Greater Aboveground Biomass Research Articles

Seeding Density Alters the Assembly of a Restored Plant Community after the Removal of a Dam in Southern Wisconsin, USA

Recently exposed reservoir sediments, prone to colonization by invasive species, provide novel settings to test hypotheses related to soil conditions and propagule supply as potential drivers of plant assembly in disturbed ecosystems. We used a dam removal site in southwestern Wisconsin to examine the relationship between the physiochemical properties of dewatered sediments, seeding density, and plant community assembly. The plant communities from five seed densities (1000, 500, 250, 125, and 0 seed m−2) were annually assessed over four years. We hypothesized (1) that the native aboveground biomass and the proportion of native to invasive (non-seeded species) aboveground biomass would increase with the seeding density and (2) that the diversity of seeded native species would increase with a higher seeding density. We found evidence that sowing at least 500 seeds m−2 of prairie species increased their abundance, establishment, and plot diversity compared to non-seeded plants that persisted four years after seeding (p < 0.05). The seeding density treatments led to the assembly of two distinct communities: “native” and “invasive”. The “native” community, assembled in plots seeded with at least 500 seeds m−2, had a greater aboveground biomass and diversity (i.e., richness) of seeded plants compared to plots with lower seed densities, and its productivity was positively related to this richness. In the “weedy” community, the diversity of invasive species had no relationship to their aboveground biomass, likely because these species share similar traits (i.e., redundancy) and may have performed similar functions within the plant community. These findings suggest that the seeding density interacted with the disturbed soil resources to increase the diversity and productivity of seeded native species and may serve as a positive feedback mechanism for the establishment of native communities in dewatered sediments.

Evidence for Reductions in Physical and Chemical Plant Defense Traits in Island Flora.

Reduced defense against large herbivores has been suggested to be part of the "island syndrome" in plants. However, empirical evidence for this pattern is mixed. In this paper, we present two studies that compare putative physical and chemical defense traits from plants on the California Channel Islands and nearby mainland based on sampling of both field and common garden plants. In the first study, we focus on five pairs of woody shrubs from three island and three mainland locations and find evidence for increased leaf area, decreased marginal leaf spines, and decreased concentrations of cyanogenic glycosides in island plants. We observed similar increases in leaf area and decreases in defense traits when comparing island and mainland genotypes grown together in botanic gardens, suggesting that trait differences are not solely driven by abiotic differences between island and mainland sites. In the second study, we conducted a common garden experiment with a perennial herb-Stachys bullata (Lamiaceae)-collected from two island and four mainland locations. Compared to their mainland relatives, island genotypes show highly reduced glandular trichomes and a nearly 100-fold reduction in mono- and sesquiterpene compounds from leaf surfaces. Island genotypes also had significantly higher specific leaf area, somewhat lower rates of gas exchange, and greater aboveground biomass than mainland genotypes across two years of study, potentially reflecting a broader shift in growth habit. Together, our results provide evidence for reduced expression of putative defense traits in island plants, though these results may reflect adaptation to both biotic (i.e., the historical absence of large herbivores) and climatic conditions on islands.

Assessing vegetation productivity and environmental impact in: A remote sensing approach

This study explores the dynamic response of vegetation productivity in semi-arid foothill rangelands of Uzbekistan, focusing on the Normalized Difference Vegetation Index (NDVI) dynamics and its correlation with climatic and environmental variables. In contrast to established relationships reported in previous studies, our findings reveal distinctive seasonal patterns in NDVI values, with higher values observed during spring (0.150-0.300) and lower values in summer (0.100-0.130). The chlorophyll and carotenoid content of A. diffusa exhibited variations in response to seasonal changes, emphasizing the importance of considering seasonal factors in rangeland health assessments. Chlorophyll and green aboveground biomass are identified as key indicators of vegetation productivity, crucial for maintaining ecosystem balance and contributing to climate regulation. Significant relationships are observed between NDVI and water resources, including precipitation and soil moisture (P ≤ 0.0001), highlighting the impact of climatic factors on vegetation cover. Positive correlations between NDVI and total green aboveground biomass underscore the relevance of NDVI as an indicator of vegetation health in foothill rangelands. This research project represents an initial step in investigating vegetation changes due to grazing in Uzbekistan, providing recommendations for sustainable rangeland utilization. Establishing an ecological monitoring system, incorporating GIS and Remote Sensing technologies, is proposed for comprehensive understanding and sustainable management of this complex ecosystem. Ongoing and future research endeavors aim to develop modern methods for rangeland vegetation monitoring, facilitating the identification of critical regions and offering solutions to prevent and mitigate desertification effects.

Street tree diversity and urban heat

Higher diversity within a city's street trees may offer greater cooling benefits than less diverse urban forests. California’s urban forests are among the most diverse in the world and offer an opportunity to test the relationship between diversity and cooling at a large scale. For 136 urban ZIP codes, we connect the most comprehensive data to date on California’s urban forests to both local station and satellite weather data for the period 2010–2018. We test whether biodiversity, measured by the Shannon-Wiener index and the new Top Diversity 50 index, is correlated with extreme heat in summer. After controlling for local averages in weather and tree canopy cover, we find that urban forest biodiversity is associated with lower maximum and higher minimum temperatures for June to September. Our specification makes it unlikely that reverse causality drives our result. Instead, we suggest that greater tree species diversity may boost daytime cooling through several pathways, including mutualism and greater aboveground biomass, a mechanical relationship where greater biodiversity implies a greater likelihood of having species with excellent shade, and cooling benefits from structural diversity in urban settings.

Unraveling the potential: assessment of the effect of Azospirillum brasilense inoculated via seeds on the growth and production of Mombaça grass

Nitrogen fertilization in pastures is considered one of the primary limiting factors that significantly enhance forage biomass production. Traditional chemical fertilizers used in crop cultivation are derived from petrochemical and mining industries. These production chains have undergone continuous and consistent structural changes year after year, affecting the prices of these inputs for farmers, consequently escalating production costs and even rendering investment in livestock farming unfeasible. For this reason, research becomes crucial to evaluate alternative techniques that can complement or fulfill the nitrogen demand in forage crops. The bacterium Azospirillum brasilense has emerged as a viable alternative to reduce costs in pasture establishment and maintenance, serving as a nitrogen source when compared to traditional sources. The objective of this study was to assess the effect of Azospirillum brasilense inoculation on the growth and production of Panicum maximum cv. Mombaça. The experimental design employed was a randomized complete block design with four treatments and four replications. Each plot consisted of three plants, resulting in a total of 48 experimental units. The treatments comprised: T1 - natural soil (NS), T2 - Azospirillum brasilense (BAC.), T3 - nitrogen topdressing (N), T4 - Azospirillum brasilense and nitrogen topdressing (BAC+N). Evaluations were conducted at 60 and 90 days after sowing (DAS), assessing the following variables: plant height (PH), number of leaves (NL), number of tillers (NT), aboveground green biomass (AGGB), aboveground dry biomass (ADBB), root fresh biomass (RFB), and root dry biomass (RDB). Significant effects (P<0.05) were observed for inoculation and nitrogen topdressing on the assessed traits: plant height, number of leaves, number of tillers, aboveground green biomass, aboveground dry biomass, root fresh biomass, and root dry biomass. Notably, nitrogen topdressing either solely or in combination with seed inoculation of the forage yielded positive outcomes for all studied variables at both 60 and 90 DAS. A favorable impact on the development of Mombaça grass was evident across all parameters studied in samples receiving nitrogen topdressing and Azospirillum spp. inoculation.

Comparing forest and grassland drought responses inferred from eddy covariance and Earth observation

Temperate forests and grasslands have different drought response strategies. Trees often control their stomatal opening to reduce water loss to prevent hydraulic failure and ensure the sustainable above-ground biomass production. In contrast, grasses generally have a less strong stomatal control and maintain high photosynthesis and transpiration until the soil moisture gets depleted. That is when their leaves wilt and the grasslands reduce their aboveground green biomass. Both the increased stomatal control and the reduction in aboveground biomass decrease the canopy-surface conductance and decrease the exchange of water and carbon between the leaves and the atmosphere. Here, we study to which extent remote sensing data reflect the drought-induced reduction in canopy-surface conductance for forests and grasslands. We use eddy covariance observations over 63 sites across the northern hemisphere to infer the conductance. We identify severe droughts from low soil moisture content and reduced canopy-surface conductance. We further analysed how the drought response is reflected in thermal and optical data derived from MODIS satellite data. The results show that the land surface temperature increases with drought-induced reductions in canopy-surface conductance for both forests and grasslands. By contrast, the optical indices (e.g., the normalized difference vegetation index) show a much stronger response for grasslands as compared to the forests. We conclude that the different canopy-level drought response strategies of trees and grasses are widespread and that these different responses are reflected in remote sensing data. Hence, a combination of thermal and optical satellite data should be used to monitor and study vegetation drought responses of forests and grasslands to ensure accurate inference on the implications on water, energy, and carbon fluxes.

Biomass estimation of World rice (Oryza sativa L.) core collection based on the convolutional neural network and digital images of canopy

ABSTRACT Above-ground biomass (AGB) is an important indicator of crop productivity. Destructive measurements of AGB incur huge costs, and most non-destructive estimations cannot be applied to diverse cultivars having different canopy architectures. This insufficient access to AGB data has potentially limited improvements in crop productivity. Recently, a deep learning technique called convolutional neural network (CNN) has been applied to estimate crop AGB due to its high capacity for digital image recognition. However, the versatility of the CNN-based AGB estimation for diverse cultivars is still unclear. We established and evaluated a CNN-based estimation method for rice AGB using digital images with 59 diverse cultivars which were mostly in World Rice Core Collection. Across two years at two locations, we took 12,183 images of 59 cultivars with commercial digital cameras and manually obtained their corresponding AGB. The CNN model was established by using 28 cultivars and showed high accuracy (R2 = 0.95) to the test dataset. We further evaluated the performance of the CNN model by using 31 cultivars, which were not in the model establishment. The CNN model successfully estimated AGB when the observed AGB was lesser than 924 g m−2 (R2 = 0.87), whereas it underestimated AGB when the observed AGB was greater than 924 g m−2 (R2 = 0.02). This underestimation might be improved by adding training data with a greater AGB in further study. The present study indicates that this CNN-based estimation method is highly versatile and could be a practical tool for monitoring crop AGB in diverse cultivars.

Restoration and resilience to sea level rise of a salt marsh affected by dieback events

AbstractThe frequency of salt marsh dieback events has increased over the last 25 years with unknown consequences to the resilience of the ecosystem to accelerated sea level rise (SLR). Salt marsh ecosystems impacted by sudden vegetation dieback events were previously thought to recover naturally within a few months to years. In this study, we used a 13‐year collection of remotely sensed imagery to provide evidence that approximately 14% of total marsh area has not revegetated 10 years after a dieback event in Charleston, SC. Dieback onset coincided with a severe drought in 2012, as indicated by the Palmer drought stress index. A second dieback event occurred in 2016 after a historic flood influenced by Hurricane Joaquin in 2015. Unvegetated zones reached nearly 30% of the total marsh area in 2017. We used a light detection and ranging‐derived digital elevation model to determine that most affected areas were associated with lower elevation zones in the interior of the marsh. Further, restoration by grass planting was effective, with pilot‐scale restored plots having greater aboveground biomass than reference sites after two years of transplanting. A positive outcome indicated that the stressors that caused the dieback are no longer present. Despite that, many affected areas have not recovered naturally, even though they are located within the typical elevation range of healthy marshes. A mechanistic modeling approach was used to assess the effects of vegetation dieback on salt marsh resilience to SLR. Predictions indicate that a highly productive restored marsh (2000 g m−2 year−1) would persist at a moderate SLR rate of 60 cm in 100 years, whereas a nonrestored mudflat would lose all its elevation capital after 100 years. Thus, rapid restoration of marsh dieback is critical to avoid further degradation. Also, failure to incorporate the increasing frequency and intensity of extreme climatic events that trigger irreversible marsh diebacks underestimates salt marsh vulnerability to climate change. Finally, at an elevated SLR rate of 122 cm in 100 years, which is most likely an extreme climate change scenario, even highly productive ecosystems augmented by sediment placement would not keep pace with SLR. Thus, climate change mitigation actions are also urgently needed to preserve present‐day marsh ecosystems.

Ecosystem engineers in the extreme: The modest impact of marmots on vegetation cover and plant nitrogen and phosphorus content in a cold, extremely arid mountain environment.

Burrowing mammals strongly impact plant communities. One of the main effects is accelerating nutrient cycling and thus promoting plant growth. This mechanism is well-studied in grasslands and alpine habitats, but less is known about this phenomenon in arid, cold mountain environments. We studied ecosystem engineering by long-tailed marmots (Marmota caudata) by measuring the content of plant nitrogen and phosphorus, as well as nitrogen stable isotopes in plant biomass and marmot feces in a distance gradient up to 20 m from marmot burrows in an extremely arid glacier valley in Eastern Pamir, Tajikistan. We also captured aerial images of the area inhabited by marmots to study the spatial distribution of vegetation. There was a weak relationship between the presence of burrows and vegetation cover on soil not covered by burrow material. Burrow mounds were not colonized by plants, as opposed to other studies, where mounds are often microhabitats that enhance plant diversity. A significant increase in N and P in aboveground green plant biomass in the proximity of burrows was found in one out of six studied plant species. Contrary to our expectations, stable N isotopes did not give further insight into N routing. We assume that plant growth is strongly limited by water availability, which prevents them from utilizing the local increase in nutrients, certainly provided by marmot activity. The results are contrary to numerous studies, which showed that the role of burrowing animals as ecosystem engineers increases with increasing abiotic stress, including aridity. This shows a lack of this type of study at the end of the gradient of abiotic factors.

Expanding wildland-urban interface alters forest structure and landscape context in the northern United States

The wildland-urban interface (WUI), where housing intermingles with wildland vegetation, is the fastest-growing land use type in the United States. Given the ecological and social benefits of forest ecosystems, there is a growing need to more fully understand how such development alters the landscape context and structure of these WUI forests. In a space-for-time analysis we utilized land cover data, forest inventory plots, and housing density data over time to examine differences in forest characteristics of the northern US across three WUI change classes: (a) forest that has been in WUI housing density levels since at least 1990 (old-WUI), (b) forest where development crossed the WUI housing density threshold after 1990 (new-WUI), and (c) forest with little to no housing development (non-WUI). Of the 184 million acres of forest in the study area, 34 million acres (19%) were in old-WUI, 12 million acres (7%) were new-WUI, and 136 million acres (74%) were non-WUI. In general, as areas transitioned from non-WUI to newer WUI to older more established WUI, the forest was associated with decreased spatial integrity, increased forest-developed edges, and lower proportions of forest in the surrounding landscape. Forest in the WUI had greater carbon storage, with greater aboveground biomass, relative stand density, and more live trees per hectare than non-WUI forest, suggesting greater capacity to sequester carbon compared to non-WUI forest. At the same time, WUI forest also had significantly reduced structural diversity compared to non-WUI forest, with fewer saplings, seedlings, and dead trees per hectare. Forest that more recently crossed the WUI housing density threshold appeared to be on a trajectory towards that of old-WUI forest. These differences in forest structure across the northern US suggest reduced capacity for forest regeneration in the WUI and the potential for changes in other ecological functions.

Richness–biomass relationships change with increasing acid rain intensity by shifting from positive to negative selection

The species interactions can be affected by environmental stress; however, how such change affects the plant species richness–biomass relationship is still unclear. Here, experimental plant communities with species richness levels of 1, 2, 4, and 8 were assembled and subjected to a simulated acid rain (SAR) intensity gradient (pH 7.0, 4.5 and 2.5). The species richness–biomass relationship was investigated and the absolute growth rate and survival rate were measured under each SAR intensity. With the increasing SAR intensity, the species richness–biomass relationships changed from positive to negative as a result of a shift in the biodiversity effects from positive to negative selection. Under a SAR intensity of pH 7.0, the absolute growth rate determined the biomass ratio of species in the mixtures. Mixtures that included Sedum lineare (with rapid growth) had a lower soil total nitrogen (TN), soil total phosphorus (TP), and greater aboveground biomass than mixtures that did not include the species, which led to a positive selection effect. Under a SAR intensity of pH 2.5, the survival rate determined the biomass ratio of species in the mixtures. Mixtures that included Sedum emarginatum and Phedimus spurius (with high survival rates) had less aboveground biomass than mixtures that did not include them, which led to a negative selection effect. Our results indicated that the mechanism by which a plant gains competitive superiority (i.e., a shift from rapid growth to a high survival rate) in response to environmental stress will affect the biodiversity effect. Considering future climate change scenarios, we suggest that changes in the competition mechanism should be integrated into future studies of the relationship between plant diversity and ecosystem functioning.

Insight into the regulatory networks underlying the high lipid perennial ryegrass growth under different irradiances.

Under favourable conditions, perennial ryegrass (Lolium perenne) engineered to accumulated high lipid (HL) carbon sink in their leaves was previously shown to also enhance photosynthesis and growth. The greater aboveground biomass was found to be diminished in a dense canopy compared to spaced pots. Besides, the underlying genetic regulatory network linking between leaf lipid sinks and these physiological changes remains unknown. In this study, we demonstrated that the growth advantage was not displayed in HL Lolium grown in spaced pots under low lights. Under standard lights, analysis of differentiating transcripts in HL Lolium reveals that the plants had elevated transcripts involved in lipid metabolism, light capturing, photosynthesis, and sugar signalling while reduced expression of genes participating in sugar biosynthesis and transportation. The plants also had altered several transcripts involved in mitochondrial oxidative respiration and redox potential. Many of the above upregulated or downregulated transcript levels were found to be complemented by growing the plants under low light. Overall, this study emphasizes the importance of carbon and energy homeostatic regulatory mechanisms to overall productivity of the HL Lolium through photosynthesis, most of which are significantly impacted by low irradiances.

Linkages between traits and decomposition of weed communities along a soil management and pedoclimate gradient in Mediterranean vineyards.

Decomposition is a major ecosystem process which improves soil quality. Despite that, only a few studies have analysed decomposition in an agricultural context, while most agrosystems (e.g. vineyards) are facing decreasing soil quality. The objective of this study is to understand the impacts of both pedoclimate and weed management on the mass loss of vineyard weed communities during the early stages of the decomposition process through their functional properties. In 16 Mediterranean vineyards representing both a pedoclimate and a soil management gradient, we measured the mass loss of green above-ground biomass of 50 weed communities during decomposition in standard conditions and key leaf traits of dominant species [e.g. leaf dry matter content (LDMC) and leaf lignin to nitrogen ratio (lignin:N)]. Both the mean [i.e. community-weighted mean (CWM)] and diversity (i.e. Rao index) were computed at the community level. Path analysis was used to quantify the effects of agro-environmental filters on the mass loss of weed communities through their functional properties. Tillage and mowing filtered more decomposable communities than chemical weeding (16 and 8 % of higher mass loss after 2 months of decomposition). Path analysis selected weed management practice type as the main factor determining mass loss through its effect on functional properties, while soil and climate had minor and no effects, respectively. Chemical weeding favoured communities with higher investment in resistant leaves (e.g. 38 % higher lignin:N, 22 % lower leaf nitrogen content) which resulted in lower mass loss compared with tilled and mowed communities. Mowing favoured communities with 47 % higher biomass and with 46 % higher nitrogen content. Weed management significantly influenced weed mass loss, while the pedoclimate had little effect. Our results suggest that mowing is a promising alternative to herbicide use, favouring higher biomass, nitrogen content and decomposability potential of weeds.

Mowing enhances the positive effects of nitrogen addition on ecosystem carbon fluxes and water use efficiency in a semi-arid meadow steppe

Grasslands are now facing a continuously increasing supply of nitrogen (N) fertilizers, resulting in alterations in ecosystem functioning, including changes in carbon (C) and water cycling. Mowing, one of the most widely used grassland management techniques, has been shown to mitigate the negative impacts of increased N availability on species richness. However, knowledge of how N addition and mowing, alone and/or in combination, affect ecosystem-level C fluxes and water use efficiency (WN) is still limited. We experimentally manipulated N fertilization (0 and 10 g N m−2 yr−1) and mowing (once per year at the end of the growing season) following a randomized block design in a meadow steppe characterized by salinization and alkalinization in northeastern China. We found that, compared to the control plots, N addition, mowing, and their interaction increased net ecosystem CO2 exchange by 65.1%, 14.7%, and 133%, and WN by 40.7%, 18.5%, and 96.1%, respectively. Nitrogen enrichment also decreased soil pH, which resulted in greater aboveground biomass (AGB). Moreover, N addition indirectly increased AGB by inducing changes in species richness. Our results indicate that mowing enhances the positive effects of N addition on ecosystem C fluxes and WN. Therefore, appropriate grassland management practices are essential to improve ecosystem C sequestration, WN, and mitigate future species diversity declines due to ecosystem eutrophication.

The ecosystem impacts of dominant species exclusion in a prairie restoration.

Dominant species often have disproportionately high abundance in restored communities compared to native remnants, which potentially could reduce the conservation value of restorations. Research is needed to determine how the abundance of dominant species in restoration plantings affects community assembly, species diversity, and ecosystem function. Most studies of dominant species in grasslands were modeled after experiments on keystone species, using the short-term experimental removal of dominants to test their functional role in ecosystems. However, the removal of established dominants constitutes a major disturbance that may influence the interpretation of their long-term functional impact. To address this, we experimentally assembled high-diversity tallgrass prairie communities that included or excluded the predicted dominant species (Andropogon gerardii and Sorghastrum nutans) from the seed mix at the time of planting, but without further manipulation of community composition. From 2013 to 2019, we measured several ecosystem functions and community dynamics in the presence or absence of dominants. Communities that included the dominant species had lower species richness, greater aboveground biomass, and reduced light availability at the soil surface. Dominant species presence also increased soil nutrient availability and rates of litter decomposition, although dominant grass litter decomposed more slowly than litter from other common species in both treatments. In the absence of the dominant grasses, communities were instead dominated by a common unplanted forb, Solidago altissima, and there was partial compensation in ecosystem functioning in these forb-dominated communities. The effects of dominant species exclusion may only be apparent in long-term studies of experimentally assembled communities that avoid the legacy effects associated with removal experiments. Furthermore, our results suggest that prairie restorations that limit or exclude the dominant grasses in seed mixes may achieve higher species diversity, increasing the conservation value of these systems.

A Microbial Mutualist Within Host Individuals Increases Parasite Transmission Between Host Individuals: Evidence From a Field Mesocosm Experiment.

The interactions among host-associated microbes and parasites can have clear consequences for disease susceptibility and progression within host individuals. Yet, empirical evidence for how these interactions impact parasite transmission between host individuals remains scarce. We address this scarcity by using a field mesocosm experiment to investigate the interaction between a systemic fungal endophyte, Epichloë coenophiala, and a fungal parasite, Rhizoctonia solani, in leaves of a grass host, tall fescue (Lolium arundinaceum). Specifically, we investigated how this interaction impacted transmission of the parasite under field conditions in replicated experimental host populations. Epichloë-inoculated populations tended to have greater disease prevalence over time, though this difference had weak statistical support. More clearly, Epichloë-inoculated populations experienced higher peak parasite prevalences than Epichloë-free populations. Epichloë conferred a benefit in growth; Epichloë-inoculated populations had greater aboveground biomass than Epichloë-free populations. Using biomass as a proxy, host density was correlated with peak parasite prevalence, but Epichloë still increased peak parasite prevalence after controlling for the effect of biomass. Together, these results suggest that within-host microbial interactions can impact disease at the population level. Further, while Epichloë is clearly a mutualist of tall fescue, it may not be a defensive mutualist in relation to Rhizoctonia solani.

Soil Organic Carbon Isotope Tracing in Sorghum under Ambient CO2 and Free-Air CO2 Enrichment (FACE)

As atmospheric carbon dioxide concentrations, [CO2Air], continue their uncontrolled rise, the capacity of soils to accumulate or retain carbon is uncertain. Free-air CO2 enrichment (FACE) experiments have been conducted to better understand the plant, soil and ecosystem response to elevated [CO2], frequently employing commercial CO2 that imparts a distinct isotopic signal to the system for tracing carbon. We conducted a FACE experiment in 1998 and 1999, whereby sorghum (C4 photosynthetic pathway) was grown in four replicates of four treatments using a split-strip plot design: (i) ambient CO2/ample water (365 μmol mol−1, “Control–Wet”), (ii) ambient CO2/water stress (“Control–Dry”), (iii) CO2-enriched (560 μmol mol−1, “FACE–Wet”), and (iv) CO2-enriched/water stressed (“FACE–Dry”). The stable-carbon isotope composition of the added CO2 (in FACE treatments) was close to that of free atmosphere background values, so the subsequent similar 13C-enriched carbon signal photosynthetically fixed by C4 sorghum plants could be used to trace the fate of carbon in both FACE and control treatments. Measurement of soil organic carbon content (SOC (%) = gC/gdry soil × 100%) and δ13C at three depths (0–15, 15–30, and 30–60 cm) were made on soils from the beginning and end of the two experimental growing seasons. A progressive ca. 0.5‰–1.0‰ δ13C increase in the upper soil SOC in all treatments over the course of the experiment indicated common entry of new sorghum carbon into the SOC pools. The 0–15 cm SOC in FACE treatments was 13C-enriched relative to the Control by ca. 1‰, and according to isotopic mass balance, the fraction of the new sorghum-derived SOC in the Control–Wet treatment at the end of the second season was 8.4%, 14.2% in FACE–Wet, 6.5% in Control–Dry, and 14.2% in FACE–Dry. The net SOC enhancement resulting from CO2 enrichment was therefore 5.8% (or 2.9% y−1 of experiment) under ample water and 7.7% (3.8% y−1 of experiment) under limited water, which matches the pattern of greater aboveground biomass increase with elevated [CO2Air] under the Dry treatment, but no parallel isotopic shifts were found in deeper soils. However, these increased fractions of new carbon in SOC at the end of the experiment do not necessarily mean an increase in total SOC content, because gravimetric measurements of SOC did not reveal a significant increase under elevated [CO2Air], at least within the limits of SOC-content error bars. Thus, new carbon gains might be offset by pre-experiment carbon losses. The results demonstrate successful isotopic tracing of carbon from plants to soils in this sorghum FACE experiment showing differences between FACE and Control treatments, which suggest more dynamic cycling of SOC under elevated [CO2Air] than in the Control treatment.

Genotype and Seasonal Variation Affect Yield and Oil Quality of Safflower (Carthamus tinctorius L.) under Mediterranean Conditions

The adoption of climate-resilient and resource-use efficient crop species and varieties is a key adaptation action for farmers in the face of climate change. Safflower, an emerging oilseed crop, has been recognized for its high oil quality and its favorable agronomic traits such as drought and cold tolerance, making it particularly suitable to Mediterranean conditions. A 2-year field study was carried out to evaluate the effects of the genotype and growing season on the crop phenology, seed and oil production, macronutrient accumulation and partitioning, and fatty acid composition of spring-sown safflower grown under rainfed conditions. The experiment was conducted during the 2012 and 2013 growing seasons on an alluvial deep loam soil (Typic Xerofluvent) at the Centre for Agri-environmental Research “E. Avanzi” of the University of Pisa (Pisa, Central Italy). Higher seed yield and yield components (plant density, plant height, branching, number of capitula per plant and seeds per capitulum) were found in almost all genotypes when the seeds were sown in mid-March 2012 compared to in late April 2013. More favorable conditions in 2012, i.e., early sowing date, higher precipitation, and quite mild temperatures, led to a better seed and oil yield and greater aboveground biomass and nitrogen uptake, with the highest amounts being removed by straw. Greater seed yield was found to be associated with a greater plant height and a higher number of capitula per plant. Oil content was negatively affected by the higher temperatures and the lower amounts of precipitation that occurred during the 2012 growing season. Seasonal variation in fatty acid composition depended on the genotype. Lower precipitation and higher temperatures during 2013 favored oleic acid content in high linoleic acid genotypes and linoleic acid in medium to high oleic acid genotypes. Among the genotypes, the linoleic-type Sabina and the oleic-type Montola 2000 performed the best in both seasons. The results, besides identifying promising safflower genotypes for spring sowing in the Mediterranean region and for future breeding programs, pointed out the importance of early sowing to contrast unfavorable environmental conditions during seed-filling, thus ensuring higher yields.

Effect of Nutrient Addition on the Productivity and Species Richness of Grassland Along With an Elevational Gradient in Tajikistan.

Grasslands provide key resource for the millions of people who are dependent on livestock in Tajikistan. Productivity and species richness (SR) are important characteristics of grassland ecosystems and are greatly affected by nutrient inputs. The effect that climate change might have on these characteristics remains unclear. Here, an in situ nitrogen (N) and phosphorus (P) fertilization experiment was conducted at four sites along with an elevational gradient (650, 1,100, 1,250, and 2,000 m) in western Tajikistan over 2 years (2018 and 2019) to examine the influences of nutrient availability and climate change on aboveground biomass (AGB) and SR; precipitation and temperature were also considered to analyze the responses. It demonstrated that enrichment with N, P, and their combinations significantly increased AGB along with an elevational gradient (p < 0.05). AGB increased as the concentrations of nutrients added increased. The maximum AGB, which was 2-fold higher compared with control, was observed when 90 kg N ha–1year–1 and 30 kg P ha–1year–1 were added. In addition, nitrogen addition alone stimulated greater AGB than P addition, although no significant difference was observed between these two treatments. Enrichment with N, P, and their combination had no significant effect on SR; however, SR significantly changed at different elevation. Elevation had direct effect on precipitation and temperature, which, in turn, resulted in variation in AGB and SR. Moreover, both nutrient and elevation had significant effect on AGB and SR, but there was no interaction effect of them. AGB and SR interacted with significant negative correlation. In the high-elevation area, plants grew better in the warmer year (2018); this indicates that grasslands in high mountain areas in Tajikistan might have higher productivity as the climate warms, which will positively affect the economic development of the country.

Could CO2-induced changes to C4 grass flammability aggravate savanna woody encroachment?

Fire plays an important role in maintaining the savanna tree-grass balance by limiting the recruitment of heat-sensitive tree seedlings. However, fire behaviour may change under increasing CO2 concentrations, due to altered flammability of the grassy layer. Here, we determined the effect of predicted future CO2 concentrations, and how it interacts with water-availability, on grass flammability and traits influential to flammability, and uncovered the physiological mechanisms underpinning these responses. Using the widespread C4 savanna grass, Themeda triandra, as a model, we found that improved water-use efficiency under elevated CO2 (800 ppm) resulted in a larger (greater aboveground biomass), but wetter (higher moisture content) grass fuel load, that cured at a slower rate under drought conditions. These changes were associated with increased time to ignition, reduced flaming times and reduced predicted rate of spread. We modelled the effect of altered grass flammability on fire behaviour at a national level (South Africa), finding large-scale reductions in fire spread under elevated CO2, mitigating the converse effects of predicted increases in aridity, and marginal increases in fireline intensity. CO2-induced reductions in fire frequency, spread or intensity could have serious implications for savanna vegetation dynamics, possibly exacerbating the woody encroachment already seen in these ecosystems across the world.