A Canopy Shift in Interior Alaskan Boreal Forests: Consequences for Above- and Belowground Carbon and Nitrogen Pools during Post-fire Succession

Global change models predict that high-latitude boreal forests will become increasingly susceptible to fire activity as climate warms, possibly causing a positive feedback to warming through fire-driven emissions of CO₂ into the atmosphere. However, fire-climate feedbacks depend on forest regrowth and carbon (C) accumulation over the post-fire successional interval, which is influenced by nitrogen (N) availability. To improve our understanding of post-fire C and N accumulation patterns in boreal forests, we evaluated above- and belowground C and N pools within 70 stands throughout interior Alaska, a region predicted to undergo a shift in canopy dominance as fire severity increases. Stands represented gradients in age and successional trajectory, from black spruce (Picea mariana) self-replacement to species replacement by deciduous species of trembling aspen (Populus tremuloides) and Alaska paper birch (Betula neoalaskana). Stands undergoing deciduous trajectories stored proportionally more of their C and N in aboveground stemwood and had 5–7 times faster rates of aboveground net primary productivity of trees compared to stands undergoing a black spruce trajectory, which stored more of their C and N in the soil organic layer (SOL), a thick layer of mostly undecomposed mosses. Thus, as successional trajectories shift, total C and N pool sizes will remain relatively unchanged, but there will be a trade-off in pool location and a potential increase in C and N longevity due to decreased flammability and decomposition rates of deciduous stemwood. Despite often warmer, drier conditions in deciduous compared to black spruce stands, deciduous stemwood has a C:N around 10 times higher than the black spruce SOL and often remains standing for many years with reduced exposure to fungal decomposers. Thus, a fire-driven shift in successional trajectories could cause a negative feedback to climate warming because of increased pool longevity in deciduous trajectories.     

High-resolution analysis of stem radius variations in black spruce [Picea mariana (Mill.) BSP] subjected to rain exclusion for three summers

Key message

A rain exclusion repeated for 3 years resulted in larger summer stem contractions in three of the sites in the third year of the experiment and in larger winter contractions in the northern sites. However, there was no pronounced stress reaction in the stem radius variations of mature black spruce since total stem expansion was not reduced.

Abstract

Future climate warming is expected to produce more severe and frequent periods of drought with consequent water stresses for boreal species. In this paper, we present a high-resolution analysis of stem radius variations in black spruce under rain exclusion. All summer long rain exclusions were applied for three consecutive summers to mature trees on four sites along a latitudinal gradient. The stem radius variations of control and treated trees were monitored year-round at an hourly resolution with automatic point dendrometers. The seasonal patterns of shrinking and swelling were analyzed using a sequential analysis technique and the daily patterns of contraction and expansion were extracted. Overall, the treated trees followed their diurnal cycles of contraction and expansion during the rain exclusions and no significant cumulative difference in stem expansion between control and treated trees was observed over the 3 years. In the third year trees subjected to rain exclusion showed larger stem contractions in summer on three out of four sites and larger winter contractions were observed on the northern sites. This study shows that repeated summer rain exclusion does not necessarily lead to a direct evident stress reaction, showing the resilience of the boreal forest.     

Changes in root size and distribution in relation to nitrogen accumulation during maize breeding in China

Background and aims

Modern maize breeding has increased maize yields worldwide. The changes in above-ground traits accompanying yield improvement are well-known, but less information is available as to the effect of modern plant breeding on changes in maize root traits.

Methods

Root growth, nitrogen uptake, dry matter accumulation and yield formation of six maize hybrids released from 1973 to 2000 in China were compared. Experiments were conducted under low and high nitrogen supply in a black soil in Northeast China in 2010 and 2011.

Results

While nitrogen accumulation, dry matter production and yield formation have been increased, modern maize breeding in China since 1990 has reduced root length density in the topsoil without much effect on root growth in the deeper soil. The efficiency of roots in acquiring N has increased so as to match the requirement of N accumulation for plant growth and yield formation. The responses of root growth, nitrogen and dry matter accumulation, and grain yield to low-N stress were similar in the more modern hybrids as in the older ones.

Conclusions

Modern maize breeding has constitutively changed root and shoot growth and plant productivity without producing any specific enhancement in root responsiveness to soil N availability.     

Spatial and temporal variation in moss-associated dinitrogen fixation in coniferous- and deciduous-dominated Alaskan boreal forests

Dominant canopy tree species have strong effects on the composition and function of understory species, particularly bryophytes. In boreal forests, bryophytes and their associated microbes are a primary source of ecosystem nitrogen (N) inputs, and an important process regulating ecosystem productivity. We investigated how feather moss-associated N₂-fixation rates and contribution to N budgets vary in time and space among coniferous and broadleaf deciduous forests. We measured N₂-fixation rates using stable isotope (¹⁵N₂) labeling in two moss species (Pleurozium schreberi and Hylocomium splendens) in broadleaf deciduous (Alaska paper birch—Betula neoalaskana) and coniferous (black spruce—Picea mariana) stands near Fairbanks, interior Alaska, from 2013 to 2015. N₂-fixation rates showed substantial inter-annual variation among the 3 years. High N₂-fixation was more strongly associated with high precipitation than air temperature or light availability. Overall, contribution of N₂-fixation to N budgets was greater in spruce than in birch stands. Our results enhance the knowledge of the processes that drive N₂-fixation in boreal forests, which is important for predicting ecosystem consequences of changing forest composition.     

Effect of ecosystem warming on boreal black spruce bud burst and shoot growth

The boreal forest is predicted to experience the greatest warming of any forest biome during the next 50–100 years, but the effects of warming on vegetation phenology are not well known. The objectives of this study were to (1) examine the effects of whole ecosystem warming on bud burst and annual shoot growth of black spruce trees in northern Manitoba, Canada and (2) correlate bud burst to cumulative degree-days (CDD). The experimental design was a complete randomized block design that consisted of four replicated blocks. Each replicate block contained four treatments: soil warming only (heated outside, HO), soil and air warming (heated inside, HI), control outside (no chamber, no heating, CO), and inside a chamber maintained at ambient conditions (no soil or air warming, control inside, CI). Bud burst was measured during the first and second years of the experiment, starting in 2004, and annual shoot growth was measured for the first 3 years (2004–2006) of the study. On average, shoot bud burst occurred 11 and 9 days earlier in 2004 and 2005, respectively, for HI than for other treatments. However, mean CDD required for bud burst for HI was within the standard deviation of CO for both years. In year 1 of the treatments, shoot bud burst occurred earlier for HI than other treatments (CI, CO, HO), but final shoot length of HI trees was less than in CO trees. In the second year of warming, final shoot length was not different for HI than CO. By the third year of warming final shoot length was significantly greater for HI than all other treatments. Empirical results from this study suggest that soil and air warming causes an earlier bud burst for all years of observation and greater shoot lengths by the third season of warming. A longer growing season and greater annual shoot growth should increase carbon uptake by boreal black spruce trees in a warmer climate.     

Boreal forest plant species responses to pH: ecological interpretation and application to reclamation

Aims

Reclamation following oil sands mining in northeastern Alberta (Canada) creates adverse reforestation soil conditions, including extreme pH values. We elucidated pH tolerance limits of boreal plant species and how pH affects nutrient uptake in these plants.

Methods

We measured growth, gas exchange, and foliar nutrient concentration of 15 common northern boreal forest plants after eight weeks exposure to root zone pH ranging from 5.0 to 9.0. Cluster analyses were used to group these species based on their pH responses.

Results

Based on their growth and gas exchange responses to pH, the 15 plant species could be divided into five groups, each of which contained species that commonly co-occur in particular boreal forest site types. For the foliar nutrient responses to pH, the 15 species could be grouped into only two categories; both showed decreases in foliar N, P, Fe and Zn concentration with increasing pH, with a more pronounced effect on the group that included trembling aspen, paper birch and chokecherry.

Conclusions

The evidence of differential adaptation to pH by habitat type suggests the importance of soil pH as a factor affecting boreal plant species distribution and could be helpful for selection of species suitable for reclamation of sites with altered soil pH.

     

Shoot development of Norway spruce (Picea abies) involves changes in piperidine alkaloids and condensed tannins

Key Message

Secondary chemistry of P. abies peaks early in shoot development. Condensed tannins accumulate already in late buds while piperidine alkaloid biosynthesis take place in early stage shoots.

Abstract

Plants protect new vegetative parts with defensive secondary metabolite compounds. We investigated how concentrations of piperidine alkaloids and condensed tannins change during bud burst and shoot growth in adult Picea abies. We detected 12 individual piperidine compounds, of which epipinidinone and 1,2-dehydropinidinone and two tentatively identified 1,6-imines are reported for the first time in P. abies. In addition three piperidine alkaloid compounds remain partly identified. We found that concentrations of both total piperidine alkaloids and condensed tannins were highest immediately after bud burst. While concentrations of condensed tannins started to increase during bud opening, the dilution effect decreased concentrations in the developing needles of mature branches. By contrast, the decrease of total alkaloid concentrations in mature shoots was not due to the dilution effect, but was connected to the disappearance of precursor components of biosynthesis. The concentrations of major alkaloid components remain stable from dormant buds to mature needles and twigs, underlining their importance for P. abies, although their real ecological significance is yet to be solved. Based on the structural features and timing of appearance of individual compounds, we also propose a hypothetical biosynthesis route for trans-substituted coniferous piperidine alkaloids.     

A novel method to measure the effect of temperature on diffusion of plant-available nitrogen in soil

Background and aims

Soil temperature influences nitrogen (N) diffusion in soil but until now, such effects have been difficult to quantify. This study aimed at estimating the effect of temperature on the diffusive fluxes of plant-available N forms in two contrasting soils.

Methods

Using a novel technique based on micro-dialysis, we established relationships between diffusive fluxes and temperature in aqueous solutions and in soil samples.

Results

Averaged for all compounds, the decreases of diffusive fluxes from the soil to the microdialysis sampler were 3.8 and 4.7% per degree Celsius in an agricultural and a boreal forest soil, respectively. The temperature-related shift of diffusive flux was, however, significantly dependent on molecular weight of the N compound. In accordance with established functions for temperature effects on diffusive fluxes, the non-linearity of this relationship resulted in a greater temperature response for small N compounds compared to larger compounds.

Conclusions

Our results show that, all other factors being equal, the relative contribution of smaller N compounds to the diffusive flux of total plant-available N increases with increasing soil temperatures.     

Macrocharcoal-Based Chronosequences Reveal Shifting Dominance of Conifer Boreal Forests Under Changing Fire Regime

Balsam fir (Abies balsamea) and black spruce (Picea mariana) forests are the main conifer forest types in the North American boreal zone. The coexistence of the two species as well as their respective canopy dominance in distinct stands raises questions about the long-term evolution from one forest type to the other in relation to environmental factors including climate and stand disturbance. We tested the hypothesis that repetitive fire events promote the succession of balsam fir forest to black spruce forest and vice versa. Postfire chronosequences of one black spruce (BSP) and one balsam fir (BFI) sites were reconstructed based on the botanical composition and ¹⁴C-dated soil macrocharcoals. The results support the hypothesis of a successional dynamics. The BSP site has been affected by fires for the last 7600 years, whereas the BFI site, after having been impacted by several fires during the first half of the Holocene, evolved in a fire-free environment for the last 4400 years. Periods of fire activity facilitated the dominance of black spruce forests. The cessation of fires around 4400 cal. years BP on BFI site marks the beginning of the transition from black spruce to balsam fir stands. This succession is a long process, due to the ability of black spruce to regenerate by layering in the absence of fire. The resulting balsam fir stands are ancient and precarious ecosystems, since fire generally leads to the return of black spruce. The increase in balsam fir to the detriment of black spruce in boreal forests is a response to a decrease in fire frequency.     

Impact of the invasive tree black locust on soil properties of Mediterranean stone pine-holm oak forests

Background and aims

Invasion by N₂-fixing species may alter biogeochemical processes. We hypothesized that the grade of invasion by the N₂-fixer black locust (Robinia pseudoacacia L.) could be related to the distribution and pools of carbon (C) and nitrogen (N) along the profile of two Mediterranean mixed forests of stone pine (Pinus pinea L.) and holm oak (Quercus ilex L.).

Methods

A low-invaded (LIN) and a high-invaded (HIN) mixed forest were studied. We assessed: N concentration in green and in senescent leaves; C and N pools along the soil profile; seasonal changes of soluble C and N fractions, and microbial activity.

Results

Compared to coexisting holm oak and stone pine, black locust had higher N content in green and in senescent leaves. In the mineral soil: N stocks were similar in LIN and HIN; water soluble C and microbial activity, were lower in HIN compared to LIN; water soluble N showed seasonal changes consistent with tree growth activity in both HIN and LIN. In the organic layer of HIN, C and N stocks were about twofold larger than expected on the basis of stand density.

Conclusion

Black locust increased C and N stocks in the upper organic layers that are more vulnerable to disturbance. However, it did not increase N stocks in the mineral soil.     

Comparative effect of inorganic N on plant growth and N<Subscript>2</Subscript> fixation of ten legume crops: towards a better understanding of the differential response among species

Aims

A better understanding of how plant growth, N nutrition and symbiotic nitrogen fixation (SNF) are influenced by soil inorganic N availability, for a wide range of legume species, is crucial to optimise legume productivity, N₂ fixation, while limiting environmental risks such as N leaching.

Methods

A comparative analysis was performed for ten legume crops, grown in a field experiment and supplied with four N fertiliser rates. Dry matter, N concentration and SNF were measured. In parallel, root elongation rates were studied in a greenhouse experiment.

Results

For most species, N fertilisation had little effect on plant growth and N accumulation. SNF was reduced by soil inorganic N available at sowing but with large differences in the magnitude of the response among species. The response varied according to plant N requirements for growth and plant ability to retrieve inorganic N. Accordingly, root lateral expansion rate measured in RhizoTubes was highly correlated with plant ability to retrieve inorganic N measured in the field experiment.

Conclusion

Combining SNF response to soil inorganic N, shoot N and plant ability to retrieve inorganic N, allowed a robust evaluation of differential response to soil inorganic N among a wide range of legume species.

     

Imbalanced plant stoichiometry at contrasting geologic-derived phosphorus sites in subtropics: the role of microelements and plant functional group

Aims

In western North America ectomycorrhizal fungi are critical to establishment of conifers in low nitrogen soils. Fire can affect both ectomycorrhizal fungi and soil properties, and inoculation with ectomycorrhizal fungi is recommended when planting on burns for restoration. The aim of this study was to examine how Suillus species used in inoculation affect whitebark pine (Pinus albicaulis L.) seedlings planted in fire-impacted soil.

Methods

In a greenhouse experiment, Suillus-colonized and uncolonized whitebark pine seedlings were planted in unsterilized and sterilized (control) soil from a recent burn. After 6 months, foliar nitrogen and carbon content, concentration, and stable isotope values were assessed, along with growth parameters.

Results

When seedlings were colonized, biomass was 61% greater, foliar nitrogen content 25% higher, foliar nitrogen concentration 30–63% lower; needles had lower δ¹⁵N and higher δ¹³C. Differences were more pronounced in sterilized soil where colonization was higher. Foliar N content was negatively correlated with δ¹⁵N values.

Conclusions

Colonization by host-specific fungi produced larger seedlings with higher foliar nitrogen content in both burn soils. The hypothesis that ectomycorrhizal fungi on roots fractionate nitrogen isotopes leading to lower δ¹⁵N in needles is supported. This helps explain restoration outcomes, and bridges the gap between field and in vitro investigations.

     

The influence of alkaline and non-alkaline parent material on Norway spruce tree chemical composition and growth rate

Background and aims

This study investigated the influence of contrasting parent materials on tree chemical composition and growth rate under field conditions. On the island of Alnö, Sweden, alkaline intrusions are interspersed into non-alkaline gneiss bedrock, which provides a unique opportunity to conduct this study with a minimum of confounding effects.

Methods

Three plots with alkaline and three plots with non-alkaline parent material were established in a homogenous Norway spruce stand. The chemical composition of soil and soil solution was determined throughout the soil profiles. The chemical composition of bark, wood and needles was determined for each plot, and the latest 5 year basal area growth increment calculated.

Results

Concentrations of Ca in needles were correlated with the soil exchangeable Ca levels. Tree growth rate was significantly higher on the alkaline plots and positively correlated with soil concentrations of Ca, Mg, P, and Zn. The tree growth rate also tended to correlate with soil N concentrations, but levelled out for the highest soil N concentrations.

Conclusions

Tree growth was enhanced on the alkaline plots and was correlated with several elements. However, none of these elements could be confirmed as the limiting one for tree growth at the current site.     

Growth and physiological responses of trembling aspen (Populus tremuloides), white spruce (Picea glauca) and tamarack (Larix laricina) seedlings to root zone pH

Background and aims

Soil pH is among the major environmental factors affecting plant growth. Although the optimum range of soil pH for growth and the tolerance of pH extremes widely vary among plant species, the pH tolerance mechanisms in plants are still poorly understood. In this study, possible mechanisms were examined to explain the differences in tolerance of boreal plants to root zone pH.

Methods

In the controlled-environment solution culture experiments, we compared growth, physiological parameters and tissue nutrient concentrations in aspen, white spruce and tamarack seedlings that were subjected to 8 weeks of root zone pH treatments ranging from 5.0 to 9.0.

Results

The pH treatments had little effect on dry weights and net photosynthesis in white spruce seedlings despite reductions in transpiration rates at higher pH levels. In aspen and tamarack, both the growth and physiological parameters significantly decreased at pH higher than 6.0. The chlorosis of young tissues in aspen and tamarack was associated with the reductions in foliar concentrations of several of the examined essential nutrients including Fe and Mn. Although the plants varied in their ability to deliver essential nutrients to growing leaves, there was no direct correlation between tissue nutrient concentrations, chlorophyll concentrations and plant growth. The results also demonstrated strong inhibition of transpiration rates by high pH.

Conclusions

The results suggest that high root zone pH can upset water balance in pH sensitive species including aspen. Although the uptake and assimilation of essential elements such as Fe and Mn contribute to plant tolerance of high soil pH, we did not observe a direct relationship between growth and foliar nutrient concentrations to account for the observed differences in growth.     

The effects of the moss layer on the decomposition of intercepted vascular plant litter across a post-fire boreal forest chronosequence

Aims

Feather mosses form a thick ground layer in boreal forests that can intercept incoming litter fall. This interception may influence the decomposition of incoming litter but this has been little explored. We investigated how the moss layer influences decomposition of intercepted litter along a 362-year fire driven forest chronosequence in northern Sweden across which soil fertility declines.

Methods

We placed leaf litter from three plant species into plots in which mosses and dwarf shrubs were either experimentally removed or left intact, at each of ten stands across the chronosequence. After one year we measured litter mass loss, and litter nitrogen and phosphorous.

Results

Litter decomposed consistently faster, and had higher nitrogen and phosphorus, in the presence of mosses and at greater depth in the moss layer. Despite an increase in moss depth across the chronosequence we did not find consistent increases in effects of moss removal on litter decomposition or on litter N or P.

Conclusions

Our findings identify a clear role of the moss layer in boreal forests in promoting the decomposition of intercepted leaf litter, and highlight that this role is relatively consistent across chronosequence stages that vary greatly in productivity and moss depth.     

Plant Community Composition as a Predictor of Regional Soil Carbon Storage in Alaskan Boreal Black Spruce Ecosystems

The boreal forest is the largest terrestrial biome in North America and holds a large portion of the world’s reactive soil carbon. Therefore, understanding soil carbon accumulation on a landscape or regional scale across the boreal forest is useful for predicting future soil carbon storage. Here, we examined the relationship between floristic composition and ecosystem parameters, such as soil carbon pools, the carbon-to-nitrogen (C/N) ratio of live black spruce needles, and normalized basal area increment (NBAI) of trees in black spruce communities, the most widespread forest type in the boreal forest of Alaska. Variability in ecosystem properties among black spruce stands was as large as that which had previously been documented among all forest types in the central interior of Alaska; we found an eightfold range in NBAI and fivefold range in mineral soil carbon and nitrogen pools. Acidic black spruce communities had significantly more carbon in the organic soil horizon than did nonacidic black spruce communities, but did not differ in any other measured ecosystem parameter. We explained 48% of the variation in total soil carbon with a combination of plant community indices and abiotic and biotic factors. Plant community composition was at least as effective as any single environmental factor or stand characteristic in predicting soil C pools in Alaskan black spruce ecosystems. We conclude that among the community properties analyzed, the presence of key groups of species, overall species composition, and diversity of certain functional types, especially Sphagnum moss species, are important predictors of soil carbon sequestration in the black spruce forest type.     

Fine root turnover and litter production of Norway spruce in a long-term temperature and nutrient manipulation experiment

Background and aims

Increased soil temperature and nutrient availability enhance soil biological activity. We studied how these affect fine root growth and survival, i.e. below-ground litter production, in relation to above-ground foliage litter production of Norway spruce (Picea abies (L.) Karst.).

Methods

The treatments, irrigation (I), soil warming + irrigation (WI), fertilization + irrigation (FI) and soil warming + fertilization + irrigation (WFI) were started in 1987 (F, I) and in 1995 (W). The annual production of fine root litter was estimated from minirhizotrons (survival) and soil-cores (biomass) and the annual above-ground litter production from litter traps.

Results and conclusions

The number and elongation of fine roots tended to be higher in WI and I compared to the other treatments, which may indicate nutrient shortage. Fine roots in the WFI treatment had the lowest median longevity and from three to fourfold higher below-ground litter production compared to WI, FI or I - higher soil temperature increased the litter input particularly into the mineral soil. Only fertilization increased the above-ground litter production. As warmer and more nutrient-rich soil significantly shortened the fine root lifespan and increased the litter input, the storage of carbon in boreal forest soil may increase in the future.     

Impacts of bud set and lammas phenology on root:shoot biomass partitioning and carbon gain physiology in poplar

Key message

Timing of bud set and occurrence of lammas in trees can alter growth partitioning (i.e., root:shoot ratios), while only bud set effectively modifies carbon gain by increasing photosynthesis-related physiological traits.

Abstract

Bud set and lammas (second bud flushing) phenology may strongly influence growth, physiology, and biomass in trees. To test effects of these phenological events, 54 individuals from 16 genotypes of black cottonwood poplar (Populus trichocarpa) were grown in a potted trial under greenhouse conditions (with extended daylengths promoting growth), followed by open-air cultivation (with natural daylengths promoting bud set and/or lammas). Trees were monitored for phenology, repeatedly measured for photosynthesis-related traits, harvested for biomass, and assessed for growth partitioning (separating above- and belowground parts). We grouped trees by phenology for comparisons: (1) trees with early summer bud set, (2) trees with early summer bud set that underwent lammas, (3) trees with late summer bud set (August), and (4) trees with bud set occurring in autumn (September). We found that bud set timing positively affected growth partitioning where earlier bud set resulted in shorter trees with higher root:shoot biomass ratios (by increasing root mass). Lammas growth altered these ratios by significantly increasing shoot growth relative to belowground growth. Trees with bud set occurring in late summer also had higher root:shoot biomass ratios (by increasing root mass) compared to trees setting bud in autumn. Occurrence of bud set coincided with modified physiology of the existing canopy where photosynthesis-related traits were enhanced relative to trees still actively growing. These physiological changes were unaltered by occurrence of lammas. This suggests that bud set prompts a significant, coordinated mechanism of higher carbon gain physiology and belowground biomass accumulation in plants within a “post-bud set” phase.

     

The natural abundance of 15N in litter and soil profiles under six temperate tree species: N cycling depends on tree species traits and site fertility

Aims

We investigated the influence of tree species on the natural ¹⁵N abundance in forest stands under elevated ambient N deposition.

Methods

We analysed δ¹⁵N in litter, the forest floor and three mineral soil horizons along with ecosystem N status variables at six sites planted three decades ago with five European broadleaved tree species and Norway spruce.

Results

Litter δ¹⁵N and ¹⁵N enrichment factor (δ¹⁵N_litter–δ¹⁵N_soil) were positively correlated with N status based on soil and litter N pools, nitrification, subsoil nitrate concentration and forest growth. Tree species differences were also significant for these N variables and for the litter δ¹⁵N and enrichment factor. Litter from ash and sycamore maple with high N status and low fungal mycelia activity was enriched in ¹⁵N (+0.9 delta units) relative to other tree species (European beech, pedunculate oak, lime and Norway spruce) even though the latter species leached more nitrate.

Conclusions

The δ¹⁵N pattern reflected tree species related traits affecting the N cycling as well as site fertility and former land use, and possibly differences in N leaching. The tree species δ¹⁵N patterns reflected fractionation caused by uptake of N through mycorrhiza rather than due to nitrate leaching or other N transformation processes.     

Biochar application to a fertile sandy clay loam in boreal conditions: effects on soil properties and yield formation of wheat, turnip rape and faba bean

Background and aims

We studied the effect of different biochar (BC) application rates on soil properties, crop growth dynamics and yield on a fertile sandy clay loam in boreal conditions.

Methods

In a three-year field experiment conducted in Finland, the field was divided into three sub-experiments with a split-plot experimental design, one for each crop: wheat (Triticum aestivum), turnip rape (Brassica rapa), and faba bean (Vicia faba). The main plot factor was BC rate (0, 5 and 10 t DM ha^?1) and the sub-plot factor was the N-P-K fertiliser rate. Soil physico-chemical properties as well as plant development, yield components and quality were investigated.

Results

BC addition did not significantly affect the soil chemical composition other than the increased C and initially increased K contents. Increased soil moisture content was associated with BC application, especially at the end of the growing seasons. BC decreased the N content of turnip rape and wheat biomass in 2010, thus possibly indicating an initial N immobilisation. In dry years, the seed number per plant was significantly higher in faba bean and turnip rape when grown with BC, possibly due to compensation for decreased plant density and relieved water deficit. However, the grain yields and N uptake with BC addition were not significantly different from the control in any year.

Conclusions

Even though BC application to a fertile sandy clay loam in a boreal climate might have relieved transient water deficit and thereby supported yield formation of crops, it did not improve the yield or N uptake.