[1] Over 1 year we followed the seasonal variations of N 2 O and CH 4 fluxes at a tropical rain forest site in Australia. In addition, meteorological parameters, litter fall and decomposition, plant species composition, and concentrations of NH 4 + /NO 3 À in the soil and N 2 O and CH 4 in the soil atmosphere were measured. N 2 O emissions showed a pronounced seasonal pattern with highest rates in the wet season (108.6 mg N m , and, thus, approximately 7 times lower than a previous estimate for the year 2000. The marked differences in N 2 O emissions between different years indicate that the interannual variability of N 2 O emissions from rain forest soils cannot be neglected. With regard to CH 4 the soil functioned throughout the entire year as a significant sink. Rates of CH 4 uptake during the dry period (35-68 mg CH 4 m À2 h À1 ) were higher as compared to the wet period (4-45 mg CH 4 m À2 h À1 ). A close linear correlation between soil moisture and magnitude of CH 4 uptake was found. The calculated annual CH 4 uptake (N = 6090) is 3.2 kg CH 4 ha À1 yr À1. This implies that tropical rain forest soils function as significant sinks for atmospheric CH 4 on a global scale.

[1] Fluxes of N 2 O, NO, NO 2 , CO 2 , and CH 4 were measured with high temporal resolution for 3 months at a tropical rain forest site in Queensland, Australia, using automated measuring systems. During this period, representing the transition between dry and wet season, huge pulses of NO emissions from the soil exceeding 500 mg N m À2 h À1were observed with the onset of the first rainfalls. . Though a significant amount of the NO emitted from the soil was redeposited to the soil surface after its oxidation to NO 2 (0.7 kg N ha À1 ), the observed magnitude of net NO x release from the soil indicates that NO x emissions from tropical rain forest ecosystems are seriously underestimated. The mean CO 2 emission was 159.0 mg C m À2 h À1 (range: 36.3-284.8 mg C m À2 h À1 ) and thus >2 magnitudes higher than NO emissions. Among the C-and N-trace gases measured, the temporal variability of CH 4 uptake was the lowest. The mean uptake rate for CH 4 was

Combined measurements of nitrification activity and N 2 O emissions were performed in a lowland and a montane tropical rainforest ecosystem in NE-Australia over a 18 months period from October 2001 until May 2003. At both sites gross nitrification rates, measured by the BaPS technique, showed a strong seasonal pattern with significantly higher rates of gross nitrification during wet season conditions. Nitrification rates at the montane site (1.48±0.24-18.75±2.38 mg N kg −1 day −1 ) were found to be significantly higher than at the lowland site (1.65±0.21-4.54±0.27 mg N kg −1 day −1 ). The relationship between soil moisture and gross nitrification rates could be described best by O'Neill functions having a soil moisture optimum of nitrification at app. 65% WFPS. At the lowland site, for which continuous measurements of N 2 O emissions were available, nitrification was positively correlated with N 2 O emission. Nitrification contributed significantly to N 2 O formation during dry season (app.85%) but less (app. 30%) during wet season conditions. In average 0.19‰ of the N metabolized by nitrification was released as N 2 O. The N 2 O fraction loss for nitrification was positively correlated with changes in soil moisture and varied slightly between 0.15 and 0.22‰. Our results demonstrate that combined N 2 O emission and microbial N turnover studies covering prolonged observation periods are needed to clarify and quantify the role of the microbial processes nitrification and denitrification for annual N 2 O emissions from soils of terrestrial ecosystems.

Some long term effects of (a) converting rainforest to grassland, and (b) rainforest regeneration on cleared land were investigated by comparing chemical properties of mineral soil (0-10 cm depth) from beneath primary rainforest, derived grassland and old secondary rainforest. Grasslands and secondary rainforest. were on land cleared at least 50 years ago. The study was undertaken on the Atherton Tableland in north east Queensland using soils formed on basalt, granite and metamorphic rocks. Organic C, kjeldahl N and labile N were 15-50% lower (P < 0.05) beneath grassland than primary rainforest for all soils, and were higher beneath secondary rainforest than grassland. Exchangeable Ca varied in a similar way in basaltic soils but did not differ between vegetation types in the other soils. Extractable Al was lower under grassland than either forest type for soils formed on granite and metamorphic rock. Total and organic P concentrations did not differ between primary forest and grassland, but were lowest under secondary rainforest for soils on metamorphic rock.

Soil and litter respiration atid nutrient coticetitratiotis(N. P, Ca. Mgand K) were tneasured in two adjacent rainforests near Lalce Eaehatn on the Atherton Tableland in north-east Queensland. One forest had soil fortued on basalt and. in physiognotnic-stritctitral classification of Webb (1968Webb ( . 1978. was structurctlly cotnplex. The other had soil formed on tnetatnorphie rock and was structurally sitnple. Respiration was measured by the alkali trap tnethod on 16 tnonthly occasions in 1986 and 1987. Soil and litter nutrient concentratiotis were higher in the cotnplex forest (with the exeept ion of soil N). The relative differettces were greater for soil than litter and more pronounced for P andCa (and also soil Mg) than other nutrients. Litter polyphenol eoneentrations were lower in the complex forest.Rates of litter respiration in the cotnplex forest were, on average, nearly twiee those of the simple forest. Soil respiration rates were occasionally slightly lower in the complex forest during the wet season but did not differ between the forests during the dry season. Highest rates oj respiration were measured dtiring the wet season although high rates for titter occasionally occurred dtiring the dry season. Cutnulative CO 2 release from the soil and overly i tig litter did not differ between forests and averaged 5134 ± 96 gCOjtn^-per year (mean ± s.e.m.) (1400g C m~-per vear). Litter respiration accounted for 14% of the annual release in the complex forest and 11% in the simple forest.