Primary productivity in patches of heterogeneous swards after 12 years of low-intensity cattle grazing

In low-intensity grazing systems, patch grazing leads to a mosaic structure of short (frequently defoliated) and tall (rarely defoliated) patches, with the stocking rate determining the proportion of these patch types on the pasture. Little is known about the long-term effects of patch grazing on the productivity of contrasting sward height patches developed under varying stocking rates. On a 12-year low-intensity cattle pasture we investigated aboveground net primary productivity (ANPP) and its seasonal variation in different patch types (‘short’, ‘medium’ and ‘tall’) under three stocking rates (‘moderate’, ‘lenient’ and ‘very lenient’) over two years. Additionally, we determined stocks of soil phosphorus, potassium and magnesium as well as soil pH. ANPP was affected by an interaction of patch type and stocking rate and ranged from less than 300 g/m² in short patches under very lenient stocking to more than 1,000 g/m² in medium patches under moderate stocking. In contrast with observations at the start of the experiment, ANPP in short patches was similar to or less than that in medium and tall patches. As topsoil phosphorus and potassium stocks were lowest in short patches, this indicates a long-term redistribution of nutrients by grazing animals, which limits short-patch productivity. Productivity of medium patches increased with stocking rate, and soil potassium concentration showed a similar trend, pointing towards enhanced nutrient cycling under more intensive stocking. We conclude that nutrient redistribution may lead to increasing trade-offs between ecological and agronomic aims in long-term low-intensity grazing systems.     

Rain Use Efficiency,Primary Production and Rainfall Relationships in Desert Rangelands of Tunisia

Desert rangelands are characterised by low and highly variable rainfall regime, low forage production and high heterogeneity in the distribution of natural resources. This study was carried out in the desert rangelands of Tunisia to evaluate the response of different rangelands to annual rainfall in terms of aboveground net primary production (ANPP) and rain use efficiency over a 10‐year period (2003–2012). In general, ANPP values were relatively low (123 kg DM ha⁻¹ y⁻¹) but would tend to increase with increasing annual rainfall for all rangeland types. The highest value of ANPP was observed from Stipagrostis pungens and Hammada shmittiana communities (sandy‐soil) during the wet year 2011. In contrast, rain use efficiency tends to decline with the highest annual rainfall and varies among rangeland types and with an average of 1·9 kg DM ha⁻¹ mm⁻¹ y⁻¹. Rain use efficiency tended to be higher during dry years and lower during wet years and tended to be higher on S. pungens and H. shmittiana (sandy‐soils) and lower on Helianthemum kahiricum (loamy soils). Therefore, understanding how rainfall affects productivity in rangelands is critical for predicting the impact of land degradation on the functioning of these ecosystems. It can be used to explain production decline associated with desertification as well as to assess rangeland conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

呼伦贝尔草甸草原地上净初级生产力对气候变化响应的模拟

利用内蒙古呼伦贝尔草原额尔古纳右旗牧业气象试验站1994-2009年牧草生长季逐月实测资料,对CENTURY模型进行检验,模拟了呼伦贝尔草甸草原1961-2010年间地上净初级生产力(ANPP)动态,并与26个气象因子进行相关性分析。模型检验结果显示,生长季内逐月地上生物量模拟值与观测值之间的相关系数为R²=0.53,斜率b=0.94,误差平方根值为72.07 g/m²,平均绝对百分比误差为38.02%。检验结果表明,CENTURY模型能够成功地模拟这类草原的季节动态和年际变化。在过去的50年中,呼伦贝尔草甸草原温度增加,降水略增,ANPP增加。相关分析表明,ANPP与生长季降水量(r=0.372)呈极显著正相关;与年平均最低气温、年平均地面气温、年平均气温、7月降水量呈显著正相关;与年平均风速(r=-0.382)呈极显著负相关;与其他气象因子无显著的相关关系。应用区域气候模式系统PRECIS输出的2021-2050年气候情景数据分析得出,在SRES B2、A2和A1B情景下,未来呼伦贝尔草甸草原平均最高气温和最低气温都将呈显著升高趋势,降水量略增,ANPP虽然在年际间存在波动,但总体呈明显增加态势,分别较基准时段增加了67.14%,69.65%和76.58%,增加速率分别为16.51,17.34和16.42 g/(m²·10 a)。在3种情景下,未来气候变化均会对呼伦贝尔草甸草原群落生产力产生显著的正面影响。     

Fall Water Effects on Growing Season Soil Water Content and Plant Productivity

Understanding fall precipitation effects on rangelands could improve forage production forecasting and inform predictions of potential climate change effects. We used a rainout shelter and water addition to test effects of seasonal precipitation on soil water and annual net primary production of C₃ perennial grass, C₄ perennial grass, annual grasses, forbs, and all plants combined. Treatments were 1) drought during September−October and April−May (DD); 2) drought plus irrigation during September−October and drought during April−May (WD); 3) year-long ambient conditions (WW); and 4) ambient plus irrigation during September−October (W + W). Treatments created conditions ranking among the driest and wettest September−October periods since 1937. Fall water effects on soil water were not detectable by May at 15 cm and 30 cm. Effects persisted into July at 60 cm and 90 cm, depths below the primary root zone. With spring drought, annual net primary production was 344 kg ha⁻¹ greater when the previous fall was wet rather than dry. No differences were detected between fall water treatments when spring was wet and fall was about 184% (1 938 ± 117 kg ha⁻¹) or 391% of the median (1 903 ± 117 kg ha⁻¹). Fall water increased C₃ perennial grass when spring was also wet and had no effect under spring drought, when forage production concerns are greatest. Fall water did not affect C₄ perennial grass, and extremely wet fall conditions reduced forb production about 50%. The greatest effect of fall water was increased annual grass production. Even record high levels of fall water had minor effects on biomass, functional group composition, and soil water that were short-lived and overwhelmed by the influence of spring precipitation. Movement of fall water to deep soil by the growing season suggests plants that would most benefit from fall precipitation are those that could use it during fall (winter annuals), or deep-rooted species (shrubs).     

浑善达克沙地地上净初级生产力动态及对气候变化的响应

利用2004?2018年多伦县生态气象观测站牧草观测资料，对CENTURY模型进行参数初始化和适用性检验，模拟了浑善达克沙地1961?2018年地上净初级生产力(above-ground?net?primary?production, ANPP)动态。模型检验结果显示，观测值与模拟值的决定系数R2 = 0.78，斜率b = 1.04，P < 0.01，误差平方根值为25.23 g·m?2，平均绝对百分比误差为45.76%。检验结果表明，CENRUTY模型可以较好地模拟浑善达克沙地地上生物量的动态变化。通过对1961年以来研究区气候变化的分析，发现该地区年平均气温与年极端最高气温均呈增加态势，且增加趋势显著，增加速率分别为0.4和0.3 ℃·(10 a)?1。年降水量与生长季降水量年际波动较大，变化趋势均不明显。ANPP年际间波动明显，但无明显变化趋势。通过因子分析法发现，增温是沙地气候变化的主要特征；Pearson相关分析表明，ANPP与生长季降水量、年极端最高气温呈极显著相关关系，牧草主要生长季降水量与年极端最高温度是影响浑善达克沙地ANPP的关键气象因子。     

Suitability of two laboratory testing methods to evaluate the side effects of pesticides on Typhlodromus pyri Scheuten (Acari: Phytoseiidae)

BACKGROUND: Laboratory results of the French ANPP/CEB guideline No. 167 and IOBC/WPRS Ring Testing Group methods for testing the side effects of pesticides on the predatory mite Typhlodromus pyri Scheuten were compared with respect to their suitability to evaluate the toxicity of three pesticides. RESULTS: Results obtained with the ANPP/CEB guideline allow the demonstration of significant differences between two slightly toxic products, a dichlofluanid 500 g kg(-1) kWP (Euparen) 50WP) and a quinoxyfen 250 g L(-1) SCC (Legend), and a highly toxic cymoxanil 60/mancozeb 200/folpet 275 g kg(-1) WP [Remiltine F Pepite) (RFP)], on the basis of bioassays conducted in the laboratory. In contrast, results obtained with the IOBC/WPRS method classified all three as harmful.CONCLUSION: The evaluation of the toxicity of RFP revealed that the concentration, the quantity of the wet deposit and the food source used in the IOBC/WPRS method maximise the toxicity, in comparison with those used in the ANPP/CEB protocol. Valid criteria in controls were all respected in the ANPP/CEB tests but not in the IOBC/WPRS samples. This result revealed difficulties related to the use of the IOBC/WPRS method in laboratories.     

开垦天然草地种植冰草和小麦对草地生产力和土壤碳储量的影响

[目的]为更加合理地利用和管理草地,保证草地可持续发展提供理论指导。[方法]选取代表性品种多年生牧草冰草和一年生作物小麦研究开垦天然草地对草地地上净初级生产力ANPP和草地土壤碳储量的影响 选取2个植被组成和土壤类型均不同的样地进行ANPP和土壤碳储量的对比研究。[结果]结果表明：ANPP和0~2×109、0~12×109g/hm2土壤碳储量显著受到样地和种植处理的影响（P〈0.05）。开垦天然草地种植冰草13/12年后,ADRI和Onefour样地的ANPP降低,而种植小麦使ANPP增加。开垦天然草地种植冰草13/12年土壤碳储量和对照相比无显著变化而种植小麦使土壤碳储量显著降低。ADRI样地3个处理的ANPP和土壤碳储量均显著高于Onefour样地的ANPP和土壤碳储量（P〈0.05）。加拿大混合普列里草地类型上,草地ANPP和土壤碳储量呈线性正相关关系（P〈0.0001）。[结论]加拿大混合普列里草地类型上,开垦天然草地种植冰草和小麦13或12年后使草地生产力发生明显变化。     

半干旱区沙质草地生态系统碳循环关键过程对水肥添加的响应

为探寻半干旱区草地生产力进一步恢复的主要限制因素,该文采用3因素2水平析因设计对草地进行水（0,80 mm）、氮（0,20 g/(m[[sup]]2[[/sup]]·a)）、磷（P2O5）（0,10 g/(m[[sup]]2[[/sup]]·a)）添加实验,研究了2004年地上净初级生产力（ANPP）与土壤呼吸的响应. 8种处理分别为添加水（W）、加氮肥（N）、加磷肥（P）、加水+氮肥（WN）、加水+磷肥（WP）、加氮肥+磷肥（NP）、加水+氮肥+磷肥（WNP）和对照（CK）,每种处理6次重复,随机分配在48个4 m × 4 m的样方中. 研究结果表明:施氮肥不仅增加了ANPP,而且推迟了植物生长高峰期; 草地生产力明显受到氮素的制约,水分和磷素并不是该生态系统的主要限制性因子; 土壤呼吸7月份最高;干旱期添加水与不添加水处理的CO2排放速率差异显著; 添加水增加了土壤CO2的排放速率,但是施磷肥对土壤呼吸存在抑制效应. 建议对半干旱区沙质草地的管理应以施氮肥为主,辅以磷肥,不宜灌溉.      

Effects of 34 Years of Experimentally Manipulated Burn Seasons and Frequencies on Prairie Plant Composition

Historically, tallgrass prairie burns occurred at many seasons and frequencies. Currently, tallgrass prescribed burns often occur annually in the spring, usually for cattle forage production. Altering burning season and frequency is known to affect plant composition and biomass production, but researchers are still uncertain how burning season and frequency interact. We present the long-term effects of a factorial combination of different burn seasons (spring, summer, autumn, or variable [rotated through seasons]) and frequencies (annual or quadrennial) on the plant composition and biomass production of an ungrazed, restored tallgrass prairie in eastern Nebraska, United States. The experimental plots were established in 1978 and visually surveyed for baseline data in 1979 and 1981. Experimental burn treatments were begun in 1982. Plots were visually surveyed until 2011 with the following results: 1) annual spring and summer burns increased C₄ graminoid abundance; 2) annual autumn burns increased forb abundance; 3) burn season had little effect on plant composition for quadrennial burns; and 4) variable season burns generally led to plant composition that was intermediate between annual spring/summer and annual autumn burns. We also clipped biomass to estimate aboveground annual net primary production (ANPP) in 2015, a year in which both annual and quadrennial burns occurred. Total ANPP did not differ significantly between burn frequencies nor between spring and autumn burns (772 g m^? 2 average) but was lower in summer burns (541 g m^? 2). ANPP results were similar to visual surveys, with significantly higher C₄ graminoid ANPP in spring than autumn burns and significantly lower forb and C₃ graminoid ANPP in spring than autumn burns. Overall, these results suggest autumn burns can increase forb and C₃ graminoid abundance, without strongly affecting total ANPP relative to spring burns. Future studies should compare plant and livestock production between spring and autumn burns in grazed fields.     

Responses of Plant Community and Soil Properties to Inter-Annual Precipitation Variability and Grazing Durations in a Desert Steppe in Inner Mongolia

Grazing can dramatically affect arid grassland communities that are very vulnerable to environmental changes due to its relatively short and sparse ground coverage, low biomass, sandy soil and inter-annual precipitation found in the desert steppe. The study investigates the effects of different grazing durations on vegetation and soil properties of a desert steppe community. The experiment was conducted in Xisu Banner in Inner Mongolia with ifve treatments：CG （continuous grazing）, 40UG （40 d ungrazed）, 50UG （50 d ungrazed）, 60UG （60 d ungrazed） and UG （ungrazed）. The biomass of both shrub and annual-biennial plant communities were signiifcantly decreased by CG. Continuous grazing and 40UG signiifcantly reduced the ANPP （aboveground net primary productivity） by the end of the three year study. 60UG treatment increased soil organic carbon （OC）, total nitrogen concentration （TN） and total phosphorus concentration （TP） concentrations and 50UG increased the TN and total phosphorus concentration （TK） concentrations, whereas CG, 40UG and 50UG decreased soil OC, TP and available phosphorus concentration （AP） concentrations. The perennial plant species of the desert steppe were generally tolerant for grazing. The annual-biennial plant species had large variability in ANPP because of the inter-annual precipitation. Our results highlight that inter-annual precipitation variations could strongly modify the community responses to grazing in arid ecosystems.