Formation of mineral-organic associations is a key process in the global carbon cycle. Recent concepts propose litter quality-controlled microbial assimilation and direct sorption processes as main ...factors in transferring carbon from plant litter into mineral-organic associations. We explored the pathways of the formation of mineral-associated organic matter (MOM) in soil profiles along a 120-ky ecosystem gradient that developed under humid climate from the retreating Franz Josef Glacier in New Zealand. We determined the stocks of particulate and mineral-associated carbon, the isotope signature and microbial decomposability of organic matter, and plant and microbial biomarkers (lignin phenols, amino sugars and acids) in MOM. Results revealed that litter quality had little effect on the accumulation of mineral-associated carbon and that plant-derived carbon bypassed microbial assimilation at all soil depths. Seemingly, MOM forms by sorption of microbial as well as plant-derived compounds to minerals. The MOM in carbon-saturated topsoil was characterized by the steady exchange of older for recent carbon, while subsoil MOM arises from retention of organic matter transported with percolating water. Overall, MOM formation is not monocausal but involves various mechanisms and processes, with reactive minerals being effective filters capable of erasing chemical differences in organic matter inputs.
Evaluating conflicting theories about the influence of mountains on carbon dioxide cycling and climate requires understanding weathering fluxes from tectonically uplifting landscapes. The lack of ...soil production and weathering rate measurements in Earth's most rapidly uplifting mountains has made it difficult to determine whether weathering rates increase or decline in response to rapid erosion. Beryllium-10 concentrations in soils from the western Southern Alps, New Zealand, demonstrate that soil is produced from bedrock more rapidly than previously recognized, at rates up to 2.5 millimeters per year. Weathering intensity data further indicate that soil chemical denudation rates increase proportionally with erosion rates. These high weathering rates support the view that mountains play a key role in global-scale chemical weathering and thus have potentially important implications for the global carbon cycle.
This study quantifies progressive pedogenesis under a super-humid climate on the west coast of South Island, New Zealand. It focuses on soil morphology, pedogenic oxides, soil mass balance, ...phosphorus transformation and linking pedogenesis trajectories to vegetation communities. The study comprises a set of dune ridges of a coastal sand dune complex covered by unmodified conifer (podocarp)-angiosperm forest. The surface ages of the chronosequence range from 370
y to 6500
y. Rapid podzolisation is characteristic for the study area. Within 1000
y, soils reach the Spodosol stage with typical eluvial–illuvial horizons and mobilisation of Fe and Al. This period is also characterised by the most rapid losses of total phosphorus at a rate of 110
g
m
−
2
ky
−
1
, a relative loss of 41%. Beyond 3000
y changes in soil chemistry and losses for all nutrients markedly slow. Soil mass balance shows that the 6500
y soil has lost 75% total P, 62% K, 52% Ca and 54% Na. Soil P fractions substantially change across the gradient. High leaching losses of apatite and non-occluded P in the first hundreds of years coincide with accumulation of organic and occluded inorganic forms in the topsoil and subsoil, which mitigate total P loss. Beyond 1000
y of pedogenesis, all P fractions decline at similar rates to low, more persistent levels with apatite/non-occluded P being the dominant P form after 6500
y of pedogenesis. This incipient steady state is assumed to be sustained by the advection of parent material-derived P through surface lowering and reduced biological cycling. Vegetation communities change from more diverse communities on young and less impoverished soils in the first 1000
y to less diverse and less variable communities beyond 1000
y of ecosystem development. The soil evolution-correlated vegetation changes documented in this study are consistent with general schemes of vegetation succession for the west coast of South Island.
► Key transformations in soils occur within the first 1000
y of pedogenesis. ► Podzolisation can trigger gleying processes by forming drainage impeding horizons. ► Holocene leaching losses of nutrients are severe and not linear with time. ► Phosphorus fractionation data is not fully consistent with the Walker & Syers model. ► Pedogenesis and vegetation communities are strongly correlated.
The inventory of soil phosphorus (P) is subject to significant changes over time. The main primary form, bedrock‐derived apatite P, becomes progressively lost through leaching, or transformed into ...more immobile and less plant‐accessible, secondary organic and mineral forms. Here we studied the rejuvenating effect of dust deposition on soil P along an active dust flux gradient downwind of a braided river. Along the gradient, we measured soil P fractions to 50 cm depth of six Spodosols and one Inceptisol, supplemented by tree foliage P concentrations. While an increasing dust flux correlates with a twofold increase of foliar P and soil organic P along the gradient, apatite P declines from ~50 to 3 g m−2 and total P shows no response. Compared to dust‐unaffected Spodosols, depth distribution of total P becomes increasingly uniform and organic P propagates deeper into the soil under dust flux. Further, the effect of topsoil P eluviation attenuates due to higher organic P content and the zone of high apatite P concentrations associated with un‐weathered subsoil becomes progressively removed from the upper 50 cm. We interpret these patterns as being consistent with upbuilding pedogenesi and conclude that dust‐derived mineral P is assimilated in the organic surface horizon and does not reach the mineral soil. Dust‐derived mineral P is temporarily stored in the living biomass and returns to the soil with plant and microbial detritus as organic P, which is subsequently buried by further dust increments. We further conclude that (1) the efficiency of P fertilization of the ecosystem by dust accession is higher than through P advection in dust‐unaffected Spodosols and (2) organic P may serve as an important source of labile P in a high‐leaching environment.
Key PointsIncrease of organic phosphorus and decrease of apatite phosphorusDust deposition positively affects foliar phosphorus concentrationsRapid assimilation of dust‐derived phosphorus through biota
•More intensive land use led to higher risk of soil structural degradation (SSD) in NZ.•Pasture production declined by 2.5% for each 1% (0.01 cm3 cm−3) decrease in macroporosity.•Compaction increased ...N2O emissions by 51–814% (grazing) and 19–1300% (traffic).•Compaction effects on contaminant losses via runoff and drainage were inconsistent.•Estimating costs of SSD is challenging due to the lack of data.
Agricultural intensification has enhanced productivity, but has also negatively affected soil structure and environmental outcomes. Agriculture is among New Zealand (NZ)'s largest industries. Like other countries, significant land use intensification over the last 20–30 years has occurred in NZ, resulting in undesirable side-effect of soil structural degradation (SSD) (e.g., soil compaction, aggregate fragmentation). Using NZ as a case study, we reviewed and, where possible, quantified the extent of SSD in NZ and its impacts and implications on production, contaminant losses via drainage and runoff, and N2O emissions. Knowledge gaps were identified that will help guide future research both in NZ and internationally. Our review revealed that SSD is common in many regions and under different land uses in NZ. At the national scale, 44% of sites monitored between 2014 and 2017 were below the national target for macroporosity (pore diameter > 30 μm). The occurrence of SSD was greater under more intensive land uses such as dairying and continuous cropping. Soil structural degradation from compaction is typically associated with reduced pasture and crop production. In NZ, pasture production was estimated to decrease by an average of 2.5% for every 1.0% (0.01 cm3 cm−3) decrease in macroporosity (0–10 cm soil). Compaction from livestock treading and wheel traffic has been shown to increase N2O emissions by 51–814% and 19–1300%, respectively, with no significant evidence that this increase is related to N loading. Effects of compaction on contaminant losses via runoff and drainage, and in particular via preferential flow, are less well researched and findings were less consistent and dependent on many factors including the degree of compaction. Important knowledge gaps include a lack of quantitative relationships between degree of SSD and soil hydraulic properties and processes (e.g., water movement and contaminant losses), and poor knowledge of critical thresholds or optimum ranges of soil physical indicators in relation to critical ecosystem services (e.g., pasture yield, gas and water regulation in soils). We also found few estimates of SSD-induced costs related to production and environmental outcomes (e.g., contaminant losses and N2O emissions) at either farm system, regional or national scales. More data are needed to better determine the true costs and implications for farm production and environmental effects associated with SSD.
•Methods and influencing factors of soil structural vulnerability are critically reviewed.•Soil structural susceptibility, vulnerability, and risk are distinguished by their controls.•Current state ...of soil structure and vulnerability need be included to assess soil structure.•Effects on ecosystem services are highlighted in soil structural vulnerability assessment.
Soil structure affects a range of soil functions (e.g., water, air, heat, and nutrient transport) and ecosystem services (e.g., production, climate regulation). Agricultural intensification is a dominant factor in global soil structural degradation. Understanding the vulnerability of soils to structural degradation may be important to land use planning and identifying management practices that mitigate the risk of degradation. We review the current methods for assessing soil structural vulnerability and the influencing factors, focussing on soil compaction and aggregate breakdown as two key measures of structural degradation. Methods for assessing risk of soil structural degradation and management practices affecting the risk are also discussed. Critical research gaps are identified, including the lack of studies that demonstrate the link between soil structural vulnerability and loss of soil functions or ecosystem services. Our review of the literature identified that the terms susceptibility, vulnerability, and risk are often used interchangeably. We propose definitions that can be used to distinguish these terms. Soil properties (relatively static), soil wetness, and land use stress (e.g., climate and management practices) are progressively included in the assessments of soil structural susceptibility, vulnerability, and risk. Existing indicators for assessing soil structural vulnerability may not be suitable to predict potential effects on ecosystem services. We highlight that soil structural vulnerability assessments should focus on key soil structural indicators (e.g., pore network-based hydraulic properties) affecting soil functions and ecosystem services. Both the state (i.e., condition) of soil structure and its vulnerability should be included for assessing soil structural degradation. To overcome the limitations of previous assessments, we developed a conceptual model linking soil structural vulnerability assessment to loss of soil functions and ecosystem services. Our review provides insights on assessment metrics and frameworks to develop management practices that improve soil structure and delivery of ecosystem services.
Chemical weathering influences many aspects of the Earth system, including biogeochemical cycling, climate, and ecosystem function. Physical erosion influences chemical weathering rates by setting ...the supply of fresh minerals to the critical zone. Vegetation also influences chemical weathering rates, both by physical processes that expose mineral surfaces and via production of acids that contribute to mineral dissolution. However, the role of vegetation in setting surface process rates in different landscapes is unclear. Here we use 10Be and geochemical mass balance to quantify soil production, physical erosion, and chemical weathering rates in a landscape where a migrating drainage divide separates catchments with an order-of magnitude contrast in erosion rates and where vegetation spans temperate rainforest, tussock grassland, and unvegetated alpine ecosystems in the western Southern Alps of New Zealand. Soil production, physical erosion, and chemical weathering rates are significantly higher on the rapidly eroding versus the slowly eroding side of the drainage divide. However, chemical weathering intensity does not vary significantly across the divide or as a function of vegetation type. Soil production rates are correlated with ridgetop curvature, and ridgetops are more convex on the rapidly eroding side of the divide, where soil mineral residence times are lowest. Hence our findings suggest fluvially-driven erosion rates control soil production and soil chemical weathering rates by influencing the relationship between hillslope topography and mineral residence times. In the western Southern Alps, soil production and chemical weathering rates are more strongly mediated by physical rock breakdown driven by landscape response to tectonics, than by vegetation.
•A drainage divide is migrating at Gunn Ridge, western Southern Alps, New Zealand.•Topography and soils respond to differences in erosion on each side of the divide.•Soil production and chemical weathering rates are strongly influenced by erosion.•The influence of vegetation on chemical weathering is masked by differences in erosion.•Silicate weathering is focused on soil-mantled portions of the landscape.
•Gradient Forest was used to study soil-type turnover along environmental gradients.•Soil-forming factors were ranked and transformed to amplify their critical parts.•The transformed variables were ...segmented into regions, at three levels of scale.•The resulting segments were clustered to produce discrete soilscapes.•Validation showed the soilscapes delineation yielded sensible results at all scales.
Soilscapes are a regionalisation of the landscape into a suite of contiguous segments with an homogeneous set of soil forming factors. The concept has been present in the soil science literature since the late 1950s, proving to be a useful framework for generalising traditional soil survey maps. This concept is inherently multi-scale, and current approaches generally build either on existing soil maps, or on cluster analysis of environmental proxies of soil forming factors. In this study, in parallel with the concept of beta-diversity in numerical ecology, we built a soilscape regionalisation for New Zealand based on detecting the turnover in soil types along different environmental gradients. It was implemented using Gradient Forest, a method that analyses the frequency of species (in our case, soil type) turnover alongside such gradients, which are then ranked relative to their ecological (in our case, pedological) relevance. Based on this analysis, the environmental covariates were transformed to amplify their most important parts in terms of soil type turnover. The transformed variables were then segmented into contiguous regions, at three different levels of scale. Finally, hierarchical clustering was used to produce discrete soilscapes, at different scales, and for the entire country. This approach was developed using pseudo-observations derived from a national scale coverage of soil types, and validated using an independent set of actual soil profile observations. Validation results reveal strong agreement between the dissimilarity quantified between soilscapes and the taxonomic distance between actual soil profile observations (R = 0.61, P < 0.001). We expect the resulting layers from this soilscape delineation exercise to be used for a diverse suite of pedometrics applications, from stratifying soil sampling schemes, to optimising the soil survey boundaries, and for digital soil mapping.
•Managing land requires a wider consideration of on-site and off-site impacts.•An ecosystems service perspective supports this wider consideration.•A framework of soil, land and landscape functions ...was devised.•This included functions describing the resistance of land to pressure.•A hypothetical example shows how the framework can inform users about suitability.
Land information has in the past focused on the key land and soil properties that physically or chemically support or limit the use of land. With the increasing focus on the environmental, social, and cultural impacts of land-use decisions beyond the boundaries of individual land parcels, there is a growing need for more extensive land resource information to support assessments of the benefits, impacts, and trade-offs of land-use decisions. We present a new framework for providing land resource information to support an ecosystem-service-based approach to land-use related policy development. The new framework, called “the Land Resource Circle”, is first conceptually defined, then its use is explored in a hypothetical example. It draws upon the literature on soil functions and their contribution to ecosystem services. In addition, it recognizes that soils differ in their capacity for resisting the various pressures due to land use and/or climate. It also recognizes that the surrounding landscape provides functionality that can affect the delivery of ecosystem services from a land parcel and its suitability for different land uses. The Land Resource Circle is designed as a flexible and comprehensive information resource that can be used to build classifications underpinning spatial planning policy and regulation and land assessment, and to increase awareness of all the ecosystem services provided by land.
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