Litter effects of two co‐occurring alpine species on plant growth, microbial activity and immobilization of nitrogen

Abstract

Litter effects of two co-occurring alpine species on plant growth, microbial activity and immobilization of nitrogen. -Oikos 104: 336-344.We measured the litter chemistry of two co-dominant alpine species, Acomastylis rossii, a forb characterized by a low growth rate and N uptake capacity, and Deschampsia caespitosa, a grass characterized by a high growth rate and N uptake capacity, and examined the effect litter of these two species had on the growth of Deschampsia phytometers in a greenhouse. We also examined the influence of litter from the two species on microbial respiration and immobilization of N, in two separate laboratory microcosm experiments and in the field. We hypothesized that Acomastylis litter would reduce plant growth more than Deschampsia litter, corresponding with either 1) suppression of microbial activity and thus a decrease in N mineralization, or 2) by stimulation of microbial biomass and increasing microbial immobilization of N. Relative to Deschampsia litter, Acomastylis litter had higher total water soluble organic carbon (DOC), and higher total phenolic concentration. Deschampsia litter had 30 times higher carbohydrate (primarily glucose and fructose) concentrations than Acomastylis litter. Soil respiration, microbial biomass N, and consumption of DOC and N were higher with the Acomastylis litter treatment than the Deschampsia litter treatment in experimental microcosms, and both respiration and microbial biomass N were higher in field soils under canopies dominated by Acomastylis relative to those dominated by Deschampsia. These results indicate that phenolics in Acomastylis are a C source for soil microorganisms, rather than an inhibitor of microbial activity. Deschampsia phytometers grew significantly less, had higher root: shoot biomass ratios, and acquired less nitrogen in the Acomastylis litter treatment relative to the control and Deschampsia litter treatments. The results of these experiments indicate that Acomastylis litter influences soil N cycling by increasing microbial activity and N immobilization, which may influence N supply to neighboring plants. This mechanism has the potential to influence competitive interactions between Acomastylis and its neighbors.

Effects of litters with different concentrations of phenolics on the competition between Calluna vulgaris and Deschampsia flexuosa

“…1), D. flexuosa was not inhibited by the presence of C. vulgaris plants. We had expected that the high concentration of phenolics in C. vulgaris litter would lead to reduced nitrogen mineralization (Kraus et al 2003;Bowman et al 2004), subsequently inhibiting the growth of grass plants on shrub litters compared with the treatments without litter amendment. However, we found no such growth inhibition of the grass plants in the shrub litter treatments although they produced less biomass compared to grass plants in the grass litter treatments.…”

Phytotoxicity, not nitrogen immobilization, explains plant litter inhibitory effects: evidence from solid‐state 13C NMR spectroscopy

“…plant extracts or glucose) to the soil can have negative effects on plant and root growth through immobilization of the available nutrients (Schmidt et al, 1997;Michelsen et al, 1999;Bowman et al, 2004). Further studies are required to determine the relative importance of phytotoxicity and nutrient immobilization during decomposition of leaf litter in plant-soil systems.…”

Phenolic Control of Plant Nitrogen Acquisition through the Inhibition of Soil Microbial Decomposition Processes: A Plant-Microbe Competition Model

“…In terms of these points, our model is consistent with that of Schimel and Weintraub (34). The dynamics of monomers (M) are represented by = (depolymerization)−(uptake by plants)− (uptake by microbes) [3] where the first term represents the increase due to depolymerization from the debris (D) pool, and the second and third terms represent decreases through uptake by both plants (P) and soil microbes (S), respectively. Uptake by microbes is assumed to decrease with phenolics (f), and uS represents the maximum uptake rate in the absence of negative effects of phenolics (i.e., f=0).…”