Soil Nutrient Dynamics Research Articles

Soil pH, Soil Organic Matter, and Crop Yields in Winter Wheat–Summer Fallow Systems

Core Ideas Continuous addition of ammonical N fertilizer increases soil acidity. Soil acidification influences nutrient dynamics and crop yields. Soil organic C and soil N decreased over years under winter wheat–summer fallow system. Soil acidifcation was not related with soil organic carbon and soil N loss over years. Soil acidification should be carefully monitored in systems using ammonical N fertilizers. Soil acidification has become a major environmental challenge for crop production in the inland Pacific Northwest (iPNW). We evaluated the effects of tillage and N‐fertilizer management on soil pH, soil organic carbon (SOC), soil N, and crop yields from 1995 through 2010 in an ongoing long‐term experiment in eastern Oregon. Tillage systems included moldboard plow (MP), disk plow (DP), and subsurface sweep (SW) and N‐fertilizer rates were 0, 45, 90, 135, 180 kg N ha−1 crop−1 in a dryland winter wheat (Triticum aestivum L.)–summer fallow (WW–SF) system. Soil pH, SOC, and N were monitored in 1995 and 2010, and crop yields were monitored every other year. Soil pH was lower in the higher N rate treatments. Long‐term N fertilizer application increased soil acidity in 0‐ to 10‐cm depth by 0.3, 0.2, and 0.3 units in MP, DP, and SW, respectively, for every 1000 kg N applied through ammonical N fertilizers. Soil pH was higher in DP than MP in 10‐ to 20‐ and 20‐ to 30‐cm depth profiles. The SOC and N concentrations in the top 30‐cm depth were lower in 2010 than in 1995 across all treatments. Wheat yield increased significantly with increase in N rates from 0 to 90 kg N ha−1 crop−1. There were no further yield increases above 90 kg N ha−1 crop−1. Soil acidification, SOC and nutrient dynamics should be carefully monitored in cropping systems using ammonical N fertilizers, particularly under high rate of N application and reduced tillage.

Improvement in Productivity, Water-Use Efficiency, and Soil Nutrient Dynamics of Summer Peanut (Arachis hypogaea L.) through Use of Polythene Mulch, Hydrogel, and Nutrient Management

ABSTRACTAgronomic management through better use of inputs benefits farmers both by enhancing productivity and profitability. A field experiment was conducted in consecutive summer seasons (2011–2013) consisting of two mulching (no mulch, polythene mulch), three hydrogel (0, 2.5, 5.0 kg ha−1), and three nutrient management treatments (organic, inorganic, and integrated) in a split–split plot design. Use of mulching and 2.5 kg hydrogel ha−1 and integrated nutrient management enhanced pod, haulm, kernel and oil yields, and net economic returns. Partial factor productivity and water-use efficiency were higher under polythene mulch and 5.0 kg hydrogel ha−1. Higher nutrient uptakes were obtained under both mulching and integrated nutrient management. Use of 2.5 kg hydrogel ha−1 resulted in more removal of N; P and K uptakes were higher in 5.0 kg hydrogel ha−1. Combination of three managements had a consequence of actual soil N loss, but gains in soil P and K after three cropping cycles.

Efficacy of Geotextile Jute Mulches on Yield, Soil Nutrient Dynamics and Weed Suppression in French bean (Phaseolus vulgaris L.)–Capsicum (Capsicum annum L.) Cropping System

Efficacy of Geotextile Jute Mulches on Yield, Soil Nutrient Dynamics and Weed Suppression in French bean (Phaseolus vulgaris L.)–Capsicum (Capsicum annum L.) Cropping System

Evaluation of the APSIM model in cropping systems of Asia

Resource shortages, driven by climatic, institutional and social changes in many regions of Asia, combined with growing imperatives to increase food production whilst ensuring environmental sustainability, are driving research into modified agricultural practices. Well-tested cropping systems models that capture interactions between soil water and nutrient dynamics, crop growth, climate and farmer management can assist in the evaluation of such new agricultural practices. One such cropping systems model is the Agricultural Production Systems Simulator (APSIM). We evaluated APSIM’s ability to simulate the performance of cropping systems in Asia from several perspectives: crop phenology, production, water use, soil dynamics (water and organic carbon) and crop CO2 response, as well as its ability to simulate cropping sequences without reset of soil variables. The evaluation was conducted over a diverse range of environments (12 countries, numerous soils), crops and management practices throughout the region. APSIM’s performance was statistically assessed against assembled replicated experimental datasets. Once properly parameterised, the model performed well in simulating the diversity of cropping systems to which it was applied with RMSEs generally less than observed experimental standard deviations (indicating robust model performance), and with particular strength in simulation of multi-crop sequences. Input parameter estimation challenges were encountered, and although ‘work-arounds’ were developed and described, in some cases these actually represent model deficiencies which need to be addressed. Desirable future improvements have been identified to better position APSIM as a useful tool for Asian cropping systems research into the future. These include aspects related to harsh environments (high temperatures, diffuse light conditions, salinity, and submergence), conservation agriculture, greenhouse gas emissions, as well as aspects more specific to Southern Asia and low input systems (such as deficiencies in soil micro-nutrients).

Effect of Tropical Legumes on Soil Nutrient Dynamics and its Consequence on Rice Production

Effect of Tropical Legumes on Soil Nutrient Dynamics and its Consequence on Rice Production

Soil Nutrient Dynamics and Yield of Cotton (Gossypium hirsutum L.) Following an Amendment with Cattle Manure

Soil Nutrient Dynamics and Yield of Cotton (Gossypium hirsutum L.) Following an Amendment with Cattle Manure

Microbial diversity and soil functions

SummarySoil is a complex and dynamic biological system, and still in 2003 it is difficult to determine the composition of microbial communities in soil. We are also limited in the determination of microbially mediated reactions because present assays for determining the overall rate of entire metabolic processes (such as respiration) or specific enzyme activities (such as urease, protease and phosphomonoesterase activity) do not allow any identification of the microbial species directly involved in the measured processes. The central problem posed by the link between microbial diversity and soil function is to understand the relations between genetic diversity and community structure and between community structure and function. A better understanding of the relations between microbial diversity and soil functions requires not only the use of more accurate assays for taxonomically and functionally characterizing DNA and RNA extracted from soil, but also high‐resolution techniques with which to detect inactive and active microbial cells in the soil matrix.Soil seems to be characterized by a redundancy of functions; for example, no relationship has been shown to exist between microbial diversity and decomposition of organic matter. Generally, a reduction in any group of species has little effect on overall processes in soil because other microorganisms can take on its function.The determination of the composition of microbial communities in soil is not necessary for a better quantification of nutrient transformations. The holistic approach, based on the division of the systems in pools and the measurement of fluxes linking these pools, is the most efficient. The determination of microbial C, N, P and S contents by fumigation techniques has allowed a better quantification of nutrient dynamics in soil. However, further advances require determining new pools, such as active microbial biomass, also with molecular techniques. Recently investigators have separated 13C‐ and 12C‐DNA, both extracted from soil treated with a 13C source, by density‐gradient centrifugation. This technique should allow us to calculate the active microbial C pool by multiplying the ratio between labelled and total DNA by the microbial biomass C content of soil. In addition, the taxonomic and functional characterization of 13C‐DNA allows us to understand more precisely the changes in the composition of microbial communities affected by the C‐substrate added to soil.

Pedotransfer Functions to Estimate Parameters for Soil Phosphorus Models

Core Ideas Equations with relatively simple parameters were provided to estimate soil solution phosphorus. A regression was fitted to estimate partition coefficients of desorption isotherms. The functions presented facilitate parameterization of existing P simulation models. Parameters of mechanistic and empirical models to simulate nutrient dynamics in soil–plant systems are not always readily available. One way to address this problem is by developing pedotransfer functions to estimate such parameters. In this study, we derive pedotransfer functions to estimate the P contents in soil solutions (Psol) of Brazilian soils and to estimate the partition coefficient of P desorption isotherms (kd,ds). We compiled data from previous studies and developed linear and nonlinear regression models to estimate P in soil solution as a function of P extracted by Mehlich‐1 (M1) and of soil clay. A regression model was also used to obtain a relationship between the partition coefficients of sorption and desorption isotherms for soils with different physicochemical characteristics. The functions presented here facilitate parameterization of existing P simulation models for Brazilian soils that are increasingly important for both scientific research and nutrient management.

Influence of the tropical millipede, Glyphiulus granulatus (Gervais, 1847), on aggregation, enzymatic activity, and phosphorus fractions in the soil

Soil macrofauna contribute to soil aggregation, as well as to enzymatic and nutrient dynamics in soils. Few studies have investigated the influence of millipede species from tropical regions on these soil variables. The objective of this study was to investigate the influence of the millipede Glyphiulus granulatus (Gervais, 1847), on aggregation, enzymatic activity, and phosphorus (P) fractions in a subtropical soil under controlled conditions. The present study was performed using 0, 2, 6, and 12 individuals per microcosm with five replicates of each density. After an incubation period of 28days, the increase in G. granulatus population density reduced the proportion of aggregates between 1.00‐2.00mm (y=236.16−1.4921x, P<0.05). The aggregates between 1.00‐2.00 and 2.00‐4.76mm were negatively correlated (r=−0.95, P<0.05). The increase population densities resulted in increased nitrogen (N) levels in the soil. The greatest population density (12 millipedes per microcosm) increased soil N content by 7%. The activity of β-glycosidase increased with densities of 6 and 12 millipedes per microcosm as compared to the control. However, the acid phosphatase activity was reduced in the presence of the millipedes, particularly at high densities, reaching 341μgp-nitrophenolg−1soilh−1 while 489μgp-nitrophenolg−1soilh−1 was found in the control treatment. The millipedes had no influence on available inorganic P fractions (H2O-Pi and NaHCO3-Pi). However, the amount of readily labile P (H2O-Pi+NaHCO3-Pi+NaHCO3-Po) was greater at the highest millipede density (12 individuals) and was mainly related to the increase of NaHCO3-Po. This indicated that the available P in soils may be conserved by cycling of organic P with high densities of such macroinvertebrates.

Effect of organic and inorganic nutrient management on soil nutrient dynamics and productivity of rice-chickpea system in lateritic soil

Field experiments were conducted to analyse the changes in soil organic carbon (SOC), NH4 +-N and NO3 −-N and the yield of paddy rice due to application of organic (vermicompost, vermiwash, Azotobacter and crop residue) and inorganic sources of N in varied amounts and timing in dry-seeded rice during wet seasons (June–October) of 2013 and 2014. The residual effect of these nutrients was also assessed on pod yield of chickpea that was grown after rice. The experiment laid in a randomized complete block design comprised eight treatment combinations of organic and inorganic nutrient management and one control, where nothing was added. Our results indicated that recommended dose of N (100 kg ha−1) through vermicompost (VC) applied full as basal and in splits (half at basal and the other half at panicle initiation stage) to rice could attain 75 and 88% grain yield of chemical fertilizer (CF), respectively. The split application of VC was comparable to CF alone and CF + VC treatment in maintaining organic carbon, NH4 +-N and NO3 −-N contents of soil at panicle initiation stage of the rice crop. The residual effect of split application of VC gave significantly higher pod yield of chickpea compared to the rest of the treatments. Hence, split application of VC to rice was effective in improving rice grain yield than its one-time application and yield of following chickpea crop in lateritic soil.

Nitrification potential in the rhizosphere of Australian native vegetation

The rhizosphere influences nutrient dynamics in soil mainly by altering microbial activity. The objective of this study was to evaluate the rhizosphere effect on nitrogen transformation in Australian native vegetation in relation to nitrification potential (NP). Microbial activity, NP, and nitrifiers (ammonia-oxidising bacteria, AOB) were compared between rhizosphere and non-rhizosphere soils of several Australian native vegetation under field conditions. These parameters were also measured with increasing distance from the rhizosphere of selected plant species using plant growth experiments. To examine the persistence of nitrification inhibitory activity of rhizosphere soil on non-rhizosphere soil, the soils were mixed at various ratios and examined for NP and AOB populations. The rhizosphere soil from all native vegetation (29 species) had higher microbial activity than non-rhizosphere soil, whereas 13 species showed very low NP in the rhizosphere when compared with non-rhizosphere soil. Nitrification potential and AOB populations obtained in the soil mixture were lower than the predicted values, indicating the persistence of a nitrification inhibitory effect of the rhizosphere soils on non-rhizosphere soils. In plant growth experiments the microbial activity decreased with increasing distance from rhizosphere, whereas the opposite was observed for NP and AOB populations, indicating the selective inhibition of nitrification process in the rhizosphere of the Australian native plants Scaevola albida, Chrysocephalum semipapposum, and Enteropogon acicularis. Some Australian native plants inhibited nitrification in their rhizosphere. We propose future studies on these selected plant species by identifying and characterising the nitrification inhibiting compounds and also the potential of nitrification inhibition in reducing nitrogen losses through nitrate leaching and nitrous oxide emission.

Nutrient Dynamics and Decomposition of Riparian Arundinaria gigantea (Walt.) Muhl. Leaves in Southern Illinois

&lt;p class="1Body"&gt;Leaf litter quality and quantity can influence soil nutrient dynamics and stream productivity through decomposition and serving as allochthonous stream inputs. Leaf deposition, nitrogen (N)-resorption efficiency and proficiency, and decomposition rates were analyzed in riparian stands of &lt;em&gt;Arundinaria gigantea &lt;/em&gt;(Walt.) Muhl.&lt;em&gt; &lt;/em&gt;in southern Illinois for the first time to determine potential nutrient cycling from riparian canebrake restoration. Leaf litter was collected from five established canebrakes monthly over one year and a decomposition study was conducted over 72 weeks. Live leaves, freshly senesced leaves, and decomposed leaves were analyzed for carbon (C) and N content. Leaf litterfall biomass peaked in November at twice the monthly average for all but one site, indicating a resemblance to deciduous leaf fall patterns. Nitrogen and C concentrations decreased 48% and 30%, respectively, between live leaves and 72 weeks following decomposition. High soil moisture appeared to slow decomposition rates, perhaps due to the creation of anaerobic conditions. Cane leaves have low resorption proficiency and nutrient-use proficiency, suggesting that these riparian canebrakes are not N limited. Giant cane should be considered in multispecies riparian buffer creation since it has this potential to supply carbon and nitrogen to the soil and to macroinvertebrates in the streams for a longer period of time and year round.&lt;/p&gt;

Agricultural land-use change in a Mexican oligotrophic desert depletes ecosystem stability

BackgroundGlobal demand for food has led to increased land-use change, particularly in dry land ecosystems, which has caused several environmental problems due to the soil degradation. In the Cuatro Cienegas Basin (CCB), alfalfa production irrigated by flooding impacts strongly on the soil.MethodsIn order to analyze the effect of such agricultural land-use change on soil nutrient dynamics and soil bacterial community composition, this work examined an agricultural gradient within the CCB which was comprised of a native desert grassland, a plot currently cultivated with alfalfa and a former agricultural field that had been abandoned for over 30 years. For each site, we analyzed C, N and P dynamic fractions, the activity of the enzyme phosphatase and the bacterial composition obtained using 16S rRNA clone libraries.ResultsThe results showed that the cultivated site presented a greater availability of water and dissolved organic carbon, these conditions promoted mineralization processes mediated by heterotrophic microorganisms, while the abandoned land was limited by water and dissolved organic nitrogen. The low amount of dissolved organic matter promoted nitrification, which is mediated by autotrophic microorganisms. The microbial N immobilization process and specific phosphatase activity were both favored in the native grassland. As expected, differences in bacterial taxonomical composition were observed among sites. The abandoned site exhibited similar compositions than native grassland, while the cultivated site differed.DiscussionThe results suggest that the transformation of native grassland into agricultural land induces drastic changes in soil nutrient dynamics as well as in the bacterial community. However, with the absence of agricultural practices, some of the soil characteristics analyzed slowly recovers their natural state.

Land-Use Conversion Changes the Multifractal Features of Particle-Size Distribution on the Loess Plateau of China.

Analyzing the dynamics of soil particle-size distributions (PSDs), soil nutrients, and erodibility are very important for understanding the changes of soil structure and quality after long-term land-use conversion. We applied multifractal Rényi spectra (Dq) and singularity spectra (f(α)) to characterize PSDs 35 years after conversions from cropland to shrubland with Caragana microphylla (shrubland I), shrubland with Hippophae rhamnoides (shrubland II), forested land, and grassland on the Loess Plateau of China. Multifractal parameters (capacity dimension (D0), entropy dimension (D1), D1/D0, correlation dimension (D2), and Hölder exponent of order zero (α0)) were used to analyze the changes of PSDs. Dq and f(α) characterized the PSDs well and sensitively represented the changes in PSDs after conversion. All types of land-use conversion significantly improved the properties of the topsoil (0–10 cm), but the effect of shrubland I and even forested land decreased with depth. All types of land-use conversion significantly increased D1 and D2 in the topsoil, and D1 and D2 in the 10–50 cm layers of shrubland II, forested land, and grassland and D1 in the 50–100 cm layers of shrubland II were significantly higher relative to the control. Both D1 and D2 were positively correlated with the contents of soil nutrients and fine particles and were negatively correlated with soil erosion, indicating that D1 and D2 were potential indices for quantifying changes in soil properties and erosion. In conclusion, all types of land-use conversion significantly improved the conditions of the topsoil, but conversion from cropland to shrubland II, forested land, and grassland, especially shrubland II and grassland, were more effective for improving soil conditions in deeper layers.

Temporal variation in soil enzyme activities after afforestation in the Loess Plateau, China

Temporal variation in soil enzyme activities has important significance for soil quality after afforestation. This study investigated the temporal variation in soil enzyme activities and their response to changes in soil properties following afforestation. Soil samples were collected during different periods of vegetation growth at sites in the Loess Plateau with different land use types: 40year-old Robinia pseudoacacia L. (RP40a), Caragana Korshinskii Kom (CK40a), and abandoned land (AL40a), as well as millet (Setaria italica) farmland (FL). Activities of four enzymes (catalase, saccharase, urease and alkaline phosphatase) that are involved in C, N, P cycling and soil water content (SWC), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and available phosphorus (AP) were measured. The results revealed that temporal variation and land-use have significant effects on the patterns of SWC, DOC, and DON, although not on that of AP. In addition, the activities of soil enzymes were highest in June, indicating that there are differences in the temporal variation of soil enzyme activities within a given land-use type, especially for alkaline phosphatase. The consistent ranking of soil enzyme activities was also significantly increased by afforestation. Furthermore, nonmetric multidimensional scaling analysis showed that the influence degree of afforestation on activities of the four enzymes was higher than that of temporal variation. Significant correlations between soil enzyme activities and soil properties indicated that soil enzyme activities are closely related to soil nutrients dynamics, particularly with respect to DON. The present study accordingly demonstrates that soil enzyme activities respond to farmland-to-forest conversion and hence have the potential to affect soil qualities in the Loess Plateau.

Unearthed! The Amazing Microbiome Exposed: The Arising Researcher

Science is at a threshold where the intertwined relationships between microorganisms and their impacts on the macroworld are challenging how we think about systems biology, ecosystem functions, and even how we define individual organisms. Over the last decade, an increasing amount of research is showing that microbial processes drive macro-ecological systems. I first began thinking about the interactions between plants and their microbiomes while I was trying to come up with a Masters research project in the summer of 2003. It was a challenge to narrow down an area related to microbiome in plant communities, which includes so many different disciplines. I finally settled on plant–microbe interactions and the regulation of plant trait expression, which cascade through ecosystems. I owe a debt of gratitude to John Klironomos for shining his flashlight into the “black box” of soil microbial communities with some very elegant “feedback” experiments with plants. In his 2002 paper, “Feedbacks with soil biota contributes to plant rarity and invasiveness in communities” (Nature 417:67–70), John paved the way for microbial perspectives to be applied to the macro-ecological phenomenon of plant invasion ecology. He showed that soil biota were regulating plant biodiversity and coexistence; microbes got put on the map as potential drivers of plant community assembly, rarity, and invasiveness. His paper was instrumental in helping many look beyond soils as a black box, and it inspired me in my own research. I have long been fascinated with microbiology and hold a deep respect for the discipline that studies the oldest life forms on earth: prokaryotes. I was exposed to many courses that dove deeply into the diversity of microbial functions, highlighting their fascinating genetic structures that allow pretty much anything to serve as a terminal electron acceptor, unlike animals that only use oxygen, O2. Simply put, microbial diversity of function was born out of the long evolutionary history the organisms have had in shaping and surviving this planet for the last 3.5 billion years. Microbial diversity in action, transforming nutrients is happening all around us: the soil biogeochemistry in our yards and gardens, fields, and forests. It is not hard to see how microbial communities that are largely responsible for soil nutrient dynamics shape the macroscale distributions of plants. For me, when I started my Masters research studying the impacts of an invasive grass on native plant communities, my natural preoccupation with microbiology kept telling me to look at the invasion process from a microbe-centric, rather than plant-centric perspective. John's work on soil feedbacks gave me the grounding to argue strongly for the role of microbes in these larger ecological patterns that I was convinced were related. Moving from just plant–plant interactions to a wider view that included plant–soil interactions made sense, because in essence soil is the functional legacy of microbes. The black box of soil still persists due to the challenge of studying things that cannot be seen with the unaided eye or cultured in the laboratory. However, advanced molecular tools have opened the door to the world of soils and related areas, such as what we think constitutes the plant genome. The microbiome is an extension of the plant genome, and this has huge implications for how we think about solving real-world problems. I was inspired by John's research and look forward to how my work on microbially mediated feedbacks between plants and soils will contribute to our understanding the role of the microbiome in plant invasions. How we view macroprocesses in plant science will continue to evolve as new microbial light continues to shed into the dark world of soils.

Impact of Bt-cotton on soil microbiological and biochemical attributes

Transgenic Bt-cotton produces Bt-toxins (Cry proteins) which may accumulate and persist in soil due to their binding ability on soil components. In the present study, the potential impacts of Bt- and non-Bt genotypes of cotton on soil microbial activity, substrate use efficiency, viable microbial population counts, and nutrient dynamics were studied. Two transgenic Bt-cotton genotypes (CIM-602 CIM-599) expressing cry1 Ac gene and two non-Bt cotton genotypes (CIM-573 and CIM-591) were used to evaluate their impact on biological and chemical properties of soil across the four locations in Punjab. Field trials were conducted at four locations (Central Cotton Research Institute-Multan, Naseer Pur, Kot Lal Shah, and Cotton Research Station-Bahawalpur) of different agro-ecological zones of Punjab. Rhizosphere soil samples were collected by following standard procedure from these selected locations. Results reveled that Bt-cotton had no adverse effect on microbial population (viable counts) and enzymatic activity of rhizosphere soil. Bacterial population was more in Bt-cotton rhizosphere than that of non-Bt cotton rhizosphere at all locations. Phosphatase, dehydrogenase, and oxidative metabolism of rhizosphere soil were more in Bt-cotton genotypes compared with non-Bt cotton genotypes. Cation exchange capacity, total nitrogen, extractable phosphorous, extractable potassium, active carbon, Fe and Zn contents were higher in rhizosphere of Bt-cotton genotypes compared with non-Bt cotton genotypes. It can be concluded from present study that the cultivation of Bt-cotton expressing cry1 Ac had apparently no negative effect on metabolic, microbiological activities, and nutrient dynamics of soils. Further work is needed to investigate the potential impacts of Bt-cotton on ecology of soil-dwelling insects and invertebrates before its recommendation for extensive cultivation.

Arctic foxes as ecosystem engineers: increased soil nutrients lead to increased plant productivity on fox dens.

Top predators can provide fundamental ecosystem services such as nutrient cycling, and their impact can be even greater in environments with low nutrients and productivity, such as Arctic tundra. We estimated the effects of Arctic fox (Vulpes lagopus) denning on soil nutrient dynamics and vegetation production near Churchill, Manitoba in June and August 2014. Soils from fox dens contained higher nutrient levels in June (71% more inorganic nitrogen, 1195% more extractable phosphorous) and in August (242% more inorganic nitrogen, 191% more extractable phosphorous) than adjacent control sites. Inorganic nitrogen levels decreased from June to August on both dens and controls, whereas extractable phosphorous increased. Pup production the previous year, which should enhance nutrient deposition (from urine, feces, and decomposing prey), did not affect soil nutrient concentrations, suggesting the impact of Arctic foxes persists >1 year. Dens supported 2.8 times greater vegetation biomass in August, but δ15N values in sea lyme grass (Leymus mollis) were unaffected by denning. By concentrating nutrients on dens Arctic foxes enhance nutrient cycling as an ecosystem service and thus engineer Arctic ecosystems on local scales. The enhanced productivity in patches on the landscape could subsequently affect plant diversity and the dispersion of herbivores on the tundra.

Soil C:N:P dynamics during secondary succession following fire in the boreal forest of central Canada

Measures of soil nutrient availability such as concentrations of nitrogen and phosphorus ([N] and [P]) are important indicators of terrestrial productivity. Optimal plant growth and ecosystem functioning are also strongly correlated with nutrient ratios in soils. Long-term trends in soil [C], [N], [P], and their stoichiometric ratios during secondary succession in the fire-driven boreal forest remain unclear. We used replicated 7- to 209-year chronosequences to examine the influence of stand age and overstory composition on [C], [N], and [P] and their ratios in the forest floor, surface (0–15cm), and subsurface (15–30cm) mineral soil in the boreal forest of central Canada. In the forest floor, [C] and [N] increased rapidly during the first three decades following fire, after which they fluctuated, but remained larger than in the youngest stands. Surface soil [C] and [N] increased from young to intermediate-aged stands, but decreased in the oldest stands. Subsurface [C] and [N] followed a similar trend, but was higher in the 7-year-old stands. Forest floor [P] followed a gradual, linear increase throughout stand development but of smaller magnitude than [C] and [N]. The temporal pattern of [P] in both mineral soil layers was lower in the 33-year-old stands of all overstory types, suggesting that P resources may be outpaced by their demand during this highly competitive stage of advanced stem exclusion during forest succession. In the forest floor and surface soil, C:N differed not only with stand age but also with overstory type, due to higher C:N in intermediate-aged conifer stands. Forest floor C:P and N:P were higher in the 33- to 146-year-old stands in all overstory types and soil layers, but particularly so in the conifer stands. In the mineral layers, C:N, C:P, and N:P all followed a similar trend. Our results demonstrate the important influence of stand age, overstory composition (as influenced by succession), and soil depth on forest soil nutrient dynamics in boreal forest ecosystems.

Herbivory and N2-fixation drive plant and soil nutrient dynamics in a southern African savanna

Herbivory and N2-fixation drive plant and soil nutrient dynamics in a southern African savanna