Limits to photosynthesis: seasonal shifts in supply and demand for CO2 in Scots pine

Boreal forests undergo a strong seasonal photosynthetic cycle; however, the underlying processes remain incompletely characterized. Here, we present a novel analysis of the seasonal diffusional and biochemical limits to photosynthesis (A(net)) relative to temperature and light limitations in high-latitude mature Pinus sylvestris, including a high-resolution analysis of the seasonality of mesophyll conductance (g(m)) and its effect on the estimation of carboxylation capacity (VCmax). We used a custom-built gas-exchange system coupled to a carbon isotope analyser to obtain continuous measurements for the estimation of the relevant shoot gas-exchange parameters and quantified the biochemical and diffusional controls alongside the environmental controls over A(net). The seasonality of A(net) was strongly dependent on VCmax and the diffusional limitations. Stomatal limitation was low in spring and autumn but increased to 31% in June. By contrast, mesophyll limitation was nearly constant (19%). We found that VCmax limited A(net) in the spring, whereas daily temperatures and the gradual reduction of light availability limited A(net) in the autumn, despite relatively high VCmax. We describe for the first time the role of mesophyll conductance in connection with seasonal trends in net photosynthesis of P. sylvestris, revealing a strong coordination between g(m) and A(net), but not between g(m) and stomatal conductance

Linking canopy-scale mesophyll conductance and phloem sugar delta C-13 using empirical and modelling approaches

Interpreting phloem carbohydrate or xylem tissue carbon isotopic composition as measures of water-use efficiency or past tree productivity requires in-depth knowledge of the factors altering the isotopic composition within the pathway from ambient air to phloem contents and tree ring. One of least understood of these factors is mesophyll conductance (g(m)). We formulated a dynamic model describing the leaf photosynthetic pathway including seven alternative g(m) descriptions and a simple transport of sugars from foliage down the trunk. We parameterised the model for a boreal Scots pine stand and compared simulated g(m) responses with weather variations. We further compared the simulated delta C-13 of new photosynthates among the different g(m) descriptions and against measured phloem sugar delta C-13. Simulated g(m) estimates of the seven descriptions varied according to weather conditions, resulting in varying estimates of phloem delta C-13 during cold/moist and warm/dry periods. The model succeeded in predicting a drought response and a postdrought release in phloem sugar delta C-13 indicating suitability of the model for inverse prediction of leaf processes from phloem isotopic composition. We suggest short-interval phloem sampling during and after extreme weather conditions to distinguish between mesophyll conductance drivers for future model development.Peer reviewe

Components explain, but do eddy fluxes constrain? Carbon budget of a nitrogen-fertilized boreal Scots pine forest

Nitrogen (N) fertilization increases biomass and soil organic carbon (SOC) accumulation in boreal pine forests, but the underlying mechanisms remain uncertain. At two Scots pine sites, one undergoing annual N fertilization and the other a reference, we sought to explain these responses.We measured component fluxes, including biomass production, SOC accumulation, and respiration, and summed them into carbon budgets. We compared the resulting summations to ecosystem fluxes measured by eddy covariance.N fertilization increased most component fluxes (P −2 yr−1. Stemwood production increases were ascribed to this partitioning shift, gross primary production (GPP), and carbon-use efficiency, in that order. The methods agreed in their estimates of GPP in both stands (P > 0.05), but the components detected an increase in net ecosystem production (NEP) (190 (54) g C m−2 yr−1; P −2 yr−1; ns).The pairing of plots, the simplicity of the sites, and the strength of response provide a compelling description of N effects on the C budget. However, the disagreement between methods calls for further paired tests of N fertilization effects in simple forest ecosystems

Limited vertical CO2 transport in stems of mature boreal Pinus sylvestris trees

Several studies have suggested that CO2 transport in the transpiration stream can considerably bias estimates of root and stem respiration in ring-porous and diffuse-porous tree species. Whether this also happens in species with tracheid xylem anatomy and lower sap flow rates, such as conifers, is currently unclear. We infused C-13-labelled solution into the xylem near the base of two 90-year-old Pinus sylvestris L. trees. A custom-built gas exchange system and an online isotopic analyser were used to sample the CO2 efflux and its isotopic composition continuously from four positions along the bole and one upper canopy shoot in each tree. Phloem and needle tissue C-13 enrichment was also evaluated at these positions. Most of the C-13 label was lost by diffusion within a few metres of the infusion point indicating rapid CO2 loss during vertical xylem transport. No C-13 enrichment was detected in the upper bole needle tissues. Furthermore, mass balance calculations showed that c. 97% of the locally respired CO2 diffused radially to the atmosphere. Our results support the notion that xylem CO2 transport is of limited magnitude in conifers. This implies that the concerns that stem transport of CO2 derived from root respiration biases chamber-based estimates of forest carbon cycling may be unwarranted for mature conifer stands.Peer reviewe

After-use of peat extraction sites – A systematic review of biodiversity, climate, hydrological and social impacts

After drainage for forestry and agriculture, peat extraction is one of the most important causes of peatland degradation. When peat extraction is ceased, multiple after-use options exist, including abandonment, restoration, and replacement (e.g., forestry and agricultural use). However, there is a lack of a global synthesis of after-use research. Through a systematic review of 356 peer-reviewed scientific articles, we address this research gap and examine (1) what after-use options have been studied, (2) what the studied and recognized impacts of the after-use options are, and (3) what one can learn in terms of best practices and research gaps. The research has concentrated on the impacts of restoration (N = 162), abandonment (N = 72), and replacement (N = 94), the latter of which consists of afforestation (N = 46), cultivation (N = 34) and creation of water bodies (N = 14). The studies on abandonment, restoration, and creation of water bodies have focused mostly on analyzing vegetation and greenhouse gas (GHG) fluxes, while the studies assessing afforestation and cultivation sites mostly evaluate the provisioning ecosystem services. The studies show that active restoration measures speed-up vegetation recolonization on bare peat areas, reduce GHG emissions and decrease negative impacts on water systems. The most notable research gap is the lack of studies comparing the environmental and social impacts of the after-use options. Additionally, there is a lack of studies focusing on social impacts and downstream hydrology, as well as long-term monitoring of GHG fluxes. Based on the reviewed studies, a comparison of the impacts of the after-use options is not straightforward. We emphasize a need for comparative empirical research in the extracted sites with a broad socio-ecological and geographical context

A test of the 'one-point method' for estimating maximum carboxylation capacity from field-measured, light-saturated photosynthesis

Simulations of photosynthesis by terrestrial biosphere models typically need a specification of the maximum carboxylation rate (Vcmax). Estimating this parameter using A–Ci curves (net photosynthesis, A, vs intercellular CO2 concentration, Ci) is laborious, which limits availability of Vcmax data. However, many multispecies field datasets include net photosynthetic rate at saturating irradiance and at ambient atmospheric CO2 concentration (Asat) measurements, from which Vcmax can be extracted using a 'one-point method'.\ud \ud We used a global dataset of A–Ci curves (564 species from 46 field sites, covering a range of plant functional types) to test the validity of an alternative approach to estimate Vcmax from Asat via this 'one-point method'.\ud \ud If leaf respiration during the day (Rday) is known exactly, Vcmax can be estimated with an r2 value of 0.98 and a root-mean-squared error (RMSE) of 8.19 μmol m−2 s−1. However, Rday typically must be estimated. Estimating Rday as 1.5% of Vcmax, we found that Vcmax could be estimated with an r2 of 0.95 and an RMSE of 17.1 μmol m−2 s−1.\ud \ud The one-point method provides a robust means to expand current databases of field-measured Vcmax, giving new potential to improve vegetation models and quantify the environmental drivers of Vcmax variation

Kriisiviestintä Kaakkois-Suomen rajavartiostossa

Tutkimuksen tarkoituksena on selvittää, kuinka kenttäjohtaja toteuttaa kriisiviestintää Kaakkois- Suomen rajavartiostossa ja mitkä ovat toiminnan mahdolliset kehittämistarpeet. Tutkielmassa tarkastellaan rajanylityspaikkojen turvallisuusuhkien kriisiviestintää Kaakkois-Suomen rajavartiostossa. Tutkimus selvittää, miten tieto välittyy rajanylityspaikalla tapahtuvasta kriisitilanteesta kansalaisille. Tutkielma oli otteeltaan kvalitatiivinen. Tutkimusmenetelmänä käytettiin sisällönanalyysiä. Tutkimusaineisto koostui suomalaisesta viestintäkirjallisuudesta, asiakirjoista, lehtiartikkeleista ja teetetystä kyselystä. Kirjallisuuden ja asiakirjojen pohjalta pyrittiin löytämään kriisiviestinnän toimintamalli, jota verrattiin kyselyn vastauksia analysoimalla muodostettuun kriisiviestinnän toteutukseen Kaakkois-Suomen rajavartiostossa. Kysely lähetettiin seitsemälle Kaakkois-Suomen rajavartiolaitoksen johtohenkilölle, joista neljä keskeisintä henkilöä vastasivat kyselyyn. Aineiston perusteella päädytään siihen tulokseen, että kriisitilanteessa kenttäjohtaja viestii oman organisaation sisällä sekä pitää yleisjohtajan tietoisena tilanteesta ja omista toimenpiteistä. Todennäköisimmät tilanteet rajanylityspaikoilla, joissa kriisiviestintää tarvitaan, ovat suuremmat onnettomuudet ja ase- tai pommiuhkatilanne. Tieto kriisitilanteesta tulee kenttäjohtajalle rajanylityspaikan partion toimesta. Kenttäjohtaja välittää tarvittavat tiedot tilanteesta yleisjohtajalle, jonka kautta tieto välittyy rajavartioston apulaiskomentajalle ja sidosryhmille. Apulaiskomentaja vastaa tiedottamisesta organisaation ulkopuolelle. Käytettävät viestintäkanavat ovat hätä- ja viranomaistiedotteet, muut median kautta välitettävät tiedotteet, Rajavartiolaitoksen esikunnan kautta valtionhallintoon välitettävät tiedotteet sekä raja.fi, rajaliikenne. fi ja sosiaalisen median internet-sivustoilla julkaistavat tiedotteet. Kenttäjohtajan kriisiviestinnän toteuttaminen on hyvällä pohjalla Kaakkois-Suomen rajavartiolaitoksessa. Tämä johtuu kenttäjohtajan sisäisen viestinnän ammattitaidosta, joka on kehittynyt päivittäistä kenttätoimintaa johtamalla. Jotta kenttäjohtajan kriisiviestintää voitaisiin kehittää, tulisi Kaakkois-Suomen rajavartiostossa järjestää kenttätoiminnan johtamisen harjoituksia, joissa kuvattaisiin laajempaa kriisitilannetta. Jokaisessa vartioston yksikössä tulisi olla saatavilla selkeä ja yksityiskohtainen kriisiviestintäohje, johon voi tarvittaessa tukeutua tapahtumapaikalla

Carbon Dioxide and Water Vapour Exchange within a Norway Spruce Canopy

Terrestrial ecosystems can act both as sinks and sources in the global carbon cycle. Forests are an important part of this system and a good understanding of their carbon balance is essential for assessments of the future climate and for evaluating mitigation strategies. Much progress has been made in understanding the main processes controlling plant-atmosphere gas exchange and their responses to environmental factors. However, most previous studies that describe the gas exchange have either been based on laboratory experiments or on short field campaigns with measurements representing a limited range of environmental conditions or positions within the canopy. The results may therefore be ecologically unrepresentative. This limits our ability to accurately represent the true interactions between the gas fluxes and their biological and meteorological regulators on a long-term basis. This thesis addresses the questions regarding spatial and temporal variety of gas exchange in a forest canopy. It is based on carbon dioxide (CO2) and water vapour (H2O) exchange measurements carried out between 2007 and 2010 at Skogaryd research site, a 60 year old Norway spruce (Picea abies (L.) Karst.) dominated mixed stand growing on drained peat soil in south-western Sweden. The measurements were conducted once every half-hour at several heights in the canopy on three adjacent trees using continuously measuring automated chambers under naturally occurring meteorological conditions. In addition, the concept of optimality of resource allocation within the canopy, with respect to maximising the canopy productivity, was investigated in two modelling based studies. Strong seasonality and vertical gradients were observed in the shoot-scale gas exchange rates. However, the relative strengths of the vertical gradients were nearly constant over the year. Therefore, no strong seasonal patterns were observed in the vertical variation of resource use efficiencies. This finding supports the use of simple resource use efficiency based models in ecological modelling. Nitrogen is often found to be a key constraint with respect to canopy assimilation in the northern forests. However, it was found that at this nitrogen rich former fen, neither the within-canopy nitrogen allocation pattern, nor the total availability of nitrogen had large effects on carbon assimilation on shoot-scale. Using optimality modelling on the stand-scale it was shown that by constraining the minimum structural allocation to the lower canopy shoots it was possible to accurately predict the observed properties of the studied stand from easily obtainable meteorological and stand properties. Stem gas exchange also exhibited strong spatial variation, and was observed to be considerably higher in the upper part of the stem during the main growing period. Ignoring this vertical variation was shown to result in considerable underestimations of the annual stem-scale gas exchange. Despite the fact that the trees at the site were accumulating large amounts of carbon, the studied stand was not a strong carbon sink on the ecosystem scale, owing to the high carbon emission from the soil. It can be concluded from the findings of this study that variation in resource use efficiency and resource availability within a forest stand is of great importance for the CO2 and H2O exchanges with the atmosphere

Increased needle nitrogen contents did not improve shoot photosynthetic performance of mature nitrogen-poor Scots pine trees

Numerous studies have shown that temperate and boreal forests are limited by nitrogen (N) availability. However, few studies have provided a detailed account of how carbon (C) acquisition of such forests reacts to increasing N supply. We combined measurements of needle-scale biochemical photosynthetic capacities and continuous observations of shoot-scale photosynthetic performance from several canopy positions with simple mechanistic modelling to evaluate the photosynthetic responses of mature N-poor boreal Pinus sylvestris to N fertilization. The measurements were carried out in August 2013 on 90-year-old pine trees growing at Rosinedalsheden research site in northern Sweden. In spite of a nearly doubling of needle N content in response to the fertilization, no effect on the long-term shoot-scale C uptake was recorded. This lack of N-effect was due to strong light limitation of photosynthesis in all investigated canopy positions. The effect of greater N availability on needle photosynthetic capacities was also constrained by development of foliar P deficiency following N addition. Thus, P deficiency and accumulation of N in arginine appeared to contribute towards lower shoot-scale nitrogen-use efficiency in the fertilized trees, thereby additionally constraining tree-scale responses to increasing N availability. On the whole our study suggests that the C uptake response of the studied N-poor boreal P. sylvestris stand to enhanced N availability is constrained by the efficiency with which the additional N is utilized. This efficiency, in turn, depends on the ability of the trees to use the greater N availability for additional light capture. For stands that have not reached canopy closure, increase in leaf area following N fertilization would be the most effective way for improving light capture and C uptake while for mature stands an increased leaf area may have a rather limited effect on light capture owing to increased self-shading. This raises the question if N limitation in boreal forests acts primarily by constraining growth of young stands while the commonly recorded increase in stem growth of mature stands following N addition is primarily the result of altered allocation and only to a limited extent the result of increased stand C-capture