Root Respiration Research Articles

Thinning-induced decrease in fine root biomass, but not other fine root traits in global forests

In forest ecosystems, changes in the expression of tree absorptive root traits following management interventions are expected to influence post-thinning forest structure and function. Fine root traits are expected to be especially responsive to forest thinning—one of the most common forest management interventions and the focus of our research here—influencing tree-level responses to environmental change, and thereby contributing to post-thinning stand-level dynamics and ecosystem processes. However, there remains limited understanding surrounding whether or not forest thinning influences the expression of root morphological, chemical, and physiological traits associated with belowground resource acquisition. We conducted a global meta-analysis to evaluate the response of 13 fine root traits to forest thinning. Our study included analysis of 769 paired observations of root traits values pre- and post-thinning, derived from 89 peer-reviewed publications. Our meta-analysis found that forest thinning leads to a decrease in fine root biomass by 11.7% on average, while other root traits including fine root length, root C and N concentrations, root lifespan, and root respiration rates, are largely unresponsive to thinning treatments. Thinning tended to reduce fine root biomass at early stand recovery stages, with increases in fine root biomass being detected at later seral stages, especially in heavy thinning experiments. The effect of thinning on fine root biomass was most pronounced in deeper soil horizons. The influence of thinning on fine root trait expression was not affected by ecosystem or stand type, with the exception of biomass which decreased in temperate and coniferous forests. Our results demonstrate variations of fine root traits to forest management, as well as the importance of stand recovery time and thinning intensity in regulating fine root trait expression in retention trees. These patterns may have strong implications for governing soil carbon stocks in managed forests associated with decreased root inputs into deeper soils. Overall, our findings can enhance our comprehension of how forest management affects fine root trait expression, and relationship between managed forests and belowground ecosystem structure and function.

Response of Root Respiration to Warming and Nitrogen Addition Depends on Tree Species.

Roots contribute a large fraction of CO2 efflux from soils, yet the extent to which global change factors affect root-derived fluxes is poorly understood. We investigated how red maple (Acer rubrum) and red oak (Quercus rubra) root biomass and respiration respond to long-term (15 years) soil warming, nitrogen addition, or their combination in a temperate forest. We found that ecosystem root respiration was decreased by 40% under both single-factor treatments (nitrogen addition or warming) but not under their combination (heated × nitrogen). This response was driven by the reduction of mass-specific root respiration under warming and a reduction in maple root biomass in both single-factor treatments. Mass-specific root respiration rates for both species acclimated to soil warming, resulting in a 43% reduction, but were not affected by N addition or the combined heated × N treatment.Notably, the addition of nitrogen to warmed soils alleviated thermal acclimation and returned mass-specific respiration rates to control levels. Oak roots contributed disproportionately to ecosystem root respiration despite the decrease in respiration rates as their biomass was maintained or enhanced under warming and nitrogen addition. In contrast, maple root respiration rates were consistently higher than oak, and this difference became critical in the heated × nitrogen treatment, where maple root biomass increased, contributing significantly more CO2 relative to single-factor treatments. Our findings highlight the importance of accounting for the root component of respiration when assessing soil carbon loss in response to global change and demonstrate that combining warming and N addition produces effects that cannot be predicted by studying these factors in isolation.

Cercospora leaf spot impacts on postharvest disease and respiration of affected sugarbeet roots.

In Michigan, sugarbeets (Beta vulgaris) are stored for up to 200 days post-harvest, during which sugar loss may occur due to energy use from respiration and factors like rot. Cercospora leaf spot (CLS) has been considered a potential predisposing factor for increased storage rot. To investigate these impacts, field and postharvest studies evaluated storage rot symptom development in sugarbeets with designated 'high' or 'low' in-season CLS severity. Root slices of sugarbeets from each CLS level were inoculated with Fusarium graminearum, Botrytis cinerea, or Penicillium vulpinum and symptoms assessed after seven days. Across three CLS-susceptible commercial varieties, there were no significant differences between storage rot susceptibility to any of the tested pathogens in hand-harvested sugarbeets, regardless of CLS level, at any storage timepoint in 2020 or 2021 (P > 0.05). In studies using CLS-susceptible and -resistant germplasm and varieties, CLS effects were inconsistent and only significant in one parameter at two of six storage timepoints across years (P < 0.05). Across storage pathogens, prior CLS level also did not impact root respiration or the change in respiration rate from initial to final storage timepoint in either 2021 or 2023 (P > 0.05). Of note, B. cinerea caused more severe symptoms than other pathogens in these studies (P < 0.05). Finally, varietal responses differed significantly to storage pathogens (P < 0.05) and may be of interest to future cultivar development efforts. This research increases our understanding of factors contributing to potential storage losses, which will improve yield and profit for sugar growers.

Greenhouse gas emissions in response to tillage, nitrogen fertilization, and manure application in the tropics

Cultivation of maize (Zea mays L.) can emit significant greenhouse gases (GHGs) due to root respiration, soil organic matter decomposition, and fertilizer losses in a tropical environment. Our objective was to examine the effect of tillage (conventional tillage [CT], minimum tillage [MT], and no-tillage [NT]), N fertilization rate (0, 90, and 120 kg N ha−1), and manure application rate (0, 5, and 10 Mg ha−1) on CO2, N2O, and CH4 emissions under maize in two growing seasons (July-October 2018 and May-August 2019) in southwest Nigeria. We measured CO2, N2O, and CH4 fluxes using the static chamber method and soil temperature and water content weekly, global warming potential (GWP), maize yield, and greenhouse gas intensity (GHGI). The CO2 and N2O fluxes peaked immediately following planting, fertilization, and intense precipitation, with most fluxes concentrated at 2–6 wk after planting. The CH4 flux showed little change throughout the duration of the study. Cumulative CO2 and N2O fluxes were greater for CT and MT than NT, but cumulative CH4 flux was greater for MT than CT and NT. Higher N fertilization rate increased N2O and CH4 fluxes. The GWP was greater for CT than MT and NT and greater for 90 than 0 kg N ha−1. Maize yield was greater for MT than CT and NT and increased with higher N fertilization rate. The GHGI was lower for MT than CT and lower for 120 than 0 and 90 kg N ha−1. Because of overall lower maize yield, MT with reduced N ferilization rate in split applications may be needed to reduce GHG emissions while sustaining yield in the sandy soils of southwest Nigeria.

Two grasses differ in their absorptive root physiological traits and rooting depth under drought in an alpine steppe.

Absorptive root traits play important roles in acquisition of water and nutrients from soil by plants. Despite numerous reports on the changes in species dominance under long-term drought in grassland community, few studies have specifically investigated absorptive root traits of these dominant species in grasslands, especially in the alpine grasslands. Here, two grass species (Leymus secalinus and Stipa purpurea) differing in their responses to drought were selected from an alpine steppe. A series of absorptive root traits were examined under drought in a 3-year glasshouse experiment. We found that drought had no effects on root morphological and architectural traits, whereas root physiological traits and rooting depth differed in their responses to drought. Specifically, drought significantly reduced root respiration and enhanced organ carbon (C) exudation rate, carboxylate exudation rate, acid phosphatase activity and rooting depth of L. secalinus. Particularly, L. secalinus released more citrate into the rhizosphere under drought than S. purpurea. In contrast, these root traits of S. purpurea remained relatively unchanged in response to the drought. These differential responses would render L. secalinus more competitive in acquisition of nutrients and water, thus contributing to its dominance in the community under drought. Moreover, root respiration was negatively correlated with organic C exudation rate, carboxylate exudation rate and acid phosphatase activity, indicating a tradeoff between root respiration and root exudates to acquire nutrients and water by optimizing C allocation under drought. Additionally, all root traits exhibited two independent dimensions in root economic space (RES) for both species under drought. These results indicate that the plant species with great capacity to acquire water and nutrients in soil by optimizing C allocation under drought will be dominant in the community of the alpine grasslands. These findings provide an important insight into species re-ordering under drought on the Tibetan Plateau.

Abiotic and Biotic Processes Controlling Deposition of Calcite and Hydrotalcite Calcretes on Niue Island, Southwest Pacific

Calcretes are indurated terrestrial carbonates that are widespread in arid and semi-arid settings and serve as important archives of present and past environments. Here, we use geochemical tools to explore the nature and origin of calcretes documented from tropical Niue Island in the Southwest Pacific. The study recognizes two types of calcretes that differ in their mineral assemblage, microfabrics, elemental chemistry, and carbon and oxygen isotopes. The calcretes common in the paleo-lagoon soils consist of 90% low-Mg calcite and ~10% highly weathered Mg-Al silicates. These pedogenic calcretes formed in the soil profiles within the vadose zone bear the following distinctions: (i) Fe/Al ratio of 0.75, identical to the ratio in soils (Fe/Al = 0.76 ± 0.5), substantiating the link between the calcretes and soils; (ii) presence of rhizoliths, root voids, micritic nodules, and clasts, which are consistent with a pedogenic calcrete fabric; and (iii) 13C and 18O depletions of −10.6‰ and −5.3‰, respectively, which are compatible with carbon sources from microbial and root respiration, as well as formation in oxygen isotope equilibrium with vadose waters. Unlike the pedogenic calcrete, a rare calcrete from the coastal terrace contains an exceptionally rare hydrotalcite [Mg6Al2(CO3)(OH)16(H2O)4] mineral (65%) coated by microbial films. We contend that the hydrotalcite-rich calcrete was deposited through interaction of dolomite with seawater, similar to the method of producing hydrotalcite in the laboratory. 13C and 18O enrichments of 0.8 to 1.7‰ and −1.0 to −1.6‰, respectively, are in agreement with (i) mixed carbon sources consisting of microbial CO2 degassing, seawater HCO3, and dolomite dissolution, and (ii) oxygen isotope equilibration with seawater-derived fluid.

Does root respiration and root anatomical traits affect crop yield under stress? A meta-analysis and experimental study

Does root respiration and root anatomical traits affect crop yield under stress? A meta-analysis and experimental study

Family ties: Root-root communication within Solanaceae

Root–root communication effects on several physiological and metabolic aspects among Solanaceae relatives were studied. We examined cherry (C) and field (F) tomato (Solanum lycopersicum) and bell pepper (B) (Capsicum annuum), comprising three degrees of relatedness (DOR): high (H-DOR; CC, FF and BB), medium (M-DOR; CF) and low (L-DOR; CB and FB). Plants were grown in pairs of similar or different plants on a paper-based and non-destructive root growth system, namely, rhizoslides. Root growth, including the proliferation of fine roots, and respiration increased as the DOR decreased and were highest in paired L-DOR plants, as was shown for root respiration that increased by 63, 110 and 88 % for C, F, and B when grown with B, B and F, respectively. On the other hand, root exudates of L-DOR plants had significantly lower levels of total organic carbon and protein than those of H-DOR plants, indicating different root–root communication between individuals with different DOR. Our findings indicate, for the first time, that carbon allocation to root growth, exudation and respiration depends on the degree of genetic relatedness, and that the degree of relatedness between individual plants plays a key role in the root-root communication within Solanaceae.

Adapting to climate change: responses of fine root traits and C exudation in five tree species with different light-use strategy.

Trees that are categorised by their light requirements have similarities in their growth strategies and adaptation mechanisms. We aimed to understand the complex responses of elevated air humidity on whole tree fine root carbon (C) exudation (ExC) and respiration rate, morphology, and functional distribution in species with different light requirements. Three light-demanding (LD) species, Populus × wettsteinii, Betula pendula, and Pinus sylvestris, and two shade-tolerant species, Picea abies and Tilia cordata saplings were grown in growth chambers under moderate and elevated air relative humidity (eRH) at two different inorganic nitrogen sources with constant air temperature and light availability. The proportion of assimilated carbon released by ExC, and respiration decreased at eRH; up to about 3 and 27%, respectively. There was an indication of a trade-off between fine root released C and biomass allocation. The elevated air humidity changed the tree biomass allocation and fine root morphology, and the responses were species-specific. The specific fine root area and absorptive root proportion were positively related to canopy net photosynthesis and leaf nitrogen concentration across tree species. The variation in ExC was explained by the trees' light-use strategy (p < 0.05), showing higher exudation rates in LD species. The LD species had a higher proportion of pioneer root tips, which related to the enhanced ExC. Our findings highlight the significant role of fine root functional distribution and morphological adaptation in determining rhizosphere C fluxes in changing environmental conditions such as the predicted increase of air humidity in higher latitudes.

Evolutionary history and root trait coordination predict nutrient strategy in tropical legume trees.

Plants express diverse nutrient use and acquisition traits, but it is unclear how trait combinations at the species level are constrained by phylogeny, trait coordination, or trade-offs in resource investment. One trait - nitrogen (N) fixation - is assumed to correlate with other traits and used to define plant functional groups, despite potential confounding effects of phylogeny. We quantified growth, carbon metabolism, fixation rate, root phosphatase activity (RPA), mycorrhizal colonization, and leaf and root morphology/chemistry across 22 species of fixing and nonfixing tropical Fabaceae trees under common conditions. Belowground trait variation was high even among closely related species, and most traits displayed a phylogenetic signal, including N-fixation rate and nodule biomass. Across species, we observed strong positive correlations between physiological traits such as RPA and root respiration. RPA increased ~ fourfold per unit increase in fixation, supporting the debated hypothesis that N-fixers 'trade' N for phosphatases to enhance phosphorus acquisition. Specific root length and root N differed between functional groups, though for other traits, apparent differences became nonsignificant after accounting for phylogenetic nonindependence. We conclude that evolutionary history, trait coordination, and fixation ability contribute to nutrient trait expression at the species level, and recommend explicitly considering phylogeny in analyses of functional groupings.

Additive effects of N addition and changing precipitation on soil respiration in a climate transitional forest

Global carbon (C) cycling can be greatly affected by the increasing nitrogen (N) deposition and changing precipitation regimes in terrestrial ecosystems. Nevertheless, whether N enrichment and precipitation variability interactively or additively influence soil C release during a long-term period remain largely elusive. Here, a seven-year (2016–2022) field experiment was conducted to explore the responses of soil respiration to N addition, decreased and increased precipitation in a subtropical-warm temperate forest in Central China. The results showed soil respiration was elevated by 11.0%, 12.2%, and 12.3% under N addition, decreased precipitation, and increased precipitation, respectively, primarily originating from the enhancements in plant root respiration. Increased precipitation led to a temporal increase in soil respiration over the experimental period, mostly due to the elevating understory richness and reducing soil C/N ratio. There were additive effects between N addition and changing precipitation on soil respiration observed in our study, suggesting that the impacts of concurrent global change drivers can be predicted from their respective influences. These findings indicated that global change may intensify soil C release from climate transition forests, thus helping to accurately assess the climate change–C feedback in natural ecosystems.

Wildfire Effects on the Soil Respiration and Bacterial Microbiota Composition in Mediterranean-Type Ecosystems

This work provides insights into the effect of fire on soil processes in Mediterranean-type ecosystems in Cyprus. Soil samples from mountainous sites that were subjected to a summer wildfire and adjacent control samples were collected. Incubations were used to estimate basal respiration and isolate soil CO2 release of heterotrophic microorganisms from autotrophic root respiration and heterotrophic respiration from litter decomposition. Physicochemical property changes, bacteria community changes using DNA extraction and 16S rRNA gene analysis, and the effects of ash and fresh litter addition were studied to reveal the microbial composition and the post-fire soil function. Laboratory incubation showed that burned soils constantly showed higher microbial respiration rates compared with control unburned areas, even six months after a fire. Adding ash to unburned samples increased microbial respiration, suggesting that increased nutrient availability positively corelates with the increased release of CO2 from fire-affected soil. Elevated temperatures due to the wildfire exerted significant effects on the composition of soil bacterial microbiota. Nevertheless, the wildfire did not affect the alpha-diversity of soil bacteria. New communities of microorganisms are still able to decompose fresh plant material after a fire, but at a slower rate than natural pre-fire populations.

Severe Preharvest Drought Elevates Respiration and Storage Rot in Postharvest Sugarbeet Roots

ABSTRACTSugarbeets are largely produced without irrigation, making drought stress inevitable when rainfall is insufficient. Whether drought stress impacts root storage, however, is currently unknown. Research was conducted to determine the effect of preharvest water stress on postharvest sugarbeet root respiration rate and susceptibility to storage rots as these traits are the primary determinants for sucrose loss and quality deterioration. Greenhouse‐grown plants were subjected to four levels of water deficit by discontinuing watering for 0, 7, 14 or 21 days prior to harvest. Plants receiving water‐restrictive treatments displayed physiological stress by leaf epinasty, reductions in net photosynthetic rate and leaf relative water content and increases in leaf temperature, whereas the water content of roots harvested from these plants progressively decreased with the severity of the preharvest water‐deficit treatment. Harvested roots from all watering treatments were stored at 10°C and 95% relative humidity for up to 12 weeks and evaluated for respiration rate and susceptibility to storage rot. Root respiration rate during storage was inversely related to root water content at harvest by second‐order equations, such that respiration was not significantly affected by minor reductions in root water content but increased exponentially for roots obtained from severely drought‐stressed plants with water contents at harvest of ≤75%. Similarly, roots with water contents ≤75% had elevated levels of electrolyte leakage, a measure of cellular membrane damage, and were more susceptible to dehydration and fungal infection during storage. In separate experiments, roots harvested from water‐stressed plants were inoculated with Botrytis cinerea or Penicillium vulpinum, two causal agents for storage rots. In these experiments, preharvest water stress quantitatively increased root rot and qualitatively altered symptoms of their infection. Overall, these results demonstrate that severe preharvest drought stress is likely to significantly increase sugarbeet root storage losses caused by root respiration and storage rots and that storage losses are likely to accelerate with time in storage. However, mild‐to‐moderate drought conditions prior to harvest are expected to have no or minimal effect on storage losses from root respiration or storage rots.

Effect of Aminating Lignin Loading with Arbuscular Mycorrhizal Fungi on Soil Aggregate Structure Improvement.

Lignin is an important component of plant fiber raw materials, and is a three-dimensional network structure aromatic polymer with abundant resources and a complex structure in nature. Lignin is generally used as industrial waste, and its potential value has not been fully utilized. Modern agriculture extensively uses chemical fertilizers, leading to the gradual degradation of soil fertility and structure, which seriously affects crop growth, nutrient transport, and root respiration function. Based on soil bulk density, porosity, aggregates, and their stability indicators, this study analyzed the effects of aminated industrial lignin and its loading with arbuscular mycorrhizal fungi on soil structure improvement and plant growth. It was hoped that resource-rich lignin could play a beneficial role in improving soil structure and promoting crop growth. The phenolic hydroxyl group of lignin was epoxidized and further aminated to load with arbuscular mycorrhizal fungi. The results indicated that amine-modified lignin could effectively load with arbuscular mycorrhizal fungi. The application of arbuscular mycorrhizal fungi-supported aminated lignin to soil aggregate structure improvement greatly reduced the bulk density of soil, and increased the porosity of soil and the content of large granular soil. Compared with unmodified soil, soil bulk density decreased by 73.08%, the porosity of soil increased by 70.43%, and the content of large granular soil increased by 56.38%. Using the improved soil for corn cultivation efficiently increased the biomass of corn. The plant height was increased by 72.16%, the root-shoot ratio was increased by 156.25%, and other indexes were also improved to varying degrees. The experimental method provides an important basis for the effective utilization of lignin materials in agriculture in the future.

Effects of Agricultural Potassium Fertilizer Application on Soil Carbon Cycle

This review examines the impact and regulatory mechanisms of potassium fertilizer on the soil carbon cycle, discussing how potassium fertilizer affects soil carbon storage and flow through various pathways. As a vital agricultural nutrient, potassium not only plays a crucial role in crop growth but also influences several aspects of the soil carbon cycle, including carbon sequestration, microbial activity, soil respiration, and the structure and enzymatic activities of the soil. The article begins by introducing the importance of the soil carbon cycle and the application of potassium in agriculture, followed by an analysis of how potassium fertilizer promotes soil organic carbon storage, including increasing the amount of plant residue returned to the soil. It then discusses the impact of potassium fertilizer on the structure and function of soil microbial communities, which play a key role in the soil carbon cycle. The article also explores the influence of potassium fertilizer on soil respiration, including its regulatory effects on microbial respiration and root respiration, and how potassium improves soil structure to affect soil respiration. Additionally, the impact of potassium fertilizer on the activity of enzymes related to carbon cycling is discussed in detail, as these enzymes play a central role in the decomposition of organic matter and nutrient cycling. Finally, the article summarizes the potential role of potassium fertilizer in improving soil health, enhancing carbon sequestration capacity, and addressing climate change, calling for more research to understand the mechanisms of potassium fertilizer and to provide a scientific basis for sustainable soil management strategies.

Soil type and temperature determine soil respiration seasonal dynamics in dairy grassland

Soil respiration rates (Rs) were measured in New Zealand dairy grassland.Both season and soil type significantly affected Rs.Soil temperature and soil type dominated overall Rs.Soil respiration (Rs), the CO2 release from root respiration and microbial metabolism, affects global soil carbon storage and cycling. Only few studies have looked at Rs in the southern hemisphere, especially regarding the interaction between soil type and environmental factors on Rs in dairy grassland. We investigated the relationship between Rs and soil temperature (Ts), soil water content (SWC), soil type, and other environmental factors based on summer and winter measurements at four sites in New Zealand. Across sites, soil respiration rates ranged from 0.29 to 14.58 with a mean of 5.38 ± 0.13 (mean ± standard error) µmol CO2 m−2 s−1. Mean summer Rs was 86.5% higher than mean winter Rs, largely driven by organic/gley and pumice soils while ultic soils showed very little seasonal temperature sensitivity. Overall mean Rs in organic/gley soils was 108.0% higher than that in ultic soils. The high Rs rate observed in organic/gley was likely due to high soil organic matter content, while low Rs in ultic and pallic soils resulted from high clay content and low hydraulic conductance. Soil temperature drove overall Rs. Our findings indicate that soil type and soil temperature together best explain Rs. This implies that a mere classification of land use type may be insufficient for global C models and should be supplemented with soil type information, at least locally.

Illuminating the “Invisible”: Substantial Deep Respiration and Lateral Export of Dissolved Carbon From Beneath Soil

AbstractDissolved organic and inorganic carbon (DOC and DIC) influence water quality, ecosystem health, and carbon cycling. Dissolved carbon species are produced by biogeochemical reactions and laterally exported to streams via distinct shallow and deep subsurface flow paths. These processes are arduous to measure and challenge the quantification of global carbon cycles. Here we ask: when, where, and how much is dissolved carbon produced in and laterally exported from the subsurface to streams? We used a catchment‐scale reactive transport model, BioRT‐HBV, with hydrometeorology and stream carbon data to illuminate the “invisible” subsurface processes at Sleepers River, a carbonate‐based catchment in Vermont, United States. Results depict a conceptual model where DOC is produced mostly in shallow soils (3.7 ± 0.6 g/m2/yr) and in summer at peak root and microbial respiration. DOC is flushed from soils to the stream (1.0 ± 0.2 g/m2/yr) especially during snowmelt and storms. A large fraction of DOC (2.5 ± 0.2 g/m2/yr) percolates to the deeper subsurface, fueling deep respiration to generate DIC. DIC is exported predominantly from the deeper subsurface (7.1 ± 0.4 g/m2/yr, compared to 1.3 ± 0.3 g/m2/yr from shallow soils). Deep respiration reduces DOC and increases DIC concentrations at depth, leading to commonly observed DOC flushing (increasing concentrations with discharge) and DIC dilution patterns (decreasing concentrations with discharge). Surprisingly, respiration processes generate more DIC than weathering in this carbonate‐based catchment. These findings underscore the importance of vertical connectivity between the shallow and deep subsurface, highlighting the overlooked role of deep carbon processing and export.

Elucidation of Shoot and Root Growth, Physiological Responses, and Quality Traits of Tomato (Solanum lycopersicon L.) Exposed to Elevated Calcium Carbonate Concentrations

The excess presence of calcium carbonate (CaCO3) in soil poses challenges for production of horticultural crops, including tomatoes. This condition is prevalent in arid and semi-arid regions of Afghanistan. The objective of this study was to evaluate the effects of elevated concentrations of CaCO3 on growth, physiology, and quality attributes of tomato. Seedlings were exposed to different concentrations of CaCO3 (0%, 2.5%, 5%, 10%, and 20% w/w) in soil. The results showed that elevated concentrations of CaCO3 (10% and 20%) significantly increased soil electrical conductivity (EC) and pH, and subsequently affected growth, physiology, and quality of tomato. CaCO3 effects resulted in an increase in leaf electrolyte leakage, leaf calcium content, root respiration rate, root ethylene production, fruit firmness, total soluble solids, ascorbic acid, and organic acids, as well as a decrease in plant height, leaf length, leaf magnesium content, leaf SPAD value, number of leaves per plant, root weight and length, and root activity. At higher concentrations, CaCO3 decreased number of flowers and fruit per plant, as well as fruit weight and diameter, consequently affecting yield production. Although elevated concentrations of CaCO3 is characteristic of soils in Afghanistan, limited information is available about this topic. These findings enhance our understanding of soil conditions in the country and provide valuable insights for farmers.

Jasmonic acid and heat stress induce high volatile organic compound emissions in Picea abies from needles, but not from roots.

Plants emit diverse volatile organic compounds (VOCs) from their leaves and roots for protection against biotic and abiotic stress. An important signaling cascade activated by aboveground herbivory is the jasmonic acid (JA) pathway that stimulates the production of VOCs. So far it remains unclear if the activation of this pathway also leads to enhanced VOC emissions from conifer roots, and how the interplay of above- and belowground defenses in plants are affected by multiple stressors. Therefore, we simultaneously analyzed needle and root VOC emissions of Picea abies saplings, as well as CO2 and H2O fluxes in response to aboveground JA treatment, heat stress and their interaction in a controlled climate chamber experiment. Continuous online VOC measurements by PTR-TOF-MS showed an inverse pattern of total needle and root VOC emissions, when plants were treated with JA and heat. While needle sesquiterpene emissions increased nine-fold one day after JA application, total root VOC emissions decreased. This was mainly due to reduced emissions of acetone and monoterpenes by roots. In response to aboveground JA treatment, root total carbon emitted as VOCs decreased from 31% to only 4%. While VOC emissions aboveground increased, net CO2 assimilation strongly declined due to JA treatment, resulting in net respiration during the day. Interestingly, root respiration was not affected by aboveground JA application. Under heat the effect of JA on VOC emissions of needles and roots was less pronounced. The buffering effect of heat on VOC emissions following JA treatment points towards an impaired defense reaction of the plants under multiple stress. Our results indicate efficient resource allocation within the plant to protect threatened tissues by a rather local VOC release. Roots may only be affected indirectly by reduced belowground carbon allocation, but are not involved directly in the JA-induced stress response.

Phosphorus addition enhances heterotrophic respiration but reduces root respiration in a subtropical plantation forest

Soil respiration (Rs) is a major component of the global carbon (C) cycle and is influenced by the availability of nutrients such as phosphorus (P). However, the response of Rs to P addition in P-limited subtropical forest ecosystems and the underlying mechanisms remain poorly understood. To address this, we conducted a P addition experiment (50 kg P ha−1 yr−1) in a subtropical Chinese fir (Cunninghamia lanceolata) plantation forest. We separated Rs into heterotrophic respiration (Rh), root respiration (Rr), and mycorrhizal hyphal respiration (Rm), and quantified soil properties, microbial biomass (phospholipid fatty acid, PLFA), fungal community composition (ITS), and the activity of extracellular enzymes. Phosphorus addition significantly increased Rs and Rh, but decreased Rr and did not influence Rm. Further, P addition increased fungal, bacterial, and total PLFAs, and phenol oxidase activity. Conversely, P application decreased root biomass and did not alter the relative abundance of symbiotrophic fungi. Phosphorus enrichment therefore enhances soil C emissions by promoting organic matter decomposition by heterotrophic activity, rather than via increases in root or mycorrhizal respiration. This advances our mechanistic understanding of the relationship between fertility and soil respiration in subtropical forests, with implications for predicting soil C emissions under global change.