•We illuminate critical issues surrounding the collection and utilization of microclimate records in ecological studies.•Microclimatic responses to structural changes in ecosystems and landscapes ...have become a growing research focus.•Vapor pressure deficit is particularly emphasized for its applications in ecology.•We underscore the significance of microclimate in modeling major ecosystem processes.
Drawing upon over 100 years of scholarly work on microclimate, we first present an overview of the history, key references, and critical issues surrounding the collection and utilization of microclimate records in ecosystem studies. We place particular emphasis on addressing specific and pressing issues related to the applications of microclimate at the community-ecosystem-landscape level, excluding those of controlled experiment such as growth chambers and greenhouses. Specifically, we: (1) highlight some key issues concerning the collection, quality assurance/quality control (QA/QC), and utilization of microclimatic data in ecosystem studies; (2) revisit microclimatic responses to the structural changes of ecosystems and landscapes; and (3) emphasize the significance of microclimate in understanding major ecosystem/landscape processes and functions. Vapor pressure deficit (VPD) is particularly emphasized for its calculation and use because of its burgeoning applications in the literature. Case studies for each of the three thematic topics are provided with selected references to demonstrate challenges and solutions. As the scientific community gears up to enhance microclimatic stations, we envision significant increases in the use of smart sensors, wireless access, networking, open databases, and computational capabilities. Understanding and addressing some of the issues raised in this synthesis paper may help advance microclimate research and foster collaboration with other relevant disciplines, such as ecosystem science.
•Increasingly warm and dry climate has a strong relationship to increasing wildfires.•High-severity fire has the strongest relationship with climate.•The relationship between climate and fire appears ...to be strengthening.•Vapor pressure deficit was associated with regional and local wildfire activity.
Over the last several decades in forest and woodland ecosystems of the southwestern United States, wildfire size and severity have increased, thereby increasing the vulnerability of these systems to type conversions, invasive species, and other disturbances. A combination of land use history and climate change is widely thought to be contributing to the changing fire regimes. We examined climate-fire relationships in forest and woodland ecosystems from 1984 to 2015 in Arizona and New Mexico using 1) an expanded satellite-derived burn severity dataset that incorporates over one million additional burned hectares when compared to MTBS data, and 2) climate variables including temperature, precipitation, and vapor pressure deficit (VPD). Regional climate-fire relationships were assessed by correlating annual area burned, area burned at high and low severity, and percent high severity with fire season (May-August) and water-year (October-September) climate variables. We also analyzed relationships between climate and high-severity fire at the scale of the individual fire using a hurdle model. We found that increasing temperature and VPD and decreasing precipitation were associated with increasing area burned regionally, and that area burned at high severity had the strongest relationships with climate metrics. The relationship between climate and fire activity in the Southwest appears to be strengthening since 2000. VPD-fire correlations were consistently as strong as, or stronger than, temperature or precipitation variables alone, both regionally and at the scale of the individual fire. Notably, at the scale of the individual fire, temperature and precipitation were not significant predictors of fire activity. Thus, our results support the use of VPD as a more integrative climate metric to forecast fire activity. We suggest that the strong relationship between VPD and fire activity may be useful to assess the likelihood of high-severity fire occurrence through continued development of the high-severity fire threshold model we present. The link between increasing aridity and increasing wildfire activity suggests a future with more fire in Southwest forests and woodlands with projected warming, underscoring the urgency of restoration in dry forests to reduce the likelihood of uncharacteristic, large high-severity fires.
•A new data-driven method is developed to partition ET based on the separation of soil and canopy conductances.•Magnitudes and trends in soil conductance, canopy conductance, E, and T:ET are ...consistent with physical understanding.•LAI only explained small variations of mean annual T:ET across sites.
Separating evapotranspiration (ET) into evaporation (E) and transpiration (T) is challenging but key for a better understanding and prediction of the hydrological cycle and plant water use. In this study, flux data at 30 routine eddy-covariance sites were used to develop a new and simple method for ET partitioning based on the separation of soil and canopy conductances, with the main assumption that the latter is proportional to gross primary productivity (GPP). The result of T:ET across different plant functional types (PFTs) was consistent with recent modeling or empirical results. The mean annual T:ET was highest for evergreen needleleaf forests (0.75 ± 0.17), followed by croplands (0.62 ± 0.16) and grasslands (0.56 ± 0.15). The leaf area index (LAI) was shown to explain only small (20%) variations of mean annual T:ET across sites. However, at each site, the correlation of T:ET with LAI was strong at the seasonal scale, where T:ET increased nonlinearly with LAI. The results did not show significant relationship of T:ET with long-term mean precipitation across sites at multiyear timescales. However, the partitioned soil evaporation after each precipitation pulse is consistent with three-stage soil evaporation theory. This ET partitioning method is an objective assessment as it is mainly data-driven. The procedure to apply this method is also simple so it can be readily applied to global flux tower networks at different temporal and spatial scales, enabling continuous estimation of T:ET to monitor ecosystem dynamics and hydrological responses to environmental change.
Recent findings were able to show significant variability of stomatal dynamics between species, but not much is known about factors influencing stomatal dynamics and its consequences on biomass ...production, transpiration and water-use efficiency (WUE).
We assessed the dynamics of stomatal conductance (g
s) to a change of irradiance or vapour-pressure deficit (VPD) in two Populus euramericana and two Populus nigra genotypes grown under control and drought conditions. Our objectives were to determine the diversity of stomatal dynamics among poplar genotypes, and if soil water deficit can alter it. Physiological and morphological factors were investigated to find their potential links with stomatal morphology, WUE and its components at the whole-plant level.
We found significant genotypic variability of g
s dynamics to both irradiance and VPD. Genotypes with faster stomatal dynamics were correlated with higher stomatal density and smaller stomata, and the implications of these correlations are discussed.
Drought slowed g
s dynamics, depending on genotype and especially during stomatal closing. This finding is contrary to previous research on more drought-tolerant species. Independently of the treatment, faster stomatal dynamics were negatively correlated with daily whole-plant transpiration, presenting new evidence of a previously hypothesized contribution of stomatal dynamics to whole-plant water use.
Changes in leaf temperature are known to drive stomatal responses, because the leaf-to-air water vapour gradient (Δw) increases with temperature if ambient vapour pressure is held constant, and ...stomata respond to changes in Δw. However, the direct response of stomata to temperature (DRST; the response when Δw is held constant by adjusting ambient humidity) has been examined far less extensively. Though the meagre available data suggest the response is usually positive, results differ widely and defy broad generalisation. As a result, little is known about the DRST. This review discusses the current state of knowledge about the DRST, including numerous hypothesised biophysical mechanisms, potential implications of the response for plant adaptation, and possible impacts of the DRST on plant-atmosphere carbon and water exchange in a changing climate.
•Build a linkage between several main climatic drivers and ET.•Separate the contribution of each climatic driver to ET changes.•Vapour pressure deficit is the primary factor over energy-limited ...regions.
Evapotranspiration (ET) is one of the most important variables in terrestrial ecosystems, linking the carbon-water-energy cycles. In this study, we first analyze the spatial patterns of annual ET changes during 1980–2010 across China using four ET products: (i) the Global Land Evaporation Amsterdam Model version 3.0a (GLEAMv3.0), (ii) the EartH2Observe ensemble (EartH2Observe-En), (iii) the Global Land Data Assimilation System version 2.0 with Noah model (GLDAS2.0-Noah), and (iv) the Modern Era Retrospective-Analysis for Research and Application-Land (MERRA-Land). The results show that the spatial distribution of annual mean ET values and long-term changes derived from these four ET products are similar. Overall, large-scale increases in ET are observed in southeastern China, while decreases in ET over the northeast. Furthermore, we apply a newly developed separation method with the Budyko framework to quantify the individual contribution of five climatic factors to ET changes, including precipitation (P), net radiation (Rn), air temperature (T), vapour pressure deficit (VPD), and wind speed (u). It is found that the dynamics of P, Rn, and VPD are all strongly correlated with ET, suggesting that they are the major climatic factors influencing ET changes. Specifically, precipitation is the dominant factor for ET in water-limited regions, while ET changes in energy-limited regions are dominated by VPD according to all ET products except the EartH2Observe-En in which Rn and VPD have comparable performance. Our study highlights the importance of VPD in ET changes across energy-limited regions of China and suggests that the role of VPD in land surface-atmosphere interactions should be considered in future studies.
This paper studies a parallel heterogeneous machine batching and scheduling problem in which weighted jobs are first batched, and the batches are then assigned and sequenced on machines of varying ...capacities. The duration of a batch is the longest time needed to process a job, and the objective is that of minimizing the makespan, or the sum of the batches durations on the machine finishing last. The authors develop polynomial-size mathematical formulations and a variable neighborhood search metaheuristic. Extensive computational results suggest that a flow-based formulation outperforms a compact formulation, despite its larger number of variables. The metaheuristic is capable of producing high-quality solutions within a limited computing time.
•We introduce two models for the (Pm|p−batch|Cmax) batch processing problem.•A variable neighborhood search (VNS) metaheuristic is developed.•The performance of the formulations, the VNS and known algorithms are compared.
Summary
Accurate representation of photosynthesis in terrestrial biosphere models (TBMs) is essential for robust projections of global change. However, current representations vary markedly between ...TBMs, contributing uncertainty to projections of global carbon fluxes. Here we compared the representation of photosynthesis in seven TBMs by examining leaf and canopy level responses of photosynthetic CO2 assimilation (A) to key environmental variables: light, temperature, CO2 concentration, vapor pressure deficit and soil water content. We identified research areas where limited process knowledge prevents inclusion of physiological phenomena in current TBMs and research areas where data are urgently needed for model parameterization or evaluation. We provide a roadmap for new science needed to improve the representation of photosynthesis in the next generation of terrestrial biosphere and Earth system models.
PDF
