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Highlights • Among-site variation in the total fine root biomass was not explained by latitude. • Fine root density increased in the organic layer towards the north. • The future climate may shift fine roots from the organic layer to the mineral soil. Abstract The geographical patterns in the distribution of fine root biomass (FRB) and in the contribution of fine roots to below-ground nitrogen and carbon stocks are poorly documented. Here, we examined FRB and the ecological factors that govern it, along a 1000 km long latitudinal gradient in unmanaged mixed boreal forests in North-East Europe. We sampled fine roots (diameter ≤2 mm; trees and field layer vegetation combined) twice per growing season in 2015 and 2016 from ten sites spaced one degree of latitude between 60°N (near St. Petersburg) and 69°N (near Murmansk, Russia). We separated living fine roots. The roots were dried and weighed; tissue carbon and nitrogen concentrations were measured. The obtained values were correlated with climatic, plant community and soil characteristics. Among-site variation in the total FRB and carbon and nitrogen concentrations were not explained by latitude or by climatic, plant community or soil characteristics. However, fine root density in the organic layer increased towards the north. The more superficial root system in the north than in the south may indicate a poleward increase in the vulnerability of boreal forests to abiotic risks (forest fires, drought). Our results suggest that the future climate may shift fine roots as well as carbon and nitrogen cycling from the organic layer to mineral soils, thereby increasing the volume of soil utilized by fine roots for water and nutrient uptake. [ABSTRACT FROM AUTHOR]

Quantification of fine root biomass is needed for estimating the role of roots as carbon (C) stores and sources of C input into the soil, as well as for modelling of forest nutrient cycling. Due to the laborious nature of root biomass determinations, there is a need to develop indirect methods that would allow fine root biomass to be estimated using data on easily measurable stand and site variables. We developed models for estimating tree fine root (diameter ⩽ 2 mm) biomass of boreal forests by compiling data from 95 Finnish forest stands (55 on upland soils and 40 on drained peatlands). Stand basal area predicted fine root biomass ( R 2 -adj. = 0.35, p < 0.001) better than any other stand variable alone. A model that included stand basal area, dominant tree species group [birch/other], soil type [upland soil/drained peatland], temperature sum and the interaction of soil type and temperature sum accounted for 46% of the variation in fine root biomass. Stand basal area, the C:N ratio of the organic layer or upper 0–20 cm peat layer and the dominant tree species group together explained 45% of the variation in fine root biomass. Temperature sum correlated with fine root biomass in opposite ways in upland soils and in drained peatlands: fine root biomass increased with decreasing temperature sum in upland soil sites, whereas in peatlands fine root biomass decreased as the temperature sum decreased. Although the models were based on a large dataset representing well the variation in stand age, basal area, site fertility and climatic conditions in northern European boreal forests, half of the variation in fine root biomass remained unexplained. More comprehensive fine root biomass sampling in relation to spatial and temporal variation in the forthcoming studies, for example in connection with monitoring campaigns, and additional predictors such as soil texture, successional stage and the fine root biomass of ground vegetation might improve the predictive power of fine root biomass models. [ABSTRACT FROM AUTHOR]

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In 1999, the area of abandoned agricultural land in Estonia formed 223,000 ha which is partly perspective for afforestation with grey alder, the most rapidly growing indigenous tree species. The production and nutrient (NPK) accumulation of a grey alder short-rotation plantation on former agricultural land was investigated. The production of above-ground biomass was estimated during 5 years after the establishment of the stand. In the fifth year after planting, the biomass of the above-ground part of the plantation was 15.9 t DM ha−1 and above-ground biomass production was 6.4 t DM ha−1 per year. In the fourth year after planting, the biomass of the below-ground part was 2.7 t DM ha−1, which accounted for 18% of total biomass. The biomass of the nodules was estimated at 169±76 kg DM ha−1 and the biomass of fine roots (d<2 mm) at 550±105 kg DM ha−1. Of fine roots 73.8% and all nodules were located in the upper 0–20 cm soil layer. In the fourth year after establishment, the amount of nitrogen introduced in the soil through leaf litter was 59.6 kg ha−1. As the site represented abandoned farm land, the pool of total soil nitrogen was relatively large (2.64 t ha−1 in the 0–20 cm layer). However, concerning phosphorus, the positive effect of grey alders was significant. While in the first year after planting the concentration of lactate soluble phosphorus in the 0–20 cm layer was 22.53 mg kg−1, then in the following years it was more than twice as high, varying from 47.2 to 59.7 mg kg−1. After the fifth year the amount of nitrogen accumulated in above-ground biomass was 147.1 kg ha−1, that of phosphorus 21.3 kg ha−1 and that of potassium 42.6 kg ha−1. Most of accumulated nitrogen and potassium (38.9 and 37.6%, respectively) was located in the leaves and most of phosphorus (61.0%) in the wood. [Copyright &y& Elsevier]

• 441 root:shoot records were compiled for 32 locations in south temperate forests. • Root:shoot ratios were size-invariant in most tree taxa assessed. • Most dicots had similar root:shoot ratios between south and north temperate forests. • Divergences in root allocation were only noted for gymnosperms and tree ferns. • Low rainfall:temperature ratio conditions led to high root biomass allocation. Accurate quantification of total forest biomass requires sound estimates of root biomass. Because roots are challenging to measure in situ , data are sparse, and this has limited our understanding of root allocation across a range of forest types. Increased sampling in the oceanic and cool temperate forests of the southern hemisphere means we are now able to better understand biomass allocation in this biome. Here we compile and systematically review root:shoot ratios for these forests and examine the taxonomic, regional, and environmental determinants of variability in biomass allocation to roots. Specifically, we assess whether limited access to resources resulting from low temperatures or low rainfall:temperature ratios increases root allocation. A literature and database search identified 441 root:shoot records from 25 studies and 32 locations around the South Pacific. Records were weighted by excavated area as a measure of sampling effort. Root:shoot ratios for eucalypts in southeast Australia (0.277) and southern beech in South America (0.275) were 6–7% above the global mean of 0.26, while southern beech (0.233) and other dicots (0.234) in New Zealand were consistent with values reported for temperate (mostly northern hemisphere) broadleaved forests. Low root:shoot ratios (of trees ≥5 cm stem diameter) relative to the global mean were noted for South American gymnosperms (0.219), seemingly driven by low values in the Cupressaceae, and New Zealand tree ferns (0.194). Size effects were taxon dependent, with a marked decline in root:shoot ratios with increasing stem size for the southern beech in South America and modest effects for other combinations of taxa and region. A clear signal of increasing root allocation with declining rainfall:temperature ratios was detected, but no major effects of temperature were noted within the range of the data. Our findings support current approaches to biomass and carbon estimation but leave room for refinement, with specific recommendations given for the New Zealand context. [ABSTRACT FROM AUTHOR]