RESUMEN
Branch/tree-level measurements of carbon (C)-acquisition provide an integration of the physical and biological processes driving the C gain of all individual leaves. Most research dealing with the interacting effects of high-irradiance environments and soil-induced water stress on the C-gain of fruit tree species has focused on leaf-level measurements. The C-gain of both sun-exposed leaves and branches of adult almond trees growing in a semi-arid climate was investigated to determine the respective costs of structural and biochemical/physiological protective mechanisms involved in the behaviour at branch scale. Measurements were performed on well-watered (fully irrigated, FI) and drought-stressed (deficit irrigated, DI) trees. Leaf-to-branch scaling for net CO2 assimilation was quantified by a global scaling factor (fg), defined as the product of two specific scaling factors: (i) a structural scaling factor (fs), determined under well-watered conditions, mainly involving leaf mutual shading; and (ii) a water stress scaling factor (fws,b) involving the limitations in C-acquisition due to soil water deficit. The contribution of structural mechanisms to limiting branch net C-gain was high (mean fs â¼0.33) and close to the projected-to-total leaf area ratio of almond branches (εâ =â 0.31), while the contribution of water stress mechanisms was moderate (mean fws,b â¼0.85), thus supplying an fg ranging between 0.25 and 0.33 with slightly higher values for FI trees with respect to DI trees. These results suggest that the almond tree (a drought-tolerant species) has acquired mechanisms of defensive strategy (survival) mainly based on a specific branch architectural design. This strategy allows the potential for C-gain to be preserved at branch scale under a large range of soil water deficits. In other words, almond tree branches exhibit an architecture that is suboptimal for C-acquisition under well-watered conditions, but remarkably efficient to counteract the impact of DI and drought events.
Asunto(s)
Dióxido de Carbono/metabolismo , Carbono/metabolismo , Prunus/fisiología , Agua/fisiología , Deshidratación , Luz , Fotosíntesis/fisiología , Hojas de la Planta/fisiología , Hojas de la Planta/efectos de la radiación , Tallos de la Planta/fisiología , Tallos de la Planta/efectos de la radiación , Transpiración de Plantas/fisiología , Prunus/metabolismo , Prunus/efectos de la radiación , Estaciones del Año , Suelo/química , ÁrbolesRESUMEN
Photosynthetic acclimation to highly variable local irradiance within the tree crown plays a primary role in determining tree carbon uptake. This study explores the plasticity of leaf structural and physiological traits in response to the interactive effects of ontogeny, water stress and irradiance in adult almond trees that have been subjected to three water regimes (full irrigation, deficit irrigation and rain-fed) for a 3-year period (2006-08) in a semiarid climate. Leaf structural (dry mass per unit area, N and chlorophyll content) and photosynthetic (maximum net CO(2) assimilation, A(max), maximum stomatal conductance, g(s,max), and mesophyll conductance, g(m)) traits and stem-to-leaf hydraulic conductance (K(s-l)) were determined throughout the 2008 growing season in leaves of outer south-facing (S-leaves) and inner northwest-facing (NW-leaves) shoots. Leaf plasticity was quantified by means of an exposure adjustment coefficient (ε=1-X(NW)/X(S)) for each trait (X) of S- and NW-leaves. Photosynthetic traits and K(s-l) exhibited higher irradiance-elicited plasticity (higher ε) than structural traits in all treatments, with the highest and lowest plasticity being observed in the fully irrigated and rain-fed trees, respectively. Our results suggest that water stress modulates the irradiance-elicited plasticity of almond leaves through changes in crown architecture. Such changes lead to a more even distribution of within-crown irradiance, and hence of the photosynthetic capacity, as water stress intensifies. Ontogeny drove seasonal changes only in the ε of area- and mass-based N content and mass-based chlorophyll content, while no leaf age-dependent effect was observed on ε as regards the physiological traits. Our results also indicate that the irradiance-elicited plasticity of A(max) is mainly driven by changes in leaf dry mass per unit area, in g(m) and, most likely, in the partitioning of the leaf N content.
Asunto(s)
Aclimatación , Luz , Fotosíntesis , Hojas de la Planta/fisiología , Prunus/fisiología , Estrés Fisiológico , Agua , Riego Agrícola , Carbono/metabolismo , Clorofila/metabolismo , Clima , Nitrógeno/metabolismo , Fenotipo , Hojas de la Planta/anatomía & histología , Tallos de la Planta/fisiología , Transpiración de Plantas , Prunus/anatomía & histología , Lluvia , Estaciones del AñoRESUMEN
Very few studies have attempted to disentangle the respective role of ontogeny and water stress on leaf photosynthetic attributes. The relative significance of both effects on photosynthetic attributes has been investigated in leaves of field-grown almond trees [Prunus dulcis (Mill.) D. A. Webb] during four growth cycles. Leaf ontogeny resulted in enhanced leaf dry weight per unit area (W(a)), greater leaf dry-to-fresh weight ratio and lower N content per unit of leaf dry weight (N(w)). Concomitantly, area-based maximum carboxylation rate (V(cmax)), maximum electron transport rate (J(max)), mesophyll conductance to CO2 diffusion (gm)' and light-saturated net photosynthesis (A(max)) declined in both well-watered and water-stressed almond leaves. Although g(m) and stomatal conductance (g(s)) seemed to be co-ordinated, a much stronger coordination in response to ontogeny and prolonged water stress was observed between g(m) and the leaf photosynthetic capacity. Under unrestricted water supply, the leaf age-related decline of A(max) was equally driven by diffusional and biochemical limitations. Under restricted soil water availability, A(max) was mainly limited by g(s) and, to a lesser extent, by photosynthetic capacity and g(m). When both ontogeny and water stress effects were combined, diffusional limitations was the main determinant of photosynthesis limitation, while stomatal and biochemical limitations contributed similarly.
Asunto(s)
Fotosíntesis/fisiología , Prunus/crecimiento & desarrollo , Prunus/fisiología , Riego Agrícola , Biomasa , Dióxido de Carbono/metabolismo , Deshidratación , Transporte de Electrón , Entropía , Células del Mesófilo/metabolismo , Modelos Biológicos , Tallos de la Planta/fisiología , Estomas de Plantas/anatomía & histología , Estomas de Plantas/fisiología , Transpiración de Plantas/fisiología , Carácter Cuantitativo Heredable , Lluvia , Estaciones del Año , Temperatura , AguaRESUMEN
We investigated seasonal trends in, and relationships between, leaf structural properties, leaf nitrogen concentration, and maximum (A(m)) and potential (A(p)) leaf net CO(2) assimilation of 1-year-old fruiting (f) and current-year non-fruiting (nf) shoots in 5-year-old almond trees (Prunus dulcis (Mill.) D.A. Webb cv Marta). These trees had been subjected in the previous 4 years to either full irrigation (FI regime) or sustained deficit irrigation (DI) at 50% of standard crop evapotranspiration during the entire growing season (DI regime) in the semiarid climate of southeast Spain. Measurements were made during an entire growing season on sun-exposed leaves. Leaf dry mass per unit area (W(a)), area and dry-mass-based leaf N concentrations (N(a) and N(w), respectively), and area and dry-mass-based A(m) (A(ma) and A(mw), respectively) were lower in f-leaves than in nf-leaves. Changes in leaf structural attributes induced by DI were more pronounced in nf-leaves than in f-leaves, the latter being little affected. Over the entire growth season, A(m) and A(p) were correlated negatively with W(a) and positively with N(w) for both the leaf classes and the irrigation regimes. When calculated with respect to total leaf N concentration, maximum photosynthetic nitrogen-use efficiency (PNUE(m)) was significantly higher in f-leaves than in nf-leaves, with no significant differences between the leaf classes among the irrigation regimes. However, when PNUE(m) was calculated with respect to photosynthetic N, no significant effect of leaf class or irrigation regime was observed. Overall, our results showed that DI and FI trees exhibited similar seasonal patterns of leaf structural properties and maximum and potential leaf net CO(2) assimilation rates, but there were distinct N-allocation patterns between f- and nf-leaves. In the DI treatment, leaf structural adjustments appeared to operate to maintain a high N status in the leaves of fruit-bearing shoots, to the detriment of N resources allocated to vegetative shoots.