Low Soil Moisture Research Articles

Use of displacement as a proxy for dike safety

Abstract. Climatic conditions and vegetation cover influence water flux in a slope which affect the pore water pressure and self weight, hence its stability. High evapotranspiration and low precipitation rates during summer cause dry soil with low soil moisture (SM) that leads to soil shrinkage, which leads to cracking and reduced shear strength, which consequently decreases the stability of slopes. Soil re-wetting increases slope weight and exerts an additional driving force on the slope. Using Earth observation (EO) data facilitates frequent, large-scale monitoring to identify the vulnerable areas along the slopes to avoid instability. Here we study the displacement of a vegetated dike subject to SM variations under varying climatic conditions. Results show that the SM and magnitude of total displacement at a desired location are highly positively correlated without time lag. This proof-of-concept study shows that near surface displacement due to interaction with the atmosphere has a strong relation with the water availability in the slope and therefore the Factor of Safety (FoS).

Performance of Dry-Seeded Rice Genotypes under Varied Soil Moisture Regimes and Foliar-Applied Hormones.

Plant hormones influence various physiological processes during the growth and development of plants, but their critical roles in influencing yield and antioxidant activities in dry-seeded rice (DSR) have not been adequately explored. This study aims to analyze the performance and antioxidant activity of contrasting genotypes of DSR in response to soil moisture regimes and foliar-applied hormones. The study comprised sixteen treatments that were evaluated under field conditions as per split-plot design in three replications. Treatments comprised combinations of two soil moisture tension regimes (10 kPa and 20 kPa) and two genotypes (PR-111, non-stay-green type and PR-123, stay-green type) applied to the main plots and foliar application of three hormones (gibberellic acid (GA3) 40 mg kg−1, abscisic acid (ABA) 20 mg kg−1, and cytokinin (CK) 40 mg kg−1)) and a control (unsprayed) to subplots. The non-stay-green genotype (PR-111) resulted in 34.6% more grain yield (6.48 t ha−1) than the stay-green genotype (PR-123) at the lower soil moisture tension regime (SMTR) (10 kPa) due to the increased number of filled grains per panicle and improvement in harvest index (HI). At the higher SMTR (20 kPa), the stay-green genotype (PR-123) produced 26.4% more grain yield (5.21 t ha−1) than non-stay green genotype (4.12 t ha−1) and showed enhanced superoxide dismutase (SOD) and peroxide dismutase (POD) activity that may have contributed in maintaining sink size through improved chlorophyll content. Grain yield (6.35 t ha−1) with foliar-applied GA3 (40 mg kg−1) at SMTR of 10 kPa was higher by 12.2% and 24.0% than with foliar-applied ABA (20 mg kg−1) and unsprayed treatments, respectively. Irrigation application at SMTR of 20 kPa and foliar application of ABA gave 24.1% higher grain yield (5.15 t ha−1) than the unsprayed treatment, but it was similar to foliar-applied GA3 and CK. This study implied that the stay-green genotype (PR-123) was more suitable under moisture stress conditions (20 kPa) in DSR, as it maintained sink size even under moisture stress conditions by improving dry matter translocation and enhancing SOD and POD activity. The study suggests the need to find out the endogenous level of these plant hormones in rice genotypes under a range of water regimes to develop high yielding and water use efficient genotypes of DSR.

Photoperiod and CO2 elevation influence morphological and physiological responses to drought in trembling aspen: implications for climate change-induced migration.

Past research suggests climate change will cause the climate envelopes of various tree species to shift to higher latitudes and can lead to a northward migration of trees. However, the success and scope of the migration are likely affected by factors that are not contained in the climate envelope, such as photoperiod and interactive effects of multiple environmental factors, and these effects are currently not well understood. In this study, we investigated the interactive effects of CO2 concentrations ([CO2]), photoperiod and soil moisture on the morphological and physiological traits of Populus tremuloides Michx. We grew seedlings under two levels of [CO2] (ambient [CO2] (AC) 400 vs elevated [CO2] (EC) 1000μmolmol-1), four photoperiod regimes (growing season photoperiods at 48 (seed origin), 52, 55 and 58°N latitude) and two soil moisture regimes (high soil moisture (HSM) vs low soil moisture (LSM), -2 MPa) for two growing seasons in greenhouses. Both morphological and physiological responses were observed. Low soil moisture reduced leaf size, total leaf area and height growth by 33, 46 and 12%, respectively, and increased root/shoot ratio by 20%. The smaller leaf area and increased root/shoot ratio allowed the seedlings in LSM to maintain higher the maximum rate of Rubisco carboxylation (Vcmax) and the maximum rate of electron transport for RuBP regeneration (Jmax) than control seedlings (55 and 83% higher in July, 52 and 70% in August, respectively). Photoperiod and [CO2] modified responses to LSM and LSM altered responses to photoperiod and [CO2], e.g., the August photosynthetic rate was 44% higher in LSM than in HSM under EC but no such a difference existed under AC. The increase in Vcmax and Jmax in response to LSM varied with photoperiod (Vcmax: 36% at 52°N, 22% at 55°N, 47% at 58°N; Jmax: 29% at 52°N, 21% at 55°N, 45% at 58°N). Stomatal conductance and its reduction in response to LSM declined with increasing photoperiod, which can have significant implications for soil moisture effect on northward migration. This study highlights the need to consider the complex interactions of [CO2], photoperiod and soil moisture when planning assisted migration or predicting the natural migration of boreal forests in the future.

Sap flow characteristics in growing and non-growing seasons in three tree species in the semiarid Loess Plateau region of China

Year-round observation suggests that sap flow in growing season represents species-specific transpiration characteristics and sap flow of deciduous broadleaved species in non-growing season is related to daily changes in stem diameter. Year-round observation is necessary to investigate species-specific characteristics of sap flow and its possible contribution in non-growing season. The middle Loess Plateau in China is characterized by temperate climate and vegetation cover of generally drought-tolerant deciduous broadleaved and some evergreen coniferous trees. In this study, Granier-type thermal dissipation probes were applied to measure year-round xylem sap flow in three species from April 2017 to April 2018. Solar radiation, air temperature, relative air humidity, precipitation, and soil moisture were monitored continuously. The results showed that the peak time of sap flux density (Fd) in the diurnal courses of Robinia pseudoacacia was later than that of Quercus liaotungensis and Platycladus orientalis. The peak time of Fd for R. pseudoacacia was significantly postponed during the period with higher soil moisture when compared with that at lower soil moisture, whereas the peak time was reached slightly earlier in the other two species. Sap flow during the non-growing season was relatively higher in P. orientalis than in the two broadleaved species. The diurnal course of Fd in non-growing season showed high values at nighttime and low values in daytime, opposite to that in growing season. Daily variation in stem diameter was inverse of the change in sap flow in the two broadleaved species, whereas the daily change in stem diameter of P. orientalis was very small and showed no clear relation with sap flow. The results suggest that changes in transpiration characteristics with soil moisture conditions vary with tree species; sap flow in deciduous broadleaved trees in non-growing season is small and closely related to daily changes in stem diameter.

Simulating the effects of water limitation on plant biomass using a 3D functional-structural plant model of shoot and root driven by soil hydraulics.

Improved modelling of carbon assimilation and plant growth to low soil moisture requires evaluation of underlying mechanisms in the soil, roots, and shoots. The feedback between plants and their local environment throughout the whole spectrum soil-root-shoot-environment is crucial to accurately describe and evaluate the impact of environmental changes on plant development. This study presents a 3D functional structural plant model, in which shoot and root growth are driven by radiative transfer, photosynthesis, and soil hydrodynamics through different parameterisation schemes relating soil water deficit and carbon assimilation. The new coupled model is used to evaluate the impact of soil moisture availability on plant productivity for two different groups of flowering plants under different spatial configurations. In order to address different aspects of plant development due to limited soil water availability, a 3D FSP model including root, shoot, and soil was constructed by linking three different well-stablished models of airborne plant, root architecture, and reactive transport in the soil. Different parameterisation schemes were used in order to integrate photosynthetic rate with root water uptake within the coupled model. The behaviour of the model was assessed on how the growth of two different types of plants, i.e. monocot and dicot, is impacted by soil water deficit under different competitive conditions: isolated (no competition), intra, and interspecific competition. The model proved to be capable of simulating carbon assimilation and plant development under different growing settings including isolated monocots and dicots, intra, and interspecific competition. The model predicted that (1) soil water availability has a larger impact on photosynthesis than on carbon allocation; (2) soil water deficit has an impact on root and shoot biomass production by up to 90 % for monocots and 50 % for dicots; and (3) the improved dicot biomass production in interspecific competition was highly related to root depth and plant transpiration. An integrated model of 3D shoot architecture and biomass development with a 3D root system representation, including light limitation and water uptake considering soil hydraulics, was presented. Plant-plant competition and regulation on stomatal conductance to drought were able to be predicted by the model. In the cases evaluated here, water limitation impacted plant growth almost 10 times more than the light environment.

P-model v1.0: an optimality-based light use efficiency model for simulating ecosystem gross primary production

Abstract. Terrestrial photosynthesis is the basis for vegetation growth and drives the land carbon cycle. Accurately simulating gross primary production (GPP, ecosystem-level apparent photosynthesis) is key for satellite monitoring and Earth system model predictions under climate change. While robust models exist for describing leaf-level photosynthesis, predictions diverge due to uncertain photosynthetic traits and parameters which vary on multiple spatial and temporal scales. Here, we describe and evaluate a GPP (photosynthesis per unit ground area) model, the P-model, that combines the Farquhar–von Caemmerer–Berry model for C3 photosynthesis with an optimality principle for the carbon assimilation–transpiration trade-off, and predicts a multi-day average light use efficiency (LUE) for any climate and C3 vegetation type. The model builds on the theory developed in Prentice et al. (2014) and Wang et al. (2017a) and is extended to include low temperature effects on the intrinsic quantum yield and an empirical soil moisture stress factor. The model is forced with site-level data of the fraction of absorbed photosynthetically active radiation (fAPAR) and meteorological data and is evaluated against GPP estimates from a globally distributed network of ecosystem flux measurements. Although the P-model requires relatively few inputs, the R2 for predicted versus observed GPP based on the full model setup is 0.75 (8 d mean, 126 sites) – similar to comparable satellite-data-driven GPP models but without predefined vegetation-type-specific parameters. The R2 is reduced to 0.70 when not accounting for the reduction in quantum yield at low temperatures and effects of low soil moisture on LUE. The R2 for the P-model-predicted LUE is 0.32 (means by site) and 0.48 (means by vegetation type). Applying this model for global-scale simulations yields a total global GPP of 106–122 Pg C yr−1 (mean of 2001–2011), depending on the fAPAR forcing data. The P-model provides a simple but powerful method for predicting – rather than prescribing – light use efficiency and simulating terrestrial photosynthesis across a wide range of conditions. The model is available as an R package (rpmodel).

Using incomplete floristic monitoring data from habitat mapping programmes to detect species trends

AbstractAimThe loss of biodiversity has raised serious concerns about the entailing losses of ecosystem services. Here, we explore the potential of repeated habitat mapping data to identify floristic changes over time. Using one German federal state as a case study, we assessed floristic changes between the 1980s and 2010s. These habitat data have great potential for analysis because of their high spatial coverage while also posing methodological challenges such as incomplete observation data. We developed a modelling approach that accounts for incomplete observations and explored the ability to detect temporal trends.LocationThe Federal State of Schleswig‐Holstein (Germany)MethodsWe compiled plant species lists from the earliest (1980s) and most recent (2010s) habitat mapping survey and aligned differing habitat definitions across mapping campaigns. A total of 5,503 mapped polygons, each with a list of species records, intersected the two surveys. We accounted for underrecorded species by assigning occurrence probabilities, based on species co‐occurrence information across all surveys, using Beals' index and tested the robustness of this approach by simulation experiments. For those species with significant increases and decreases in occurrence probability, we linked these trends to the species' functional characteristics.ResultsWe found a systematic loss of species that are moderately threatened. Species that indicate low nitrogen supply and high soil moisture declined, suggesting a shift towards a more eutrophic and drier landscape. Importantly, assessing specific plant traits associated with losses, we also detected a decrease in species with reddish and blueish flowers and species providing nectar, pointing to a decrease of insect‐pollinated taxa.Main conclusionsThe identified changes raise concerns that plant biodiversity has fundamentally changed over the last three decades, with concomitant consequences for ecosystem services, especially pollination. Given the general lack of historical standardized data, our approach for trend analyses using incomplete observation data may be widely applicable to assess long‐term biodiversity change.

Biogeochemical controls on nitrogen transformations in subtropical estuarine wetlands

Changes in soil moisture and salinity are expected to alter gross nitrogen (N) transformations, which can control microbial N dynamics in estuarine wetlands. However, the effects of soil moisture and salinity on microbial N limitation remain poorly understood. To this end, we used a15N pool dilution approach to characterize the changes in soil gross N transformations with the variations of soil moisture in subtropical estuarine wetlands along a low-level salinity gradient. The results showed that soil gross N mineralization (GNM) increased with the increasing soil moisture. Ammonia immobilization (AIM) and microbial N immobilization (MIM) increased with the increasing soil salinity. High gross nitrification rates were generally found in the wetlands with relatively high ammonia content and low soil moisture. The ratios of MIM to GNM (MIM/GNM), as an indicator of microbial N limitation, decreased in response to the enhancing soil moisture and increased with the increasing soil salinity. Ammonia supply capacity (GNM–AIM) decreased with increasing soil salinity but increased with the increasing soil moisture. These results together indicated that microbial N limitation became stronger in the wetlands characterized with high soil salinity and low soil moisture. Soil moisture and salinity exhibited also indirect effects on microbial N limitation through affecting organic N content, ecological stoichiometry, microbial biomass and enzyme activity. Therefore, soil moisture and salinity levels are crucial for controlling soil N transformations with important implications on microbial N removal and retention in estuarine wetlands.

Effect of different abiotic factors on symptom expression and severity of bakanae disease of rice (Oryza sativa)

The bakanae disease incited by Fusarium fujikuroi Nirenberg is becoming a serious threat to cultivation of rice, especially aromatic rice worldwide. The present study was conducted in the year 2016–17 at ICAR- Indian Agricultural Research Institute, New Delhi to study the effect of different abiotic factors (soil moisture, soil pH, soil type, and temperature) individually and in combination in causation of different kind of bakanae disease symptoms and severity. The highest disease severity (93.33%) was observed at 30% soil moisture conditions. Variation in disease severity was significant in interaction of moisture and soil type and temperature and soil type, whereas, it was non-significant in interaction of moisture and temperature and soil type, moisture and temperature. It was observed that elongation symptoms were more prevalent in high moisture conditions, whereas rotting symptoms were more prevalent in low soil moisture.

Alpine Hummocks Drive Plant Diversity and Soil Fertile Islands on the Tibetan Plateau

Earth hummocks are widely distributed in arctic, sub-Arctic and alpine regions and have important roles in determining plant diversity and the nutrient content of soils. We investigated the impact of the spatial heterogeneity on soil properties and plant communities caused by the hummocks on the Tibetan Plateau. The results indicated alpine hummocks created higher plant diversity and soil fertile island patterns under Kobresia Genus communities. Vegetation height, cover, above-ground and underground biomass, species richness and diversity at the top of well-developed hummocks were the significantly higher than those in the inter-hummocks and surrounding flat ground. The soil organic carbon content in surface soil layer (0-50 cm) at the hummock top was 154.6% and 172.3% higher than those in inter-hummock area and the flat ground, respectively. From the developing to well-developed stage, K. littledalei became the dominant population at hummock top instead of K. humilis, and fertile islands gradually formed with higher soil organic carbon and total nitrogen, lower soil moisture and wider soil temperature variation. RDA analysis further indicated the interactions of plant community succession and soil fertile island could create positive feedbacks to nutrient-rich patches.

Physiological screening of cotton (Gossypium hirsutum L.) genotypes against drought tolerance

Cotton is a vital fiber and oilseed crop badly affected by soil moisture deficit stress. Screening of cotton germplasm is a prerequisite to classify the cotton genotypes as a drought sensitive and tolerant. With the aim to separate the distinct genotypes, eight cotton genotypes (BH-190, Ali Akbar-802, NIAB-86, NIBGE-115, FH-942, IUB-13, MNH-886, and FH Lalazar) were grown under normal moisture (08 irrigations/ 28 acre inches) and moisture stress (03 irrigations at 60, 90 and 120 DAS/ water deficit of 15 inches) environments. The assessment was done through different physiological parameters (stomatal conductance, osmotic and water potential, photosynthetic rate, relative water contents and canopy temperature). Cell injury and yield were also evaluated. The experimental design was Randomized Complete Block Design (RCBD) in factorial way with three replicates. The data obtained was investigated statistically at 5% probability and Least Significant Difference (LSD) test was used to isolate the significant means (treatment). The results indicated that water stress adversely reduced the values of all the above stated parameters. The cotton genotype BH-190 had significantly greater (p<0.05) yield and physiological attributes and found extra water deficit stress tolerant. While cotton genotype FH Lalazar had least value of these attributes as compared to all remaining cotton genotypes and thus considered as water deficit stress sensitive genotype. So, it can be concluded from the results of this experiment that the physiological screening of low soil moisture stress tolerant varieties could be a superior way to mitigate impact of drought stress on the cotton cultivated in drought susceptible regions. Keywords: Cotton (Gossypium hirsutum L.); Drought tolerant; Physiological; Screening http://dx.doi.org/10.19045/bspab.2020.90017

Conservation tillage and residue management improves soil properties under a upland rice–rapeseed system in the subtropical eastern Himalayas

AbstractPoor soil properties and low soil moisture content (SMC) are major limitations for cultivating a second crop after the rainy season rice (Oryza sativa L.) in the uplands of the Eastern Himalayas. Information on impact of conservation tillage and residue management (RM) to alleviate soil constraints is limited in the region. Thus, a field study was conducted in a rice–rapeseed (Brassica campestris Var. Toria) system under rainfed conditions with two tillage systems (CsT—conservation and CT—conventional) and five RM practices (100% NPK fertilizer, 50% NPK; 50% NPK + in‐situ rice residue retention [ISRR, 5 Mg ha−1], 50% NPK + weed biomass [WB, 10 Mg ha−1] fresh weight basis (FW)]; 50% NPK + green manuring [GM, 10 Mg ha−1 FW]), and their impact on soil quality parameters were assessed after 3 years. Significantly lower bulk density and penetration resistance (0–15 cm) and higher water infiltration rate were recorded under CsT than CT. The soil water holding capacity (WHC) and SMC in rapeseed were significantly higher under CsT than those under CT at 0–15 cm and 15–30 cm depths. The WHC and SMC were the maximum under 50% NPK + GM/WB and the minimum under sole application of 50% NPK. After 3 years, there were 5.7% higher available nitrogen (N), 7.3% phosphorus (P), and 3% potassium (K) (kg ha−1) in 0–15 cm depth under CsT than those under CT, respectively. Similarly, SOC stock (0–30 cm), soil microbial biomass carbon (SMBC), and dehydrogenase activity (DHA) under CsT were significantly higher than CT. Application of 50% NPK + WB/GM/ISRR registered significantly higher available NPK, SMBC, and DHA in soil than those under 50% and 100% NPK. Thus, CsT along with 50% NPK + WB/GM/ISRR are recommended for improving soil properties under the rice–rapeseed system of the region.

English

The experiment was conducted by using seven released coffee varieties at three locations in southern Ethiopia, Halaba, Loka Abaya and Dilla, to select coffee varieties with higher yield and tolerant to low soil moisture stress. It was arranged in RCBD having three replications. The result indicated that the varieties showed significant difference on main stem diameter, plant height at harvesting, plant height up to the first branch, number of primary branches, number of secondary branches, number of tertiary branches, number of main stems, fruiting nodes per branch (FNPB), number of beans per cherry (NBPC), canopy diameter, leaf area, number of leaves per branch, number of leaves per tree (NLPT), hundred bean weight (HBW), weight of fresh husk (WHF), weight of dried husk (WHD), weight of fresh husked bean (WHBF), and weight of dried husked bean (WHBD). Stand count at harvest (STCNT), leaf length (LL), leaf width (LW), bean thickness (BTH), bean length (BL), bean yield per tree (YPT), bean yield per plot (YPP), bean yield per hectare (YPHA) and weight of husked clean coffee (WHCC) were not statistically significant. Location specific significant variations were observed on some of the variables such as stand count, leaf length, and leaf width at Halaba; yield per tree, yield per plot, yield per hectare and weight of husked clean coffee were significant at all the three locations despite their non-significant value while combined. The coffee variety Catimor J-19 performed best at all location with respect to fresh bean yield and dried clean coffee followed by Angafa. Thus they can be promoted for larger commercial production at tested locations and locations with similar agro-ecological conditions. Key words: Coffea arabica, husked coffee, clean coffee, agroecology.

Nitrogen and Phosphorus Absorption and Yield of Tomato Increased by Regulating the Bacterial Community under Greenhouse Conditions via the Alternate Drip Irrigation Method

Alternate drip irrigation (ADI) is a useful irrigation method for water conservation and the regulation of soil quality; however, knowledge about the underlying mechanism of soil-root-bacterium interactions is limited. To determine the mechanism by which ADI transforms soil nutrients and thereby promotes plant growth and to provide a basis for the reasonable selection of drip irrigation methodology, the present study investigated the effects of ADI on the composition and potential function of the bacterial community in tomato rhizosphere soils under greenhouse conditions and analyzed the soil-root-bacterium interactions under ADI. The results revealed that, compared with the soils of the plots treated with surface drip irrigation with plastic film mulching (DI-PFM), the soils of the plots treated with ADI presented an optimized bacterial community structure and optimized soil nitrogen (N) and phosphorus (P) metabolism. The soil available N contents under ADI with lower irrigation limits of 50%, 60%, and 70% of field capacity (A50, A60, and A70 treatments, respectively) were 1.48, 2.19, and 1.91 times greater than those under DI-PFM, respectively; similarly, the soil available P contents were 1.49, 1.65, and 2.91 times greater; the total phosphorus (TP) contents in the tomato roots were 1.06, 1.94, and 1.59 times greater, respectively; and the TP contents in the tomato plants were 1.03, 1.75, and 2.84 times greater, respectively. In addition, the total nitrogen (TN) contents in the tomato roots under ADI with lower irrigation limits of 60% and 70% of field capacity were 1.07 and 1.14 times greater than those under DI-PFM, and the TN contents in the tomato stems were 1.21 and 1.12 times greater than those under DI-PFM. However, compared with DI-PFM, ADI improved tomato yields by 24.23% under only 70% of field capacity. Therefore, ADI significantly enhanced soil-root interactions and stimulated the activation of soil N and P, but only a proper low soil moisture content (SMC) led to significantly increased tomato yields.

Impact of invasive species on soil hydraulic properties: importance of functional traits

To understand the effects of invasive species on soil hydraulic properties is a challenging task for Neotropical dry ecosystems because the relative paucity of knowledge of linkages between functional traits of species in response to drought conditions and land-cover transformation contexts. We tested whether functional strategies vary between native and invasive plants and if these differences have impact on processes at ecosystem level. Eight functional traits in wood and leaves of all woody species reported in our study area were measured. Over two contrasting climatic seasons and three vegetation covers, we measured four water regulation properties of soils. We found that forest covers showed higher values of hydraulic conductivity, water infiltration rate, volumetric water content and lower penetration resistance (lower compaction) of soils for both climatic seasons than other vegetation covers. In contrast, zones dominated by invasive species and degraded covers showed greater similarity between hydraulic properties in the soil and high variation among climatic seasons. Additionally, evergreen and deciduous species were functionally different, and invasive evergreen legumes were characterized by acquisitive hydraulic traits but leaf, height and wood density related with conservative strategies. The dominance of functional traits, mainly hydraulic traits, was correlated with volumetric moisture content of the soil. The functional differences between invasive and native species explained the lower soil moisture and greater soil compaction values in invasive covers compared to the forest covers. These results confirm that introduction of invasive species have an impact on soil ecosystem properties on tropical dry forests. Additionally, it is possible that invasive species can help to recover some hydraulic properties and can facilities the restoration processes in degraded areas where the native species failed to colonize.

Effects of precipitation intermittency on vegetation patterns in semi-arid landscapes

Patterns of vegetation are a characteristic feature of many semi-arid regions. The limiting resource in these ecosystems is water, which is added to the system through short and intense rainfall events that cause a pulse of biological processes such as plant growth and seed dispersal. We propose an impulsive model based on the Klausmeier reaction–advection–diffusion system, analytically investigate the effects of rainfall intermittency on the onset of patterns, and augment our results by numerical simulations of model extensions. Our investigation focuses on the parameter region in which a transition between uniform and patterned vegetation occurs. Results show that decay-type processes associated with a low frequency of precipitation pulses inhibit the onset of patterns and that under intermittent rainfall regimes, a spatially uniform solution is sustained at lower total precipitation volumes than under continuous rainfall, if plant species are unable to efficiently use low soil moisture levels. Unlike in the classical setting of a reaction–diffusion model, patterns are not caused by a diffusion-driven instability but by a combination of sufficiently long periods of droughts between precipitation pulses and water diffusion. Our results further indicate that the introduction of pulse-type seed dispersal weakens the effects of changes to width and shape of the plant dispersal kernel on the onset of patterns.

Enhanced‐efficiency nitrogen fertilizers reduce winter losses of nitrous oxide, but not of ammonia, from no‐till soil in a subtropical agroecosystem

AbstractNitrogen (N) gas losses can be reduced by using enhanced‐efficiency N (EEN) fertilizers such as urease inhibitors and coating technologies. In this work, we assessed the potential of EEN fertilizers to reduce winter losses of nitrous oxide (N2O‐N) and ammonia (NH3‐N) from a subtropical field experiment on a clayey Inceptisol under no‐till in Southern Brazil. The EEN sources used included urea containing N‐(n‐butyl) thiophosphoric triamide (UR+NBPT), polymer‐coated urea (P‐CU) and copper‐and‐boron‐coated urea (CuB‐CU) in addition to common urea (UR) and a control treatment without N fertilizer application. N2O‐N and NH3‐N losses were assessed by using the static chamber method and semi‐open static collectors, respectively. Both N2O‐N and NH3‐N exhibited two large peaks with an intervening period of low soil moisture and air temperature. Although the short‐term effect was limited to the first few days after application, UR + NBPT urea decreased soil N2O‐N emissions by 38% relative to UR. In contrast, urease inhibitor technology had no effect on NH3‐N volatilization. Both coating technologies (CuB‐CU and P‐CU) were ineffective in reducing N losses via N2O production or NH3 volatilization. The N2O emission factor (% N applied released as N2O) was unaffected by all N sources and amounted to only 0.48% of N applied—roughly one‐half the default factor of IPCC Tier 1 (1%). Based on our findings, using NBPT‐treated urea in the cold winter season in subtropical agroecosystems provides environmental benefits in the form of reduced soil N2O emissions; however, fertilizer coating technologies provide no agronomic (NH3) or environmental (N2O) advantages.

Trait-environment interactions affect plant establishment success during restoration.

Establishment and persistence are central to community assembly and are determined by how traits interact with the environment to determine performance (trait-environment interactions). Community assembly studies have rarely considered such trait-environment interactions, however, which can lead to incorrect inferences about how traits affect assembly. We evaluated how functional traits, environmental conditions, and trait-environment interactions structure plant establishment, as a measure of performance. Within 12 prairie restorations created by sowing 70 species, we quantified environmental conditions and counted individuals of each seeded species to quantify first-year establishment. Three trait-environment interactions structured establishment. Leaf nitrogen interacted with herbivore pressure, as low leaf nitrogen species established relatively better under higher herbivory than species with high leaf nitrogen. Soil moisture interacted with root mass fraction (RMF), with low-RMF species establishing better with low soil moisture and higher-RMF species better on wetter soils. Specific leaf area (SLA) interacted with light availability, as low-SLA species established better under high light conditions and high-SLA species under low light conditions. Our work illustrates how community assembly can be better described by trait-environment interactions than correlating traits or environment with performance. This knowledge can assist species selection to maximize restoration success.

Throughfall Reduction × Fertilization: Deep Soil Water Usage in a Clay Rich Ultisol Under Loblolly Pine in the Southeast USA

Forests in the Southeast USA are predicted to experience a moderate decrease in precipitation inputs over this century that may result in soil water deficiency during the growing season. The potential impact of a drier climate on the productivity of managed loblolly pine (Pinus taeda L.) plantations in the Southeast USA is uncertain. Access to water reserves in deep soil during drought periods may help buffer these forests from the effects of water deficits. To better understand the potential impact of drought on deep soil water, we studied the combined effects of throughfall reduction and fertilization on soil water usage of a clay rich Piedmont Ultisol to a depth of 3 m in a 6-year-old loblolly pine plantation by applying a throughfall reduction treatment (ambient versus ~30% throughfall reduction) and a fertilization treatment (no fertilization versus fertilization). Throughfall reduction lowered soil moisture for all depths and differences were significant in the surface soils (0-0.3 m) (1.2-3.6%) and deep soils (below 2 m) (2.6-3.6%). Fertilization also lowered soil moisture for all depths and differences were significant at 0.3-0.6 m (2.9%) and 1.94-3.06 m (4.5%). Fertilization when combined with the throughfall reduction treatment significantly decreased soil water at 0.1-0.9 m depth. Soils of all depths were rarely depleted of plant available water with the exception of 0-0.1 m, mainly during the growing season. Under throughfall reduction treatment, soil below 0.9 m consistently accounted for more than half of the change in plant available water during months when transpiration exceeded precipitation. When considering the whole soil profile in this clay rich Ultisol, soil water storage buffered transpirational demand in the face of increasing dryness.

Distinct xylem responses to acute vs prolonged drought in pine trees.

Increasing dryness challenges trees' ability to maintain water transport to the leaves. Most plant hydraulics models use a static xylem response to water stress. Yet, in reality, lower soil moisture and warmer temperatures during growing seasons feed back onto xylem development. In turn, adjustments to water stress in the newly built xylem influence future physiological responses to droughts. In this study, we investigate the annual variation of anatomical traits in branch xylem in response to different soil and atmospheric moisture conditions and tree stress levels, as indicated by seasonal predawn leaf water potential (ΨL,pd). We used a 6-year field experiment in southwestern USA with three soil water treatments applied to Pinus edulis Engelm trees-ambient, drought (45% rain reduction) and irrigation (15-35% annual water addition). All trees were also subject to a natural 1-year acute drought (soil and atmospheric) that occurred during the experiment. The irrigated trees showed only moderate changes in anatomy-derived hydraulic traits compared with the ambient trees, suggesting a generally stable, well-balanced xylem structure under unstressed conditions. The artificial prolonged soil drought increased hydraulic efficiency but lowered xylem construction costs and decreased tracheid implosion safety ((t/b)2), suggesting that annual adjustments of xylem structure follow a safety-efficiency trade-off. The acute drought plunged hydraulic efficiency across all treatments. The combination of acute and prolonged drought resulted in vulnerable and inefficient new xylem, disrupting the stability of the anatomical trade-off observed in the rest of the years. The xylem hydraulic traits showed no consistent direct link to ΨL,pd. In the future, changes in seasonality of soil and atmospheric moisture are likely to have a critical impact on the ability of P. edulis to acclimate its xylem to warmer climate. Furthermore, the increasing frequency of acute droughts might reduce hydraulic resilience of P. edulis by repeatedly creating vulnerable and less efficient anatomical structure.