Luisina Carbonell-Silletta

Water potential gradients drive water flow within and between soils and plants, and the internal plant water potential controls a wide range of physiological processes including photosynthesis, growth, and mortality. Notwithstanding this clear relevance for many critical aspects of ecosystem function, water potential data have historically been relatively inaccessible and unnetworked. The absence of a centralized repository for plant water potential time series limits our ability to integrate a wealth of ecophysiological information from other networks and from remote sensing. Closing this gap is necessary to address unresolved questions about plant responses to drought and heat stress, and to make confident predictions about plant and ecosystem function in a warming world. Here, we introduce the PSInet database -- a global collection of plant water potential time series from 285 datasets representing 523 species. We present the workflow that guided database development and evaluate its key features. Through a series of preliminary analyses, we then highlight the potential of the PSInet database for applications including: a) advancing plant water use strategy frameworks; b) disentangling the impacts of soil versus atmospheric drought stress; c) assessing the long-held assumption of pre-dawn equilibration of ecosystem water potential; d) understanding the risk of drought-driven mortality; and e) benchmarking remote-sensing data products and land-surface models.

Vegetation activity in arid ecosystems is traditionally interpreted as a direct response to precipitation pulses. However, the extent to which vegetation dynamics are regulated by antecedent soil water storage and its interaction with atmospheric demand remains poorly understood. Here, we combined six years of near-surface GCC from PhenoCam, field NDVI, and satellite-derived vegetation indices to examine the ecohydrological controls of vegetation activity and phenological dynamics in a Patagonian steppe in southern Argentina. Vegetation activity and phenological metrics describing both timing and magnitude were more strongly associated with antecedent soil water storage (SWS) integrated across the 2-m soil profile than with precipitation alone. This suggests that vegetation responses are better explained by hydrological memory than by recent rainfall pulses. However, this control changed with atmospheric demand: under low vapor pressure deficit (VPD) vegetation activity was mainly associated with shallow SWS, whereas under high VPD, deeper SWS became the primary driver. Across phenological metrics, SWS showed a pervasive influence, while atmospheric variables exerted more selective but biologically critical effects. In addition, integrated canopy greenness was positively correlated with grass aboveground net primary productivity, supporting its use as a proxy for seasonal productivity. Our results demonstrate that vegetation activity and phenology in the Patagonian steppe are governed by the interaction between antecedent SWS and atmospheric demand. By identifying profile-scale water availability as a key ecohydrological control, this study highlights the need to incorporate both hydrological memory and atmospheric demand into monitoring and modeling approaches under increasing aridity.

Changes in water and nitrogen availability can affect the structure and function of arid ecosystems. How these resources affect aboveground primary productivity (ANPP) remains far from clear. We examined the N and water limitation of ANPP from the species to the community level and the response of ANPP to annual precipitation in a Patagonian steppe. We conducted a 7‐year field experiment with water addition (+W), nitrogen addition (+N) and +NW. Destructive methods for grasses and allometric relationships for shrubs were used to assess ANPP and vegetation indices (NDVI and MSAVI2) to estimate community ANPP. An increase in ANPP of one grass species (Papposstipa humilis) and a decrease of the grass Poa ligularis under +N were observed. Some shrub species exhibited mortality under nitrogen addition. Nitrogen exerted a positive effect on grass ANPP and amplified the sensitivity of grass ANPP to annual precipitation. However, +N had not effects on the shrub ANPP and shrub ANPP‐precipitation relationship. Water addition by itself had no effect on ANPP for either shrubs or grasses. However, shrubs responded positively to an unusually wet year regardless of treatment and were also more sensitive to changes in annual precipitation than grasses. Total ANPP increased significantly in +N relative to the C and +W but without changes in the sensitivity to annual precipitation. The results suggest that the responses of grasses and shrubs to water inputs are driven by soil moisture redistribution and rooting depth and that grass and community ANPP are more limited by N than by water.

Changes in water and nitrogen availability can affect the structure and function of arid ecosystems. How these resources affect aboveground primary productivity (ANPP) remains far from clear. We examined the N and water limitation of ANPP from the species to the community level and the response of ANPP to annual precipitation in a Patagonian steppe. We conducted a 7-year field experiment with water addition (+W), nitrogen addition (+N), and +NW. Destructive methods for grasses and allometric relationships for shrubs were used to assess ANPP and vegetation indices (NDVI and MSAVI2) to estimate community ANPP. An increase in ANPP of one grass species ( Papposstipa humilis ) and a decrease of the grass Poa ligularis under +N were observed. Some shrubs species exhibited mortality under nitrogen addition. Nitrogen exerted a positive effect on grass ANPP and amplified the sensitivity of grass ANPP to annual precipitation. However, +N had not effects on the shrub ANPP and shrub ANPP-precipitation relationship. Water addition by itself had no effect on ANPP for either shrubs or grasses. However, shrubs responded positively to an unusually wet year regardless of treatment and were also more sensitive to changes in annual precipitation than grasses. Total ANPP increased significantly in +N relative to the C and +W, but without changes in the sensitivity to annual precipitation. The results suggest that the responses of grasses and shrubs to water inputs is driven by soil moisture redistribution and rooting depth and that grass and community ANPP is more limited by N than by water.

Water availability is one of the factors affecting plant growth and development, especially in arid and semiarid environments. Changes in precipitation due climate change alter water availability to plants impacting on plant physiology. Numerous studies have focused on plant response to reduced precipitation and less on the effects of increased precipitation. The main objective of this study was to evaluate biophysical and physiological leaf traits in response to experimental water addition in four dominant shrubs and one grass species in a Patagonian steppe, during the dry season. The experiment consisted of two treatments: control and water addition, increasing the average annual rainfall by 25% during 6 years. We measured leaf wettability, water status, transpiration, photosynthesis, stomatal conductance, water use efficiency and foliar water uptake (FWU). In addition, we determined the phenotypic plasticity index of these evaluated traits. We expected lower FWU and higher transpiration and photosynthesis rates due changes in leaf surface properties under water addition treatment. All study species responded significantly to treatment with higher loss of water per transpiration and lower FWU. Also, all species increased photosynthesis rate and water use efficiency (WUE). However, water potential and leaf wettability did not change with higher precipitation. Thus, higher phenotypic plasticity was observed in functional than in morphological traits. Since functional traits were more sensitive than leaf surface traits, plants may quickly take advantage when environmental conditions tend to be more favourable to growth. Our findings suggest that plants of Patagonian steppe have adaptive ability to respond to environmental changes through plastic responses.

Stored water in inner tissues influences the plant water economy, which might be particularly relevant for trees facing increasing dry conditions due to climate change. We studied the water storages in the inner bark and the sapwood of Araucaria araucana. This species has an extremely thick inner bark and thus it can be used as a model system to assess the impact of internal water storage on plant water balance. Specifically, we analyzed the water circulation pathways in and out of the elastic water storages by using simultaneously frequency domain moisture sensors and dendrometers inserted in the inner bark and in the sapwood, and sap flow determinations during the dry season. The daily patterns of water content and expansion and contraction of the stem tissues were similar to the sap flow pattern. The whole-stem water content and diameter increased in the morning and decreased in the afternoon, contrary to typical pattern observed in most tree species. An osmotic gradient favoring the water influx from sapwood to inner bark was observed in the morning. There were no lags in the onset of sap flow between different stem heights at the time that recharge of reservoirs occurred. Sap flow at 6 m height was higher than basal sap flow in the afternoon, when the sapwood water content started to decline followed by the water content of the inner bark. Inner bark and sapwood contributed with 5 to 11% to total daily transpiration allowing the maintenance of high water potentials in the dry season. Our results suggest that the stored water in the stems, the atypical dynamic of recharge and discharge of water from reservoirs and the high tissue capacitance may make an important contribution to the survival of A. Araucana during drought periods by maintaining the water balance.

Los capítulos del presente libro representan un conjunto de reflexiones, saberes, análisis y, desde luego, propuestas que se derivan de avances y resultados de investigaciones presentadas en diferentes eventos (como seminarios, simposios y congresos) que el equipo de la Red Temática Ibero-Latinoamericana de Investigación e Intervención en Educación Ambiental para el Desarrollo (REDIILECAD) ha trabajando desde hace más de una década en vinculación con programas de licenciatura y posgrado, especialmente con el Doctorado en Ciencias en Educación Agrícola Superior (DCEAS), adscrito al Departamento de Sociología Rural de la Universidad Autónoma Chapingo (UACh) de México. De tal manera que en los resultados y avances de investigación aquí presentados se aprecia una estrecha vinculación entre el DCEAS, el Instituto de Investigaciones Socioambientales Educativas y Humanísticas para el Medio Rural (IISEHMER), la Dirección General de Investigación y Posgrado (DGIP), el Consejo Nacional de Ciencia y Tecnología (Conacyt) (particularmente con el Programa Nacional de Posgrados de Calidad [PNPC]) y la REDIILECAD. Vale decir que las mismas líneas de generación y aplicación del conocimiento (LGAC) del DCEAS se comparten en los estudios posgraduales de la UACh y el IISEHMER.

Aims: Soil respiration and N-mineralization are key processes in C and N cycling of terrestrial ecosystems. Both processes are limited by soil temperature, moisture and nutrient content in arid and cold ecosystems, but how nutrient addition interacts with water addition requires further investigation. This study addresses the effects of water and N+P additions on soil respiration and mineralization rates in the Patagonian steppe.Methods: We measured soil respiration and N-mineralization throughout seasons in control, fertilized, irrigated and irrigated-fertilized plots. We also analyzed root density and soil physico-chemical properties.Results: The soil CO₂ effluxes in the Patagonian steppe were controlled by soil temperature, soil water content and root density. Increases in water addition had no effects on soil respiration, except when combined with N+P addition. However, soil nutrient enrichment without water addition enhanced soil respiration during the plant growing season. We found a linear positive relationship between root density and soil respiration, without interaction with treatments. N+P addition had negative impacts on N-mineralization, resulting in a strong N-immobilization. However, soil ammonium and nitrate content increased with N+P addition all over the seasons.Conclusion: Moderate increases in the precipitation through small pulses lead to no long-term response of soil processes in arid and cold Patagonian ecosystems. However, soil CO₂ effluxes are likely to increase with nutrient additions, such as anthropogenic N deposition, and microbial biomass could retain more nutrients in the soil. Therefore, high levels of N enrichment in arid ecosystems may strengthen the positive feedback between C cycle and climate change.

Stored water in inner tissues can affect plant water balance and its freezing resistance. We studied the water storages in the inner bark and sapwood of Araucaria araucana, a species with thick inner bark. Specifically, we analyzed its daily behavior, the driving force to radial water movement and its freezing resistance. The whole-stem water content and diameter and sap flow increased in the morning and decreased in the afternoon. An osmotic gradient between stem tissues was involved in the morning water storage recharge. There were no lags in the onset of sap flow between different stem positions, however sap flow at 6m height was higher than basal sap flow in the afternoon, at the time that sapwood water content started to decline followed by the inner bark. Extracellular freezing was delayed down to -6˚C in the inner bark and to -8˚C in the leaves. The unusual diurnal pattern of internal water use may enhance freezing resistance as a consequence of the lower water content and higher osmotic potential when the lowest temperatures occur. The contribution of stem tissues to daily water use and the pattern of ice nucleation observed make this species less susceptible to drought and very low temperatures.