浙西北丘陵地区次生林与杉木林土壤水溶性有机碳季节动态

为了解浙江省西北部丘陵地区森林土壤水溶性有机碳含量及动态规律,以达到成熟林状态的次生林和杉木林为对象,分别对其春、夏、秋、冬4个季节的0 ～ 10、10 ～ 20 cm土层水溶性有机碳含量进行了研究.结果表明:1)0 ～10和10 ～ 20 cm土层,次生林与杉木林水溶性有机碳含量没有显著差异;2)次生林和杉木林土壤水溶性有机碳含量季节动态基本一致,均表现为冬季＞春季＞秋季＞夏季;3)0 ～10和10 ～ 20 cm土层次生林与杉木林水溶性有机碳含量与土壤温度、降水量均呈显著负相关,与土壤湿度相关性不显著,与凋落物量呈正相关,且在0 ～10 cm土层显著.     

华西雨屏区香樟人工林土壤表层细根生物量和碳储量

2010年11月-2011年12月, 研究了华西雨屏区31年生香樟人工林土壤表层(0～30 cm)细根生物量及碳储量.结果表明: 香樟人工林土壤0～30 cm层细根总生物量(活根+死根)和碳储量的平均值分别为1592.29 kg·hm^-2和660.68 kg C·hm^-2,其中活细根贡献率分别为91.1%和91.8%.随着土壤深度的增加,香樟1～5级活细根和死细根的生物量及碳储量均显著减少;随着根序等级的升高,香樟活细根生物量及碳储量显著增加.香樟细根总生物量及碳储量均在秋季最高、冬季最低,死细根生物量及碳储量为冬季最高、夏季最低;1级根和2级根生物量及碳储量均在夏季最高、冬季最低,而3~5级根则为秋季最高、冬季最低.土壤养分和水分的空间异质性是导致细根生物量和碳储量变化的主要原因.     

Occurrence and impact of Agrilus spp. and associated egg parasitoids in hazel groves of Northwest Italy

In several hazel (Corylus avellana L.) groves in the area of Langhe (Piedmont, Northwest Italy), many hazel branches suddenly withered, and in some cases, the whole tree died, with heavy economic losses for the farmers. Symptoms of jewel beetle attacks were detected on the trees. Eight Agrilus species were caught by traps from 2007 to 2009 in the surveyed hazel groves; among them, only four species have been known to develop on hazel. On the traps, Agrilus olivicolor Kiesenwetter was the most abundant species, while almost only Agrilus viridis (L.) was sampled by plant beating from 2008 to 2010. Moreover, almost all adults emerged from field‐collected hazel wood belonged to this latter species that proved to be the main responsible for the severe attacks on the hazel trees. Agrilus viridis adults emerged from late May to late June, and generally lived until the end of August, while egg masses were observed from late May to late July. The egg parasitoid Oobius zahaikevitshi Trjapitzin was found in all of the investigated groves; adults emerged already from the first egg masses collected on hazel trees in late May‐early June. O. zahaikevitshi was able to largely reduce A. viridis populations, with a parasitism rate of more than 50% in some groves. Recent attacks of A. viridis were related to a long period of drought; however, appropriate agronomic practices to minimize the effects of water stress and to conserve natural enemies, such as O. zahaikevitshi, could be more effective to protect hazel groves against boring beetle attacks.     

Quantitative and qualitative numerical alterations in splenocyte subpopulations of the cotton rat (Sigmodon hispidus) across seasons

Abstract

Previous research in our laboratory has documented seasonal alterations in humoral and cell‐mediated immunity in cotton rat (Sigmodon hispidus) populations. Based on these observations, we hypothesized that these seasonal differences in immune function were attributable in part to qualitative and quantitative numerical changes in specific splenocyte subpopulations. Lymphocytes were harvested from spleens of 139 cotton rats collected from a tallgrass prairie in central Oklahoma from December 1991 to September 1992. Unique splenocyte subpopulations were identified using fluorescein conjugated cell surface markers (concanavalin‐A, peanut agglutinin, soybean agglutinin, Helix pomatia agglutinin, pokeweed mitogen, and rabbit‐anti‐rat immunoglobulin‐G). All subpopulations examined were more abundant in fall and winter than spring and summer. Several plausible explanations for seasonal variation in abundance of splenocyte subpopulations are discussed.     

A decade of seasonal dynamics and co-occurrences within freshwater bacterioplankton communities from eutrophic Lake Mendota,WI, USA

With an unprecedented decade-long time series from a temperate eutrophic lake, we analyzed bacterial and environmental co-occurrence networks to gain insight into seasonal dynamics at the community level. We found that (1) bacterial co-occurrence networks were non-random, (2) season explained the network complexity and (3) co-occurrence network complexity was negatively correlated with the underlying community diversity across different seasons. Network complexity was not related to the variance of associated environmental factors. Temperature and productivity may drive changes in diversity across seasons in temperate aquatic systems, much as they control diversity across latitude. While the implications of bacterioplankton network structure on ecosystem function are still largely unknown, network analysis, in conjunction with traditional multivariate techniques, continues to increase our understanding of bacterioplankton temporal dynamics.     

Crossing the threshold: an amphibian assemblage highly infected with Batrachochytrium dendrobatidis in the southern Brazilian Atlantic forest

The fungal infection caused by Batrachochytrium dendrobatidis (Bd) in amphibians is known to be lethal when infection intensity values exceed loads of 10,000 zoospores per individual. We investigated Bd infection intensity in 100 anurans of southern Brazil. Almost half of the individuals were infected and the intensity ranged from four to about 156,000 zoospore genomic equivalents. We found no clinical signs of chytridiomycosis and no evidence of mortality. However, we observed a reduction in the number of infected individuals with loads above 10,000 zoospores. This fact could be considered indirect evidence that individuals with high loads are removed from the population.     

桂西南喀斯特季节性雨林枯立木的空间格局及生境关联性分析

枯立木是森林生态系统物质循环和能量流动的重要组成部分,对森林群落动态和演替具有重要作用。该研究以位于桂西南的弄岗北热带喀斯特季节性雨林15 hm~2森林动态监测样地为平台,以样地中2011年第一次植被调查数据胸径(diameter at breast height,DBH)≥1 cm的枯立木为研究对象,在充分考虑空间自相关的基础上分析其不同径级(小径级,1 cm≤DBH5 cm;中径级,5 cm≤DBH15 cm;大径级,15 cm≤DBH)的空间分布格局、枯立木多度与环境因子的相关性及生境关联性等。结果表明:枯立木所有个体和小径级分别在0~4 m和0~5 m尺度上表现为聚集分布,其它尺度为随机分布;中径级和大径级在0~30 m尺度上均为随机分布。大径级与凹凸度表现为显著负相关,所有个体和小径级与干旱度指数和样方内所有植株个体数为显著正相关,所有个体和小径级与样方内最大胸径和平均胸径呈显著负相关。所有个体和小径级与3种生境类型间的关联性并不显著;中径级与山坡呈正关联性、与山脊呈负关联性、与山谷无显著关联性;大径级与山谷呈正关联性、与山坡无显著关联性、与山脊呈负关联性。在喀斯特季节性雨林中,枯立木空间分布格局总体表现为随机分布,仅小径级在小尺度内聚集分布,而较大径级在样地中表现出一定的生境关联性;树木死亡过程可能是小尺度内密度制约、大尺度内生境过滤和个体自然衰老等生态学过程形成的。     

The timing of frugivore‐mediated seed dispersal effectiveness

The seed dispersal effectiveness framework allows assessing mutualistic services from frugivorous animals in terms of quantity and quality. Quantity accounts for the number of seeds dispersed and quality for the probability of recruitment of dispersed seeds. Research on this topic has largely focused on the spatial patterns of seed deposition because seed fates often vary between microhabitats due to differences in biotic and abiotic factors. However, the temporal dimension has remained completely overlooked despite these factors—and even local disperser assemblages—can change dramatically during long fruiting periods. Here, we test timing effects on seed dispersal effectiveness, using as study case a keystone shrub species dispersed by frugivorous birds and with a fruiting period of 9 months. We evaluated quantity and quality in different microhabitats of a Mediterranean forest and different periods of the fruiting phenophase. We identified the bird species responsible for seed deposition through DNA barcoding and evaluated the probability of seedling recruitment through a series of field experiments on sequential demographic processes. We found that timing matters: The disperser assemblage was temporally structured, seed viability decreased markedly during the plant's fruiting phenophase, and germination was lower for viable seeds dispersed in the fruiting peak. We show how small contributions to seed deposition by transient migratory species can result in a relevant effectiveness if they disperse seeds in a high‐quality period for seedling recruitment. This study expands our understanding of seed dispersal effectiveness, highlighting the importance of timing and infrequent interactions for population and community dynamics.     

Persistence of the flowerbud weevil Anthonomus santacruzi in optimal versus marginal areas: implications for the biological control of the invasive tree Solanum mauritianum in South Africa

Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was released in South Africa to offset the extensive reproductive output of the invasive tree Solanum mauritianum Scopoli (Solanaceae). Widespread establishment has occurred predominantly in the coastal areas of KwaZulu-Natal province, with limited success in higher-altitude inland areas. Irrespective of location, populations exhibit peaks in the austral autumn and decline during winter. In this study, we evaluated the persistence of A. santacruzi populations in climatically-optimal coastal areas versus climatically-marginal inland areas. The weevil’s pre- and post-winter abundance was surveyed at six coastal and six inland sites during 2018, and compared between areas and seasons. The 2018 pre-winter data were also compared to 2016 pre-winter data collected at the same sites. During 2018, pre- and post-winter numbers were six times and 22 times higher, respectively, at optimal sites than at marginal sites, with substantial winter declines at all sites. Post-winter weevil numbers at optimal sites were significantly higher than pre-winter numbers at marginal sites. Pre-winter numbers at optimal sites were not significantly different between 2016 and 2018, but at marginal sites were significantly lower in 2018. Inflorescences of S. mauritianum at marginal sites contained significantly more floral material and fruit than those at optimal sites, during both seasons in 2018. Significant negative correlations between A. santacruzi numbers and floral/fruit production suggest some impact on the reproductive output of S. mauritianum. Since A. santacruzi populations are barely persisting in marginal areas, releases in other South African provinces should target locations that are below 300?m in altitude.