Temperate oceanic treelines - Low temperature effects on photosynthesis and growth

Altitudinal treelines form where tree growth is limited by low growing season temperatures. However, exactly what aspects of temperature are critical remains unclear. Temperate New Zealand treelines are at a lower altitude than in comparable temperate regions elsewhere. Past studies have shown them to be warmer, and suggested that New Zealand montane trees are not capable of growing at cool temperatures. A detailed study at six sites showed that New Zealand treelines are not anomalously warm, but instead are within the global range of growing season soil temperature at treeline. The thermal environment in summer did not differ between abrupt and gradual treelines, but winters were much colder at the former. The consistency of mean daily minimum air temperature during the growing season at 20 oceanic treelines across the New Zealand archipelago suggests that thermal thresholds to tree growth are better described by minimum temperature, rather than often-used mean temperature. Extreme freezing temperatures are unlikely to control treeline position through dieback of adult trees, as the frost tolerance of trees of all species studied was in excess of the extreme minimum temperatures experienced at the New Zealand treeline. Overall, the proposition that an absence of hardy taxa in New Zealand has resulted in low treelines appears incorrect. In controlled environment experiments, the response of photosynthesis and growth to growing season temperatures differed between the six treeline species. Three species showed evidence of reduced growth activities at low temperature (carbon sink limitation), whereas one species showed reduced growth at low temperature because of limited carbon acquisition (carbon source limitation). Different measures of sink- and source activities provided support for both hypotheses for two other species. These results highlight species-specificity in the temperature response of photosynthesis and growth as well as the complexity in the interpretation of carbon sink and source limitation hypotheses. A combined approach in the field will be required to untangle the processes and thresholds that interact to determine tree growth and treeline positions

Partitioning the impact of environmental drivers and species interactions in dynamic aquatic communities

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Musters, C. J. M., Ieromina, O., Barmentlo, S. H., Hunting, E. R., Schrama, M., Cieraad, E., Vijver, M. G., & van Bodegom, P. M. Partitioning the impact of environmental drivers and species interactions in dynamic aquatic communities. Ecosphere, 10(11), (2019): e02910, doi:10.1002/ecs2.2910.Temperate aquatic communities are highly diverse and seasonally variable, due to internal biotic processes and environmental drivers, including human‐induced stressors. The impact of drivers on species abundance is supposed to differ fundamentally depending on whether populations are experiencing limitations, which may shift over the season. However, an integrated understanding of how drivers structure communities seasonally is currently lacking. In order to partition the effect of drivers, we used random forests to quantify interactions between all taxa and environmental factors using macrofaunal data from 18 agricultural ditches sampled over two years. We found that, over the agricultural season, taxon abundance became increasingly better predicted by the abundances of co‐occurring taxa and nutrients compared to other abiotic factors, including pesticides. Our approach provides fundamental insights in community dynamics and highlights the need to consider changes in species interactions to understand the effects of anthropogenic stressors.The authors are grateful to B. Schaub of Water Board Rijnland for his help, E. Gertenaar for assistance in the fieldwork, M. Wouterse for DOC measurements, and B. Koese for help with taxonomic identification of macrofaunal samples. CM designed the study, did the statistical modeling and analyses, and wrote the draft paper; OI did field sampling and taxonomic identification and constructed the datasets; OI and HB structured the data; EH, MS, ES, MV, and PvB contributed to the study design and the conceptual improvement of the manuscript; all authors substantially revised the subsequent drafts

Drivers of plant traits that allow survival in wetlands

Plants have developed a suite of traits to survive the anaerobic and anoxic soil conditions in wetlands. Previous studies on wetland plant adaptive traits have focused mainly on physiological aspects under experimental conditions, or compared the trait expression of the local species pool. Thus, a comprehensive analysis of potential factors driving wetland plant adaptive traits under natural environmental conditions is still missing.In this study, we analysed three important wetland adaptive traits, i.e. root porosity, root/shoot ratio and underwater photosynthetic rate, to explore driving factors using a newly compiled dataset of wetland plants. Based on 21 studies at 38 sites across different biomes, we found that root porosity was affected by an interaction of temperature and hydrological regime; root:shoot ratio was affected by temperature, precipitation and habitat type; and underwater photosynthetic rate was affected by precipitation and life form. This suggests that a variety of driving mechanisms affect the expression of different adaptive traits.The quantitative relationships we observed between the adaptive traits and their driving factors will be a useful reference for future global methane and denitrification modelling studies. Our results also stress that besides the traditionally emphasized hydrological driving factors, other factors at several spatial scales should also be taken into consideration in the context of future functional wetland ecology.Environmental Biolog

Figure 2. Root porosity vs. Leaf nitrogen

The original root porosity and leaf nitrogen data used to make the Figure 2. in the manuscript. More data description can be found in the Appendix_FEPANSA1

Figure 3. ROL vs. Leaf nitrogen

The original radial oxygen loss (ROL) and leaf nitrogen data used to make the Figure 3 in the manuscript. More data description can be found in the Appendix_FEPANSA1

Data from: Are ecophysiological adaptive traits decoupled from leaf economics traits in wetlands?

Wetland plants have developed a suite of traits, such as aerenchyma, radial oxygen loss, and leaf gas films, to adapt to wetland environment featured by e.g. a low redox potential and a lack of electron acceptors. These ecophysiological traits are critical for the survival and physiological functioning of wetland plants. Most studies on these traits typically focus on a single trait and a single or few species at the time. Next to these traits, traits of the leaf economics spectrum (LES) that reflect resources acquisition and allocation in plant species have also been frequently measured in wetlands. However, the performance of the LES has rarely been examined among wetland plants. Both suites of traits are critical for ‐but affect different aspects of‐ wetland plant functioning and survival. The interactions between them, potentially causing synergies or trade‐offs, reflect wetland plant strategies to simultaneously deal with stress tolerance and resources utilization, and have ramifications for the functioning of wetland ecosystems. Based on a literature review and quantitative analysis of available data, we provide evidence suggesting that LES and ecophysiological traits may be decoupled (e.g., for root porosity & radial oxygen loss vs. leaf nitrogen) or coupled (e.g., for iron tolerance vs. SLA) in wetlands, depending on the trait combination concerned. This rather complex relationship between wetland adaptation traits and LES traits indicates that there can be multiple mechanisms behind the strategies of wetland plants. We further illustrate how adaptation and LES traits together contribute to wetland ecosystem functions, such as denitrification and methane emission. We highlight that both suites of traits should be considered simultaneously when applying trait‐based methods to wetland ecology

Sudden cold temperature regulates the time-lag between plant CO2 uptake and release

Since substrates for respiration are supplied mainly by recent photo-assimilates, there is a strong but time-lagged link between short-term above- and belowground carbon (C) cycling. However, regulation of this coupling by environmental variables is poorly understood. Whereas recent studies focussed on the effect of drought and shading on the link between above- and belowground short-term C cycling, the effect of temperature remains unclear. We used a 13CO2 pulse-chase labelling experiment to investigate the effect of a sudden temperature change from 25 to 10◦C on the short-term coupling between assimilatory C uptake and respiratory loss. The study was done in the laboratory using two-month-old perennial rye-grass plants (Lolium perenne L.). After label application, the δ13 C signal of respired shoot and root samples was analysed at regular time intervals using laser spectroscopy. In addition, δ13C was analysed in bulk root and shoot samples. Cold temperature (10◦C) reduced the short-term coupling between shoot and roots by delaying belowground transfer of recent assimilates and its subsequent respiratory use, as indicated by the δ13 C signal of root respiration (δ13C RR). That is, the time lag from the actual shoot labelling to the first appearance of the label in 13CRR was about 1.5 times longer under cold temperature. Moreover, analysis of bulk shoot and root material revealed that plants at cold temperature invest relatively more carbon into respiration compared to growth or storage. While the whole plant C turnover increased under cold temperature, the turnover time of the labile C pool decreased, probably because less 13C is used for growth and/or storage. That is, (almost) all recent C remained in the labile pool serving respiration under these conditions. Overall, our results highlight the importance of temperature as a driver of C transport and relative C allocation within the plant–soil system.ISSN:1810-6277ISSN:1810-628

Artificial light at night affects plant‐herbivore interactions

Artificial light at night (ALAN) affects species' physiology and behaviour, and the interactions between species. Despite the importance of plants as primary producers, it remains poorly understood whether and how effects of ALAN on plants cascade through the food web. We assess the extent to which ALAN of different spectra result in plant-mediated insect herbivory damage. In a 6-month field experiment, we exposed plants of differing palatability to three colours of ALAN and a dark control, and assessed plant traits (growth rate, leaf size, foliar density and thickness) and insect herbivory (represented by insect damage as loss of foliage to leaf-chewing insects, and gall abundance by phloem-feeding herbivory). We found evidence for plant trait-mediated ALAN effects on herbivory for oak, but not for blueberry. In oak, ALAN of different colours changed the direction of relationships of insect damage with relative growth rate and with leaf thickness. Moreover, we found that the effects of ALAN on herbivory damage differed markedly between forest types within the same locale, particularly in the red light treatment. Synthesis and applications. Our results provide evidence that continuous night-time light, as provided by street lighting around the world, affects food web interactions. The nature of these effects differed by species and appeared to depend on forest type and the light spectrum employed, thus underlining the context dependency of ALAN in different ecosystems and environmental settings. These findings highlight the complexity of using spectral manipulation as a mitigation measure, and the need for further consideration of ALAN in environmental management and planning, to limit the exposure and impact of cascading effects of artificial light at night on food webs and communities