ABSTRACTLianas (woody vines and climbing monocots) are increasing in abundance in many tropical forests with uncertain consequences for forest functioning and recovery following disturbances. At a global scale, these increases are likely driven by disturbances and climate change. Yet, our understanding of the environmental variables that drive liana prevalence at regional scales is incomplete and geographically biased towards Latin America. To address this gap, we present a comprehensive study evaluating the combined effects of climate, soil, disturbance and topography on liana prevalence in the Australian Wet Tropics. We established 31 20 × 20 m vegetation plots along an elevation gradient in low disturbance (canopy closure ≥ 75%) and high disturbance (canopy closure ≤ 25%) forest stands. In these plots, all tree and liana (defined as all woody dicot vines and climbing monocots, i.e., rattans) stems ≥ 1 cm DBH were measured and environmental data were collected on climate, soil and topography. Generalised linear models were used with multi‐model averaging to quantify the relative effects of the environmental variables on measures of liana prevalence (liana–tree basal area ratio, woody vine basal area and stem density and rattan stem density). Liana prevalence decreased with elevation but increased with disturbance and mean annual precipitation. The increase in the liana–tree ratio with precipitation was more pronounced for highly disturbed sites. Like other tropical regions, disturbance is an important driver of liana prevalence in Australian rainforests and appears to interact with climate to increase liana–tree ratios. The observed increase in liana–tree ratio with precipitation contrasts findings from elsewhere but is confounded by correlated changes in elevation and temperature, which highlights the importance of regional studies. Our findings show that forests with high disturbance and climatic conditions favourable to lianas are where lianas most likely to outcompete trees and impede forest recovery.

Land use conversion of natural ecosystems to intensive agriculture can alter soil biogeochemical processes and nutrient cycling, while increasing potential for land degradation. The disturbance of soil microbial community, due to land use conversion, may also lead to detrimental effects on soil ecosystem processes and services. Therefore, the objective of this study was to examine how sugarcane cultivation alters soil nitrogen (N) bioavailability and associated microbial processes in tropical Australia. Two adjacent paired sites (native forest vs sugarcane cultivation for 78 years; pasture vs sugarcane cultivation for 78 years) were selected and five composite surface soils (0–10 cm) were collected from each site. Sugarcane cultivations decreased total organic carbon (OC; 45–48

Forest ecosystems can store massive amounts of organic carbon (OC) deep in their soils. Soil OC (SOC) is composed of several complex organic compounds of which groupings of these organic compounds can provide an insight into evaluating the formation and fate of SOC. However, there is little information available regarding the chemical composition of deep forest SOC and how they compare to upper soil depths. The objective of this study was to explore the SOC chemistry changes with increasing soil depth on a fine spatial scale in a planted forest soil derived from young volcanic erupted airfall deposits. Soil core samples to 1 m depth were collected from Puruki Experimental Forest (New Zealand) and examined for incremental depth changes in SOC functional groups, or chemical shift regions, using solid-state 13C cross polarisation magic angle spinning nuclear magnetic resonance (13C CPMAS-NMR) spectroscopy. The results showed that soil depth was a driver of change in soil chemical shift regions. The presence of a coarse-textured soil horizon, lapilli layer, at depth was a driver of significant (p < 0.05) differences between SOC functional groups. In the upper soil profile (0–10 cm), the chemical shift distribution was dominated by O-alkyl C (39%) followed by alkyl C (32%), aromatic C (23%), and carboxyl C (6%). In the deep soil layers, we found alkyl C increased below the lapilli layer (varying depth > 50 cm) compared to above the lapilli layer. In the deep soil layers the alkyl C was the dominant functional group (55%), followed by O-alkyl C (28%). Furthermore, there was a decrease at depth in aromatic (12%) and carboxyl C (5%). The A/O-A ratio increased with depth from soil above the lapilli layer compared to soils below the lapilli layer indicating a greater degree of organic matter decomposition and a corresponding decrease in the labile OC fractions. Within the lapilli layer the SOC functional groups and A/O-A ratio were highly variable. These results highlight that changes in SOC chemical composition occur with increasing soil depth, a property of deep soil that is frequently understudied, and are highly influenced by the multi layered nature of soil derived from volcanic airfall deposits.

Microplastics (MPs) are a major emerging contaminant in agroecosystems, due to their significant resistance to degradation in terrestrial environments. Although previous investigations have reported the harmful effects of MPs contamination on soil biological properties, still little is known about the characteristics and fate of MPs in biosolid-amended soils and their risks to soil biota, particularly earthworms. We determined microplastics' concentration, size distribution, and chemical composition in 3 sewage sludge biosolids and 6 biosolid-amended agricultural soils. In addition, we assessed the potential short-term risks of MPs to earthworms' (Amynthas Gracilis and Eisenia Fetida) survival rate and fitness in an environmentally relevant exposure study (28 days). Biosolid-amended soils (1000-3100 MPs kg(-1) dry mass) showed approximate to 30 times lower MPs content than investigated biosolids (55400-73800 MPs kg(-1) dry mass), with microplastic fragment to fibre ratios between 0.2 and 0.6 and 0.3-0.4 in soils and biosolids, respectively. Total MPs dry mass was also approximate to 19 times lower in assessed soils (12-26 mg kg(-1)) than biosolids (328-440 mg kg(-1)). On average 77% and 80% of plastic fragments had a lower dimension than 500 mu m, while 50% and 67% of plastic fibres had a length of less than 1000 mu m in soil and biosolid samples, respectively. Polyethylene (23.6%) was the major source of microplastic contamination in biosolid-amended soils, while polyethylene terephthalate (41.6%) showed the highest concentration in biosolid samples. Spiked polyethylene MPs did not show any significant effect on earthworms' survival rate (93-99%). However, biosolid application significantly (P < 0.05) decreased survival rate of Eisenia Fetida (81%) but showed no significant effect on Amynthas Gracilis (93%). Biosolid amendment significantly (P < 0.05) decreased earthworms' growth rate, with higher impact on Eisenia Fetida than Amynthas Gracilis, while there were no significant differences between control and microplastic spiked treatments. The overall decrease in MPs con-centration of earthworm casts, compared with initial MPs concentrations in soil, indicated that the investigated species did not bioaccumulate MPs during the exposure experiment.

Biochar–bioenergy coproduction from biomass pyrolysis has the potential to contribute to climate change mitigation. Biochar produced at various pyrolysis temperatures (<600°C) has been widely studied. However, the effect of biochars, produced at high pyrolysis temperature (≥600°C), on soil nitrogen (N) dynamics and nitrous oxide (N 2 O) emission is largely unknown. A pot trial was performed to examine the effect of high pyrolysis temperature (600, 700, 850 and 950°C) woody biochars on soil N dynamics, microbial gene abundance and N 2 O emissions with (+N) and without N (−N) fertilization from an acid soil. Results showed that all biochar treatments significantly lowered the N 2 O emissions in both fertilized and unfertilized regimes. However, the suppressive effect on N 2 O emission among different high pyrolysis temperatures was not statistically different. Biochar amendment significantly decreased the concentration of soil NH 4 + , and lower levels of soil NO 3 − were observed at the later stage of experiment. Under −N, plant biomass and N uptake were significantly lowered in all biochar treatments. Under +N, biochar addition significantly increased plant biomass, while only the 700°C biochar significantly increased N uptake. This suggests that single application of biochar could limit soil mineral N bioavailability and further decrease plant growth and N uptake in the plant–soil system. Biochar amendments tended to increase nitrous oxide reductase ( nosZ ) gene abundance, but this effect was only significant for biochar produced at 950°C under +N. In conclusion, high pyrolysis temperature biochars can be effectively used to reduce N 2 O emission, while increases in nosZ gene abundance and decreases in NH 4 + and NO 3 − concentrations in the acid soil are likely to be responsible for the reduction in N 2 O emission. Thus, woody biochars as a by‐product produced at high pyrolysis temperature have the potential to mitigate soil N 2 O emission via modifying N transformation and further affect climate change.

Few studies have focused on the effects of long-term forest plantations on the soil profile of carbon (C) and nitrogen (N) stocks. In this study, we selected 78-year-old tree plantations that included three coniferous tree species (i.e., slash pine, hoop pine and kauri pine) and a Eucalyptus species in subtropical Australia. We measured soil extractable organic C (EOC) and N (EON) contents and total C and N stocks under different tree species on the forest floor and along a soil profile to 100 cm depth. The results showed that Eucalyptus had significantly higher soil EOC contents (3.3 Mg ha−1) than the other tree species (EOC of 1.9–2.3 Mg ha−1) and had significantly higher EON (156 kg ha−1) contents than slash pine (107 kg ha−1). Eucalyptus had significantly higher soil C (58.9 Mg ha−1) and N (2.03 Mg ha−1) stocks than the other tree species (22.3–27.6 Mg C ha−1 and 0.71–1.23 Mg N ha−1) at 0–100 cm depth. There were no differences in soil C stocks at the 0–100 cm depth among the coniferous tree species. Forest floor C stocks had stronger effects on mineral soil total N stocks than fine root biomass, whereas fine root biomass exerted stronger effects on soil total C stocks at the 0–100 cm depth than forest floor C and N stocks. Our results addressed large differences in soil C and N stocks under different tree species, which can provide useful information for local forest management practices in this region.

Bauxite residue sand (BRS) is the primary growth medium for rehabilitating Alcoa's residue storage areas in south-west Western Australia. Successful revegetation of highly alkaline BRS can be hindered by its low nitrogen (N) use efficiency. Biochar, a carbon (C)-rich material, has been suggested to have the potential to improve water and nutrient retention in soil. However, little is still known about the effect of biochar amendment on N use efficiency in the alkaline BRS environment. This incubation study aimed to evaluate the impact of biochars with different characteristics on N retention and dynamics in BRS. The BRS (pH 9.5 after being pre-treated with 1% gypsum and leached with water) was amended with the acidic biochar (pH 3.86; AC, from wild fire) and alkaline biochars (pH 9.58-10.8; greenwaste, GW; Jarrah, JL; mallee, ML) at a rate of 10% (w/w). The N loss via NH3 volatilization was much lower from the AC treatment (24% of di-ammonia phosphate (DAP)-N added) than the alkaline biochars treatments (76-80% of the DAP-N added). The AC treatment can retain about 73% of N added to BRS, compared with <25% in alkaline biochar treatments. This can be attributed to the acidic nature and the greater NH4'-N sorption capacity arising from the presence of a high density of the oxygen-containing functional groups on the surface of acidic biochar as revealed by the FTIR spectroscopy. These results imply acidic biochar can be used as an effective amendment for increasing N use efficiency by plants growing in alkaline BRS. (C) 2016 Elsevier B.V. All rights reserved.

Micro-flora differences in various soil layers covered with coniferous,coniferous-broadleaf mingled and broadleaf forest were studied by phospholipids fatty acid spectrum analysis.The results showed that the relative biomass of total microorganisms,bacteria,fungus and actinomycetes in the forestry soils decreased significantly or remarkably with the increase of soil depth,and the vertical differences of the biomass were much significant in the soils covered with coniferous-broadleaf mingled and broadleaf forest.The bacteria and fungus,whose biomasses were 69.92%-77.08% and 20.64%-30.01% of total microorganism respectively,were dominative and secondary micro-flora in the forestry soils,and the biomass of pseudomonas was 26.80%-38.38% of total bacteria,were main species of soil bacteria,which showed distinct characteristics of soil micro-flora in subtropical area.The relative biomasses of total microorganisms and bacteria in both 0-20 cm and 20-40 cm layers covered with coniferous-broadleaf mingled forest were significantly higher than those covered with coniferous and broadleaf forest,and those of fungus in two layers covered with coniferous-broadleaf mingled and coniferous forest were remarkably higher than those covered with broadleaf forest.The bacteria diversities in 0-20 cm layer covered with coniferous-broadleaf mingled forest were higher than those covered with broadleaf and coniferous forest,and those in 20-40 cm layer covered with coniferous-broadleaf mingled and broadleaf forest were higher than those covered with coniferous forest.