Using branch and basal trunk sap flow measurements to estimate whole-plant water capacitance: a caution

Thermometric sap flow sensors are widely used to measure water flow in roots, stems and branches of plants. Comparison of the timing of flow in branches and stems has been used to estimate water capacitance of large trees. We review studies of sap flow in branches and present our own data to show that there is wide variation in the patterns and timing of sap flow of branches in different parts of the crown, owing to the course of daily solar illuminance. In contiguous forest, east-facing and upper branches are illuminated earlier than west-facing and lower branches and most capacitance studies do not include adequate information about branch sampling regimes relative to the overall pattern of crown illuminance, raising questions about the accuracy of capacitance estimates. Measuring only upper branches and normalising these results to represent the entire crown is dangerous because flows at the stem base likely peak in response to maximum crown illuminance (and transpiration) and this will differ compared to the timing of peak flows in upper branches. We suggest that the magnitude of flow lags between branches and stems needs further study, with careful attention to branch position and method application before a robust understanding of capacitance, particularly in woody tissues of large trees, can be formed. We did not detect flow lags in the world’s tallest and largest tree species Sequoia sempervirens and Sequoiadendron giganteum, despite measurement along large pathlengths (∼57 and 85 m), which raises questions as to why large flow lags are often recorded for much smaller species. One conspicuous possibility is the different methods used among studies. Constant-heating methods such as the thermal dissipation probe (and also heat balance methods) include heat capacitance behaviour due to warming of wood tissues, which delays the response of the sensors to changing sap flow conditions. We argue that methods with intrinsic heat-capacitance present dangers when trying to measure water-capacitance in trees. In this respect heat pulse methods hold an advantage.     

Combining sap flow and trunk diameter measurements to assess water needs in mature olive orchards

Sap flux (Q) and trunk diameter variation (TDV) are among the most useful plant-based measurements to detect water stress and to evaluate plant water consumption. The usefulness of both methods decreases, however, when applied to species that, like olive, have an outstanding tolerance to drought and a remarkable capacity to take up water from drying soils. Evidence shows that this problem is greater in old, big trees with heavy fruit load. Our hypothesis is that the analysis of simultaneous measurements of Q and TDV made in the same trees is more useful for assessing irrigation needs in old olive orchards than the use of any of these two methods alone. To test our hypothesis, we analysed relations between Q, TDV, midday stem water potential (Ψ_stem), relative extractable water and atmospheric demand in an olive orchard of 38-year-old ‘Manzanilla’ trees with heavy fruit load. Measurements were made during one irrigation season (May-October), in fully irrigated trees (FI, 107% of the crop evapotranspiration, ET_c, supplied by irrigation), and in trees under two levels of deficit irrigation (DI60, 61% ET_c; DI30, 29% ET_c). Time courses of Q and TDV measured on days of contrasting weather and soil water conditions were analysed to evaluate the usefulness of both methods to assess the crop water status. We calculated the daily tree water consumption (E_p) from Q measurements. For both DI treatments we calculated a signal intensity by dividing daily E_p values of each DI tree by those of the FI tree (SI−Ep). We did the same with the maximum daily shrinkage (MDS) values (S_I−MDS). Neither SI−Ep nor S_I−MDS rendered useful information for assessing the crop water needs. On the contrary, the daily difference for maximum trunk diameter (MXTD) between each of the DI trees and the FI tree (D_MXTD) clearly indicated the onset and severity of water stress. A similar analysis with the E_p values, from which DEp values were derived, showed the effect of water stress on the water consumption of the trees. We concluded that the simultaneous use of D_MXTD and DEp values provides more detailed information to assess water needs in mature olive orchards than the use of Q or TDV records alone.     

Sapflow+: a four-needle heat-pulse sap flow sensor enabling nonempirical sap flux density and water content measurements

? To our knowledge, to date, no nonempirical method exists to measure reverse, low or high sap flux density. Moreover, existing sap flow methods require destructive wood core measurements to determine sapwood water content, necessary to convert heat velocity to sap flux density, not only damaging the tree, but also neglecting seasonal variability in sapwood water content. ? Here, we present a nonempirical heat-pulse-based method and coupled sensor which measure temperature changes around a linear heater in both axial and tangential directions after application of a heat pulse. By fitting the correct heat conduction-convection equation to the measured temperature profiles, the heat velocity and water content of the sapwood can be determined. ? An identifiability analysis and validation tests on artificial and real stem segments of European beech (Fagus sylvatica L.) confirm the applicability of the method, leading to accurate determinations of heat velocity, water content and hence sap flux density. ? The proposed method enables sap flux density measurements to be made across the entire natural occurring sap flux density range of woody plants. Moreover, the water content during low flows can be determined accurately, enabling a correct conversion from heat velocity to sap flux density without destructive core measurements.     

Irrigation effects on daily and seasonal variations of trunk sap flow and leaf water relations in olive trees

Irrigation effects on whole-plant sap flow and leaf-level water relations were characterised throughout a growing season in an experimental olive (Olea europaea L.) orchard. Atmospheric evaporative demand and soil moisture conditions for irrigated and non-irrigated olive trees were also monitored. Whole-plant water use in field-grown irrigated and rain fed olive trees was determined using a xylem sap flow method (compensation heat-pulse velocity). Foliage gas exchange and water potentials were determined throughout the experimental period. Physiological parameters responded diurnally and seasonally to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. There was a considerable degree of agreement between daily transpiration deduced from heat-pulse velocity and that determined by calibration using the Penman–Monteith equation in the field. Summer drought caused decreasing leaf gas exchange and water potentials, and a progressive increase in hydraulic conductance (stronger in non-irrigated than irrigated trees), probably attributable to modifications in hydraulic properties at the soil-root interface. Negligible hysteresis, attributable to low plant capacitance, was observed in the relationship between leaf water potential and sap flow. A proportional decrease in maximum daily leaf conductance with increasing vapour pressure deficit was observed, while mean daytime canopy stomatal conductance decreased with the season. As a result, plant water use was limited and excessive drought stress prevented. Non-irrigated olive trees recovered after the summer drought, showing a physiological behaviour similar to that of irrigated trees. In addition to physiological and environmental factors, there are endogenous keys (chemical signals) influencing leaf level parameters. Olive trees are confirmed to be economical and sparing users of soil water, with an efficient xylem sap transport, maintenance of significant gas exchange and transpiration, even during drought stress.     

Effect of stem water content on sap flow from dormant maple and butternut stems: induction of sap flow in butternut

Sap flow from excised maple stems collected over the winter (1986/87) was correlated with stem water content. Stem water content was high in the fall (>0.80) and decreased rapidly during 2 weeks of continuous freezing temperatures in late winter (<0.60). Exudation of sap from stem segments subjected to freeze/thaw cycles was small (<10 mL/kg) in the fall, but substantial exudation (45-50 mL/kg) occurred following the decline in water content. These observations are consistent with Milburn's and O'Malley's models (J.A. Milburn, P.E.R. O'Malley [1984] Can J Bot 62: 2101-2106; P.E.R. O'Malley, J.A. Milburn [1983] Can J Bot 61:3100-3106) of sap absorption into gas-filled fibers during freezing. Exudation volume was increased 200 to 300% in maple stems originally at high water content (>0.80) after perfusion with sucrose and dehydration at −12°C. Sap flow was also induced in butternut stem segments after the same treatment. Thus, sap flow may not be unique to maples. Sap flow could not be increased in stem segments dehydrated at 4°C. Migration of water molecules from small ice crystals in fibers to larger crystals in vessels while stems were frozen may account for increase exudation after dehydration at −12°C. This would result in preferential dehydration of fibers and a distribution of gas and sap favorable for stem-based sap flow.     

Using flow cytometry to estimate pollen DNA content: improved methodology and applications

Background and Aims

Flow cytometry has been used to measure nuclear DNA content in pollen, mostly to understand pollen development and detect unreduced gametes. Published data have not always met the high-quality standards required for some applications, in part due to difficulties inherent in the extraction of nuclei. Here we describe a simple and relatively novel method for extracting pollen nuclei, involving the bursting of pollen through a nylon mesh, compare it with other methods and demonstrate its broad applicability and utility.

Methods

The method was tested across 80 species, 64 genera and 33 families, and the data were evaluated using established criteria for estimating genome size and analysing cell cycle. Filter bursting was directly compared with chopping in five species, yields were compared with published values for sonicated samples, and the method was applied by comparing genome size estimates for leaf and pollen nuclei in six species.

Key Results

Data quality met generally applied standards for estimating genome size in 81 % of species and the higher best practice standards for cell cycle analysis in 51 %. In 41 % of species we met the most stringent criterion of screening 10 000 pollen grains per sample. In direct comparison with two chopping techniques, our method produced better quality histograms with consistently higher nuclei yields, and yields were higher than previously published results for sonication. In three binucleate and three trinucleate species we found that pollen-based genome size estimates differed from leaf tissue estimates by 1·5 % or less when 1C pollen nuclei were used, while estimates from 2C generative nuclei differed from leaf estimates by up to 2·5 %.

Conclusions

The high success rate, ease of use and wide applicability of the filter bursting method show that this method can facilitate the use of pollen for estimating genome size and dramatically improve unreduced pollen production estimation with flow cytometry.     

Water uptake by seminal and adventitious roots in relation to whole-plant water flow in barley (Hordeum vulgare L.)

Prior to an assessment of the role of aquaporins in root water uptake, the main path of water movement in different types of root and driving forces during day and night need to be known. In the present study on hydroponically grown barley (Hordeum vulgare L.) the two main root types of 14- to 17-d-old plants were analysed for hydraulic conductivity in dependence of the main driving force (hydrostatic, osmotic). Seminal roots contributed 92% and adventitious roots 8% to plant water uptake. The lower contribution of adventitious compared with seminal roots was associated with a smaller surface area and number of roots per plant and a lower axial hydraulic conductance, and occurred despite a less-developed endodermis. The radial hydraulic conductivity of the two types of root was similar and depended little on the prevailing driving force, suggesting that water uptake occurred along a pathway that involved crossing of membrane(s). Exudation experiments showed that osmotic forces were sufficient to support night-time transpiration, yet transpiration experiments and cuticle permeance data questioned the significance of osmotic forces. During the day, 90% of water uptake was driven by a tension of about -0.15 MPa.     

Diurnal changes in the radius of a subalpine Norway spruce stem: their relation to the sap flow and their use to estimate transpiration

Diurnal changes in the stem radius of a subalpine mature Norway spruce were measured simultaneously with the flow of sap in xylem. Matric potentials in the soil were > -35 kPa. The kinetics of the flow were closely related to the changes in the radius of the stem resulting from depletion of its extensible tissues. The radius of the stem oscillated daily and, fairly independently of this, fluctuated over several days. The daily shrinkage (_d) was correlated with the daily flow through its base (Q_d). When the crown transpired little and was nearly saturated during rainy days, ASd tended to increase relative to Q_d. Using a linear relation, the estimates of flow by _d deviated less than ± 10% from the values measured by heat balance, provided that the periods of calibration in their ratio of dry to rainy days were comparable to those estimated. If the two periods differed in this respect, the estimates of flow deviated up to 42%. A quadratic relation yielded estimates that depended less on weather. It reduced maximal deviations to ±22%. Since _d additionally may represent the time pattern of the daily transpiration better than Q_d, analysing changes in the radius of stems may supplement or partly replace measurements of sap flow in stems.     

Effect of soil temperature on stem sap flow,shoot gas exchange and water potential of Picea engelmannii (Parry) during snowmelt

Summary The effect of cold soils on stem sap flow, shoot gas exchange and water potential of Picea engelmannii (Parry) was investigated during the snowmelt period in the Medicine Bow Mountains, Wyoming, USA. Shoot net photosynthetic rates were higher in young trees (1.5–1.8 m in height) growing in cold soils (<3.5° C) associated with snowpack, than trees in warm soils until about 1500 h. Higher shoot photosynthetic rates of trees in cold soils continued after snow was removed and could not be completely explained by higher visible irradiance over highly reflective snow. Following soil warming higher photosynthetic rates were evident in these trees for five days. High nutrient availability associated with snowmelt may improve shoot nutrient status leading to higher gas-exchange rates during snowmelt. Shoot conductance to water vapor was higher in trees in cold soil until midday, when declining shoot conductance led to lower intercellular CO₂ concentrations. Midday through afternoon shoot water potentials of trees in cold soils were similar or higher than those of trees in warm soils and the lower afternoon shoot conductances in cold soils were not the result of lower bulk shoot water potentials. Decline in net photosynthesis of trees in cold soils at 1500 h paralleled increases in intercellular CO₂ concentrations, implying a nonstomatal limitation of photosynthesis. This scenario occurred consistently in mid-afternoon following higher morning and midday photosynthesis in cold soils, suggesting a carbohydrate feedback inhibition of photosynthesis. Diurnal patterns in stem sap flow of all trees (cold and warm soils) reflected patterns of shoot conductance, although changes in stem sap flow lagged 1–3 h behind shoot conductance apparently due to stem water storage. Total daily stem sap flow was similar in trees in cold and warm soils, although diel patterns differed. The morning surge and night-time drop in sap flow commenced 1–2 h earlier in trees in cold soils. Overnight stem sap flow was lower in trees in cold soils, possibly due to higher resistance to root water uptake in cold soils, which may explain lower predawn shoot water potentials. However, midday shoot water potentials of trees in cold soils equalled or exceeded those of trees in warm soils. Higher resistance to root water uptake in P. engelmannii in cold soils was apparently overshadowed by transpirational forces and significant shoot water deficits did not develop.     

Marine reserve effects on fishery profits: a comment on White et al. (2008)

A recent study ( White et al. 2008 ) claimed that fishery profits will often be higher with management that employs no‐take marine reserves than conventional fisheries management alone. However, this conclusion was based on the erroneous assumption that all landed fish have equal value regardless of size, and questionable assumptions regarding density‐dependence. Examination of an age‐structured version of the White et al. (2008) model demonstrates that their results are not robust to these assumptions. Models with more realistic assumptions generally do not indicate increased fishery yield or profits from marine reserves except for overfished stocks.     

Using otolith weight to estimate the age of haddock (Melanogrammus aeglefinus): a tree model application

In this study, we investigated whether otolith weight can be used to estimate fish age with the same level of accuracy as that of the traditional annuli counting technique in a commercially important species such as haddock (Melanogrammus aeglefinus). Results indicate that this method is highly effective for young fish (around 97% correct classification), whereas its powers of prediction decrease with the increasing age of the fish. For older fish, the otolith weight cannot be an accurate estimator of fish age if the weight overlap between the different age classes is too large. Nevertheless, the otolith weight technique is strictly dependent on correct age determination through the counting of annuli of those individuals used in the calibration. Hence, an increase in the accuracy of ageing obviously determines an increase of the power of otolith weight to estimate fish age. Therefore, we suggest that otolith weight could represent a routine technique for determination of the age structure of haddock populations. This technique has the merit to be objective, fast, 100% repeatable and has the same level of accuracy as that of annuli counting.     

Kauri seeds and larval somersaults: The larval trunk of the seed mining basal moth Agathiphaga vitensis (lepidoptera: Agathiphagidae)

The trunk morphology of the larvae of the kauri pine (Agathis) seed infesting moth Agathiphaga is described using conventional, polarization, and scanning electron microscopy. The pine seed chamber formed by the larva is also described and commented on. The simple larval chaetotaxy includes more of the minute posture sensing setae, proprioceptors, than expected from the lepidopteran larval ground plan. The excess of proprioceptors is suggested to be necessary for sensory input concerning the larval posture within the seed chamber. The trunk musculature includes an autapomorphic radial ventral musculature made up of unique multisegmental muscles. The combined presence of additional proprioceptors and the unique ventral musculature is proposed to be related to the larval movement within the confined space of the seed chamber, especially to a proposed somersault movement that allows the larva to orientate itself within the chamber. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Using banded sunflower moth (Lepidoptera: Tortricidae) egg density to estimate damage and economic distance in oilseed sunflower

The banded sunflower moth, Cochylis hospes Walsingham (Lepidoptera: Tortricidae), is an important economic pest of sunflower in the Upper Great Plains of North America. Economic losses due to reductions in seed number, weight, and quality can be significant. Previously, the potential for economic losses were estimated by sampling for adult moths. However, sampling for moths can be difficult and inaccurate. An alternative is to sample for banded sunflower moth eggs, which can be accurately counted in the field by using a binocular 3.5 headband magnifier. The egg counts are used to calculate the economic injury level (EIL) (EIL = C/VWPK), where C is the cost of treatment per unit area, V is the crop market value per unit of weight, W is the slope of the regression between banded sunflower moth egg densities and weight loss per plant, P is a term for plant population per unit area, and K is the control treatment efficacy. Estimates of populations of banded sunflower moth eggs are taken from the center of 400-m spans along all field sides. From these samples and the calculated EIL, a map of the extent of the economically damaging banded sunflower moth population throughout the field is made using economic distance; ED = e ( ( (EIL/E)-1.458)/-0.262). Economic distance estimates the distance an economic population extends into the field interior along a transect from the sampling site. By using egg samples to calculate the EIL and mapping the distribution of economic populations throughout a field, producers can then make more effective pest management decisions.     

Using parentage analysis to estimate rates of straying and homing in Chinook salmon (Oncorhynchus tshawytscha)

We used parentage analysis based on microsatellite genotypes to measure rates of homing and straying of Chinook salmon (Oncorhynchus tshawytscha) among five major spawning tributaries within the Wenatchee River, Washington. On the basis of analysis of 2248 natural‐origin and 11594 hatchery‐origin fish, we estimated that the rate of homing to natal tributaries by natural‐origin fish ranged from 0% to 99% depending on the tributary. Hatchery‐origin fish released in one of the five tributaries homed to that tributary at a far lower rate than the natural‐origin fish (71% compared to 96%). For hatchery‐released fish, stray rates based on parentage analysis were consistent with rates estimated using physical tag recoveries. Stray rates among major spawning tributaries were generally higher than stray rates of tagged fish to areas outside of the Wenatchee River watershed. Within the Wenatchee watershed, rates of straying by natural‐origin fish were significantly affected by spawning tributary and by parental origin: progeny of naturally spawning hatchery‐produced fish strayed at significantly higher rates than progeny whose parents were themselves of natural origin. Notably, none of the 170 offspring that were products of mating by two natural‐origin fish strayed from their natal tributary. Indirect estimates of gene flow based on F_ST statistics were correlated with but higher than the estimates from the parentage data. Tributary‐specific estimates of effective population size were also correlated with the number of spawners in each tributary.     

The behaviour and form of Psephenus herricki (DeKay) (Coieoptera: Psephenidae) in relation to water flow*

1. Psephenus herricki (DeKay) larvae were observed in aquaria and artificial streams using videomacroscopic techniques. Dye visualization was used to determine flow around the organisms. 2. The highly flattened larvae of Psephenus herricki are able to withstand and/or avoid the force of flowing water in streams through a number of mechanisms. The legs are vital: if they cannot gain purchase the larvae can be dislodged by the lifting forces acting on the body. At the flow rates tested (up to 50 cm s^?1), suction under the carapace is not needed to maintain position. 3. Active pumping of water through lateral slots of the carapace and out from under the body posteriorly greatly reduces turbulence around the body and may act to decrease drag at high Reynolds numbers. 4. An interpretation of the flattened body-shape of Psephenus herrickilarvae as an adaptation to fast currents and/or to prevent the larvae from being removed from the substrate by a predator is of questionable ecological significance because individuals are usually found in crevices and on the undersides of stones.     

Using exon and intron sequences of the gene Mp20 to resolve basal relationships in Cicindela (Coleoptera:Cicindelidae)

The genus Cicindela (Coleoptera: Cicindelidae) is a species-rich cosmopolitan group of tiger beetles useful for comparing clade diversification worldwide. Knowledge about relationships of major groups is important for this analysis but basal nodes in Cicindela have been difficult to resolve with standard mtDNA markers. Here we developed the Mp20 gene, a single-copy nuclear marker coding for a muscle-associated protein in insects, for phylogenetic analysis of basal groups of Cicindela. Nearly full-length sequences were obtained for 51 cicindelids, including major taxonomic groups from all continents. Sequences of Mp20 were between 1.2 and 1.7 kb and spanning three introns. Phylogenetic signal of exon and intron sequences was compared with that from four gene regions of mtDNA (COI, COIII, Cytb, 16S rRNA; 2.4 kb total). Because introns differed in length, sequence alignment was conducted using various procedures of phenetic and parsimony-based character coding of indels to assess their phylogenetic information content, but major nodes were recovered consistently. Mp20 sequences contributed two thirds of the total support of the combined analysis, with most signal from the introns. We found major clades of Cicindela to be geographically largely coincident with continental regions, confined to Australasia, the Holarctic, the Indian subcontinent, Africa, and South and Central America. Clock estimates using various maximum-likelihood (ML) branch length calculations resulted in roughly similar divergence times whether Mp20 exon, introns, or mtDNA were used, and they were not greatly affected by different procedures for coding and optimizing indel characters. Based on existing clock calibrations in Cicindela, basal splits of continental lineages occurred in the mid-Miocene, placing the radiation of basal groups of Cicindela to a period when their open-vegetation habitats expanded globally.     

Binomial sampling to estimate rust mite (Acari: Eriophyidae) densities on orange fruit

Binomial sampling based on the proportion of samples infested was investigated for estimating mean densities of citrus rust mite, Phyllocoptruta oleivora (Ashmead), and Aculops pelekassi (Keifer) (Acari: Eriophyidae), on oranges, Citrus sinensis (L.) Osbeck. Data for the investigation were obtained by counting the number of motile mites within 600 sample units (each unit a 1-cm2 surface area per fruit) across a 4-ha block of trees (32 blocks total): five areas per 4 ha, five trees per area, 12 fruit per tree, and two samples per fruit. A significant (r2 = 0.89), linear relationship was found between ln(-ln(1 -Po)) and ln(mean), where P0 is the proportion of samples with more than zero mites. The fitted binomial parameters adequately described a validation data set from a sampling plan consisting of 192 samples. Projections indicated the fitted parameters would apply to sampling plans with as few as 48 samples, but reducing sample size resulted in an increase of bootstrap estimates falling outside expected confidence limits. Although mite count data fit the binomial model, confidence limits for mean arithmetic predictions increased dramatically as proportion of samples infested increased. Binomial sampling using a tally threshold of 0 therefore has less value when proportions of samples infested are large. Increasing the tally threshold to two mites marginally improved estimates at larger densities. Overall, binomial sampling for a general estimate of mite densities seemed to be a viable alternative to absolute counts of mites per sample for a grower using a low management threshold such as two or three mites per sample.