Midday Water Potential Research Articles

Effects of irrigation on ecophysiology, sugar content andthiol precursors (3-S-cysteinylhexan-1-ol and 3-S-glutathionylhexan-1-ol) on Vitis vinifera cv. Sauvignon Blanc

Climate change has an important impact on the phenological phases of the grapevine. The consequences are directly reflected in quantitative and qualitative characteristics of the grapes. In fact, there is a decrease in the skin-to-pulp ratio (therefore a decrease in production with an excess of alcohol) and a consequent reduction in the aromatic potential of white grapes (lowering of the quality of musts). Volatile tioles are important aromatic compounds found in various foods and drinks; in particular they contribute to forming the aroma of some types of white wines as they are characterized by extremely low perception thresholds.This work aimed to evaluate the effects of water stress on ecophysiology, technological maturity and on the thiol precursors of Vitis vinifera L. cv. Sauvignon Blanc vineyards in the Tuscan region (Italy) during two seasons. To this end, three treatments were established: WW (well watered), MW (medium watered), and WS (water stress with no irrigation). During the seasons, measurements were made of single-leaf gas exchange, pre-dawn and leaf midday water potential, leaf temperature, chlorophyll fluorescence, as well chlorophyll content. In addition, the parameters of plant yield, technological maturity (° Brix, acidity, pH and berries weight) and the precursors of 3-Mercaptohexanol (3MH) were analyzed: 3-S-cysteinylhexan-1-ol (Cys-3MH) and 3-S-glutathionylhexan-1-ol (GSH-3MH).Well watered treatments (WW) showed less negative water potential, a higher rate of photosynthesis, of stomatal conductance, a lower leaf temperature (°C). Furthermore, WW showed higher levels of precursors accumulation (Cys-3MH and GSH-3MH) than the other treatments during two seasons. Technological analyses (° Brix and acidity) showed significant differences between WW and WS treatments. The lower berry weight was found in the WS treatment.Finally as a result of climate change, precision irrigation has proved to be a good technique to rebalance the gap between technological and aromatic maturity in Sauvignon Blanc grapes.

Chitosan Improves Morphological and Physiological Attributes of Grapevines Under Deficit Irrigation Conditions

Abstract This study aimed to estimate the morphological and physiological effects of chitosan foliar spray and/or three irrigation levels of 100%, 60%, and 40% of field capacity on grapevines grown in plastic containers to simulate water shortage conditions. The results showed that water irrigation deficit significantly reduced leaf area, trunk cross-sectional area, plant dry weight, root dry weight, relative chlorophyll content, leaf total carbohydrates, catalase activity, leaf midday water potential (ψ), relative water content (RWC), and crop evapotranspiration (ETc), but increased the proline content. Under well-watered condition, foliar-applied chitosan, in particular, 5 and 10 g·dm−3 increased plant growth and biomass production compared with untreated plants. Also, chitosan sprays during deficit irrigation conditions significantly improved plant tolerance to water deficit by enhancing the morphological and physiological parameters of grapevines. The results of this work suggest the opportunity to grow grapevines under deficit irrigation conditions using chitosan foliar spray. Increased plant biomass and root weight, and the positive impacts of chitosan as antitranspirant on increased ψ, RWC, and decreased ETc play the main role in drought stress avoidance mechanisms in grapevines raised under moderate deficit irrigation conditions.

Leaf water relations reflect canopy phenology rather than leaf life span in Sonoran Desert trees.

Plants from arid environments display covarying traits to survive or resist drought. Plant drought resistance and ability to survive long periods of low soil water availability should involve leaf phenology coordination with leaf and stem functional traits related to water status. This study tested correlations between phenology and functional traits involved in plant water status regulation in 10 Sonoran Desert tree species with contrasting phenology. Species seasonal variation in plant water status was defined by calculating their relative positions along the iso/anisohydric regulation continuum based on their hydroscape areas (HA)-a metric derived from the relationship between predawn and midday water potentials-and stomatal and hydraulic traits. Additionally, functional traits associated with plant water status regulation, including lamina vessel hydraulic diameter (DHL), stem-specific density (SSD) and leaf mass per area (LMA) were quantified per species. To characterize leaf phenology, leaf longevity (LL) and canopy foliage duration (FD) were determined. Hydroscape area was strongly correlated with FD but not with leaf longevity (LL); HA was significantly associated with SSD and leaf hydraulic traits (DHL, LMA) but not with stem hydraulic traits (vulnerability index, relative conductivity); and FD was strongly correlated with LMA and SSD. Leaf physiological characteristics affected leaf phenology when it was described as canopy FD better than when described as LL. Stem and leaf structure and hydraulic functions were not only relevant for categorizing species along the iso/anisohydric continuum but also allowed identifying different strategies of desert trees within the 'fast-slow' plant economics spectrum. The results in this study pinpoint the set of evolutionary pressures that shape the Sonoran Desert Scrub physiognomy.

Physiological and Biochemical Responses of Ungrafted and Grafted Bell Pepper Plants (Capsicum annuum L. var. grossum (L.) Sendtn.) Grown under Moderate Salt Stress.

The response of grafted bell pepper plants (Capsicum annuum L. var. grossum (L.) Sendtn.) to salt stress was investigated by analyzing the photosynthetic traits and mineral content of the plants and the metabolic composition of the fruit. The bell pepper variety “Vedrana” was grafted onto the salt-tolerant rootstock “Rocal F1” and grown at two salinities (20 mM and 40 mM NaCl) and control (0 mM NaCl) during the spring–summer period. On a physiological level, similar stomatal restriction of photosynthesis in grafted and ungrafted plants indicated that grafting did not alleviate water balance disturbances under increased salt exposure. Measurements of midday water potential did not show improved water status of grafted plants. The similar metabolic changes in grafted and ungrafted plants were also reflected in similarly reduced fruit yields. Thus, this grafting did not reduce the risk of ionic and osmotic imbalance in pepper plants grown under moderate salt treatment. Changes in the biochemical profiles of the pepper fruit were seen for both added-salt treatments. The fruit phenolic compounds were affected by rootstock mediation, although only for the July harvest, where total phenolics content increased with 40 mM NaCl treatment. Fruit ascorbic acid content increased with the duration of salt stress, without the mediation of the rootstock. The high salt dependence of this quality trait in pepper fruit appears to lead to more limited rootstock mediation effects.

Bigleaf Maple Within-Crown Leaf Morphology and Seasonal Physiology

We investigated the influences of height, light availability, leaf structure, and season on bigleaf maple (Acer macrophyllum Pursh) leaf physiology in northern California to improve our understanding of productivity and carbon sequestration in western forests. Using hydrated cuttings and lab-based measurements, we found that leaf mass-to-area ratio and maximum photosynthetic capacity increased with height and distance from the bole. In situ, we measured leaf physiology throughout tree crowns from June through September and found that predawn water potential was remarkably constant, indicating sustained access to water. We also found that midday water potential generally decreased with height and distance from the bole, noticeably decreased at the end of the growing season, and did not fall below –2 MPa, suggesting ample access to water and/or stomatal regulation to maintain hydrated water status. At midday, light availability and stomatal conductance of water vapor generally increased with height and distance from the bole. Stomatal conductance peaked in the treetop in June, in the mid-crown in July and August, and in the low-crown in September, demonstrating temporal and spatial optimization of crown resources in response to changing light quality, climatic conditions, and water status across the season to maximize carbon uptake at the tree level. Together, our water potential and light measurements suggest that light availability is a stronger determinant of leaf morphology and physiology than hydraulic limitation in this species. These findings provide information on seasonal physiology in a widespread deciduous hardwood species, thereby strengthening our understanding of forest productivity in a predominantly coniferous region.

Weak Tradeoff and Strong Segmentation Among Plant Hydraulic Traits During Seasonal Variation in Four Woody Species.

Plants may maintain long-term xylem function via efficiency-safety tradeoff and segmentation. Most studies focus on the growing season and community level. We studied species with different efficiency-safety tradeoff strategies, Quercus acutissima, Robinia pseudoacacia, Vitex negundo var. heterophylla, and Rhus typhina, to determine the seasonality of this mechanism. We separated their branches into perennial shoots and terminal twigs and monitored their midday water potential (Ψmd), relative water content (RWC), stem-specific hydraulic conductivity (Ks), loss of 12, 50, and 88% of maximum efficiency (i.e., P12, P50, P88) for 2 years. There were no correlations between water relations (Ψmd, RWC, Ks) and embolism resistance traits (P12, P50, P88) but they significantly differed between the perennial shoots and terminal twigs. All species had weak annual hydraulic efficiency-safety tradeoff but strong segmentation between the perennial shoots and the terminal twigs. R. pseudoacacia used a high-efficiency, low-safety strategy, whereas R. typhina used a high-safety, low-efficiency strategy. Q. acutissima and V. negundo var. heterophylla alternated these strategies. This mechanism provides a potential basis for habitat partitioning and niche divergence in the changing warm temperate zone environment.

Drought effects on resource partition and conservation among leaf ontogenetic stages in epiphytic tank bromeliads.

Studying the response to drought stress of keystone epiphytes such as tank bromeliads is essential to better understand their resistance capacity to future climate change. The objective was to test whether there is any variation in the carbon, water and nutrient status among different leaf ontogenetic stages in a bromeliad rosette subjected to a gradient of drought stress. We used a semi-controlled experiment consisting in a gradient of water shortage in Aechmea aquilega and Lutheria splendens. For each bromeliad and drought treatment, three leaves were collected based on their position in the rosette and several functional traits related to water and nutrient status, and carbon metabolism were measured. We found that water status traits (relative water content, leaf succulence, osmotic and midday water potentials) and carbon metabolism traits (carbon assimilation, maximum quantum yield of photosystem II, chlorophyll and starch contents) decreased with increasing drought stress, while leaf soluble sugars and carbon, nitrogen and phosphorus contents remained unchanged. The different leaf ontogenetic stages showed only marginal variations when subjected to a gradient of drought. Resources were not reallocated between different leaf ontogenetic stages but we found a reallocation of soluble sugars from leaf starch reserves to the root system. Both species were capable of metabolic and physiological adjustments in response to drought. Overall, this study advances our understanding of the resistance of bromeliads faced with increasing drought stress and paves the way for in-depth reflection on their strategies to cope with water shortage.

Physiological responses of rosewoods Dalbergia cochinchinensis and D. oliveri under drought and heat stresses.

Dalbergia cochinchinensis and D. oliveri are classified as vulnerable and endangered, respectively, in the IUCN Red List and under continued threat from deforestation and illegal harvesting for rosewood. Despite emerging efforts to conserve and restore these species, little is known of their responses to drought and heat stress, which are expected to increase in the Greater Mekong Subregion where the species co‐occur and are endemic. In this study of isolated and combined drought and heat effects, we found that D. oliveri had an earlier stomatal closure and more constant midday water potential in response to increasing drought level, suggesting that D. oliveri is relatively isohydric while D. cochinchinensis is relatively anisohydric. Heat shock and drought had synergistic effects on stomatal closure. Our results indicate contrasting relationships in water relations, photosynthetic pigment levels, and total soluble sugars. An increase in chlorophyll a was observed in D. cochinchinensis during drought, and a concomitant increase in carotenoid content likely afforded protection against photo‐oxidation. These physiological changes correlated with higher total soluble sugars in D. cochinchinensis. By contrast, D. oliveri avoided drought by reducing chlorophyll content and compromising productivity. Anisohydry and drought tolerance in D. cochinchinensis are adaptations which fit well with its ecological niche as a pioneering species with faster growth in young trees. We believe this understanding of the stress responses of both species will be crucial to their effective regeneration and conservation in degraded habitats and in the face of climate change.

Tree growth, transpiration, and water-use efficiency between shoreline and upland red maple (Acer rubrum) trees in a coastal forest

Coastal shoreline forests are vulnerable to seawater exposure, the impacts of which will increase due to sea-level rise, but the long-term adaptation strategies and vulnerability of coastal forests are not well understood. We used whole-tree transpiration, leaf water potential, tree-ring width, and tree-ring δ13C (a proxy for intrinsic water use efficiency, iWUE) to examine the long-term adaptation strategies of red maple (Acer rubrum) trees at the coastal interface (i.e., shoreline) and nearby upland in Maryland, USA. Red maple trees that grew along the shoreline and were exposed to slightly saline water (up to two PSU) had higher transpiration rates than those growing in the nearby upland forest during a wet year, but these differences disappeared during a normal precipitation year. Shoreline trees grew more slowly than upland trees over the last four decades, but these growth differences have disappeared in the last six years. Shoreline and upland red maple trees had similar variation in iWUE, indicating that higher transpiration rates of the seawater-exposed trees did not translate into differences in water use efficiency. There were no differences in predawn and midday water potential between upland and shoreline trees, suggesting no additional water stress occurs in shoreline trees. These findings indicate that mature red maple in our coastal study site maintains gas exchange and growth at a consistent or homeostatic level under slight soil salinity.

Water relations and drought response of Pinus strobiformis

Southwestern white pine (Pinus strobiformis Engelm.) faces dual threats of climate change shifting its environmental niche and mortality due to a nonnative, invasive fungal pathogen. To inform efforts to sustain this species, we established experimental field trials in three common gardens along an elevational gradient with drought treatments to assess trait responses in southwestern white pine. We measured predawn and midday water potential on 44 maternal families from 10 populations at each garden. We used regression between predawn and midday water potentials to estimate hydroscape area, an index of stomatal regulation of transpiration. We measured leaf carbon isotope ratio and estimated carbon isotope discrimination and leaf mass per area to understand the effects of gardens and treatments on stomatal aperture and leaf structure. Water stress caused by experimental drought and temperature decreased leaf carbon isotope discrimination and leaf mass per area, indicating formation of thin leaves with low stomatal conductance in response to heat and drought. The hydroscape area of southwestern white pine suggests tight control of transpiration via stomatal closure, similar to other isohydric pines. Families with greater stomatal closure (inferred from carbon isotope ratio) at the warm, dry garden had higher survival than other families, suggesting an important role of isohydry in acclimation of southwestern white pine to expected habitat drying and warming.

Fundamental intra-specific differences in plant–water relations in a widespread desert shrub (Artemisia tridentata)

Big sagebrush (Artemisia tridentata) is a widespread and locally dominant shrub that is a key driver of water fluxes and storage in western North America. There are several recognized subspecies of big sagebrush that occupy different microsites across the landscape according to moisture availability, yet little is known about how these subspecies vary in drought tolerance or water management strategies. We measured diurnal and seasonal (i.e., early-, mid-, and late summer) variation in water status and transport efficiency, transpiration, and stomatal regulations in two subspecies of big sagebrush (A.t. wyomingensis and A.t. vaseyana) at the Reynolds Creek Critical Zone Observatory in southwestern Idaho. We hypothesized that water status, transport efficiency, and stomatal regulations would be greater in A.t. vaseyana compared to A.t. wyomingensis, because the first subspecies occupies wetter microsites. Predawn and midday water potentials were up to 2× more negative in A.t. wyomingensis compared to A.t. vaseyana, and transpiration was up to ~ 4× greater in A.t. vaseyana compared to A.t. wyomingensis. A.t. vaseyana was more isohydric with ~ 1.5× greater stomatal sensitivity to atmospheric vapor pressure deficit and a smaller hydroscape, compared to A.t. wyomingensis. Our data demonstrate that there are fundamental differences in plant–water relations among these subspecies that constitute the vast, but not homogeneous sagebrush landscapes. These important differences can have implications for modeling water fluxes in big sagebrush-dominated communities at shrub to ecosystem scales.

Association between Fruit Development and Mature Fruit Drop in Huanglongbing-affected Sweet Orange

In the past decade, FL citrus industry has been struck by Huanglongbing (HLB), a disease caused by the phloem-limited bacterium Candidatus Liberibacter asiaticus (CLas). Besides tree decline, HLB causes a sharp increase in mature fruit drop before harvest, leading to a substantial reduction in citrus production. The aim of the study was to provide insights in HLB-associated mature fruit drop. For HLB-affected ‘Valencia’ and ‘Hamlin’ sweet orange (Citrus sinensis), trees exhibiting severe symptoms (“severe trees”) had a significantly higher rate of mature fruit drop compared with mildly symptomatic ones (“mild trees”). Interestingly, dropped fruit were smaller than those still attached to tree branches regardless of the symptom levels of trees; overall, fruit of severe trees were smaller than mild trees. The result suggests a negative effect of HLB on fruit growth that may lead to a high incidence to drop subsequently at maturity. This possibility is further supported by the difference in immature fruit size as early as 2 months after bloom between severe and mild trees. Although HLB-triggered phloem plugging due to callose deposition in citrus leaves, which results in disrupted carbohydrate transport, has been documented in literature, the results of the histological analysis demonstrated no consistent pattern of callose deposition in the mature fruit pedicel in relation to the drop incidence. Additionally, sugar concentration in juice was not significantly different between dropped and attached fruit, providing evidence that carbohydrate shortage is not the case for dropped fruit and thus not the predominant cause of HLB-associated mature fruit drop. Notably, the midday water potential was significantly lower for severe than mild trees during the preharvest period (2 weeks before harvest of the current crop) in late March, which was also the second week after full bloom of return flowering. This suggests that altered tree water status due to HLB might limit fruit growth during the initial stage of fruit development (immediately after flowering) and/or increase the incidence of mature fruit abscission, leading to elevated preharvest fruit drop. Together, the results suggest that in the presence of HLB, strategies to increase fruit size and minimize additional stresses (especially drought) for the trees may improve mature fruit retention.

Impacts of precommercial thinning on gas exchange, midday water potential, and chlorophyll content in Pinus nigra subsp. pallasiana stand from the semiarid region

The net photosynthetic rate (A), stomatal conductance (gs), and transpiration rate (E), chlorophyll content, and midday xylem water potential (Ψmd) of Pinus nigra Arn. subsp. pallasiana (Lamb.) Holmboe trees were studied in a natural stand (Burdur-Aziziye, Turkey) for the first (2015), second (2016) and third (2017) years after precommercial thinning (PCT) to better understand the physiological and biochemical responses of trees in a semiarid region. In this study, three treatments (control, 2–2.5 × 2–2.5 m and 3–3.5 × 3–3.5 m spacing) were applied. Soil water content (SWC) and soil temperature (ST) was greater in both PCT treatments than in the control treatments. In general, the control treatment had a lower Ψmd compared with PCT treatments. A, gs, and E are generally higher than PCT treatments applied with 3–3.5 m spacing. The lowest gs and E were determined in the control trees. Ψmd and A were positively correlated with SWC, but negatively correlated with ST. The decrease in stress level, improvement in resources, and reduced competition for resources by fewer trees increased the A and gs in trees in the PCT treatments. Chlorophyll a, chlorophyll b, and total chlorophyll content are higher in the control treatments as compared to PCT treatments. SWC, ST, Ψmd, A, gs, E, and photosynthetic pigment showed seasonal changes. The two PCT treatments were generally similar in the ecophysiological changes in plots and a longer time is needed to decide for PCT treatments applied with 3–3.5 m spacing. According to the results obtained, it is recommended that PCT be applied with spacings of 2–2.5 × 2–2.5 m.

Subtle precipitation differences yield adaptive adjustments in the mesic Nothofagus dombeyi

Climate change is impacting on natural systems and forests worldwide have suffered from massive mortality due to extreme droughts. That is the case of mesic Nothofagus dombeyi forests of northern Patagonia, whereas no climate-driven mortality was recorded towards drier areas. The aim was to examine population differences in relation to a small precipitation gradient at morphological, physiological, and genetic scales. Adaptive differences between seedlings collected from dry and mesic sites of N. dombeyi on the eastern slopes of the Andes were studied combining common garden and water stress manipulative experiments with genomic analyses. We recorded mortality, plant architectural and leaf traits during cultivation in the greenhouse. A set of plants were subjected to water deficit experiments and water potential was measured. Genomic differences were analyzed by Single Nucleotide Polymorphisms (SNPs). Plants from the mesic site grew taller with more branches and number of larger leaves, and greater stomatal density under optimum conditions yet with slightly more negative midday water potentials due to induced desiccation. Adaptive SNPs yielded similar divergence than quantitative traits which were greater than that of neutral SNPs. Five adaptive loci had a significant association to whole plant and leaf traits. These results show that in spite of the small climatic differences between sites and continuous gene flow populations showed adaptive adjustments and differed significantly in growth, ecophysiology, and genetically. This information can be used in climate-oriented restoration efforts.

Vertical gradients in foliar physiology of tall Picea sitchensis trees.

In tall conifers, leaf structure can vary dramatically with height due to decreasing water potential (Ψ) and increasing light availability. This variation in leaf structure can have physiological consequences such as increased respiratory costs, reduced internal carbon dioxide conductance rates and ultimately reduced maximum photosynthetic rates (Amax). In Picea sitchensis (Bong.) Carrière, the leaf structure varies along the vertical gradient in ways that suggest compensatory changes to enhance photosynthesis, and this variation seems to be driven largely by light availability rather than by Ψ. These trends in leaf structure coupled with remarkably fast growth rates and dependence on moist environments inspire two important questions about P. sitchensis: (i) does foliar water uptake minimize the adverse effects of decreasing Ψ with height on leaf structure, and (ii) do trends in leaf structure increase photosynthetic rates despite increasing height? To answer these questions, we measured foliar water uptake capacity, predawn (Ψpd) and midday water potential and gas-exchange rates as they varied between 25- and 89-m heights in 300-year-old P. sitchensis trees in northwestern California. Our major findings for P. sitchensis include the following: (i) foliar water uptake capacity was quite high relative to published values for other woody species; (ii) foliar water uptake capacity increased between the crown base and treetop; (iii) wet season Ψpd was higher than predicted by the gravitational potential gradient, indicating foliar water uptake; and (iv) the maximum photosynthetic rate increased with height, presumably due to shifts in leaf structure between the crown base and treetop, mitigating height-related decreases in Amax. These findings suggest that together, the use of fog, dew and rain deposits on leaves and shifts in the leaf structure to conserve and possibly enhance photosynthetic capacity likely contribute to the rapid growth rates measured in this species.

基于叶片水势的内蒙古典型草原植物水分适应特征研究

PDF HTML阅读 XML下载 导出引用 引用提醒 基于叶片水势的内蒙古典型草原植物水分适应特征研究 DOI: 10.5846/stxb201903190512 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划（2014CB138802）；国家科技支撑计划（2015BAC02B05） The adaptability of plants to water based on leaf water potential in typical steppe in Inner Mongolia Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:水分是限制草原生态系统植物生存、繁殖和扩散最重要的生态因子，植物通过多样的水分适应策略适应干旱环境。为了解典型草原植物水势特征及其影响因素，在2017年和2018年的生长季对内蒙古典型草原71种植物的叶片黎明水势、午后水势、叶片和根系功能性状进行了测定与分析。结果表明：测定的71种植物叶片的黎明水势分布于-2.67—-0.63 MPa，午后水势分布于-4.67—-1.01 MPa；一年生植物的叶片具有最高的黎明水势、午后水势和最小的水势日差值（叶片的黎明水势与午后水势的差值），多年生禾草的叶片具有最低的黎明水势、午后水势和最大的水势日差值；71种植物对水分的适应策略可分为高水势保持型、低水势忍耐型和变水势波动型；叶片午后水势与叶片干物质含量和根系深度呈极显著的负相关关系（P<0.01），但与比叶面积呈极显著的正相关关系（P<0.01）。本研究有助于从植物生理学的角度上准确认识典型草原植物的水分适应性及水分生态特征。 Abstract:Water is the most important eco-factor which strongly constrains the survival, reproduction, and dispersal of plants in typical steppes. Plants can adapt to arid environments through various water strategies. To elucidate the characteristics of leaf water potential and its relationships with the functional traits of leaves and roots in the typical steppes in Inner Mongolia, we measured the predawn water potential, midday water potential, and functional traits of leaves and roots in 71 plant species during the growing seasons in 2017 and 2018. We had the following key results. The predawn and midday water potential of all the 71 species ranged from -2.67 to 0.63 MPa and from -4.67 to -1.01 MPa, respectively. Among five plant functional groups, the annual plants had the highest predawn and midday water potential, and the smallest diurnal range of water potential (i.e. the difference between predawn water potential and midday water potential); the perennial grasses followed the opposite patterns. The water-adaptive strategies of 71 plant species were quantitatively classified into three types: high water potential type, low water potential type, and fluctuant water potential type. Across 71 plant species, their midday water potentials exhibited significantly negative correlations with their leaf dry matter content and root depths (P<0.01), and significantly positive correlations with their specific leaf area (P<0.01). Our findings might help us to understand the water adaptability and water ecological characteristics of plant species in the typical steppes in Inner Mongolia from the perspective of plant physiology. 参考文献 相似文献 引证文献

Six co-occurring conifer species in northern Idaho exhibit a continuum of hydraulic strategies during an extreme drought year

As growing seasons in the northwestern USA lengthen, on track with climate predictions, the mixed conifer forests that dominate this region will experience extended seasonal drought conditions. The year of 2015, which had the most extreme drought for the area on record, offered a potential analogue of future conditions. During this period, we measured the daily courses of water potential and gas exchange as well as the hydraulic conductivity and vulnerability to embolism of six dominant native conifer species, Abies grandis, Larix occidentalis, Pinus ponderosa, Pinus monticola, Pseudotsuga menziesii and Thuja occidentalis, to determine their responses to 5 months of record-low precipitation. The deep ash-capped soils of the region allowed gas exchange to continue without significant evidence of water stress for almost 2 months after the last rainfall event. Midday water potentials never fell below −2.2 MPa in the evergreen species and −2.7 MPa in the one deciduous species. Branch xylem was resistant to embolism, with P50 values ranging from −3.3 to −7.0 MPa. Root xylem, however, was more vulnerable, with P50 values from −1.3 to −4.6 MPa. With predawn water potentials as low as −1.3 MPa, the two Pinus species likely experienced declines in root hydraulic conductivity. Stomatal conductance of all six species was significantly responsive to vapour pressure only in the dry months (August–October), with no response evident in the wet months (June–July). While there were similarities among species, they exhibited a continuum of isohydry and safety margins. Despite the severity of this drought, all species were able to continue photosynthesis until mid-October, likely due to the mediating effects of the meter-deep, ash-capped silty-loam soils with large water storage capacity. Areas with these soil types, which are characteristic of much of the northwestern USA, could serve as refugia under drier and warmer future conditions.

The adjustment of Prosopis tamarugo hydraulic architecture traits has a homeostatic effect over its performance under descent of phreatic level in the Atacama Desert

Prosopis tamarugo undergoes several modifications of its hydraulic architecture, which has a homeostatic effect on its performance under descent of phreatic level. Groundwater extraction for mining has generated a large area of descent of phreatic level in the Llamara Salt Flat, Atacama Desert, where Prosopis tamarugo lives as a strict phreatophyte. We study different hydraulic architecture traits of P. tamarugo after 12 years of exposure to a descent of phreatic level of ~ 11 m to assess its acclimation capacity. Under this condition, tree size was reduced making the structure of trees shrubbier. At branch level, leaf shedding increased Huber Value and theoretical leaf-specific hydraulic conductivity. At vascular tissue level, vessel composition decreased significantly due to an increase in vessel density and a slight decrease in mean vessel area. This meant that there were no differences of theoretical sapwood-specific hydraulic conductivity and wood density between conditions of descent of phreatic level. Although the theoretical hydraulic efficiency is high under descent of phreatic level, a lower midday water potential indicates other possible factors that may affect its performance (e.g., microclimate, daily loss of conductivity and a high root resistances). The above is consistent with a higher leaf mass per area of the remaining leaves, but no differences were observed in stomatal conductance, leaf 13C isotopic composition and predawn water potential between descent condition. While the adjustment of hydraulic architecture traits has a homeostatic effect on P. tamarugo performance, it is necessary to evaluate the limits of its resistance to contribute to its conservation in a context of intervention of its habit, mainly due to demographic growth and non-metallic mining.

Stem cycle analyses help decipher the nonlinear response of trees to concurrent warming and drought

High-resolution analysis of stem radius variation can quantify the impact of warming and drought on stem water balance and stem growth in black spruce [ Picea mariana (Mill.) B.S.P.)]. Drought affected plant water status and stem growth. However, warming affects the components of the circadian stem cycle differently if the impacts occur in the daytime or nighttime. The interactive effect of abiotic stresses had less impact on the circadian stem cycle than when the stresses occurred independently. Warming and recent droughts in boreal regions reflect the multiple dimensions of climate change. How these climate-related stresses will affect the stem growth of trees remains to be described. Plant water relations can detect the dynamics of stem depletion and replenishment under conditions of climate-forced stress. This study aimed to verify the impacts of a combination of asynchronous warming (nighttime versus daytime warming) and drought on stem water balance and stem growth in black spruce [Picea mariana (Mill.) B.S.P.)]. We investigated the water status and variations in stem radius of black spruce saplings growing in a controlled environment from May through August. We grew four-year-old saplings in warmer conditions either during the day (DW) or night (NW) at temperatures ca. 6 °C warmer than the ambient air temperature (CT). We then simulated a one-month drought in June. Automatic point dendrometers provided a high-resolution analysis of variations in stem radius, and we also monitored leaf water potentials and volumetric soil water content during the entire experimental period. We detected significant reductions in stem radius variation under water deficit conditions. In the daytime warming scenario, we observed a significant increase in the duration of contraction and a decrease in expansion of the stems. The amplitude of this contraction and expansion was reduced under the nighttime warming conditions. The main effect of warming was to enhance drought stress by accelerating soil water depletion. Changes in predawn water potential drove the duration of stem circadian cycles under conditions of daytime warming, whereas irreversible growth dynamics drove these cycles under nighttime warming conditions due to the midday water potential. The interaction of night/daytime asynchronous warming and drought reduced the amplitude rather than the duration of stem contraction and expansion. Water deficit decreased stem growth during the growing season. Asymmetric warming (as a single independent treatment) affected the timing and magnitude of stem circadian cycles. Under daytime warming scenarios, the duration of contraction and expansion were regulated mainly by predawn water potential, inducing longer (shorter) durations of contraction (expansion). Under nighttime warming, the smaller amplitudes of stem contraction and expansion were associated with midday water potential. Therefore, the interaction of abiotic stresses had less of an impact on the circadian stem cycle components than when these stresses were applied independently.

Effects of dry-season irrigation on leaf physiology and biomass allocation in tropical lianas and trees.

Lianas are more abundant in seasonal forests than in wetter forests and are thought to perform better than trees when light is abundant and water is limited. We tested the hypothesis that lianas perform better than trees during seasonal drought using a common garden experiment with 12 taxonomically diverse species (six liana and six tree species) in 12 replicated plots. We irrigated six of the plots during the dry season for four years, while the remaining six control plots received only ambient rainfall. In year 5, we measured stem diameters for all individuals and harvested above- and belowground biomass for a subset of individuals to quantify absolute growth and biomass allocation to roots, stems, and leaves, as well as total root length and maximum rooting depth. We also measured rate of photosynthesis, intrinsic water use efficiency (iWUE), pre-dawn and midday water potential, and a set of functional and hydraulic traits. During the peak of the dry season, lianas in control plots had 54% higher predawn leaf water potentials (ΨPD ), and 45% higher photosynthetic rates than trees in control plots. By contrast, during the peak of the wet season, these physiological differences between lianas and trees become less pronounced and, in some cases, even disappeared. Trees had higher specific leaf area (SLA) than lianas; however, no other functional trait differed between growth forms. Trees responded to the irrigation treatment with 15% larger diameters and 119% greater biomass than trees in control plots. Liana growth, however, did not respond to irrigation; liana diameter and biomass were similar in control and irrigation plots, suggesting that lianas were far less limited by soil moisture than were trees. Contrary to previous hypotheses, lianas did not have deeper roots than trees; however, lianas had longer roots per stem diameter than did trees. Our results support the hypothesis that lianas perform better and experience less physiological stress than trees during seasonal drought, suggesting clear differences between growth forms in response to altered rainfall regimes. Ultimately, better dry-season performance may explain why liana abundance peaks in seasonal forests compared to trees, which peak in abundance in less seasonal, wetter forests.