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Water management is an important practice that affects fruit size and quality. Effective implementation of irrigation scheduling requires knowledge of the appropriate indicators and thresholds, which are established manly based on the effects of water deficits on final fruit quality. Few studies have focused on the real-time effects of water status on fruit and shoot growth. To establish soil water potential (jsoil) thresholds to trigger irrigation of peach at pivotal fruit developmental stages, photogrammetry, 13C labelling, and other techniques were used in this study to investigate real-time changes in stem diameter, fruit projected area, net leaf photosynthetic rate (Pn), and allocation of photoassimilates to fruit under soil water potential conditions ranging from saturation to stress in 6-year-old 'Shimizu hakuto' peach. Stem growth, fruit growth, and Pn exhibited gradually decreasing sensitivity to water deficits during fruit developmental stages I, II, and III. Stem diameter growth was signifi- cantly inhibited when jsoil dropped to -8.5, -7.6, and -5.4 kPa, respectively. Fruit growth rate was low, reaching zero when the jsoil was -9.0 to -23.1, -14.9 to -21.4, and -16.5 to -23.3 kPa, respectively, and Pn decreased significantly when the jsoil reached -24.2, -22.7, and -20.4 kPa, respectively. In addition, more photoassimilates were allocated to fruit under moderate jsoil conditions (-10.1 to -17.0 kPa) than under other jsoil values. Our results revealed three jsoil thresholds, -10.0, -15.0, and -15.0 kPa, suitable for triggering irrigation during stages I, II, and III, respectively. These thresholds can be helpful for controlling excessive tree vigor, maintaining rapid fruit growth and leaf photosynthesis, and promoting the allocation of more photoassimilates to fruit. [ABSTRACT FROM AUTHOR]

Background and Objective The history of using American mesquite (Prosopis juliflora) for desertification control especially sand stabilization in Iran, is long. Considering the non-native nature of this species, attention should be paid to its ecological requirements, especially water needs or evapotranspiration (ET). This can contribute to the sustainability of sand stabilization programs and fine dust control and play an influential role in ecosystem development. Determining plants' evapotranspiration rates through lysimetry is one of the most accurate direct measurement methods. Methodology The experiment using weighing and drainage lysimeters began in 2021 by planting seedlings inside lysimeters located at the Yazd Shahid Sadoughi Desert Research Station. It continued for two years. Nine lysimeters with a volume of 1.95 m³ (height: 170 cm, diameter: 121 cm) and a surface area of 1.15 m² were used. The ET rates and the crop coefficient (Kc) of Prosopis juliflora were studied under different soil moisture levels, including field capacity (no stress), 67% of field capacity (mild stress), and 34% of field capacity (severe) for various growth stages. Irrigation was performed by drip irrigation based on a fraction of field capacity with an appropriate number of droppers calculated for each treatment. For field capacity, 67% and 34% of field capacity treatments, 6, 4, and 2 droppers with an 8 liters per hour flow rate were used, respectively. Each treatment was irrigated twice with the appropriate amount of water based on soil moisture levels. Results The results showed that Prosopis juliflora, under lysimeter conditions and the local climate, had an annual ET rate of 496.5 mm and a Kc 0.21. These values for the 67% and 34% field capacity treatments were 445.4 mm with Kc 0.18 and 275.2 mm with Kc 0.11, respectively. The ET rates of Prosopis juliflora at different growth stages revealed that the highest ET occurred during the development period of 124 days. This corresponds to rapid shoot, branch, and leaf growth. The ET rates in different irrigation regimes for field capacity, 67%, and 34% of soil moisture were 322.1 mm, 281.7 mm, and 158.3 mm, respectively. The lowest ET rate was associated with the final growth stage. The Kc for various growth stages in the field capacity treatment were 0.19, 0.24, and 0.14 for the first, second, and third growth periods, respectively. Under these conditions, a sigmoid growth curve (initial growth, development, and end of growth) can be defined for this plant. Conclusion It is recommended for afforestation with this species in Iran's southern regions, considering its optimal planting density to reduce competition. It is also recommended to pay attention to its ET rate, especially during the hot months of the year when it can exceed 2.5 mm per day. By examining and calculating the ET rates of mature trees with appropriate efficiency in sand stabilization and dust control, it was found that to create a canopy cover area, as mentioned, it is necessary to have 4846 m3 of water per hectare (equivalent to 484.6 mm per year) available to the plant. In other words, with this amount of ET, the plant can expand its canopy cover area to 19.5 m2 and, with 155 individuals per hectare (8×8 meters), cover 30% of the area, which is suitable for sand stabilization. [ABSTRACT FROM AUTHOR]

Non-invasive techniques such as RGB, thermal imaging, and optical sensing can provide information on plant water stress before it occurs. In the present study, the maize crop (Var. DMRH 1301) was cultivated with three different sowing dates (1, 15, and 30 June) under rainfed condition. The RGB and thermal images along with crop growth parameters were recorded periodically along with soil moisture in maize. A deep learning model (DarkNet53) was applied on RGB as well as thermal images for the identification of water stress. The occurrence of rainfall and thereby soil moisture had a significant effect on crop canopy temperature under different dates of sowing. The canopy temperature histogram under water stress showed bimodal distribution whereas unimodal distribution was observed under non-stress condition. The maximum accuracy of the DarkNet53 model at 20 epochs and 8 batch size for the identification of water stress in RGB and thermal imagery was 94.1 and 99.6%, respectively. The testing accuracy of identification of water stress for RGB imagery were 94.1, 90.5, and 92.3% and for thermal imagery 95.7, 91.5, and 99.6% in early, timely and late sown maize, respectively. Overall, thermal imagery input had higher accuracy for water stress identification. The present study showed that non-destructive, rapid vision-based techniques using digital imagery can helpto characterize plant growth, water stress, and thereby, yield. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the effects of different tillage on the main soil physical properties in the conditions of Ezareni Farm, Iasi, Romania. The study was conducted at the Ezareni Farm within the Didactic Station of the University of Life Sciences,,Ion Ionescu de la Brad'' Iasi. The study was carried out on a cambic chernozem soil type. Two tillage systems, the conservative or no- tillage (NT) and the conventional one (CT), have been evaluated. The soil bulk density, the soil moisture and water stable aggregates were determined for each tillage system. The bulk density was determined measuring both the soil weight and volume at sampling. These soil samples were taken from four different layers: 0-10, 10-20, 20-30 and 30-40 cm. Regarding the water stability of soil aggregates, the soil samples were also taken at different depths and the soil moisture content was evaluated. Soil samples were taken down to a depth of 90 cm. Sampling was carried out in three replicates for each depth. The no-till system had a highly significant effect on the bulk density of the soil, particularly at a depth of 10-20 cm (NT2), with 1.50 g/cm³ being the highest value obtained. The same effect was observed for soil aggregate stability under the same treatment and at the same depth, where the highest value was 90.16%. Regarding to soil moisture, it took the second year of study to obtain a significant effect. [ABSTRACT FROM AUTHOR]

Copyright of Atatürk University Journal of Agricultural Faculty is the property of Ataturk University Coordinatorship of Scientific Journals and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights • Established irrigation thresholds, for different growth stages of tilled DSR, to realize higher yield and water productivity in DSR. • Irrigation threshold of −15 kPa at all growth stages recorded better crop growth and grain yield. • Irrigations at −30 kPa up to the end of vegetative phase and −15 kPa thereafter in DSR, proved as safer irrigation threshold. • Best DSR treatment (irrigations at −15 kPa at all stages) did not match the yield potential of transplanted puddled rice (TPR). Abstract Water and labour scarcity besides increasing cost of cultivation in transplanted puddle rice (TPR) warrants to develop and adopt input use efficient and cost effective direct seeded rice (DSR) method of cultivation. Though DSR saves substantial amount of irrigation but there are contradictory observations on yield realization. Therefore, a two year field study was undertaken with the aim to develop efficient irrigation strategy for maximizing tilled DSR yield with minimum irrigation input. Total 08 irrigation strategies, based on 03 soil matric potential (SMP) levels (−15, −30 and −45 kPa) and their combinations based on crop growth stages, were evaluated for fine grain aromatic (Basmati) rice variety 'CSR30'. Responses of respective irrigation strategies were evaluated on crop water use and its components, biometric parameters and yield attributes and yield of DSR. Performance of DSR was also compared with standard TPR practice. Soil profile moisture content ranged from 32 to 39, 27–39 and 22–39% in −15, −30 and −45 kPa irrigation regimes, respectively. Irrigation input in DSR method of cultivation varied between 709–1541 mm as compared to 1807 mm of TPR. With different irrigation strategies, DSR grain yield and irrigation water productivity (IWP) varied from 1.72 to 2.89 Mg/ha and 0.19–0.24 kg/m3, respectively. Irrigation threshold −15 kPa at all stages in DSR produced the highest yield and crop water productivity (CWP; 0.48 kg/m3), but with lowest IWP. Irrigations at or below −30 kPa during initial phase (<90 DAS) and at −15 kPa during remaining period produced comparable yield with significantly higher IWP. Though TPR registered lower IWP (0.18 kg/m3) as compared to the best DSR treatment but recorded about 11% higher grain yield with significantly higher crop water productivity (0.58 kg/m3) than DSR. Water balance studies revealed better utilization of precipitation in DSR due to irrigations at more negative SMP. Overall, study suggests irrigation scheduling at < −30 kPa during initial phase and −15 kPa during the remaining crop season proved to be the optimum irrigation threshold for maximizing DSR yield with limited irrigation input. [ABSTRACT FROM AUTHOR]

Copyright of Acta Agriculturae Slovenica is the property of Biotechnical Faculty of the University of Ljubljana and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights • A new data-driven method is developed to partition ET based on the separation of soil and canopy conductances. • Magnitudes and trends in soil conductance, canopy conductance, E, and T:ET are consistent with physical understanding. • LAI only explained small variations of mean annual T:ET across sites. Abstract Separating evapotranspiration (ET) into evaporation (E) and transpiration (T) is challenging but key for a better understanding and prediction of the hydrological cycle and plant water use. In this study, flux data at 30 routine eddy-covariance sites were used to develop a new and simple method for ET partitioning based on the separation of soil and canopy conductances, with the main assumption that the latter is proportional to gross primary productivity (GPP). The result of T:ET across different plant functional types (PFTs) was consistent with recent modeling or empirical results. The mean annual T:ET was highest for evergreen needleleaf forests (0.75 ± 0.17), followed by croplands (0.62 ± 0.16) and grasslands (0.56 ± 0.15). The leaf area index (LAI) was shown to explain only small (20%) variations of mean annual T:ET across sites. However, at each site, the correlation of T:ET with LAI was strong at the seasonal scale, where T:ET increased nonlinearly with LAI. The results did not show significant relationship of T:ET with long-term mean precipitation across sites at multiyear timescales. However, the partitioned soil evaporation after each precipitation pulse is consistent with three-stage soil evaporation theory. This ET partitioning method is an objective assessment as it is mainly data-driven. The procedure to apply this method is also simple so it can be readily applied to global flux tower networks at different temporal and spatial scales, enabling continuous estimation of T:ET to monitor ecosystem dynamics and hydrological responses to environmental change. [ABSTRACT FROM AUTHOR]

Soil Temperature (ST) data, obtained from either field works or satellite imagery, has frequently been studied for Soil Moisture (SM) estimation. However, a combination of ST data at different depths and soil surface temperature, i.e., Surface Radiometric Temperature (SRT) or Land Surface Temperature (LST), has not yet been well investigated for accurate SM prediction. In this study, an empirical model was first developed to estimate SM at 5 cm Depth (SM5D) over areas with no or sparse vegetation cover using the field SRT and field ST data at 5 cm Depth (ST5D). A Root Mean Square Error (RMSE) and a correlation coefficient (r) of 0.037 m3 m−3 and 0.8 were obtained using this model, respectively. Then, the SRT was substituted by the LST obtained from Landsat thermal bands and ST5D was estimated using the ST data collected at the nearest weather station to the study area by developing a regression equation. The second model demonstrated an RMSE and r of 0.035 m3 m−3 and 0.71, respectively. Overall, it was concluded that the proposed models had high potential for SM estimation using the ST data at different depths collected in the field or acquired by optical satellites. [ABSTRACT FROM AUTHOR]

Background and Aims: Available soil water is an important factor determining grapevine yield and grape composition. The aim of this study was to determine the impact of water availability on the yield components and the composition of must and wine of Vitis vinifera L. cv. Verdejo. Methods and Results: The irrigation strategies [rainfed (R0), drip irrigated at 25% ETo (R25) and 50% ETo (R50) applied weekly from the end of the vegetative main shoot growth until harvest] were imposed on white Verdejo grapevines over three consecutive seasons (2012–2014). The 50% ETo treatment resulted in the highest yield. Increasing water availability also reduced the concentration of volatile phenols in all seasons, and of the C6 compounds in 2014 alone. The highest concentration of five individual volatile compounds was associated with the lowest water availability (R0). Conclusions: High water availability increased yield and its components, mainly in the wettest season. Volatile compounds in wine were modified by water regime, with their concentration increased by the most severe deficit irrigation regime (R0). The effect of the year on must and wine composition was greater than the in‐season effects of water availability treatment. Significance of the Study: This study has described the effect of soil water availability on yield and its components and the composition of must and wine of Verdejo. [ABSTRACT FROM AUTHOR]

Aims: Root shrinkage in drying soil has been shown repeatedly. The aim of this study was to investigate the dynamics of root-soil contact and its relationship with plant water status during soil drying.Methods: The development of root-soil contact of Vicia faba L. during a drying period was studied. Plants (N = 4) were grown in cylinders filled with a sandy soil. Samples were repeatedly scanned with an X-ray CT scanner to visualize root-soil contact. Soil matric potential, transpiration rate, and stomatal conductance were measured daily.Results: Root-soil contact was lower in taproots than in lateral roots at any time. Transpiration rate and stomatal conductance decreased before roots started to shrink. Root-soil contact decreased significantly over the course of the drying period, starting at soil matric potentials below −20 kPa. Root shrinkage did not differ significantly between taproots and laterals.Conclusions: This study confirms previous findings with Lupinus albus roots in that roots shrink after transpiration rate decreases. The dynamics of root shrinkage are governed by soil water availability and transpirational demand. [ABSTRACT FROM AUTHOR]

Abstract: Soil moisture controls microbial activity and soil carbon cycling. Because microbial activity decreases as soils dry, decomposition of soil organic matter (SOM) is thought to decrease with increasing drought length. Yet, microbial biomass and a pool of water‐extractable organic carbon (WEOC) can increase as soils dry, perhaps implying microbes may continue to break down SOM even if drought stressed. Here, we test the hypothesis that WEOC increases as soils dry because exoenzymes continue to break down litter, while their products accumulate because they cannot diffuse to microbes. To test this hypothesis, we manipulated field plots by cutting off litter inputs and by irrigating and excluding precipitation inputs to extend or shorten the length of the dry season. We expected that the longer the soils would remain dry, the more WEOC would accumulate in the presence of litter, whereas shortening the length of the dry season, or cutting off litter inputs, would reduce WEOC accumulation. Lastly, we incubated grass roots in the laboratory and measured the concentration of reducing sugars and potential hydrolytic enzyme activities, strictly to understand the mechanisms whereby exoenzymes break down litter over the dry season. As expected, extending dry season length increased WEOC concentrations by 30% above the 108 μg C/g measured in untreated plots, whereas keeping soils moist prevented WEOC from accumulating. Contrary to our hypothesis, excluding plant litter inputs actually increased WEOC concentrations by 40% above the 105 μg C/g measured in plots with plants. Reducing sugars did not accumulate in dry senesced roots in our laboratory incubation. Potential rates of reducing sugar production by hydrolytic enzymes ranged from 0.7 to 10 μmol·g−1·h−1 and far exceeded the rates of reducing sugar accumulation (~0.001 μmol·g−1·h−1). Our observations do not support the hypothesis that exoenzymes continue to break down litter to produce WEOC in dry soils. Instead, we develop the argument that physical processes are more likely to govern short‐term WEOC dynamics via slaking of microaggregates that stabilize SOM and through WEOC redistribution when soils wet up, as well as through less understood effects of drought on the soil mineral matrix. [ABSTRACT FROM AUTHOR]

We conducted an experiment with two agricultural soils with acidic and alkaline pH levels to assess the effects of zinc oxide nanoparticles (nZnO) on the bacterial community. The effect of the nZnO concentrations (0, 0.1, 1, 10, 100, 1000 mg Zn/kg soil) and contact time between nanoparticles and soil (180 days) was considered. We measured the microbial respiration rate, nitrogen transformation, enzymatic activities (dehydrogenase (DH), acidic phosphatase (ACP), and alkaline phosphatase (ALP)), and the community-level physiological profile (CLPP) soil parameters. Respiration potential and nitrogen transformation were negatively affected only at the highest nZnO concentration. The changes in enzymatic activities were very variable with time and between both soils. A stimulating effect of the nanoparticles on microbial activity was clearly shown at 30 days after the nZnO application in both soils, except for the 1000 mg/kg in calcareous soil, after which time in the latter, the functional richness of the bacterial community was reduced to virtually zero. However, values of the enzymatic activities demonstrated that there was self-adaptation of microbial communities over the study period (180 days). The nZnO 1000 mg/kg dose produced an increase in bacterial growth in the acidic soil, without apparent changes in their metabolic profiles over time. A good correlation was found between microbial respiration rates (calcareous and acidic soils) and microbial metabolic activity (acidic soil) based on extracted Zn concentrations. Our findings suggest the necessity of additional studies to examine the effects of nZnO in natural microorganism populations in soil with different pH levels for extended periods of time. [ABSTRACT FROM AUTHOR]

Abstract: Predicting species responses to climate change involves understanding both the direct effects of environmental change, as well as indirect effects mediated by altered interspecific interactions. Indirect effects may be particularly important for understanding native species responses in systems invaded by highly competitive exotic species. For instance, Mediterranean climate regions are predicted to experience more frequent drought, and are increasingly invaded by exotic annual plants. For native shrubs in these regions, seedling establishment is episodic, and associated with high rainfall years. However, exotic annual plants also often increase in abundance with high rainfall, suggesting competition from exotic annual species could alter the relationship between rainfall and shrub seedling establishment. Theories such as the stress gradient hypothesis predict competition intensity should increase with resource supply, but there have been few evaluations of competitive interactions across experimental gradients of soil moisture availability. Here we examined how competition from an exotic annual influenced native shrub establishment, across an experimental soil moisture gradient. Seedlings of two native shrub species (Encelia californica and Eriogonum fasciculatum) were grown with and without an exotic grass competitor (Avena fatua) across eight water availability levels, and monitored for growth and survival. These species are common and abundant in the Mediterranean climate region of coastal Southern California, where climate change projections include long‐term drought for the coming decades. Without competition, shrub seedlings achieved higher growth and survival at high water availability levels. However, when grown in competition with the exotic grass, shrub seedlings had higher growth and/or survival under relatively dry conditions, suggesting competition can modify and even reverse species responses to changing rainfall patterns, compared to predictions made in the absence of competitors. The exotic grass strongly reduced soil nitrate and water availability when it was planted with the native shrub seedlings, and the exotic grass responded with positive but saturating growth with increasing levels of water addition. Synthesis. This experiment demonstrates that competition from invasive species can alter native species responses to climate change; consistent with ecological theories predicting a positive association between the supply of limiting resources and the intensity of competition. [ABSTRACT FROM AUTHOR]

Snow strongly affects ecosystem functioning in alpine environments with potential carry-over effects outside of snow periods. However, it is unclear whether changes in snow cover affect microbial community functioning in summer. In a field experiment, we tested whether manipulation of snow cover affected the functional capabilities of the microbial community either directly, or indirectly through concomitant changes in the vegetation. While 23 years of differential snow depth and persistence fundamentally changed the vegetation composition, the microbial community's ability to catabolize a range of carbon compounds was not altered. Instead, soil moisture content was the key driver of carbon catabolism by the microbial community. [ABSTRACT FROM AUTHOR]

Soil moisture is one of the main reasons for the decline of predictive accuracy of soil attributes (organic carbon, salt, etc.) in using spectrum analysis method. By comparing the two methods of external parameter orthogonization (EPO) and non-negative matrix factorization (NMF), the purpose of this article is to explore a method and technology route of removing the effect of soil moisture (SM) and improving the estimation precision of soil salt content (SSC) based on hyperspectra. Firstly, we used Kenli county of Shandong province as the research area, and took 96 soil samples in the fields. The samples’ hyperspectra in situ and indoor after air-dry were measured respectively by spectra radiometer, and then transformed to the first deviation. The content of soil salinity and moisture were measured in laboratory. Then, the spectral characteristics of soil salt content and the effect of soil moisture on it were analyzed by comparison. Next, the external parameter orthogonization and non-negative matrix factorization were respectively used to correct and fuse the soil spectra in situ (Situ-spectra), and to remove the SM effect, and form the EPO correction spectra (EPO-spectra) and the NMF fusion spectra (NMF-spectra) of the Situ-spectra. Finally the estimation models of SSC were built respectively by the multiple step linear regression (MSLR) and the partial least squares regression (PLSR) based on the Situ-spectra, EPO-spectra and NMF-spectra, and were verified and compared to analyze the change of the SSC prediction precision. The results indicated that the soil salt content was high the soil salt content gradient was obvious, and the dispersion degree of soil salt content was high. However the soil moisture content was about 30 times of the soil salt content in the study area. The correlation between soil salinity and spectra is better at the band ranges of 1440 - 1660 nm, 1830 - 1860 nm, 1960 - 2110 nm. The soil moisture had great effect on the Situ-spectra and soil salt content spectral characteristics. Therefore, it is necessary to remove soil moisture impact. The EPO method can reduce the correlation between spectra and soil moisture in most spectral regions, and at the same time weaken the correlation between spectra and soil salinity in local bands. In comparison, the NMF method can effectively reduce the correlation between spectra and soil moisture, and increase the correlation between spectra and soil salinity. Both the EPO and NMF can improve the accuracy of the soil salt content estimation based on Situ-spectra. After adoption of EPO, the validation coefficient of determination (R2) increased between 0.08 and 0.09, and the relative prediction deviation (RPD) increased between 0.08 and 0.69%. At the same time, after adoption of NMF, the validation R2 increased between 0.27 and 0.38 and reached above 0.80, the RPD increased between 1.04 and 1.06, and reached above of 2.37. Thus the result of NMF was more significant than that of EPO for the removal of the SM effect. The method of EPO combined with PLSR or NMF combined with MSLR can be used as the technical route of removing the soil moisture effect and building soil salt content calibration model. The results can effectively promote the quantitative remote sensing extraction and real-time, in-situ monitoring of the saline soil information. [ABSTRACT FROM AUTHOR]

Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water supply regimes on water resources in tropical regions. This interaction is a major issue because climate change is expected to increase the length of drought periods in many tropical regions and soil water availability in deep soil layers is likely to have a major influence on tree growth during dry periods in tropical planted forests. A process-based model (MAESPA) was parameterized in a throughfall exclusion experiment in Brazil to gain insight into the combined effects of K deficiency and rainfall reduction (37% throughfall exclusion) on the water used by the trees, soil water storage and water table fluctuations over the first 4.5 years after planting Eucalyptus grandis trees. A comparison of canopy transpiration in each plot with the values predicted for the same soil with the water content maintained at field capacity, made it possible to calculate a soil-driven tree water stress index for each treatment. Compared to K-fertilized trees with undisturbed rainfall (+K+W), canopy transpiration was 40% lower for K deficiency (−K+W), 20% lower for W deficit (+K−W) and 36% lower for combined K deficiency and W deficit (−K−W) on average. Water was withdrawn in deeper soil layers for −W than for +W, particularly over dry seasons. Under contrasted K availability, water withdrawal was more superficial for −K than for +K. Mean soil water content down to 18 m below surface (mbs) was 24% higher for −K+W than for +K+W from 2 years after planting (after canopy closure), while it was 24% lower for +K−W and 12% lower for −K−W than for +K+W. The soil-driven tree water stress index was 166% higher over the first 4.5 years after planting for −W than for +W, 76% lower for −K than for +K, and 14% lower for −K−W than for +K+W. Over the study period, deep seepage was higher by 371 mm yr −1 (+122%) for −K than for +K and lower by 200 mm yr −1 (−66%) for −W than for +W. Deep seepage was lower by 44% for −K−W than for +K+W. At the end of the study period, the model predicted a higher water table for −K (10 mbs for −K+W and 16 mbs for −K−W) than for +K (16 mbs for +K+W and 18 mbs for +K−W). Our study suggests that flexible fertilization regimes could contribute to adjusting the local trade-off between wood production and demand for soil water resources in planted forests. [ABSTRACT FROM AUTHOR]

Mixed forest plantations now emerge as an alternative to traditional plantations in the tropics and represent ecological gains associated with production, wood quality and nutrient cycling. Mixed plantations with higher diversity may also be advantageous concerning their use of soil water. To shed light onto water-related issues of mixing Eucalyptus and a high diversity of tropical native trees, we explored the following questions: What is the impact of high diversity mixed plantations of Eucalyptus intercropped with native trees on soil water? How does the mixture affect the physiology of water use in native trees? Firstly, we tested the hypothesis that stands of Eucalyptus mixed with a high diversity of native trees consume less water compared to Eucalyptus monocultures, by measuring the temporal dynamics of soil water. Secondly, we tested how mixing with Eucalyptus affects the hydraulic performance of fast- and slow-growing native species in these forestry systems. This is the first time a large experiment has been implemented to compare the effects of monospecific Eucalyptus plantations, native species mixtures and mixed plantations of Eucalyptus and native species on soil water dynamics under controlled conditions in terms of site, age, soil type, topography and climate. We found that high diversity mixed plantations of Eucalyptus and native trees use less soil water, than Eucalyptus monocultures. However, the soil under the mixtures was drier than in native species stands. The mixing with Eucalyptus affected the hydraulic performance of native species by decreasing the leaf water potential and stomatal conductance of the fast-growing species, suggesting that fast-growing species performance may be especially constrained by competition for water from Eucalyptus . These findings have important implications for forest management and ecological restoration in the tropics. They will help to further develop silvicultural options to adapt to climate change and improve plantation forestry by using mixed plantations for production purposes or rehabilitation of degraded lands. [ABSTRACT FROM AUTHOR]

Improvements in soil water balance modeling can be beneficial for optimizing irrigation management to account for spatial variability in soil properties and evapotranspiration (ET). A remote-sensing-based ET and water balance model was tested for irrigation management in an experiment at two University of Nebraska-Lincoln research sites located near Mead and Brule, Nebraska. Both fields included a center pivot equipped with variable rate irrigation (VRI). The study included maize in 2015 and 2016 and soybean in 2016 at Mead, and maize in 2016 at Brule, for a total of 210 plot-years. Four irrigation treatments were applied at Mead, including: VRI based on a remote sensing model (VRI-RS); VRI based on neutron probe soil water content measurement (VRI-NP); uniform irrigation based on neutron probe measurement; and rainfed. Only the VRI-RS and uniform treatments were applied at Brule. Landsat 7 and 8 imagery were used for model input. In 2015, the remote sensing model included reflectance-based crop coefficients for ET estimation in the water balance. In 2016, a hybrid component of the model was activated, which included energy-balance-modeled ET as an input. Both 2015 and 2016 had above-average precipitation at Mead; subsequently, irrigation amounts were relatively low. Seasonal irrigation was greatest for the VRI-RS treatment in all cases because of drift in the water balance model. This was likely caused by excessive soil evaporation estimates. Irrigation application for the VRI-NP at Mead was about 0 mm, 6 mm, and –12 mm less in separate analyses than for the uniform treatment. Irrigation for the VRI-RS was about 40 mm, 50 mm, and –98 mm greater in separate analyses than the uniform at Mead and about 18 mm greater at Brule. For maize at Mead, treatment effects were primarily limited to hydrologic responses (e.g., ET), with differences in yield generally attributed to random error. Rainfed soybean yields were greater than VRI-RS yields, which may have been related to yield loss from lodging, perhaps due to over-irrigation. Regarding the magnitude of spatial variability in the fields, soil available water capacity generally ranked above ET, precipitation, and yield. Future research should include increased cloud-free imagery frequency, incorporation of soil water content measurements into the model, and improved wet soil evaporation and drainage estimates. [ABSTRACT FROM AUTHOR]

The semi-arid region of the Loess Plateau is typical of rain-fed agricultural production in Northwestern China. In this area, the ridge mulched system (RM) is a widely-used measure to increase crop yield. The purpose of this study was to investigate the effect of RM on soil water and inorganic nitrogen (N) distribution, and grain yield of maize ( Zea mays L.). The study was conducted over three consecutive years and consisted of four treatments (each replicated three times): i) RM with N application rate of 260 kg N ha −1 (RM-N260); ii) RM with 180 kg N ha −1 (RM-N180); iii) a traditional flat cultivation system without mulching (F) with 260 kg N ha −1 (F-N260); iv) F with 180 kg N ha −1 (F-N180). Mean soil water content during the maize growing season was increased by RM in 2013 only. However, RM increased the soil water storage significantly at the 3-leaf (V3) and 6-leaf stage (V6), and decreased evapotranspiration (ET) during pre-silking stage in all years. Compared to F, RM significantly improved maize grain yield by 79–123% in 2013, 23–25% in 2014, and 11–12% in 2015. Following three years of maize cultivation, soil inorganic N content increased substantially (two- to three-fold) in the RM system and 60% of the total inorganic N was accumulated in the top soil layers (0–60 cm) under the mulched ridge. Relative changes were much smaller in F, and most of inorganic N was stored in 0–20 cm and 100–160 cm soil layers. Generally, RM resulted in higher soil water storage during the pre-silking stage, which was the main reason for the improved maize grain yield. The nitrate leaching risk was reduced in RM-N180 compared with F, but nitrate leaching from the furrows between ridges was observed in RM-N260. However, the large increase in soil inorganic N content in RM-N180 after three years’ cultivation indicates an oversupply of N and a potential risk of N losses to the environment over the longer term. Our study indicates, therefore, that RM is a suitable system for maize cropping in the semi-arid region of the Loess Plateau, with benefits in water and N use efficiency, but recommendations for appropriate N application rates are required to ensure long term agricultural sustainability, accounting for grain yields and environmental impacts. The mechanisms for inorganic N accumulation under the RM system are not fully understood and warrant further investigation. [ABSTRACT FROM AUTHOR]

Chestnut orchards are facing new limitations due to scarce of soil water during summer times, mainly attributed to the low precipitation amount typically occurred on such period. The present study aims to define a methodology to improve in a smart way the utilization of water on chestnut irrigation. Based on leaf gas exchanges parameters, there is done a transposition for the soil water content and matric potential, to allow an optimization of the irrigation scheduling in chestnut trees. Trial was installed in a loamy soil at the northeast of Portugal between 2013 and 2016 with micro-sprinkler and drip irrigation system. Stem water potential, photosynthetic rate, soil water content and soil water potential were monitored during the vegetative cycle (June–October). The stem water potential was dependent on air’s temperature and soil moisture. The higher photosynthetic rate (9–11 μmolCO 2 ·m −2  s −1 ) was reached when midday stem water potential ranged between −1.2 to −0.5 MPa and the regression between stem water potential and soil water content on the top 10–40 cm of soil was of r 2  = 0.38. According to these, it was admissible to trigger irrigation when the probe registers 16% and watering must keep soil’s moisture near 23%. The regression between stem and soil water potential was of r 2  = 0.43 and irrigation scheduling may be triggered when ‘Watermark’ sensor at 30–60 cm soil depth is above −100 cbar to promote good tree water status although this last is air temperature dependent. [ABSTRACT FROM AUTHOR]

This study was carried out in Estahban, Iran, during 2013 and 2014 to identify the optimal time and amount of supplemental irrigation at different distances from tree trunks on a rainfed fig orchard. This region is distinguished as the largest producer of dried figs in Iran and the world and its production is highly dependent on precipitation. A split–split plot statistical design with four replicates was used to conduct the experiment. Irrigation treatments based on the position of application around trees were: in a micro-catchment close to tree trunks; in three holes inside of tree canopies with a mean canopy of 3.2 m diameter (placed 1–1.1 m from tree trunks); and in four holes outside of tree canopies placed 2.1–2.2 m from tree trunks were used in this experiment. Irrigation time treatments consisted of: (a) in early spring; (b) in mid-summer and the three different volumes of irrigation water were used: no supplemental irrigation (control), and either 1000 or 2000 l of irrigation water per tree. Results showed a high evaporation rate in the area which used nearly half of the rainfall during autumn and winter. There was a significant positive correlation between soil water content (SWC) and temporal rainfall distribution as r **  = 0.63 (p < 0.001) over two years. Under drought conditions, irrigated trees showed higher ET a that was close to the ET a in years with normal rainfall. Compared to irrigation in summer, irrigation in early spring kept higher SWC for a longer time period in the soil profile and irrigation far from trees increased soil surface evaporation especially in summer. This study suggests that using supplemental irrigation with 2000 l per tree of water in early spring near tree trunk could provide higher SWC and lower surface evaporation for rainfed fig orchards during drought conditions. [ABSTRACT FROM AUTHOR]

Potential yield of a crop is limited by the factor which most restricts its productivity. In dryland cropping systems this factor is often the available soil water. Nitrogen fertiliser is also a high cost input in crop production systems. Conservation of these resources is essential to increase agricultural productivity and profitability. A field experiment and computer simulation modelling were conducted for the dryland farming system of south eastern Australia to investigate the effect of summer fallow management on growth and yield of canola ( Brassica napus L.). A factorial experiment with two residual nitrogen levels and three residual soil water conditions was conducted. Soil water content and crop growth were monitored. At harvest, canola grain yield and above-ground biomass were measured. The biophysical model APSIM was used to analyse the effect of seasonal variation on crop yield by simulating canola grain yield at different residual water and nitrogen levels. The field experiment and simulation modelling indicated that in seasons with high in-crop rainfall, high residual soil water does not increase crop yield. However, residual nitrogen increases crop yield if in-crop rainfall is high. Irrespective of the in-crop rainfall, controlling summer weeds increases crop yield due to residual mineral N and/or residual soil water. [ABSTRACT FROM AUTHOR]

Marginal quality saline sodic water will be important for agricultural production in water limited environments, and has been demonstrated as suitable for irrigation on a soil-specific basis. Suitability is usually demonstrated as the threshold electrolyte concentration ( C TH ), defined as a 10–20% reduction in saturated hydraulic conductivity. Others have suggested that the aggregate-dispersion boundary may be used as this threshold, which is also known as the threshold turbidity concentration ( C TU ). Using a saturated hydraulic conductivity approach, this work sought to quantify the extent of reduction at the C TU and compare this to traditional C TH approaches to define the practicality of the thresholds. The C TU was determined as the point where dispersed clay was detected, and subsequently compared to the C TH with the difference between these compared within the measured domain. The reduction in saturated hydraulic conductivity from a Ca dominant stable condition was determined at each threshold value. It was found that saturated hydraulic conductivity at the C TU reduced by between 44 and 78% for the five Vertisol soils investigated, demonstrating that the C TU varied between soils and was substantially more than the 10–20% reduction in hydraulic conductivity at the C TH . Discussion on application of these thresholds to practical irrigation is provided, and suggests that irrigation water quality application can be optimised on a soil-specific basis. Results reinforce that management guidelines should not be based on the C TU , or at the aggregation-dispersion boundary. [ABSTRACT FROM AUTHOR]

Agricultural soils are strong sources of the potent greenhouse gas N 2 O but soil N 2 O emissions and its microbial mechanism in greenhouse field, especially ammonia-oxidizing microorganisms are unclear. We characterized a potential response in soil N 2 O production and its influencing factors, such as soil temperature, moisture, pH, and inorganic nitrogen to different irrigation methods named drip irrigation (DI), subsurface irrigation (SI) and furrow irrigation (FI) in a long-term irrigation field in greenhouse. The abundance and metabolic activity of ammonia oxidizing archaea (AOA) and bacteria (AOB) in greenhouse soils were also investigated using amoA gene as a molecular biomarker by quantitative PCR and 13 CO 2 -DNA-stable isotope probing (SIP) methods. Results showed that N 2 O flux peaks would obviously occur within 1–8 days after each irrigation. The soil N 2 O flux in FI treatment was significantly higher than that in DI and SI treatments ( P <  0.05). Correlation analysis between soil N 2 O flux and its influencing factors indicated that soil moisture and nitrate nitrogen were substantially affecting soil N 2 O emissions compared with soil temperature, pH and ammonium nitrogen. The copy numbers of AOA amoA gene in FI treatment were significantly higher than those in DI and SI treatments ( P <  0.05), while there is no significant difference of AOB amoA gene among the three treatments. Also, the copy numbers of AOA amoA gene were significantly higher than those of AOB amoA gene. The 13 CO 2 -DNA-SIP and phylogenetic tree results indicated only AOB dominantly involved in Nitrosospira genera was active during the nitrification process in the three irrigation methods. Our findings provided direct evidence that drip irrigation and subsurface irrigation could effectively reduce soil N 2 O emissions in greenhouse. AOA was dominant in abundance, while AOB played a key role in microbial community under the conditions of this experiment. Future characterization of the mechanisms for ammonia oxidation requires deeper studies in the greenhouse field. [ABSTRACT FROM AUTHOR]

The combined application of different functional chemicals creates challenges both in modeling water flow in soil and quantification of water extraction by crops in dry land farming. In the present study, 2-year laboratory and field experiments were conducted in a typical dry land of northern China in order to: (i) develop a model to describe patterns of water flow in soil under two typical chemicals Superabsorbent polymer (SAP) and Fulvic acid (FA) combined applied in the soil-maize system and (ii) use the stable hydrogen and oxygen analysis method to further quantify the soil water extraction by crops as affected by SAP and FA. Two root water extraction (RWE) terms based on density of root length (DRL) and density of root nitrogen mass (DRNM), respectively, were established to describe the rate of RWE, demonstrating that the values simulated from DRNM were verified to be closer to measured values. A particular model was further developed to simulate flow of water in different soil layers, and its authenticity was confirmed for describing the patterns of soil water flow under multi-chemicals application. The results of hydrogen and oxygen isotope abundance estimated from multi-source mass balance method (IsoSource model) suggested that main depth of water extraction as affected by multi-chemicals decreased first and then increased, and mainly concentrated in the shallow soil layers, 0–20 cm soil layer for jointing stage, 20–40 cm soil layer for heading stage, 0–20 cm soil layer for grain filling stage. Combined application of SAP and FA played a synergistic role in promoting the rainfall WUE of maize. [ABSTRACT FROM AUTHOR]

The implementation of rotational tillage with straw mulching during a fallow period seems to be an effective management strategy to help store water for spring-sown crop. A site-specific field study was conducted according to rainfall conditions to determine the effect of rotational tillage on soil water regime, water use efficiency and grain yield in semi-arid region on the loess plateau of China. Six tillage practices were tested: NT/ST rotation (no-tillage was applied in the first year and rotated with sub-soiling in the second year), ST/CT rotation (sub-soiling was applied in the first year and rotated with conventional tillage in the second year), CT/NT rotation (conventional tillage was applied in the first year and rotated with no-tillage in the second year), NT (no-tillage was applied every year), ST (sub-soiling was applied every year), CT(conventional tillage was applied every year). The results showed that the rotational tillage increase average SWS (soil water at sowing) by 5.2 mm in dry years, 0.8 mm in normal years, and 13.2 mm in humid years when compared to CT. Soil water depletion was consistent with rainfall totals, and the lowest depletion value recorded in the NT/ST and followed by NT treatment. The grain yield was positively related with rainfall, and average grain yields for three rainfall conditions were ranked as NT/ST > CT/NT > ST/CT > ST > NT = CT, while the soil water use efficiency (WUE) was ranked in the order of NT/ST, >CT/NT > ST, ST/CT > NT > CT. Grain yields of rotational tillage NT/ST, ST/CT and CT/NT are higher than the yield of NT by 6.5%–12.0%, higher than the yield of ST by 1.7%–7.0%, and 7.6%–13.2% higher than CT, respectively. Hence, rotational tillage could improve soil water storage, thus significantly increasing crop grain yield and water use efficiency. The method could have important applications in semi-arid areas. [ABSTRACT FROM AUTHOR]

Adapting groundnut production to the high climatic variability and extremes prevailing in Limpopo (South Africa) requires season- and site-specific exploitation of genotype x environment x management interactions. Notably, the El Niño-Southern Oscillation phenomenon (ENSO) causes distinctive seasonal rainfall anomalies in the province: Weather records over the period 1955–2010, showed El Niño years with an average of 296 mm growing season rainfall, neutral years with 349 mm and La Niña with 434 mm. We hypothesized that (i) early planting date is crucial for ensuring high productivity of groundnut and (ii) early maturing cultivars can ensure satisfactory production even in El Niño years, both options aiming at escaping prolonged periods of drought. To evaluate our hypotheses, we conducted a three year on-station trial with three planting dates and two cultivars, a one year trial at two sites comparing the two cultivars, tested crop model APSIM against field trial data, and, finally, performed long-term gridded crop model simulation runs for all cultivated land (i.e. 14,739 grid cells at a resolution 0.01°) in Limpopo exploring the effect of the cultivars and planting dates on groundnut yield. Field trials showed that early planting was superior to later plantings, irrespective of the weather year. Even in the very dry El Niño year 2016, yields of more than 1000 kg/ha were achieved with early planting, while planting later was not possible due to severe soil water deficits. Cultivar ICGV 03796 performed slightly better than ICGV 99257 due to faster ground cover closure, but no difference in phenology was observed. After evaluation of the model against the field trial data was found satisfactory, APSIM simulations showed that highest yields were achieved in La Niña years (median 996 kg/ha across all grids) and smallest in El Niño years (654 kg/ha across all grids). However, as in the field trials, we observed on average over all grid cells higher grain yields for early planting for all weather years as effective rainfall captured was higher than for later plantings. Longer growth duration by cultivar ICGV 03796 appeared to be more productive than an earlier maturing cultivar that we added into the simulation analysis as a third cultivar. However, a closer look at the spatial pattern of the simulation analysis revealed that for the generally drier regions of Limpopo, this cultivar with shorter growth duration would indeed be more productive in El Niño years. It showed that such season-specific adaptation would increase yields only by 2.9% for Limpopo province in total, but yield gains of more than 10% could be obtained for 11.3% of the grid cells in El Niño years. Hence, this study demonstrated that management recommendations at provincial scale explicitly need to consider in more detail a site- and season-specific approach. [ABSTRACT FROM AUTHOR]

Many lichen secondary metabolites have functions related to the environmental conditions of lichen habitats but few studies have compared soil characteristics with lichen species composition or their secondary products. The goal of this study was to investigate the relationship between soil characteristics with lichen species composition and secondary metabolites. Five locations were chosen in Manitoba, each with five sites (transects), and each transect with five quadrats (1 m × 1 m). All species were collected from each of the quadrats, presence of secondary metabolites was determined by thin layer chromatography, and soil characteristics were examined. The results revealed that rounded sand grains were significantly higher in southeastern Manitoba than in other locations, corresponding to a distinct species composition. Angular grains were significantly higher in northern locations, corresponding to a different group of species. Some of the significant relationships between soil characteristics and secondary metabolites include correlations of atranorin with pH, organic matter, and sand content; fumarprotocetraric acid with organic matter and sand content; and usnic acid with pH and organic matter. A better understanding of the role of lichens with respect to soil characteristics will be important for improving soil stabilization in land reclamation. [ABSTRACT FROM AUTHOR]

To derive ozone (O3) dose-response relationships for three European oak species (Quercus ilex, Quercus pubescens, and Quercus robur) under a range of soil water availability, an experiment was carried out with 2-year-old potted seedlings exposed to three levels of water availability in the soil and three levels of O3 pollution for one growing season in an ozone free-air controlled exposure (FACE) facility. Total biomass losses were estimated relative to a hypothetical clean air at the pre-industrial age, i.e., at 10 ppb as daily average (M24). A stomatal conductance model was parameterized with inputs from the three species for calculating the stomatal O3 flux. Exposure-based (M24, W126, and AOT40) and flux-based (phytotoxic O3 dose (POD)0-3) dose-response relationships were estimated and critical levels (CL) were calculated for a 5% decline of total biomass. Results show that water availability can significantly affect O3 risk assessment. In fact, dose-response relationships calculated per individual species at each water availability level resulted in very different CLs and best metrics. In a simplified approach where species were aggregated on the basis of their O3 sensitivity, the best metric was POD0.5, with a CL of 6.8 mmol m−2 for the less O3-sensitive species Q. ilex and Q. pubescens and of 3.5 mmol m−2 for the more O3-sensitive species Q. robur. The performance of POD0, however, was very similar to that of POD0.5, and thus a CL of 6.9 mmol m−2 POD0 and 3.6 mmol m−2 POD0 for the less and more O3-sensitive oak species may be also recommended. These CLs can be applied to oak ecosystems at variable water availability in the soil. We conclude that PODy is able to reconcile the effects of O3 and soil water availability on species-specific oak productivity. [ABSTRACT FROM AUTHOR]

A unique database of stand volume growth, estimated as periodic annual volume increment (in m3 ha−1 per year over the period 2001-2005) from 728 European beech (Fagus sylvatica L.) sites distributed across Italy, was used to assess the effects of ambient ozone (O3), expressed as annual average (M24), accumulated exposure above a 40 ppb hourly threshold (AOT40), and total stomatal ozone flux (POD0). Growth data were from the National forest inventory of Italy, while climate data and ozone concentrations were computed by the WRF and CHIMERE models, respectively. Results show that the growth increased with increasing solar radiation and air temperature and decreased with increasing number of cold days, while effects of soil water content and O3 were not significant. In contrast, the literature results suggest that European beech is sensitive to both drought and O3. Ozone levels resulted to be very high (48 ppb M24, 51,200 ppb h AOT40, 21.08 mmol m−2 POD0, on average) and thus able to potentially affect European beech growth. We hypothesize that the high-frequency signals of soil water and O3 got lost when averaged over 5 years and recommended finer time-resolution investigations and inclusion of other factors of variability, e.g., thinning, tree age, and size. [ABSTRACT FROM AUTHOR]

Free-living biological N 2 fixation (BNF) in soil, litter and moss is an important pathway for external nitrogen (N) inputs to unmanaged terrestrial ecosystems. However, how free-living BNF responses to temperature, moisture and their interaction have not been well understood, especially in the subtropical regions. Here we investigated the responses of BNF in soil, litter and moss to temperature (15, 25 and 35 °C) and moisture (low, intermediate and high levels) over a one-week period under laboratory conditions. The samples were collected in a subtropical karst forest, southwest China. We found that the responses of BNF in moss, litter and soil to temperature and moisture were divergent. Litter and soil BNF rates increased with temperature under the three moisture levels. However, moss BNF rates were decreased, not changed or increased by warming under low, intermediate and high moisture levels, respectively. At each temperature, the BNF rates increased with moisture for moss and litter. However, the patterns of moisture responses were different at the three temperatures for soil BNF, which was not changed and increased by moisture at 15 °C and 25 °C, respectively; and was greatest under intermediate moisture, but lowest under low moisture at 35 °C. The temperature sensitivity of BNF was generally highest for litter, intermediate for soil and lowest for moss. In contrast, the moisture sensitivity of BNF was generally highest for moss, intermediate for soil, and lowest for litter. Our findings suggest that different temperature or moisture sensitivities of BNF for the three substrates should be integrated into terrestrial ecosystem models in order to better predict N inputs via BNF under climate change. [ABSTRACT FROM AUTHOR]

The species of passion fruit ( Passiflora spp.) are cultivated commercially for food, medicinal and ornamental purposes, especially in tropical regions of the planet subject to intense seasonal drought. This study assessed biometric, physiological, and anatomical responses of P. edulis , P. gibertii , P. cincinnata , P. alata and P. setacea to controlled water deficit. Seedlings with five months of age were subjected to soil water deficit imposed by irrigation suspension until the complete stomatal closure. All assessed species were susceptible to water deficit, with 50–75% reduction in vegetative growth, even though distinct mechanisms of coexistence with this stress were demonstrated by the evaluated genotypes. P. gibertii and P. edulis showed vigorous growth, quick closing and stomatal opening in response to soil water content, the first being more efficient in extracting water from the substrate even with lowest soil water storage. The effects of water deficit were postponed in P. setacea and P. cincinnata , which showed reduced leaf area and stomatal conductance even under irrigation, particularly in P. setacea . P. alata showed large leaf area but lower stomatal conductance and decreased root system by irrigation suspension. P. alata was the species that showed the most anatomical changes resulting from water deficit, such as reductions in the thickness of the leaf blade, adaxial epidermis, palisade parenchyma, and spongy parenchyma. On the other hand, P. setacea was the species that showed greatest ability to survive under water restriction due to tolerate prolonged drought periods with minor anatomical changes when compared to the control. [ABSTRACT FROM AUTHOR]

Our goal was to describe stomatal conductance (gs) and the site-scale environmental parameters that best predict gs in Kruger National Park (KNP), South Africa. Dominant grass and woody species were measured over two growing seasons in each of four study sites that represented the natural factorial combination of mean annual precipitation [wet (750 mm) or dry (450 mm)] and soil type (clay or sand) found in KNP. A machine-learning (random forest) model was used to describe gs as a function of plant type (species or functional group) and site-level environmental parameters (CO2, season, shortwave radiation, soil type, soil moisture, time of day, vapor pressure deficit and wind speed). The model explained 58% of the variance among 6,850 gs measurements. Species, or plant functional group, and shallow (0–20 cm) soil moisture had the greatest effect on gs. Atmospheric drivers and soil type were less important. When parameterized with three years of observed environmental data, the model estimated mean daytime growing season gs as 68 and 157 mmol m-2 sec-1 for grasses and woody plants, respectively. The model produced here could, for example, be used to estimate gs and evapotranspiration in KNP under varying climate conditions. Results from this field-based study highlight the role of species identity and shallow soil moisture as primary drivers of gs in savanna ecosystems of KNP. [ABSTRACT FROM AUTHOR]

Pest outbreaks are driving tree dieback and major influxes of deadwood into forest ecosystems. Understanding how pulses of deadwood impact the climate system requires understanding which factors influence greenhouse gas production during wood decay. Recent analyses identify stem diameter as an important control, but report effects that vary in magnitude and direction. This complexity may reflect interacting effects of soil contact, geometry and variable tissue properties. To dissect these effects, we implemented a three-way factorial experiment in Fraxinus americana, (white ash), an iconic North American species threatened by an invasive beetle. Soil contact accelerated decay rates by an order of magnitude with an effect that varied with stem diameter, not bark presence. After experimentally controlling surface area-to-volume ratio, half-buried wide stems decayed more slowly than half-buried narrow stems but more quickly than the aggregate decay rate of buried and suspended stems. These results closely matched variation in moisture content within and among samples, suggesting that limited vertical conduction of soil moisture through deadwood mediates the effect of stem diameter on wood decay. Soil contact also influenced greenhouse gas concentrations reinforcing recent evidence that deadwood acts as a source for CO2 and CH4 while acting as a sink for N2O. Our results suggest that managing tree species affected by pest outbreaks, including F. americana, for biomass salvage and greenhouse gas mitigation requires understanding traits that mediate wood permeability and diffusivity to soil moisture and greenhouse gases. [ABSTRACT FROM AUTHOR]

Sugar maple (Acer saccharum), an economically important timber and syrup species, is not expected to flourish under projected future climates. The objectives of our study were to (1) tease apart the effects of warming and soil moisture availability on transpiration rates of mature sugar maple trees with a full-factorial soil warming × water addition experiment and (2) determine the primary environmental driver(s) of sugar maple transpiration in the upper Midwestern United States. Over three growing seasons, we monitored sap flux of 33 trees in eight 100-m2 plots, two replicates each of four treatments: (1) heat (soil warmed +4°C), (2) water (1.3 × ambient growing season precipitation, (3) heat + water, and (4) control. As expected, sugar maple transpiration decreased under the heat treatments in all years and increased in water treatments in years 1 and 2, all mediated primarily by soil moisture. However, under the heat + water treatment, supplemental water compensated for the warming-induced soil evaporation only in year 1 (2011), which was the driest year. Despite clear evidence of a soil moisture-mediated treatment effect, light was the dominant driver of seasonal variation in sap flux in this sugar maple-dominated ecosystem with relatively short growing seasons. However, sap flux was reduced with decreases in soil moisture, and therefore, net C gain likely was as well. Overall, our results suggest that even though this northern temperate species is primarily limited by light, sugar maple productivity may be reduced by a warming climate on drier sites within its current range, if warming is not accompanied by a sufficient increase in precipitation. [ABSTRACT FROM AUTHOR]

The experiment was conducted during the agricultural season 2016-2017 with the aim of studying the effect of salinity with a concentration of 3% and nanocarbon compounds (0, 0.5, 1) g/L and yeast suspension with concentration (0.3, 6) g/L and their interactions in some characteristics of vegetative growth and yield and its Components in Vinga unguiculatal. The results showed that the use of salinity with a concentration of 3% caused a moral decreased in the studied characteristics. While the spraying of the nano-carbon spray and yeast suspension led to significant increase in vegetative growth characters which included (vegetation length, number of branch, leaf area, number of leaves and Shoot dry weight) and the quantitative and qualitative characters yield Included (number of pods, weight of pods, Plant yield, protein and carbohydrate ratio in seeds). For the interaction, the combination of the nanocarbon at 1 g/L with salt-irrigated plants with a concentration of 3% recorded higher values in the studied characteristics in comparison with control. [ABSTRACT FROM AUTHOR]

Large-scale vegetation restoration on the Loess Plateau in China has been performed by the central government in recent decades; however, the planting of incompatible vegetation during these efforts has resulted in serious environmental problems, such as dry soil layers, that are widespread and difficult to ameliorate. To determine the proper evaluation indices for plant available soil water content (PASWC) in commonly reforested plants and crops, we examined the physiological responses of Robinia pseudoacacia (tree), Amorpha fruticosa (shrub), Medicago sativa (perennial leguminous herb) and Zea mays (crop) to prolonged drought; these plants were planted widely in the semiarid Loess Plateau region of China. Leaf water status, gas exchange and fluorescence parameters did not show marked changes at the beginning of the prolonged drought but changed rapidly as PASWC continued to decrease. These data were fitted with a sigmoid function ( P < 0.0001). In addition, different physiological parameters showed different PASWC thresholds; the fluorescence parameters exhibited the lowest PASWC threshold among the four species, with an upper threshold that was less than 50% of the PASWC for all but Z. mays . In this study, the photosynthesis rate was a better indicator of the PASWC, and the upper and lower thresholds of PASWC of the normalized photosynthesis rate were 64.1% and 47.6%, 83.0% and 44.1%, 82.7% and 35.2%, 82.9% and 39.3% for R. pseudoacacia , A. fruticosa , M. sativa and Z. mays , respectively. The current study also suggests that R. pseudoacacia is a suitable afforestation species in areas with higher levels of rainfall. These results provide important information for determining the PASWC and the supply capacity of soil water on the Loess Plateau. [ABSTRACT FROM AUTHOR]

'Hass' and 'Fuerte' avocado plants were grown under well-watered or waterlogged conditions. Results indicated significant effects on the majority of the allometric parameters in waterlogged plants, with 'Fuerte' displaying a more pronounced growth inhibition. Waterlogged conditions caused a progressive and simultaneous decline in net photosynthetic rate and stomatal conductance, earlier in 'Fuerte' than in 'Hass'. Maximal potential quantum yield of PSII was unaffected by the soil water regime and/or variety and leaf water potential values in waterlogged plants were not more negative compared with control plants. 'Fuerte' waterlogged plants exhibited increased contents of thiobarbituric acid reactive substances, whereas oxidative injury was not detected in 'Hass'. Finally, none of the two cultivars displayed valuable antioxidant potential, as evidenced by the decreased activities of the antioxidant enzymes superoxide dismutase, guaiacol peroxidase, glutathione peroxidase, and ascorbate peroxidase. [ABSTRACT FROM AUTHOR]

Water movement through the soil-plant-atmosphere continuum can be tracked through its hydrogen and oxygen isotopic composition. How the isotopic composition of water evolves as it moves through this continuum provides critical information on ecosystem hydrology and climate change. Cryogenic vacuum extraction is the most applied method to extract waters from soil and plant material for such studies. However, recent experiments where oven dried soils were spiked with a reference water suggest potential for these techniques to bias results. We present results from a greenhouse-based plant water uptake and cryogenic vacuum distillation experiment using Salix viminalis cuttings. We tested the capacity for cryogenic vacuum extraction to recover irrigation water and the plant-available water pool from 4 soils that were subject to continuous irrigation as would occur in nature. Results show that δ2H and δ18O values of extracted soil waters reflect those of irrigation water, but with some influence of evaporation that varied with differences in soil humic and clay content. This suggests that isotope effects observed in laboratory experiments with oven-dried soils may not be relevant under natural conditions. Cryogenic vacuum extraction also recovered xylem water δ2H values that matched the δ2H values of extracted soil water but revealed small, consistent offsets between xylem and soil water δ18O values of 0.84 ± 1.13‰. Although these effects may not significantly bias water isotope sourcing applications, they do result in large extrapolation errors when estimating original source water isotope composition from extracted xylem waters using the back extrapolation to the global meteoric water line method. [ABSTRACT FROM AUTHOR]

Soil moisture varies within landscapes in response to vegetative, physiographic, and climatic drivers, which makes quantifying soil moisture over time and space difficult. Nevertheless, understanding soil moisture dynamics for different ecosystems is critical, as the amount of water in a soil determines a myriad ecosystem services and processes such as net primary productivity, runoff, microbial decomposition, and soil fertility. We investigated the patterns and variability in in situ soil moisture measurements converted to plant-available water across time and space under different vegetative cover types and topographic positions at the Marcell Experimental Forest (Minnesota, USA). From 0- to 228.6-cm soil depth, plant-available water was significantly higher under the hardwoods (12%), followed by the aspen (8%) and red pine (5%) cover types. Across the same soil depth, toeslopes were wetter (mean plant-available water = 10%) than ridges and backslopes (mean plant-available water was 8%), although these differences were not statistically significant ( p < .05). Using a mixed model of fixed and random effects, we found that cover type, soil texture, and time were related to plant-available water and that topography was not significantly related to plant-available water within this low-relief landscape. Additionally, during the 3-year monitoring period, red pine and quaking aspen sites experienced plant-available water levels that may be considered limiting to plant growth and function. Given that increasing temperatures and more erratic precipitation patterns associated with climate change may result in decreased soil moisture in this region, these species may be sensitive and vulnerable to future shifts in climate. [ABSTRACT FROM AUTHOR]

The complex interaction process of the abiotic factors (sunlight, air temperature and soil water) in regulating maize (Zea mays L.) photosynthesis has not been fully understood. Our field experiment explored the changed sensitivity (or role) of the abiotic factors in regulating maize photosynthesis under a drought development process. The experiment established a scenario with a long-term drought and an instantaneous cloud cover. The results revealed that long-term drought stress causes the sensitivity (or role) of sunlight and temperature exchanged in regulating maize photosynthesis. The maize photosynthesis was more sensitive to instantaneous sunlight rather than temperature in the absence of drought. However, a diminishing photosynthetic sensitivity to sunlight but an increasing photosynthetic sensitivity to temperature was observed with drought development process. The variable photosynthetic sensitivity indicated that the roles of temperature and sunlight in regulating maize photosynthesis were exchanged, so it is expected that higher photosynthetic rate could be achieved by adjusting temperature rather than sunlight after severe drought. Nevertheless, further studies are needed to provide more evidence and mechanism explanations. [ABSTRACT FROM AUTHOR]

The Mediterranean basin is extremely vulnerable to climate change, and one of the areas most impacted by human water demand. Yet the green roofs increasingly created both for aesthetic reasons and to limit pollution and urban runoff are themselves very water-demanding. Successful green roof installation depends on the establishment of the vegetation, and the substrate is the key element: it conserves water, and provides the nutrients and physical support indispensable for plant growth. Since typical Mediterranean plant communities require no maintenance, this study seeks to develop techniques for creating maintenance- and watering-free horizontal green roofs for public or private buildings in a Mediterranean context. The innovative aspect of this study lies in creating two soil mixes, fine elements (clay and silt) and coarse elements (pebbles of all sizes), in two different thicknesses, to assess vegetation development. Monitoring of substrate moisture was carried out and coupled with local rainfall measurements during summer and autumn. As expected, substrate moisture is mainly influenced by substrate depth (the deeper, the moister) and composition (the finer the particles (clays and silts), the higher the moisture content). Vegetation cover impacts moisture to a lesser extent but is itself affected by the composition and depth of the substrates. These results are subsequently discussed with relation to the issue of sustainable green roofs in Mediterranean climates. Considering applications of our results, for an optimal colonization of a Mediterranean vegetation, a substrate thickness of 15 cm composed mainly of fine elements (75% clay-silt and 25% pebble-sand) would be recommended in green roofs. [ABSTRACT FROM AUTHOR]

Hybridization between shortleaf pine ( Pinus echinata Mill.) and loblolly pine ( Pinus taeda L.) has dramatically increased and may threaten the genetic integrity of shortleaf pine. Shortleaf pine is presumed to be more drought tolerant than loblolly pine, but the drought hardiness of the hybrid pine is not known. We determined biomass partitioning in response to water stress and measured whole-plant transpiration of shortleaf, loblolly, and hybrid pine seedlings. Water stress decreased total seedling biomass, increased biomass partitioning to foliage, and decreased biomass partitioning to coarse roots. Shortleaf pine seedlings partitioned more biomass to coarse roots than loblolly pine, and hybrid pine was intermediate between the parent species. We found no differences in the level of soil moisture at which seedlings of different species began to limit transpiration. Our results suggest that the transpiration response of shortleaf pine and hybrid pine is similar to that of loblolly pine when exposed to water stress. However, greater partitioning to coarse root may allow shortleaf and hybrid pines to better withstand drought due to greater potential belowground carbohydrate supply. [ABSTRACT FROM AUTHOR]

Contrasting phenotypes of foundation species are known to differentially affect understorey plants. However, there is little knowledge on both the mechanisms of competition (resource competition versus interference) of stress-tolerant phenotypes and the importance of indirect interactions. In an oromediterranean community from Mount Lebanon we assessed the effects on understorey forbs of two contrasting phenotypes, a tight competitive from stressful habitat and a loose facilitative from more benign habitat. In a dry south and a wet north exposure we assessed short-term resource effects removing shrub canopy and long-term soil effects (including litter interference) with the comparison of forb performances in adjacent naturally open areas vs no shrub. Indirect effects were quantified through the removal of grasses. Abundance, richness and biomass of forbs were measured in all treatments after one year of experiment, together with litter depth and soil moisture. We found strong direct negative soil effects of the tight phenotype on all forb performances and in particular in south exposure. These effects were due to litter interference on water availability, but not to resource competition. They were likely explained by the high hydrophobicity of organic matter accumulating in the stressful habitat of the tight phenotype. We also found an indirect competition of the loose phenotype for forb richness, due to its direct positive soil effect on competitive grasses, and in particular in south exposure. Our results improve our knowledge on the importance of litter interference in dry nutrient-poor habitats and the role of indirect interactions in phenotypic effects on understorey species. [ABSTRACT FROM AUTHOR]