Tree physiology最新文献

Camellia oleifera has constantly been threatened by drought and insufficient soil nutrients. Our study used RNA sequencing (RNA-Seq) to investigate the molecular responses to nitrogen application under drought conditions. Concurrently, we also analyzed associated leaf functional traits. The results showed that supplemental nitrogen effectively alleviated drought-induced stress in C. oleifera. Fertilization increased leaf chlorophyll and flavonoid concentrations, restored non-structural carbohydrate balance and enhanced antioxidant capacity under drought conditions under drought, thereby enhancing drought resistance. RNA-Seq identified differentially expressed genes predominantly engaged in drought stress response mechanisms such as light harvesting, starch and sucrose metabolic pathways, and flavonoid biosynthesis. Under drought conditions, nitrogen application activated CoHEMA, CoHEMB, CoCHI and CoLAR while repressing CoSGR, CoUFGT, CoSPS and CoInv expression, thereby enhancing chlorophyll content and maintaining flavonoid-sucrose homeostasis to meet the metabolic demands of C. oleifera survival. Co-expression network analysis revealed two highly interconnected modules (pink and blue), primarily enriched in carbon metabolism, nitrogen metabolism and secondary metabolite metabolism. The two modules strongly correlated with opposite effects on physiological indicators. In addition, nitrogen fertilizer treatment identified numerous transcription factors associated with drought response. Heterologous expression in Nicotiana tabacum confirmed that CoWHY1 promoted chlorophyll accumulation by regulating the expression of HEMA1 and SGR. This study provides molecular insights into the impact of soil nutrients on the drought response of C. oleifera foliage, setting the groundwork for nutrient management in economic trees under drought conditions.

Proanthocyanidins (PAs), or condensed tannins, are widespread plant secondary metabolites common in trees. Proanthocyanidins play roles in plant defense and soil nutrient cycling, and have applications in human medicine and diet. Although PA function in plant shoots is well studied, there is less information on the role of PAs in roots. Proanthocyanidins can act as anti-fungal compounds, suggesting PAs in roots could negatively affect beneficial mycorrhizal fungi, and thus nutrient uptake. Poplars (Populus spp.) are known to produce a wide range of phenolic compounds, and for this work a transformable (P. tremula L. x P. tremuloides Michx.) hybrid was utilized. Transgenic lines with high and low tissue PA concentrations were used to test the hypothesis that high root PA levels would impede mycorrhizal colonization, and consequently, nitrogen uptake. Plants were grown in a sandwich tissue culture system allowing co-culture of the mycorrhizal fungi and roots. Plants from each line were inoculated with either the ectomycorrhizal (EcM) fungus Laccaria bicolor (Maire) P.D. Orton or the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis (Błaszk., Wubet, Renker & Buscot) C. Walker & A. Schüßler, or were kept as a non-inoculated control. Uptake of ammonium and nitrate by plant roots was measured by 15N-labeling. Successful EcM colonization on poplar roots was confirmed in all the plant lines, while no AM structures were observed. The low-PAs/phenolics line was less colonized by EcM fungi. When inoculated with EcM fungi, plants from all lines tended to have lower root PA concentrations. No significant differences in nitrogen uptake among plant lines were observed, but ammonium uptake was greater than nitrate uptake. Results suggest that PA content is reduced during colonization and that phenylpropanoids may play essential roles in establishing ectomycorrhizal symbioses.

Drought-induced tree mortality and dieback is expected to become an increasingly significant issue as climate change increases the frequency, severity and duration of droughts. The primary proposed mechanism of drought-induced decline is hydraulic failure, which is mechanistically linked to xylem architecture. However, annual variation of xylem anatomical traits has largely been overlooked as a possible driver of tree decline, with a focus instead on traditional ring-width based dendrochronological methods. Here, we employ a quantitative wood anatomy approach to examine whether differences in xylem vessel lumen area were related to decline risk during a recent drought-induced decline of chestnut oak (Quercus prinus) from Southern Indiana, USA. Our results show that over at least the past 60 years, healthy trees built consistently wider vessels than those that succumbed. This phenomenon has now been observed across three continents, and in both tracheid- and vessel-bearing species, indicating that conduit size may be related to drought survival, likely as an indicator of long-term stress. Moreover, an analysis of the sensitivity of vessel lumen area to climate variables suggests that early winter warming may promote the production of wider vessels in the following year. In contrast, a negative correlation between prior year growing season length and vessel lumen area suggests that extended growing seasons may lead to narrower, potentially more vulnerable xylem vessels. These effects were less pronounced in the declining trees, hinting that already-stressed trees were less sensitive or physiologically unable to respond to climatic variability. Designing studies aimed at understanding the drivers of intra-specific variation in xylem conduit architecture could improve our ability to predict tree dieback and mortality under future climate scenarios.

Water uptake and distribution are critical for drought recovery, yet previous drought conditions have been shown to impair water transport by affecting soil-root contact and xylem conductivity. In order to investigate these dynamics, the approach of applying δ2H-labeled water as a controlled irrigation was adopted, with this irrigation being administered to a mixed stand of mature European beech (Fagus sylvatica (L.)) and Norway spruce (Picea abies Karst. (L)) trees in control (CO) and throughfall exclusion (TE) plots following 5 years of experimental summer drought. The δ2H concentrations were measured in soil, stem, twig and leaf water before and after rewetting to assess water pool turnover. The labeled water infiltrated the upper 70 cm of soil in both treatments within 48 h. However, a notable delay in water uptake and distribution was exhibited by TE trees in comparison with CO trees, where the label was detected in stems and leaves within 24 h. The TE beech demonstrated water uptake after 4 days, while TE spruce exhibited a more pronounced delay of 7 days. Despite this delay, TE trees exhibited a higher turnover of stem water pools (>75%) compared with CO trees (<50%), while leaf water turnover remained similar between treatments. The delayed uptake in TE trees may be attributed to fine root loss in both species and the suberization of surviving fine roots in spruce, which likely reduced water absorption efficiency. Additionally, the depleted stem water reserves in TE spruce may have delayed internal redistribution. These findings underscore the importance of considering species-specific recovery dynamics and provide valuable insights into the long-term impacts of drought on tree water relations.

Root and leaf traits are expected to converge on the plant economics spectrum (PES). Some studies have focused on correlation between specific root length (SRL) and specific leaf area (SLA), which reflect resource acquisition per invested mass in root and leaf, respectively. However, the results have been inconsistent amongst previous studies. We hypothesized that this discrepancy was due to overlooked variations in root traits depending on mycorrhizal types because SRL can be influenced by not only PES but also mycorrhizal types. To assess how mycorrhizal type inherently mediates the coordination of root and leaf traits, we determined the leaf and root traits of current-year seedlings of 33 species encompassing different leaf habits and mycorrhizal types, AM (arbuscular mycorrhizal) and ECM (ectomycorrhizal) species, grown under a common condition. Root and leaf traits correlated with the first axis of the principal component analysis, and this axis represented PES. Root diameter (RD) also correlated with the second axis, which differed between mycorrhizal types. Specific root length (SRL) and SLA were correlated positively to each other, but ECM species had higher SRL than AM species when compared at the same SLA. This was because (i) SRL is negatively related to root tissue density (RTD) and RD, (ii) RTD was negatively correlated with SLA and (iii) RD was smaller in ECM. Leaf and root traits are tightly coordinated with each other across species, but the relationship shifts between the mycorrhizal types.

Climate change is intensifying drought conditions in the Eastern Mediterranean, posing a significant threat to its unique forest ecosystems. While residual water loss from leaves (i.e., minimal leaf conductivity) after stomatal closure has been identified to play an important role in drought susceptibility across different tree species worldwide, the role of bark as an additional source of residual transpiration (i.e., bark conductivity-gbark) still remains largely underexplored. This study investigates gbark and bark structural traits in two co-occurring Mediterranean pine species, Pinus brutia Ten. and P. nigra Arnold, in Cyprus. Since P. brutia typically occurs in hotter and drier areas, we expected a lower gbark associated with thicker outer bark. Contrary to our initial hypothesis, P. brutia exhibited significantly higher gbark and thinner outer bark than P. nigra on branches of similar diameter (~1 cm). Along with its higher gbark, P. brutia also showed traits associated with an acquisitive growth strategy, including thicker inner bark and potentially greater bark photosynthetic capacity. Contrary to species-specific relationships, gbark showed a negative relationship with outer bark thickness across the species level. These findings suggest that bark structure and function are intricately linked to species-specific growth strategies.

Small Auxin Upregulated RNA (SAUR) genes constitute the largest family of early auxin-responsive genes and are critically involved in plant growth and development. However, their functional roles in root morphogenesis and terpenoid metabolism, particularly in gymnosperms, remain largely unexplored. In this study, we identified 58 SAUR genes in the Ginkgo biloba L. genome and performed comprehensive analyses of their phylogenetic relationships, gene structures, conserved motifs and chromosomal distributions. Most GbSAUR genes lack introns and contain conserved auxin-responsive elements, suggesting a potential for rapid transcriptional activation in response to auxin signaling. Notably, GbSAUR48 exhibited high and specific expression in root tissues. Functional characterization revealed that overexpression of GbSAUR48 in G. biloba significantly enhanced lateral root formation and increased the accumulation of ginkgolides A and B. Conversely, virus-induced gene silencing of GbSAUR48 suppressed lateral root development and reduced terpenoid lactone content. Further quantitative real-time PCR analysis showed that key genes involved in ginkgolide biosynthesis, GbCYP7005C1, GbCYP7005C3 and GbCYP867E38, were upregulated in overexpression lines and downregulated in silenced plants. These findings indicate that GbSAUR48 plays a dual regulatory role in promoting both lateral root development and terpenoid lactone biosynthesis. This study provides novel insights into the multifunctionality of SAUR genes in gymnosperms and highlights their importance in regulating secondary metabolism in G. biloba.

Mangroves are vital components of coastal blue carbon ecosystems due to their high carbon sequestration capacity, offering a nature-based strategy for climate change mitigation and adaptation. However, their photosynthetic carbon assimilation is highly susceptible to increased salinity. Previous studies have shown that the net photosynthesis rate (Anet) in mangrove plants under salt stress was limited by stomatal conductance (gs) and biochemical factors, but the role of mesophyll conductance to CO2 (gm)-a diffusion component increasingly highlighted as a significant constrain on photosynthesis in various plant species-has not been explicitly considered. In this study, we revisit the physiological mechanisms underlying photosynthetic response of mangrove plants to salt stress. We experimentally examined variations in a comprehensive set of photosynthetic parameters (i.e., with gm included) and leaf structural components in two common coastal woody species of southern China, Kandelia obovata Sheue, H.Y. Liu & J. Yong and Aegiceras corniculatum (L.), across different salinity gradients. Our results demonstrate that both species exhibited optimal photosynthetic performance at 10‰ salinity; however, A, gs and gm significantly declined with increasing salinity level. However, maximum carboxylation rate (Vcmax) did not decrease significantly in K. obovata, while it showed a significant decline in A. corniculatum. Photosynthetic limitation analysis showed that gm was the dominant limiting factor across salinity treatments, except in Kandelia obovata at 20‰ salinity. In K. obovata, the decline in gm correlated with reductions in chloroplast surface area exposed to intercellular airspace per unit leaf area (Sc/S), whereas no such structural relationship was observed in A. corniculatum. Overall, our results demonstrate that increased mesophyll resistance to CO2 diffusion was a primary cause of photosynthetic decline under salt stress, with species-specific structural regulation of gm. These findings enhance our understanding of mangrove responses to salinity and providing guidance for species selection and management strategies to maintain productivity and carbon sequestration in coastal blue carbon ecosystems under future climate change.

The survival of mistletoe and its host under frequent drought stress has become a major focus of many studies but few studies have addressed the leaf hydraulic relations between mistletoes and their hosts that may provide new insights into their adaptation. Here, leaf water potential (ψ) at predawn and midday (ψpd,  ψmid), leaf hydraulic conductance (Kleaf), stomatal conductance (gs), transpiration rate (E), net assimilation (An), pressure-volume curve traits, vein structure and anatomy were tested among mistletoe Loranthus tanakae and two of its hosts Quercus mongolica and Pyrus ussuriensis. We found that compared with the two host species, the mistletoe L. tanakae exhibited more negative ψpd, ψmid, higher Kleaf, less negative ψ at the induction of 50% loss of Kleaf (Kleaf  P50), a less negative turgor loss point and a narrower leaf hydraulic safety margin (ψmid -Kleaf  P50). Furthermore, the mistletoe also exhibited higher gs, E and An, and lower intrinsic water-use efficiency, a rapid decrease in the Kleaf to gs ratio in response to decreasing ψleaf, along with higher vein density and midrib xylem conduit area than its hosts. Our results suggest that the mistletoe L. tanakae exhibits profligate traits with a high-water consumption to sustain aerial parasitic life, but more hydraulic vulnerability to drought. Therefore, their populations may face an extinction threat under increasing drought and heat stress with future climate change.

Pigment dynamics in temperate evergreen forests remain poorly characterized, despite their year-round photosynthetic activity and importance for carbon cycling. Developing rapid, nondestructive methods to estimate pigment composition enables high-throughput assessment of plant acclimation states. In this study, we investigate the seasonality of eight chlorophyll and carotenoid pigments and hyperspectral reflectance data collected at both the needle (400-2400 nm) and canopy (420-850 nm) scales in longleaf pine (Pinus palustris Mill.) at the Ordway Swisher Biological Station in north-central Florida, USA. Needle spectra were obtained at three distinct times throughout the year, while tower-based spectra were collected continuously over a 9-month period. Seasonal trends in photoprotective pigments (e.g. lutein and xanthophylls) and photosynthetic pigments (e.g. chlorophylls) aligned closely with seasonal changes in photosynthetically active radiation and gross primary productivity. To track inter-tree and seasonal variability in pigment pools with hyperspectral reflectance data, we used correlation analyses and ridge regression models. Ridge regression models using the full hyperspectral range outperformed predictions using standard linear regression with specific wavelengths in a normalized difference index fashion. Ridge regression successfully predicted all pigment pools (R2 > 0.5) with comparable accuracy at both the needle and canopy scales. The models performed best for lutein, neoxanthin, antheraxanthin, and chlorophyll a and b-which had greater inter-tree and seasonal variation-and achieved moderate accuracy for violaxanthin, alpha-carotene and beta-carotene. These results provide a foundation for scaling biochemical traits from ground-based sensors to airborne and satellite platforms, particularly in ecosystems with subtle changes in pigment dynamics.