Tree species impact the terrestrial cycle of silicon through various uptakes

Abstract

The quantification of silicon (Si) uptake by tree species is a mandatory step to study the role of forest vegetations in the global cycle of Si. Forest tree species can impact the hydrological output of dissolved Si (DSi) through root induced weathering of silicates but also through Si uptake and restitution via litterfall. Here, monospecific stands of Douglas fir, Norway spruce, Black pine, European beech and oak established in identical soil and climate conditions were used to quantify Si uptake, immobilization and restitution. We measured the Si contents in various compartments of the soil-tree system and we further studied the impact of the recycling of Si by forest trees on the DSi pool. Si is mainly accumulated in leaves and needles in comparison with other tree compartments (branches, stembark and stemwood). The immobilization of Si in tree biomass represents less than 15% of the total Si uptake. Annual Si uptake by oak and European beech stands is 18.5 and 23.3 kg ha -1 year -1 , respectively. Black pine has a very low annual Si uptake (2.3 kg ha -1 year -1 ) in comparison with Douglas fir (30.6 kg ha -1 year -1 ) and Norway spruce (43.5 kg ha -1 year -1 ). The recycling of Si by forest trees plays a major role in the continental Si cycle since tree species greatly influence the uptake and restitution of Si. Moreover, we remark that the annual tree uptake is negatively correlated with the annual DSi output at 60 cm depth. The land-ocean fluxes of DSi are certainly influenced by geochemical processes such as weathering of primary minerals and formation of secondary minerals but also by biological processes such as root uptake.

Historical land use change has lowered terrestrial silica mobilization

“…Developing forests form net sinks for DSi: unfortunately, at present, little or no research exists that addresses Si dynamics in developing forests. An equilibrium state will eventually be reached: this stage is characterized by a large, slowly growing soil ASi stock 15 . The forest vegetation stimulates bedrock weathering of silicates through increases in soil CO 2 content, production of organic acids and stabilization of organic soil cover 16,17 .…”

Experimental Evidence of Large Changes in Terrestrial Chlorine Cycling Following Altered Tree Species Composition

“…Triplicate samples of litterfall and ligneous parts of standing biomass (stem, bark, and branches), 31 as well as samples of bulk humus layer soil (eight replicates per stand) and mineral soil (triplicate soil profiles, n = 6 per profile) collected in 2005, and yearly samples of living foliage (2002−2006; five replicates per stand), were analyzed as described below. The tree biomass and litterfall were estimated according to ref 31. We also had access to data on the Cl − content in atmospheric deposition, throughfall and stemflow for the same period.…”

“…Throughfall was collected every month by double gutters (three replicates per forest stand). 31 Stemflow was collected by means of plastic collars attached to the trunks of 10 trees per stand selected to represent different growth classes. The Cl − concentrations were analyzed using ion chromatography (MIC-2, Metrohm).…”

Silicon uptake by wheat: Effects of Si pools and pH

“…Two obstacles occur for comparison of Si-uptake rates from the present study with literature: First, in field studies Si uptake of plants is often referred to area instead of plant biomass (e.g., Cornelis et al, 2010). Second, Si uptake of plants, measured either in plant biomass or by monotoring Si concentration in the culture solution, is usually related on dry weight of root biomass (e.g., Tamei and Ma, 2003), while in the present study, rates were calculated using total biomass within each individual plant pot (see Eq.…”

“…This was already shown for grasses (Fraysse et al, 2006) and forest soils. Comparing Si-uptake rates of different tree species, Cornelis et al (2010) pointed out the important role of biogenic Si and its recycling for the global Si cycle.…”