How is the water footprint of the species Vachellia farnesiana, Amburana cearensis, and Handroanthus impetiginosus influenced by abiotic stresses as water deficit and salinity?

In semi-arid regions, is necessary to explore strategies to mitigate abiotic stresses such as water deficit and salinity. This study aimed to evaluate the stress tolerance capacity of three species subjected to different water regimes and salinity levels, based on dry matter production and water use efficiency (WUE). The species Handroanthus impetiginosus, Vachellia farnesiana, and Amburana cearensis were evaluated in combination with different water regimes (50%, 75%, and 100% of reference evapotranspiration - ET0) and salinity levels (0.18, 1.50, and 1.90 dS m-1). The results show that biomass accumulation increased at 50% and 75% ET0, while the WUE decreased at 100% ET0. The salinity level (1.90 dS m-1) caused reductions in leaf dry biomass (LDB), total dry biomass (TDB), LDB/TDB ratio, and WUE. The negative effects of high salinity on plant height were greater with the application of 75% ET0. The highest WUE was obtained at 50% ET0 for A. cearensis and H. impetiginosus, while V. farnesiana obtained the highest WUE at 75% ET0. A. cearensis exhibited the highest biomass accumulation (2.58 g) and WUE (0.21 g L-1). Overall, the species can tolerate drought and salinity conditions, being sensitive to high salinity concentrations during their initial growth.

Cactus-sorghum intercropping combined with management interventions of planting density, row orientation and nitrogen fertilisation can optimise water use in dry regions

Some strategies can optimise the use of water in crops under deficit, either by increasing yield or by reducing actual crop evapotranspiration (ET), to promote the sustainable intensification of production systems. The objective was to evaluate how the spacing, planting orientation, nitrogen fertilisation and intercropping strategies impact the dynamics of water in the soil, ET partitioning, and water use indicators for forage cactus and cactus-sorghum intercropping. Four experiments were conducted between 2018 and 2020 in the Brazilian semi-arid region. In the first two sites (I and II), the cladodes of the intercropped forage cactus and sorghum were spaced at 0.10, 0.20, 0.30, 0.40 and 0.50 m with rows-oriented east-west and north-south. In site III, the intercropped rows were spaced at 1.00, 1.25, 1.50 and 1.75 m. Site IV, which contained the forage cactus crop exclusively, was treated with four nitrogen levels (50, 150, 300 and 450 kg N ha-1). The management interventions improved water use more by increasing dry matter than by reducing ET in the cropping system. Intercropping promoted the greatest increase in water productivity (130 %). Increasing N doses in the forage cactus-only crop reduced ET by up to 39 % but increased deep drainage losses by up to 365 %. The most promising management practices for optimising water resources were as follows: spacing of 0.10 m between cactus plants in the intercropping trial under east-west row orientation, as it promoted greater water use efficiency (76 %); spacing of 0.30 m in the north-south orientation; and row spacing of 1.50 m, as it improved water productivity (6.89 kg m-3). Thus, interventions in management should be adopted to optimise water use in intercropping systems with forage cactus, aiming at sustainable intensification in dry environments.

Monitoring Energy Balance, Turbulent Flux Partitioning, Evapotranspiration and Biophysical Parameters of Nopalea cochenillifera (Cactaceae) in the Brazilian Semi-Arid Environment

The in-situ quantification of turbulent flux and evapotranspiration (ET) is necessary to monitor crop performance in stressful environments. Although cacti can withstand stressful conditions, plant responses and plant-environment interactions remain unclear. Hence, the objective of our study was to investigate the interannual and seasonal behaviour of components of the surface energy balance, environmental conditions, morphophysiological parameters, biomass yield and water relations in a crop of Nopalea cochenillifera in the semi-arid region of Brazil. The data were collected from a micrometeorological tower between 2015 and 2017. The results demonstrate that net radiation was significantly higher during the wet season. Latent heat flux was not significant between the wet season and dry season. During the dry-wet transition season in particular, sensible heat flux was higher than during the other seasons. We observed a large decline in soil heat flux during the wet season. There was no difference in ET during the wet or dry seasons; however, there was a 40% reduction during the dry-wet transition. The wet seasons and wet-dry transition showed the lowest Evaporative Stress Index. The plants showed high cladode water content and biomass during the evaluation period. In conclusion, these findings indicate high rates of growth, high biomass and a high cladode water content and explain the response of the cactus regarding energy partitioning and ET.

Understanding interactive processes: a review of CO2 flux, evapotranspiration, and energy partitioning under stressful conditions in dry forest and agricultural environments

Arid and semiarid environments are characterized by low water availability (e.g., in soil and atmosphere), high air temperature, and irregularity in the spatio-temporal distribution of rainfall. In addition to the economic and environmental consequences, drought also causes physiological damage to crops and compromises their survival in ecosystems. The removal of vegetation is responsible for altering the energy exchange of heat and water in natural ecosystems and agricultural areas. The fluxes of CO₂ are also changed, and environments with characteristics of sinks, which can be sources of CO₂ after anthropic disturbances. These changes can be measured through methods such as sap flow, eddy covariance, remote sensing, and energy balance. Despite the relevance of each method mentioned above, there are limitations in their applications that must be respected. Thus, this review aims to quantify the processes and changes of energy fluxes, CO₂, and their interactions with the surfaces of terrestrial ecosystems in dry environments. Studies report that the use of methods that integrate data from climate monitoring towers and remote sensing products helps to improve the accuracy of the determination of energy fluxes on a global scale, also helping to reduce the dissimilarity of results obtained individually. Through the collection of works in the literature, it is reported that several areas of the Brazilian Caatinga biome, which is a Seasonally Dry Tropical Forest have been suffering from changes in land use and land cover. Similar fluxes of sensible heat in areas with cacti and Caatinga can be observed in studies. On the other hand, one of the variables influenced mainly by air temperature is net radiation. In dry forest areas, woody species can store large amounts of carbon in their biomass above and belowground. The use of cacti can modify the local carbon budget when using tree crops together. Therefore, the study highlights the complexity and severity of land degradation and changes in CO₂, water, and energy fluxes in dry environments with areas of forest, grassland, and cacti. Vegetation energy balance is also a critical factor, as these simulations are helpful for use in forecasting weather or climate change. We also highlight the need for more studies that address environmental conservation techniques and cactus in the conservation of degraded areas.

Genotypic differences relative photochemical activity, inorganic and organic solutes and yield performance in clones of the forage cactus under semi-arid environment

Plants with the crassulacean acid metabolism commonly present good adaptation to arid and semi-arid environments, but it highly depends on the type of species. In this study, chlorophyll fluorescence, the concentration of inorganic and organic solutes and the productive performance were evaluated along with their relationships in different clones of the genera Opuntia and Nopalea. The experiment was conducted from 2016 to 2018. Four clones of genus Opuntia were evaluated: 'Orelha de Elefante Mexicana' (OEM), 'Orelha de Elefante Africana' (OEA), V19 and F8; and two clones of genus Nopalea: 'IPA Sertânia' and 'Miúda'. The experiment was arranged in a randomised block design, with six treatments and three replications. The following parameters were measured when harvesting: initial, maximum and variable fluorescence; the quantum yield of PSII (Fv/Fm); light-induction curves of the photochemical parameters (ΔF/Fm', qP, NPQ and ETR); the chlorophyll and carotenoid content; carbohydrates; the sodium (Na⁺) and potassium (K⁺) content; morphometry; and dry matter accumulation. The values for the effective quantum yield of PSII (ΔF/Fm') and the alterations in photochemical quenching were higher in the OEM clone (P < 0.05). There was a difference between clones for non-photochemical quenching, with the F8 clone having the highest values. The Fv/Fm was 0.87 for the OEM. 'IPA Sertânia' obtained the greatest Chl a/b, and the highest values for carbohydrate concentration were found in the OEA clone. The OEM clone showed the greatest accumulation of K⁺, in addition to a higher cladode area index and greater dry matter accumulation. The results of this study show the high physiological tolerance of the forage cactus to a semi-arid environment, which varies according to the clone.

Agronomic characteristics of the Pennisetum glaucum submitted to water and saline stresses

Agricultural production in semi-arid regions is limited due to water availability. In addition, the water quality available for irrigation is often compromised due to the high salt content present. Millet is a forage species considered tolerant to water deficit and moderately salt tolerant. In view of the above, the objective was to evaluate the growth of millet under water and saline stress associates. The experiment was carried out in a randomized block design, in a 4x3 factorial scheme, composed of four levels of water replacement, based on crop evapotranspiration (ETc): 25%.ETc, 50%.ETc, 75%.ETc and 100%.ETc and three levels of water salinity (0.03, 2.0 and 4.0 dS m-1). With 25%.ETc independent of salinity, all morphological characteristics of millet were affected, occurring death of plants in the initial growth phase. In the absence of salt and greater availability of water, greater plant growth occurred. With respect to salinity, there was a reduction in the increment of all variables evaluated, with the highest reduction at the highest saline level (4.0 dS m-1). Water and salt stresses, when associated, reduce the growth of millet, since concentrations above 2.0 dS m-1 and less than 50%.ETc compromise its full development, providing declines in yield.