Changes In Soil Nitrogen Research Articles

Effect of peanut straw mulching on the soil nitrogen change and functional genes in the Camellia oleifera intercropping system

Effect of peanut straw mulching on the soil nitrogen change and functional genes in the Camellia oleifera intercropping system

Increased nitrogen accumulation in mulberry trees due to the secretion of glomalin-related soil protein induced by arbuscular mycorrhizal fungi

In the initial stages of restoring areas affected by rocky desertification, plant survival is strongly influenced by nitrogen nutrition. Mycorrhization is a unique type of inter-root engineering that improves nitrogen acquisition efficiency by plant roots. We selected potted mulberry trees inoculated, two dominant arbuscular mycorrhizal fungi (AMF) with Funneliformis mosseae (Fm) and Rhizophagus intraradices (Ri), to clarify the effects of AMF on the root nitrogen content of mulberry trees. Meanwhile, the key factors of soil nitrogen changes caused by AMF were analyzed, based on the primary role of soil nitrogen as the source of root nitrogen. Simultaneously, the potential of AMF to promote the acquisition of different forms of nitrogen by mulberry roots was investigated. Our findings indicate that the inoculation of mulberry plants with Fm and Ri, improved plant height and increased nitrogen accumulation in the roots and shoots. Additionally, AMF regulates nitrogen transformation, significantly increasing soil nitrate nitrogen (NO3−-N) and dissolved organic nitrogen (DON) levels. The results indicated that soil NH4+-N, NO3−-N, and DON contributed to the observed changes in root nitrogen accumulation. The largest contribution (22.0 %) to the overall effect size was made by NO3−-N. AMF stimulated soil microbial activity and significantly increased soil glomalin-related soil protein (GRSP), enzyme activity, and soil microbial biomass (SMB). Urease activity and microbial biomass carbon (MBC) both increased exponentially by 118.7 % and 115.2 %, respectively. Higher GRSP, enzyme activity, and SMB were positively correlated with changes in soil nitrogen patterns, and GRSP had the most significant effect on changes in the soil nitrogen dynamics. Our study confirmed that inoculation with AMF not only regulates soil nitrogen dynamics but also diversifies plant nitrogen sources. This is achieved by increasing plant growth and enhancing soil microbial activity. Ultimately, this enhances plant root nitrogen nutrition. Therefore, AMF promote root nitrogen accumulation and enhance root nitrogen uptake through GRSP-regulated soil nitrogen, providing a theoretical basis for the management of rocky desertification.

Effects of nitrogen addition and drought on the relationship between nitrogen- and water-use efficiency in a temperate grassland

BackgroundNitrogen- and water-use efficiency (NUE and WUE) reflect the capacity of plants to take up and utilize resources in the environments. Although N deposition and drought are known to affect plant growth and persistence, it remains elusive how plants adjust NUE, WUE and their relationship to adapt to the concurrent N deposition and drought under the context of global change. We conducted a field experiment in a temperate grassland in Inner Mongolia, in which N addition (10 g m–2 yr−1), drought (reduced 66% precipitation during growing season) and their combination were manipulated, and we explored the responses of both instantaneous (NUEINST and WUEINST) and long-term (NUELT and WUELT) WUE and NUE for six common plant species (Leymus chinensis, Stipa baicalensis, Thermopsis lanceolata, Potentilla bifurca, Thalictrum squarrosum, Klasea centauroide).ResultsAcross all the six species, NUEINST decreased and WUEINST increased with both N addition and drought; NUELT decreased with both N addition and drought, while WUELT decreased with N addition and increased with drought. A significant interactive effect between N addition and drought was detected, in that, drought weakened the negative effect of N addition on WUELT and NUELT, and N addition weakened the negative effect of drought on NUELT, but enhanced the positive effect of drought on WUELT. As a consequence, drought caused a trade-off between NUE and WUE, and N addition brought forth positive correlation between NUE and WUE. Meanwhile, the relationship between NUE and WUE varied among the species of different functional groups.ConclusionsOur study demonstrated that NUE, WUE and their relationship play an important role in determining their responses and adaptability to changes in soil nitrogen and water availability induced by N deposition and drought. Our results shed light on the antagonistic, synergetic and neutral effects between nitrogen deposition and drought on resource use efficiency, and further clarified the different adaptability among species of different functional groups, which will conduce to a comprehensive understanding on the role of NUE and WUE in plant persistence and coexistence in grassland ecosystems.

Soil nitrogen fertilization reduces relative leaf nitrogen allocation to photosynthesis.

The connection between soil nitrogen availability, leaf nitrogen, and photosynthetic capacity is not perfectly understood. Because these three components tend to be positively related over large spatial scales, some posit that soil nitrogen positively drives leaf nitrogen, which positively drives photosynthetic capacity. Alternatively, others posit that photosynthetic capacity is primarily driven by aboveground conditions. Here, we examined the physiological responses of a non nitrogen-fixing plant (Gossypium hirsutum) and a nitrogen-fixing plant (Glycine max) in a fully factorial combination of light by soil nitrogen availability to help reconcile these competing hypotheses. Soil nitrogen stimulated leaf nitrogen in both species, but the relative proportion of leaf nitrogen used for photosynthetic processes was reduced under elevated soil nitrogen in all light availability treatments due to greater increases in leaf nitrogen content than chlorophyll and leaf biochemical process rates. Leaf nitrogen content and biochemical process rates in G. hirsutum were more responsive to changes in soil nitrogen than G. max, likely due to strong G. max investments in root nodulation under low soil nitrogen. Nonetheless, whole plant growth was significantly enhanced by increased soil nitrogen in both species. Light availability consistently increased relative leaf nitrogen allocation to leaf photosynthesis and whole plant growth, a pattern that was similar between species. These results suggest that the leaf nitrogen-photosynthesis relationship varies under different soil nitrogen levels and that these species preferentially allocated more nitrogen to plant growth and non-photosynthetic leaf processes, rather than photosynthesis, as soil nitrogen increased.

Impacts of soil nutrition on floral traits, pollinator attraction, and fitness in cucumbers (Cucumis sativus L.)

Annual plants allocate soil nutrients to floral display and pollinator rewards to ensure pollination success in a single season. Nitrogen and phosphorus are critical soil nutrients whose levels are altered by intensive land use that may affect plants’ fitness via pollinator attractiveness through floral display and rewards. In a controlled greenhouse study, we studied in cucumbers (Cucumis sativus) how changes in soil nitrogen and phosphorus influence floral traits, including nectar and pollen reward composition. We evaluated how these traits affect bumble bee (Bombus impatiens, an important cucumber pollinator) visitation and ultimately fruit yield. While increasing nitrogen and phosphorus increased growth and floral display, excess nitrogen created an asymptotic or negative effect, which was mitigated by increasing phosphorus. Male floral traits exhibited higher plasticity in responses to changes in soil nutrients than female flowers. At 4:1 nitrogen:phosphorus ratios, male flowers presented increased nectar volume and pollen number resulting in increased bumble bee visitation. Interestingly, other pollinator rewards remained consistent across all soil treatments: male and female nectar sugar composition, female nectar volume, and pollen protein and lipid concentrations. Therefore, although cucumber pollination success was buffered in conditions of nutrient stress, highly skewed nitrogen:phosphorus soil ratios reduced plant fitness via reduced numbers of flowers and reward quantity, pollinator attraction, and ultimately yield.

Soil Greenhouse Gas Emissions and Nitrogen Change for Wheat Field Application of Composted Sewage Sludge

This study aimed at assessing the character of greenhouse emissions under different rates of composted sewage sludge as a nitrogen fertilization substitute, founding the characteristic of soil nitrogen change and, ultimately, providing a theoretical basis for the rational utilization of composted sewage sludge in calcareous soil. Compost sludge as a nitrogen fertilizer substitute has emission reduction effects on N2O, CH4 and CO2. Compared with that of the single fertilizer application, the GHGI under the 20% sludge replacement treatment was significantly reduced by 20.15%, and the global warming potential was significantly reduced by 11.53%, while the wheat yield was increased by 4.78%. Compost sludge as a nitrogen substitute significantly increased the soil organic carbon at the jointing stage and reached a 100% replacement ratio at the maturity stage. During the jointing and mature stages, the total nitrogen content of the soil increased significantly at the 100% replacement ratio, while the soil nitrate nitrogen content only increased significantly at the 50% and 100% replacement ratio. Our findings highlight the impact of sludge compost on greenhouse gas emissions and soil nitrogen and guide the use of sludge compost in wheat fields.

Effect of nitrogen limitation and soil biophysics on Holocene greening of the Sahara

Abstract. The so-called Green Sahara (GS), which was a wet and vegetative Sahara region in the early to mid-Holocene, provides useful information on our climate simulation because it is a consequence of complex interaction between biophysical and climatic processes. It is still a challenge to simulate the GS in terms of vegetative extent and precipitation using current climate models. This study attempts to simulate the Green Sahara 8000 years ago by using the state-of-the-art Earth system model CESM that incorporates the nitrogen cycle and the soil–precipitation feedbacks. Our study puts more emphasis on the impact of soil biophysical properties (e.g., bare-soil albedo, porosity, heat capacity, and hydraulic conductivity) and soil nitrogen influenced by soil organic matter on the simulation of the GS. In this coupled simulation, vegetation interacts with changes in soil properties and soil organic matter by phenology, decomposition, and allocation of carbon and nitrogen. With changes in the Earth's orbit and dust in the early to mid-Holocene, the model simulates increased precipitation in North Africa but does not capture the extent of the GS. Our analysis shows that the Holocene greening is simulated better if the amount of soil nitrogen and soil texture is properly modified for the humid and vegetative GS period. Soil biochemical and physical properties increase precipitation and vegetation cover in North Africa through their influence on photosynthesis and surface albedo as well as their consequent enhanced albedo–precipitation and evapotranspiration–precipitation feedbacks. Our findings suggest that future climate simulation needs to consider consequent changes in soil nitrogen and texture with changes in vegetation cover and density for proper climate simulations.

Soil Carbon Turnover and Changes in Soil Nitrogen under the Agropastoral System in Brazilian Savannas (Cerrados)

Soil Carbon Turnover and Changes in Soil Nitrogen under the Agropastoral System in Brazilian Savannas (Cerrados)

Enhanced atmospheric nitrogen deposition triggered little change in soil microbial diversity and structure in a desert ecosystem

Enhanced atmospheric nitrogen deposition can greatly influence the soil nitrogen content and soil microorganisms in terrestrial ecosystems. However, there is a lack of knowledge about the response of soil microbes to changes in soil nitrogen, particularly in desert ecosystems. To address this, we used long-term artificial nitrogen addition to simulate atmospheric nitrogen deposition in a desert ecosystem in Ningxia, China. We adopted a high-throughput sequencing method (16S rRNA and ITS) to explore the effects of different amounts of atmospheric nitrogen deposition on soil microbial diversity and community structure. Six years of nitrogen addition (6 g N m −2 y −1 ) significantly increased the soil organic carbon content and the total soil nitrogen content ( p < 0.05) and promoted the growth of Leymus secalinus . However, it did not significantly change the diversity and the structure of soil microbial communities ( p > 0.05). Further analysis revealed that nitrogen addition substantially reduced the number of positive correlations between soil microbial species and the number of core microbial species. Our results suggest that for desert ecosystems, at present, atmospheric nitrogen deposition may increase soil nitrogen use by some vegetation but it does not alleviate the competition for soil nitrogen between soil microbes and vegetation. Moreover, although enhanced atmospheric nitrogen deposition did not significantly change the soil microbial community structure, it may negatively affect the interactions among soil microbial species. This would hinder soil microbial adaptation to the changing environment and the development of desert ecosystems. • The current atmospheric nitrogen deposition cannot significantly change the diversity and structure of microbial community. • Vegetation (e.g. Leymus secalinus ) may be more competitive than soil microorganisms when using soil nitrogen in deserts. • The environmental factors hardly had significant correlations with soil bacterial community composition. • TN, soil pH and SOC had significant correlations with soil fungal community composition. • Enhanced atmospheric nitrogen deposition may negatively affect the interactions among soil microbial species.

Anthropogenic and climatic shaping of soil nitrogen properties across urban-rural-natural forests in the Beijing metropolitan region

Global urbanization has profoundly altered regional biogeochemical cycles across urban-rural-natural continuums. A better insight in the changes in soil nitrogen (N) properties across urban-rural-natural forests sheds lights on the impacts of urbanization on regional N cycles and ecological consequences. Based on a systematic survey in forest patches of twenty parks across the urban-rural-natural gradients in the Beijing metropolitan region, China, we analyzed the spatial variations of three soil N properties (i.e., total N, alkali-hydrolyzable N, and δ15N) and their potential drivers that are indicative for anthropogenic N sources (trunk road density for traffic N emissions; cropland share for agricultural N emissions), climate conditions (mean annual temperature, MAT; mean annual precipitation, MAP), forest conditions (forest coverage and the number of common tree species) and time for soil N accumulation since park establishment (park age). Soil total N concentration, alkali-hydrolyzable N concentration and δ15N values in the surface (0–10 cm) and subsurface layers (10–20 cm) all showed a decrease up to 40 km (i.e., the urban fertile island phenomenon) from the urban core and then an increase to values in peri-urban natural forests as high as those in urban forests. The spatial variations of the surface and subsurface soil total N concentrations and alkali-hydrolyzable N concentrations were, respectively, mainly and exclusively explained by park age, while trunk road density, MAP and MAT played a less important role in regulating the soil N variation in the surface layer. The spatial variations of the surface and subsurface soil δ15N values were respectively, mainly, and exclusively controlled by cropland share, while park age and MAP played a limited role in regulating the soil δ15N variation in the surface layer but not in the subsurface layer. Our findings reveal the way in which anthropogenic and climatic drivers shape soil N properties across the urban-rural-natural forests.

Mycorrhizal effects on decomposition and soil CO2 flux depend on changes in nitrogen availability during forest succession

Abstract Mycorrhizal fungi play a central role in plant nutrition and nutrient cycling, yet our understanding on their effects on free‐living microbes, soil carbon (C) decomposition and soil CO2 fluxes remains limited. Here we used trenches lined with mesh screens of varying sizes to isolate mycorrhizal hyphal effects on soil C dynamics in subtropical successional forests. We found that the presence of mycorrhizal hyphae suppressed soil CO2 fluxes by 17% in early‐successional forests, but enhanced CO2 losses by 20% and 32% in mid‐ and late‐successional forests respectively. The inhibitory effects of mycorrhizal fungi on soil CO2 fluxes in the young stands were associated with changes in soil nitrogen (N) mineralization and microbial activities, suggesting that competition between mycorrhizae and saprotrophs for N likely suppressed soil C decomposition. In the mid‐ and late‐successional stands, mycorrhizal enhancement of CO2 release from soil likely resulted from both hyphal respiration and mycorrhizal‐induced acceleration of organic matter decay. Synthesis. Our results highlight the sensitivity of mycorrhizal fungi‐saprotroph interactions to shifts in nutrient availability and demand, with important consequences for soil carbon dynamics particularly in ecosystems with low nutrient conditions. Incorporating such interactions into models should improve the simulations of forest biogeochemical cycles under global change.

Do predators have a role to play in wetland ecosystem functioning? An experimental study in New England salt marshes.

The historical ecological paradigm of wetland ecosystems emphasized the role of physical or “bottom‐up” factors in maintaining functions and services. However, recent studies have shown that the loss of predators in coastal salt marshes can lead to a significant reduction in wetland extent due to overgrazing of vegetation by herbivores. Such studies indicate that consumers or “top‐down” factors may play a much larger role in the maintenance of wetland ecosystems than was previously thought. The objective of this study was to evaluate whether altering top‐down control by manipulating the presence of predators can lead to measurable changes in salt marsh ecosystem properties. Between May and August of 2015 and 2016, we established exclosure and enclosure cages within three New England coastal wetland areas and manipulated the presence of green crab predators to assess how they and their fiddler and purple marsh crab prey affect changes in ecosystem properties. Predator presence was associated with changes in soil nitrogen and aboveground biomass at two of the three field sites, though the magnitude and direction of these effects varied from site to site. Further, path analysis results indicate that across field sites, a combination of bottom‐up and top‐down factors influenced changes in measured variables. These results challenge the growing consensus that consumers have strong effects, indicating instead that predator impacts may be highly context‐dependent.

Impact of Parthenium hysterophorus L. invasion on soil nitrogen dynamics of grassland vegetation of Indo-Gangetic plains, India.

The noxious plant species Parthenium hysterophorus L. has become a major concern for the conservation of many natural and managed areas. The species is known for its various adverse effects on the invaded ecosystems, particularly in terms of biodiversity loss. Currently, P. hysterophorus is a leading invasive species widespread in the grasslands of productive and diversity rich Indo-Gangetic plains of India and is responsible for various changes in the ecosystem. The present study addresses the changes that P. hysterophorus can bring in the vegetation structure (species richness, species evenness, and species composition) of the grasslands of Indo-Gangetic plain. To broaden our understanding of the invasion success and facilitated expansion, we also focus on the variability of soil nitrogen pool and processes as a consequence of invasion. We report that in the presence of P. hysterophorus, the species diversity, evenness, composition and richness were altered, affecting many native and non-native flora of the ecosystem. The effect was more prominent during the second and third year of the study with more increase in the invasion outcomes. Significant changes in soil nitrogen (N) dynamics, particularly, increased available (N), N-mineralization and microbial biomass N have been found in the invaded plots along with changes in vegetation of the grassland community. Overall, the result suggested that the invasive species, P. hysterophorus, modifies the soil and this modification is correlated with changes in vegetation structure and this situation is likely to further facilitate severe alterations in the ecosystem and could favor encroachment of other non-native species in the area.

Litter inputs drive patterns of soil nitrogen heterogeneity in a diverse tropical forest: Results from a litter manipulation experiment

Plant functional traits affect soil nutrient cycling in many ecosystems, but high levels of diversity make it challenging to identify their influence in tropical rainforests. Here, we used a litter manipulation experiment to demonstrate that differences in litter chemistry alone are sufficient to drive changes in soil nitrogen (N) cycling within a two-year period in a lowland tropical rainforest. Previously, we used airborne imaging spectroscopy to identify ten 0.25 ha plots on the Osa Peninsula of southwestern Costa Rica, each containing 10–20 emergent trees, with relatively high or low mean canopy N content (± 0.4 standard deviations of the landscape mean; n = 5 each). Plots with high canopy N content had higher soil inorganic N concentrations, faster net N cycling rates, and greater nitrous oxide (N2O) emissions. Because abiotic conditions were similar among the plot types, we hypothesized that litter inputs drove the formation of these high and low soil N patches. We tested this hypothesis with a reciprocal litter transplant experiment. After two years of monthly treatments, litter inputs from the high canopy N plots increased soil N availability in the low canopy N plots by 30% but had no measurable effects on net N cycling rates or N2O emissions. Surprisingly, litter inputs from the low canopy N plots increased soil N availability and net nitrification in the high canopy N plots. While somewhat counterintuitive from a canopy N perspective, these results may reflect a more nuanced effect of litter chemistry. Although low canopy N plot litter had lower N content than high canopy N plot litter, it leached relatively more and higher quality soluble carbon (C), which we speculate may have had a positive priming effect, releasing N from more recalcitrant compounds. Additionally, low canopy N plot litter supported higher rates of free-living N fixation, which could have directly increased soil N availability. Overall, our results show that tropical tree assemblages with differing foliar chemistry can directly influence soil properties through litter inputs, and that this effect may be mediated not only by litter N, but also relative C solubility and chemistry.

Influence of fire retardant and pyrogenic carbon on microscale changes in soil nitrogen and phosphorus

During wildfire season in the western US, fire retardant chemicals are dropped from aircraft in an effort to control the spread of fire. Fire retardant dropped on sites that are not actively burning results in exceptionally high soil nitrogen (N) and phosphorus (P) “fertilization” effect on wildland soils impacting terrestrial and aquatic ecosystems. Herein, we used microdialysis to evaluate the short-term spatiotemporal dynamics of soil inorganic N and ortho-P fluxes in response to wood pyrogenic carbon (PyC) on soils receiving fire retardant (Phos-Chek) in a 28-d column experiment. Retardant additions to soil induced dramatic increases in soil inorganic N and ortho-P flux rates. The addition of wood PyC to soils with retardant significantly and immediately reduced ortho-P flux rates at multiple depths (1, 5, and 10 cm) and reduced NH4+ flux rates at 10 cm while retaining flux rates at 1 and 5 cm. These effects were observed throughout the course of the experiment and were more pronounced towards the end of the experiment. By d-28, PyC significantly reduced the NH4+, NO3−, and ortho-P accumulation on ionic resins at soil column bottoms by 50%, 52%, and 43%, respectively. The application of wood PyC may be effective at buffering excess nutrient fluxes from fire retardant and reduce short-term nutrient leaching in unburnt forest soils exposed to fire retardant.

Soil Microbial Community Assembly and Interactions Are Constrained by Nitrogen and Phosphorus in Broadleaf Forests of Southern China

Subtropical and tropical broadleaf forests play important roles in conserving biodiversity and regulating global carbon cycle. Nonetheless, knowledge about soil microbial diversity, community composition, turnover and microbial functional structure in sub- and tropical broadleaf forests is scarce. In this study, high-throughput sequencing was used to profile soil microbial community composition, and a micro-array GeoChip 5.0 was used to profile microbial functional gene distribution in four sub- and tropical broadleaf forests (HS, MES, HP and JFL) in southern China. The results showed that soil microbial community compositions differed dramatically among all of four forests. Soil microbial diversities in JFL were the lowest (5.81–5.99) and significantly different from those in the other three forests (6.22–6.39). Furthermore, microbial functional gene interactions were the most complex and closest, likely in reflection to stress associated with the lowest nitrogen and phosphorus contents in JFL. In support of the importance of environmental selection, we found selection (78–96%) dominated microbial community assembly, which was verified by partial Mantel tests showing significant correlations between soil phosphorus and nitrogen content and microbial community composition. Taken together, these results indicate that nitrogen and phosphorus are pivotal in shaping soil microbial communities in sub- and tropical broadleaf forests in southern China. Changes in soil nitrogen and phosphorus, in response to plant growth and decomposition, will therefore have significant changes in both microbial community assembly and interaction.

The response of grassland mycorrhizal fungal abundance to a range of long-term grazing intensities

Keystone root symbiotic arbuscular mycorrhizal fungi play a major role in maintaining plant biodiversity, increasing plant productivity and enhancing storage of carbon in soil. AM fungi are ubiquitous and found in most ecosystems including grasslands currently experiencing increasing pressures form human activity. Grazing is known to impact AM fungi but very little is known about how AM fungi are affected by different levels of grazing intensity. Here we report on results from a long-term experimental site in a typical steppe in the north of China, containing seven levels of field-manipulated grazing intensities maintained for over 13 years. We assessed arbuscular mycorrhizal fungal abundance, represented by soil hyphal length density and mycorrhizal root colonization (mycorrhizal root frequency, intensity and arbuscule intensity) within the farm-scale field experiment. We also measured environmental variables to explain the responses of mycorrhizal fungi to grazing intensity. Our results showed that with an increase in grazing intensity, soil hyphal length density linearly decreased. There was, however, no significant trend for mycorrhizal root colonization variables in relation to grazing intensity. Mycorrhizal root frequency was negatively correlated with topographic-induced changes in soil nitrogen and phosphorus, while arbuscule intensity was marginally negatively correlated with soil available phosphorus. Further, we found a possible hump-shaped relationship between the ratio of external to internal AM fungal structures and grazing intensity. Our finding showed that external AM fungal structure was clearly impacted by grazing intensity but that this was not the case for internal mycorrhizal structures. This indicated that mycorrhizal functioning was impacted by the intensity of grazing as the mycorrhizal structures responded differently. Indeed the ratio of the foraging extra-radical mycorrhizal hyphae to intra-radical mycorrhizal structures was highest at moderate grazing intensity but strongly decreased by high grazing intensity. Our study suggests that the impacts of grazing intensity on the plant-AMF association could lead to further knock-on effects on the plant-soil system via the feedbacks that exist between plant and AMF communities.

Changes in Soil Nitrogen, Phosphorus, and Carbon Stocks in a Forest Ecosystem at Different Successional Stages in Leyte, Philippines

Forests play a vital role in the global carbon cycle since these are sources and sinks of carbon. This study was conducted to evaluate the changes in soil carbon stocks and some essential nutrients of different succession stages in two different soil types in Leyte Province. A space-fortime substitution approach was done in this study. Measurements of the physical, chemical, and biological properties of the soils were done following standard methods. The sites were characterized as Ultisol (Site 1 – Baybay, Leyte) and Andisol (Site 2 – Ormoc City). Results showed no significant differences among all the soil properties in the different forest succession stages in each site. However, variation in soil properties between sites was clearly observed. Site 2 had higher soil porosity and water holding capacity, but had lower bulk density than Site 1. Soils in Site 2 were more acidic, had higher total organic carbon, total N, and CEC but had pot, lower exchangeable bases and CEC than in Site 1. Both sites had low eff available P. The C:N ratios in all forest successions were significantly lower in Site 1 than in Site 2. This conforms to the results of substrate-induced respiration, where Site 1 was more active in CO evolution than Site 2. 2 Moreover, the soils in Site 2 significantly contained more SOC stocks (108- -1 -1 180 Mg C ha ) than in Site 1 (49-76 Mg C ha ). However, SOC stocks did not vary significantly in both sites. This result implies that the determination of soil physico-chemical properties is important in evaluating the changes of C:N ratios as well as of SOC stocks. In this study, Andisols had higher potential in storing organic C than Ultisols.

Soil nitrous oxide flux following land-use reversion from Miscanthus and SRC willow to perennial ryegrass.

Decarbonization of the world's energy supply is essential to meet the targets of the 2016 Paris climate change agreement. One promising opportunity is the utilization of second generation, low input bioenergy crops such as Miscanthus and Short Rotation Coppice (SRC) willow. Research has previously been carried out on the greenhouse gas (GHG) balance of growing these feedstocks and land‐use changes involved in converting conventional cropland to their production; however, there is almost no body of work understanding the costs associated with their end of life transitions back to conventional crops. It is likely that it is during crop interventions and land‐use transitions that significant GHG fluxes might occur. Therefore, in this study, we investigated soil GHG fluxes over 82 weeks during transition from Miscanthus and SRC willow into perennial ryegrass in west Wales, UK. This study captured soil GHG fluxes at a weekly time step, alongside monthly changes in soil nitrogen and labile carbon and reports the results of regression modelling of suspected drivers. Methane fluxes were typically trivial; however, nitrous oxide (N2O) fluxes were notably affected, reverted plots produced significantly more N2O than retained controls and Miscanthus produced significantly higher fluxes overall than willow plots. N2O costs of reversion appeared to be contained within the first year of reversion when the Miscanthus plots produced an average pregrass flux of 0.13 mg N2O m−2 hr−1 while for willow, this was 0.03 mg N2O m−2 hr−1. Total N2O emission from reversion increased the carbon cost over the lifetime of the Miscanthus from 6.50 to 9.91 Mg CO2 eq. ha−1 while for the willow, this increase was from 9.61 to 10.42 Mg CO2 eq. ha−1. Despite these significant increases, the carbon cost of energy contained in these perennial crops remained far lower than the equivalent carbon cost of energy in coal.

Availability and species diversity of forest products in a Neotropical rainforest landscape

Abstract Tropical rainforests harbor a high diversity of tree species, offering a potentially rich array of timber (TFP) and non-timber (NTFP) forest products. The supply of such products has been commonly evaluated at the local (plot) scale; however, little is known about how their availability and diversity change at the landscape scale, particularly in heterogeneous environments. This information is critical in designing landscape forest management programs. Here, we assess the extent to which the frequency, abundance, diversity, composition and productivity (aboveground biomass) of tree assemblages with potential forest products (PFPs) change across three landscape units (LUs) that differ in soil and topographic conditions. The study was carried out in a well-conserved old-growth tropical rainforest in southeastern Mexico. Three plots (0.5 ha each) were established per LU, in which all trees ≥ 10 cm were inventoried, taxonomically identified and assigned to eight forest product categories. General linear models, multiple regression and ordination analysis (CCA) were used to assess structural and compositional changes in the tree assemblages supplying different PFPs among LUs and along soil physicochemical gradients. More than half (94 species, 57%) of the total number of identified species (165) had one or more PFPs, mostly related to timber products. Ordination analysis showed that the abundance of species with different PFPs has a heterogeneous distribution among LUs, mostly related to changes in soil nitrogen, pH and aluminum saturation. Variation among LUs in terms of tree biomass was strongly driven by soil available phosphorus and soil physiological depth. Each LU had a different potential to provide forest products, producing a diverse mosaic of PFPs within the landscape. Decisions concerning sustainable forest management should consider such variability in the availability and diversity of forest products across landscapes, as well as the environmental factors that govern this spatial variation.