Biomass Production and Net Ecosystem Exchange Following Defoliation in a Wet Sedge Community

Riparian ecosystems provide many ecosystem services, including serving as an important forage resource for livestock grazing operations. We evaluated defoliation impacts on above- and belowground production, and net ecosystem exchange of CO₂ (NEE), in a wet sedge (Carex nebrascensis Dewey)-dominated plant community. In June or July of 2004–2005, experimental plots were clipped to 10 cm stubble height and paired control plots left unclipped. All plots were clipped to 2.5 cm in mid-September, and end-of-season and season-long aboveground production calculated. Root ingrowth cores were used to estimate annual root production and root length density (RLD). A portable gas exchange system and plexiglass chamber were used to measure NEE in 2005. An elevated water table in 2005 vs. 2004 was associated with higher (P &spilt; 0.001) season-long aboveground production (about double), but lower (P ≤ 0.05) belowground production (about half). Total productivity did not differ between years, but below-:aboveground ratios were 3× higher in 2004 vs. 2005. RLD was not different between years (P &spigt; 0.05). Clipping reduced (P ≤ 0.05) end-of-season aboveground standing crop by 33% to 73% depending on clipping month and year. Effects of clipping month on season-long aboveground production were inconsistent between years; June clipping decreased (P ≤ 0.05) production (-10%) in 2005 and July clipping decreased (P ≤ 0.05) production (-25%) in 2004. NEE for June-clipped plots recovered within 1 mo of clipping, whereas NEE for plots clipped in July remained below unclipped levels at the end of the growing season. Water table levels strongly influenced below-:aboveground ratios, although total production was relatively stable between years. Year effects overwhelmed clipping effects on season-long aboveground production. Defoliation after mid-summer did not allow recovery of photosynthetic capacity by the end of the growing season, suggesting the potential for long-term impact with regular late-season defoliation.     

Spatial and Temporal Variability in Aboveground Net Primary Production of Uruguayan Grasslands

Aboveground net primary production (ANPP) is a variable that integrates many aspects of ecosystem functioning. Variability in ANPP is a key control for carbon input and accumulation in grasslands systems. In this study, we analyzed the spatial and temporal variability of ANPP of Uruguayan grasslands during 2000–2010. We used enhanced vegetation index (EVI) data provided by the MODIS-Terra sensor to estimate ANPP according to Monteith's (1972) model as the product of total incident photosynthetically active radiation, the fraction of the radiation absorbed by green vegetation, and the radiation use efficiency. Results showed that ANPP varied spatially among geomorphological units, increasing from the north and midwest of Uruguay to the east and southeast. Hence, Cuesta Basáltica grasslands were the least productive (399 g DM · m^-2 · yr^-1), while grasslands of the Sierras del Este and Colinas y Lomas del Este displayed the highest productivity (463 and 465 g DM · m^-2 · yr^-1, respectively). This pattern is likely related to differences in soil depth and associated variation in water availability among geomorphological units. Seasonal variability in ANPP indicated peak productivity in the spring in all units, but differences in annual trends over the 10-yr study period suggested that ANPP drivers are operating spatially distinct. Understanding the spatial and temporal variability of ANPP of grasslands are prerequisites for sustainable management of grazing systems.     

Defoliation Timing Effects on Spotted Knapweed Seed Production and Viability

Spotted knapweed (Centaurea stoebe L.), a perennial invasive forb that reproduces largely by seed, often forms new flowers after prescribed sheep grazing or mowing is applied during the bolting or flowering stage. It is unknown if these new flowers produce viable seeds by the end of the growing season. The purpose of this 2-yr study was to determine the appropriate timing (or timings) or combination (or combinations) of timings of defoliation on spotted knapweed to reduce its viable seed production. Spotted knapweed plants on foothill rangeland in west-central Montana were hand-clipped at seven different timings and frequencies of defoliation: June (bolting stage); July (late-bud–early flowering stage); August (full-flowering stage); June + July; June + August; July + August; or June + July + August. Unclipped plants were controls. Plants clipped in the bolting stage were defoliated at 35–40% relative utilization. Plants clipped at all other timings had 100% of their buds and flowers removed, plus 3 cm of each bud or flower stem. Plant response was evaluated from mid-August through September, whenever the seed heads of each treatment’s plants reached maturity but while their seed-head bracts remained tightly closed. Clipping at any timing or combination of timings reduced the number of buds and flower heads per plant (P < 0.01), number of seeds per plant (P < 0.01), percentage of viability of seeds (P < 0.01), and number of viable seeds per plant (P < 0.01) compared with no clipping. Clipping during the bolting stage reduced the number of viable seeds by nearly 90% compared with no clipping. Clipping during the late-bud–early-flower or full-flower stage reduced the number of viable seeds by nearly 100% compared with no clipping. Spotted knapweed defoliation via prescribed sheep grazing or mowing in summer should suppress viable seed production of spotted knapweed.     

不同放牧率对草原牧草再生性能和地上净初级生产力的影响

在生长季研究不同放牧率对草原牧草再生性能和地上净初级生产力的影响。结果表明,随着放牧率的增大,地上现存量呈线性下降,但地上净初级生产力(地上现存量＋家畜采食量)以2.67只羊/hm²处理最大,即存在超补偿性生长。地上最大现存量和最大净初级生产力出现的日期随着放牧率的增大有提前的趋势,二者随着放牧年限的延长均有较大幅度的下降。但降水可以缓和或加剧此变化的趋势。在冷蒿小禾草退化草原上,1.33和2.67只羊/hm²始牧时期为5月中下旬为宜,而重度放牧宜在6月上、中旬;重牧或过度放牧可降低牧草早期的再生能力,但可加快后期的再生速度,即后期牧草补偿性生长较明显。     

Estimating Aboveground Net Primary Production in Grasslands: A Comparison of Nondestructive Methods

Aboveground net primary production (ANPP) is an important ecosystem property that is affected by environmental variability. ANPP in grasslands is typically measured by clipping peak live plant material. However, this method is time intensive (and therefore expensive), making it difficult to capture spatial and temporal variability. Additionally, it is impractical to use a destructive method to estimate ANPP in long-term, permanent plots. Thus, many double-sampling techniques have been developed to reduce costs and increase sample size. The objective of our study was to assess the accuracy and precision of nondestructive techniques to estimate ANPP as supplements to the traditional method of peak biomass harvest at two grassland sites. We harvested biomass and compared estimates from the same plots to 1) canopy interception using a point frame, 2) green cover estimates derived from a digital camera, and 3) reflectance measurements using a handheld radiometer. We calculated the optimum allocation of sampling effort to direct and indirect methods to minimize sampling cost yet achieve a desired precision. We found that the point frame technique explained the highest proportion of the variability in biomass at both sites (R² = 0.91, 0.90). However, our cost-optimization analysis revealed that the radiometer technique, although less accurate (R² = 0.38, 0.51), could achieve a desired precision for lower labor costs than the point frame. The radiometer and point frame methods will be a useful tool for grassland ecologists and rangeland managers who desire fast, nondestructive estimates of ANPP.     

Grazing Abandonment Delays the Effect of Temperature on Aboveground Net Primary Production in Atlantic Grasslands

We used an Atlantic grassland system on the Iberian Peninsula to ascertain whether monthly climate variability explains variation in monthly aboveground net primary production (ANPP) and to test whether climate-ANPP relationships depend on grazing regime. In 2005, large herbivores (beef cattle, dairy sheep, and horses) were excluded through fencing three 2 500-m² plots, each located in a different location; adjacent grazed plots of equal size were established. ANPP was measured monthly during the next three growing periods (2006 ? 2008), and locally measured climate data were obtained from a public database. Because between-site variation in annual ANPP was not significant, we used data averaged across sites to test for the effect of monthly climate variability on monthly ANPP by means of dynamic regression. Enhanced ANPP was found after grazing abandonment, probably due to the sudden dominance of productive graminoids. Variation in monthly rainfall did not contribute to explain monthly ANPP under grazing or grazing exclusion. Simultaneous mean monthly air temperature explained monthly ANPP under grazing. By contrast, the effect of temperature on ANPP under grazing exclusion was delayed by 1 mo. We suggest that this delay can be explained by the development of a thick organic layer (litter) that insulated the soil in the grazing exclusion plots. However, changes in floristic composition and, consequently, in phenology might also have contributed to the differential response.     

Defoliation Effects on Herbage Production and Root Growth of Wet Meadow Forage Species

Root growth is important to the competitive ability of plants, and understanding how herbage defoliation affects root growth has implications for development of management strategies. Objectives were to determine the effects of defoliation intensity and frequency on root characteristics and herbage production of slender wheatgrass (Elymus trachycaulus [Link.] Shinners), Nebraska sedge (Carex nebrascensis C. Dewey), and “Steadfast” birdsfoot trefoil (Lotus corniculatus L.). Plants of each species were transplanted into containers that had been placed in the ground at wet meadow field sites the prior year. There were eight replications of a control and five defoliation treatments, which were combinations of different frequencies (two or five times) and intensities (light or heavy) and haying. Treatments were applied for a single growing season, and aboveground biomass was collected. Containers were extracted in October, and plant crowns, rhizomes, and roots were separated from the soil. Defoliation treatment did not affect total root weight, length, and surface area of Nebraska sedge or birdsfoot trefoil (P>0.10). Slender wheatgrass total root weight was less when defoliated five times (4.46 g·container^?1) than when defoliated twice (6.62 g·container^?1) during the growing season. More frequent defoliation of slender wheatgrass also reduced length (20%) and surface area (21%) compared to less frequent defoliation. However, defoliation frequency did not affect aboveground biomass. Defoliation intensity did not affect aboveground production or root characteristics of the three species. Abundant soil moisture in meadows likely buffers negative effects of defoliation. For all species, two defoliation events (e.g., haying followed by grazing) does not appear to negatively affect root growth and herbage production.     

Glyphosate Alters Aboveground Net Primary Production,Soil Organic Carbon,and Nutrients in Pampean Grasslands (Argentina)

We have previously demonstrated that recurrent application of glyphosate causes dramatic shift in the vegetation structure of the native grasslands of Flooding Pampa. As these structural changes might alter functional processes such as primary production, carbon, nitrogen and phosphorus cycling, this study aims to evaluate functional changes associated with the application of glyphosate in these temperate grasslands. We measured aboveground net primary production (ANPP) during two consecutive years, and the concentration of organic carbon, nitrogen and phosphorus in the soil during the following six years after primary production measurements ended in glyphosate treated and non- treated (control) paddocks of a commercial livestock far. We related the vegetation data, basal cover, species richness and diversity, obtained in a previous study conducted in the same paddocks of the livestock farm, with ANPP data obtained in this one. Late summer applications of glyphosate greatly reduced the biomass contribution of warm-season perennial grasses and legumes and increased the contribution of cool season annual grasses, altering the seasonal pattern of ANPP. As the reduction of the spring and summer productivity could not be compensated by the increase of cool-season productivity, the annual ANPP was lower in the glyphosate-treated paddocks than in control paddocks. Glyphosate applications also decreased soil organic carbon and phosphorus concentration, probably because of the reduction of ANPP, the changes of its seasonal distribution and the shift in the floristic composition of the community, which may modify the amount and quality of the litter. We found a linear positive relationship between basal cover, species richness and species diversity with ANPP, which suggest that the negative effects on ecosystem functioning would be directly related with the changes in vegetation structure caused by glyphosate application.     

Fire,Defoliation, and Competing Species Alter Aristida purpurea Biomass,Tiller, and Axillary Bud Production

Aristida purpurea (purple threeawn) is a competitive native perennial grass with monoculturistic tendencies and poor palatability. We examined effects of fire, defoliation, and interspecific/intraspecific planting for 1) threeawn responses in the presence of threeawn, Bouteloua gracilis, or Pascopyrum smithii, and 2) B. gracilis and P. smithii response with threeawn. Biomass, aboveground production, tillers, and axillary buds were analyzed following two fire and four clipping treatments applied to three species–pair combinations in a completely randomized factorial design with nine replications. Fire killed 36% of threeawn. Fire reduced surviving threeawn biomass 61% and reduced production 27%. Threeawn production was greatest when neither plant was clipped and least when competing species were moderately clipped, or when both plants were severely clipped. Tiller counts of burned threeawn were similar among clipping treatments, and less than non-clipped or moderately clipped plants not burned. Fire decreased threeawn axillary buds on average by 25%. Moderately clipped plants had greater production than those from other clipping treatments across species. Average threeawn percentage of pot biomass was greater with B. gracilis (46 ± 3% SE) than P. smithii (38 ± 3% SE). Fire reduced threeawn from 60 ± 3% to 23 ± 3% of pot biomass, indicating good potential for rapid reductions in threeawn dominance and restoration of plant diversity with fire.     

锡林郭勒草原地上净第一性生产力遥感反演方法初探

探索了利用遥感方法进行牧草消耗量估测，进而进行大面积天然草原地上净第一性生产力估测的方法和技术流程。并以锡林郭勒草原为例，提出了利用MODIS-NDVI反演最高生物量期的牧草采食消耗昔，再利用地面获取的旬度采食系数，推算整个生长季的牧草采食消耗量的思路。在获得草原放牧消耗量基础上，反演了草原净第一性生产力。由于野外测量草原净第一性生产力和消耗量数据的难度较大，所以该方法中的定量分析缺乏对研究区草原净第一性生产力分布特征和消耗量的直接验证，有关反演的方法和可靠性仍有待于进一步验证。     

Estimating Aboveground Net Primary Production (ANPP) Using Landsat 8-Based Indices: A Case Study From Hir-Neur Rangelands,Iran

Aboveground Net Primary Production (ANPP), an indicator of ecosystems’ ability to capture and convert solar energy, is critical to evaluate and manage ecosystem carbon balance index including rangelands. Measuring ANPP over a large area is difficult at it varies with different factors including climate and anthropogenic, while satellite-based information shows strong opportunity. The aim of this study was to estimate the ANPP of Plant Functional Types (PFTs) using Landsat-8 imagery over the rangelands of Hir-Neur from Ardabil Province, Iran as a case study area. Landsat-8 Operational Land Imager (OLI) satellite images were collected on 9^th June 2017 aligning with the field sampling of PFTs ANPP. Eleven sampling sites with 10 plots at each site (locations recorded with a Global Positioning System, GPS) were selected along a transect with elevation gradient and the ANPP of PFTs were recorded. Twenty-two vegetation indices were calculated from the Landsat-8 imagery and the index values were extracted for the sampling plots. Correlation between derived indices and field collected ANPP data were calculated. Predictive relationships between PFTs and total ANPP and satellite indices were developed using a 3^rd-order polynomial model and the model was used to map the whole study area. The best estimation of PFTs and total ANPP was obtained using the Vegetation Index (VI3) for grasses (R²=0.47), Iron Oxide (IO) for forbs (R²=0.51), and Renormalized Difference Vegetation Index (RDVI) for shrubs (R²=0.50). The Difference Vegetation Index (DVI) was the best estimator for the total ANPP (R²=0.49). The overall accuracies of the maps were acceptable (MAE, MDE, RMSE <0.5). Results showed a difference when using PFTs for ANPP estimation in comparison with direct ANPP estimation. Thus, direct estimation of ANPP from the satellite based indices would be more accurate. This study also showed promising capabilities of the indices based on PFTs and total ANPP for estimating aboveground biomass, supply-demand balance and carbon balance at the study area and elsewhere with similar ecological conditions. This study also showed opportunity to select the most appropriate vegetation indices for the estimation of PFTs and the total ANPP.     

净能体系的优势及其在猪生产中的作用

净能体系相对于消化能体系和代谢能体系来说,能够更精确地评估饲料的能量含量,也能够更精确地预测猪的性能表现,在猪生产中采用净能体系将能给生产者带来更多利益。笔者就净能体系与消化能体系、代谢能体系的比较以及净能体系在猪生产中的作用进行了综述。     

松嫩平原西部草地净初级生产力时空格局

基于改进CASA模型估算得到的草地NPP,分析了2000～2009年松嫩平原西部草地NPP时空分布特征及变化趋势.结果表明:2000～2009年松嫩平原西部草地NPP总量在8.46～11.22Tg C之间,平均值为9.92Tg C,呈波动上升趋势;受气温、降水及太阳辐射季节变化的影响,NPP存在明显的季节变化,积累期主要集中在水热条件搭配较好的4～10月,占年度NPP总量的99.60％;2000～2009年,春、夏、秋、冬四季草地NPP平均值分别为6.82gC· m-2·a-1、79.68gC· m-2·a-1、13.57gC·m-2·a-1、0.09gC·m-2·a-1,即夏季＞秋季＞春季＞冬季.空间上,松嫩平原西部草地NPP由南向北呈明显增加趋势,最低值分布在吉林省境内的中部地区;2000～2009年,黑龙江省各年草地NPP均高于吉林省,说明在松嫩平原西部黑龙江省草地长势优于吉林省;基于像元的NPP年际变化趋势分析表明,占研究区总面积3/4的草地NPP表现为增加趋势,NPP显著增加的草地面积是显著降低面积的7.6倍,说明2000～2009年间松嫩平原西部草地长势呈明显好转趋势.     

不同披碱草属植物的形态分化和分类功能的构建

形态学是分类学中最常用的方法,但形态指标复杂多变且不易操作,因此有价值的形态指标尤为重要。披碱草属(Elymus)植物在我国分布广泛,形态特征差异较大,且其分类一直存在较多争议,集中体现了禾本科分类学上的难题。为了筛选具有较大分类价值的形态特征,本研究对我国9种披碱草40个种群材料的28个形态指标进行数量化测定,依据分类功能良好的指标应符合种内变异小而种间变异大的要求,通过UPGMA法(unweighted pairgroup method with arithmetic average)进行系统关系分析,并采用软件NTSYS-PC进行相关性和显著性分析,从4种组合的分类情况筛选分类功能指标,推荐14种有价值的指标用于披碱草属植物的分类。     

青海高原草地净初级生产力和降水利用效率时空特征

为了探究青海高原草地净初级生产力（Net primary productivity,NPP）和降水利用效率（Precipitation use efficiency,PUE）的时空特征,基于遥感估算的NPP数据和降水空间插值数据,采用地理空间统计法分析了2001—2017年青海高原草地NPP和PUE的时空特征。结果表明：2001—2017年青海高原草地NPP均值为42.81 gC·m^-2,其中高值区域主要分布在青海高原的东部和南部,低值区域主要分布在青海高原的西北部。2001—2017年青海高原草地NPP年际变化总体较为平稳,以年均速率0.09 gC·m^-2呈微弱的波动上升。2001—2017年青海高原草地PUE均值为0.089 gC·m^-2·mm^-1,其中高值区域主要分布在青海高原的东部和南部,低值区域主要分布在青海高原的西部和西北部。2001—2017年青海高原草地PUE年际变化呈微弱的波动下降趋势,下降速率为年均0.0023 gC·m^-2·mm^-1。2001—2017年青海高原草地PUE年际变化整体上与降水年际变化为负相关。本研究为青海高原草地可持续利用提供了重要理论参考和数据支撑。     

基于单片机的肉蛋鸡LED自动调节组合灯设计

基于禽类视觉和处理光信息的特殊性及单色光对禽类的不同作用,利用单片机、LED发光技术设计的肉蛋鸡生产光源由主控机构和LED组合灯具组成。利用SN3352芯片,设计恒流LED驱动电路,用主动散热和被动散热解决灯具的散热问题,采用模块式设计思想,设计LED组合灯具;在主控机构单片机的控制下,实现了肉鸡/蛋鸡在不同生长阶段对光质、光强、光周期、照光方式的自动调节。表明单片机内蛋鸡促产光源适用于多种禽类和牲畜照射,在畜禽养殖业具有广阔的应用前景。     

牧压和肥力对亚热带山地牧草净生产的影响

在亚热带山地湿润环境条件下, 研究牧压和土壤肥力对人工草地净生产的影响。三年试验结果表明, 绵羊在轮牧下, 产草量和磷肥对全年及各月牧草净生产具有显著影响。禁牧时, 夏季地上生物量积累到一定程度后, 只有很少量的净生产。放牧时, 产草量在1000kgDM/hm²左右时, 净生产最大, 当产草量低于300kgDM/hm²以下时, 净生产量则降低。每年施一次 P2O536～ 60kg/hm², 可以显著增加牧草净生产, 尤以春末夏初时施肥更为显著。最低产草量出现在不施肥处理     

单细胞蛋白和菌体蛋白饲料的生产及发展前景

阐述了单细胞蛋白饲料的基本概念、特点、生产工艺、安全性以及单细胞蛋白饲料的意义和发展前景,以期为更好地利用单细胞蛋白和菌体蛋白饲料提供参考.     

星星草群落地上生产结构、现存量季节动态和净初级生产力的研究

对星星草（Ｐｕｃｃｉｎｃｅｌｌｉａｔｅｎｕｉｆｌｏｒａ）群落的生产结构、现存量季节动态和地上净初级生产力（ＡＮＰＰ）的研究结果表明：同化系统（ＡＳ）和非同化系统（ＵＡＳ）的现存量分别集中分布于地上０～２０ｃｍ和０～３０ｃｍ的范围内，属典型的下繁型草地群落。其ＡＳ．ＵＡＳ和地上总现存量（Ｙ）在空间不同层次（ｘ）的积累规律表现为变型双曲线函数Ｙ＝ａ＋ｂ／ｘ形式。星星草种群及其群落地上生物量增长规律符合Ｌｏｇｉｓｔｉｃ增长模型；其地上现存量季节动态呈二次抛物线方程Ｙ＝ａ＋ｂｘ＋ｃｘ２形式。该群落的ＡＮＰＰ为２００．９８／ｍ２·ａ。