Tree diversity promotes predator but not omnivore ants in a subtropical Chinese forest

1. Epigeic ants are functionally important arthropods in tropical and subtropical forests, particularly by acting as predators. High predation pressure has been hypothesised to be a mechanism facilitating high diversity across trophic levels. 2. In this study, standardised pitfall traps were used in a highly diverse subtropical forest to test if and how ant species richness is related to tree species richness and a comprehensive set of other environmental variables such as successional age, soil properties or elevation. 3. A total of 13 441 ant individuals belonging to 3839 species occurrences and 71 species were collected, of which 26 species were exclusive predators and 45 species were omnivores. 4. Occurrence and species richness of total and omnivore ants were positively related to soil pH. Predator ant occurrence was unrelated to all environmental variables tested. 5. The species richness of predator ants increased with tree species richness but decreased with leaf functional diversity and shrub cover. Elevation negatively influenced only total ant species richness. 6. The evenness of predators increased with tree species richness, while the evenness of all ants decreased with shrub cover. Omnivore ant evenness decreased with tree evenness, but increased with successional age. 7. The results highlight the value of diverse forests in maintaining species richness and community evenness of a functionally important predator group. Moreover, the results stress the importance of analysing trophic groups separately when investigating biodiversity effects.     

Tree diversity promotes predatory wasps and parasitoids but not pollinator bees in a subtropical experimental forest

From regional to global scales, anthropogenic environmental change is causing biodiversity loss and reducing ecosystem functionality. Previous studies have investigated the relationship between plant diversity and functional insect communities in temperate and also in tropical grasslands and forests. However, few studies have explored these dynamics in subtropical forests. Here, cavity-nesting Hymenoptera and associated parasitoids were collected across a controlled tree diversity experiment in subtropical China to test how predatory wasps, bees and parasitoids respond to tree species richness. Abundance and species richness of predatory wasps and parasitoids were positively correlated with tree species richness, while bee abundance and bee species richness were unrelated to tree species richness. Our results indicate that tree species richness increases the abundance and species richness of important communities such as predators and parasitoids. Moreover, the results highlight the importance of subtropical forests in maintaining abundance and species richness of key functional insect groups.     

Reprint of: Tree diversity promotes predatory wasps and parasitoids but not pollinator bees in a subtropical experimental forest

From regional to global scales, anthropogenic environmental change is causing biodiversity loss and reducing ecosystem functionality. Previous studies have investigated the relationship between plant diversity and functional insect communities in temperate and also in tropical grasslands and forests. However, few studies have explored these dynamics in subtropical forests. Here, cavity-nesting Hymenoptera and associated parasitoids were collected across a controlled tree diversity experiment in subtropical China to test how predatory wasps, bees and parasitoids respond to tree species richness. Abundance and species richness of predatory wasps and parasitoids were positively correlated with tree species richness, while bee abundance and bee species richness were unrelated to tree species richness. Our results indicate that tree species richness increases the abundance and species richness of important communities such as predators and parasitoids. Moreover, the results highlight the importance of subtropical forests in maintaining abundance and species richness of key functional insect groups.     

Local-scale spatial diversity patterns of ectomycorrhizal fungal communities in a subtropical pine-oak forest

This study aimed to analyze spatial patterns of soil ectomycorrhizal fungal (EMF) communities at the local scale in a subtropical pine-oak forest located in the Nearctic-Neotropical transition in central Mexico, to underpin biodiversity conservation strategies in forest fragments of this region. We used a spatially-explicit nested square sampling design with the same sampling representativeness at all scales and replicated three times. We detected 674 EMF OTUs within 19,200 m² and 65 OTUs on average per sample. Seventy percent of OTUs were detected in only 1–4 samples. Average community similarity was below 5%, showed minor change within 14 and 339 m distance and increased with the spatial grain used to compare the data. We found a high species-area relationship and beta diversity coefficients for soil fungi indicating that, at the local scale, increasing area by a constant factor of four represented an increase in OTU richness by a factor of two.     

Tree species diversity influences herbivore abundance and damage: meta-analysis of long-term forest experiments

Plant monocultures are commonly believed to be more susceptible to herbivore attacks than stands composed of several plant species. However, few studies have experimentally tested the effects of tree species diversity on herbivory. In this paper, we present a meta-analysis of uniformly collected data on insect herbivore abundance and damage on three tree species (silver birch, black alder and sessile oak) from seven long-term forest diversity experiments in boreal and temperate forest zones. Our aim was to compare the effects of forest diversity on herbivores belonging to different feeding guilds and inhabiting different tree species. At the same time we also examined the variation in herbivore responses due to tree age and sampling period within the season, the effects of experimental design (plot size and planting density) and the stability of herbivore responses over time. Herbivore responses varied significantly both among insect feeding guilds and among host tree species. Among insect feeding guilds, only leaf miner densities were consistently lower and less variable in mixed stands as compared to tree monocultures regardless of the host tree species. The responses of other herbivores to forest diversity depended largely on host tree species. Insect herbivory on birch was significantly lower in mixtures than in birch monocultures, whereas insect herbivory on oak and alder was higher in mixtures than in oak and alder monocultures. The effects of tree species diversity were also more pronounced in older trees, in the earlier part of the season, at larger plots and at lower planting density. Overall our results demonstrate that forest diversity does not generally and uniformly reduce insect herbivory and suggest instead that insect herbivore responses to forest diversity are highly variable and strongly dependent on the host tree species and other stand characteristics as well as on the type of the herbivore.     

Tree functional diversity affects litter decomposition and arthropod community composition in a tropical forest

Disturbance can alter tree species and functional diversity in tropical forests, which in turn could affect carbon and nutrient cycling via the decomposition of plant litter. However, the influence of tropical tree diversity on forest floor organisms and the processes they mediate are far from clear. We investigated the influence of different litter mixtures on arthropod communities and decomposition processes in a 60‐year‐old lowland tropical forest in Panama, Central America. We used litter mixtures representing pioneer and old growth tree species in experimental mesocosms to assess the links between litter types, decomposition rates, and litter arthropod communities. Overall, pioneer species litter decomposed most rapidly and old growth species litter decomposed the slowest but there were clear non‐additive effects of litter mixtures containing both functional groups. We observed distinct arthropod communities in different litter mixtures at 6 mo, with greater arthropod diversity and abundance in litter from old growth forest species. By comparing the decay of different litter mixtures in mesocosms and conventional litterbags, we demonstrated that our mesocosms represent an effective approach to link studies of litter decomposition and arthropod communities. Our results indicate that changes in the functional diversity of litter could have wider implications for arthropod communities and ecosystem functioning in tropical forests.     

Ant community structure during forest succession in a subtropical forest in South-East China

Understanding how communities respond to environmental gradients is critical to predict responses of species to changing habitat conditions such as in regenerating secondary habitats after human land use. In this study, ground-living ants were sampled with pitfall traps in 27 plots in a heterogeneous and diverse subtropical forest to test if and how a broad set of environmental variables including elevation, successional age, and tree species richness influence ant diversity and community composition. In total, 13,441 ant individuals belonging to 71 species were found. Ant abundance was unrelated to all environmental variables. Rarefied ant species richness was negatively related to elevation, and Shannon diversity decreased with shrub cover. There was considerable variation in ant species amongst plots, associated with elevation, successional age, and variables related to succession such as shrub cover. It is shown that younger secondary forests may support a species-rich and diverse community of ants in subtropical forests even though the species composition between younger and older forests is markedly different. These findings confirm the conservation value of secondary subtropical forests, which is critical because subtropical forests have been heavily exploited by human activities globally. However, the findings also confirm that old-growth forest should have priority in conservation as it supports a distinct ant community. Our study identifies a set of ant species which are associated with successional age and may thus potentially assist local conservation planning.     

Different patterns of ecosystem carbon accumulation between a young and an old-growth subtropical forest in Southern China

Using long-term (22 years) measurements from a young and an old-growth subtropical forest in southern China, we found that both forests accumulated carbon from 1982 to 2004, with the mean carbon accumulation rate at 227 ± 59 g C m⁻² year⁻¹ for young forest and 115 ± 89 g C m⁻² year⁻¹ for the old-growth forest. Allocation of the accumulated carbon was quite different between these two forests: the young forest accumulated a significant amount of carbon in plant live biomass, whereas the old-growth forest accumulated a significant amount of carbon in the soil. From 1982 to 2004, net primary productivity (NPP) increased for the young forest, and did not change significantly for the old-growth forest. The increase in NPP of the young forest resulted from recruitment of some dominant tree species characteristic of the subtropical mature forest in the region and an increase in tree density; decline of NPP of the old-growth forest was caused by increased mortality of the dominant trees.     

南亚热带常绿阔叶林群落及其卫星样地物种多样性特征

群落生物多样性的研究一直备受关注。鼎湖山植被资源丰富,对其典型植物群落及其卫星样地物种多样性状况进行探索是一项非常有意义的研究工作。以鼎湖山20 hm~2样地及其周边5个1 hm~2卫星样地为研究对象,分别从种面积关系、α多样性和β多样性几个角度进行分析,研究发现：(1)20 hm~2南亚热带常绿阔叶林鼎湖山(DHS)大型固定样地经过10年的更新演替,总个体数出现了爆发式增长。DHS样地周边5个卫星样地之间总个体数差异较大,按个体数进行排序：1号(南亚热带山地常绿阔叶林)> 3号(南亚热带常绿阔叶林)> 5号(南亚热带针阔混交林)>4号(南亚热带常绿针叶林)>2号(南亚热带沟谷雨林)卫星样地。(2)DHS大样地的物种并未达到饱和,卫星样地群落可以有效补充该区域的物种。(3)DHS大样地的α多样性较高;卫星样地之中,2号样地的物种多样性最高,其次是3号样地,继而是1号和4号样地,最后是5号样地。除了2号样地由于大量大树和巨树的存在使得物种均匀度提升,从而导致多样性指数值偏大以外,其它样地的结果呈现出海拔高度与多样性正相关。(4)DHS大样地与其3号卫星样地处于相近...     

Tree species influences soil microbial community diversity but not biomass in a karst forest in southwestern China

中国西南喀斯特森林树种对土壤微生物群落多样性和生物量的影响陆地生态系统中植物种对土壤微生物群落结构的影响不一,而喀斯特生态系统中植物种对土壤微生物群落结构影响的研究尚未见报道。本研究利用磷酸脂肪酸(PLFA)法,分析了黔中高原型喀斯特常绿落叶阔叶混交林5个优势树种—窄叶石栎(Lithocarpus confinis Huang)、圆果化香(Platycarya longipes Wu)、滇鼠刺(Itea yunnanensis Franch.)、安顺润楠(Machilus cavaleriei H. Lév.)、云贵鹅耳枥(Carpinus pubescens Burkill)—与土壤理化性质对土壤微生物群落组成和生物量的影响。在测试的212个土壤样品 中共检测出132种PLFA,每个样品土壤微生物平均PLFA数量和生物量分别为65.97和11.22 µg g^–1。土壤表层(0–10 cm)的土壤微生物PLFA数量与下层(10–20 cm)土壤接近,但前者土壤微生物生物量显著高于后者(P < 0.05)。树种影响土壤微生物PLFA数量,但对土壤微生物生物量没有影响。云贵鹅耳枥附近的土壤微生物PLFA数量显著高于其他树种(P < 0.05),而其他树种土壤微生物PLFA数量接近。土壤微生物 生物量与表层土壤的理化性质无显著相关,但与下层土壤的有机碳、全氮和全磷含量呈显著正相关 (P < 0.05)。总之,黔中高原型喀斯特森林真菌/细菌生物量比率低,微生物总生物量低,但微生物群落多样性高。树种对土壤微生物群落多样性产生影响。     

Diet optimization in a generalist herbivore: The moose

In an attempt to understand the foraging of a generalist herbivore, a linear programming optimization model was constructed to describe moose feeding in summer. The model attempts to predict the amounts of aquatic vegetation, deciduous leaves, and forbs a moose should consume each day; and to determine whether or not its feeding is constrained by the maximum feeding time available each day, its daily rumen processing capacity, its sodium requirements, and its energy metabolism. The model can be solved for two alternative strategies: time minimization and energy maximization. The energy-maximizing strategy appears to predict the observed diet chosen by an average moose very well. Also, the diets selected by moose of each sex and various reproductive states appear to fit the energy-maximizing strategy. In addition, it is demonstrated that a moose's body size at weaning, size at first reproduction, and maximum size are related to foraging efficiency. Furthermore, there appears to exist an optimum adult body size for feeding. The general conclusion arrived at is that the foraging of a generalist herbivore can be predicted in a quantitative manner, at least in this case, as has been shown for other types of consumers (carnivores and granivores).     

Distinct patterns of soil bacterial and fungal community assemblages in subtropical forest ecosystems under warming

Climate change globally affects soil microbial community assembly across ecosystems. However, little is known about the impact of warming on the structure of soil microbial communities or underlying mechanisms that shape microbial community composition in subtropical forest ecosystems. To address this gap, we utilized natural variation in temperature via an altitudinal gradient to simulate ecosystem warming. After 6 years, microbial co-occurrence network complexity increased with warming, and changes in their taxonomic composition were asynchronous, likely due to contrasting community assembly processes. We found that while stochastic processes were drivers of bacterial community composition, warming led to a shift from stochastic to deterministic drivers in dry season. Structural equation modelling highlighted that soil temperature and water content positively influenced soil microbial communities during dry season and negatively during wet season. These results facilitate our understanding of the response of soil microbial communities to climate warming and may improve predictions of ecosystem function of soil microbes in subtropical forests.     

Ecological stoichiometry of the epiphyte community in a subtropical forest canopy

Epiphytes in tree canopies make a considerable contribution to the species diversity, aboveground biomass, and nutrient pools in forest ecosystems. However, the nutrient status of epiphytes and their possible adaptations to nutrient deficiencies in the forest canopy remain unclear. Therefore, we analyzed the stoichiometry of five macroelements (C, N, P, K, and Ca) in four taxonomic groups (lichens, bryophytes, ferns, and spermatophytes) to investigate this issue in a subtropical montane moist evergreen broad‐leaved forest in Southwest China. We found that the interspecific variations in element concentrations and mass ratios were generally greater than the intraspecific variations. And there were significant stoichiometric differences among functional groups. Allometric relationships between N and P across the epiphyte community indicated that P might be in greater demand than N with an increase in nutrients. Although canopy nutrients were deficient, most epiphytes could still maintain high N and P concentrations and low N:P ratios. Moreover, ferns and spermatophytes allocated more limited nutrients to leaves than to stems and roots. To alleviate frequent drought stress in the forest canopy, vascular epiphytes maintained several times higher K concentrations in their leaves than in the tissues of lichens and bryophytes. Our results suggest that epiphytes may have evolved specific nutrient characteristics and adaptations, so that they can distribute in heterogeneous canopy habitats and maintain the stability of nutrient metabolism.     

南亚热带混交人工林树种丰富度与土壤微生物多样性和群落组成的关系

森林植被与土壤微生物作为森林生态系统的重要组成部分,它们之间的相互作用对维持森林生态系统功能和稳定性起着重要作用。以往多在天然草地和森林生态系统开展植物多样性与土壤微生物多样性关系的研究,但人工构建的多树种混交林生态系统中树种多样性对土壤微生物群落组成的影响及其机制尚不完全清楚。因此,以南亚热带人工块状造林后自然恢复形成的多树种混交森林生态系统为研究对象,利用高通量测序技术研究了随树种丰富度(1—10种)变化土壤细菌和真菌多样性的变化规律及主要影响因子。结果表明,随树种丰富度增加,土壤真菌α多样性显著提高,但土壤细菌α多样性差异不显著;不同树种丰富度梯度间土壤细菌和真菌的群落结构组成均差异显著;Pearson相关分析表明土壤细菌α多样性主要受土壤pH和土壤铵态氮影响,而土壤pH和有效磷是土壤真菌α多样性的主要影响因子。距离冗余分析(db-RDA)表明,对土壤细菌群落组成产生显著影响的环境因子分别为土壤pH、硝态氮和芳香碳组分,而土壤有机碳、硝态氮、细根生物量和氧烷基碳组分是影响土壤真菌群落组成的主要因子。本研究的结果说明了南亚热带人工林不同树种混交后形成多树种混交林生态系统的过程中,树...     

亚热带两种森林土壤担子菌漆酶基因多样性比较

漆酶是降解森林凋落物中木质素的关键酶之一,直接影响着森林生态系统碳循环过程.运用TA克隆、测序技术,研究了两种亚热带森林(原生常绿落叶阔叶混交林和人工马尾松林)凋落物层(O层)和土壤表层(A层,0～20 cm)降解木质素的担子菌漆酶基因多样性.结果表明:同一土壤层位,原生林土壤中担子菌漆酶基因多样性和种群丰富度高于马尾松林;同一森林生态系统,原生林土壤O层中担子菌漆酶基因多样性和种群丰富度略高于土壤A层,而马尾松林则O层明显低于A层;两森林土壤具有相同含漆酶基因的担子菌优势种群,且大部分优势种群与伞菌目小菇属或侧耳属有较高的氨基酸相似性;与原生林土壤A层和马尾松林土壤O层相比,原生林土壤O层和马尾松林土壤A层中含漆酶基因的担子菌种群分布相对均匀;马尾松林O层与A层之间漆酶基因核苷酸序列的相似性较原生林土壤O层与A层之间的高.表明植被和土壤层位显著影响漆酶基因多样性和群落结构,而植被和土壤层位引起的担子菌可利用底物和土壤pH值的差异可能直接驱动这种影响.