Impact of land degradation on soil respiration in a steppe (Stipa tenacissima L.) semi-arid ecosystem in the SE of Spain     

A. Rey  E. Pegoraro  A. Were  J. Raimundo 《Soil biology & biochemistry》2011,43(2):393-1861

Climate change scenarios predict increases in temperature, changes in precipitation patterns, and longer drought periods in most semi-arid regions of the world. Ecosystems in these regions are prone to land degradation, which may be aggravated by climate change. Soil respiration is one of the main processes responsible for organic carbon losses from arid and semi-arid ecosystems. We measured soil respiration over one year in two steppe ecosystems having different degrees of land degradation under three ground-covers: with vegetation, bare soil, and an intermediate situation between plants and bare soil.The largest differences in soil respiration rates between the sites were observed in spring, coinciding with the highest level of plant activity. The degraded site had drier and hotter soils with less soil water availability and a longer drought period. As a result, vegetation on the degraded site did not respond to spring rainfall events. Soil respiration showed a strong seasonal variability, with average annual rates of 1.1 and 0.8 μmol CO₂ m⁻² s⁻¹ in the natural and degraded sites, respectively. We did not observe significant differences in soil respiration rates associated with ground-cover i.e., the temporal variation was much larger than the spatial variation. At both sites, soil moisture was the controlling driver of soil respiration for most of the year, when temperatures were above 20 °C and constrained the response to temperature for the few months when the temperature was below 20 °C. An empirical model based on soil temperature and soil moisture explained 90% and 72% of the seasonal variability of soil respiration on the natural and degraded sites, respectively. For the first time, this study suggests that land degradation may alter the carbon balance of these ecosystems through changes in the temporal dynamics of soil respiration and plant productivity, which have important negative consequences for ecosystem functioning and sustainability.  相似文献   

Rhizospheric and heterotrophic respiration of a warm-temperate oak chronosequence in China     

Junwei Luan  Shirong Liu  Jingxin Wang 《Soil biology & biochemistry》2011,43(3):503-512

Plot trenching and root decomposition experiments were conducted in a warm-temperate oak chronosequence (40-year-old, 48-year-old, 80-year-old, and 143-year-old) in China. We partitioned total soil surface CO₂ efflux (R_S) into heterotrophic (R_H) and rhizospheric (R_R) components across the growing season of 2009. We found that the temporal variation of R_R and R_H can be well explained by soil temperature (T₅) at 5 cm depth using exponential equations for all forests. However, R_R of 40-year-old and 48-year-old forests peaked in September, while their T₅ peaks occurred in August. R_R of 80-year-old and 143-year-old forests showed a similar pattern to T₅. The contribution of R_R to R_S (RC) of 40-year-old and 48-year-old forests presented a second peak in September. Seasonal variation of R_R may be accounted for by the different successional stages. Cumulative R_H and R_R during the growing season varied with forest age. The estimated R_H values for 40-year-old, 48-year-old, 80-year-old and 143-year-old forests averaged 431.72, 452.02, 484.62 and 678.93 g C m⁻², respectively, while the corresponding values of R_R averaged 191.94, 206.51, 321.13 and 153.03 g C m⁻². The estimated RC increased from 30.78% in the 40-year-old forest to 39.85% in the 80-year-old forest and then declined to 18.39% in the 143-year-old forest. We found soil organic carbon (SOC), especially the light fraction organic carbon (LFOC), stock at 0-10 cm soil depth correlated well with R_H. There was no significant relationship between R_R and fine root biomass regardless of stand age. Measured apparent temperature sensitivity (Q₁₀) of R_H (3.93 ± 0.27) was significantly higher than that of R_R (2.78 ± 0.73). Capillary porosity decreased as stand age increased and it was negatively correlated to cumulative R_S. Our results emphasize the importance of partitioning soil respiration in evaluating the stand age effect on soil respiration and its significance to future model construction.  相似文献   

Trichothecene genotypes of Gibberella zeae from winter wheat fields in the eastern USA     

D. G. Schmale  A. K. Wood‐Jones  C. Cowger  G. C. Bergstrom  C. Arellano 《Plant pathology》2011,60(5):909-917

Fusarium head blight (FHB), caused principally by Gibberella zeae (Fusarium graminearum), is a devastating disease of small grains such as wheat and barley worldwide. Grain infected with G. zeae may be contaminated with trichothecene mycotoxins such as deoxynivalenol (DON) and nivalenol (NIV). Strains of G. zeae that produce DON may also produce acetylated derivatives of DON: 3‐acetyl‐DON (3‐ADON) and 15‐acetyl‐DON (15‐ADON). Gradients (clines) of 3‐ADON genotypes in Canada have raised questions about the distribution of G. zeae trichothecene genotypes in wheat fields in the eastern USA. Tri3 and Tri12 genotypes were evaluated in 998 isolates of G. zeae collected from 39 winter wheat fields in New York (NY), Pennsylvania (PA), Maryland (MD), Virginia (VA), Kentucky (KY) and North Carolina (NC). Ninety‐two percent (919/998) of the isolates were 15‐ADON, 7% (69/998) were 3‐ADON, and 1% (10/998) was NIV. A phylogenetic analysis based on portions of three genes (PHO, RED and URA) from 23 isolates revealed two species of Fusarium (F. graminearum sensu stricto and one isolate of F. cerealis (synonym F. crookwellense)). An increasing trend of 3‐ADON genotypes was observed from NC (south) to NY (north). Punctuated episodes of atmospheric transport may favour a higher frequency of 3‐ADON genotypes in the northeastern USA, near Canada, compared with the mid‐Atlantic states. Discoveries of the NIV genotype in NY and NC indicate the need for more intensive sampling in the surrounding regions.  相似文献   

双江县竹类资源及主要竹种竹材造纸性能评定   总被引：3，自引：0，他引：3  

辉朝茂  王文久 《西南林学院学报》1993,13(2):79-86

本文系统记载了双江县竹类资源及其分布情况,计有竹种11属23种,竹林面积4816.4公顷,竹材蓄积量36.93万吨。对5种主要竹种进行了造纸性能分析及综合评定,提出了适宜该区发展的优良竹种,可为该县竹业生产及纸厂建设提供可靠依据。  相似文献   

负水头条件下的水平一维土壤吸渗特征   总被引：4，自引：1，他引：4       下载免费PDF全文

辛琛  王全九  樊军 《农业工程学报》2007,23(9):20-26

该文分析了不同负水头条件下土壤水分运动特征，并通过室内模拟试验研究了不同负水头条件下水平一维土壤的吸渗特征，根据Brooks-corey模型推求了描述负水头条件下土壤吸渗公式，并分析了各参量间的函数关系。分析了Philip吸渗公式在负水头条件下的适用性，并对所建立的公式进行检验。研究结果表明：上述理论关系可以很好描述负水头条件下水平一维土壤吸渗过程。  相似文献   

基于不等扬程的离心式长轴泵的优化设计与试验     

朱荣生  贺博  付强  王秀礼  张亮亮 《农业工程学报》2015,31(5):38-45

为使离心式长轴泵能够在不同工况下高效运行,该文以500GJC-32.3×3型离心式长轴泵为例,对其进行优化,首先根据传统方法估算离心式长轴泵叶轮参数,通过正交方法对离心式长轴泵叶轮进行优化设计,对正交试验结果进行极差分析,得到了叶轮几何参数对离心式长轴泵扬程和效率影响的主次顺序。综合考虑各参数对离心式长轴泵性能的影响,选取重要因素,基于不等扬程设计理论,采用控制变量法对叶轮进行多方案优化设计,对比不同方案计算结果可知:基于不等扬程理论优化设计的叶轮具有较好的水力性能,选择合适的后盖板无穷叶片数理论扬程系数,可使叶轮水力性能趋于最佳。对于该型离心式长轴泵,当后盖板无穷叶片数理论扬程系数取1.1时可获得较优的水力性能,对比较优方案的试验与计算结果可知:二者变化趋势相同,扬程、效率、轴功率的最大误差分别为4.02%、5.58%、3.59%,在(0.8~1.2)倍设计流量工况下,扬程、效率、轴功率的误差小。同时由试验可知:该型离心式长轴泵在设计流量时扬程大于97 m,效率高于82%,最高效率点出现在1.1倍设计工况附近为83.22%,曲线具有较宽的高效区和无过载特性,能够满足设计要求,在丰水期和枯水期均能高效稳定的运行,同时可降低电机的配套功率,减少一次成本投入。因此,该文的研究结果对离心式长轴的优化设计有较好的参考价值。  相似文献   

Root colonisation by arbuscular mycorrhizal, fine endophytic and dark septate fungi across a pH gradient in acid beech forests     

Jacqueline W.M. Postma  Pål Axel Olsson  Ursula Falkengren-Grerup 《Soil biology & biochemistry》2007,39(2):400-408

Colonisation by root endophytes can be beneficial to plants growing on acid, nutrient-poor soils. Arbuscular mycorrhizal (AM) fungi can supply herbs with nutrients and may give protection against aluminium toxicity. Two other root colonising fungi, fine endophytes (FE) and dark septate fungi (DSE), are less well known but are potentially of benefit to their host plant. AM fungi are the most prevalent symbionts in herbs at neutral to acidic soil pH. At extremely low pH, fungal growth can be limited and AM colonisation is usually rare. Fine and dark septate endophytes, on the other hand, have been observed more often under these conditions. In order to relate endophyte colonisation to a gradient in soil pH, we investigated root colonisation by AM, FE and DSE in Maianthemum bifolium, Galium odoratum, Mercurialis perennis and Stellaria nemorum, from a range of acidic beech forests. With decreasing pH, colonisation by AM decreased, whereas the other two endophytes increased. AM and FE colonisation were inversely correlated in Maianthemum bifolium. We compared changes in root colonisation with those in chemical composition of soil and leaf samples and found a positive correlation between leaf magnesium concentrations and the presence of DSE in Galium odoratum. Aluminium concentration in Maianthemum bifolium tended to be lower when FE colonisation was high, suggesting a possible role for the fungi in plant protection against Al. We suggest that FE and DSE may replace AM fungi in herbaceous vegetation at extremely low pH, counteracting some of the negative effects of high soil acidity on plants.  相似文献   

关于河源梁涧区重点治理分析──以32条重点治理小流域为例     

高永海 《水土保持通报》1994,14(5):42-47

河源梁涧区为黄土丘陵沟壑区的重要地貌类型。该对河源梁涧区的地形地貌特征作了详细描述，通过实地调查，并结合３２条重点小流域治理，对该区进行了系统的分析及经验总结，特别是对固沟保涧，引洪漫地作了深入的分析，提出了河源梁涧区的治理模式，对该区治理与开发具有拽导意义。  相似文献   

基于FLOW-3D的田间便携式短喉槽水力性能数值模拟     

肖苡辀  王文娥  胡笑涛 《农业工程学报》2016,32(3):55-61

田间量水是实现灌区计划用水和节水农业的关键技术,但由于试验条件、测量方法和精度的限制,传统的水工模型试验分析田间量水设施的水力性能存在一定局限性。该文基于FLOW-3D软件,采用RNG k-ε三维湍流模型、Tru VOF方法、FAVOR(fractional area volume obstacle representation)技术模拟喉口宽度为51 mm的田间便携式短喉槽过槽水流的三维流场。与试验结果对比表明:过流能力、水流流态以及水深与试验结果较为吻合,误差小于10%,采用的数值模拟方法能够有效地模拟田间便携式短喉槽水力性能,在确定数值模拟可靠性的前提下,对其水力性能进行分析。数值模拟结果显示:佛汝德数、流速在自由出流工况下沿程增大,在淹没出流条件下先增大后减小,并由佛汝德数分析结果确定了临界水深断面所在区域为喉口段后半部分;通过回归分析得到的田间便携式短喉槽上游水深与流量计算公式最大测流误差为-5.63%,满足灌区量水精度的要求;该量水槽最大水头损失占总水头的12.10%,相比于长喉道量水槽的13%较小。该研究对提高量水设备研发效率、降低研发成本与周期、促进中国灌区流量精准测量设备的推广具有实用价值。  相似文献   

Estimation of the amount of nutrients in livestock manure   总被引：1，自引：0，他引：1  

Kazunori KOHYAMA  Masayuki HOJITO  Hiroyuki SASAKI  Shoji MATSUURA 《Soil Science and Plant Nutrition》2006,52(4):576-577

  相似文献