Fu-Sheng Chen

Nitrogen and phosphorus additions alter nutrient dynamics but not resorption efficiencies of Chinese fir leaves and twigs differing in age

It is unclear how or even if phosphorus (P) input alters the influence of nitrogen (N) deposition in a forest. In theory, nutrients in leaves and twigs differing in age may show different responses to elevated nutrient input. To test this possibility, we selected Chinese fir (Cunninghamia lanceolata) for a series of N and P addition experiments using treatments of +N1 - P (50 kg N ha(-1) year(-1)), +N2 - P (100 kg N ha(-1) year(-1)), -N + P (50 kg P ha(-1) year(-1)), +N1 + P, +N2 + P and -N - P (without N and P addition). Soil samples were analyzed for mineral N and available P concentrations. Leaves and twigs in summer and their litters in winter were classified as and sorted into young and old components to measure N and P concentrations. Soil mineral N and available P increased with N and P additions, respectively. Nitrogen addition increased leaf and twig N concentrations in the second year, but not in the first year; P addition increased leaf and twig P concentrations in both years and enhanced young but not old leaf and twig N accumulations. Nitrogen and P resorption proficiencies in litters increased in response to N and P additions, but N and P resorption efficiencies were not significantly altered. Nitrogen resorption efficiency was generally higher in leaves than in twigs and in young vs old leaves and twigs. Phosphorus resorption efficiency showed a minimal variation from 26.6 to 47.0%. Therefore, P input intensified leaf and twig N enrichment with N addition, leaf and twig nutrients were both gradually resorbed with aging, and organ and age effects depended on the extent of nutrient limitation.

Degradation of litter quality and decline of soil nitrogen mineralization after moso bamboo (Phyllostachys pubscens) expansion to neighboring broadleaved forest in subtropical China

AimsMoso bamboo (Phyllostachys pubescens) is a typical native invasive plant imposing serious threats on ecosystem processes and functions. A primary concern is alterations of litter and soil N mineralization in evergreen broadleaved forests coupled with bamboo population expansion.MethodsWe conducted a field study to determine the litter production, quality, N resorption efficiency, and soil N mineralization rates in bamboo-dominated forest (BDF) and adjacent uninvaded evergreen broadleaved forest (EBF) in subtropical China.ResultsThe mean annual litter production for BDF was 5.82xa0Mgxa0ha−1, 36.0xa0% lower than that for EBF (9.09xa0Mgxa0ha−1). Litter N concentration was also lower, but C: N was higher after bamboo expansion, coupled with higher N resorption efficiency for Moso bamboo and lower litterfall, resulting in potential N return decreasing as much as 60.41xa0kgxa0Nxa0ha−1xa0yr−1 to the soil. The soil N net nitrification and mineralization rates exhibited lower values in BDF than in EBF. In addition, annual soil N mineralization rate was positively correlated with litter production but negatively with C: N ratio of litter.ConclusionsExpansion of bamboo into neighboring EBF decreased litter production and quality, reduced soil N mineralization rate, and ultimately retarded N cycling. These effects should be carefully considered in the design of restoration strategies for ecosystems impacted by bamboo species.

Topsoil and Deep Soil Organic Carbon Concentration and Stability Vary with Aggregate Size and Vegetation Type in Subtropical China

The impact of reforestation on soil organic carbon (OC), especially in deep layer, is poorly understood and deep soil OC stabilization in relation with aggregation and vegetation type in afforested area is unknown. Here, we collected topsoil (0–15 cm) and deep soil (30–45 cm) from six paired coniferous forests (CF) and broad-leaved forests (BF) reforested in the early 1990s in subtropical China. Soil aggregates were separated by size by dry sieving and OC stability was measured by closed-jar alkali-absorption in 71 incubation days. Soil OC concentration and mean weight diameter were higher in BF than CF. The cumulative carbon mineralization (Cmin, mg CO2-C kg-1 soil) varied with aggregate size in BF and CF topsoils, and in deep soil, it was higher in larger aggregates than in smaller aggregates in BF, but not CF. The percentage of soil OC mineralized (SOCmin, % SOC) was in general higher in larger aggregates than in smaller aggregates. Meanwhile, SOCmin was greater in CF than in BF at topsoil and deep soil aggregates. In comparison to topsoil, deep soil aggregates generally exhibited a lower Cmin, and higher SOCmin. Total nitrogen (N) and the ratio of carbon to phosphorus (C/P) were generally higher in BF than in CF in topsoil and deep soil aggregates, while the same trend of N/P was only found in deep soil aggregates. Moreover, the SOCmin negatively correlated with OC, total N, C/P and N/P. This work suggests that reforested vegetation type might play an important role in soil OC storage through internal nutrient cycling. Soil depth and aggregate size influenced OC stability, and deep soil OC stability could be altered by vegetation reforested about 20 years.

Aluminum and nutrient interplay across an age-chronosequence of tea plantations within a hilly red soil farm of subtropical China

Abstract Aluminum (Al) and nutrients are key factors to influence tea (Camellia sinensis L.) productivity and quality, while how they interplay in tea plantations under the pressure of global change and increasing fertilization is little studied. In this study, we selected the tea plantations along an age-chronosequence to study Al fractions using a sequential extraction procedure, and nutrient concentrations in topsoil and subsoil and various plant organs. Our results indicated that Al levels and nutrient concentrations in soils and plants generally increased with planting year (P < 0.05), and soil Al bioavailability was positively correlated with Al concentrations in most plant organs. Significant negative relations among pH and most extractable Al fractions in both soil layers suggested that decreased pH would directly alter soil-plant Al cycling due to exogenous nitrogen (N) fertilizer and atmospheric acid deposition. Topsoil total phosphorus (P) was positively correlated with most Al fractions, and root P was positively correlated with root Al concentration, both of which indicate that P and Al were synchronously absorbed by roots in acid tea soils. In addition, topsoil organic carbon was positively correlated with both active and inert Al fractions, indicating that above-ground organic litters would be the main source of elevated Al levels in older tea plantations. Clearly, Al enrichment in tea leaves with increasing planting year needs to be considered under management practices with heavy N and P fertilizers and increasing atmospheric acid deposition in subtropical China.

Exogenous nutrients and carbon resource change the responses of soil organic matter decomposition and nitrogen immobilization to nitrogen deposition.

It is unclear whether exogenous nutrients and carbon (C) additions alter substrate immobilization to deposited nitrogen (N) during decomposition. In this study, we used laboratory microcosm experiments and 15N isotope tracer techniques with five different treatments including N addition, N+non-N nutrients addition, N+C addition, N+non-N nutrients+C addition and control, to investigate the coupling effects of non-N nutrients, C addition and N deposition on forest floor decomposition in subtropical China. The results indicated that N deposition inhibited soil organic matter and litter decomposition by 66% and 38%, respectively. Soil immobilized 15N following N addition was lowest among treatments. Litter 15N immobilized following N addition was significantly higher and lower than that of combined treatments during the early and late decomposition stage, respectively. Both soil and litter extractable mineral N were lower in combined treatments than in N addition treatment. Since soil N immobilization and litter N release were respectively enhanced and inhibited with elevated non-N nutrient and C resources, it can be speculated that the N leaching due to N deposition decreases with increasing nutrient and C resources. This study should advance our understanding of how forests responds the elevated N deposition.

Long-term fertilization increases soil nutrient accumulations but decreases biological activity in navel orange orchards of subtropical China

PurposeWith its high economic benefits, navel orange (Citrus sinensis) has been widely planted and fertilizer has been increasingly applied in the subtropical China in the last 30xa0years. Comprehensive assessments are needed to explore the long-term fertilization impacts on soil chemical and biological properties in the navel orange orchards.Materials and methodsThrough a large number of soil and leaf samples from the young, middle-aged, and mature navel orange orchards, this study examined the impacts of stand age (corresponding to the fertilization year using compound chemical fertilizer) on seasonal variations in major soil properties and leaf nutrients in the subtropical China.Results and discussionSoil total nitrogen (N) and mineral N were significantly higher in the middle-aged and mature orchards than in the young orchard. Total phosphorus (P), available P, labile P, slow P, occluded P, weathered mineral P, total exactable P, and residual P generally increased with fertilization years (Pu2009<u20090.05), and the increasing percentages for soil P fractions were much higher than those for N variables. The total N and P use efficiencies (plant uptake/soil input) were 20–34 and 10–15xa0%, respectively. Soil microbial biomass, invertase, urease, and acid phosphatase activities showed significant seasonal variations and decreased with fertilization years. Leaf N concentration significantly decreased with fertilization years, but no difference was found for P.ConclusionsSoil self-fertilization was impeded, and less fertilizer amount should be applied especially in the older navel orange orchards since N and P accumulations do not increase leaf nutrients but worsen soil biological quality.

Accumulation of residual soil microbial carbon in Chinese fir plantation soils after nitrogen and phosphorus additions

Nitrogen (N) and phosphorus (P) additions can affect soil microbial carbon (C) accumulation. However, the mechanisms that drive the changes in residual microbial C that occur after N and P additions have not been well-defined for Chinese fir plantations in subtropical China. We set up six different treatments, viz. a control (CK), two N treatments (N1: 50xa0kgxa0ha−1xa0a−1; N2: 100xa0kgxa0ha−1xa0a−1), one P treatment (P: 50xa0kgxa0ha−1xa0a−1), and two combined N and P treatments (N1P: 50xa0kgxa0ha−1xa0a−1 of N +xa050xa0kgxa0ha−1xa0a−1 of P; N2P: 100xa0kgxa0ha−1xa0a−1 of N +xa050xa0kgxa0ha−1xa0a−1 of P). We then investigated the influences of N and P additions on residual microbial C. The results showed that soil pH and microbial biomass decreased after N additions, while microbial biomass increased after P additions. Soil organic carbon (SOC) and residual microbial C contents increased in the N and P treatments but not in the control. Residual microbial C accumulation varied according to treatment and declined in the order: N2Pxa0>xa0N1Pxa0>xa0N2xa0>xa0N1xa0>xa0Pxa0>xa0CK. Residual microbial C contents were positively correlated with available N, P, and SOC contents, but were negatively correlated with soil pH. The ratio of residual fungal C to residual bacterial C increased under P additions, but declined under combined Nxa0+xa0P additions. The ratio of residual microbial C to SOC increased from 11 to 14% under the N1P and N2P treatments, respectively. Our results suggest that the concentrations of residual microbial C and the stability of SOC would increase under combined applications of N and P fertilizers in subtropical Chinese fir plantation soils.

Increasing acidity of rain in subtropical tea plantation alters aluminum and nutrient distributions at the root-soil interface and in plant tissues

Background and aimsAcid rain alters aluminum (Al) and nutrient cycling in tea (Camellia sinensis) plantations. However, the underlying mechanisms of the interaction among Al, nitrogen (N) and phosphorus (P) dynamics in response to increasing acidity of rain remain unclear.MethodsA typical tea plantation was selected for an experimental treatment by pHxa04.5, 3.5, and 2.5 acid rains and control in southern China. After 3xa0years, rhizosphere and bulk soils were collected to analyze extractable Al fractions and available nutrients. Roots, stems, young and old twigs, tea and mature leaves were sampled to measure total Al, total N and P concentrations.ResultsExtractable Al fractions in rhizosphere soils generally increased with increasing rain acidity until pHxa03.5 and dropped treated by pHxa02.5 acid rain. In contrast, NO3−-N, mineral N and available P in rhizosphere soils monotonically decreased with increasing acidity. Average total Al and total P in plant tissues, respectively increased and decreased with increasing acidity. Soluble sugar in tea leaves was directly and inversely related to Al/N and N/P, respectively. Free amino acids were inversely related to Al/P.ConclusionProlonged elevation of rain acidity altered Al and nutrient stoichiometry in rhizosphere soils and plant tissues, and severe acid rain decreased tea quality.

Soil phosphorus functional fractions and tree tissue nutrient concentrations influenced by stand density in subtropical Chinese fir plantation forests

Stand density regulation is an important measure of plantation forest management, and phosphorus (P) is often the limiting factor of tree productivity, especially in the subtropics and tropics. However, the stand density influence on ecosystem P cycling is unclear in Chinese fir (Cunninghamia lanceolata) plantations of subtropical China. We collected rhizosphere and bulk soils, leaves and twigs with different ages and roots with different orders to measure P and nitrogen (N) variables in Chinese fir plantations with low density (LDCF) and high density (HDCF) at Fujian and Hunan provinces of subtropical China. Rhizosphere soil labile P, slow P, occluded P and extractable P were higher in LDCF than HDCF at two sites. Meanwhile, P and N concentrations of 1-year-old leaves and twigs were higher in LDCF than HDCF and leaf N/P ratio generally increased with increasing leaf age at two sites. Rhizosphere vs. bulk soil labile P and occluded P were greater in LDCF than HDCF at Fujian. Nitrogen resorption efficiencies (NRE) of leaves and twigs were higher in LDCF than HDCF at Fujian, while their P resorption efficiencies (PRE) were not different between two densities at two sites. The average NRE of leaves (41.7%) and twigs (65.6%) were lower than the corresponding PRE (67.8% and 78.0%, respectively). Our results suggest that reducing stem density in Chinese fir plantations might be helpful to increase soil active P supplies and meet tree nutrient requirements.

Isolation and characterization of two phosphate-solubilizing fungi from rhizosphere soil of moso bamboo and their functional capacities when exposed to different phosphorus sources and pH environments

Phosphate-solubilizing fungi (PSF) generally enhance available phosphorus (P) released from soil, which contributes to plants’ P requirement, especially in P-limiting regions. In this study, two PSF, TalA-JX04 and AspN-JX16, were isolated from the rhizosphere soil of moso bamboo (Phyllostachys edulis) widely distributed in P-deficient areas in China and identified as Talaromyces aurantiacus and Aspergillus neoniger, respectively. The two PSF were cultured in potato dextrose liquid medium with six types of initial pH values ranging from 6.5 to 1.5 to assess acid resistance. Both PSF were incubated in Pikovskaya’s liquid media with different pH values containing five recalcitrant P sources, including Ca3(PO4)2, FePO4, CaHPO4, AlPO4, and C6H6Ca6O24P6, to estimate their P-solubilizing capacity. No significant differences were found in the biomass of both fungi grown in media with different initial pH, indicating that these fungi could grow well under acid stress. The P-solubilizing capacity of TalA-JX04 was highest in medium containing CaHPO4, followed by Ca3(PO4)2, FePO4, C6H6Ca6O24P6, and AlPO4 in six types of initial pH treatments, while the recalcitrant P-solubilizing capacity of AspN-JX16 varied with initial pH. Meanwhile, the P-solubilizing capacity of AspN-JX16 was much higher than TalA-JX04. The pH of fermentation broth was negatively correlated with P-solubilizing capacity (p<0.01), suggesting that the fungi promote the dissolution of P sources by secreting organic acids. Our results showed that TalA-JX04 and AspN-JX16 could survive in acidic environments and both fungi had a considerable ability to release soluble P by decomposing recalcitrant P-bearing compounds. The two fungi had potential for application as environment-friendly biofertilizers in subtropical bamboo ecosystem.