Low Soil Moisture Research Articles

Feasibility and limitation of calculative determination of hygrothermal conditions in historical buildings: Case study of st. Martin church in Wiśniowa

The aim of this paper is to examine the perspective of implementing of the calculation model to forecast the inner climate development in historic buildings. Accuracy of calculations is very important issue, as environmental factors, especially air temperature and moisture, strongly influence condition of building and collection. Hence, the indoor conditions in a 18th century wooden church in Wiśniowa (Poland) as well as the external climate were monitored over three years. The results of year-round simulations were compared with the results of experimental studies and referred to the assessment criteria indices (among others Normalized Mean Bias Error, Coefficient of Variation of the Root Mean Square Error, Coefficient of Determination and Goodness of Fit) and the conservation criteria of the model accuracy. As a result of model calibration, sufficient compliance was obtained except for Goodness of Fit. The key turned out to consider the mass of the wooden furnishings and altars, lowering soil moisture and increasing the precision of determining internal heat and moisture gains.

Drought, axe and goats. More variable and synchronized growth forecasts worsening dieback in Moroccan Atlas cedar forests

Understanding how climate warming and land-use changes determine the vulnerability of forests to drought is critical. However, we still lack: (i) robust quantifications of long-term growth changes during aridification processes, (ii) links between growth decline, changes in forest cover, stand structure and soil conditions, and (iii) forecasts of growth variability to projected climate warming. We investigated tree-ring records over the past 400–700 years, quantified changes in grazing area and forest cover during the 20th century, sampled current stand structure, and analyzed soil organic carbon δ13C and total nitrogen δ15N of Atlas cedar (Cedrus atlantica (Endl.) Manetti ex Carrière) Moroccan forests to characterize their dieback. Atlas cedar forests experienced massive dieback after the 1970s, particularly in the xeric High Atlas region. Forest cover increased in the less xeric regions (Middle Atlas and Rif) by almost 20%, while it decreased about 18% in the High Atlas, where soil δ13C and δ15N showed evidences of grazing. Growth declined and became more variable in response to recent droughts. The relative growth reduction (54%) was higher in the Middle Atlas than elsewhere (Rif, 32%; High Atlas, 36%). Growth synchrony between forests located within the Middle and High Atlas regions increased after the 1970s. Simulations based on a worst-case emission scenario and rapid warming forecast a stronger limitation of growth by low soil moisture in all regions, but particularly in the Middle Atlas and after the mid-21st century. Climate warming is expected to strengthen growth synchronization preceding dieback of conifer forests in xeric regions. The likelihood of similar dieback episodes is further exacerbated by historical degradation of these forests.

Variations in the top-layer soil freezing/thawing process from 2009 to 2018 in the Maqu area of the Tibetan Plateau

Considerable progress has been made in understanding the variation rules of the freezing/thawing period and soil water-heat exchange. With the use of meteorological and soil observation data, this study highlighted the importance of vegetation cover and soil moisture for the beginning of the freezing/thawing period, and an improved calculation equation of the soil moisture content was presented, which could be used to simulate the variation in soil moisture during the freezing/thawing period. Our analyses showed that the temperature changes at the beginning of the soil freezing month (December) and the soil thawing month (February) were significantly different from 2009 to 2018. The rate of air temperature increase in December reached 0.38 °C/a. However, the air temperature in February changed little. As a result, the beginning of the soil freezing period was clearly lagged, while the beginning of the soil thawing period fluctuated little. The total soil thawing time increased by 25 days over 10 years. Furthermore, it was shown that the surface vegetation cover and soil moisture affected the beginning of the freezing/thawing time. In general, the soil freezing/thawing state at sites with low vegetation cover and soil moisture content was more likely to change. To further study the freezing/thawing mechanism, the relationship between the soil temperature and soil moisture during the freezing/thawing period was expressed as a fitting function of the relationship between soil water and heat. It was shown that the relationship between the soil moisture and soil temperature followed the new fitting function in both warm and cold years.

Water Use Efficiency of Acacia seyal (Del.) in extreme arid environment prevails in South-Western Desert, Egypt

The present investigation involves the studies of water use efficiency of Acacia seyal (Del.) seedlings under extreme arid conditions. Experiments were performed in a hyper arid environment to study the effects of drought stress using different water regimes at 12%, 9%, 6%, 4% and 2%. Calculated instantaneous water use efficiency was measured under full Photosynthetic Active Radiation range (0-2500μmols-1m-2). Acacia seyal showed maximum photosynthesis rate at 9% soil moisture content, and at high Photosynthetic Active Radiation levels. Maximum transpiration rate recorded at 9% soil moisture content at highest Photosynthetic Active Radiation. The maximum instantaneous water use efficiency was noticed at 4% soil moisture content at high Photosynthetic Active Radiation level. Acacia seyal maximized photosynthesis rate and minimized transpiration rate, giving maximum instantaneous water use efficiency at the high Photosynthetic Active Radiation and low soil moisture content levels.

Soil moisture dominates dryness stress on ecosystem production globally

Dryness stress can limit vegetation growth and is often characterized by low soil moisture (SM) and high atmospheric water demand (vapor pressure deficit, VPD). However, the relative role of SM and VPD in limiting ecosystem production remains debated and is difficult to disentangle, as SM and VPD are coupled through land-atmosphere interactions, hindering the ability to predict ecosystem responses to dryness. Here, we combine satellite observations of solar-induced fluorescence with estimates of SM and VPD and show that SM is the dominant driver of dryness stress on ecosystem production across more than 70% of vegetated land areas with valid data. Moreover, after accounting for SM-VPD coupling, VPD effects on ecosystem production are much smaller across large areas. We also find that SM stress is strongest in semi-arid ecosystems. Our results clarify a longstanding question and open new avenues for improving models to allow a better management of drought risk.

Dung beetle species introductions: when an ecosystem service provider transforms into an invasive species.

Dung beetle introduction programmes were designed to accelerate exotic livestock dung degradation and to control dung breeding pestiferous flies and livestock parasites. The introduction programmes provided exotic dung beetle species with an opportunity to cross natural barriers and spread beyond their native range. There are no reports that explain what probable adaptation mechanisms enable particular dung beetle species to be the most successful invader. Here we identify the morphological, biological, physiological, ecological and behavioural attributes of the four most widespread and successful dung beetle species in introduced areas on a global scale in relation to the assumption that these species are different from other exotic and native dung beetles. We have recognised Digitonthophagus gazella (Fabricius), Onthophagus taurus (Schreber), Euoniticellus intermedius (Reiche) and Aphodius fimetarius (Linnaeus) as the most successful invaders based on their spread, predominance, distribution range and the reports of invasion. Each of these four species has different natural history traits that increase their fitness making them successful invaders. D. gazella has high fecundity and spreading ability, can instantly locate and colonise fresh and nutritious dung, and has a broad thermal window. O. taurus has morphological plasticity, high fecundity, high brood survival rate due to bi-parenting, and is adapted to extreme thermal and moisture conditions. E. intermedius has remnant-dung feeding abilities, a wide thermal window, functioning best at upper-temperature levels, and successful breeding and survival abilities at extremely low soil moisture conditions. A. fimetarius is small-sized, has high breeding and dispersal abilities, and is adapted to lower thermal and upper moisture extremes and variable soil conditions. Discussed here are perspectives on adaptive attributes of dung beetle species that are important to consider during their selection for redistributions. We have elaborated on the fitness and success characteristics of the four species individually. Further, we recommend a prior-introduction baseline monitoring of native dung beetle assemblages so as to evaluate the future impact of exotic dung beetle introductions on the recipient ecosystem.

Heat shock protein and aquaporin expression enhance water conserving behavior of citrus under water deficits and high temperature conditions

Citrus is most important fruit crop of the world grown throughout the subtropics and semi-arid to humid tropics. Water deficit and high temperature are two major abiotic stresses that affect the plant physiology negatively and ultimately reduced crop yield and performance. The objective of this study was to evaluate the responses of ten genetically diverse citrus selections against the water deficit, heat, and their combinations. Treatments consisted of moderate and high heat (38 °C and 46 °C), water deficit (50% and 25% field capacity) and combined (38 °C with 50% field capacity and 46 °C with 25% field capacity) stress. We measured the effects of water potential, moisture contents and gas exchange on the expression of heat shock proteins (HSPs) and major intrinsic proteins (MIPs). Brazilian sour orange (Citrus aurantium L.) and Keen sour orage (C. aurantium L) performed well by avoiding desiccation and maintaining photosynthesis, stomatal conductance, water potential and moisture content under high temperature and low soil moisture. While, Savage citrange (Poncirus trifoliata × Citrus sinensis) proved the most sensitive to all stress conditions. Genome wide analysis indicated that CsHsp70 had NBD sugar kinase actin Hsp70 protein and molecular charpones Dnak, while CsHsp70.1 had chloroplast protein with Dnak and CsHsp90 had Hsp90 protein. Brazilian sour orange expressed HSPs under heat, MIPs under water deficit and both under combined stress conditions. CsHsp70, CsHsp70.1 and CsHsp90 showed high expression from 1.5 to 6.0 h and then gradually decreased till 24.0 h under heat and combined stress in Brazilian sour orange. CsHsp70 in Savage citrange exhibited slight expression under heat and combined stress after 6.0 h. High expression of CsTIP2 and CsTIP1 was observed from 1.5 to 24.0 h under water deficit, whereas CsTIP1 expressed under heat and combined stress after 1.5 h. Whereas, Savage citrange exhibited little expression of the same genes under stress. It was concluded that the differences among these varieties are in tolerance to heat and water deficit is associated with capacity for upregulation of HSPs and MIPs.

Hot Pepper Fusarium Wilt (Fusarium oxysporum f. sp. capsici): Epidemics, Characteristic Features and Management Options

Hot pepper (Capsicum annum L.) is one of the important cash crops to Ethiopian smallholder farmers and an important agricultural commodity which contribute to export earnings. In Ethiopia, this high value crop is constrained by powdery mildew, Phytophthora leaf blight, Fusarium wilt, bacterial leaf spot, bacterial wilt, bacterial soft rot and pepper motile virus. Among this diseases, wilt disease caused by Fusarium oxysporum f.sp. capsici (FOC) is one of the major pathogen that constrained production and productivity of hot pepper in Ethiopia mainly the Central Rift valley. In Ethiopia, hot pepper fusarium wilt is reported in all production regions in different magnitude. The highest wilt incidence due to fusarium is 90% in some Farmers association of Alaba districts in South Nation Nationalities and peoples of Ethiopia. The economic yield losses due to Fusarium wilt has been estimated at 68 to 71%. Infection and disease development in Fusarium wilt is favored by warm soil temperature, low soil moisture, susceptible host, virulent pathogen and 5.0 to 6.0 pH levels; are some of epidemic factors. Fusarium is reproduced by sexually by teleomorphs and asexually by microconidia, macroconidia and chlamydospore. From the Central rift valley of Ethiopia, 49 FOC isolates were identified based on micro and macroscopic characteristics and the isolate having pink colony color, 3-5 septa forming conidia on potato dextrose agar, perform the most pathogenic ability to Mareko Fana Variety. This pathogen has an over wintering stage called chlamydospore which can exist in the soil for more than ten years without the host. Hot pepper fusarium wilt can be managed by host resistance, biological agent, botanicals and fungicide. In Ethiopia, pepper screening for resistant source, in vitro evaluation of bioagents and fungicides were done. In this review attempt has been made to summarize relevant scientific studies on this economically important crop, hot pepper fusarium wilt and associated factors in Ethiopia as well as its different disease management options, challenges and future prospects.

Effects of canopy cover and neighboring vegetation on the early development of planted Austrocedrus chilensis and Nothofagus dombeyi in north Patagonian degraded forests

Austrocedrus chilensis and Nothofagus dombeyi, are endemic forest species of ecological and productive importance in the Andean-Patagonian region of Argentina. Both species grow in pure or mixed stands. In the last decades, several A. chilensis stands have been degraded by different disturbances that have compromised their natural regeneration. Plantation of seedlings of both species may be an alternative to help restore degraded A. chilensis stands. In this study we determined, in degraded A. chilensis stands grown in a xeric and a mesic site, the effects of canopy cover, the presence/absence of neighboring herbaceous vegetation and the interaction between these factors, on the performance (i.e. survival and growth) of planted N. dombeyi and A. chilensis seedlings, during three growing seasons. Results showed that in both xeric and mesic sites, survival and growth of either species were reduced when canopy cover was below 30%. Removal of neighboring vegetation improved survival of both species at the xeric site, and improved growth of both species at the mesic site. Canopy cover and removal of neighboring vegetation seem to interact by improving survival and growth of A. chilensis, while for N. dombeyi the effects of these factors, when present, are independent, both improving survival and growth. Austrocedrus chilensis has greater capacity than N. dombeyi to tolerate the high radiation and low soil moisture combination, so this species is more recommendable for planting at most exposed conditions (no canopy cover at xeric sites), but both species could be successfully used for restoring degraded A. chilensis stands.

Spring enhancement and summer reduction in carbon uptake during the 2018 drought in northwestern Europe.

We analysed gross primary productivity (GPP), total ecosystem respiration (TER) and the resulting net ecosystem exchange (NEE) of carbon dioxide (CO2) by the terrestrial biosphere during the summer of 2018 through observed changes across the Integrated Carbon Observation System (ICOS) network, through biosphere and inverse modelling, and through remote sensing. Highly correlated yet independently-derived reductions in productivity from sun-induced fluorescence, vegetative near-infrared reflectance, and GPP simulated by the Simple Biosphere model version 4 (SiB4) suggest a 130–340 TgC GPP reduction in July–August–September (JAS) of 2018. This occurs over an area of 1.6 × 106 km2 with anomalously low precipitation in northwestern and central Europe. In this drought-affected area, reduced GPP, TER, NEE and soil moisture at ICOS ecosystem sites are reproduced satisfactorily by the SiB4 model. We found that, in contrast to the preceding 5 years, low soil moisture is the main stress factor across the affected area. SiB4’s NEE reduction by 57 TgC for JAS coincides with anomalously high atmospheric CO2 observations in 2018, and this is closely matched by the NEE anomaly derived by CarbonTracker Europe (52 to 83 TgC). Increased NEE during the spring (May–June) of 2018 (SiB4 −52 TgC; CTE −46 to −55 TgC) largely offset this loss, as ecosystems took advantage of favourable growth conditions.This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

Primary productivity of managed and pristine forests in Sweden

Land use is affecting 70% of global ecosystems and their functioning. Forest management is a regionally dominant land use and affects forest ecosystems by changing both structure and functioning, but its impact on primary productivity is not well known. Here we investigated the effect of forest management on primary productivity by comparing managed secondary forests with relatively pristine unmanaged primary forests in Sweden. As proxy for primary productivity we used the satellite-based vegetation index NIRv which has been shown to be closely and linearly related to primary productivity. We produced a digital map of 390 primary forests across Sweden, and extracted NIRv over these and surrounding secondary forests forming spatially proximate pairs. By comparing the primary and secondary forests NIRv in the pairs we found that secondary forests on average show higher NIRv, but the highest values were found in primary forests. The difference in NIRv between pairs is related to their difference in mean stand age, and at equal stand age the NIRv of primary forests is higher than in their paired secondary forests. Overall, management leads to increased NIRv through regeneration of forests stands that reduce their mean age. However, primary forests show higher NIRv when controlling for age, despite being found on higher altitudes and on steeper slopes with lower soil moisture, which suggests that forest management other than regeneration is not increasing primary productivity of Swedish forests.

Applicability of cosmic-ray neutron sensor for measuring soil moisture at the agricultural-pastoral ecotone in northwest China

Accurate monitoring of soil moisture is crucial in hydrological and ecological studies. Cosmic-ray neutron sensors (CRNS) measure area-average soil moisture at field scale, filling a spatial scale gap between in-situ observations and remote sensing measurements. However, its applicability has not been assessed in the agricultural-pastoral ecotone, a data scarce semi-arid and arid region in Northwest China (APENC). In this study, we calibrated and assessed the CRNS (the standard N0 method) estimates of soil moisture. Results show that Pearson correlation coefficient, RP, and the root mean square error (RMSE) between the CRNS soil moisture and the gravimetric soil moisture are 0.904 and less than 0.016 m3 m−3, respectively, indicating that the CRNS is able to estimate the area-average soil moisture well at our study site. Compared with the in-situ sensor network measurements (ECH2O sensors), the CRNS is more sensitive to the changes in moisture in its footprint, which overestimates and underestimates the soil moisture under precipitation and dry conditions, respectively. The three shape parameters a0, a1, a2 in the standard calibration equation (N0 method) are not well suited to the study area. The calibrated parameters improved the accuracy of the CRNS soil moisture estimates. Due to the lack of low gravimetric soil moisture data, performance of the calibrated N0 function is still poor in the extremely dry conditions. Moreover, aboveground biomass including vegetation biomass, canopy interception and widely developed biological soil crusts adds to the uncertainty of the CRNS soil moisture estimates. Such biomass impacts need to be taken into consideration to further improve the accuracy of soil moisture estimation by the CRNS in the data scarce areas such as agricultural-pastoral ecotone in Northwest China.

Variations in nitrous oxide emissions as manipulated by plastic film mulching and fertilization over three successive years in a hot pepper-radish rotated vegetable production system

Plastic film mulching (FM) is widely applied in agro-ecosystems to improve soil hydrothermal conditions for better crop productivities. However, effects of such FM practices on nitrous oxide (N2O) emissions are not well known in high nitrogen (N) input vegetable fields. Using static chambers under no-mulching (NM) and FM with four N application rates N2O emissions were monitored in a hot pepper (Capsicum annuum)-radish (Raphanus sativus) rotation in southwest China over three years (Cycle 1, 2 and 3) from May 2014 to February 2017. These four N application rates for each vegetable crop were 0, 150, 300 and 450 kg N ha−1 and 0, 100, 200 and 300 kg N ha-1 in the respective hot pepper and radish seasons. Compared to NM, FM insignificantly reduced N2O emissions in the hot pepper season owing to lower soil moisture, while significantly increased N2O emissions in the radish season owing to higher soil NH4++NO3− and temperature. Additionally, FM had no remarkable effects on N2O EFs or crop yields of hot pepper or radish. N application exerted stronger effects on N2O emissions under FM and NM in Cycle 1 than in other two cycles during the hot pepper season owing to higher temperature and rainfall, resulting in very high N2O EFs (2.56 %–7.43 %). The average seasonal EF was 1.52 % (0.15 %–7.43 %), while the average annual EF was 1.74 % (0.16 %–5.32 %), which was comparable to the 2006 IPCC defaulted of 1.00 %. Yield-scaled N2O emissions under FM were significantly increased in the radish season, but not in the hot pepper season. Additionally, N application remarkably increased N2O emissions and crop yields in the hot pepper season, with a bigger effect on N2O emissions than on crop yields, leading to increased yield-scaled N2O emissions with increasing N application between 0 and 450 kg N ha-1. Moreover, the stimulation effect of N application on crop yield was strongest under 150 kg N ha-1 with lower yield-scaled emissions. In addition, N application remarkably increased N2O emissions and crop yields, but were more prominent on crop yields than N2O emissions during the radish season, resulting in insignificant increase of yield-scaled N2O emissions between 0 and 300 kg N ha-1. Our results demonstrated that no-mulching with 150 or 300 kg N ha-1 fertilization in the hot pepper or radish season is a more suitable agronomic practice to simultaneously mitigate N2O emissions while increasing crop yields in subtropical vegetable fields.

Soil Microbiomes With the Genetic Capacity for Atmospheric Chemosynthesis Are Widespread Across the Poles and Are Associated With Moisture, Carbon, and Nitrogen Limitation.

Soil microbiomes within oligotrophic cold deserts are extraordinarily diverse. Increasingly, oligotrophic sites with low levels of phototrophic primary producers are reported, leading researchers to question their carbon and energy sources. A novel microbial carbon fixation process termed atmospheric chemosynthesis recently filled this gap as it was shown to be supporting primary production at two Eastern Antarctic deserts. Atmospheric chemosynthesis uses energy liberated from the oxidation of atmospheric hydrogen to drive the Calvin-Benson-Bassham (CBB) cycle through a new chemotrophic form of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), designated IE. Here, we propose that the genetic determinants of this process; RuBisCO type IE (rbcL1E) and high affinity group 1h-[NiFe]-hydrogenase (hhyL) are widespread across cold desert soils and that this process is linked to dry and nutrient-poor environments. We used quantitative PCR (qPCR) to quantify these genes in 122 soil microbiomes across the three poles; spanning the Tibetan Plateau, 10 Antarctic and three high Arctic sites. Both genes were ubiquitous, being present at variable abundances in all 122 soils examined (rbcL1E, 6.25 × 103–1.66 × 109 copies/g soil; hhyL, 6.84 × 103–5.07 × 108 copies/g soil). For the Antarctic and Arctic sites, random forest and correlation analysis against 26 measured soil physicochemical parameters revealed that rbcL1E and hhyL genes were associated with lower soil moisture, carbon and nitrogen content. While further studies are required to quantify the rates of trace gas carbon fixation and the organisms involved, we highlight the global potential of desert soil microbiomes to be supported by this new minimalistic mode of carbon fixation, particularly throughout dry oligotrophic environments, which encompass more than 35% of the Earth’s surface.

Climatology of Planetary Boundary Layer Height-Controlling Meteorological Parameters Over the Korean Peninsula

Planetary boundary layer (PBL) height plays a significant role in climate modeling, weather forecasting, air quality prediction, and pollution transport processes. This study examined the climatology of PBL-associated meteorological parameters over the Korean peninsula and surrounding sea using data from the ERA5 dataset produced by the European Centre for Medium-range Weather Forecasts (ECMWF). The data covered the period from 2008 to 2017. The bulk Richardson number methodology was used to determine the PBL height (PBLH). The PBLH obtained from the ERA5 data agreed well with that derived from sounding and Global Positioning System Radio Occultation datasets. Significant diurnal and seasonal variability in PBLH was observed. The PBLH increases from morning to late afternoon, decreases in the evening, and is lowest at night. It is high in the summer, lower in spring and autumn, and lowest in winter. The variability of the PBLH with respect to temperature, relative humidity, surface pressure, wind speed, lower tropospheric stability, soil moisture, and surface fluxes was also examined. The growth of the PBLH was high in the spring and in southern regions due to the low soil moisture content of the surface. A high PBLH pattern is evident in high-elevation regions. Increasing trends of the surface temperature and accordingly PBLH were observed from 2008 to 2017.

Consumer control and abiotic stresses constrain coastal saltmarsh restoration

Die-off of coastal wetlands has been reported worldwide. Planting habitat-forming species is an important strategy to reverse the decline of coastal wetlands. However, how abiotic environmental stresses and consumers affect the establishment of the planted vegetation species is unclear. We reported a large-scale restoration project in the Liaohe estuary, China, where native pioneer plant Suaeda salsa was planted. We evaluated the growth performance of the planted S. salsa, and identified the constraints on the establishment of planted S. salsa. Results showed that the growth performance (density, coverage and survival rate) of planted S. salsa was better in the low restored marsh than that in the high restored marsh. The death of planted S. salsa was primarily driven by crab herbivory, followed by abiotic stresses (low soil moisture and high salinity) in the high restored marsh, whereas plant death was only driven by crab herbivory in the low restored marsh. Herbivory strength in the high marsh was significantly higher than that in the low marsh. Our findings challenge the bottom-up paradigm used as the foundation for coastal restoration, and highlight the overlooked role of consumers. Therefore, protection measures against consumer pressure, especially in physically harsh conditions, should be considered to enhance the success of coastal wetland restoration.

The intra- and inter-annual responses of soil respiration to climate extremes in a semiarid grassland

Increasing frequency and magnitude of climate extremes could fundamentally affect terrestrial carbon (C) cycling. However, as the second-largest terrestrial C flux, soil respiration (SR) responses to climate extremes are not well understood. Here, we investigated the effects of drought, heat wave and drought plus heat wave on SR in a semiarid grassland during the growing season over 3 years. The results indicated that drought consistently reduced the growing-season mean SR, especially during the period of drought treatment, while heat wave, alone or when combined with drought, had little effect on SR. The decreased SR under drought at the intra-annual timescale could be primarily attributable to restriction of low soil moisture to microbial biomass, as there were no consistent changes in plant community (aboveground biomass, richness and abundance). In contrast, the inter-annual variation in SR was positively related to plant community abundance, richness and aboveground biomass in additional to soil water availability, but was not significantly affected by microbial biomass. Our study highlighted that incorporating microbial biomass in C cycling models can improve simulation of seasonal dynamics of soil respiration while incorporating plant community characteristics can benefit prediction of variation in SR across multiple years in semiarid grasslands.

Cold Pool Responses to Changes in Soil Moisture

AbstractThis study examines the role of soil moisture in modulating convective cold pool properties in an idealized modeling framework that uses a cloud‐resolving model coupled to an interactive land surface model. Five high‐resolution simulations of tropical continental convection are conducted in which the initial soil moisture is varied. The hundreds of cold pools forming within each simulation are identified and composited across space and time using an objective cold pool identification algorithm. Several important findings emerge from this analysis. Lower soil moisture results in greater daytime heating of the surface, which produces a deeper, drier subcloud layer. As a result, latent cooling through the evaporation of precipitation is enhanced, and cold pools are stronger and deeper. Increased propagation speed, combined with wider rain shafts, results in wider cold pools. Finally, the rings of enhanced water vapor that surround each cold pool when soil is wet disappear when the soil moisture is reduced, due to the suppression of surface latent heat fluxes. Instead, short‐lived “puddles” of enhanced water vapor permeate the cold pools. The results are nonlinear in that the properties of the cold pools in the two driest‐soil simulations depart substantially from the cold pool properties in the three simulations initialized with wetter soil. The dividing line between the resulting wet‐soil and dry‐soil regimes is the permanent wilting point. Below the permanent wilting point, transpiration is subdued due to a sharp increase in water stress. These results emphasize the role of land surface‐boundary layer‐cloud interactions in modulating cold pool properties.

How do soil microbial communities respond to fire in the intermediate term? Investigating direct and indirect effects associated with fire occurrence and burn severity

Fires transform soil microbial communities directly via heat-induced mortality and indirectly by altering plant and soil characteristics. Emerging evidence suggests the magnitude of changes to some plant and soil properties increases with burn severity, but the persistence of changes varies among plant and soil characteristics, ranging from months to years post-fire. Thus, which environmental attributes shape microbial communities at intermediate time points during ecosystem recovery, and how these characteristics vary with severity, remains poorly understood. We identified the network of properties that influence microbial communities three years after fire, along a burn severity gradient in Sierra Nevada mixed-conifer forest. We used phospholipid fatty acid (PLFA) analysis and bacterial 16S-rDNA amplicon sequencing to characterize the microbial community in mineral soil. Using structural equation modelling, we applied a systems approach to identifying the interconnected relationships among severity, vegetation, soil, and microbial communities. Dead tree basal area, soil pH, and extractable phosphorus increased with severity, whereas live tree basal area, forest floor mass, and the proportion of the ≥53 μm soil fraction decreased. Forest floor loss was associated with decreased soil moisture across the severity gradient, decreased live tree basal area was associated with increased shrub coverage, and increased dead tree basal area was associated with increases in total and inorganic soil nitrogen. Soil fungal abundance decreased across the severity gradient, despite a slightly positive response of fungi to lower soil moisture in high severity areas. Bacterial phylogenetic diversity was negatively related to severity and was driven by differences in nutrients and soil texture. The abundance of Bacteroidetes increased and the abundance of Acidobacteria decreased across the severity gradient due to differences in soil pH. Overall, we found that the effects of burn severity on vegetation and soil physicochemical characteristics interact to shape microbial communities at an intermediate time point in ecosystem recovery.

Influences of litter diversity and soil moisture on soil microbial communities in decomposing mixed litter of alpine steppe species

Many studies have examined the effects of plant diversity and soil water availability on litter decomposition, but little is known about how these two factors interactively influence soil microbial communities, especially in alpine ecosystems. Therefore, the objective of this work was to investigate how litter diversity influences soil microbial communities under different moisture conditions in an alpine steppe ecosystem in Northern Tibet. We collected litter of four abundant plant species (Stipa purpurea, Sp; Carex moorcroftii, Cm; Leontopodium pusillum, Lp; and Artemisia nanschanica, An), and used phospholipid fatty acid (PLFA) analysis to measure soil microbial biomass and community structure. A fully factorial litter mixing experiment under different soil moisture conditions (i.e., 20%, 30% and 40% water holding capacity) was employed. The results showed that litter composition, rather than species richness, significantly affected soil microbial biomass and community composition. The presence of Sp, Cm and An exerted positive or negative effects on soil microbial communities. Litter quality (i.e., C:N ratio) could explain the effects of litter composition on soil microbial communities. High soil moisture facilitated the growth of gram-negative bacteria, while gram-positive bacteria and fungi were more abundant in lower moisture soil. We did not detect any interactive effects of litter species richness and soil moisture on the microbial communities. However, the effects of litter composition on soil microbial communities were dependent on soil moisture condition. These findings indicate that litter composition, rather than species richness, shows interactive effects with soil moisture on soil microbes, and both factors are important in regulating ecosystem functions.