Cytochemical changes in the developmental process of Nostoc sphaeroides (cyanobacterium)

There are several apparent developmental stages in the life cycle of Nostoc sphaeroides Kützing, an edible cyanobacterium found mainly in paddy fields in central China. The cytochemical changes in developmental stages such as hormogonia, aseriate stage, filamentous stage and colony in N. sphaeroides were examined using fluorescent staining and colorimetric methods. The staining of acidic and sulfated polysaccharides increased with development when hormogonia were used as the starting point. Acidic polysaccharides (AP) were most abundant at the aseriate stage and then decreased, while the sulfated polysaccharides (SP) were highest at the colony stage. Quantitatively, along the developmental process from hormogonia to colony, total carbohydrates first increased, then became stable, and then reached their highest level at the colony stage, while reducing sugars were highest at the hormogonia stage and then decreased sharply once development began. SP were not detectable in the hot water soluble polysaccharides (HWSP), and hormogonia had the lowest content of AP, while old colonies had the highest. The AP content of the aseriate stage, filamentous stage and young colony stage were very similar. The evolutionary relationships reflected in the developmental stages of N. sphaeroides are discussed.     

不同耕作模式下稻田水中氮磷动态特征及减排潜力

通过微区模拟稻田试验, 研究了夏季施肥免耕、浅耕和深耕3种耕作模式下不同滞水时间稻田排水中氮磷的动态特征及总氮、总磷流失潜能。结果表明:(1)3个耕作处理5 d后的稻田滞排水中TN、NH⁺₄-N、TP和DP 均处于较低的浓度水平, 免耕的田面水中NO^-₃-N浓度较低。(2)不同耕作模式滞水5 d后TN的绝对流失量均处于较低水平。深耕处理的稻田水中TN的流失潜能相对较小。不同耕作模式处理后氮素的相对流失形态与潜能以TN为主。(3)浅耕处理田面水中TP绝对流失量和相对流失潜能最少。不同耕作模式滞水5 d后排水可显著减少田面水中TP流失。不同耕作模式处理田面水中磷素流失形态随时间呈TP与DP交替变化。因此, 从减少田面水中氮磷的绝对流失量出发, 夏季浅耕不失为最佳清洁耕作模式;同时滞水5 d后排水能有效减少田面水中氮磷的流失量, 减少稻田排水对面源污染的影响。     

Converting paddy fields to Lei bamboo (Phyllostachys praecox) stands affected soil nutrient concentrations, labile organic carbon pools, and organic carbon chemical compositions

Background and aims

Land-use change often markedly alters soil carbon (C) and nitrogen (N) pool sizes with implications for climate change and soil sustainability. The objective of this research was to study the effect of converting paddy fields to Lei bamboo (Phyllostachys praecox) stands on soil C and N and other nutrient pools as well as the chemical structure of soil organic C (SOC) in the soil profile.

Methods

Soils (Anthrosols) from four adjacent paddy field–bamboo forest pairs with a known land-use history were sampled from Lin’an County, Zhejiang Province. Soil water soluble organic C (WSOC), hot water soluble organic C (HWSOC), microbial biomass C (MBC), readily oxidizable C (ROC), water soluble organic N (WSON), and other soil chemical and physical properties were determined. Soil organic C functional group compositions were determined by ¹³C-nuclear magnetic resonance (NMR).

Results

Concentrations of soil available P, available K, and different N forms increased (P?<?0.05) by the land-use conversion. Higher concentrations of SOC and total N (TN) were observed in the subsoil (20–40 and 40–60 cm soil layers) but not in the topsoil (0–20 cm layer) in the bamboo stands than in the paddy fields. The storage of SOC and TN in the entire soil profile (0–60 cm) increased by 56.7 and 70.7 %, respectively, after the land-use change. The increases in the SOC stock of the three soil layers were 11.0, 14.3, and 9.5 Mg C ha^?1, respectively. The conversion decreased WSOC concentrations in the subsoil but increased the ROC concentration in the topsoil. Solid-state NMR spectroscopy of soil samples showed that the conversion increased (P?<?0.05) the O-alkyl C content while decreased the aromatic C content, alkyl C to O-alkyl C ratio (A/O-A), and aromaticity of SOC.

Conclusions

Conversion of paddy fields to bamboo stands increased soil nutrient availability, and SOC and TN stocks. Effects of land-use change on C pools and C chemistry of SOC varied among different soil layers in the profile. The impact of the land-use conversion on soil organic C pools was not restricted to the topsoil, but changes in the subsoil were equally large and should be accounted for.     

Long-Term Nitrogen Addition Leads to Loss of Species Richness Due to Litter Accumulation and Soil Acidification in a Temperate Steppe

Background

Although community structure and species richness are known to respond to nitrogen fertilization dramatically, little is known about the mechanisms underlying specific species replacement and richness loss. In an experiment in semiarid temperate steppe of China, manipulative N addition with five treatments was conducted to evaluate the effect of N addition on the community structure and species richness.

Methodology/Principal Findings

Species richness and biomass of community in each plot were investigated in a randomly selected quadrat. Root element, available and total phosphorus (AP, TP) in rhizospheric soil, and soil moisture, pH, AP, TP and inorganic N in the soil were measured. The relationship between species richness and the measured factors was analyzed using bivariate correlations and stepwise multiple linear regressions. The two dominant species, a shrub Artemisia frigida and a grass Stipa krylovii, responded differently to N addition such that the former was gradually replaced by the latter. S. krylovii and A. frigida had highly-branched fibrous and un-branched tap root systems, respectively. S. krylovii had higher height than A. frigida in both control and N added plots. These differences may contribute to the observed species replacement. In addition, the analysis on root element and AP contents in rhizospheric soil suggests that different calcium acquisition strategies, and phosphorus and sodium responses of the two species may account for the replacement. Species richness was significantly reduced along the five N addition levels. Our results revealed a significant relationship between species richness and soil pH, litter amount, soil moisture, AP concentration and inorganic N concentration.

Conclusions/Significance

Our results indicate that litter accumulation and soil acidification accounted for 52.3% and 43.3% of the variation in species richness, respectively. These findings would advance our knowledge on the changes in species richness in semiarid temperate steppe of northern China under N deposition scenario.     

我国稻田氮磷流失现状及影响因素研究进展

水稻是我国主要的粮食作物,分析现阶段我国稻田氮磷流失现状及影响因素,对明确不同区域水稻化肥减施潜力具有重要意义.本研究对我国主要稻区地表径流氮磷流失现状特征和降雨、种植模式、栽培技术、施肥管理、水分管理方式及其他影响因素进行了总结.六大稻区全氮(TN)、全磷(TP)径流损失量范围分别在5.09～21.32和0.70～3.22 kg·hm^-2,均以华南双季稻区最高,TN径流损失量以华北单季稻区最低,TP径流损失量以西南高原单双季稻区最低.各稻区农户习惯施肥的水稻田田面水TN、TP峰值普遍高于径流水.水稻施肥后一周内为氮磷流失高峰期.与优化施肥相比,农户习惯施肥仍具有20%左右的氮磷减施潜力.各因素中,降雨和施肥管理是影响稻田径流氮磷流失的主要因素,而施肥管理和水分管理则最具可控性,具体调控措施包括化肥减量、施用新型肥料、有机肥代替化肥和节水灌溉等.整体上我国稻田氮磷流失风险在南方更突出.应以资源高效利用模式进行水稻种植以降低养分流失风险.未来研究应侧重稻田面源污染监测、氮磷流失风险评估、氮磷流失特征和机理、化肥减施增效新技术等方向.     

三峡库区消落带落羽杉(Taxodium distichum)与柳树(Salix matsudana)人工植被对土壤营养元素含量的影响

落羽杉与柳树被认为是三峡库区消落带植被修复的适生树种。2012年7月(T1)及2013年7月(T2)在消落带人工基地取样,研究了消落带人工植被(处理组)及裸地土壤(对照组)的营养元素含量,并对植被生长情况进行调查。结果表明:(1)对比处理组与对照组养分含量发现,T1时除土壤p H值外,其他养分含量在处理组与对照组间均存在差异。T2时只有p H值、磷(包括有效磷AP、全磷TP)、速效钾(AK)含量在处理组与对照组中差异显著。(2)对同一植被类型而言,T2时落羽杉土壤p H值与土壤有机质含量(OM)均显著低于T1,同样,T2时柳树实生土壤OM也显著降低;处理组土壤中碱解氮(AN)、AP、全钾(TK)含量极显著的低于淹水前,而TP含量却显著升高;与T1相比,T2时裸地土壤除AN含量降低、AK含量显著升高外,其它养分含量均未呈现显著差异。(3)相关性分析表明,土壤p H值与TP含量呈现极显著负相关,而OM与AN、AP、TK分别呈现出极显著正相关。AN、AP分别与TP表现出极显著负相关关系,而与TK表现出极显著正相关关系。TK与TP也呈现极显著的负相关关系。此外,植物高度、基径与冠幅三项生长指标与土壤中的p H值、OM、AN、AP(高度除外)、TK呈现出负相关的现象。研究表明,落羽杉与柳树人工植被对土壤养分的影响主要出现在水淹之前,进一步证实在三峡库区消落带开展科学的植被修复与重建值得提倡和肯定。     

Community structure and abundance of ammonia-oxidizing archaea and bacteria after conversion from soybean to rice paddy in albic soils of Northeast China

Community composition of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the albic soil grown with soybean and rice for different years was investigated by construction of clone libraries, denaturing gradient gel electrophoresis (DGGE), and quantitative polymerase chain reaction (q-PCR) by PCR amplification of the ammonia monooxygenase subunit A (amoA) gene. Soil samples were collected at two layers (0–5 and 20–25 cm) from a soybean field and four rice paddy fields with 1, 5, 9, and 17 years of continuous rice cultivation. Both the community structures and abundances of AOA and AOB showed detectable changes after conversion from soybean to rice paddy judged by clone library, DGGE, and q-PCR analyses. In general, the archaeal amoA gene abundance increased after conversion to rice cultivation, while bacterial amoA gene abundance decreased. The abundances of both AOA and AOB were higher in the surface layer than the bottom one in the soybean field, but a reverse trend was observed for AOB in all paddy samples regardless of the duration of paddy cultivation. Phylogenetic analysis identified nine subclusters of AOA and seven subclusters of AOB. Community composition of both AOA and AOB was correlated with available ammonium and increased pH value caused by flooding in multiple variance analysis. Community shift of AOB was also observed in different paddy fields, but the two layers did not show any detectable changes in DGGE analysis. Conversion from soybean to rice cultivation changed the community structure and abundance of AOA and AOB in albic agricultural soil, which requires that necessary cultivation practice be followed to manage the N utilization more effectively.     

基于GIS和地统计学的黄泛区土壤磷空间变异——以周口为例

土壤中的磷是衡量土壤肥力的重要指标,其含量的高低对土壤理化性质、植物生长以及微生物的活动等都有重要影响.本文以周口黄泛区土壤为例,通过土样采集和室内试验分析,运用地统计分析及GIS空间模拟等方法,分析土壤全磷和速效磷的空间分布特征.结果表明: 研究区土壤全磷和速效磷含量比较高,且表层(0～20 cm)含量均高于第二层含量(20～40 cm).两层土壤全磷和速效磷均属于中等程度变异,并且速效磷的变异程度高于全磷;两层土壤全磷为中等程度的各向异性,最适模型为高斯模型,表层具有较强的空间相关性,第二层则具有中等的空间相关性. 两层土壤速效磷的各向异性均较弱,最适模型为线性模型,两层均呈现较弱的空间相关性. 两层全磷含量从西南到东北方向呈现缓慢上升的变异趋势,而从西北到东南方向呈逐渐下降的变异趋势. 表层速效磷含量在西南到东北方向先升后降,在东南到西北方向呈先降后升的变异趋势;第二层速效磷含量在西南到东北方向上呈现先降后升的趋势,而在西北到东南方向则呈上升趋势.表层土壤全磷含量较高,第二层含量属于中等水平;表层速效磷含量较高,而第二层含量较低.土地利用方式、耕作制度和施肥等人为因素是影响该区土壤磷分布趋势和空间变异的主要因素.     

水位控制对农田泥炭藓产量的影响

为明确不同水位控制下农田土壤因子与泥炭藓产量之间的关系,解析影响泥炭藓产量的主要土壤因子,以贵州省龙里县水苔村种植年限相同的泥炭藓为研究对象,分析不同水位条件下泥炭藓生理生态指标与土壤因子的特征,并结合冗余分析,讨论水位和土壤因子的交互作用对泥炭藓生理生态指标的影响。结果表明：水苔村种植泥炭藓有1科1属5种,其中泥炭藓原亚种(Sphagnum palustre L. ssp.palustre)为优势种。泥炭藓生理生态指标均随水位升高逐渐上升,表明高水位有利于泥炭藓生长;土壤含水量(SWC, Soil Water Content)和孔隙度(STP, Soil Porosity)随水位升高逐渐增大,表明水位升高有助于增强土壤透水、透气及蓄水保墒能力;总氮(TN, Total Nitrogen)、总磷(TP, Total Phosphorus)、总钾(TK, Total Potassium)、有效磷(AP, Available Phosphorus)随水位升高逐渐降低,表明水位升高加速氮磷钾等营养元素淋失;脲酶(URE, Urease)和过氧化氢酶(CAT, Catalase)随水位升高逐渐...     

不同林龄杉木人工林土壤C:N:P化学计量特征及其与土壤理化性质的关系

为了阐明林龄对杉木人工林土壤理化性质及碳氮磷(C∶N∶P)生态化学计量特征的影响,在福建农林大学三明莘口林场选取4个林龄(4, 20, 24, 33a)的杉木人工林为研究对象,测定0—20,20—40,40—60 cm深度土壤的水分-物理性质、pH、总碳(TC)、全氮(TN)、全磷(TP)、全钾(TK),探讨它们随林龄的变化及其与C∶N∶P化学计量比之间的关系,为杉木人工林持续经营管理提供科学依据。结果表明:(1)随着林龄的增加,质量含水量、田间持水量和毛管孔隙度先减小后增加,在20 a达到最小,TN和TP也有相似的变化趋势,但在24 a林分的深层土壤达到最小,TC和TK保持不变;(2)随着林龄的增加,C∶N保持不变,C∶P和N∶P在24 a成熟林达到最大,但只在20—60 cm达到显著差异;(3)TC与多数水分-物理性质及3个生态化学计量比显著相关,质量含水量和孔隙度与C∶N∶P生态化学计量比均显著相关,TP与C∶P和N∶P显著负相关。土壤物理性质与土壤养分循环存在一定关联,有机质与土壤结构及养分平衡的调节有关,研究区杉木林发育过程中土壤腐殖质化进程较缓慢,24 a成熟林杉木的生长受到土壤磷的限制,在杉木速生阶段适当增施磷肥,保证林木的良好生长,促进土壤与植物的良性养分循环。     

Composition Shifts of Arbuscular Mycorrhizal Fungi between Natural Wetland and Cultivated Paddy Field

The community assembly change of arbuscular mycorrhizal fungi (AMF) during the reclamation of wetlands to paddy fields is mostly unknown. In this study, we applied the high-throughput sequencing technique to investigate the composition of the AMF community in natural wetland (common wild rice and Leersia hexandra Swartz) and paddy field (Asian cultivated rice), as well as the soil elements effective on the community of AMF. Soil properties including soil organic carbon, available nitrogen (AN), available phosphorus (AP), available potassium, and pH were also measured. Operational taxonomic units (OTUs) of nine genera in four orders (Glomerales, Diversisporales, Archaeosporales, and Paraglomerales) of AMF were detected. All detected AMF genera were found in the wild rice wetland, while about half of the detected AMF genera were absent in paddy field; however, the absolute amount of total AMF in the paddy field and wetland was not different. Among all measured soil properties, AMF community was affected significantly by soil AN and AP. Results indicate that agricultural managements affect AMF community significantly, but do not have negative effects on the absolute amount of all the AMF genera. Soil AP may be the main factor resulting in the decreased AMF genus in paddy field. In addition, AMF may have contributed to the survival and evolution of plants.     

三峡水库峡谷地貌区消落带土壤氮磷钾、有机质含量和pH值的时空动态

基于三峡水库巫山段和秭归段消落带海拔155～172 m区段经历水库水位涨落前(2008年)和经历1次(2009年)、4次(2012年)、7次(2015年)水库水位涨落后土壤化学性质的长期定位监测,研究峡谷地貌区消落带土壤氮(N)、磷(P)、钾(K)、有机质(OM)含量和pH值的时空动态变化规律,并对其养分状态进行评价.结果表明: 随着经历水库水位涨落次数的增多,消落带土壤全氮(TN)、速效氮(AN)、速效钾(AK)和OM含量减少,全磷(TP)、全钾(TK)、速效磷(AP)含量和pH值增加;经历水库水位涨落前和经历1次水库水位涨落后,消落带各土层的TP、TK和AP含量为巫山样地>秭归样地,经历4次和7次水库水位涨落后,变为秭归样地>巫山样地;随着经历水库水位涨落次数的增多,消落带大多数土壤化学指标含量在土层间的差异减小.对照全国第二次土壤普查养分分级标准,经历7次水库水位涨落后,秭归样地土壤TP和AP含量达到极高等级,巫山样地土壤AP含量为高等级,其他指标为中等及以下等级.三峡水库的水文特征、人为活动的干扰,以及不同土壤化学指标性质的差异,是峡谷地貌区消落带土壤N、P、K、OM含量和pH值时空变化的主要驱动因素.     

Seasonal Patterns of Nitrogen and Phosphorus Limitation in Four German Lakes and the Predictability of Limitation Status from Ambient Nutrient Concentrations

To identify the seasonal pattern of nitrogen (N) and phosphorus (P) limitation of phytoplankton in four different lakes, biweekly experiments were conducted from the end of March to September 2011. Lake water samples were enriched with N, P or both nutrients and incubated under two different light intensities. Chlorophyll a fluorescence (Chla) was measured and a model selection procedure was used to assign bioassay outcomes to different limitation categories. N and P were both limiting at some point. For the shallow lakes there was a trend from P limitation in spring to N or light limitation later in the year, while the deep lake remained predominantly P limited. To determine the ability of in-lake N:P ratios to predict the relative strength of N vs. P limitation, three separate regression models were fit with the log-transformed ratio of Chla of the P and N treatments (Response ratio = RR) as the response variable and those of ambient total phosphorus:total nitrogen (TN:TP), dissolved inorganic nitrogen:soluble reactive phosphorus (DIN:SRP), TN:SRP and DIN:TP mass ratios as predictors. All four N:P ratios had significant positive relationships with RR, such that high N:P ratios were associated with P limitation and low N:P ratios with N limitation. The TN:TP and DIN:TP ratios performed better than the DIN:SRP and TN:SRP in terms of misclassification rate and the DIN:TP ratio had the highest R² value. Nitrogen limitation was predictable, frequent and persistent, suggesting that nitrogen reduction could play a role in water quality management. However, there is still uncertainty about the efficacy of N restriction to control populations of N₂ fixing cyanobacteria.     

Micro-scale spatial heterogeneity and the loss of carbon,nitrogen and phosphorus in degraded grassland in Ordos Plateau,northwestern China

The micro-scale spatial distribution and loss of carbon, nitrogen and phosphorus were examined in degraded grassland near Ordos, in the Mu Us Sand-land, northwestern China. Five communities that represented a series of successionally degraded stages in desertification were chosen for the work. The dominant plant of Community 1 was the steppe grass Stipa bungeana; Community 2 was dominated by a mix of S. bungeana and the shrub Artemisia ordosia; Community 3 was A. ordosia; Community 4 was a mix of A. ordosia and the desert grass Cynanchum komorovii; and Community 5 was C. komorovii. The soils in root-spheres and in the bare openings between plants in five successionally degraded plant communities were analyzed for total organic carbon (TOC), total nitrogen (TN), inorganic nitrogen (IN), total phosphorus (TP), and available phosphorus (AP). The results showed that the heterogeneity process of the soil chemistry was characterized first by TOC heterogeneity and later by TN heterogeneity. The heterogeneity process of TP was only characterized in the community 3. No significant heterogeneity was present for AP in the five community stages. At the beginning of degradation, invasion by the shrub A. ordosia of S. bungeana grassland was found to lead to competition for soil elements between S. bungeana and A. ordosia and made the Community 2 soil environment temporarily homogeneous. In Community 3, however, the soil elements became spatially heterogeneous, and this led to the development of `islands of fertility'. The concentrations of soil elements (TOC, TN and IN) were greatest in the shrub root-spheres. With further desertification (from Community 4 to Community 5), the islands of fertility began to collapse, and the concentrations of the main soil elements declined rapidly. The dynamics of soil phosphorus under progressive desertification were different from those of the other soil elements. TP decreased from form Community 1 to Community 5, while the AP concentration did not change in mid-level desertification (Community 3), but increased with serious desertification (Community 5).     

天山高寒草原土壤团聚体结构与养分含量对模拟氮磷沉降的响应

为更好地理解高寒草原土壤团聚体结构及其养分含量对氮(N)、磷(P)沉降增加的响应,于2018年开始依托全球营养网络(Nutrient Network)在巴音布鲁克草原生态系统研究站开展模拟氮磷沉降的短期(<5年)氮磷添加控制实验,设置对照(CK)、N添加、P添加、NP交互添加4个处理。N、P添加量均为10 g m^-2 a^-1。于2021年8月采集植物与土壤样品,采用湿筛法分析土壤水稳定性团聚体组成,测定全土和各粒级团聚体有机碳(SOC)、总氮(TN)、总磷(TP)、速效氮(AN)和速效磷(AP)含量。研究结果表明：(1)巴音布鲁克高寒草原各粒级土壤团聚体比例从低到高依次为：0.053—0.25 mm、<0.053 mm、0.25—2 mm、和>2 mm,以>2 mm团聚体占主导,其比例在45.48%—71.81%之间。(2)N添加显著降低了0—10 cm土壤层>2 mm团聚体比例和团聚体稳定性,而P添加则显著降低了10—20 cm土壤层>2 mm团聚体比例和团聚体稳定性。(3)0—10 cm土壤层各粒级团聚...     

鄂西南亚热带常绿落叶阔叶混交林土壤空间异质性

大样地是监测森林生物多样性及生态因子动态变化的重要平台,以湖北木林子国家级自然保护区常绿落叶阔叶混交林为对象,依托15 hm2动态监测样地,对每个400 m2样方进行取样并测定7个化学性质指标,运用地统计与多元统计方法,分析了该大样地内不同土壤因子的富集程度、空间格局、变异性、相关性。结果如下:1)研究区土壤酸性较强,有机质、有效氮、全氮、有效钾丰富,有效磷、全磷亏缺;2)有效氮、全氮、有效磷呈东高西低,p H呈西高东低,有效钾呈斑块状分布,有机质呈中间高,西北与东南低的"凸"型分布,其中以有效钾空间结构最复杂(A=50 m,D=1.96),p H空间结构最简单(A=180 m,D=1.83);3)土壤因子的块基比范围为0.14—0.69,14对因子显著相关(P0.05),其中以全磷的空间自相关最强,并与其余因子显著相关;4)土壤因子的变异系数范围为0.05—0.34,其中全磷、有效磷变异系数最高,分别为0.29和0.34,p H变异系数最低(0.05),土壤全磷在主成分中具有最大载荷(2.27)。结果表明:1)木林子常绿落叶阔叶混交林土壤酸性较强,除了磷素亏缺,其余土壤养分富集;2)土壤的变异性不强,空间分布具有明显的自相关特征,并具有一定的尺度效应;3)除了土壤有效磷以外的土壤因子之间存在较为普遍的相互联系;4)土壤全磷对于土壤的综合变异最具代表性。     

拉萨河流域洪积扇不同植被类型土壤化学计量特征

洪积扇是拉萨河流域珍贵的土地资源,而明悉其土壤养分状况是对其进行科学合理开发利用的基础。为此,在拉萨河流域选取了10个洪积扇,于2020年7-8月调查了其上的植物群落组成并采集对应土壤,测定了土壤有机碳（SOC）、全氮（TN）、全磷（TP）、全钾（TK）、碱解氮（AN）、速效磷（AP）和速效钾（AK）的含量并计算其化学计量比。结果表明：10个洪积扇的60个样方中共发现植物种87种,分属于29科79属,其中禾本科和菊科的物种居多;洪积扇SOC、TN、TP、AN和AK的平均含量分别为34.38 g/kg、2.77 g/kg、0.39 g/kg、130.78 mg/kg和189.79 mg/kg,均表现为草地>灌丛>农田,其中SOC、TN、AN和AP含量在草地和农田下差异显著（P<0.05）;土壤TK的平均含量为19.68 g/kg,表现为农田>草地>灌丛;土壤AP的平均含量为3.36 mg/kg,表现为农田>灌丛>草地;土壤C：N的均值为12.75,表现为农田>灌丛>草地;土壤C：P、N：P和N：K的均值分别为102.50、8.10和0.16,均表现为草地>灌丛>农田,总体来说洪积扇土壤P元素较为稀缺;土壤N：K与SOC、TN、TP、TK、AN、AP、AK均极显著相关（P<0.01）,SOC和TN与植物群落盖度极显著正相关（P<0.01）;典范对应分析（CCA）进一步表明土壤养分及其计量比对洪积扇植物群落组成影响显著（P=0.002）,且TP、K：P和AP是影响洪积扇植物群落组成的主要土壤生态化学计量因子。综上所述,拉萨河流域洪积扇植物种相对丰富,但分布不均匀,组成不稳定。SOC、TN、TK含量相对较高但C：N值低,表现为有机质矿化速率高而土壤肥力低下;土壤TP和AP的含量均较低,洪积扇植物群落在生长发育过程中受到土壤P元素的限制。此外,研究还发现土壤N：K同C：N：P一样可作为评价土壤养分状况的生态化学计量指标。     

喀斯特不同土地利用类型裂隙土壤有机碳及磷素赋存特征

以喀斯特石漠化区不同土地利用类型裂隙土壤为研究对象，运用野外调查和实验室内分析相结合方法，探索其有机碳和磷素含量变化及其赋存特征，以期为喀斯特地区开展石漠化治理和植被恢复提供理论依据。结果表明：4种土地利用类型裂隙土层土壤有机碳赋存含量变化范围为16.067-39.436 g/kg，总体呈现出随土层深度增加而降低的变化趋势；土壤全磷、有效磷赋存含量变化范围分别为0.093-0.274 g/kg、3.836-8.025 mg/kg，整体上在裂隙表层显著高于其他土层，具有上层高下层低的特点；同时，土壤有机碳和磷素总体上属于中度变异。乔木林地和灌丛地的C/P总体上表现出随土层的加深而减小的趋势，而草地和撂荒地先减小后增加，土壤C/P在各土地利用类型裂隙土层变化范围为86.499-268.343，磷的有效性较低；随土层深度的增加，各土地利用类型裂隙土壤有机碳、全磷和有效磷含量逐渐在减少，有机碳对土壤碳磷比、有效磷含量变化有一定影响。     

黄壤稻田土壤微生物生物量碳磷对长期不同施肥的响应

本研究以进行了22年的黄壤稻田长期定位试验为依托,分析了不同施肥模式下土壤碳(C)、磷(P)与微生物生物量C(MBC)、P(MBP)的变化及其耦合特征,旨在探讨黄壤地区合理培肥模式以提高土壤磷素有效性.试验包括10个处理,分别为不施肥(CK)、单施氮肥(N)、磷钾配合(PK)、氮钾配合(NK)、氮磷配合(NP)、氮磷钾配合(NPK)、单施有机肥(M)、3种有机无机肥配施(1/4M+3/4NP、0.5MNP、MNPK).结果表明:与不施肥相比,N和NK处理土壤有机碳(TOC)、全磷(TP)、MBC、MBP均有不同程度的降低,施磷处理(PK、NP、NPK)则有不同程度的提升;与不施肥和施用无机肥相比,施用有机肥各处理TOC、MBC、MBP及MBP/TP均显著增加,其中M和MNPK处理增幅最大.MBC/MBP、TOC/MBP、MBC/TP以施用有机肥处理最低,N处理最高.土壤MBC、MBP及其耦合关系与土壤TOC和有效磷均呈极显著相关,TOC是影响MBC、MBP、MBP/TP的直接因素,而有效磷则是影响MBC/MBP、TOC/MBP、MBC/TP的直接因素.土壤MBP及碳、磷耦合关系各指标可以有效区分单施化肥和施用有机肥的不同施肥方式,可作为评价黄壤稻田磷素肥力的生物学指标.配施有机肥是增加黄壤稻田磷有效性、提高土壤供磷潜力和保持土壤生物健康的有效途径.