N-transfer through aspen litter and feather moss layers after fertilization with ammonium nitrate and urea

Abstract

When fertilizer is broadcast in boreal forest stands, the applied nutrients must pass through a thick layer of either feather moss or leaf litter which covers the forest floor. In a growth chamber experiment we tested the transfer of N through living feather moss or aspen litter when fertilized with urea ((NH 2 ) 2 CO) or NH 4 NO 3 at a rate of 100 kg ha −1 and under different watering regimes. When these organic substrates were frequently watered to excess they allowed the highest transfer of nutrients through, although 72% of the applied fertilizer was captured in the substrates. In a field experiment we also fertilized moss and aspen litter with urea ((NH 2 ) 2 CO) or NH 4 NO 3 at a more operationally relevant rate of 330 kg ha −1 . We captured the NO 3 − or NH 4 + by ion exchange resin at the substrate-mineral soil interface. In contrast to the growth chamber experiment, this fertilizer rate killed the moss and there was no detectable increase in nutrient levels in the aspen litter or feather moss layers. Instead, the urea was more likely transferred into the mineral soil; mineral soil of the urea treatment had 1.6 times as much extractable N compared to the NH 4 NO 3 treatment. This difference between the growth chamber and field studies was attributed to observed fertilizerdamage to the living moss and possibly damage to the litter microflora due to the higher rate of fertilization in the field. In addition, the early and substantial rainfall after fertilization in the field experiment produced conditions for rapid leaching of N through the organic layers into the mineral soil. In the field, only 8% of the urea-N that was applied was captured by the ion exchange resin, while 34% was captured in for the NH 4 NO 3 fertilization. Thus, the conditions for rapid leaching in the field moved much of the N in the form of urea through the organic layers and into the mineral soil before it was hydrolyzed.

Bryophytes attenuate anthropogenic nitrogen inputs in boreal forests

“…However, the total bryophyte effect (decreased N‐fixation plus sequestration of N into tissues) does not account for enough N capital to fully explain the high δ 15 N response threshold at which P. sylvestris and soil N availability and mineralization rates changed (Tables 1 and 2). Other important processes, such as sequestration of N into humic substances (Nadelhoffer et al , 1999), N volatilization (Startsev et al , 2008), N leaching (Akselsson & Westling, 2005), and N uptake by shrubs (Nilsson & Wardle, 2005; Nordin et al , 2006) may limit the availability of anthropogenic N r to trees when the bryophyte layer becomes N saturated.…”

Influences of evergreen gymnosperm and deciduous angiosperm tree species on the functioning of temperate and boreal forests

“…Conversely, air humidity may be higher in some EG stands than in DA stands (Nihlgård, 1969) providing favourable growing conditions for mosses (Frisvoll & Presto, 1997). Almost all absorbed water, and the majority of absorbed nutrients, are provided by direct precipitation or forest throughfall; only the very top of the soil is exploited (Anderson & Bourdeau, 1955;Binkley & Graham, 1981;Weber & Van Cleve, 1984;Startsev et al, 2008). A thick moss layer may not be observed in some EG forests, such as frequently thinned stands.…”

“…Because mosses have no root (only short rhizoids), no or limited cuticle, and very high SLA, they rely mainly on atmospheric inputs for their water and nutrient supply. Almost all absorbed water, and the majority of absorbed nutrients, are provided by direct precipitation or forest throughfall; only the very top of the soil is exploited (Anderson & Bourdeau, 1955;Binkley & Graham, 1981;Weber & Van Cleve, 1984;Startsev et al, 2008). Moss may thus act as an intercepting layer for water and nutrients, reducing their movement and recycling.…”

Moss-cyanobacteria associations as biogenic sources of nitrogen in boreal forest ecosystems

“…Assuming the fixed N 2 is transferred to the soil, questions about the amount, extent and rates of the transferred N emerge. Several studies have shown that mosses represent a short-term (<1 year) N-sink due to efficient capturing and retaining of N from the atmosphere (Startsev and Lieffers, 2006; Startsev et al, 2008; Friedrich et al, 2011). However, mosses can turn into a long-term (>1 year) N source after disturbances like drying-rewetting and fire events (Carleton and Read, 1991; Wilson and Coxson, 1999), upon which N is released from cyanobacterial-N-enriched moss tissue and made available for N-cycling in soils.…”