Heatwave breaks down the linearity between sun-induced fluorescence and gross primary production.

Sun-induced fluorescence in the far-red region (SIF) is increasingly used as a remote and proximal-sensing tool capable of tracking vegetation gross primary production (GPP). However, the use of SIF to probe changes in GPP is challenged during extreme climatic events, such as heatwaves. Here, we examined how the 2018 European heatwave (HW) affected the GPP-SIF relationship in evergreen broadleaved trees with a relatively invariant canopy structure. To do so, we combined canopy-scale SIF measurements, GPP estimated from an eddy covariance tower, and active pulse amplitude modulation fluorescence. The HW caused an inversion of the photosynthesis-fluorescence relationship at both the canopy and leaf scales. The highly nonlinear relationship was strongly shaped by nonphotochemical quenching (NPQ), that is, a dissipation mechanism to protect from the adverse effects of high light intensity. During the extreme heat stress, plants experienced a saturation of NPQ, causing a change in the allocation of energy dissipation pathways towards SIF. Our results show the complex modulation of the NPQ-SIF-GPP relationship at an extreme level of heat stress, which is not completely represented in state-of-the-art coupled radiative transfer and photosynthesis models.

Dynamics of sun-induced chlorophyll fluorescence and reflectance to detect stress-induced variations in canopy photosynthesis.

Passive measurement of sun-induced chlorophyll fluorescence (F) represents the most promising tool to quantify changes in photosynthetic functioning on a large scale. However, the complex relationship between this signal and other photosynthesis-related processes restricts its interpretation under stress conditions. To address this issue, we conducted a field campaign by combining daily airborne and ground-based measurements of F (normalized to photosynthetically active radiation), reflectance and surface temperature and related the observed changes to stress-induced variations in photosynthesis. A lawn carpet was sprayed with different doses of the herbicide Dicuran. Canopy-level measurements of gross primary productivity indicated dosage-dependent inhibition of photosynthesis by the herbicide. Dosage-dependent changes in normalized F were also detected. After spraying, we first observed a rapid increase in normalized F and in the Photochemical Reflectance Index, possibly due to the blockage of electron transport by Dicuran and the resultant impairment of xanthophyll-mediated non-photochemical quenching. This initial increase was followed by a gradual decrease in both signals, which coincided with a decline in pigment-related reflectance indices. In parallel, we also detected a canopy temperature increase after the treatment. These results demonstrate the potential of using F coupled with relevant reflectance indices to estimate stress-induced changes in canopy photosynthesis.

Leaf and canopy photosynthesis of a chlorophyll deficient soybean mutant.

The photosynthetic, optical, and morphological characteristics of a chlorophyll-deficient (Chl-deficient) "yellow" soybean mutant (MinnGold) were examined in comparison with 2 green varieties (MN0095 and Eiko). Despite the large difference in Chl content, similar leaf photosynthesis rates were maintained in the Chl-deficient mutant by offsetting the reduced absorption of red photons by a small increase in photochemical efficiency and lower non-photochemical quenching. When grown in the field, at full canopy cover, the mutants reflected a significantly larger proportion of incoming shortwave radiation, but the total canopy light absorption was only slightly reduced, most likely due to a deeper penetration of light into the canopy space. As a consequence, canopy-scale gross primary production and ecosystem respiration were comparable between the Chl-deficient mutant and the green variety. However, total biomass production was lower in the mutant, which indicates that processes other than steady state photosynthesis caused a reduction in biomass accumulation over time. Analysis of non-photochemical quenching relaxation and gas exchange in Chl-deficient and green leaves after transitions from high to low light conditions suggested that dynamic photosynthesis might be responsible for the reduced biomass production in the Chl-deficient mutant under field conditions.

WhiteRef: a new tower-based hyperspectral system for continuous reflectance measurements.

Proximal sensing is fundamental to monitor the spatial and seasonal dynamics of ecosystems and can be considered as a crucial validation tool to upscale in situ observations to the satellite level. Linking hyperspectral remote sensing with carbon fluxes and biophysical parameters is critical to allow the exploitation of spatial and temporal extensive information for validating model simulations at different scales. In this study, we present the WhiteRef, a new hyperspectral system designed as a direct result of the needs identified during the EUROSPEC ES0903 Cost Action, and developed by Fondazione Edmund Mach and the Institute of Biometeorology, CNR, Italy. The system is based on the ASD FieldSpec Pro spectroradiometer and was designed to acquire continuous radiometric measurements at the Eddy Covariance (EC) towers and to fill a gap in the scientific community: in fact, no system for continuous spectral measurements in the Short Wave Infrared was tested before at the EC sites. The paper illustrates the functioning of the WhiteRef and describes its main advantages and disadvantages. The WhiteRef system, being based on a robust and high quality commercially available instrument, has a clear potential for unattended continuous measurements aiming at the validation of satellites' vegetation products.

Fractionated Seminal Plasma of Boar Ejaculates Analyzed by LC-MS/MS: Its Effects on Post-Thaw Semen Quality.

This study aimed to characterize the protein composition of fractionated seminal plasma (SP) by liquid chromatography mass spectrometry (LC-MS/MS) analysis and investigate its effects on survival of frozen-thaw (FT) boar spermatozoa following storage. Seminal plasma (SP) was fractionated by gel filtration chromatography to give two fractions, SP1 with more than 40 kDa (>40 kDa) and SP2 with less than 40 kDa (<40 kDa). SP1 and SP2 were subjected to LC-MS/MS and bioinformatics analysis. Following cryopreservation, FT boar semen (n = 7) was thawed in Beltsville Thawing Solution (BTS), BTS + SP1 or BTS + SP2, stored at different periods and subjected to post-thaw (PT) quality assessment. A total of 52 and 22 abundant proteins were detected in SP1 and SP2, respectively. FN1, ANGPTL1, and KIF15 proteins were more abundance in SP1, whereas a high abundance of spermadhesins (PSP-I and PSP-II) was detected in SP2. Proteins of the fractionated SP were involved in various biological processes, such as cell motility and signal transduction. The dominant pathway of SP1 proteins was the apelin signaling pathway (GNA13, MEF2D, SPHK2, and MEF2C), whereas a pathway related to lysosome (CTSH, CTSB, and NPC2) was mainly represented by SP2 proteins. In most of the boars, significantly higher motility characteristics, membrane integrity, and viability were observed in FT spermatozoa exposed to SP1 or SP2 compared with BTS. The results of our study confirm that a combination of several proteins from the fractionated SP exerted beneficial effects on the sperm membrane, resulting in improved quality characteristics following PT storage.

Gene promoter polymorphisms in boar spermatozoa differing in freezability.

Single nucleotide polymorphisms (SNPs) in the 5'-flanking regulatory regions of genes could affect their expression levels. This is a follow-up study aimed to identify polymorphic variants in the 5'-flanking regulatory regions of genes expressed in boar spermatozoa, and to predict the interactions of such variants with transcription factors (TFs) on the gene promoter activity, using bioinformatics. Five and six boars were classified as having good and poor semen freezability (GSF and PSF, respectively) according to post-thaw (PT) assessment of sperm motility and membrane integrity characteristics. The 5'-flanking region sequences of the 14 genes (FOS, NFATC3, EAF2, FGF-14, BAMBI, RAB33B, CKS2, LARS2, SLC25A16, ACADM, CPT2, CCT3, DTD2 and CCDC85A) were PCR amplified and analyzed by Sanger sequencing method. A total of 32 polymorphic variants were identified in the 5'-flanking regions of the genes, including 4 insertion/deletion (indel) polymorphisms, and 8 unknown (novel) SNPs. Multiple sequence alignment analysis revealed a 26-bp indel variant in the 5'-flanking region of the LARS2 gene, which showed greater protein expression in spermatozoa from boars of the PSF group. It was found that 17 polymorphic variants, observed in the differentially expressed (DE) genes, showed significant allele frequency differences between the GSF and PSF groups. Polymorphic variants in the 5'-flanking regulatory regions of the genes contributed to the decrease or increase in the binding affinity for different testis-specific TFs, such as SMAD1, NF-1, FOXMI, RXRA, STAT4 and C/EBPß. This study provides more insights into the mechanisms responsible for variations in transcriptional activity in promoters of genes expressed in boar spermatozoa. The allelic variants are promising genetic markers for predicting the freezability of boar spermatozoa.

Improving remote estimation of winter crops gross ecosystem production by inclusion of leaf area index in a spectral model.

The hysteresis of the seasonal relationships between vegetation indices (VIs) and gross ecosystem production (GEP) results in differences between these relationships during vegetative and reproductive phases of plant development cycle and may limit their applicability for estimation of croplands productivity over the entire season. To mitigate this problem and to increase the accuracy of remote sensing-based models for GEP estimation we developed a simple empirical model where greenness-related VIs are multiplied by the leaf area index (LAI). The product of this multiplication has the same seasonality as GEP, and specifically for vegetative periods of winter crops, it allowed the accuracy of GEP estimations to increase and resulted in a significant reduction of the hysteresis of VIs vs. GEP. Our objective was to test the multiyear relationships between VIs and daily GEP in order to develop more general models maintaining reliable performance when applied to years characterized by different climatic conditions. The general model parametrized with NDVI and LAI product allowed to estimate daily GEP of winter and spring crops with an error smaller than 14%, and the rate of GEP over- (for spring barley) or underestimation (for winter crops and potato) was smaller than 25%. The proposed approach may increase the accuracy of crop productivity estimation when greenness VIs are saturating early in the growing season.