Tree Physiology

Journal Information
ISSN / EISSN : 0829-318X / 1758-4469
Published by: Oxford University Press (OUP) (10.1093)
Total articles ≅ 4,514
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Dar Dror,
Published: 14 October 2021
While atmospheric CO2 concentration ([CO2]) continues to rise, the question of how tree carbon allocation is affected by this change remains. Studies show that carbon assimilation increases under elevated CO2 (eCO2). Yet, no detailed study determined the fate of the surplus carbon, i.e., its compartment and physiological process allocation, nor in multiple species together. In this project we grew 2-year old saplings of four key Mediterranean tree species (the conifers Cupressus sempervirens and Pinus halepensis, and the broadleaf Quercus calliprinos and Ceratonia siliqua) to [CO2] levels of 400 or 700 ppm for 6 months. We measured the allocation of carbon to below- and above-ground growth, respiration, root exudation, storage, and leaf litter. Additionally, we monitored intrinsic water-use efficiency, soil moisture, soil chemistry, and nutrient uptake. Net assimilation, water-use efficiency, and soil nitrogen uptake significantly increased at eCO2 across the four species. Broadleaf species showed soil water savings which were absent in conifers. All other effects were species-specific: Cupressus had higher leaf respiration; Pinus had lower starch in branches and transiently higher exudation rate; and Quercus had higher root respiration. eCO2 did not affect growth, nor litter production. Our results are pivotal to understanding the sensitivity of tree carbon allocation to the change in [CO2] when water is abundant. Species-specific responses should be regarded cautiously when predicting future changes in forest function at a higher CO2 world.
Chiaki Tsuji, Masako Dannoura, Dorine Desalme, Nicolas Angeli, Satoru Takanashi, Yuji Kominami, Daniel Epron
Published: 12 October 2021
Tree species that close stomata early in response to drought are likely to suffer from an imbalance between limited carbohydrate supply due to reduced photosynthesis and metabolic demand. Our objective was to clarify the dynamic responses of non-structural carbohydrates to drought in a water-saving species, the hinoki cypress (Chamaecyparis obtusa Sieb. et Zucc.). To this end, we pulse-labeled young trees with 13CO2 ten days after the beginning of the drought treatment. Trees were harvested seven days later, early during drought progression, and 86 days later when they had suffered from a long and severe drought. The labeled carbon was traced in phloem extract, in the organic matter and starch of all the organs, and in the soluble sugars (sucrose, glucose, and fructose) of the most metabolically active organs (foliage, green branches, and fine roots). No drought-related changes in labeled C partitioning between below-ground and above-ground organs were observed. The C allocation between non-structural carbohydrates was altered early during drought progression: starch concentration was half lower in the photosynthetic organs, while the concentration of almost all soluble sugars tended to increase. The preferential allocation of labeled C to glucose and fructose reflected an increased demand for soluble sugars for osmotic adjustment. After three months of a lethal drought, the concentrations of soluble sugars and starch were admittedly lower in drought-stressed trees than in the controls, but the pool of non-structural carbohydrates was far from completely depleted. However, the allocation to storage had been impaired by drought; photosynthesis and the sugar translocation rate had also been reduced by drought. Failure to maintain cell turgor through osmoregulation and to refill embolized xylem due to the depletion in soluble sugars in the roots could have resulted in tree mortality in hinoki cypress, though the total pool of carbohydrate was not completely depleted.
Zhipeng Gao, Lin Guo, Muthusamy Ramakrishnan, Yu Xiang, Chen Jiao, Jiaweng Jiang, Kunnummal K Vinod, Zhangjun Fei, Feng Que, Yulong Ding, et al.
Published: 11 October 2021
The key molecular mechanisms underlying the sectionalized growth within bamboo or other grass internodes remain largely unknown. Here, we genetically and morphologically compared the culm and rhizome internode division zones (DZs) of a slow-growing bamboo variant (sgv) having dwarf internodes, to those of the corresponding wild-type (WT). Histological analysis discovers that the sgv has an irregular internode DZ. However, the shoot apical meristems in height, width, outside shape, cell number and cell width of the sgv and the WT were all similar. The DZ irregularities first appeared post apical meristem development, in 1-mm sgv rhizome internodes. Thus, the sgv is a DZ irregularity bamboo variant, which has been first reported in bamboo according to our investigation. Transcriptome sequencing analysis finds that a number of cell wall biogenesis and cell division related genes are dramatically downregulated in the sgv DZ. Interestingly, both transcriptomic and brassinosteroid (BR) contents detecting as well as qRT-PCR analyses show that these irregularities have resulted from the BR signaling pathway defects. BR defect might also cause the erect leaves and branches as well as the irregular epidermis of the sgv. These results suggest that BR signaling pathway plays critical roles in bamboo internode division zone and leaf development from a mutant perspective, and also explain the upstream mechanisms causing the dwarf internode of the sgv bamboo.
Jimei Han, , Jeffrey M Warren, Anirban Guha, David A Mclennan, Wangfeng Zhang, Yali Zhang
Published: 7 October 2021
The induction and relaxation of photochemistry and non-photochemical quenching (NPQ) are not instantaneous and require time to respond to fluctuating environments. There is a lack of integrated understanding on how photochemistry and NPQ influence photosynthesis in fluctuating environments. We measured the induction and relaxation of chlorophyll a fluorescence and gas exchange in poplar and cotton at varying temperatures under saturating and fluctuating lights. When the light shifted from dark to high, the fraction of open reaction centers in photosystem II (qL) gradually increased while NPQ increased suddenly and then remained stable. Temperature significantly changed the response of qL but not that of NPQ during the dark to high light transition. Increased qL led to higher photosynthesis but their precise relationship was affected by NPQ and temperature. qL was significantly related to biochemical capacity. Thus, qL appears to be a strong indicator of the activation of carboxylase, leading to the similar dynamics between qL and photosynthesis. When the light shifted from high to low intensity, NPQ is still engaged at a high level, causing a stronger decline in photosynthesis. Our finding suggests that the dynamic effects of photochemistry and NPQ on photosynthesis depend on the phases of environmental fluctuations and interactive effects of light and temperature. Across the full spectra of light fluctuation, the slow induction of qL is a more important limiting factor than the slow relaxation of NPQ for photosynthesis in typical ranges of temperature for photosynthesis. The findings provided a new perspective to improve photosynthetic productivity with molecular biology under natural fluctuating environments.
Stacy Welker, Myrtho Pierre, James P Santiago, , ,
Published: 7 October 2021
Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), is a phloem-limited disease which disrupts citrus production in affected areas. In HLB-affected plants, phloem sieve plate pores accumulate callose, and leaf carbohydrate export is reduced. However, whether HLB causes a reduction in carbohydrate phloem translocation speed, and the quantitative relationships among callose, CLas population, and phloem translocation are still unknown. In this work, a procedure was developed to concurrently measure sugar transport, callose deposition, and relative pathogen population at different locations throughout the stem. Increasing quantities of CLas genetic material were positively correlated with quantity and density of callose deposits, and negatively correlated with phloem translocation speed. Callose deposit quantity was position- and rootstock dependent, and were negatively correlated with phloem translocation speed, suggesting a localized relationship. Remarkably, callose accumulation and phloem translocation disruption in the scion was dependent on rootstock genotype. Regression results suggested that the interaction of Ct values and number of phloem callose depositions, but not their size or density, explained the effects on translocation speed. Sucrose, starch, and sink 14C label allocation data support the interpretation of a transport pathway limitation by CLas infection. This work shows that the interaction of local accumulation of callose and CLas affect phloem transport. Further, the extent of this accumulation is attenuated by the rootstock and provides important information about the disease mechanism of phloem-inhabiting bacteria. Together, these results constitute the first example of a demonstrated transport limitation of phloem function by a microbial infection.
Yu-E Ding, Ying-Ning Zou, ,
Published: 7 October 2021
The circadian rhythm of plants is associated with stress responses; however, it is not clear whether increased host plant drought tolerance by arbuscular mycorrhizal fungi (AMF) is associated with changes in the circadian clock. The present study aimed to analyze the effect of Funneliformis mosseae (Nicol. & Gerd.) Schüßler & Walker on the circadian clock gene expression patterns in trifoliate orange (Poncirus trifoliata L. Raf.), along with gas exchange, abscisic acid (ABA) levels, and antioxidant enzyme gene expression under well-watered (WW) and drought stress (DS) conditions. Plant growth, net photosynthetic rate, stomatal conductance, and ABA levels were significantly higher in AMF- than in non-AMF-inoculated plants, regardless of soil water regimes. Six circadian clock genes, including PtPRR7, PtLHY, PtCCA1, PtGI, PtPIF3, and PtSRR1, were identified and showed rhythmic expression patterns over the course of the day. AMF inoculation reduced the expression of most circadian clock genes in different time periods. However, AMF treatment significantly increased PtPRR7 and PtGI expression at 17:00 p.m. under WW and DS conditions, PtLHY expression at 1:00 a.m., and PtSRR1 expression at 21:00 p.m. At 1:00 a.m., AMF inoculation up-regulated the expression of the circadian clock genes PtPRR7, PtCCA1, PtLHY, and PtPIF3 and the antioxidant enzyme genes PtFe-SOD, PtMn-SOD, PtCu/Zn-SOD, PtPOD, and PtCAT1. Correlation analysis revealed that these changes in circadian clock gene expression were associated with antioxidant enzyme gene expression, root ABA and gas exchange. We concluded that mycorrhizal fungi have the ability to regulate the daily rhythm of the circadian clock in trifoliate orange plants in response to drought.
Anne Griebel, Jennifer Peters, Daniel Metzen, Chelsea Maier, Craig Barton, Heather Speckman, Matthias Boer, Rachael Nolan, Brendan Choat, Elise Pendall
Published: 6 October 2021
Mistletoes are important co-contributors to tree mortality globally, particularly during droughts. In Australia, mistletoe distributions are expanding in temperate woodlands, while their hosts experienced unprecedented heat and drought stress in recent years. We investigated whether the excessive water use of mistletoes increased the probability of xylem emboli in a mature woodland during the recent record drought that was compounded by multiple heatwaves. We continuously recorded transpiration ($T_{SLA}$) of infected and uninfected branches from two eucalypt species over two summers, monitored stem and leaf water potentials ($\Psi $), and used hydraulic vulnerability curves to estimate percent loss in conductivity (PLC) for each species. Variations in weather (vapour pressure deficit, photosynthetic active radiation, soil water content), host species and % mistletoe foliage explained 78% of hourly $T_{SLA}$. While mistletoe acted as an uncontrollable sink for water in the host even during typical summer days, daily $T_{SLA}$ increased up to 4-fold in infected branches on hot days, highlighting the previously overlooked importance of temperature stress in amplifying water loss in mistletoes. The increased water use of mistletoes resulted in significantly decreased host $\Psi _{leaf}$ and $\Psi _{trunk}$. It further translated to an estimated increase of up to 11% PLC for infected hosts, confirming greater hydraulic dysfunction of infected trees that place them at higher risk of hydraulic failure. However, uninfected branches of Eucalyptus fibrosa had much tighter controls on water loss than uninfected branches of Eucalyptus moluccana, which shifted the risk of hydraulic failure towards an increased risk of carbon starvation for E. fibrosa. The contrasting mechanistic responses to heat and drought stress between both co-occurring species demonstrates the complexity of host–parasite interactions and highlights the challenge in predicting species-specific responses to biotic agents in a warmer and drier climate.
, Sandra Jämtgård, Ram Oren, Linda Gruffman, Sabine Kunz, Torgny Näsholm
Published: 28 September 2021
Boreal trees are capable of taking up organic nitrogen (N) as effectively as inorganic N. Depending on the abundance of soil N forms, plants may adjust physiological and morphological traits to optimize N uptake. However, the link between these traits and N uptake in response to soil N sources is poorly understood. We examined Pinus sylvestris seedlings’ biomass growth and allocation, transpiration, and N uptake in response to additions of organic (the amino acid arginine) or inorganic N (ammonium-nitrate). We also monitored in-situ soil N fluxes in the pots following an addition of N, using a microdialysis system. Supplying organic N resulted in a stable soil N flux, whereas the inorganic N resulted in a sharp increase of nitrate flux followed by a rapid decline, demonstrating a fluctuating N supply and a risk for loss of nitrate from the growth medium. Seedlings supplied with organic N achieved a greater biomass with a higher N content, thus reaching a higher N recovery compared with those supplied inorganic N. In spite of a higher N concentration in organic N seedlings, root-to-shoot ratio and transpiration per unit leaf area were similar to those of inorganic N seedlings. We conclude that enhanced seedlings’ nutrition and growth under the organic N source may be attributed to a stable supply of N, owing to a strong retention rate in the soil medium.
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