Heljä-Sisko Helmisaari

Seasonal and yearly variations of fine-root biomass and necromass in a Scots pine (Pinus sylvestris L.) stand

Abstract Seasonal variations of the Scots pine (Pinus sylvestris L.), dwarf shrub and grass fine-root biomass and necromass were studied in a pole stage Scots pine stand in eastern Finland during three successive growing seasons. The biomass of Scots pine fine roots varied annually and seasonally in the humus layer between 19±5 g m−2 to 139±22 g m−2, in the upper mineral soil layer between 90±14 g m−2 to 279±0 g m−2, and in the lower mineral soil layer between 68±17 g m−2 to 217±73 g m−2. The seasonal minimum and maximum of understory vegetation fine-root biomass were in the humus layer 35±6 g m−2 and 235±42 g m−2, in the upper mineral soil layer 26±0 g m−2 and 165±0 g m−2, and in the lower mineral soil layer 14±0 g m−2 and 36±5 g m−2. The seasonal fine-root necromass varied in the humus layer from 2±0 g m−2 to 1398±236 g m−2, in the upper mineral soil layer from 86±0 g m−2 to 1267±366 g m−2, and in the lower mineral soil layer from 8±0 g m−2 to 753±306 g m−2. The major part of the living Scots pine fine roots (62%) was in the mineral soil immediately below the humus layer, but almost all dwarf shrub roots and grass roots were in the humus and in the upper mineral soil layers. Most dead fine roots (82%) were in the humus layer and in the uppermost mineral soil layer. The variations of Scots pine fine-root biomass, dwarf shrub and grass fine-root biomass and necromass did not show a distinct and clear pattern within any growing season although there were significant differences between the same month during different growing seasons. Some of the observed variations could be explained by climatic factors related to drought.

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.

Assessing fine-root biomass and production in a Scots pine stand – comparison of soil core and root ingrowth core methods

Soil core and root ingrowth core methods for assessing fine-root (< 2 mm) biomass and production were compared in a 38-year-old Scots pine (Pinus sylvestris L) stand in eastern Finland. 140 soil cores and 114 ingrowth cores were taken from two mineral soil layers (0–10 cm and 10–30 cm) during 1985–1988. Seasonal changes in root biomass (including both Scots pine and understorey roots) and necromass were used for calculating fine-root production. The Scots pine fine-root biomass averaged annually 143 g/m2 and 217 g/m2 in the upper mineral soil layer, and 118 g/m2 and 66 g/m2 in the lower layer of soil cores and ingrowth cores, respectively. The fine-root necromass averaged annually 601 g/m2 and 311 g/m2 in the upper mineral soil layer, and 196 g/m2 and 159 g/m2 in the lower layer of soil cores and ingrowth cores, respectively. The annual fine-root production in a Scots pine stand in the 30 cm thick mineral soil layer, varied between 370–1630 g/m2 in soil cores and between 210 – 490 g/m2 in ingrowth cores during three years. The annual production calculated for Scots pine fine roots, varied between 330–950 g/m2 in soil cores and between 110 – 610 g/m2 in ingrowth cores. The horizontal and vertical variation in fine-root biomass was smaller in soil cores than in ingrowth cores. Roots in soil cores were in the natural dynamic state, while the roots in the ingrowth cores were still expanding both horizontally and vertically. The annual production of fine-root biomass in the Scots pine stand was less in root ingrowth cores than in soil cores. During the third year, the fine-root biomass production of Scots pine, when calculated by the ingrowth core method, was similar to that calculated by the soil core method. Both techniques have sources of error. In this research the sampling interval in the soil core method was 6–8 weeks, and thus root growth and death between sampling dates could not be accurately estimated. In the ingrowth core method, fine roots were still growing into the mesh bags. In Finnish conditions, after more than three growing seasons, roots in the ingrowth cores can be compared with those in the surrounding soil. The soil core method can be used for studying both the annual and seasonal biomass variations. For estimation of production, sampling should be done at short intervals. The ingrowth core method is more suitable for estimating the potential of annual fine-root production between different site types.

Temporal variation in nutrient concentrations of Pinus sylvestris needles

Temporal variation in nutrient concentrations of Scots pine (Pinus sylvestris L.) needles was studied during a three‐year period in three stands of differing stages of development. Concentrations of N, P and K varied significantly between years; this variation was related to differences in needle dry weight. Concentrations of all measured nutrients (N, P, K, Ca, Mg, Mn, Cu, Zn, Fe, B) and Al varied between seasons; this variation was related to nutrient mobility and the annual physiological cycle. Concentrations of the mobile nutrients N, P and K decreased in spring and early summer during shoot and needle elongation and increased in late summer and autumn during needle senescence and litterfall. Concentrations of Mg, Cu, Zn and B followed somewhat similar patterns. The poorly mobile nutrients Ca, Mn and Fe accumulated gradually in needles during each growing season. Needle nutrient concentrations were stable during the nonactive period.

Nutrient cycling in Pinus sylvestris stands in eastern Finland

Nutrient cycling within three Pinus sylvestris stands was studied in eastern Finland. The aim of the study was to determine annual fluxes and distribution of N, P, K, Ca, Mg, Mn, Zn, Fe, B, and Al in the research stands. Special emphasis was put on determining the importance of different fluxes, especially the internal cycle within the trees in satisfying the tree nutrient requirements for biomass production. The following nutrient fluxes were included, input; free precipitation and throughfall, output; percolation through soil profile, biological cycle; nutrient uptake from soil, retranslocation within trees, return to soil in litterfall, release by litter decomposition. The distribution of nutrients was determined in above- and belowground tree compartments, in ground and field vegetation, and in soil.

Fine-root biomass and necromass in limed and fertilized Norway spruce (Picea abies (L.) Karst.) stands

Abstract Fine-root biomass, biomass production and necromass were studied using soil cores and ingrowth cores in Finland and Sweden in four Picea abies stands repeatedly limed and fertilized with N, and PK separately and in combination. The fine-root biomass was smaller than control, though not always significantly, in those plots that had received lime (Ca, NCa, PKCa) or PK alone. These plots also had a large fine-root necromass. The lower fine-root biomass values in the PK-, Ca-, PKCa- and NCa-plots may have been caused by smaller fine-root production and greater mortality since in these plots the ingrowth of fine roots was also the smallest, and the proportion of dead fine roots in the soil cores and in the ingrowth cores highest. The negative effect of fertilizers with lime or PK alone, and PKCa on the stem volume growth may be related to the smaller fine-root biomass and, especially, fine root growth. Those plots that had received nitrogen alone, or together with PK had similar or larger fine-root biomass than control, except in the Heinola experiment which was situated on a fertile soil type in southern Finland. The larger biomass values were caused by higher fine-root production since the ingrowth of fine roots was also greatest in these plots. The results suggest that the differences in the above-ground growth between stands of varying nutritional treatment on the same site may be related to the correspondent differences in the fine-root biomass, and especially, fine-root growth.

Nutrient retranslocation in three Pinus sylvestris stands

Abstract Retraslocation of N, P, K, Ca, Mg, Mn, Zn, Fe, B and Al from senescing needles of Scots pine (Pinus sylvestris L.) was studied in control and fertilized stands of three different ages (sapling stand, pole stage stand and mature stand: 15 years old 35 years old and 100 years old, respectively) in eastern Finland during 1983–1987. The two oldest stands had parallel research plots, one of which, in each stand, was fertilized with ammonium nitrate (nitrogen 150 kg ha−1). Between 70 and 85% of the contents of nitrogen, phosphorus and potassium and between 30 and 60% of magnesium was retranslocated from senescing needles. There were no significant (P Retranslocation supplied 30–50% of nitrogen 23–37% of phosphorus, 17–31% of potassium and 7–20% of magnesium required for annual biomass production. There were no significant differences between stands or between unfertilized and fertilized plots in the retranslocation importance. However, in the pole stage stand, retranslocation supplied each year 13–34% less of the nitrogen requirements in the fertilized plot than in the unfertilized plot.

Acidity and nutrient content of throughfall and soil leachate in three Pinus sylvestris stands

The quantity and quality of throughfall and soil leachate were measured in 1983–1985 in three Scots pine stands of different age situated in Ilomantsi, eastern Finland. Soil leachate was collected using percolation lysimeters. Free precipitation pH varied from 4.0 to 5.2. Throughfall was more acidic than free precipitation. The closed canopy layer intercepted about 70% of the free precipitation. The canopy acted as a sink for nitrate and ammonium, and as a source for Mn, K, Mg and Ca. The quality of the throughfall and soil leachate varied seasonally. The hydrogen ion input into the soil was greatest at snow melt. The major part of the nitrogen load was deposited during winter. Part of the winter‐time nitrate load was leached through the surface soil. However, during the growing season all the nitrogen was efficiently taken up or immobilized. Basic cations K, Ca and Mg, as well as Mn, Fe and Al, were leached from the upper soil layers. Manganese was leached especially at snow melt. The output of magnesium...

Optimal co‐allocation of carbon and nitrogen in a forest stand at steady state

Nitrogen (N) is essential for plant production, but N uptake imposes carbon (C) costs through maintenance respiration and fine-root construction, suggesting that an optimal C:N balance can be found. Previous studies have elaborated this optimum under exponential growth; work on closed canopies has focused on foliage only. Here, the optimal co-allocation of C and N to foliage, fine roots and live wood is examined in a closed forest stand. Optimal co-allocation maximizes net primary productivity (NPP) as constrained by stand-level C and N balances and the pipe model. Photosynthesis and maintenance respiration increase with foliar nitrogen concentration ([N]), and stand-level photosynthesis and N uptake saturate at high foliage and fine-root density. Optimal NPP increases almost linearly from low to moderate N availability, saturating at high N. Where N availability is very low or very high, the system resembles a functional balance with a steady foliage [N]; in between, [N] increases with N availability. Carbon allocation to fine roots decreases, allocation to wood increases, and allocation to foliage remains stable with increasing N availability. The predicted relationships between biomass density and foliage [N] are in reasonable agreement with data from coniferous stands across Finland. All predictions agree with our qualitative understanding of N effects on growth.

Compensatory fertilization of Scots pine stands polluted by heavy metals

The results from four compensatory fertilization experiments located at different distances (0.5, 2, 4 and 8 km) along a heavy metal deposition gradient extending from the Harjavalta Cu-Ni smelter in SW Finland are presented. The experiments were established in middle-age Scots pine stands growing on dryish sites of sorted glaciofluvial sediments. The soil type in all the experiments is ferric podsol. The treatments in the experiments consisted of liming, a powdered slow-release mineral mixture and stand-specific fertilization which comprised at least methylene urea and ammonium nitrate.Monitoring of deposition and soil solution and studies on soil chemical and microbiological properties, on the nutrient status of trees and needle litterfall, on fine root dynamics and on the growth of the tree stands were carried out during a 5-year period.There was a severe shortage of exchangeable Ca and Mg in the organic layer of the most polluted stands. Although the uppermost mineral soil layer had relatively high exchangeable Ca and Mg concentrations, the trees were not able to utilize these nutrient reserves presumably due to the toxic effects of Cu and Ni on the plant roots and mycorrhizas.The treatments that included limestone markedly decreased the Cu and Ni concentrations in the soil solution and soil organic layer, presumably due to immobilisation through precipitation or absorption. The Ca and Mg concentrations correspondingly increased, which certainly contributed to the partial recovery of fine root and stand growth. The powdered mineral mixture and the combination of methylene urea and ammonium nitrate had no short-term effect on the microbial biomass and activity. All the fertilizer treatments increased volume growth in the most polluted stand. The stand-specific fertilization increased needle mass in heavily polluted stands, but the response of the needle mass to fertilizer treatments was low in the less polluted stands. No clear evidence was found to support the role of nutrient status in tree resistance.