Rehabilitation of bauxite residue to support soil development and grassland establishment

Rehabilitation(amendment and vegetation establishment)on bauxite residue is viewed as a promising strategy to stabilize the surface and initiate soil development.However,such approaches are inhibited by high pH,high exchangeable sodium(ESP)and poor nutrient status.Amendment with gypsum is effective in improving residue physical and chemical properties and promoting seed establishment and growth.Application of organics(e.g.compost)can address nutrient deficiencies but supplemental fertilizer additions may be required.A series of germination bioassays were performed on residue to determine candidate species and optimum rehabilitation application rates.Subsequent field trials assessed establishment of grassland species Holcus lanatus and Trifolium pratense as well as physical and chemical properties of amended residue.Follow up monitoring over five years assessed elemental content in grassland and species dynamics.With co-application of the amendments several grassland species can grow on the residue.Over time other plant species can invade the restored area and fast growing nutrient demanding grasses are replaced.Scrub species can establish within a 5 Yr period and there is evidence of nutrient cycling.High pH,sodicity and nutrient deficiencies are the major limiting factors to establishing grassland on residue.Following restoration several plant species can grow on amended residue.

Analysis of Post-Burial Soil Developments of Pre-AD 79 Roman Paleosols near Pompeii(Italy)

The AD 79 eruption of Somma-Vesuvius completely buried the ancient landscape around Pompeii (Italy) to some extent conserving the pre-AD 79 Roman paleosols of the Sarno River plain. To estimate potential post-burial soil developments of these paleosols detailed soil liquid and solid phase analysis were carried out. Firstly, an in-situ soil hydrological monitoring was conducted within a pre-AD 79 paleosol in natural undisturbed stratification. The results show that soil water flow and nutrient transport from the overlying volcanic deposits into the pre-AD 79 paleosol take place. Secondly, to estimate their influence on the paleosol’s mineral soil properties, the solid phase of four pre-AD 79 paleosols and associated modern unburied soils were analysed and compared. By combining the data from the soil liquid and solid phase analysis, potential post-burial changes in the paleosols were estimated. Finally, a rise of the mean groundwater table was determined since AD 79. This distinguishes the Sarno River plain into two different zones of post-burial soil developments: 1) lower altitudes where formerly terrestrial paleosols are now influenced by groundwater dynamics and 2) higher altitudes where the paleosols are still part of the vadose zone and rather influenced by infiltration water or interflow. Thus, the mechanism of potential post-burial soil development being active in the pre-AD 79 paleosols is not uniform for the entire Sarno River plain but strongly depends on the paleotopographic situation.

Temporal and environmental factors drive community structure and function of methanotrophs in volcanic forest soils

Methanotrophs,organisms that obtain oxygen by oxidizing methane,are recognized as the only known biological sink for atmospheric CH_4,and forest soil methanotrophs play crucial roles in mitigating global warming.The succession patterns of methanotrophic communities and functions in Wudalianchi volcano forest soils could provide a basis for the study of evolutionary mechanisms between soil microorganisms,the environment,and carbon cycling of temperate forest ecosystems under climate change.In this study,the characteristics and drivers of methanotrophic community structure and function of two volcanic soils at different stages of development are analyzed,including an old volcano and a new volcano,which most recently erupted 300 years and 17-19×10^(5)years ago,respectively,and a non-volcano hills as control,based on space for time substitution and Miseq sequencing and bioinformation technology.The results showed that CH_(4) fluxes were significantly higher in old-stage volcano forest soils than new-stage forest soils and non-volcano forest soils.There were significant differences in the community composition and diversity of soil methanotrophs from different volcano forest soils.Methylococcus was the dominant genus in all soil samples.Additionally,the relative abundance of Methylococcus,along with Clonothrix,Methyloglobulus,Methylomagum,Methylomonas and Methylosarcina,were the important genera responsible for the differences in methanotrophic community structure in different volcano forest soils.The relative abundance of methanotroph belonging toγ-proteobacteria was significantly higher than that belonging toα-proteobacteria(P<0.05).Chao1,Shannon and Simpson indices of soil methanotrophic community were significantly lower in new-stage volcanos and were significantly affected by bulk density,total porosity,p H,nitrate,dissolved organic carbon and dissolved organic nitrogen.There were significant differences in community structure between new-stage and old-stage volcanoes.Bulk density and p H are important soil properties contributing to the divergence of methanotrophs community structure,and changes in soil properties due to soil development time are important factors driving differences in methanotrophs communities in Wudalianchi volcanic soils.

基于CiteSpace的草原土壤近三十年研究态势分析

利用文献计量软件CiteSpace对CNKI(1992~2021年)和WOS数据库(1995~2021年)草地土壤领域的文献资料做可视化分析和系统梳理。结果表明,在CNKI数据库中,《草业科学》《草业学报》《生态学报》《应用生态学报》刊载草原土壤研究成果较多;高中心性的龙瑞军、张法伟是承接作者;中国科学院大学为数据库发文量排名第一的机构;依据发文量特征将我国草原土壤研究历程划分为起步(1992~2002年)、平稳发展(2003~2012年)和波动发展(2013~2021年)三阶段,并讨论了早期萌芽研究阶段及各阶段对应的主题。在WOS数据库中,Agriculture Ecosystems&Environment、Rangeland Ecology Management、Plant and Soil、Journal of Arid Environments上刊载草原土壤研究成果较多;高中心性的白永飞、韩兴国是前沿作者;中国科学院为数据库发文量排名第一的机构;中国发文量大,但中心性不及美国、德国等国家。最后综合分析草原土壤研究热点和前沿,指出全球气候变化背景下土壤碳氮收支问题是未来草原土壤研究主要方向。

Fractions and Bioavailability of Soil Inorganic Phosphorus in the Loess Plateau of China under Different Vegetations

Plants play an important role in soil phosphorus nutrition. However, the effect of plants on phosphorus nutrition in soils of the Loess Plateau of China is not well understood. This study was conducted to reveal the relationships between plants and phosphorus＇ fractions and availability in the Loess Plateau of China. Twenty-two plant communities were surveyed and soil samples under different plant canopies were collected for the determination of soil properties and inorganic phosphorus fractionation. The results showed that Leguminosae and Lilaceae reduced pH and increased organic matter, cation exchange capacity, total and Olsen phosphorus in soils under their canopies, while Labiatae and Rosaceae increased pH and decreased organic matter, cation exchange capacity, total and Olsen phosphorus in soils under their canopies. The contents of Ca2P, CasP, AI-P and Fe-P were highly related with soil Oisen phosphorus. They were all higher in soils under Leguminosae and Lilaceae and lower in softs under Labiatae and Rosaceae. The results of this study indicate that Leguminosae and Lilaceae improved phosphorus nutrition in soils, yet Labiatae and Rosaceae impeded the improvement of phosphorus nutrition in soils under their canopies, which will be of more help to instruct vegetation restoration in the region and provide information for soil development.

高山冰川区冰碛土形成过程、成土特征及滑坡灾变机制研究进展

冰碛土作为冰川搬运、堆积消融后的主要产物,广泛发育于我国环青藏高原边缘高山冰川区。受高海拔山区地形地貌及极端气候的影响,呈现宽级配、强渗透、非均质、无分选及无层理等特征,是诱发高山冰川区冰碛土滑坡地质灾害的主要物质来源。系统掌握高山冰川区冰碛土的形成过程及灾变演化特征对于科学认知孕灾机制具有重要现实价值。据此,首先论述了高山冰川区冰川作用及冰碛地貌特征,阐明了冰碛土的演化过程及发育条件,并针对我国环青藏高原边缘高山冰川区冰碛土的分布特征进行分析。其次,总结了冰碛土的相关分类指标,并探讨了不同沉积部位、沉积时间及沉积成因下冰碛土的典型成土特征。最后,梳理了冰碛土滑坡的主要致灾因素及结构特征,并剖析了在极端气候环境下冰碛土滑坡的发育特征及灾变演化过程。研究表明:(1)高山冰川区冰碛土发育主要受冰川冰进及冰退作用控制,在西部高海拔地区、高山系成群分布且气候垂直变化明显区域广泛发育。(2)不同沉积部位及沉积时间分布的冰碛土结构呈现显著区域分异性,主要表现为高海拔冰川源头的现代冰碛土具有结构松散、磨圆度差且层理不发育等特征,而古冰碛土分布海拔跨度大且结构相对致密。(3)不同类型冰碛土边坡结构引发的界面型滑坡破坏模式包括:浅表层冰碛层降/融水蠕滑型、冰水堆积-古冰碛层界面控制型及冰碛层-湖相沉积接触风化型等3类,其内部富冰带的滞水促滑效应是引发冰碛土界面型滑坡灾害的主要诱因。该研究旨在为揭示高山冰川区冰碛土地质特征及滑坡灾变机制提供基础参考。

碎石土滑坡的发育机制分析及防治对策研究

[目的]以甘肃礼县夹关沟滑坡为例,计算其在降水和地震作用下的稳定性系数,对其发育机制进行分析,并针对不同情况下碎石土滑坡的发育提供防治对策。[方法]选取强度折减法,利用的本构模型为莫尔-库伦模型,同时利用Midas有限元软件对夹关沟滑坡进行数值模拟。[结果]碎石土边坡天然条件下的稳定性系数为1.271 9,处于基本稳定;降雨条件下稳定性系数为1.125,处于不稳定状态;地震条件下稳定性系数为1.006 8,处于不稳定状态。[结论]在降水作用时,滑坡内部岩体受到入渗水的侵蚀,在坡面松散堆积物和下伏基岩层顶部的位置逐渐形成饱水带,成为滑坡失稳滑动的潜在滑移面;在地震作用时,滑坡体松散堆积物的抗滑力逐渐减小,直到小于其自重时,滑坡发生失稳滑动,再加上河道侵蚀冲刷的影响,滑坡前缘处不断受到河水的侵蚀冲刷,形成不合理的切坡,导致滑坡内部的应力发生重分布,在外力作用下,滑坡容易发生失稳滑动。

沙质草原风蚀坑土壤粒度组成及养分特征

为探究草原风蚀坑发育土壤质量的演化特征及对草原生态系统结构和功能的影响,以多伦县典型沙质草原不同发育阶段的风蚀坑为研究对象,周围未风蚀草地为对照(CK),通过野外实地观测、室内指标测定等手段分析草原风蚀坑的土壤粒度组成及养分特征。结果表明,研究区土壤平均粒径为1.65~3.55μm,未风蚀草地、消亡阶段土壤的平均粒径显著高于其他发育阶段,其中活跃发展阶段的土壤平均粒径最低。风蚀坑在发育过程中土壤粒径逐渐粗化,至活跃发展阶段粗砂含量增至9.72%,土壤颗粒分布情况最差。粉粒在活跃发展阶段和活化阶段分别降低至0.87%和0.88%。当风蚀坑逐渐走向消亡,至消亡阶段时土壤颗粒变细,粗砂减少,黏粒不断增加。风蚀坑的土壤有机质、速效钾、速效磷含量间存在显著差异,而碱解氮含量差异不显著。风蚀坑发育会造成土壤有机质和速效钾大量流失,速效磷含量在风蚀坑开始发展时减少,至活跃发展阶段时又有所增加,碱解氮含量在整个发育过程中变化较小。

The Chemistry of Serpentine Soils Developed Over A Podiform Chromite Deposit,Western Sierra Nevada,USA

The Chinese Camp mining district in the western Sierra Nevada of California,USA,contains a serpentinized,ultramafic dunite intrusion with podiform chromite deposits.Serpentine soils have developed over this intrusion,creating a unique ecosystem of endemic vegetation and soils characterized by low Ca/Mg ratios and high Ni and Cr contents.The vegetation and red coloration make it easy to visually distinguish between soils developed over intruded,serpentinized bedrock and unmineralized,adjacent andesite bedrock(Fig.1).The purpose of our study was to compare soil chemistry and vegetative parameters among 3 study-design levels:1)undisturbed serpentine soil,2)undisturbed background soil(non-serpentine,developed over andesite),and 3)serpentine soil disturbed by mining activities.Within each of these l e v*e ls,3 random locations were chosen where weestablished 3,30-m transects(spaced 120-degrees apart).One soil sample was collected at a random location along each transect(0-15 cm depth after removing litter/O horizon).This scheme resulted in the collection of 9replicate soil samples per study-design level.Samples were analyzed for total metal content by ICP-AES/MS(inductively coupled plasma atomic emission spectroscopy/mass spectroscopy),p H,electrical conductivity,and total C/N/S.The vegetative parameter of%canopy cover was measured with a line-point intercept survey along each transect,using 0.6m intervals.Above-ground net primary productivity(ANPP)was estimated by harvesting all aboveground living plant material within a 0.5 m quadrant at 3 random locations along each transect,drying,and weighting the material.Significant differences among design levels were observed for ANPP,canopy cover,total P,total N,and Ca/Mg,where the median values for these parameters decreased in the order undisturbed background>undisturbed serpentine>mining-disturbed serpentine.The highest concentrations of Cr and Ni were found in undisturbed serpentine(medians of 1960 ppm and 2529ppm,respectively)followed by mining-disturbed serpentine(medians of 420 and 2120,respectively)then undisturbed non-serpentine(medians 47.0 and 32.2 ppm,respectively).Soil p H varied significantly among the design levels with a median 5.74 in undisturbed background,median 6.25 in undisturbed serpentine,and median of 7.17 in mining-disturbed serpentine.These data document the distinct differences in soil chemistry and vegetation parameters between undisturbed serpentine soil and adjacent,undisturbed background soil.Efforts toward mining reclamation must recognize these differences and include the correct baseline conditions in the reclamation plan.

Cropland physical disturbance intensity： plot-scale measurement and its application for soil erosion reduction in mountainous areas

Various kinds of human disturbances on cropland are the main reasons for soil erosion and land degradation.Farming practices in mountainous areas vary greatly among cropland plots because of the heterogeneity of biophysical conditions and differences in farmers'management behavior.The main purpose of this paper is to develop a composite index of cropland physical disturbance intensity(CLDI)to reflect the plot-scale discrepancy of potential soil erosion in mountainous areas.The study was based on both plot survey and household interview data,collected from six typical catchments in mountainous areas of southwestern China.Four kinds of physical disturbance practices and two kinds of conservation practices during one crop rotation period were synthesized to develop the CLDI index.The rough set theory was referenced to avoid subjectivity during weight allocation.The results show that conventional tillage,deep fertilization,and manual weeding are the main causes of cropland soil erosion,whereas manure application in combination with seasonal fallow reduces soil erosion.Different crop types as well as cropland location factors determine the spatial pattern of CLDI.Crop rotation modes with major crops of tobacco and maize resulted in a maximal CLDI,and cropland plots with a distance radius of 150 meters away from households received the most intensive physical disturbance.These results are critical to help better protect rural environments in mountainous areas.Based on the results,methods to reduce cropland soil erosion are suggested.

不同发育阶段柠条灌丛堆土壤生态化学计量学特征

采用空间代替演替时间的研究方法,以我国宁夏南部荒漠草原不同生长期(生长期、成熟期、衰退期)柠条灌丛堆为研究对象,分析了0~20 cm土层土壤有机碳、全氮、全磷等养分含量及其生态化学计量比随发育阶段的变化和垂直分布特征。结果表明:在柠条灌丛堆的不同生长发育阶段,各土层中有机碳、全氮、全磷的含量分别在2.18~4.25 g/kg、0.13~0.20 g/kg、0.22~0.29 g/kg之间,与全国土壤养分平均水平相比,体现出碳、氮、磷元素的极度匮乏;在不同发育阶段,柠条灌丛堆成熟期土壤有机碳和全氮的含量显著高于生长期和衰退期;在垂直方向上,随着土壤深度的增加,土壤有机碳、全氮含量逐渐降低,表现出明显的“肥岛效应”;而全磷含量在柠条灌丛堆的不同发育阶段随土层深度变化未呈现出明显变化;不同发育阶段的柠条灌丛堆各土层土壤碳氮比、碳磷比、氮磷比分别在14.93~27.89、10.50~15.83、0.59~0.84之间,碳氮比高于全国平均水平,而碳磷比、氮磷比均低于全国平均水平,氮是主要的土壤养分限制因子。相关性分析表明,有机碳与全磷和碳磷比呈显著正相关,全氮与全磷呈显著正相关(P<0.05);有机碳与速效磷、电导率和碳氮比呈极显著正相关,与pH呈极显著负相关;全氮分别与氮磷比和碳氮比呈极显著正、负相关;全磷与碳磷比和氮磷比呈极显著负相关(P<0.01)。柠条灌丛堆的发育主要受氮限制,可在其生长过程中适当添加氮肥以保证土壤养分的良性循环。

土壤类型及含水量对花蓟马蛹期发育及羽化的影响

基于花蓟马Frankliniella intonsa(Trybom)偏好土壤内化蛹的习性,研究不同土壤及含水量对花蓟马化蛹及羽化的影响,以期为花蓟马蛹控制技术提供重要依据。采集黏土、壤土和沙土3种土壤并在105℃条件下烘干,在3种土壤中添加纯水至其含水量达到3.00%、5.00%、10.00%、15.00%、20.00%和25.00%,随后将花蓟马老熟2龄若虫引入不同类型及含水量的土壤,观察其化蛹与羽化。土壤类型及含水量均显著影响了花蓟马的羽化,且2种因素之间交互作用显著(P<0.05)。在所有供试土壤中,随着土壤含水量的增加,花蓟马羽化率表现出先升高后降低的趋势。其中,花蓟马在含水量为10.00%沙土中羽化率最高,可达77.50%;在黏土中,当土壤含水量为15.00%时,花蓟马羽化率最高达63.33%;而在壤土中,当土壤含水量为15.00%和20.00%时,花蓟马的羽化率最高,分别为50.00%和47.50%。此外,研究发现花蓟马的羽化高峰在15.00%含水量的沙土中出现在第4天,而在其他含水量沙土以及所有含水量的黏土和壤土中其羽化高峰为第3天。土壤类型与含水量共同制约着花蓟马的化蛹及羽化,田间可以通过控制土壤湿度来干预花蓟马的化蛹及羽化。

黄土丘陵区生物结皮对土壤磷素有效性及碱性磷酸酶活性的影响

黄土丘陵区生物结皮广泛发育,可影响土壤磷素有效性。目前鲜见生物结皮对土壤磷素有效性的研究报道。本文以该区不同年限退耕地的生物结皮为研究对象,通过野外调查和室内分析,研究了生物结皮对土壤全磷、有效磷及碱性磷酸酶活性的影响。结果表明,1)生物结皮的形成可显著提高结皮层土壤全磷含量,而下层(0—10 cm)全磷含量差异不显著;2)生物结皮的形成可显著提高结皮层土壤有效磷含量,研究区生物结皮层土壤有效磷含量为3.27～5.87 mg/kg,占到同层土壤全磷含量的0.57%～0.95%,生物结皮层磷酸酶活性高于下层(0—10 cm)3～81倍;3)生物结皮对土壤磷素有效性及碱性磷酸酶活性的影响与生物结皮发育阶段有关;4)生物结皮主要通过提高结皮层土壤碱性磷酸酶活性和有机质含量,降低土壤pH,进而提高了土壤磷素有效性。本文研究结果表明,生物结皮的形成有助于提高黄土丘陵区退耕地土壤磷素有效性。

甘肃小陇山日本落叶松人工林不同发育阶段土壤理化性质的变化

采用时序研究法对甘肃小陇山林区日本落叶松人工林不同发育阶段(6、15、23、35 a)的土壤物理性质、化学性质进行多因子综合比较,利用主成分分析的方法,以主成分特征贡献率为权重,计算土壤肥力综合指标值,分析土壤性质的演变规律。结果表明:日本落叶松人工林发育至近熟林阶段,土壤物理性质变差,表现为土壤密度最大1.62g·cm-3,毛管孔隙度和最大持水量降至最低,分别为29.69%、24.45%,并且土壤有机质、氮、磷、钾、镁、钙含量也明显降低;而到成熟林阶段,土壤理化性质有显著改善,土壤密度降低为1.21 g·cm-3、毛管孔隙度和最大持水量恢复至45.56%、42.65%,土壤养分含量也有了很大的提高,甚至超过了中龄林阶段的水平;同时幼龄林、中龄林、近熟林和成熟林土壤性质综合得分分别为-0.329、0.188、-0.565、0.739,也表明近熟林土壤性质最差,成熟林土壤性质最好。

江西省大岗山湿地松林土壤性质的变化

重点论述在江西省大岗山山下林场清除灌丛和其它次生植被的迹地上栽植湿地松 ,发育至中龄林、近熟林时土壤性质的变化规律。研究结果表明 :次生植被的土壤容重明显比湿地松中龄林和近熟林的高 ,次生植被土壤的最大持水量则明显地低于中龄林和近熟林 ,非毛管孔隙度和总孔隙度也明显比中龄林和近熟林土壤的低 ;在中龄林土壤中细菌和放线菌的数量最少 ,真菌数量则随着树龄不断增大呈增加的趋势 ;湿地松中龄林的土壤氧化还原酶活性明显比次生植被和近熟林的低 ,土壤有机养分含量随着树龄增大有提高趋势 ,但速效

土壤含水量和土壤类型对豆大蓟马蛹期发育和羽化的影响

豆大蓟马Megalurothrips usitatus(Bagrall)是近年来严重制约海南豇豆生产的重要害虫。针对该蓟马在土壤中化蛹的习性,本文研究了在室内条件下不同土壤含水量和土壤类型对豆大蓟马化蛹的影响。结果表明,土壤含水量和土壤类型显著影响豆大蓟马蛹的发育历期和羽化率,土壤含水量为15%且土壤类型为砂壤土时,豆大蓟马的发育历期最短为3.62±0.15 d,羽化率最高为52.08%±0.07%,低含水量(5%)和高含水量(25%)均不利于豆大蓟马化蛹。土壤类型以砂壤土最适宜豆大蓟马化蛹,粘土最不适合豆大蓟马化蛹,其羽化率最低为19.17%±0.02%。

黄土丘陵区不同类型生物结皮下土壤微生物的分布特征

【目的】分析黄土丘陵区不同类型生物结皮的发育特征及土壤微生物的分布特征,以明确生物结皮形成过程对土壤微生物的影响。【方法】采用野外调查和室内分析相结合的方法,调查黄土丘陵区浅色藻结皮、深色藻结皮、藻+少量藓结皮、藓+少量藻结皮及藓结皮5类生物结皮的发育特征,并测定生物结皮层及结皮下0~2cm土层的土壤微生物数量和化学性质,最后分析了不同生物结皮发育特征和土壤化学性质与土壤微生物数量之间的相关性。【结果】研究区浅色藻结皮、深色藻结皮、藻+少量藓结皮、藓+少量藻结皮及藓结皮的结皮厚度分别为1.13,3.26,6.31,8.91,12.61mm,藻盖度分别为100%,98.67%,71.61%,27.33%,7.80%,藓盖度分别为0%,0.80%,24.90%,65.87%,81.30%。不同类型生物结皮土壤细菌数量占微生物总数的比例为53.12%~72.09%,放线菌所占比例为27.49%~46.80%,真菌所占比例为0.08%~0.92%。在生物结皮层,土壤微生物总数和细菌数量从浅色藻结皮到藓结皮总体呈增加趋势,藓结皮土壤细菌、放线菌和真菌数量显著高于其他生物结皮;在结皮下0~2cm土层,土壤微生物总数和放线菌数量表现为藓结皮>浅色藻结皮>深色藻结皮>藓+少量藻结皮>藻+少量藓结皮,藓结皮土壤细菌、放线菌和真菌数量显著高于其他生物结皮。在生物结皮层,藓结皮土壤细菌比例较藻结皮有所增加,放线菌比例相应减少,藓结皮真菌比例最高;藓结皮下0~2cm土层真菌比例显著大于其他生物结皮。垂直分布上,生物结皮层土壤细菌数量和比例、真菌数量和比例均大于结皮下0~2cm土层,但放线菌数量和比例小于结皮下0~2cm土层。在生物结皮层和结皮下0~2cm土层,不同类型生物结皮土壤化学性质存在明显差异。生物结皮层微生物总数、细菌数量和比例、真菌数量与藓盖度和结皮厚度呈显著或极显著正相关关系,放线菌比例与藓盖度和结皮厚度呈显著负相关关系。土壤微生物总数、细菌数量和比例、真菌数量和比例与土壤碳氮含量、碳氮比、电导率呈显著或极显著正相关关系,细菌数量和比例、真菌数量和比例与土壤pH值呈显著或极显著负相关关系。【结论】生物结皮对半干旱地区土壤微生物具有重要影响,藓结皮较其他生物结皮可显著提高土壤微生物数量。

杉木人工林不同发育阶段土壤性质变化的研究

通过对杉木幼龄林、中龄林、近熟林、成熟林和过熟林5个发育阶段下土壤主要理化性质和生物学性质的分析,探讨了杉木不同发育阶段对土壤性质的影响。结果表明:土壤密度、孔隙度、饱和持水量和田间持水量均受到林木生长的显著影响,这种影响在表层最强烈;土壤有机质含量、全氮量、碱解氮含量和速效钾含量以及土壤细菌、放线菌和真菌数量都表现出幼龄林阶段较高、其后开始明显下降且多数指标在近熟林阶段达到最低、成熟林阶段显著提高、至过熟林阶段达到整个生长发育最高水平的规律性变化。相关分析表明:土壤理化性质表现出的规律性变化与不同阶段下土壤微生物状况的改变密切相关。土壤有效磷含量仅在近熟林—成熟林阶段有显著增加,其他阶段变化不显著。在中龄林和近熟林阶段土壤出现明显的负向极化变化趋势,在该阶段进行整地、施肥等营林措施可能会对林木生长有良好的促进作用。

我国水土保持“十一五”建设目标与任务

我国是世界上水土流失最严重的国家之一。多年来,水土流失防治工作取得巨大进展。遥感调查表明,20世纪80年代以来,我国水土流失加剧的趋势初步得到控制,但总体形势依然严峻。“十一五”期间,水土保持工作要以科学发展观为指导,围绕全面建设小康社会的目标,加强预防监督,抓紧重点治理,促进生态自我修复,搞好科技推广,完善监测预报,基本遏制水土流失、生态恶化的趋势。

不同树龄杨树人工林的根系呼吸季节动态

根系呼吸是准确评估森林生态系统土壤碳收支的一个重要依据。基于LI-COR-6400-09土壤呼吸系统连续2a测定的3个生长阶段杨树人工林的根系呼吸数据,分析了根系呼吸的季节变化规律及树龄、土壤水热因子和细根生物量对它的影响。结果表明:3个不同树龄人工林的根系呼吸速率均呈明显的季节变化,最大值出现在夏初,最小值出现在秋末,基本上与表层土壤温度的季节变化相一致。根系呼吸的峰值早于土壤温度和细根生物量的峰值,说明林木根系的季节生长节律、地下碳分配模式都可能影响根系呼吸的季节变化。2年生人工林的根系呼吸速率最高,平均为3.78μmolCO2m-2s-1,并随树龄增长呈下降趋势。3个树龄人工林根系呼吸占土壤呼吸的比例介于38.6%-58.0%之间,且2年生人工林最大。不同林龄之间根系呼吸的差异主要与根系的生长周转速率及代谢活性随生长阶段的变化有关。总的来说,表层土壤温度和细根生物量的协同作用可解释根系呼吸速率变化的76%。此外在评估一个轮伐期内的根系呼吸强度时,应考虑不同生长阶段对它的影响。