Ecosystem openness to nitrogen (N) and phosphorus (P) is determined by the balance of N and P inputs (e.g. fertiliser) and outputs (biomass removal). Plant biodiversity enhances nutrient use efficiency due to species' complementary uptake driven by their variation in roots and growth requirements. It remains unclear how biomass removal (e.g. via mowing) can intensify the effect of N and P input on ecosystem openness, N and P removal and balance, and to what degree these processes are related to plant biodiversity. To assess this, a field experiment was conducted to examine the effects of N fertiliser (0 vs. 4 g N m-2 yr-1), P fertiliser (0 vs. 1 g P m-2 yr-1) and mowing frequency (3-4 vs. 6-8 mowing events year-1) to induce variation in N and P availability as well as plant species diversity. We showed that a greater plant N uptake and N loss were driven by N fertilisation where we observed an increase of delta 15N (as a measure of openness) of the plant community over time. Phosphorus removal and loss were enhanced by higher mowing frequency with a negative balance when no fertiliser was applied, likely due to mowing-induced variation in community composition, shortening of the vegetative stage and a greater biomass removal. Furthermore, N fertilisation (without P application) enhanced P removal causing a negative P balance, likely because of N-induced promotion of vegetative growth and biomass production. Biodiversity enhanced the ability of plant communities in taking up more N and thereby increasing removal with mowing as revealed by greater plant delta 15N with increased plant diversity, likely due to a greater resource use efficiency. Moreover, the relationship between N and P removal to Shannon-Weiner biodiversity index varied over the year that could be driven by seasonal variation in plant species growth, nutrient demand and availability. Our results provide important information about managing N and P retention and removal through mowing frequency and fertilisation and highlight that these nutrient dynamics are mediated by plant biodiversity.Read the free for this article on the Journal blog.

Grains of Australian native grasses have been important components of traditional Aboriginal diets for millennia and have the potential for increased utilisation in contemporary food systems. This study assessed the macronutrient profiles of whole grains from Dactyloctenium radulans (Button Grass), Astrebla lappacea (Curly Mitchell Grass), Panicum decompositum (Native Millet), and Microlaena stipoides (Weeping Grass) compared to wheat, barley, and sorghum using proximate analysis, Osborne protein fractionation, gel electrophoresis, and carbohydrate assays. Key results were that Native Millet had high lipid content (8.0 g/100 g dry weight basis (db)), Curly Mitchell Grass had high protein (29.1 g/100 g db) and low carbohydrate content (64.0 g/100 g db), and there were substantial differences in prolamin and glutelin fractions across the species. All four native grains were gluten-free, and their starch amylose content ranged from 25.7% (Button Grass) to 41.2% (Curly Mitchell Grass), which affects starch properties. Button Grass had the highest dietary fibre content (21.9 g/100 g db), while Weeping Grass had the highest beta-glucan levels (8.6 g/100 g db), supporting functional food applications. Our findings highlight the potential for an expanded range of food applications for these grains and their contribution to human nutrition, together with implications for supporting Indigenous-led enterprises.

Soil carbon (C) sequestration depends on the formation of particulate- and mineral-associated organic matter (POM and MAOM). These soil organic matter (SOM) pools are largely derived from rhizodeposition, but how the quality and quantity of rhizodeposits affect the direct contribution of root-derived C (ex-vivo pathway) and microbially processed root-derived C (in-vivo pathway) to the formation of each pool remains unclear. To test this, we induced variation in quality and quantity of plant C inputs by imposing defoliation frequencies (3-4 vs. 6-8 clipping events year-1), and varying N fertiliser (0 vs. 40 kg N ha-1 yr-1) application rate for five years in a grassland. Two 2-hour 13CO2 pulse labelling events were applied in mid- and late summer to estimate the shortterm incorporation of root-derived C in SOM pools. Water soluble metabolites in soil and near edge X-ray absorption fine structure (NEXAFS) spectroscopy of POM and MAOM fractions were used to characterise the organic C. Results showed that N fertilisation increased microbial utilisation of the rhizodeposited C and the contribution of in-vivo pathway to MAOM-C, as supported by increased concentration of trehalose (microbederived metabolite) associated with MAOM-C. Moreover, N fertilisation increased POM-C accumulation via exvivo pathway, as shown by increased abundance of carboxylic C groups, likely reflecting increased fine root biomass and rhizodeposited C. At the same time, N fertilisation increased the abundance of O-alkyl C functional groups in POM-C fraction that are mostly microbially driven likely suggesting that decaying microbes or mycorrhizal hyphae also contribute to POM-C highlighting the co-contribution of the in-vivo pathway with N addition. Moreover, both ex-vivo and in-vivo pathways contributed into MAOM-C at low rhizodeposition rate (e.g. in highly defoliated treatment particularly when no N was applied) as shown by increased abundance of the aromatic C with side chain and N-substituted aromatic C and increased concentration of metabolites such as malic acid and mannose, which can originate from both plants and microbes. Our results shed light on how variation in root biomass, rhizodeposition, and N availability affects the contribution of ex-vivo and in-vivo pathways in the formation of root-derived C in POM and MAOM fractions.

[This corrects the article DOI: 10.1007/s12298-026-01753-z.].

Earthworms affect soil organic carbon (SOC) decomposition and C stabilization into mineral associated organic matter (MAOM) following fresh organic matter input. However, it remains untested how these earthworminduced C dynamics vary with the rate of fresh organic matter input and soil texture and how they are associated with soil microbial C use efficiency (CUE). Herein, we conducted a 48-day incubation to investigate the impact of earthworms on soil C dynamics following litter input, as well as the relationships of C dynamics with microbial CUE. The experimental set-up consisted of three factors including earthworms (with and without), 13Clabeled grass litter input rate (0, 1 and 6 g C kg- 1 soil) and soil texture (grassland soils with either clay or sand addition). Earthworms increased SOC decomposition without litter input by 9 % - 13 %, while amplifying the priming effect (PE) in soil with clay and sand addition at the highest litter addition by 24 % - 139 %, but decreasing the PE in soil with sand and low litter addition by 32 %. In soil with sand addition, earthworms increased MAOM formation efficiency from litter (fraction of added litter C stabilized in MAOM) by 17 % - 23 %, and the litter C sequestration quotient (litter-derived C in MAOM divided by the sum of litter derived C in MAOM and respiration) by 10 % - 27 %. However, earthworm-induced changes in SOC decomposition, PE and MAOM formation were not associated with earthworm-induced changes in microbial CUE. In conclusion, earthworms can facilitate SOC accrual more in soils with sand addition through disproportional amplification of SOC stabilization compared with SOC loss through decomposition. The influence of earthworms on SOC accrual is more likely driven by physicochemical protection of SOC rather than by changes in microbial metabolism.

Plants depend on nitrogen (N) for their growth, development, and metabolic functions. However, the regulatory mechanisms modulating N assimilate allocation under varying N forms are unclear. This study examines N metabolism and spatial distribution in maize seedlings subjected to four N treatments (T1 to T4): T1, 1 mM NO3− (sole NO3−); T2, substitution of 1 mM NO3− with 1 mM NH4+ (N form substitution, NFS); T3, 1 mM NH4+ (sole NH4+); and T4, 0.5 mM NH4NO3 (mixed N supply). The NFS treatment induced significant physiological and molecular adaptations, such as enhanced growth and total biomass under fluctuating N conditions. NFS-treated plants exhibited improved photosynthesis, increased protein and amino acid synthesis, and increased NO₃⁻ and NH₄⁺ accumulation. Activities of key N metabolism enzymes, such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT), were significantly upregulated, supporting efficient assimilation of both NO3− and NH4+. Furthermore, spatial and diurnal analyses revealed dynamic N partitioning and adaptive regulation, with NFS-treated plants maintaining consistently higher NO3− and NH4+ levels in leaves, roots, sheaths, and developing ears. These findings highlight the robust plasticity of maize N metabolism under NFS conditions and provide valuable insights into optimizing N use efficiency (NUE) for sustainable crop production. Future studies will focus on exploring these adaptive mechanisms across different maize genotypes and under field conditions to improve NUE and productivity in varying N environments.

Nitrogen (N) is primarily taken up by most plant species in the form of nitrate (NO3-) and ammonium (NH4+) to support growth and metabolic functions. However, the regulatory mechanisms modulating carbon (C) assimilate allocation under varying N forms remain unclear. This study investigated C metabolism and its spatial distribution in maize seedlings subjected to five N treatments (T1-T5): T1, nitrogen-free (control N); T2, 1 mM NO3- (sole NO3-); T3, 1 mM NH4+ (sole NH4+); T4, 0.5 mM NH4NO3 (mixed N supply); and T5, substitution of 1 mM NH4+ with 1 mM NO3- (NH4+→NO3-) at 10 days after seedling transfer (DAT). NH4+ treatment triggered significant physiological and molecular adaptations, such as enhanced growth, improved photosynthetic performance, and increased sucrose and starch accumulation. These elevated carbohydrate levels were closely associated with increased activity of sucrose-metabolizing enzymes (SuSy, SPS, and INVs) and starch-metabolizing enzymes (AGPase, SS, AMY, and BAM), alongside the upregulation of key genes involved in sucrose metabolism (ZmSPS1, ZmSuSy1, and ZmINVs), sucrose transport (ZmSWEET14, ZmSUT2, and ZmSTP2), and starch metabolism (ZmSS1, ZmAGPase1, ZmAMY1, and ZmBAM1). Spatial and diurnal analyses revealed dynamic patterns of C partitioning across the leaves, roots, and leaf sheaths. These findings advance our understanding of how different N forms, particularly NH4+, regulate C metabolism and shoot-root allocation to facilitate carbon utilization in sink tissues to improve plant resilience to N fluctuations. Future research will focus on exploring these adaptive mechanisms across diverse maize genotypes under field conditions, with the goal of improving nitrogen use efficiency (NUE) and productivity in variable N environments.

Phosphorus (P) availability affects carbon (C) allocation to roots for nutrient acquisition and biological nitrogen fixation (BNF), which in turn impacts yield. It is unclear how P availability and inter-specific interactions affect these processes in intercropping systems. Methods: A pot experiment was conducted using a factorial randomized block design with four replicates, where wheat and chickpea were grown alone or together, with 44 mg P kg−1 (equivalent to 50 kg P ha⁻1) or without additional P fertilizer. We evaluated yield, BNF based on 15N natural abundance, plant P content, and C allocation to root biomass and respiration. Results: Phosphorus availability strongly modulated the coupling between C allocation and BNF that depended on interspecific interactions. Under intercropping, chickpea exhibited greater increases in yield and P uptake with P fertilization than in monocropping, reflecting enhanced competition for P when intercropped with wheat. Intercropping significantly increased BNF in chickpea that was further marginally increased by P fertilization, while both intercropping and P fertilization sharply increased specific root respiration, indicating higher metabolic investment to support BNF. However, chickpea allocated less C to root biomass under P fertilization and intercropping, suggesting a strategic shift in C partitioning from root growth to BNF. In contrast, wheat maintained C allocation to roots in both cropping systems under P fertilization, highlighting species-specific strategies for nutrient capture and symbiotic relationships. Conclusion: Our findings highlight the importance of optimizing nutrient management for BNF and P uptake in P-deficient soils and in intercropping systems.

Nitrogen (N) and phosphorus (P) play important roles in increasing agricultural productivity. However, excessive use of N and P fertilization can result in low N and P fertilizer use efficiencies (REN and REP) and loss of N and P through gaseous emission and leaching, but which also depend on soil pH conditions. In a full factorial glasshouse experiment using pots with 2.5 kg soil and adding N (0 and 100 kg N ha-1), P (0 and 50 kg P ha-1) fertilizer and lime (0, 3.5, 14 t ha-1, 100 % calcium carbonate equivalent) we investigated the main and interactive effects of our treatments on REN and REP in wheat (Triticum aestivum) grown in a P-poor soil. The REN was close to zero without P fertilization regardless of liming, but increased to 46 % with P fertilization (averaged across liming treatment) because of strong P limitation. Likewise, N fertilization increased REP from 6 % to 8 % averaged across the liming treatment. However, liming decreased REN (only when P fertilizer was added), possibly because of enhanced net N mineralization in the soil making plants less dependent on N fertilizer with liming, and increased REP, possibly because of reduced fertilizer P-immobilization in the soil with low pH. Overall, N and P fertilizer and lime addition changed REN and REP by changing wheat growth along with N and P uptake, thereby affecting soil available nutrients, nitrous oxide emissions and N and P loss through leaching. We highlight the importance of adjusting N and P fertilization with liming to optimize REN and REP and reduce N and P loss.

Sugars are essential for plant development, with nitrogen (N) availability playing a critical role in their distribution across plant organs, ultimately shaping growth patterns. However, the regulatory mechanisms modulating carbon (C) assimilate allocation and utilization under different N forms are not well understood. This study examined C fixation, utilization, and spatial re-distribution in the roots of hydroponically grown maize seedlings subjected to four N treatments: 1 mM NO3− (low N; LN), 2 mM NO3− (medium N; MN), 10 mM NO3− (high N; HN), and 1 mM NH4+ (low ammonium; LA). LN treatment significantly increased soluble sugar, sucrose, and starch contents while promoting greater root biomass at the expense of shoot biomass, leading to a higher root to shoot assimilate allocation. The activities of sugar and starch metabolism enzymes were more tightly regulated under LN, indicating enhanced C utilization and increased competition for assimilates. Key genes involved in sugar (ZmSPS, ZmSuSy, ZmSWEET6, ZmSUC2, ZmSTP2, and ZmAINV1) and starch (ZmAGPASE and ZmSS) metabolism were upregulated under LN, correlating with increased root sucrose and starch accumulation and enhanced enzyme activity. Sucrose and starch accumulated predominantly in the brace and lateral roots. This pattern suggests that excess C accumulation results from inefficient C utilization in sink tissues rather than impaired C assimilation. These findings provide new insights into how LN modulates C partitioning in roots for stress adaptation, highlighting the importance of improving C utilization in sink tissues to mitigate N deficiency and enhance plant growth.

Plants depend on nitrogen (N) to support their growth, development, and essential metabolic activities. However, the mechanisms modulating the distribution of N assimilates under supplemental N (SN) condition is unknown. This study examines carbon (C) metabolism and spatial distribution in maize seedlings subjected to three N treatments (T1 to T3): T1, 1 mM NO₃⁻ (low N, LN); T2, supplementation of 1 mM NO₃⁻ with 2 mM NO₃⁻ (1 mM NO₃⁻ → 2 mM NO₃⁻, SN); and T3, 2 mM NO₃⁻ (medium N, MN). SN treatment induced significant physiological and molecular adaptations, such as enhanced growth and total biomass under fluctuating N conditions. SN-treated plants exhibited enhanced photosynthetic activity and significantly greater accumulation of soluble sugars, sucrose, and starch compared to those under LN and MN treatments. Activities of key C metabolism enzymes, such as sucrose phosphate synthase (SPS), sucrose synthase (SuSy) and invertases (INVs), starch synthase (SS), AGPase, α-amylase (AMY) and β-amylase (BAM) were significantly upregulated, supporting efficient C metabolism. Molecular analysis revealed transcriptional reprogramming under SN, marked by the upregulation of genes related to sucrose (ZmSPS1, ZmSuSy1, ZmINVs, ZmSUT2, ZmSTP2, ZmSUC2 and ZmSWEET14) and starch (ZmSS1, ZmAGPase1, ZmAMY1 and ZmBAM1) metabolism and transport. The spatial and diurnal analysis revealed dynamic C partitioning and adaptive regulation, with SN plants maintaining higher sucrose and starch levels in the leaves, sheath and roots. These findings highlight the robust plasticity of maize C metabolism under SN conditions and provide valuable insights into optimizing nitrogen use efficiency (NUE) for sustainable crop production. Future studies will focus on exploring these adaptive mechanisms across different maize genotypes and under field conditions to improve NUE and productivity in varying N environments.

Many agricultural soils suffer from phosphorus (P) deficiency. Intercropping could improve plant P uptake efficiency and yield compared to monocropping systems. How P fertilization affects yield and P uptake in intercropping remains unclear. In this meta-analysis (including 907 observations from 39 studies) we evaluated how P fertilization influences yield, P and nitrogen (N) uptake in both intercropping and monocropping systems, and their Land Equivalent Ratios (LER) for different crops, soil types, management practices, and climatic conditions. Across all observations, P fertilization increased yields in both cropping systems. However, monocropping exhibited a greater increase in yield. Despite this, the LER increased under P fertilization, indicating that intercropping use land resources more efficiently, likely because certain crops respond more strongly to P fertilization compared to their companion crops. Most pronounced P fertilizer-induced increases in LER were observed in intercropping systems that had no cereals, while cereal yields in intercropping systems increased as much or less compared to monocropping. Positive relationships were observed between increased P and N uptake and yield with P fertilization in both systems. Notably, intercropping demonstrated enhanced efficiency in converting P uptake into yield gains compared to monocropping. P fertilization improves yield, LER, and P uptake in non-cereal intercropping systems while cereal-based intercropping may be more favourable under low P availability conditions. Our findings further emphasize the role of fertilizer duration, soil factors (clay content and pH) and climate in increasing yields and LER with P fertilization, stressing the need for region-specific P management strategies.

Nitrogen (N) deficiency in maize regulates carbon (C) metabolism by enhancing sugar and starch metabolism and related gene expression in both shoots and roots, while increasing root competition for assimilates causing carbohydrate accumulation in leaves and sheaths due reduced translocation to sink tissues. Soluble sugars are vital for plant development, with nitrogen (N) availability playing a key role in their distribution across plant organs, ultimately shaping growth patterns. However, the regulatory mechanisms governing carbon (C) assimilate allocation and utilization under different N forms remain unclear. This study examined C fixation, utilization, and spatial distribution in hydroponically grown maize seedlings subjected to four N treatments: 1 mM NO3⁻ (low N, LN), 2 mM NO3⁻ (medium N), 10 mM NO3⁻ (high N), and 1 mM NH4⁺ (low ammonium, LA). LN treatment significantly increased soluble sugar and starch contents while promoting greater root biomass at the expense of shoot biomass, leading to a higher root-to-shoot assimilate allocation. The activities of sugar and starch metabolism enzymes were more tightly regulated in both shoots and roots under LN, indicating enhanced C utilization and increased competition for assimilates, particularly in the root. Key genes involved in above-ground sugar and starch metabolism, ZmSPS1, ZmSuSy1, ZmCINV1, ZmVINV1, ZmCWINV1, ZmSTP2, ZmSUC2, ZmSWEET14, ZmSS1, ZmAMY1, ZmBAM1, and ZmAGPase1, were upregulated under LN, correlating with enhanced enzyme activity and resulting increased sugar and starch accumulation. Starch and sucrose accumulated more in LN-treated leaves than in other N treatments, with starch primarily stored in leaf tips and sucrose concentrated in the leaf sheath. This pattern suggests that excess C accumulation results from inefficient C utilization in sink tissues rather than impaired C assimilation. These findings provide new insights into how LN modulates C partitioning between leaves and roots for stress adaptation, highlighting the importance of improving C utilization in sink tissues to mitigate N deficiency and enhance plant growth.

The contributions of de novo synthesis to terpene emissions from Eucalyptus globulus subsp. globulus were determined by fumigating branchlets with 13CO2 in a gas exchange system. Of more than thirty-four terpenes emitted by this species, only four, i.e., isoprene, iso-valeraldehyde, cis-ocimene, and trans-caryophyllene, incorporated 13C into the terpene carbon skeleton during the ~5–6 h experiment. 13C incorporation into isoprene and iso-valeraldehyde reached a maximum of ca. 82% of the carbon skeleton, similar to cis-ocimene, with a maximum of 77% 13C incorporation after ~2.5 h exposure to 13CO2. Only ca. 20% of carbon was labelled in trans-caryophyllene after 5–6 h. the incorporation of 13C was observed only in compounds emitted from leaves, and was not detected in either individual oil glands or in bulk leaf tissue. The results suggest the de novo synthesis of some terpenes (isoprene, cis-ocimene, trans-caryophyllene, and iso-valeraldehyde) and their emission is independent of emissions of terpenes stored in oil glands.

Plant inputs from root exudates and litter can improve soil aggregation and enhance soil organic carbon (SOC) content, but they can also increase SOC decomposition referred to as the priming effect. While bacteria and fungi are considered as key microbes for organic matter decomposition, their role in decomposing plant inputs and SOC, and their contribution to forming aggregates and SOC protection is still not fully understood. We conducted a 16-day incubation study to investigate the role of bacteria and fungi on decomposition and protection of C derived from glucose (labile C as a surrogate for root exudates) and wheat root biomass added to soil. Bronopol and captan were used to suppress bacterial and fungal activity, respectively, in the soil. Because glucose and wheat root biomass were enriched in 13C, we were able to estimate their decomposition and priming effect, microbial C use efficiency (CUE), and recovery in different aggregate size classes. As expected, the decomposition of both substrates was reduced significantly when biocides were added, and the decomposition rate of glucose was significantly higher than of wheat root biomass. Fungi were more important than bacteria in causing a priming effect, as indicated by the reduced SOC decomposition in the presence of substrates when captan was added. The mean weight diameter of aggregates at the end of the incubation was significantly reduced when captan was added, either alone or in combination with bronopol, independent of substrate type, suggesting that fungi also played an important role in soil aggregation. However, recovery of C derived from wheat root biomass in macroaggregates was highest when both biocides were added, suggesting that decomposition by both bacteria and fungi may have outweighed the protection of wheat C in new macroaggregates. While we observed variation in the microbial CUE among substrate and biocide treatments, we found no relationship with soil aggregation. We conclude that both bacteria and fungi were important for decomposition of added substrates to the soil, but that fungi can play a larger role in both soil C loss through priming effects and C protection through aggregation.

Organic amendments to soil often enhance soil organic matter (SOM) decomposition, also referred to as a priming effect (PE). However, decomposition of the organic amendment itself could also be altered when mixed in soil, with important consequences for the net soil carbon (C) balance and nutrient cycling, but this has rarely been explored. We examined decomposition and gross nitrogen (N) mineralisation of compost (C:N = 29) and SOM (C:N = 12) separately and when mixed, at two different moisture levels (45 and 85% water holding capacity) in a 42-day laboratory incubation study. As observed by many others, compost addition enhanced decomposition of SOM (i.e., causing a PE) at both moisture levels. In contrast, decomposition of compost was strongly reduced when mixed with soil, particularly at the highest moisture level, which more than compensated for the PE. These results indicate that the microbial decomposer community had a greater preference for decomposing SOM than decomposing compost when mixed, possibly because decomposition of SOM released more N than decomposition of compost in meeting the microbial demand for N. This was supported by higher gross N mineralisation rates at the end of the incubation period in compost-soil mixtures compared to what would be expected from gross N mineralisation rates in their separate components. It is also possible that mineral adsorption of organic compounds derived from compost caused greater protection against microbial decomposition of compost, and thus reduced compost decomposition when mixed into soil. We conclude that mixing compost in soil could result in greater net soil C gains compared to having compost and soil separate, particularly under moist conditions.

Food availability determines the amount of energy animals can acquire and allocate to reproduction and other necessary functions. Female animals that are food limited thus experience reduced energy available for reproduction. When this occurs, females may reduce frequency of reproductive events or the number or size of offspring per reproductive bout. We assessed how maternal diet affects reproductive output in adult female Murray River short-necked turtles, Emydura macquarii, from four wetlands in Victoria. We previously found that turtle diets differ in the composition of plants and animals between our study wetlands. In this study, we tested whether differences in turtle diet composition (i.e. plants and animals) at these wetlands were associated with differences in clutch mass, individual egg mass, bulk egg composition and hatching success. We found total clutch mass increased with maternal body size at each site. At sites where filamentous green algae were scarce and E. macquarii were carnivorous, females produced smaller clutches relative to body size compared to females from sites where algae were abundant, and turtles were more herbivorous. Individual egg mass, bulk egg composition and hatching success did not differ across wetlands. Isotopic analysis revealed significant positive relationships between the carbon and nitrogen isotopes (δ13C, δ15N) of the eggs and those of the mothers, indicating that mothers allocated ratios of carbon and nitrogen isotopes to their eggs similar to those present in their tissues. Our study suggests that at sites where females are more carnivorous due to a relative absence of algae, females produce smaller clutches, but other aspects of their reproduction are not significantly impacted. The reduction in clutch size associated with differences in the availability of dietary plants and animals may have long-term consequences for E. macquarii and other freshwater turtle species that are experiencing population declines.

Rhizodeposition is organic matter released by living plant roots that can be transformed by microbes into particulate organic matter (POM), but that can also become more stable through the adsorption of organic matter onto soil minerals (mineral-associated organic matter, MAOM), thereby playing an important role in mitigating climate change. We examined how root-derived carbon (C) as a proxy for rhizodeposition contributed to POM and MAOM formation in a grassland affected by nitrogen (N) fertilisation and defoliation frequency, and to what degree rhizodeposition was incorporated into microbial biomass. We applied N fertiliser (0 vs. 40 kg N ha−1 yr−1) and defoliation frequencies (3–4 vs. 6–8 clipping events year−1, simulating low and high grazing intensity) for three years, then used a 13CO2 pulse labelling technique to examine the incorporation of rhizodeposition into microbial biomass, POM and MAOM fractions. With N fertilisation, rhizodeposition contributed less to the formation of MAOM compared to the formation of POM, while defoliation frequency decreased the contribution of rhizodeposition into both POM and MAOM, particularly with N fertilisation. Although the MAOM fraction was relatively rich in N (C: N ratio of 10.5 vs. 13.5 for POM), our results suggest that adding inorganic N promoted the formation of POM more than of MAOM from rhizodeposition. A large proportion of rhizodeposition was taken up by microbes that eventually could contribute to POM and MAOM formation. Our results provide insightful information regarding the stabilisation of rhizodeposition into different soil organic matter pools.

Both root exudates and root litter can improve soil structure (i.e., soil aggregation) and enhance soil carbon (C) content for optimal soil functioning in the ecosystem. While soil bacteria and fungi are considered as key microbes for the decomposition of organic plant inputs, their role in decomposing and stabilizing root exudates and litter in aggregates are still not fully understood. We conducted a 16-day incubation study to investigate the role of soil bacteria vs fungi in the decomposition of 13C labeled glucose (labile C as a surrogate for root exudates) and 13C labeled wheat root biomass (complex C). Bronopol and captan were used to suppress bacterial and fungal activity, respectively, in the soil. During the incubation period, we measured total soil respiration, microbial biomass C (MBC), and calculated the decomposition, microbial C use efficiency (CUE) and the soil priming effects of added glucose and wheat root litter. We further separated three aggregate size classes (macroaggregates, microaggregates, and silt and clay fraction) and measured the total aggregate C content and the 13C recovered in each aggregate size class from the added labile C (glucose) and complex C (wheat root biomass). As expected, the decomposition of both substrates was reduced significantly when biocides were added, and the decomposition rate of glucose was significantly higher than of wheat root litter. The MBC decreased at the end of incubation, particularly when bronopol was added alone or in combination with captan. The biocide manipulation of the microbial communities caused differences in the microbial CUE that were substrate-dependent. However, the microbial CUEs of the substrates were not related to soil aggregation. The mean weight diameter (MWD) of aggregates at the end of the incubation was significantly reduced when captan was added, either alone or in combination with bronopol, independent of substrate type, suggesting that fungi played an important role in soil aggregation. On the other hand, fungi were also important for soil organic matter decomposition, as indicated by the reduced soil priming effect when captan was added, particularly for wheat root biomass. We conclude that while both bacteria and fungi were important for decomposition of added substrates to the soil, fungi played a larger role in both soil C protection through aggregation and C loss through priming effects.

Utilization of grains of local grasses by Australia's First Nations people for food and connection to Country has largely been lost due to colonization. Native Australian grain production has the potential to deliver environmental, economic, nutritional and cultural benefits to First Nations people and the wider community. Revitalization of the native grain food system can only be achieved if relevant properties of the grains are elucidated. This study aimed to characterize the grain structure and histochemistry of four Australian native grasses: Dactyloctenium radulans (Button Grass), Astrebla lappacea (Curly Mitchell Grass), Panicum decompositum (Native Millet) and Microlaena stipoides (Weeping Grass). For these species, as well as wheat and sorghum, whole-grain images were obtained via stereo microscopy, starch and the embryo were visualized, and sections of fixed grains were imaged via bright-field and fluorescence microscopy. The shape, size and colour of the whole native grains varied between the species. The aleurone layer was one-cell thick in the native species, as in the domesticated grains, except for Weeping Grass, which had a two-cell-thick aleurone. In the native grains, endosperm cell walls appeared thinner than in wheat and sorghum. Starch granules in Button Grass, Curly Mitchell Grass and Native Millet were found mainly in the central region of the starchy endosperm, with very few granules in the sub-aleurone layer, whereas Weeping Grass had abundant starch in the sub-aleurone. Protein appeared most abundant in the aleurone and sub-aleurone layers of the native grains, although in Button Grass, the starchy endosperm was observed to be rich in protein, as in wheat and sorghum. As a proportion of the whole grain, the embryo was larger in the native species than in wheat. The differences found in the grain properties among the four native Australian species have important implications for the agri-food industry in a changing climate.