Relative Soil Water Research Articles

Photosynthetic characteristics of Tamarix chinensis under different groundwater depths in freshwater habitats

Groundwater is the major source of water for Tamarix chinensis growth in the Yellow River Delta (YRD) region, and the groundwater depth (GWD) dramatically influences the physiological activities of T. chinensis. The quantitative response of the photosynthetic physiological process of T. chinensis to the GWD in freshwater habitats remains unclear. In this study, the response characteristics of gas exchange parameters in the leaves of three-year-old T. chinensis seedlings were measured and analyzed at a graded series of seven GWDs (0 m, 0.3 m, 0.6 m, 0.9 m, 1.2 m, 1.5 m and 1.8 m). The GWD thresholds corresponding to drastic changes in the photosynthetic efficiency and the GWDs of several levels of photosynthetic productivity and efficiency were also determined. In the freshwater habitats of the YRD, variations in GWD significantly altered the relative soil water content (RSWC) and thus influenced the photosynthetic efficiency of T. chinensis. RSWC at 0 ≤ GWD ≤ 0.9 m and GWD at 1.2 m ≤ GWD ≤ 1.8 m directly influenced the photosynthetic physiology of T. chinensis. When the GWD was 1.2 m, net photosynthetic rate (Pn), apparent quantum efficiency and water use efficiency (WUE) values all peaked. Thus, T. chinensis exhibited a high light and water use efficiency, wide ecological amplitude in terms of light, and high photosynthetic capacity. The optimum GWD for photosynthetic carbon assimilation and WUE in T. chinensis was determined to be 1.2 m. At a deep (≥1.64 m) or shallow (≤0.53 m) GWD, both Pn and WUE in T. chinensis clearly decreased below the corresponding mean values. The main causes for the reduction in Pn in these two GWD ranges (≤0.53 m, ≥1.64 m) were stomatal and nonstomatal limitations, respectively. Additionally, a moderate GWD of 1.09–1.25 m corresponded to the “high-productivity and high-efficiency GWD” range, in which T. chinensis displayed a high photosynthetic yield and WUE. Overall, the photosynthetic capacity of T. chinensis shows characteristics of high tolerance to moderate GWDs from 1.09 m to 1.25 m but intolerance at both shallow (≤0.53 m) and deep (≥1.64 m) GWDs in freshwater habitats.

Export of nutrients to the sea in a karstic basin in the west of Cuba

Few studies relate soil water erosion and associated nutrient losses in flat karst landscapes to marine waters. This is due to the complexity of these peculiar ecosystems, given their scarce distribution in the world (20%) and the low erosion rates. Adding that in Cuba these marine waters, where these soils discharge are oligotrophic with a strong historical reduction of their nutrients as a result anthropic-engineering causes; therefore, these are one of their main sources of nutrients. The present research constitutes an approximation of the influence of soil erosion on La Teresa basin, a karstic environment where there are practically no permanent surface streams, to the marine platform of the Batabanó Gulf. The influence of soil erosion and its associated nutrients (0.064 kg ha−1 yr−1 (2.3 t) of P, 1 kg ha−1 yr−1 (35 t) of N) on marine waters coincides with the oligotrophication effect suffered by the island's water bodies reported by Baisre (Biogeochemistry 79:91–108, 2006) and Baisre and Arboleya (Fish Res 81:283–292, 2006) as a result of the damming by agricultural programs.

Analysis of floodplain forest sensitivity to drought.

Floodplain forests are very complex, productive ecosystems, capable of storing huge amounts of soil carbon. With the increasing occurrence of extreme events, they are today among the most threatened ecosystems. Our study's main goal was to assess the productivity of a floodplain forest located at Lanžhot in the Czech Republic from two perspectives: carbon uptake (using an eddy covariance method) and stem radius variations (using dendrometers). We aimed to determine which conditions allow for high ecosystem production and what role drought plays in reducing such production potential. Additionally, we were interested to determine the relative soil water content threshold indicating the onset and duration of this event. We hypothesized that summer drought in 2018 had the most significant negative effects on the overall annual carbon and water budgets. In contrast with our original hypothesis, we found that an exceptionally warm spring in 2018 caused a positive gross primary production (GPP) and evapotranspiration (ET) anomaly that consequently led in 2018 to the highest seasonal total GPP and ET from all of the investigated years (2015–2018). The results showed ring-porous species to be the most drought resistant. Relative soil water content threshold of approximately 0.45 was determined as indicating the onset of drought stress.This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

Dynamics of soil penetration resistance in water-controlled environments

In water-controlled environments, because rainfall is one of the primary hydroclimatic forcings, its variability can affect the dynamics of soil water content and other related processes such as soil penetration resistance (PR), plant growth, and food production. The objective of this study was to simulate the relative soil water content (s) and PR year-round considering semi-arid rainfall conditions for different soil classes. An experiment was conducted to obtain relative soil water content (s) and PR data in sandy soil and this information was combined with a data set of four soils from a similar experiment conducted on different soil texture classes. The relative soil water content and PR were simulated at a daily timescale using a stochastic soil water balance model for the five soils. The parameters of the PR-s model can be estimated from the soil texture and bulk density. Under rainfed conditions, there is a short window for tillage (plowing and cultivation) of sandy soils compared with clay soils. During the majority of a typical hydrological year, the PR reaches high values (greater than 5.0 MPa) imposing a moderate to high physical limitation for root growth in sandy soils. In the same soils, limiting PR is reached at s levels very close to the field capacity during the drying process. This indicates that an extra input of water through irrigation may be required during the establishment of crops with a well-developed root system in order to prevent impairments to root growth. The daily PR values modeled over the course of a hydrological year followed a beta distribution with shape parameters (α and β) which were strongly correlated with the frequency of rainfall events during the wet season (λwet). The modeling framework presented here for simulating relative soil water content and soil penetration resistance can be applied to agricultural systems in order to prevent physical limitations on crop growth and to plan tillage management schedules.

Sap flow of Amorpha fruticosa: implications of water use strategy in a semiarid system with secondary salinization

A. fruticosa (Amorpha fruticosa L.) is widely used for revegetation in semiarid lands that undergo secondary salinization. Understanding A. fruticosa plants response to soil water and salt stress is essential for water irrigation management and proper revegetation practices. In this study, we measured sap flow, stomatal conductance, meteorological and soil characteristics in an A. fruticosa community that recently experienced secondary salinization in northwestern China. Results of our study showed that daytime and nocturnal sap flows averaged 804.37 g·cm−2·day−1 and 46.06 g·cm−2·day−1, respectively, during the growing season. Within individual days, the highest sap flow appeared around noon local time and followed a similar pattern of photosynthetically active radiation (PAR). Despite the significant effect of meteorological factors on the characteristics of sap flow, our study highlighted that the sap flow of A. fruticosa is strongly regulated by the availability of soil relative extractable water (REW). The daytime sap flow, which is predominant compared to nocturnal sap flow, was strongly affected by PAR, air temperature and vapor-pressure deficit. With water stress in the top 40 cm of the soil (REW0–40 cm < 0.4), daytime sap flow displayed a strong relationship with soil water content (SWC) (positive) and soil electrical conductivity (EC) (negative) in the relatively shallow soil profile (up to 40 cm). For the nocturnal sap flow, our results suggest that in the absence of soil water stress (REW0–40 cm > 0.4), the nocturnal sap flow is mainly used to replenish the stem water content and sustain nocturnal transpiration. Under soil water stress, nocturnal sap flow is mainly used to replenish stem water content. The results of our study indicate that it is necessary to shorten the irrigation cycle during the primary growing period (May–July) of A. fruticosa. Moreover, in the absence of soil water stress (REW0–40 cm > 0.4), A. fruticosa can survive well in an saline environment with soil EC < 5 mS·cm−1.

Soil water availability threshold indicator was determined by using plant physiological responses under drought conditions

Soil water shortage is a critical limiting factor that threaten the growth of vegetation and their sustainability in semi-arid areas. Grasses directly respond to the soil water availability (SWA), and the soil water shortage degree can be studied through plant physiological response thresholds under soil drought stress. In this study, the lower-and-optimal limitation of SWA was evaluated with pots along the soil water gradient by quantifying plant gas exchange parameters. These parameters showed a strong cubic relationship with the relative soil water content (RWC) in four forage species. The lower limitation of RWC was obtained for Onobrychis viciifolia (4.0%–20.2%), followed by Astragalus adsurgens (15.5%–25.5%), Elymus nutans (16.1%–27.2%), and Lolium multiflorum (24.6%–35.8%). The average RWC was of 74.83%, and the water saturation point of water use efficiency (WSPWUE) showed a similar critical scope in the four species: Onobrychis viciifolia (71.2%–82.8%), Astragalus adsurgens (72.1%–84.2%), Elymus nutans (79.3%–85.1%), and Lolium multiflorum (76.7%–85.6%). The highest productivity with the highest availability of water (HPHAW) for Onobrychis viciifolia, Astragalus adsurgens, Elymus nutans and Lolium multiflorum was of 71.2%–82.8%, 72.1%–84.2%, 79.3%–85.1% and 76.7%–85.6%, respectively. The lower limitation of RWC, the maximum water use efficiency (WUEmax) and HPHAW in legumes were lower than those values obtained in gramineae, suggesting that legumes were more susceptible to soil drought stress. We concluded that plant gas exchange parameters acted as indicators for SWA under drought conditions, and represented a valuable tool for identifying SWA threshold response in environmental changes.

Plastic-Covered Ridge-Furrow Planting Combined with Supplemental Irrigation Based on Measuring Soil Moisture Promotes Wheat Grain Yield and Irrigation Water Use Efficiency in Irrigated Fields on the Loess Plateau, China

The purpose of this study was to investigate whether combining plastic-covered ridge and furrow planting (RF) and supplemental irrigation based on measuring soil moisture (SIMSM) can increase the grain yield and water use efficiency (WUE) of wheat (Triticum aestivum L.) in irrigated fields of Loess Plateau, China. In 2016–2018, the experiment was conducted at Doukou experimental farm (34°36′ N, 108°52′ E) with two plant systems (RF and traditional planting (TF)) and three irrigation treatments (S1 and S2: SIMSM with a target relative soil water content of 85% and 100%, respectively). The results suggest that under the TF system, SIMSM decreased the grain yield and nitrogen utilization. The reason for this may be the local low precipitation. However, the combination of RF and S2 significantly increased the WUE, protein and wet gluten concentration in the grain. In addition, the grain yield of the RF plus S2 treatment was not significantly different than that of the traditional irrigation method. These results suggest that combining RF and SIMSM with a target relative soil water content of 100% is beneficial to the synergistic improvement of the wheat yield, the wheat quality, and the water and fertilizer use efficiency in irrigated fields on the Loess Plateau.

Introducing water stress hysteresis to the Feddes empirical macroscopic root water uptake model

During wetting-drying cycles, divergence is often found between the immediately improved soil water conditions after re-watering and the recovery of plant water status from stress, which ensues only gradually. Such an apparent hysteresis effect of water stress (HEWS) is usually neglected in simulating root-water-uptake (RWU) by empirical models. To consider HEWS in the empirical macroscopic RWU model of Feddes, a water stress recovery coefficient (δ) was introduced based on two lysimetric experiments under greenhouse and field conditions for winter wheat. The integrated effects of historical water stress events were investigated by assuming that the normalized influence weight of each past stress event declines with the increase of time interval before simulation as an exponential function of attenuation rate. Although δ could be described by an exponential function of an integrative index representing the general historical stress extent (R2 = 0.65, P < 0.001), with an attenuation rate smaller than 0.13, it is challenging to establish such a function practically. An attenuation rate close to zero means HEWS is mainly dominated by the water stress on the previous day, validated by a significant relationship between the relative transpiration or stomatal conductance on the day after irrigation and the water stress extent on the day before irrigation. Therefore, a simplification, substituting the integrative index in the exponential function with the stress extent on the previous day, was proposed for estimating δ. Compared to the traditional RWU model, the revised model considering HEWS was more successful in simulating relative transpiration and soil water dynamics. Root mean square error of relative transpiration was reduced by 65.9 % and of soil water by 30 % in the greenhouse experiment and by 7.4 % and 12.5 %, respectively, in the field experiment.

Photosynthetic CO&lt;sub&gt;2&lt;/sub&gt; response to soil water and its simulation using different models in leaves of two species

CO2 concentrations and soil moisture conditions are important factors in photosynthesis of trees. This study investigated the photosynthetic CO2 responses in the leaves of Prunus sibirica L. and Pinus tabulaeformis Carr. under eight soil water conditions in a semiarid loess hilly region. CO2-response curves and physiological parameters were fitted using a rectangular hyperbola model, nonrectangular hyperbola model, exponential equation, and modified rectangular hyperbola model. Results revealed the relative soil water content (RWCs) for P. sibirica required to maintain higher photosynthetic rate ranging from 46.5 to 81.6%, and that for P. tabulaeformis ranging from 35.4 to 84.5%. When RWCs exceeded these ranges, the net photosynthetic rate of both species decreased. CO2-response curves and three parameters, carboxylation efficiency, CO2-compensation point, and photorespiration rate, were well fitted by the four models when RWCs was appropriate for P. sibirica and P. tabulaeformis. When RWCs exceeded the optimal ranges, only the modified rectangular hyperbola model could precisely simulate the CO2-response curves and photosynthetic parameters of both species.

Simulating the Influences of Soil Water Stress on Leaf Expansion and Senescence of Winter Wheat

Current crop models usually need a lot of input information to simulate crop leaf area index and have relatively large simulation errors under soil water stress, which need to be improved. In this study, based on experiments conducted in glass soil columns and field under rainout shelters in four years (2012-2016) in Yangling, Shaanxi Province in China, we attempted to establish a dynamic model for simulating leaf expansion and senescence of winter wheat under soil water stress. First, a temperature response function was established with four cardinal temperatures (base temperature, lower optimum temperature, higher optimum temperature, and maximum temperature). Then two soil water stress functions were established to quantify the effect of soil water stress on the processes of leaf expansion and leaf senescence of main stem per plant. The first order derivative of a logistic function was then modified with the temperature and soil water stress response function and was used to simulate the daily rate of leaf area expansion and senescence of main stem. The parameters of the new model were estimated using the Solver add-in in MS Excel and then validated based on the data of soil column experiments in 2014-2015 growing season. Then the new model was evaluated with another dataset of column experiments conducted in 2015-2016. Furthermore, the influence of soil water stress on wheat tillering was included in the new model based on open field experiments in 2012-2013 growing season. Then, the new leaf area index (LAI) simulation model was further verified with the data of open field experiments under rainout shelter (2013-2014) and rainfed condition (2004-2005, 2005-2006, and 2008-2009) in different sites. A comparison was conducted between new LAI model and the original LAI module of CERES-Wheat. The results showed that the leaf expansion rate was not affected when the relative soil water availability was greater than 0.7; water stress inhibited the leaf expansion when relative soil water availability was between 0.2 and 0.7; leaves withered and yellowed when relative soil water availability was less than 0.2. The overall average root mean square error (RMSE) and residual accumulation coefficient (CRM) were 9.78 cm2 plant−1, -0.03, and 6.51 cm2 plant−1; 0.05 for model calibration and validation, respectively. The RMSE of LAI decreased by an average of 47.89% compared with the original LAI module of CERES-Wheat. The results of this study can help to improve the current CERES-Wheat model for model applications in the arid and semi-arid regions of China.

The Effects of Temperature and Humidity on a Field Population of Bradysia odoriphaga (Diptera: Sciaridae).

The production of Chinese chives is reduced throughout China due to a root-feeding dipteran pest Bradysia odoriphaga Yang et Zhang (Diptera: Sciaridae), therefore deciphering the conditions influencing its growth and development are important in developing ecological control strategies. A study was conducted from 2014 to 2017 to determine the relationship between the abundance of B. odoriphaga and temperature (atmospheric and soil), soil water content, and atmospheric humidity in a Chinese chive field in Beijing City, China. Numbers of adults peaked in March and October to November and were lowest in July to August and December to next February; numbers of larvae were highest in December to next February and lowest in July to August. From 2014 to 2017, the numbers of adults and larvae were significantly correlated with monthly mean atmospheric temperatures and soil temperatures, but were not significantly correlated with monthly mean atmospheric relative humidity and soil water content. However, for both adults and larvae, numbers were significantly greater with high soil water contents compared with drought treatment. The results of this study suggest that the very low soil water contents, high atmospheric temperatures, and high soil temperatures were critical for regulating field populations of B. odoriphaga.

Special issue in honour of Prof. Reto J. Strasser - Comparative analysis of drought stress response of maize genotypes using chlorophyll fluorescence measurements and leaf relative water content

The initial photochemical quantum efficiency of photosystem II (Fv/Fm) and performance index (PI), describing the ability of the photosynthetic apparatus to collect light energy, have been used to screen tolerance to drought stress by ten maize accessions, monitored by leaf relative water content (RWC) and soil water content (SWC). The Fv/Fm, PI, and RWC values were significantly reduced in drought-stressed plants. The analysis of chlorophyll a fluorescence induction rise from the basic dark-adapted fluorescence yield to the maximum (OJIP transient), distinguished accession Zea 1006 from Libya and Zea 612 from Italy, as the most tolerant and the least tolerant genotypes. The maize genotypes were classified using the Principal Component Analysis (PCA) and clustering methods, based on Fv/Fm and PI values, leaf RWC and SWC. Genotypes from Egypt and Libya were differentiated from genotypes from Europe, Russia and the USA.

Belowground soil water response in the afforestation-cropland interface under semi-arid conditions

Agroforestry is an effective measure to control soil erosion and maintain or increase productivity in semi-arid areas. However, the belowground soil water responses in the afforestation-cropland interface (ACI) is not well known. This study analyzed the variability of soil water storage (SWS) and deficit in three ACIs taking into account the distance between the forest and cropland. The variations of soil water content up to 4 m depth and at five distances from the interface (−5 m (in forest), 0 m (interface), 1 m, 3 m and 5 m (in cropland)) were estimated in three artificial forests (Salix matsudana, Sophora japonica, and Populus cathayana) and their adjacent croplands (maize). The results showed that soil water at the interfaces was significantly affected by forest. This effect was effective up to 160–170 cm of soil depth, and the ACI of S. matsudana had the greatest impact on the farmland soil water. There was no significant relative soil water deficit between 1 and 3 m length, and the ACI of P. cathayana showed the lowest changes in the lateral direction. The SWS of S. japonica in the ACI was clearly higher than the other two artificial forests (P < 0.05). Our findings indicated that S. japonica was the most suitable forest species for agriculture sustainability in the study area. The tree species and the distance between cropland and forest should be considered during the establishment of agroforestry systems. This study provided insights for water conservation and effective management of ACIs in semi-arid areas.

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.

Nitrogen supply modulates nitrogen remobilization and nitrogen use of wheat under supplemental irrigation in the North China Plain

Excessive nitrogen (N) input and irrigation exacerbate N leaching in winter wheat production in the North China Plain (NCP). To explore the optimal N for better N remobilization and higher N utilization of wheat under water-saving irrigation will be conductive to less environmental contamination. A field experiment was conducted at 300 (N300), 240 (N240), 180 (N180), and 0 (N0) kg N ha−1 of N application under supplemental irrigation (SI) that brought the relative soil water content (RSWC) to 70% at jointing and 65% at anthesis. Compared with N0, N180 improved the free amino acid content in the flag leaf and grain after anthesis, dry matter and plant N accumulation at maturity, N translocation amount of vegetable organs and its contribution to grain from anthesis to maturity. Compared to N240 and N300, N180 increased the N translocation efficiency of vegetable organs, and reduced the soil NO3-N residue in the 60–180 cm soil layer, which contributing to no significant reduction in grain yield and grain protein yield, but higher grain N recovery efficiency (GREN), N recovery efficiency (REN), and N partial factor productivity (PFPN). Positive relationships were found between leaf N translocation efficiency and grain yield, grain protein yield, PFPN, GREN, and REN. Therefore, N180 is appropriate to obtain a steady grain yield over 7.5 t ha−1 for at least 2 years under SI based on RSWC in the NCP.

Simulation of plant height of winter wheat under soil Water stress using modified growth functions

Plant height is an important trait that influences the yield and sustainability of wheat productions. It is also an important objective for agronomic breeding and a critical indicator to represent the status of crop growth and nitrogen absorption in the vegetative stage. Wheat is the main crop in arid regions. However, there is insufficient understanding of wheat plant height response to soil water stress. In this study, we tried to explore a new algorithm for simulating dynamics of winter wheat height under different scenarios of soil water stress based on soil column and field experiments conducted under rainout shelters between 2012 and 2016 at Yangling, Shaanxi province, China. First, we established a temperature response function of wheat plant height based on four cardinal temperatures (i.e. base temperature, lower optimal temperature, higher optimal temperature, and ceiling temperature). And we also constructed a water stress response function of wheat plant height using relative soil water availability (Aw) as water stress index. Then, these two functions were used as multipliers to modify the first-order derivative of six distinct growth functions (i.e. Gompertz, Logistic, Mischerlich, Richards, Von Bertalanffy, and Weibull) to represent the elongation rate of wheat plant height under soil water stresses. Consequently, six modified simulation models for wheat plant height were established and identified as Mod-Geo, Mod-Log, Mod-Mis, Mod-Ric, Mod-Von, and Mod-Wei, respectively, among which an optimal simulation model was selected for winter wheat growth under soil water stresses. Based on experimental data of 2014–2015 used for model calibration, it was found that when Aw was greater than 0.65, elongation rate of wheat height was not influenced by soil water content; when Aw was between 0.3 and 0.65, elongation rate of wheat height gradually reduced following an exponential function driven by water stress; when Aw was less than 0.30, elongation rate of wheat height rapidly and linearly reduced driven by water stress until Aw was close to 0 at which the elongation stopped. After that, the data of soil column experiment of 2014–2015 growing season were used to assess the parameters of the six newly established models. The results of model calibration showed that the mean value of the Willmott Index of Agreement (WIA) between measured and simulated wheat heights of the six cultivars were all less than 0.90 for all treatments in the experiment, except for the Mod-Log model (0.95). The data of soil column experiment in 2015–2016 seasons were used to validate the six calibrated new models. The results of model validation with mean value of WIA 0.93 which were even better than model calibration. Finally, the data of two growing seasons (2012–2013 and 2013–2014) of field experiments conducted under a giant rainout shelter were used for further verification of the six new models under field conditions. Among the six different plant height simulation model, Mod-Log model obtained the best values of RMSE and WIA.

Relating modelled habitat suitability for Abies balsamea to on-the-ground species structural characteristics in naturally growing forests

Abstract Modelling tree habitat suitability (HS) is a common practice to assess tree species distribution across a broad range of spatial scales. However, it is seldom used to test the extent that modelled HS-scores (probability of species occurrence) can represent on-the-ground measures of species-structural characteristics. In this study, we compare four parametric and non-parametric models generated with the R-package, sdm, to assess the potential for these models to estimate tree species distribution of balsam fir [Abies balsamea (L.) Mill.] in naturally-growing forests across an extensive landscape. Central to this development are inventory plot data of species presence-absence and four abiotic factors linked to plant growth and distribution. The study’s abiotic factors include: (1) photosynthetically active radiation; (2) growing degree-days; (3) relative extractable soil water content; and (4) near-surface wind speed, all expressed spatially at 30-m resolution. To gauge whether modelled HS can explain structural characteristics in balsam fir-dominated stands, field-based estimates of site index (SI) and cumulative aboveground biomass (ABG) were compared against independently-derived HS-scores. The results showed that: (i) random forest was the most successful at representing species distribution of balsam fir among the four methods considered; (ii) overall growing conditions for balsam fir was observed to be most favourable on north-facing slopes, particularly in the northwest part of the target landscape, where near-surface air temperatures are cooler, soils are moderately wetter, and wind speeds are lower; (iii) tree-based calculations of SI were partially characterised by patterns in modelled HS-scores, due to scale differences (i.e., from individual tree to 30-m grid cells) and an inadequate number of sample trees; and (iv) patterns of cumulative AGB were more accurately represented by species HS. Modelled HS-scores, as potential indicators of tree species habitat preference, AGB, and species distribution, can offer key ecological information essential to inform forest management and conservation planning at the landscape level.

Norway spruce responses to drought forcing in areas affected by forest decline

Aim of study: To assess the crown condition and radial growth of Norway spruce in plots with an increasing frequency and strength of drought during the last decades.Area of the study: Northern Moravia, Czech Republic.Materials and methods: Crown condition assessment and dendrochronology analysis were used.Main results: Tree-ring width (TRW) was significantly influenced by previous autumn and current summer climate. The temporal variability of the growth-climate relationship shows that the impact of water sufficiency (precipitation, relative soil water content, drought index) markedly increased mainly during the 2000s and the 2010s. Most climate-growth relationships were significant only in the last two or three decades. The observed crown conditions and their relationships with TRW also indicate stress intensification during the same period. Our results suggest that water availability was the main factor affecting radial growth and the occurrence of negative pointer years and was probably also the factor triggering the decline.Research highlights: In these current site and climate conditions, the silviculture of Norway spruce is extremely risky in the study area. Our results have also shown that the observed climate change is too dynamic for long-term forest plans, especially with regard to recommended forest species composition.Keywords: defoliation; Picea abies; tree-ring width; precipitation; PDSI; available soil water.

Effects of High Temperature and Drought Stress on the Expression of Gene Encoding Enzymes and the Activity of Key Enzymes Involved in Starch Biosynthesis in Wheat Grains.

High temperature (HT) and drought stress (DS) play negative roles in wheat growth, and are two most important factors that limit grain yield. Starch, the main component of the wheat [][endosperm, accounts for 65–75% of grain weight, and is significantly influenced by environmental factors. To understand the effects of post-anthesis HT and DS on starch biosynthesis, we performed a pot experiment using wheat cultivar “Zhengmai 366” under field conditions combined with a climate-controlled greenhouse to simulate HT. There were two temperature regimes (optimum day/night temperatures of 25/15°C and high day/night temperatures of 32/22°C from 10 days after anthesis to maturity) accompanied by two water treatments (optimum of ∼75% relative soil water content, and a DS of ∼50% relative soil water content). Optimum temperature with optimum water treatment was the control (CK). We evaluated the expression patterns of 23 genes encoding six classes of enzymes involved in starch biosynthesis in wheat grains using real-time qPCR. HT, DS, and HT+DS treatments altered gene expression profiles. Compared to the CK, expression of 22 of the 23 genes was down regulated by HT, and only one gene (ISA2) was up-regulated by HT. Actually ISA2 was the only gene up-regulated by all three stress treatments. The expression of 17 genes was up-regulated, while six genes, including granule-bound starch synthase (GBSSI), AGPS2, BEIII, PHOL, ISA1, and AGPL2, were down-regulated by DS. Eleven genes were down-regulated and 12 were up-regulated by HT+DS. The activity of ADP-Glc pyrophosphorylase, starch synthases, GBSS, SS, and starch branching enzymes in the stress treatments (HT, DS, and HT+DS) often appeared to peak values in advance and declined significantly to be lower than that in the CK. The genes that coordinated participation in the enzymes formation can serve as an indicator of the enzymes activity potentially involved in starch biosynthesis. HT, DS, and HT+DS altered the timing of starch biosynthesis and also influenced the accumulation of amylose, amylopectin, total starch, and sucrose. Under HT, DS, and HT+DS, the key enzymes activity and their genes expression associated with the conversion of sucrose to starch, was reduced, which was the leading cause of the reductions in starch content. Our study provide further evidence about the effects of stress on starch biosynthesis in wheat, as well as a physiological understanding of the impact of post-anthesis heat and DS on starch accumulation and wheat grain yield.

Light-response curve of photosynthesis and model fitting in leavesof Mangifera indica under different soil water conditions

A pot experiment was performed to study the light-response curve of photosynthesis (PN-PAR curve) of Mangifera indica and the applicability of light-response models under different soil water conditions. The experimental data were fitted and analyzed using the rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, the modified rectangular hyperbola model, and the kinetic model. The results showed that the optimal range of relative soil water content (RSWC) for the normal photosynthesis of M. indica was 45.1-77.3%. The modified rectangular hyperbola model could well fit the PN-PAR curves and photosynthetic parameters under wide range of soil water conditions (RSWC 23.3-77.3%). The rectangular hyperbola model, the nonrectangular hyperbola model, the exponential model, and the kinetic model could only be used to fit the PN-PAR curves of M. indica under mild and moderate drought stress (RSWC 45.1-77.3%).