Photosynthesis and growth reduction with warming are driven by nonstomatal limitations in a Mediterranean semi-arid shrub

Whereas warming enhances plant nutrient status and photosynthesis in most terrestrial ecosystems, dryland vegetation is vulnerable to the likely increases in evapotranspiration and reductions in soil moisture caused by elevated temperatures. Any warming‐induced declines in plant primary production and cover in drylands would increase erosion, land degradation, and desertification. We conducted a four‐year manipulative experiment in a semi‐arid Mediterranean ecosystem to evaluate the impacts of a ~2°C warming on the photosynthesis, transpiration, leaf nutrient status, chlorophyll content, isotopic composition, biomass growth, and postsummer survival of the native shrub Helianthemum squamatum. We predicted that warmed plants would show reduced photosynthetic activity and growth, primarily due to the greater stomatal limitation imposed by faster and more severe soil drying under warming. On average, warming reduced net photosynthetic rates by 36% across the study period. Despite this strong response, warming did not affect stomatal conductance and transpiration. The reduction of peak photosynthetic rates with warming was more pronounced in a drought year than in years with near‐average rainfall (75% and 25–40% reductions relative to controls, respectively), with no indications of photosynthetic acclimation to warming through time. Warmed plants had lower leaf N and P contents, δ (13)C, and sparser and smaller leaves than control plants. Warming reduced shoot dry mass production by 31%. However, warmed plants were able to cope with large reductions in net photosynthesis, leaf area, and shoot biomass production without changes in postsummer survival rates. Our findings highlight the key role of nonstomatal factors (biochemical and/or nutritional) in reducing net carbon assimilation rates and growth under warming, which has important implications for projections of plant carbon balance under the warmer and drier climatic scenario predicted for drylands worldwide. Projected climate warming over the coming decades could reduce net primary production by about one‐third in semi‐arid gypsum shrublands dominated by H. squamatum

The gap between mycorrhizal science and application: existence, origins, and relevance during the United Nation's Decade on Ecosystem Restoration

During the United Nation's Decade on Ecosystem Restoration, planting material shortages are constraining restoration, while climate change exacerbates the need for restoration and reduces recruitment. Concurrently, research shows that native mycorrhizal fungi (symbiotic with plant roots) appropriate to plant provenance and site conditions significantly accelerate restoration, support crucial ecosystem services, and provide natural climate solutions (sequestering carbon), and nature-based solutions for climate change (climate adaptation). We reviewed 130 management plans for natural areas in the United States to evaluate whether restoring native mycorrhizal communities has translated into implementation. Although management plans frequently discussed the ecosystem services mycorrhizal fungi provide, nearly one half (46%) viewed fungi solely as pathogens or ignored them altogether. Only 8% of plans mentioned mycorrhizal fungi. Only one plan mentioned that mycorrhizae were potentially helpful to natural regeneration, while one other mentioned utilizing soil as a restoration tool. Our examination of publicly available data and case studies suggests that relatively meager protections for fungi, limited research funding and resulting data, research difficulty, and limited access to mycology experts and training contribute to this gap between science and implementation. A database of literature showcasing mycorrhizal ecosystem services and benefits is provided to highlight when and why mycorrhizae should be considered in management, regeneration, and restoration. Three action items are recommended to safeguard native mycorrhizal fungal communities and accelerate restoration and regeneration. Ten implementation tips based in scientific literature are provided to clarify the need and methods for mycorrhizal restorationAchievement Rewards for College Scientists Foundation. Grant Number: Mrs. John Van Denburgh Scholar Arizona Mushroom Society, Dr. Chester Leathers Graduate Student Scholarship Northern Arizona University, Lucking Family Professorship, Presidential Fellowship United States National Science Foundation. Grant Number: Macrosystems DEB-1340852Peer reviewe

Data from: Leaf carbon and oxygen isotopes are coordinated with the leaf economics spectrum in Mediterranean rangeland species

The leaf economics spectrum (LES) describes covariation of traits relevant to carbon and nutrient economics across plant species, but much less is known about the relationship between the LES and leaf water economy. We propose an approach combining the measurement of two leaf traits related to water use economy, leaf carbon (δ13C) and oxygen (δ18O) isotopic composition, and the measurement of leaf morphological and nutrient traits to investigate the link between leaf carbon and nutrient economics and water use. We tested the relationships between leaf traits linked to carbon and nutrient use within the LES and water use traits using leaf δ18O as a proxy of stomatal conductance (gs) and δ13C as a proxy of intrinsic water use efficiency (WUEi) across 15 Mediterranean rangeland species grown in an irrigated common garden and in a natural grassland in Southern France. The target species spanned a wide range of variation in leaf morphological and nutrient trait values and a wide range of leaf δ18O and δ13C values. PCA analysis revealed multiple associations among leaf morphology, nutrients and isotopic composition, with the first axis alone explaining 56.0% of the total variation across species. Leaf δ18O and δ13C covaried with leaf morphology and leaf nutrient concentrations along a single resource use axis. Species with high leaf δ18O and δ13C (low gs and high WUEi) exhibited a resource-conservative strategy (high LDMC, low leaf N, P and K) whereas species with low leaf δ18O and δ13C (high gs and low WUEi) showed a more resource-acquisitive strategy (high SLA and leaf N, P and K). These leaf trait syndromes and resource use strategies were strongly conserved across sites with contrasting environmental conditions, indicating that foliar δ18O and δ13C can be included as an integral part of the LES for this set of rangeland species. Overall, the data suggest a tight coupling and coordination between water, carbon and nutrient use strategies across herbaceous plant species. A dual δ18O and δ13C isotope approach combined with LES trait measurements is a promising tool to more comprehensively assess the diversity of resource use strategies among coexisting plant species

Simulated climate change in a semiarid shrubland decreased the phylogenetic diversity of arbuscular mycorrhizal fungal communities

Comunicación oral presentada en: International Society for Microbial Ecology Latin American Congress (ISMELAT). Bototá, Colombia, 27-30 de julio (2021) On line.In this study, we carried out a 9-year manipulative field experiment in a semiarid shrubland in Southeastern Spain (Sorbas, Almería) dominated by several shrub species, such as Helianthemum squamatum, Helianthemum syriacum, Teucrium turredanum, Santolina viscosa, Coris hispánica and Gypsophila struthium. The AM fungal community associated with soil was characterized by DNA sequencing using Illumina technology. We simulated the warmer and drier climate conditions (~2-7ºC temperature increase by using open top chambers and ~30% rainfall reduction using rainout shelters), in order to investigate the effect of increased temperature, rainfall reduction and their combination on the taxonomic and phylogenetic diversity of arbuscular mycorrhizal fungi communities in these areas. Warming factor had a significant effect on AMF community composition, favoring the presence of Glomeraceae family members mostly under the W+RR treatment. Rainfall reduction and its interaction with warming did not show a significant effect on AMF community composition. Indicator species analyses found that six VTs were indicators only for the W+RR treatment, the majority belonging to Glomeraceae family. In the phylogenetic diversity index, the W+RR treatment had the smallest and more negative value than rest of climate change treatments (-1.07 ± 0.41) and it was found to be significantly different from the generated null values (t = -2.70, p < 0.05). This means that the AM fungal communities associated with W+RR treatment exhibited a significant phylogenetic clustering. In conclusion, the combination of experimental warming and rainfall reduction significantly reduced the AMF phylogenetic/functional diversity with predominance of Glomeraceae members which were linked to decreased water content in the soil. This finding indicates that environmental filtering has selected AMF species with functional traits well-suited to cope with environmental stresses, which allowed them to survive under future climate changes in semiarid conditions

Long-term nutrient imbalances linked to drought-triggered forest dieback

Drought-induced forest dieback is causing reductions in productivity, increasing tree mortality and impairing terrestrial carbon uptake worldwide. However, the role played by long-term nutrient imbalances during drought-induced dieback is still unknown. To improve our knowledge on the relationships between dieback and nutrient imbalances, we analysed wood anatomical traits (tree-ring width and wood density), soil properties and long-term chemical information in tree-ring wood (1900–2010) by non-destructive Micro X-ray fluorescence (μXRF) and destructive (ICP-OES) techniques. We studied two major European conifers with ongoing drought-induced dieback in mesic (Abies alba, silver fir) and xeric (Pinus sylvestris, Scots pine) sites. In each site we compared coexisting declining (D) and non-declining (ND) trees. We used dendrochronology and generalized additive and linear mixed models to analyse trends in tree-ring nutrients and their relationships with wood traits. The D trees presented lower growth and higher minimum wood density than ND trees, corresponding to a smaller lumen area of earlywood tracheids and thus a lower theoretical hydraulic conductivity. These differences in growth and wood-anatomy were more marked in silver fir than in Scots pine. Moreover, most of the chemical elements showed higher concentrations in D than in ND trees during the last two-five decades (e.g., Mn, K and Mg), while Ca and Na increased in the sapwood of ND trees. The Mn concentrations, and related ratios (Ca:Mn, Mn:Al and P:Mn) showed the highest differences between D and ND trees for both tree species. These findings suggest that a reduced hydraulic conductivity, consistent with hydraulic impairment, is affecting the use of P in D trees, making them more prone to drought-induced damage. The retrospective quantifications of Mn ratios may be used as early-warning signals of impending dieback