Spatial heterogeneity in species composition constrains plant community responses to herbivory and fertilisation

Environmental change can result in substantial shifts in community composition. The associated immigration and extinction events are likely constrained by the spatial distribution of species. Still, studies on environmental change typically quantify biotic responses at single spatial (time series within a single plot) or temporal (spatial beta diversity at single time points) scales, ignoring their potential interdependence. Here, we use data from a global network of grassland experiments to determine how turnover responses to two major forms of environmental change – fertilisation and herbivore loss – are affected by species pool size and spatial compositional heterogeneity. Fertilisation led to higher rates of local extinction, whereas turnover in herbivore exclusion plots was driven by species replacement. Overall, sites with more spatially heterogeneous composition showed significantly higher rates of annual turnover, independent of species pool size and treatment. Taking into account spatial biodiversity aspects will therefore improve our understanding of consequences of global and anthropogenic change on community dynamics

QTL and Drought Effects on Leaf Physiology in Lowland Panicum virgatum

Switchgrass is a key component of plans to develop sustainable cellulosic ethanol production for bioenergy in the USA. We sought quantitative trait loci (QTL) for leaf structure and function, using the Albany full-sib mapping population, an F1 derived from lowland tetraploid parents. We also assessed both genotype × environment interactions (G×E) in response to drought and spatial trends within experimental plots, using the mapping population and check clones drawn from the parent cultivars. Phenotypes for leaf structure and physiological performance were determined under well-watered conditions in two consecutive years, and we applied drought to one of two replicates to test for G×E. Phenotypes for check clones varied with location in our plot and were impacted by drought, but there was limited evidence of G×E except in quantum yield (ΦPSII). Phenotypes of Albany were also influenced by plant location within our plot, and after correcting for experimental design factors and spatial effects, we detected QTL for leaf size, tissue density (LMA), and stomatal conductance (gs). Clear evidence of G×E was detected at a QTL for intrinsic water use efficiency (iWUE) that was expressed only under drought. Loci influencing physiological traits had small additive effects, showed complex patterns of heritability, and did not co-localize with QTL for morphological traits. These insights into the genetic architecture of leaf structure and function set the stage for consideration of leaf physiological phenotypes as a component of switchgrass improvement for bioenergy purposes

Effects of nitrogen fertilization and bioenergy crop species on central tendency and spatial heterogeneity of soil glycosidase activities

Extracellular glycosidases in soil, produced by microorganisms, act as major agents for decomposing labile soil organic carbon (e.g., cellulose). Soil extracellular glycosidases are significantly affected by nitrogen (N) fertilization but fertilization effects on spatial distributions of soil glycosidases have not been well addressed. Whether the effects of N fertilization vary with bioenergy crop species also remains unclear. Based on a 3-year fertilization experiment in Middle Tennessee, USA, a total of 288 soil samples in topsoil (0–15 cm) were collected from two 15 m2 plots under three fertilization treatments in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) using a spatially explicit design. Four glycosidases, α-glucosidase (AG), β-glucosidase (BG), β-xylosidase (BX), cellobiohydrolase (CBH), and their sum associated with C acquisition (Cacq) were quantified. The three fertilization treatments were no N input (NN), low N input (LN: 84 kg N ha−1 year−1 in urea) and high N input (HN: 168 kg N ha−1 year−1 in urea). The descriptive and geostatistical approaches were used to evaluate their central tendency and spatial heterogeneity. Results showed significant interactive effects of N fertilization and crop type on BX such that LN and HN significantly enhanced BX by 14% and 44% in SG, respectively. The significant effect of crop type was identified and glycosidase activities were 15–39% higher in GG than those in SG except AG. Within-plot variances of glycosidases appeared higher in SG than GG but little differed with N fertilization due to large plot-plot variation. Spatial patterns were generally more evident in LN or HN plots than NN plots for BG in SG and CBH in GG. This study suggested that N fertilization elevated central tendency and spatial heterogeneity of glycosidase activities in surficial soil horizons and these effects however varied with crop and enzyme types. Future studies need to focus on specific enzyme in certain bioenergy cropland soil when N fertilization effect is evaluated

Nutrient addition shifts plant community composition towards earlier flowering species in some prairie ecoregions in the U.S. Central Plains

e0178440, 15 p.The distribution of flowering across the growing season is governed by each species' evolutionary history and climatic variability. However, global change factors, such as eutrophication and invasion, can alter plant community composition and thus change the distribution of flowering across the growing season. We examined three ecoregions (tall-, mixed, and short-grass prairie) across the U.S. Central Plains to determine how nutrient (nitrogen (N), phosphorus, and potassium (+micronutrient)) addition alters the temporal patterns of plant flowering traits. We calculated total community flowering potential (FP) by distributing peakseason plant cover values across the growing season, allocating each species' cover to only those months in which it typically flowers. We also generated separate FP profiles for exotic and native species and functional group. We compared the ability of the added nutrients to shift the distribution of these FP profiles (total and sub-groups) across the growing season. In all ecoregions, N increased the relative cover of both exotic species and C3 graminoids that flower in May through August. The cover of C4 graminoids decreased with added N, but the response varied by ecoregion and month. However, these functional changes only aggregated to shift the entire community's FP profile in the tall-grass prairie, where the relative cover of plants expected to flower in May and June increased and those that flower in September and October decreased with added N. The relatively low native cover in May and June may leave this ecoregion vulnerable to disturbance induced invasion by exotic species that occupy this temporal niche. There was no change in the FP profile of the mixed and short-grass prairies with N addition as increased abundance of exotic species and C3 graminoids replaced other species that flower at the same time. In these communities a disturbance other than nutrient addition may be required to disrupt phenological patterns

Effects of precipitation changes on aboveground net primary production and soil respiration in a switchgrass field

Switchgrass (Panicum virgatum L.) is widely selected as a model feedstock for sustainable replacement of fossil fuels and climate change mitigation. However, how climate changes, such as altered precipitation (PPT), will influence switchgrass growth and soil carbon storage potential have not been well investigated. We conducted a two-year PPT manipulation experiment with five treatments: −50%, −33%, +0%, +33%, and +50% of ambient PPT, in an “Alamo” switchgrass field in Nashville, TN. Switchgrass aboveground net primary production (ANPP), leaf gas exchange, and soil respiration (SR) were determined each growing season. Data collected from this study was then used to test whether switchgrass ANPP responds to PPT changes in a double asymmetry pattern as framed by Knapp et al. (2017), and whether it is held true for other ecosystem processes such as SR. Results showed that the wet (+33%, and +50%) treatments had little effects on ANPP and leaf gas exchange compared to the ambient precipitation treatment, regardless of fertilization or not. The −33% treatment did not change ANPP and leaf photosynthesis, but significantly decreased transpiration and enhanced water use efficiency (WUE). Only the −50% treatment significantly decreased ANPP and LAI, without changing leaf photosynthesis. SR generally decreased under the drought treatments and increased under the wet treatments, while there was no significant difference between the two drought treatments or between the two wet treatments. Our results demonstrate that switchgrass ANPP responded in a single negative asymmetry model to PPT changes probably due to relative high PPT in the region. However, even in such a mesic ecosystem, SR responded strongly to PPT changes in an “S” curve model, suggesting that future climate changes may have greater but more complex effects on switchgrass belowground than aboveground processes. The contrasting models for switchgrass ANPP and SR in response to PPT indicate that extreme wet or dry PPT conditions may shift ecosystem from carbon accumulation toward debt, and in turn provide government and policy makers with useful information for sustainable management of switchgrass

Soil extracellular oxidases mediated nitrogen fertilization effects on soil organic carbon sequestration in bioenergy croplands

Nitrogen (N) fertilization significantly affects soil extracellular oxidases, agents responsible for decomposition of slow turnover and recalcitrant soil organic carbon (SOC; e.g., lignin), and consequently influences soil carbon sequestration capacity. However, it remains unclear how soil oxidases mediate SOC sequestration under N fertilization, and whether these effects co-vary with plant type (e.g., bioenergy crop species). Using a spatially explicit design and intensive soil sampling strategy under three fertilization treatments in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) croplands, we quantified the activities of polyphenolic oxidase (PHO), peroxidase (PER), and their sum associated with recalcitrant C acquisition (OX). The fertilization treatments included no N fertilizer input (NN), low N input (LN: 84 kg N ha−1 year−1 in urea), and high N input (HN: 168 kg N ha−1 year−1 in urea). Besides correlations between soil oxidases and SOC (formerly published), both descriptive and geostatistical approaches were applied to evaluate the effects of N fertilization and crop type on soil oxidases activities and their spatial distributions. Results showed significantly negative correlations between soil oxidase activities and SOC across all treatments. The negative relationship of soil oxidases and SOC was also evident under N fertilization. First, LN significantly depressed oxidases in both mean activities and spatial heterogeneity, which corresponded to increased SOC in SG (though by 5.4%). LN slightly influenced oxidases activities and their spatial heterogeneity, consistent with insignificant changes of SOC in GG. Second, HN showed trends of decrease in soil oxidase activities, which aligned with the significantly enhanced SOC in both croplands. Overall, this study demonstrated that soil oxidase activities acted as sensitive and negative mediators of SOC sequestration in bioenergy croplands and optimizing fertilizer use particularly in switchgrass cropland can improve for both carbon sequestration and environmental benefit

A Randomised Phase 2 Trial of Intensive Induction Chemotherapy (CBOP/BEP) and Standard BEP in Poor-prognosis Germ Cell Tumours (MRC TE23, CRUK 05/014, ISRCTN 53643604)

AbstractBackgroundStandard chemotherapy for poor-prognosis metastatic nonseminoma has remained bleomycin, etoposide, and cisplatin (BEP) for many years; more effective regimens are required.ObjectiveTo explore whether response rates with a new intensive chemotherapy regimen, CBOP/BEP (carboplatin, bleomycin, vincristine, cisplatin/BEP), versus those in concurrent patients treated with standard BEP justify a phase 3 trial.Design, setting, and participantsWe conducted a phase 2 open-label randomised trial in patients with germ cell tumours of any extracranial primary site and one or more International Germ Cell Cancer Collaborative Group poor-prognosis features. Patients were randomised between 2005 and 2009 at 16 UK centres.InterventionBEP (bleomycin 30 000 IU) was composed of four cycles over 12 wk. CBOP/BEP was composed of 2×CBOP, 2×BO, and 3×BEP (bleomycin 15 000 IU).Outcome measurements and statistical analysisPrimary end point was favourable response rate (FRR) comprising complete response or partial response and normal markers. Success required the lower two-sided 90% confidence limit to exclude FRRs <60%; 44 patients on CBOP/BEP gives 90% power to achieve this if the true FRR is ≥80%. Equal numbers were randomised to BEP to benchmark contemporary response rates.Results and limitationsA total of 89 patients were randomised (43 CBOP/BEP, 46 BEP); 40 and 41, respectively, completed treatment. CBOP/BEP toxicity, largely haematologic, was high (96% vs 63% on BEP had Common Terminology Criteria for Adverse Events v.3 grade ≥3). FRRs were 74% (90% confidence interval [CI], 61–85) with CBOP/BEP, 61% with BEP (90% CI, 48–73). After a median of 58-mo follow-up, 1-yr progression-free survival (PFS) was 65% and 43%, respectively (hazard ratio: 0.59; 95% CI, 0.33–1.06); 2-yr overall survival (OS) was 67% and 61%. Overall, 3 of 14 CBOP/BEP and 2 of 18 BEP deaths were attributed to toxicity, one after an overdose of bleomycin during CBOP/BEP. The trial was not powered to compare PFS.ConclusionsThe primary outcome was met, the CI for CBOP/BEP excluding FRRs <61%, but CBOP/BEP was more toxic. PFS and OS data are promising but require confirmation in an international phase 3 trial.Patient summaryIn this study we tested a new, more intensive way to deliver a combination of drugs often used to treat men with testicular cancer. We found that response rates were higher but that the CBOP/BEP regimen caused more short-term toxicity. Because most patients are diagnosed when their cancer is less advanced, it took twice as long to complete the trial as expected. Although we plan to carry out a larger trial, we will need international collaboration.Trial registrationISRCTN53643604; http://www.controlled-trials.com/ISRCTN53643604

Nutrient addition increases grassland sensitivity to droughts

Grasslands worldwide are expected to experience an increase in extreme events such asdrought, along with simultaneous increases in mineral nutrient inputs as a result of human industrialactivities. These changes are likely to interact because elevated nutrient inputs may alter plantdiversity and increase the sensitivity to droughts. Dividing a system?s sensitivity to drought intoresistance to change during the drought and rate of recovery after the drought generates insights intodifferent dimensions of the system?s resilience in the face of drought. Here, we examine the effects ofexperimental nutrient fertilization and the resulting diversity loss on the resistance to and recoveryfrom severe regional droughts. We do this at 13 North American sites spanning gradients of aridity, 5annual grasslands in California and 8 perennial grasslands in the Great Plains. We measured rate ofresistance as the change in annual aboveground biomass (ANPP) per unit change in growing seasonprecipitation as conditions declined from normal to drought. We measured recovery as the change inANPP during the post drought period and the return to normal precipitation. Resistance and recoverydid not vary across the 400 mm range of mean growing season precipitation spanned by our sites inthe Great Plains. However, chronic nutrient fertilization in the Great Plains reduced drought resistanceand increased drought recovery. In the California annual grasslands, arid sites had a greater recoverypost-drought than mesic sites, and nutrient addition had no consistent effects on resistance orrecovery. Across all study sites, we found that pre-drought species richness in natural grasslands wasnot consistently associated with rates of resistance to or recovery from the drought, in contrast toearlier findings from experimentally assembled grassland communities. Taken together, these resultssuggest that human-induced eutrophication may destabilize grassland primary production, but theeffects of this may vary across regions and flora, especially between perennial and annual-dominatedgrasslands.Fil: Bharath, Siddharth. University of Minnesota; Estados UnidosFil: Borer, Elizabeth. University of Minnesota; Estados UnidosFil: Biederman, Lori A.. owa State University; Estados UnidosFil: Blumenthal, Dana M.. State University of Colorado - Fort Collins; Estados UnidosFil: Fay, Philip A.. United States Department of Agriculture; Estados UnidosFil: Gherardi, Laureano. Arizona State University; Estados UnidosFil: Knops, Johannes M. H.. United States Department of Agriculture; Estados UnidosFil: Leakey, Andrew D. B.. State University of Colorado - Fort Collins; Estados UnidosFil: Yahdjian, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Seabloom, Eric. University of Minnesota; Estados Unido