Tulio Arredondo

Plant species richness and ecosystem multifunctionality in global drylands

Global Ecosystem Analysis The relationship between species richness and the functional properties of their ecosystems has often been studied at small scales in experimental plots. Maestre et al. (p. 214; see the Perspective by Midgley) performed field measurements at 224 dryland sites from six continents and assessed 14 ecosystem functions related to carbon, nitrogen, and phosphorus cycling. Positive relationships were observed between perennial plant species richness and ecosystem functionality. The relative importance of biodiversity was found to be as large as, or larger than, many key abiotic variables. Thus, preservation of plant biodiversity is important to buffer negative effects of climate change and desertification in drylands, which collectively cover 41% of Earths land surface and support over 38% of the human population. Plant species richness is positively related to ecosystem multifunctionality in drylands at a global scale. Experiments suggest that biodiversity enhances the ability of ecosystems to maintain multiple functions, such as carbon storage, productivity, and the buildup of nutrient pools (multifunctionality). However, the relationship between biodiversity and multifunctionality has never been assessed globally in natural ecosystems. We report here on a global empirical study relating plant species richness and abiotic factors to multifunctionality in drylands, which collectively cover 41% of Earth’s land surface and support over 38% of the human population. Multifunctionality was positively and significantly related to species richness. The best-fitting models accounted for over 55% of the variation in multifunctionality and always included species richness as a predictor variable. Our results suggest that the preservation of plant biodiversity is crucial to buffer negative effects of climate change and desertification in drylands.

Decoupling of soil nutrient cycles as a function of aridity in global drylands

The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems. It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes. Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability. The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients. Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. We find a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition. Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems.

Increasing aridity reduces soil microbial diversity and abundance in global drylands.

Significance Climate change is increasing the degree of aridity in drylands, which occupy 41% of Earth’s surface and support 38% of its population. Soil bacteria and fungi are largely responsible for key ecosystem services, including soil fertility and climate regulation, yet their responses to changes in aridity are poorly understood. Using a field survey conducted in drylands worldwide and DNA-sequencing approaches, we found that increases in aridity reduce the diversity and abundance of soil bacteria and fungi. This study represents an important advancement in our understanding of soil microbial communities and their likely responses to ongoing climate change. Soil bacteria and fungi play key roles in the functioning of terrestrial ecosystems, yet our understanding of their responses to climate change lags significantly behind that of other organisms. This gap in our understanding is particularly true for drylands, which occupy ∼41% of Earth´s surface, because no global, systematic assessments of the joint diversity of soil bacteria and fungi have been conducted in these environments to date. Here we present results from a study conducted across 80 dryland sites from all continents, except Antarctica, to assess how changes in aridity affect the composition, abundance, and diversity of soil bacteria and fungi. The diversity and abundance of soil bacteria and fungi was reduced as aridity increased. These results were largely driven by the negative impacts of aridity on soil organic carbon content, which positively affected the abundance and diversity of both bacteria and fungi. Aridity promoted shifts in the composition of soil bacteria, with increases in the relative abundance of Chloroflexi and α-Proteobacteria and decreases in Acidobacteria and Verrucomicrobia. Contrary to what has been reported by previous continental and global-scale studies, soil pH was not a major driver of bacterial diversity, and fungal communities were dominated by Ascomycota. Our results fill a critical gap in our understanding of soil microbial communities in terrestrial ecosystems. They suggest that changes in aridity, such as those predicted by climate-change models, may reduce microbial abundance and diversity, a response that will likely impact the provision of key ecosystem services by global drylands.

Climate and soil attributes determine plant species turnover in global drylands

AIM Geographic, climatic, and soil factors are major drivers of plant beta diversity, but their importance for dryland plant communities is poorly known. This study aims to: i) characterize patterns of beta diversity in global drylands, ii) detect common environmental drivers of beta diversity, and iii) test for thresholds in environmental conditions driving potential shifts in plant species composition. LOCATION 224 sites in diverse dryland plant communities from 22 geographical regions in six continents. METHODS Beta diversity was quantified with four complementary measures: the percentage of singletons (species occurring at only one site), Whittakes beta diversity (β(W)), a directional beta diversity metric based on the correlation in species occurrences among spatially contiguous sites (β(R2)), and a multivariate abundance-based metric (β(MV)). We used linear modelling to quantify the relationships between these metrics of beta diversity and geographic, climatic, and soil variables. RESULTS Soil fertility and variability in temperature and rainfall, and to a lesser extent latitude, were the most important environmental predictors of beta diversity. Metrics related to species identity (percentage of singletons and β(W)) were most sensitive to soil fertility, whereas those metrics related to environmental gradients and abundance ((β(R2)) and β(MV)) were more associated with climate variability. Interactions among soil variables, climatic factors, and plant cover were not important determinants of beta diversity. Sites receiving less than 178 mm of annual rainfall differed sharply in species composition from more mesic sites (> 200 mm). MAIN CONCLUSIONS Soil fertility and variability in temperature and rainfall are the most important environmental predictors of variation in plant beta diversity in global drylands. Our results suggest that those sites annually receiving ~ 178 mm of rainfall will be especially sensitive to future climate changes. These findings may help to define appropriate conservation strategies for mitigating effects of climate change on dryland vegetation.

Soil fungal abundance and plant functional traits drive fertile island formation in global drylands

Dryland vegetation is characterized by discrete plant patches that accumulate and capture soil resources under their canopies. These “fertile islands” are major drivers of dryland ecosystem structure and functioning, yet we lack an integrated understanding of the factors controlling their magnitude and variability at the global scale. We conducted a standardized field survey across 236 drylands from five continents. At each site, we measured the composition, diversity and cover of perennial plants. Fertile island effects were estimated at each site by comparing composite soil samples obtained under the canopy of the dominant plants and in open areas devoid of perennial vegetation. For each sample, we measured 15 soil variables (functions) associated with carbon, nitrogen and phosphorus cycling and used the relative interaction index to quantify the magnitude of the fertile island effect for each function. In 80 sites, we also measured fungal and bacterial abundance (quantitative PCR) and diversity (Illumina MiSeq). The most fertile islands, i.e. those where a higher number of functions were simultaneously enhanced, were found at lower elevation sites with greater soil pH values and sand content under semiarid climates, particularly at locations where the presence of tall woody species with a low-specific leaf area increased fungal abundance beneath plant canopies, the main direct biotic controller of the fertile island effect in the drylands studied. Positive effects of fungal abundance were particularly associated with greater nutrient contents and microbial activity (soil extracellular enzymes) under plant canopies. Synthesis. Our results show that the formation of fertile islands in global drylands largely depends on: (1) local climatic, topographic and edaphic characteristics, (2) the structure and traits of local plant communities and (3) soil microbial communities. Our study also has broad implications for the management and restoration of dryland ecosystems worldwide, where woody plants are commonly used as nurse plants to enhance the establishment and survival of beneficiary species. Finally, our results suggest that forecasted increases in aridity may enhance the formation of fertile islands in drylands worldwide.

Fine-Scale Spatial Genetic Structure in Perennial Grasses in Three Environments

Abstract Past research has shown that changes in grazing-resistance traits may be associated with genetic changes in plant populations. Little is known about spatial genetic relationships within plant populations (spatial genetic structure) and any grazing effects on these relationships. Here we present observations of the fine-scale spatial genetic structure in three grass species in semiarid environments (Arizona, Mexico, and Argentina). In each environment, populations of a dominant grass species were sampled from two sites with contrasting livestock grazing histories. Plant genotypes were described with the use of amplified fragment length polymorphism markers. In Arizona, populations of sideoats grama (Bouteloua curtipendula var. caespitosa Gould and Kapadia) differed in that one has never experienced livestock grazing, whereas cattle have grazed the other. In the other two environments, populations exposed to long-term heavy grazing were examined, along with those that experienced either moderate grazing (Mexico, blue grama [Bouteloua gracilis {Willd. ex Kunt} Lag. ex Griffiths]) or extended exclusion of livestock (Argentina [Poa ligularis Nees ex Steud.]). Based on independent analysis of each population, we observed no differences in average gene diversity between populations of each species. With the use of analysis of molecular variance we found slight but significant genetic differentiation between populations with different grazing histories in Arizona and Argentina. Significant genetic structure was present in all populations and indicated an inverse relationship between spatial and genetic distance. Interestingly, this relationship was most pronounced in the cattle-free sideoats grama population, suggesting larger genetic neighborhood areas in the absence of livestock. Less distinct differences in spatial genetic structure associated with grazing history were evident in the other two species. We hypothesize that livestock grazing may lead to increased homogeneity in genetic structure at the landscape scale. Effectively examining this hypothesis presents many experimental challenges.

Initial response of phenology and yield components of wheat (Triticum durum L., CIRNO C2008) under experimental warming field conditions in the Yaqui Valley

This work evaluates the experimental warming effects on phenology and grain yield components of wheat in the Yaqui Valley, Sonora, México, using CIRNO C2008 variety from Triticum durum L., as a model during the cropping cycle of 2016–2017 (December to April). Infrared radiators were deployed to induce experimental warming by 2 °C above ambient crop canopy temperature, in a temperature free-air controlled enhancement system. Temperature was controlled by infrared temperature sensors placed in eight plots which covered a circle of r = 1.5 m starting five days after germination until harvest. The warming treatment caused a reduction of phenophases occurrence starting at the stem extension phenophase. Such phenological responses generated a significant biological cycle reduction of 14 days. Despite this delay, CIRNO C2008 completed its biological cycle adequately. However, plant height under the warming treatment was reduced significantly and differences were particularly observed at the final phenophases of the vegetative cycle. Plant height correlated negatively with spikes length, spikes mass, and number of filled grains. Warming also reduced grain yield in 33%. The warming treatment caused a stress intensity (SI = 1-yield warming/yield control) of 39.4% and 33.2% in biomass and grain yield, respectively. The differences in stress intensities between biomass and grain yield were based on plant height reduction. Grain mass was not affected, demonstrating the crop capability for remobilization and adequate distribution of elaborated substances for the spikes under warming conditions.