Soil Total Phosphorus Content Research Articles

Short Term Effects of a Changing Carbon Input on the Soil Respiration of Picea schrenkiana Forests in the Tianshan Mountains, Xinjiang

The impact of exogenous carbon input changes on forest soil respiration provides the basis for an intensive analysis of the forest carbon cycle. Based on a plant residue addition and removal control experiment, this study investigated the short-term soil respiration response to carbon input changes of Picea schrenkiana on the Tianshan Mountains during their growing season with five different carbon input treatments:control, double litter, no root, no litter, and no input. The results revealed that, during the entire observation period, the cumulative soil respiration rates were 3.38, 3.94, 2.65, 2.87, and 2.01 μmol·(m2·s)-1 in the double litter, control, no litter, no root, and no input treatments, respectively. Compared with the control treatment, the cumulative soil CO2 efflux increased by 402.65 g·m-2 in the double litter treatment, whereas it decreased by 515.00, 354.73, and 967.15 g·m-2 in the no litter, no root, and no input treatments, respectively. The mineral soil respiration, litterfall respiration, and root respiration contributed 59.46%, 21.49%, and 14.79%, respectively, to the total soil respiration rate. PCA analysis revealed that the soil respiration rate was positively correlated with the soil temperature, soil moisture, soil total phosphorus content, pH, and soil organic carbon content, and negatively correlated with the soil bulk density, while the soil total nitrogen content, carbon nitrogen ratio, and soil electrical conductivity had no effect on the soil respiration rate.

Responses of soil nutrients to vegetation restoration in China

Although vegetation restoration is known to improve soil quality and increase soil microbial activity, its effects on soil nutrients remain largely uncertain because of the complex relationship between plant growth and nutrient cycling. In order to evaluate the responses of soil nutrients to vegetation restoration, we used a standardized procedure to collect 586 and 395 observations for soil total nitrogen (TN) and total phosphorus (TP) in the top 30 cm of soil from 101 published field studies to conduct a meta-analysis in China. Our results revealed that soil TN and TP increased by 47% and 25% following vegetation restoration. Restoration actions made a larger contribution to recovery soil nutrients, and the recovery effects depended on land use history more than restoration approach and age. Vegetation restoration, especially on farmland with broadleaf species, could provide substantial opportunities for TN and TP sequestrations in the top 30 cm of soil. Passive approach (restoration by natural succession) performed better than active approach (restoration with human intervention) for enhancing soil TP content, but the recovery levels of soil TN were insignificantly different between two restoration approaches. Meanwhile, soil TN significantly increased with time after restoration. Soil nutrient dynamics were largely controlled by soil properties and were closely coupled with SOC stock dynamics. The magnitude and direction of the dynamics of soil TN and TP differed among four ecological regions, indicating geographical and climatic heterogeneities had significant impacts on soil nutrient recovery. Dynamics of soil nutrients were significantly influenced by soil properties, geographical locations, and climatic characteristics of the study sites, and these findings could facilitate priority setting and selection of treatment methods for vegetation restoration to enhance soil nutrients.

Effects of fire intensity on leaf functional traits and functional diversity of Larix gmelinii community

Fire is an important ecological factor in boreal coniferous forest, which directly affects plant taxonomic and functional diversity and consequently forest succession. We analyzed the changes of soil nutrient contents, leaf functional traits, taxonomic and functional diversity of a Larix gmelinii community under different fire intensity levels (low, medium, heavy). The forest stand had been naturally recovered for 12 years in Yakeshi area. The results showed that fire significantly reduced soil total nitrogen content, but did not affect soil total phosphorus content. Low and medium fire intensities could maintain higher species diversity and functional diversity of the community. Medium fire disturbance significantly increased species diversity of the community, with maximum species richness index, Shannon index, Simpson index and Pielou evenness index. Fire disturbance reduced functional richness and functional divergence of the community, which were the largest in medium and low fire intensity respectively (except unburned). Functional evenness and Rao qua-dratic entropy index increased after forest fire disturbance, and the largest was in the low intensity burned area. With the increases of fire intensity, leaf dry matter content, leaf tissue density and leaf total phosphorus content showed a significantly increased trend, while specific leaf area, leaf water content, leaf total nitrogen content and leaf N:P showed the trend unburned ＞ medium fire ＞ low fire ＞ heavy fire, leaf thickness increased first and then decreased. Fire intensity had significant effects on leaf functional traits and functional diversity of forest community. Moderate fire distur-bance could promote forest restoration.

Environmental factors influencing spatial variability of soil total phosphorus content in a small watershed in Poyang Lake Plain under different levels of soil erosion

Soil erosion can change the migration and deposition patterns of soil particles and alter the regional geographic environment; therefore, it plays an important role in the biogeochemical cycle of soil total phosphorus (STP). Quantifying the influence of environmental factors on STP content under soil erosion is critical for understanding the lateral transfer of STP from soil. Here, we explored the influence of environmental factors on STP content under different levels of soil erosion in the small watershed of Nanliao River, a tributary of Xiu River in the western part of Poyang Lake Plain in Jiangxi Province, China. Soil erosion ranged from 0 to 176.26 t hm−2 a−1 (15.41 t hm−2 a−1 on average) across the watershed in 2018, indicating a mild erosion level on the whole. The STP content varied between 0.06 and 1.19 g/kg (0.6 g/kg on average) with a coefficient of variation of 43.33%, indicating moderate variation. An exponential model with a small nugget effect (7.35%) and a small range (2.25 km) could estimate 86.5% of spatial variability in STP content. The STP content showed a strong spatial autocorrelation, and the soil rich in STP was mostly distributed along the Nanliao River. There was a negative correlation between STP content and soil erosion (r = –0.149, P < 0.01). Each of the 10 selected environmental factors could explain 2.7–21.3% of spatial variability in STP content. Elevation, soil particle size, soil pH, and their interactions with other factors were the main factors influencing STP content, although their influence differed across various erosion levels. This study could provide useful data for controlling STP loss and reducing the impacts of soil erosion on the ecological environment in the Poyang Lake Plain.

Response of understory species distribution of Robinia pseudoacacia plantation to environmental factors in loess hilly region, China.

We explored the distribution characteristics and influencing factors of understory species in Robinia pseudoacacia plantation in Wuqi, Ansai, Mizhi, Yichuan and other places, in combination with niche breadth, soil, altitude and other environmental factors. We analyzed the response mechanism of species distribution to environmental factor to provide a scientific basis for the mana-gement of R. pseudoacacia plantation in loess hilly region. The results showed that the broadly distributed understory species in R. pseudoacacia plantation were Setaria viridis, Heteropappus altaicus, Artemisia scoparia, Poa sphondylodes, Artemisia leucophylla, Ixeris sonchifolia, and Incarvillea sinensis. With the increasing rehabilitationage, the dominant understory species distribution followed the order: Artemisia capillaries → P. sphondylodes → A. scoparia → others (Rubia cordifolia, Rosa rubus and so on) → A. leucophylla → S. viridis. Results from principal component analysis showed that soil total phosphorus (25.6%), altitude (20.3%) and soil total nitrogen (19.3%) were the key factors influencing understory species distribution in R. pseudoacacia plantation. Soil organic carbon content, soil total nitrogen content, soil total phosphorus content, soil water content and the number of understory species distribution in R. pseudoacacia plantation were generally positively correlated with the degree of correlation varying across different species. There was no correlation between the slope aspect and the understory species distribution in R. pseudoacacia plantation. In conclusion, topography and soil factors played important roles in driving understory species distribution. The steeper the slope, the higher the altitude, the fewer understory species in R. pseudoacacia plantation. Understory species distribution was mainly affected by soil total phosphorus content and altitude. The understory species distribution reflected the differences of soil nutrient status, which had a certain guiding role in the management of R. pseudoacacia plantation.

Relationship between the main functional traits of fine root and the rhizosphere soil nutrients of different diameter classes in Zenia insignis plantation.

Fine roots are sensitive to changes in the soil environment, and play an important role in plant growth and development. To clarify the relationship between fine root traits and rhizosphere soil nutrient characteristics, fine roots of trees belonging to different diameter classes in six-year-old Zenia insignis plantation were sampled. The results showed that root biomass, root length density and root volume density increased with the increases of diameter class. Specific root length and specific root area showed the trend of first rising and then falling and rising again with the increases of diameter class. Root tissue density did not change with diameter class. There were significant diffe-rences in soil pH, water content, total carbon, total phosphorus, ammonium nitrogen, nitrate nitrogen and total available nitrogen contents of rhizosphere soil belonging to different diameter classes. The concentrations of soil total carbon, total nitrogen, nitrate nitrogen and total available nitrogen in the rhizosphere soil of large diameter trees were relatively higher, while the soil water content, total phosphorus and ammonium nitrogen contents of small diameter trees were relatively higher. The concentrations of soil total nitrogen, total carbon, nitrate nitrogen and total available nitrogen were significantly positively correlated with root biomass, root length density and root volume density. The concentrations of soil total phosphorus was significantly positively correlated with root tissue density of fine roots, but negatively correlated with specific root length and specific root area. Soil water content was significantly positively correlated with root biomass and root volume density. Soil pH was significantly positively correlated with the specific root length and specific root area of fine roots, but negatively correlated with root tissue density. Our results provide scientific basis for the selection of excellent germplasm resources of Z. insignis.

Different responses of soil element contents and their stoichiometry (C:N:P) to yak grazing and Tibetan sheep grazing in an alpine grassland on the eastern Qinghai – Tibetan Plateau’

The alpine grassland of the Qinghai–Tibetan Plateau has long been subjected to grazing by local livestock, yak and Tibetan sheep. Although there is plenty of evidence that grazing influences the vegetation community structure and functions, researches on how grazing of different livestock affects element contents in soil and their stoichiometry and how they relate to plant community remain inadequate in the region. We quantified the concentration and distribution of carbon (C), nitrogen (N) and phosphorus (P), and investigated the robustness of soil stoichiometry (C:N:P) under yak grazing and Tibetan sheep grazing through a manipulated grazing experiment on an alpine grassland. Our results showed that: (1) Yak grazing increased the soil total carbon content (STC) but decreased the soil total phosphorus content (STP), whereas Tibetan sheep grazing decreased STC but increased STP. Neither of the two livestock species had impact on the soil total nitrogen content (STN). (2) Yak grazing and sheep grazing had no impact on soil stoichiometry except for C:P. (3) Only STP and C:P were affected by the mixing ratio of yak to sheep. The plant biomass loss and the shifts in plant community structure may account for the opposite responses of STC and STP to yak grazing and sheep grazing, whereas the dung chemical property of different livestock species might also contribute to the response of STP. The higher soil C:N and lower soil N:P ratios indicated that plant growth may be limited more by N than by P in the region.

沙质草地营造樟子松林后土壤容重的变化及其影响因子

PDF HTML阅读 XML下载 导出引用 引用提醒 沙质草地营造樟子松林后土壤容重的变化及其影响因子 DOI: 10.5846/stxb201808161750 作者: 作者单位: 辽宁工程技术大学,辽宁工程技术大学,辽宁工程技术大学,辽宁工程技术大学,辽宁工程技术大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金面上项目（31570709） Changes in soil bulk density and its influencing factors after sandy grassland afforestation with Pinus sylvestris var. mongolica Author: Affiliation: Liaoning Technical University,Liaoning Technical University,Liaoning Technical University,Liaoning Technical University,Liaoning Technical University Fund Project: The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用野外调查和室内试验相结合，以辽宁省章古台地区不同生长阶段（包括幼龄林、中龄林、成熟林和过熟林）的20块樟子松人工固沙林样地（以临近的7块天然草地为对照）为研究对象，研究了沙质草地营造樟子松人工林后不同生长阶段0-100 cm土层土壤容重的变化及其影响因子。结果表明：天然沙质草地营造樟子松人工固沙林后，不同生长阶段樟子松林在0-10 cm土层土壤容重变化的变异系数为78%，其他土层变异系数范围为1.08%-4.35%。随着樟子松人工林林龄的增加，土壤容重变化量在0-20 cm和60-100 cm层逐渐降低，在20-60 cm层先降低，到37年左右后逐渐升高，过熟林较成熟林显著增大。林龄对不同土层容重变化的决定系数由大到小依次为40-60、60-80、20-40、10-20、0-10、80-100 cm层。土壤容重变化在60-80 cm层与土壤粗颗粒（粒径>0.05 mm）含量、在0-10、20-40 cm和60-80 cm层与土壤全氮含量、在0-10、20-60 cm和80-100 cm层与土壤全磷含量、在20-40 cm和80-100 cm层与土壤全钾含量显著负相关，且土壤全氮和全磷含量对土壤容重的影响效果随土层深度的增加逐渐降低，土壤容重变化在10-20 cm层与土壤含水率、在20-40 cm层与土壤有机碳含量呈显著的正相关。总体上，沙质草地营造樟子松人工林可以改善土壤结构，提高土壤质量，建议采取封育禁牧等营林措施增加樟子松林下枯落物积累，提高土壤养分含量，同时对37年樟子松人工林逐渐进行更新。 Abstract:Using a combination of field surveys and laboratory analysis, in the Zhanggutai area of Liaoning province, 20 forest plantations of Pinus sylvestris var. mongolica in different growth stages (including young forests, mid-aged forests, mature forests, and over-mature forests) and 7 neighboring control grasslands were selected. In this paper, the changes in soil bulk density and its influencing factors were studied in the 0-100 cm soil layer of different growth stages after sandy grassland afforestation with P. sylvestris var. mongolica. The results showed that after sandy grassland afforestation, the variance coefficient of soil bulk density was 78% in the 0-10 cm soil layer and the variance coefficient in other soil layers ranged from 1.08% to 4.35%. As the stand age increased, the magnitude of soil bulk density decreased gradually in 0-20 and 60-100 cm soil layers, however, the magnitude decreased firstly and then increased after 37 years in 20-60 cm soil layers, and the magnitude in over-mature forests was significantly higher than that in mature forests. In different soil layers, the coefficients of determination of stand ages for the magnitude of soil bulk density in decreasing order were 40-60, 60-80, 20-40, 10-20, 0-10, and 80-100 cm soil layers. The coarse-textured soil (particle size>0.05 mm) in the 60-80 cm soil layer; soil total nitrogen content in 0-10, 20-40, and 60-80 cm soil layers; soil total phosphorus content in 0-10, 20-60, and 80-100 cm soil layers; and soil total potassium content in 20-40 and 80-100 cm soil layers were significantly negatively correlated with soil bulk density, and the impact of soil total nitrogen and soil total phosphorus content on soil bulk density changes gradually decreased as the soil layer depth increased. However, soil moisture in the 10-20 cm soil layer and soil organic carbon content in the 20-40 cm soil layer were significantly positively correlated with soil bulk density. On the whole, sandy grassland afforestation with P. sylvestris var. mongolica can improve soil structure and quality. It is suggested that enclosure and grazing prohibition are effective to increase leaf litter accumulation and improve soil nutrient content in P. sylvestris var. mongolica plantations. In addition, 37 year old P. sylvestris var. mongolica plantations need to be regenerated gradually. 参考文献 相似文献 引证文献

Effect of poultry wastewater irrigation on nitrogen, phosphorus and carbon contents in farmland soil

Abstract The goal of this study was to assess the suitability of poultry wastewater for the irrigation of farmland soil as a possible substitute for regular water and fertilizers. The vertical and spatial variability of soil total nitrogen (STN), soil total phosphorus (STP) and soil organic carbon (SOC) was analyzed during the growing season of summer maize in two types of soil: an experimental group (EG) soil, irrigated once only with poultry wastewater, and a control group (CG) soil, irrigated once only with regular water. Results revealed no difference in STP concentration, SOC concentration, nitrogen storage and phosphorus storage between EG and CG soils (all p&gt;0.05); STN concentration in the 5–15 cm layer and carbon storage were higher in EG soil (p&lt;0.05) while remaining within safety limits. Overall, single-time irrigation by poultry wastewater enhances nitrogen and carbon content of soil and does not pose a serious risk of pollution for ground water.

Factors that influence soil total phosphorus sources on dam fields that are part of ecological construction programs on the Loess Plateau, China

Terraces and check-dam construction are widely used to control soil and water on the Loess Plateau, China. However, it is not known whether dam fields behave as soil phosphorus sources or sinks. This study quantitatively assessed the effects of check-dam and terrace construction on soil total phosphorus (STP). It also investigated the factors that influenced STP. A total of 1010 soil samples (five land uses and five soil depths) were collected in a small watershed on the Loess Plateau. The probability density function of the Weibull distribution was used to analyze the STP sources on the dam field land. The results showed that the highest STP concentration was recorded in the dam field land. Furthermore, the STP concentration mean values for the five land-use types decreased in the following order: dam field > terraced land > grassland > forestland > sloping cropland. The highest clay content value was also recorded in the dam field land. Soil total phosphorus was significantly and positively correlated to soil organic carbon (SOC), but negatively correlated to sand content (P < 0.01) in all areas. Across the entire soil profile down to 60 cm depth, the STP levels for the five land-uses were dam field, 2.78 kg/m2; terrace, 2.86 kg/m2; grassland, 2.98 kg/m2; forestland, 2.84 kg/m2; and sloping cropland, 2.83 kg/m2. The percentage contributions made by the four land use types to the soil total phosphorus deposited in the dam field were 50% (sloping cropland), 33% (grassland) and 17% (forestland). Therefore, check dam constructions behave as a sink for soil phosphorus on the Loess Plateau, China.

Vertical distribution of soil total nitrogen and soil total phosphorus in the critical zone on the Loess Plateau, China

It is important to determine the vertical distributions of soil total nitrogen (STN) and soil total phosphorus (STP) as well as the factors that influence them in the Earth's critical zone (CZ) in order to understand the N/P cycle in the CZ. However, few data are available regarding the vertical distributions of STN and STP in deep soil profiles in the CZ. Thus, this study investigated the vertical distributions of the STN and STP as well as related factors in a deep soil profile on the Loess Plateau, China. Soil drilling was used to collect 703 soil samples throughout the soil profile from five sites. The STN decreased initially at all of the sampling sites (except at Shenmu), before fluctuating with increasing depth throughout the profile, whereas the STP exhibited a fluctuating trend at all sites. The mean STN and STP concentrations ranged from 0.12 g kg−1 to 0.25 g kg−1 and from 0.45 g kg−1 to 0.58 g kg−1, respectively. The adjusted r2 values based on stepwise multiple linear regressions for STN and STP ranged from 35% to 83% and from 4% to 17%, respectively, and thus, STN was explained better by the measured soil variables compared with STP. The mean STN and STP stocks ranged from 1.87 to 3.90 mg ha−1 and from 6.75 to 9.09 mg ha−1, respectively. The results of this study facilitate evaluations of STN and STP stocks and studies of the N/P cycle in the CZ on the Loess Plateau.

Effects of mulching management on biomass of Phyllostachys praecox and soil fertility

We analyzed the dynamics of stand growth and soil nutrient availability during the degradation processes of Phyllostachys praecox plantation, taking the advantage of bamboo forest stands with different mulching ages (0, 3, 6, 9 and 12 a). The results showed the aboveground and belowground biomass of bamboo forest reached the maximum value when they were covered by three years, which was significantly increased by 14.6% and 146.6% compared with the control. The soil nutrient content was affected by the mulching age and soil layer. Soil nutrients gradually accumulated in upper layer. Soil organic carbon and total nitrogen content were increased with the increases of coverage years. The soil total phosphorus content at different soil layers showed a trend of decreasing first and then increasing. It was the lowest level in the surface layer (0-20 cm) and the bottom (40-60 cm) in 6 years, and the subsurface (20-40 cm) soil reached the lowest level in three years. The total potassium content kept increasing in 0-20 cm soil layer, but decreased during the first three years of mulching and then increased in 20-60 cm soil layer. The comprehensive index of soil fertility quality was greatly improved after nine years mulching, with fertility of subsurface soil being better than that of surface and bottom soils. There was no relationship between the soil fertility index and biomass of different organs in bamboo in the different mulching ages. In the subsurface, however, nitrogen content was negatively related to leaf biomass and potassium was negatively correlated with the biomass of leaves and whip roots. Our results indicated that excessive accumulation of soil nutrients seriously inhibited the propagation and biomass accumulation of P. praecox after long-term mulching management and a large amount of fertilizer, which further aggravated the degradation of bamboo plantation.

Effects of selective cutting on soil phosphorus forms and availability in Korean pine broad-leaved forest in Xiaoxing'an Mountains of China.

In order to clarify the effects of selective cutting on soil phosphorus availability in Korean pine broad-leaved forest, surface soil (0-10 cm) samples from original Korean pine broad-leaved forest and natural forests with mild, medium and intensive cutting disturbances were collected. The Sui modified Hedley phosphorus fractionation method was used to continuously extract soil samples and analyzed the differences and changes of soil phosphorus fractions from different experimental stands. The results showed that the soil total phosphorus content of Korean pine broad-leaved forest varied from 1.09 to 1.66 g·kg-1, with the original stand and intensive cutting disturbance stand being the maximum and minimum one, respectively. The differences of soil total phosphorus content among cutting disturbance levels were significant. The Olsen phosphorus and phosphorus activation coefficients changed with an amplitude of 7.26-17.79 mg·kg-1 and 0.67%-1.07%, respectively. Both of them significantly decreased with the increase of selective cutting disturbance level. The concentrations of all P fractions except HCl-Po, i.e., H2O-Pi, NaHCO3-P, NaOH-P, HCl-Pi, Residual-P, decreased with increasing cutting disturbance levels compared with original forest. The correlation coefficient between H2O-Pi and soil Olsen phosphorus was the highest (0.98), though it only accounted for 1.5%-2.2% of the total phosphorus. NaOH-P content contributed to more than 48.0% of the total phosphorus, acknowledged as the potential source of soil phosphorus. In conclusion, selective cutting disturbance could constrain phosphorus storage and soil phosphorus availabi-lity of the Korean pine broad-leaved forests by significantly reducing the content of soil inorganic phosphorus and NaOH-Po, and such trends were positively dependent on the intensity of selective cutting.

Arbuscular mycorrhizal fungal community structure and diversity are affected by host plant species and soil depth in the Mu Us Desert, northwest China

ABSTRACTThe vertical diversity and distribution of arbuscular mycorrhizal (AM) fungi were investigated in the Mu Us Desert, northwest China. Soils were sampled to 50 cm in depth in the rhizospheres of Hedysarum laeve, Artemisia ordosica, and Psammochloa villosa and 44 AM fungal species belonging to 10 genera were isolated. Several of these species have peculiar morphological features, which are distinct from other habitats. AM fungal diversity and distribution differed significantly among the three host plants and the five soil layers. Spore density, species richness, and the Shannon-Wiener index of AM fungi were 0.55–4.3 spores g−1 soil, 7–36 and 1.78–2.89, respectively. Spore density and species richness had a significant positive correlation with soil total phosphorus content (0.0377–0.1129 mg g−1), and a negative correlation with soil pH (7.19–7.64). Nonmetric multidimensional scaling, PerMANOVA, and structural equation model analysis demonstrated that host plant species and soil depth significantly and directly influenced the structure of AM fungal communities. We concluded that diversity and distribution of AM fungi might be influenced by plant species, soil depth patterns, and soil nutrient availability in desert ecosystems. This research into AM fungal communities may lead to the development of AM fungi treatment for the mitigation of soil erosion and desertification using mycorrhizal plants, such as H. laeve, A. ordosica, and P. villosa.

Responses of soil nutrients and microbial communities to three restoration strategies in a karst area, southwest China

Ecological restoration is widespread in the karst region, southwest China, but the impacts of different restoration strategies on soil fertility indices have rarely been compared. Here soil nutrients and microbial communities were measured 16 years after agricultural abandonment in a karst area, southwest China. Three restoration strategies were included, i.e., i) restoration with an economic tree species Toona sinensis (TS), ii) restoration with Guimu-1 hybrid elephant grass (GG), iii) restoration with a combination of Zenia insignis and Guimu-1 hybrid elephant grass (ZG). Cropland under maize-soybean rotation (CR) was used as reference. Soil organic carbon level was more than doubled in TS, and that in GG and ZG was elevated by about 50% relative to CR. Soil total nitrogen concentration in GG was not significantly different from CR, but that in TS and ZG was increased by 93% and 55% relative to CR. Similar to nitrogen, soil total phosphorus concentration in GG was not changed relative to CR, but that in TS and ZG were significantly increased. Microbial biomass carbon and nitrogen concentrations were significantly increased in TS and GG by 124% and 82%, respectively, compared to CR, but those in ZG and CR were similar. The abundance of total PLFAs (phospholipid fatty acids) was significantly increased by 55–69% following agricultural abandonment, and there was no significant difference among the three restoration strategies. The patterns of the other microbial groups and the ratio of fungal to bacterial (F:B) PLFAs were largely similar to that of total PLFAs. Soil organic carbon was identified as the primary factor affecting the abundance of soil microbial communities. Our findings suggest that the three restoration strategies, particularly TS are efficient in improving soil fertility.

Spatial patterns of soil organic carbon fractions and their control in temperate grasslands of China

Soil organic carbon (SOC) fractions (light fraction organic carbon, LFOC; heavy fraction organic carbon, HFOC), which have different sensitivities to environmental change, have been widely used as an effective way to assess the soil carbon pool. To explore the spatial patterns of SOC, its fractions (LFOC, HFOC), and their influential factors in temperate grasslands of China, 16 study sites were selected without significant human disturbance along temperature and precipitation gradients in Inner Mongolia, China. These study sites covered three community types: meadow steppe, typical steppe, and desert steppe. Soil samples were collected from five discrete depth intervals (0–10cm, 10–20cm, 20–40cm, 40–60cm, and 60–100cm) for each study site in July 2013, the peak period for plant growth. The variations in SOC, LFOC, HFOC, and their major influential factors were analyzed in the three community types and at five soil depths. The effects of abiotic and biotic factors on SOC and its fractions were evaluated. The coefficient of variation for LFOC was lower than that for HFOC among the different grassland types and higher among the different vertical depths. The LFOC in the 0–10cm soil layer was significantly higher than that in the substratum, whereas HFOC did not differ significantly among the different soil depths. LFOC/SOC in meadow steppe, typical steppe, and desert steppe (7.34%, 8.29%, and 9.41%, respectively) appeared to be lower when compared with previous studies (3%–48%). Both LFOC and HFOC were significantly positively correlated with mean annual precipitation (MAP), soil moisture, aboveground biomass, root biomass, soil microbial biomass carbon (MBC), clay content, soil total nitrogen content (STN), and soil total phosphorus content (STP), and negatively correlated with mean annual temperature (MAT), soil temperature, and soil pH. Among these factors, root biomass, MBC, STN, and STP were the most important influential factors for LFOC, whereas soil moisture, MAP, STN, and STP were the most important for HFOC. STN had a greater influence on LFOC than on HFOC, whereas STP had a greater influence on HFOC than on LFOC. In conclusion, labile C occurred in the surface soil and was closely correlated with biotic factors, whereas steady fraction C did not significantly change with soil depth and was more closely correlated with abiotic factors in temperate grasslands. Our results emphasize the importance of STN and STP in affecting the variation in SOC fractions, and could provide a theoretical basis for accurately predicting SOC stabilization and its response to global climate change.

Soil‐nutrient availability and the nutrient‐use efficiencies of forests along an altitudinal gradient on Yakushima Island, Japan

AbstractThe vegetation on Yakushima Island, Japan, grows on soils derived from Akahoya volcanic ash, released from the Kikai Caldera about 7300 years ago. The eruption was devastating and it is believed that primary succession and soil formation reinitiated across all altitudes at this point. We hypothesize that the concentrations of soil total phosphorus (P) and labile P fractions increase with increasing altitude because the soil formation has progressed less in upslope areas as a result of the cooler temperature and because of the ample P source of the volcanic ash. Conversely, we hypothesize that the concentration of soil inorganic nitrogen (N) decreases with increasing altitude. Available soil P and N would result in increasing P limitation downslope and increasing N limitation upslope, respectively. We studied soil P fractions and soil inorganic N, and P‐ and N‐use efficiencies of the seven forests on Yakushima along an elevation gradient (170–1550 m a.s.l.). Contrary to our hypotheses, soil total P, labile soil P fractions, and inorganic N decreased with increasing altitude. The P‐ and N‐use efficiencies of the forests were negatively correlated with the concentration of soil total active P (total P minus occluded P) and inorganic N, respectively. We suggest that progressive soil acidity and slower decomposition under cooler and wetter environments upslope must have dissolved the P contained in volcanic ash and accelerated P leaching. Forest ecosystems on Yakushima that show a distinct altitudinal zonation are, therefore, characterized by increasing P and N shortage with increasing altitude.

Influences of stand characteristics and environmental factors on forest biomass and root–shoot allocation in southwest China

Tree biomass and it's allocation pattern may respond to the environmental conditions and are quite important for understanding the global carbon cycling, climate change, and forest management. However, how stand characteristics (e.g. tree age, density) and environmental factor (e.g. climate, site conditions, and soil chemistry) influence the biomass and biomass allocation in southwest of China has not been well investigated. We analyzed 318 field measurements of forest biomass in this region, which 62 sites were obtained from our field measurements and the others from the national forest inventory. The results showed that the average above-ground biomass (AGB) and below-ground biomass (BGB) were 134Mg/ha and 28Mg/ha, respectively. The root/shoot biomass ratio (R/S) ranged between 0.06 and 0.81, with an average of 0.22. Forest stand characteristics explained 43% and 21% of the variation in AGB and BGB, respectively, while climate only explained 2–4%, reflecting the strong effect of forest features on biomass. However, only 5% of the R/S ratio was explained by climate, soil chemistry, and stand characteristics, suggesting that these factors had no significant effect on biomass allocation. In addition, the scaling exponents between AGB and BGB did not differ significantly from 1, and did not vary with mean annual temperature, mean annual precipitation, longitude, latitude, altitude, soil pH, soil total nitrogen concentration, and stand age, but did vary with soil total phosphorus concentration, stand density, and forest type. Our findings suggest that stand characteristics have a marked impact on forest biomass, and root biomass scales isometrically with above-ground biomass in southwest China.

Soil Nutrient Assessment and Characterization in a Degraded Central Florida Swamp

Flatford Swamp, a 2800-acre forested wetland in east Manatee County, Florida, serves as the headwaters of the Myakka River. Over the last two decades, Flatford swamp has experienced significant tree mortality. The cause of this mortality, as well as dramatic encroachment of several invasive herbaceous and shrub species, is thought to be linked to hydrologic alterations that resulted in increased inundation during the wet and dry seasons. A biogeochemical characterization of wetland soils was conducted to (1) establish a baseline spatial distribution of soil P and N in Flatford Swamp, (2) determine if soil biogeochemistry could be related to tree mortality, and (3) determine if soil biogeochemical conditions may affect future restoration efforts. Mean total nitrogen and total carbon in sampled soils ranged from 13.8 to 24.9 mg kg−1 and 211 to 468 mg kg−1, respectively, indicating that soils are predominantly organic. Environmental conditions suggest that the nitrate-reduction process occurs readily in Flatford Swamp, and thus N abatement will continue naturally during restoration. Soil total phosphorus content is significantly higher than expected and is likely one of several contributing factors that led to observed changes in vegetation community structure. Levels of total sulfur, total calcium, and conductivity, indicative of agricultural use of groundwater for irrigation, suggest sulfide toxicity as a plausible contributing mechanism in the observed dieback of Nyssa sylvatica var. biflora.

Spatial distribution of soil total phosphorus in Yingwugou watershed of the Dan River, China

P is an essential and commonly limiting element for plants. P losses from agricultural production systems are known to contribute to accelerated eutrophication of natural waters. In this study, soil total phosphorus (STP) concentration and STP mass were estimated from a soil survey of a small watershed of the Dan River, China, after which the spatial heterogeneity of STP distribution and impacts of land-use types, elevation, slope and aspect on STP were assessed. A total of 190 sites were sampled, and 539 soil samples from a soil profile of 40cm were collected by field sampling in a 100m×100m grid. The results indicated that classical kriging could successfully interpolate STP concentration in the watershed. The STP concentration showed a downward trend with increasing soil depth. The STP variability in the three soil layers was moderate, and there were significant differences among soil layers (p<0.01). Statistical analysis by ANOVA indicated that land use had a great impact on STP concentration, and the spatial variation of STP concentrations among the land use types was significant (p<0.05). The STP mass of different land-use types followed the order of forestland>cropland>grassland. On average, the mean STP masses of forestland, cropland and grassland at a depth of 0–40cm were 0.39, 0.35 and 0.28kg/m2, respectively. The topographic factors of altitude and aspect exerted the greatest influence on STP concentration, and the STP concentration increased with decreasing altitude; however, STP concentration and slope showed no significant correlation. The soil bulk density also played a very important role in the assessment of STP mass. In conclusion, the soils in the source area of the middle Dan River would increase STP with conversions from cropland to forest.