Mineral nutrient economy in competing species of Sphagnum mosses

Abstract

Bog vegetation, which is dominated by Sphagnum mosses, depends exclusively on aerial deposition of mineral nutrients. We studied how the main mineral nutrients are distributed between intracellular and extracellular exchangeable fractions and along the vertical physiological gradient of shoot age in seven Sphagnum species occupying contrasting bog microhabitats. While the Sphagnum exchangeable cation content decreased generally in the order Ca 2+ ‡ K + , Na + , Mg 2+ > Al 3+ > NH 4 + , intracellular element content decreased in the order N > K > Na, Mg, P, Ca, Al. Calcium occurred mainly in the exchangeable form while Mg, Na and particularly K, Al and N occurred inside cells. Hummock species with a higher cation exchange capacity (CEC) accumulated more exchangeable Ca 2+ , while the hollow species with a lower CEC accumulated more exchangeable Na + , particularly in dead shoot segments. Intracellular N and P, but not metallic elements, were consistently lower in dead shoot segments, indicating the possibility of N and P reutilization from senescing segments. The greatest variation in tissue nutrient content and distribution was between species from contrasting microhabitats. The greatest variation within microhabitats was between the dissimilar species S. angustifolium and S. magellanicum. The latter species had the intracellular N content about 40% lower than other species, including even this species when grown alone. This indicates unequal competition for N, which can lead to outcompeting of S. magellanicum from mixed patches. We assume that efficient cation exchange enables Sphagnum vegetation to retain immediately the cationic nutrients from rainwater. This may represent an important mechanism of temporal extension of mineral nutrient availability to subsequent slow intracellular nutrient uptake.

Biochemical determinants of litter quality in 15 species of Sphagnum

“…The desiccation avoidance strategy is possible only when the cell walls are strong enough to prevent collapse of the large capillary spaces as discussed above. (2) Low nutrient availability in rainfed hummocks can be partly compensated by the greater CEC of hummock-forming sphagna provided by sphagnan (consistent with Clymo (1963);Painter (2003); Hájek and Adamec (2009)) as the cationic nutrients from atmospheric deposition can be retained on the cation-exchange sites before assimilation. Although CEC can be considered a measure of sphagnan, their correlation was not as high as expected, obviously due to the non-exhaustive sphagnan isolation.…”

Seasonal Net Ecosystem Carbon Exchange of a Regenerating Cutaway Bog: How Long Does it Take to Restore the C‐Sequestration Function?

“…A lower Sphagnum NPP may be caused by the higher biomass of vascular plants in the later regeneration stages, causing shading (Berendse et al 2001). Another possible cause is a change in species composition: early stages were dominated by the more minerotrophic species Sphagnum fallax , while other ombrotrophic species such as Sphagnum magellanicum , Sphagnum rubellum , and Sphagnum fuscum also occurred locally in site C. These changes in species composition also suggest a decrease in nutrient availability from site A to site C (Hajek & Adamec 2009; Grosvernier et al 1997).…”

Long-term vegetation changes in bogs exposed to high atmospheric deposition, aerial liming and climate fluctuation

“…Limpens & Berendse (2003) have demonstrated growth reduction of S. magellanicum subjected to high N deposition. In addition, Hájek & Adamec (2009) found that intracellular N content was about 40% lower in S. magellanicum than in the competing species S. angustifolium . The results indicate unequal competition for N, which can lead to out‐competing of S. magellanicum from mixed patches.…”