Impacts of species diversity on root systems

Trees need root systems for anchorage and for water and nutrient uptake. Root systems consist of stumps, coarse roots and fine roots.  Coarse roots have diameter larger than 2 mm, and fine roots less than 2 mm. Stumps and coarse roots are needed for anchorage and transportation of water and nutrients and their lifespan is long. Fine roots are short living and they take up water and nutrients from soil. In most forests there are in addition to trees also other plants growing in understory. Their roots are mostly fine, less than 2 mm in diameter. The tops of trees can reach the height of 10-30m from the soil surface, but the majority of roots in forests grow within 20-30 cm from the soil surface.

In forest ecosystems, the fine roots play a significant role in carbon and nutrient cycling and allocation. Even up to 75% of the carbohydrates produced by forest trees can be allocated below-ground for building and maintaining root systems. Because fine roots are short living they sequestrate significant amounts of carbon into soil. If fine root production and turnover is changed by tree species richness, it has a significant impact on forest ecosystem carbon sequestration.

In FunDivEurope project our objectives were to study the impacts tree species richness on fine roots in forest ecosystems. We determined fine root biomass with the coring method and fine root production with the ingrowth bag method in six countries representing the most common forest types in Europe.

We hypothesised that fine root biomass and production are higher between mixed stands compared to monocultures. That can be the case if there is higher complementary and lower competition between tree species in mixtures. What we found was not what we hypothesised, on the contrary, species richness did not affect fine root biomass or production or tree biomass allocation between roots and shoots.

We also hypothesized that a higher number of tree species results in a more effective utilisation of the soil resources. That can occur if roots fill soil more evenly in mixtures in horizontal and vertical directions than in monoculture. But the depth distribution of root systems in soil was not affected by species richness. However, our results indicated that species identity has an impact on root biomass. We found tree species, like Norway spruce, which are highly competitive in mixtures. Thus the selection of species into mixtures can have an impact on water, carbon and nutrient fluxes in forest ecosystems.

The unconsolidated mineral or organic material on the immediate surface of the earth that serves as the natural medium for the growth of land plant ( SAF dictionary, 2008).
The processes by which elements are extracted from their mineral, aquatic, or atmospheric sources or recycled from their organic forms, converting them to the ionic form in which biotic uptake occurs and ultimately returning them to the atmosphere, water, or soil. (MA 2003). the exchange or transformation of elements among the living (organic and biotic) and nonliving (inorganic and abiotic) components (SAFnet, 2008)
Rate of biomass produced by an ecosystem, generally expressed as biomass produced per unit of time per unit of surface or volume. Net primary productivity is defined as the energy fixed by plants minus their respiration. (MA 2003)
The part of a plant that grows typically underground gets water and nourishment from the ground, sand holds the plant in place. http://www.merriam-webster.com/dictionary/root
Inter-or intraspecific interaction between individuals whereby one or more of the interacting individuals is adversely affected. (Sage Publication, 2014, Volume I pp. 204).
Leena Finér - Root Systems and Species Diversity

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