Vegetation Biomass Research Articles

Plastic mulches improve yield and reduce spotted-wing drosophila in primocane raspberry

Plastic mulches are increasingly used by growers producing perennial fruit crops to improve vegetative and fruit biomass, promote earlier yield, increase fruit quality, and enhance weed suppression. In this two-year study, we evaluated how black, white, and metallic plastic mulches impact primocane raspberry vegetative biomass, fruit yield and quality, and spotted-wing drosophila (Drosophila suzukii; SWD) infestation in a humid continental climate. All three plastic mulches increased vegetative biomass compared to the control with grass within the row. Marketable fruit yield was increased by 68-139%, 44-76%, and 33-110% in the black, white, and metallic plastic mulch plots, respectively, compared to the control. The black mulch extended fruit production by two weeks compared to the other treatments. Increases in vegetative and fruit biomass may be attributable to increased soil temperature under the black plastic mulch and increased reflection of photosynthetic active radiation (PAR) in the white and metallic mulches. None of the plastic mulches impacted the fruit quality parameters assessed, including soluble solids content, pH, titratable acidity, anthocyanin concentration, and total phenolics, compared to the control. All three plastic mulches reduced the proportion of unmarketable fruit, likely due to their 40-71% reduction in SWD larval infestation of fruit compared to the control. Overall, black, white, and metallic plastic mulches are an effective cultural practice for managing SWD while simultaneously increasing fruit and vegetative biomass.

Greenhouse gas emissions and carbon sequestration associated with Integrated Crop–Livestock–Forestry (ICLF) systems

Greenhouse gas (GHG) emissions from the Agriculture, Forest, and Other Land Use sector account for 23% of net global anthropogenic emissions. However, effective conservation agriculture practices can sequester carbon (C) up to 1 m in soil depth and vegetation biomass. Integrated Crop–Livestock–Forestry (ICLF) systems attempt to ensure sustainable agricultural production by combining various agricultural, livestock, and forestry production systems. This bibliographic review aims to present and discuss ICLF systems and their advantages and disadvantages compared with conventional systems, achieving a better understanding of the sources and sinks of GHGs (CH4, N2O, and CO2). Integrated systems exist in tropical and temperate climates with different practices, arrangements, designs, and modalities. Intercropping species with different root structures provides more ecological interactions that enhance biodiversity, soil quality, and C sequestration while reducing GHG emissions. Yet, ICLF systems are complex and require technical assistance and support for being implemented, besides an extensive initial investment that increases the cost of operation. A relevant carbon sink in ICLF systems is carbon from tree biomass, where the wood can be used for various purposes. Timber for sawmills and general construction has a longer C immobilization time. Methane from enteric fermentation is the greatest contributor to GHG emissions in livestock and ICLF systems. Nitrous oxide is released primarily from synthetic fertilizers (when applied), manure deposited on pastures, and the decomposition of plant residues. Carbon dioxide is emitted to a lesser extent from the application of lime and urea. Many studies do not include all compartments in the C balance and often focus on only one GHG or compartment of C. Accordingly, more studies on the sources and sinks of C and their potential to offset GHG emissions in terms of CO2 equivalent are urged.

Assessment of the Effects of Fencing Enclosure on Soil Quality Based on Minimum Data Set in Biru County of the Qinghai–Tibet Plateau, China

Fencing enclosures play an important role in improving ecological quality. There is a direct impact of implementing fencing enclosures on the change in soil quality. The soil quality index was used to examine the effects of fencing enclosures for different years (7 and 11 years) on soil quality in Biru County of Qinghai–Tibet Plateau, China. The fencing enclosure significantly increased soil water content, non-capillary porosity, soil organic matter, total nitrogen, total phosphorus, and alkali-hydrolyzable nitrogen, and significantly decreased the soil bulk density. The soil quality gradually improved as the fencing enclosure time length increased, probably due to the increase of vegetation coverage and biomass under the fencing enclosure. The minimum data set was composed of soil organic matter, capillary porosity, total potassium, and non-capillary porosity. The minimum data set was significantly correlated with the total data set and could replace the total data set for soil quality evaluation in the fencing enclosure project area. In summary, our study reflects that fencing enclosures significantly improve soil quality, and the implementation of the fencing enclosure project will effectively curb land degradation in Biru County of the Qinghai–Tibet Plateau, China.

Analysis of Resource Potential of Emergent Aquatic Vegetation in the Curonian Lagoon of the Baltic Sea

This paper presents results of an aquatic vegetation resource potential assessment. The study is aimed at assessing the perspective of biotechnological approaches to reducing the biogenic pollution of water bodies by the removal of aquatic vegetation. The article analyzes the dominant species of aquatic vegetation in the Curonian Lagoon, and their productivity and resource potential. It was established that the concentrations of protein and fat in the biomass of four dominant plants are extremely low, making it impossible to speak of their values in terms of biomass processing. Based on elemental composition, we can conclude that the biomass of Phragmites australis should have a high calorie content because it has a high carbon and hydrogen content (49.6% and 7.1%, respectively), resulting in a high energy value. Synchronous thermal analysis revealed that the maximum energy values of biomasses of Phragmites australis and Scirpus lacustris have a net calorific value of 12.62 and 12.55 MJ/kg, respectively. At the same time, the biomass of these plants has a low ash content (around 6.6–7.6%) and a low sulfur content (less than 0.41%). An analysis of the composition of aquatic vegetation biomass samples allowed us to establish that, given the permissible collection time (no earlier than September), the search for directions in the utilization of aquatic vegetation should focus on processing cellulose with the production of crystalline cellulose, biochar, or biofuel via anaerobic digestion. The removal of the excess biomass of aquatic vegetation (Phragmites australis) will allow the reduction of the nitrogen and phosphorus load in the water body by 140 kg/ha and 14 kg/ha, respectively.

Effects of long‐term fixed fire regimes on African savanna vegetation biomass, vertical structure and tree stem density

Abstract Fire plays an integral role in shaping the vegetation structure of savanna ecosystems. However, the effects of fire regime characteristics, such as frequency and season of burn, on savanna vegetation structure, biomass and tree abundance across landscape types are largely unknown. We used high‐resolution airborne light detection and ranging (LiDAR) to investigate the long‐term effects of fire manipulation on savanna vegetation in Kruger National Park, South Africa. We analysed the effects of fire exclusion and experimental burns every 1, 2, 3, 4 and 6 years and during different seasons on aboveground biomass (AGB), tree stem densities and vegetation vertical height profiles across a rainfall gradient and on contrasting geologies. Across savanna types, and especially in drier savannas, fire season was more influential for constraining AGB than fire frequency. Plots experiencing fires during the late‐ and mid‐dry season had 44.50% and 43.60%, respectively, lower AGB relative to unburnt plots than wet‐season fires. However, in mesic savannas, fire frequency interacted with fire season to influence AGB: plots subjected to high frequency, dry‐season fires had 55.35% lower AGB than unburnt plots, whereas plots burnt in the wet season at lower frequencies had lower AGB (24.40% lower than unburnt plots) than plots subjected to high frequency, wet‐season fires (13.74% lower AGB than unburnt plots). Fire regimes had variable effects on tree densities, and effects varied with the savanna type. Woody vertical vegetation profiles showed the largest differences in response to dry‐season fires, with the greatest divergence in vegetation height classes <5 m. Synthesis and applications. Understanding the influence of fire regimes on vegetation structure has important implications for the management of savanna heterogeneity and for predicting trajectories of change in savanna vegetation as fire regimes vary with climate change. We show that the magnitude of the effect of fire on woody vegetation structure varies with savanna context. Our results suggest that heterogeneous vegetation structure can be achieved by applying fires in the dry season in mesic savannas, whereas in dry savannas, variation in fire regimes is less consequential for constraining biomass accumulation and altering vegetation structure.

Aggregate‐associated soil organic carbon fractions in subtropical soil undergoing vegetative restoration

AbstractPrecise assessment of soil organic carbon (SOC) storage requires understanding how vegetation and soil physico‐chemical properties differ in SOC fractions. Therefore, we aimed to analyze the dynamics of aggregate‐associated, labile organic carbon (LOC) fractions corresponding to depth to clarify the effect of vegetation and soil properties on water stable aggregate (WSA) mineral adsorption in subtropical, red soil with five vegetation restoration regimes. The results showed that the large macro‐aggregate fraction dominated the degraded red soil, which had the highest content of dissolved organic carbon (DOC). WSA‐associated, easily oxidized organic carbon (EOC) varied from 6.26 to 20.02 g/kg and was not affected by vegetation types. Schima superba pure forest significantly increased DOC (0.38 g/kg on average) and particulate organic carbon (POC, 7.92 g/kg on average), which had the highest biomass. Along with soil depth, WSA‐associated POC declined, while exhibiting a growth trend with decreasing particle size, for example, the highest POC was found in <0.053 mm aggregates. The redundancy analysis ordination indicated that soil porosity and total nitrogen (TN) were the main soil parameters that explained the most variance. Meanwhile, the vegetation biomass, except for litter, were all significantly positively correlated with <0.053 mm aggregates. Leaf biomass played the most important role on DOC in macro‐aggregates with a 53.42% contribution. For aggregate‐related POC, the largest contribution was from the interactions between branch biomass and pH (47.78%) followed by TN (35.1%) of micro‐aggregate‐related POC. Leaf biomass, <0.053 mm aggregates, and TN can be used as indicators to evaluate the impact of vegetation restoration on WSA‐associated SOC fractions. Broad‐leaved forest or in combination with indigenous coniferous species was a better choice for SOC sequestration improvement in the study area for managing C supply, process, and flux in subtropical terrestrial ecosystems.

Differential developmental rates and demographics in Red Kangaroo (Osphranter rufus) populations separated by the dingo barrier fence.

Decommissioning the dingo barrier fence has been suggested to reduce destructive dingo control and encourage a free transfer of biota between environments in Australia. Yet the potential impacts that over a century of predator exclusion might have had on the population dynamics and developmental biology of prey populations has not been assessed. We here combine demographic data and both linear and geometric morphometrics to assess differences in populations among 166 red kangaroos (Osphranter rufus)-a primary prey species of the dingo-from two isolated populations on either side of the fence. We also quantified the differences in aboveground vegetation biomass for the last 10 years on either side of the fence. We found that the age structure and growth patterns, but not cranial shape, differed between the two kangaroo populations. In the population living with a higher density of dingoes, there were relatively fewer females and juveniles. These individuals were larger for a given age, despite what seems to be lower vegetation biomass. However, how much of this biomass represented kangaroo forage is uncertain and requires further on-site assessments. We also identified unexpected differences in the ontogenetic trajectories in relative pes length between the sexes for the whole sample, possibly associated with male competition or differential weight-bearing mechanics. We discuss potential mechanisms behind our findings and suggest that the impacts of contrasting predation pressures across the fence, for red kangaroos and other species, merit further investigation.

Recycled water use with added microbial consortia in the cultivation of aromatic plants

Research objective: This research aims to evaluate the potential of biologically purified water with added beneficial microorganisms for soil and plants for possible use in agriculture. In such a way that this type of water, which is not always accepted by growers, can instead be positively perceived by technicians in the sector and by those who often have no other water resources to irrigate their plants. Materials and Methods: The experiments, which began in April 2023, were conducted to the Abbey of S. Antimo in Piombino (LI) on different types of aromatic plants (rosemary, sage, mint, thyme). The experimental groups were: control; aqueduct water; aqueduct water with added microorganisms; recycled water; recycled water with added microorganisms. On 17 May 2023, plant height, number of leaves, vegetative weight, volume and length of roots, number of microorganisms in the substrate, number of dead plants and pH of the substrate were determined. Results and Discussion: The experiment showed that it is possible to use recycled water supplemented with microorganisms to significantly improve plant height, leaf number, and vegetative and root biomass, reducing plant mortality on aromatic species such as mint, rosemary, thyme and sage. In general, a significant increase in plant height and number of leaves as well as vegetative and root biomass was observed in plants treated with microorganisms The trial significantly showed how water inoculated with plant-stimulating microorganisms can significantly increase the vegetative and root biomass of various aromatic plant species. This aspect was also found in other horticultural species. Conclusions: The possible use of these waters in agriculture requires a careful study of the microbial communities present in them, which are often not suitable for plant growth. This experiment aimed to assess whether the use of plant-specific micro-organisms added to previously biologically treated water could improve the adaptation and growth performance of certain aromatic species. The results were significant and certainly deserve further studies on other horticultural species.

Plant extracts from mediterranean vegetation in the cultivation and defence of Plectranthus coleidos and Plectranthus amboinicus

Research objective: This research aims to evaluate the biostimulant potential of some Mediterranean vegetation extracts for the stimulation and defence of some Plectranthus amboinicus and Plectranthus coleidos plants. This is to increase knowledge on these plant extracts that could be used for the formulation of new plant biostimulants. Materials and Methods: The experiments, which started in May 2022, were conducted in the greenhouses of CREA-OF in Pescia (Pt), Tuscany, Italy (43°54′N 10°41′E) on Plectranthus amboinicus and Plectranthus coleidos. The experimental groups were: group control; group with oak macerated; group with myrtus macerated; group with wild fennel macerated; group with lentiscus macerated; group with inula macerated. On January 20, 2023, plant height, leaves number, vegetative weight, roots volume and length, the number of microorganisms in the substrate, plant dead number and pH were determined. Results and Discussion: The experiment showed that the use of plant extracts as biostimulants can significantly improve vegetative and root growth and reduce plant mortality of Plectranthus amboinicus and Plectranthus coleidos. In general, a significant increase in plant height and number of leaves as well as vegetative and root biomass was observed in plants treated with all plant biostimulants, particularly with the treatments of macerated oak, macerated fennel and macerated inula. The treatments with macerated oak and macerated fennel were the best in all two Plectranthus species. Observations conducted on treatments with phytotherapeutic agents demonstrate their effectiveness as stimulants of the plants' self-defence mechanisms. In addition, some preparations appear to act as repellents and substances that make many pests lose their appetite or stimulus to feed. Their activity seems to be determined by the minerals and certain molecules present in the plants used to prepare the macerates. This is why some of these substances have been placed under observation by scientific research to verify their effects. However, the objective difficulty of obtaining reproducible results limits research and experimentation activities in this field and directs them towards the characterisation of the active ingredients that play a primary role in insecticide, fungicide, bactericide or herbicide action. Conclusions: Herbal medicines are always used in aqueous form by performing the treatment with an atomiser or, more rarely, by adding the extract to irrigation water. The extract is obtained by steeping the herbs in water or by preparing an infusion or decoction. The test showed that the use of extracts obtained from plants by macerating Mediterranean shrub species can have biostimulant activity against aromatic succulents such as Plectranthus amboinicus and Plectranthus coleidos. Very interesting aspects especially with regard to the study of new formulations obtained from plants and applicable in organic farming.

Sweet potato ADP-glucose pyrophosphorylase small subunit affects vegetative growth, starch content and storage root yield

The development of storage roots is a key factor determining the yields of crop plants, including sweet potato. Here, using combined bioinformatic and genomic approaches, we identified a sweet potato yield-related gene, ADP-glucose pyrophosphorylase (AGP) small subunit (IbAPS). We found that IbAPS positively affects AGP activity, transitory starch biosynthesis, leaf development, chlorophyll metabolism, and photosynthesis, ultimately affecting the source strength. IbAPS overexpression in sweet potato led to increased vegetative biomass and storage root yield. RNAi of IbAPS resulted in reduced vegetative biomass, accompanied with a slender stature and stunted root development. In addition to the effects on root starch metabolism, we found that IbAPS affects other storage root development-associated events, including lignification, cell expansion, transcriptional regulation, and production of the storage protein sporamins. A combinatorial analysis based on transcriptomes, as well as morphological and physiological data, revealed that IbAPS affects several pathways that determine development of vegetative tissues and storage roots. Our work establishes an important role of IbAPS in concurrent control of carbohydrate metabolism, plant growth, and storage root yield. We showed that upregulation of IbAPS results in superior sweet potato with increased green biomass, starch content, and storage root yield. The findings expand our understanding of the functions of AGP enzymes and advances our ability to increase the yield of sweet potato and, perhaps, other crop plants.

Space–time home‐range estimates and resource selection for the Critically Endangered Philippine Eagle on Mindanao

Quantifying home‐range size and habitat resource selection are important elements in wildlife ecology and are useful for informing conservation action. Many home‐range estimators and resource selection functions are currently in use. However, both methods are fraught with analytical issues inherent within autocorrelated movement data from irregular sampling and interpretation of resource selection model parameters to inform conservation management. Here, we apply satellite remote sensing technologies to provide updated estimates of home‐range size and first estimates of fine‐scale resource selection for six adult Philippine Eagles Pithecophaga jefferyi using a space–time autocorrelated kernel density estimate (AKDE) home‐range estimator and non‐parametric resource selection functions. All six adult Eagles showed distinct site fidelity, with continuous range residency between 2 and 18 km, 1 month after tagging. The space–time AKDE home‐range estimators had a median 95% home‐range size = 68 km2 (95% confidence interval (95% CI) 62–74 km2, range: 39–161 km2), with the median 50% core range size = 13 km2 (95% CI 11–14 km2, range 9–33 km2). From the resource selection functions, all adult Philippine Eagles used habitat high in photosynthetic leaf and canopy structure but avoided areas of old‐growth biomass and denser areas of vegetation. This is possibly due to foraging forays into secondary forest and fragmented agricultural areas away from nesting sites. For the first time, we determine two important fine‐scale spatial processes for this Critically Endangered raptor that can help in directing conservation management. Rather than employing traditional home‐range estimators and resource selection functions, we recommend that analysts consider space–time approaches and non‐parametric resource selection functions to animal movement data to explore fully space–time and resource selection.

Levoglucosan and its isomers in terrestrial sediment as a molecular markers provide direct evidence for the low-temperature fire during the mid-Holocene in the northern Shandong Peninsula of China

Black carbon and charcoal's limitation in detecting low-temperature fires could be a major obstacle in observing paleofire. To reconstruct a low-temperature fire pattern and vegetation changes in the Changyi in the northern Shandong Peninsula over the last 5000 years, we used molecular biomarker (levoglucosan and its isomers) and hydrocarbons (n-alkanes), along with charcoal and black carbon in the sediment sites. An increase in the amounts of coniferous flammable fuels could provide the biomass required to maintain low-temperature conditions for smoldering fires during the prehistoric period when wildfires occurred during 5300–5100 yr BP. These fires primarily coincided with cooling climate events that began approximately 5300 yr BP onward. Significant levoglucosan fluxes at approximately 4400–3600 yr BP and 1300–1000 yr BP were thought to be closely linked to intensive anthropogenic burning practices and the climate-controlled sedimentary wet environments, coinciding with the periods of the Longshan (4600–4000 yr B.P), Yueshi Cultures （4000–3500 yr B.P）and Tang Dynasty（1300–1100 yr B.P）. During those times, the original forest landscape in the study region was gradually replaced by a fire-prone open forest, where low-temperature smoldering fires could be sustained by the abundance of biomass for producing fuel from open forests. In contrast, the levoglucosan fluxes remained at low values between the intervals of 3600–3200 yr BP and 1000–0 yr BP, whereas the charcoal fluxes showed a significant increase in the Changyi profile. Moreover, the positive correlation between the levoglucosan and char fluxes in sediments suggested that levoglucosan could be an indicator of regional fires or biomass burning at low temperatures. The ratios between levoglucosan and its isomers indicated that levoglucosan are derived from the combustion of softwood at the study site. Futhermore, Levoglucosan in sediments was used in this study to document the changes in vegetation and low-temperature regional biomass burning, as well as the shifts in human land use and the cultural development in response to climate change. Compared to the two biomass-burning proxies (black carbon and charcoal), levoglucosan in sediments can additionally provide supplementary information to understand paleofire.

Effects of vegetation restoration on soil properties and vegetation attributes in the arid and semi-arid regions of China

Driven by the goal of reversing desertification and recovering degraded lands, a wide range of vegetation restoration practices (such as planting and fencing) have been implemented in China's drylands. It is essential to examine the effects of vegetation restoration and environmental factors on soil nutrients to optimize restoration approaches. However, quantitative evaluation on this topic is insufficient due to a lack of long-term field monitoring data. This study evaluated the effects of sandy steppe restoration and sand dune fixation in the semi-arid desert, and natural and artificial vegetation restoration in the arid desert. It considered soil and plant characteristics using long-term (2005–2015) data from the Naiman Research Station located in the semi-arid region and Shapotou Research Station in the arid region of China's drylands. Results showed the sandy steppe had higher soil nutrient contents, vegetation biomass and rate of accumulating soil organic matter (OM) than the fixed dunes and moving dunes. Soil nutrient contents and vegetation biomass of the natural vegetation of Artemisia ordosica were higher than those of the artificial restoration of Artemisia ordosica since 1956. Artificial restoration had a higher rate of accumulating soil OM, total nitrogen (TN) and grass litter biomass than natural restoration. Soil water indirectly affected soil OM by affecting vegetation. Grass diversity was the main influencing factor on soil OM variance in the semi-arid Naiman desert while shrub diversity was the main factor in the arid Shapotou desert. These findings indicate that sand fixation in the semi-arid desert and vegetation restoration in the arid desert bring benefits for soil nutrient accumulation and vegetation improvement, and that natural restoration is preferable to artificial restoration. Results can be used to formulate sustainable vegetation restoration strategies, such as encouraging natural restoration, considering local resource constraints, and giving priority to restoring shrubs in arid areas with limited water.

Simulating dynamic fire regime and vegetation change in a warming Siberia

BackgroundClimate change is expected to increase fire activity across the circumboreal zone, including central Siberia. However, few studies have quantitatively assessed potential changes in fire regime characteristics, or considered possible spatial variation in the magnitude of change. Moreover, while simulations indicate that changes in climate are likely to drive major shifts in Siberian vegetation, knowledge of future forest dynamics under the joint influence of changes in climate and fire regimes remains largely theoretical. We used the forest landscape model, LANDIS-II, with PnET-Succession and the BFOLDS fire extension to simulate changes in vegetation and fire regime characteristics under four alternative climate scenarios in three 10,000-km2 study landscapes distributed across a large latitudinal gradient in lowland central Siberia. We evaluated vegetation change using the fire life history strategies adopted by forest tree species: fire resisters, fire avoiders, and fire endurers.ResultsAnnual burned area, the number of fires per year, fire size, and fire intensity all increased under climate change. The relative increase in fire activity was greatest in the northernmost study landscape, leading to a reduction in the difference in fire rotation period between study landscapes. Although the number of fires per year increased progressively with the magnitude of climate change, mean fire size peaked under mild or moderate climate warming in each of our study landscapes, suggesting that fuel limitations and past fire perimeters will feed back to reduce individual fire extent under extreme warming, relative to less extreme warming scenarios. In the Southern and Mid-taiga landscapes, we observed a major shift from fire resister-dominated forests to forests dominated by broadleaved deciduous fire endurers (Betula and Populus genera) under moderate and extreme climate warming scenarios, likely associated with the substantial increase in fire activity. These changes were accompanied by a major decrease in average cohort age and total vegetation biomass across the simulation landscapes.ConclusionsOur results imply that climate change will greatly increase fire activity and reduce spatial heterogeneity in fire regime characteristics across central Siberia. Potential ecological consequences include a widespread shift toward forests dominated by broadleaved deciduous species that employ a fire endurer strategy to persist in an increasingly fire-prone environment.

Movement drives population dynamics of one of the most mobile ungulates on Earth: Insights from a mechanistic model.

Long-distance movements are hypothesized to positively influence population size and stability of mobile species. We tested this hypothesis with a novel modeling approach in which moving herbivores interact with the environment created by a dynamic global vegetation model using highly mobile Mongolian gazelles in the eastern Mongolian grasslands as a case study. Gazelle population dynamics were modeled from 1901 to 2018 under two scenarios, one allowing free movement and one restricting movement. Gazelles were 2.2 times more abundant when they could move freely and were extirpated in 71% of the study area when mobility was restricted. Mobility resulted in greater population increases during times of abundant forage and smaller population decreases during drought. Reduced thermoregulatory costs associated with climate change, combined with an increase in vegetation biomass, increased gazelle abundance. Since high abundances often resulted in overgrazing and, thus, extirpation when movement was restricted, mobility had an important role in maintaining higher densities. The novel modeling approach shows how accounting for not just herbivore but also plant ecophysiology can improve our understanding of the population dynamics of highly mobile herbivores, in particular when examining the effects of habitat and climate change. Since the model simulates herbivores based on general physiological mechanisms that apply across large herbivores and the vegetation model can be applied globally, it is possible to adapt the model to other large-herbivore systems.

Assessment of dynamic drought-induced ecosystem risk: Integrating time-varying hazard frequency, exposure and vulnerability

Terrestrial ecosystems, occupying 28.26% of Earth's surface, are extensively at risk from droughts, which is likely to propagate into human communities owing to loss of vital services. Ecosystem risk also tends to fluctuate within anthropogenically-forced nonstationary environments, raising considerable concerns about effectiveness of mitigation strategies. This study aims to assess dynamic ecosystem risk induced by droughts and identify risk hotspots. Bivariate nonstationary drought frequency was initially derived as a hazard component of risk. By coupling vegetation coverage and biomass quantity, a two-dimensional exposure indicator was developed. Trivariate likelihood of vegetation decline was calculated under arbitrary droughts to intuitively determine ecosystem vulnerability. Ultimately, time-variant drought frequency, exposure and vulnerability were multiplied to derive dynamic ecosystem risk, followed by hotspot and attribution analyses. Risk assessment implemented in the drought-prevalent Pearl River basin (PRB) of China during 1982–2017 showed that meteorological droughts in eastern and western margins, although less frequent, were prolonged and aggravated in contrast to prevalence of less persistent and severe droughts in the middle. In 86.12% of the PRB, ecosystem exposure maintains high levels (0.62). Relatively high vulnerability (>0.5) occurs in water-demanding agroecosystems, exhibiting a northwest-southeast-directed extension. A 0.1-degree risk atlas unveils that high and medium risks occupy 18.96% and 37.99% of the PRB, while risks are magnified in the north. The most pressing hotspots with high risk continuing to escalate reside in the East River and Hongliu River basins. Our results provide knowledge of composition, spatio-temporal variability and driving mechanism of drought-induced ecosystem risk, which will assist in risk-based mitigation prioritization.

Continuous ground monitoring of vegetation optical depth and water content with GPS signals

Abstract. Satellite microwave remote sensing techniques can be used to monitor vegetation optical depth (VOD), a metric which is directly linked to vegetation biomass and water content. However, these large-scale measurements are still difficult to reference against either rare or not directly comparable field observations. So far, in situ estimates of canopy biomass or water status often rely on infrequent and time-consuming destructive samples, which are not necessarily representative of the canopy scale. Here, we present a simple technique based on Global Navigation Satellite Systems (GNSS) with the potential to bridge this persisting scale gap. Because GNSS microwave signals are attenuated and scattered by vegetation and liquid water, placing a GNSS sensor under a vegetated canopy and measuring changes in signal strength over time can provide continuous information about VOD and thus on vegetation biomass and water content. We test this technique at a forested site in southern California for a period of 8 months. We show that variations in GNSS signal-to-noise ratios reflect the overall distribution of biomass density in the canopy and can be monitored continuously. For the first time, we show that this technique can resolve diurnal variations in VOD and canopy water content at hourly to sub-hourly time steps. Using a model of canopy transmissivity to assess these diurnal signals, we find that temperature effects on the vegetation dielectric constant, and thus on VOD, may be non-negligible at the diurnal scale or during extreme events like heat waves. Sensitivity to rainfall and dew deposition events also suggests that canopy water interception can be monitored with this approach. The technique presented here has the potential to resolve two important knowledge gaps, namely the lack of ground truth observations for satellite-based VOD and the need for a reliable proxy to extrapolate isolated and labor-intensive in situ measurements of biomass, canopy water content, or leaf water potential. We provide recommendations for deploying such off-the-shelf and easy-to-use systems at existing ecohydrological monitoring networks such as FluxNet or SapfluxNet.

The Transcription Factor HaHB11 Boosts Grain Set and Yield in Rice Plants, Allowing Them to Approach Their Ideal Phenotype.

The ideal rice phenotype is that of plants exhibiting fewer panicles with high biomass, large grain number, flag leaf area with small insertion angles, and an erected morphology improving light interception. The sunflower transcription factor HaHB11, homeodomain-leucine zipper I, confers increased seed yield and abiotic stress tolerance to Arabidopsis and maize. Here, we report the obtaining and characterization of rice plants expressing HaHB11 driven by its promoter or the 35S constitutive one. Transgenic p35S:HaHB11 plants closely resembled the ideal high-yield phenotype, whereas those carrying the pHaHB11:HaHB11 construct were hard to distinguish from the wild type. The former had an erected architecture, enhanced vegetative leaf biomass, rolled flag leaves with a larger surface, sharper insertion angles insensitive to brassinosteroids, and higher harvest index and seed biomass than the wild type. The combination of the distinct features exhibited by p35S:HaHB11 plants, including the increased number of set grains per panicle, supports the high-yield phenotype. We wondered where HaHB11 has to be expressed to achieve the high-yield phenotype and evaluated HaHB11 expression levels in all tissues. The results indicate that its expression is particularly necessary in the flag leaf and panicle to produce the ideal phenotype.

Early afforestation on islands of proglacial Lake Ojibway as evidence of post-glacial migration outposts

At the end of the last glacial period in the northern hemisphere, meltwater from receding ice sheets accumulated into large proglacial lakes, potentially limiting postglacial afforestation. We explored whether former islands of proglacial Lake Ojibway (Canada) (hilltops in the current landscape) could have acted as migration outposts and thus accelerated the postglacial migration. We extracted sediments from two small lakes located on “paleo-islands” and used XRF to detect changes in soil erosion and vegetation biomass. We also used plant macro-remains and wood charcoal to determine if (and which) tree species colonized the sites and to detect local fire events. Organic sediment accumulation started around 9657 and 9947 cal. yr BP at Lakes Perché and Despériers, respectively, before the level of Lake Ojibway started to decrease and liberate parts of the studied landscape ca 9400 cal. yr BP. Lithogenic elements (Ti, K, Sr, Fe, Zr, and Rb) decreased between the beginning of organic sediment accumulation and 8800–8700 cal. yr BP, indicating reduced soil erosion, possibly due to soil stabilization by vegetation. Then, the S/Ti ratio, a proxy of organic matter increased around 8800 and 8400 cal. yr BP. The earliest tree macro-remains ( Larix laricina and Pinus spp.) were found between 9850 and 9500 cal. yr BP. Local fires were detected around 9820 and 8362 cal. yr BP. Early afforestation occurred on the islands of Lake Ojibway, 200 and 450 years before its level started to decrease, confirming that some islands acted as migratory outposts accelerating postglacial migration.

Mixed-Species Acacia Plantation Decreases Soil Organic Carbon and Total Nitrogen Concentrations but Favors Species Regeneration and Tree Growth over Monoculture: A Thirty-Three-Year Field Experiment in Southern China

Mixed-species plantations of trees with N-fixing species have the potential of promoting forest productivity and soil fertility. However, few studies in the literature have addressed the advantages of mixed-species plantations of leguminous trees over monocultures of leguminous trees based on in situ inventories over a long time period. Here, we monitored the dynamics of tree community composition, vegetation biomass, soil nutrients, and soil microbial phospholipid fatty acids (PLFAs), in an Acacia mangium monoculture plantation during 33 years of development and compared it with a mixed-species plantation of A. mangium associated with 56 native species which were underplanted 14 years after the initial establishment. Leaf N and phosphorus (P) concentrations of three main species in the overstory and understory of the A. mangium monoculture were measured. Our results showed that the soil organic carbon (SOC), total nitrogen (TN), and available phosphorus (AP) concentrations significantly increased over time during the approximately thirty years of A. mangium monoculture plantation, while the disadvantages were associated with new species regeneration and the increment of vegetation biomass. In the A. mangium monoculture plantation, leaf N concentration of A. mangium,Rhodomyrtus tomentosa, and Dicranopteris dichotoma continuously increased from 21 to 31 years, while the leaf P concentration of A. mangium and R. tomentosa decreased. The mixed-species plantations of A. mangium with native tree species had lower SOC and soil TN concentrations, more new tree species recruitment in the understory, and faster vegetation biomass increment than the A. mangium monoculture. However, the PLFAs of soil microbial groups were slightly different between the two types of plantations. We conclude that improved soil N nutrient condition by A. mangium monoculture benefits N absorption by A. mangium, R. tomentosa, and D. tomentosa, while low soil AP limits P absorption by A. mangium and R. tomentosa. Meanwhile, transforming the A. mangium monoculture into a mixed-species plantation via the introduction of multiple native species into the A. mangium monoculture decreases SOC and TN concentrations but the advantages include improving forest regeneration and maintaining forest growth in a long-term sequence. These findings provide useful and practical suggestions for managing forest monocultures of A. mangium in subtropical regions.