Soil Hypoxia Research Articles

Construction of a High-Resolution Waterlogging Disaster Monitoring Framework Based on the APSIM Model: A Case Study of Jingzhou and Bengbu

This study investigates waterlogging disasters in winter wheat using the Agricultural Production Systems Simulator (APSIM) model. This research explores the effects of soil hypoxia on wheat root systems and the tolerance of wheat at different growth stages to waterlogging, proposing a model to quantify the degree of waterlogging in wheat. Remote sensing data on soil moisture and wheat distribution are utilized to establish a monitoring system for waterlogging disasters specific to winter wheat. The analysis focused on affected areas in Bengbu and Jingzhou. Experimental results from 2017 to 2022 indicate that the predominant levels of waterlogging disasters in Bengbu and Jingzhou were moderate and mild, with the proportion of mild waterlogging ranging from 30.1% to 39.3% and moderate waterlogging from 14.8% to 25.6%. A combined analysis of multi-source remote sensing data reveals the key roles of precipitation, evapotranspiration, and altitude in waterlogging disasters. This study highlights regional disparities in the distribution of waterlogging disaster risks, providing new strategies and tools for precise assessment of waterlogging disasters.

Rhizosphere Ventilation Effects on Root Development and Bacterial Diversity of Peanut in Compacted Soil

Soil compaction is one of the crucial factors that restrains the root respiration, energy metabolism and growth of peanut (Arachis hypogaea L.) due to hypoxia, which can be alleviated by ventilation. We therefore carried out a pot experiment with three treatments: no ventilation control (CK), (2) ventilation volumes at 1.2 (T1), and 1.5 (T2) times of the standard ventilation volume (2.02 L/pot). Compared to no-ventilation in compacted soil, ventilation T1 significantly increased total root length, root surface area, root volume and tips at the peanut anthesis stage (62 days after sowing), while T2 showed a negative impact on the above-mentioned root morphological characteristics. At the podding stage (S2, 95 days after sowing), both ventilation treatments improved root morphology, especially under T1. Compared to CK, both ventilation T1 and T2 decreased the activities of enzymes involving the anaerobic respiration, including root lactate dehydrogenase, pyruvate decarboxylase and alcohol dehydrogenase. The activities of antioxidant enzymes of root superoxide dismutase, peroxidase and catalase also decreased at S1, while superoxide dismutase and peroxidase significantly increased under T1 at S2. The ventilation of compacted soil changed soil nitrogen-fixing bacterial communities, with highest bacterial alpha diversity indices under T1. The Pearson correlation analyses indicated a positive relationship between the relative abundance of Bradyrhizobiaceae and root activity, and between unclassified_family of Rhizobiales and the root surface area, while Enterobacteriaceae had a negative impact on the root nodule number. The Pearson correlation test showed that the root surface, tips and activity positively correlated with root superoxide dismutase and peroxidase activities. These results demonstrate that soil ventilation could enhance plant root growth, the diversity and function of soil nitrogen-fixing bacterial communities. The generated results from this present study could serve as important evidence in alleviating soil hypoxia caused by compaction.

Effects of aeration treatments on root and rhizome growth parameters of Phyllostachys violascens (Lei bamboo) under intensive cultivation: A field study

Aeration through underground tunneling in mulched Phyllostachys violascens (Lei bamboo) forests can improve soil quality. Nevertheless, the effect of soil ventilation on the growth of bamboo roots and rhizomes at different distances, directions and depths of the forest are still unclear. In a field experiment, four treatments including organic mulching without aeration (MNA), organic mulching with aeration (MA), non-mulched with aeration (NMA), and non-mulched and non-aeration treatment (control) were set up to investigate the effects of soil aeration treatment on bamboo root and rhizome growth at different depths and radii distances from the bamboo trunk in both perpendicular (PD) and horizontal (HD) aeration directions. The results show that root and rhizome quantity and quality decreased vertically and linearly in the soil layers and this trend was more significant in the PD direction and near the trunk. MA treatment induced the most significant effects on the determined root and rhizome growth parameters. At 10 cm depth, the number of rhizomes in CK was 70.8 %, 77.1 %, and 18.8 % higher than that in MA, NMA, and MNA plots, respectively. However, fewer rhizomes appeared in CK and MNA plots at 20 and 30 cm depths relative to 10 cm while the number was increased by 149 % in MA and 151 % NMA plots at 20 cm. This suggest that in CK and MNA plots, soil hypoxia and soil acidification were prevalent which inhibited rhizome growth by inducing rhizome up-floating and preventing root elongation, respectively. Also, the root morphological parameters including lengths, surface areas, and volumetric areas were significantly increased in MA and MNA treatments compared to the control and NMA. For example, root length, surface area, and volumetric area in MA were increased by 56 %, 44.9 %, and 28.3 % while that in MNA increased by 40 %, 55.8 %, and 81.0 % compared with roots from the control plot. This study provides both a theoretical and practical guide for improving soil quality and bamboo growth under intensive management using aeration treatment.

Subsurface aeration mitigates organic material mulching-induced anaerobic stress via regulating hormone signaling in Phyllostachys praecox roots.

Organic material mulching has been used extensively to allow Phyllostachys praecox to promote growth and development of shoots. However, the bamboo forest always showed a significant degradation, probably due to anaerobic damage caused by the mulching after several years. Therefore, we have innovatively proposed an improvement measure to aerate the underground pipes for the first time. We investigated the role of subsurface pipe aeration in regulating root hypoxia to reduce the stress and to identify the degradation mechanism. Results showed that aeration increased oxygen concentration, shoot yield and root growth compared with mulching, and the aeration enhanced the concentration of indole-3-acetic acid (IAA) and the expression of Aux/IAAs (Aux1, Aux2, Aux3, and Aux4). Aeration reduced gibberellin (GA), ethylene (ETH), and abscisic acid (ABA) contents as well as anaerobic enzyme activities (alanine transaminase, AlaAT; alcohol dehydrogenase, ADH; pyruvate decarboxylase, PDC; and lactate dehydrogenase, LDH), which alleviated root damage in anoxic conditions. Furthermore, correlation showed that the activities of ADH, LDH, PDC, and AlaAT showed significant linear correlations with soil oxygen levels. RDA analyses showed that ABA, IAA, and ETH were found as the key driving hormones of Aux/IAAs in the root of the forest mulched with organic material. Here we show that subsurface aeration increases soil oxygen concentration, shoot yield, root growth and regulates phytohormone concentrations and Aux/IAAs expression, which reduces anaerobic enzyme activities. Consequently, subsurface pipe aeration is an effective measure to mitigate the degradation of bamboo forests caused by soil hypoxia that results from organic material mulching.

Root hypoxia causes oxidative damage on photosynthetic apparatus and interacts with light stress to trigger abscission of lower position leaves in Capsicum

Oxidants produced by roots in hypoxic soil and stress caused by intense light are two causes of reduced photosynthetic capacity and efficiency. Moreover, they promote the formation of leaf abscission zones, which has detrimental effects on crop growth. It remains unclear how leaf position, an endogenous factor in nonstress-induced senescence, affects leaf senescence caused by oxidative stress. Thus, we used Capsicum plants to examine how leaf senescence and abscission changed photosynthetic capacity and efficiency at five leaf positions. We analyzed the association between photosynthetic changes and leaf abscission. Our results demonstrated that hypoxia resulted in lower root biomass, lower water uptake in leaves, and lower leaf carotenoid content. Moreover, the interaction between hypoxia and intense light stress causes lower carotenoid and chlorophyll content, suggesting that leaf oxidative stress levels affect the degree of photoprotection conferred by the presence of carotenoids. We also found a significant reduction in the maximum quantum yield of photosystem II under hypoxia conditions, especially in leaves at lower positions on the plant. Finally, we observed that the combined stress of hypoxia and intense light induced abscission at these lower leaf positions. Our results suggested that the level of oxidative damage in respective leaf caused by hypoxia and high light stress is significantly affected by leaf position, and stress interactions cause abscission in the lower leaves near the roots.

Can aeration improve bamboo soil fertility of soil below bamboo and fungal diversity under mulching conditions?

AbstractAeration can alleviate soil hypoxia stress of Phyllostachys praecox bamboo under mulching conditions, but how aeration affects soil properties, soil fungal community structure, and bamboo development is unclear. We studied the responses of soil properties, fungal community structure, bamboo shoots, and rhizome growth to organic mulching (TM), mulching with aeration (TA1 and TA2), and no‐mulching treatments (CK) from a field experiment in March and July, 2019. During the mulching period (March), the aeration improvement treatment (TA2) improved soil O2 content, bamboo shoots yield, and soil nutrient availability significantly when compared with TM. TA2 treatment showed significantly higher relative abundances of the genus Trichoderma and functional group endophyte than TM treatment, which might be conducive to soil nutrient transformation and bamboo growth. The TA2 treatment had higher fungal diversity indices than that of the TA1 treatment, suggesting that optimal aeration conditions enhance soil fungal diversity. The fungal community structure also showed strong temporal dynamics in all treatments. Mantel test results indicated soil O2 is the primary factor driving fungal community structure under mulching conditions, while has no impact on the fungal community in summer; fungal community structure was primarily controlled by soil pH in summer. Structural equation model revealed soil NO3−‐N content was responsible directly for bamboo rhizome growth and shoot yield. Our results indicate short‐term mulching is beneficial to soil nutrients improvement and bamboo yield increase, while rational aeration can further facilitate sustainable plantation development under hypoxic soil conditions.

Exogenously applied spermidine alleviates hypoxia stress in Phyllostachys praecox seedlings via changes in endogenous hormones and gene expression

BackgroundHypoxia stress is thought to be one of the major abiotic stresses that inhibits the growth and development of higher plants. Phyllostachys pracecox is sensitive to oxygen and suffers soil hypoxia during cultivation; however, the corresponding solutions to mitigate this stress are still limited in practice. In this study, Spermidine (Spd) was tested for regulating the growth of P. praecox seedlings under the hypoxia stress with flooding.ResultsA batch experiment was carried out in seedlings treated with 1 mM and 2 mM Spd under flooding for eight days. Application of 1 mM and 2 mM Spd could alleviate plant growth inhibition and reduce oxidative damage from hypoxia stress. Exogenous Spd significantly (P < 0.05) increased proline, soluble protein content, catalase (CAT), superoxide dismutase (SOD), and S-adenosylmethionine decarboxylase (SAMDC) activity, enhanced abscisic acid (ABA) and indole-3-acetic acid (IAA) content, and reduced ethylene emission, hydrogen peroxide (H2O2), superoxide radical (O2·−) production rate, ACC oxidase (ACO) and ACC synthase (ACS) to protect membranes from lipid peroxidation under flooding. Moreover, exogenous Spd up-regulated the expression of auxin-related genes auxin responsive factor1 (ARF1), auxin1 protein (AUX1), auxin2 protein (AUX2), auxin3 protein (AUX3) and auxin4 protein (AUX4), and down-regulated the expression of ethylene-related ACO and ACS genes during flooding.ConclusionThe results indicated that exogenous Spd altered hormone concentrations and the expression of hormone-related genes, thereby protecting the bamboo growth under flooding. Our data suggest that Spd can be used to reduce hypoxia-induced cell damage and improve the adaptability of P. praecox to flooding stress.

Aeration increases soil bacterial diversity and nutrient transformation under mulching-induced hypoxic conditions

Soil oxygen (O2) deficiency induced by organic mulching is easy to overlook. Aeration has been shown to potentially alleviate soil hypoxia stress. However, the responses of soil bacterial communities to such mulching-induced hypoxic conditions and aeration remain elusive. Therefore, a three-year field experiment, consisting of mulching (T1), mulching with aeration (TA1, poor aeration; TA2, strong aeration), and no-mulching (CK) treatments, was conducted in bamboo (Phyllostachys praecox) plantations. According to our results, the strong aeration treatment (TA2) alleviated soil acidification, increased soil nutrient availability, and significantly increased soil O2 content by 18.44% (P < 0.05) when compared with T1. In addition, TA2 significantly increased soil β-glucosidase, invertase, urease, and acid phosphatase activities compared with CK and T1 (P < 0.05). The alpha diversity indices with TA2 treatment were the highest, indicating that aeration increased the species richness and diversity of bacteria. The changes in bacterial community composition associated with TA2 treatment (i.e., an increase in Firmicutes, Verrucomicrobia, and Faecalibacterium abundance and a decrease in Chloroflexi and Bradyrhizobium abundance) were mainly related to nutrient and O2 content. Mantel Test results suggested that soil O2 content and temperature were the key factors shaping bacterial community composition. Structural equation modeling revealed that soil O2 content had a positive and direct influence on bacterial community diversity. Functional annotation of prokaryotic taxa predicted that TA2 significantly increased the relative abundance of bacterial communities associated with nitrification, nitrogen fixation, and ureolysis. Our results demonstrated that optimal soil aeration conditions (17.60% of O2 content) could enhance the diversity and function of soil bacterial communities. Overall, the findings of this study could serve as a benchmark for alleviating soil hypoxia caused by organic mulches, which is important for increasing the functionality of nutrient cycling bacterial communities in the soil.

Iron toxicity increases oxidative stress and impairs mineral accumulation and leaf gas exchange in soybean plants during hypoxia.

Iron toxicity is a major challenge faced by plants in hypoxic soils; however, the consequences of such combined stress for soybean (Glycine max) remain to be determined. Here we assessed the physiological responses of soybean plants exposed to hypoxia and a high concentration of iron. Soil-grown plants cultivated in a greenhouse until the vegetative stage were transferred to a hydroponic system containing nutrient solution and subjected to two oxygen conditions (normoxia (6.2 mg L-1) and hypoxia (0.33 mg L-1)) and two iron concentrations (Fe-EDTA) (0.09 and 1.8 mM) for 72 h. During hypoxia, high concentrations of iron in the nutrient solution resulted in increased iron accumulation in roots and leaves. Under this condition, the concentrations of zinc, nitrogen, potassium, and calcium decreased in the roots, while the concentration of nitrogen and magnesium decreased in the leaves. Additionally, during hypoxia, the higher concentration of iron led to an increase in the activity of the antioxidant enzymes in roots and leaves, while decreased the levels of the photosynthetic pigments, leaf gas exchange, and plant growth. In conclusion, high iron concentration in the root medium results in a considerably more severe damage condition to soybean plants under hypoxia compared to plants grown under low iron availability.

Flood signals in tree-ring δ18O and wood anatomical parameters of Lagerstroemia speciosa: Implications for developing flood management strategies in Bangladesh

Bangladesh consists of 80% of the flood plain of the Ganges-Brahmaputra-Meghna river system (GBM), making the country one of the highest flood prone countries of the world. Due to the high rate of discharge of the GBM caused by the summer monsoon and the snowmelt of the Eastern Himalaya and Southern Tibetan Plateau due to climate change, Bangladesh witnessed 16 flood events over 1954–2017. We performed a multiproxy tree-ring analysis to investigate the impact of extreme flood events on tree growth, xylem anatomical parameters and oxygen isotope composition of tree-ring cellulose (δ18Otr) in a Bangladeshi moist tropical forest and to establish relationships between water level of the regional rivers and tree-ring parameters. By using pointer year analysis and comparing the pointer years with historical flood records (a cut-off threshold of the country's flooded land area of 33.3%), we identified the three extreme flood events (hereafter called flood years) 1974, 1988, and 1998 in Bangladesh. Superposed epoch analysis revealed significant changes in Tree-ring width (TRW), total vessel area (TVA), vessel density (VD), and δ18Otr during flood years. Flood associated hypoxic soil conditions reduced TRW up to 53% and TVA up to 28%, varying with flood events. In contrast, VD increased by 23% as a safety mechanism against flood induced hydraulic failure. Tree-ring δ18O significantly decreased during the flood years due to the amount effect in regional precipitation. Bootstrapped Pearson correlation analysis showed that wood anatomical variables encoded stronger river level signals than TRW and δ18Otr. Among the wood anatomical parameters, VD showed a strong relationship (r = −0.58, p < 0.01) with the water level of the Manu River, a regional river of the north-eastern part of Bangladesh, indicating that VD can be used as a reliable proxy for river level reconstruction. Our analyses suggest that multiproxy tree-ring analysis is a potential tool to study tropical moist forest responses to extreme flood events and to identify suitable proxies for reconstructing hydrological characteristics of South Asian rivers.

Drip irrigation with nanobubble oxygenated treated wastewater improves soil aeration

Long-term drip irrigation with treated wastewater (TWW) is known to enhance oxygen deficiency (hypoxia), especially in fine-textured soils. Hypoxia conditions around plant roots negatively affect growth and yield. Experiments were conducted to evaluate the response of lettuce grown in well-aerated (sandy) and poorly aerated (clayey) soils to surface and subsurface drip irrigation with nanobubbles oxygenated TWW (ONB-TWW). Oxygen mass balances show that irrigation with ONB-TWW supplied about 1% of the daily OCO2 emissions. Nevertheless, our results show that both surface and subsurface drip irrigation with ONB-TWW increased the lettuce yield regardless of the soil type or the amount of oxygen added to the soil out of the daily oxygen consumption in it. Irrigation with ONB-TWW significantly reduced membrane leakage and osmotic potential in the roots and leaves in both well-aerated and poorly aerated soils, concomitantly improving root viability and chlorophyll content in the leaves of the plants grown in the poorly aerated clayey soil. The results suggest that drip irrigation with ONB-TWW, should be considered as a viable method to improve oxygen availability in soils and to alleviate soil hypoxia. Further study is needed to elucidate the mechanisms by which ONB promote plant health and growth.

Soil oxygen and water dynamics underlying hypoxic conditions in the root-zone of avocado irrigated with treated wastewater in clay soil

Alternative water sources for agriculture are in high demand in a world with diminishing fresh water (FW) availability. Treated wastewater (TWW) offers a reliable alternative, but increasing evidence is pointing to damage to TWW irrigated orchards planted in clay soils related to soil hypoxia. The mechanisms responsible for this hypoxia have not been extensively studied to date. The aim of this study was to elucidate meaningful insights into the mechanisms responsible for the hypoxia in TWW irrigated orchards planted in clay soils using a novel approach whereby parameters describing the soil oxygen and water temporal dynamics are analyzed. To that end, soil oxygen and soil water tension (SWT) measurements from a two year field experiment comparing TWW to FW irrigation in an avocado orchard planted in a clay soil (60 % clay) were used. The deterioration in oxygen levels occurred as the irrigation season progressed, and the oxygen availability decreased with depth (10–35 cm depth). During August-September, when the lowest oxygen concentrations were measured, the water content at which oxygen supply matched oxygen consumption at 35-cm depth did not differ between treatments (∼50 mbar), but the TWW irrigated soil experienced ∼47 % more time at wetter conditions. Lower oxygen decline rates were observed in the TWW irrigated plots which countered the previous concept that TWW leads to increased soil oxygen consumption. The findings point towards the rate of soil drying as the prime cause of differences – TWW irrigated plots dried in a rate which is nearly 4-times smaller than that in FW irrigated plots during the dark and light hours, reflecting slower drainage and water uptake respectively. It is suggested that soil hypoxia induced by the low soil drainage in TWW irrigated clay soils impairs tree water uptake, which further hinders the soil oxygen levels. Based on these results management tools are suggested to allow sustainable irrigation with TWW in the future. Furthermore, the work demonstrates how analysis of parameters describing the oxygen hourly changes can be utilized to gain mechanistic insights unto processes affecting the oxygen regime in the soil.

Reversible and irreversible root phenotypic plasticity under fluctuating soil physical conditions

Roots grow in a highly heterogeneous physical environment due to the spatial complexity of soil structure. Thereby, the root growth zone repeatedly experiences soil physical stress such as hypoxia or increased penetration resistance. To mimic the highly variable physical environment surrounding the root growth zone, we subjected pea and wheat seedlings to periodic soil physical stress. One day of soil hypoxia or increased penetration resistance reduced root elongation rate of both species by at least 20 %. Upon stress release, root elongation rate of pea could recover within one day, while no such recovery occurred in wheat. Similarly, the diameter of the root elongation zone in pea increased by 15 % and 20 % due to hypoxia and increased penetration resistance, respectively, but decreased again once the stresses were released. In contrast, the diameter of the elongation zone of wheat roots started to decrease with the onset of soil physical stress and this trend continued upon stress release. Hence, root responses to short-term soil physical stress were reversible in pea and irreversible in wheat, indicating reversible and irreversible root phenotypic plasticity, respectively. This suggests that strategies to cope with periodic soil physical stress may vary among species. The differentiation between reversible and irreversible phenotypic plasticity is crucial to advance our understanding on soil exploration, resource acquisition, whole plant growth, and ultimately crop yield formation on structured soil.

Leaf anatomical traits and their ecological significance for Acrostichum aureum (Pteridaceae), a remarkable fern species growing in mangroves

Mangroves are naturally stressful habitats, with high salinity, regular flooding, strong winds, high temperatures, and muddy, hypoxic soils, requiring adaptations in plant anatomy. In this sense, we present a description of the leaf anatomy of Acrostichum aureum, a remarkable fern species growing in mangroves, focusing on novelties and the significance of the traits for adaptation to mangrove conditions. The leaves were amphistomatic with anomocytic stomata at the same level as the other epidemic cells, and there was a uniseriate hypodermis on both surfaces of the lamina. A dense spongy parenchyma was present in the lamina with limited number of intercellular spaces. We observed sclerenchyma fibers in the costae (3–5 layers) immediately below the epidermis and surrounding the vascular bundles, which were amphicrival (1) and bicollateral (4) in the costae, and collateral and bicollateral in the mesophyll (4–6). In the costae, the endodermis was uniseriate with Casparian strip. The pericycle was interrupted, uniseriate, with varied cell sizes, indicating activity. Idioblasts containing isolated calcium oxalate crystals with a prismatic shape occurred in the epidermis, hypodermis, and sclerenchyma. Some anatomical traits of A. aureum are similar to those reported to angiosperms in mangroves, such as the presence of a thick cuticle, amphistomaty, hypodermis, CaOx crystals, and intercellular spaces, indicative of ecological convergence. These traits are potentially involved in promoting resistance to water loss, enhanced photosynthesis, avoidance of photoinhibition, mechanical resistance, resistance to herbivory, homeostasis, and detoxification.

Exogenous Peroxidase Mitigates Cadmium Toxicity, Enhances Rhizobial Population and Lowers Root Knot Formation in Rice Seedlings

Soil cadmium (Cd) causes toxicity and oxidative stress, alters biochemical processes and root knot formation in rice. Irrigation of exogenous peroxidase (POX) together with its co-substrate H2O2 (POXRice+H2O2), is likely to have protective effect upon the biochemical and nodular changes in rice grown in Cd-rich soil. Exposure to Cd concentration of 1.00mg/L increased oxidative stress, loss of cell viability, electrolyte leakage and root knot formation, whereas it significantly lowered the chlorophyll level and rhizobium growth in rice. Irrigation of exogenous POXRice+H2O2 to Cd-stressed rice seedlings reversed the Cd-induced alterations in rice to levels similar in control (non-stressed) seedlings. Results provided strong evidence of exogenous POXRice+H2O2-mediated reversal and restoration of physiological and biochemical processes as well as increased resistance of rice seedlings to root knot formation. Irrigation with POXRice+H2O2 appeared to contribute towards bringing normoxic conditions in the otherwise hypoxic soil environment by enhancing the O2 in pot-experiments due to reduced Cd uptake, enhanced mineral homeostasis of essential elements viz. P, Fe, Mo, Mg and Mn for maintenance of root architecture damaged by lipid peroxidation and reduction in oxidative stress by reducing Cd-induced reactive oxygen species generation. Therefore, the mitigation of Cd-toxicity in rice through this novel approach appeared to be a promising mode to limit Cd-uptake, modulate protective and tolerance mechanisms for sustainable rice yield in Cd-contaminated rice-croplands and prevent nematode attack in rice, however, more detailed studies are needed prior to large scale applications.

Effects of solid oxygen fertilizers and biochars on nitrous oxide production from agricultural soils in Florida

Elevated levels of nitrous oxide (N2O) emissions are a matter of concern in agricultural soils especially when flooding (hypoxic conditions) results from over irrigation or frequent rains. This study is the first to report the use of two solid oxygen fertilizers (SOFs, calcium peroxide and magnesium peroxide) to reduce N2O production in mineral and organic soils amended with N fertilizer in a short-term laboratory incubation besides two biochars. In general, organic soil had greater N2O production than mineral soil. Soils amended with nitrogen fertilizer exhibited increased N2O production, by 74 times in mineral soil and 2 times in organic soil. Both solid oxygen fertilizers in mineral soil (98–99%) and calcium peroxide in organic soil (25%) successfully reduced N2O production than corresponding N fertilized treatments. Additionally, a greater level of available nitrate–N (52–57 and 225 mg kg−1 in mineral and organic soil, respectively) was recorded with the solid oxygen fertilizers. Corn residue biochar with N fertilizer increased N2O production in mineral soil but decreased in organic soil, while pine bark biochar with N did not affect the N2O production in either soil. Depending on soil, appropriate SOFs applied were able to reduce N2O production and maintain greater nitrate–N levels in flooded soil. Thus, solid oxygen fertilizers can potentially be used as an effective way to reduce N2O emission from hypoxic soil in agricultural production systems.

Effect of soil aeration treatment on the physiological and biochemical characteristics of Phyllostachys praecox under the organic material mulching

Phyllostachys praecox is one of the bamboo species that cultivated extensively in southern China. An organic material mulching technique is commonly adopted in winter to increase the yield of bamboo shoots and profits. However, P. praecox is inevitable to be declined when using the technique continuously. Accordingly, we conducted an aeration study to explore the mechanism of the bamboo recession. P. praecox were subjected to mulching and aeration treatments for 50 days, antioxidant enzymes, anaerobic respiratory metabolizing enzymes, and photosynthesis characteristics were investigated in root and leaf tissues. The mulching treatment led to bamboo hypoxia stress, while the aeration improved bamboo growth. Compared with mulching treatment, the aeration treatment significantly increased the soil oxygen content. Aeration treatment led to increases in the bamboo root respiratory activity by 19.74%, but decreased ADH, LDH, PDC, SOD, CAT, APX, GR activities by 64.98%, 36.58%, 57.78%, 21.57%, 33.33%, 22.60%, and 32.06%, respectively. Moreover, the aeration treatment greatly enhanced chlorophyll synthesis and improved bamboo photosynthesis. Soil hypoxia induced by the organic material mulching inhibited bamboo growth, which might be the critical factor in the bamboo recession. Our results indicated aeration was conducive to preventing the degeneration of the P. praecox bamboo forest.

Variation in root growth responses of sweet potato to hypoxia and waterlogging

Climate change increase the probability of soil waterlogging due to severe rainfall. A low oxygen concentration in soil (hypoxia) is a major problem associated with waterlogging, and root development is an important indicator of resistance. However, little is known about the root development responses of sweet potato to hypoxia under waterlogging. In this study, the root hypoxia tolerance of four sweet potato cultivars was investigated using three environments (hydroponics, soil in pots, and upland field). In the hydroponic experiment, at 4 days after transplanting (DAT), the plants were transferred to either normoxia (control) or hypoxia and grown for 7 more days. In the soil pot experiment, seedlings at 7 DAT were grown for another 7 days under one of two treatments: drained (control) or waterlogging conditions. The root systems of individual plants were scanned with an image scanner using the WinRhizo software to measure root morphological traits. All the cultivars were tested for tuberous root performance under field waterlogging conditions imposed at the seedling stage. The obtained results showed that the root development responses to hypoxia were clearly associated and contributed to waterlogging tolerance in sweet potato plants. Of the four sweet potato varieties investigated, we identified Cuc Nhanh as the most waterlogging-tolerant variety and hence, it was noted as a promising and important genetic plant resource. The results of this study on root responses, hypoxia, and waterlogging relationships are fundamental towards exploring the mechanisms underlying hypoxia and waterlogging adaptation.

Mitigation of the Impact of Vascular Wilt and Soil Hypoxia on Cape Gooseberry Plants by Foliar Application of Synthetic Elicitors

Physalis peruviana L. crops are exposed to different stress conditions that limit their productivity. Within these conditions, abiotic stress caused by water and biotic stress by Fusarium oxysporum f. sp. physali (Foph) are frequent at commercial levels. The foliar application of synthetic elicitors can be a tool to mitigate the negative impacts of these stresses. The objective of this study was to evaluate the interaction between Foph inoculation and three foliar applications of brassinosteroids (BR), salicylic acid (SA), and a commercial elicitor based on botanical extracts (BE) of Echinacea purpurea, Potentilla erecta, and Aloe vera on the physiological [stomatal conductance (gS), leaf water potential (Ψwf), chlorophyll fluorescence, and growth] and biochemical [photosynthetic pigments, malondialdehyde (MDA) production, and proline content] responses of cape gooseberry plants subjected to a 6-day waterlogging period. The established treatments were as follows: 1) waterlogged plants without Foph; 2) waterlogged plants with Foph; 3) waterlogged, noninoculated (Foph−) plants treated foliarly with BR, SA, or BE; and 4) waterlogged, inoculated (Foph+) plants treated foliarly with BR, SA, or BE. The results showed that the foliar application of BR or SA reduced vascular wilt development in plants subjected to a hypoxia period. In addition, three applications of BR, SA, or BE favored gS, Ψwf, growth, and chlorophyll fluorescence parameters in cape gooseberry plants under the interaction between Foph and oxygen deficit in the soil. Also, higher photosynthetic pigment and proline contents were observed in plants treated with elicitors under stress combination, whereas a lower MDA production was evidenced in this group of plants. In conclusion, BR, SA, or BE can help mitigate the negative effects of the simultaneous occurrence of Foph and a waterlogging condition for 6 days in cape gooseberry plants.

Energy use efficiency of root growth – a theoretical bioenergetics framework

ABSTRACTMetabolic efficiency of root growth is a crucial physiological parameter, contributing to the amount of photosynthate that plants need to invest into soil exploration. Common measurements of metabolic efficiency usually rely on CO2 respiration measurements with the underlying assumption that all metabolic processes are taking place under aerobic conditions. In this conceptual paper, we introduce energy use efficiency based on the quantification of heat dissipation and energy fluxes as an alternative metric to quantify the metabolic efficiency of root growth. In a theoretical framework, we adopted recently published heat dissipation data from wheat seedlings and show that energy use efficiency decreases in response to (i) soil hypoxia and (ii) increased soil penetration resistance. In contrast to traditional CO2 respiration measurements, heat dissipation measurements account for both aerobic as well as anaerobic respiration in growing roots. Hence, we advocate that the quantification of heat dissipation provides a more complete picture of the metabolic efficiency of root growth than CO2 respiration measurements alone. We therefore propose that energy use efficiency should be included in future studies assessing the metabolic efficiency of root growth.