Krista Lõhmus

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m−2, and that of spruce and pine 297 g m−2 and 277 g m−2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.

Gaseous fluxes in the nitrogen and carbon budgets of subsurface flow constructed wetlands

In 2001 and 2002, fluxes of N(2)O, CH(4), CO(2) and N(2) were measured in two constructed wetlands (CW) for domestic wastewater treatment in Estonia. The difference between the median values of N(2)O, CH(4), and N(2) fluxes in the horizontal subsurface flow (HSSF) CWs was non-significant, being 1.3-1.4 and 1.4-4.1 mg m(-2) d(-1) for N(2)O-N and CH(4)-C, and 0.16-0.17 g N m(-2) d(-1) for N(2)-N respectively. The CO(2)-C flux was significantly lower (0.6 g C m(-2) d(-1)) in one of the HSSF filters of a hybrid CW, whereas the single HSSF and VSSF filters emitted 1.7 and 2.0 g C m(-2) d(-1). The median value of CH(4)-C emission in CWs varied from 1.4 to 42.6 g C m(-2) d(-1), being significantly higher in the VSSF filter beds. We also estimated C and N budgets in one of the HSSF CWs (312.5 m(2)) for 2001 and 2002. The total C input into this system was similar in 2001 and 2002, 772 and 719 kg C year(-1), but was differently distributed between constituent fluxes. In 2001, the main input flux was soil and microbial accumulation (663 kg C year(-1) or 85.8% of total C input), followed by plant net primary production (NPP) (10.2%) and wastewater inflow (3.9%). In 2002, 55.7% of annual C input was bound in plant NPP, whereas the increase in soil C formed 28.5% and wastewater inflow 15.7%. The main C output flux was soil respiration, including microbial respiration from soil and litter, and the respiration of roots and rhizomes. It formed 120 (97.5%) and 230 kg C year(-1) (98.2%) in 2001 and 2002 respectively. The measured CH(4)-C flux remained below 0.1% of total C output. The HSSF CW was generally found to be a strong C sink, and its annual C sequestration was 649 and 484 kg C year(-1) per wetland in 2001 and 2002 respectively. However, negative soil and microbial accumulation values in recent years indicate decreasing C sequestration. The average annual N removal from the system was 38-59 kg N year(-1) (46-48% of the initial total N loading). The most important flux of the N budget was N(2)-N emission (22.7 kg in 2001 and 15.2 kg in 2002), followed by plant belowground assimilation (2.3 and 11.9 kg N year(-1) in 2001 and 2002), and above-ground assimilation (1.9 and 9.2 kg N year(-1), respectively). N(2)O emission was low: 0.37-0.60 kg N year(-1)(.).

The role of soil conditions in fine root ecomorphology in Norway spruce (Picea abies (L.) Karst.)

The present study is an attempt to investigate the pattern of morphological variability of the short roots of Norway spruce (Picea abies (L.) Karst.) growing in different soils. Five root parameters – diameter, length and dry weight of the root tip, root density (dry weight per water-saturated volume) and specific root area (absorbing area of dry weight unit) were studied with respect to 11 soil characteristics using CANOCO RDA analysis. The investigation was conducted in seven study areas in Estonia differing in site quality class and soil type. Ten root samples per study area were collected randomly from the forest floor and from the 20 cm soil surface layer. Eleven soil parameters were included in the study: humus content, specific soil surface area, field capacity, soil bulk density, pH (KCl and H2O dilutions), N and Ca concentrations, Ca/Al and C/N ratios, and the decomposition rate of fine roots (<2 mm dia.). Root morphological characteristics most strongly related to the measured soil characteristics in the different sites were specific root area, root density and diameter of the short roots, the means varying from 29 to 42 m2 kg−1, from 310 to 540 kg m−3 and from 0.26 to 0.32 mm, respectively; root density being most sensitive. The most favourable site and soil types resulting in fine roots with morphological characteristics for optimizing nutrient uptake (e.g. low short root density and high specific root area) were Umbric Luvisol (Oxalis), Dystric Gleysol (Oxalis) and Gleyic Luvisol (Hepatica). These soil types correspond to highly productive natural forest stands of Norway spruce in Estonia. All measured soil variables explained 28% of total variance of the root characteristics. The most important variables related to root morphology were the humus content, field capacity and specific soil surface area.

Ectomycorrhizal root tips in relation to site and stand characteristics in Norway spruce and Scots pine stands in boreal forests

Variations in ectomycorrhizal (EcM) short root tips of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in 16 stands throughout Finland were studied, and their relationships with latitude, organic layer C:N ratio, temperature sum and foliage biomass were determined. There were no significant differences in EcM root tip frequency (number per milligram of fine roots) or root tip mass between tree species or between northern and southern sites. The EcM root tip number per unit area of the organic layer plus the 0-30 cm mineral soil layer varied between 0.8 and 2.4 million per m(2) for Norway spruce and between 0.7 and 2.9 million per m(2) for Scots pine, and it was higher in the northern Scots pine stands than in the southern Scots pine stands. Over 80% of the EcM root tips of both species were in the organic layer and the upper 0-10 cm mineral soil layer. We related EcM root tips to foliage mass because these two components are the most important functional units in boreal tree physiology. Both species, especially the Scots pine trees, had more EcM root tips in relation to foliage mass in northern Finland than in southern Finland. Scots pine trees had more EcM root tips in relation to foliage mass than Norway spruce in the same climatic region. The EcM root tip:foliage biomass ratio of Norway spruce was positively related to the C:N ratio in the organic layer, whereas that of Scots pine was negatively related to the temperature sum. The number of EcM root tips per milligram of fine root biomass was constant, implying that trees of both species increase nutrient uptake by increasing fine root production and hence their total number of EcM tips and the area of soil occupied by mycelia. Both tree species responded to nitrogen (N) deficiency by maintaining more EcM tips per foliage unit, and this may be related to a higher proportion of N uptake in an organic form.

Climate change at northern latitudes: rising atmospheric humidity decreases transpiration, N-uptake and growth rate of hybrid aspen.

At northern latitudes a rise in atmospheric humidity and precipitation is predicted as a consequence of global climate change. We studied several growth and functional traits of hybrid aspen (Populus tremula L.×P. tremuloides Michx.) in response to elevated atmospheric humidity (on average 7% over the ambient level) in a free air experimental facility during three growing seasons (2008–2010) in Estonia, which represents northern temperate climate (boreo-nemoral zone). Data were collected from three humidified (H) and three control (C) plots, and analysed using nested linear models. Elevated air humidity significantly reduced height, stem diameter and stem volume increments and transpiration of the trees whereas these effects remained highly significant also after considering the side effects from soil-related confounders within the 2.7 ha study area. Tree leaves were smaller, lighter and had lower leaf mass per area (LMA) in H plots. The magnitude and significance of the humidity treatment effect – inhibition of above-ground growth rate – was more pronounced in larger trees. The lower growth rate in the humidified plots can be partly explained by a decrease in transpiration-driven mass flow of NO3 − in soil, resulting in a significant reduction in the measured uptake of N to foliage in the H plots. The results suggest that the potential growth improvement of fast-growing trees like aspens, due to increasing temperature and atmospheric CO2 concentration, might be smaller than expected at high latitudes if a rise in atmospheric humidity simultaneously takes place.

Tree fine root Ca/Al molar ratio – Indicator of Al and acidity stress

Abstract High soil acidity and elevated soil Al concentrations limit plant growth in many terrestrial ecosystems. Aluminium toxicity can be ameliorated by Ca. Thus, Ca/Al molar ratios in soil solution and in plant tissues have been proposed as superior indicators than Al concentration itself for evaluating the Al toxicity stress to trees (Cronan & Grigal, J Environ Qual 1995;24:209 – 226). This article presents an overview of publications since 1995 where the reduced Ca/Al ratio in fine tree roots has been used as an indicator of stress for Al and/or soil acidity. The main aim of this review was to evaluate the use and the critical threshold of the fine root Ca/Al ratio as a potential indicator for Al toxicity stress to trees in acid soils. Based on the reviewed literature, the fine root Ca/Al molar ratio was strongly negatively related to Al stress in small tree seedlings in controlled environments, whereas the response was not clear under field conditions where other environmental factors interact. Fine root Ca/Al ranged from 0.03 to 17 in tree seedlings and from 0.1 to 18 in mature trees depending on experimental and site conditions, as well as the tolerance and uptake mechanisms of the different tree species. Fine root Ca/Al was positively related to the soil solution Ca/Al molar ratio. Fine root Ca/Al ratios were related positively to fine root length, growth, specific root length, and biomass, and negatively to root diameter, callose formation, respiration chain activity, starch concentration, and root necromass. A number of relationships have been also found between the fine root Ca/Al and above-ground seedling and/or mature tree growth and nutrient uptake. The critical thresholds for the Ca/Al fine root ratio of 0.2 suggested by Cronan and Grigal (1995) is estimated to represent 90% risk of inverse impact on root and above-ground tree growth. Values of Ca/Al molar ratio in the fine roots of mature trees were only rarely determined below the critical 0.2. The caveats for the use and the interpretation of Ca/Al ratio in fine roots have been addressed in detail. A protocol for root processing and elemental analysis to obtain reliable and comparable results of Ca and Al concentrations in roots is also provided. The article concludes with recommendations for a wider use of the Ca/Al ratio in roots as a bioindicator of Al toxicity to trees in acid soils.

Humidity-driven changes in growth rate, photosynthetic capacity, hydraulic properties and other functional traits in silver birch (Betula pendula)

A study was performed on saplings of silver birch (Betula pendula Roth) growing at the free air humidity manipulation site, which was established to investigate the effect of increased air humidity on tree performance and canopy functioning. The aim of the experiment was to simulate the impact of the increasing atmospheric humidity on forest ecosystems predicted for northern Europe. Artificially elevated relative humidity (RH), which causes transpirational flux to decrease, diminished nutrient supply to the foliage; leaf nitrogen content, phosphorus content and P:N ratio decreased. The changes in leaf nutritional status brought about a considerable decline in both photosynthetic capacity (Amax, Vcmax, Jmax) and tree growth rate. The manipulation induced diverse changes in tree hydraulic architecture and other functional traits. Different segments of the soil-to-leaf water transport pathway responded differently: leaf hydraulic conductance (KL) decreased, while hydraulic conductance of root systems (KR) and leaf-specific conductivity of stem-wood increased in response to elevated RH. Humidification caused the Huber values of stems to increase, thus reflecting changes in allocation patterns; relatively more resources were allocated to vascular tissue and less to foliage. The elevated RH induced substantial changes in specific leaf area (increased), branch- (decreased) and stem-wood density (decreased). The observed responses suggest that the expected climate-change-induced increase in the growth rate of trees at northern latitudes (boreal areas) due to the earlier start of the growing season in spring or higher carbon assimilation rate could be smaller or null if temperature rise is accompanied by a rise in atmospheric absolute humidity.

Decomposition and nitrogen dynamics of fine roots of Norway spruce ( Picea abies (L.) Karst) at different sites

Long-term decomposition and nitrogen dynamics of Norway spruce finest (<1 mm in diameter) and fine (<2 mm in diameter) roots were estimated using the root litter-bag techniques. The seasonal decomposition of the finest roots was investigated in a 40-year-old high site quality stand grown on brown lessive soil at different depths as part of productivity studies. The fine root decomposition studies were conducted on 8 permanent plots in the Estonia with the aim to describe the site variation. The initial material was collected from one of stands (high quality site) and incubated at the depth of 10 cm in 1989 (at one site 1990). The bags were collected once or twice a year except for one site, where the seasonal dynamics was investigated. In all initial and decomposing root samples oven-dry weight, ash and energy content and nitrogen concentration was determined. After five years the finest roots had lost 40% of their initial dry weight, half of it during the first year. The initial concentration of nitrogen was 1.29%, the mean concentrations varied during the incubation from 1.47 to 1.78%. After the first year fine roots had lost 21.0 to 32.7% of their initial dry weight, after two years the weight loss was 22.5 to 43.2%. The initial N concentration in fine roots was 0.73% and in the first years it varied from 0.97 to 1.40% at different sites.

Gaseous Fluxes from Subsurface Flow Constructed Wetlands for Wastewater Treatment

Abstract We measured nitrous oxide (N2O), dinitrogen (N2), and methane (CH4) fluxes in two constructed wetlands (CW) in Estonia using the closed chamber method and the He-O method in the period from October 2000 to March 2003. Emission rates of N2O-N, N2-N and CH4-C from both CWs varied significantly on a both spatial and temporal scale, ranging from 1 to 2,600, 170 to 130,000, and –1.7 to 87,200 μ g m− 2 h− 1 respectively. The average flux of N2O from the microsites in the Kodijärve horizontal subsurface flow (HSSF) CW and Kõo hybrid CW ranged from 27 to 370 and from 72 to 500 μ g N2O-N m−2 h−1, respectively, whereas the average dinitrogen flux from the microsites in the HSSF CW in Kodijärve was 2–3 magnitudes higher than the N2O flux, ranging from 19,500 to 33,300 μ g N2-N m− 2 h− 1. The average methane emissions from the microsites in the Kodijärve HSSF CW and the Kõo hybrid CW ranged from 31 to 12,100 and from 950 to 5,750 μ g CH4-C m− 2 h−1, respectively. The highest emission values for all three gases were observed in the warm period. There was a significant relationship between emission rates and water table depth: CH4 and N2 emission increased and N2O emission decreased when the water table did rise. Although the emission of N2O and CH4 from CWs was found to be relatively high, their global warming potential (GWP) in the time horizon of 100 years is not significant, ranging from 4.5 to 16.3 tonnes of CO2 equivalents per ha per year in Kodijärve and from 12.1 to 17.3 t CO2 equivalents ha− 1 yr−1 in Kõo.

Cattail population in wastewater treatment wetlands in Estonia: biomass production, retention of nutrients, and heavy metals in phytomass.

Abstract The aim of this article is to evaluate and compare common cattail (Typha latifolia) biomass production and annual accumulation of nitrogen, phosphorus, carbon, and heavy metals (Cd, Cu, Pb, Zn) in phytomass in 3 treatment wetland systems in Estonia. The biomass samples (roots/rhizomes, shoots with leaves, and spadixes) and litter were collected from 1 × 1 m plots—15 plots in Tänassilma seminatural wetland, 15 plots in Põltsamaa constructed wetland, and 10 plots in Häädemeeste constructed wetland.The highest average total cattail phytomass was 2.54 kg DW m−2 in Häädemeeste. In Tänassilma and Põltsamaa this value was 2.3 and 2.11 kg DW m−2, respectively. The average total aboveground biomass production and roots/rhizomes phytomass was not significantly different in three studied wetland systems. We have found significantly less spadixes and litter in Tänassilma than in Põltsamaa and Häädemeeste. In Põltsamaa, the N and P content in all plant fractions were higher than in other test areas.The Cd concentration in all samples (shoots, spadixes, litter) varied from < 0.01 to < 0.02 mg/kg. The average concentration of Zn in litter varied from 12.2 mg kg−1 in Häädemeeste to 12.6 mg kg−1 in Tänassilma and 13.3 mg kg−1 in Põltsamaa. There has been found a significantly higher average contents of Cu (39.3 mg kg−1), Pb (30.4 mg kg−1), and Zn (412.3 mg kg−1) in Tänassilma than those in Häädemeeste or Põltsamaa: Cu—11.6 and 15.9, Pb—2.3 and 3.3, and Zn—57.5 and 73.2 mg kg−1, respectively. The highest heavy metal retention (303.2 mg Pb m−2, 29.4 mg Zn m−2, 22.9 mg Cu m−2, and 0.35 mg Cd m−2) was observed in root and rhizome samples from the Tänassilma wetland.