Nitrogen Limitation of Production and Decomposition in Prairie, Mountain Meadow, and Pine Forest

Abstract

The responses of decomposition and primary production to nitrogen supply were investigated in a shortgrass prairie, a mountain meadow, and a lodgepole pine forest. Nitrogen (N) supply was increased by applying ammonium nitrate, or decreased by applying sucrose. The litterbag technique was used to follow decomposition ofleaves of the dominant plants: blue grama (Bouteloua gracilis) from the prairie, western wheatgrass (Agropyron smithii) from the meadow, and lodgepole pine (Pinus contorta) from the forest.Soil from beneath the litterbags was sampled at the time of litterbag retrieval in order to detect interactions between decomposition and properties of the underlying soil. There was no consistent effect of soil properties on decomposition rate, but there was a significant effect of litter type on N mineralization in the underlying soil.Decomposition was fastest in the forest, intermediate in the prairie, and slowest in the meadow. Blue grama decomposed faster than the other litters. Each litter type decomposed faster than expected when placed in its ecosystem of origin. This interaction suggests that decomposers in an ecosystem are adapted to the most prevalent types of litter.Nitrogen supply had a small but significant effect on decomposition rate. Within an ecosystem, there was a positive association between decomposition and accumulation of N within the litter, but this relationship was 'reversed when comparing across ecosystems, possibly because of the overriding effects of differences among ecosystems in abiotic factors.Aboveground net primary production was estimated in the grasslands by a single harvest at the end of the growing season, and growth increment of boles was measured in the forest. These indices of primary production showed a greater relative response to N fertilization than did decomposition, suggesting that primary production is the more N-limited process.

The effect of resource history on the functioning of soil microbial communities is maintained across time

“…1), suggesting "home-field advantage" (Gholz et al, 2000;Hunt et al, 1988). Our study design further demonstrates this "homefield advantage" phenomenon (Gholz et al, 2000;Hunt et al, 1988) for the first time through the generation of experimental resource histories. These gains in function are consistent with the expected properties of microbial communities -fast growth rates, physiological flexibility and rapid evolutionthat enable them to respond rapidly to new conditions (Allison and Martiny, 2008).…”

“…Interestingly, the soil inoculum sourced from the hardwood environment (inoculum B) had the greatest initial litter mineralization ( Fig. 1), suggesting "home-field advantage" (Gholz et al, 2000;Hunt et al, 1988). Our study design further demonstrates this "homefield advantage" phenomenon (Gholz et al, 2000;Hunt et al, 1988) for the first time through the generation of experimental resource histories.…”

Relationship of host recurrence in fungi to rates of tropical leaf decomposition

“…Evidence from some reciprocal leaf decomposition experiments have shown faster decomposition in leaf litter placed in the community of origin rather than in another plant community, suggesting that some detrital communities may be adapted to breaking down particular types of substrata. This pattern is referred as 'home-court advantage', and has been found for low-quality leaf litter in forest plantations in Brazil (De Asiss Olivereira et al, 1998) and for some temperate pine and aspen forests (Hunt et al, 1998;González et al, 2003). In our study, microfungal decomposers showed faster decomposition of their own substratum or substrata that were related or similar to their source leaves as compared to unrelated and dissimilar substrata.…”

Despite strong seasonal responses, soil microbial consortia are more resilient to long-term changes in rainfall than overlying grassland

“…In contrast, soil bacterial and archaeal communities remained statistically indistinguishable among treatments after 5 years and through most of the 2-year sampling period that followed (Figure 2a). Research has shown that many characteristics of a plant assemblage-composition (Hunt et al, 1988;Bardgett et al, 1999;Smalla et al, 2001;Wieland et al, 2001;Nunan et al, 2003;Ayres et al, 2006), diversity (Gruter et al, 2006) and production (Zak et al, 2003)-can affect the microbial composition of underlying soils. Any snapshot measurement in our experiment might have affirmed this idea for our grassland system as well, but analyzing across seasons we find a soil community characterized by marked seasonal dynamics and longer-term decoupling from aboveground change.…”