming experiment called Boreal Forest Warming at an Ecotone in Danger (B4WarmED) that addresses the potential for projected climate warming to alter tree function, species composition, and ecosystem processes at the boreal‐temperate ecotone. The experiment includes two forested sites in northern Minnesota, USA, with plots in both open (recently clear‐cut) and closed canopy habitats, where seedlings of 11 tree species were planted into native ground vegetation. Treatments include three target levels of plant canopy and soil warming (ambient, +1.7 °C, +3.4 °C). Warming was achieved by independent feedback control of voltage input to aboveground infrared heaters and belowground buried resistance heating cables in each of 72‐7.0 m² plots. The treatments emulated patterns of observed diurnal, seasonal, and annual temperatures but with superimposed warming. For the 2009 to 2011 field seasons, we achieved temperature elevations near our targets with growing season overall mean differences (?T_below) of +1.84 °C and +3.66 °C at 10 cm soil depth and (?T^above) of +1.82 °C and +3.45 °C for the plant canopies. We also achieved measured soil warming to at least 1 m depth. Aboveground treatment stability and control were better during nighttime than daytime and in closed vs. open canopy sites in part due to calmer conditions. Heating efficacy in open canopy areas was reduced with increasing canopy complexity and size. Results of this study suggest the warming approach is scalable: it should work well in small‐statured vegetation such as grasslands, desert, agricultural crops, and tree saplings (<5 m tall).