Whole-tree sap flow is substantially diminished by leaf herbivory

Ecohydrological models consider the relationship between tree size and structure (especially leaf area index) and water use but generally treat herbivory as a source of unwanted noise in the data. Little is known of how insect damage to leaves influences whole-plant water use in trees. Water use is driven by environmental demand and the total leaf area through which transpiration can occur, but the effects of insects are expected to be complex. Different kinds of insects could have different effects; for example, chewing insects reduce leaf area, whereas sucking and tissue mining insects reduce leaf function without reducing area. Further, plants respond to herbivory in a range of ways, such as by altering leaf production or abscising leaves. We examined the effect of insects on Eucalyptus blakelyi in a woodland near Canberra, Australia, using sap flow velocity as a measure of whole-plant water use. We applied insecticide to 16 trees matched to an untreated control group. After 6 months, we examined the effects on sap flow velocity and crown condition. There was a general increase in sap flow velocity as trees produced leaves over the growing season, but the increase in sap flow for trees without insecticide protection was half that of the protected trees (increase: 4.4 vs. 9.0 cm/h, respectively). This dramatic effect on sap flow was consistent with effects on crown condition. Unprotected trees had 20% less leaf mass per unit stem in the crown. In addition, unprotected trees had a 20% greater loss of leaf functional area from necrosis. It should be noted that these effects were detected in a year in which there was not an outbreak of the psyllids (Homoptera) that commonly cause severe leaf damage to this tree species. It is predicted that the effect in a psyllid outbreak year would be even more substantial. This result underscores the significant impact that insect herbivores can have on an ecological process of significance to the ecosystem, namely, the movement of water from the soil to the atmosphere.     

Demonstration of the root surface electrogenic ion pump activity revealed from the seasonal inversion in the phase relation between electro-radicogram and the diurnal oscillation of air temperature in a field tree (Diospyros kaki)

Re-examination of the electro-radicogram (ERG) obtained during past 10 years research (Masaki and Okamoto in Trees (Berl) 21:433–442, 2007) enabled us to discriminate the excess activity of the electrogenic ion pump in the root surface cell membrane over that of the xylem pump during most of the foliate phase. The trans-root electric potential (TRP) is defined as the difference between V _ps (electric potential difference between symplast and bulk water phase surrounding the root) and V _px (electric potential difference between symplast and xylem apoplast). The diurnal oscillation of TRP followed that of the air temperature and/or light intensity with a delay of several hours during defoliate phase. This means the superiority of the electrogenic activity of the xylem pump over that of the root surface pump. However, after leaf expansion, TRP began to oscillate inversely with the temperature change with a short delay, indicating the superiority of the electrogenic activity of the surface ion pump over that of the xylem pump. An experimental lumbering of the surroundings of the kaki tree in foliate phase prominently increased the ERG amplitude, keeping the inverted phase relation, with the increase in transpiration caused by the increased illumination. An incidental sudden fall of the temperature and illumination caused an inverse reaction.     

The impact of salt stress on the water status of barley plants is partially mitigated by elevated CO2

With the changing climate, plants will be facing increasingly harsh environmental conditions marked by elevated salinity in the soils and elevated concentrations of CO₂ in the atmosphere. These two factors have opposite effects on water status in plants. Therefore, our objective was to determine the interaction between these two factors and to determine whether elevated [CO₂] might alleviate the adverse effects of salt stress on water status in two barley cultivars, Alpha and Iranis, by studying their relative water content and their water potential and its components, transpiration rate, hydraulic conductance, and water use efficiency. Both cultivars maintained their water status under salt stress, increasing water use efficiency and conserving a high relative water content by (1) reducing water potential via passive dehydration and active osmotic adjustment and (2) decreasing transpiration through stomatal closure and reducing hydraulic conductance. Iranis showed a greater capacity to achieve osmotic adjustment than Alpha. Under the combined conditions of salt-stress and elevated [CO₂], both cultivars (1) achieved osmotic adjustment to a greater extent than at ambient [CO₂], likely due to elevated rates of photosynthesis, and (2) decreased passive dehydration by stomatal closure, thereby maintaining a greater turgor potential, relative water content, and water use efficiency. Therefore, we found an interaction between salt stress and elevated [CO₂] with regard to water status in plants and found that elevated [CO₂] is associated with improved water status of salt-stressed barley plants.     

作物光合、蒸腾与水分高效利用的试验研究

通过田间试验,对作物光合、蒸腾、气孔行为及其影响因素进行了研究。结果表明,光合与蒸腾的非线性关系可以用抛物线方程表述,其中光合速率最高时的蒸腾速率为临界值,超出该值即为奢侈蒸腾,干旱处理的临界值较低,通过合适的调控措施,抑制奢侈蒸腾并不影响光合生产,综合分析光合速率、蒸腾速率与气孔导度的关系,气孑L导度大于0．12mol·m^-2·s^-1,实施提高气孔阻力并抑制蒸腾的措施,既节约水分又促进光合作用,增加产量．光合速率基本上随光合有效辐射的增加而提高,并有光饱和点存在,水分条件影响叶片光合作用达到饱和的早晚,干旱处理的光饱和点远远低于湿润处理,强光需要水分充足相耦合,才能充分发挥光能利用率,蒸腾与辐射的线性关系十分显著。从光合有效辐射入手,在光合有效辐射大于1000μmol·m^-2·s^-1时实施措施,既可大大降低蒸腾,又可改善光合,节水增产效果不言而喻。     

不同供水条件下侧柏和刺槐幼树的蒸腾耗水与土壤水分应力订正

采用旱棚人工控水,对侧柏、刺槐不同水量全生长期均衡供水条件下,2～3年生幼树的生理需水规律、蒸腾耗水与土壤水分的关系进行了研究.结果表明,刺槐蒸腾耗水量随土壤供水能力的增大而增加.其中以生长前期和生长盛期耗水为主,约占年蒸腾耗水量的80.5%;刺槐年均生理需水量是侧柏的5.13倍.侧柏蒸腾耗水量在土壤相对含水率为40%～100%有一峰值.当土壤相对含水率≤87.84%时,蒸腾耗水量随土壤相对含水率增加而增大;反之则减小.侧柏蒸腾耗水量以生长盛期最大,约占年蒸腾量的46.27%,生长后期次之,生长前期较小.并求出了两树种蒸腾耗水的土壤水分应力订正函数及在非充分供水条件下实际蒸腾耗水的时间-水分函数.     

Transpiration and whole-tree conductance in ponderosa pine trees of different heights

Changes in leaf physiology with tree age and size could alter forest growth, water yield, and carbon fluxes. We measured tree water flux (Q) for 14 ponderosa pine trees in two size classes (12 m tall and ∼40 years old, and 36 m tall and ∼ 290 years old) to determine if transpiration (E) and whole-tree conductance (g _t) differed between the two sizes of trees. For both size classes, E was approximately equal to Q measured 2 m above the ground: Q was most highly correlated with current, not lagged, water vapor pressure deficit, and night Q was <12% of total daily flux. E for days 165–195 and 240–260 averaged 0.97 mmol m^–2 (leaf area, projected) s^–1 for the 12-m trees and 0.57 mmol m^–2 (leaf area) s^–1 for the 36-m trees. When photosynthetically active radiation (I _P) exceeded the light saturation for photosynthesis in ponderosa pine (900 μmol m^–2 (ground) s^–1), differences in E were more pronounced: 2.4 mmol m^–2 (leaf area) s^–1 for the 12-m trees and 1.2 mmol m^–2 s^–1 for the 36-m trees, yielding g _t of 140 mmol m^–2 (leaf area) s^–1 for the 12-m trees and 72 mmol m^–2 s^–1 for the 36-m trees. Extrapolated to forests with leaf area index =1, the 36-m trees would transpire 117 mm between 1 June and 31 August compared to 170 mm for the 12-m trees, a difference of 15% of average annual precipitation. Lower g _t in the taller trees also likely lowers photosynthesis during the growing season. Received: 19 April 1999 / Accepted: 23 March 2000     

拟单性木兰不同季节断根和剪枝后蒸腾和光合特性的变化

在2005年春季、夏季和秋季,对10a生拟单性木兰(Parakmeriaomeiensis)进行断根和剪枝处理,模拟移栽,用LICOR-6400测定了植株叶片的蒸腾速率、光合速率等生理指标,探讨这些生理指标对不同季节移栽成活率的影响。结果表明,春季处理后叶片能迅速关闭部分气孔,蒸腾速率和光合速率都减小,两者最低时约为对照的60%,生理机能的减弱有利于维持地上、地下部分的平衡,因而最有利于植株成活。夏季处理后叶片气孔导度显著增加,光合速率和蒸腾速率也随之增大,最高时约为对照的2倍左右,此时,若主要依靠剪枝来降低水分消耗,很难保证水分代谢平衡,移栽成活率低。秋季处理后植株叶片气孔导度高于对照,光合速率和蒸腾速率也增加,但增加幅度相对夏季较小,前期最高约增加40%,此时移栽可以通过适当的剪枝和增加土壤水分含量等措施提高成活率。可见,与水分相关的生理机能的调节机制,决定了移栽后的成活水平,即处理后能迅速调节自身生理机能、减少水分消耗的植株,成活率就高,反之就低。     

Photosynthesis and transpiration of healthy and diseased spruce trees in the course of three vegetation periods

Summary CO₂- and H₂O-gas exchange of 20- to 25-year-old spruce trees from a plantation in the Hunsrück mountains were investigated over a period of 3 years. All measurements were made as pair comparisons, i.e., in each case the gas exchange of a damaged tree and of a relatively healthy tree in its immediate vicinity was measured simultaneously. A second plantation in the Westerwald mountains consisted of 18-year-old apparently healthy spruce trees. Pair comparison at this location meant comparison of two healthylooking trees. The investigations at both locations included diurnal course measurements of photosynthesis and transpiration, and light saturation curves and CO₂-saturation curves of photosynthesis. The reduced photosynthesis parameters of the phenotypically damaged trees at the Hunsrück location indicates massive damage to the photosynthetic apparatus. Measurements of H₂O-gas exchange showed that there are disturbances in stomatal regulation of the needles of damaged trees. As a result, the water use efficiency of these needles proved to be significantly lower. In addition, apparent photorespiration of the damaged trees was decreased, whereas their light- and CO₂-compensation points and their dark respiration were increased. In contrast to the Hunsrück plantation, no such effects were detectable when the healthy-looking Westerwald trees were subjected to pair comparison of gas exchange. Reduced photosynthetic capacity and disturbances of the stomatal regulation of the phenotypically damaged Hunsrück trees may be due to damage in the cellular membranes. Furthermore, a comparison of three growing seasons led to the conclusion that the gas exchange of spruce trees in their natural habitat is markedly influenced by climatic conditions.     

The effects of water and multi-nutrient stress on xylem sap chemistry,photosynthesis and transpiration of seedlings of two Eucalypts

Summary Ten seedlings each of Eucalyptus kitsoniana Maiden and Eucalyptus globulus Labill. were subjected to two levels of water stress and two levels of nutrient stress (macro and micro-nutrients) in a greenhouse for 3 weeks. The objectives were to determine the degree to which seedlings show differences in sap chemistry, photosynthesis and transpiration that relate to the environments in which these two species live. Whole plants were then extracted for xylem sap using a pressure chamber and the sap was analyzed for 14 elements using an inductively coupled plasma spectrometer and a nitrometer. For E. kitsoniana water and nutrient stress, applied separately or in combination, significantly reduced leaf conductance, transpiration, photosynthesis and midday water potential. Nutrient stress alone had less effect than water stress on most functions measured. Water stress alone reduced the root/shoot ratio; the combination of water and nutrient stress increased the root/shoot ratio, primarily because of reduced shoot weight. In E. kitsoniana, water stress alone or in combination with nutrient stress increased the xylem sap concentrations of B and Si. Multi-nutrient stress alone, or in combination with water stress, significantly decreased sap Zn and K. For this species, sap N was decreased by nutrient stress, but increased by water stress. E. globulus had significantly lower transpiration rates and less root mass than E. kitsoniana. Slightly lower leaf conductance and photosynthesis were not significant in E. globulus compared to E. kitsoniana. Water and nutrient stress reduced conductance, transpiration (except for nutrient stress) and photosynthesis, and the effects of water stress on E. globulus were greater than the effects of nutrient stress. Midday water potential was reduced by water stress. Water or nutrient stress alone did not alter seedling root/shoot ratio, but the combination of water and nutrient stress significantly increased the root/shoot ratio for both species. For E. globulus, sap concentrations of Mn, Na, Si and K were increased by water stress (alone or in combination with nutrient stress). Sap N increased with water stress or combined stresses, but decreased under nutrient stress alone. When the two species were compared, E. globulus generally had lower or similar nutrient concentrations in the sap, with Ca, Mg, Mn and P significantly lower than in E. kitsoniana. Seedlings of these two species show strong site adaptations to water and nutrient availability.     

Seasonal changes in CO2 and H2O gas exchange of young European beech (Fagus sylvatica L.)

Summary The CO₂ and H₂O gas exchange of young beech trees (Fagus sylvatica L.) were measured over a growing season. Of particular interest was the adaptation of gas exchange to the low level of photon flux density in the understorey of the old beech. The recorded diurnal courses were subdivided into several classes of irradiance. The most frequent class was from only 30–40 E * m^-2 * s^-1. Even at the highest irradiance values, no light saturation in assimilation occurred. The light compensation point lies below 3 E * m^-2 * s^-1, because net dark respiration values are very low. Calculated from the initial slope of the light response curves a mean value of 0.02 mol CO₂ * mol photons^-1 shows a very efficient use of light be the young trees. At the optimal phase of assimilation, the relationship between the daily sum of irradiance and net photosynthesis is highly significantly correlated. Under the local climatic situation, the stomatal opening primarily depends on irradiance. In response to a change in irradiance, stomatal opening also changes rapidly. Therefore, there is only a loose relationship between transpiration rate and vapour pressure saturation deficit. Towards autumn, the transpiration coefficient (E/A-ratio, estimated under light saturation) increases strongly because net photosynthesis decreases simultaneously.