Changes In Biomass Research Articles

Systematic reduction in seed rain of large‐seeded and endozoochorous species in pastures compared to forests along a tropical elevational gradient

AbstractQuestionsHow do seed rain biomass and richness change from old‐growth tropical forests to pastures at different elevations? How do seed mass and seed dispersal mode change from forests to pastures across these elevations? What implications do these changes have for the recovery of deforested areas in tropical mountains?LocationOld‐growth montane forests and livestock pastures along an elevational gradient (1,000–3,000 m a.s.l.), located at Podocarpus National Park, San Francisco Reserve and surrounding agricultural lands, Andes of southern Ecuador.MethodsWe collected seed rain for a 3‐month period using 324 traps installed at eighteen 1‐ha plots across elevations. Half of the traps were installed in nine 1‐ha forest plots, and the other half in nine 1‐ha pasture plots. For each trap, we identified the seeds and measured seed rain biomass and richness. We also recorded seed traits and calculated community‐weighted means of seed mass and seed dispersal mode (proportion of endozoochory).ResultsForests received a higher seed rain biomass than pastures, but only at the lowest elevation. Seed rain richness did not differ between habitat types at all elevations. Community‐weighted means of seed mass and the proportion of endozoochorous species declined from forests to pastures, especially at the lower elevations.ConclusionsAlthough seed rain biomass and richness were overall similar between forests and pastures, large‐seeded and endozoochorous species were generally poorly represented in the seed rain of pastures compared with that of forests. These findings show that biomass and richness of seed rain may be insufficient to quantify the restoration potential of natural seed rain in deforested areas. Information on seed traits, such as seed mass and seed dispersal mode, is important to optimize restoration efforts towards the regeneration of diverse old‐growth forests along elevational gradients in tropical mountains.

Temporal Changes in Biochemical Responses to Salt Stress in Three Salicornia Species.

Halophytes adapt to salinity using different biochemical response mechanisms. Temporal measurements of biochemical parameters over a period of exposure to salinity may clarify the patterns and kinetics of stress responses in halophytes. This study aimed to evaluate short-term temporal changes in shoot biomass and several biochemical variables, including the contents of photosynthetic pigments, ions (Na+, K+, Ca2+, and Mg2+), osmolytes (proline and glycine betaine), oxidative stress markers (H2O2 and malondialdehyde), and antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) activities of three halophytic Salicornia species (S. persica, S. europaea, and S. bigelovii) in response to non-saline, moderate (300 mM NaCl), and high (500 mM NaCl) salinity treatments at three sampling times. Salicornia plants showed maximum shoot biomass under moderate salinity conditions. The results indicated that high Na+ accumulation in the shoots, coupled with the relative retention of K+ and Ca2+ under salt stress conditions, contributed significantly to ionic and osmotic balance and salinity tolerance in the tested Salicornia species. Glycine betaine accumulation, both constitutive and salt-induced, also seems to play a crucial role in osmotic adjustment in Salicornia plants subjected to salinity treatments. Salicornia species possess an efficient antioxidant enzyme system that largely relies on the ascorbate peroxidase and peroxidase activities to partly counteract salt-induced oxidative stress. The results also revealed that S. persica exhibited higher salinity tolerance than S. europaea and S. bigelovii, as shown by better plant growth under moderate and high salinity. This higher tolerance was associated with higher peroxidase activities and increased glycine betaine and proline accumulation in S. persica. Taking all the data together, this study allowed the identification of the biochemical mechanisms contributing significantly to salinity tolerance of Salicornia through the maintenance of ion and osmotic homeostasis and protection against oxidative stress.

Impact of changes in root biomass on the occurrence of internal browning in radish root

The purpose of this study was to investigate the effects of root biomass during the later stage of growth on fatty acid composition and lipid peroxidation, and to clarify the physiological mechanisms by which these differences affect internal browning (IB) development in radish roots. Therefore, we controlled the enlargement of roots by changing the thinning period and generated plots composed of roots with different biomass in the latter half of growth. The earlier the radish seedlings were thinned, the more vigorous the root growth from an earlier stage was achieved. Earlier thinning caused IB from the early stage of root maturation, and IB severity progressed with subsequent age progression; however, IB damage did not occur when root size during the later growth stage was kept small by later thinning. Higher levels of hydrogen peroxide, peroxidase activity, NADPH-dependent reactive oxygen species (ROS) burst-related genes, and carbonyl compounds were detected in earlier-thinned large-sized roots compared to later-thinned small-sized ones. Compared with the latter small-sized roots, the former large-sized roots had a lower ratio of linoleic acid (18:2) and a higher ratio of α-linolenic acid (α-18:3). Furthermore, in earlier-thinned large-sized roots, higher levels of phospholipase- and/or lipoxygenase-related genes were detected compared to later-thinned small-sized ones. These facts suggest the possibility that root biomass in the later stage of growth affects the desaturation of membrane fatty acids, ROS concentration, and activity of fatty acid degrading enzymes, and controls the occurrence of IB injury through membrane oxidative degradation.

Estimating fish production in wetlands

Fish production integrates changes in biomass from growth, reproduction, and mortality, and is a useful indicator for fisheries management. However, calculation of fish production has been limited by the intensive requirements for data on abundance, biomass, age structure, and vital rates, and so it is uncommon to find estimates of fish production for wetlands. We developed an approach to directly estimate production that is suitable for data-limited systems: a continuous time model of production describing individual growth over short time intervals with continuous time models of abundance and biomass over longer timescales. We applied this model for 18 Great Lakes coastal wetlands (GLCWs) on Lake Ontario, including Big Island Wetland (BIW). In BIW, most species were dominated in abundance and biomass by younger cohorts and, as a result, these young, fast-growing individuals contributed disproportionately to fish production. In total, BIW produced 336.1 kg·ha·year of fish and the other 17 neighbouring ranged between 447.7 and 1119.9 kg·ha·year. These are some of the first estimates of fish production for GLCWs, highlighting their value for managing Great Lakes fisheries.

The Arctic Plant Aboveground Biomass Synthesis Dataset

Plant biomass is a fundamental ecosystem attribute that is sensitive to rapid climatic changes occurring in the Arctic. Nevertheless, measuring plant biomass in the Arctic is logistically challenging and resource intensive. Lack of accessible field data hinders efforts to understand the amount, composition, distribution, and changes in plant biomass in these northern ecosystems. Here, we present The Arctic plant aboveground biomass synthesis dataset, which includes field measurements of lichen, bryophyte, herb, shrub, and/or tree aboveground biomass (g m−2) on 2,327 sample plots from 636 field sites in seven countries. We created the synthesis dataset by assembling and harmonizing 32 individual datasets. Aboveground biomass was primarily quantified by harvesting sample plots during mid- to late-summer, though tree and often tall shrub biomass were quantified using surveys and allometric models. Each biomass measurement is associated with metadata including sample date, location, method, data source, and other information. This unique dataset can be leveraged to monitor, map, and model plant biomass across the rapidly warming Arctic.

The below-ground biomass contributes more to wetland soil carbon pools than the above-ground biomass—a survey based on global wetlands

Abstract The biomass of wetland plants is highly responsive to environmental factors and plays a crucial role in the dynamics of the soil organic carbon (SOC) pool. In this study, we collected and analyzed global data on wetland plant biomass from 1980 to 2021. By examining 1134 observations from 182 published papers on wetland ecosystems, we created a comprehensive database of wetland plant above-ground biomass (AGB) and below-ground biomass (BGB). Using this database, we analyzed the biomass characteristics of different climate zones, wetland types and plant species globally. Based on this, we analyzed the differences between the biomass of different plant species and the linkage between AGB and BGB and organic carbon. Our study has revealed that wetland plant AGB is greater in equatorial regions but BGB is highest in polar areas, and lowest in arid and equatorial zones. For plant species, the BGB of the Poales is higher than the AGB but Caryophyllales, Cyperales and Lamiales have higher AGB. Moreover, our findings indicate that BGB plays a more significant role in contributing to the organic carbon pool compared to AGB. Notably, when BGB is less than 1 t C ha−1, even slight changes in biomass can have a significant impact on the organic carbon pool. And we observed that the SOC increases by 5.7 t C ha−1 when the BGB content is low, indicating that the SOC is more sensitive to changes in biomass under such circumstances. Our study provides a basis for the global response of AGB and BGB of wetland plants to organic carbon.

Water quality in a shallow eutrophic lake is unaffected by extensive thinning of planktivorous and benthivorous fish species

Ambitious to fulfill the European Water Framework Directive obligations, the European governments support projects to rehabilitate lakes with poor water quality. However, most lake restorations having relied on biomanipulation by fish thinning have failed to improve or even maintain water quality. Previous attempts removed all target fish species simultaneously, thus making it impossible to assess the specific impact of each feeding group on water chemistry. Lake Bromme was selected for extensive, time-selective fish biomanipulation to improve water clarity and promote submerged macrophytes and piscivorous fish stocks over a three-year monitoring period. Thinning of adult benthivorous bream (Abramis brama) and tench (Tinca tinca) was conducted throughout year one while thinning in years two and three targeted planktivorous roach (Rutilus rutilus), juvenile bream, and small perch (Perca fluviatilis). Yearly fish surveys assessed changes in fish population structure and biomass. Water quality parameters were monitored continually, and the cover of submerged macrophytes was surveyed annually via sonar. We found no improvement in water clarity or reductions of nutrients, organic particles, chlorophyll concentrations, or watercolor, despite a 6-fold thinning of total estimated fish biomass, from 112 to 19 kg ha−1. Over the period, the macrophyte cover increased from 0.8 to 13.5 %, but no recruitment of large piscivorous fish (perch and pike (Esox lucius) > 10 cm) was detected. We found higher correlations of particle concentration and water clarity to water temperature than to wind speed, which indicates sediment particle resuspension by the remaining fish community (mostly carp Cyprinus carpio) that forage on benthos in shallow lakes. Further system-ecological research in Lake Bromme should evaluate whether thinning the stock of carp and increasing plant cover may improve water quality and test which optical properties sustain high water turbidity and prevent shallow, eutrophic lakes like Lake Bromme from responding to intense fish thinning.

Effects of the Replacement of Chemical Fertilizers with Organic Fertilizers in Different Proportions on Microbial Biomass and Enzyme Activities of Soil Aggregates in Gravel-Mulched Field

Gravel-mulched fields are a unique form of drought-resistant agriculture in the northwest region of China. In recent years, continuous cropping obstacles caused by the perennial cultivation of a single crop have seriously constrained the sustainable development of sand fields. This study aimed to explore the distribution patterns of different particle sizes of aggregates (>2, 1–2, 0.25–1, and <0.25 mm) and the relationships between their microbial biomass and enzyme activities under different organic fertilization and to explore the effective measures for improving soil fertility in a gravel-mulched field with an 8-year positioning test. The results indicate that the mass percentage of soil aggregates of ≥1 mm and their mean weight diameter (MWD), microbial biomass (carbon and nitrogen, bacteria, fungi, actinomycetes, and total phospholipid fatty acids), and their related enzyme activities (leucine aminopeptidase, LAP; N-acetyl-β-d-glucosidase, NAG; β-glucosidase, BG; and polyphenol oxidase, PPO) in aggregates of different particle sizes increased with the increase in the proportion of organic fertilizers replacing the N fertilizer. Among them, the organic fertilizer replacing more than 50% of chemical nitrogen fertilizers exerted the most significant effect. With the decrease in agglomerate particle size, the contents of microbial carbon and nitrogen showed a decreasing trend, whereas LAP, NAG, and BG activities followed an increasing trend, and the change in microbial biomass was not obvious. The correlation analysis showed highly significant positive correlations between the MWD of soil aggregates, microbial biomass, and the activities of LAP, NAG, BG, and PPO. Therefore, the replacement of more than 50% of chemical fertilizer with organic fertilizer was observed to be conducive to promoting the formation of large aggregates in sandy soils and increasing the microbial biomass and enzyme activities in different sizes of aggregates.

Spatiotemporal variability and drivers of modeled primary production rates in the Northern Humboldt Current System

A coupled physical-biogeochemical model was employed to explore the spatiotemporal dynamics of primary production (PP) rates within the Northern Humboldt Current System (NHCS). The coastal zone spanning 250 km from the shore, from 3°to 18°S, stands out as a highly productive upwelling region, exhibiting an average surface PP value of 2.5 mol C m−3 yr−1. Correspondingly, the average vertically integrated PP within the euphotic layer amounts to 13 mol C m−2 yr−1. In this context, summer emerges as the peak of productivity, yielding 18 mol C m−2 yr−1, while winter signifies the period of least productivity, with 9 mol C m−2 yr−1. Our study revealed that surface PP variability is primarily driven by changes in surface chlorophyll and phytoplanktonic biomass (mainly diatoms), followed by changes in photosynthetically active radiation (PAR) levels. During summertime, these three drivers contribute to substantial positive anomalies in surface PP. However, the reduction in nutrient availability resulting from weakened upwelling-favorable winds has a slight negative impact on surface PP rates. Yet, this decline is offset by a positive thermal effect during the warmer season. In contrast, during the winter season, a significant decrease in surface chlorophyll concentrations due to a vertical redistribution into a deeper mixed layer significantly diminishes surface PP. Furthermore, the reduction in both PAR levels and biomass concentrations has a comparable effect, further contributing to the decrease in surface PP rates during wintertime. At a depth of 20 m, changes in PP are primarily driven by variations between the opposing influences of PAR and chlorophyll concentrations. While PAR adheres to the seasonal cycle of warming and cooling throughout the year, chlorophyll-driven anomalies exhibit an inverse pattern to those at the surface, influenced by the vertical dilution effect within the mixed layer. Overall, this study provides valuable insights into the complex interplay of drivers that govern PP dynamics across various depths within one of the world’s most productive marine regions.

Different responses of lipids and lignin phenols to nitrogen addition in meadow grassland soil

PurposeNitrogen (N) enrichment can affect the composition and stability of soil organic carbon (SOC) pools by altering vegetation and soil properties. However, the response of plant-derived carbon components in soil to different N addition levels is unclear. We investigated the changes and potential driving processes of plant-derived carbon components (especially lignins and lipids) in meadow grassland soils under long-term N addition in eastern Inner Mongolia, China.Materials and methodsBiomarker technology was utilised to analyse changes in plant-derived carbon components (C>20 free lipids, bound lipids, and lignin phenols) in soil under different N addition levels, including changes in soil chemical properties, enzyme activity, plant biomass, and diversity under N addition, as well as the specific pathways involved.Results and discussionWe found that high levels of N addition significantly reduced the concentration of soil lignin phenols whereas increased the accumulation of lipids (free and bound lipids). Compared with changes in plant biomass and diversity, soil chemical properties and enzyme activity play a more significant role in regulating the accumulation and degradation of plant-derived carbon. Structural equation modelling (SEM) showed that decreases in lignin phenol concentration were related to specific biochemical decomposition processes (increased polyphenol oxidase activity and decreased C/N). The increase in lipids associated with the protective effects of minerals mediated by pH.ConclusionsIn general, plant-derived carbon components showed inconsistent responses to N addition, lignin phenol concentration decreased and lipid concentration increased, which was mainly related to the change of soil biochemical properties. Plant-derived carbon components only showed significant changes under high N addition levels. Furthermore, our research indicates that SOC sequestration and functioning are highly dependent on soil biochemical properties, which weakens the influence of changes in plant carbon input on soil carbon storage.

Effects of grazing and climate change on aboveground standing biomass and sheep live weight changes in the desert steppe in Inner Mongolia, China

CONTEXTThe Stipa breviflora desert steppe ecosystem is fragile and sensitive to climate change and grazing disturbance. Previous studies have reported the effects of climate change and grazing on aboveground standing biomass of the plant community and sheep live weight, however, the interaction between climate change and grazing remains unclear. Process models have become ideal tools for the evaluation of the effects of grazing management practices under climate change. OBJECTIVEWe used the Soil-Plant-Atmosphere Continuum System (SPACSYS) model to investigate aboveground standing biomass and the live weight of sheep in the desert steppe of Inner Mongolia under future climate change scenarios and different grazing management. The results will be used to inform adaptive management strategies. METHODSThe grazing experiment consisted of four treatments: no grazing (0 sheep ha−1 half year−1), light stocking rate (0.91 sheep ha−1 half year−1), moderate stocking rate (1.82 sheep ha−1 half year−1), and high stocking rate (2.71 sheep ha−1 half year−1). We used observed data on soil temperature, soil volumetric water content, changes to sheep live weight, and aboveground standing biomass of plant community to provide parameterization and validation for the SPACSYS model. We then predicted aboveground standing biomass of the plant community and sheep live weight changes for different grazing management under three representative concentration pathways (RCP) scenarios (RCP 2.6, RCP 4.5, and RCP 8.5) from 2021 to 2100. RESULTS AND CONCLUSIONSModerate and high stocking rates decreased aboveground standing biomass and sheep live weight changes more than the light stocking rate. A light stocking rate can maintain higher aboveground standing biomass and sheep live weight as well as meet production requirements. Therefore, a light stocking rate is a potentially effective management approach to improve food production security and combat global climate change in the desert steppe. SIGNIFICANCEThe model can inform management strategies for grazing in the desert steppe under climate change, supporting efforts to maintain the stability of the steppe ecosystem and increase economic benefits, while also providing a theoretical basis for adaptive management in the desert steppe.

Long‐term organic management: Mitigating land use intensity drawbacks and enhancing soil microbial redundancy

AbstractBackgroundSoils under organic farming systems exhibit better quality and higher biological activity than conventional systems. Manure addition, especially coupled with reduced or no tillage, significantly enhances microbial biomass and activity by improving soil physical properties and providing carbon (C) and nitrogen (N) sources. While several studies have examined the effects of transitioning from conventional to organic farming on soil chemistry and biochemistry, limited research has explored the influence of land use variations on soil fertility within long‐term organic farming systems.AimsTherefore, the aim of this study was to assess how three different land uses—pasture, vegetable crops, and orchard—affected soil fertility under a long‐term organic farming system.MethodsSoil samples were collected from the 0 to 15 cm layer of plots used for pasture, vegetable crops and orchard, being the latter cover cropped with legumes, and analyzed to determine chemical and biochemical soil parameters.ResultsContrary to expectations, high land use intensity (vegetable crops and orchard soils) resulted in increased soil organic C and total N, compared to low intensity (pasture). Such an increase was ascribed to farmyard manure addition that counteracted the negative impact of tillage. Consequently, microbial biomass C and activity also increased. The greatest availability of organic substrates favored bacteria, particularly gram‐positive strains, shaping the microbial community. However, despite changes of microbial biomass and of the main microbial groups, microbial activity was only slightly affected, suggesting high functional redundancy of microorganisms in long‐term organic farming soil.ConclusionsResults suggested that if land use intensification provides for organic supply, its negative impact on soil fertility may be mitigated.

Polarimetric Measures in Biomass Change Prediction Using ALOS-2 PALSAR-2 Data

The use of multiple synthetic aperture radar polarizations can improve biomass estimations compared to using a single polarization. In this study, we compared predictions of aboveground biomass change from ALOS-2 PALSAR-2 backscatter using linear regression based on (1) the cross-polarization channels, (2) the co- and cross-polarizations from fully polarimetric SAR, (3) Freeman–Durden polarimetric decomposition, and (4) the polarimetric radar vegetation index (RVI). Additionally, the impact of forest structure on the sensitivity of the polarimetric backscatter to AGB and AGB change was assessed. The biomass consisted of mainly coniferous trees at the hemi-boreal test site Remningstorp, located in southern Sweden. We found some improvements in the predictions when quad-polarized data (RMSE = 79.4 tons/ha) were used instead of solely cross-polarized data (RMSE = 84.9 tons/ha). However, when using Freeman–Durden decomposition, the prediction accuracy improved further (RMSE = 69.7 tons/ha), and the highest accuracy was obtained with the radar vegetation index (RMSE = 50.4 tons/ha). The corresponding R2 values ranged from 0.45 to 0.82. The bias was less than 1 t/ha for all models. An analysis of forest variables showed that the sensitivity to AGB was reduced for high values of basal-area-weighted mean height, basal area, and stem density when predicting absolute AGB, but the best change prediction model was sensitive to changes larger than the apparent saturation point for AGB state estimates. We conclude that by using fully polarimetric SAR images, forest biomass changes can be estimated more accurately compared to using single- or dual-polarization images. The results were improved the most (in terms of RMSE and R2) by using the Freeman–Durden decomposition model or the RVI, which captured especially the large changes better.

Study on the future development prospects of biomass energy in towns, townships, and subdistricts under multi-scenarios —A case study of Harbin City

Biomass energy is the most likely new energy source to replace fossil fuels. This study presents a prediction method for biomass energy supply-demand and changes in supply-demand patterns that connects the past and future. In the study, carbon peaking and carbon neutrality are taken as the time base. The FLUS model is used to simulate future land allocation in four basic scenarios: natural development scenario, agricultural development scenario, low-carbon development scenario and industrial development scenario; and townships, towns, and subdistricts are taken as the basic statistical unit. Based on this, we have examined the suitability of future development of biomass energy in rural and urban areas in each scenario, as well as its contribution to the future energy system transformation that substitutes for fossil energy. This method has been applied to the case study of townships, towns, and subdistricts in Harbin City in China. The study results show that: The degrees to which biomass energy potential can substitute for fossil energy in the four scenarios in 2030 reach 4.21%, 5.62%, 5.47%, and 3.82%, respectively. Under agricultural development scenario, the supply-demand balance areas account for 48.94%, meaning this scenario has the largest potential for energy development and transition; low-carbon development scenario sees the highest degree of spatial supply-demand match, and thus enjoys the most advantages in energy transportation. The degrees to which biomass energy potential can substitute for fossil energy under the four scenarios in 2060 reach 2.01%, 6.96%, 5.35%, and 1.26% respectively. Agricultural development scenario still has the largest development potential, with the proportion of supply-demand balance areas jumping to 50.46%; Finally, low supply-high demand mismatch clusters are mainly concentrated in the main urban area and the central areas of townships, towns, and subdistricts. The high supply-low demand mismatch clusters are mainly distributed in the northeast. Under low-carbon development scenario, the low supply-high demand mismatch ratio has been reduced to 0.92%, the lowest supply-demand mismatch among all scenarios. Therefore, low-carbon development scenario enjoys the most spatial match advantages. This study will serve as an assessment method to advance the spatial development of biomass, and provide a geospatial basis for optimizing the layout of future energy development. Compared with previous studies, it has more spatial attributes, better reflects the complexity of biomass energy changes and is more connected with the measurement results and future policy making. In future research, we will combine multiple types of clean energy into the comparison and combined use to form a more comprehensive and specific research framework for new energy conversion. Longer-term macro-planning will go beyond the application boundaries of this research.

Lithological features of Lake Bannoe sediments (Southern Urals) as an indicator of environmental and climate changes in the Holocene

Research subject. Bottom sediments of Lake Bannoe (Southern Urals). Aim. Identification of lithologic features of Lake Bannoe sediments, which could reflect sedimentation conditions in the Holocene. Materials and methods. The detailed complex analysis included radiocarbon dating, grain-size analysis, X-ray diffraction analysis, electron microscopy, X-ray fluorescence and isotope analysis, coercive spectrometry and pollen analysis. Results. Radiocarbon dating showed that sedimentation in Lake Bannoe began no later than ~13 thousand years ago. Combination of data from various laboratory studies unraveled four lithological zones and the corresponding stages in the sedimentation history. The grain size, allothigenic particles, carbonate minerals, organic matter and isotopic composition of carbon and oxygen are the most informative indicators. Grain size variations and the ratio between allothigenic and carbonate components reflect changes in the Lake’s depth and clastic material supply, which, in turn, is associated with humidity. Organic matter parameters (TOC, δ13Corg, C/N ratio) can be considered as indicators of climate-sensitive changes in bioproductivity of the sedimentation basin. They also reflect the ratio of exogenous and endogenous organic matter in the sedimentary environment. The isotopic composition of carbon and oxygen (δ13Ccarb, δ18Ocarb) in sedimentary carbonates is an informative indicator of lithological zones and climatic events of the Holocene due to its sensitivity to changes in biomass, temperature fluctuations, and fresh water inflow. The paramagnetic component k_para was used as an indicator of the allothigenic material input into the lake basin for the first time in this region. Conclusions. The granulometric, mineral, and chemical composition, as well as the magnetic properties of Lake Bannoe sediments reflect the history of Lake sedimentation in the Southern Urals, which agrees mainly with the climate stages of the Holocene.

Contrasting depth‐related fine root plastic responses to soil warming in a subtropical Chinese fir plantation

Abstract Warming‐induced soil drought, especially in topsoil, may enlarge the spatial mismatch between nutrients and water along the soil profile, which impedes the uptake of not only water but also nutrients by trees. Therefore, coordinating the acquisition of soil water and nutrients along the soil profile is an important strategy for trees to cope with global warming. This study examined soil depth‐related changes in nutrient concentrations, biomass and morphology of fine roots in a Chinese fir plantation after 3 years of large‐scale manipulative soil warming. Soil warming (ambient +4°C) increased fine root nitrogen (N) concentrations but decreased fine root phosphorus (P) concentrations across soil depths. Warming did not affect total fine root biomass and its vertical distribution. At the 0–10 cm depth, warming increased specific root length (SRL), specific root area (SRA), fine root diameter (RD) and root length density (RLD) but reduced root tissue density (RTD). In the 40–60 cm layer, warming reduced RD, SRL and RLD while increasing RTD mainly for roots of the 1–2 mm diameter class. Synthesis. We concluded that roots of Chinese fir plantations could adapt to warming‐induced moderate water stress through contrasting depth‐related root morphological adjustments, probably to optimize the acquisition of both soil water and nutrients. The results of this study are crucial for understanding the adaptation strategies of subtropical forests under future climate conditions.

A general, resource‐based explanation for density dependence in populations of large herbivores

AbstractThe discipline of ecology seeks to understand how ecosystems, communities, and populations are regulated. A ubiquitous mechanism of population regulation of consumers is that capturing energy and nutrients in sufficient quantities for survival and reproduction becomes more difficult as population density increases. Extensive evidence has revealed that populations of large herbivores are often regulated by density dependence, defined as the reduction in the per‐capita population growth rate that occurs as populations grow large. Diminished body mass of individuals has been repeatedly observed in high‐density populations, implicating compromised nutrition as the primary cause of density dependence. However, there is no general explanation for why these nutritional deficiencies occur. Recent work demonstrated that reduced food intake rates resulting from the functional response of herbivores to depleted plant biomass does not provide a sensible explanation for density dependence because rates of food intake of herbivores are often insensitive to changes in plant biomass. A new model of feedbacks from plant biomass to herbivores shows how reduced nutrition of herbivores can result from increased dilution of nutrients in the plant tissue they consume as populations grow, even when their rate of consumption of plants remains constant. The model contains parameters that can be scaled to body mass, allowing unusually general predictions. The model shows that convex, concave, and linear relationships between the per‐capita growth rate and population density can arise from the effects of depletion of plant biomass by herbivore foraging. The model is the first to explicitly include spatial variance in the nutritional quality of plants as a general driver of herbivore population dynamics. I show how regulation of herbivore abundance by plant nutrients can occur, even when a large fraction of the consumable plant biomass remains uneaten, providing a simple, mechanistic explanation for bottom‐up control of population dynamics of primary consumers in a “green world.”

Microbial nutrient limitation along a 2-million-year dune chronosequence

Long-term ecosystem development is characterized by a switch from nitrogen (N) to phosphorus (P) limitation of plant communities as soils age, which leads to changes in plant biomass, diversity, and foliar nutrient concentrations. Similar effects occur belowground, although the extent to which nutrient availability is the primary driver of long-term changes in soil microbial communities remains uncertain. To investigate this, we assessed proxies for soil microbial nutrient limitation along the Jurien Bay dune chronosequence in Western Australia, where a long-term decline in P availability is reflected in strong variation in plant and microbial community composition over 2 million years of soil development. We quantified carbon (C), N, and P in the soil microbial biomass, assayed soil enzymes involved in the acquisition of those nutrients from soil organic matter, and used microbial stoichiometric ratios and vector analysis of enzyme activities to assess whether long-term changes in soil nutrient availability are reflected in nutrient demand by soil microbes. Concentrations of microbial nutrients peaked in Holocene soils (1–6.5 ky), although differences in microbial P were not significant. There were no significant differences in microbial nutrient ratios (C:N, C:P, and N:P) along the chronosequence. Acid phosphatase activity increased continually throughout the chronosequence, while the activities of leucine aminopeptidase and β-glucosidase were greatest in Holocene soils and declined with increasing soil age. Corresponding vector lengths indicated greater investment in C-degrading enzymes in Holocene soils (≤6.5 ky), while vector angles indicated greater investment in the acquisition of P compared with N in Pleistocene soils (≥120 ky). Overall, these findings show that changes in nutrient availability during long-term pedogenesis at Jurien Bay are reflected in microbial investment in nutrient acquisition, but that the soil microbial biomass exhibits a remarkable degree of homeostasis despite major shifts in nutrient availability and community composition over 2 million years of ecosystem development.

Chondrichthyes in the north-western Ionian Sea (central Mediterranean): Species diversity, abundance and spatio-temporal changes

This study provides an updated list of fish in the Class Chondrichthyes sampled during all research projects conducted in the north-western Ionian Sea from 1985 to 2020. A total of 36 Chondrichthyes species belonging to 8 orders and 19 families were detected, most of them distributed over a wide depth range, between shelf and slope. For species assessed by the International Union for Conservation of Nature (IUCN), 8 species are listed as Critically Endangered, 3 as Endangered, 6 Vulnerable and 5 as Near Threatened species. The distribution of cartilaginous fish was examined exploring the historical series of MEDITS data (1995–2020. Changes in the species diversity and in their abundance with time and space were detected and some environmental and anthropogenic drivers that could have caused these changes were analysed. An increase in the presence, number of species and biomass of Chondrichthyes was detected from 1995 to 2020. The GAM analyses seem to indicate that the observed increase in species number and biomass is due to the decrease in fishing capacity and increase in salinity and temperature on the bottom. Furthermore, for the most abundant species, Galeus melastomus, an increase of biomass, size and a deeper distribution over the last 26 years were detected. Significant changes in biomass were also observed for other abundant species in the study area (Scyliorhinus canicula and Raja miraletus). The increase in biomass over time, different from several Mediterranean observations, is discussed in relation to the presence of refuge areas in the north-western Ionian Sea.

A positive feedback to climate change: The effect of temperature on the respiration of key wood-decomposing fungi does not decline with time.

Heterotrophic soil microorganisms are responsible for ~50% of the carbon dioxide released by respiration from the terrestrial biosphere each year. The respiratory response of soil microbial communities to warming, and the control mechanisms, remains uncertain, yet is critical to understanding the future land carbon (C)-climate feedback. Individuals of nine species of fungi decomposing wood were exposed to 90 days of cooling to evaluate the medium-term effect of temperature on respiration. Overall, the effect of temperature on respiration increased in the medium term, with no evidence of compensation. However, the increasing effect of temperature on respiration was lost after correcting for changes in biomass. These results indicate that C loss through respiration of wood-decomposing fungi will increase beyond the direct effects of temperature on respiration, potentially promoting greater C losses from terrestrial ecosystems and a positive feedback to climate change.