昆明海口林场滇藏钝果寄生的调查及寄生特性分析

桑寄生科(Loranthaceae)植物是常见的半寄生灌木,其过度繁殖会影响天然林和人工林生态、经济和社会效应的发挥.前期调查发现,昆明海口林场部分地区具有桑寄生危害,其主要种类为滇藏钝果寄生.为监控滇藏钝果寄生在林场的传播扩散,了解其寄生初期的选择偏好,本研究以昆明市海口林场滇藏钝果寄生危害最严重地区为中心,对其周边4个区域的传播情况进行样方调查,统计滇藏钝果寄生的寄主选择模式、构建寄生强度与寄主生长特征的归回关系.结果 表明,滇藏钝果寄生于郁闭度最低(30％)、坡度最大(27°)的样方2 (M2,中心样方)中危害严重,其余4个样方(M1,M3,M4,M5;周边样方)的感染程度较低,尚处于扩散初期.滇藏钝果寄生在所调查样地中具有明显的寄主选择性,几乎仅存在于槲栎中,但其扩散与槲栎在群落中的百分率无明显相关性.采用逐步回归法构建槲栎生长特征与寄生强度的线性关系,其冠幅和胸径可依次引入回归模型中,修正后的拟合度R2为0.526,方程式为y=-0.467+0.152x1+0.110x2.滇藏钝果寄生于样方M2和M1中的寄生高度百分率集中分布于40％～80％之间,而于M3、M4和M5中变幅较大,无明显集中区.该研究结果可为滇藏钝果寄生的生态防治提供科学基础.     

Screening and Verification of Low Nitrogen Tolerant and Nitrogen Sensitive Cotton Germplasm

[Objective] The aim of this study is to evaluate nitrogen efficient cotton germplasms and improve nitrogen use efficiency. [Method] Eighty cotton germplasms were selected and evaluated in the hydroponic experiment under low (0.25 mmol·L^－1) and high (5 mmol·L^－1) nitrogen concentration. Different traits for screening were identified and nitrogen use efficiency types were classified. Field experiments were also performed for comparison and confirmation of the identified germplasms. [Result] The results showed that there were significant differences in the total plant dry matter, shoot nitrogen accumulation and nitrogen absorption efficiency in cotton germplasms at the two nitrogen levels. Based on coefficient of variation, principal component analysis and correlation, six traits including total plant dry matter, shoot dry matter, root dry matter, total nitrogen accumulation, shoot nitrogen accumulation and nitrogen absorption efficiency were used as screening indicators. According to the Heatmap clustering analysis and the nitrogen efficiency comprehensive index, two germplasms (Lu05R59 and CCRI 69) were identified as low nitrogen tolerant and nitrogen efficient, and two germplasms (Coker 201 and Xinluzhong 30) as low nitrogen sensitive and nitrogen inefficient. The results of field experiment were consistent with the results of the hydroponic culture at the seedling stage. [Conclusion] It was finally determined that Lu05R59 and CCRI 69 were the low nitrogen tolerant and nitrogen efficient germplasms, and Coker 201 and Xinluzhong 30 were low nitrogen sensitive and nitrogen inefficient germplasms. The results of these studies provide the possibility for screening and rapid identification of nitrogen use efficiency in cotton at the seedling stage, and provide the ideal materials and theoretical basis for further study of cotton nitrogen efficient.     

Waterlogging tolerance of pea at germination

Peas (Pisum sativum L.) are exposed to waterlogging at germination when grown as relay in rice‐based cropping. Ninety‐one germplasm accessions were evaluated in relay (sown in waterlogged soil), and subsequently 10 diverse genotypes compared under relay and sole cropping (conventional tillage sowing) over two seasons in Bangladesh. Contrasting genotypes, BM‐3, NL‐2 and Kaspa, were further evaluated in three waterlogging treatments (drained control, 4 and 8 days waterlogging) in the glasshouse. Conspicuous variation in waterlogging tolerance at germination was observed in the field and confirmed under controlled conditions. In relay sowing in 2011, emergence of a few genotypes was affected by waterlogging. In 2012, emergence in relay was severely affected (12 plants/m²) compared to sole sowing (37 plants/m²). Among genotypes BM‐3 had 6 plants/m² emerge, which all subsequently died, in contrast to NL‐2 in which emergence was 13 plants/m² with all plants surviving. In the glasshouse, there was 14% emergence in BM‐3, 40% in NL‐2 and 55% in Kaspa after 8 days of waterlogging. Such marked differences in waterlogging tolerance at germination in the model pea are the first reported and illustrate prospects for selection to improve adaptation to relay sowing in South Asia.     

Migration pathways,speed and mortality of Atlantic salmon (Salmo salar) smolts in a Scottish river and the near‐shore coastal marine environment

Long‐distance migration of Atlantic salmon (Salmo salar) is known to result in high levels of mortality. For a species experiencing global population decline, it is thus vital to better understand migration behaviour, both in the river and marine stages. Atlantic salmon smolts (n = 50) were tracked using acoustic telemetry in the River Deveron, Scotland, and adjacent coastal area. Higher rates of mortality were observed in the river (0.77% per km) than the early marine stage of migration (0.0% per km). Mortality likely resulted from predation. Higher swim speeds were recorded in the early marine stage compared with the river (marine = 7.37 ± 28.20 km/day; river = 5.03 ± 1.73 km/day [mean ± SD]), a potential predator avoidance behaviour. The majority of smolts leaving the river did so in darkness and on a flooding tide. Overall river and marine migration success were linked to nights of lower lunar brightness. Marine migration speed decreased with increasing environmental noise levels, a finding with implications for fisheries management. The migration pathway in the early marine environment did not follow obvious geographical features, such as the coastline. Thus, we suggest that early marine environment pathways are more influenced by complex water currents. These findings highlight factors that influence smolt migration survival and behaviour, areas on which future research should focus.     

Stable isotopes and gut contents indicate differential resource use by coexisting asp (Leuciscus aspius) and pikeperch (Sander lucioperca)

Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0%–65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions.     

Responses of carbon metabolism and antioxidant system of summer maize to waterlogging at different stages

A field experiment was performed to explore responses of carbon metabolism, antioxidant system and endogenous hormone content of summer maize hybrids DengHai605 (DH605) and ZhengDan958 (ZD958) to waterlogging at the third leaf stage (V3), the sixth leaf stage (V6) and the 10th day after the tasselling stage (10VT). Results showed that waterlogging significantly decreased the contents of zeatin riboside (ZR), indole‐3‐acetic acid (IAA) and gibberellic acid (GA), compared to those of CK. However, leaf abscisic acid (ABA) content was significantly increased by waterlogging at different stages, with the most significant increase was found in the treatment of waterlogging at V3 (V3‐W), with an increase of 30% and 29% for DH605 and ZD958, respectively. Waterlogging significantly decreased antioxidative enzyme activities, accelerating leaf senescence, resulted in the disorder of leaf gas exchange parameters and chlorophyll fluorescence parameters. In addition, waterlogging decreased key enzyme activities of carbon metabolism (ribulose bisphosphate carboxylase and phosphoenolpyruvate carboxylase), with the most significant reduction in V3‐W, with a decrease of 46% and 49% for DH605, and 53% and 55% for ZD958, respectively. Visibly, waterlogging disturbed carbon metabolism, affected plant endogenous hormone content, accelerated leaf senescence and eventually resulted in a significant reduction in photosynthetic characteristic and grain yield. V3 was most susceptible to waterlogging, followed by V6 and 10VT.     

Quantifying trophic interactions and niche sizes of juvenile fishes in an invaded riverine cyprinid fish community

Quantifying feeding interactions between nonindigenous and indigenous fishes in invaded fish communities is important for determining how introduced species integrate into native food webs. Here, the trophic interactions of invasive 0+ European barbel Barbus barbus (L.) and the three other principal 0+ fishes in the community, Squalius cephalus (L.), Leuciscus leuciscus (L.) and Phoxinus phoxinus (L.), were investigated in the River Teme, a River Severn tributary in Western England. B. barbus has been present in the River Teme for approximately 40 years. Analyses of stomach contents from samples collected from three sites between June and September 2015 revealed that, overall, fishes displayed a generalist feeding strategy, with most prey having low frequency of selection. Relationships of diet composition versus body length and gape height were species‐specific, with increasing dietary specialisms apparent as the 0+ fishes increased in length and gape height. The trophic niche size of invasive B. barbus was always significantly smaller than S. cephalus and L. leuciscus and was significantly smaller than P. phoxinus at two sites. This was primarily due to differences in the functional morphology of the fishes; 0+ B. barbus were generally restricted to foraging on the benthos, whereas the other fishes were able to forage on prey present throughout the water column. Nevertheless, the invasive B. barbus were exploiting very similar prey items to populations in their native range, suggesting these invaders were strongly pre‐adapted to the River Teme and this arguably facilitated their establishment and invasion.     

Thresholds,sensitive stages and genetic variability of finger millet to high temperature stress

Finger millet [Eleusine coracana (L.) Gaertn.] is an important coarse cereal crop grown in the arid and semi‐arid regions and often experiences high temperature (HT) stress. The objectives of this research were (i) to quantify effects of season‐long HT stress on physiological and yield traits, (ii) to identify the developmental stages most sensitive to HT stress and (iii) to quantify the genetic variability for HT stress tolerance in finger millet. Research was conducted in controlled environment conditions. HT stress decreased the chlorophyll index, photosystem II activity, grain yield and harvest index. Maximum decrease in number of seeds per panicle and grain yield per plant was observed when stress was imposed during booting, panicle emergence or flowering stages. Maximum genotypic variation was explained by panicle width and number of seeds per panicle at optimum temperature (OT) and grain yield per plant at HT and number of seeds at HT. Based on the stress response and grain yield, tolerant or susceptible genotypes were identified. Finger millet is sensitive to HT stress during reproductive stages, and there was genotypic variability among the finger millet genotypes for number of seeds per panicle and grain yield under HT, which can be exploited to enhance stress tolerance.     

Factors determining the adoption of laser land leveling in the irrigated rice–wheat system in Haryana,India

Laser land leveling has been increasingly adopted in the irrigated rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system in the state of Haryana (India), located in the north-western Indo-Gangetic Plains. Still, many farmers have applied it to only a fraction of their land. In this study, we used data collected from 621 farm households in Haryana and applied a double-hurdle model for assessing the factors that determine the adoption and intensity of laser-leveling technology. The results show that large land holders are more likely to laser level their farm land; however, we found a negative association between land holdings and the proportion of laser-leveled land. Information about technology through farmer-to-farmer communication and through private traders, participation in agricultural training and membership in local agricultural institutions increased both the likelihood and the intensity of adoption. Our findings call for a closer collaboration among the various stakeholders, specifically to promote farmer-to-farmer communication through increased participation in local institutions and increase the rate of adoption of laser leveling technology.