Soil N dynamics in relation to leaf litter quality and soil fertility in north‐western Patagonian forests

Abstract

Summary 1We examined the relationships among soil N dynamics, soil chemistry and leaf litter quality in 28 forest stands dominated by conifers, woody broad-leaf deciduous species or broad-leaf evergreens. Potential net N mineralization, net nitrification and microbial biomass N were used as indicators of soil N dynamics; pH, organic C, total N, exchangeable cations and extractable P as indicators of soil chemistry and N concentration, lignin concentration, C : N ratio and lignin : N ratio in senescent leaves as indicators of leaf litter quality. N dynamics were assessed in two consecutive years with contrasting precipitation. 2 Net N mineralization was lower in stands of the three conifers and one of three broadleaf evergreen species than in stands of the other six broad-leaf species (40-77 vs. 87-250 mg N kg − 1 after 16-week incubations) and higher in the wetter year. 3 The proportion of N nitrified was high beneath most species regardless of mineralization rates, soil N fertility and leaf litter quality, and was significantly higher for the wetter year. Ammonium was the predominant form of N in three sites affected by seasonal waterlogging and in two sites the predominant form changed from ammonium in the drier year to nitrate during the wetter year, probably due to differences in soil texture affecting soil moisture. 4 Net N mineralization was linearly related to microbial biomass N, implying that the microbial activity per biomass unit was quite similar beneath all species. Constant microbial biomass during the wetter year suggested that as mineralization/nitrification increased, there was a higher potential risk of N losses. 5 Although the litter lignin : N ratio allowed differentiation of soil N dynamics between broad-leaf species and conifers, its constant value (23-28) in all broad-leaf species made it a poor predictor of the differences found within this group. Across all sites and between broad-leaf species, soil N dynamics were best explained by a combination of leaf litter lignin and soil chemistry indicators, particularly soil total N for net N mineralization and net nitrification, and soil organic C for microbial biomass N.

Can biosolids compost improve, in the short term, native vegetation and soils fertility in burned Nothofagus pumilio forest in Patagonia, Argentina?

“…Comparing previous studies on soil fertility variables in post-fire Challhuaco Valley (Satti et al 2003, Alauzis et al 2004, Kitzberger et al 2005 with the results obtained in the present study, a lack of recovery in soil fertility eight years after fire (carbon, nitrogen, microbial nitrogen flush, pH, potassium and extractable phosphorus, for example) can be observed. This indicates the high disturbance intensity and the low post-disturbance resilience of these forests.…”

“…Alauzis et al (2004) found that four years after fire, burnt soils showed no recovery compared to soil in unburnt conditions. The main effects on organic carbon, total nitrogen, extractable phosphorus and microbial biomass were recorded by these and other authors (Diehl et al 2003, Satti et al 2003, Kitzberger et al 2005.…”

“…With reference to microsite conditions, there is seasonal variability in soils nutrient contents, independent of the microsite considered (control treatment; tables 2 and 3), in agreement with Alauzis et al (2004). In many cases, litter quality exerts important feedback on nitrogen dynamics, regulating rates of decomposition, nitrogen availability, net primary production and responses to disturbance (Satti et al 2003).…”

Effects of Nitrate and Labile Carbon on Denitrification of Southern Temperate Forest Soils

“…Soils of unpolluted, old-growth temperate forests in Chile and Argentina present a high ratio of net nitrification in relation to net mineralized N; either potential (Pérez et al, 1998;Satti et al, 2003) or in situ (Pérez et al, 1998;Decker and Boerner, 2003). However nitrate pools in forest soils and nitrate losses to stream waters are extremely low because of a high N retention in soil organic matter (Perakis and Hedin, 2001).…”

“…The evidence shows that forest logging increases N availability through higher rates of mineralization (Reynolds et al, 2000;Thibodeau et al, 2000;Hope et al, 2003;Lindo and Visser, 2003;Inagaki et al, 2008) and decomposition (Prescott, 1997;Brais et al, 2002), leading to increased availability of labile C (Chatterjee et al, 2008) and higher denitrification (Robertson and Tiedje, 1988). However, the effects of altering the inputs of reactive N and land use change in N transformations are less understood in southern temperate forests, where N is strongly limiting for tree growth (Perakis and Hedin, 2001;Vann et al, 2002;Satti et al, 2003;Diehl et al, 2008), and soils are dominated by recalcitrant forms of C, as indicated by the relatively high soil C/N ratios (Pérez et al, 2009). Such analysis is relevant because one of the important microbial transformations in the context of global change is denitrification, as it may counteract eutrophication in aquatic ecosystems and also may be a significant source of N 2 O, an important greenhouse gas.…”