Metla Project 3262

Nitrogen dynamics in peat and the effect of nitrogen on tree growth

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Duration: 1999-2003   Keywords: microbes, mycorrhiza, nutrients, peat nitrogen, tree growth
Research Programme: Ecologically and economically sustainable forestry on drained peatlands

Objectives

The objectives of the study are to determine
  1. soluble nitrogen compounds in peat which are available for tree nutrition and how do they vary according to the total N content of peat and fluctuate during the growing season in different temperature sums on drained peatland forests.
  2. What kind of variables in peat soil (characterization of organic components and microbial activity) are good indicators to predict tree growth.
  3. The effect of the nitrogen content of peat on the microbial activity in different temperature sums.
  4. Does the total nitrogen content of the peat affect mycorrhizal infection of the Scots pine roots? The effect of mycorrhizal fungi on the utilization of organic pool of nitrogen in peat by the trees.
  5. The effect of physical and chemical characteristics of peat on nitrogen mineralization and utilization of inorganic and organic nitrogen sources in different temperature sums.
  6. The limit values of nitrogen concentration and other characteristics in peat for adequate nitrogen supply and satisfactory growth of trees.
  7. The aim is also to create an improved classification method of drained peatland forest sites for forest improvement actions.


Results

Peat properties and ground vegetation along different trophic levels on an afforested mire and the effect of fertilization was studied (Hartman, Kaunisto & Silfverberg 2001). The concentrations of nitrogen, phosphorus and iron in peat were in close positive correlation and also with the proportion of the Carex peat component. This implies that the potentially best sites (high N) for growing trees were the least susceptible to leaching of fertiliser phosphorus (high Fe). The occurrence of forest mosses increased with the increasing total nitrogen concentration of peat indicating that the development of peatland sites from pristine to the transformed stage had occurred faster on the nitrogen-rich, Carex-dominated sites than on the nitrogen-poor sites.

Effect of fertilization and peat nitrogen status on the nutrition and growth of Scots pine (Pinus sylvestris L.) was investigated (Kaunisto & Pietiläinen 2002, manuscript). Ammonium is the major inorganic form of nitrogen in the most superficial 0-5 cm peat layer. The ammonium and total nitrogen concentrations as well as the C/N ratio of the surface 0-5 cm peat layer explain the nitrogen nutrition of trees better than nitrogen in deeper peat layers. Stand growth is explained quite equally by the peat total nitrogen and iron concentrations and the C/N ratio by both 0-5, 5-10 cm surface peat layers and they can be used quite reliably for estimating tree growth.

Wood production capacity on drained peatlands depends on the site type and temperature sum. Site type is closely related to the peat total nitrogen concentration. This study aims at clarifying nitrogen nutrition of Scots pine in different peat total nitrogen and air temperature sum conditions (Pietiläinen & Kaunisto 2002, manuscript). Three fertilized and refertilized pine-growing mires in the temperature sum regions of 850, 950 and 1080 d.d. with a wide peat nitrogen gradient in each site were selected for the study. The nutrient deficiencies that appeared after the basic fertilization were cured after the refertilization. The mean foliar phosphorus and potassium contents of the needles were significantly lower in the coldest area than in the warmest area. In the coldest region, 26 years after the refertilization, the pine stands suffered from a severe nitrogen deficiency (N = 1.12 %) and in the warmest region, 15 years after the refertilization the mean nitrogen content was 1,54 %. Regardless of the peat total nitrogen concentrations in the top 10 cm layer the needle nitrogen concentrations in the coldest temperature sum region were below the severe deficiency limit (N = 1.2 %) and PK-fertilization would not be profitable, even 26 years after the basic fertilization, because of the nitrogen deficiency. In the region of 950 d.d. the mean peat total nitrogen content was 1.45 % when the foliar nitrogen content was over the slight deficiency level (N = 1.30 %) and in the region of 1080 d.d. the total peat nitrogen was correspondingly1.31%. In the temperature sum regions of 950 and 1080 d.d. the pine stands surpassing the above mentioned peat total nitrogen border values can benefit from PK fertilisation.

Fluctuation in the concentrations of soluble nitrogen compounds was followed during the growing seasons 1999 and 2000 in pine stand on drained peatland forest (Potila & sarjala 2002 manuscript). A gradient in the total nitrogen content of peat was from 1.2 to 2.7 % on the experimental plots of the area. Correlations between the total N in peat and DON (dissolved organic nitrogen) were negative whereas ammonium correlated positively with the total N in peat at the beginning of the growing season. The proportion of ammonium of the total dissolved N varied between 20-60 %. Microbial biomass and ergosterol were found to depend on the nitrogen content of the peat. The relationship between total N in peat, temperature sum and peat organic components was studied in controlled conditions. Growth chambers were programmed to run different temperature sums in peat (> 0 °C) (749d.d.-1309d.d. at the end of the experiment). Proportion of DON from the total dissolved nitrogen was found to be dominant especially under low nitrogen level and low temperature sum. This emphasizes the role of mycorrhiza in the uptake of nitrogen by Scots pine. Organic components in peat were identified (Karsisto, Hartman, Potila & Sarjala 2002, manuscript): 15 free amino acids, 8 phenolic, 9 fatty acids, 3 resin acids and 4 sterols. The data revealed that concentrations of the resin acids were affected more by the temperature sum than by the peat. Both the temperature sum and the peat affected significantly the phenolic acids and sterols, whereas the amino acids were affected only by the peat. Significant differences in fatty acids were found both between the peats and the temperature sums. Experiments are being carried out on the effect of some mycorrhizal fungi on growth and N uptake of Scots pine seedlings on different types of natural non-sterile peat taken from drained peatland forest. According to preliminary studies Suillus variegatus enhanced most the growth and N uptake of the pine seedlings (Sarjala unpublished).

Project leader: Sarjala, Tytti
The Finnish Forest Research Institute, Parkano Office, Kaironiementie 15, FI-39700 PARKANO, FINLAND
Phone: +358 29 532 4064
E-mail: tytti.sarjala@metla.fi

Other researchers: Hartman, Markus, VA (2000-03), Jokela, Anne, PA (2003-04), Karsisto, Marjut, VA (1999-2003), Kaunisto, Seppo (1999,2001-2002), Koskela, Merja-Leena, ES (2000), Niemi, Karoliina (2002-03), Pietiläinen, Pekka, MU (1999-2003), Potila, Hannamaria, PA (1999-2003), Silfverberg, Klaus, VA (1999-2001), Vuosku, Jaana, PA (2002-04)


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Updated 12.06.2012
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