Biophysical Control Research Articles

Plasma membrane abundance dictates phagocytic capacity and functional cross-talk in myeloid cells.

Professional phagocytes like neutrophils and macrophages tightly control what they consume, how much they consume, and when they move after cargo uptake. We show that plasma membrane abundance is a key arbiter of these cellular behaviors. Neutrophils and macrophages lacking the G protein subunit Gβ4 exhibited profound plasma membrane expansion, accompanied by marked reduction in plasma membrane tension. These biophysical changes promoted the phagocytosis of bacteria, fungus, apoptotic corpses, and cancer cells. We also found that Gβ4-deficient neutrophils are defective in the normal inhibition of migration following cargo uptake. Sphingolipid synthesis played a central role in these phenotypes by driving plasma membrane accumulation in cells lacking Gβ4. In Gβ4 knockout mice, neutrophils not only exhibited enhanced phagocytosis of inhaled fungal conidia in the lung but also increased trafficking of engulfed pathogens to other organs. Together, these results reveal an unexpected, biophysical control mechanism central to myeloid functional decision-making.

Environmental and biological controls on the interannual variations of evapotranspiration in a natural oak forest

Investigating the interannual variation (IAV) of evapotranspiration (ET) is important for understanding the water cycle in forest ecosystems. However, there has been little research on interannual variability of ET in warm-temperate forests under a changing environment. In this study, 6-year eddy covariance data (2017–2022) in a warm-temperate natural oak forest in central China were used to examine the IAV of ET and its driving factors. The mean and standard deviation of annual ET from 2017 to 2022 were 610 and 122.8 mm (with a coefficient of variation (CV) of 20 %), respectively. The annual ET did not exhibit an obvious trend over the six years with a larger IAV. Environmental factors had a greater impact on the IAV of annual ET compared to the biological factors, with reference crop evapotranspiration (ET0) exerting the most significant influence on ET. The IAV of monthly ET was primarily controlled by precipitation during the early growing season, but it changed to be controlled by radiation and temperature (i.e., atmospheric evaporation demand) during the mid-growing season. We concluded that atmospheric evaporation demand rather than water supply dominated the IAV of annual ET in the warm-temperate natural oak forest in central China, and occasional seasonal drought only affected the ET in a short time-scale (no more than three years). There is a need to measure three components of ET (transpiration, canopy interception evaporation and soil evaporation) in order to better understand the IAV of ET and the underlying biophysical control mechanisms.

Biophysical Control of the Glioblastoma Immunosuppressive Microenvironment: Opportunities for Immunotherapy.

GBM is the most aggressive and common form of primary brain cancer with a dismal prognosis. Current GBM treatments have not improved patient survival, due to the propensity for tumor cell adaptation and immune evasion, leading to a persistent progression of the disease. In recent years, the tumor microenvironment (TME) has been identified as a critical regulator of these pro-tumorigenic changes, providing a complex array of biomolecular and biophysical signals that facilitate evasion strategies by modulating tumor cells, stromal cells, and immune populations. Efforts to unravel these complex TME interactions are necessary to improve GBM therapy. Immunotherapy is a promising treatment strategy that utilizes a patient's own immune system for tumor eradication and has exhibited exciting results in many cancer types; however, the highly immunosuppressive interactions between the immune cell populations and the GBM TME continue to present challenges. In order to elucidate these interactions, novel bioengineering models are being employed to decipher the mechanisms of immunologically "cold" GBMs. Additionally, these data are being leveraged to develop cell engineering strategies to bolster immunotherapy efficacy. This review presents an in-depth analysis of the biophysical interactions of the GBM TME and immune cell populations as well as the systems used to elucidate the underlying immunosuppressive mechanisms for improving current therapies.

Biological and environmental controls on nighttime water-use behaviors in Populus simonii in semi-arid areas of the Chinese Loess plateau

Recent studies have revealed that the active nighttime water-use behaviors by trees have critical physio-ecological significance in survival and growth in adversity. However, the characteristics and biophysical control of nighttime water-use of silvicultural trees are not clear. We continuously monitored sap flow and leaf water potential (predawn and midday) of Populus simonii of different tree sizes as well as environmental factors during the 2021 and 2022 growing seasons (May-September) in a semi-arid area of Loess Plateau. Our results showed that both nighttime water-use (WUn) and the ratio of nighttime to daily water-use (WUn%) increased significantly with tree size, and had larger values in the drought year than in the normal year. The WUn% of different tree sizes ranged from 10.24 to 13.01% and can reach up to 36.49% during prolonged soil drought. Besides, the WUn% of different tree sizes were significantly positively and negatively correlated with nighttime vapor pressure deficit (VPDn) and soil water content, respectively. By partitioning the components of WUn, we found that as tree size increased, the stem water refilling (RE) and nighttime transpiration increased obviously, but the ratio of RE to WUn (RE%) did not change. The RE of different tree sizes constituted the major part of WUn with an average RE% of 65.7–68.0%, and the RE% was larger in the drought year than in the normal year. Additionally, the RE% of different tree sizes increased with decreasing predawn leaf water potential (Ѱpd) during the soil dry stage and with increasing VPDn during the soil wet stage. Given the increased risk of atmospheric drought and soil drought, it can be expected from our findings that the nighttime water-use behaviors of trees become more active in the future, which represents a significant performance of drought adaptation strategies of silvicultural species.

Forest reorganisation effects on fuel moisture content can exceed changes due to climate warming in wet temperate forests.

The distributions of vegetation and fire activity are changing rapidly in response to climate warming. In many regions, climate effects on dead fuel moisture content (FMC) are expected to increase future wildfire activity. However, forest FMC is largely driven by microclimate conditions, which are moderated from open weather by vegetation canopies. As shifts in vegetation increase under climate warming, the extent to which future fire activity will be driven by climate directly or associated vegetation shifts remains unresolved. Here, we present a study aimed at quantifying the relative magnitudes of (i) direct climate warming, and (ii) vegetation change, on FMC. Field sites to evaluate these effects were established in a natural laboratory of altered forest states to mature wet temperate forest in south-eastern Australia. FMC was estimated using a process-based model and 48 years of reconstructed climate data. Canopy effects on microclimate were captured by transferring inputs from climate to microclimate using models parameterised with field observations. To evaluate the relative magnitude of climate and vegetation effects, we calculated the maximum difference in mean annual FMC across annual climate replicates and compared this to FMC differences across reorganising forest sites. Our results show vegetation effects on FMC can exceed those related to expected climate change. Changes to forest structure and composition increased (+15.7%) and decreased (-12.3%) mean annual FMC, with a larger negative effect when forest cover was completely removed (-18.5%). In contrast, the largest climate effect on FMC was -6.6% across 48-years of data. Our study demonstrates that the magnitude of vegetation effects on FMC can exceed expected climate change effects. Models of future fire activity that do not account for changing vegetation effects on microclimate are omitting a key biophysical control on FMC and therefore may not be accurately predicting future fire activity.

Biophysics at the edge of life and death: Radical control of apoptotic mechanisms

Recent studies have furthered our understanding of how dying and living cells interact in different physiological contexts, however the signaling that initiates and mediates apoptosis and apoptosis-induced proliferation are more complex than previously thought. One increasingly important area of study is the biophysical control of apoptosis. In addition to biochemical regulation, biophysical signals (including redox chemistry, bioelectric gradients, acoustic and magnetic stimuli) are also known yet understudied regulators of both cell death and apoptosis-induced proliferation. Mounting evidence suggests biophysical signals may be key targets for therapeutic interventions. This review highlights what is known about the role of biophysical signals in controlling cell death mechanisms during development, regeneration, and carcinogenesis. Since biophysical signals can be controlled spatiotemporally, bypassing the need for genetic manipulation, further investigation may lead to fine-tuned modulation of apoptotic pathways to direct desired therapeutic outcomes.

Semi-Synthetic Click-Gelatin Hydrogels as Tunable Platforms for 3D Cancer Cell Culture.

Basement membrane extracts (BME) derived from Engelbreth-Holm-Swarm (EHS) mouse sarcomas such as Matrigel® remain the gold standard extracellular matrix (ECM) for three-dimensional (3D) cell culture in cancer research. Yet, BMEs suffer from substantial batch-to-batch variation, ill-defined composition, and lack the ability for physichochemical manipulation. Here, we developed a novel 3D cell culture system based on thiolated gelatin (Gel-SH), an inexpensive and highly controlled raw material capable of forming hydrogels with a high level of biophysical control and cell-instructive bioactivity. We demonstrate the successful thiolation of gelatin raw materials to enable rapid covalent crosslinking upon mixing with a synthetic poly(ethylene glycol) (PEG)-based crosslinker. The mechanical properties of the resulting gelatin-based hydrogels were readily tuned by varying precursor material concentrations, with Young's moduli ranging from ~2.5 to 5.8 kPa. All hydrogels of varying stiffnesses supported the viability and proliferation of MDA-MB-231 and MCF-7 breast cancer cell lines for 14 and 21 days of cell culture, respectively. Additionally, the gelatin-based hydrogels supported the growth, viability, and osteogenic differentiation of patient-derived preosteoblasts over 28 days of culture. Collectively, our data demonstrate that gelatin-based biomaterials provide an inexpensive and tunable 3D cell culture platform that may overcome the limitations of traditional BMEs.

Investigating biophysical control of marine phytoplankton dynamics via Bayesian mechanistic modeling

Marine phytoplankton possess a key position in multiple ecological, biological, and environmental processes; therefore, constructing a systematic and comprehensive mechanistic understanding of the leading mechanisms and key biophysical drivers of phytoplankton dynamics is crucial for evaluating biophysical forcings and ecological responses. Here, we develop a process-based model to improve the characterization of controlling mechanisms and assess the relative importance of nutrients, light, temperature, and oceanic mixing for explaining chlorophyll-a variability in the western North Pacific Ocean. The model is calibrated using 20-year observational data of chlorophyll-a concentrations from 1993 to 2012 in a Bayesian framework to provide data-driven inference and a rigorous uncertainty quantification of important biophysical rates. The model explains approximately 61% of the variability in chlorophyll-a. Our results, supported by cross-validation, show that the chlorophyll-a concentration is much more responsive to temperature variability than nutrients, light, or mixing. By synthesizing the effects of multiple nutrients (i.e., nitrogen, phosphorus, silica, and iron) on phytoplankton dynamics, we find that iron and nitrogen largely determine the chlorophyll-a variability. Sensitivity analysis shows that future warming conditions with +3°C change in temperature will impede phytoplankton production by 24% due to an intensified phytoplankton mortality impact. Our findings highlight the potential of “deductive-and-inductive” modeling approaches combining embedded biophysical mechanisms and probabilistic uncertainty quantification to effectively integrate and leverage sporadic ocean monitoring efforts and ultimately improve the marine water quality predictions.

Upscaling Gross Primary Production from Leaf to Canopy for Potato Crop (Solanum tuberosum L.)

Estimating gross primary production (GPP) is important to understand the land–atmosphere CO2 exchange for major agroecosystems. Eddy covariance (EC) measurements provide accurate and reliable information about GPP, but flux measurements are often not available. Upscaling strategies gain importance as an alternative to the limitations of the use of the EC. Although the potato provides an important agroecosystem for worldwide carbon balance, there are currently no studies on potato GPP upscaling processes. This study reports two GPP scaling-up approaches from the detailed leaf-level characterization of gas exchange of potatoes. Multilayer and big leaf approaches were applied for extrapolating chamber and biometric measurements from leaf to canopy. Measurements of leaf area index and photosynthesis were performed from planting to the end of the canopy life cycle using an LP-80 ceptometer and an IRGA Li-Cor 6800, respectively. The results were compared to concurrent measurements of surface–atmosphere GPP from the EC measurements. Big-leaf models were able to simulate the general trend of GPP during the growth cycle, but they overestimated the GPP during the maximum LAI phase. Multilayer models correctly reproduced the behavior of potato GPP and closely predicted both: the daily magnitude and half-hourly variation in GPP when compared to EC measurements. Upscaling is a reliable alternative, but a good treatment of LAI and the photosynthetic light-response curves are decisive factors to achieve better GPP estimates. The results improved the knowledge of the biophysical control in the carbon fluxes of the potato crop.

Canopy Transpiration and Stomatal Conductance Dynamics of Ulmus pumila L. and Caragana korshinskii Kom. Plantations on the Bashang Plateau, China

Constructing protective forests to control water and soil erosion is an effective measure to address land degradation in the Bashang Plateau of North China, but forest dieback has occurred frequently due to severe water deficits in recent decades. However, transpiration dynamics and their biophysical control factors under various soil water contents for different forest functional types are still unknown. Here, canopy transpiration and stomatal conductance of a 38-year-old Ulmus pumila L. and a 20-year-old Caragana korshinskii Kom. were quantified using the sap flow method, while simultaneously monitoring the meteorological and soil water content. The results showed that canopy transpiration averaged 0.55 ± 0.34 mm d−1 and 0.66 ± 0.32 mm d−1 for U. pumila, and was 0.74 ± 0.26 mm d−1 and 0.77 ± 0.24 mm d−1 for C. korshinskii in 2020 and 2021, respectively. The sensitivity of canopy transpiration to vapor pressure deficit (VPD) decreased as soil water stress increased for both species, indicating that the transpiration process is significantly affected by soil drought. Additionally, canopy stomatal conductance averaged 1.03 ± 0.91 mm s−1 and 1.34 ± 1.22 mm s−1 for U. pumila, and was 1.46 ± 0.90 mm s−1 and 1.51 ± 1.06 mm s−1 for C. korshinskii in 2020 and 2021, respectively. The low values of the decoupling coefficient (Ω) showed that canopy and atmosphere were well coupled for both species. Stomatal sensitivity to VPD decreased with decreasing soil water content, indicating that both U. pumila and C. korshinskii maintained a water-saving strategy under the stressed water conditions. Our results enable better understanding of transpiration dynamics and water-use strategies of different forest functional types in the Bashang Plateau, which will provide important insights for planted forests management and ecosystem stability under future climate changes.

Biophysical impacts of northern vegetation changes on seasonal warming patterns

The seasonal greening of Northern Hemisphere (NH) ecosystems, due to extended growing periods and enhanced photosynthetic activity, could modify near-surface warming by perturbing land-atmosphere energy exchanges, yet this biophysical control on warming seasonality is underexplored. By performing experiments with a coupled land-atmosphere model, here we show that summer greening effectively dampens NH warming by −0.15 ± 0.03 °C for 1982–2014 due to enhanced evapotranspiration. However, greening generates weak temperature changes in spring (+0.02 ± 0.06 °C) and autumn (−0.05 ± 0.05 °C), because the evaporative cooling is counterbalanced by radiative warming from albedo and water vapor feedbacks. The dwindling evaporative cooling towards cool seasons is also supported by state-of-the-art Earth system models. Moreover, greening-triggered energy imbalance is propagated forward by atmospheric circulation to subsequent seasons and causes sizable time-lagged climate effects. Overall, greening makes winter warmer and summer cooler, attenuating the seasonal amplitude of NH temperature. These findings demonstrate complex tradeoffs and linkages of vegetation-climate feedbacks among seasons.

Environmental and stomatal control on evapotranspiration in a natural oak forest

AbstractEvapotranspiration (ET) is an important component in water budgets in forest ecosystems, and the associated latent heat flux has important implications for regional climate. However, biophysical control mechanisms on variations in ecosystem ET on intra‐annual scales may have year‐to‐year variations in different years with contrasting precipitation and soil water contents. Related research is lacking in natural oak forests in Central China. Based on eddy‐covariance technique, we investigated variations of ET and controlling factors in a natural oak forest in central China over three years (2017–2019) with contrasting soil water contents (SWCs) and precipitation. The ET of the oak forest was mainly affected by surface conductance (gs) in growing seasons, and the restriction from stoma on ET was aggravated in dry year. High vapour pressure deficit (VPD) promoted gs and ET in wet year but decreased gs and ET in dry year. There was a positive relationship between shallow soil water contents and gs in dry year but no relationship between the two variables in wet year. The ET were 738.1, 750.6 and 513.1 mm, respectively, for 2017–2019, with a coefficient of variation (CV) of 20%, while the corresponding precipitation (P) were 1239.4, 855.8 and 645.6 mm, with a CV of 33%. Annual ET was the lowest in the year with the lowest P, SWC and gs. Short‐term droughts (periods with relative extractable water content less than 0.1 for less than 15 days) only constrained gs and ET in short timescales (e.g., hours). Long‐term droughts (periods with relative extractable water content less than 0.1 for more than 15 days) evidently decreased the gs, thus reducing the ET and affecting energy partitioning in the corresponding period. ET/P were 0.6, 0.88 and 0.79 in 2017–2019, respectively, indicating that ET consumed most of the rain. The ratios of latent heat flux (LE) to net radiation (Rn) were 0.86, 0.88 and 0.6 during growing seasons in 2017–2019, respectively. Our study suggested that the natural oak forest has high ET rate and soil moisture affects the variations of ET.

Contrasting Biophysical Controls on Carbon Dioxide and Methane Outgassing From Streams

AbstractSmall headwater streams are recognized for intense outgassing to the atmosphere of climate‐relevant carbon dioxide (CO2) and methane (CH4). Though these headwaters are markedly oversaturated for both CO2 and CH4, the origins and controls over the fate of these two carbon‐gases are still poorly constrained, especially for the stronger greenhouse gas CH4. Here, by measuring stream‐based production of CO2 and CH4, concurrently with their rates of outgassing to the atmosphere, we identify distinct biophysical control mechanisms for each gas. We show that while CO2 is largely imported from the catchment in proportion to discharge, CO2 outgassing can be modulated by in‐stream metabolism to offset outgassing by up to 30% in spring and summer. In contrast, CH4 shows a non‐linear response to seasonal changes in discharge and is predominantly produced in the streambed in relation to sediment type. Further, once released from the streambed, outgassing of CH4 at the surface and flow‐driven dilution occur far more rapidly than biological methane oxidation and CH4 leaves the water largely unaltered by biology. Incorporating the intense carbon cycling of headwater streams into the global carbon cycle will require distinct parameterizations for each carbon gas in Earth system models.

Patterns and Controls of the Latent and Sensible Heat Fluxes in the Brazilian Pampa Biome

Energy and water exchange between the surface and the atmosphere are important drivers to Earth’s climate from local to global scale. In this study, the energy dynamic and the biophysical mechanisms that control the energy partitioning over a natural grassland pasture over the Brazilian Pampa biome are investigated using two micrometeorological sites located 300 km apart, in Southern Brazil. The latent heat flux, LE, was the main component of the energy balance in both autumn-winter (AW) and spring-summer (SS) periods. Annually, approximately 60% of the available energy is used for evapotranspiration (ET). However, the Bowen ratio presents seasonal variability greater in AW than SS. Global radiation, Rg, is the atmospheric variable controlling LE and sensible heat flux, H. Hysteresis curves in the daily cycle were observed for ET and surface conductance, Cs, regarding the environmental variables, net radiation, vapor pressure deficit, and air temperature. Among the variables analyzed in the Pampa biome, surface conductance and evapotranspiration respond more strongly to the vapor pressure deficit. The hysteresis cycles formed by ET and conductance show a substantial biophysical control in the ET process. The results obtained here allowed a comprehension of the biophysical mechanisms involved in the energy partition process in natural grassland. Therefore, this study can be used as a base for research on land-use changes in this unique ecosystem of the Pampa biome.

Physiological and nutritional constraints on zooplankton productivity due to eutrophication and climate change predicted using a resource-based modeling approach

Emerging evidence suggests that zooplankton production is affected by physiological and nutritional constraints due to climate change and eutrophication, which in turn could have broad implications for food-web dynamics and fisheries production. In this study, we developed a resource-based zooplankton production dynamics model that causally links freshwater cladoceran and copepod daily production-to-biomass (P/B) ratios with water temperature, phytoplankton biomass and community composition, and zooplankton feeding selectivity. This model was used to evaluate constraints on zooplankton growth under four hypothetical scenarios: involving natural plankton community seasonal succession; lake fertilization to enhance fisheries production; eutrophication; and climatic warming. Our novel modeling approach predicts zooplankton production is strongly dependent on seasonal variation in resource availability and quality, which results in more complex zooplankton dynamics than predicted by simpler temperature-dependent models. For mesotrophic and hypereutrophic lakes, our study suggests that the ultimate control over zooplankton P/B ratios shifts from physiological control during colder periods to strong resource control during warmer periods. Our resource-based model provides important insights into the nature of biophysical control of zooplankton under a changing climate that has crucial implications for food web energy transfer and fisheries production.

Spatiotemporal Development and Dissipation of Hypoxia Induced by Variable Wind‐Driven Shelf Circulation off the Pearl River Estuary: Observational and Modeling Studies

AbstractObservations reveal the high spatiotemporal variability of the hypoxia in the western and eastern coastal transition zones (WCTZ and ECTZ) off the Pearl River Estuary (PRE). We utilized data from cruise observations, buoy mooring, and a three‐dimensional model based on ROMS to investigate the hypoxia variability response to the typical synoptic variation of the summer monsoon, i.e., from prevailing upwelling‐favorable wind (UFW), the ensuing episodic upwelling relaxation (URW), downwelling (DFW), to downwelling relaxation wind (DRW). During the UFW, we found that the northeastward shelf current converges with nutrient‐rich river plume, forms strong stratification, and provides hubs for depositing detritus for hypoxia to develop in the CTZ. The ensuing URW and DFW forcing alters the transport to advect the plume and detritus westward, weakens vertical mixing, and enhances hypoxia in the WCTZ. Correspondingly, opposite conditions occur in the ECTZ as the plume veers westward during the URW and DFW. Contrarily, the weakening westward transport during the DRW forcing restores the biophysical conditions to their states when there is an UFW event. We found that varying wind‐driven circulation interacts with the plume to jointly regulate the transport of nutrient and detritus, water vertical mixing, and residence time, and, thus, the hypoxia variability in the CTZ. The variability of hypoxia in the CTZ is less controlled by the river discharges once biogeochemical conditions become saturated. Our study illustrates the biophysical control of hypoxia variability that is frequently observed in estuaries and coastal oceans.

Biophysical control on nighttime sap flow in Salix psammophila in a semiarid shrubland ecosystem

The impact of extreme desert conditions on long-term nighttime sap flow dynamics in desert-dwelling shrubs is poorly understood. Based on heat-balance measurements in a semiarid area of northwest China, we investigated the nighttime sap flow (transpiration) dynamics in Salix psammophila as affected by changes in site biophysical variables over a six-year period (2012-2017). Nocturnally, sap flow rate per leaf area (Jsn) formed a positive linear relationship with air temperature (Ta), water vapor pressure deficit (VPD) and stomatal conductance (Gs), when Ta < 17 °C, VPD < 1 kPa, and Gs < 0.004 mol m−2 s−1, remaining unchanging or forming a negative linear relationship, when Ta, VPD and Gs were greater than these limits. This relationship was modified by soil water content (SWC) through its effects on Gs. The multiple regression model showed that together Ta, VPD and Gs explained 63% of the variation in Jsn. Seasonally, pairwise relationships between Ta and VPD and Gs and SWC explained 76 and 70% of the variation in Jsn during wet and dry years, respectively. Interannually, Ta and Gs were able to explain a significant portion of observed variation in Jsn, individually explaining about 74 and 83% of that variation. Interannual control on Jsn also varied with SWC, Ta and Gs explaining 84% of the variation. The diminished sensitivity of Jsn to both Ta and VPD and increased sensitivity to SWC during dry years, suggested that the shrubs had a physiological capacity to adapt to dry soil conditions. Daytime sap flow rates (Jsd) were significantly greater than those at night (i.e., Jsn), with an interannual mean difference of 0.15 ± 0.04 g cm−2 d−1 and coefficient of variation of 27%. In addition, Jsn formed a positive linear association with Jsd during the growing season. Mean Jsn contributed to the daily total sap flow (i.e., Jsn/Js24-h × 100) by 8-14% over the six years, with an interannual mean of 11%. Our findings underscore the importance of nighttime sap flow in S. psammophila and the importance of temperature and SWC in controlling nighttime water losses through transpiration. It is suggested that the proportion of nighttime sap flow could increase during plant acclimatization in response to increasing temperature and water shortages with future climate change.

Biophysical Control on Variability in Phytoplankton Production and Composition in the South-Western Tropical Indian Ocean During Monsoon 2014

The existing oligotrophic conditions in the southwest tropical Indian Ocean (SWTIO) is believed to be one of the causes for low phytoplankton productivity (PP) observed in this area. Though many remote sensing based studies on PP have been carried out in SWTIO; studies on in situ estimation of PP and its cause(s) of variability are scarce. Thus, to understand the controlling environmental forcings on the variability in phytoplankton biomass (chlorophyll-a; Chl-a), community structure and productivity, time series (TS; @6h intervals for 10 days) plus point measurements (RT) were carried out in the SWTIO during southwest monsoon (June) of 2014. Strong thermohaline stratification resulted in shallow (35-40m) mixed layer (ML). Subsurface Chl-a maximum (SCM) was observed to oscillate within 40-60m with majority of peaks at ~50m, and existed just beneath the ML depth. Light availability at the time of sampling was highly conducive for algal growth; whereas nutrient ratios indicated N- and Si-limitation suggesting unfavourable conditions for diatoms and/or silicoflagellates growth within the ML. Furthermore, HPLC-based pigments analysis confirmed dominance of nano-sized plankton (53%) followed by pico-plankton (25%) and micro-plankton (22%). Column integrated production (IPP) varied from 176 - 268 (241+43 mgC m-2 d-1) and was relatively stable during the observation period, except a low value on 11-June, which was ascribed to the drastic dropdown in the daily incident PAR due to overcast sky. Vertical profiles of PP and Chl-a resembled each other and maximum PP usually corresponded with SCM depths. The Chl-a-specific PP (PB) was mostly higher within the ML and showed no surface photoinhibition, due to the dominance of smaller phytoplankton (less prone to pigment packaging effect) in the surface layer. Comparatively, higher PB within the ML is indicative of phytoplankton healthiness during the sampling time, whereas low PB below the SCM was due to light limitation. Highest integrated Chl-a (39 mg m-2) and IPP (328 mgC m-2 d-1) observed at RT-2 was clearly linked to low sea surface height anomaly (SSHA), cyclonic disturbance and associated positive Ekman pumping. Conversely, high SSHA and strong stratification conditions prevailed at TS, RT-4 and RT-6 stations leading to comparatively low IPP.

The nuclear envelope: LINCing tissue mechanics to genome regulation in cardiac and skeletal muscle.

Regulation of the genome is viewed through the prism of gene expression, DNA replication and DNA repair as controlled through transcription, chromatin compartmentalisation and recruitment of repair factors by enzymes such as DNA polymerases, ligases, acetylases, methylases and cyclin-dependent kinases. However, recent advances in the field of muscle cell physiology have also shown a compelling role for 'outside-in' biophysical control of genomic material through mechanotransduction. The crucial hub that transduces these biophysical signals is called the Linker of Nucleoskeleton and Cytoskeleton (LINC). This complex is embedded across the nuclear envelope, which separates the nucleus from the cytoplasm. How the LINC complex operates to mechanically regulate the many functions of DNA is becoming increasingly clear, and recent advances have provided exciting insight into how this occurs in cells from mechanically activated tissues such as skeletal and cardiac muscle. Nevertheless, there are still some notable shortcomings in our understanding of these processes and resolving these will likely help us understand how muscle diseases manifest at the level of the genome.

A multiple-temporal scale analysis of biophysical control of sap flow in Salix psammophila growing in a semiarid shrubland ecosystem of northwest China

With increased usage of plantations in the control of desertification and water shortages in the Mu Us Desert, water use by desert-dwelling shrubs, such as Salix psammophila has become a serious topic in the management of ecologically-important plants. However, our understanding of the unevenness in water consumption across multiple timescales is still limited for many desert shrub species. Interannual variation in water consumption and its environmental controls are scarcely documented. To attend to this deficit, sap-flow measurements were continuously collected in a region of the Mu Us Desert from 2012 to 2017 to investigate the biophysical controls on sap-flow and water-consumption dynamics in S. psammophila. Diurnally, sap flow per leaf area (Js) was shown to be controlled by shortwave radiation (Rs), peaking in summer about two hours ahead of Rs, and about three to five hours ahead of air temperature (Ta) and vapor pressure deficit (VPD), respectively. Seasonal patterns in Js varied with precipitation and subsequent changes in soil volumetric water content (VWC). Soil volumetric water content was observed to modify the influence of the other environmental variables on Js (i.e., Ta, Rs, and VPD), with Js being more responsive to the site variables, when VWC > 0.09 m3 m−3, and less responsive, when <0.09 m3 m−3. Furthermore, Ta and VPD were responsible for most of the variation observed in Js during the leaf-expansion stage. Meanwhile, VWC and leaf area index (LAI) became more important during the leaf-expanded stage, and Rs during the leaf-defoliation stage. Interannually, LAI and meteoric water input to soils was responsible for most of the variation observed in Js. Reduction in Js sensitivity to biophysical factors under water-stressed conditions across temporal scales and the hysteresis effect point to species acclimatization to dry soil conditions. This study has the potential to help: (i) clarify the temporal dynamics in Js for S. psammophila across multiple timescales; and (ii) contribute to the sustainable management and control of desertification in the region under future climate change and projected increases in severe drought.