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Strategy of deep soil water acquisition is critical to plantu2019s adaption to drought stress. However, it is unknown how the deep soil water acquisition determines speciesu2019 distribution and resource economy strategy in an experimental context. With data from 13 woody shrub species of subtropical coniferous forests, we investigated the associations of deep water acquisition patterns (ability of deep water use and plasticity of deep water use between season), plant hydraulic traits (leaf water potential, water use efficiency), species distribution (relative occurrence frequency and importance), and economic traits across organs (first-order root diameter of shallow soil, wood density, specific leaf area, and leaf nitrogen concentration). Higher ability of deep resource utility acted synergistically with higher intrinsic water use efficiency to promote plantsu2019 adaption to seasonal drought, but was not a necessary trait possessed by the common species. Species with higher plasticity of deep water use (rather than higher ability of deep water use) had lower wood density, but not smaller first-order root diameter, indicating species being fast in deep soil resource acquisition not necessarily being fast in shallow fine root resource acquisition.Our result provide new insight in the mechanisms through which deep soil resource acquisition trait interacted with shallow soil and aboveground resource acquisition traits to integrate the whole-plant economic spectrum and thus community assembly process.

On the basis of Kranz type leaf anatomy, 107 species in 11 families out of 682 species in 47 famines surveyed were identified as C4 plants. The families in which C4 representatives were found ¡nclude the Aizoaecae, Amaranthaecae, Boraginaceac, Compositae, Convolvulaceae, Cyperaceae, Euphorbiaceae, Gramineae, Nyctaginaceae, Portulacaceae, and Zygophyliaceae. Several of the species identified have not been reported in previously published lists of C4 plants.The presence of C4 photosynthesis was restricted to plants of herbaceous life form from open habitats. When the altitudinal distributions of C3 and C4 representatives in the 11 C4 families were compared, relative abundance of C4 species and elevation were found to be highly correlated. The possible reasons for this are discussed. La identificación de especies vegetales según su sistema de fijación fotosintética de carbono (C3, C4 o CAM) ha llegado a ser una técnica útil para el entendimiento de su ecofisiología. Ciertas generalizaciones sobre la distribución ecológica de las plantas C4 pueden hacerse basadas en las características fisiológicas anteriormente mencionadas. Como se esperaría, las plantas C4 se encuentran en ambientes cálidos con alta intensidad luminosa, donde el agua puede ser un factor limitante. Estas condiciones ambientales generales predominan en muchas regiones tropicales y la abundancia de especies C4 en estas regiones es bien conocida, pero es escasa la información sobre las condiciones ecológicas específicas que favorecen la abundancia, dominancia o ausencia de especies C4 en determinados habitats tropicales. Este estudio intenta correlacionar algunos parámetros ecológicos con la distribución de especies C4 dentro de una región geográfica restringida.

International audience; The Araucariaceae is an iconic tree family. Once globally important, the Araucariaceae declined dramatically over the Cenozoic period. Increasing aridity is thought to be responsible for extinction and range contraction of Araucariaceae in Australia, yet little is known about how these trees respond to water stress. We examined the response to water stress of the recently discovered tree Wollemia nobilis Jones, W.G., Hill, K.D. & Allen, J.M. (Araucariaceae) and two closely related and widespread tree species, Araucaria bidwillii Hook. and Araucaria cunninghamii Mudie, and the island-endemic species, Araucaria heterophylla (Salisb.) Franco. Leaf water potential in all Araucaria spp. remained remarkably unchanged during both dehydration and rehydration, indicating strong isohydry. The xylem tensions at which shoot and stem hydraulic conductances were reduced to 50% (P50shoot and P50stem) were closely correlated in all species. Among the four species, W. nobilis exhibited greater resistance to xylem hydraulic dysfunction during water stress (as indicated by P50shoot and P50stem). Unexpectedly, W. nobilis also experienced the highest levels of crown mortality in response to dehydration, suggesting that this was the most drought-sensitive species in this study. Our results highlight that single traits (e.g., P50) should not be used in isolation to predict drought survival. Further, we found no clear correlation between species’ P50 and rainfall across their distributional range. Diversity in drought response among these closely related Araucariaceae species was surprisingly high, considering their reputation as a functionally conservative family.

Hydraulic architecture was studied in shrub species differing in rooting depth in a cold desert in Southern Argentina. All species exhibited strong hydraulic segmentation between leaves, stems and roots with leaves being the most vulnerable part of the hydraulic pathway. Two types of safety margins describing the degree of conservation of the hydraulic integrity were used: the difference between minimum stem or leaf water potential (⍦) and the ⍦ at which stem or leaf hydraulic function was reduced by 50% ⍦ - ⍦50), and the difference between leaf and stem ⍦50. Leaf ⍦50 -⍦ stem ⍦50 increased with decreasing rooting depth. Large diurnal decreases in rootspecific hydraulic conductivity suggested high root vulnerability to embolism across all species. Although stem ⍦50 became more negative with decreasing species-specific Ysoil and minimum stem⍦, leaf ⍦50 was independent of ⍦ and minimum leaf ⍦. Species with embolism-resistant stems also had higher maximum stem hydraulic conductivity. Safety margins for stems were >2.1 MPa, whereas those for leaves were negative or only slightly positive. Leaves acted as safety valves to protect the integrity of the upstream hydraulic pathway, whereas embolism in lateral roots may help to decouple portions of the plant from the impact of drier soil layers. Fil: Bucci, Sandra Janet. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina Fil: Scholz, Fabian Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina Fil: Peschiutta, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina Fil: Arias, Nadia Soledad. Universidad Nacional de la Patagonia "san Juan Bosco". Facultad de Ingenieria - Sede Comodoro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Meinzer, Frederick. United States Department of Agriculture; Argentina Fil: Goldstein, Guillermo Hernan. University Of Miami; Estados Unidos. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución. Laboratorio de Ecología Funcional; Argentina

International audience; Co-occurring species often have different strategies for tolerating daily cycles of water stress. One underlying parameter that can link together the suite of traits that enables a given strategy is wood density. Here we compare hydraulic traits of two pioneer species from a tropical forest in Panama that differ in wood density: Miconia argentea and Anacardium excelsum. As hypothesized, the higher wood density of Miconia was associated with smaller diameter vessels and fibres, more water stress-resistant leaves and stems, and roughly half the capacitance of the lower wood density Anacardium. However, the scaling of hydraulic parameters such as the increases in leaf area and measures of hydraulic conductivity with stem diameter was remarkably similar between the two species. The collection of traits exhibited by Miconia allowed it to tolerate more water stress than Anacardium, which relied more heavily on its capacitance to buffer daily water potential fluctuations. This work demonstrates the importance of examining a range of hydraulic traits throughout the plant and highlights the spectrum of possible strategies for coping with daily and seasonal water stress cycles.

International audience; Deep root water uptake and hydraulic redistribution (HR) play a major role in forest ecosystems during drought, but little is known about the impact of climate change on root-zone processes influencing HR and its consequences on water and carbon fluxes. Using data from two old growth sites in the western USA, two mature sites in the eastern USA, one site in southern Brazil, and simulations with the process-based model MuSICA, our objectives were to show that HR can 1) mitigate the effects of soil drying on root functioning, and 2) have important implications for carbon uptake and net ecosystem exchange (NEE). In a dry, old-growth ponderosa pine (USA) and a eucalyptus stand (Brazil) both characterized by deep sandy soils, HR limited the decline in root hydraulic conductivity and increased dry season tree transpiration (T) by up to 30%, which impacted NEE through major increases in gross primary productivity (GPP). The presence of deep-rooted trees did not necessarily imply high rates of HR unless soil texture allowed large water potential gradients to occur, as was the case in the wet old-growth Douglas-fir/mixed conifer stand. At the Duke mixed hardwood forest characterized by a shallow clay-loam soil, modeled HR was low but not negligible, representing annually up to 10% of T, and maintaining root conductance high. At this site, in the absence of HR, it was predicted that annual GPP would have been diminished by 7-19%. At the coastal loblolly pine plantation, characterized by deep organic soil, HR limited the decline in shallow root conductivity by more than 50% and increased dry season T by up to 40%, which increased net carbon gain by the ecosystem by about 400 gC m-2 yr-1, demonstrating the significance of HR in maintaining the stomatal conductance and assimilation capacity of the whole ecosystem. Under future climate conditions (elevated atmospheric [CO2] and temperature), HR is predicted to be reduced by up to 50%; reducing the resilience of trees to droughts. Under future conditions, T is predicted to stay the same at the Duke mixed hardwood forest, but to decline slightly at the coastal loblolly pine plantation and slightly increase at the old-growth ponderosa pine stand and the eucalyptus plantation. As a consequence, water use efficiency in all sites was predicted to improve dramatically under future climate conditions. Our simulations also showed that the negative effect of drier nights on HR would be greater under future climate conditions. Assuming no increase in stomatal control with increasing drier nights, increased vapor pressure deficit at night under future conditions was sufficient to drive significant nighttime T at all sites , which reduced HR, because the plant and the atmosphere became a sink for hydraulically redistributed water . We concluded that the predicted reductions in HR under future climate conditions are expected to play an important regulatory role in land–atmosphere interactions by affecting whole ecosystem carbon and water balance. We suggest that root distribution should be treated dynamically in response to climate change and that HR and its interactions with rooting depth and soil texture should be implemented in soil–vegetation–atmosphere transfer models.

The objective of this study was to characterize and understand morphological and physiological variation in traits related to water economy, at the plant and stand level, along a gradient of tree density in a Neotropical savanna (Cerrado). Cerrado plots subjected to long-term fertilization and gallery forests were also included in the analysis to expand the axes of ecosystem variation. Consistent changes in stand level biophysical traits observed along the gradient of increasing tree density included a decrease in weighted-average wood density, and increases in leaf surface area per plant, leaf specific hydraulic conductivity, specific leaf area and stomatal conductance. A conceptual model of biophysical, morphological and physiological trait interactions was developed in an attempt to explain determinants of hydraulic architecture and variations in water economy of Cerrado trees. Consistent with the model minimum leaf water potentials were higher, during the dry season, in low wood density trees compared to high wood density trees, and higher leaf water potential was associated with higher stomatal conductance. On the other hand, variations in stand level physiological and morphological traits along the tree density gradient could not be explained by variations in single environmental factors. Some of the potential contributing factors are: higher concentration and availability of soil nutrients in the upper portion of the gradient where tree density is greatest and constrains to tree establishment and growth by waterlogging and presence of concretions in the soil profile where tree density is lowest. O objetivo deste estudo foi caracterizar e compreender as variações morfológicas e fisiológicas em atributos relacionados à economia da água, em nível de indivíduo e de parcela, que ocorrem ao longo de um gradiente de densidade arbórea em uma savana neotropical (cerrado). Parcelas de vegetação de cerrado submetidas a um experimento de adubação de longo prazo e matas de galeria também foram incluídas na análise, a fim de expandir os eixos de variação do ecossistema. Mudanças consistentes em atributos biofísicos em nível de parcela foram observadas ao longo do gradiente de densidade crescente de árvores. Estas incluíram uma diminuição na densidade média ponderada da madeira, aumentos na área foliar por planta, na condutividade hidráulica específica da folha, na área foliar específica e na condutância estomática. Um modelo conceitual das interações entre as características biofísicas, morfológicas e fisiológicas foi desenvolvido em uma tentativa de explicar os determinantes da arquitetura hidráulica e variações na economia de água de árvores do Cerrado. Consistente com o modelo, os valores mínimos de potencial hídrico durante a estação seca foram maiores nas árvores de baixa densidade de madeira, em comparação com árvores de alta densidade de madeira, enquanto os maiores valores de potencial hídrico foliar estiveram associados com maior condutância estomática. Por outro lado, ao longo do gradiente de densidade arbórea, as variações em nível de parcela das características morfológicas e fisiológicas não puderam ser explicadas por variações de um único fator ambiental. Alguns dos fatores contribuintes potenciais são: maior concentração e disponibilidade de nutrientes do solo na porção superior do gradiente de densidade arbórea onde há um maior número de árvores e restrições no estabelecimento e crescimento pela inundação periódica e pela presença de concreções no perfil do solo onde a densidade de árvores é mais baixa.

We determined adjustments in physiology and morphology that allow Neotropical savanna trees from central Brazil (Cerrado) to avoid water deficits and to maintain a nearly constant internal water balance despite seasonal changes in precipitation and air saturation deficit (D). Precipitation in the study area is highly seasonal with about five nearly rainless months during which D is two fold higher compared to wet season values. As a consequence of the seasonal fluctuations in rainfall and D, soil water potential changes substantially in the upper 100 cm of soil, but remains nearly constant below 2 m depth. Hydraulic architecture and water relations traits of Cerrado trees adjusted during the dry season to prevent increasing water deficits and insure homeostasis in minimum leaf water potential ψL and in total daily water loss per plant (isohydry). The isohydric behavior of Cerrado trees was the result of a decrease in total leaf surface area per tree, a strong stomatal control of evaporative losses, an increase in leaf-specific hydraulic conductivity and leaf hydraulic conductance and an increase in the amount of water withdrawn from internal stem storage, during the dry season. Water transport efficiency increased in the same proportion in leaves and terminal stems during the dry season. All of these seasonal adjustments were important for maintaining ψL above critical thresholds, which reduces the rate of embolism formation in stems and help to avoid turgor loss in leaf tissues still during the dry season. These adjustments allow the stems of most Cerrado woody species to operate far from the point of catastrophic dysfunction for cavitation, while leaves operate close to it and experience embolism on a daily basis, especially during the dry season. O objetivo deste estudo foi determinar os ajustamentos na morfologia e fisiologia que permitem árvores das savanas neotropicais do Brasil Central (Cerrado) de evitar déficits hídricos e de manter um balanço hídrico interno praticamente constante apesar das variações sazonais da precipitação e no déficit de saturação do ar (D). A precipitação na área de estudo é fortemente sazonal, com cerca de cinco meses praticamente sem chuva durante os quais D é duas vezes maior aos valores medidos na época chuvosa. Como conseqüência da flutuação sazonal das chuvas e de D, o potencial hídrico do solo muda substancialmente, nos primeiros 100 cm do solo, mas permanece quase constante abaixo de 2 m de profundidade. A arquitetura hidráulica e os parâmetros relacionados a relações hídricas das árvores do Cerrado se ajustaram durante a estação seca para evitar o déficit hídrico crescente e assegurar a homeostase nos valores mínimos de potencial hídrico foliar ψL e na perda total diária de água pela planta (iso-hidria). O comportamento iso-hídrico das árvores do Cerrado foi o resultado de uma diminuição da superfície foliar total por árvore, um forte controle estomático das perdas por evaporação, um aumento na condutividade hidráulica específica da folha e na condutância hidráulica foliar e um aumento da quantidade de águas retirada dos reservatórios internos do caule, durante a estação seca. A eficiência no transporte de água aumentou, nas mesmas proporções, nas folhas e nos ramos terminais durante a estação seca. Todos estes ajustamentos sazonais foram importantes para a manutenção de ψL acima de limiares críticos, com isto contribuindo para uma redução na formação de embolismos nos ramos e ajudando a evitar a perda de turgor em tecidos foliares durante a época seca. Esses ajustes permitem que os ramos das espécies lenhosas do Cerrado operem bem distanciados do ponto de disfunção catastrófica para a cavitação, enquanto as folhas operam próximas e sofrem embolismos em uma base diária, especialmente durante a estação seca.