Cessation of grazing causes biodiversity loss and homogenization of soil food webs

There is widespread concern that cessation of grazing in historically grazed ecosystems is causing biotic homogenization and biodiversity loss. We used 12 montane grassland sites along an 800 km north-south gradient across the UK, to test whether cessation of grazing affects local α- and β-diversity of below-ground food webs. We show cessation of grazing leads to strongly decreased α-diversity of most groups of soil microbes and fauna, particularly of relatively rare taxa. By contrast, the β-diversity varied between groups of soil organisms. While most soil microbial communities exhibited increased homogenization after cessation of grazing, we observed decreased homogenization for soil fauna after cessation of grazing. Overall, our results indicate that exclusion of domesticated herbivores from historically grazed montane grasslands has far-ranging negative consequences for diversity of below-ground food webs. This underscores the importance of grazers for maintaining the diversity of below-ground communities, which play a central role in ecosystem functioning.

Combined effects of warming and drought on plant biomass depend on plant woodiness and community type: a meta-analysis

Global warming and precipitation extremes (drought or increased precipitation) strongly affect plant primary production and thereby terrestrial ecosystem functioning. Recent syntheses show that combined effects of warming and precipitation extremes on plant biomass are generally additive, while individual experiments often show interactive effects, indicating that combined effects are more negative or positive than expected based on the effects of single factors. Here, we examined whether variation in biomass responses to single and combined effects of warming and precipitation extremes can be explained by plant growth form and community type. We performed a meta-analysis of 37 studies, which experimentally crossed warming and precipitation treatments, to test whether biomass responses to combined effects of warming and precipitation extremes depended on plant woodiness and community type (monocultures versus mixtures). Our results confirmed that the effects of warming and precipitation extremes were overall additive. However, combined effects of warming and drought on above- and belowground biomass were less negative in woody- than in herbaceous plant systems and more negative in plant mixtures than in monocultures. We further show that drought effects on plant biomass were more negative in greenhouse- than in field studies, suggesting that greenhouse experiments may overstate drought effects in the field. Our results highlight the importance of plant system characteristics to better understand plant responses to climate change.

A global database of soil nematode abundance and functional group composition

As the most abundant animals on earth, nematodes are a dominant component of the soil community. They play critical roles in regulating biogeochemical cycles and vegetation dynamics within and across landscapes and are an indicator of soil biological activity. Here, we present a comprehensive global dataset of soil nematode abundance and functional group composition. This dataset includes 6,825 georeferenced soil samples from all continents and biomes. For geospatial mapping purposes these samples are aggregated into 1,933 unique 1-km pixels, each of which is linked to 73 global environmental covariate data layers. Altogether, this dataset can help to gain insight into the spatial distribution patterns of soil nematode abundance and community composition, and the environmental drivers shaping these patterns.

Reduced tillage, but not organic matter input, increased nematode diversity and food web stability in European long-term field experiments

Soil nematode communities and food web indices can inform about the complexity, nutrient flows and decomposition pathways of soil food webs, reflecting soil quality. Relative abundance of nematode feeding and life‐history groups are used for calculating food web indices, i.e., maturity index (MI), enrichment index (EI), structure index (SI) and channel index (CI). Molecular methods to study nematode communities potentially offer advantages compared to traditional methods in terms of resolution, throughput, cost and time. In spite of such advantages, molecular data have not often been adopted so far to assess the effects of soil management on nematode communities and to calculate these food web indices. Here, we used high‐throughput amplicon sequencing to investigate the effects of tillage (conventional vs. reduced) and organic matter addition (low vs. high) on nematode communities and food web indices in 10 European long‐term field experiments and we assessed the relationship between nematode communities and soil parameters. We found that nematode communities were more strongly affected by tillage than by organic matter addition. Compared to conventional tillage, reduced tillage increased nematode diversity (23% higher Shannon diversity index), nematode community stability (12% higher MI), structure (24% higher SI), and the fungal decomposition channel (59% higher CI), and also the number of herbivorous nematodes (70% higher). Total and labile organic carbon, available K and microbial parameters explained nematode community structure. Our findings show that nematode communities are sensitive indicators of soil quality and that molecular profiling of nematode communities has the potential to reveal the effects of soil management on soil quality.

Evolution of plant parasitism in the phylum Nematoda

Within the species-rich and trophically diverse phylum Nematoda, at least four independent major lineages of plant parasites have evolved, and in at least one of these major lineages plant parasitism arose independently multiple times. Ribosomal DNA data, sequence information from nematode-produced, plant cell wall-modifying enzymes, and the morphology and origin of the style(t), a protrusible piercing device used to penetrate the plant cell wall, all suggest that facultative and obligate plant parasites originate from fungivorous ancestors. Data on the nature and diversification of plant cell wall-modifying enzymes point at multiple horizontal gene transfer events from soil bacteria to bacterivorous nematodes resulting in several distinct lineages of fungal or oomycete-feeding nematodes. Ribosomal DNA frameworks with sequence data from more than 2,700 nematode taxa combined with detailed morphological information allow for explicit hypotheses on the origin of agronomically important plant parasites, such as root-knot, cyst, and lesion nematodes.

Inositol polyphosphates regulate Ca2+ efflux in a cardiac membrane subtype distinct from junctional sarcoplasmic reticulum

The membrane location and mechanism of inositol 1,3,4,5-tetrakisphosphate (InsP4)-regulated Ca2+ uptake in cardiac membrane vesicles was investigated. In canine and rat membranes separated by sucrose density gradient centrifugation, InsP4-regulated Ca2+ uptake was slightly more enriched in low density than in higher density membranes. Membranes supporting InsP4-regulated Ca2+ uptake were correspondingly enriched in type 1 InsP3 receptors. Junctional sarcoplasmic reticulum (J-SR), enriched in sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) and ryanodine receptors, separated predominantly with higher density membranes. In membranes supporting InsP4-regulated Ca2+ uptake, Ca2+ uptake was facilitated by a high Ca2+ affinity carrier that was insensitive to thapsigargin. Ca2+ uptake in J-SR was mediated by thapsigargin-sensitive SERCA2a. Net Ca accumulation was enhanced by oxalate in both SR subtypes. Although Ca2+-carrier-mediated Ca2+ uptake was ATP independent, ATP indirectly regulated net Ca2+ accumulation by modifying Ca2+ efflux via a Ca2+ channel with properties of type 1 InsP3 receptors. In the presence of < or = 0.1 mM ATP, InsP4 enhanced Ca2+ accumulation whereas InsP4 inhibited Ca2+ uptake at higher ATP concentrations. In the presence of 0.15 mM ATP, InsP4 stimulated Ca2+ efflux from vesicles preloaded with Ca. Several other InsP4 isomers and 1,3,4-InsP3 also stimulated Ca2+ efflux but with slightly less potency than 1,3,4,5-InsP4. Ruthenium red enhanced net Ca accumulation by the Ca2+ carrier and reduced the potency of ATP, InsP4, and InsP3 to stimulate Ca2+ efflux in vesicles. In summary, this investigation shows that a Ca2+ carrier facilitates Ca loading in a sarcoplasmic reticulum subtype distinct from J-SR. InsP4 and InsP3 are proposed to regulate Ca2+ efflux in low density SR by acting on an ATP-modulated Ca2+ channel with properties of type 1 InsP3 receptors.

Mechanisms of prostaglandin F2 alpha and histamine-induced contractions in human chorionic vasculature

We investigated the signaling pathways modulating histamine- and prostaglandin F2 alpha (PGF2 alpha)-induced contractions of human chorionic vasculature. Neomycin, a phospholipase C (PLC) inhibitor, attenuated PGF2 alpha and histamine contractile responses 40 and 60%, respectively. AIF4-, a G protein stimulant, induced a strong contraction alone but blocked histamine- and PGF2 alpha-induced contractions. Staurosporine (100 nM), a protein kinase C (PKC) inhibitor, attenuated the PGF2 alpha-dependent contractions by 50% but did not affect the histamine response. However, higher nonspecific inhibitory concentrations of staurosporine (1-2 microM) abolished histamine and PGF2 alpha contractile responses, presumably by inhibiting other protein kinases. Although, the PKC phorbol 12-myristate 13-acetate (PMA) did not affect basal tension or PGF2 alpha-dependent contractions, the histamine response was attenuated by 30%. Sodium nitroprusside (SNP), a guanylyl cyclase stimulant, strongly attenuated histamine- and PGF2 alpha-induced contractions. Tension increases were similarly attenuated by forskolin and isobutylmethylxanthine (IBMX), which increase intracellular cyclic AMP. In vessel rings prelabeled with [3H]myoinositol, PGF2 alpha and histamine increased [3H]inositol phosphate (IP) production 400 and 100%, respectively, indicating that PLC is stimulated by both agonists. Neomycin inhibited histamine- and PGF2 alpha-induced increases in [3H]IP production 60 and 40%, respectively. Staurosporine (0.1-1 microM) and PMA did not affect histamine- or PGF2 alpha-stimulated IP production. AIF4-alone increased IP production but blocked histamine- and PGF(2 alpha)-dependent IP increases. These observations suggest that at least part of the contractile responses due to PGF2 alpha and histamine are associated with stimulation of PLC through an AIF4(-)-sensitive G protein. The role of PKC is variable, because PGF2 alpha but not histamine tension responses were attenuated by PKC inhibition. In addition, therapeutic agents that increase cyclic AMP and cyclic GMP attenuated histamine- and PGF2 alpha-induced contractions in human chorionic vasculature, although histamine responses were relatively more sensitive to these agents.

Inositol tetrakisphosphate stimulates a novel ATP-independent Ca2+ uptake mechanism in cardiac junctional sarcoplasmic reticulum

The effects of inositol phosphates on Ca2+ uptake in cardiac junctional sarcoplasmic reticulum (JSR) vesicles was investigated. Inositol 1,3,4,5-tetrakisphosphate (IP4) selectively increased Ca2+ uptake 2.8 fold over basal levels whereas 1,3,4-IP3, 1,4,5-IP3 or 1,4-IP2 were without effect. Stimulation of Ca2+ uptake by IP4 was maximal within 15-60 sec at 30 degrees C and ATP-independent. Following incubation of JSR with ruthenium red, Ca2+ uptake in the presence or absence of IP4 was further enhanced 2.5 fold. Both basal and IP4-stimulated Ca2+ uptake were half-maximal and maximal in the presence of 60 nM and 180 nM Ca2+, respectively. These studies indicate that IP4 stimulates an ATP-independent Ca2+ uptake mechanism in cardiac JSR which may function to promote rapid Ca2+ loading.

Regulation of the tension of human chorionic vasculature by histamine and prostaglandin F2 alpha

The calcium dependence of potassium chloride-, prostaglandin F2 alpha (PGF2 alpha)-, and histamine-induced contractions of human chorionic vasculature segments was investigated. In physiologic buffer that contained 1.5 mM calcium chloride, 60 mM potassium chloride induced a rapid and sustained contraction of the vasculature. Potassium chloride-induced contractions were completely inhibited by the calcium channel blockers diltiazem and nifedipine or by excluding Ca2+ from the medium. Histamine (100 microM) induced a rapid increase in vascular tension in physiologic buffer which rapidly faded or desensitized after maximal tension was obtained. The maximal contractile responses to histamine were reduced approximately 50% by diltiazem and nifedipine in physiologic buffer or by suspension in calcium-free medium (OCaPB). Pretreatment of vessels with 20 mM caffeine in OCaPB completely abolished histamine-dependent contractile responses. Prostaglandin F2 alpha (100 nM)-induced increases in vascular tension developed slowly but remained maximal for at least 40 minutes. Contractile responses to PGF2 alpha were reduced 50% to 65% by diltiazem and nifedipine in physiologic buffer or by suspension in OCaPB. Caffeine pretreatment failed to alter the contractile response to PGF2 alpha in OCaPB. The differences in responsiveness of potassium chloride, histamine, and PGF2 alpha under the various conditions used suggest that these agents act by different mechanisms to elicit contractions in chorionic vessels. The potential roles of PGF2 alpha, histamine, and calcium channel blockers in modulating the fetoplacental circulation is discussed.