The ecosystem wilting point defines drought response and recovery of a Quercus-Carya forest

Soil and atmospheric droughts increasingly threaten plant survival and productivity around the world. Yet, conceptual gaps constrain our ability to predict ecosystem-scale drought impacts under climate change. Here, we introduce the ecosystem wilting point (Ψ_EWP), a property that integrates the drought response of an ecosystem's plant community across the soil–plant–atmosphere continuum. Specifically, Ψ_EWP defines a threshold below which the capacity of the root system to extract soil water and the ability of the leaves to maintain stomatal function are strongly diminished. We combined ecosystem flux and leaf water potential measurements to derive the Ψ_EWP of a Quercus-Carya forest from an “ecosystem pressure–volume (PV) curve,” which is analogous to the tissue-level technique. When community predawn leaf water potential (Ψ_pd) was above Ψ_EWP (=−2.0 MPa), the forest was highly responsive to environmental dynamics. When Ψ_pd fell below Ψ_EWP, the forest became insensitive to environmental variation and was a net source of carbon dioxide for nearly 2 months. Thus, Ψ_EWP is a threshold defining marked shifts in ecosystem functional state. Though there was rainfall-induced recovery of ecosystem gas exchange following soaking rains, a legacy of structural and physiological damage inhibited canopy photosynthetic capacity. Although over 16 growing seasons, only 10% of Ψ_pd observations fell below Ψ_EWP, the forest is commonly only 2–4 weeks of intense drought away from reaching Ψ_EWP, and thus highly reliant on frequent rainfall to replenish the soil water supply. We propose, based on a bottom-up analysis of root density profiles and soil moisture characteristic curves, that soil water acquisition capacity is the major determinant of Ψ_EWP, and species in an ecosystem require compatible leaf-level traits such as turgor loss point so that leaf wilting is coordinated with the inability to extract further water from the soil.     

Complete ammonia oxidization in agricultural soils: High ammonia fertilizer loss but low N2O production

The contribution of agriculture to the sustainable development goals requires climate-smart and profitable farm innovations. Increasing the ammonia fertilizer applications to meet the global food demands results in high agricultural costs, environmental quality deterioration, and global warming, without a significant increase in crop yield. Here, we reported that a third microbial ammonia oxidation process, complete ammonia oxidation (comammox), is contributing to a significant ammonia fertilizer loss (41.9 ± 4.8%) at the rate of 3.53 ± 0.55 mg N kg⁻¹ day⁻¹ in agricultural soils around the world. The contribution of comammox to ammonia fertilizer loss, occurring mainly in surface agricultural soil profiles (0–0.2 m), was equivalent to that of bacterial ammonia oxidation (48.6 ± 4.5%); both processes were significantly more important than archaeal ammonia oxidation (9.5 ± 3.6%). In contrast, comammox produced less N₂O (0.98 ± 0.44 μg N kg⁻¹ day⁻¹, 11.7 ± 3.1%), comparable to that produced by archaeal ammonia oxidation (16.4 ± 4.4%) but significantly lower than that of bacterial ammonia oxidation (72.0 ± 5.1%). The efficiency of ammonia conversion to N₂O by comammox (0.02 ± 0.01%) was evidently lower than that of bacterial (0.24 ± 0.06%) and archaeal (0.16 ± 0.04%) ammonia oxidation. The comammox rate increased with increasing soil pH values, which is the only physicochemical characteristic that significantly influenced both comammox bacterial abundance and rates. Ammonia fertilizer loss, dominated by comammox and bacterial ammonia oxidation, was more intense in soils with pH >6.5 than in soils with pH <6.5. Our results revealed that comammox plays a vital role in ammonia fertilizer loss and sustainable development in agroecosystems that have been previously overlooked for a long term.     

Human appropriation of net primary production as driver of change in landscape-scale vertebrate richness

Aim

Land use is the most pervasive driver of biodiversity loss. Predicting its impact on species richness (SR) is often based on indicators of habitat loss. However, the degradation of habitats, especially through land-use intensification, also affects species. Here, we evaluate whether an integrative metric of land-use intensity, the human appropriation of net primary production, is correlated with the decline of SR in used landscapes across the globe.

Location

Global.

Time period

Present.

Major taxa studied

Birds, mammals and amphibians.

Methods

Based on species range maps (spatial resolution: 20 km × 20 km) and an area-of-habitat approach, we calibrated a “species–energy model” by correlating the SR of three groups of vertebrates with net primary production and biogeographical covariables in “wilderness” areas (i.e., those where available energy is assumed to be still at pristine levels). We used this model to project the difference between pristine SR and the SR corresponding to the energy remaining in used landscapes (i.e., SR loss expected owing to human energy extraction outside wilderness areas). We validated the projected species loss by comparison with the realized and impending loss reconstructed from habitat conversion and documented by national Red Lists.

Results

Species–energy models largely explained landscape-scale variation of mapped SR in wilderness areas (adjusted R²-values: 0.79–0.93). Model-based projections of SR loss were lower, on average, than reconstructed and documented ones, but the spatial patterns were correlated significantly, with stronger correlation in mammals (Pearson's r = 0.68) than in amphibians (r = 0.60) and birds (r = 0.57).

Main conclusions

Our results suggest that the human appropriation of net primary production is a useful indicator of heterotrophic species loss in used landscapes, hence we recommend its inclusion in models based on species–area relationships to improve predictions of land-use-driven biodiversity loss.     

High-temperature stress in crops: male sterility,yield loss and potential remedy approaches

Global food security is one of the utmost essential challenges in the 21st century in providing enough food for the growing population while coping with the already stressed environment. High temperature (HT) is one of the main factors affecting plant growth, development and reproduction and causes male sterility in plants. In male reproductive tissues, metabolic changes induced by HT involve carbohydrates, lipids, hormones, epigenetics and reactive oxygen species, leading to male sterility and ultimately reducing yield. Understanding the mechanism and genes involved in these pathways during the HT stress response will provide a new path to improve crops by using molecular breeding and biotechnological approaches. Moreover, this review provides insight into male sterility and integrates this with suggested strategies to enhance crop tolerance under HT stress conditions at the reproductive stage.     

Peptide-protein interaction markedly alters the functional properties of the catalytic subunit of aspartate transcarbamoylase.

Interaction of a 70-amino acid zinc-binding polypeptide from the regulatory chain of aspartate transcarbamoylase (ATCase) with the catalytic (C) subunit leads to dramatic changes in enzyme activity and affinity for ligand binding at the active sites. The complex between the polypeptide (zinc domain) and wild-type C trimer exhibits hyperbolic kinetics in contrast to the sigmoidal kinetics observed with the intact holoenzyme. Moreover, the Scatchard plot for binding N-(phosphonacetyl)-L-aspartate (PALA) to the complex is linear with a Kd corresponding to that evaluated for the holoenzyme converted to the relaxed (R) state. Additional evidence that the binding of the zinc domain to the C trimer converts it to the R state was attained with a mutant form of ATCase in which Lys 164 in the catalytic chain is replaced by Glu. As shown previously (Newell, J.O. & Schachman, H.K., 1990, Biophys. Chem. 37, 183-196), this mutant holoenzyme, which exists in the R conformation even in the absence of active site ligands, has a 50-fold greater affinity for PALA than the free C subunit. Adding the zinc domain to the C trimer containing the Lys 164-->Glu substitution leads to a 50-fold enhancement in the affinity for the bisubstrate analog yielding a value of Kd equal to that for the holoenzyme. A different mutant ATCase containing the Gln 231 to Ile replacement was shown (Peterson, C.B., Burman, D.L., & Schachman, H.K., 1992, Biochemistry 31, 8508-8515) to be much less active as a holoenzyme than as the free C trimer. For this mutant holoenzyme, the addition of substrates does not cause its conversion to the R state. However, the addition of the zinc domain to the Gln 231-->Ile C trimer leads to a marked increase in enzyme activity, and PALA binding data indicate that the complex resembles the R state of the holoenzyme. This interaction leading to a more active conformation serves as a model of intergenic complementation in which peptide binding to a protein causes a conformational correction at a site remote from the interacting surfaces resulting in activation of the protein. This linkage was also demonstrated by difference spectroscopy using a chromophore covalently bound at the active site, which served as a spectral probe for a local conformational change. The binding of ligands at the active sites was shown also to lead to a strengthening of the interaction between the zinc domain and the C trimer.     

Zinc-mediated interaction of copper chaperones through their heavy-metal associated domains

BackgroundA copper chaperone CCS is a multi-domain protein that supplies a copper ion to Cu/Zn-superoxide dismutase (SOD1). Among the domains of CCS, the N-terminal domain (CCS^dI) belongs to a heavy metal-associated (HMA) domain, in which a Cys-x-x-Cys (CxxC) motif binds a heavy metal ion. It has hence been expected that the HMA domain in CCS has a role in the metal trafficking; however, the CxxC motif in the domain is dispensable for supplying a copper ion to SOD1, leaving an open question on roles of CCS^dI in CCS.MethodsTo evaluate protein-protein interactions of CCS through CCS^dI, yeast two-hybrid assay, a pull-down assay using recombinant proteins, and the analysis with fluorescence resonance energy transfer were performed.ResultsWe found that CCS specifically interacted with another copper chaperone HAH1, a HMA domain protein, through CCS^dI. The interaction between CCS^dI and HAH1 was not involved in the copper supply from CCS to SOD1 but was mediated by a zinc ion ligated with Cys residues of the CxxC motifs in CCS^dI and HAH1.ConclusionWhile physiological significance of the interaction between copper chaperones awaits further investigation, we propose that CCS^dI would have a role in the metal-mediated interaction with other proteins including heterologous copper chaperones.     

Higher-order interactions of Bcr-Abl can broaden chronic myeloid leukemia (CML) drug repertoire

Bcr-Abl, a nonreceptor tyrosine kinase, is associated with leukemias, especially chronic myeloid leukemia (CML). Deletion of Abl's N-terminal region, to which myristoyl is linked, renders the Bcr-Abl fusion oncoprotein constitutively active. The substitution of Abl's N-terminal region by Bcr enables Bcr-Abl oligomerization. Oligomerization is critical: it promotes clustering on the membrane, which is essential for potent MAPK signaling and cell proliferation. Here we decipher the Bcr-Abl specific, step-by-step oligomerization process, identify a specific packing surface, determine exactly how the process is structured and identify its key elements. Bcr's coiled coil (CC) domain at the N-terminal controls Bcr-Abl oligomerization. Crystallography validated oligomerization via Bcr-Abl dimerization between two Bcr CC domains, with tetramerization via tight packing between two binary assemblies. However, the structural principles guiding Bcr CC domain oligomerization are unknown, hindering mechanistic understanding and drugs exploiting it. Using molecular dynamics (MD) simulations, we determine that the binary complex of the Bcr CC domain serves as a basic unit in the quaternary complex providing a specific surface for dimer–dimer packing and higher-order oligomerization. We discover that the small α1-helix is the key. In the binary assembly, the helix forms interchain aromatic dimeric packing, and in the quaternary assembly, it contributes to the specific dimer–dimer packing. Our mechanism is supported by the experimental literature. It offers the key elements controlling this process which can expand the drug discovery strategy, including by Bcr CC-derived peptides, and candidate residues for small covalent drugs, toward quenching oligomerization, supplementing competitive and allosteric tyrosine kinase inhibitors.     

Upper thermal limits predict herpetofaunal responses to forest edge and cover

Amphibians and reptiles are sensitive to changes in the thermal environment, which varies considerably in human-modified landscapes. Although it is known that thermal traits of species influence their distribution in modified landscapes, how herpetofauna respond specifically to shifts in ambient temperature along forest edges remains unclear. This may be because most studies focus on local-scale metrics of edge exposure, which only account for a single edge or habitat patch. We predicted that accounting for the combined effect of multiple habitat edges in a landscape would best explain herpetofaunal response to thermally mediated edge effects. We (1) surveyed herpetofauna at two lowland, fragmented forest sites in central Colombia, (2) measured the critical thermal maximum (CT_max) of the species sampled, (3) measured their edge exposure at both local and landscape scales, and (4) created a thermal profile of the landscape itself. We found that species with low CT_max occurred both further from forest edges and in areas of denser vegetation, but were unaffected by the landscape-scale configuration of habitat edges. Variation in the thermal landscape was driven primarily by changes in vegetation density. Our results suggest that amphibians and reptiles with low CT_max are limited by both canopy gaps and proximity to edge, making them especially vulnerable to human modification of tropical forest. Abstract in Spanish is available with online material.