Aino Smolander

Soil microbial activities and characteristics of dissolved organic C and N in relation to tree species

Abstract The aim of this study was to compare soil microbial biomass and activities with the characteristics of water-extractable organic matter in different types of forest stands. The study was carried out in adjacent 70-year-old stands dominated by silver birch (Betula pendula Roth.), Norway spruce (Picea abies (L.) Karst.) or Scots pine (Pinus sylvestris L.) growing in originally similar soil on Hylocomium–Myrtillus site type in northern Finland. The birch stand was a pure single-species stand, but the coniferous stands were mixed with birch. Soil samples were taken from the humus layer. Water extracts were analyzed for the concentrations of dissolved organic C and N (DOC and DON) and characterized according to chemical composition using a resin fractionation technique and molecular size distribution. C and N in the soil microbial biomass and rates of C mineralization, net N mineralization and net nitrification were measured. Soil pH varied from 4.0 to 4.3 and was highest in the birch stand. The C-to-N ratio of the soil organic matter was higher in the pine stand than in the other stands. Per unit organic matter, the amounts of C and N in the soil microbial biomass were highest in the birch stand. In laboratory incubation experiments, both the rate of C mineralization and that of net N mineralization were much higher in soils from the birch and spruce stands than in soil from the pine stand. This was also the order for concentrations of both DOC and DON. The DOC-to-DON ratio was similar in the birch and spruce soils but higher in the pine soil. The distributions of both different chemical and molecular size fractions were relatively similar in all soils, except for differences in some fractions of DON. The hydrophobic acid fraction was the major carrier of both DOC and DON, accounting for about 60% of DOC and 40–55% of DON. The DOC-to-DON ratio was especially low in the hydrophilic neutral fraction and in the smallest molecular size fraction (

Microbial community structure and characteristics of the organic matter in soils under Pinus sylvestris, Picea abies and Betula pendula at two forest sites

Abstract Microbial biomass C (Cmic), C mineralization rate, phospholipid fatty acid (PLFA) profiles and community level physiological profiles (CLPPs) using Biolog were determined from the humus and mineral soil layers in adjacent stands of Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and silver birch (Betula pendula Roth) at two forest sites of different fertility. In addition, the Fourier-transformed infrared (FTIR) spectra were run on the samples for characterization of the organic matter. Cmic and C mineralization rate tended to be lowest under spruce and highest under birch, at the fertile site in all soil layers and at the less fertile site in the humus layer. There were also differences in microbial community structure in soils under different tree species. In the humus layer the PLFAs separated all tree species and in the mineral soil spruce was distinct from pine and birch. CLPPs did not distinguish microbial communities from the different tree species. The FTIR spectra did not separate the tree species, but clearly separated the two sites.

Microbial biomass C and N, and respiratory activity in soil of repeatedly limed and N- and P-fertilized Norway spruce stands

Abstract Our aim was to assess long-term effects of repeated liming and N and P additions on soil microbial biomass and activity. The experimental sites were four, 40–60 yr old, Norway spruce (Picea abies L.) stands growing on mineral soil sites. During the 30 yr study period, the cumulative amount of finely-ground limestone totalled 6000 kg ha−1, and fertilizer N and P totalled 530–950 and 70–115 kg ha−1, respectively. The main effects of the additions, expressed on an organic matter basis, were as follows: liming increased, and N addition decreased, both the fumigation-extraction (FE) and substrate-induced-respiration (SIR) derived microbial biomass C, microbial biomass N and its proportion of total soil N, and microbial respiration rate. Nitrogen addition increased slightly the soil ergosterol content, indicating an increase in fungal biomass or a change in fungal population structure. There were no significant differences in microbial C:N ratio and respiration: biomass ratio between the treatments. No clear effects of P addition were observed.

Nitrogen transformations in soil under Pinus sylvestris, Picea abies and Betula pendula at two forest sites

Abstract Microbial biomass N, net ammonification, net nitrification, denitrification potential, numbers of nitrifiers and the pH-dependency of nitrification were measured from the humus layer and mineral soil layers in adjacent stands of Scots pine ( Pinus sylvestris L.), Norway spruce ( Picea abies (L.) Karst.) and silver birch ( Betula pendula L.). The trees had been established at two forest sites of different fertility approximately 60 years ago. The aim was to see whether the microbial and chemical characteristics of the soils differed under different tree species. The soil pH(H 2 O) varied from 3.8 to 5.0 and was lowest in spruce soil at both sites in all soil layers. Microbial biomass N, ammonification, nitrification and denitrification all differed in soils of pine, spruce and birch. The flush of N from fumigation varied from 36 to 67 μg N cm −3 fresh soil in the humus layer, and from 13 to 50 μg cm −3 in the mineral soil layers. Denitrification potential with added nitrate was 2–29 ng N 2 O-N cm −3 soil h −1 in the humus layer and 0–28 ng in the mineral soil layers. Both tended to be lowest under spruce and highest under birch, at the fertile site in all soil layers and at the less fertile site in the humus layer. In the mineral soil layers of the fertile site and in the humus layer and upper mineral soil layer of the less fertile site the content of mineral N was highest under birch. Different populations of nitrifiers existed in the soils, regarding numbers, activity and pH-dependency. Only the nitrifier community in pine humus layer from the fertile site was adapted to acidic (pH 4.1) conditions. In an aerobic soil suspension the cumulative nitrate production of it was 32 μg cm −3 soil in three weeks, compared to negligible production in the other soils. When the pH of the suspensions was raised to 6.0, all soils from the fertile site produced nitrate, but the production at the less fertile site was still negligible. Higher C-to-N ratios probably explained the low nitrification activity and numbers of nitrifiers at the less fertile site. Thus, there were differences in N transformations under pine, spruce and birch, but the changes depended also on the fertility of the site.

Wood-ash fertilization and fire treatments in a Scots pine forest stand: Effects on the organic layer, microbial biomass, and microbial activity

We studied the reactions of humus layer (F/H) microbial respiratory activity, microbial biomass C, and the fungal biomass, measured as the soil ergosterol content, to the application of three levels of wood ash (1000, 2500, and 5000 kg ha-1) and to fire treatment in a Scots pine (Pinus sylvestris L.) stand. Physicochemical measurements (pH, organic matter content, extractable and total C content, NH4+and total N content, cation-exchange capacity, base saturation) showed similarity between the fire-treated plots and those treated with the lowest dose of wood ash (1000 kg ha-1). The ash application did not change the level of microbial biomass C or fungal ergosterol when compared to the control, being around 7500 and 350 μg g-1 organic matter for the biomass C and ergosterol, respectively. The fire treatment lowered the values of both biomass measurements to about half that of the control values. The fire treatment caused a sevenfold fall in the respiration rate of fieldmoist soil to 1.8 μl h-1 g-1 organic matter compared to the values of the control or ash treatments. However, in the same soils adjusted to a water-holding capacity of 60%, the differences between the fire treatment and the control were diminished, and the ash-fertilized plots were characterized by a higher respiration rate compared to the control plots. The glucose-induced respiration reacted in the same way as the water-adjusted soil respiration. The metabolic quotient, qCO2, gradually increased from the control level with increasing applications of ash, reaching a maximum in the fire treatment. Nitrification was not observed in the treatment plots.

Inhibition of nitrification in forest soil by monoterpenes

Nitrate production was detected in untreated soil of a Norway spruce (Picea abies L.) stand only after clear-cutting the stand. The aim of this study was to determine whether allelochemical inhibition of nitrification by monoterpenes played any role in inhibiting nitrification in the stand. Therefore, soils from a clear-cut plot and from a forest plot were studied. In the field, monoterpenes (mostly α- and β-pinenes), measured by soil microair diffusive samplers, were intensively produced in the forest plot, but not in the clear-cut plot. In the laboratory, soil samples taken from the forest plot produced only small amounts of monoterpenes, indicating that monoterpenes were mainly produced by the roots and not to great extent by the soil microbial population. The effect of a mixture of monoterpenes (seven major monoterpenes detected in the field) on net nitrification, net N mineralization and denitrification activities of soil from the clear cut plot, and on carbon mineralization of soils from both the forest and clear-cut plots, was studied in the laboratory. In both aerobic incubation experiments and in soil suspensions with excess NH4-N, nitrification was inhibited by exposure to the vapours of monoterpenes at similar concentrations at which they had been detected in forest plot. This indicates direct inhibition of nitrification by monoterpenes. Exposure to monoterpenes did not affect denitrification. However, it increased respiration activity of both soils. This could also indicate indirect inhibition of nitrification by monoterpenes, due to immobilization of mineral N. Thus it seems that monoterpenes could play a role in inhibiting nitrification in the forest soil.

Nitrogen and carbon transformations before and after clear-cutting in repeatedlyN-fertilized and limed forest soil

Abstract Nitrogen and carbon transformations were monitored in a Norway spruce ( Picea abies L.) stand in the summer before clear-cutting, and for the following three summers. During 30 y before the clear-cutting the stand had been repeatedly limed (total 6 t limestone ha −1 ), fertilized with N (total about 900 kg N ha −1 ), and both treatments were combined. Aerobic incubation experiments in the laboratory showed that, before clear-cutting, nitrification took place only in the soil that had been both limed and N-fertilized. Clear-cutting increased soil pH and net formation of mineral N, and initiated nitrification in all soils. These effects were observed throughout the study period. The only exception was the soil that had been both limed and N-fertilized, where the effect of clear-cutting on these N transformations was negligible or even suppressive. Generally, the greatest response in N transformations to clear-cutting was observed in the control soil. There was a small increase in microbial biomass C and N, and C mineralization in the first summer after clear-cutting. Net formation of mineral N correlated positively with pH at a lower pH range (pH 3.9–4.9) and negatively at a higher pH range (pH 4.9–6.9). C mineralization correlated positively with microbial biomass C, but there was no linear relationship between net formation of mineral N and microbial biomass N. C mineralization and net N mineralization were not correlated.

Microbial biomass and activity in soil and litter underPinus sylvestris, Picea abies andBetula pendula at originally similar field afforestation sites

Microbial biomass C and N, and activities related to C and N cycles, were compared in needle and leaf litter, and in the uppermost 10 cm of soil under the litter layer in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) stands, planted on originally similar field afforestation sites 23–24 years ago. The ground vegetation was differentiated under different tree species, consisting of grasses and herbs under birch and pine, and mosses or no vegetation with a thick layer of needles under spruce. The C:N ratio of the soils was 13–21 and the soil pHCaCl2 3.8–5.2. Both showed little variation under different tree species. Microbial biomass C and N, C mineralization, net ammonification, reduction) did not differ significantly in soil under different tree species either. Birch leaf litter had a higher pHCaCl2 (5.9) than spruce and pine needle litter (pH 5.0 and 4.8, respectively). The C:N ratio of spruce needles was 30, and was considerably higher in pine needles (69) and birch leaves (54). Birch leaves tended to have the highest microbial biomass C and C mineralization. Spruce needles appeared to have the highest microbial biomass N and net formation of mineral N, whereas formation of mineral N in pine needles and birch leaves was negligible. Microbial biomass C and N were of the same order of magnitude in the soil and litter samples but C mineralization was tenfold higher in the litter samples.

Influences of evergreen gymnosperm and deciduous angiosperm tree species on the functioning of temperate and boreal forests

It has been recognized for a long time that the overstorey composition of a forest partly determines its biological and physical–chemical functioning. Here, we review evidence of the influence of evergreen gymnosperm (EG) tree species and deciduous angiosperm (DA) tree species on the water balance, physical–chemical soil properties and biogeochemical cycling of carbon and nutrients. We used scientific publications based on experimental designs where all species grew on the same parent material and initial soil, and were similar in stage of stand development, former land use and current management. We present the current state of the art, define knowledge gaps, and briefly discuss how selection of tree species can be used to mitigate pollution or enhance accumulation of stable organic carbon in the soil. The presence of EGs generally induces a lower rate of precipitation input into the soil than DAs, resulting in drier soil conditions and lower water discharge. Soil temperature is generally not different, or slightly lower, under an EG canopy compared to a DA canopy. Chemical properties, such as soil pH, can also be significantly modified by taxonomic groups of tree species. Biomass production is usually similar or lower in DA stands than in stands of EGs. Aboveground production of dead organic matter appears to be of the same order of magnitude between tree species groups growing on the same site. Some DAs induce more rapid decomposition of litter than EGs because of the chemical properties of their tissues, higher soil moisture and favourable conditions for earthworms. Forest floors consequently tend to be thicker in EG forests compared to DA forests. Many factors, such as litter lignin content, influence litter decomposition and it is difficult to identify specific litter‐quality parameters that distinguish litter decomposition rates of EGs from DAs. Although it has been suggested that DAs can result in higher accumulation of soil carbon stocks, evidence from field studies does not show any obvious trend. Further research is required to clarify if accumulation of carbon in soils (i.e. forest floor + mineral soil) is different between the two types of trees. Production of belowground dead organic matter appears to be of similar magnitude in DA and EG forests, and root decomposition rate lower under EGs than DAs. However there are some discrepancies and still are insufficient data about belowground pools and processes that require further research. Relatively larger amounts of nutrients enter the soil–plant biogeochemical cycle under the influence of EGs than DAs, but recycling of nutrients appears to be slightly enhanced by DAs. Understanding the mechanisms underlying forest ecosystem functioning is essential to predicting the consequences of the expected tree species migration under global change. This knowledge can also be used as a mitigation tool regarding carbon sequestration or management of surface waters because the type of tree species affects forest growth, carbon, water and nutrient cycling.

PHENOLIC COMPOUNDS AND TERPENES IN SOIL ORGANIC HORIZON LAYERS UNDER SILVER BIRCH, NORWAY SPRUCE AND SCOTS PINE

The aim of this study was to monitor the concentration of some plant secondary metabolites, such as low- and high-molecular-weight phenolics, condensed tannins (proanthocyanidins), and sesqui-, di- and triterpenes, in litter (L), fermentation (F) and humified (H) layers of the soil organic horizon in stands dominated by silver birch (Betula pendula Roth.), Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.), and from samples taken from birch leaves and spruce and pine needles. Concentrations of low- and high-molecular-weight phenolics and terpenes from the four most dominant species of ground vegetation taken from the stands were also determined. In general, the L layer showed higher concentrations of both phenolic compounds and terpenes than the F and H layers did. Concentrations of terpenes decreased relatively more with soil depth than did concentrations of total phenolics (=low + high) or condensed tannins. Of the total phenolics, the proportion of low-molecular-weight phenolics increased from the L to the H layer with all tree species. Concentrations of all terpenes were highest under pine and lowest under birch. Concentrations of the studied secondary metabolites in the ground vegetation species were similar under different tree species. Blueberry (Vaccinium myrtillus L.) and lingonberry (Vaccinium vitis-idaea L.) contained considerably higher concentrations of total phenolics than did feather moss (Pleurozium schreberi (Brid.) Mitt.) and wavy hair-grass (Deschampsia flexuosa (L.) Trin.). Concentration of total phenolics in soil correlated positively with soil respiration and microbial biomass C, and terpenes showed positive correlation with soil C-to-N ratio.