Water Stress Strengthens Mutualism Among Ants, Trees, and Scale Insects

Abiotic environmental variables strongly affect the outcomes of species interactions. For example, mutualistic interactions between species are often stronger when resources are limited. The effect might be indirect: water stress on plants can lead to carbon stress, which could alter carbon-mediated plant mutualisms. In mutualistic ant–plant symbioses, plants host ant colonies that defend them against herbivores. Here we show that the partners\u27 investments in a widespread ant–plant symbiosis increase with water stress across 26 sites along a Mesoamerican precipitation gradient. At lower precipitation levels, Cordia alliodora trees invest more carbon in Azteca ants via phloem-feeding scale insects that provide the ants with sugars, and the ants provide better defense of the carbon-producing leaves. Under water stress, the trees have smaller carbon pools. A model of the carbon trade-offs for the mutualistic partners shows that the observed strategies can arise from the carbon costs of rare but extreme events of herbivory in the rainy season. Thus, water limitation, together with the risk of herbivory, increases the strength of a carbon-based mutualism

Mammal and tree diversity accumulate different types of soil organic matter in the northern Amazon

Diversity of plants and animals influence soil carbon through their contributions to soil organic matter (SOM). However, we do not know whether mammal and tree communities affect SOM composition in the same manner. This question is relevant because not all forms of carbon are equally resistant to mineralization by microbes and thus, relevant to carbon storage. We analyzed the elemental and molecular composition of 401 soil samples, with relation to the species richness of 83 mammal and tree communities at a landscape scale across 4.8 million hectares in the northern Amazon. We found opposite effects of mammal and tree richness over SOM composition. Mammal diversity is related to SOM rich in nitrogen, sulfur and iron whereas tree diversity is related to SOM rich in aliphatic and carbonyl compounds. These results help us to better understand the role of biodiversity in the carbon cycle and its implications for climate change mitigation.Xunta de Galicia | ED481D 2019/024Xunta de Galicia | ED431C2021/32European Commission | Ref. H2020, n. 947921National Science Foundation (NSF) | BE/CNH 05 0809

Data from: Water stress strengthens mutualism among ants, trees, and scale insects

Abiotic environmental variables strongly affect the outcomes of species interactions. For example, mutualistic interactions between species are often stronger when resources are limited. The effect might be indirect: water stress on plants can lead to carbon stress, which could alter carbon-mediated plant mutualisms. In mutualistic ant–plant symbioses, plants host ant colonies that defend them against herbivores. Here we show that the partners' investments in a widespread ant–plant symbiosis increase with water stress across 26 sites along a Mesoamerican precipitation gradient. At lower precipitation levels, Cordia alliodora trees invest more carbon in Azteca ants via phloem-feeding scale insects that provide the ants with sugars, and the ants provide better defense of the carbon-producing leaves. Under water stress, the trees have smaller carbon pools. A model of the carbon trade-offs for the mutualistic partners shows that the observed strategies can arise from the carbon costs of rare but extreme events of herbivory in the rainy season. Thus, water limitation, together with the risk of herbivory, increases the strength of a carbon-based mutualism

A Plant Growth-Promoting Microbial Soil Amendment Dynamically Alters the Strawberry Root Bacterial Microbiome.

Despite growing interest in utilizing microbial-based methods for improving crop growth, much work still remains in elucidating how beneficial plant-microbe associations are established, and what role soil amendments play in shaping these interactions. Here, we describe a set of experiments that test the effect of a commercially available soil amendment, VESTA, on the soil and strawberry (Fragaria x ananassa Monterey) root bacterial microbiome. The bacterial communities of the soil, rhizosphere, and root from amendment-treated and untreated fields were profiled at four time points across the strawberry growing season using 16S rRNA gene amplicon sequencing on the Illumina MiSeq platform. In all sample types, bacterial community composition and relative abundance were significantly altered with amendment application. Importantly, time point effects on composition are more pronounced in the root and rhizosphere, suggesting an interaction between plant development and treatment effect. Surprisingly, there was slight overlap between the taxa within the amendment and those enriched in plant and soil following treatment, suggesting that VESTA may act to rewire existing networks of organisms through an, as of yet, uncharacterized mechanism. These findings demonstrate that a commercial microbial soil amendment can impact the bacterial community structure of both roots and the surrounding environment

Pringle.etal.PlosBiology

Raw data files and ReadMe file

Study sites and precipitation gradient.

<p>(A) Map showing the 26 study sites and (B) their annual precipitation. Additional work was conducted at three of the sites, Chamela (white circle), Huatulco (gray diamond), and Santa Rosa (black triangle), that spanned the Mesoamerican dry-forest precipitation gradient.</p

Summary of the data and results used to support carbon-limitation hypothesis.

*<p>Bold indicates significance at <i>p</i><0.05 level.</p>**<p>Mechanistic hypothesis illustrated in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001705#pbio-1001705-g001" target="_blank">Figure 1</a> schematic.</p

Tree NSC pools and water stress.

<p>Total NSCs, starch and sucrose pools in main stems in (A) the late dry season (April 2009) at a wetter site (Santa Rosa; black bars) and a drier site (Chamela; white bars) and (B) the early dry season (October 2009; gray bars) and the late dry season (April 2009; white bars) at the drier site. Bars indicate means, and error bars indicate SE; values are based on plant dry weights. Starch bars are open, glucose (free sugars) bars have diagonal lines, and sucrose bars have vertical lines. Asterisks (*) indicate <i>p</i><0.05 by two-tailed <i>t</i> tests.</p

Insurance model of indirect carbon trading.

<p>Equilibrium (A) tree carbon pools, <i>C^*</i>, and (B) ant colony size, <i>W^*</i>, as allocated in each mutualist's evolutionary stable strategy as a function of growing-season (rainy-season) duration. (C) Tree carbohydrate investment in ants, <i>a</i>, and (D) ant investment in colony growth, <i>u</i>, as a function of the season length T_s in the evolutionary stable strategy, while keeping the time a tree needs to replace its leaf area, <i>τ</i>, constant. Parameter values are: <i>h</i> = 0.1, <i>L_max</i> = 10, <i>τ</i> = 5, <i>μ</i> = 0.01, <i>k</i> = 10, and <i>q₀</i> = 1.</p