Leaf Area-specific Hydraulic Conductivity Research Articles

Effect of domestication on water transport in Jatropha curcas seedlings: Relevance of xylem vessels of organs and aquaporin activity in roots

Plant domestication may lead to the suppression of attributes that enable survival in adverse environments. In this context, considering the scarcity of information on water transport in Jatropha curcas L., an experiment was conducted to compare the anatomical variables and hydraulic parameters of roots, stems, and leaves as well as the contribution of aquaporins in water transport of roots between wild and domesticated genotypes. Under irrigation, it was observed 10.2% larger xylem vessel diameters in roots but 7.9% and 11.3% smaller xylem vessel diameters in stems and leaves, respectively, of domesticated genotypes as compared to their wild counterparts. Overall, domestication resulted in 57.5% lower hydraulic resistivity in roots, 87.2% higher hydraulic resistivity in leaves, 22.4% higher vein length per leaf area, 10.5% lower net photosynthetic rate, 36.7% and 42.6% lower theoretical leaf area-specific hydraulic conductivity in roots and stems, respectively. Conversely, in domesticated genotypes, theoretical mass-specific hydraulic conductivity was respectively 58.4% and 57.7% higher in roots and stems. Furthermore, in these genotypes, the root volume was 13% smaller and the contribution of aquaporins to the hydraulic conductivity of roots was greater. In conclusion, domestication has driven the selection of genotypes with roots that are more efficient in conducting water through effects on the anatomy of xylem vessels and activity of aquaporins. However, leaves of such genotypes are more conservative in anatomical and photosynthetic terms. • Domestication of J. curcas resulte in water transport efficient genotypes. • Such efficiency resulted from aquaporin activity and from changes on xylem anatomy. • Domestication improved leaf water distribution, without changes on photosynthesis.

Hydraulic conductivity in stem of young plants of Jatropha curcas L. cultivated under irrigated or water deficit conditions

Jatropha curcas L. can survive situations of water deficiency, in which carbon assimilation and growth rates are severely affected, which can ultimately result in low productivity. With the objective of evaluating the hydraulic conductivity of stem xylem and its relationship with leaf gas exchange under water deficiency, two-month old plants of ten genotypes of J. curcas from an improved population were cultivated under water restriction (soil water content of 14%) or under full irrigation (soil water content of 22%) for 60 days. Water deficit led to significant increase of leaf area-specific hydraulic conductivity (LSCn) in genotype CNPAE 517 and decrease in CNPAE 556, 557, 559, 569 and 570. Of those five genotypes, only in CNPAE 556 there was no decrease of leaf water potential measured around 4 h. Genotypes CNPAE 516, 517 and 520 can be highlighted, where elevated rate of net photosynthesis were observed even under water restriction. Changes in the anatomy of the xylem vessels, as well as in root biomass when submitted to water deficiency favored a greater or lesser drought tolerance of the genotypes when the native or potential hydraulic conductivity were analyzed. In summary, high plasticity for hydraulic and anatomical traits, as observed for the genotypes CNPAE 516, 517 and 520 must be considered for further investigation on the tradeoffs between hydraulic conductivity and productivity, in the search for genetic material suitable for cultivation in areas subject to short periods of soil water deficit.

Impacts of long-term precipitation manipulation on hydraulic architecture and xylem anatomy of piñon and juniper in Southwest USA.

Hydraulic architecture imposes a fundamental control on water transport, underpinning plant productivity, and survival. The extent to which hydraulic architecture of mature trees acclimates to chronic drought is poorly understood, limiting accuracy in predictions of forest responses to future droughts. We measured seasonal shoot hydraulic performance for multiple years to assess xylem acclimation in mature piñon (Pinus edulis) and juniper (Juniperus monosperma) after 3+years of precipitation manipulation. Our treatments consisted of water addition (+20% ambient precipitation), partial precipitation-exclusion (-45% ambient precipitation), and exclusion-structure control. Supplemental watering elevated leaf water potential, sapwood-area specific hydraulic conductivity, and leaf-area specific hydraulic conductivity relative to precipitation exclusion. Shifts in allocation of leaf area to sapwood area enhanced differences between irrigated and droughted KL in piñon but not juniper. Piñon and juniper achieved similar KL under ambient conditions, but juniper matched or outperformed piñon in all physiological measurements under both increased and decreased precipitation treatments. Embolism vulnerability and xylem anatomy were unaffected by treatments in either species. Absence of significant acclimation combined with inferior performance for both hydraulic transport and safety suggests piñon has greater risk of local extirpation if aridity increases as predicted in the southwestern USA.

Heavy browsing affects the hydraulic capacity of Ceanothus rigidus (Rhamnaceae).

Defoliation by herbivores can reduce carbon assimilation, change plant water relations, and even shift the biotic structure of plant communities. In this study, we took advantage of a long-term deer exclosure experiment to examine the consequences of persistent deer herbivory on plant water relations and the xylem structure-function relationships in Ceanothus rigidus, a maritime chaparral shrub in coastal California. Browsed plants had thicker stems with many intertwined short distal twigs, and significantly higher sapwood-to-leaf area ratios than their non-browsed counterparts. Leaf area-specific hydraulic conductivity was similar in both browsed and non-browsed plants, but xylem area-specific conductivity was significantly lower in the browsed plants. Vessel diameters were equivalent in both plant groups, but the number of vessels on a transverse area basis was nearly 40% lower in the browsed plants, accounting for their lower transport efficiency. Mid-day in situ water potentials and losses of hydraulic conductivity due to embolism were similar in both groups of plants but stomatal conductance was higher in the browsed shrubs in the early part of the growing season. We discuss our findings in the context of whole-plant ecophysiology, and explore the consequences of herbivory on hormonal signals, wood anatomy, and xylem function.

Limits to the height growth of Caragana korshinskii resprouts

Predawn leaf water potential (LWP), the LWP between 09:00 and 10:30 h (termed minimum LWP), stem xylem hydraulic conductivity, foliar nitrogen, leaf gas exchange and leaf traits were measured on the same days in adults and 1-year-old to 7-year-old resprouts that had regrown after removing all the aboveground shoots. Height growth and accumulation of aboveground biomass quickly decreased with resprout age and there was no difference between 7-year-old resprouts and the uncut adults. Predawn LWP showed no significant difference between resprouts and adults, but the minimum LWP decreased gradually from -2.0 MPa in 1-year-old resprouts to -3.0 MPa in 7-year-old resprouts. The decrease in minimum LWP was associated with increased hydraulic resistance, as indicated by the gradual decrease in leaf area-specific hydraulic conductivity (KL) and sapwood area-specific hydraulic conductivity (KS) and the associated increase in stem native percentage loss of hydraulic conductivity in older than 2-year-old resprouts. The leaf nitrogen content per unit area (Narea) also decreased steadily from 3.6 g m(-2) in 1-year-old resprouts to 1.7 g m(-2) in 7-year-old resprouts. With the decline in LWP and Narea, the rate of leaf photosynthesis per unit area (Aarea) decreased from 20 μ mol m(-2) s(-1) in 1-year-old resprouts to 11 μ mol m(-2) s(-1) in 7-year-old resprouts. In adults, although KS decreased further compared with 7-year-old resprouts, the minimum LWP, KL, Narea and the rate of photosynthesis increased by 0.3 MPa, 29, 34 and 23%, respectively. The results show that a progressive loss of stem hydraulic conductivity and a steady decrease in foliar nitrogen with age were associated with a decrease in the photosynthetic rate of Caragana korshinskii Kom. resprouts, possibly changing the allocation of photosynthetic assimilates and slowing resprout height growth.

Allocation to leaf area and sapwood area affects water relations of co-occurring savanna and forest trees

Water availability is a principal factor limiting the distribution of closed-canopy forest in the seasonal tropics, suggesting that forest tree species may not be well adapted to cope with seasonal drought. We studied 11 congeneric species pairs, each containing one forest and one savanna species, to test the hypothesis that forest trees have a lower capacity to maintain seasonal homeostasis in water relations relative to savanna species. To quantify this, we measured sap flow, leaf water potential (Psi(L)), stomatal conductance (g (s)), wood density, and Huber value (sapwood area:leaf area) of the 22 study species. We found significant differences in the water relations of these two species types. Leaf area specific hydraulic conductance of the soil/root/leaf pathway (G (t)) was greater for savanna species than forest species. The lower G (t) of forest trees resulted in significantly lower Psi(L) and g (s) in the late dry season relative to savanna trees. The differences in G (t) can be explained by differences in biomass allocation of savanna and forest trees. Savanna species had higher Huber values relative to forest species, conferring greater transport capacity on a leaf area basis. Forest trees have a lower capacity to maintain homeostasis in Psi(L) due to greater allocation to leaf area relative to savanna species. Despite significant differences in water relations, relationships between traits such as wood density and minimum Psi(L) were indistinguishable for the two species groups, indicating that forest and savanna share a common axis of water-use strategies involving multiple traits.

Control of transpiration in three coffee cultivars: the role of hydraulic and crown architecture

Water use and hydraulic architecture were studied in the coffee (Coffea arabica) cultivars San Ramon, Yellow Caturra and Typica growing in the field under similar environmental conditions. The cultivars differed in growth habit, crown architecture, basal sapwood area and total leaf surface area. Transpiration per unit leaf area (E), stomatal conductance (g s), crown conductance (g c), total hydraulic conductance of the soil/leaf pathway (G t) and the stomatal decoupling coefficient, omega (Ω) (Jarvis and McNaughton 1986) were assessed over a range of soil moisture and during partial defoliation treatments. The relationship between sap flow and sapwood area was linear and appeared to be similar for the three cultivars. Variation in g c, E, and G t of intact plants and leaf area-specific hydraulic conductivity (k l) of excised lateral branches was negatively correlated with variation in the ratio of leaf area to sapwood area. Transpiration, g c, and g s were positively correlated with G t. Transpiration and G t varied with total leaf area and were greatest at intermediate values (10 m2) of leaf area. Omega was greatest in Yellow Caturra, the cultivar with the greatest leaf area and a dense crown, and was smallest in Typica, the cultivar with an open crown. Differences in omega were attributable primarily to differences in leaf boundary layer conductance among the cultivars. Plants of each cultivar that were 40% defoliated maintained sap flows comparable to pretreatment plants, but expected compensatory increases in g s were not consistently observed. Despite their contrasting crown morphologies and hydraulic architecture, the three cultivars shared common relationships between water use and hydraulic architectural traits.