Dynamic of Boron in Forest Ecosystems Traced by its Stable Isotopes: A Modeling Approach
Abstract
Boron is an essential micronutrient for the growth of plants and its biogeochemical cycle appears to be strongly impacted by vegetation recycling. For instance, fluxes associated to vegetation cycling 5 to 10 times greater than the total B supply have been reported for two ecosystems developed under tropical and temperate climates (1). As for other nutrients, the distribution and seasonal variations of B among and in different pools of an ecosystem are probably influenced by biotic processes but the connection between plant demand, boron cycling and responses to external forcing remain to be established.In this regard, B stable isotopes can be used effectively to trace processes which transfer matter to or out and from one compartment to another in an ecosystem as they are potentially fractionated during B uptake by roots and strong evidences exist that intra-plant B isotopic fractionations exist.
Here we explore through a modeling approach the B isotopic signatures of different pools in terrestrial ecosystems and how the impacts on boron cycling by external forcing are reflected in the changes of its isotopic compositions across the ecosystems. To model the effect of vegetation recycling, we defined a boron plant demand and included an active uptake when the plant demand was not fulfill by passive uptake. We ascribed B isotopic fractionations to the active uptake of boron and during B transport within the plant. The model predicts a progressive boron enrichment in the soil solution of the upper soil layer along with the increase of boron cycling by vegetation in agreement with the general observation that limiting nutrients accumulate in the top soil through litter decay and throughfall. Concomitantly, the difference between the B isotopic composition of the upper layer soil solution and the inputs follows that of the vegetation pools and shows an increase with B recycling by vegetation. Finally, we examined the pattern of B isotopic compositions of soil solutions and by extension those of streams or rivers, as a signature of biotic demand in terrestrial ecosystems under different climatic or anthropogenic forcing. (1) Gaillardet and Lemarchand, Advance in Isotope Geochemistry, 2018. Work supported by the NNSFC grants No 41473023 and U1612442- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H41Q1981C
- Keywords:
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- 1041 Stable isotope geochemistry;
- GEOCHEMISTRY;
- 1813 Eco-hydrology;
- HYDROLOGY