Soil Stoichiometry Research Articles

Soil properties and microbial respiration activities of riparian forest wetland in the north of permafrost zone, the Great Hing'an Mountains, Northeast China

Riparian wetlands in permafrost regions are critical regions for hydrological, ecological, and biochemical processes. We studied the soils of riparian and transition wetlands and analyzed physicochemical properties, stoichiometry, and microbial respiration activities (microbial biomass carbon, basal respiration, microbial entropy, and metabolic entropy) of the humus layer and diffe-rent soil layers. The results showed that the main differentiation of soil physical and chemical pro-perties in riparian forest wetlands was below 20 cm. Compared to the wetlands of transition zone, total carbon content, total nitrogen content, C/P and N/P decreased significantly with soil depth in riparian forest wetlands. These changes in soil stoichiometry were mainly caused by soil nitrogen content. Such a result meant that the transferring of nitrogen was relatively fast and that there was nitrogen limitation. The main differentiation of Na, Mg, K and Ca in soil occurred in the 30 cm layer of the transition zone and the 20 cm layer of the riparian forest wetlands. The correlations between soil Mg content and total C, total N, total P contents were significant. It meant that the soil Mg was an important element to riparian wetlands in the Great Hing'an Mountains. Microbial respiration activities of the humus layer in riparian forest wetlands and transition zone were higher than those in the other soil layers, indicating that the content of labile carbon fractions was high. The correlations between soil microbial respiration activities and soil properties, stoichiometry, nutrient elements were different in riparian wetland and transition zone. Soil total nitrogen contents were significantly correlated with soil microbial respiration activities in riparian wetland, indicating that soil microbial respiration activities were limited by nitrogen in riparian wetland of the Great Hing'an Mountains.

Soil freezing-thawing induces immediate shifts in microbial and resource stoichiometry in Luvisol soils along a postmining agricultural chronosequence in Western Germany

Freeze-thaw (FT) events exert a great physiological stress on soil microorganisms and hence impact biogeochemical processes in soils. As numerous environmental factors affect microbial and chemical responses to FT, a better understanding of the leverage factors that regulate the responses to FT events is required. To date, FT-induced shifts and transformations in microbial and resource stoichiometry have received particularly little attention. We exposed fifteen Luvisol soils with different time after restoration and corresponding differences in soil organic C contents from a postmining agricultural chronosequence to a single FT event and analysed changes in soil chemistry and microbial stoichiometry one hour and eighteen hours after thawing. FT considerably altered soil biochemical attributes within the first hours of thawing. Microbial biomass C declined substantially after FT, and its relative losses were positively correlated with enhanced dissolved organic C contents. Thus, microbial cell lysis likely led to the significant increase of dissolved organic C. Moreover, microbial biomass C losses were disproportionally higher in C-rich soils, suggesting that soil microorganisms in high-C soils might be particularly prone to FT stress. Microbial biomass N marginally decreased one hour after thawing, yet returned to initial levels eighteen hours after thawing. The alternating responses of microbial biomass C and N caused a strong stoichiometric reduction of the microbial C:N ratio. The resulting microbial oversaturation with N relative to C is likely the first step in the chain of processes that generally lead to the high N losses commonly recorded in agricultural soils in the aftermath of FT events. Metabolic activity of the soil microbial community increased with the relative decline of the microbial biomass C:N ratio eighteen hours after thawing, suggesting increased levels of microbial metabolic expenditure due to stoichiometric shifts. The strength of the FT-driven biochemical responses was strongly dependent on soil organic C content, indicating that high-C soils might be especially vulnerable to initial C and N losses due to shifts in microbial stoichiometry.

Stoichiometric theory shapes enzyme kinetics in paddy bulk soil but not in rhizosphere soil

AbstractThe available carbon (C) to phosphorus (P) ratio in the soil is regulated by extracellular hydrolases for C and P acquisition by microbes and plants. However, the stoichiometric relationship between acquiring C and P in paddy rhizosphere and bulk soils remains unclear. The objective was to explore the underlying mechanisms of C and P acquisition stoichiometry in rhizosphere and bulk soils in response to P fertilization and cellulose addition. Amendment with either cellulose or P separately caused a significant increase in the maximal velocity (Vmax) of C acquisition enzymes (β‐1,4‐glucosidase and β‐cellobiohydrolase) but decreased that of P acquisition enzymes (acid and alkaline phosphomonoesterases) in bulk soil. In contrast, lower Vmax values of C and P acquisition enzymes were observed in rhizosphere soil than in bulk soil. The co‐application of cellulose and P increased the Vmax of P acquisition enzymes in rhizosphere soil but decreased that of only alkaline phosphomonoesterase in bulk soil. Results show that P availability and labile‐C content co‐regulated the P/C acquisition ratio, and two inverse linear relationships were observed. Specifically, the P/C acquisition ratio was negatively related to both the dissolved organic C/Olsen‐P ratio and the microbial biomass C/P ratio in rhizosphere soil. However, the P/C acquisition ratio was positively related to both the dissolved organic C/Olsen‐P ratio and the microbial biomass C/P ratio in bulk soil. Overall, microbes mineralized less organic P to acquire P in paddy soil rhizosphere (i.e., containing higher labile‐C) than in bulk soil (i.e., having lower labile‐C contents).

Changes in soil total, microbial and enzymatic C-N-P contents and stoichiometry with depth and latitude in forest ecosystems

Soil microorganisms and their extracellular enzymes are key factors determining the biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P). Relevant studies mainly focus on surface soils (0–20 cm), while deep soils (>20 cm) are often neglected, let alone comparing multiple ecosystems simultaneously. In this study, we studied the latitudinal (19–48°N) and vertical (0–100 cm) patterns of soil total, microbial and enzymatic C-N-P contents and ratios (stoichiometry) in eight temperate, subtropical and tropical forest ecosystems in eastern China. We found that the C-N-P contents and their stoichiometry in soil, microbial biomass and extracellular enzymes all varied significantly with depth and latitude. Soil total C, N and P declined with depth, as did microbial biomass and enzyme activity, while microbial and enzymatic C:N ratios showed increasing or no trend with increasing soil depth. Moreover, soil total and microbial C-N-P contents in surface soils (0–20 cm) showed positive correlations with increasing latitude, and such correlations tended to be weaker or disappeared in deep soils (>20 cm). Overall, changes in total, microbial and enzymatic C-N-P contents and ratios among latitudes suggested a shift from relative N limitation in the north to relative P limitation in the south.

Wildfire alters the linkage between total and available soil C:N:P ratios and the stoichiometric effects on fine root growth in a Chinese boreal larch forest

Background and aimsWildfire is a primary driver of forest ecosystem functioning, and fire-induced changes in nutrient cycling and the balance of multiple nutrients may influence plant growth response to burning. However, the relationship between total and available soil stoichiometry and stoichiometric effects on the growth of fine roots following forest fires remain unclear.MethodsWe measured the total and available soil C, N, and P concentrations, their ratios, and fine root biomass (FRB) at unburned control, 1-year-postfire, and 11-year-postfire sites in a Chinese boreal larch forest. We analyzed the relationship between soil stoichiometry and FRB.ResultsWildfire significantly reduced the total and available soil C:N:P ratios and FRB immediately postfire. Eleven years postfire, most indicators recovered to the prefire levels except for total soil C:P and N:P ratios, and available C:N ratio. Wildfire increased the associations between total and available soil C:N:P ratios, as well as between FRB and soil C:N:P ratios, but reduced the relationship between FRB and soil nutrient supply. However, these effects became weaker over time.ConclusionsThe effects of wildfire on biogeochemical processes in boreal ecosystems extend to the relationship between total and available soil stoichiometry. Wildfires strengthen the linkage between fine roots and soil stoichiometry but weaken the effects of soil nutrient supply in the Great Xing’an Mountains. Therefore, the effects of wildfire on the coupling of soil C, N, and P cycling can produce a more complex soil-plant interaction in the early succession stage of boreal larch forest.

Revisiting the quantitative contribution of microbial necromass to soil carbon pool: Stoichiometric control by microbes and soil

Quantitative assessments of soil microbial necromass improve our knowledge of soil carbon (C) sequestration, which is vital for addressing climate change and food security. Here, we revisit the quantitative contribution of microbial necromass to soil organic C (SOC) pool by using an optimized strategy that considers the stoichiometric differences of microbes and the full range of the microbial necromass proportion in soil nitrogen (N) pool. We derive a more applicable estimate of the microbial necromass contribution to SOC pool, reporting a narrower average range (24%–60%) compared with those in recent publications. We further find that the potential contribution of microbial necromass to SOC pool is controlled by the stoichiometry (C/N ratio) of microbes and soil. We suggest soil C sequestration strategy by increasing microbial necromass should well be exploited to improve soil N availability and use microbial species associated with high biomass C/N ratio to boost C accrual.

Ecoenzymatic stoichiometry and microbial nutrient limitation of shrub rhizosphere soils in response to arbuscular mycorrhizal fungi inoculation

Ecoenzymatic stoichiometry and microbial nutrient limitation of shrub rhizosphere soils in response to arbuscular mycorrhizal fungi inoculation

Forest soil nutrient stocks along altitudinal range of Uttarakhand Himalayas: An aid to Nature Based Climate Solutions

Understating of forest functioning is crucial for ensuring the sustainable flow of forest ecosystem services. Climate regulation service of a forest ecosystem can be ensured through emission reduction by increasing carbon sequestration in forests. However, understanding about the functioning of forests for carbon sequestration is constrained due to lack of information on nutrient stocks and stoichiometry of soils of forests of India. Present study focuses to examine the stoichiometry of major nutrients; nitrogen (N), phosphorus (P), carbon (C) of forest soil to understand the dynamics of the forests of Uttarakhand, India. The study also attempted to supplement the information about the soil carbon sequestration potential of important tree species of the forest. Soil samples were collected randomly for the evaluation of physico-chemical characteristics and stoichiometry of forest soil at four altitudinal ranges i.e., <1000, 1000–1500, 1500–2000, and >2000 m a.s.l in the Himalayan region of Uttarakhand, India. The analysis shows that total nitrogen, total phosphorous, and soil organic carbon contents in forest soil were 0.35 ± 0.11%, 0.10 ± 0.04% and 3.36 ± 0.84%, respectively, which increases with altitude. The stoichiometric ratios viz., C:N:P, N:P, C:N, and C:P, and N:P were reported of 51.6:5.4:1, 4.30 ± 2.39, 9.60 ± 1.48, and 41.94 ± 23.35, respectively which were invariant with altitude. The low C:N ratio may be attributed to either increase in the nitrous oxide (N2O) emissions with an increase in nitrogen, or low in carbon stock leading to decrease in carbon dioxide (CO2) and methane (CH4) emissions. Moreover, the soil C sequestration potential in the forest tree species follow the order of Abies pindrow > Cedrus deodara > Quercus leucotrichophora > Pinus roxburghii. The information of the study would facilitate for broadening the understanding about the soil properties and stoichiometry of forest ecosystem and would provide an aid to forest management besides contributing to the mitigations strategies of the forests.

Effects of addition of nitrogen-enriched biochar on bacteria and fungi community structure and C, N, P, and Fe stoichiometry in subtropical paddy soils

Biochar can be a soil amendment that increases nutrient retention and carbon (C) sequestration in rice paddy systems. However, biochar can lose nutrient during its production processes so modifications such as coating with the nitrogen (N) that can slowly release nutrients to soil following application are necessary. Dynamic changes in paddy soil microbial communities affect the biogeochemical cycling of soil nutrients; however, the effects of addition of N-enriched biochar on paddy soil microorganisms and nutrient stoichiometry are unclear. Here, we investigated the effects of N-enriched biochar on soil bacteria and fungi community structure and on carbon (C), N, phosphorous (P), and iron (Fe) stoichiometry in subtropical paddy soils. The soil concentrations of TC, TN and TP increased by 0.27–18.55%, 1.31–18.15% and 10.35–54.24% respectively under the nitrogen rich biochar treatment. Under N-enriched biochar application, ratios of N/P and C/P decreased, while P-fixation capacity increased; the decrease in N/P ratio indicated that rice productivity was N-limited. The quantity of soil fungi increased by 42.07% and 10.89% in early and late rice, respectively in the treatment group applying 4t ha−1 of N-enriched biochar. Relative abundance of the bacteria Bacillus, Geobacter, and Sideroxydans decreased with N-enriched biochar, whereas that of Thiobacillus and Thermomonas increased; relative abundance of the fungi Spicellomyces and Crustoderma increased with biochar. Relative abundance of the bacteria Bacteroides was negatively correlated with TC and Fe3+ (P < 0.05) and Sideroxydans and Geoyhrx was negatively correlated with soil TP (P < 0.05). Relative abundance of the fungi genera Westerdykella, Synchytrium, Russula, and Orbilia was positively correlated with soil TC (P < 0.05), Trapelia, Leptosphaerulina, and Tremella was positively correlated with soil TN (P < 0.05), and relative abundance of Leucanium, Monoblepharis was positively correlated with soil TP (P < 0.05). Overall, application of N-enriched biochar to paddy soils affected the microbial community composition through changes in soil physicochemical properties that led to shifts in microbial community function and associated improvements in soil nutrient enrichment.

Microbial Resource Limitation in Aggregates in Karst and Non-Karst Soils

Karst is a widespread ecosystem with properties that affect the microbial activity and storage and cycling of soil organic carbon. The mechanisms underlying microbial resource availability in karst, which limit the microbial growth and activity in soil aggregates, remain largely unknown. We assessed the microbial resource limitations using exoenzymatic stoichiometry and key extracellular enzyme activities in bulk soil and aggregates in karst and non-karst forest soils. Soil organic carbon, total nitrogen, and microbial biomass carbon and nitrogen were significantly higher in bulk soil and the aggregate fractions in karst forests. However, the microbial biomass accumulation was higher in finer aggregates than in macroaggregate fractions. This may be attributed to the surface area of finer aggregates that increase the microbial C accumulation. In karst forests, the activity of extracellular enzymes β-d-glucosidase, β-N-acetylglucosaminidase, α-glucosidase, and α-d-1,4-cellobiosidase was two to three times higher in microaggregates (0.053–0.25 mm) and mineral fractions (&lt;0.053 mm) than in macroaggregates. This coincided with the distribution of microbial biomass carbon and phosphorus in finer aggregate fractions. The microorganisms in bulk soil and aggregates in karst forests were largely co-limited by carbon and phosphorus and rarely by nitrogen and only by phosphorus in non-karst soils. The microbial phosphorus limitation in non-karst soils was alleviated in finer soil aggregates, while these fractions reflected slightly higher. microbial C limitations than bulk and other aggregates in karst forests. The patterns of microbial resource limitations in the bulk and aggregate fractions in karst ecosystems reflected the regulation of enzyme activity and soil organic carbon accumulation in finer aggregate fractions but not in other aggregates.

The Linkage of Soil CO2 Emissions in a Moso Bamboo (Phyllostachysedulis (Carriere) J. Houzeau) Plantation with Aboveground and Belowground Stoichiometry

Understanding the effects of soil stoichiometry and nutrient resorption on soil CO2 emissions is critical for predicting forest ecosystem nutritional demands and limitations tooptimal forest growth. In this study, we examined the effects of above- and belowground stoichiometry on soil CO2 emissions and their mediating effect on soil respiration in subtropical moso bamboo (Phyllostachys edulis) plantations. Our results showed that the soil respiration rate did not differ significantly among four bamboo stands. Nitrogen (N) and phosphorous (P) concentrations were higher in bamboo leaves than litter, whereas the C:N and C:P ratios showed the opposite trend. Significant positive correlations of soil cumulative CO2 emission with litter C:P (p = 0.012) and N:P (p = 0.041) ratios indicated that litter stoichiometry was a better predictor of soil respiration than aboveground stoichiometry. Cumulative soil CO2 emissions were significantly negatively correlated with soil microbe C:N (p = 0.021) and C:N (p = 0.036) ratios, and with soil respiratory quotients (p &lt; 0.001). These results suggest that litter and soil stoichiometry are reliable indicators of the soil respiration rate. This study provides important information about the effects of ecosystem stoichiometry and soil microbial biomass on soil CO2 emissions and highlights them editing role of soil nutritional demands and limitations in the association between soil respiration rates and aboveground plant tissues.

The stoichiometric signature of high‐frequency fire in forest floor food webs

AbstractFire regimes are shifting under climate change. Decadal‐scale shifts in fire regime can disrupt the biogeochemical cycling of carbon (C), nitrogen (N), and phosphorus (P) within forest ecosystems, but the full extent of these disruptions is unknown. It is also unclear whether these disruptions have consequences for the ecological characteristics (e.g., biomass, abundance, and composition) of microbial and invertebrate communities, which together comprise the majority of terrestrial biodiversity and underpin many ecosystem processes. The theoretical framework of ecological stoichiometry has great potential in this context, but it has rarely been used to develop an integrated understanding of the biogeochemical and ecological effects of altered fire regime across trophic levels. Using one of the world's longest‐running fire experiments, located in Queensland, Australia, we carried out a comprehensive investigation into the stoichiometric consequences of a decadal‐scale divergence in prescribed fire frequency and their links to coinciding changes in various ecological characteristics of forest floor microbial and invertebrate communities. Compared to long‐term fire exclusion, forty‐three years of biennial burning led to significantly N‐depleted and/or P‐enriched stoichiometry in soil, leaf litter, leaf litter–associated microbial biomass, and certain groups of invertebrates, although total invertebrate community stoichiometry was not affected. Microbial biomass was 42% lower in biennially burned soils. Invertebrate community composition differed between fire regime treatments on some sampling dates, but fire regime did not have consistent effects on invertebrate biomass or abundance. Microbial biomass and the abundances of some invertebrate taxa were depressed at particularly low and/or high resource N:P, consistent with a coupling of these variables to the stoichiometric effects of decadal‐scale fire regime. Litter transplants likewise indicated that some invertebrate abundances were sensitive to litter properties over 12 months. Together, our results indicate that long‐term changes in fire regime can decouple the within‐ecosystem cycling of N and P, with N and P cycling growing more and less conservative, respectively, under high‐frequency fire in a way that propagates throughout forest floor food webs. Our study provides new insights into the coupled biogeochemical and ecological responses of forest ecosystems to novel fire regimes and establishes a basis for a stoichiometric framework for fire ecology.

How C: N: P stoichiometry in soils and carbon distribution in plants respond to forest age in a Pinus tabuliformis plantation in the mountainous area of eastern Liaoning Province, China.

Carbon distribution in plants and ecological stoichiometry in soils are important indicators of element cycling and ecosystem stability. In this study, five forest ages, young forest (YF), middle-aged forest (MAF), near-mature forest (NMF), mature forest (MF), and over-mature forest (OMF) in a Pinus tabuliformis plantation were chosen to illustrate interactions among the C: N: P stoichiometry in soils and carbon distribution in plants, in the mountainous area of eastern Liaoning, China. Carbon content was highest in the leaves of MAF (505.90 g⋅kg−1) and NMF (509.00 g⋅kg−1) and the trunks of YF (503.72 g⋅kg−1), MF (509.73 g⋅kg−1), and OMF (504.90 g⋅kg−1), and was lowest in the branches over the entire life cycle of the aboveground components (335.00 g⋅kg−1). The carbon content of the fine roots decreased with soil layer depth. In YF, MAF, and NMF carbon content of fine roots at 0.5 m was always higher than that of fine roots at 1 m; however, it was the opposite in MF and OMF. The carbon content of the leaves changed with forest age; however, carbon content of branches, trunks and fine roots did not change significantly. Soil total carbon (TC), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) content was highest in the OMF. Soil TC, TN and AP content, and TC: TN, TC: TP and TN: TP ratio decreased with increasing soil depth. Soil TC, TN, and TP content had a significant effect on the carbon content of fine roots (p < 0.05). The leaf carbon content and soil element content changed obviously with forest age, and the soil TN, TP and AP increased, which might reduce the carbon content allocation of fine roots.

Drivers of soil respiration in response to nitrogen addition in a Mediterranean mountain forest

Atmospheric nitrogen (N) deposition rates affect soil N dynamics, influencing soil respiration (RS) rates. However, for the Mediterranean region, the effect of changes in atmospheric N deposition on RS are not well constrained yet. We investigated the interplay between increased N deposition and tree species composition on RS at a Scots pine—Pyrenean oak ecotone in Central Spain, and whether the observed responses were mediated by changes on selected soil properties. Throughout 3 years, we simulated two N deposition rates—10 (medium) and 40 kg N ha−1 a−1 (high)—over the background deposition (control) in neighbouring stands in which tree species composition (pine or oak) shapes soil stoichiometry and microbial communities. We monitored RS on a monthly basis during 3 years; in addition, we performed targeted measurements 24 h after the N fertilization events to assess short-term soil responses. During winter and summer, RS did not respond to enhanced N deposition rates. In spring and autumn, higher RS rates were observed in the medium-fertilization, but the size and duration of this effect was tree species dependent. We suggest that climate seasonality modulates the response of RS to N availability, with tree species effects becoming relevant only when environmental conditions are adequate. RS in fertilized plots was larger from February to May and in September under pine, while under oak a response was observed only in April, probably due to differences in native soil stoichiometry under each tree species. Overall, RS showed high stability during 3 years of N enrichment in this Mediterranean ecotone area. However, we observed short-term soil responses after N fertilization events—loss of base cations, soil acidification and reduced microbial biomass—which emphasize the need to investigate consequences for the belowground C and N cycles if chronic N enrichment persists in the long run.

C:N:P stoichiometry responses to 10 years of nitrogen addition differ across soil components and plant organs in a subtropical Pleioblastus amarus forest

How stoichiometry in different ecosystem components responds to long-term nitrogen (N) addition is crucial for understanding within-ecosystem biogeochemistry cycling processes in the context of global change. To explore the effects of long-term N addition on nutrient stoichiometry in soil and plant components in forest ecosystem, a 10-year N addition experiment using ammonium nitrate (NH4NO3) was conducted in a bamboo forest in the Rainy Zone of West China, where the background N deposition is the highest in the world. Four N treatment levels (+0, +50, +150, +300 kg N ha−1 yr−1) (CK, LN, MN, HN) were applied monthly since November 2007, and then, the C:N:P stoichiometry of soil, microbial biomass, and enzymes in rhizosphere soil and bulk soil, and plant organs were measured. N addition decreased the stoichiometry of C:N:P of soil, microbial biomass, and enzymes. Soil C:N:P change under N addition treatments was stronger in bulk soil, while C:N:P changes for microbial biomass and enzyme activity were significant in rhizosphere soil. N addition significantly decreased TOC in bulk soil. Changes in MBC:MBN:MBP in rhizosphere and bulk soil were mainly caused by MBN and MBP, and MBP performance was consistent with that of AP. The main variable leading to the change of enzyme C:N:P in rhizosphere soil was BG and AP, and in bulk soil was LAP + NAG activity. Plant root C:P and N:P increased with N addition, while those for leaves and twigs did not. N addition significantly reduced the pH of both rhizosphere and bulk soils. These results suggest that the stoichiometry responses of rhizosphere and bulk soils were different due to the influence of plant roots. Soil acidification, enhanced aluminum toxicity potential, decreased root biomass and enhanced microbial P limitation caused by N addition were the important mechanisms that promoted stoichiometry changes in this ecosystem. Under the chronic input of N deposition, the stoichiometry between plant and soil evolved in different directions, which may lead to the decoupling of plants from soils.

Effects of transforming forest land into terraced land on the characteristics of soil carbon, nitrogen, phosphorus and their stoichiometry in North Guangdong, China.

To examine the effects of land use change on soil stoichiometry, we selected four kinds of land use soils in northern Guangdong: forest land (FL), sloping orchard (SO), dry land terraces (DLT) and paddy terraces (PT) to explore the changes of the contents, stocks and stoichiometry of organic carbon, nitrogen and phosphorus in the 20 a process of transforming from forest land into terraced land. Results showed that land use significantly changed the contents and stoichiometric characteristics of soil carbon, nitrogen and phosphorus. With the increase of soil depth, organic carbon (OC) and total nitrogen (TN) contents of DLT and PT decreased significantly, while FL and SO showed a "V"-shaped change trend. There was no difference in total phosphorus (TP) content among the four land use types. The OC content of PT was the highest, with an average value of 12.36 g·kg-1, followed by FL (10.32 g·kg-1) and DLT (8.80 g·kg-1), while SO was the lowest (5.96 g·kg-1). TN content was decreased in order of PT (1.01 g·kg-1)>DLT (0.78 g·kg-1)>FL (0.66 g·kg-1)>SO (0.33 g·kg-1). TP content of DLT (0.71 g·kg-1) was the highest, and SO (0.22 g·kg-1) was the lowest. C:N was between 8.87 and 22.94, and SO was the highest. C:P was between 8.73 and 81.74, N:P was between 0.77 and 5.13, with both of which being the highest in FL. Land use, soil depth and their interaction significantly affected the contents, stocks, and stoichiometric ratio of soil carbon, nitrogen and phosphorus, with soil bulk density, pH, and clay content as important influencing factors. The research results could provide a scientific basis for land use of subtropical low mountain forest land and rational fertilization of terraced ecosystems.

Response of water use efficiency and plant-soil C:N:P stoichiometry to stand quality in Robinia pseudoacacia on the Loess Plateau of China

The evaluation of stand quality is of great significance for forest management and sustainable development. Water use efficiency (WUE) and the carbon (C), nitrogen (N), and phosphorus (P) stoichiometric characteristics of plants and soil are important indexes used to evaluate plant water and nutrients adaptation strategies. However, little is known about the effects of stand quality on WUE and plant‑soil C:N:P stoichiometry. In this study, the growth characteristics of Robinia pseudoacacia plantations and understory plants in an age series of 8-, 15-, 25-, and 35-year-old stands were investigated, and the leaf-level WUE and C:N:P stoichiometry in plants and soil were measured on the Loess Plateau. The results showed that the species richness, Shannon-Weiner diversity index, and evenness index reached their peaks in the 35-year-old stands with increasing afforestation age. WUE reached its highest value in the 35-year-old stands but was only significantly higher than that in the 8-year-old stands. Stand age had different effects on C, N, and P nutrients and stoichiometry in leaves, fine roots, and soil. The most obvious trend was that soil total P decreased significantly with increasing afforestation age, and the leaf N:P ratio was greater than 16 in the four stand ages, which indicated that P was the main limiting factor in R. pseudoacacia plantations. Leaf nutrients and stoichiometry are closely related to forest growth characteristics, while root nutrients and stoichiometry are more related to understory plant composition and diversity. Importantly, the WUE had no significant change with the increase in the stand quality index, and the response of soil stoichiometry to stand quality was stronger than that of plant stoichiometry. These results help us further understand coordinated plant-soil restoration after afforestation.

Short-term effects of grazing intensity on soil stoichiometric characteristics of typical grassland in the agro-pastoral ecotone of northern China.

Grazing is the dominant land use way for natural grasslands. Different grazing intensities could affect soil stoichiometry in grasslands by influencing the selective feeding by livestock, litter input, and microbial community structure. In this study, a grazing experiment was carried out in a grassland of agro-pastoral ecotone in Northern China for three years (2017-2019). The concentrations of total carbon (TC), total nitrogen (TN), dissolved organic carbon (DOC), dissolved nitrogen (DN), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) in soils were measured. We analyzed the stoichiometric characteristics of those parameters. The results showed that different grazing intensities (1, 2, 4 sheep·0.2 hm-2) had no significant effect on soil TC after three years. The moderate grazing intensity significantly reduced soil TN in 10-20 cm layer in 2019. The light, moderate, and heavy grazing intensities significantly increased soil C/N at 10-20 cm layer, while grazing intensities did not affect soil DOC, DN and DOC/DN. The soil DOC and DN content showed a decreasing trend with the increase of grazing intensity in 2019. It indicated that continuous high intensity grazing might reduce soil dissolved nutrients. The light grazing inten-sity increased soil MBC, while heavy grazing intensity reduced soil MBC significantly, with the increase of grazing year. Different grazing intensities did not affect soil MBN and MBC/MBN.

Soil Stoichiometry Mediates Links Between Tree Functional Diversity and Soil Microbial Diversity in a Temperate Forest

Interactions between plants and soil microbial communities underpin soil processes and forest ecosystem function, but the links between tree diversity and soil microbial diversity are poorly characterized. Differences in both the taxonomic and functional diversity of trees and microbes can shape soil nutrient status and carbon storage, but the stoichiometry of carbon and nutrients in the soil also influences resource availability to plant and microbial communities. Given the key role of resource availability in plant–soil interactions, we hypothesized that relationships between tree diversity metrics and soil bacterial or fungal diversity are mediated by soil stoichiometry. To test our hypothesis, we measured tree diversity metrics (tree species richness, functional trait diversity and functional trait composition) and soil stoichiometry in a temperate forest in China, and we determined soil microbial diversity by Illumina sequencing. We used structural equation models to assess the relationships between tree diversity metrics and soil bacterial or fungal diversity and to evaluate the influence of soil stoichiometry. Overall, microbial diversity was strongly related to soil stoichiometry, whereby fungal diversity was associated with high soil N/P ratios, whereas bacterial diversity was related to high soil C/P ratios. Soil bacterial and fungal diversity were more closely related to tree functional trait diversity and composition than to tree species richness, and the links between tree and soil microbial diversity were mediated by soil stoichiometry. The strong links between tree functional traits, soil stoichiometry and soil bacteria or fungi suggest that resource quality plays a key role in plant–microbial interactions. Our results highlight the importance of nutrient stoichiometry in linkages between tree functional diversity and soil microbial diversity.

Stoichiometric imbalance of soil carbon and nutrients drives microbial community structure under long-term fertilization

Fertilization affects soil microbial community by altering soil organic carbon (C) and nutrients availability. However, it remains unclear how changes in stoichiometric C, N, and P ratios resulting from fertilization affect microbial community. We investigated a 26-year field experiment receiving inorganic fertilizers (N, NP, PK, and NPK), organic N combination (with manure and straw), natural recovery (fallow), and no fertilizer (control). The aim of this study was to explore the responses of microbial community to C: N:P stoichiometry in soil and microbial biomass of topsoil (0–20 cm) and subsoil (20–40 cm). Results showed that compared to control treatment, organic application increased the ratio of fungi to bacteria (F:B) in topsoil and gram-negative bacteria to gram-positive bacteria (G−:G+) in subsoil. However, application of inorganic decreased both the F: B and G−:G+ ratio in topsoil. Increasing soil C, N and P availability resulted from inorganic fertilizers and organic combination fertilization caused stoichiometric imbalance between soil and microbial biomass. As a result, the F:B and G−:G+ ratio were positively related to C:N imbalance but negatively associated with N:P imbalance in topsoil. Redundancy analysis (RDA) showed that main factors regulating microbial community were pH, C:P and N:P imbalances in topsoil, whereas TDN, N:P imbalance, DOC and soil C:N in subsoil. Furthermore, C:P and N:P imbalance explained 16.4% in topsoil, and N:P imbalance explained 22.0% in subsoil of microbial community variation. These results reveal the shifts of soil microbial community are driven by changes in soil pH and C, N and P stoichiometric imbalance from long-term fertilization.