Open Data

Communities of soil insects in tropical rainforests are among the richest and most complex, but the mechanisms structuring them remain mostly unknown. Identifying whether nutrient availability plays a relevant role in the assembly of these communities poses several challenges due to the diverse nutritional requirements of insects. We investigated the importance of nutrient availability in accounting for the abundance, richness and composition of soil-insect communities in two tropical rainforests. We sampled soil insects 72 one square-meter sampling points across three topographic levels at two sites in French Guiana, counted all specimens and characterized each assemblage using DNA metabarcoding. We then determined the importance of nutrient availability by measuring 19 nutrient concentrations and ratios from pools of litter and topsoil.We collected 18,000 specimens from 17 different orders.Despite an extraordinary diversity and spatial heterogeneity, the concentrations of sodium (Na), potassium (K), magnesium (Mg) and calcium (Ca) positively correlated with either the abundance or the richness of the communities. We found similar relationships when analyzing the data separately for Blattodea, Coleoptera, Hymenoptera and Orthoptera, the most abundant insect orders with the most OTUs. These micronutrients were also important predictors of the composition of the assemblages. We did not find effects for nitrogen or phosphorus, and only the concentration of carbon in the litter strongly influenced the compositions of the hymenopteran and orthopteran communities. This lack of effect indicated that the availability of macronutrients was not a relevant driver of the communities in tropical rainforests as it is for plants and microbes, in contrast to micronutrients.Our results demonstrated that the availability of micronutrients played a large role in species selection during the assembly of the soil-insect communities in these tropical rainforests.The high unexplained variance, however, suggests that additional neutral and niche deterministic processes, such as stochastic population drift and biotic interactions, likely play complementary roles in structuring insect communities in the soils of tropical rainforests.

热带雨林土壤昆虫群落是全球物种最丰富、结构最复杂的昆虫群落之一，但其构建机制大多仍未明晰。由于昆虫营养需求存在多样性，明确养分有效性是否对这类群落的组装发挥关键作用，面临诸多挑战。本研究针对两处热带雨林，探究养分有效性对土壤昆虫群落的个体数量、物种丰富度及群落组成的影响。研究团队在法属圭亚那的两个研究点，沿三种地形梯度设置了72个1平方米的采样点采集土壤昆虫，计数所有标本，并通过DNA宏条形码（DNA metabarcoding）对每个群落进行特征分析。随后通过测定枯落物与表层土壤中的19种养分浓度及其比值，量化养分有效性的重要性。本次研究共采集到17个昆虫目、总计18000头昆虫标本。尽管群落呈现出极高的物种多样性与空间异质性，但钠（Na）、钾（K）、镁（Mg）及钙（Ca）的浓度，均与土壤昆虫群落的个体数量或物种丰富度呈显著正相关。针对个体数量与操作分类单元（Operational Taxonomic Units, OTUs）最多的蜚蠊目（Blattodea）、鞘翅目（Coleoptera）、膜翅目（Hymenoptera）及直翅目（Orthoptera）分别进行数据分析时，也得到了一致的相关关系。上述微量养分同样是群落组成的重要预测因子。但并未发现氮（N）或磷（P）对群落产生显著影响；仅枯落物中的碳浓度，对膜翅目与直翅目群落的组成存在显著影响。这一结果表明，与微量养分不同，大量养分的有效性并未如对植物与微生物那样，成为热带雨林土壤昆虫群落的关键驱动因子。本研究结果证实，微量养分的有效性在上述热带雨林土壤昆虫群落的组装过程中，对物种筛选发挥了重要作用。然而，仍存在大量未被解释的变异，这表明还有其他中性过程与生态位确定性过程——比如种群随机漂变与生物间相互作用——可能在热带雨林土壤昆虫群落的构建中发挥互补作用。