Decreasing Soil Water Content Research Articles

Habitat loss weakens the positive relationship between grassland plant richness and above-ground biomass.

Habitat loss and fragmentation per se have been shown to be a major threat to global biodiversity and ecosystem function. However, little is known about how habitat loss and fragmentation per se alters the relationship between biodiversity and ecosystem function (BEF relationship) in the natural landscape context. Based on 130 landscapes identified by a stratified random sampling in the agro-pastoral ecotone of northern China, we investigated the effects of landscape context (habitat loss and fragmentation per se) on plant richness, above-ground biomass, and the relationship between them in grassland communities using a structural equation model. We found that habitat loss directly decreased plant richness and hence decreased above-ground biomass, while fragmentation per se directly increased plant richness and hence increased above-ground biomass. Fragmentation per se also directly decreased soil water content and hence decreased above-ground biomass. Meanwhile, habitat loss decreased the magnitude of the positive relationship between plant richness and above-ground biomass by reducing the percentage of grassland specialists in the community, while fragmentation per se had no significant modulating effect on this relationship. These results demonstrate that habitat loss and fragmentation per se have inconsistent effects on BEF, with the BEF relationship being modulated by landscape context. Our findings emphasise that habitat loss rather than fragmentation per se can weaken the positive BEF relationship by decreasing the degree of habitat specialisation of the community.

Habitat loss weakens the positive relationship between grassland plant richness and above-ground biomass

Habitat loss and fragmentation per se have been shown to be a major threat to global biodiversity and ecosystem function. However, little is known about how habitat loss and fragmentation per se alters the relationship between biodiversity and ecosystem function (BEF relationship) in the natural landscape context. Based on 130 landscapes identified by a stratified random sampling in the agro-pastoral ecotone of northern China, we investigated the effects of landscape context (habitat loss and fragmentation per se) on plant richness, above-ground biomass, and the relationship between them in grassland communities using a structural equation model. We found that habitat loss directly decreased plant richness and hence decreased above-ground biomass, while fragmentation per se directly increased plant richness and hence increased above-ground biomass. Fragmentation per se also directly decreased soil water content and hence decreased above-ground biomass. Meanwhile, habitat loss decreased the magnitude of the positive relationship between plant richness and above-ground biomass by reducing the percentage of grassland specialists in the community, while fragmentation per se had no significant modulating effect on this relationship. These results demonstrate that habitat loss and fragmentation per se have inconsistent effects on BEF, with the BEF relationship being modulated by landscape context. Our findings emphasise that habitat loss rather than fragmentation per se can weaken the positive BEF relationship by decreasing the degree of habitat specialisation of the community.

Enhancing Faba Bean Yields in Alpine Agricultural Regions: The Impact of Plastic Film Mulching and Phosphorus Fertilization on Soil Dynamics

Plastic film mulching is widely used in water and temperature-limited regions to enhance crop yields. Phosphorus (P) fertilization can address deficiencies in soil P availability. In this four-year field experiment conducted in an alpine agricultural area, we explored the effects of nitrogen (N) and P supply imbalance on faba bean cultivation, particularly examining intensified N competition between soil microbes and plants. The randomized block design comprised three film mulching treatments—no film mulching with flat planting (NMF), double ridges and furrows mulched with one plastic film (DRM), and three ridges and furrows mulched with one plastic film (TRM)—and three P levels—P0 (0 kg P ha−1), P1 (9.10 kg P ha−1), and P2 (18.2 kg P ha−1). The results indicated that NMF enhanced soil available N and microbial biomass N (MBN) during early growth stages, consequently improving faba bean yield, nodule weight, total N, and microbial biomass carbon (MBC) compared to DRM and TRM. DRM and TRM exhibited higher soil available N and MBN during later growth stages and higher soil temperature and water content, soil water storage (SWS), soil organic C (SOC), and soil C/N ratio than NMF. In NMF and DRM, P fertilization increased grain yield, nodule weight, SOC, total N, soil C/N ratio, soil available N, and MBC but decreased MBN during early growth stages, and decreased soil water content and SWS. TRM exhibited the opposite trend. P fertilization increased soil total P and available P. Overall, NMF combined with P fertilization (~18.2 kg P ha−1) significantly improved faba bean yield. However, it may also accelerate SOC decomposition, highlighting the need to consider N fertilizer application in this alpine agricultural region.

Silicon via fertigation with and without potassium application, improve physiological aspects of common beans cultivated under three water regimes in field

Frequent droughts have led to an expansion of irrigated common bean (Phaseolus vulgaris L.) cultivation areas. An effective strategy to enhance water use efficiency and optimize crop growth is the application of silicon (Si) and potassium (K). However, the interaction between Si dosage, water regimes, and plant potassium status, as well as the underlying physiological mechanisms, remains unknown. This study aimed to assess the effects of Si doses applied via fertigation under various water regimes, in the presence and absence of potassium fertilization, on gas exchange, water use efficiency, and growth of Common beans in field conditions. Two experiments were conducted, one with and one without K supply, considering that the potassium content in the soil was 6.4 mmolc dm-3 in both experiments and a replacement dose of 50 kg ha was applied in the with K treatment, with the same treatments evaluated in both potassium conditions. The treatments comprised a 3 × 4 factorial design, encompassing three water regimes: 80% (no deficit), 60% (moderate water deficit), and 40% (severe water deficit) of soil water retention capacity, and four doses of Si supplied via fertigation: 0, 4, 8, and 12 kg ha−1. Where it was evaluated, content of photosynthetic pigments, fluorescence of photosynthesis, relative water content, leaf water potential and electrolyte extravasation, dry mass of leaves, stems and total. The optimal doses of Si for fertigation application, leading to increased Si absorption in plants, varied with decreasing soil water content. The respective values were 6.6, 7.0, and 7.1 kg ha−1 for the water regimes without deficit, with moderate water deficit, and with severe water deficit. Fertigation application of Si improved plant performance, particularly under severe water deficit, regardless of potassium status. This improvement was evident in relative water content, leaf water potential, and membrane resistance, directly impacting pigment content and gas exchange rates. The physiological effects resulted in enhanced photosynthesis in water-deficient plants, mitigating dry mass production losses. This research demonstrates, for the first time in common bean, the potential of Si to enhance irrigation efficiency in areas limited by low precipitation and water scarcity.

Transcriptomic and metabolomic analysis of grain weight potential induced by water stress in wheat

The sink strength of developing ovary in wheat determines the grain weight potential. The period from booting to grain setting stage is critical for the growth and development of ovary and potential sink capacity determination. However, the underlying regulation mechanism during this period by which wheat plant balance and coordinate the florets number and ovary/grain weight under water stress has not been clarified. Therefore, we designed two irrigation treatments W0 (no seasonal irrigation) and W1 (additional 75 mm irrigation at jointing stage), and analyzed the responses of the ovary/grain weight to water stress covering the phenotypic, metabolomic, and transcriptomic levels. Results showed that W0 irrigation treatment decreased soil water content, plant height, and green area of flag leaf, thus reduced grain number, especially the inferior grain, but improved the grain weight of superior grain and inferior grain as well as average grain weight at maturity, meanwhile the average ovary/grain weight and volume during -3 to 10 days after anthesis (DAA) also increased. Transcriptomic analysis indicated that the genes involved in both the sucrose metabolism and phytohormone signal transduction were prominently accelerated by W0 treatment, accompanied by increased enzyme activities of soluble acid invertase (SAI) and sucrose synthase (Sus) and elevated abscisic acid (ABA) and indole-3-acetic acid (IAA) levels. The sucrose content was thus decreased, while glucose and fructose content were increased. In addition, several TaTPP genes (especially TaTPP-6) were downregulated and the IAA biosynthesis genes TaTAR1 and TaTAR2 genes were upregulated under W0 treatment before anthesis, which improved IAA level further. Collectively, water stress reduced vegetative organs growth and eliminated most of the inferior grains, but improved the ABA and IAA levels of the surviving ovaries/grains, promoting enzyme activity of Sus and degrading sucrose into glucose and fructose; as a result, the strong sucrose utilization ability, the enhanced enzyme activity of SAI and the ABA- and IAA-mediated signaling jointly improved the weight and volume of surviving ovaries/grains, and finally achieved the trade-off between ovary/grain weight and number in wheat under water stress.

Management impacts on whole soil warming responses of CO2 production and efflux in temperate climate

Although global warming has the potential to increase soil CO2 efflux, the magnitude of these changes are uncertain, as CO2 production rates in deep soil are poorly constrained. In particular, management effects on the warming responses at depth are unknown. Here, we conducted an in-situ soil warming experiment down to 2.0-m depth in an agricultural Cambisol to study the warming responses of (1) CO2 production across different depths and (2) CO2 efflux from topsoil in different seasons under two management practices. To this end, we measured whole-soil profile water content, CO2 production and CO2 efflux under continuous grassland and cropland in response to elevated temperature (+4°C).Warming decreased soil water content for both management practices. We found contrasting warming effects on surface CO2 efflux, depending on season and land management practices. Subsoil CO2 production was more sensitive to warming than topsoil CO2 production with grassland subsoil showing a greater warming response than cropland subsoil. Topsoil CO2 production decreased in response to warming in the cropland but not the grassland. We concluded that warming responses of CO2 production and efflux are affected by soil management practices. Their effect on biological processes (roots and microbial activity) and factors affecting gas diffusivity, such as soil water availability and soil physical organization need to be assessed to model warming effects on carbon exchange between soil and the atmosphere in agricultural systems.

Artificial light at night (ALAN) causes shifts in soil communities and functions.

Artificial light at night (ALAN) is increasing worldwide, but its effects on the soil system have not yet been investigated. We tested the influence of experimental manipulation of ALAN on two taxa of soil communities (microorganisms and soil nematodes) and three aspects of soil functioning (soil basal respiration, soil microbial biomass and carbon use efficiency) over four and a half months in a highly controlled Ecotron facility. We show that during peak plant biomass, increasing ALAN reduced plant biomass and was also associated with decreased soil water content. This further reduced soil respiration under high ALAN at peak plant biomass, but microbial communities maintained stable biomass across different levels of ALAN and times, demonstrating higher microbial carbon use efficiency under high ALAN. While ALAN did not affect microbial community structure, the abundance of plant-feeding nematodes increased and there was homogenization of nematode communities under higher levels of ALAN, indicating that soil communities may be more vulnerable to additional disturbances at high ALAN. In summary, the effects of ALAN reach into the soil system by altering soil communities and ecosystem functions, and these effects are mediated by changes in plant productivity and soil water content at peak plant biomass. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Biodegradable mulch films improve yield of winter potatoes through effects on soil properties and nutrients

Biodegradable mulch films are recognized as a promising substitute of polyethylene (PE) films to alleviate the “white pollution”. Biodegradable mulch films with optimum degradation rates increase crop yield even compared to PE films. However, the mechanisms underlying this yield-increasing effect remains elusive. In this study, three biodegradable film treatments (BFM1, BFM2 and BFM3) and one PE film treatment (PFM) were used to evaluate their effects on soil and winter potatoes, and a partial least squares path model (PLS-PM) was constructed to investigate their relationships. The degradation rates of films under different treatments were ranked as BFM3 > BFM2 >BFM1 > PFM, and presented distinctive effects on soil properties and nutrients, structure of soil bacterial community, and yield traits of winter potatoes. The PLS-PM showed that mulch treatments affected potato yield through effects on soil properties (soil water and temperature) and soil nutrients (TOC, DOC, TN and NO3--N). The disintegration of the biodegradable films decreased soil water content and temperature, and reduced the loss of soil nutrients in the topsoil at the later growth stage of winter potatoes compared to PE films. Additionally, the elevated content of soil TN and NO3--N under treatment BFM1 may play a key role in its yield-increasing effect on potatoes compared to treatments PFM and BFM2. Thus, biodegradable mulch films with proper degradation rates regulate soil TN and NO3--N through their effects on soil water and temperature, and subsequently improve the yield of winter potatoes compared to PE mulch films.

Temporal effects of thinning on soil organic carbon and carbon cycling-related enzyme activities in oak-pine mixed forests

Thinning, a common practice in forest management, has complex effects on soil organic carbon dynamics. In this study, we examined the effects of precommercial thinning on soil organic carbon (SOC) and carbon cycling-related enzyme activities in a thinning chronosequence (4–12 year recovery period) of oak-pine mixed forests in the Qinling Mountains, China. Three treatments were selected, namely, the control (CK) with no thinning, the a4 treatment (thinning 4 years ago), and the a12 treatment (thinning 12 years ago). Soil physicochemical properties, such as SOC, microbial biomass carbon (MBC), easily oxidizable organic carbon (EOC), dissolved organic carbon (DOC), and carbon cycling-related enzyme activities (hydrolase: β-glucosidase [BG], cellobiohydrolase [CBH], and invertase [INV]), were assessed. Our results indicated that thinning significantly reduced SOC by an average of 51.67% in a4 compared to CK, whereas SOC in a12 gradually returned to the unthinned level. The levels of EOC, MBC, BG, and CBH were significantly lower under the a4 and a12 treatments than under the CK treatment. Furthermore, the level of MBC was significantly higher in the a12 treatment than in the a4 treatment. There were no significant differences in DOC or INV among treatments. The structural equation model showed that thinning might regulate SOC by initially decreasing soil water content, MBC, and carbon cycling-related enzyme activities, followed by them gradually recovering to unthinned levels. These findings provide a scientific basis for understanding the response of SOC to forest thinning.

Rock fragment content alters spatiotemporal patterns of soil water content and temperature: Evidence from a field experiment

Soil water and temperature play a crucial role on hydrological and heat cycling in terrestrial ecosystems, yet rock fragment content in affecting soil water content, temperature, and their relationship is still poorly understood, particularly in dynamic water-heat environments in stony region. In this study, we conducted a field experiment with rock fragment content ranging from 0% to 75%, and investigated soil water content and soil temperature across soil profiles from 2018 to 2022. Soil water content and temperature showed apparent spatiotemporal dynamics under varying rock fragment content. Increased rock fragment content significantly decreased soil water content, but the effect in wet season was stronger than that in dry season. Soil water content increased first and then decreased with increasing soil depths in the conditions of 0% and 25% rock fragment content, but monotonically increased in soils with 50% and 75% rock fragment content. Presence of rock fragment raised annual mean soil temperature, and rock fragment content posed various impacts on soil temperature which depended on seasons and soil layers. Among the rock fragment content gradient, 25% rock fragment content posed a consecutive warming effect on soils in each season. Negative correlation between soil water content with soil temperature was observed both in 10 cm and 30 cm soil layers during wet season, while positive correlation in 30 cm soil layer during dry season. These results indicated that rock fragment content can drive the change in spatiotemporal patterns of soil water content and temperature, and presence of rock fragment strengthened coupling relationship between soil water content and temperature during the wet period.

Metatranscriptomic response of the wheat holobiont to decreasing soil water content

Crops associate with microorganisms that help their resistance to biotic stress. However, it is not clear how the different partners of this association react during exposure to stress. This knowledge is needed to target the right partners when trying to adapt crops to climate change. Here, we grew wheat in the field under rainout shelters that let through 100%, 75%, 50% and 25% of the precipitation. At the peak of the growing season, we sampled plant roots and rhizosphere, and extracted and sequenced their RNA. We compared the 100% and the 25% treatments using differential abundance analysis. In the roots, most of the differentially abundant (DA) transcripts belonged to the fungi, and most were more abundant in the 25% precipitation treatment. About 10% of the DA transcripts belonged to the plant and most were less abundant in the 25% precipitation treatment. In the rhizosphere, most of the DA transcripts belonged to the bacteria and were generally more abundant in the 25% precipitation treatment. Taken together, our results show that the transcriptomic response of the wheat holobiont to decreasing precipitation levels is stronger for the fungal and bacterial partners than for the plant.

Revealing the Effect of Saline Water Drip Irrigation on Soil Microorganisms in Cotton Fields Based on Metagenomics

Saline water irrigation has become an important means to alleviate the shortage of freshwater in arid areas. However, long-term saline water irrigation can cause soil salinity accumulation, affect soil microbial community structure, and then affect soil nutrient transformation. In this study, we used metagenomics to investigate the effects of long-term saline water drip irrigation on soil microbial community structure in a cotton field. In the experiment, the salinity of irrigation water (ECw) was set to two treatments:0.35 dS·m-1 and 8.04 dS·m-1 (denoted as FW and SW, respectively), and the nitrogen application rates were 0 kg·hm-2and 360 kg·hm-2 (denoted as N0 and N360, respectively). The results showed that saline water irrigation increased soil water content, salinity, organic carbon, and total nitrogen content and decreased soil pH and available potassium content. Nitrogen fertilizer application increased soil organic carbon, salinity, and total nitrogen content and decreased soil water content, pH, and available potassium content. The dominant bacterial phyla in each treatment were:Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, and Gemmatimonadetes. Saline water irrigation significantly increased the relative abundances of Actinobacteria, Chloroflexi, Gemmatimonadetes, and Firmicutes but significantly decreased the relative abundances of Proteobacteria, Acidobacteria, Cyanobacteria, and Nitrospira. Nitrogen fertilizer application significantly increased the relative abundances of Chloroflexi and Nitrospira but significantly decreased the relative abundances of Acidobacteria, Gemmatimonadetes, Planctomycetes, Cyanobacteria, and Verrucomicrobia. LEfSe analysis showed that saline water irrigation had no significant effect on the number of potential biomarkers, and nitrogen fertilizer application decreased the number of potential biomarkers in soil microbial communities. The correlation network diagram showed that the 20 genera had different degrees of correlation, including 44 positive correlations and 48 negative correlations. The core species in the network diagram were Nocardioides, Streptomyces, Pyrinomonas, Candidatus_Solibacter, and Bradyrhizobium spp. Saline water irrigation increased the relative abundances of the denitrification genes nirK, nirS, nasB, and norC and decreased the relative abundances of the nitrification genes amoB, amoC, and nxrA, whereas nitrogen fertilizer application increased the relative abundances of the nitrification genes amoA, amoB, amoC, hao, and nxrA and decreased the relative abundances of the denitrifying genes narB, napA, nasA, and nosZ. Saline water irrigation could adversely affect soil physicochemical properties; SWC, EC1:5, and BD were the main driving factors affecting soil microbial community structure and function genes; and soil microorganisms adapted to soil salt stress by regulating species composition.

Herbaceous plant species and their combinations positively affect soil microorganisms and processes and modify soil physicochemical properties in a mesocosm experiment

Although herbaceous plant species have the potential to affect soil abiotic and biotic properties, and thus ecosystem processes, they still remain an underappreciated component of forest ecosystems. We performed an outdoor pot experiment to assess the influence of four herbaceous plant species and their combinations on beech and riparian forest soils. The following plant cover treatments were used in the experiment: (1) bare (unplanted) soil, (2) Aegopodium podagraria, (3) Allium ursinum, (4) Anemone nemorosa, (5) Ficaria verna, (6) two-species combination (A. podagraria + A. ursinum), and (7) four-species combination. After 15 months of the experiment, the soils were collected from the pots and analyzed for microbiological properties, i.e., basal respiration, substrate-induced respiration (SIR), phospholipid fatty acid (PLFA) concentrations, enzymatic activity, and physicochemical properties, including moisture, pH, total and available nutrient contents. Herbaceous plants strongly influenced beech and riparian forest soils. Plant growth, either in monocultures or in combinations, resulted in high microbial performance. On the contrary, bare soils were characterized by the lowest values of many microbial indices. Overall, species combinations and A. podagraria had the strongest positive effects on microbes and processes, though the latter mainly in riparian soil; they increased PLFA-biomass (total, bacteria, G+ and G- bacteria, saprotrophic fungi), SIR-biomass, soil respiration, acid phosphatase, alkaline phosphatase, arylsulfatase, and/or urease activity. Plant species combinations and A. podagraria (in riparian soil) also stood out from other treatments in their effects on soil physicochemical properties, decreasing soil water content and the availability of some nutrients (N-NO3, P-PO4). Moreover, A. podagraria increased organic C and total N in riparian soil. Concluding, our experiment showed that the presence of herbaceous plant species positively influences microbes in beech and riparian forest soils, and this effect becomes stronger as plant species diversity increases. Herbaceous plant species are an important component of temperate forests because they play a significant role in supporting soil microorganisms and processes, maintaining soil health in these ecosystems. As such, they should be included in forest management practices.

Asymmetric responses of biocrust respiration to precipitation manipulation under a changing semiarid climate

Global climate change is expected to cause both increased and reduced precipitation in the next decades, especially in drylands with semi-arid climates. Biocrusts are an essential soil surface cover in global drylands, and they strongly influence most soil properties and support fundamental ecosystem functions, especially soil carbon (C) cycling. Nevertheless, the response patterns and mechanisms of biocrust respiration rate (Rs) to precipitation changes remain uncertain under changing semi-arid climates. In our study, a field experiment for biocrusts with natural precipitation (CK) and six levels of precipitation manipulation (–50 %, –30 %, –10 %, +10 %, +30 %, and +50 % of CK) were conducted from 2019 to 2021 in a semi-arid climate region of the northern Chinese Loess Plateau. We continuously measured the biocrust Rs of all the treatments in the growing seasons, and the fundamental properties of biocrusts and their temperature and water content at 5 cm depth were also measured. Our results showed that the increased precipitation inhibited biocrust Rs, while moderately reduced precipitation stimulated biocrust Rs. As compared with the CK, the precipitation manipulations of +10 %, +30 %, and +50 % decreased biocrust Rs by 8.9 %, 15.3 %, and 22.1 %, respectively, while the treatments of –10 % and –30 % increased biocrust Rs by 25.5 % and 8.0 %, respectively. However, the precipitation manipulation of –50 % suppressed biocrust Rs by 19.3 %. More importantly, the responses of biocrust Rs to precipitation changes were negative and asymmetric, which indicated a higher sensitivity of biocrust Rs to reduced precipitation in comparison to increased precipitation. Moreover, the increased precipitation (+10 % to + 50 %) raised soil water content (by 29.7 %–55.0 %), moss biomass (by 12.5 %–50.0 %), and organic matter content (by 11.3 %–12.4 %). In contrast, the reduced precipitation (–10 % to –30 %) decreased soil water content (by 5.2 %–17.6 %) and moss biomass (by 12.5 %–25.8 %). The structural equation modeling analysis showed that the responses of biocrust Rs to precipitation manipulation were mainly and directly influenced by soil temperature and biocrust properties. Although soil water content did not have a direct significant effect on biocrust Rs, it indirectly influenced biocrust Rs by affecting the fundamental properties of soil and biocrusts. Consequently, the changed soil properties and biocrust characteristics caused by precipitation shifts aggravated the negative responses of biocrust Rs to precipitation manipulation. Our findings emphasize that biocrusts have a negative and asymmetric response of Rs to precipitation changes, implying that the intensified precipitation variation in semi-arid regions caused by global climate change in future may positively affect the stability of soil C stocks contributed by biocrusts and thus reduce soil C efflux in drylands.

Applicability of the microdialysis technique in dry soils: Impact of soil water content depends on perfusion flow rate

Plant nutrient acquisition largely depends on the availability and constant replenishment of nutrients at root surfaces. The main process providing nutrients for root uptake is diffusion which is critically affected by soil physicochemical and biological factors. The effective diffusion path length increases with decreasing soil water content thus limiting diffusive nutrient supply in dry soils. Microdialysis, an increasingly popular sampling tool for monitoring nutrient fluxes in soil in situ, could be used to measure such a limitation provided it operates reliably under dry soil conditions. However, due to its mode of operation, the performance of microdialysis could be impeded in dry soils since a significant amount of perfusate might be lost via leaching to the surrounding soil. Until now, however, no data is available on the applicability of microdialysis in dry soils. In this project, we estimated leaching losses of perfusate to eight soils with different texture maintained at 10, 20, 30, 50 and 80% (w/w) of maximum water-holding capacity in dependence of perfusion flow rate. We found that microdialysis operates reliably even in dry soils when using a high perfusion flow rate (10 μl min−1). At lower perfusion flow rates (1 or 5 μl min−1), however, significant amounts of perfusate were leaching out to soils. Diffusive fluxes of nitrate and ammonium were strongly affected by soil water content, but not fluxes of phosphate. Even at the highest flow rate (where no losses of perfusate where observed) concentrations of both inorganic N forms in dialysates decreased with decreasing soil water content. Overall, we conclude that microdialysis can be applied in dry soils without high risk of perfusate leaching when a high perfusion flow rate (10 μl min−1) is used. Further, our results highlight that microdialysis can be used in much dryer soils than previously suggested (70% MWHC) and allows monitoring the effect of soil water content on nutrient supply for root uptake via diffusion.

Metatranscriptomic response of the wheat holobiont to decreasing soil water content

Metatranscriptomic response of the wheat holobiont to decreasing soil water content

Canopy Transpiration and Stomatal Conductance Dynamics of Ulmus pumila L. and Caragana korshinskii Kom. Plantations on the Bashang Plateau, China

Constructing protective forests to control water and soil erosion is an effective measure to address land degradation in the Bashang Plateau of North China, but forest dieback has occurred frequently due to severe water deficits in recent decades. However, transpiration dynamics and their biophysical control factors under various soil water contents for different forest functional types are still unknown. Here, canopy transpiration and stomatal conductance of a 38-year-old Ulmus pumila L. and a 20-year-old Caragana korshinskii Kom. were quantified using the sap flow method, while simultaneously monitoring the meteorological and soil water content. The results showed that canopy transpiration averaged 0.55 ± 0.34 mm d−1 and 0.66 ± 0.32 mm d−1 for U. pumila, and was 0.74 ± 0.26 mm d−1 and 0.77 ± 0.24 mm d−1 for C. korshinskii in 2020 and 2021, respectively. The sensitivity of canopy transpiration to vapor pressure deficit (VPD) decreased as soil water stress increased for both species, indicating that the transpiration process is significantly affected by soil drought. Additionally, canopy stomatal conductance averaged 1.03 ± 0.91 mm s−1 and 1.34 ± 1.22 mm s−1 for U. pumila, and was 1.46 ± 0.90 mm s−1 and 1.51 ± 1.06 mm s−1 for C. korshinskii in 2020 and 2021, respectively. The low values of the decoupling coefficient (Ω) showed that canopy and atmosphere were well coupled for both species. Stomatal sensitivity to VPD decreased with decreasing soil water content, indicating that both U. pumila and C. korshinskii maintained a water-saving strategy under the stressed water conditions. Our results enable better understanding of transpiration dynamics and water-use strategies of different forest functional types in the Bashang Plateau, which will provide important insights for planted forests management and ecosystem stability under future climate changes.

Variety-specific response of bulk stomatal conductance of grapevine canopies to changes in net radiation, atmospheric demand, and drought stress.

In wine growing regions around the world, climate change has the potential to affect vine transpiration and overall vineyard water use due to related changes in daily atmospheric conditions and soil water deficits. Grapevines control their transpiration in response to such changes by regulating conductance of water through the soil-plant-atmosphere continuum. The response of bulk stomatal conductance, the vine canopy equivalent of stomatal conductance, to such changes were studied on Cabernet-Sauvignon, Merlot, Tempranillo, Ugni blanc, and Semillon vines in a non-irrigated vineyard in Bordeaux France. Whole-vine sap flow, temperature and humidity in the vine canopy, and net radiation absorbed by the vine canopy were measured on 15-minute intervals from early July through mid-September 2020, together with periodic measurements of leaf area, canopy porosity, and predawn leaf water potential. From these data, bulk stomatal conductance was calculated on 15-minute intervals, and multiple linear regression analysis was performed to identify key variables and their relative effect on conductance. For the regression analysis, attention was focused on addressing non-linearity and collinearity in the explanatory variables and developing a model that was readily interpretable.Variability of vapour pressure deficit in the vine canopy over the day and predawn water potential over the season explained much of the variability in bulk stomatal conductance overall, with relative differences between varieties appearing to be driven in large part by differences in conductance response to predawn water potential between the varieties. Transpiration simulations based on the regression equations found similar differences between varieties in terms of daily and seasonal transpiration. These simulations also compared well with those from an accepted vineyard water balance model, although there appeared to be differences between the two approaches in the rate at which conductance, and hence transpiration is reduced as a function of decreasing soil water content (i.e., increasing water deficit stress). By better characterizing the response of bulk stomatal conductance, the dynamics of vine transpiration can be better parameterized in vineyard water use modeling of current and future climate scenarios.

Potential soil methane oxidation in naturally regenerated oak-dominated temperate deciduous forest stands responds to soil water status regardless of their age—an intact core incubation study

Key messagePotential CH4 oxidation in the top soil layer increased with decreasing soil water content in spring but was inhibited during severe summer drought in naturally-regenerated oak-dominated temperate deciduous forest stands regardless of their age. No direct effect of mineral nitrogen on soil CH4 oxidation was found. Soil CH4 oxidation in temperate forests could be reduced by extreme climatic events.ContextThe oxidation of atmospheric methane (CH4) by methanotrophic bacteria in forest soils is an important but overlooked ecosystem service.AimOur objective was to determine which factors drive variations in soil CH4 oxidation in oak-dominated temperate deciduous forest stands of different ages.MethodsSoil samples were collected in 16 stands aged 20 to 143 years in periods of high and low soil water content (SWC). The potential rate of soil CH4 oxidation was measured by incubating the first five centimetres of intact soil cores at 20 °C.ResultsSWC was the main driver accounting for variations in CH4 oxidation. In spring, a two-fold reduction in SWC greatly increased CH4 oxidation. But when the soil was dry in late summer, a further reduction in SWC led to a decrease in CH4 oxidation in the top soil layer. No direct effect of mineral nitrogen on soil CH4 oxidation was found.ConclusionsWith regard to soil CH4 oxidation, naturally regenerated forest stands contribute equally to climate change mitigation regardless of their age. Considering future climate scenarios for Europe, soil CH4 sink in temperate forests could be reduced, due to both an increase in the number of flooding episodes in spring and drier summers.

Effect of shrub encroachment on land surface temperature in semi-arid areas of temperate regions of the Northern Hemisphere

Under the influences of climate change and human activities, grassland ecosystems are being invaded by shrubs around the world, especially in temperate semi-arid regions of the Northern Hemisphere. Shrub encroachment can not only affect the properties of grassland ecosystem, but also have an important impact on regional or global climate by affecting biogeochemical and biophysical processes. Although shrub encroachment has become a serious ecological problem in the northern temperate region during the past decades, the possible effects of shrub encroachment on regional climate in northern temperate grasslands remain unclear due to a lack of in situ and long-term environmental records. Based on the satellite-derived land use data, land surface temperature (LST), evapotranspiration, leaf area index, and albedo data, this study quantified, for the first time, the biophysical effects of shrub encroachment on regional climate in semi-arid areas of temperate regions of the Northern Hemisphere. The results indicate that shrub encroachment tends to increase the average annual daytime and mean LST in most of the northern temperate semi-arid region due to increased bare soil fraction. In contrast, shrub encroachment could decrease the daytime LST in relatively humid region of southwest of North America by increasing evapotranspiration (vegetation coverage) and decreasing bare soil fraction. In the arid center region of Central Asia, grassland conversion to shrubland slightly decreases the surface temperature during both daytime and nighttime due to increased albedo caused by decreasing soil water content. Our findings imply that the biophysical effects of shrub encroachment on regional climate should be considered in climate models if they are to accurately simulate climate change in temperate regions of the Northern Hemisphere. More attention should be paid to the climate feedbacks of shrub encroachment, especially considering the distinct effects in different regions and how these climate feedbacks are likely to further impact ecosystem properties.