Constraints on the utilisation of the invasive Chinese tallow tree Sapium sebiferum by generalist native herbivores in coastal prairies

Abstract.  1. Introduced plants generally have lower generalist herbivore loads than native plants. Herbivores may be avoiding a potentially edible food source (Behavioural Constraint Hypothesis) or defences of introduced plants may be unusually toxic (Novel Defence Hypothesis).
2. To examine these hypotheses, acridid grasshoppers ( Melanoplus angustipennis and Orphullela pelidna ) were enclosed in a Texas grassland. Each enclosure contained native prairie vegetation and a seedling of either introduced Sapium sebiferum (Chinese tallow tree) or native Celtis laevigata (hackberry). Sapium invades many ecosystems in the south-east U.S.A. Celtis seedlings also establish in these ecosystems.
3. Although grasshoppers usually feed sparingly on Sapium , in field enclosures they fed heavily on this introduced tree species, supporting a role for behavioural avoidance. In laboratory feeding trials, M. angustipennis grasshoppers preferred Sapium foliage over the foliage of three native tree species. In a greenhouse experiment, M. angustipennis individuals fed more on Sapium in prairie mesocosms if they were conditioned on Sapium .
4. In another field experiment with single seedlings in enclosures, grasshoppers consumed similar amounts of Sapium from its introduced (Texas, U.S.A.) and native (China) ranges, suggesting that Sapium may have been a suitable host plant since it was introduced. Behavioural avoidance by generalist herbivores may contribute to Sapium 's low herbivore load in its introduced range.     

Effects of simulated herbivory and resources on Chinese tallow tree (Sapium sebiferum, Euphorbiaceae) invasion of native coastal prairie

Trade-offs associated with maintaining herbivory resistance and herbivory tolerance are frequently inferred in plant life histories. Invasive success for many non-native plants is often attributed to novel resistance that repels native herbivores. Chinese tallow tree (Sapium sebiferum, Euphorbiaceae) is a non-native invader that threatens ecosystems throughout the southeastern United States, including imperiled coastal prairie regions. Low herbivore loads due to costly resistance are generally assumed to give Sapium a competitive advantage over native plants. We predicted that if Sapium experienced higher damage levels it would show significant decreases in growth and reduced ability to compete with native prairie vegetation. We conducted full-factorial, paired greenhouse and field experiments designed to assess the effects of simulated leaf herbivory on Sapium growth in the presence of prairie vegetation at different levels of light and nitrogen. Contrary to our expectations, neither low-intensity, chronic defoliation nor high-intensity, acute defoliation negatively affected Sapium seedlings in any resource combination in either experiment. These studies reveal that Sapium possesses considerable phenotypic plasticity, and herbivory tolerance is a newly appreciated trait that likely contributes to its invasive potential.     

Potential distribution of the invasive tree Triadica sebifera (Euphorbiaceae) in the United States: evaluating climex predictions with field trials

Models that project introduced species distributions based on the climates in native and potential introduced ranges can provide valuable insights on the extent of a species' future spread. Yet, the lack of direct field evaluation of these range projections remains a major limitation. We evaluated results from the climex model in conjunction with results from seed and plant field trials in assessing environmental constraints to spread of the invasive tree Triadica sebifera (Chinese tallow tree) in the southeastern USA. climex incorporates key climatic parameters to generate large‐scale projections of potential distributions based on the climate across the species' current distribution. By employing field trials within microhabitats within and beyond the tree's current range, we were able to determine seed and young plants' response to the heterogeneity of the environment at regional scales. Based on projections of the climex model, T. sebifera has the potential to spread 500 km northward beyond its current distribution in the southeastern USA; minimum temperature and limited precipitation are the key climatic constraints in the eastern and western USA, respectively. climex results correlate strongly with seed germination across sites in the southeastern USA. These results do not however correlate with plant growth rates, which were often higher in sites with low projected climatic suitability. Competition and herbivory were not constraints on the growth of T. sebifera in our field trials and were therefore not responsible for the lack of correlation between model results and plant growth rates. If the minimum and maximum temperatures were to rise by 2 °C, the range of T. sebifera could extend northward 700 km beyond its current distribution. While both climex and the field trials indicate that T. sebifera is capable of extensive northward spread in the eastern USA, results of field trials indicate that the patterns of invasion within the region are likely to vary substantially with local site conditions.     

滨海盐土土壤水分的高光谱参数及估测模型

基于滨海盐土5个试验点的土壤含水量和室内土壤表面高光谱反射率,综合分析了350～2500 nm波段范围内土壤含水量与土壤光谱之间的关系,并基于比值光谱指数(RSI)、归一化光谱指数(NDSI)和差值光谱指数(DI)确定了光谱参数,进而构建土壤含水量估测定量模型.结果表明： 滨海盐土原始光谱反射率与土壤含水量呈显著负相关关系,且最大负相关出现在1930 nm(r=0.86)附近.对RSI、NDSI和DI的直线回归方程、幂函数回归方程进行对比,以RSI(R₁₄₀₇,R₁₄₅₉)为自变量构建的土壤含水量指数函数线性回归方程决定系数最大(0.780),标准误较小(0.016),拟合方程为y=0.00001e^9.72053x.估测模型能够更好地监测滨海盐土土壤水分状况.基于RSI(R₁₄₀₇,R₁₄₅₉)构建的模型可实现对江苏省滨海盐土土壤水分的精确监测.     

Effects of nutrient loading and extreme rainfall events on coastal tallgrass prairies: invasion intensity, vegetation responses, and carbon and nitrogen distribution

Soil fertility and precipitation are major factors regulating transitions from grasslands to forests. Biotic regulation may influence the effects of these abiotic drivers. In this study, we examined the effects of extreme rainfall events, anthropogenic nutrient loading and insect herbivory on the ability of Chinese tallow tree ( Sapium sebiferum ) to invade coastal prairie to determine how these factors may influence woody invasion of a grassland. We manipulated soil fertility (NPK addition) and simulated variation in frequency of extreme rainfall events in a three growing season, full factorial field experiment. Adding water to or pumping water out of plots simulated increased and decreased rainfall frequencies. We added Sapium seeds and seedlings to each plot and manipulated insect herbivory on transplanted Sapium seedlings with insecticide. We measured soil moisture, Sapium performance, vegetation mass, and carbon and nitrogen in vegetation and soils (0–10 cm deep, 10–20 cm deep). Fertilization increased Sapium invasion intensity by increasing seedling survival, height growth and biomass. Insect damage was low and insect suppression had little effect in all conditions. Recruitment of Sapium from seed was very low and independent of treatments. Vegetation mass was increased by fertilization in both rainfall treatments but not in the ambient moisture treatment. The amount of carbon and nitrogen in plants was increased by fertilization, especially in modified moisture plots. Soil carbon and nitrogen were independent of all treatments. These results suggest that coastal tallgrass prairies are more likely to be impacted by nutrient loading, in terms of invasion severity and nutrient cycling, than by changes in the frequency of extreme rainfall events.     

人工植被对崇明东滩滨海盐土水盐空间异质性的影响

运用经典统计学和地统计学相结合的方法,于2012年6月研究了上海市崇明东滩滨海盐土上3种人工植被表层土壤(0～20cm)水盐的空间异质性.结果表明:不同样地的土壤含水量大小顺序为:落羽杉林>狗牙根草丛>夹竹桃灌丛,其变异系数分别为13.9%、13.4%和12.9%;土壤电导率为:夹竹桃灌丛>落羽杉林>狗牙根草丛,其变异系数分别为79.2%、55.4%和15.9%;二者均属中等程度变异.不同样地土壤水盐的理论变异模型各不相同,其中土壤电导率的拟合效果更好,R2在0.97～0.99.当植被从夹竹桃灌丛→狗牙根草丛→落羽杉林,土壤含水量的空间异质性程度由弱变强,其中夹竹桃的变异性是随机的;植被从狗牙根草丛→夹竹桃灌丛→落羽杉林,土壤电导率的空间异质性由中等相关变为强相关.不同植被下土壤电导率空间自相关性多为正相关,土壤水分多呈负相关.狗牙根草丛的土壤水盐均呈条带状分布,落羽杉林地土壤水盐均呈大斑块连续状分布,而夹竹桃灌丛的土壤水分呈小斑块破碎状分布,盐分呈条带状分布.     

黄土丘陵区坡面整地和植被耦合下的土壤水分特征

水分是干旱半干旱地区植被恢复的主要环境制约因子。在黄土高原小流域,合理整地能够有效截留降雨补给土壤水,进而促进植被恢复。选择地处甘肃定西的半干旱黄土小流域为研究区,基于野外实测数据,分析不同植被和整地方式(柠条水平阶、山杏水平沟、侧柏反坡台,油松反坡台)综合影响下的土壤水分特征。采用最优分割法将不同整地方式土壤水分垂直层次划分为活跃层,次活跃层和相对稳定层。结果表明:生长季不同整地方式土壤水分的变化与降水量的变化密切相关,不同月份以及不同深度各整地方式土壤水分之间差异显著(P0.05)。根据土壤水分垂直变化特征,山杏水平沟水分活跃层与次活跃层为0—80cm,其深度范围均大于其他3种整地方式,而柠条水平阶土壤水分均在30 cm以下较为稳定,其深度范围均小于其他3种整地方式。不同整地方式土壤水分含量具体表现为:山杏水平沟侧柏反坡台柠条水平阶油松反坡台。     

黄土高原半湿润区苜蓿草地土壤干层形成及水分恢复

研究了黄土高原地区不同生长年限苜蓿草地0～1000 cm土层土壤水分消耗规律.结果表明,荒地与苜蓿草地土壤干层出现的区域及发生的程度不同:荒地在80～100 cm土层深度,出现轻度干层;生长年限低于8a(含8a)的苜蓿草地,在250～350 cm土层出现轻度干层,生长年限超过8a,出现中度干层,干层范围延至500 cm土层以下.苜蓿生长超过18a,0～200 cm上层土壤水分开始恢复,年均恢复1.49%;但在200～1000 cm土壤深层,18、26年生苜蓿草地土壤含水量仅为10.20%,深层土壤通体干化,水分难以恢复.     

Influence of soil moisture on egg cold hardiness in the migratory locust Locusta migratoria (Orthoptera: Acridiidae)

Abstract.  The present study investigates the influence of environmental moisture on cold hardiness of the migratory locust, Locusta migratoria . The water content of locust eggs kept in soil at 30 °C varies according to the moisture content of the substrate. In turn, it can significantly affect the supercooling point of locust eggs (range from −26 to −14.8 °C) and the mortality when exposed to subzero temperatures. Environmental moisture influences the supercooling capacity of eggs and their survival at low temperature. When locust eggs of the same water content are exposed to subzero temperatures under different soil moistures, their mortality varies between short-time exposure and long-time exposure at subzero temperatures. Given a short-time exposure, mortality in wet soil is lower than in dry soil due to the buffering effect of soil water against temperature change. The pattern of egg mortality is reversed after long-time exposure at low temperature, suggesting that inoculative freezing may be an important mortality factor. It is suggested that interactions between soil moisture and low temperature can influence the cold hardiness of locust eggs, and partial dehydration is beneficial to over-wintering eggs of the migratory locust.     

The role of light,soil and human factors on the probability of occurrence of an invasive and three native plant species in coastal transitions of coastal Mississippi,USA

Aims Understanding relationships between the distributions of species and their surrounding environment provides a basis for forecasting how species will respond to future environmental changes. In this study, we examined the effects of environmental factors and human developmental features associated with disturbances on probability of occurrence of juveniles of invasive Triadica sebifera and three native plant species, Baccharis halimifolia, Ilex vomitoria and Morella cerifera within a typical coastal transition in coastal Mississippi, USA.Methods We recorded presence of juveniles of focal species and measured environmental factors (soil salinity, canopy openness, soil texture and soil carbon to nitrogen ratio) along an 11.3 km transect located at Grand Bay National Estuarine Research Reserve. Further, we documented anthropogenic features and associated activities as a proxy for human disturbance.Important findings With the exception of I. vomitoria, all other species occurrences were significantly influenced by an interaction between soil salinity and canopy openness. The occurrence of I. vomitoria sharply decreased with salinity. B. halimifolia occurrence peaked at moderate levels of salinity and low to moderate levels of canopy openness. Occurrences of M. cerifera and the invasive T. sebifera were highest at low levels of salinity and canopy openness. These results indicate that salinity is a strong driver that limits distribution of juvenile native and invasive species in coastal transitions. Logistic regression confirmed the positive effects of anthropogenic disturbances on T. sebifera and I. vomitoria occurrence. It appears that while soil salinity is likely to drive retreat of the seaward boundaries of woody plant species distributions, increased human developments along the coast likely enhance the inland spread of species, in particular the invasive T. sebifera by increasing disturbances and facilitating dispersal. Results from this study can offer insight for the development of T. sebifera management and preventive measures for further spread along coastal areas of the southeastern USA.     

喀斯特山区洼地表层土壤水分的时空变异

研究用地统计学方法在桂西北典型喀斯特洼地研究了表层土壤水分（0～15cm）的时空变异特征及其分布格局。结果表明在取样时段内洼地表层土壤水分总体不高（15．0％～27．5％）,呈现弱至中等变异特征,并且中等变异一般与含水量较低相对应。洼地表层土壤水分的半变异函数参数及其影响因素产生一定的季节变化;块金值、基台值和变程的变化范围分别是0．01～2．74,2．04～7．52和6．0～36．8。块金值和基台值的变化大致与平均含水量呈相反变化趋势;变程在采样初期和中期与土壤水分的变化趋势相反,在后期变化趋势相同,结果说明平均含水量对表层土壤水分的时空变异具有持续主导作用,结合研究目标可以有效指导后续的土壤采样。在剔除趋势效应后,表层土壤水分呈明显的斑块或条带状分布,样块土壤水分不仅具有空间分布的差异而且具有明显季节变化,其中旱、雨季的土壤水分分布特征明显不同。在喀斯特山区特殊地貌中,土壤平均含水量、地形、微地貌（石丛）和人为管理等因素是造成洼地表层土壤水分时空变异及其分布差异的主要影响因素。     

黄土丘陵区沙打旺草地土壤水分过耗与恢复

研究了黄土丘陵区沙打旺 (Astragalusadsurgens)草地土壤水分的动态规律和恢复过程及人为调控土壤水分的效果。结果表明 :沙打旺在该区生长年限为 6～ 7a,生物量形成的高峰期在第 3～ 4年 ,之后土壤水分大量亏缺 ,生物量逐年下降 ,第 6年生物量和水分均下降到最低点。同时土壤水分的消耗深度与根系的分布相一致 ,土壤干层主要集中在根系分布的密集区 0 .3～0 .8m。随着沙打旺生长年限的延长及根系的下扎 ,土壤干层逐渐加深 ,3～ 6年生沙打旺草地土壤干层平均厚度为 2 .3m;土壤水分要自然恢复到种植前的含水量需要 6～ 7a;通过水平阶和水平沟整地进行人工调控 ,土壤水分比自然恢复可提前 2～ 3a,一般需要 4～ 5 a的时间即可恢复正常     

Chemotaxonomy of the tribe Antidesmeae (Euphorbiaceae): antidesmone and related compounds

Selected species of the tribe Antidesmeae (Euphorbiaceae, subfamily Phyllanthoideae) have been screened for antidesmone occurrence and its content by quantitative HPLC (UV) and qualitative LC-MS/MS analysis. The LC-MS analysis allowing the additional detection of 17,18-bis-nor-antidesmone, 18-nor-antidesmone, 8-dihydroantidesmone and 8-deoxoantidesmone was carried out in the selected reaction monitoring (SRM) mode. Leaf material from herbarium specimens of 13 Antidesma spp., Hyeronima alchorneoides and Thecacoris stenopetala (all subtribe Antidesminae), as well as Maesobotrya barteri, Aporosa octandra (both Scepinae) and Uapaca robynsii (Uapacinae) were analysed. Additionally, freshly collected samples of different plant parts of two Antidesma spp. were investigated to ensure the significance of the results on herbarium specimens and to compare the antidesmone content in bark, root and leaves. Antidesmone could be unambiguously identified in 12 of 13 Antidesma spp., as well as in the two other investigated genera of subtribe Antidesminae, in levels of up to 65 mg/kg plant dry weight. Antidesmone was not found in specimens from other subtribes. Antidesmone-derived compounds occur in much lower concentrations than antidesmone.     

土壤水分胁迫对设施番茄根系及地上部生长的影响

为了研究土壤水分胁迫对番茄生长的影响,以番茄‘金粉2号’(Jingfen 2)品种为试材,于2013年5—8月间在南京信息工程大学可控试验温室设计正常灌溉(T1)、轻度胁迫(T2)、中度胁迫(T3)、重度胁迫(T4)4个土壤水分处理,观测不同处理番茄植株根系及地上部分的生长状况。结果表明:不同处理的番茄根系生长指标(根系总长度、总表面积、总平均直径、根尖数)的最大值均表现为:T2T3T1T4,比较峰值发现,T2、T3和T4的根系总长度分别为T1的1.8、1.0和0.4倍,总表面积分别为T1的2.3、1.1和0.4倍,总平均直径分别为T1的1.3、1.1和0.6倍,根尖数分别为T1的1.1、1.0和0.5倍;T1、T2和T3处理的番茄根系均集中分布在5—10 cm土层内,而在T4处理下根系集中分布在15—25 cm土层内;番茄的株高、茎粗和叶面积指数大小表现为:T1T2T3T4,T2、T3和T4的番茄株高分别比T1下降11.49%、28.6%和43.98%,茎粗以T4处理最低,为T1的73.57%,T2、T3和T4的叶面积指数分别为T1的81.33%、64.62%和43.37%,各处理间叶面积指数在5%水平下呈现显著性差异。相关分析表明,番茄地上部分和地下部分各项生长指标与土壤体积含水率呈正相关。研究认为轻度土壤水分胁迫对番茄植株地上部分的生长影响不显著,利于根系生长,中、重度土壤水分胁迫明显抑制了番茄植株地上部分的生长,降低根系在土壤中的分布层,研究为设施番茄水分管理提供科学依据。     

土壤含水量对桔小实蝇蛹期存活的影响

浸水时间、土壤含水量对桔小实蝇Bactroceradorsalis(Hendel)蛹的存活及成虫羽化的影响的研究结果表明:(1)不同浸水时间对桔小实蝇蛹存活率的影响不同。浸水时间越长,蛹存活率越低;浸水对初期蛹的影响较大,蛹龄越大,浸水作用效果越低。浸水时间(TW)、蛹期(AP)和蛹存活率(SP)之间关系符合以下模型:SP=0.4165-0.00307TW+0.2290AP-0.00004496T2W-0.0002528A2P+0.00008258TWAP。(2)土壤含水量对桔小实蝇成虫羽化影响明显。当土壤含水量较低或较高时,羽化率都明显受到抑制。相对含水量在30%～80%之间,蛹的羽化率较高。相对含水量(Ws)和成虫羽化率(E)之间存在以下关系:E=0.396+0.01985W-0.000181W2。     

Patterns of asymmetry in the twining vine Dalechampia scandens (Euphorbiaceae): ontogenetic and hierarchical perspectives

We studied patterns of fluctuating asymmetry (FA) in leaves of four populations of the neotropical vine Dalechampia scandens to obtain insight into the origin of leaf FA and the level at which it is controlled. We analysed correlations in signed and unsigned asymmetry at different organizational levels. We also analysed the ontogeny of FA during leaf expansion to test whether asymmetry is regulated during cell expansion, and whether fast-expanding leaves are more or less asymmetrical. Signed asymmetry was negatively correlated between successive leaves, that is, when the right side of a leaf was larger than the left side, the next leaf on the shoot tended to show the opposite pattern. The magnitude of FA, however, was very weakly correlated among successive leaves or among leaves measured on different shoots. The direction of asymmetry did not change during leaf expansion, but the relative asymmetry, that is, asymmetry corrected for difference in trait size, decreased during expansion. We found a weak negative relationship between leaf expansion rate and relative asymmetry on the fully expanded leaves. These results suggest that leaf asymmetry in Dalechampia originates from perturbations in cell proliferation in the stem, creating asymmetries in opposite directions in successive leaves. These asymmetries persist during leaf expansion, but tend to be reduced by unknown mechanisms.     

Phenotypic plasticity of Capsella bursa-pastoris (Brassicaceae) and its effect on fitness in response to temperature and soil moisture

Capsella bursa-pastoris is one of the most common plants on earth. Although phenotypic plasticity of ecologically important traits possibly contributes to its wide geographic range, little is known about the plasticity of C. bursa-pastoris and its effects on its fitness. In a laboratory, we assessed the phenotypic plasticity in response to two representative climatic conditions: temperature and soil moisture. In addition, we quantitatively evaluated the relationship between phenotypic plasticity and fruit production. Most measured morphological and physiological traits exhibited plastic responses to temperature and fitness based on fruit production was maintained across temperatures. In contrast, no plasticity to soil moisture was detected, and plants produced fewer fruits in dry soil. Selection analysis revealed that the plasticity of the flowering time and the water-use efficiency had positive effects on fruit production over the tested temperature regime. These experimental results suggest that phenotypic plasticity probably enables C. bursa-pastoris to cope with heterogeneous temperature environments and thereby probably contributes to its wide geographic range.     

Growth,development and yield of pawpaw (Carica papaya L.) ‘Homestead selection’ in response to soil moisture stress

Summary The effects of four soil water potential regimes under greenhouse conditions on growth, development, and yield of ‘Homestead selection’ pawpaw were investigated. The objectives were to determine the critical soil water potential regime and the moisture sensitive stages of growth of pawpaw. Repeated cycles of stress to −6.0 bar soil water potential imposed as from vegetative phase prevented fruit formation by constantly causing flower abscission. The stressed plants were stunted in size. The −2.0 bar soil water potential value was considered the critical level for normal growth and reproductive development of pawpaw. The mid-vegetative, flowering and fruit enlargement phases were moisture sensitive.     

水分和温度对若尔盖湿地和草甸土壤碳矿化的影响

土壤碳矿化及其温度和水分敏感性是研究生态系统碳循环的重要指标。本文以若尔盖高寒湿地和草甸为对象,在不同水分（70%,100%,130%饱和含水量（SSM））和温度（5,10,15,20,25℃）培养下定期测定土壤碳矿化速率（或土壤微生物呼吸速率）,探讨水分和温度对高寒湿地和草甸土壤碳矿化的影响,为揭示未来暖干化对若尔盖地区碳贮存及其碳汇功能的潜在影响提供科学依据。实验结果表明：增温显著促进了高寒湿地和草甸土壤碳矿化,而水分过高会抑制土壤碳矿化;此外,高寒湿地土壤碳矿化速率高于高寒草甸。土壤水分和草地类型对土壤碳矿化温度敏感性（Q10）的影响比较复杂。高寒草甸Q10随水分升高而显著升高,培养7天时的Q10变化趋势为70% SSM（1.21）< 100% SSM（1.76）< 130% SSM（2.80）,培养56天的Q10从1.17上升为4.53。高寒湿地的Q10在培养7天差异不显著,但整个56天培养期内Q10随水分升高而显著增加。在评估暖干化对若尔盖地区碳贮量和碳汇功能的影响时,应更加重视高寒草甸和高寒湿地Q10对水分和温度变化的不同响应。     

Effect of habitat type and soil moisture on pupal stage of a Mediterranean forest pest (Thaumetopoea pityocampa)

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