Soil Nutrient Ratios Research Articles

Riparian plant-soil-microbial C:N:P stoichiometry: are they conserved at plant functional group level?

As a consequence of the tight linkages between plants, soil, and microorganisms, we hypothesized the variations in plant species would change soil and microbial stoichiometry. Here, we examined the plant leaf carbon (C):nitrogen (N):phosphorus (P) ratios of nine species coming from three plant functional groups (PFGs) in the riparian zones of Hulunbuir steppe during near-peak biomass. The soil C:N:P, microbial biomass carbon (MBC):microbial biomass nitrogen (MBN), and extracellular enzyme's C:N:P were also assessed using the soils from each species. We found that plant tissue, soil nutrient, microbial, and enzyme activity stoichiometry significantly differed among different PFGs. Plant leaf and soil nutrient ratios tended to be similar (p > 0.05) between different species within the same PFGs. The variations in leaf C:N:P significantly correlated with the changes in soil C:N:P and MBC:MBN ratios. The homeostatic coefficients (H) < 1 suggested the relationships between plants and their resources C:N:P ratios might be non-homeostatic in the examined riparian zone. By assessing plant tissue and its soil nutrient stoichiometry, this study provided a perspective to understand the linkages of plant community, soil nutrient, and microbial characteristics.

Effects of slope aspect on soil enzyme activity and microbial nutrient limitation in subalpine region of wes-tern Sichuan, China.

Exploring the resource limitation of soil microbial metabolism is essential to understand ecosystem functions and processes. However, the spatially divergent patterns and drivers of soil microbial nutrient limitation cha-racteristics in montane ecosystems at small scales, especially at the slope aspect scale, are still unclear. In this study, we measured soil enzyme activities involved in carbon (C), nitrogen (N) and phosphorus (P) cycle and quantified the microbial nutrient limitations by enzyme stoichiometry in two representative mountain sites in subalpine region of western Sichuan, including the sunny and shady slopes with different vegetation types (shrubland and forest, respectively) in Miyaluo of Lixian County, and with the same vegetation type (shrubland) in Yakexia of Heishui County. The results showed that soil enzyme activities and their stoichiometric ratios were significantly different between slope aspects in Miyaluo, while the differences were not significant in Yakexia. The stoichiometry ratio of C-, N- and P-acquiring enzymes on the sunny slope of Miyaluo was 1:0.96:0.92, approaching the 1:1:1 ratio at the global scale, but deviated from 1:1:1 on the shady slope of Miyaluo (1:1.39:0.75) and the different slopes of Yakexia (1:1.09:1.35). There was no significant difference in vector length between slope aspects at both sites, indicating no significant effect of slope aspect on the microbial C limitation. The vector angle was significantly higher on the sunny slope (43.6°) than that on the shady slope (28.7°) in Miyaluo, suggesting that the microorganisms were mainly N-limited. Partial least squares path model showed that the vector angle was mainly directly influenced by the soil nutrient ratios. The vector angle ranged from 50.3° to 51.4°, and did not differ between slope aspects in Yakexia. Therefore, differences in vegetation types between slope aspects drove variations in soil enzyme activity and microbial nutrient limitation through soil properties. It would provide a scientific basis for predicting the spatial pattern of soil enzyme activity and microbial nutrient limitation.

Flooding dominates soil microbial carbon and phosphorus limitations in Poyang Lake wetland, China

Soil microbial metabolic limitations influence the equilibrium between microbial metabolic requirements and the accessibility of soil substrates and nutrients. Although extensive research has examined the effects of hydrological regime changes on soil microbial activity and community structures, our understanding of their effects on soil microbial metabolic limitations remains inadequate. In this study, we quantified and evaluated soil microbial metabolic limitations along a flooding duration (FD) gradient over a three-year period in the Poyang Lake wetland, China, using vector analysis of extracellular enzyme stoichiometry. Our results revealed that the lengths and angles of the vector analyses ranged from 1.32 to 1.58 and 56.82° to 65.19°, respectively, across all samples, indicating that soil microbial metabolism was primarily limited by C and P. Both the vector length and angle showed negative correlations with FD, suggesting that microbial C and P limitations significantly decreased with increasing FD. Flooding regime primarily affected microbial C and P limitations through direct effects, as well as indirect effects resulting from plant features (e.g., plant community diversity, biomass, and nutrient properties) and soil nutrient ratios. Among hydrological, vegetational, and edaphic variables, flooding was the dominant driver of microbial C and P limitations. Overall, our research highlights the importance of hydrological regimes in regulating soil microbial metabolic limitations and provides valuable perspectives for understanding and predicting soil C and nutrient cycling in floodplain wetlands.

Yield Variability in Oil Palm Plantations in Tropical India Is Influenced by Surface and Sub-Surface Soil Fertility and Leaf Mineral Nutrient Contents

Oil palm (Elaeis guineensis Jacq.), an industrial oilseed crop, is the most prominent oil-producing crop in the world and one of the highest dry matter producers among C3 plants. It removes large amounts of soil nutrients to support its substantial biomass and oil production. Thus, maintaining adequate levels of limiting nutrients at favorable ratios in the soil is crucial to sustain the required palm nutritional status and oil production over extended periods. We evaluated the levels and ratios of the available soil and leaf nutrients in high-yielding (HYOPP) and low-yielding (LYOPP) oil palm plantations from two locations in southern India and assessed their relations to develop effective nutrient management for sustaining fresh fruit bunch (FFB) production. The FFB yield varied from 2.00 to 31.0 t ha−1 (location 1) and 6.84 to 30.9 t ha−1 (location 2), and the FFB yields of the high- and low-yield population at each location differed significantly. Wide ranges of soil properties, available nutrients, and leaf nutrients concentrations were observed at 0–20- and 20–40-cm soil depths at both locations. The soil nutrient ratios at both sampling depths of the HYOPP were significantly different than the LYOPP at location 1. The mean leaf N (2.09%) and K (0.68%) concentrations at location 2 were significantly higher than those in location 1 (1.85% and 0.54, respectively). The mean leaf concentrations at both locations followed the order N (1.85%, 2.09%) &gt; Ca (1.65%, 1.36%) &gt; K (0.54%, 0.68%) &gt; Mg (0.49%, 0.47%) &gt; S (0.16%, 0.18) &gt; P (0.11%, 0.12%) &gt; B (35.8 mg kg−1, 27.5 mg kg−1). We observed positive and significant correlations between the available N and P at 0–20 cm and between the available N and K as well as Ca and S at both soil depths for HYOPPs. In LYOPPs, the available N was significantly correlated with the available P, K, Ca, and Mg at both soil depths and with the available S at 0–20 cm. The FFB yield of LYOPPs was positively and significantly correlated with the available P and S at the 0–20-cm soil depth and with the available N and P at the 20–40-cm soil depth. Except for a negative correlation (p &lt; 0.05) with exchangeable Ca at the 20–40-cm soil depth, the FFB yield in HYOPPs had no significant correlation with the available soil nutrients at both depths. The FFB yield of LYOPPs had a positive significant (p &lt; 0.01) correlation with the leaf P and K concentrations, while the yield of HYOPPs had a negative correlation (p &lt; 0.01) with the leaf P. Fertilizer accounts for a large part of the on-farm cost in oil palm plantations, and an evidenced approach for fertilizer management based on nutrient contents and ratios in the soil and in the plant is useful for sustainable and profitable production of palm oil.

Allometric scaling of biomass with nitrogen and phosphorus above- and below-ground in herbaceous plants varies along water-salinity gradients.

Biomass allocation affects the ability of plants to acquire resources and nutrients; a limited allocation of nutrients, such as nitrogen and phosphorus, affects ecological processes. However, little research has been conducted on how plant allocation patterns change and on the trade-offs involved in allocation strategies when microhabitat gradients exist. We selected a 3.6 km transect in the Ebinur Lake Wetland Natural Reserve of Xinjiang, China, to investigate the relationships between plant traits (biomass and N and P concentrations) of herbaceous plants and environmental factors (soil moisture, salinity and nutrient content), and to determine the allometric scaling of biomass and stoichiometric traits between the above- and below-ground plant parts. The results show that the biomass and stoichiometric traits of plants reflected both the change of micro-environment and the natural characteristics of plants. With a decrease of the soil water availability and salinity, above- and below-ground N and P concentrations decrease gradually; scaling relationships exist between above- and below-ground plant parts, for biomass and N and P concentrations. Biomass allocation is influenced by soil nutrient ratios, and the allocation strategy tended to be conserved for N and variable for P. Second, the scaling relationships also show interspecific differences; all scaling exponents of Suaeda prostrata are larger than for other species and indicate a ‘tolerance’ strategy, while other species tend to increase the below-ground biomass and N and P concentrations, i.e. a ‘capture’ strategy.

Tree-scale spatial responses of extracellular enzyme activities and stoichiometry to different types of fertilization and cover crop in an apple orchard

The effects of cover crops and fertilization on the soil properties of apple orchards have been studied widely, but our knowledge of the variations in the soil enzyme activity and stoichiometry remains limited, particularly the tree-scale spatial responses. In this study, field experiments were conducted in two main plots comprising cover crop (CC) and no cover crop (NC) treatments with four sub-plots comprising no fertilization, manure (M), N, P, and K fertilizer (NPK), and NPK fertilizer combined with manure (NPKM). We determined the activities of C, N, and P acquisition enzymes comprising β-1,4-glucosidase, (BG), β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and alkaline phosphatase (PHOS), the soil nutrient contents, and microbial biomass. Cover crop and fertilization significantly affected the soil nutrient contents, microbial biomass, and enzyme activities. Cover crop growth decreased the BG:NAG + LAP and BG:PHOS enzyme activity ratios (before mowing and mulching the cover crop). Fertilization also influenced the BG:NAG + LAP, BG:PHOS, and NAG + LAP:PHOS ratios. The soil enzyme activities were affected by the soil nutrient contents and microbial biomass, especially at distances 90 and 120 cm from the trees, as well as by the manure application treatments (M and NPKM). The soil enzyme ratios and microbial biomass ratio were influenced by the soil properties, especially at distances of 90 and 120 cm form the trees. The relationships among the soil properties, microbial biomass ratio, and soil enzyme ratios were affected by the growth of the cover crop and apple trees. The chemical fertilizer treatments (NPK and NPKM) significantly increased the negative relationships between the soil nutrient ratios and enzyme ratios. Our findings demonstrate that the C:N:P stoichiometry of the soil microbes and enzyme activities were affected by the cover crop and fertilization, and the spatial effects were detected at the tree-scale in an apple orchard.

English

Nutrients are essential for plant growth and development, and soil nutrient ratios play key roles in coffee quality. The objective of this study was to investigate the influence of soil nutrient ratios on the quality of wild Arabica coffee in Ethiopia. Results revealed that the balance between the soil nutrients was well correlated with coffee quality attributes. The balance between magnesium and calcium (Mg:Ca) and the balance between nitrogen and phosphorus (N:P) were found to be very important factors for bean size. Increase in Ca relative to Mg increased bean size, and vice versa. The higher the concentration of available P in relation to soil organic carbon (P:C) or total N (P:N), the better the cup quality of the coffee, and vice versa. The Mg:K ratio, P:N ratio, P:C ratio and P:Zn ratio were very important factors for cup quality. Although the ratio between Mg and K was important for cup quality, it was not apparent for bean size. The ratio between Ca and Mg was of no or little importance for coffee cup quality as opposed to that of bean size. Therefore, coffee growers should make careful decisions depending on the demands of the buyers/consumers and environmental requirements. Key words: Arabica coffee, bean size, cup quality, coffee forest, nutrient ratios.

Mercury Stoichiometric Relationships in a Subtropical Peatland

Spatially variable areas, or hotspots, of elevated mercury (Hg) concentrations in soil, water, and wildlife occur throughout the Everglades wetland ecosystem. This study investigates the stoichiometric controls of Hg relative to soil, water, and biotic components. Surface water, porewater, soil, periphyton, and Gambusia spp. (mosquitofish) were collected from hotspots and non-spot stations and analyzed for various parameters, including total mercury (THg), organic carbon (OC), total carbon (TC), total phosphorus (TP), and total nitrogen (TN) between late 2010 and early 2013. Soil nutrient ratios were significantly different between hotspot and non-hotspot stations, indicating a difference in trophic status and position along the decay continuum or differences in limiting nutrients. Overall, soil total Hg concentrations were negatively correlated with soil TC/TN, while soil TC/TP and soil TN/TP molar ratios and soil THg were negatively correlated at hotspot stations. Meanwhile, mosquitofish THg was negatively correlated with soil TC/TN molar ratio and positively correlated with soil TC/TP and TN/TP molar ratios, suggesting trophic truncation. Soil, surface water, and porewater THg, TC, and OC interactions resulted in significant differences between hotspot and non-hotspot stations and between molar ratios of C, N, and P. Periphyton-surface water THg/OC homeostasis and soil nutrient ratios significantly explained mosquitofish THg concentrations, further indicating a trophic influence on mosquitofish THg and potential hotspot dynamics. Several factors and processes including bottom-up trophic interaction and vegetation influence on Hg accumulation dynamics and food-chain length explain the development and persistence of Hg hotspot formation within the Everglades system.

Impact of glyphosate-resistant corn, glyphosate applications and tillage on soil nutrient ratios, exoenzyme activities and nutrient acquisition ratios.

We report results of the last two years of a 7 year field experiment designed to test the null hypothesis: applications of glyphosate on glyphosate-resistant (GR) and non-resistant (non-GR) corn (Zea mays L.) under conventional tillage and no-till would have no effect on soil exoenzymes and microbial activity. Bulk soil (BS) and rhizosphere soil (RS) macronutrient ratios were not affected by either GR or non-GR corn, or glyphosate applications. Differences observed between exoenzyme activities were associated with tillage rather than glyphosate applications. In 2013, nutrient acquisition ratios for bulk and rhizosphere soils indicated P limitations, but sufficient assimilable N. In 2014, P limitations were observed for bulk and rhizosphere soils, in contrast to balanced C and N acquisition ratios in rhizosphere soils. Stoichiometric relationships indicated few differences between glyphosate and non-glyphosate treatments. Negative correlations between C:P and N:P nutrient ratios and nutrient acquisition ratios underscored the inverse relation between soil nutrient status and microbial community exoenzyme activities. Inconsistent relationships between microbial community metabolic activity and exoenzyme activity indicated an ephemeral effect of glyphosate on BS exoenzyme activity. Except for ephemeral effects, glyphosate applications appeared not to affect the function of the BS and RS exoenzymes under conventional tillage or no-till. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Tree species and soil nutrients drive tropical reforestation more than associations with mycorrhizal fungi

The relative benefits that mycorrhizal fungi confer to host plants and reforestation efforts may differ due to the host tree species and soil nutrient status. Our research objective was to examine the effects of mycorrhizal fungi, host tree species, and soil nutrient availability on nutrient acquisition in tropical reforestation. Four tree species (Pinus caribaea, Quercus insignis, Swietenia macrophylla, and Terminalia amazonia) were planted across eight sites and subjected to five nutrient treatments in southern Costa Rica. After two years, there were strong growth differences based upon tree species but not mycorrhizal fungi. Site variation, specifically base cation availability, and nutrient treatments also influenced tree growth and tissue nutrient concentrations. In a complementary greenhouse experiment isolating fungal from tree species effects, the ratio of nutrients in treatments was more important to tree growth responses to fungal symbionts than individual nutrients. These results show that soil nutrient availability may be more important to tree species’ nutrient acquisition than mycorrhizal fungi. This study highlights the importance of tree species selection and replication across sites with different soil nutrient ratios in order to make management recommendations for reforestation success.

Linking spatial patterns of leaf litterfall and soil nutrients in a tropical forest: a neighborhood approach.

Leaf litter represents an important link between tree community composition, forest productivity and biomass, and ecosystem processes. In forests, the spatial distribution of trees and species-specific differences in leaf litter production and quality are likely to cause spatial heterogeneity in nutrient returns to the forest floor and, therefore, in the redistribution of soil nutrients. Using mapped trees and leaf litter data for 12 tree species in a subtropical forest with a well-documented history of land use, we: (1) parameterized spatially explicit models of leaf litter biomass and nutrient deposition; (2) assessed variation in leaf litter inputs across forest areas with different land use legacies; and (3) determined the degree to which the quantity and quality of leaf litter inputs and soil physical characteristics are associated with spatial heterogeneity in soil nutrient ratios (C:N and N:P). The models captured the effects of tree size and location on spatial variation in leaf litterfall (R² = 0.31-0.79). For all 12 focal species, most of the leaf litter fell less than 5 m away from the source trees, generating fine- scale spatial heterogeneity in leaf litter inputs. Secondary forest species, which dominate areas in earlier successional stages, had lower leaf litter C:N ratios and produced less litter biomass than old-growth specialists. In contrast, P content and N:P ratios did not vary consistently among successional groups. Interspecific variation in leaf litter quality translated into differences in the quantity and quality (C:N) of total leaf litter biomass inputs and among areas with different land use histories. Spatial variation in leaf litter C:N inputs was the major factor associated with heterogeneity in soil C:N ratios relative to soil physical characteristics. In contrast, spatial variation soil N:P was more strongly associated with spatial variation in topography than heterogeneity in leaf litter inputs. The modeling approach presented here can be used to generate prediction surfaces for leaf litter deposition and quality onto the forest floor, a useful tool for understanding soil-vegetation feedbacks. A better understanding of the role of leaf litter inputs from secondary vegetation in restoring soil nutrient stocks will also assist in managing expanding secondary forests in tropical regions.

C:N:P stoichiometry and nutrient limitation of the soil microbial biomass in a grazed grassland site under experimental P limitation or excess

IntroductionThe availability of essential nutrients, such as nitrogen (N) and phosphorus (P), can feedback on soil carbon (C) and the soil microbial biomass. Natural cycles can be supplemented by agricultural fertiliser addition, and we determined whether the stoichiometry and nutrient limitation of the microbial biomass could be affected by an unbalanced nutrient supply.MethodsSamples were taken from a long-term trial (in effect since 1968) with annual applications of 0, 15 and 30 kg P ha−1 with constant N and potassium. Soil and microbial biomass CNP contents were measured and nutrient limitation assessed by substrate-induced respiration. Linear regression and discriminant analyses were used to identify the variables explaining nutrient limitation.ResultsSoil and biomass CNP increased with increasing P fertiliser, and there was a significant, positive, correlation between microbial biomass P and biomass C, apart from at the highest level of P fertilisation when the microbial biomass was over-saturated with P. The molar ratios of C:N:P in the microbial biomass remained constant (homeostatic) despite large changes in the soil nutrient ratios. Microbial growth was generally limited by C and N, except in soil with no added P when C and P were the main limiting nutrients. C, N and P, however, did not explain all the growth limitation on the soils with no added P.ConclusionsIncreased soil C and N were probably due to increased net primary production. Our results confirm that C:N:P ratios within the microbial biomass were constrained (i.e. homeostatic) under near optimum soil conditions. Soils with no added P were characterised by strong microbial P limitation and soils under high P by over-saturation of microorganisms with P. Relative changes in biomass C:P can be indicative of nutrient limitation within a site.

A comparison between Northern and Southern Hemisphere tundras and related ecosystems

Climatic, edaphic, and vegetation parameters are compared among three Subantarctic islands and one Maritime Antarctic island, and Northern Hemisphere tundras and tundra-like ecosystems (ranging from higharctic to cool-temperate oceanic and temperate alpine), mainly by Principal Component Analyses (PCA). All analyses of abiotic variables emphasized the extreme oceanicity of the Southern Hemisphere sites and showed the strong influence of seaspray on soil nutrient ratios in the southern sites. Analyses of climate classified all the southern sites as “Cold Oceanic” within a series of very oceanic climates that were distinct from the continental/subalpine climates more typical of the northern sites. Four factorial groups were derived from the vectors in PCA of soils and climate combined. Each was a grouping of several variables that was essentially independent of the other groups. They were: general climatic severity, soil base status, supply of “labile” nutrients, and a combined index of oceanicity with organic/mineral balance and drainage. The ecological significance of these is discussed. The range of soil nutrient levels in the southern sites is approximately equal to that of the northern sites; however, in the southern sites soil nutrient levels are inversely related to climatic severity while in the north the reverse is true. The two most important causes of these opposed trends are the relative ages of the sites and the much greater effects of sea-based vertebrates (e.g. seals and seabirds) in the southern islands. Cluster analyses of component scores derived from climatic and soil data linked the southern sites with northern sites at higher latitudes, indicating the effect of the Antarctic continent on the Southern Ocean (hence on the overall climate of the southern islands) and of wind-chill on the aerial and soil climates of the southern sites. Vegetation patterns (derived from PCA of life form data) were more complex because of the serial replacement of one lifeform by onother along continuous environmental gradients. Wind exposure was an important element in the first two vectors derived from the PCA of the botanical data. The Southern Hemisphere sites exhibited almost the full range of vegetation types found in the Northern Hemisphere, despite their floristic poverty. Variation within individual islands was comparable with that found at considerably higher (up to 30° more) northern latitudes and reflects the overriding importance of wind exposure in the southern islands. Subarctic ecosystems are generally less severe forms of Arctic ones, and decreasing latitude leads to increasingly milder environments with no great changes overall in continentality. In contrast, the Subantarctic combines elements from the extremes of the range of northen tundras (i.e. high-Arctic and cool-temperate oceanic) with its own peculiar features (e.g. animal influences) to produce ecosystems that are qualitatively different both from Subarctic systems and from the continental Antarctic regions to which they are geographically closest.