Heljä-sisko Helmisaari - Academia.edu (original) (raw)

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Papers by Heljä-sisko Helmisaari

Trends in Ecology & Evolution, 2020

Plant growth is usually constrained by the availability of nutrients, water, or temperature, rath... more Plant growth is usually constrained by the availability of nutrients, water, or temperature, rather than photosynthetic carbon (C) fixation. Under these conditions leaf growth is curtailed more than C fixation, and the surplus photosynthates are exported from the leaf. In plants limited by nitrogen (N) or phosphorus (P), photosynthates are converted into sugars and secondary metabolites. Some surplus C is translocated to roots and released as root exudates or transferred to root-associated microorganisms. Surplus C is also produced under low moisture availability, low temperature, and high atmospheric CO 2 concentrations, with similar below-ground effects. Many interactions among above-and belowground ecosystem components can be parsimoniously explained by the production, distribution, and release of surplus C under conditions that limit plant growth. What Drives Carbon Allocation in Plants? Highlights Plant growth is normally constrained by nutrients, water or temperature, not photosynthesis, and plants often have surplus carbohydrates. Secondary metabolites are produced in N-limited plants primarily to dispose of surplus carbon, although they may subsequently help reduce browsing damage. Surplus carbohydrates are translocated from leaves and below ground some are discharged via exudates and mycorrhizal fungi. Root exudates contain more of the elements that plants have in surplus, and less of those in short supply. The abundance and type of mycorrhizal fungi is influenced by the amount and composition of surplus carbon in roots. Surplus carbon provides an alternative lens though which to view interactions between plants and soil organisms.

Forest Ecology and Management, 2019

Roots and rhizospheres in forest ecosystems: Recent advances and future challenges ☆ ☆ This artic... more Roots and rhizospheres in forest ecosystems: Recent advances and future challenges ☆ ☆ This article is part of the Special Issue "Roots and Rhizospheres in Forest Ecosystems: Recent Advances and Future Challenges" published at the journal Forest Ecology and Management 431, 2018.

Julkaisussa: Mälkönen, E. …, 1994

Water, Air, & Soil Pollution, 1995

Distribution and fluxes of copper within Pinus sylvestris stands were studied during 1992-1994 al... more Distribution and fluxes of copper within Pinus sylvestris stands were studied during 1992-1994 along a heavy-metal pollution gradient in southwestern Finland. The stands are situated at distances of 0.5, 4 and 8 km from a copper-nickel smelter that started operating in 1945 at Hmjavalta. According to the results, copper concentrations in the soil, in the understorey vegetation and in the trees increased steeply towards the smelter. Almost 50 years' accumulation of heavy metals in the soil has caused direct toxic effects to soil microbes, thus decreasing decomposition and nutrient mineralisation. During the past few years, sulphur and heavy metal emissions from the copper and nickel smelter have been radically decreased. Ilowever, the heavy metals which have been accumulating in the soil for decades continue to affect the vegetation for a I(mg time through soil processes. Consequently, long term accumulation in the soil has to be taken into account when determining the critical loads of forest ecosystems for heavy metals.

University of Nova Gorica, Slovenia, 2010

Technical University of Crete, 2008