间伐和凋落物处理对华北落叶松人工林土壤磷形态的影响

土壤磷在维持生态系统功能稳定性中发挥重要作用,研究间伐和凋落物处理下的土壤磷组分特征及转化机理,对森林生态系统磷素管理和可持续发展具有重要意义。采用Tiessen改良的Hedley分级方法,探究了不同间伐强度(未间伐、轻度间伐、中度间伐、重度间伐)和凋落物处理(对照、加倍、去凋、切根去凋)下土壤磷形态的变化特征及其驱动因子。结果显示:随着间伐强度的增大,土壤活性磷(Resin-Pi、NaHCO_3-Pi和NaHCO_3-Po)、土壤微生物量磷和酸性磷酸酶活性呈先增加后降低的趋势,且在中度间伐最高。凋落物加倍(DL)显著增加了土壤活性磷(Resin-Pi、NaHCO_3-Pi和NaHCO_3-Po)、土壤微生物量磷和酸性磷酸酶活性。稳定态磷(HCl-Pi、浓HCl-Pi和浓HCl-Po)、残留态磷(Residual-P)不受间伐和凋落物处理的影响。冗余分析(RDA)显示,土壤微生物量磷、酸性磷酸酶活性和土壤有机碳是引起华北落叶松人工林表层土壤磷组分变化的重要因子。研究表明,适度的间伐和增加凋落物能够显著提高华北落叶松人工林表层土壤磷素的活化能力。本研究为华北落叶松人工林的可持续经营提供依据。     

模拟氮沉降对中亚热带米槠天然林土壤解磷微生物群落和功能潜力的影响

解磷微生物是森林土壤磷循环的关键驱动因素,对亚热带低磷土壤尤为重要。由于微生物对环境变化较为敏感,氮沉降下土壤微生物如何变化以及如何影响土壤磷有效性尚不清楚。为此,依托福建三明森林生态系统与全球变化国家野外科学观测研究站建立的米槠天然林长期氮沉降观测平台,借助16S rRNA和ITS高通量测序以及PICRUSt功能预测方法,探索氮添加对土壤解磷微生物群落和功能潜力的影响。结果表明:氮添加显著增加了土壤有效氮含量,但显著降低了Resin-P、NaHCO₃-P和TPo,表明氮沉降改变了土壤养分平衡,加剧了磷限制。此外,氮添加降低了根瘤菌和伯克霍尔德菌等解磷细菌的丰度,却增加了青霉菌和曲霉菌等解磷真菌的丰度。PICRUSt功能预测进一步发现,存在15种能够编码磷酸酶的基因,并且与对照相比,施氮后酸性磷酸酶、碱性磷酸酶和植酸酶等酶基因丰度显著增加。综上,本研究发现施氮加剧了亚热带米槠天然林土壤的磷限制,同时增加了解磷真菌的丰度和磷酸酶的基因丰度来促进有机磷矿化,这可能是氮沉降下驱动米槠天然林土壤磷转化的主要微生物机制。     

Responses of soil chemical and biological properties to nitrogen addition in a Dahurian larch plantation in Northeast China

Soil microbial properties play a key role in belowground ecosystem functioning, but are not well understood in forest ecosystems under nitrogen (N) enrichment. In this study, soil samples from 0–10 cm and 10–20 cm layers were collected from a Dahurian larch (Larix gmelinii Rupr.) plantation in Northeast China after six consecutive years of N addition to examine changes in soil pH, nutrient concentrations, and microbial biomass and activities. Nitrogen addition significantly decreased soil pH and total phosphorus, but had little effect on soil total organic carbon (TOC) and total N (TN) concentrations. The NO ₃ ^? -N concentrations in the two soil layers under N addition were significantly higher than that in the control, while NH ₄ ⁺ -N concentrations were not different. After six years of N addition, potential net N mineralization and nitrification rates were dramatically increased. Nitrogen addition decreased microbial biomass C (MBC) and N (MBN), and MBC/TOC and MBN/TN in the 0–10 cm soil layer, but MBC/MBN was increased by 67% in the 0–10 cm soil layer. Soil basal respiration, microbial metabolic quotient (qCO₂), and β-glucosidase, urease, acid phosphomonoesterase and nitrate reductase activities in the two soil layers showed little change after six years of N addition. However, soil protease and dehydrogenase activities in the 0–10 cm layer were 41% and 54% lower in the N addition treatment than in the control, respectively. Collectively, our results suggest that in the mid-term N addition leads to a decline in soil quality in larch plantations, and that different soil enzymes show differentiated responses to N addition.     

Wheat, canola and grain legume access to soil phosphorus fractions differs in soils with contrasting phosphorus dynamics

Despite the high phosphorus (P) mobilizing capacity of many legumes, recent studies have found that, at least in calcareous soils, wheat is also able to access insoluble P fractions through yet unknown mechanism(s). We hypothesized that insoluble P fractions may be more available to non-legume plants in alkaline soils due to increased dissolution of the dominant calcium(Ca)-P pool into depleted labile P pools, whereas non-legumes may have limited access to insoluble P fractions in iron(Fe)- and aluminium(Al)-P dominated acid soils. Four crop species (faba bean, chickpea, wheat and canola) were grown on two acid and one alkaline soil under glasshouse conditions to examine rhizosphere processes and soil P fractions accessed. While all species generally depleted the H₂O-soluble inorganic P (water Pi) pool in all soils, there was no net depletion of the labile NaHCO₃-extractable inorganic P fraction (NaHCO₃ Pi) by any species in any soil. The NaOH-extractable P fraction (NaOH Pi) in the alkaline soil was the only non-labile Pi fraction depleted by all crops (particularly canola), possibly due to increases in rhizosphere pH. Chickpea mobilized the insoluble HCl Pi and residual P fractions; however, rhizosphere pH and carboxylate exudation could not fully explain all of the observed Pi depletion in each soil. All organic P fractions appeared highly recalcitrant, with the exception of some depletion of the NaHCO₃ Po fraction by faba bean in the acid soils. Chickpea and faba bean did not show a higher capacity than wheat or canola to mobilize insoluble P pools across all soil types, and the availability of various P fractions to legume and non-legume crops differed in soils with contrasting P dynamics.     

Effects of nitrogen addition on litter decomposition, soil microbial biomass, and enzyme activities between leguminous and non-leguminous forests

Anthropogenic nitrogen (N) deposition is an expanding problem that affects the functioning and composition of forest ecosystems, particularly the decomposition of forest litters. Legumes play an important role in the nitrogen cycle of forest ecosystems. Two litter types were chosen from Zijin Mountain in China: Robinia pseudoacacia leaves from a leguminous forest (LF) and Liquidambar formosana leaves from a non-leguminous forest (NF). The litter samples were mixed into original forest soils and incubated in microcosms. Then, they were treated by five forms of N addition: NH₄ ⁺, NO₃ ^?, urea, glycine, and a mixture of all four. During a 6-month incubation period, litter mass losses, soil microbial biomass, soil pH, and enzyme activities were investigated. Results showed that mixed N and NO₃ ^?-N addition significantly accelerated the litter decomposition rates of LF leaves, while mixed N, glycine-N, and urea-N addition significantly accelerated the litter decomposition rates of NF leaves. Litter decomposition rates and soil enzyme activities under mixed N addition were higher than those under single form of N additions in the two forest types. Nitrogen addition had no significant effects on soil pH and soil microbial biomass. The results indicate that nitrogen addition may alter microbial allocation to extracellular enzyme production without affecting soil microbial biomass, and then affected litter decomposition process. The results further reveal that mixed N is a more important factor in controlling litter decomposition process than single form of N, and may seriously affect soil N cycle and the release of carbon stored belowground.     

Higher plant diversity enhances soil stability in disturbed alpine ecosystems

Genotypic differences in acquiring immobile P exist among species or cultivars within one species. We investigated the P-efficiency mechanisms of rapeseed (Brassica napus L.) in low P soil by measuring plant growth, P acquisition and rhizosphere properties. Two genotypes with different P efficiencies were grown in a root-compartment experiment under low P (P15: 15 mg P kg^?1) and high P (P100: 100 mg P kg^?1) treatments. The P-efficient genotype produced more biomass, and had a high seed yield and high P acquisition efficiency under low P treatment. Under both P treatments, both genotypes decreased inorganic P (Pi) and organic P (Po) fractions in the rhizosphere soil. However there was no decrease in NaHCO₃-Po at P100. For the P15 treatment, the concentrations of NaHCO₃-Po and NaOH-Po were negatively correlated with soil acid phosphatase activity. The P-efficient genotype 102 differed from the P-inefficient genotype 105 in the following ways. In the rhizosphere the soil pH was lower, acid phosphatase activity was higher, and depletion of P was greater. Further the depletion zones were wider. These results suggested that improving P efficiency based on the character of P efficiency acquisition in P-efficient genotype would be a potential approach for maintaining rapeseed yield potential in soils with low P bioavailability.     

亚热带米槠天然林凋落物和根系输入变化对土壤磷组分的影响

植物残体添加和去除试验(The Detritus Input and Removal Treatments, DIRT)是研究地上凋落物以及植物根系对土壤营养物质循环过程及机制探究的一种试验设计。于2012年6月选择福建省三明森林生态系统与全球变化研究站的米槠常绿阔叶天然林,设置5种处理:对照(CT)、去除凋落物(NL)、去除根系(NR)、去除凋落物与根系(NI)、添加双倍凋落物(DL),在2018年12月对各处理不同土层(0—10cm、10—20cm)土壤磷组分及其影响因子进行研究,结果表明:(1)在0—10cm土层中DL处理总磷含量显著大于NL处理,NI处理无机磷含量最低,在10—20cm中DL处理有机磷含量显著大于其他处理;(2)DL处理活性磷(Resin-P、NaHCO₃-Pi、NaHCO₃-Po)含量在0—10cm土层中显著大于其他处理。在10—20cm土层中NR处理活性磷以及中等活性磷显著大于NL处理。残留态磷(Residual-P)含量最高,但在各处理与土层之间并没有明显差异;(3)酸性磷酸酶在0—10 cm土层不同处理间的变化...     

Elevated CO2 temporally enhances phosphorus immobilization in the rhizosphere of wheat and chickpea

Aims

The efficient management of phosphorus (P) in cropping systems remains a challenge due to climate change. We tested how plant species access P pools in soils of varying P status (Olsen-P 3.2–17.6 mg?kg^?1), under elevated atmosphere CO₂ (eCO₂).

Methods

Chickpea (Cicer arietinum L.) and wheat (Triticum aestivum L.) plants were grown in rhizo-boxes containing Vertosol or Calcarosol soil, with two contrasting P fertilizer histories for each soil, and exposed to ambient (380 ppm) or eCO₂ (700 ppm) for 6 weeks.

Results

The NaHCO₃-extractable inorganic P (Pi) in the rhizosphere was depleted by both wheat and chickpea in all soils, but was not significantly affected by CO₂ treatment. However, NaHCO₃-extractable organic P (Po) accumulated, especially under eCO₂ in soils with high P status. The NaOH-extractable Po under eCO₂ accumulated only in the Vertosol with high P status. Crop species did not exhibit different eCO₂-triggered capabilities to access any P pool in either soil, though wheat depleted NaHCO₃-Pi and NaOH-Pi in the rhizosphere more than chickpea. Elevated CO₂ increased microbial biomass C in the rhizosphere by an average of 21 %. Moreover, the size in Po fractions correlated with microbial C but not with rhizosphere pH or phosphatase activity.

Conclusion

Elevated CO₂ increased microbial biomass in the rhizosphere which in turn temporally immobilized P. This P immobilization was greater in soils with high than low P availability.     

不同林分土壤磷形态与磷酸酶特征

以湖南省平江县国有芦头林场的次生林以及经人工翻垦种植的油茶(Camellia oleifera)、黄桃(Amygdalus persica)、杨梅(Myrica rubra)和杉木(Cunninghamia lanceolata)四种人工林为研究对象,比较了不同林分土壤理化性质、磷酸酶活性与磷形态特征,分析了三者之间的相关性,探讨了次生林转变为人工林后,土壤磷形态和磷酸酶的变化特征以及驱动土壤磷素形态变化的关键因子。结果表明：(1)次生林土壤有机碳(SOC),全氮(TN)、铵态氮(NH⁺₄-N)含量与磷酸酶活性显著高于其他四种林分。(2)五种林分中土壤残余磷(Residual-P)含量最高,是林地土壤主要的磷素存在形态。林分转变后,黄桃林与杉木林树脂提取态无机磷(Resin-Pi)显著增加,黄桃林与油茶林NaHCO₃提取态磷(NaHCO₃-Pi、NaHCO₃-Po)含量显著增加,而四种人工林的NaOH提取态有机磷(NaOH-Po)含量均显著降低。可利用磷、中等可利用磷与稳定态磷...     

Soil Biochemical Responses to Nitrogen Addition in a Bamboo Forest

Many vital ecosystem processes take place in the soils and are greatly affected by the increasing active nitrogen (N) deposition observed globally. Nitrogen deposition generally affects ecosystem processes through the changes in soil biochemical properties such as soil nutrient availability, microbial properties and enzyme activities. In order to evaluate the soil biochemical responses to elevated atmospheric N deposition in bamboo forest ecosystems, a two-year field N addition experiment in a hybrid bamboo (Bambusa pervariabilis × Dendrocalamopsis daii) plantation was conducted. Four levels of N treatment were applied: (1) control (CK, without N added), (2) low-nitrogen (LN, 50 kg N ha⁻¹ year⁻¹), (3) medium-nitrogen (MN, 150 kg N ha⁻¹ year⁻¹), and (4) high-nitrogen (HN, 300 kg N ha⁻¹ year⁻¹). Results indicated that N addition significantly increased the concentrations of NH₄ ⁺, NO₃ ⁻, microbial biomass carbon, microbial biomass N, the rates of nitrification and denitrification; significantly decreased soil pH and the concentration of available phosphorus, and had no effect on the total organic carbon and total N concentration in the 0–20 cm soil depth. Nitrogen addition significantly stimulated activities of hydrolytic enzyme that acquiring N (urease) and phosphorus (acid phosphatase) and depressed the oxidative enzymes (phenol oxidase, peroxidase and catalase) activities. Results suggest that (1) this bamboo forest ecosystem is moving towards being limited by P or co-limited by P under elevated N deposition, (2) the expected progressive increases in N deposition may have a potential important effect on forest litter decomposition due to the interaction of inorganic N and oxidative enzyme activities, in such bamboo forests under high levels of ambient N deposition.     

Effects of Nitrogen Addition on Litter Decomposition and CO2 Release: Considering Changes in Litter Quantity

This study aims to evaluate the impacts of changes in litter quantity under simulated N deposition on litter decomposition, CO₂ release, and soil C loss potential in a larch plantation in Northeast China. We conducted a laboratory incubation experiment using soil and litter collected from control and N addition (100 kg ha⁻¹ year⁻¹ for 10 years) plots. Different quantities of litter (0, 1, 2 and 4 g) were placed on 150 g soils collected from the same plots and incubated in microcosms for 270 days. We found that increased litter input strongly stimulated litter decomposition rate and CO₂ release in both control and N fertilization microcosms, though reduced soil microbial biomass C (MBC) and dissolved inorganic N (DIN) concentration. Carbon input (C loss from litter decomposition) and carbon output (the cumulative C loss due to respiration) elevated with increasing litter input in both control and N fertilization microcosms. However, soil C loss potentials (C output–C input) reduced by 62% in control microcosms and 111% in N fertilization microcosms when litter addition increased from 1 g to 4 g, respectively. Our results indicated that increased litter input had a potential to suppress soil organic C loss especially for N addition plots.     

Soil nutrients and microbial biomass in three contrasting Mediterranean forests

Aims

The extent to which the spatial and temporal patterns of soil microbial and available nutrient pools hold across different Mediterranean forest types is unclear impeding the generalization needed to consolidate our understanding on Mediterranean ecosystems functioning.

Methods

We explored the response of soil microbial, total, organic and inorganic extractable nutrient pools (C, N and P) to common sources of variability, namely habitat (tree cover), soil depth and season (summer drought), in three contrasting Mediterranean forest types: a Quercus ilex open woodland, a mixed Q. suber and Q. canariensis woodland and a Pinus sylvestris forest.

Results

Soil microbial and available nutrient pools were larger beneath tree cover than in open areas in both oak woodlands whereas the opposite trend was found in the pine forest. The greatest differences in soil properties between habitat types were found in the open woodland. Season (drought effect) was the main driver of variability in the pine forest and was related to a loss of microbial nutrients (up to 75 % loss of N_mic and P_mic) and an increase in microbial ratios (C_mic/N_mic, C_mic/P_mic) from Spring to Summer in all sites. Nutrient pools consistently decreased with soil depth, with microbial C, N and P in the top soil being up to 208 %, 215 % and 274 % larger than in the deeper soil respectively.

Conclusions

Similar patterns of variation emerged in relation to season and soil depth across the three forest types whereas the direction and magnitude of the habitat (tree cover) effect was site-dependent, possibly related to the differences in tree species composition and forest structure, and thus in the quality and distribution of the litter input.     

Phosphorus acquisition characteristics of cotton (Gossypium hirsutum L.), wheat (Triticum aestivum L.) and white lupin (Lupinus albus L.) under P deficient conditions

A rhizobox experiment was conducted to examine the P acquisition characteristics of cotton (Gossypium hirsutum L.), wheat (Triticum aestivum L.) and white lupin (Lupinus albus L.) under P-deficient conditions. We aimed to identify whether cotton is physiologically efficient at acquiring P through release of protons, phosphatases or carboxylates. Plants were pre-grown in the upper compartment of rhizoboxes filled with a sand and soil mixture to create a dense root mat against a 53 μm polyester mesh. For each species, two P treatments (0 and 20 mg P kg^?1) were applied to the upper compartment in order to create P-deficient and P-sufficient plants. At harvest, the upper compartment with intact plants was used for collection of root exudates while the lower soil compartment was sliced into thin layers (1 mm) parallel to the rhizoplane. Noticeable carboxylates release was only detected for white lupin. All P-deficient plants showed a capacity to acidify their rhizosphere soil to a distance of 3 mm. The activity of acid phosphatase was significantly enhanced in the soil-root interfaces of P-stressed cotton and wheat. Under P-deficient conditions, the P depletion zone of cotton from the lower soil compartment was narrowest (<2 mm) among the species. Phosphorus fractionation of the rhizosphere soil showed that P utilized by cotton mainly come from NaHCO₃–P_i and NaOH–P_o pools while wheat and white lupin markedly depleted NaHCO₃–P_i and HCl–P pools, and the depletion zone extended to 3 mm. Wheat also depleted NaOH–P_o to a significant level irrespective of P supply. The study suggests that acquisition of soil P is enhanced through P mobilization by root exudates for white lupin, and possibly proton release and extensive roots for wheat under P deficiency. In contrast, the P acquisition of cotton was associated with increased activity of phosphatases in rhizosphere soil.     

Nitrogen and phosphorus requirement of the microbiota in soils of the Bornhöved Lake district

Estimating in situ N and P status of the soil microbiota is complicated because microbiological features reflect potentials rather than field conditions. Complementary microbiological assays were, therefore, combined to evaluate the N and P requirement of the microbiota in seven agricultural, grassland and forest topsoils of the Bornhöved Lake district as follows: (i) the sensitivity of the substrate-induced respiration (SIR) to supplemental addition of N and P was monitored during microbial growth and (ii) soil protease and phosphatase activities were analysed and related to soil mass and microbial biomass content. Nitrogen addition increased the maximal SIR rate in all except one soil indicating that the growth of organisms is restricted by this element when easily degradable C source is present. Supplemental N (and in some cases also P) retarded the respiratory response within the first 24 h which suggests microbial sensitivity and/or greater anabolic efficiency. With additional N the maximal SIR rate was most strongly enhanced in topsoils of the beech forest and the dystric alder forest. Thus, the microbial growth in these soils that were below litter horizons seems to be mostly restricted by N. Supplemental P positively affected respiratory response of soils under monoculture, wet grassland and dystric alder forest. In the dystric alder forest soil, high rates of alkaline and unbuffered phosphatase activity were observed when activity was related to either soil mass or microbial biomass content. The data of proteolytic and phospholytic enzymes are discussed with reference to nutrient deficiency and microbial strategy for N and P adsorption.     

Characterization of Phosphorus in Animal Manures Collected from Three (Dairy,Swine, and Broiler) Farms in China

In order to identify the phosphorus species and concentration in animal manure, we comparatively characterized phosphorus in dairy manure, swine manure, and broiler litter, using a sequential procedure, a simplified two-step procedure (NaHCO₃/NaOH+EDTA), and a solution Phosphorus-31 Nuclear Magnetic Resonance (³¹P-NMR) spectroscopy procedure. In the sequential procedure, deionized water extracted 39, 22, and 32%; NaHCO₃ extracted 48, 26, and 37%; NaOH extracted 8, 9, and 13.8%; and HCl extracted 3, 42.8, and 17% of the total phosphorus in dairy manure, swine manure and broiler litter, respectively. Total phosphorus extracted by the NaHCO₃/NaOH+EDTA procedure was 7.5, 32.4, and 15.8 g P kg⁻¹ for dairy manure, swine manure, and broiler litter, respectively. The solution ³¹P-NMR procedure detected that 9, 34, and 29% of total phosphorus was phytic acid in dairy manure, swine manure, and broiler litter, respectively. These results show that phosphorus forms, availability, and quantities differ between animal manures, which provides valuable information for P characterization of animal manures in China.     

Carbon and nitrogen status of litterfall, litter decomposition and soil in even-aged larch, red pine and rigitaeda pine plantations

The carbon (C) and nitrogen (N) status in forest ecosystems can change upon establishment of plantations because different tree species have different nutrient cycling mechanisms. This study was carried out to evaluate C and N status of litterfall, litter decomposition and soil in three adjacent plantations consisting of one deciduous (larch: Larix leptolepis) and two evergreen (red pine: Pinus densiflora; rigitaeda pine: P. rigida × P. taeda) species planted in the same year (1963). Both the pine plantations showed comparatively higher C input from needle litter but significantly lower N concentration and input than the larch plantation (P < 0.05). During the decomposition process, the deciduous larch needle litter showed low C concentration and C remaining in soil, but high N concentration and N remaining in soil compared to the two evergreen pine needle litters. However, the soil C and N concentration and their content at a soil depth of 0–10 cm were not affected significantly (P > 0.05) by the plantation type. These results demonstrate the existence of considerable variation in C and N status resulting from needle litter input and litter decomposition in these three plantations grown at sites with similar environmental conditions.     

Effects of long-term nitrogen deposition on phosphorus leaching dynamics in a mature tropical forest

Elevated anthropogenic nitrogen (N) deposition is suggested to affect ecosystem phosphorus (P) cycling through altered biotic P demand and soil acidification. To date, however, there has been little information on how long-term N deposition regulates P fluxes in tropical forests, where P is often depleted. To address this question, we conducted a long-term N addition experiment in a mature tropical forest in southern China, using the following N treatments: 0, 50, 100, and 150 kg N ha^?1 year^?1. We hypothesized that (i) tropical forest ecosystems have conservative P cycling with low P output, and (ii) long-term N addition decreases total dissolved phosphorus (TDP) leaching losses due to reduced litter decomposition rates and stimulated P sorption deriving from accelerated soil acidification. As hypothesized, we demonstrated a closed P cycling with low leaching outputs in our forest. Under experimental N addition, TDP flux in throughfall was significantly reduced, suggesting that N addition may result in a less internal P recycling. Contrary to our hypothesis, N addition did not decrease TDP leaching, despite reduced litter decomposition and accelerated soil acidification. We find that N addition might have negative impacts on biological P uptake without affecting TDP leaching, and that the amount of TDP leaching from soil could be lower than a minimum concentration for TDP retention. Overall, we conclude that long-term N deposition does not necessarily decrease P effluxes from tropical forest ecosystems with conservative P cycling.     

Long‐term nitrogen addition modifies microbial composition and functions for slow carbon cycling and increased sequestration in tropical forest soil

Nitrogen (N) deposition is a component of global change that has considerable impact on belowground carbon (C) dynamics. Plant growth stimulation and alterations of fungal community composition and functions are the main mechanisms driving soil C gains following N deposition in N‐limited temperate forests. In N‐rich tropical forests, however, N deposition generally has minor effects on plant growth; consequently, C storage in soil may strongly depend on the microbial processes that drive litter and soil organic matter decomposition. Here, we investigated how microbial functions in old‐growth tropical forest soil responded to 13 years of N addition at four rates: 0 (Control), 50 (Low‐N), 100 (Medium‐N), and 150 (High‐N) kg N ha^?1 year^?1. Soil organic carbon (SOC) content increased under High‐N, corresponding to a 33% decrease in CO₂ efflux, and reductions in relative abundances of bacteria as well as genes responsible for cellulose and chitin degradation. A 113% increase in N₂O emission was positively correlated with soil acidification and an increase in the relative abundances of denitrification genes (narG and norB). Soil acidification induced by N addition decreased available P concentrations, and was associated with reductions in the relative abundance of phytase. The decreased relative abundance of bacteria and key functional gene groups for C degradation were related to slower SOC decomposition, indicating the key mechanisms driving SOC accumulation in the tropical forest soil subjected to High‐N addition. However, changes in microbial functional groups associated with N and P cycling led to coincidentally large increases in N₂O emissions, and exacerbated soil P deficiency. These two factors partially offset the perceived beneficial effects of N addition on SOC storage in tropical forest soils. These findings suggest a potential to incorporate microbial community and functions into Earth system models considering their effects on greenhouse gas emission, biogeochemical processes, and biodiversity of tropical ecosystems.     

Fate of ammonium 15N in a Norway spruce forest under long-term reduction in atmospheric N deposition

In the last decades, in particular forest ecosystems became increasingly N saturated due to elevated atmospheric N deposition, resulting from anthropogenic N emission. This led to serious consequences for the environment such as N leaching to the groundwater. Recent efforts to reduce N emissions raise the question if, and over what timescale, ecosystems recover to previous conditions. In order to study the effects on N distribution and N transformation processes under the lowered N deposition treatment, we investigated the fate of deposited NH₄ ⁺-¹⁵N in soil of a N-saturated Norway spruce forest (current N deposition: 34 kg ha^?1 year^?1; critical N load: 14 kg ha^?1 year^?1), where N deposition has been reduced to 11.5 kg ha^?1 year^?1 since 14.5 years. We traced the deposited ¹⁵N in needle litter, bulk soil, and amino acids, microbial biomass and inorganic N in soil. Under reduced N deposition, 123 ± 23% of the deposited N was retained in bulk soil, while this was only 72 ± 15% under ambient deposition. We presume that with reduced deposition the amount of deposited N was small enough to become completely immobilized in plant and soil and no leaching losses occurred. Trees receiving reduced N deposition showed a decline in N content as well as in ¹⁵N incorporation into needle litter, indicating reduced N plant uptake. In contrast, the distribution of ¹⁵N within the soil over active microbial biomass, microbial residues and inorganic N was not affected by the reduced N deposition. We conclude that the reduction in N deposition impacted only plant uptake and drainage losses, while microbial N transformation processes were not influenced. We assume changes in the biological N turnover to start with the onset of the decomposition of the new, N-depleted litter.     

亚热带不同海拔黄山松林土壤磷组分及微生物特征

磷是亚热带地区植物生长必需的养分元素之一,海拔梯度可能会改变土壤-植物-微生物系统并影响土壤磷形态及有效性。了解不同海拔土壤磷组分状况,对维持山地森林生态系统可持续发展具有重要的意义。以戴云山地区不同海拔梯度(1300m和1600 m)黄山松林为研究对象,分析了土壤磷组分、微生物群落特征和磷酸酶活性。结果显示:海拔显著影响黄山松林土壤磷组分,与海拔1300 m相比,海拔1600 m处土壤总磷含量减少了48.4%—49.8%,且各磷组分(易分解态磷、中等易分解态磷和难分解态磷)含量也显著降低,淋溶层(A层)土壤的降低程度分别为45.7%、58.6%和38.7%,淀积层(B层)为82.6%、59.9%和31.1%。海拔对土壤微生物群落特征和酶活性亦有显著影响,各类微生物群落和总微生物磷脂脂肪酸含量(PLFAs),以及磷酸双酯酶(PD)活性均表现为海拔1600 m 1300 m,但酸性磷酸单酯酶(ACP)活性呈相反的趋势。冗余分析(RDA)表明,土壤磷组分主要受有机碳(SOC)调控,且SOC与有机磷组分(Na HCO3-Po和Na OH-Po)呈显著正相关;磷酸酶和外生菌根真菌(EMF)也是影响土壤磷组分变化的重要因素。研究表明,土壤有机质含量和微生物群落结构及功能的变化可能是不同海拔黄山松林土壤磷有效性的关键调控因素。